WO1996032576A1

WO1996032576A1 - Operation and control of a free piston aggregate

Info

Publication number: WO1996032576A1
Application number: PCT/NL1996/000157
Authority: WO
Inventors: Theodorus Gerhardus Potma
Original assignee: T. Potma Beheer B.V.
Priority date: 1995-04-10
Filing date: 1996-04-10
Publication date: 1996-10-17
Also published as: EP0839265A1; AU5163896A; CA2217864A1

Abstract

A device is provided for generating a fast movement for controlling a free piston aggregate in particular, comprising a cylinder (72) with therein a first adjusting piston (51) with a first position and a second position, which adjusting piston, together with the cylinder, forms a first displacement space (61) that is minimal in the first position and a second displacement space (79) that is minimal in the second position, in which, in the first position, both displacement spaces are under low pressure and the first adjusting piston closes off a first supply port for a first main (59) with medium under high pressure, and in which means are present to initially move the first adjusting piston (51) from the first position in order to open the first supply gate, so that the medium under high pressure quickly moves the first adjusting piston (51) to the second position. In addition, the invention relates to the charging of the combustion space of a free piston aggregate and the corresponding charging device and to the supply and discharge of liquid to the compression spaces on either side of the compression piston of the free piston combination.

Description

Operation and control of a free piston aggregate

The invention relates to the operation and control of a free piston aggregate.

In general, the aggregate in question is a free piston aggregate in which the compression of combustion gas takes place with the aid of a hydraulically moved free piston and in which the free piston mainly supplies hydraulic energy. More specifically, the aggregate in question is the so-called Potma or TP-aggregate, which was first described in the Dutch patent application 68.14405, in which only one piston is used per combustion cylinder and the frequency and power control are realized by keeping the free piston in a stationary position at the end of each expansion stroke during a longer or shorter waiting period.

In the free piston aggregates the movement of the free piston or, rather, the free piston combination, is not a forced movement, such as is the case in a crank-connecting rod engine. In the latter case the combustion piston is connected to the crankshaft and makes a forced harmonic movement, while the movement and timing of the free piston must take place by operation and control of the (combusti¬ on)gas and liquid flow, the pressure of which determines the movement of the free piston. This operation and control for attaining an optimal movement of the free piston largely takes place by remotely operating certain gas and liquid valves by means of electric control signals going out from the central control electronics. The main points here are the quick opening and closing of specific valves with sufficiently large passages that influence specific flows of liquids and gases, which determine the free piston movement and thus also the optimal action of the free piston aggregate.

A disadvantage of the known free piston aggregates is that hydraulic throttling losses usually occur when some valves do not open or close quickly enough and/or have a passage that is too small. Another disadvantage is that imperfect gas-filling of the combustion cylinder takes place in the known free piston aggregates, owing to the fact that the charging device is mechanically coupled to the movement of the combustion piston, which is not optimal, also in view of the electronically controlled waiting periods of the free piston. A third disadvantage is that the known free piston aggregates have a rather intricate conduit and valve configuration. A fourth disadvantage is that, in the known conduit configuration of free piston engines, flow and leakage losses occur at the fast-moving pistons and rods and during the waiting periods of the free piston.

It is an object of the invention to provide an improved free piston aggregate.

According to a first aspect of the invention a device for generating a fast movement as described in claim 1 is provided to that end.

Claims 2 - 9 provide advantageous embodiments for this device.

A device is herewith provided for generating a relatively large and powerful and, in particular, fast movement, controlled remotely and with very littly energy, which movement can be implemented within a very short period of time after the control signal. The movement is mainly used for operating various types of hydraulic and pneumatic valves, either sliding valves or completely sealing seating valves. Each time, the movement is brought about by one or more hydraulically operated adjusting piston(s) .

The device for the valve operation according to the inven¬ tion always comprises a hydraulic adjusting piston, with which the valve disc of the valve that has to be operated is adjusted. The fast movement from the initial position to the final position of the valve takes place under the influence of hydraulic (high) pressure on one side of the adjusting piston. The high pressure medium flows towards the pressure side of the adjusting piston via a main that, in the initial position, is closed by the adjusting piston itself. The adjusting piston must therefore be moved across a very small initial distance in order to open this main.

This initial movement may take place with mechanical, electromagnetical and electrodynamical means because no (high) pressure is exerted on the two sides of the adjus¬ ting piston in the initial position and the adjusting piston can move freely to the extent that, in the case of movement from the initial position, no pressure build-up can occur by displacement of liquid as a result of said movement.

The initial movement is preferably achieved with hydraulic means under the influence of an electric signal to fast- working electrovalves with a small passage, in which, via a narrow auxiliary channel, pressure medium flows towards the pressure side of the adjusting piston. In the starting position, the pressure side of the adjusting piston is connected with low pressure, as a result of which a pos¬ sible leakage flow to said pressure side cannot lead to pressure build-up and unwanted movement of the adjusting piston.

With the device according to the invention it is possible to realize a double-acting embodiment by using a second adjusting piston, as a result of which the valve operated by the adjusting pistons will be able to open very quickly after a control signal as well as close very quickly after a control signal.

Claims 10 - 21 offer an application of the device for operating a gas valve for a combustion chamber, and the gas or supply valves and re-setting valves used therewith.

According to a second aspect of the invention, a method and a device for charging the combustion chamber of a free piston aggregate are provided, as described in claims 22 - 26.

With this aspect of the invention, a method and a device are provided with which the fresh air or gas supply to the combustion chamber is controlled. The method and the device are such, that the quantity of fresh gas and thus also the development of the pressure in the combustion cylinder can be operated and controlled remotely, for every stroke, by the control electronics.

The operation and control of the fresh gas flow towards the combustion cylinder takes place by means of a piston gas pump that is hydraulically driven with the same fre¬ quency as the free piston. The gas pump piston draws in fresh gas during the final part of the compression stroke of the free piston and/or during the initial part of the expansion stroke. Then, before the beginning of the next compression stroke, the compression of the drawn-in fresh gas in the gas pump cylinder commences. The moment the delivery stroke of the gas piston begins is determined with a control signal from the control electronics to a fast-working hydraulic valve that admits pressure medium to the hydraulic piston that activates the pump piston.

The gas pump cylinder is connected to the combustion cylinder via a conduit in which a non-return gas valve or an operated gas valve are present. The non-return valve opens when the pressure in the gas pump cylinder is higher than the pressure in the combustion cylinder. In this case, the beginning of the delivery stroke of the gas pump piston is regulated in such a way that the non-return valve opens during the compression stroke of the free piston within a period of time beginning shortly before the exhaust ports of the combustion cylinder close until well before the end of the compression stroke of the com¬ bustion piston. In the case of an actuated gas valve to the combustion cylinder, the gas pressure in the gas pump cylinder can rise considerably higher than the pressure in the combustion cylinder before said valve is opened. The moment of opening is then determined by the control electronics. In this case too, however, the moment of opening will lie within the indicated period of time, since, when opening takes place well before the exhaust ports close, fresh air or fresh combustion gas will disap- pear through the exhaust ports without having been used, as a result. The gas from the gas pump reaches the combus¬ tion cylinder via a conduit that debouches in the head or in the cylinder wall of the combustion cylinder. The actuated gas valve is opened by an adjusting piston, as described before.

The moment the gas valve opens, the gas pump piston will usually still be moving and the delivery action will continue during the compression stroke of the combustion piston as well, with the advantage that the pressure difference at which fresh gas is supplied (and therewith the quantity of pressure energy needed for each stroke) can be as low as possible on average. The moment the delivery stroke of the gas pump commences and ends is principally determined by the operation of the hydraulically actuated valve that controls the supply and discharge to the hydraulic cylinder of the gas pump. By controlling the opening and closing times of this hydraulic valve and of the gas valve, the quantity of supplied fresh air or fresh combustion gas per stroke can be operated and controlled by the control electronics.

According to a third aspect of the invention, a free piston aggregate is provided such as described in the claims 27 - 53, and a release valve used therewith.

With this aspect of the invention, a specific embodiment is given of the liquid supply and discharge to the first and second displacement space on either side of the hydraulic compression piston of the free piston com¬ bination. It involves various conduit configurations with or without non-return valves and/or valves that can be quickly and remotely actuated, with which the movements of the free piston are controlled. Depending on the indicated configuration, specific advantages are attained leading to limitation of the occurring leakage loss and/or simplification of the embodiment. The attained simplification consists of a limitation of the number of valves and/or a limitation of the number of displacement spaces upto two at the least by integrating the energy and the compression piston, in addition to which the minimally required number of high pressure accumulators can be reduced to two in certain cases.

The embodiments have the advantage that leakage via rod and piston seals at the hydraulic compression piston is reduced as a result of the fact that the supply of hydraulic medium from spaces with high pressure via con¬ duits to the compression cylinder is prevented during the waiting period of the free piston near the lower dead centre with the aid of non-return valves and actuated valves in said conduits. This embodiment according to the invention has a great number of variants and examples of application. In one of the variants, the second displacement space is permanently connected to a space with a pressure that is as low as possible and said second displacement space is therefore never connected to a space with high pressure when the machine is working normally. However, in order to prevent too strong a spring-back of the free piston after the end of the expansion stroke, a new device is required for release of the pressure medium in the first displacement space as soon as the free piston comes to a standstill in the lower dead centre. In other variants a simplified embodiment is described in which the conduit to the first displacement space as well as the conduit to the second displacement space are provided with a fast-working actuated valve, as a result of which ports in the cylinder wall of the hydraulic compression cylinder are prevented, the interception of the free piston at the end of the expansion stroke is improved, the leakage via the piston and rod seals is reduced and a number of valves can be integrated into a compact combination of valves. Finally, an embodiment is described in which, under cer- tain circumstances, the third displacement space can be integrated with the first and second, while, for a number of embodiments, the number of hydraulic accumulators can be reduced from three to two as well.

The invention will be elucidated below on the basis of a number of figures.

Figure 1 shows a known embodiment of a hydraulic free piston aggregate;

figure 2 shows a single-acting valve actuation with one adjusting piston;

figure 3 shown a double-acting valve actuation with two adjusting pistons;

figure 4 shows a valve actuation with an auxiliary adjus- ting piston;

figure 5 shows a charging of the combustion part of a free piston aggregate with a separate hydraulically driven piston gas pump;

figure 6 shows embodiments of an actuated gas valve in the head or wall of the combustion cylinder;

figure 7 shows embodiments of the supply and discharge of hydraulic medium to the hydraulic compression cylinder of the free piston aggregate;

figure 8 shows a release device for pressure medium in the first and third displacement space of the free piston aggregate,*

figure 9 shows an embodiment with two actuated valves to the hydraulic compression cylinder of the free piston aggregate;

figure 10 shows an embodiment with upto two integrated displacement spaces and upto two integrated accumulators.

Figure 1 shows a known hydraulic free piston engine or free piston aggregate. The way it works is described below. The combustion piston 7 moves within the combustion cylinder 15, which combustion piston 7 is connected via rod 35 to the hydraulic piston 8 and to the plunger 9. The piston 8 moves within a cylinder 17 and, therewith, forms the first displacement space 1 (with pressure Ptc) and the second displacement space 2 (with pressure Pec) . The left- hand annular piston surface of piston 8 is smaller than the right-hand annular piston surface. Together with the plunger cylinder 18, the plunger 9 forms the third displacement space 3. The combustion engine portion especially comprises the combustion cylinder 15 and the combustion piston 7 and acts as a two-stroke combustion engine with exhaust- 13 and inlet-channel 14. During the expansion stroke (the movement to the right) , hydraulic medium is forced from space 1 into high pressure compres- sion accumulator 4 in which the pressure Pea prevails. The supply into accumulator 4 first goes mainly via the wide channel 19 and, after it has been closed by the piston 8, via non-return valve 11. Liquid is also forced from space

3 (with pressure Pac) into the high pressure accumulator 5, in which pressure Paa prevails, via non-return valves

32 and 30. Liquid under high pressure Pea is also supplied from accumulator 4 to displacement space 2 via channel 10. By supplying energy to accumulator 4 and 5, the piston 8 comes to a standstill in the lower dead centre (LDC) at the end of the expansion stroke. In order to start the compression stroke (movement to the left) , the valve 12 must open. The time that passes from the moment the free piston comes to a standstill in the LDC and the moment the starting valve 12 opens and the compressions stroke com- mences, is the waiting period of the free piston. This waiting period is controlled with starting valve 12, and thus the stroke frequency of the free piston is also determined, as well as the quantity of pressurized oil produced per unit of time.

After the starting valve 12 has been opened the compressi¬ on stroke commences, during which the pressure medium flows with high pressure from the compression accumulator

4 to space 1 and with low pressure P_L from the low pressure accumulator 6 to space 3. At the same time, liquid flows from the second displacement space 2 into compression ac¬ cumulator 4. During the movement to the left the piston plunger combination is slowed down by the compressed gases in the combustion cylinder 15 and finally comes to a standstill in the upper dead centre (UDC) , i.e. the left¬ most position. Just before the UDC is reached, combustion commences and the pressure within the combustion cylinder very quickly rises.

The free piston starts the expansion stroke and subse¬ quently comes to a standstill in the LDC. At this moment liquid under high pressure is still present in space 1 and space 3.

Owing to the elasticity of the liquid, the free piston rebounds to the left even before the starting valve 12 opens. During this movement to the left a counterforce is experienced, however, under the influence of the pressure Ptc in the second displacement space 2 that is connected to the accumulator 4. Owing to this counterforce, the free piston comes to a standstill again within a very short period of time, even before channel 19 is released by the piston 8. Subsequently, the free piston moves to the left again, until the pressure in space 1 has risen so much that the piston comes to a standstill. In this way the free piston oscillates with diminishing amplitude near the LDC and finally comes to a complete standstill, especially as a result of frictional losses. The high pressure in space 2 is necessary in order to prevent the free piston, under the influence of the elasticity of the oil in space 1 and 3, from rebounding too far upto past the port of channel 19, as a result of which an unwanted new stroke is made and the operation can no longer be controlled with starting valve 12.

In this embodiment of the free piston engine, space 2 is under high pressure during the waiting period and oil will leak via the rod seal 16. Here, it is difficult to seal properly because of the varying temperatures caused by the proximity of the hot combustion piston to which rod 25 is attached. The combination of varying temperatures, extremely high piston speed and high pressure is undesired from a viewpoint of limitation of leakage losses. During the waiting period, leakage also occurs from ac¬ cumulator 4 via channel 19 along the seal between piston 8 and the cylinder wall. Differences in temperature occur less frequently here, but there is a longer leakage gap, however, owing to the larger diameter of piston 8.

Figure 2a shows the basic embodiment of the movement device according to the invention. The adjusting piston 51 moves within cylinder 72. This adjusting piston 51, in the depicted first position or initial position, closes the main 59 in the wall of the cylinder. The piston or plunger combination 51 (figure 2b), together with the cylinder 72, forms a first displacement space 61 and a second displace¬ ment space 79. The piston or plunger combination can move towards the second, most right-hand position and, via rod 28, moves the mass M that mainly consists of a valve slide or valve of an air- or hydraulic piston or a gas valve.

In the first position of the adjusting piston 51 the first displacement space is connected to low pressure P_L. The second displacement space 79 is also connected to low pressure P_L via a large channel 72a. The main 59 is under high pressure Ph. The adjusting piston 51 can move from the first position without pressure build-up by displacing hydraulic medium in space 79. After a small first or initial movement to the right the adjusting piston 51 opens the main channel 59, causing hydraulic medium under high pressure to flow in and causing the adjusting piston 51 or the plungers 51 with the mass M to move to the second end position very quickly. The means for generating the initial movement are described in the figure descrip¬ tion and at figures 2c - 2e, as well as the means to move the adjusting piston back to the first position again.

Figure 2 shows a drawing of the movement device according to the invention, which is used for operating a hydraulic valve 96. To this end, the valve 96, which may serve as starting valve 12 of the free piston aggregate, is operated by the fast-working adjusting piston 51 that moves under the influence of a medium under high pressure that flows in via electrovalve 74 in auxiliary channel 56 and via main 59 that is opened by the adjusting piston 51. In the initial position valve 96 is closed. Via re-setting valve 68 the main 59 (with large passage) is under high pressure Ph and auxiliary channel 56 is connected to low pressure Pi via actuating valve 73. The adjusting piston 51 does not start moving because space 61 is under low pressure and main 59 is closed off and the very slight hydraulic imbalance is compensated by the left seating seal with spring 58.

As soon as the control electronics close off the electri¬ cally operated actuating valve 73 and open actuating valve 74, space 61 is pressurized, causing the adjusting piston 51 to move and, subsequently, main 59 to open, after which a fast movement to the right takes place and valve 96 opens.

Under the influence of the pressure difference between Px and Py, which pressures may be deduced from the present pressures in the free piston aggregate, the re-setting valve 68 switches and moves to the left. For Px a choice can be made out of Pea, Pec or Pec, to be combined with

P_τc, Pea and Pec, respectively for Py. In this case Px-Py will first become negative during the compression stroke

(68 switches to the left) while Px-Py will become positive (68 switches to the right) at the end of said stroke and during the expansion stroke. In the left position of valve 68 the main 59 will come under low pressure, after which the adjusting piston 51, under the spring force of spring 83, moves to the left and closes the valve 96. The star- ting valve 96 is now closed again.

Meanwhile, the control electronics have closed actuating valve 74 and opened 73, causing space 61 to be connected to low pressure.

At a certain moment in time, the pressure difference Px-Py reverses its sign, as a result of which re-setting valve 68 switches to the right. Main 59 will now be under high pressure again and the initial position has been reached again.

In figure 2c, the possibility of channels to the high pressure level Ph and the low pressure level PI are also indicated on the righthand side in cylinder 71, with small non-return valves 115 and 116 in said channels. If neces¬ sary, these serve to decelerate the adjusting piston 51 that moves quickly to the right, by means of pressure build-up in space 79 during the final part of the stroke to the right of adjusting piston 51.

The valve operation according to figure 2c brings about a fast-working and electrically controllable valve adjust¬ ment, in which use can be made of small and very fast-wor¬ king electrovalves (73, 74), which may be obtained on the market, and of standard sliding valves (96) .

In figure 2d the initial movement is brought about mecha¬ nically with the aid of a short, powerful current surge through coil 128, as a result of which, via the pin con¬ nected to the coil cup 128, a force is exerted to the right on the adjusting piston 51. The moment port 47 is closed, the port to channel 59 is opened. The non-return valve 59a, to be mounted if necessary, makes it possible to close port 47 slightly earlier, as a result of which the possibility of a brief leakage from channel 59 via space 61 into port 47 and to low pressure P_L in space 79 is prevented or greatly reduced. After channel 59 has been switched back to low pressure via the (non-depicted) re¬ setting valve 68, the adjusting piston moves to the left again under the influence of spring 55. The port to chan¬ nel 59 closes first or simultaneously with port 47. If channel 59 should close slightly earlier, the remaining kenetic energy is converted to throttling heat via the leakage gap at channel 59.

In figure 2e port 72a is connected to the pressure Pac in the third displacement space 3 of the energy cylinder of the free piston aggregate and channel 59 is connected to the pressure Paa in the energy accumulator 5. During the waiting period of the free piston in the expansion positi¬ on and during the compression stroke, the pressure Pac is lower than Paa. The adjusting piston 51 can then open valve 96 and, under the influence of the pressure diffe- rence Paa-Pac, will remain in the second position. After the expansion stroke has commenced, Pac rises to a level that is equal to or higher than Paa, as a result of which the adjusting piston, owing to the spring force and the slight pressure difference present, moves back to the first position during the expansion stroke. The time that is required for this back-movement can be influenced by the spring force and possibly by a resistance with, para¬ llel thereto, a non-return valve in channel 59 in order to achieve that valve 96 closes shortly before the end of the expansion stroke and, before that moment, maintains a large passage from the first displacement space 1 to the compression accumulator 4.

In the double-acting movement device according to the invention of figure 3, the valve actuating rod 28 is operated by two adjusting pistons 51 and 52. The opening of valve 96 takes place by adjusting piston 51 in a way that corresponds with the one described at figure 2c. After the starting valve has been opened, the adjusting piston 51 opens channel 63 and brings it into connection with the pressure Ph in adjusting cylinder 71, causing re¬ setting valve 68 to switch to the right, counter to the spring force of spring 67. By switching the re-setting valve 68, channel 59 and thus also 63 will be put under low pressure and main 60 under high pressure. The spring 67 cannot switch valve 68 to the left, however, because non-return valve 65, bridged by the pre-stressed non¬ return valve 66, prevents it from doing so. The pressure required to open 66 cannnot be generated by spring 67. Owing to the pressure in main 60, the adjusting piston 52 can now move to the left after an electric command from the control electronics of the free piston aggregate, closing electrovalve 73 and opening 76. Valve 96 will now close. This closing takes place by adjusting piston 52 in a way that corresponds with the one described for adjus¬ ting piston 51. As soon as valve 96 (which may serve as starting valve 12) is closed, the adjusting piston 52 connects channel 64 to the space 62 under high pressure. Re-setting valve 68 switches to the left, as a result of which the initial position is reached again.

Figure 4 indicates how, in the case of a heavy adjusting piston and the mass moved by it, the speed of response of the adjusting piston 51 can be increased by means of an auxiliary adjusting piston 51a. It works as follows.

After the actuating valve 74 has been opened, space 61 will be pressurized. The actuating valve switches very quickly, but has a very small passage, which decelerates a quick start of the relatively large adjusting piston 51. Therefore the auxiliary adjusting piston 51a is present, which, owing to its small mass, low spring force of spring 83a and small piston surface, can move to the left more quickly, opening channel 59a in the process, which has a larger passage than actuating valve 74. Owing to this larger passage to space 61, the adjusting piston 61 can now also move more quickly and open main 59. When the adjusting piston 51 moves back under the influence of low pressure in space 61, the auxiliary adjusting piston 51a returns to its initial position under the influence of the spring force of spring 83a.

Figures 5a-d depict the free piston engine of figure 1 with the charging device.

In figures 5a and 5b the gas supply channel 46 debouches in the head of the combustion cylinder, but channel 46 can also debouch in the wall of the combustion cylinder 15 and be closed off there by the combustion piston 7. This embodiment of figures 5c and d entails that the closing of the gas supply from pressure space 137 is now attended to by the combustion piston. This ensures guaranteed, extre¬ mely fast closing. The supply valve 45 is embodied as an actuated valve 45a (figure 5c) or as a non-return valve 45 (figure 5d) and can now close much more slowly during the period of time that passes from the moment the combustion piston closes off channel 27 until the moment the combus¬ tion piston re-opens channel 27 during expansion.

The exhaust port 13 of the combustion cylinder is also indicated. Port 46, with non-return valve 45 or actuated valve 45a, is connected via channel 44 to the charging cylinder 42 within which the scavenging piston 128 moves. This piston 128 is connected via rod 119 to the hydraulic piston 121 which moves within the hydraulic cylinder 127. Via fast-working and remotely operable valves 123, 124 or the valves 123 - 126, the spaces 120, 122 may be connected to high or low pressure. Air supply to the charging cylinder 137 takes place via the channel with non-return valve 41, in which the valve 41 is an operated valve or a non-return valve.

The charging device works as follows. Proceeding from the depicted initial position with the combustion piston 2 in the lower dead centre (LDC) , the combustion piston 7 moves to the left and compresses the gas in cylinder 15 as soon as the exhaust port 13 is closed by the piston 7. Before the moment the combustion piston 7 commences the compres¬ sion stroke starting from the LDC, the supply of hydraulic medium under high pressure to the hydraulic cylinder 127 is opened, under the influence of which the scavenging piston 128 moves upwards. The scavenging piston 128 can generally compress the gas in the scavenging cylinder faster than the combustion piston 7 compresses the gas in the combustion cylinder, because, among other things, the scavenging piston is comparatively much lighter and/or makes a shorter stroke. As a result of this and of a commencement of the scavenging piston before the beginning of the compression stroke of the combustion piston, the gas pressure in the scavenging cylinder 137 can be higher than the gas pressure in the combustion cylinder 15 at the beginning of the compression stroke, causing gas to flow from the scavenging or charging cylinder 137 via non¬ return valve 45 into the combustion cylinder 15. This gas supply is ended shortly after the scavenging piston has reached the end of its stroke or by the fact that the scavenging piston is brought to a standstill by the clo¬ sing of the supply of hydraulic medium to cylinder 127 with the aid of the hydraulic valves present. Subsequent¬ ly, the combustion piston 7 continues its movement to the left until the upper dead centre (UDC) is reached.

The scavenging piston must commence its movement to the left before the combustion piston has started its own movement to the left. As a result, the very moment the combustion piston commences there will be an over-pressure present in the scavenging cylinder and gas will flow to combustion cylinder 15 via channel 44, 46. This flow of gas subsequently increases as a result of the quickly rising gas pressure in the scavenging cylinder. After the supply of hydraulic pressure medium into cylinder 127 has stopped, the speed of the scavenging piston will quickly drop to zero, causing the pressure difference between scavenging and combustion cylinder to decrease as well. As a result of the fact that the combustion piston 7 con¬ tinues moving upwards, the pressure in the combustion cylinder continues to rise, initially resulting in an equilibrium of pressure, followed by an over-pressure in the combustion cylinder. Non-return valve 45 will now close. Subsequently, the scavenging piston 128, under the influence of the remaining gas pressure in the scavenging cylinder 137 and as a result of the pressure of hydraulic medium in the space above the hydraulic piston 128, will move downwards, in the course of which the pressure in the scavenging cylinder 137 decreases and, finally, air or gas is drawn in via non-return valve 41 and air filter 118, until the scavenging piston reaches the initial position again. The important aspect of this device is the pos¬ sibility to control the amount of supplied air or gas via channel 46 by letting the movement of the scavenging piston to the left take place sooner or later. When the scavenging piston starts comparatively long before the combustion piston does, an over-pressure will already have built up in the scavenging cylinder the moment the combus¬ tion piston commences and gas will already flow into the combustion cylinder. Owing to the fact that, generally speaking, the exhaust port 13 is still open here, the supplied air from the scavenging cylinder will be able to leave the combustion cylinder again via the exhaust port. This is, of course, effective scavenging. After the ex¬ haust port has been closed, the remaining volume of air in the scavenging cylinder will be fed under low pressure into the combustion cylinder and participate in the com¬ bustion process. When the scavenging piston commences later, at a moment in time chosen in such a way that the supply of gas is just commencing via conduit 46 the moment the combustion piston closes off the exhaust port, all the air supplied from the scavenging cylinder will be used for charging. If commencement takes place at an even later moment in time, the charging will diminish because the pressure in the combustion cylinder at which supply from the scavenging cylinder takes place, is higher. The degree and nature of the charging can therefore be remotely controlled by the control electronics, in addition to which the early start may also result in a comparatively big charging.

By using an actuating valve 45a in the head or wall of the combustion cylinder, the operation and control of the fresh gas filling of said cylinder is enhanced even fur¬ ther. The actuated gas valve makes it possible to start the charging piston sooner and to build up the pressure in the pump cylinder 137 further, until approximately the moment the exhaust port 13 closes and the gas valve opens. The greater pressure difference between pump cylinder 137 and combustion cylinder 15 will cause the fresh gas to flow to the combustion space more quickly and more gas to be supplied during the very short period of time of 5 - 10 m.sec. that is available therefor. On the other hand, said greater pressure difference increases the amount of energy that is required for the charging by the required higher end pressure. The opening and closing times of the hydrau¬ lic valves 123 - 126 and the gas valve 45a must therefore be optimized by the control electronics in order to attain a mimimal energy demand for each desired air addition via channel 46. This is possible with the charging device according to the invention.

For the control of the movement of the charging piston 128, the hydraulic valves 123 - 126 are used. The hydrau¬ lic piston 121 can also be embodied as a single-acting or double-acting adjusting piston 51 and 52, just like those in figures 2c, 3, 6g of 6i. The valves 123 and 124 can be embodied as a three-way valve that is moved by a double- or single-acting adjusting piston or as two open-close valves that are operated by a single-acting adjusting piston 51. The charging piston 128 can also be controlled by a four- way valve moved by a single- or double-acting adjusting piston as described at figures 2, 3, 6g or 6i, for instance.

The charging device according to the invention can also be used for the supply of fuel. To this end, fuel is injected on the places indicated with a triangle. Injection im¬ mediately into the combustion cylinder is possible too, of course. Injection of fuel into the charging part has the advantage that more time is available for evaporation and mixing before the fuel reaches the combustion cylinder as an air-fuel mixture, together with the charging air.

Figure 6a shows an embodiment of the supply valve 45a that is to be mounted into the wall of the cylinder. One objec¬ tion here is the present space 46 in which air or gas remains behind that is brought into contact with the burning gas mixture in the combustion cylinder during the expansion stroke. The volume 46 causes a small pressure drop in the combustion cylinder as soon as the port in the cylinder wall is opened. This pressure drop decreases the energetic efficiency of the machine.

When combustible gas is fed in from the first pressure space, the dead volume of gas 46 will not participate in the combustion cycle, as a result of which the fuel effi¬ ciency of the machine will decrease further.

It is therefore important to make the dead volume 46 as small as possible.

Figure 6b shows an embodiment of the supply valve 45a with a very small dead volume. When gas pressure is present in the combustion cylinder during the second part of the expansion stroke, the valve may not open and must then be kept closed by a considerable force on valve stem 28. Figure 63 shows an embodiment of the supply valve 45a with a minimal dead volume, a passage that is as large as possible and a light valve disc 45a. Here, the valve disc is a ring or band around the outer wall 38 of the cylinder, in which the wall is provided with holes 46 all around, which holes are opened or closed by rotation of the valve disc 45. To this end the valve disc, too, is provided with holes 36 that correspond with the holes 46 in the cylinder wall 38 when the valve is open. The rotation of the valve disc is made possible on account of the fact that it is provided with a cam 37 to which the operating rod 28 is attached. By moving the rod 28 back and forth, the valve disc is rotated.

If there is a ring 45a, it must consist of two parts that are connected to each other after they have been placed in a slot around the combustion cylinder. If a band is used, it must have a joint that is bridged by spring tension or by a fixed connection.

Figure 6d shows how the band-shaped valve disc can be locked up between two annular sealing surfaces 38 and 39. The divided band can now have a light-weight construction and will be able to contact the outer sealing area 39 when there is pressure in the combustion space, and be able to contact the inner sealing area 38 when there is pressure from outside the combustion cylinder (in the pressure space that encloses the outer side of the combustion cylinder here) . The surface 39 has holes 35 that corres- pond with the holes 46.

Figures 6e - 6i relate to the hydraulic valve control. The supply valve 45a can also be operated mechanically in a way that is customary for crankshaft combustion enginges, with rotary cams, the movement being transferred to the valve disc mechanically or hydraulically. Owing to the very fast opening and closing on account of the very short period of time of 5 - 10 msec that are available for the total charging period, valve operating times of a few milliseconds are necessary here. Major forces occur as a result, which preferably should be generated by hydrau- lically operated adjusting cylinders. The fast movements do call for comparatively large adjusting pistons, high hydraulic pressures, large passages, while electric or mechanical control valves are necessary that are light to operate and work fast.

These combined requirements can be better met when the valve controls according to the invention, described in the following, is used. The valve controls in figures 6e and 6f are, on account of the constructive adaptation and the necessary fast opening and fast closing, rather meant to be mounted in the upper area of the cylinder head, while the figures 6g - 6i show valve controls that are more suitable for valves that are placed in the wall of the combustion cylinder.

Figures 6e and 6f show the usual embodiment of a spring- loaded sealing gas valve in the head of the combustion cylinder. The valve stem 28 is moved by two adjusting pistons 51 and 52, in a way as described at figure 3. In the depicted closed position in figure 6e, no resulting force is exerted on the first adjusting piston by the medium in space 61. In this embodiment, the opening of the valve is commenced with the aid of the fast little elec- trovalves 73 and 74. Via the large main 59, the pressure medium can now flow in, on account of which the first adjusting piston 51 opens the valve 45a with considerable force and high speed. When this movement to the right takes place, the liquid escapes from the second displacement space 62, via the second main 60 and subse- quently via the re-setting valve 68 into a space with low pressure P_L. At the same time liquid with low pressure P_L flows via channel 70 into the displacement space 53 of holding cylinder 89.

As soon as the first adjusting piston 51 has reached the open position or second end position, the following takes place. Channel 63 is connected to the first displacement space 61 with high pressure by the first adjusting piston, while channel 64 is connected to the space 79 with low pressure by the second adjusting piston 52. This will cause the re-setting valve 68 to move quickly to the right. As a result, the pressure in the first displacement space 61 decreases via main 59 and the pressure in the second displacement space 62 increases via main 60 and the pressure in the displacement space 53 of the holding cylinder 89 increases via channel 70.

In this second end position, the second displacement space 62 is connected via auxiliary channel 57 to low pressure and the connection between main 60 and the second displacement space is closed off by the second adjusting piston as well. The valve disc 1 is now kept open by the pressure in the holding cylinder 89, opposing the spring force of spring 55, while the first and second displacement spaces are connected to low pressure and the first and second adjusting piston do not exert a resulting force on the valve disc 1.

Owing to the fact that channels 63 and 64 are now con¬ nected to the pressure-free spaces 61 and 79, re-setting valve 68 would be able to spontaneously switch back to the left position under the influence of spring 67. The non¬ return valve 66 through which the through-flow must take place is spring-loaded, however, and the power of spring 67 is not large enough to open the non-return valve 66.

A stable open or second position of the supply valve 1 is obtained with this. The closing of the supply valve is subsequently started with the aid of electrovalves 73 and 76. Valve 73 is closed first, after which 76 is opened. This causes main 60 to be opened by the second adjusting piston 52, after which the valve disc moves to the left with great force and speed. When the closed position is reached, channel 64 is connected to the high pressure in the second displacement space 62, while channel 63 is connected to the low pressure in space 79 via non-return valve 66. The re-setting valve 68 switches to the left as a result and the initial position is reached again.

Figure 6f shows an embodiment with a small first adjusting piston 51 and a larger second adjusting piston 52. The first displacement space 61 is brought under pressure by closing valve 73 and then opening valve 74, starting from the position depicted in the drawing. The first adjusting piston starts off the initial movement to the right and, after a slight displacement, opens the main 59 after which the first adjusting piston quickly reaches the second end position. When this open position of the supply valve 1 is reached, channel 63 is connected to the high pressure in displacement space 61 and channel 64 is connected to the low pressure in space 79, causing the re-setting valve 68 to switch to the right. Main channel 60 is now brought under high pressure, so that after the closing of valve 75 and the opening of valve 76 the closing movement of supply valve 1 will commence. The permanent high pressure in displacement space 61 and the force to the right that the first adjusting piston continues to exert are unable to prevent the closing movement from taking place because the piston surface of the second adjusting piston 52 is larger than the surface of 51.

When the closed position is reached, channel 64 is brought under pressure and channel 63 is connected to the low pressure space 79, causing the re-setting valve 68 to switch to the left and return to the depicted position. Valve 73 is open then, and 74 is closed so that a stable closed position of the supply valve 1 is attained.

The embodiment according to figure 6f has a disadvantage as compared to that of figure 6e in that there is a larger adjusting cylinder and it has the advantage that there is a simpler re-setting valve and no holding piston.

Figure 6g shows an embodiment that corresponds to the embodiment of figure 6e as far as its operation is con¬ cerned. In this case there is no holding piston 89 because the band or ring-shaped valve member 1 stays in any position when the operating force is cut off. Another difference is the operation of the re-setting valve 68. Here, the re-setting valve is operated by pressure dif¬ ferences that occur in the displacement spaces of a free piston aggregate. Operation as indicated in figure 6e is possible here as well, however.

As far as the operating pressures indicated in figure 6g for the re-setting valve 68 are concerned, i.e. Ptc, Pea, Pec, the following serves to elucidate. In figure 1 of the free piston aggregate, 2 is the back pressure cylinder with the pressure Ptc, 1 is the compression cylinder with the pressure Pec and 4 is the energy cylinder with the pressure Pac. The pressures in the pressure accumulators 4, 5 and 6 are: Pea, Paa and P_L. During the compression stroke (the movement to the left) liquid is forced through pipe 10 to the accumulator 4. The pressure Ptc is therefore higher than Pea in accumulator 4. For Pec the reverse holds during the compression stroke: Pec is lower than Pea. During the expansion stroke the following ap¬ plies: Pec is larger than Ptc and Ptc is smaller than Pea and Pac is larger than Paa. The pressure differences Ptc- Pca and Pea-Pec and Ptc-Pec are positive during the compression stroke and negative during the expansion stroke. By connecting these pressures to points Px and Py, the re-setting valve 68 in figure 6g will therefore switch to the right during the compression stroke and to the left during the expansion stroke. The speed-dependent component of these pressure differences is largest in the second half of the compression stroke and the first half of the expansion stroke because the piston speeds are highest then. When choosing the connecting points of x and y on the conduit system of the free piston, the speed and ac- celerating component in the pressure difference must be taken into account in order to be able to use them op¬ timally.

The pre-stressed non-return valves 91 and 92 that do not open until a certain pre-pressure has been reached, ensure that valve 68 does not switch until the pressure dif¬ ference Px-Py has reached a certain threshold value.

Figure 6h shows a valve embodiment with a very small dead space 46 in accordance with what is stated at figure 6.

During the second half of the expansion stroke there is rather high gas pressure in the combustion cylinder. Valve

45a may not open then and counterforce cylinder 80 is present to ensure this, exerting a permanent force to the right that is large enough to keep valve 45a closed during the second part of the expansion stroke. This permanent force could also be exerted by a strong spring, for that matter, which spring would have to be strong enough to ensure that the valve 45a cannot be opened under the influence of the pressure of the gas medium.

In this embodiment only a first adjusting piston 51 is present that is larger than the counterforce piston 81 and can therefore quickly open the adjusting piston (opposing the action of the counterforce piston) in accordance with the procedure described above. In the open position of valve 1 oil flows under high pressure via channel 65 to the operating cylinder of the non-return valve 68, which will switch to the right as a result. This will cause the pressure in the main 59 and in the first displacement space 61 to fall out. The first adjusting piston will now move to the right (to the closed position) under the influence of the counterforce piston 81. In order to prevent too fast a closing, an adjustable restriction 84 might be necessary that slows down the flow into counterforce cylinder 80.

In this embodiment the re-setting valve 68 may also be operated by pressure differences that occur in the free piston aggregate as described at figure 6g. In that case, non-return valve 82 and the adjustable restriction 84 are unnecessary and the conduits 65 and 87 are left out. Valve 1 will open quickly and will not close until re-setting valve 68 has been switched by the external pressures Pec, Ptc and Pea.

Figure 6i shows an embodiment in which, just as in figure 6h, only a first adjusting piston 51 is present to quickly open the band-shaped supply valve 1, also indicated in figure 6d.

Starting from the position in the drawing, first the electrovalve 73 will close and electrovalve 74 will open. High-pressure oil now flows through the auxiliary channel 56 to the first displacement space 61. Piston 51 commences the movement to the right and opens main 59. The supply valve 1 will now open quickly, during which holes 46, 36 and 35 correspond with one another. In the open position channel 63 is opened by the first adjusting piston 51. Oil under high pressure flows via non-return valve 65 to the operating cylinder of the re-setting valve 68. This valve now switches to the right, causing channel 97 to be brought under pressure and piston 98 and the first adjus- ting piston 51 to move to the left. If necessary, this movement is slowed down by the adjustable restriction 95 that is bridged by non-return valve 96 (for the purpose of quickly opening the supply valve 1) .

When the closed position is reached, channel 64 is con¬ nected to high pressure by piston 98, causing the adjus¬ ting valve 68 to switch to the left. Electrovalve 74 had already closed when the open position was reached and 73 is opened before the closed position is reached so that the initial position is reached again.

Generally speaking, it can be said that the electrovalves 73 - 76 may also be replaced by mechanically operated valves that are moved by a rotary cam. This also holds for the re-setting valves 68 that can be switched either mechanically via a rotary cam or electrically or with the aid of the pressures occurring in the free piston ag¬ gregate or by opening and closing the ports in the adjus- ting cylinders. The described control of the supply valve 45a with the aid of a first and/or second adjusting piston can also be used for controlling other gas or liquid valves or valves that form a part of known crank shaft or free piston engines. In this way, the control in figures 6e and 6f, for instance, can also be used for the electrohydraulic operation of inlet and exhaust valves of known two-stroke and four-stroke engines. The valves can then be opened and/or closed very quickly and be controlled by the electronics, the camshaft being left out. In many instances in which the actuated valves open near the lower dead centre and close before the end of the expansion stroke, one re-setting valve can operate several adjusting cylinders.

In view of the high valve speeds, buffering may be neces¬ sary. To that end, figure 6j shows the known pos¬ sibilities. 140 and 146 are restrictions that are adjus- table or not

As indicated above, use may also be made of a gas non¬ return valve 45 in channel 44 to cylinder 15. In that case closing takes place slowly via a spring and for those reasons valve 45 is preferably placed in the wall of the combustion cylinder. A closing time then runs from the moment the combustion piston port in the cylinder wall closes off until the moment said piston re-opens the port.

It is an object of the invention to reduce the occurring leakage losses by means of a specific control of the flows of liquid to the hydraulic compression cylinder 17 and also to keep the spring-back of the free piston small. A first embodiment thereof is shown in figure 7a, in which the dotted line indicates the non-return valve 107. This valve offers passage to compression accumulator 4 via the port in the cylinder wall and channel 19, but prevents the flow of liquid from accumulator 4 to the port in the cylinder wall and, therewith, leakage via the piston sealing to the first displacement space 1. In this em¬ bodiment according to the invention, the liquid, during the entire compression stroke, will only be able to flow to the first displacement space via the starting valve 12. To that end, starting valve 12 must be dimensioned more largely and may not close until after the UDC. At the description of the valve embodiments there is an in¬ dication as to how such a valve may be realized.

Figure 7a also shows a drawing of a second embodiment according to the invention. In the drawing the combustion portion has been left out because, in figure 7a and those following, it is the same as the one in figure 1.

In this second embodiment the second displacement space is connected to accumulator 4 via channel 10. In channel 10 a non-return valve 26 is accommodated that only offers passage to the accumulator, but that blocks the flow from the accumulator to the second displacement space and, therewith, also leakage loss via channel 10 and the rod seal 16.

The embodiment is also characterized by the connection between the first and second displacement space via chan¬ nel 29, in which a non-return valve 27 is accommodated that only offers passage in the direction of the second displacement space 2. Channel 29 connects the right part of space 1 with the left part of space 2 and has a connec¬ tion via channel 28 with a port in the wall of the hydraulic cylinder 17 that is closed by piston 8 during the final part of the expansion stroke and the first part of the compression stroke. (Channels 19 and 28 are not interconnected via the ports in the wall of the cylinder 77) . This embodiment works as follows.

At the end of the expansion stroke the free piston comes to a standstill. The piston 8 will spring back to the left under the influence of the compressibility of the volume of oil in spaces 1 and 3. Meanwhile, the piston undergoes a counterforce under the influence of the pressure in the second displacement space 2, which occurs as a result of the initial pressure and the rise in pressure caused by compression of the (rather large) volume of oil in space 2 during the spring-back, and channel 29 is closed by non¬ return valve 27 while channel 10 only offers passage when the pressure via valve 26 to accumulator 4 is high enough. Under the influence of the pressure build-up in space 2, the piston comes to a standstill and subsequently moves to the right. This movement to the right and leakage via rod seal 16 cause the pressure in space 2 to fall. After several oscillations of very small, declining amplitude, the free piston comes to a complete standstill, while the pressure in spaces 1, 2 and 3 drops below level Pea, depending on the leakage proportion between the gap seal of piston 8 and the rod seal 16.

A combination with the non-return valve 107 described above, will cause the leakage during the waiting periods to become low because, during said waiting period, both the high pressure accumulators 4 and 5 are closed and the pressure in the displacement spaces can fall to the minimum level P_L.

After opening the starting valve 12, the compression stroke commences and moves the free piston to the left. While doing so, the liquid in the second displacement space 2 is pressed to accumulator 4 under high pressure. As soon as the piston 8 opens the port of channel 28 in the wall of the cylinder 17, the liquid can flow from the second displacement space to the first displacement space via a large channel 28, 29. Therefore, in the presence of channel 28, non-return valve 27 may be small.

At the end of the expansion stroke, channel 28 is closed again by piston 8. At a further movement to the right, the liquid flows from space 1 into space 2 via non-return valve 27 until the piston comes to a standstill in the LDC.

The starting valve 12 can be embodied in accordance with figure 2. This valve is operated by an adjusting piston 51 in conformity with earlier descriptions. Here, valve 12 corresponds with the actuated valve 96 and is opened by means of a control signal from the control electronics of the free piston aggregate and must open quickly enough to be able to handle the increasing flow of oil to the first displacement space withouth great flow losses. Valve 96 is closed in the initial position of the free piston in the LDC. After the opening, the compression stroke commences. Under the influence of this pressure difference Ptc-Pcc that is created between points Px and Py of the re-setting valve 68 in figure 2c, for instance, valve 68 switches to the left, after which valve 96 closes. After the UDC, the pressure difference Ptc-Pea reverses the sign and switches 68 to the right, as a result of which the initial position is reached again.

Figure 7b shows an embodiment of the hydraulic portion of the free piston engine in which channel 28 as in figure 71 has been left out. The non-return valves 26 and 27 must have greater dimensions here. For the rest, the operation and the technical effect are comparable to the embodiment of figure 7a.

Figure 7c shows an embodiment of non-return valve 27, 30 or 11, in which the closing force of the valve may be enhanced hydraulically. To this end a piston 90 is pre¬ sent, which will exert a force onto valve disc 93 in the closing direction of the non-return valve when there is pressure difference over said piston. Space 98 is con- nected to the discharge channel 29 of the non-return valve. As long as space 104 is kept at the same pressure level as 98, only the valve spring provides the per¬ manently present closing force.

As soon as the pressure in space 104 is decreased with respect to that in space 98, an extra closing force develops. This extra closing force is necessary at valve 11 in those cases in which channel 19 has been left out for the sake of minimal leakage and at valve 27 if channel 28 has been left out. This device is also necessary for valve 30 if valve 32 has been left out. At two of the present discharge channels the second (smaller) valve may be provided with a heavy spring to prevent after-flow after the free piston has come to a standstill in the LDC. The enhancement of the closing force according to the invention therefore serves to achieve that the valves in question, notwithstanding the weak closing spring, never- theless close quickly after the free piston has come to a standstill in the LDC. To that end, the enhancement of the closing force is activated during the final part of the expansion stroke. The fast closing decreases the springing back of the free piston after the LDC because the pressure fall in spaces 1 and 3 commences earlier. Enhancement of the closing force according to the invention is a general¬ ly usable means for fast closing non-return valves with nevertheless little flow losses.

On account of the fact that, in the cases indicated, the non-return valve in question must handle the entire dis¬ charge from spaces 1 and 3, even at the highest speed of the free piston, and must therefore have a relatively large and heavy construction, the enhancement of the valve force is necessary in the indicated embodiments according to the invention. The activation of the enhancement of the closing force takes place by connecting space 99 to a level of low pressure with the aid of electrically or hydraulically operated valves or by connection to a point of the conduit system at which the development of the pressure already follows the desired pattern, as is described at figures 7f and 7g, for instance.

Figure 7d shows an embodiment of the hydraulic portion of the free piston engine in which space 2 is permanently connected to a pressure accumulator 33 in which there is a pressure Pm that is lower than Pea but high enough to prevent cavitation in space 2 during the expansion stroke. Owing to the fact that Pm is lower than Pea, the leakage via the rod seal 16 will decrease as well. At the same time, however, a stronger spring-back of the free piston with respect to the embodiment according to figure 1 will take place. In order to overcome this drawback, a release valve is suggested in the embodiments according to the invention, which release valve is described at figures 8a and 8b. Figure 7e shows an embodiment of the free piston aggregate according to the invention in which channel 19 (whether or not provided with non-return valve 107) of figures 1, 2, 3 and 4 has been left out. The advantage of leaving out channel 19 is that, during the waiting period of the free piston, leakage can no longer occur from the high pressure accumulator 4 via channel 19. In this embodiment, the flow of liquid from accumulator 4 takes place via starting valve 12 during the entire compression stroke. This valve 12 must therefore offer a large passage and may only close after the UDC. By subsequently closing the starting valve 12 shortly before the LDC is reached, a small non-return valve 11 may be used. In order to ensure that this is accomplished, the operation of valve 12 may for instance be carried out according to figure 3, in which the control electronics determine the exact closing time.

Figure 7f shows an embodiment in which both channel 19 and channel 28 have been left out. The statement at figure 7b applies here as well.

The enhancement of the closing force may be easily ob¬ tained here for valve 27, by connecting space 104 of figure 7c to main 60 of figure 3. On account of the fact that channel 60 is connected to low pressure during the closed position of the starting valve 12 and said closed position only occurs during the final part of the expan¬ sion stroke and during the waiting period, also the enhan¬ cement of the closing force will be active during said period.

Figure 7g shows an embodiment in which channels 19 and 28 have been left out and displacement space 2 is permanently connected to accumulator 105 with pressure Pm. It should be noted that the non-return valve 32 to accumulator 5 has been left out here too. This means that enhancement of closing force must be applied for valve 30. The control of the enhancement of the closing force may here be obtained by connecting space 104 of figure 7c to channel 94 of figure 7g with a port in the cylinder wall 17, or to main 60 of figure 3. Owing to the fact that channel 94 is only connected to the lower pressure Pm during the righthand position of the free piston, the hydraulic enhancement of the closing force is only active during that time.

Figure 8a shows a drawing of the signaller for a release valve 100 in figure 8b. This release valve is necessary because the pressure in displacement space 2 to Pm has been decreased, which may cause the spring-back of the free piston to increase too much. The signaller works as follows. Piston 90 is connected to the valve disc 93 of the non-return valve of figure 7c. The spring-mounted pin 106 breaks off the connection with piston 90 just before non-return valve 93 closes. The free piston then still moves to the LDC and will come to a standstill at a known period of time after pin 106 has broken off the contact with piston 90. Breaking off the contact with the pin 106 that has electrically insulated bearings entails the breaking of the electric contact of point 109 with mass. This results in an electric signal to the control electronics of the free piston engine. The control electronics convert this signal into a starting signal for the release valve, taking correction data, if any, into account. This starting signal arrives at exactly the right moment when, as a result of the opening of the release valve 100 on time, the liquid pressure in displacement spaces 1 and 3 has fallen to P_L the moment the piston comes to a standstill in the LDC. Spring-back no longer takes place then and the problems connected therewith stay away.

Figure 8b shows a diagram of the release valve 100. This valve is operated by an adjusting piston 51 and functions in accordance with the description for the starting valve of figure 2. In this case, however, valve 96 of the star- ting valve 96, present as well, is constructed in such a way that, simultaneously with the opening of the connec¬ tion between space 1 and the compression accumulator 4, the connection between channel 113 and low pressure P_L is interrupted and vice versa. As a result, the release valve 10 only has effect as along as starting valve 12 is closed and is put out of operation when valve 12 opens. In the case of the highest stroke frequency and a zero waiting period, the starting valve will open before the free piston reaches the LDC. The release valve will not be in operation then, but that is unnecessary in this situation anyhow, because the free piston has to start on the next compression stroke after it has reached the LDC.

In this embodiment, channel 59 in figure 8b can be con¬ nected to channel 59 of figures 2 or 3 or be operated by an electrovalve or another valve that connects 59 to a space of high or low pressure.

As far as the connection of space 1 and space 3 to the release valve 100 is concerned, it is necessary to accom¬ modate the non-return valves 111 and 112 in order to prevent an unwanted flow from space 1 to space 3 or vice versa from occurring.

In figure 9a an embodiment of a free piston aggregate with valve kl is given. It works as follows. In the depicted position the starting valve 12 and valve kl are closed and the free piston is located at the expansion-end position near the lower dead centre. In order to start the free piston 8, both the starting valve 12 and valve kl are opened. Pressure oil now flows via the starting valve into the first displacement space 1 and from the second displacement space 2 into the compression accumulator 4 via valve Kl. During the first part of the expansion or energy stroke to the right, pressure oil flows from the first displacement space 1 via the starting valve 12 and via non-return valve 11 into the compression accumulator 4, while pressure oil flows from the first displacement space l into the second displacement space via non-return valve 27. Shortly before the end of the expansion stroke (in the position indicated by the dotted line) valve kl and starting valve 12 are both closed.

During the subsequent final part of the expansion stroke, the hydraulic medium flows from the first displacement space 1 via non-return valve 11 into accumulator 4 and pressure medium flows from the first displacement space 1 via non-return valve 27 into the second displacement space 2 until the free piston 8 comes to a standstill in the lower dead centre.

The non-return valves 11 and 27 will now close and the initial position is reached again. When the free piston springs back to the left, the pressure in the second displacement space will rise, causing said spring-back to be very slight.

In embodiment 9b a valve kl is present in conduit 29. This valve is bridged by non-return valve 27. During the compression stroke of the free piston 8 less oil will now flow through the starting valve 12, as a result of which a smaller one may be used.

In figure 9c conduit 10 has been added to embodiment 9b again. This has been done for the purpose of preventing high rises in pressure in the first displacement space during the spring-back of the free piston. In order to decrease leakage when the piston is at a standstill, non¬ return valve 26 has been introduced.

In embodiments 9a and 9b starting valve 12 and valve kl must open simultaneously in order to ensure an immediate start. In embodiment 9c kl may open a bit later than 12. In all embodiments 9a - 9c kl may close a bit sooner or later than starting valve 12. In all embodiments 9a - 9c, 11 and 27 are small non-return valves with a relatively high closing force.

In figure 9d the embodiment of valves 12 and kl is given. These valves must open very quickly and also close at a rather specific moment in time and are controlled by a signal of little energy issued by the control electronics of the free piston aggregate. In order to meet these requirements and the requirement of a large passage, these valves may be operated as indicated in figure 3.

In figure 9d, which corresponds with figure 3, the adjus- ting piston operates a sliding or scavenging valve 132 that opens both the starting valve and kl in one position, and, in the other position, closes both the valves. In the embodiment that is in conformity with figures 9b and 9e, conduit 24 is connected to space 1, while conduit 29 is connected to space 2 and conduit 23 to accumulator 4. Valve 132 can also be moved by a single adjusting piston according to figure 2e.

In figure 9e the non-return valve 11 and the starting valve 12 are combined, while the non-return valves 27 and kl are combined as well. The operation of the adjusting pistons 51 and 52 is described at figure 6f. Operation in conformity with figure 6i and figure 2c is possible as well.

In figure 9f a single adjusting piston 51 is used that can press open the two non-return valves 11 and 27. The way the adjusting piston works is described at 2e. Here, pressure Paa must be larger than or equal to Pea.

In the embodiment according to 9f it is also possible to connect channel 59 to pressure Pea in accumulator 4 and 72a to pressure Pec in the first displacement space 1. In this case, as soon as pressure Pec in space 1 has risen until above the value Pea in accumulator 4 during the expansion stroke of the free piston after the non-return valve 11 has been opened, adjusting piston 51 will move to the left under the influence of the pressure difference Pcc-Pca and the spring force. After this, non-return valves 11 and 27 operate independently of the adjusting piston 51. These valves may be provided with a relatively strong closing spring that does not bring about any extra loss of pressure when said non-return valves are kept open by adjusting piston 51 until just before the end of the expansion stroke. A decelerated movement to the left of 51 may therefore be needed and, if necessary, is achieved with non-return valve 121 and the flow resistance 122. Actuation by means of adjustion piston 51 in conformity with figure 9f, as described here, may also be used, com¬ bined with only non-return valve 11 as starting valve, or combined with valves 96 and 136. When these movements with an adjusting piston 51 take place, 72a is always connected to the outlet of the actuated valve. The movement of non¬ return valve 11 on its own, or 11 and 27, may also be brought about with an actuation in conformity with figure 2c or 2d, while the re-setting valve 68, however, is operated via channels in the wall of the adjusting cylinder in accordance with the operation of re-setting valve 68 in figures 6h and 6i.

The yoke 142 that is moved by the adjusting pistons pushes both the non-return valves 11 and 27 open at the same time. After the closing movement of yoke 142 to the left has taken place, valves 11 and 27 work as normal non¬ return valves, offering passage from space 1 via conduit 24 into accumulator 4 via conduit 23 and into space 2 via conduit 29, respectively. The combined valve in figure 9e holds all the valves shown in figures 9b and 9c. The non¬ return valves 11 and 27 may also be placed one after the other and as shown in figure 9f.

Figures 10a - 10c show embodiments in which the third and second displacement spaces are integrated. The supply to the energy accumulator 5 takes place from space 2 via non¬ return valve 30, except in figure 10c. In embodiment 10a the low pressure accumulator 6 and the compression ac¬ cumulator 4 are integrated as well. In embodiment 10c the energy and compression accumulators are integrated. All this will result in low-leakage embodiments according to the invention, which are relatively simple but do have the disadvantage that the lowest pressure level (which was P_L at first) will end up being higher and the pressure variations in the energy accumulator 5 should be small by preference or necessity. For some applications this need not be a problem, however.

In figure 10a, which has been derived from the embodiment according to figures 7a and 7b, liquid is pressed into the energy accumulator 5 during the compression stroke with a pressure Paa that is higher than Pea. The compression pressure Pea is the lowest system pressure and is kept as low as possible by giving piston 8 a relatively large diameter. The energy supplied from accumulator 4 to the free piston, less the hydraulic energy given out at ac¬ cumulator 5, is available for the gas compression. At the expansion stroke all the energy given out by the combus¬ tion gases to the free piston is supplied to the compres¬ sion accumulator 4. The energy users are connected between Paa and Pea. The pressures Pea and Paa are basically constant. However, Paa may be increased by supplying liquid to 5 at an increased pressure Paa during a part of the compression stroke and by supplying liquid to 4 during the remaining part of the stroke. This can be done with the aid of a short-circuit conduit 38 with a cut-off valve. This conduit is indicated in the figure by means of the dotted line. When the cut-off valve is open, the increased pressure in 5 is attainable.

The embodiments 10b and 10c have been derived from those in figures 7b and 7d. The free piston engine pumps liquid from the medium pressure accumulator with pressure Pm (the lowest system pressure here) into the energy accumulator 5 or into the integrated accumulator 4/5.

In embodiment 10b, Pea is lower than Paa. In 10c, Paa and Pea are equal and high. The pressure ratios are determined by the difference between the left- and righthand piston surface of piston 8. Pressure Pm is so high that cavitati- on in the second displacement space still cannot take place during the expansion stroke. The pressure level Paa is basically constant but may be increased in 10b by partial supply from space 2 during the compression stroke via conduit 38.

Figures lOd and lOe show an embodiment in which the func- tion of the first and third displacement space is integra¬ ted. Paa is equal to or higher than Pea depending on the fuel supply. The users are connected between 4 and 5.

Figure lOd has been derived from the embodiment according to figures 7d and 7g, while the embodiment lOe has been derived from figures 7a, 7b, 7e and 7f. In lOd, the stroke volume of the second displacement space can be kept relatively small and Pm can be kept relatively low by using the release valve of figures 8a and 8b.

JK/ES

Claims

C L A I M S

1. Device for generating a fast movement for controlling a free piston aggregate in particular, comprising a cylinder (71) , therein a first adjusting piston (51) with a first position and a second position, which adjusting piston, together with the cylinder, forms a first displacement space (61) that is minimal in the first position and a second displacement space (79) that is minimal in the second position, in which, in the first position, both displacement spaces are under low pressure and the first adjusting piston closes off a first supply port for a first main (59) with medium under high pressure, and in which means are present to initially move the first adjus¬ ting piston (51) from the first position in order to open the first supply gate, so that the medium under high pressure quickly moves the first adjusting piston (51) to the second position.

2. Device according to claim 1, in which the means for initially moving the first adjusting piston (51) mechanically engage the first adjusting piston and are electromagnetically, electrodynamically or mechanically movable.

3. Device according to claim 1, in which the means for initially moving the first adjusting piston (51) hydraulically act on the first adjusting piston and comprise an auxiliary channel (56) with an operable valve (74) for supplying medium under high pressure, so as to supply the medium under high pressure to the first displacement space (61) after the valve (74) has been opened, in order to cause the initial movement of the first adjusting piston.

4. Device according to claim 3, in which an auxiliary cylinder with an auxiliary adjusting piston (37) is provided, which auxiliary adjusting piston, in a first position, closes off an additional port of the first main (59) to the first displacement space (61) and, in a second position, after the valve (74) has been opened, opens the additional port in order to quickly let medium under high pressure out of the first main act on the first adjusting piston for the initial movement thereof.

5. Device according to claim 1, 2, 3 or 4, in which the first adjusting piston (51) is connected to a rod (28) that protrudes outwards from the cylinder, in which the movement of the rod operates a valve or piston, particu- larly for a free piston aggregate.

6. Device according to claim 1, 2, 3 or 4, in which a discharge conduit (72a) is connected to the second displacement space (79) and to the discharge conduit (24) for the valve that has to be operated, and in which the first main (59) is connected to the supply conduit (23) for the valve that has to be operated.

7. Device according to any one of the preceding claims, in which discharge conduits for medium under low pressure in the first position of the adjusting piston (51) , on either side of the adjusting piston, are in connection with the displacement space.

8. Device according to any one of the preceding claims, in which means are present for moving the first adjusting piston (51) from the second position to the first position after closing off the first main (59) for medium under high pressure.

9. Device according to claim 8, in which a second adjus¬ ting piston (52) in the cylinder (71) is connected to the first adjusting piston (51) , which second adjusting piston

(52) in the second position of the first adjusting piston closes off a second supply port for a second main for medium under high pressure, in which analogous means are present for initially moving the second adjusting piston

(52) from the second position in order to open the second supply port and for moving the first adjusting piston to the first position.

10. Device according to claim 8 or 9, which is connected to a gas valve for a combustion chamber of a free piston aggregate in particular, in which control electronics of the free piston aggregate control the means for the initial movement of the first and second adjusting piston.

11. Admission valve according to claim 10, in which the valve disc of the admission valve (1) is constructed as a closing dish or plate valve with a seating in or near the inner wall of the combustion cylinder (14) , in which the valve closes by a movement of the valve disc (1) , which is directed at the inner side of the combustion cylinder.

12. Device according to claim 10, in which the gas valve is a body in the shape of a ring or a band (45) with a plurality of holes (36) , which ring or band is provided around the cylinder wall (15) with correspondingly placed holes (46) therein, such, that the holes (46) in the first position of the first adjusting piston (51) are covered by the ring or band (45) and, in the second position, cor- respond with the holes (36) , by movement of the ring or band with the aid of the device.

13. Admission valve according to claim 10 or 11, in which the second adjusting piston (52) is larger than the first adjusting piston (51) and in which the first main (59) continues to be connected to high pressure while the second main (60) , during the movement from the first end position to the second end position, is connected to low pressure via a switch back valve (68) and is connected to high pressure during the movement from the second end position to the first end position via said switch back valve (68) .

14. Admission valve with a first and second adjusting piston according to claim 10 or 11, in which, during the movement from the first end position to the second end position, the first main (59) is connected to high pres¬ sure via a re-setting valve and the second main (60) is connected to low pressure while, during the movement from the second end position to the first end position, the first main (59) is connected to low pressure via said re- setting valve (68) , and the second main (60) is connected to high pressure.

15. Admission valve according to claim 13 or 14, in which the first main (59) is connected to high pressure via a re-setting valve during the movement from the first to the second end position, while said main is connected to low pressure via said re-setting valve during the movement from the second end position to the first end position.

16. Admission valve according to claim 13, 14 or 15, in which another cylinder with piston (80, 81) is present besides the adjusting cylinder(s), which other cylinder exerts a force in the direction of the closed position or in the direction of the open position when high pressure is admitted, in which the conduit to said cylinder is per¬ manently under pressure or is connected to the second main or, during the movement from the first end position to the second end position, is connected to low pressure via the present re-setting valve (68) and, during the movement from the second end position to the first end position, is connected with high pressure via said re-setting valve. - kβ -

17. Re-setting valve according to claim 13 or 14, in which the re-setting valve (68) is moved under the influence of the differential pressures in the operating cylinders of said re-setting valve, in which one operating cylinder is connected to the first adjusting cylinder (71) via a channel (63) , in which said channel (63) is connected to high pressure in the second end position and to low pres¬ sure in the first end position by the first adjusting piston, while the other operating cylinder is connected to the second adjusting cylinder via another channel (64) , in which said other channel (64) is connected to low pressure in the second end position and to high pressure in the first end position by the second adjusting piston.

18. Re-setting valve for an admission valve with an adjus¬ ting piston according to claim 17, in which the other channel (64) is connected by a piston (98) that moves along with the valve disc (1) , in a manner similar to the one described in claim 17.

19. Re-setting valve for an admission valve with an adjus¬ ting piston according to claim 15, in which an operating cylinder is permanently connected to low pressure while the other operating cylinder is connected to the adjusting cylinder via two channels (63, 87), in which one channel (87) is connected to low pressure and the other channel (63) is closed off by the adjusting piston in the first end position, while, in the second end position, one of the channels (87) is closed off by the adjusting piston while the other (63) is connected to the displacement space (61) of the adjusting cylinder by the adjusting piston, a non-return valve (65) being accommodated in the other channel (63) , which opens in the direction of the operating cylinder of the re-setting valve.

20. Re-setting valve for an admission valve according to any one of the claims 13 - 16, in which the re-setting valve (68) is moved under the influence of the pressure differences between the pressure in the counter pressure cylinder (Ptc) of the free piston aggregate, the pressure in the compression pressure accumulator (Pea) and the pressure (Ptc) yet again on the one hand, and the pressure in the compression accumulator (Pea) , the pressure in the compression cylinder (Pec) and the pressure (Pec) yet again, on the other hand.

21. Re-setting valve according to any one of the claims

17 - 20, in which the re-setting valve is also used for operating other adjusting cylinders that are part of known combustion engines.

22. Method for pressure-charging the combustion space of a free piston aggregate with the aid of a pressure-charging device, comprising a hydraulic piston (121) that is con¬ nected to a scavenging piston (128) in a pressure-charging cylinder (42) , which hydraulic cylinder is operated with the aid of fast-working valves, in which the control elec¬ tronics for the free piston aggregate excite the hydraulic cylinder from its rest position before the control elec¬ tronics operate the combustion piston of the free piston aggregate starting from the LDC.

23. Pressure-charging device for use in the method of claim 22, comprising a hydraulic piston (121) that is connected to a scavenging piston (128) in a pressure- charging cylinder (42) , which pressure-charging cylinder can draw in gas via a non-return valve and can discharge compressed gas to the combustion space of the free piston aggregate, the hydraulic cylinder being controllable with the aid of two supply conduits for high and low pressure, which can be closed off by fast-working valves, said valves being operable by the control electronics of the free piston aggregate.

24. Pressure-charging device according to claim 23, provi¬ ded with valve control devices for the valves according to any one of claims 1 - 9.

25. Pressure-charging device according to claim 23 or 24, in which the discharge conduit to the combustion space for the compressed gas is provided with a gas valve as descri¬ bed in one of the claims 10 - 16.

26. Pressure-charging device according to claim 23, 24 or

25, in which fuel is supplied either for the scavenging cylinders or in the scavenging cylinders, or between the scavenging and combustion cylinders or in the combustion cylinder.

27. Free piston aggregate with a hydraulic compression piston (8) in a compression cylinder and a first displace¬ ment space (1) and a second displacement space (2) on either side thereof, and with a plunger piston (9) that forms a third displacement space (3) together with a plunger cylinder, which third displacement space is con¬ nected to an energy accumulator (5) via a non-return valve (30) , in which the first displacement space is connected to a compression accumulator (4) by means of a conduit with a non-return valve (11) and a parallel stop valve (12) , in which the stop valve is operable by the device according to any one of claims 1 - 9.

28. Free piston aggregate according to claim 27, in which one or more conduits of the compression accumulator (4) to the compression cylinder (17) are provided with valves that prevent flow to the compression cylinder during the waiting period of the compression piston (8) .

29. Free piston aggregate according to claim 28, in which a conduit (10) connects the second displacement space to the compression accumulator (4) , in which a valve is placed that allows passage in the direction of the compression accumulator (4) and in which a conduit (29) connects the second displacement space (2) to the first displacement space (1) , in which a valve (27) is provided that allows passage to the second displacement space.

30. Free piston aggregate according to claim 28, in which the second displacement space (2) is connected to a medium pressure accumulator (105) .

31. Free piston aggregate according to claim 28, in which a channel (28) is provided that connects the first displa¬ cement space (1) to the second displacement space (2) via a port in the wall of the hydraulic cylinder (17) , which port is closed by the hydraulic piston (8) during the final part of the compression stroke or the first part of the expansion stroke.

32. Free piston aggregate according to claim 31, in which a non-return valve (107) is accommodated in the channel

(19) of the compression accumulator (14) to the first displacement space (1) , which non-return valve only admits flow from the first displacement space (1) to the compression accumulator (14) .

33. Free piston aggregate according to claim 30, in which the second displacement space is connected to an accumula¬ tor (33) in which a pressure Pm is present that is at least high enough to prevent cavitation in the second displacement space during the expansion stroke but is lower than Pea.

34. Free piston aggregate according to claim 28, 31, 32 or 33, in which one or more non-return valves (27, 11, 30), which are accommodated in the channels for discharge of liquid from first and/or third displacement spaces, are provided with a device with which the closing force on the valve disc of the non-return valve can be operably increased during the expansion stroke.

35. Free piston aggregate according to claim 34, in which the operable increase of closing force is achieved with a hydraulic piston that exerts a force in the closing direc¬ tion of the valve on the movable valve disc of the non¬ return valve under the influence of the pressure(s) in the single or double-acting cylinder in which the piston moves.

36. Free piston aggregate according to claim 33, with hydraulic increase of closing force by means of a piston acting in a double-acting cylinder according to claim 35, in which the lower side (98) of the cylinder is connected to the discharge channel (29) of the non-return valve and the bar or lid side (104) is connected to a channel (94) that connects to a port in the wall of the hydraulic cylinder (17) of the free piston engine, said port being connected to the first (1) or the second displacement space (2) by the piston (8) of the free piston.

37. Free piston aggregate according to any one of claims 28 - 36, in which the first or the third displacement space is provided with a signaller (106) that breaks off an electric contact (109) with the metal of the free piston aggregate just before the free piston (8) comes to a standstill at the end of the expansion stroke, which break-off of contact is transmitted to the control elec- tronics of the free piston aggregate, in which these control electronics, at a specific period of time after the contact has been broken off, give the starting signal for the opening of a release valve (100) that connects the first and/or third displacement space to a space with low pressure.

38. Free piston aggregate according to claim 37, in which the control electronics adapt the time that passes between the signal from the signaller and the starting signal to the release valve, depending on certain measuring signals such as the liquid temperature of the liquid in the first displacement space, for instance.

39. Free piston aggregate according to claim 37 or 38, in which the signaller consists of a plug pin that moves as a spring with the valve disc of a non-return valve, past which non-return valve the liquid leaves the first or the third displacement space at the end of the expansion stroke in which the electric contact is broken off before the valve disc (93) closes off the non-return valve owing to the fact that the moving pin is checked by a stop and the valve disc, moving further, breaks off the contact with the pin (106) .

40. Free piston aggregate according any one of claims 28 - 36, in which the control electronics, during the final part of the expansion stroke, receive a signal that is proportional to the speed of the hydraulic piston (8) and also a signal that is proportional to the pressure in the first or third displacement space and, on the basis of these signal data, always issues the starting signal for the release valve (100) at such a moment in time, that the residual pressure in the first or the third displacement space is as low as possible the moment the free piston in the LDC comes to a standstill.

41. Release valve according to claim 37, 38, 39 or 40, in which this valve is a stop valve that is operated by an adjusting piston constructed in the same way and function¬ ing as the adjusting piston(s) that operate the starting valve (12) as indicated in claim 8 or 9.

42. Free piston aggregate according to any one of claims 28 - 41, with a starting valve (12) and a release valve (100) , in which the starting valve opens the supply from the compression accumulator to the first displacement space and simultaneously closes off the connection from the release valve to the space with low pressure via conduit (113) and, when closing off the former connection, simultaneously opens the latter connection.

43. Free piston aggregate according to any one of claims 27 - 40, or 42, in which the third displacement space (3) has been left out and in which liquid is pressed from the second displacement space (2) via a non-return valve (30) into the energy accumulator (5) during the compression stroke.

44. Free piston aggregate according to claim 43, in which a channel (38) is present that is connected to a port in the wall of the hydraulic cylinder (17) , said port being closed by the hydraulic piston (8) during the first part of the compression stroke and being opened during the second part of the compression stroke, in which the chan¬ nel (38) is also connected to the second displacement space (2) .

45. Free piston aggregate according to any one of claims 27 - 40 or 42, in which the third displacement space has been left out while liquid is pressed from the second displacement space via a non-return valve (30) into the energy accumulator (5) during the compression stroke, in which liquid flows via a non-return valve (37) into the second displacement space (2) from an accumulator (105) with a pressure Pm during the expansion stroke.

46. Free piston aggregate according to claim 45, in which the energy accumulator (5) has been left out and in which liquid is pressed from the second displacement space (2) via a non-return valve (26) into the compression accumula¬ tor (4/5) during the compression stroke, said compression accumulator here merging with the energy accumulator.

47. Free piston aggregate according to any one of claims 27 - 40 or 42, in which the third displacement space has been left out, in which the inflow of liquid from the compression accumulator (4) into the first displacement space takes place via a non-return valve (31) and liquid is pressed from the first displacement space via one or more non-return valves (30, 32) into the energy accumu- lator (5) during the expansion stroke, the users being connected between the compression accumulator and the energy accumulator.

48. Free piston aggregate according to any one of claims 27 - 40 or 42, in which the third displacement space has been left out, in which the inflow of the liquid from the compression accumulator (4) into the first displacement space takes place via a non-return valve (31) , in which liquid is pressed from the first displacement space via one or more non-return valves (30, 32) to the energy accumulator (5) during the expansion stroke.

49. Free piston aggregate according to any one of claims 27 - 40 or 42 - 48, in which non-return valve (11) and starting valve (12) are integrated and replaced by a non¬ return valve that offers a passage from the first displa¬ cement space into the compression accumulator, in which said non-return valve (11) can be opened by an adjusting piston (51) , opposing the closing force and the closing pressure.

50. Free piston aggregate according to claim 28, in which the plunger cylinder (18) and the plunger piston (9) have been left out and in which the energy discharge takes place via a liquid piston pump for pumpage of an external medium or via an air piston compressor for supplying compressed air or via a linear generator for supplying electrical energy in which the pump piston or the air piston or the anchor of the generator are attached to the free piston via a rod (9) with rod closure to the first displacement space.

51. Closing force amplification for non-return valves according to claim 34 or 35, in which said closing force amplification is also used for the hydraulic inlet valves (31, 37) of the free piston aggregate and/or for the non- return valves of known piston pumps for pumpage of gas or liquid.

52. Free piston aggregate according to claim 28, in which a remote controlled valve (kl) is present in a conduit (10) between the compression accumulator (4) and the second displacement space (2) or in a conduit (29) between the first (1) and second (2) displacement space, in which a non-return valve (27) is also present in the conduit (29) .

53. Free piston aggregate according to claim 52, in which valve (kl) is bridged by a non-return valve (27) that opens in the direction of the second displacement space, in which a non-return valve is present in the conduit between the second displacement space and the compression accumulator (4) , which non-return valve opens in the direction of the compression accumulator.

54. Free piston aggregate according to any one of claims 27 - 53, in which in a device according to claim 6 the first main (59) is connected to the energy accumulator (5) and the discharge conduit (72a) is connected with medium under pressure (Pac) in the third displacement space.

55. Free piston aggregate according to any one of claims 27 - 54, in which a device according to any one of claims 1 - 9 is provided, the adjusting piston (51) of which opens one or more non-return valves (11, 27) , opposing the closing force.

ES