WO1992002712A1

WO1992002712A1 - A valve control arrangement

Info

Publication number: WO1992002712A1
Application number: PCT/GB1991/001260
Authority: WO
Inventors: Keith Leslie Richards; Richard Anthony Ashen
Original assignee: Keith Leslie Richards; Richard Anthony Ashen
Priority date: 1990-07-27
Filing date: 1991-07-26
Publication date: 1992-02-20
Also published as: AU8294491A; GB9016600D0

Abstract

A valve control arrangement for opening and closing the valves in, for example, an internal combustion engine comprises an electrically powered magnetic valve drive (9-14). A sensor (17) is provided for monitoring actual valve position. In addition means are provided for monitoring the operating conditions of the engine or the like in which the valve is fitted and for generating a desired valve position based upon the those operating conditions. The desired valve position and the actual valve position are compared and the valve drive (9-14) is controlled such that the actual valve position follows or approximates to the desired valve position.

Description

A Valve Control Arrangement.

THE PRESENT INVENTION relates to a valve control arrangement and more particularly to a valve control arrangement which is suitable for use with an internal combustion engine in order to control the opening and closing of the engine valves.

In a conventional internal combustion engine each of the cylinders are provided with one or more ports through which combustible air is introduced into the cylinders and the exhaust remains are ejected after combustion is completed. The ports are opened or closed by poppet valves which close aσainst specially prepared seats sealing the cylinders during the process of combustion. The valves are controlled by a rotary cam and spring assembly. Thus, a respective spring normally retains each valve in the closed position and a rotary cam opens the valve either by acting upon the valve stem directly or via a rocker arm which may be connected to the cam shaft by a push rod.

The valve timing, that is to say the point at which the valve opens and closes and the duration of opening in relation to the position of the engine crankshaft is critical to the efficient operation of the engine. The valve timing and valve lift or travel are dictated by the cam profile. It is therefore most important that the cam shaft and in particular the cams formed thereon are produced to a very high degree of accuracy since small errors can give rise to grea-^"* reduced engine efficiency.

The cam profile has a major affect upon the power and torque outputs of the engine and is designed over as wide a speed and load range as possible but at best can only be a compromise depending upon the specific requirement of the engine as a power source and in fact the engine output will only be at an optimum over a very small speed and load range. Thus whenever the engine is operating at conditions other than those for which the cam profile has been specifically designed, it will be operating at a reduced efficiency.

The present invention seeks to provide an improved valve control arrangement which, when used in an internal combustion engine, overcomes the above-mentioned problems.

According to the present invention there is provided a valve control arrangement for opening and closing a valve in dependence upon operating conditions of an engine or the like in which the valve is fitted, the arrangement comprising an electrically powered magnetic drive for opening and closing the valve, means for monitoring the actual valve position, means for monitoring said operating conditions, means for generating a desired valve position based upon the operating conditions monitored, means for comparing the desired valve position with the monitored valve position and for controlling the drive such that the actual valve position follows or approximates to the desired valve position.

Preferably the electrically powered magnetic drive for opening and closing the valve comprises coil means within which a permanent magnet or magnets mounted on part of the valve is received, the permanent magnet or magnets being freely movable in the direction of valve travel.

Conveniently the coil means comprise a pair of coils, each having an annular permanent magnet received within its central region. Advantageously the dimension of each coil in the direction of valve travel is equal to or greater than the maximum valve travel such that the permanent magnets are always disposed within the central regions of their respective coils.

Preferably the coils are energized by means of a push-pull circuit.

Conveniently the current supplied to the coils is controlled by the drive controlling means and is varied in order to vary the rate and direction of valve travel so that the actual valve position follows the desired valve position.

Advantageously the permanent magnets are mounted upon an armature which is connected to part of the valve with a heat insulating material positioned between the armature and the valve part upon which it is mounted.

Preferably the means for monitoring the actual valve position comprise a position sensor which engages the armature connected to part of the valve.

Conveniently the arrangement includes a spring which serves to move the valve to the closed position when the electrically powered magnetic drive is not energized.

Advantageously the arrangement includes a microprocessor for generating the desired valve position, comparing actual valve position with the desired position and controlling the electrically powered magnetic drive accordingly. This invention also provides an internal combustion engine incorporating a valve control arrangement as described above.

In order that the present invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view of a valve control arrangement in accordance with the present invention when mounted upon an internal combustion engine;

FIGURE 2 is a schematic block diagram of a logic circuit for an engine management system used with an engine having a valve control arrangement in accordance with this invention; and

FIGURE 3 is a schematic block diagram of a control circuit for driving a valve in a valve control arrangement according to this invention.

Referring to the accompanying drawings, Figure 1 shows part of a cylinder head 1 of an internal combustion engine, the cylinder head defining a port 2 which may be either the inlet port or the outlet port associated with one cylinder of the engine. It will of course be appreciated that the present invention may be utilized in connection with engines having various inlet and exhaust port arrangements or with engines in which fuel is injected directly into the cylinders and which therefore are only provided with exhaust ports which are opened and closed by way of valves. Since the valve control arrangement of the present invention is the same whether used on an inlet port or an exhaust port a description of only one such arrangement, as illustrated in Figure 1, will be given.

The port 2 is provided with a valve 3 in the form of poppet valve comprising an elongate stem 4 having a valve head 5 formed at one end thereof. The valve head forms a seal with a valve seat 6 defined at the end of the port 2 when the valve is in the closed position.

The valve 3 is mounted upon the cylinder head 1 and the valve stem 4 is received within a valve guide 7 such that the valve is constrained to move linearly along the longitudinal axis of the valve stem.

In Figure 1 of the d awings the valve is shown in the closed position i.e. with the valve head 5 in engagement with the valve seat 6 formed around the and of the port 2. The valve may be moved downwardly such that the valve head 5 moves away from the valve seat 6 thereby opening the end of the port 2 and allowing eith - an air fuel mixture to flow into the engine cylinder or exhaust remairs to be extracted from the cylinder.

Movement of the valve is controlled by a valve control arrangement including a linear drive assembly 8 mounted upon the cylinder head 1.

The drive assembly 8 comprises an armature 9 mounted upon the upper end of the valve stem with a heat insulating sleeve 10 disposed between the armature and the valve stem in order to prevent the armature from being heated excessively during operation. The armature 9 is mounted upon the valve stem by any appropriate means. The armature 9 has upper and lower annular permanent magnets 11 mounted at its opposite ends. The annular magnets 11 are formed typically in four quadrants which are joined together around the upper and lower ends of the armature 9. The upper permanent magnets define a south pole on its radially innermost face which is mounted upon the armature 9 and a north pole on its radially outermost face. The lower permanent magnet defines a north pole on its radially innermost face which is connected to the armature 9 and a south pole on its radially outermost face.

The armature is effectively an extension of the valve stem 4 and is freely movable along the longitudinal axis of the valve stem. The armature and the permanent magnets mounted thereon are disposed within upper and lower coils 12, 13 such that the coils surround the upper and lower permanent magnets. The armature having the permanent magnets fixed thereon and thus the valve 3 is freely movable along the longitudinal axis of the valve stem within the coils 12, 13 under the influence of the forces generated by the magnetic fields when the coils are energized.

The coils 12, 13 are mounted within a stator housing 14 which in turn is mounted upon the cylinder head 1 with an insulating spacer 15 disposed therebetween. The housing 14 is provided with a cover 16 through which a position sensor 17 extends in order to engage the upper end of the armature 9. The position sensor 17 serves to track the actual position of the valve 3 and this information is relayed to the drive control circuit as shown in Figure 3 where the signal from the valve position sensor is used in a feedback loop in the control circuit so as to ensure that the valve is as close as possible to its desired position, as will be explained in greater detail hereinafter. It is envisaged that the sensor 17 will be an electromechanical position sensor such as a linear voltage displacement transducer, although other types of position sensors could be used.

The coils 12, 13 are energized by means of a 'push-pull' circuit contained in the drive control, the coils thus creating magnetic fields of opposite sense which causes movement of the valve. The flux path created by the permanent magnets is shown at 18 in Figure 1 and passes radially across the upper coil, down through the stator housing, radially across the lower coil and up through the armature 9. Over the depth of each of the coils 12, 13 the magnetic force generated at a particular radius when the coils are energized is of constant value and is proportional to the current flowing in the coils. Outside the coils the magnetic force drops off. The coils are so dimensioned that the permanent magnets 11 are always within the depth of the coil and are therefore subjected to a constant driving force when the coils are energized. The depth of each coil, i.e. its dimension in the direction parallel to the longitudinal axis of the valve stem, is therefore equal to or greater than the maximum valve lift. Controlling the current supply to the coils 12, 13 therefore enables the valve to be driven in either direction between the open and closed positions at any desired rate so that it can track a desired valve profile.

When the coils 12, 13 are not energized a light compression spring 19 which extends between the cylinder head 1 and the armature 9 serves to return the valve 3 to the closed position with the valve head in engagement with the valve seat.

The engine with which the valve drive assembly is to be used is provided with a microprocessor-based engine management system 20 which monitors various engine operating parameters by way of appropriate sensors and which generates a valve operating function dependant upon those operating parameters. Signals representing the valve operating function are sent from the engine management system to a drive control circuit 21 which generates a desired valve opening/closing profile for the particular engine operating conditions and which controls the current supplied to the coils 12, 13 so that the valve 3 follows the desired profile as closely as possible. The actual position of the valve, as sensed by the position sensor 17, is compared with the desired valve position in the drive control circuit 21 and any error is corrected by varying the current supplied to the coils.

Looking at the engine management system and the drive control circuit in more detail, the microprocessor-based management system of Figure 2 comprises a number of discrete circuits linked in a logical manner to provide a series of outputs essential for the correct operation of the linear drive assemblies 8. These circuits include an engine analyser 22 which monitors various parameters such as ignition setting, fuel injection timing, coolant temperature, engine speed, engine torque, throttle position, crankshaft angle, top dead centre position and the like and a combustion analyser 23 which monitors parameters such as exhaust gas products, fuel flow, air temperature, air humidity, air mass flow, engine knock and the like by way of appropriate sensors.

The engine analyser circuit and the combustion analyser circuit feed their signals into an engine operational profile circuit 24 which reviews these inputs and, using the resident software and memory 25 in the management system, outputs a number of variables, as can be seen from Figure 2 of the drawings, including inlet and exhaust valve opening and closing profiles, inlet and exhaust valve opening and closing angles, valve lift, ignition setting, fuel injection settings, top dead centre signals and signals representing crankshaft angle. These variables are output onto appropriate data buses.

The valve opening and closing profiles are output in the form of a profile number and the profile nur^ers comprise a set of standardized curves coverinc the equivalent of a range of cam profiles from 'soft' profiles (i.e. gentle opening and closing of the valve) through 'medium' profiles to 'hard' profiles (i.e. short opening and closing of the valve) suitable for high performance engine operation.

The timing pulses required by the management system 20 in order to synchronize the engine valve sequence are provided by two transducers, one of which detects the angular position of the crankshaft corresponding to the 'top dead centre' position of the piston in cylinder number one whilst a second transducer measures the angular position of the crankshaft relative thereto, possibly using a tooth wheel creating electrical pulses corresponding to the tooth positions. These electrical pulses are used to provide the necessary timing pulses in order to ensure correct operation of the engine valves.

The engine management system also incorporates a display 26 which may be used to display various parameters, such as engine speed, fuel consumption, coolant temperature, oil temperature, oil pressure, vehicle speed or even an indication of actual valve position compared with the desired position i.e. the error in the valve position. The valve drive control circuit 21 of Figure 3 reads the values of various parameters output onto data buses by the engine management system and in particular details relating to the desired valve profile i.e. the profile number, valve lift, opening angle, closing angle as well as the actual monitored crankshaft angle and the angle to which the top dead centre position of cylinder number one corresponds. The drive control circuit generates, in real time, a desired valve profile corresponding to the profile number stored in the circuit memory. The standardized profile, corresponding to the profile number desired, is then modified to take account of the desired valve lift and opening and closing angles.

The valve lift can be used in order to control engine speed and if desired the valve profile could be modified to give zero lift for an inlet valve so that one engine cylinder (or more if desired) is shut off. This can make the engine more economical.

The desired valve profile is then fed via a comparator 27 to a drive amplifier 28 which serves to energize the coils 12, 13 so as to move the valves to the desired positions matching the instantaneous output from the amplifier. When the valves are being driven to the closed position the control circuit automatically damps the valve travel during the final stage of closure in order to prevent valve bounce.

The signal corresponding to the actual valve position generated by the position sensor 17 is feed into the comparator 27 which evaluates any difference between the desired valve position and the actual valve position and any error which is detected results in the current in - li ¬ the appropriate coil being adjusted in order to minimize the error in position.

The starting point for the profile generated by the drive control circuit 21 is controlled by the signals corresponding to the crankshaft position and the top dead centre position. The drive control circuit includes a built-in offset value for each cylinder relative to the first cylinder in order to ensure that the valves are timed correctly for their cylinder and are not all opened and closed simultaneously.

In addition the valve control arrangement enables crossover i.e. the period when both the inlet valve and the exhaust valve in an internal combustion are open, to be minimized or eliminated, thereby reducing pollution caused by unburnt fuel passing directly out through the exhaust port.

It will be appreciated that controlling the valves in the manner described above obviates the problems associated with cam-operated valves. Thus, the valve timing is operated in dependence upon the engine operating conditions and is not specifically suited to only one set of operating conditions. In addition the valve control arrangement enables crossover i.e. the period when both the inlet valve and the exhaust valve in an internal combustion are open, to be minimized or eliminated, thereby reducing pollution caused by unburnt fuel passing directly out through the exhaust port.

It will be appreciated that various modifications may be made to the above described embodiment without departing from the scope of the present invention. Whilst the invention has been described for use with an internal combustion engine, a valve control arrangement in accordance with this invention may also find other applications where it is desired to control valve operation in a manner related to the operating conditions of the engine or machine in which the valves are fitted.

Claims

1. A valve control arrangement for opening and

a valve in dependence upon operating conditions of an engine or the like in which the valve is fitted, the arrangement comprising an electrically powered magnetic drive for opening and closing the valve, means for monitoring the actual valve position, means for monitoring said operating conditions, means for generating a desired valve position based upon the operating conditions monitored, means for comparing the desired valve position with the monitored valve position and for controlling the drive such that the actual valve position follows or approximates to the desired valve position.

2. A valve control arrangement according to Claim 1 wherein the electrically powered magnetic drive for opening and closing the valve comprises coil means within which a permanent magnet or magnets mounted on part of the valve is received, the permanent magnet or magnets being freely movable in the direction of valve travel.

3. A valve control arrangement according to Claim 2 wherein the coil means comprise a pair of coils, each having an annular permanent magnet received within its central region.

4. A valve control arrangement according to Claim 3 wherein the dimension of each coil in the direction of valve travel is equal to or greater than the maximum valve travel such that the permanent magnets are always disposed within the central regions of their respective coils.

5. A valve control arrangement according to Claim 3 or Claim 4 wherein the coils are energized by means of a push-pull circuit.

6. A valve control arrangement according to Claim 3, 4 or 5 wherein the current supplied to the coils is controlled by the drive controlling means and is varied in order to vary the rate and direction of valve travel so that the actual valve position follows the desired valve position.

7. A valve control arrangement according to any one of Claims 3 to 6 wherein the permanent magnets are mounted upon an armature which is connected to part of the valve with a heat insulating material positioned between the armature and the valve part upon which it is mounted.

8. A valve control arrangement according to Claim 7 wherein the means for monitoring the actual valve position comprise a position sensor which engages the armature connected to part of the valve.

9. A valve control arrangement according to any one of the preceding claims wherein the arrangement includes a spring which serves to move the valve to the closed position when the electrically powered magnetic drive is not energized.

10. A valve control arrangement according to any one of the preceding claims wherein the arrangement includes a microprocessor for generating the desired valve position, comparing actual valve position with the desired position and controlling the electrically powered magnetic drive accordingly.

11. An internal combustion engine incorporating a valve control arrangement in accordance with any one of the preceding claims.

12. A valve control arrangement substantially as herein described with reference to and as shown in the accompanying drawings.