SE1251365A1 - Control of at least one state in a system - Google Patents

Abstract

A method and a system for controlling at least one state in a system against a reference value are presented, said at least one state comprising an inertia and said control being performed by utilizing a control signal. According to the present invention, said control is model based, where the model comprises a force equation related to said system. Furthermore, a magnitude of said control signal is proportional to a change of said at least one state. 2

Description

lO l5 20 Fg. “P-, w_l, _¿Ü _ p, - $ ï..p, æï§__š -___ § .year 5 * (eq. L) where: - Kp constitutes a gain constant; - KI constitutes an integration constant; and - KD constitutes a derivation constant.

A PID controller regulates in three ways, through a proportional gain (P; Kp), through an integration (I; Ki), and through a derivation (D; Kg).

The constants Kp, Ki and Kd affect the system as follows.

An increased value for the gain constant Kp leads to the following change of the PID controller: - increased speed; - reduced stability margins; - improved compensation of process disturbances; and - increased control signal activity.

An increased value for the integration constant Ki leads to the following change of the PID controller: - better compensation of low-frequency process disturbances (eliminates residual errors in case of step disturbances); - increased speed; and - reduced stability margins 10 l5 20 25 An increased value for the derivative constant Kd leads to the following change of the PID controller: - increased speed - increased stability margins; and - increased control signal activity.

As mentioned above, there are also other types / variants of controllers / control algorithms which have a function similar to that of the PID controller.

Brief description of the invention Prior art controllers / control algorithms, such as for example the PID controller, have a large number of parameters which need to be calibrated in order for the control of the systems they are intended to control to be accurate and correct. This means that the calibration often needs to be performed by someone who has a good knowledge of the system to be controlled and who also has a good understanding of the controller function. Unfortunately, the person who owns or uses the system rarely has the detailed knowledge of the system and / or the control algorithm that is needed for the calibration to provide an optimal control system. The fact that, for example, the PID controller is so common in control systems is partly due to the fact that it is relatively robust against incorrect calibration.

Thus, the PID controller often provides a functioning control system.

Rarely, however, is this control system optimized for controlling the system it is intended to control. In other words, the PID controller provides a control that works for most systems, but at the same time the PID control is not very accurate. Thus, the PID control seldom follows the desired reference values particularly well, which often leads to substandard performance and / or unnecessary costs. For example, it can be mentioned that a PID control in a cruise control system in a vehicle adapts relatively poorly to a reference speed that the cruise control has calculated that the vehicle must maintain in order to minimize fuel consumption, which leads to unnecessarily high fuel consumption in the vehicle.

The same applies to other known controllers that have a similar function as the PID controller.

A problem with the PID controller, which is also a contributing factor to the PID control becoming inaccurate, is that the PID algorithm gives rise to upper and / or lower loops for the control signal to the system to be controlled, i.e. the input signal u ( t). These upper and / or lower loops are due at least in part to a twist in the controller due to the gain from the I-part, i.e. from the integrating part (I; Ki) of the algorithm. The distortion works much like a memory that remembers too far back in time, which puts the controller at risk of compensating for old errors. Corresponding problems also exist for other controllers which include an at least partially integrating function.

It is an object of the present invention to provide a control system which solves the above-mentioned problems with previously known control systems.

This object is achieved by the above-mentioned method according to the characterizing part of claim 1. The object is also achieved by the above-mentioned control system according to the characterizing part of claim 27, as well as by the above-mentioned computer program and computer program product.

By means of the present invention, at least one state in a system is controlled against a reference value, where at least one state has an inertia, for example a mass inertia, a thermal inertia or a moment of inertia as explained above. The control according to the invention is based on a model which comprises a force equation which is related to the system to be regulated. The control of the at least one state is performed by utilizing a control signal, which according to the invention must be proportional to the change, i.e. the derivative, of the at least one state being controlled.

Thus, the control of the states of the present invention is based on the systems which include the respective states. In other words, the systems are regulated based on the systems themselves, since the regulation of the systems is performed based on models of the systems to be regulated. In this way, there is a good knowledge of the systems that are to be regulated within the control algorithm, which means that the control algorithm can be made stable.

Since the control according to the invention is based on the system to be regulated, a regulation as powerful or sensitive as the system requires is obtained. This results in an adaptive adjustment of the control, where the adjustment follows the system's change. This means that a very precise control of the system can be obtained when the present invention is used.

The control according to the invention does not have to utilize predetermined gain factors as required in, for example, PID control, which means that the control can be easily adapted to the system to be controlled. In addition, the number of parameters that must be radically calibrated with the present invention decreases compared to, for example, a PID controller.

Since a physical model for the system to be regulated is the basis for the regulation, considerably less knowledge in control technology is required to set up the control system. Substantially no detailed knowledge of control technology or control algorithms is required to operate the control system of the present invention.

The control according to the present invention adapts quickly and well to the reference value because over- and / or under-throws of the control signal which previously known control algorithms have had problems do not arise in the control according to the present invention. In particular it can be mentioned that the twisting of previously known regulators due to the reinforcement from the I-part can be avoided with the invention.

According to an embodiment of the invention, the system to be regulated is a cruise control system in a vehicle, which has an inertia which is related to a mass m of the vehicle.

The condition here constitutes an actual speed what for the vehicle. When the present invention is applied to such a cruise control system, the fuel consumption of the vehicle can be reduced because the control more accurately follows the reference speed determined by the cruise control system.

According to an embodiment of the invention, the system to be controlled is an engine in a vehicle, which has an inertia based on an inertia moment] of the engine. The at least one condition here includes an actual engine speed. By control according to the present invention, the engine speed can be controlled very precisely without much calibration work.

According to an embodiment of the invention, the system to be controlled is a temperature control system, which has an inertia based on a thermal inertia K. The at least one state here comprises an actual temperature Tha. This results in a very precise adjustment of the actual temperature 10 l5 20 25 Täa to the desired reference value, which in certain environments, for example in laboratories, is absolutely crucial operations and in other environments, for example in office premises and vehicle cabins, increases the comfort for eg staff .

According to an embodiment of the invention, the system to be controlled is a system for acceleration limitation in a vehicle, which has an inertia based on a mass m of the vehicle. What at least one condition includes has an actual acceleration aa ”for the vehicle. As a result, a very good control of the vehicle acceleration can be obtained.

According to an embodiment of the invention, the system to be controlled is a system for braking the vehicle, which has an inertia based vehicle mass m. It includes at least one condition having an actual speed as for the vehicle. In this way, essentially all therefore suitable types of braking systems for a vehicle can be controlled very precisely.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further elucidated below with reference to the accompanying drawings, in which like reference numerals are used for like parts, and in which: Figure 1 shows an example of a capture sequence versus a reference value, Figure 2 shows an example of a capture sequence versus a reference value, Figures 3a and 3b shows an example of mass determination of a vehicle, and Figure 4 shows a control unit. Description of preferred embodiments The present invention relates in one aspect to a method for controlling one or more states in a system against a reference value and in one aspect to a control system arranged to control this at least one state against the reference value. Conditions for the systems that can be regulated according to the present invention have an inertia, which means that there is a resistance to change for the condition, for example against a change in movement or against a change in temperature. Changes to the permits therefore take place over a period of time and not momentarily.

Many systems have built-in inertia for their states.

Essentially all such systems can be controlled by utilizing the present invention. A couple of embodiments of the present invention will be described below. However, one skilled in the art will recognize that the present invention is generally applicable to substantially all systems where the state of the systems has some sort of reluctance to change, that is, some kind of inertia.

For example, with the present invention, in temperature control systems, the temperature can be controlled toward a temperature reference value. In an engine control system in a vehicle, the engine speed can be controlled to a reference speed. In a cruise control system in a vehicle, the vehicle speed can be controlled towards a reference speed. In a brake control system in a vehicle, the vehicle speed can be controlled towards a reference value in the form of a maximum speed. In a control system for acceleration limitation, the vehicle acceleration can be controlled towards a reference acceleration. These embodiments and applications of the invention will be described in more detail below. The control of the at least one state in the system to be regulated according to the invention is model-based. The model applied here is related to the system to be regulated in that the model includes a force equation or another equation that is related to this system. Thus, a model of the system is developed at least in part by setting up a force equation for at least a part of the system.

Furthermore, in controlling the system, the control of the state is performed by utilizing a control signal, the model-based control causing a magnitude of this control signal to be proportional to a change for the at least one state. Thus, a control unit provides the control signal based on the model so that its magnitude is proportional to a change in the state.

Regulating systems based on the appearance and characteristics of the systems themselves make the regulation of the systems very precise. Unlike previously known control systems, in which the systems to be regulated have been forced into the control algorithms of the control systems, for example in the form of amplification parameters, the control algorithm according to the present invention is based entirely on the system to be regulated, so an optimally adapted control can be provided. .

The number of parameters that must be calibrated in the control system prior to control is radically reduced with the present invention compared to prior art controllers. This also means that considerably less knowledge in control technology is required to set up the control system so that good control is obtained.

In addition, the control according to the present invention minimizes upper and / or lower hoses of the control signal which have arisen in previously known controllers due to the integrating memory part of its control algorithms, i.e. for example the I-part of a PID controller. .

According to an embodiment of the invention, the system to be regulated is a cruise control system in a vehicle, which has an inertia is related to a mass m of the vehicle. The condition to be controlled here constitutes an actual speed for the vehicle, ie the actual speed the vehicle will maintain as a result of the cruise control. The reference value against which the permit is controlled here constitutes a reference speed vmf for the vehicle.

There are a variety of types of cruise control vehicles. In some of these types of cruise control, the driver sets the reference speed himself. In other types of cruise control, the driver sets a set speed vw, based on which the cruise control then determines the magnitude of the reference speed væf sent to the speed controller, whereby the reference speed væf may have a different value than the set speed væt.

According to the embodiment, the model takes into account a difference between an actual acceleration aad for vehicles, i.e. the actual acceleration resulting from the cruise control, and a reference acceleration amf for the vehicle. This difference is due to a time parameter T, which is described in more detail below. The time parameter I determines what the appearance of the oscillation process for the actual velocity vmï against the reference velocity væf looks like in such a way that a smaller value of the time parameter I gives a fast oscillation process and a larger value of the time parameter I gives a slow oscillation process. This is shown schematically in Figure 1, where the dashed straight horizontal line is a reference velocity against which actual velocities for different values of I turn. As illustrated in Figure 1, the smallest value l0 l5 20 25 30 ll on the time parameter I == 2 (solid curve) gives the fastest acquisition course, the greater care on the time parameter T == 5 (dotted curve) gives a slower course in the course, and the largest value on the time parameter T == 8 (dashed curve) the slowest indentation process.

According to the embodiment, the time parameter I is thus the only parameter that must be calibrated in order for the control to have the desired course. In other words, the care of the time parameter I determines how long it takes for the actual speed vwx to become equal to the reference speed væf.

Thus, according to the invention, the time parameter I should be adjusted to give an optimal appearance for the system to be regulated of the oscillation process for the actual speed in relation to the reference speed vmf. It is relatively simple and intuitive for a user of a control system according to the present invention to realize the effect of an adjustment of the size of the time parameter I on the control.

Thus, only one parameter, the time parameter I, needs to be calibrated, as it is also easy to understand and explain the effect this parameter has on the regulation. This is a considerable simplification and improvement for the user compared to previous controllers, such as for PID controllers, where a number of parameters, which for the user have an incomprehensible effect on the control, must be adjusted to adapt the control to the system to be regulated. For example, parameters for the P-part, the I-part and the D-part must be calibrated when a PID controller is to be adapted to a system it is to regulate.

The impact of these adjustments of the P-, I- and D-parts on the regulation is at best incomprehensible to the user and at worst totally incomprehensible. The present invention therefore presents a considerable simplification of the calibration that needs to be done to perform the control of the system.

According to an embodiment of the present invention, the value of the time parameter I is related to a driving mode, also called driving mode, of the vehicle. This is shown schematically in Figure 2.

The value of the time parameter I is seen here as related to an aggressiveness of the regulation. Therefore, in a normal driving mode, for example referred to as "standard" (dotted curve), the time parameter I can be given a medium value.

For a more aggressive driving mode, for example called "power" (dashed curve), the time parameter I is given a relatively small value if the actual speed is lower than the reference speed vmf. For this driving mode, the time parameter I is given a relatively large value if the actual speed vmï is higher than the reference speed vmf, as shown in Figure 2.

The more aggressive driving mode power thus swings in quickly as it approaches the reference speed vmf from below (from a lower speed), but swings in slowly as it approaches the reference speed væf from above (from a higher speed).

The driving mode power thus quickly tries to reach the reference speed weave from below and meets early from the top, which gives a powerful impression, a higher average speed and a time gain in comparison with the other driving modes.

I / I / For a less aggressive driving mode, for example called eco (solid curve), the time parameter T is given a relatively large value if the actual speed is lower than the reference speed vwf. Correspondingly, the time parameter I for this driving mode is given a relatively small value if the actual speed is higher than the reference speed væf, l0 l5 20 25 l3 as shown in Figure 2. The less aggressive driving mode eco thus turns in quickly as it approaches the reference speed væf from above (from a higher speed), but turns in slowly as it approaches the reference speed vwf from below (from a lower speed), which gives a soft impression, as well as a lower average speed and thus a lower total fuel consumption. In addition, the amount of braked energy is also reduced with driving mode eco, since a vehicle, for example, under a road section comprising an uphill slope followed by a downhill slope has a lower speed at the top of the crest. Due to the lower speed at the top, less braking is required under the downhill slope, whereby less energy is braked away.

As can be seen from the unrestricted example shown in Figure 2, the control according to the present invention can be easily adjusted so that different driving modes for the vehicle are obtained. The only parameter that needs to be changed to achieve this is the time parameter I, which is a considerable simplification compared to previously known control systems.

According to an embodiment where the invention is applied to cruise control, the force equation described by the model of the system to be regulated is related to an appearance according to: Fk + l = m * (i- am) + Fk, where (eq. 1) - Fku is a force which will act on said vehicle at the next iteration of the equation is calculated; - nï is the mass of the vehicle; - vmf is the reference speed; - what is the actual speed; - I is the time parameter; 10 15 20 25 14 - amï is the actual acceleration of the vehicle; and - Pa is a current force acting on the vehicle.

O _ v _11 As can be seen from Equation 1, the term l fl ä-52 corresponds to a reference acceleration amf, which means that the magnitude of the difference of the time parameter I has a direct effect on the difference between the reference acceleration amf and the actual acceleration aan. In this way, a simple adjustment of the value of the time parameter I can affect the entire control according to the present invention, in the manner described above.

When the present invention is applied to a cruise control system, the fuel consumption of the vehicle can be reduced because the control more accurately follows the reference speed determined by the cruise control system. This is because the control according to the invention is based on a physical model of the cruise control system, i.e. the control is based on the system to be regulated.

The signal for the actual acceleration aan that the vehicle can provide often contains noise. This signal can be generated in a variety of ways in the vehicle. For example, the acceleration can be determined by deriving the actual vehicle speed what, by using the force equation, or by using an accelerometer. Regardless of how the signal for the actual acceleration aan has been generated, it is often noisy, which makes it difficult to base the regulation on because it risks becoming unstable.

Therefore, according to an embodiment of the present invention, the force equation is adjusted to compensate for the noise of the signal for the actual acceleration aad. The adjusted force equation then has an appearance according to: 10 15 20 25 15 _ h Vref -Vact Fk + 1 _ çm * _ am) + Fk, where (eq. 2) - EH4 is a force which will act on the vehicle at the next iteration ; h is a discretionary factor, which indicates a resolution in the control system, where this resolution may be related to the sampling time / time step of the control system, which may be, for example, 0.01 seconds; - y is a calibration time; - nï is the mass of the vehicle; - vmf is the reference speed; - what is the actual speed; - I is the time parameter; - aan is the actual acceleration; and - Fk is a current force which acts on the vehicle.

The value of the calibration time y indicates how fast the actual acceleration aaa approaches the reference acceleration awf. In other words, the value of the calibration time y indicates how fast (Vre f - ”act T - aMI) == 0 in equation 2.

By utilizing the compensated force equation in Equation 2, oscillation problems can be avoided for the control as the signal for the actual acceleration add is noisy. Problems related to incorrect estimates of the vehicle mass m in the model can also be avoided by this embodiment of the invention.

According to this embodiment, the control of the system is made oscillation-free, i.e. the control of the state is made non-oscillative, by giving the time parameter I a value which is at least four times greater than the value of the calibration time y, I21l * y. When I21l * y the oscillation of the actual l0 l5 20 25 16 value takes place against the reference value completely without upper and / or lower loops. Oscillations in the actual oscillation process of the actual value against the reference value are thus avoided r24 *) /.

According to another embodiment, the time parameter I is given a value which is at least more than four times as large as the value of the calibration time y, T >> 4 * y. For example, here the time parameter I can be given the value 5 * y, r == 5 * y, which gives an additional 20% stability margin compared to the value I == 4 * y. Higher values for the time parameter I can also be used, for example r == 6 * y, or T == 7 * y, which gives additional margins against oscillation in the control. The higher values for the time parameter I can be used to provide additional margins against incorrect estimates of the vehicle mass m.

According to an embodiment of the present invention, the system to be controlled is a system for acceleration limitation in a vehicle. The condition to be controlled then constitutes an actual acceleration add for the vehicle and the reference value used in the control constitutes a reference acceleration amf for the vehicle.

The inertia of the acceleration limitation system is based here on the mass of the vehicle m. The physical model on which the regulation is based takes into account a difference between the actual acceleration aan and the reference acceleration awf, as the force equation has an appearance according to: Fk + 1 = m * (a, e, - aa ,,) + F,., where (eq. 3) - EH4 is the force that will act on the vehicle at the next iteration; -in is the mass of the vehicle; - aæf is the reference acceleration; 10 15 20 25 30 17 - aan is the actual acceleration; and - Fk is a former current force which acts on the vehicle.

Thus, by this embodiment of the invention, the actual acceleration aaa is controlled against reference acceleration amf so that a limitation of the actual acceleration aaa is obtained.

Since the control is based on a physical model of the acceleration limitation system, this gives an exact control of the actual acceleration aan, which is also easy to calibrate. The magnitude of the time parameter I determines in the manner described above what the oscillation process looks like when the actual acceleration aaa approaches reference acceleration aæf, so that different values of the time parameter I give different behavior for the acceleration limitation system.

According to an embodiment of the present invention, the system to be regulated constitutes a system for braking the vehicle.

Substantially any type of vehicle braking system can be regulated according to this embodiment, for example a service brake, a retarder, or an electromagnetic brake, which can for instance be constituted by an electric motor in a hybrid vehicle. The at least one condition here constitutes an actual vehicle speed va fl and the reference value constitutes a maximum vehicle speed vmax, the value of which can be based, for example, on a speed limit for a road section. The inertia of the vehicle braking system is based on the vehicle mass m.

For this embodiment of the invention, the model of the vehicle braking system takes into account a difference between the actual vehicle acceleration aaa and the reference acceleration amf for the vehicle when power equation has an appearance according to: Bk fl = m * (e-acw.) + Bk, where (eq. 4) 1 . ' 10 - BM4 is a force which will act on said vehicle at the next iteration of the algorithm; - n1 is the vehicle mass; - weave is the reference velocity; - what is the actual speed; - I is the time parameter; - aad is the actual vehicle acceleration; and - Bk is the current braking force which acts on vehicles.

As can be seen from Equation 4, the difference between the actual vehicle acceleration aaa and the reference acceleration aæf depends on the time parameter I since the reference acceleration aæf Vmax -Vact corresponds to the term In the same way as described above, the magnitude of the time parameter I determines the maximum vehicle speed vmax. In this way, the vehicle braking system can be easily calibrated, and possibly given a changed behavior, only by changing the value of the time parameter T, at the same time as a very precise control is obtained. Also for this embodiment, the above-described adjustment of the force equation can be applied to the force equation in Equation 4 by introducing the ratio å in Equation 4, where h is a discretionary factor and y is a calibration time, whereby problems related to noise of the actual acceleration aan and / or misestimations of the vehicle mass m is minimized.

As mentioned above, the control system can be made oscillation-free, i.e. non-oscillatively by giving the time parameter I a suitable value, which is a value which is at least four times greater than the value of the calibration time V, I 211 * y. Even larger margins against oscillations / oscillation can be obtained by using larger values of the time parameter T, for example = 5 * y, I = 6 *) /, or r = 7 * y.

According to an embodiment of the present invention, the system to be controlled is an engine in a vehicle. The state to be controlled in this control then constitutes an actual speed waa for said motor and the reference value against which the actual speed waa is to be controlled constitutes a reference speed wmf for the motor. The inertia of the engine system here consists of an inertia moment] for the engine. The model of the engine system, on which the control is based, takes into account here a difference between a change of an actual speed w¿Ü for the engine and a change of a reference speed wgj for the engine. The difference here is due to a time parameter I, wref -wact because the term includes time parameter I, so the course of the actual speed maa oscillation towards the reference speed wæf can be controlled by the magnitude of the time parameter I, in the same way as described above for different embodiments.

According to the embodiment, the force equation of the model has an appearance according to: Tk + 1: f * (d _ mass) + Tkf where T (eq. 5) - Ykil is a torque which will be emitted by the motor at the next iteration of the algorithm; -] is the moment of inertia of the motor; - aq fi- is the reference speed of the motor; - wad is the actual engine speed; I is the time parameter; l0 l5 20 25 20 - w¿ fl is a change in the actual speed; and - T; is the torque currently emitted by the engine.

An accurate and easily calibrated control of the engine system is obtained by the control algorithm in Equation 5.

According to an embodiment of the present invention, the system to be controlled constitutes a temperature control system for a limited volume, wherein the inertia of the temperature control system is based on a thermal inertia K for the volume. The at least one state here constitutes an actual temperature Tha for the limited volume and the actual temperature Tha is controlled against a reference temperature Ræf for the volume.

The model of the temperature control system takes into account a difference between a change of an actual temperature Tan for the volume and a change of a reference temperature Rgf for this volume. The difference here depends on the time parameter I and an equation for temperature control which according to the model of the temperature control system has an appearance according to: Pk flfl r fl e- (eq. E) I out) + Pk, where - HH4 is a thermal effect which will be emitted in the limited volume at the next iteration of the algorithm; - K is the thermal inertia of the limited volume; - æf is the reference temperature; - T¿ï is the actual temperature; - I is the time parameter; - Täï is a change in the actual temperature; and - PQ is a current thermal effect which is emitted in the limited volume.

The aggressiveness of the oscillation process of the actual temperature Tha against the reference temperature fl wf can be easily set by adjusting the value of the model time parameter T, thereby changing the nature of the oscillation process as described in detail above.

According to an embodiment of the present invention, the system to be regulated constitutes any suitable system connected to a power take-off in the vehicle. Some vehicles, such as trucks and tractors, have power outlets to which a user can connect virtually any equipment, such as a crane, a cement mixer, or various types of power units. In vehicles with previously known control systems implemented, the user has then been able to choose between a predetermined number of preset calibrations of the PID controller for this power take-off, which has not been satisfactory for the users. The large variation between the different types of systems that can be connected to the power take-off means that regulators with a relatively large number of different properties are required to operate these systems satisfactorily.

When the present invention is used for the power take-off, in the manner described above, the control of the system connected to the power take-off can be given a desired character / aggressiveness by a simple adjustment of time parameter I. Hereby the aggressiveness of the control can be chosen substantially freely by the user. can be optimized against the system to be regulated. This results in a very well-adapted control of all the various arbitrary suitable systems which can be connected to the power take-off in the vehicle.

According to one embodiment, time parameter I is given a relatively large value when regulation of systems connected to the power take-off takes place, for example I == 4 * y, == 5 * y, I == 6 * y, or I == 7 * y, which gives l0 l5 20 25 22 safety margins for the control to remain non-oscillating.

The present invention can also be used to determine the vehicle mass m. This is done by analyzing the oscillation processes of actual state values against the reference value. Here the appearance of the actual swing-in process, for example for the actual vehicle speed, is compared with an expected appearance for the same swing-in course, for example with an expected appearance for this vehicle speed vaaßmwa If these two swing-in runs differ, it may be that the estimation of the vehicle mass is incorrect. which makes the regulation according to the invention somewhat inaccurate, whereby the actual vehicle speed has a different appearance than it should have. Therefore, the estimation of the vehicle mass m can be adjusted based on this analysis of the oscillation processes. In order to be able to estimate a ratio between the actual mass nz for the vehicle and the estimated mass rn * for the vehicle, a mathematical analysis of a swing-in process is made, which is described below.

The vehicle always follows the force equation (Newton's second law): -F "V¿l = I% w wwwmg (ekV- 7) When the vehicle is really controlled by the controller, ie when the controller gets what it requests and when the control system is not saturated with maximum torque or towing torque, the velocity profile of the actual vehicle speed vaa will follow a predefined profile which depends only on the two parameters I and Y, which can be deduced as below.

The vehicle is controlled, when the controller really controls, by the equation: lO l5 20 23 F I hm Vref _ Vacgk _ a M am + Fk, where (eq. 8) - EH4 is a force which will act on the vehicle at the next iteration; - h is a discretionary factor; - y is a calibration time; - nï is the mass of the vehicle; - weave is the reference velocity; Liquid is the actual velocity; - I is the time parameter; ammk is the actual acceleration; and - Fk is a current force which acts on the vehicle.

By combining the power equation (equation 7) and the power update equation (equation 8), the expression is obtained: hm * Vref _ Vacßk maacgk fl + Fomgivníng, k +] I T I _ aaczgk + Famgívníngk + maacßk 9) (eq.

Assume that the ambient force F 'is constant from one sample environment to another, which is a reasonable assumption in, for example, a cruise control system, which is relatively slow. Then, after a little algebraic rearrangement, the expression is obtained: 1 m * Vref _ vactk (aactk _ aacl k + 1) o --_ í-aaayk + í Y m T h (eq. 10) If a velocity error is defined as 8 == væ, -VM, and uses (aacßk _ aact, k + 1) h the acceleration is obtained instead of the following ordinary that the term is the numerical derivative of differential equation of the second order for the velocity error of 10 l5 20 24 one also transitions from discrete time to continuous time: (eq. .ll)> | = -; L = 2L is the ratio between the mass estimated so far etc. and the actual mass nz.

From equation ll, the mass ratio; L can be easily solved and calculated.

The problem is that both å and É are often very noisy, which is why the estimate thus also often becomes noisy.

To minimize the problem of noise in measurement signals, the equation is integrated from the moment the controller actually starts to steer the vehicle at time t = 0 until the system has stabilized around the reference after time t = T. Then an expression is obtained for the mass ratio according to: <° i (0) - ~ ° l (T) «(s (T) -s (o)) + í8 (1) df u = 1 ~ v (eq. L2) Equation 12 years easy to realize in a discreet control system and it is guaranteed to converge as long as the speed converges towards the reference.

When this value for the mass ratio 1L is calculated according to equation 12, a new mass estimate n fl y can be obtained by multiplying the old estimate nf by the calculated mass ratio uz (equation 13). This can be repeated at each indentation towards the reference.

A non-limiting simulated example of mass estimation according to this embodiment is shown in Figures 3a and 3b, where the solid curve corresponds to an inversion where the mass estimation is correct and the dotted curve corresponds to an inversion with incorrect mass estimation. For the correct mass estimate, the oscillation becomes oscillation-free (shown in Figure 3a) and the mass ratio LL = 1 (shown in Figure 3b).

For the incorrect mass estimate, the indentation has an overshoot (shown in Figure 3a) and the mass ratio; L = 05 (shown in Figure 3b). The mass here is thus 50 6 underestimated.

Figure 3b clearly shows that the algorithm converges towards the mass ratio values LL = 1 and U fl = Q5 for correct and incorrect mass estimation, respectively, which makes the algorithm very useful for correcting incorrect mass estimates. In addition, the algorithm can be implemented with very low complexity addition.

Those skilled in the art will appreciate that the method of the present invention described above may additionally be implemented in a computer program, which when executed in a computer causes the computer to perform the method. The computer program usually consists of a computer program product 403 stored on a digital storage medium, the computer program being included in a computer program readable medium of the computer program product. Said computer readable medium consists of a suitable memory, such as for example: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk drive, etc .

Figure 4 schematically shows a control unit 400. The control unit 400 comprises a calculation unit 401, which may be constituted by substantially any suitable type of processor or microcomputer, e.g. a Digital Signal Processor (DSP), or an Application Specific Integrated Circuit (ASIC) function.

The calculation unit 401 is connected to a memory unit 402 arranged in the control unit 400, which provides the calculation unit 401 e.g. the stored program code and / or the stored data calculation unit 401 is needed to be able to perform calculations. The calculation unit 401 is also arranged to store partial or final results of calculations in the memory unit 402.

Furthermore, the control unit 400 is provided with devices 411, 412, 413, 414 for receiving and transmitting input and output signals, respectively. These input and output signals may contain waveforms, pulses, or other attributes, which of the input signals receiving devices 411, 413 may be detected as information and may be converted into signals which may be processed by the computing unit 401. These signals are then provided to the computing unit 401. The devices 412 , 414 for transmitting output signals are arranged to convert signals obtained from the calculation unit 401 for creating output signals by e.g. modulate the signals, which can be transmitted to other parts of the control system and / or to systems controlled according to the present invention.

Each of the connections to the devices for receiving and transmitting input and output signals, respectively, may consist of one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Orientated Systems Transport bus), or any other bus configuration; or by a wireless connection.

One skilled in the art will appreciate that the above-mentioned computer may be the computing unit 401 and that the above-mentioned memory may be the memory unit 402. In general, control systems in modern vehicles consist of a communication bus system consisting of one or more communication buses for interconnecting a number of electronic controllers (ECUs), or controllers, and various components located on the vehicle. Such a control system can comprise a large number of control units, and the responsibility for a specific function can be divided into more than one control unit. Vehicles of the type shown thus often comprise considerably more control units than what is shown in Figure 4, which is a choice for those skilled in the art.

The present invention is in the embodiment shown implemented in the control unit 400. However, the invention can also be implemented in whole or in part in one or more other control units already existing with the vehicle or in a control unit dedicated to the present invention.

Those skilled in the art will also appreciate that the above system may be modified according to the various embodiments of the method of the invention.

In addition, the invention relates to a motor vehicle, for example a truck or a bus, comprising at least one control system according to the invention.

The present invention is not limited to the above-described embodiments of the invention but relates to and encompasses all embodiments within the scope of the appended independent claims.

Claims (32)

l0 l5 20 25 28 Patent claim A method for controlling at least one state in a system against a reference value, said at least one state comprising an inertia and said control being performed using a control signal characterized in that - said control is model based, where the model comprises a force equation, or other equation related to said system; and - a magnitude of said control signal is proportional to a change of said at least one state. A method according to claim 1, wherein said system is a cruise control system in a vehicle, said at least one condition constitutes an actual speed for said vehicle, said reference value constitutes a reference velocity web for said vehicle, and said inertia is related to a mass m for said vehicle. A method according to claim 2, wherein said model takes into account a difference between an actual acceleration aad for said vehicle and a reference acceleration amf for said vehicle, wherein said difference depends on a time parameter I. A method according to any one of claims 2-3, wherein said force equation has an appearance according to: "ref -vact TP¿ + 1 == n1 * (- add) - + P}, where - EH4 is a force which will act on said vehicle at the next iteration; -1n is said mass of said vehicle; vmf is said reference speed; - what is said actual speed; - I is a time parameter; l0 l5 20 25 29 - awï is an actual acceleration for said vehicle; and - Fk is a current force which acts on said vehicle. The method of claim 2, wherein said force equation is adjusted to compensate for an actual acceleration signal aad for said vehicle being noisy. A method according to claim 5, wherein said force equation has an appearance according to: P} +1 ==% n1 * (5É¿fÉï5- aan) -kF¿, where - HH4 is a force which will act on said vehicle at the next iteration ; - h is a discretionary factor; - y is a calibration time; -in is said mass for said vehicle; vmf is said reference speed; - what is said actual speed; - I is a time parameter; aaa is an actual acceleration for said vehicle; and - Fk is a current force which acts on said vehicle. A method according to claim 6, wherein said control is made oscillation-free in that said time parameter I is at least four times greater than said calibration time y, r24 * y. A method according to any one of claims 2-7, wherein said model comprises a time parameter I of a magnitude which determines the appearance of an oscillation process of said actual speed vm1 against said reference speed vwf. 10 15 20 25 30 A method according to claim 8, wherein said size of said time parameter I is related to a driving mode of said vehicle. A method according to any one of claims 2-9, wherein a swing-in process for said actual speed with respect to said reference speed vmf is used to determine said mass m for said vehicle. A method according to claim 1, wherein said system is an engine in a vehicle, said at least one condition constitutes an actual speed waa for said engine, said reference value constitutes a reference speed wmf for said engine, and said inertia is based on an inertia moment] for said engine. A method according to claim 11, wherein said model takes into account a difference between a change of an actual speed w¿a for said motor and a change of a reference speed w fl f for said motor, said difference being due to a time parameter I. A method according to any one of claims 11-12, wherein said force equation has an appearance according to: m1 = 1 * (i- w; ...) + T., where - RH4 is a torque which will be emitted by said motor at the next iteration; -] is said moment of inertia of said motor; - ay fl- is said reference speed; - maa is the said actual speed; - I is a time parameter; - w¿ fl is a change of said actual speed; and - T; is a current torque emitted by said motor. 10 15 20 25 31 A method according to any one of claims 11-13, wherein said model comprises a time parameter I of a magnitude which determines the appearance of an oscillation process of said actual speed wan against said reference speed wwf. The method of claim 1, wherein said system is a temperature control system, said at least one state constitutes an actual temperature T @ ï for a limited volume, said reference value constitutes a reference temperature @ æf for said volume, and said inertia is based on a thermal inertia of said volume. volume. The method of claim 15, wherein said model takes into account a difference between a change in an actual temperature Tan for said volume and a change in a reference temperature Rgf for said volume, said difference being due to a time parameter I. A method according to any one of claims 15-16, wherein said equation has an appearance according to: 1% + 1:} (* (E fl I3EE_ I ga) + Pk, where - HH4 is a thermal effect which will be emitted in said volume at the next iteration; - K is said thermal inertia; - Ræf is said reference temperature; - ad is said actual temperature; - I is a time parameter; - Tha is a change of said actual temperature; and - Fk is a current thermal effect given in said volume . A method according to any one of claims 15-17, wherein said model comprises a time parameter I of a magnitude which determines the appearance of a turn-in process for said actual temperature Tàa against said reference temperature fl æf. The method of claim 1, wherein said system is an acceleration limitation system in a vehicle, said at least one state constituting an actual acceleration am1 of said vehicle, said reference value constituting a reference acceleration; for said vehicle, and said inertia is based on a mass m for said vehicle. The method of claim 19, wherein said model takes into account a difference between said actual acceleration aa 'and said reference acceleration amf'. A method according to any one of claims 19-20, wherein said force equation has an appearance according to: Fk + 1 I m * (aref _ aact) + Fkr where - HH4 is a force which will act on said vehicle at the next iteration; -in is said mass for said vehicle; - amf is said reference acceleration; - aan is said actual acceleration; and - Fk is a former current force which acts on said vehicle. A method according to claim 1, wherein said system is a system for braking a vehicle, said at least one condition constitutes an actual speed for said vehicle, said reference value constitutes a maximum speed vmax for said vehicle, and said inertia is based on a mass m for said vehicle. A method according to claim 22, wherein said model takes into account a difference between an actual acceleration aaa l0 15 20 25 30 33 for said vehicle and a reference acceleration amf for said vehicle, wherein said difference depends on a time parameter T. A method according to any one of claims 22-23, wherein said force equation has an appearance according to: Bk + 1 I m * (_ aact) + Bk: where - Bmg is a force which will act on said vehicle on the next iteration; -in is said mass for said vehicle; vmf is said reference speed; - what is said actual speed; - I is a time parameter; - amï is an actual acceleration for said vehicle; and - Bk is a current braking force which acts on said vehicle. A computer program comprising program code, which when said program code is executed in a computer causes said computer to perform the method according to any one of claims 1-24. A computer program product comprising a computer readable medium and a computer program according to claim 25, wherein said computer program is included in said computer readable medium. A control system arranged to control at least one state in a system against a reference value, said state comprising an inertia and said control system is arranged to perform said control by utilizing a control signal characterized by - a model unit, arranged to provide a model comprising a force equation related to said system, said control being model based; and - a control unit, arranged to provide said control signal 34 so that a magnitude of said control signal is proportional to a change of said at least one state. A control system according to claim 27, wherein said system is a cruise control system in a vehicle, said at least one state constitutes an actual speed vmx for said vehicle, said reference value constitutes a reference speed mwf for said vehicle, and said inertia is related to a mass m for said vehicle. A control system according to claim 27, wherein said system is an engine in a vehicle, said at least one condition constitutes an actual speed wad for said engine, said reference value constitutes a reference speed wnf for said engine, and said inertia is based on an inertia moment] for said engine. A control system according to claim 27, wherein said system is a temperature control system, said at least one state constitutes an actual temperature T @ ï for a limited volume, said reference value constitutes a reference temperature Éæf for said volume, and said inertia is based on a thermal inertia for said volume. volume. A control system according to claim 27, wherein said system is an acceleration limitation system in a vehicle, said at least one state constitutes an actual acceleration aa 'for said vehicle, said reference value constitutes a reference acceleration aaf for said vehicle, and said inertia is based on a mass m for said vehicle. A control system according to claim 27, wherein said system is a system for braking said vehicle, said at least one condition constitutes an actual speed vwï for said vehicle, said reference value constitutes a maximum speed vm fl x for said vehicle, and said inertia is based on a mass m for said vehicle.