METHOD AND CONTROL CIRCUIT FOR DETERMINING A MANIPULATED VARIABLE FOR ADJUSTING AN INTAKE MANIFOLD PRESSURE

Abstract

The present invention relates to a method for determining a manipulated variable for adjusting an intake manifold pressure in an internal combustion engine on the basis of a target intake manifold pressure, whereby the target intake manifold pressure is corrected as a function of a limit value of the manipulated variable and/or as a function of a variable that has been influenced by the limit value of the manipulated variable. Moreover, the invention relates to a control circuit for carrying out such a method.

Claims

1. A method for determining a manipulated variable for adjusting an intake manifold pressure in an internal combustion engine on the basis of a target intake manifold pressure, comprising: correcting the target intake manifold pressure as a function of a limit value of the manipulated variable and/or as a function of a variable that has been influenced by the limit value of the manipulated variable.

2. The method according to claim 1, whereby the limit value of the manipulated variable comprises a maximum opening surface area of a throttle valve in the intake manifold and/or a minimum opening surface area of the throttle valve and/or whereby the variable that has been influenced by the limit value of the manipulated variable is a variable containing an opening surface area of the throttle valve that has been limited by the maximum opening surface area of the throttle valve and/or by the minimum opening surface area of the throttle valve.

3. The method according to claim 1, whereby the manipulated variable is determined by means of a PI control (proportional-integral control) of the corrected target intake manifold pressure, by means of a non-linear transformation of the regulated target intake manifold pressure into an unlimited manipulated variable and by means of a limitation of the unlimited manipulated variable by means of the limit value of the manipulated variable.

4. The method according to claim 1, whereby, on the basis of the limit value of the manipulated variable or on the basis of the variable that has been influenced by the limit value of the manipulated variable, a correction value of the target intake manifold pressure to correct the target intake manifold pressure is determined by means of a transformation (50, 70).

5. The method according to claim 2, whereby the maximum opening surface area of the throttle valve is transformed into a maximally achievable intake manifold pressure, and the minimum opening surface area of the throttle valve is transformed into a minimally achievable intake manifold pressure, and the target intake manifold pressure is limited as a function of the transformed maximally achievable intake manifold pressure and as a function of the transformed minimally achievable intake manifold pressure.

6. The method according to claim 1, whereby the transformation of the maximum opening surface area of the throttle valve into the maximally achievable intake manifold pressure is based on the following relationship:
p.sup.*,max=p.sub.sr+{tilde over (p)}.sub.sr+bA.sub.eff.sup.max; and whereby the transformation of the minimal opening surface area of the throttle valve into the minimally achievable intake manifold pressure is based on the following relationship:
p.sup.*,min=p.sub.sr+{tilde over (p)}.sub.sr+bA.sub.eff.sup.min wherein p.sub.sr stands for a prognosticated change in the intake manifold pressure, {tilde over (p)}.sub.sr stands for a measured intake manifold pressure, b stands for a variable that is influenced by a flow through the throttle valve, by a leakage of the throttle valve, by a mass flow through the throttle valve and by the P controller, A.sub.eff.sup.max stands for the maximum opening surface area of the throttle valve, and A.sub.eff.sup.min stands for the minimum opening surface area of the throttle valve.

7. The method according to claim 2, whereby the difference between an unlimited opening surface area of the throttle valve and the limited opening surface area of the throttle valve is transformed into a pressure differential, and the target intake manifold pressure is adapted as a function of the transformed pressure differential.

8. The method according to claim 1, whereby the following applies for the determination of the transformed pressure differential p*.sub.sr:
p*.sub.sr=c(A.sub.efcLimA.sub.effUnLim), wherein c stands for a variable that has been influenced by the P controller and by a flow factor through the throttle valve, A.sub.efcLim stands for the limited opening surface area of the throttle valve, and A.sub.efcUnLim stands for unlimited opening surface area of the throttle valve.

9. A control circuit for determining a manipulated variable for adjusting an intake manifold pressure in an internal combustion engine on the basis of a target intake manifold pressure, comprising: a correction unit for correcting the target intake manifold pressure as a function of a limit value of the manipulated variable and/or as a function of the variable that has been influenced by the limit value of the manipulated variable.

10. The control circuit according to claim 9, which, on the basis of the limit value of the manipulated variable or on the basis of the variable that has been influenced by the limit value of the manipulated variable, also comprises an inverse transformation means that is configured to determine a correction value for the target intake manifold pressure for correcting the target intake manifold pressure by means of a transformation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be explained by way of examples and making reference to the accompanying drawings. The following is shown:

[0040] FIG. 1: schematically, a depiction of a drive arrangement and of a control unit with a control circuit for determining an opening surface area of the throttle valve;

[0041] FIG. 2: schematically, a conventional control circuit;

[0042] FIG. 3: schematically, a first embodiment of a control circuit according to the invention, with a limitation of the target intake manifold pressure;

[0043] FIG. 4: a flow diagram of a method for determining a manipulated variable for adjusting an intake manifold pressure in an internal combustion engine, with the control circuit of the first embodiment;

[0044] FIG. 5: schematically, a second embodiment of a control circuit according to the invention, with a limitation of the target intake manifold pressure; and

[0045] FIG. 6: a flow diagram of a method for determining a manipulated variable for adjusting an intake manifold pressure in an internal combustion engine, with the control circuit of the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0046] FIG. 1 shows a section of a drive arrangement 1. The drive arrangement 1 has an intake manifold 10, a throttle valve 11, an internal combustion engine 12, an exhaust gas turbocharger 13 and an exhaust gas channel 14. The throttle valve 11 is arranged in the intake manifold 10 and is configured to regulate the feed of fresh air into the internal combustion engine 12. The internal combustion engine 12 is connected to the intake manifold 10 and to the exhaust gas channel 14. The exhaust gas turbocharger 13, which is provided to regulate the charge pressure in the intake manifold 10, has a turbine 130 and a compressor 131 that is connected to the turbine 130 via a shaft. The turbine 130 is arranged in the exhaust gas channel 14 and it is driven by exhaust gas that is flowing out of the internal combustion engine 12. The compressor 131 is arranged in the intake manifold 10 and, driven by the turbine 130, it compresses the air in the intake manifold 10.

[0047] The drive arrangement 1 also comprises an engine control unit 2 that has a control circuit 20 for adjusting an intake manifold pressure.

[0048] In conventional drive devices, the control circuit 20 is often configured as described with reference to FIG. 2. FIG. 2 shows a control circuit 3 with an intake manifold sensor 30, a disturbance variable observer 31, a PI controller that comprises a P controller 32P and an I controller 32I, a non-linear transformer 33, a manipulated variable limiter 34 and a conversion and adjustment unit 35.

[0049] The sensor 30 for the intake manifold pressure measures the current actual intake manifold pressure p.sub.sr and sends a measurement signal {circumflex over (p)}.sub.sr representing the detected actual intake manifold pressure p.sub.sr to a first differentiator 36a that is situated upstream from the I controller 32I, to the disturbance variable observer 31 that is situated upstream from the first differentiator 36a, and to a second differentiator 36b.

[0050] The disturbance variable observer 31 is provided to determine an anticipated intake manifold pressure {tilde over (p)}.sub.sr on the basis of a target intake manifold pressure p*.sub.sr and on the basis of the measurement signal {circumflex over (p)}.sub.sr by means of a model that describes the influence of the throttle valve on the intake manifold pressure as well as by means of a model of the intake manifold pressure. In this context, the anticipated intake manifold pressure {tilde over (p)}.sub.sr indicates which actual intake manifold pressure will set in.

[0051] The first differentiator 36a forms a difference between the measurement signal {circumflex over (p)}.sub.sr and the anticipated intake manifold pressure {tilde over (p)}.sub.sr and forwards it to the I controller 32I. The I controller 32I subjects the difference between the measurement signal {circumflex over (p)}.sub.sr and the anticipated intake manifold pressure {tilde over (p)}.sub.sr to an integral control and forwards the result p.sub.sr to a third differentiator 36c that is situated downstream from the second differentiator 36b and upstream from the P controller 32P.

[0052] The second differentiator 36b forms a difference from the target intake manifold pressure p*.sub.sr and the measurement signal {circumflex over (p)}.sub.sr and forwards it to the third differentiator 36c. The third differentiator 36c forms a difference from the difference between the target intake manifold pressure P*.sub.sr and the measurement signal {circumflex over (p)}.sub.sr and the result p.sub.sr of the I controller and forwards the result to the P controller 32P.

[0053] The P controller 32P subjects the result of the third differentiator 36c to a proportional control and forwards the result to the non-linear transformer 33. The transformer 33 carries out a non-linear transformation in order to determine a target opening surface area of the throttle valve and forwards this target opening surface area to the manipulated variable limiter 34. By means of a maximally possible opening surface area A.sub.eff.sup.max of the throttle valve and a minimally possible opening surface area A.sub.eff.sup.min of the throttle valve, which are prescribed by the configuration of the throttle valve and by its installation in the intake manifold, the manipulated variable limiter 34 corrects the target opening surface area of the throttle valve and forwards the corrected target opening surface area of the throttle valve to the calculation and adjustment unit 35. The manipulated variable limiter 34 checks whether the target opening surface area of the throttle valve falls between the maximally possible opening surface area A.sub.eff.sup.max of the throttle valve and the minimally possible opening surface area A.sub.eff.sup.min of the throttle valve, and then adapts the opening surface area of the throttle valve only if this is not the case. On the basis of the corrected opening surface area of the throttle valve (limited opening surface area of the throttle valve), the calculation and adjustment unit 35 calculates a position of the throttle valve and then adjusts this position of the throttle valve. In this manner, the actual intake manifold pressure p.sub.sr is adjusted.

[0054] The control circuit 3 described with reference to FIG. 2 entails the drawback that, if the target intake manifold pressure tends to move towards a value at which the opening surface area of the throttle valve is greater or smaller than the maximally or minimally possible opening surface area of the throttle valve, no correction is possible over a prolonged period of time, as a result of which the I term rises steadily (windup). If the target intake manifold pressure subsequently tends to move towards a value at which the opening surface area of the throttle valve assumes a value between the maximally and minimally possible opening surface area of the throttle valve, then marked overshooting of the controller can occur since the high I term first has to be reduced once again by means of overshooting. For this reason, up until now, the I controller in the first case had to be frozen, which entails a demanding re-initialization procedure.

[0055] Below, two embodiments of a control circuit according to the invention will be described on the basis of the control circuit 3 shown in FIG. 2, and these embodiments render the freezing of the I controller and thus also the re-initialization procedure superfluous, thereby considerably simplifying the control of the intake manifold pressure.

[0056] FIG. 3 shows a first embodiment of a control circuit 4 according to the invention. In addition to the components of the control circuit 3 of FIG. 2, the control circuit 4 has an inverse transformation means 40 and a target variable limiter 41. Taking into account the measurement signal {circumflex over (p)}.sub.sr and the result p.sub.sr of the I controller 32I, the inverse transformation means 40 is configured to transform the maximally possible opening surface area A.sub.eff.sup.max of the throttle valve into a maximally achievable target intake manifold pressure p.sup.*,max and to transform the minimally possible opening surface area A.sub.eff.sup.min of the throttle valve into a minimally achievable target intake manifold pressure p.sup.*,min. The target variable limiter 41 is configured to correct the target intake manifold pressure p*.sub.sr as a function of the maximally achievable target intake manifold pressure p.sup.*,max and as a function of the minimally achievable target intake manifold pressure p.sup.*,min. In this process, the target variable limiter 41 functions analogously to the manipulated variable limiter 34.

[0057] FIG. 4 shows a flow diagram of a method 5 to correct the target intake manifold pressure by means of the control circuit 4 of the first embodiment.

[0058] In 50, the maximally possible opening surface area of the throttle valve is transformed into a maximally achievable intake manifold pressure. The transformation takes place on the basis of the above-mentioned relationships

[00003]$\begin{array}{cc}{p}^{*,\max }=.Math..Math.p_{\mathrm{sr}}+{\tilde{p}}_{\mathrm{sr}}+\frac{{}_{\mathrm{mult}}}{36000.Math.K_4}.Math.\left(A_{\mathrm{eff}}^{\max }+A_{\mathrm{efcOffset}}-{}_{\mathrm{off}}\right).Math..Math.\mathrm{and}& \left(1.Math.a\right)\\ p^{*,\min }=.Math..Math.p_{\mathrm{sr}}+{\tilde{p}}_{\mathrm{sr}}+\frac{{}_{\mathrm{mult}}}{36000.Math.K_4}.Math.\left(A_{\mathrm{eff}}^{\min }+A_{\mathrm{efcOffset}}-{}_{\mathrm{off}}\right)& \left(2.Math.a\right)\end{array}$

[0059] In 51, the target intake manifold pressure is limited as a function of the transformed maximally achievable intake manifold pressure p.sup.*,max and as a function of the transformed minimally achievable intake manifold pressure p.sup.*,min. The target variable limiter 41 checks whether the target intake manifold pressure p*.sub.sr falls between the maximally achievable intake manifold pressure p.sup.*,max and the minimally achievable intake manifold pressure p.sup.*,min and it adapts the target intake manifold pressure p*.sub.sr only if this is not the case.

[0060] Owing to the correction of the target intake manifold pressure p*.sub.sr by means of the limitation procedure, it no longer happens that the target intake manifold pressure tends to move towards a value at which the opening surface area of the throttle valve exceeds the maximally possible opening surface area of the throttle valve or falls below the minimally possible opening surface area of the throttle valve, since an achievable opening surface area of the throttle valve or an achievable position of the throttle valve exists in order to set each corrected target intake manifold pressure. Consequently, the control circuit can be continuously corrected and freezing of the I controller as well as a re-initialization procedure become superfluous.

[0061] FIG. 5 shows a second embodiment of a control circuit 6 according to the invention. In addition to the components of the control circuit 3 shown in FIG. 2, the control circuit 6 comprises an inverse transformation means 60 and a correction unit 61. The inverse transformation means 60 is configured to transform a difference between the unlimited opening surface area A.sub.efcUnLim of the throttle valve and the limited opening surface area A.sub.efcLim of the throttle valve into a pressure differential p*.sub.sr. The correction unit 61 is configured as an adder that adds the pressure differential p*.sub.sr and the target intake manifold pressure p*.sub.sr and then outputs the sum as the corrected target intake manifold pressure p*.sub.sr.

[0062] FIG. 6 shows a flow diagram of a method 7 to correct the target intake manifold pressure by means of the control circuit 6 of the second embodiment.

[0063] In 70, a difference A.sub.efcLimA.sub.efcUnLim between the unlimited opening surface area A.sub.efcLim of the throttle valve and the limited opening surface area A.sub.efcUnLim of the throttle valve is formed, and the difference A.sub.efcLimA.sub.efcUnLim of the throttle valve is transformed into the pressure differential p*.sub.sr in accordance with the above-mentioned relationship given below:

p*.sub.sr=K.sub.5 360000 .sub.mult(A.sub.efcLimA.sub.effUnLim)(3a)

[0064] In 71, the sum is formed from the pressure differential p*.sub.sr and the target intake manifold pressure p*.sub.sr and then it is output as the corrected target intake manifold pressure p*.sub.sr.

[0065] The inverse transformation means 60 and the correction unit 61, together with the second and third differentiators, the P controller, the non-linear transformer and the manipulated variable limiter, form an algebraic loop. If necessary, the algebraic loop can be resolved, for instance, as a fixed-point iteration.

[0066] Once again, the case in which the target intake manifold pressure tends to move towards a value at which the opening surface area of the throttle valve is greater than or smaller than the maximally or minimally possible opening surface area of the throttle valve is effectively prevented by the correction of the target intake manifold pressure p*.sub.sr. Consequently, the control circuit can be continuously corrected and freezing of the I controller as well as a re-initialization procedure become superfluous.

LIST OF REFERENCE NUMERALS

[0067] 1 drive device [0068] 10 intake manifold [0069] 11 throttle valve [0070] 12 internal combustion engine [0071] 13 exhaust gas turbocharger [0072] 130 turbine [0073] 131 compressor [0074] 14 exhaust gas channel [0075] 2 engine control unit [0076] 20 control circuit for adjusting an intake manifold pressure [0077] 3 conventional control circuit [0078] 30 sensor for the intake manifold pressure [0079] 31 disturbance variable observer [0080] 32P P controller [0081] 32I I controller [0082] 33 non-linear transformer [0083] 34 manipulated variable limiter [0084] 35 conversion and adjustment unit [0085] 36a, 36b, 35c differentiator [0086] 4 control circuit according to the first embodiment [0087] 40 inverse transformation means [0088] 41 target variable limiter [0089] 5 method for correcting the target intake manifold pressure by means of the control circuit 4 [0090] 50 transformation of the maximally and minimally possible opening surface areas of the throttle valve [0091] 51 limiting the target intake manifold pressure [0092] 6 control circuit according to the second embodiment [0093] 60 inverse transformation means [0094] 61 correction unit [0095] 7 method for correcting the target intake manifold pressure by means of the control circuit 6 [0096] 70 transformation of the maximally and minimally possible opening surface areas of the throttle valve [0097] 71 limiting the target intake manifold pressure