GB2279769A

GB2279769A - Method and equipment for use in controlling engine operation

Info

Publication number: GB2279769A
Application number: GB9413328A
Authority: GB
Inventors: Gerhard Stumpp; Gerhard Engel; Manfred Birk; Peter Rupp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-07-05
Filing date: 1994-07-01
Publication date: 1995-01-11
Anticipated expiration: 2014-07-01
Also published as: GB2279769B; DE4322319A1; DE4322319C2; GB9413328D0; FR2707348B1; FR2707348A1

Description

2279769 - 1 METHOD AND EQUIPMENT FOR OBTAINING A CONTROL VALUE FOR USE IN

CONTROLLING ENGINE OPERATION The present invention relates to a method and equipment for obtaining a control value for use in controlling operation of an internal combustion engine, especially a compression-ignition engine.

A method and a device for the control of an internal combustion engine are described in DE-OS 42 07 541, in which a first regulator is provided to compare a target value with an actual value and, starting therefrom, presets a control magnitude. A second regulator similarly compares an actual value and a target value and, in dependence on the comparison result, generates a second control signal for the drive control of a setting member. The two regulators are connected one after the other as cascade regulators in such a manner that the control signal of the first regulator serves as target value for the second regulator. In this method and this device, the dynamic behaviour of the engine is not always satisfactory. Thus, especially during acceleration, the exhaust gas composition or the acceleration of the motor vehicle driven by the engine is not optimal.

controlled engine.

There is thus scope for improvement in engine control methods and equipment with respect to dynamic behaviour and accuracy of the controlled engine.

According to a first aspect of the present invention there is provided a method of obtaining a control value for use in controlling operation of an internal combustion engine, comprising the steps of determining a first actual value dependent on the lambda value of the engine exhaust gas, determining a first control value in dependence on the first actual value and a first target value, determining a second actual value dependent on the engine induction air quantity, and determining a second control value in dependence on the second actual value and a second target value, the second target value being set in the presence and the first target value in the absence of a given engine operating condition.

According to a second aspect of the invention there is provided equipment for obtaining a control value for use in controlling operation of an internal combustion engine comprising means for determining a first actual value dependent on the lambda value of the engine exhaust gas, determining a first control value in dependence on the first actual value and a first target value, determining a second actual value dependent on the engine induction air quantity, and determining a second control value in dependence on the second actual value and a second target value, the second target value being set in the presence and the first target value in the absence of a given engine operating condition.

Examples of the method and embodiments of the equipment of the present invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic block diagram of principal parts of control means for an internal combustion engine; Fig. 2 i Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 s a block diagram of first equipment embodying the invention; is a diagram showing the relationship between injected fuel quantity and target value of an air quantity regulator in the equipment; is a block diagram of second equipment embodying the invention; is a block diagram of third equipment embodying the invention; is a block diagram of a fourth equipment embodying the invention; is a block diagram of a fifth equipment embodying the invention; and is a block diagram of a sixth equipment embodying the invention; Referring now to the drawings there is shown in Fig. 1 the principal elements of control means for a compressionignition internal combustion engine 100. The control means is not, however restricted to compression- ignition engines and can be used for other types of engine. In that case, appropriate components must be The control means can be realised by a hardware circuit computer in conjunction with an appropriate program exchanged. or by a sequence.

The control means comprises a first setting member 110, which influences exhaust gas return rate, arranged in the region of the engine 100. The setting element is preferably an appropriate valve in a duct which connects the engine exhaust pipe with the engine induction duct. A second setting member 120 is similarly arranged in the region of the engine 100 and determines the quantity of fuel fed to the engine. In the case of a diesel engine, the second setting member can be a regulating rod or an electromagnetic valve which fixes the beginning and end of injection, whereas in the case of an engine with applied ignition it can serve for the influencing of a throttle flap.

In addition, an air mass meter 130, which delivers a signal MLI indicating the inducted quantity of air, is arranged in the region of the engine 100. Also present is a lambda sensor 135, which provides a lambda value;,. This value is a measure of the oxygen concentration in the exhaust gas, preferably a value proportional to the oxygen concentration.

An exhaust gas return control 140 is acted on by the air quantity signal MLI and the lambda value X, as well as by an output signal QK of a quantity presetting device 160. The control acts on the first setting member 110 by a control magnitude which is designated as drive control signal TV. The control 160 acts on a quantity control 150 by the fuel quantity signal QK. This quantity control 150 translates this fuel quantity signal QK into a drive control signal for action on the second setting member 120.

The quantity presetting device 160 is connected with inter alia an accelerator pedal setting transmitter 168 and with sensors 164. The transmitter 168 produces a signal which corresponds to the intention of the driver. The sensors 164 detect operating parameters, for example rotational speed N of the engine, fuel injection instant, pressure and temperature of in particular the inducted air.

In operation of the control means, starting from the accelerator pedal setting and the parameter values from the sensors 164, the quantity presetting device 160 determines the fuel quantity QK to be injected. quantity signal QK setting member 120.

The quantity control 150 translates this into a drive control signal for the second In the simplest case, the quantity-presetting device is a pump characteristic values field in which the relationship between each quantity of fuel to be injected and the corresponding drive control signal, for example a voltage for a regulating rod setting member, is filed. According to the position of the second setting member 120, a corresponding quantity of fuel is admetered to the engine 100.

In addition, the output signal QK of the device 160 is applied to the exhaust gas return control 140. Starting from the signal QK and the further magnitudes of inducted air quantity MLI and lambda value X- of the exhaust gas the control 140 determines the signal TV for drive control of the first setting member 110, which influences the proportion of the exhayst gas conducted back into the engine induction duct.

It is a problem with such control means that, due to mechanical tolerances and drift phenomena, the relationship between the signal QK and the actually injected quantity of fuel changes in the course of operation of the engine. Since the output signal of the device 160 is used by the exhaust gas return control 140, a false exhaust gas return rate can result in some circumstances. Appropriate measures must be taken in order to compensate for this. Moreover, the output signal of the lambda sensor 135 suffers from an appreciable delay time and reacts very slowly to corresponding changes.

The exhaust gas return control 140 is illustrated in greater detail in Fig. 2. Elements, which have alreayd been described in connection with Fig. 1, are denoted by the same reference numerals.

The control 14 essentially consists of a regulator 200, which is also designated as an air quantity regulator. The regulator 200 forms a second control magnitude, which is also designated as a control signal TV, for action on the first setting member 110. The regulator 200 processes the output signal of a comparison point 210 as input magnitude. The input values at the comparison point 210 are a second actual value, which corresponds to the output signal MLI of the air quantity meter 130 and has a negative sign. and a second target value MLS, which corresponds to the output signal of a maximum value selector 220 and has a positive sign.

The input values at the maximum value selector 220 are the output value of a control 230, which is also designated as a preliminary control magnitude, and the output value, which is also designated as a second control magnitude, of a regulator 240. The fuel quantity signal QK is applied as input magnitude to the control 230. The regulator 240 processes the output signal of a comparison point 245. The input values at the comparison point 250 are a first target value of a first target value presetting device 250, which has a positive sign, and a first actual value MLB of a first actual value presetting device 270, which is also designated as an air quantity computation and has a negative sign. The output signal of a delay device 260, which is in turn acted on by the fuel quantity signal QK, is fed to both the device 250 and the device 270. The device 270 also processes the output signal of the lambda sensor 135, in order to provide the actual value MLB.

The illustrated equipment is essentially a cascade regulating system with a subordinate air quantity regulator and a superordinate lambda regulator. The preliminary control 230, which is connected in parallel with the superordinate lambda regulator, is provided for improvement of the dynamic range.

This equipment operates as follows: The control 230 presets a preliminary control magnitude starting from the fuel quantity QK.

This preliminary control magnitude is also denoted as a control value in the following. Preferably, this control value is chosen so that it assumes a constant value for all fuel quantities. In the simplest case, the value is fixed. However, the value can be taken from a characteristic values field, for example in dependence on engine rotational speed and injected fuel quantity. The value provided by the control 130 is compared in the maximum selection 220 with the output signal value of the regulator 240.

The regulator 240 is a lambda regulator. The target value presetting device 250 presets a target value for the regulator 240. This is compared with an actual value which is preset by the air quantity computation device 270.

The device 250 forms the first target value starting from the fuel quantity signal QK delayed by the delay device 260. In this case, a linear relationship preferably exists between the fuel quantity QK and the corresoonding target value. The regulator in this embodiment processes a magnitude representing inducted air quantity. This means that the target value represents an air quantity target value. A linear relationship between air quantity and injected quantity of fuel corresponds to a constant lambda value as a function of the quantity of fuel. It is, however, also possible for the target value to be filed in a characteristic values field in dependence on rotational speed and quantity of fuel. The device 270 determines the actual value of the air quantity starting from the injected fuel quantity QK and the output signal of the lambda probe 135. The following relationship exists between the air quantity MLI and the other two magnitudes:

MLI = 14.5 X QK.

A lean probe, which supp 1 i es an output signal which corresponds to the oxygen concentration in the exhaust gas, is preferably used as the-lambda probe 135.

1 The lambda regulator 240, which is preferably a proportional integral regulator, produces the second control value starting from the deviation between the output signal of the first target value presetting device 250 and the first actual value presetting device 270. This control value is a measure of the deviation between the actual oxygen concentration and the oxygen concentration to be expected based on the fuel quantity signal QK.

The selector 220 selects the greater one of the output signal values of the control 230 and the regulator 240 and conducts it as second target value MLS to the comparison point 210 upstream of the air quantity regulator 200. The selected value MLS is then compared with the air quantity MLI measured by the air quantity meter 130.

In dependence on the result of the comparison of these two signal val ues, the air quantity meter 200, which is preferably a proportional - integral regulator, forms the second control signal value TV for action on the exhaust gas return setti-ng member 110.

The value TV is preferably a keying ratio.

This procedure offers the ad vantage that the rapid air quantity regulator 200 is active in a].] operational states. The maximum value selector 220 decides whether a constant air quantity or a constant lambda value is regulated towards. The constant air quantity is preset by the control 230 and the constant lambda value by the device 250. The selector 220 applies the greater one of these two values to the regulator 200. Thus, a constant air quantity is regulated towards for small quantities of fuel and a constant lambda value is regulated towards for small quantities of fuel and a constant lambda value is regulated towards for large quantities of fuel.

This means that the control 230 is active in the case of small quantities of fuel and the lambda regulator 240 is active in the case of large quantities of fuel. The transfer between these two branches takes place by means of the maximum value selector 220.

The relationship between the injected fuel quantity QK and the target value MLS of the regulator 200 is shown in Fig. 3. The presetting for the lambda regulator is entered in dashed lines and corresponds to the output signal of the device 250. Since the device 250 presets a constant lambda value for all fuel quantities QK, a linear relationship results between air quantity target value MLS and the quantity of fuel.

The output signal of the control 230 is entered in chain dotted lines. The control presets a constant air quantity target value MLS as a function of the fuel quantity QK. It is achieved by the selector 220 that the output signal of the control 230 is used as target value MLS for small quantities and the output signal of the regulator 240 is used as target value MLS for large quantities of fuel. This is denoted by a solid line.

A further embodiment, in which a different form of transfer between the lambda regulator 240 and the control 230 takes place, is illustrated in Fig. 4. Corresponding elements, which have already been described in connection with Fig. 2, are denoted by the same reference numerals. It is significant that the maximum value selector 220 is replaced by a switching means 400, a logical interlinking point 420 and a logical switch-off system 410. This means that the output signal value of the regulator 240 is applied, 11 preferably with positive sign, by way of the switching means 400 to one input of the interlinking point 420, at the other input of which the output signal value of the control 230 is present, preferably also with positive sign. The output signal of the interlinking point 420 then serves as target value and is fed with positive sign to the comparison point 210.

A fuel quantity signal QK, a rotational speed signal N and possibly further operating parameters are applied as inputs to the logical switch off system 410. The system 410 acts on the switching means 400 by a drive control signal shown by a dashed line.

The switch-off system 410 in conjunction with the switching means 400 takes over the function of the selector 220 in Fig. 2.

For small quantities of fuel, the switching means 400 is in its open state and merely the output signal of the control 230 is passed to the interlinking point 420 and thus determines the target value for the air quantity regulator. For large quantities of fuel, the switching means 400 is closed by the system 410.

The system 410 differentiates, in dependence on the characteristic of the optimum target values, between operating ranges in which an almost constant air quantity is preset as a function of the fuel quantity and ranges in which an almost constant lambda value is preset in dependence on the fuel quantity. Thus, for examkple, the switch is opened for small fuel quantities and for low rotational speeds which lie below about 1,500 revolutions per minute. In the remaining operating ranges, it is closed. On switching on of the lambda regulator 240, the integral proportion is preset as 0. On switching off, the setting magnitude of the regulator 240 is lowered to 0 with delay.

This means that the control 230 fixes the target value for the air quantity regulator in the case of small quantities of fuel. In this case, merely the air quantity regulator 200 is effective. The lambda regulator 240 is activated only for greater quantities of fuel in that the switching means 400 closes. This means that the control 230 presets a base value for the air quantity target value MLS, on which the control magnitude of the lambda regulator 240 is superimposed. This logical interlinking preferably takes place additively, but can take place multiplicatively or in another manner.

Only a low accuracy of this value is required in the case of small fuel quantities. In the case of large fuel quantities, the air quantity must be set as accurately as possible. If too little air is set or too great an exhaust gas return is set, this can lead to inacceptable levels of sootemission. If, thereagainst, a lower exhaust gas return rate is set for the sake of safety, excessive output of nitrogen oxide results.

It is therefore provided that for large quantities of fuel this base value is supplied by the control 230 and corrected by means of the lambda regulator 240.

A further refinement provides that the control 230 simulates a course of the air quantity value illustrated in Figure 3. For this purpose a constant air quantity value is preset for small fuel quantities and a linearly rising air quantity target value is preset for greater fuel quantities.

This procedure offers the advantage that target value errors, due to an inexactly known fuel quantity QK, are avoided by the lambda regulator 240 in the range of the critical large quantities of fuel, as both regulators influence the setting member as cascade regulators. This means that the lambda regulator 240 corrects the air quantity target value MLS for great fuel quantities.

Fig. 5 shows a further embodiment of the equipment. Apart from the elements, which have already been described in connection with the preceding figures and are denoted by the same reference numerals, the following changes are provided: The output signal MLI of the air quantity meter 130 is applied, as in the previous figures, to the comparison point 210 and also to a dead time member 500 and from there by way of a delay member 510 to the comparison point 245. In this embodiment, the regulator 240 is dispensed with or replaced by a proportional member. In addition, the control 230 is structured so that the characteristic course as a function of the fuel quantity exactly corresponds to the corresponding air requirement. The comparison result from the comparison point 245 is then applied directly by way of the switching means 400 to the logical interlinking point 420.

By means of the dead time member 500 and the delay member 510, the temporal behaviour of the measured air quantity signal MLI and the air quantity preset by the quantity computation are matched to each other in time. The signal presented by the lambda probe suffers from an appreciable time delay as well as a dead time. This dead time and the time delay are compensated for by the dead time member 500 and the delay member 510.

The measured quantity MLI is then compared in the comparison point 245 with the air quantity which is computed starting out from the fuel quantity signal QK and the measured lambda value. The signal present at the output of the interlinking point 245 is a measure of the error of the fuel quantity signal, i.e. the deviation of the fuel quantity signal from the actually injected fuel quantity. Starting from this error signal, the output signal of the control 230 is then corrected at the point 420.

The logical switch-off system ensures that this correction takes place only in certain operational states, preferably when the fuel quantity QK is above a threshold value.

In this embodiment, the lambda regulator is reduced to a comparison of the air quantity measured by means of the air quantity meter 130 with the air quantity MLB computed by means of the output signal of the lambda sensor and the fuel quantity value QK. The difference, which is formed starting from both these signals, serves for the correction of the target value preset by the control 230.

The difference present at the output of the comparator 245 corresponds to the error of the target value which is based on the erroneous fuel quantity QK. This error in the fuel quantity indicates the difference between the expected quantity of fuel and the actually injected quantity of fuel for a certain fuel quantity value.

In the embodiment according to Fig. 6, the air quantity computation device 270, the dead time member 500 and the delay device 510 are replaced by an observer 600. The output signals of the regulator 200 and the lambda sensor 135 and the fuel quantity signal QK are fed to the observer. The observer 600 supplies a computed air quantity MLB to the interlinking point 245.

This observer determines the target value for the air quantity with the aid of a model starting from the control signal TV of the air quantity regulator 200 and the fuel quantity value QK. A more rapid, dynamically improved air quantity signal can be obtained by means of this observer.

The observer operates as follows: Starting from the fuel quantity QK and the lambda value of the exhaust gas, an air quantity is determined as for the air quantity computation by the device 270.

The observer contains a simple path model which replicates the transmission behaviour of the path, i.e. the engine. The path model essentially comprises time members for the replication of the dynamic behaviour of the path. This path model, apart from the control magnitude TV takes into consideration the rotational speed N and the fuel quantity QK. Starting from these and possibly further magnitudes, the path model determines a value for the air quantity. This model value is then compared with the air quantity value computed starting from the lambda value. The path model is then adapted by means of this comparison value.

In pleace of the ocntrol magnitude TV, a magnitude can be used which represents a measure of the stroke of the exhaust gas return valve. Preferably, the target value for the stroke is used. Alternatively, the target air quantity can also be used.

The' observer 600 can also be used in conjunction with the embodiments according to Figs. 2, 4, and 5. In this case, the observer takes the place of the air quantity computation device 270.

A further embodiment is illustrated in Fig. 7. In this embodiment, the difference signal, which is present at the logical interlinking point 245 and is a measure of the quantity error, is used for adaptation of the pump characteristic values field or quantity control 150. Corresponding elements of the earlier figures are identified by the same reference numerals.

The difference signal is applied by way of a switching means 705 to a first correction block 710 and by way of a switching means 715 to a second correction block 720. The two switching means are controlled in their drive by an adaptation control 700.

In certain operating ranges, in which multiplicative errors predominate, the adaptation control 700 closes the switching means 715. In thse operating ranges, the correction block 720 learns a correction factor. The correction block preferably operates a a slow integrator. The correction factor is used constantly for multiplicative correction of-the fuel quantity signal.

Accordingly, a corresponding additive correction value is learned by the correction block 710 in operating conditions in which the additive errors predominate. This correction value is used constantly for the additive correction of the fuel quantity signal.

When the difference at the logical interlinking point 245 is zero, i.e. the measured air quantity MLI and the computed air quantity MLB are equal, this means that the error between the fuel quantity value and the actually injected fuel quantity has become zero. By means of this procedure, the quantity errors in the pump characteristic values field can be minimised.

The fuel quantity is corrected starting out from the difference between the measured air quantity value and the air quantity value computed from the lambda value. Alternatively or additionally, the values stored in dependence on the quantity of fuel in the pump characteristic values field can be corrected.

A further embodiment is illustrated in Fig. 8. Corresponding elements of the earlier figures are again denoted by the same reference numerals. The significant difference from the preceding equipment is that a cascade structure is not provided here, but rather a parallel structure.

The fuel quantity value QK is applied to a first characteristic values field 800 and a second characteristic value field 810. The output signal of the field 800 is applied with positive sign to the interlinking point 210, to which the output signal of the air quantity meter 130 is fed with negative sign. The interlinking point 210 is connected by way of the air quantity regulator 200 with the input of a minimum value selector 820.

The output signal of the second field 810 is applied with positive sign to the interlinking point 245, at the second input of which the output signal of the lambda sensor 135 is present with negative sign. The output of the interlinking point 245 is also connected with the selector 820 by way of the lambda regulator 240.

The selector 820 acts on the -exhaust gas return setting member 110 by the drive control signal TV.

Starting from the fuel quantity and possibly further operating parameters, the field 800 presets a target values MLS for the regulator 200. The field 810 correspondingly presets a target value for the regulator 240. The interlinking point 210 compares the target value MLS for the regulator 200 with the actually measured air quantity value MLI. Starting therefrom, the regulator 200 determines a setting magnitude. An analogous procedure is performed for the regulator 240. The two setting magnitudes are then compared with each other in the minimum value selector 820 and the smaller one of these signals is employed as the drive control signal TV for the exhaust gas return setting member 110.

In this equipment, too, the air quantity regulation is active for small fuel quantities and the lambda regulation is active for large fuel quantities. The air quantity regulation is dynamically better than the lambda regulation, which suffers from dead time. In the region of constant target air quantity, the exhaust gas return is limited more accurately than by the lambda regulation, since the fuel quantity error is not effective. In the range of high oxygen concentrations, the actual quantity error is less than the lambda error.

Claims

A method of obtaining a control value for use in controlling operation of an internal combustion engine, comprising the steps of determining a first actual value dependent on the lambda value of the engine exhaust gas, determining a first control value in dependence on the first actual value and a first target value, determining a second actual value dependent on the engine induction air quantity, and determining a second control value in dependence on the second actual value and a second target value, the second target value being set in the presence and the first target value in the absence of a given engine operating condition.
2. A method as claimed in claim 1, comprising the step of setting a constant air quantity in the case of a small fuel quantity and a constant lambda value in the case of a" large fuel quantity.
3. A method as claimed in claim 1 or claim 2, comprising the step of selecting the smaller of the first control value and the second control value for application to a device for influencing engine induction air composition.
4. A method as claimed in claim 1, comprising the step of determining at least one of the lambda value and the induction air quantity by measurement at the engine.

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5. A method as claimed in claim 1, comprising the step of determining a third control value in dependence on engine fuel feed quantity.
6. A method as claimed in claim 5, comprising the step of selecting the greater of the first control value and the third control value as the second target value.
7. A method as claimed in claim 5, comprising the steps of correcting the third control value in dependence on the first control value and selecting the corrected third control value as the second target value.
8. A method as claimed in claim 7, wherein the step of correcting is carried out only in a given operational state or given operational states of the engine.
9. A method as claimed in claim 1, wherein the first control value is determined in dependence on the difference between a measured value and a calculated value of engine induction air quantity.the calculated value being derived from at least the lambda val ue.
10. A method as claimed in claim 9, wherein the calculated valve is additionally derived from an engine fuel feed quantity value.
11. A method as claimed in claim 10, wherein the calculated valve is additionally derived from the second control value and is formed by an observer.
12. A method as claimed in claim 9, comprising the step of correcting at least one of a fuel pump characteristic values field and a fuel feed quantity value in dependence on said difference.
13. A method as claimed in any one of the preceding claims, wherein the engine is a compression-ignition engine.
14. A method as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.
15. Equipment for obtaining a control value for use in controlling operation of an internal combustion engine comprising means for determining a first actual value dependent on the lambda value of the engine exhaust gas, determining a first control value in dependence on the first actual value and a first target value, determining a second actual value dependent on the engine induction air quantity, and determining a second control value in dependence on the second actual value and a second target value, the second target value being set in the presence and the first target value in the absence of a given engine operating condition.

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16. Equipment as claimed in claim 15, the means for determining the first control value and the second control value comprising, respectively, first regulating means and second regulating means.
17. Equipment as claimed in claim 15 or claim 16, wherein the engine is a compression-ignition engine.
18. Equipment substantially as hereinbefore described with reference to the accompanying drawings.