GB2279698A

GB2279698A - Control of i.c. engine exhaust gas recirculation

Info

Publication number: GB2279698A
Application number: GB9413300A
Authority: GB
Inventors: 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: DE4322270B4; GB9413300D0; DE4322270A1; JPH0763124A; FR2707346A1; FR2707346B1; GB2279698B

Description

2279698 METHOD AND CONTROL MEANS FOR CONTROLLING ENGINE OPERATION The

present invention relates to a method and control means for controlling 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. This applies particularly to systems which operate with only a slow lambda regulator and without a subordinate air quantity regulator. Thus, especially during acceleration, the exhaust gas composition or the acceleration of the motor vehicle driven by the engine is not optimal.

There is thus scope for improvement in engine control methods and control means with respect to exhaust gas behaviour of the controlled engine.

According to a first aspect of the present invention there is provided a method of controlling operation of an internal combustion engine equipped with a setter for setting a rate of return of exhaust gas for induction by the engine, the method comprising the steps of determining a stroke magnitude in dependence on at least one of a rotational speed of an engine component and a fuel f eed quantity for the engine, determining a control magnitude for the setter in dependence on at least the stroke magnitude, and correcting at least one of the stroke magnitude and the control magnitude in dependence on engine operating conditions.

According to a second aspect of the invention there is provided control means for controlling operation of an internal combustion engine with a setter for setting a rate of return of exhaust gas for induction by the engine, the control means caTprising -means for determining a stroke magnitude in dependence on at least one of a rotational speed of an engine component and a fuel feed quantity for the engine, means for determining a control magnitude for the setter in dependence on at least the stroke magnitude, and means for correcting at least one of the stroke magnitude and the control magnitude in dependence on engine operating conditions.

Examples of the method and embodiments of the control means 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 embodying the invention; Fig. 2 is a block diagram of an exhaust gas return control of the control means; Fig. 3 is a block diagram of an exhaust gas return characteristic field;

Fig. 4 is a block diagram of a first form of air quantity regulator in the control means; and Fig. 5 is a block diagram of a second form of air quantity regulator in the control means.

Referring now to the drawings there is shown in Fig. 1 the principal elements of control means for a compression-ignition 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 exchanged. The control means can be realised by a hardware circuit or by a computer in conjunction with an appropriate program 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 X. 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, as well as by an output signal QK of a quantity presetting device 160. The control 140 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. The quantity control 150 translates this quantity signal QK into a drive control signal for the second setting member 120. In the simplest case, the qu anti ty-presetti ng 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 exhaust gas conducted back into the engine induction duct.

The exhaust gas return control 140 is illustrated in more detail in the block diagram of Figure 2. Elements already illustrated in Fig. 1 are identified by the same reference numerals.

The output signal of a target value presetting device 200, is applied by way of a logical interlinking point 202 to an exhaust gas return characteristic values field 210. The device 200 processes the fuel quantity signal QK as well as further magnitudes, for example the rotational speed signal N, as input magnitudes. These are detected by the sensors 160 and 164.

thus an air quantity target value MLS The air quantity target value MLS is also applied to a logical interlinking point 204, at the second input of which the output signal of an actual value transmitter 206 is present. The output of the logical interlinking point 204 is in turn connected with an air quantity regulator 208, which produces a signal acting on a second input of the interlinking point 202.

Also applied to the exhaust gas return characteristic values field 210 are the rotational speed signal N by way of a delay member

212 and a fuel quantity signal QK by way of a delay member 214. The field 210 is connected with a valve characteristic curve device 220, which produces a keying ratio signal TV acting on a logical interlinking point 225. An output signal of a first correction characteristic curve device 230, which processes the rotational speed signal N as input magnitude, is applied to a second input of the interlinking point 225.

The output signal of the interlinking point 225 is applied to a first input of a further logical interlinking point 235, to a second input of which is applied an output signal of a second correction characteristic curve device 240. The device 240 processes the fuel quantity signal QK as input magnitude. The output signal TX of the interlinking point 235 serves for action on the exhaust gas return setting member 110.

In a particularly advantageous refinement, the output signal of the rotational speed sensor 164 is applied to the device 230 by way of a so-called lead/lag member. This lead/lag member is realised in such a manner that the rotational speed signal N is applied directly to one input of a logical interlinking point 270 and from there to the device 230. The rotational speed signal N is also applied by way of a DT1 member 260 to a further input of the interlinking point 270. The two magnitudes are preferably interlinked additively in the logical interlinking point 270.

Correspondingly, the output signal QK of the quantity presetting device 160 can be applied to the drive 240 by way of a lead/lag member. This lead/lag member is realised in such a manner that the quantity signal QK is applied directly to one input of a logical interlinking point 275 -and from there to the device 240.

The quantity signal QK is also applied by way of a DT1 member 265 to a further input of the interlinking point 275. The two magnitudes are preferably interlinked additi'vely at the interlinking point 275.

These lad/lag members substanti al ly improve the dynamic behaviour of the system. A change in the input magnitude at the DT1 member 260 or 265 causes a briefly rising output signal which after a certain time decays to zero. Accordingly, a short term increase of the signal by the D-component is caused by the lead/lag member in the case of signal changes.

The control 140 shown in Fig. 2 operates as follows: The air quantity target value MLS is preset by the target value presetting device 200 in dependence on the fuel quantity QK and further operating parameters such as the rotational speed N. The device 200 is preferably a characteristic values field. In order to ensure as rapid as possible a change in the exhaust gas return rate in the case of a changing air quantity target value, the air quantity target value is fed directly to the exhaust gas return characteristic values field 210.

The air quantity target value MLS is furthermore compared at the point 204 with the output signal of the actual value transmitter 206. This transmitter can have various forms,for example it can be an air quantity meter which measures the inducted quantity of air and is arranged in the induction duct of the engine. It is also possible to compute the actual air quantity starting from different operating parameters such as the lambda value of the exhaust gas and/or the temperature and pressure values of the inducted air.

On the basis of the output signal from the point 208 the regulator 208 computes a correction magnitude for the air quantity target value. The output signal MLS of the target value presetting device 200 is corrected by this correction value at the interlinking point 202. The interlinking point 202 preferably interlinks the two signals additively. However, other forms of interlinking, for example multiplicative, can be provided.

The direct action on the field 210 by the air quantity target value acts as preliminary control. Due to the substantial path dead time, in particular for a large exhaust gas return quantity, the exact preliminary control improves the dynamic behaviour of the overall system. This preliminary control is corrected at the interlinking point 202 by the output signal of the air quantity regulator 208. This regulator can be realised as an air quantity regulator and/or a lambda regulator or as a cascade regulator.

The regulator 208 preferably has a proportional component and a integral component. In a refinement, the integral component (I component) is frozen when the output signal of the exhaust gas return characteristic values field exceeds or falls below certain val ues. These values correspond to stroke values at which the valve is disposed against its mechanical abutments. This means that when the valve reaches its abutment, the I-component of the regulator remains at its instantaneous value.

The regulator corrects this target magnitude in such a manner that an exact regulation of the setting mechanism results.

The relationship between a stroke magnitude H, which in the following signifies a stroke H of an exhaust gas return valve, and the air quantity target value MLS is stored in the exhaust gas return characteristic values field 210. Preferably, the rotational speed N and the fuel quantity QK are taken into consideration as further magnitudes.

If a charger is provided, changes in the rotational speed and the fuel quantity QK act with a delay, caused by the charger, on the need for returned exhaust gas. In order to take these dynamic properties of the charger into consideation, the delay members 212 and 214 are provided to delay the rotational speed and the fuel quantity signals.

The field 210 can be real i sed as a multidimensional characteristic values field or by means of three characteristic curves. One realisation with three characteristic curves is illustrated in Fig. 3. Already-described elements are identified by the same reference numerals. The output signal of the target value presetting device 200 passes by way of of a logical interlinking point 340 to the logical interlinking point 202 and from there to a stroke characteristic curve device 350.

The interlinking point 340 is acted on by the output signals of a first characteristic curve device 320 and a second characteristic curve device 330. The output magnitude of the delay member 212 is fed to the first device 320 and the output magnitude of the delay member 214 is fed to the second device 330.

An air quantity is filed in the first device 320 in dependence on the delayed fuel quantity signal QK. A higher air quantity is issed for a rising fuel quantity. A linear relationship exists to a first approximation. An air quantity is filed in the second device 330 in dependence on the delayed rotational speed N. A higher quantity is issued for a rising rotational speed. A linear relationship exists to a first approximation. These output magnitudes are logically interlinked at the interlinking point 340 with the output signal of the target value presetting device 200.

This interlinking is preferably additive. It can, however, take place in another manner, for example multiplicatively.

The relationship between the thus corrected air quantity and the stroke H of the valve is filed in the stroke characteristic curve device 350. The strokes become smaller for increasing air quantity. The relationship between air quantity and stroke is strongly non-linear, so that, for the same change in stroke, large changes in the air quantity result for small strokes and small changes in the air quantity result for large strokes.

The valve is closed for a stroke of about 0 millimetres and completely opened for a stroke of, for example, 6 millimetres. These values are typical values, but differ for different types of valves.

Subsequently, the stroke H is converted by means of the valve characteristic curve device 220 into the keying ratio TV. The device 220 contains the relationship between stroke and the keying ratio. This relationship is subsequently linear. For example, a stroke of 0 millimetres corresponds to a keying ratio of 15% and a stroke of 6 millimetres corresponds to a keying ratio of 30%.

For a constant keying ratio, changes in the stroke of the exhaust gas return valve and thereby changes in the exhaust gas return rate result for increasing rotational speed. This effect is based on flow forces which act on the valve. At a high rotational speed above about 3000 revolutions per minute, these effects lead to a greater stroke than for low rotational speeds with the same keying ratio. A corresponding effect occurs for large fuel quantities.

These effects lead to the valve no longer closing at high rotational speed or large quantities of fuel when the drive control has a keying ratio of 15%. In order to ensure reliable closing of the valve, the drive control has to have a lower keying ratio for high rotational speeds and large quantities of fuel.

The stroke is restricted to 0 to 6 millimetres for physical reasons and the keying ratio could therefore be limited to values between 15 and 30% if the above effects were not to arise. Due to the described effects, a greater range must be provided for the keying ratio in order that the valve reliably reaches its end positions.

This lea ds to the regulator also traversing the entire range of the keying ratio. When the valve is situated in one of its end positions, the regulator requires a certain time until it again reaches a keying ratio which effects a change in the stroke. This causes a poor dynamics and consequently an unfavourable behaviour of the entire regulating system. For this reason, the range in which the keying ratio moves should be preset as exactly as possible. However, this is only possible when the above effects are compensated for.

In order to compensate for these disturbances, the first correction device 230 is provided for taking into consideration the stroke changes at constant keying ratio and variable rotational speed. A correction value for the correction of the keying ratio in dependence on rotational speed is filed in this device. The output signal of the device 220 and the correction value of the first correction device 230 are logically interlinked at the interlinking point 225. This signal is then logically interlinked at the second interlinking point 235 with the output signal of the second correction device 240, which takes the influence of the injected fuel quantity QK into consideration. Each correction value can be added to or subtracted from the keying ratio TV at the respective interlinking point. Alternatively, a multiplicative interlinking can be provided, i.e. the device 230 or 240 presets a factor by which the keying ratio is multiplied.

Preferably, no correction is carried out for low rotational speeds or small fuel quantities and the correction becomes progressively larger for increasing fuel quantity or increasing rotational speed. The setting member 110 is then acted on by the corrected keying ratio M.

- 13 By means of this correction, the stroke of the valve can be kept constant independently of counterforces at the valve.

Moreover, dynamic influences by a charger can be taken into consideration. In a particularly advantageous refinement, an anti reset windup function is provided. When the stroke and/or the keying ratio reaches a value which corresponds to the mechanical abutment of the valve, the instantaneous value of the considered magnitude is kept constant until a change in the air quantity target value appears.

In a further refinement, tolerances of the valve and/or influences of the temperature of the coil of the valve are corrected. Valve tolerances lead to, in particular, additive errors and the influence of the coil temperature leads to multiplicative errors. Accordingly, the output signal of the regulator 208 can be fed to a correction device 300, shown in dashed lines in Fig. 2.

The correction device 300 applies a signal to a logical interlinking point 310 between the devices 210 and 220.

Starting from the output signal of the regulator 208, the correction device 300 computes multiplicative and/or additive correction factors by which the output signal H of the field 210 is then corrected multiplicatively and/or additively. By this means valve tolerances and the influence of the coil temperature can be compensated for.

In a further advantageous refinement, the keying ratio at which the valve stroke of 0 millimetres results or at which the valve closes is learned. For this purpose, the keying ratio is wobbled in idling. This means that the keying ratio fluctuates at a frequency of about 0.1 hertz between a first value at which the valve is reliably closed and a second value at which the valve is reliably open. The first value is, for example, 10% and the second value is, for example, 40%. At the same time, a measurement magnitude is observed which changes greatly at the instant of the closing or the opening of the valve. Such a magnitude can be the lambda value, i.e. the oxygen concentration of the exhaust gas.

By reference to this value, it can be recognised at which keying ratio the valve closes reliably. The thus learned keying ratio at which the valve closes can then be used in place of the usual value.

Alternatively, the keying ratio can be wobbled at only a small amplitude. In this case, the change in the lambda value is greatest for small strokes of the valve, thus directly after the opening of the valve.

A realisation of the air quantity regulator 208 with a cascade structure is illustrated in Fig. 4. Already-described elements are identified by the same reference numerals.

The output signal of the target value presetting device 200 is applied by way of a time delay device 400 and a comparison point 410 to a lambda regulator 420, the output magnitude of which is applied by way of a comparison point 430 to an air quantity regulator 440.

The logical interlinking point 202 is acted on by the output magnitude of the regulator 440.

An actual value presetting device 415 acts on the comparison point 410 and the actual value presetting device 206 acts on the comparison point 430 by an actual value.

The delayed output signal of the device 200 is applied as target value to the comparison point 410, where it is compared with the actual value of the actual value presetting device 415. The delay device 400 preferably operates in dependence on the rotational speed. A smaller delay is chosen for higher rotational speed.

The actual value presetting device 415 supplies an actual lambda value, preferably that measured by means of the lambda probe 135. Starting from the deviation between the target value and the actual value, the lambda regulator 420 determines a setting magnitude. The regulator 420 preferably has a proportional-integral behaviour.

Alternatively, the actual value presetting device 415 can compute an air quantity value starting from the lambda value measured by the lambda probe 135 and from the fuel quantity QK. In this case, a corresponding air quantity magnitude must be used as target magnitude.

The output magnitude of the lambda regulator 420 serves as target value which is compared at the comparison point 430 with the actual value of the actual value presetting device 206. The air quantity regulator 440 then forms a control magnitude starting from the difference between the actual value and the target value. The air quantity is then corrected appropriately, as already described for Fig. 2, by this control magnitude at the logical interlinking point 202.

A refinement of this cascade regulator is illustrated in Fig. 5. In this refinement, the output signal of the target value presetting device 200 is applied by way of a logical interlinking point 500 to the interlinking point 430. In addition, this manner is applied by way of a dead-time member 510 and a delay member 520 to the comparison point 410. The output magnitude of the lambda regulator 420 is applied by way of switching means 530 to the interlinking point 500. In this refinement, the lambda regulator operates only in certain operational states in which the exhaust gas emissions are particularly critical, particularly in the case of high quantities of fuel or full load. In these operating conditions, the switching means is closed and the lambda regulator forms a correction magnitude for correction of the target value for the air quantity regulator. The dynamic behaviour of the actual lambda value and of the target value are matched to each other by means of the dead-time member 510 and the delay member 520.

Claims

1. A method of controlling operation of an internal combstion engine equipped with a setter for setting a rate of return of exhaust gas for induction by the engine, the method comprising the steps of determining a stroke magnitude in dependence on at least one of a rotational speed of an engine component and a fuel feed quantity for the engine, determining a control magnitude for the setter in dependence on at least the stroke magnitude, and correcting at least one of the stroke magnitude and the control magnitude in dependence on engine operating conditions.

2. A method as claimed in claim 1, wherein the stroke magnitude is determined in dependence on at least one of the rotational speed, the fuel feed quantity and a target air induction quantity for the engine by reference to at least one of a characteristic values field and a characteristic curve for exhaust gas return rate.

3. A method as claimed in claim 1 or claim 2, wherein the step of determining the stroke magnitude comprises applying a signal indicative of the rotational speed or fuel feed quantity to a characteristic values field for exhaust gas return rate with a delay.

4. A method as claimed in any one of the preceding claims, wherein the control magnitude is determined in dependence on the stroke magnitude by reference to a stroke characteristic curve.

5. A method as claimed in any one of the preceding claims, wherein the step of correcting is carried out with a correction magnitude determined in dependence on at least one of the rotational speed and the f uel feed quantity by reference to a correction characteristic values field.

6. A method as claimed in claim 1, wherein the step of detemining the stroke magnitude comprises forming a target value in dependence on at least one of the rotational speed and the fuel f eed quantity, forming a regulating value by applying the target value to a regulator, logically interlinking the regulating value and the target value and applying a value formed by the interlinking to a characteristic values field for exhaust gas return rate.

7. A method as cl aimed in claim 6, wherein the step of determining the stroke magnitude comprises determining a correction value in dependence on the regulating value and correcting an output value of the field by the correction value.

8. A method as claimed in any one of the preceding claims, wherein the step of determining the control magnitude is carried out when the setter is disposed in an end position thereof.

9. A method as claimed in claim 6 or claim 7. wherein the regulator is a cascade regulator 11 - 19

10. A method as claimed in any one of the preceding claims, wherein the engine is a compression-ignition engine.

11. A method as cl aimed in cl aim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

12. Control means for controlling operation of aninternal combustion engine equippped with a setter for setting a rate of return of exhaust gas for induction by the engine, the control means comprising means for determining a stroke magnitude in dependence on at least one of a rotational speed of an engine component and a fuel feed quantity for the engine, means for determining a control magnitude for the setter in dependence on at least the stroke magnitude and means for correcting at least one of the stroke magnitude and the control magnitude in dependence on engine operating conditions.

13. Control means as claimed in claim 12, wherein the engine is a compression-ignition engine.

14. Control means substantially as hereinbefore described with reference to the accompanying drawings.

15. A compression-ignition internal combustion engine equipped with control means as claimed in any one of claims 12 to 14.