GB2251094A

GB2251094A - Control system for a fuel-injected, compression ignition internal combustion engine

Info

Publication number: GB2251094A
Application number: GB9120638A
Authority: GB
Inventors: Reinhard Fenchel; Dieter Seher
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-10-04
Filing date: 1991-09-27
Publication date: 1992-06-24
Anticipated expiration: 2011-09-27
Also published as: GB2251094B; JPH04246262A; FR2667651A1; FR2667651B1; GB9120638D0; DE4031367A1

Description

2231094 Control system for a fuel-injected, compression-ignition internal

combustion engine The present invention relates to a control means for a fuelinjected, compression-ignition internal combustion engine.

In DE-OS 35 22 414 (US-A-4 619 233) there is described a control system for an internal combustion engine in which the instant of fuel injection is fixed by a first setting mechanism and the quantity of fuel to be injected by a second setting mechanism. A stroke slide is provided as the first setting mechanism. In this system resetting of the first setting mechanism also acts on the quantity of the fuel. In order to compensate for this influencing, the setting signal for the second setting mechanism, which determines the quantity of fuel to be injected, is corrected by means of a correction factor. This correction factor depends on the engine rotational speed and the actual position of the first setting mechanism.

Such a correction by means of a factor dependent only on rotational speed and actual position of the slide is not sufficient for exact setting of the injected fuel quantity and inaccuracies in the quantity of fuel may result. A different quantity of fuel results according to setting of the slide for a fixed setting of the second setting mechanism, yet it is desirable for the magnitudes of injection start and fuel quantity to be able to be set completely independently of each other. It has proved that adequate correction is not possible by a correction factor which takes into consideration only the rotational speed and the position of the slide.

2 - Thus, the quantity of fuel to be injected cannot be set completely independently of the beginning of injection by means of the prior art system and inaccuracies result in the injected fuel quantity.

There is thus a need for improvement in such control means so as to provide enhanced accuracy of fuel metering.

According to the present invention there is provided control means for a fuel-injected, compression-ignition internal combustion engine, the control means comprising first setting means for determining the start of fuel injection in dependence on a first target value, storage means for storing the first target value in dependence on engine operating parameters, second setting means for determining the quantity of fuel to be injected in dependence on a second target value, and means for correcting the second target value in dependence on a value indicative of injection start and a value indicative of fuel quantity.

Such control means may ensure that there is a constant injected quantity for a fixedly preset target value for the injected quantity for any desired engine rotational speed and any desired setting of the first setting means. This can be achieved by taking into account all influences on the quantity of fuel by way of a multi -dimensional characteristics or values field. The correction of the second target value can take place through the characteristics field in dependence on the setting position of the first setting mechanism, the engine rotational speed, the setting of the second setting means or the target value of injected quantity. In one preferred embodiment it is, for example, possible to keep the engine torque independent of the beginning of injection.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings in which:

Fig. 1 is a schematic block diagram of control means embodying the invention; Fig. 2 is a diagram showing dependence of conveyed quantity of fuel on cam angle; and Fig. 3a to 3c are diagrams of possible constructions of components of the control means.

Referring now to the drawings there is shown in Fig. 1 a control system based on a stroke slide pump, although other forms of fuel pump, in which the injection start and the injected quantity of fuel can be set independently of each other, are usable. The system comprises a first setting mechanism 80 which determines the beginning of conveying or the beginning of injection and a second setting mechanism 130 which determines the quantity of fuel to be injected, each mechanism being set by way of a respective regulating loop. An internal combustion engine 10 receives the fuel necessary for combustion by way of a high-pressure fuel pump 20. A sensor 30 detects the respective fuel injection start, which means the beginning of injection or the beginning of conveying of the fuel pump. The sensgr 30 can, however, be arranged to detect the actual position of the first setting mechanism 80.

A sensor 40 provides a signal which is indicative of the quantity of fuel fed to the engine 10. Usually, this is the position of a regulating rod of the pump (regulating travel RWI). In other pump types, however, it is feasible to use a signal indicative of the injection duration or other signal which represents a measure of the injected fuel quantity.

In addition, different sensors 50 detect the operational state of the engine 10. Thus, for example, a sensor is provided to detect the rotational speed N of the engine 10.

The output signal of the sensor 30 is applied, by way of a first input of a subtraction point 60, to a first regulator 70, which drives the first setting mechanism 80. As indicated above, the first setting mechanism 80 influences injection start. The output signal SBS of a characteristics field 90, which presets a target value for injection start, is present at a second input of the subtraction point 60. The field 90 receives signals in respect of the engine rotational speed and the desired quantity QK of fuel from a computing unit 100.

The sensor 40 detects the actual value RWI of the regulating travel of the pump regulating rod and feeds a signal representing this value to a first input of a further subtraction point 110. In dependence on the output signal of the subtraction point 110, a second regulator 120 determines a signal for a second setting mechanism 130. In this embodiment, this setting mechanism serves to reset the pump regulating rod.' An output signal of a characteristic field 140, which presets a target value for the regulating rod position, is applied to a second input of the subtraction point 110. The field 140 receives different signals from the computing unit 110, for example, a signal which indicates engine rotational speed and a signal which indicates the desired quantity QK of fuel. In addition, the output signal of the first regulator 70 or of the field 90 is applied to the field 140.

The computing unit 100 includes an engine characteristics field 170, to which are applied the output signal of the field 90 or of the regul ator 70. Signals indicating desired -engine torque MD and the engine rotational speed N are also applied to the field 170.

The computing unit 100 processes different signals, including signals derived from the engine by means of sensors 50 and also signals of further sensors 160, for example for air temperature, air pressure and/or fuel temperature. A device 150 delivers a signal which indicates the wish of a driver of a vehicle equipped with the engine, this signal being an accelerator pedal value transmitter in the simplest case.

In use of the control system, the computing unit 100 computes the desired quantity QK of fuel in dependence on different parameters such as the wish of the driver, desired engine torque and external environmental influences as well as in dependence on different operating parameters of the engine.

It is particularly advantageous if the computing unit processes a signal indicat.ive of desired engine torque MD. In this case, the field 170 is necessary and serves to set the quantity QK of fuel to be injected in dependence on different magnitudes, such as the torque.

The signal QK, which corresponds to the desired quantity of fuel, as well as the engine rotational speed signal N are fed on the one hand to the field 90 for the injection start control and on the other hand to the field 140 for the regulating rod travel.

In certain cases, it is advantageous if a torque regulation is deployed, for example if different target values for injection start can be predetermined for one engine operating point. An engine operating point is defined as a constant torque and constant rotational speed. The field 170 determines a value for the quantity

QK of fuel to be injected in dependence on the desired torque, the rotational speed N and the injection start. In that case it is particularly advantageous if a value for the quantity of fuel to be injected is read out from the field 170 in dependence on a comparison between desired and actual torque values.

A target value SBS for injection start is read out from the field 90 and is compared in the subtraction point 60 with the actual value SBI of injection start detected by the sensor 30. The first regulator 70 then computes a driving signal for the first setting mechanism 80 in dependence on the comparison between the target value and the actual value for injection start. The regulator 70 contains, for this purpose, a preliminary/characteristics field which issues a value indicative of the position of the first setting mechanism.

The field 140 feeds a target value RW for the regulating travel to thesecond regulator 120 in'dependence on the rotational speed and the desired quantity of fuel. The target value is compared in the subtraction point 110 with the actual regulating travel RWI detected by the sensor 40. The regulator 120 generates a signal in dependence on this comparison result and the signal correspondingly sets the setting mechanism.

The first setting mechanism 80 fixes injection start by the fuel pump and the second setting mechanism 130 fixes injection duration by the fuel pump. The two setting mechanisms 80 and 130 can be designed as pure control setting mechanisms, i.e. the setting mechanism assumes the position preset by the regulator output signal. On the other hand, however, it can be advantageous if each regulator presets the current flowing through the associated setting mechanism, with this current being detected by a respective sensor. A regulator then compares the value of the detected current with a target value determined by the respective current regulator and computes a new setting current in dependence on the comparison result.

In the case of the first setting mechanism 80, it is particularly advantageous if the regulator 70 determines a target value for the setting mechanism position. A sensor then detects the position of the mechanism 80. A first setting regulator regulates the actual position of the mechanism 80 to the target value.

Such a regulating system may operate satisfactorily only if the resetting of the beginning of injection has no influence on the injected quantity. If this is not the case, this influence should be taken into consideration. Thus, in the embodiment of the present invention the influence of injection start on the injected fuel quantity is taken into consideration in that a signal indicative of injection start is fed to the field 140 for the regulating travel.

Thus, in effect, a signal which indicates the position of the first setting mechanism 80 can be fed to the field 140. Such a signal is, for example, the output signal of the first regulator 70. If the equipment comprises a first setting regulator which regulates the position of the first setting mechanism to a position determined by the first regulator 70, then the actual value or the target value of this first setting regulator can also be used. If this is not the case, the output signal of the first regulator 70 is utilised. Thi s signal corresponds to the target value of the first setting regulator.

It is particularly advantageous if the output signal of the field 90 for the target value of injection start is utilised for correction. This has the advantage that no reporting-back of the setting mechanism position is necessary.

Such a regulating system may operate satisfactorily only if the resetting of injection start has no influence on the torque delivered by the engine. If this is not the case, this influence should be taken into consideration. Thus, in the described embodiment of the present invention, the influence of injection start on delivered torque is taken into consideration in that a signal indicative of injection start is fed to the field 170. In that case, it is particularly advantageous if the output signal of the field 90 is utilised for correction.

The necess.ity of correction of the regulating travel in dependence on the injection start is illustrated in Figure 2, in which camshaft angle NW is entered on the x-axis and injected quantity QK of fuel on the y-axis. Two metering of different durations are entered for each of two different injection starts.

Also entered is the injected quantity of fuel. A metering with injection start SBA and a metering with injection start SSB, each with the durations D1 and D2, are shown. In that case, the metering duration D2 is longer by the factor 2 than the metering duration D1.

If metering takes place with the conveying duration D1 at the injection start SBA, then a quantity QA1 results. At the injection start SBB, thereagainst, a quantity QB1 results. The quantity QB1 is greater by a factor F1, in this example 1.2, than the quantity QA1.

If a metering takes place with the duration D2 at the injection start SBA, a conveyed quantity QA2 results. For metering at the injection start SBB, thereagainst, a quantity QB2 results. The quantity QB2 is greater by the factor F2 than the quantity QA2. Thus, different factors result for the ratio of quantity QB (metering at SBB) to the quantity QA (metering at SBA) in dependence on the conveying duration and thereby on the regulating travel (regulating rod position). If the correction of the target value for the regulating rod position depends, as in the state of the art, only on the beginning of conveying and the rotational speed, then false values result. In the embodiment of the present invention the correction additionally depends on the injection duration or on a signal which represents a measure for the duration of the fuel metering. Coming into consideration as such a signal are the conveying duration, the injection duration, the target value RW for regulating travel, the target value for injected quantity, the actual value RWI for regulating travel or the spacing between injection start and injection end.

For carrying out correction of the regulating travel in dependence on injection start and injected fuel quantity, there are different possibilities as illustrated in Figs. 3a, 3b and 3c. Fig. 3a shows a particularly simple and advantageous possibility. The regulating travel target value is filed in the field 140 in dependence on desired injected quantity, the rotational speed and a signal indicative of injection start. The target value issued by the field 90 for the injection start can, for example, be used as such a signal. Alternatively, the actual value or target value of the setting regulator for the position of the first setting mechanism or the setting mechanism current can be used or the output signal of the first regulator 70.

If none of these signals is available, a suitable substitute magnitude can be utilised. In the case of systems controlled by an electromagnetic valve, it may be feasible to utilise the switching instants of the valve.

The field 140 takes into consideration that the target value RW for the second setting mechanism 130 must be corrected in dependence on the beginning of conveying, the rotational speed and the target value for injected quantity.

A complete correction of the influence of the beginning of conveying on the injected quantity of fuel is made possible by this procedure. The preferably four-dimensional pump characteristics field 140 represents the inversion of the hydraulic properties of the pump, i.e. the conveyed quantity characteristics field. It is valid for the conveyed quantity field that the injected quantity depends on the actual value of the regulating travel, the rotational speed and the beginning of conveying. It is then valid for the pump characteristics field that the target value for the regulating travel represents a function of the desired quantity of fuel, the rotational speed and beginning of conveying. This ensures a constant injected quantity for a fixedly determined fuel quantity wish at desired rotational speed and desired beginning of conveying. The influence of the fuel temperature on the conveyed quantity can, for example, be taken into consideration through enlargement of the field by one dimension.

This field in that case takes into consideration that the target value for quantity QK of fuel to be injected must be corrected in dependence on injection start.

The form of the field 140 is illustrated in detail in Fig 3b. Such fields are in general three-dimensional, but a four-dimensional characteristics field is necessary here and for that purpose several three-dimensional fields are arranged one beside the other. Consequently, simpler and cheaper storage components can be used. The individual characteristics fields 310, 320, and 330 are each provided for a respective constant injection start value. The computation of the respective' target value for regulating travel in dependence on injection start SB is effected by means of interpolation within a computing stage 300.

In a first form of realisation, the fields 310, 320 and 330 are, respectively, a field for each end abutment of the setting mechanism for injection start and a field for a mean position of the setting mechanism for the injection start. A regulating travel target value RW(G) for the greatest possible injection start value SM is filed in the field 310, a target value RW(M) for the injection start mean value SBM is filed in the field 320, and a target value RW(K) for the smallest possible injection start value SM is filed in the- field 330.

Referring to Fig. 3c, injection start SB is detected in a first step 350. The injection start can be the beginning of conveying by the pump or the actual beginning of injection. It is possible to draw upon the measured position of the first setting mechanism, the target value for the beginning of injection or the target current value for the setting mechanism regulator.

The detection of injection start is followed by a decision stage 360 which checks whether the injection start SB is greater than a threshold value, in particular whether the injection start is greater or smaller than the mean injection start value SW. If this is the case, computation takes place in a stage 370 according to the formula:

RW = RW(M) + (RW(G) RW(M)) ( SBX - SBM)/(SBG - SBM).

In that case, RW denotes the desired target value for regulating travel for the actual injection start SU. The target value RW is t computed by the computing unit 300 according to the above formula and issued.

If th@ stage 360 shows that the injection start is smaller than the threshold value, a computation takes place in a stage 380 5 according to the formula:

RW - RW(K) + (RW(M) - RW(K)) ( SBX - SM)/(SBM - SM).

In a second form of realisation, the regulating travel RW(M) is filed in a field 320 in dependence on rotational speed and quantity of fuel for a mean value of injection start. Furthermore, difference field values (DRW(K) for smaller value of injection start are filed in the field 310 and difference field values DRW(G) for greater values of injection start are filed in the field 330, in both cases in dependence on rotational speed and quantity of fuel.

The computation takes place in the stages 370 and 380 shown in Fig. 3c, wherein small values of injection start there is used the formula:

RW = RW(M) + DRW(K) ( SBM - SBX)/(SBM - SM).

For large values of injection start, there is used the formula:

RW = RW(M) + DRW(G) 58X - SBM)/(SBG - SBM).

The engine characteristics field 170 also has a corresponding f orm. In that case, only the regulating travel value RW need be replaced by the quantity QK of fuel to be injected, and the quantity QK of fuel to be injected need be replaced by the torque value MD. A complete correcti- on of the influence of injection start on the delivered torque is made possible by this procedure. It is true for the field 170 that the quantity QK of fuel to be injected represents a function of the desired torque, the rotational speed and the beginning of injection. This procedure may ensure a constant torque at any desired rotational speed and injection start.

This method is used to particular advantage in fuel pumps in which injection start can be set independently of conveyed quantity, for example stroke slide pumps. In this pump type, the first setting mechanism is provided for the pump slide position and the second setting mechanism for the pump regulating rod. The rod determines the quantity of fuel to be injected, whereas the position of the slide determines the beginning of injection.

In such a system, it is particularly advantageous if the target or actual value for the slide position is- used instead of the beginning of injection for correction. This value can be derived simply from the output signal of the field 90. Further sensors are not required, which offers the advantage that no sensors can fail. The system thus has a higher operational reliability by comparison with equipment in which the beginning of injection is detected by means of a separAte sensor.

In a further refinement the actual slide position is detected. This signal is fed to the field 140 or to the field 170. This equipment has the disadvantage that the sensor can fail, but the advantage by comparison with the use of the target value that a very accurate signal in respect of injection start is present.

This system can also be used for fuel pumps in which the beginning and end of injection are fixed by means of electromagnetic valves. In these systems, the instant of switching-on or switching off of a valve determines the beginning or end of conveying by the fuel pump. For utilisation with such a pump the above-described system is to be designed appropriately to draw upon appropriate signals.

Claims

1. Control means for a fuel-injected, compression-ignition internal combustion engine, the control means comprising first setting means for determining the start of fuel injection in dependence on a first target value, storage means for storing the first target value in dependence an engine operating parameters, second setting means for determining the quantity of fuel to be injected in dependence on a second target value, and means for correctJng the second target value in dependence on a value indicative of injection start and a value indicative of fuel quantity.

2. Control means as claimed in claim 1 comprising means for determining said value indicative of fuel qu,antity in dependence on at least one of a value indicative of desired fuel quantity and a value indicative of desired engine torque and for correcting the fuel quantity value in dependence on a value indicative of injection start.

3. Control means as" claimed in either claim 1 or claim 2, comprising storage means for storing said value indicative of fuel quantity in dependence on values indicative of engine speed, injection start and desired torque.

- 17

4. Control means as claimed in any one of the preceding claims, comprising storage means for storing the second target value in dependence on values indicative of engine speed, injection start and fuel quantity.

5. Control means as' claimed in any one of claims 1 to 3, comprising storage means for storing the second target value with account taken of necessary correction of the second target value by values indicative of injection start, engine speed and injection duration.

6. Control means as claimed in any one of the preceding claims, wherein the first target value is indicative of a desired setting of the first setting means, and the value indicative of injection start is provided by the first target value or by a value indicative of actual setting of the first setting means.

7. Control means as claimed in any one of the preceding claims, comprising means for determining the first target value in dependence on values indicative of engine speed and desired fuel quantity.

8. Control means as claimed in any one of the preceding claims, the first setting means comprising a fuel pump slide.

9. Control means as claimed in any one of the preceding claims, the second setting means comprising a fuel pump regulating rod.

10. Control means as claimed in any one of claims 1 to 3, comprising storage means for storing the second target value,the storage means being arranged to determine the second target value by interpolation proceeding from three stores each for a respective fixed value for injection start.

11. Control means as claimed in any one of claims 1 to 3, comprising storage means for storing the second target value, the storage means comprising a store for a mean value for injection start and further stores for difference values, or for large and small values, for injection start.

12. Control means substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

13. Control means as claimed in claim 12 and modified substantially as hereinbefore described with reference to any one of Figs. 3a, 3b and 3c of the accompanying drawings.

14. A fuel-injected, compression ignition internal combustion engine equipped with control means as' claimed in any one of the preceding claims.