GB2276250A

GB2276250A - Fuel feed control

Info

Publication number: GB2276250A
Application number: GB9404319A
Authority: GB
Inventors: Roland Gronenberg; Peter Schmitz; Dietbert Schoenfelder; Peter Lutz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-03-17
Filing date: 1994-03-04
Publication date: 1994-09-21
Anticipated expiration: 2014-03-04
Also published as: DE4308422A1; GB9404319D0; DE4308422C2; ITMI940441A0; IT1269523B; GB2276250B; JP3609442B2; ITMI940441A1; JPH074297A

Description

2276250 FUEL FEED CONTROL The present invention relates to a method of

controlling an engine fuel feed system and to a system in which such a method can be performed.

In DE-OS 42 04 091 there is described a method and a device for controlling a diesel engine with a fuel-admetering system controlled by an electromagnetic valve. This admetering system includes an electronic control unit which, starting from at least a fuel conveying duration value, computes a drive-off instant for the valve.

The drive-on duration has been used as a parameter of the quantity field in known systems of that kind. This had the consequence of a falling injected fuel quantity in the case of constant drive-on duration and rising engine speed. Thus, falling characteristic curves appear in the quantity characteristic field.

These falling characteristic curves have a stabilising effect on engine operation.

The actual start of conveying is ascertained interpolatively in the device described in DE-OS 42 04 091. This means that the actual instant of the beginning of injection is made available during the same injection phase. Starting from this ascertained injection start, the valve drive-off instant can be fixed very precisely. This results in a reduction of the quantity scatter between the individual injection phases. However, since the conveying duration enters into the quantity characteristics field as

2 a val ue in p] ace of the drive-on duration val ue, rising characteristics - seen dynamically - then result. This means that rising fuel quantities occur in the case of constant conveying duration and rising engine speed. These risin-g quantity characteristics lead to instabilities in engine operation.

It would thus be desirable to eliminate these instabilities in fuel feed systems in which fuel feed is controlled by an electromagnetic valve.

According to a first aspect of the present invention there is provided a method of controlling a fuel-admetering system, which is controlled by an electromagnetic valve and in which electronic control means determines a drive-off instant for the valve starting from at least a conveying duration value, wherein locally falling characteristics are presettable through correction of the conveying duration value.

Preferably correction of the conveying duration value takes place in dependence on a correction factor and a further value, which can correspond to change in engine speed between the instant of detection of a wean speed value and an instant of injection.

For preference, a correction factor is associated with each operating point. This factor can correspond to the slope in the respective operating point. It may be of advantage if the maximum slope serves as the correction factor.

According to a second aspect of the invention there is provided control means for controlling a fuel-admetering system, which is controlled by an electromagnetic valve and in which 3 electronic control means determines a driveoff instant for the valve starting from at least a conveying duration value, comprising correction means to produce locally falling characteristics through correction of the conveying duration value.

The stability of the engine - operation may be able to be substantially improved by correction of the conveying durationvalue in the sense that locally falling characteristics arise.

An example of the method and an embodiment of a system of the invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a block schematic diagram of a fuel feed system embodying the invention; Fig. 2 is a series of diagrams illustrating valve operation in the system; Fig. 3 is a flow chart illustrating steps in calculation of a valve control signal by electronic control means in the system when performing a method exemplifying the invention; Fig. 4a is a diagram showing a fuel quantity values field; and Fig. 4b is a further diagram showing a fuel quantity values field.

Referring now to the drawings, there is shown in Fig. 1 control equipment for a fuel pump, controlled by an electromagnetic valve, for a compression ignition or diesel engine. The control equipment is, however, also usable for the control of an applied 4 ignition internal combustion engine, in particular for the control of the injected quantity of fuel. Fuel is fed by way of a fuel pump 10, which comprises a pump piston 15, to the individual cylinders of the engine (not shown). In that case, a respective fuel pump 10 can be associated with each cylinder, thus a pump-nozzle system, or a fuel pump feeds the fuel to the individual cylinders in alternation, thus a distributor pump.

The fuel pump 10 is connected with an electromagnetic valve 20. The valve 20 is responsive to switching pulses supplied from a power output stage 40 of an electronic control unit 30, which inter alia comprises a fixed value storage device 35. A transmitter 70, which is arranged at the output stage 40, at the valve 20 or at an injection nozzle,- supplies signals FBI to the electronic control unit 30. In this case, the signal FBI preferably indicates the actual start of fuel conveying.

The pump is driven by way of a shaft 60. Angle marks are arranged on an increment wheel 55 mounted on the shaft 60. Each two marks define an increment. The increment wheel has at least one increment gap as a reference point, which can be realised by, for example, an omitted mark or other appropriate measure. A measuring device 50 detects pulses initiated by the angle marks, and thereby the rotational movement of the increment wheel 55, and supplies corresponding signals in the form of pulses to the unit 30.

The increment wheel can also be arranged on the crankshaft.

The increment wheel supplies a signal KW in respect of the angular setting of shaft 60 and a signal N which indicates the instantaneous rotational speed of the shaft. Additional magnitudes, such as mean rotational speed NM, air temperature T and load L, which corresponds to the setting of an accelerator pedal of a vehicle equipped with the engine are also led to the control unit 30 from further sensors 80.

The mean rotational speed NM is detected over a larger angular range. Preferably, a transmitter is provided which, in the course of one revolution of the engine crankshaft or the camshaft, supplies only a snall number of pulses, for example one to four pulses.

These are then evaluated for ascertaining of the mean rotational speed W. The evaluation is carried out in such a manner that the mean rotational speed NM is preferably averaged over an engine cycle or over a combustion process.

In operation, the control unit 30 determines the desired fuel conveying start FBS (Fig. 3) and the desired fuel conveying duration FDS (Fig. 3) of the fuel pump 10 in dependence on the magnitudes detected by means of the sensors 80-and the rotational movement of the shaft 60 detected by way of the measuring equipment 50.

Starting from these target values for conveying start FBS and conveying duration FDS, the unit then computes a drive-on instant E and a driveoff instant A for the power output stage 40 with the use of the signal FBI for the actual injection start. The power output stage 40 then acts on the valve 20 by a corresponding current.

One or more of such magnitudes as mean rotational speed, air temperature, lambda value of the exhaust gas, fuel temperature, load (characterising the setting of the accelerator pedal or desired 6 speed of travel) or other magnitudes can be used as operating parameter magnitudes. The rotational movement of the shaft 60 can be that of a pump drive shaft 60, the or a camshaft of the engine and/or the engine crankshaft. The camshaft of the engine or a shaft coupled therewith can function as pump drive shaft. The pump drive shaft drives the pump piston 15 in such a manner that the fuel in the fuel pump 10 is placed under pressure. The electromagnetic valve 20 controls the pressure build-up.

The valve 20 is preferably so arranged that no substantial pressure build-up takes place when the valve is open. A pressure in the fuel pump builds up only after the valve 20 is closed. At an appropriate pressure in the fuel pump, an injection valve opens and the fuel passes by way of an injection nozzle into the combustion chamber of the engine.

The transmitter 70 serves for checking the instant at which the valve opens or closes. The transmitter 70 can also be mounted at the injection nozzle and then generates a signal which identifies the actual start or the end of the fuel injection into the combustion chamber.

In place of the output signal of the transmitter 70, a signal can be used which indicates the setting of the valve 20. Such a signal is obtained through evaluation of the current flowing through the valve or the voltage across the valve.

In Fig. 2, different signals are entered in diagrams as a function of the setting KW of the shaft 60. The drive-on signal for the valve output stage or for the valve are shown in the first 7 diagram. At the drive-on instant E, the valve is acted on by vol tage. At the drive-off instant A, the valve is separated from the supply voltage. The time span between the drive-on instant E and the drive-off instant A is denoted as drive-on duration AD.

In the second diagram, the stroke of the valve needle is shown for a relatively low rotational speed. The valve needle is in its rest position until the drive-on instant E. From this instant onwards, it moves within a certain time to its second position. The instant at which the magnetic valve needle has reached its new position is denoted as conveying start FBI. This time span, which elapses between the drive-on instant E and the conveying start FBI, is shown as switchon time TE in the first diagram.

The valve needle remains in this position until the drive-off instant A. From this instant onwards, the needle goes slowly back is into its rest position. This time span between the drive-off instant A and the reaching of the rest position is shown as switch off time TA in the first diagram. When the needle reaches its rest position, the injection ends. This instant is denoted as conveying end FEI. The time duration between the actual conveying start FBI and the actual conveying end FEI is denoted as conveying duration FD. The angle which the shaft 60 has traversed in this time is a measure for the supplied or injected quantity of fuel.

In the third diagram, the relationships are shown for higher rotational speeds. Since the switch-on time TE is almost constant, the needle reaches its second position only at a substantially later angular setting. The switch-off time TA is shorter than the switch- 8 on time TE, for which reason the influence of the rotational speed on the switch-off time TA is substantially less and the effective conveying duration FD becomes shorter as rotational speeds rise.

The injection usually ends already substantially earlier, namely shortly after the beginning of the opening movement, since the pressure collapses even then. This means that the physically effective conveying duration FD is even shorter than shown in Fig.

2. The time between the drive-off instant A and the movement of the valve needle is the opening delay time TV. Thus, the difference TE - TA is responsible for the shortening of the conveying duration FD or the difference TE - TV is responsible for the shortening of the physical conveying duration FD.

When the conveying duration FD is preset as an angular magnitude, the injected quantity of fuel to a first approximation depends merely on the conveying duration FD. For equal conveying duration FD, the same quantity of fuel is injected. This means that a smaller conveying duration FD and thereby a smaller injected quantity of fuel results for rising rotational speed with equal drive-on duration AD. This effect is desired because it promotes engine stability. If the rotational speed rises between the computation of the drive-on duration AD, this leads to the injected quantity of fuel being reduced.

Fig. 3 shows program steps of the control unit 30 for determining the drive-off instant A. In a first step 310, the target values for the conveying start FBS and conveying duration FDS are computed starting from mean rotational speed and accelerator 9 pedal setting as well as possibly in dependence on further operating parameter magnitudes. The magnitudes of mean rotational speed and pedal setting as well as the further magnitudes are preferably detected anew at the beginning of the step 310. In a following step 320, the drive-on instant E is then computed with the use of the instantaneous rotational speed N as well as the setting KW of the shaft 60. This computation is described in, for example, DE-OS 42 04 091.

In a step 330, the actual conveying start FBI is then detected. Subsequently, in a step 350, the drive-off instant A is computed starting from the actual conveying start FBI of the conveying duration FD, the instantaneous rotational speed N and the setting KW of the shaft 60. The magnitudes of instantaneous rotational speed and shaft setting are detected anew at the beginning of the step 350. This computation is illustrated in, for example, DE-OS 42 04 091.

It has now proved that the injected quantity of fuel rises when the rotational speed rises between the determination of the conveying duration FDS in the step 310 and the output of the drive off pulse A in the step 350. This effect does not occur in the case of use of the drive-on duration AD in place of the conveying duration FD, since the shortening of the conveying duration due to the switch-on time TE reduces the injected quantity of fuel.

The target values for the conveying duration FDS and the conveying start FBS are filed in characteristic curve value fields.

In particular, the conveying duration is filed in such a field as a function of the fuel quantity QK to be injected and of the mean rotational speed NM. A quantity field inverse thereto is illustrated in Figs. 4a and 4b.

- 10 In Fig. 4a, the fuel quantity QK in cubic millimetres per strokeH is entered as a function of mean rotational speed NM. The drive-on duration AD is chosen as parameter.

If a certain drive-on duration is now considered, falling characteristic curves result for increasing rotational speed. These falling characteristics lead to stabilisation of the engine operation. This is important particularly in dynamic travel operation states.

If the rotational speed rises between the computation of the target values in the step 310 and the computation of the drive-off pulse A in the step 350, a value for the conveying duration FDS is read out in the step 310. which corresponds to a low rotational speed of, for example, 1000 revolutions per minute. In that case, a fuel quantity of 10 cubic millimetres per stroke is injected for a drive-on duration of 180. If the rotational speed rises to 1500 revolutions per minute before injection, a fuel quantity of about 2 cubic millimetres per stroke then results for a drive-on duration AD of 18.

In Fig. 4b, the fuel quantity QK is entered as a function of mean rotational speed W. In this case, however, the conveying duration FD is chosen as parameter. It now proves that the injected quantity of fuel is almost constant or rises slightly as a function of the rotational speed for a certain conveying duration.

For a rotational speed of 1500 revolutions and a conveying duration of 150, an injected quantity of fuel of 40 cubic millimetres per stroke results. If the rotational speed rises before injection to 2000 revolutions, an injected quantity of fuel of 45 cubic millimetres per stroke results for the same conveying duration. This increased quantity of injected fuel in turn leads to an acceleration of the engine, which leads to a further rise in rotational speed and thereby to a further increase in the injected quantity of fuel.

In order to avoid these instabilities, the target value read out of the field in step 310 is corrected in step 340 for the conveying duration FDS. The conveying duration FDS is corrected in such a manner that a constant or a falling quantity of fuel is injected also for a mean rotational speed rising between the computation of the conveying duration and the injection. This means that locally falling characteristics result. The corrected conveying duration FM can, for example, be computed as follows, starting from the conveying duration FDS read out from the field:

FM = FDS - NA K.

The magnitude NA corresponds to the change in the instantaneous rotational speed between the instant of the detection of the mean rotational speed and the instant of the injection. This magnitude is obtained through multiplication of the rotational speed gradient referred to the shaft 60 with the spacing between the shaft angle at the instant at which the rotational speed was ascertained for the characteristic field computation, and the instant of the injection.

The factor K is the slope dQ/dFD in the field.

- 12 If the respective sloDe dQ/dFD of the corresponding operating point is chosen for the value K, horizontal characteristics can be achieved at each operating point even in dynamic operating states.

In practice, it is simpler to preset a single value K for the entire field range. This value should preferably correspond to the maximum slope dQ/dFD of the field illustrated in Fig. 4b. Thus, seen dynamically, a falling characteristic, which according to actual field slope has a value between 0 and - K,results at each point in the field. Such a dynamically locally falling characteristic is indicated in Fig. 4b by a dashed line for an arbitrary operating point.

With a method and system embodying the invention it may be possible to achieve a dynamically stable engine operation with a maximum Possible accuracy of fuel injection. The accuracy of the fuel feed is improved through computation of the drive-off instant A starting from the actual injection start FBI. The stability is achieved through the correction of the conveying duration FD.

- 13

Claims

1 A method of controlling operation of an engine fuel fee-d system comprising an electromagnetic valve for controlling fuel feed and electronic means operable to determine, in dependence on at least a value indicative of fuel conveying duration, an instant for termination of driving of the valve, the method comprising the step of so correcting the fuel conveying duration value as to permit setting of a locally falling course of a parameter of fuel feed by the valve.

2. A method as claimed in claim 1, wherein the step of correcting is carried out in-dependence on a correction factor and a further value.

3. A method as claimed in claim 2, wherein the fuel conveying duration value is determined in- dependence on detected mean rotational speed of a component of an engine equipped with the system and the instant for termination of valve driving is determined in dependence on detected instantaneous speed of the component, the further value being indicative of change in the component speed between the detection of the mean speed and the detection of the instantaneous speed.

4. A method as claimed in claim 2 or claim 3, wherein a respective such -correction factor is associated with each operating point of an engine equipment with the system.

14 -

5. A method as claimed in claim 4, wherein each correction factor corresponds to the slope, at the respective engine operating point, of a plot of fuel feed quantity against fuel conveying duration in a values field.

6. A method as claimed in claim 2 or claim 3, wherein the correction factor corresponds to a maximum value of the slope of a plot of fuel feed quantity against fuel conveying duration in a values field.

7. A method as claimed in claim 1 and substantially as 10 hereinbefore described with reference to the accompanying drawings.

8. An engine fuel feed system comprising an electromagnetic valve for controlling fuel feed and' electronic means operable to determine, in dependence on at least a value indicative of fuel conveying duration, an instant for termination of driving of the 15 valve, the electronic means including correction means to so correct the fuel conveying duration value as to set a locally falling course of a parameter of fuel feed by the valve.

9. A system substantially as hereinbefore - described with reference to the accompanying drawings.