GB2241354A

GB2241354A - Controlling electromagnetic valve of a fuel pump

Info

Publication number: GB2241354A
Application number: GB9102186A
Authority: GB
Inventors: Hans-Joachim Siebert; Nestor Rodriguez-Amaya; Joachim Tauscher; Herbert Graf; Werner Zimmermann; Alfred Schmitt; Pierre Lauvin; Anton Karle
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-02-10
Filing date: 1991-02-01
Publication date: 1991-08-28
Anticipated expiration: 2011-02-01
Also published as: KR910015786A; FR2658246A1; DE4004110C2; JP3224553B2; JPH04214942A; FR2658246B1; GB9102186D0; KR0185589B1; GB2241354B; DE4004110A1

Abstract

To control actuation of an electro-magnetic valve (20, Fig 1) of a fuel pump (10) for an internal combustion engine, drive signals for the valve are determined in dependence on markings on an increment wheel (55) mounted on a shaft of the engine, a fuel conveying start WB and end WE being determined by the valve. To determine a drive signal for the valve, Fig. 5c, the markings on the shaft are counted and interpolation, B1 or B2, of shaft position between markings is carried out in dependence on the rotational speed of the shaft. Variations in rotational speed are accurately tracked by determining the speed from the two markings prior to interpolation; the speed is updated throughout the fuel pulse. <IMAGE>

Description

k,1 - 1 METHOD OF AND EQUIPMENT FOR CONTROLLING ACTUATION OF AN

ELECTROMAGNETIC VALVE OF A FUEL PUMP The present invention relates to a method of and equipment for controlling actuation of an electromagnetic valve of a fuel pump for an internal combustion engine, especially for a fuel injected Diesel engine.

A method and equipment for that purpose are disclosed in German (Federal Republic) laid-open specification (DE-OS) 35 40 811. In this specification there is described a system for the control of a fuel pump, which itself is controlled by an electromagnetic valve, for a Diesel engine. The pump has a piston which moves in a pumping chamber and is driven by a camshaft of the engine. The piston disposes the fuel in the chamber under pressure and the fuel then passes by way of a fuel duct to the individual cylinders of the engine. The electromagnetic valve is arranged between a fuel tank and the pump chamber and an electronic control device delivers control pulses to the valve, which closes and opens in dependence on these pulses.

The pump piston thus conveys fuel into the engine combustion chambers in dependence on the switching state of the valve. The drive pulses determine the exact injection start and, by way of the injection end, the quantity of fuel to be injected. A mechanical determination of quantity by way of control grooves is not necessary. An increment wheel is provided on the camshaft for fixing the drive pulses. A counter, which counts markings on the wheel, starts counting after issue of a synchronising pulse. After counting of a preset number of markings, the control equipment delivers a drive pulse to the valve which defines the injection start. The conveying end is fixed by further counting of the increment markings.

This equipment has the disadvantage that fuel metering is relatively inaccurate. Since the drive pulses are fixed by counting from the increment wheel, the metering accuracy depends on the fineness of the wheel markings. The conveying start and end are not able to be determined very precisely. Due to production tolerances, only a finite number of teeth can be arranged on the wheel and the markings on the wheel therefore have a relatively large spacing, which is disadvantageous for metering accuracy.

A method in which the exact conveying start can be fixed by way of an electromagnetic valve between pump working chamber and fuel supply is also known from German (Federal Republic) laid-open specification (DE- OS) 35 40 313. The injection end and thereby the quantity of fuel to be injected are fixed by mechanical components. Calculation of a drive pulse for the injection start is carried out in similar manner to the method described in DE-OS 35 40 811. The teeth on an increment wheel are again counted down in response to issue of a synchronising pulse. If the injection start lies between two markings of the increment wheel, the remaining balance is interpolated. The interpolation is carried out in dependence on a rotational speed value averaged over several working cycles.

In that case, there is the problem that the rotational speed can fluctuate during a working cycle of the engine and also from cycle to cycle. When an averaged rotational speed value is used as in DE-OS 35 40 313, the interpolation becomes very inaccurate if the speed changes during the metering. The system of DE-OS 35 40 313 attempts to compensate for these difficulties by a correction factor dependent on a parameter 1 i i 1 1 1 i i field, but this correction does not provide sufficiently accurate values for injection start. Since the injection end is fixed by mechanical components, an error at the conveying start also effects a quantity error.

It would thus be desirable to determine valve drive instants for fixing injection start and injection end as accurately as possible.

According to a first aspect of the present invention there is provided a method of controlling actuation of an electromagnetic valve of a fuel pump for an internal combustion engine, wherein the pump is operable to convey fuel under pressure to the cylinders of the engine and the start and end of the fuel conveying are fixed by the valve, the method comprising the step of determining drive signals for the valve in dependence on markings on a shaft of the engine by counting down the markings and by carrying out interpolation over time between the markings in dependence on instantaneous rotational speed detected immediately before the interpolation.

According to a second aspect of the present invention there is provided equipment for controlling actuation of an electromagnetic valve of a fuel pump for an internal combustion engine, wherein the pump is operable to convey fuel under pressure to the cylinders of the engine and the start and end of the fuel conveying are fixed by the valve, the equipment comprising means to determine drive signals for the valve in dependence on markings on a shaft of the engine by counting down the markings and by carrying out interpolation over time between the markings in dependence on instantaneous rotational speed detected immediately before the interpolation.

Due to the interpolation between the individual markings, the - 4 accuracy of the conveying or injection start as well as of the conveying or injection end can be determined relatively accurately. The reference to the instantaneous rotational speed value immediately before the interpolation has the result that the accuracy of the interpolated value 5 may be able to be substantially increased. An example of the method ment of the invention will now be more particularly described with reference to the Fig. 1 and an embodiment of.the equip- Fig. 2 Fig. 5 accompanying drawings, in which: is a schematic diagram of fuel conveying control equipment for an internal combustion engine; is a set of diagrams showing the relationship between cam stroke, drive signal of an electromagnetic valve, valve stroke and a synchronising pulse in operation of such equipment; Fig. 3 is a set of diagrams showing fuel quantity scatter for different fuel conveying starts; Fig. 4 is a schematic block diagram of a control device of the equipment, in particular a device for forming a valve drive signal; is a set of diagrams showing the relationship of the drive signal to camshaft rotational speed and to markings on an angle increment wheel of the camshaft; and Fig. 6 is a set of diagrams showing the sequence of different signals serving for regulation of injection start.

Referring now to the drawings, there is shown in Fig. 1 control equipment for a fuel pump, which is controlled by an electromagnetic valve, for a Diesel engine. Fuel is fed to the individual cylinders 1 1 i s i I i - 5 of the engine by way of a fuel pump 10, which has a pump piston 15 driven by a camshaft 60 and which is disposed in flow connection with an electromagnetic valve 20. The valve 20 is acted on by switching pulses from an electronic control unit 30 by way of a power output stage 40. The 5 control unit 30 comprises, inter alia, a regulator 32. A transmitter 70, which is arranged at the valve 20 or at a fuel injector (not shown), supplies signals to the control unit 30.

Angle markings are provided on an increment wheel 55 mounted on the camshaft 60. The wheel has at least one increment gap IL, which can be defined by an absent tooth, by a tooth differing from the remaining teeth, or by another appropriate measure. A measuring device 50 detects pulses initiated by the angle markings and thereby the rotational movement of the wheel 55, and supplies corresponding signals to the control unit 30. 15 A measuring device 90 recognises marks 92 on a transmitter wheel 95 mounted on the engine crankshaft and also supplies corresponding signals to the control unit 30. Data concerning additional magnitudes, such as rotational speed n, temperature T and load FP (accelerator pedal setting) are passed to the control unit 30 by way of further inputs 80. 20 The control unit 30 determines a fuel conveying start WB and a fuel conveying angle WD of the fuel pump 10 in dependence on the magnitudes supplied by way of the inputs 80 and the rotational movement of the pump camshaft 60 detected by way of the measuring device 50. Starting out from these values for the conveying start WB and the conveying angle WD, the unit 30 then computes the start and the end of a drive signal AS for the power output stage 40. The computation takes place in such a way that the valve 20 at the instant WB assumes a first setting - 6 in which the pump conveys and injects, and at the instant WE assumes a second setting in which the fuel pump no longer injects. The computation can be based on, inter alia, one or more of rotational speed n, temperature T or a signal FP which indicates the setting of the acceleratorpedal or a desired speed of travel.

The camshaft 60 drives the pump piston 15 in such a manner that the fuel in the pump 10 is set under pressure. In that case, the electromagnetic valve 20 controls the pressure build-up. The valve 20 can be so arranged at the pump that the fuel conveying is initiated through closing of the magnetic valve or that the fuel conveying starts through opening of the valve. Methods exemplifying the invention can be used for both variants of the valve function.

If the valve 20 is so arranged that there is no pressure build-up when the valve is opened, a pressure in the pump 10 builds up only when the valve 20 is closed. A valve (not illustrated) opens at a.ppropriate pressure in the fuel pump and the fuel passes by way of the injector into a combustion chamber of the engine.

The transmitter 70 serves to check the instant at which the valve 20 opens or closes. It is particularly advantageous when the transmitter 70 is arranged at the injector, because it then produces a signal which denotes the actual start SB or end of the fuel injection into the combustion chamber.

The regulator 32 compares the output signal of the transmitter 70 and the signal of the measuring device 90 with a preset target value.

When a deviation occurs, the regulator changes the value of the conveying start WB correspondingly. In place of the output signal of the transmitter 70, it is possible to use a signal which indicates the position in which i 1 - 7 the valve 20 is disposed. Such a signal can be obtained through evaluation of the current flowing through or the voltage present across the valve.

Fig. 2a shows the cam stroke NH over somewhat more than a combustion cycle, Fig. 2b shows the drive signal AS for the valve 20, Fig. 2c shows the valve stroke MH and Fig. 2d shows the synchronising pulse S. The conveying start WB and the conveying end WE are defined starting out from this synchronising pulse S. The electronic control unit 30 delivers a drive signal AS for the valve 20 at an angle.WD after the synchronising pulse S. After a short delay time VT, the valve 20 passes over into its second switching state. From this instant FB onwards, the pump 10 conveys.

After passage of the angle WD, which fixes the conveying duration D, the drive signal AS for the valve is again withdrawn. After a further delay time, the valve opens and the conveying ends at FE. Between the closing at FB and the opening at FE of the valve 20, the cam moves through the distance H, the cam stroke. This cam stroke H determines the injected quantity of fuel, which is directly proportional to the cam stroke H.

When the cam speed c is constant, the quantity of fuel injected does not depend on the conveying start WB. The ratio of cam stroke to elapsed time is denoted as cam speed c. If the cam speed c is not constant, a change in quantity, which must be allowed for, results when there is a change in the conveying start and when the duration D of the drive signal for the valve 20 is unchanged. The inconstant cam speed can be due to, for example, a change in rotational speed in th e course of the injection.

In Fig. 3a the cam stroke NH is recorded as a function of time. The cam speed c is recorded in Fig. 3b and rises as a function of time.

- 8 In Fig. 3c, the voltage UM across the valve 20 for two injection phases 21 (shown by a solid line) and Z2 (shown by a dashed line) is recorded as a function of time. In that case, the starts (WB) of the injection phases differ by only a small amount DFB. The conveying angle WD remains the same in both phases. If the cam speed rises with time, a cam stroke H1 results for the first injection phase and a cam stroke H2 for th e second injection phase. The-cam moves during the first phase by a smaller stroke H1 than in the case of the second phase H2. Consequently, a larger quantity of fuel is injected in the second phase than in the 10 first phase.

A pure time control is not possible in view of the different rotational speed courses during injection. The rotational speed changes are caused by, for example, elasticity in the drive connection between crankshaft and camshaft.

The fuel quantity Q injected into the engine thus depends not only on the closing time of the valve 20, but also on the instantaneous rotational speed N. In this case, there applies the relationship Q = conveying rate x WD, wherein the conveying rate denotes the quantity of fuel injected per unit of angle. The conveying angle WD = 6 x N x D, wherein D signifies 20 the conveying duration.

Figs. 4 to 6 illustrate a method for reducing the dependence of the injected fuel quantity on unsystematic changes in rotational speed.

Fig. 4 illustrates the electronic control unit 30 in more detail, wherein the unit consists of an admetering computer 120, parameter fields

K1 and K2 and a computer 110. A signal from a rotational speed sensor 125, which detects the instantaneous rotational speed N of the camshaft, is delivered to the computer 120. Signals which indicate the desired 1 i - 9 conveying angle WD and desired conveying start WB are also applied to the computer 120. The signals WD and WB respectively originate from the fields K1 and K2. The mean rotational speed nM and the desired fuel quantity Q serve at in put magnitudes for each of the fields K1 and K2. The signal Q originates from the computer 110, which computes the desired fuel quantity Q in dependence on different input rhagnitudes provided by means of sensors detecting, for example, mean rotational speed nM, temperature T, accelerator pedal setting FP and possibly other operating parameter magnitudes.

The conveying angle WD is read out from the field K1 in dependence on the values for injected quantity Q and mean rotational speed nM and determines the quantity of fuel to be injected. This is the angle traversed by the camshaft while the fuel pump conveys. The mean rotational speed nM can be derived from different sensors, preferably a sensor which detects pulses from a pulse wheel on the crankshaft or camshaft.

In that case, the rotational speed is averaged over a larger angular range or over several rotations of the shaft. This signal can also be derived from a substitute rotational speed sensor, such as for example an injection start sensor.

The conveying start WB is read out from the field K2 in dependence on the injected quantity Q and the mean rotational speed nM. This is the angle at which the injection shall start. The computer 120 translates these angle signals WD and WB into time magnitudes with the aid of the instantaneous rotational speed N. These magnitudes determine the drive signal for the valve 20. The computer 120 thus fixes the instants at which the voltage present across the magnetic valve changes (see Fig.

2b). These values are delivered to the power stage 40, which translates 10 them into a drive signal AS.

The translation of the angular magnitudes into the time magnitudes is now described with reference to Fig. 5. Fig. 5a shows a usual rotational speed course during an injection phase or admetering. The rotational' speed decreases linearly as a function of time in the course of the phase. The pulses which the measuring device 50 derives from'the markings of the increment wheel 55 are shown in Fig. 5b. Each mark on the wheel produces a pulse in the device 50. It is particularly advantageous if the spacing between two angle marks, the measuring angle MW, is smaller than the smallest conveying angle WD. A measuring angle of 3' is particularly advantageous, in which case 120 angle marks at a 30 spacing are applied to the wheel. Such a wheel is particularly suited to engines with four, five, six and eight cylinders. As already mentioned, at least one increment gap IL, which produces a synchronising pulse S, is present on the wheel for synchronisation. The angles for the conveying start WB and the conveying end WE are indicated starting out from this synchronising pulse.

The fuel metering takes place over the conveying angle WD, which lies between the conveying start WB and the conveying end WE. The angle for WB is divided into an integral angle component WBG for the conveying start and a remaining angle RB for the conveying start or the corresponding remaining time TB. The angle for WE is divided into the integral angle part WEG and the remaining angle RWE or the corresponding remaining time TE. The recalculation of the angles RWB and RWE into the times- TB and TE takes place by reference to the instantaneous rotational speed N. In that case, the respective remaining time T is derived from the remaining angle RW and the instantaneous rotational speed N by the formula i 1 1 T = U/(6N).

The rotational speed base for the interpolation of the times TB and TE is obtained from a measurement angle MW which lies as close as possible to the respective interpolation distance. Errors can be kept small through the use of a rotational speed value which is as up-todate as possible.

A first computation is characterised by B1 in Fig. 5b. The camshaft traverses the measurement angle MW in the measurement time MT. A first value for the instantaneous rotational speed N is computed and the interpolation performed in the computation time TR. After the computation time TR, the actual remaining time TB is left. The computation time TR must, in any event, end before the injection phase. If the conveying start WB has not yet been reached, a renewed interpolation takes place. The instantaneous rotational speed N is detected over a first measurement angle and the interpolation.is performed in the computation time TR of the second computation B2. The interpolation error due to changing camshaft rotational speed can be kept small through repeated computation of the instantaneous rotational speed value. The detection of the instantaneous camshaft rotational speed N and the interpolation must start, at the latest, in advance of the conveying start WB by the measurement time MT and the computation time TR. The detection of the camshaft rotational speed and the interpolation are thus carried out, with particular advantage, in a time interval equal to the sum of the measurement time MT and the computation time TR just before the desired conveying start WB.

The process is repeated for the conveying end. In a further computation time, a first value for the instantaneous rotational speed - 12 is computed anew and the interpolation is performed. The actual remaining time TE is left after the computation time. The computation time must end before the end of the injection phase. If the conveying end angle WE has not yet been reached, a renewed interpolation takes place. The instantaneous rotational speed N is detected over a further measurement angle and the interpolation is performed. As before, the interpolation error due to changing camshaft rotational speed can be kept small through repeated computation of the instantaneous rotational speed value, and the detection of the instantaneous speed N and the interpolation must start, at the latest, in advance of the conveying end WE by the measure- ment time MT and the computation time TR. The detection of the camshaft rotational speed and the interpolation are thus carried out, with particular advantage, in a time interval equal to the sum of the measurement time MT and the computation time TR just before the desired conveying end WE. The actual conveying start is utilised in the computation of the conveying end. Errors in the computation of the remaining time of the conveying start can be corrected in the computation of the conveying end.

In systems with preliminary injection, the computation of the con veying start and conveying end for the preliminary and the main injection take place according to the described method. Since the angles for conveying start and conveying end are formed through counting down integral angle marks and subsequent time interpolation, an increment angle time system can be regarded as an admetering principle.

At least one increment gap IL is necessary on the increment wheel, as already described, for the purpose of cylinder synchronisation.

j 1 Alternatively, Z-gaps can be provided, in which case a cylinder identifi cation is then necessary. The synchronising gap could also be replaced by a corresponding synchronising mark which differs from the remaining marks.

In order to achieve optimum combustion, the injection should take place at the correct position of the piston. The conveying start and thus the injection start are therefore referred to the piston top dead centre and thereby to the crankshaft. An optimum setting of the conveying start is achieved when the conveying start is referred to signals from a sensor at the crankshaft.

If the initiation of the conveying start takes place on the basis of signals from the camshaft, then deviations of the actual conveying start from the preset optimum conveying start may result. These deviations are due to different influences, for example elasticity in the camshaft drive from the crankshaft. Such systematic deviations can be eliminated by means of a regulating circuit.

Fig. 6 serves to explain such a regulating circuit. The occurrence of the synchronising pulse 5 as a functidn of time is entered in Fig. 6a. Fig. 6b shows the drive signal AS. The signal SB, which denotes the actual injection start, is shown as a function of time in Fig. 6c. This signal SB originates from the transmitter 70. The signal OT of the measuring device 90 is shown in Fig. 6d. The signal OT is closely correlated with the top dead centre of the piston. The spacing SBI between the signal SB, which denotes the actual injection start, and the signal OT of the measuring device 90 is delivered to the regulator 32 as shown in Fig. 6e. The spacing SBI can be indicated in angle magnitudes or in time units. The regulator 32 has at least proportional - 14 behaviour, but it i.s of particular advantage if it also has an integral component. The regulator 32 compares the signal SBI, which indicates the actual injection start, with a preset target value SBS. A correction of the conveying start takes place in dependence on this comparison. For the next injection phase or admetering, the drive signal is initiated 5 not at the conveying start WB, but at the corrected conveying'start W.

The initiation of the drive signal is referred to a synchronisation mark S, which is applied to the camshaft. The position of the actual injection start SBI is detected relative to a measuring mark OT on the crankshaft. The measuring mark is in that case preferably arranged in the region of the piston top dead centre. It is thereby possible for the injection start to take place at the optimum instant with respect to crankshaft angle. The signal processing takes place in angle magnitudes, in time magnitudes or in a combination of both.

Relatively accurate fuel injection can be achieved by such a system, since the conveying start is regulated from a crankshaft signal and quantity computation takes place in dependence on the camshaft rotation.

In order to eliminate disturbing influences, the increment wheel can alternatively be arranged at the crankshaft. A segment wheel is then arranged on the camshaft for the purpose of synchronisation of the cylinders. A system in which a respective increment wheel is arranged on the camshaft and on the crankshaft would be particularly advantageous.

i i j

Claims

1. A method of controlling actuation of an electromagnetic valve of a fuel pump for an internal combustion engine, wherein the pump is operable to convey fuel under pressure to the cylinders of the engine and the start and end of the fuel conveying are fixed by the valve, the method comprising the step of determining drive signals for the valve in dependence on markings on a shaft of the engine by counting down the markings and by carrying out interpolation over time between the markings in dependence on instantaneous rotational speed detected-immediately before the interpolation.

2. A method as claimed in claim 1, wherein the drive signals are additionally determined in dependence on the instantaneous rotational speed and on a determined angle and determined start for the fuel conveying.

3. A method as claimed in claim 2, comprising the step of determining each of the conveying angle and the conveying start from a respective field of stored values in dependence on a desired fuel quantity value and a mean rotational speed value.

4. A method as claimed in claim 3, comprising the step of determining the desired fuel quantity in dependence on engine operating parameter values.

5. A method as claimed in any one of the preceding claims, wherein the shaft is a camshaft of the engine and the markings are applied to - 16 an increment wheel of the camshaft.

6. A method as claimed in claim 5, wherein the markings are arranged at a spacing of 3'.

7. A method as claimed in any one of the preceding claims, Wherein the instantaneous rotational speed is determined constantly and the latest value used for the interpolation.

8. A method as claimed in claim 7, wherein the detection of the instantaneous speed and the interpolation are carried out during a time interval which precedes the desired conveying start and which is equal to the 10 sum of a measurement time and a calculation time.

9. A method as claimed in any one of the preceding claims, comprising the steps of comparing a signal indicative of actual fuel injection my - start with a target value and correcting the conveying start in dependence on the comparison result.

10. A method as claimed in claim 10, comprising the step of determining the signal indicative of injection start by comparison of a signal denoting the start of injection into a cylinder and a signal referred to piston top dead centre in that cylinder.

11. Equipment for controlling actuation of an electromagnetic valve of a fuel pump for an internal combustion engine, wherein the pump is' operable to convey fuel under pressure to the cylinders of the engine i 1 - 17 and the start and end of the fuel conveying are fixed by the valve, the equipment comprising means to determine drive signals for the valve in dependence on markings on a shaft of the engine by counting down the markings and by carrying out interpolation over time between the markings in dependence on instantaneous rotational speed detected immediately before the interpolation.

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

4

13. Equipment as claimed in claim 11 and substantially as hereinbefore descy,ibed with reference to the accompanying drawings.

Published 1991 at The Patent Office. Concept House. CardlIT Road. Newport. Gwent NP9 1RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Paint. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed ky Multiplex techniques ltd. St Man, Cray. Kent.