An electronic control device for modulating fuel quantities in an internal combustion engine

Abstract

 A device for electronically controlling adjusting devices in an internal combustion engine in which the adjusting devices can be controlled, by comparing differentiated engine speed dependent signals with predeterminable threshold values, in such a way that shuddering oscillations of the internal combustion engine are counteracted. A time control is included which is initiated when the adjusting devices are actuated to perform fuel quantity modulation and which is arranged to switch off the fuel quantity modulation after an elapsed time period, whose value is dependent upon the prevailing operating conditions of the engine.

Description

State of the Art.

[0001] The present invention is concerned with electronic control devices for modulating fuel quantities in internal combustion engines, in accordance with the pre-characterising clause of claim 1.

[0002] In motor vehicles, the interaction of the internal combustion engine elastic suspension and oscillating masses often stimulates shuddering oscillations which interfere with the behaviour of the motor vehicle. Such oscillations can also be brought about by acceleration or deceleration (overrun) operation.

[0003] German Offenlegungsschrift No. 29 06 782 describes a device for damping shuddering oscillations in an internal combustion engine, whereby it is assumed that clearly measurable fluctuations in speed are associated with the shuddering oscillations. These measured fluctuations in speed are derived from the differential of an engine speed signal. The differentiated speed signal is itself then fed to the fuel quantity control means in order to counteract the shuddering oscillations.

[0004] The latter known device, which intervenes directly in the fuel quantity control, is, however, not suitable for all operating conditions of a motor vehicle or of an associated internal combustion engine, because the connection of the differentiated speed signal to the fuel quantity control means can also lead to instabilities in the control loop.

[0005] Our German Application No. P 37 05 278.0 describes a device for damping shuddering oscillations in internal combustion engines, wherein such shuddering oscillations are effectively damped, particularly during acceleration and in overrun operation, but which does not intervene directly in the fuel quantity control loop. In this latter device, the derivative of the speed-dependent signal is compared with a predetermined threshold value, above which the fuel quantity is arranged to be modulated in such a way that shuddering oscillations of the internal combustion engine are counteracted. In preferred embodiments, the fuel quantity is only modulated if the first derivative of the speed signal exceeds a first threshold value and the second derivative of the speed signal differs from zero by a predetermined amount.

[0006] The output of the above described system is a switching signal which is used for control of the solenoid or solenoids of the fuel injection valves of the engine. A problem arises with the known system in that the use of such a switching signal itself can cause oscillations to occur in the control of the solenoids.

Advantages of the Invention.

[0007] The device in accordance with the characterising clause of claim 1 overcomes the disadvantages of the known devices and prevents the occurrence of such control oscillation.

[0008] In particular, as a result of the time control provided by the present invention, the effect of the shuddering damping remains steady in that, when there is only slight shuddering, only a small reduction in the injection quantity is effected, whereas when there is heavy shuddering, a considerable reduction in the injection quantity is effected.

[0009] By using the feature of claim 2, the system can be adapted in an extremely sensitive manner to the operating conditions of the engine.

Drawings.

[0010] The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:

Fig.1 is a simplified flow diagram illustrating how control oscillations can occur in the known devices of P 37 05 278.0; and

Fig.2 is a simplified circuit diagram of part of a fuel injection system incorporating one embodiment of a device in accordance with the present invention for damping shuddering oscillations.

[0011] Referring firstly to Fig.1, there is illustrated diagrammatically a flow diagram for the conventional control of shuddering vibrations in a motor vehicle engine wherein, during an acceleration operation, upon a predetermined engine speed increase being detected and the switching threshold of a fuel control solenoid being exceeded, the fuel control solenoid is actuated such as to cut off or reduce the amount of fuel supplied to the engine. Upon a a consequential reduction of the engine speed, the fuel control solenoid is de-actuated again. Thus, there is formed within the engine control system a closed loop in which oscillation can occur and which has a system-­dependent resonant frequency.

[0012] The present invention seeks to break this closed loop and prevent the establishment of the shuddering vibrations usually associated with such loops.

[0013] Referring now to Fig.2, an engine speed detector 10 operates in conjunction with the engine crankshaft or camshaft to produce a series of engine-speed dependent pulses on line 12. The pulsed output from the detector 10 is fed to a divider 14, usually having a variable division ratio. The engine speed is determined in block 16 from the pulses detected in the detector 10. The speed signal which has been determined in this way is filtered in a filter 18 in order to eliminate interference.

[0014] The filtered speed signal is differentiated in circuit block 20 to provide the first derivative of speed (ṅ) and is then fed to a comparator 22 where it is compared with a predetermined threshold value for the speed-dependent derivative. The resulting output of the comparator 22 is fed to an input S of a decision stage 24 which provides an output signal which is fed to one input of an AND gate 26.

[0015] The speed signal from the filter 18 is also fed to a window comparator 27 for limiting the speed range in which fuel quantity correction is to take place. The window comparator 27 causes a signal to be passed to a second input of the AND gate 26 when the speed signal from the filter 18 lies between upper and lower predetermined values, in this case between an upper limit of 3000 rpm and a lower limit of 1000 rpm. Only when the comparator 27 supplies an output signal to the AND gate 26 does the AND gate 26 enable the decision stage 24 to provide an output on line 28 to a control device 30 which controls the supply of fuel to the engine cylinders.

[0016] The control system as described thus far is similar to that described in our earlier German Application P 37 05 278.0. However, in the system of P 30 05 278.0, the first derivative of speed (ṅ) is applied to one input of two different comparators arranged such that the shuddering damping is switched on at a first threshold of ṅ and is switched off at a second threshold. Reference is hereby directed to P 37 05 278.0 for a fuller description to the latter system.

[0017] As illustrated in Fig.1 of the present drawings, a problem with the basic device of P 37 05 278.0 is that, as a result of the generation of the switching signal, control oscillation can occur in the system, the frequency of which corresponds to the resonance frequency of the system.

[0018] In order to avoid control oscillation arising in this manner, in place of the second switching threshold of P 37 05 278.0, the embodiment of the present Fig.2 includes a single predetermined threshold ṅ for the switching on and switching off of the shuddering damper, together with a time control which (normally) acts to switch off the damper before the ṅ threshold is reached.

[0019] The time control arrangement includes a counter 32 which is arranged to start counting when ṅ exceeds the ṅ threshold and the shuddering damper solenoid is switched on by the provision of a signal at the output of the comparator 22. In dependence upon operating parameters of the engine, such as speed n, ṅ,

, water temperature etc., a variable comparative value is established in circuit block 36 via a multidimensional characteristic field 34 in accordance with techniques well known to those familiar with this art. When the counter value reaches the comparative value established in the circuit element 36, a comparator 38 outputs a signal to one input of an AND gate 40 which, provided that the comparator 22 is still showing ṅ to be above the ṅ threshold, forwards this signal to the R input of the decision stage 24 to switch the shuddering damper solenoid off.

[0020] It will be appreciated that the use of the multidimensional characteristic field enables the system to be adapted in an extremely sensitive manner to the operating conditions of the engine. Furthermore, as a result of the time control provided by the present invention, the shuddering damping remains steady, that is, when there is only slight shuddering, only a small reduction in the injection quantity is effected, whereas when there is heavy shuddering, a considerable reduction in the injection quantity is effected. Control oscillation is thus prevented, or at least substantially reduced by this provision.

Claims

1. An electronic control device for modulating fuel quantities in an internal combustion engine, having an electrically controllable adjusting device for the supply of fuel to the engine cylinders, and wherein the first derivative of an engine speed-­dependent signal is compared with a predetermined threshold value above which the fuel quantity is modulated by means of said adjusting device in such a way that shuddering oscillations of the internal combustion engine are counteracted, characterised in that when the adjusting device is actuated to perform fuel quantity modulation, a time control is initiated which is adapted to switch off the fuel quantity modulation after an elapsed time period, whose value is dependent upon the prevailing operating conditions of the engine.

2. An electronic control device according to claim 1, wherein the time control includes a counter (32) which is arranged to be switched on when the adjusting device is actuated to perform fuel quantity modulation, the count value being compared with a comparative value established by means of a multi­dimensioned characteristic field (34) such that, upon attainment of such comparative value, a signal is established to terminate fuel quantity modulation.

3. An electronic control device according to claim 2, wherein the first derivate (ṅ) of the speed-dependent signal is compared in a comparator (22) with a predetermined threshold value for ṅ, and wherein the counter (32) output is compared in a comparator (38) with the comparative value established by the multi-dimensioned characteristic field (34) to provide an output signal for switching off the fuel quantity modulation when equivalence of count value and the comparative value occurs.

Drawing