GB2302418A

GB2302418A - Method and apparatus for diagnosing a diesel engine

Info

Publication number: GB2302418A
Application number: GB9611404A
Authority: GB
Inventors: Karl-Martin Kutteruf; Uwe Fischer; Karlheinz Steinle
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-06-20
Filing date: 1996-05-31
Publication date: 1997-01-15
Anticipated expiration: 2016-05-31
Also published as: DE19522271A1; GB9611404D0; DE19522271B4; GB2302418B

Description

1 Method and device for diagnosing a diesel engine

Background art

2302418 The invention relates to a method of diagnosing a diesel engine, whereby by means of a pressure sensor disposed on a line between an.injection pump and an injection nozzle a pressure characteristic signal is removed, whereby with simultaneous amplitude-dependent adjustment of a trigger level individual injection pulses of the pressure characteristic signal are acquired and from the interval of the individual injection pulses the engine speed is determined and whereby the pressure characteristic signal is evaluated for diagnostic purposes, the invention further relating to a device for diagnosing a diesel engine which comprises, for picking off a pressure characteristic signal between a diesel injection pump and an injection nozzle, a clip-on sensor and, connected in series thereto, a signal acquisition circuit, a triggering device, an evaluation circuit equipped with a speed-measuring stage, and an information output device.

In a known method of said type, an attempt is made to draw conclusions about malfunctions of a diesel injection pump from failed triggering of a speed-measuring circuit. During said process, dips in the graph of speed against time (cf. Fig.1) during an acceleration process are evaluated. The dips in speed occur because the injection quantity and hence also the amplitude of the clip-on sensor signal fall off sharply upon attainment of a limit speed. Since the trigger level is not adjusted quickly enough, instances of failed triggering o5.-cur, with the added result that a plurality of successive individual injection pulses of a pressure characteristic signal are not acquired and a sharply reduced speed is erroneously determined. From the dips in speed, negative

2 gradients of the injection quantity are consequently detectable. From such dips at specific instants, an attempt is made to form a diagnosis.

Advantages of the invention The object of the invention is to provide a method and a device of the type described initially, by means of which the true speed may be reliably acquired and reliable information may be obtained for diagnosis of the engine.

In the case of the method, said object is achieved in that, besides the amplitudes of the individual injections, the glitch-afflicted signal characteristic is additionally acquired, that upon failed triggering of an individual injection pulse, before the next individual injection pulse is received the maximum value of the glitch-afflicted signal characteristic since the preceding individual injection pulse, at which triggering occurred, is used to adjust the trigger level, and that upon a failed triggering the speed is determined on the basis of double the angle of rotation compared to a normal triggering. In the case of the device, to achieve the object of the invention it is provided that the triggering device comprises an amplitude acquisition device, a signal recording device and an adjusting device for the trigger level, by means of which, upon a failed triggering, triggering may be effected at the next individual injection pulse, and that provided in the speed-measuring stage is a circuit part, by means of which the speed upon a failed triggering may be determined on the basis of the double trigger interval as in the case of a normal trigger sequence.

By said means, instances of failed triggering are clearly recognized and taken into account when evaluating the speed, with the result that the true speed is reliably acquired and indicated. From the speed, it is possible to obtain further information about the engine performance, i.a. the duration of 3 the acceleration process, the limit speed, the minimum speed after closing the throttle, the rate of the speed increase and/or the rate of the speed decrease. Information about faults may be obtained, for example, by relating the measured speed characteristics or characteristic values thereof to standard data, which characterize proper functioning, or to fault data, which contain typical fault patterns. In so doing, it is also possible to incorporate fault patterns learned in the course of time into the data store. It is relatively easy to recognize limit speeds which are too low or a motor output which is too low.

A rapid adjustment of the trigger level given a relatively high signal-tonoise ratio is achieved in that the trigger level, immediately after acquisition of the amplitude of an individual injection pulse, is adapted to said injection pulse and set, for example, to a value of between 50 and 9011 of said amplitude. In so doing, it is advantageous if the change in the trigger level is effected digitally, for which purpose a suitable program may be selected.

A reliable adjustment upon instances of failed triggering and an uncorrupted determination of the speed is achieved in that the failed triggering is monitored and located by acquiring the time interval between at least two preceding successive trigger events and in that the reduction of the trigger level is effected on the basis of the maximum value of the glitchafflicted signal characteristic after, for example, one and a half times the time interval since the last trigger event has elapsed. In the continued absence of the trigger event, the described process may be repeated.

A further diagnostic aid consists of additionally generating an envelope curve relating to the pressure signal characteristic on the basis of the amplitude of the individual injection pulses or the surface below the individual injection pulses. The envelope curve based on the amplitude of the 4 individual injection pulses may be obtained by simple means, while the envelope curve based on the surface integrals below the individual injection pulses results in good suppression even of high glitches since their surface integral in the short term is low compared to the surface integrals of the individual injection pulses.

An advantageous development of the device is such that triggering at the next individual injection pulse may be effected by reducing the trigger level on the basis of the maximum value of the recorded pressure characteristic signal since the preceding normal triggering. Thus, even in the event of a failed triggering the speed is reliably determined, in the manner already described above. The additional determination of the envelope curve may be effected, for example, by a refinement which is such that there is provided, between the signal acquisition circuit and the evaluation circuit and parallel to the triggering device, an envelope curve-determining circuit by means of which the envelope curve of the pressure characteristic signal based on the amplitudes of the individual injection pulses or on the surfaces below the individual injection pulses may be determined. In such a case, speed acquisition, on the one hand, and determination of the envelope curve, on the other hand, may also be independently effected and evaluated by the evaluation circuit and passed on to the information output device for user display.

For various diagnoses a structure is advantageous, which is such that the evaluation circuit comprises an appraisal stage with stored standard data and/or fault pattern data and the diagnosis may be effected on the basis of a comparison and appraisal based on the standard data and/or fault pattern data. The evaluation device may be designed in such a way that the appraisal stage has a correlation unit, in which a correlation may be effected between the actual speed data or envelope curve data and/or the standard data and fault pattern data. Thus, the actual acquired data may be suitably displayed for the user in an appropriate manner and optionally indicating the most likely faults.

There follows a detailed description of an embodiment of the invention with reference to the drawings. The drawings show:

Fig. 1 Fig. 2 Fig. 3 Fig. 4 a characteristic of speed as a function of time, of the type determined by means of a measuring device according to prior art, a diagram with individual injection pulses and the respective position of the adjusted trigger level, a speed-time curve of the type obtained by the measures of the present invention, as well as an envelope curve on the basis of the amplitudes of the corresponding individual injection pulses, and diagrammatic view of a device for diagnosing diesel engine in the form of a block diagram.

Figure 1 shows a speed curve plotted against time. The rising edge represents an increasing speed, after which a dip may be seen, which does not correspond to the true speed but is attributable to the reduced injection quantity at the limit speed, the amplitude of the individual injection pulses being so low that they are not acquired on account of the relatively slow adjustment of the trigger level. As a result, the speed is incorrectly determined on the basis of an actually nonexistent over-long time interval. After a certain time, the trigger level is lowered in line with the reduced amplitude of the individual injection pulses so that the speed at its constant value is again determined. Upon a further drop in the amplitudes of the individual injections, instances of 6 failed triggering once more occur, resulting in a measured speed which is too low, as the dip in the falling edge reveals.

Figure 2 shows the adjustment of the trigger level TP as a function of the amplitudes of the individual injection pulses EP. The trigger level TP lies, for example, between 50 and 90-05,;, e.g. at 7516 of the preceding individual injection pulse, so that glitches SP likewise indicated in Figure 2 are reliably suppressed. Upon the drop in the peak values of the individual injection pulses, a failed triggering occurs at the second last individual injection pulse as a result of the trigger level TP being too high. However, a signal recording device for acquiring the glitch- af f licted signal characteristic is also provided. on the basis of said acquired signal characteristic, the maximum value of the signal characteristic is located when, during a time interval corresponding, for example, to one and a half times a preceding time interval t, between two successive individual injection pulses, no trigger event has occurred. The trigger level TP is then adapted to said maximum value before arrival of the next individual injection pulse, so that the latter is in turn acquired. In the event of such a failed triggering, the speed is determined on the basis of double the interval of two successively acquired individual injection pulses so that the measured speed corresponds almost exactly to the true speed.

Figure 4 shows in a block diagram the individual stages of the device for diagnosing a diesel engine. A signal acquisition circuit ES receives the signal supplied by a clip-on sensor KG which is clipped onto a line between an injection pump and an injection nozzle. The pressure characteristic signal with the individual injection pulses produced by the acquisition circuit ES is supplied, on the one hand, to a triggering device T for adjustment of the trigger level TP and, on the other hand, to an envelope curve-determining circuit HKS for 7 determination of an envelope curve HK (cf. Figure 3). The triggering device T and the envelope curve-determining circuit HKS supply their results to an evaluation circuit AW, in which the speed z and/or the envelope curve HK are evaluated in order to form a diagnosis. For example, the actual acquired data may be related to stored standard data or fault pattern data. To said end, the evaluation circuit AW is provided with. an appraisal stage having, for example, a correlation unit, in order to determine the most likely faults. The results are passed on to an information output device for appropriate user display.

In Figure 3, speed z is shown against time t in the top curve, while the bottom curve reproduces - for the same individual injection pulses - the envelope curve HK of the individual injection pulse amplitudes or the pressure pulses p. The speed is associated, in said case, with the same individual injection pulses as in Figure 1. However, on account of the described triggering and evaluation, there are no corrupting dips in the speed because the speed is correctly determined even in the event of failed triggering. It is evident from the envelope curve HK that the amplitude of the individual injection pulses EP remains constant over a wide stretch of the rising edge of the speed z and upon the transition to the constant speed, in line with the reduced injection quantity and/or reduced amplitude of the individual injection pulses EP, drops to a lower value which becomes lower still upon a drop in the speed z.

From the characteristic of speed against time, the duration of the acceleration process, the limit speed, the minimum speed after closing the throttle, the rate of the speed increase and/or the rate of the speed decrease may be determined and faulty values located. From the envelope curve it is possible to determine, for example, the maximum amplitude during acceleration, the minimum amplitude during speed limiting and also the duration of the acceleration process. It is obvious 8 that evaluation of both curve shapes provides an even more comprehensive diagnostic capability than evaluation of the individual curves.

9

Claims

Claims

1. Method of diagnosing a diesel engine, whereby by means of a pressure sensor disposed on a line between an injection pump and an injection nozzle a pressure characteristic signal is removed, whereby with simultaneous amplitudedependent adjustment of a trigger level individual injection pulses of the pressure characteristic signal are acquired and from the interval of the individual injection pulses the engine speed is determined and whereby the pressure characteristic signal is evaluated for diagnostic purposes, characterized in that besides the amplitudes of the individual injections, the glitch-afflicted signal characteristic is additionally acquired, that upon failed triggering of an individual injection pulse, before the next individual injection pulse is received the maximum value of the glitch-afflicted signal characteristic since the preceding individual injection pulse, at which triggering occurred, is used to adjust the trigger level and that upon a failed triggering the speed is determined on the basis of double the angle of rotation compared to a normal triggering.

2. Method according to claim 1, characterized in that the trigger level immediately after acquisition of the amplitude of an individual injection pulse is set to a value of between 50 and 90% of said amplitude.

Method according to claim 1 or claim 2, characterized in that the change in the trigger level is effected digitally.

4. Method according to one of the preceding claims, characterized in that the failed triggering is monitored and located by acquiring the time interval between at least two preceding successive trigger events and that the reduction of the trigger level is effected on the basis of the maximum value of the glitch-afflicted signal characteristic after one and a half times the time interval since the last trigger event has elapsed.

Method according to one of the preceding claims, characterized in that an envelope curve relating to the pressure signal characteristic is generated on the basis of the amplitude of the individual injection pulses or the surface below the individual injection pulses.

Device for diagnosing a diesel engine which, for picking off a pressure characteristic signal between a diesel injection pump and an injection nozzle, comprises a clipon sensor and, connected in series thereto, a signal acquisition circuit, a triggering device, an evaluation circuit equipped with a speed-measuring stage, and an information output device, characterized in that the triggering device (T) comprises an amplitude acquisition device, a signal recording device and an adjusting device for the trigger level (TP), by means of which, upon a failed triggering, triggering may be effected at the next individual injection pulse (EP), and that provided in the speed-measuring stage is a circuit part, by means of which the speed upon a failed triggering may be determined on the basis of double the 11 trigger interval as in the case of a normal trigger sequence.

7.

Device according to claim 6, characterized in that triggering at the next individual injection pulse (EP) may be effected by reducing the trigger level (TP) on basis of the maximum value of the recorded pressure characteristic signal since the preceding normal triggering.

8. Device according to claim 6 or claim 7, characterized in that provided between the signal acquisition circuit (ES) and the evaluation circuit (AW) and parallel to the triggering device (T) is an envelope curvedetermining circuit (HKS), by means of which the envelope curve of the pressure characteristic signal based on the amplitudes of the individual injection pulses (EP) or on the surfaces below the individual injection pulses (EP) may be determined.

9. Device according to one of claims 6 to 8, characterized in that the evaluation circuit (AW) comprises an appraisal stage with stored standard data and/or fault pattern data and that the diagnosis may be effected on the basis of a comparison and an appraisal based on the standard data and/or fault pattern data.

10. Device according to claim 10, characterized in that the appraisal stage has a correlation unit, in which a correlation may be effected between the actual speed data and/or envelope curve data and/or the standard and fault pattern data.

12 11. A method of diagnosing a diesel engine substantially as herein described with reference to the accompanying drawings.

12. A device for diagnosing a diesel engine substantially as herein described with reference to the accompanying drawings