Method and unit for diagnosing malfunctioning of the injectors of an internal combustion engine high-pressure injection system

Abstract: The diagnostic method includes the steps of generating an acceleration signal (S) related to the intensity of vibration in an engine; comparing the amplitude of the acceleration signal (S) with a predetermined reference amplitude value (S th ); generating a fault indicator when the amplitude of the acceleration signal (S) exceeds the predetermined reference amplitude value (S th ); determining a crossover drive angle value (A o ) upon the amplitude of the acceleration signal (S) exceeding the predetermined reference amplitude value (S th ); comparing the crossover drive angle value (A o ) with a predetermined reference angle value (A th ); and generating a fault signal in the event the crossover drive angle value (A o ) is less than the predetermined reference angle value (A th ).

Description: The present invention relates to a method and unit for diagnosing malfunctioning of the injectors of an internal combustion engine high-pressure injection system. As is known, high-pressure injection systems comprise a number of injectors for supplying fuel to an internal combustion engine. One problem of such systems is that, if one or more of the injectors should become jammed in the open position, fuel is supplied continuously to the cylinders, thus resulting, not only in excessive fuel consumption, but also in abnormal combustion characterized by pressure peaks and a considerable increase in temperature inside the cylinders. Being withstandable by the engine for no more than a short period of time, the above phenomena may result in serious damage to the engine, e.g. to the connecting rod, piston or the injector nozzles. DE-A-35 06 114 discloses diagnosing knocking of an internal combustion engine caused by malfunction of high-pressure injectors directly injecting fuel into the engine, comprising the steps of generating an acceleration signal related to the intensity of vibration in the engine, frequency analysing the acceleration signal using a discrete Fourier transformation to obtain a vibration spectrum, comparing the vibration spectrum with a reference spectrum and determining a fault condition when the amplitudes of the vibration spectrum exceeds the amplitudes of the reference spectrum. US-A-4 518 268 discloses a system for analysing a diesel engine including glow plugs and transmitting data regarding faults within the diesel engine. The system includes a vibration sensor interconnected to the diesel engine and influenced by the temperature of the vapour within the internal chamber over a working cycle of the diesel engine and providing a temperature signal representing the temperature. A display is connected to the sensor for receiving the temperature signal and responsively providing a display representative of the operational characteristics of the engine. It is an object of the present invention to provide a method and unit for diagnosing a jammed open condition of the injectors and so enabling fuel supply to the cylinder to be cut off immediately in the event of an injector jamming in the open position. According to the present invention, there is provided a method of diagnosing a jammed open condition of injectors of a diesel engine high-pressure common rail injection system, as defined in claim 1. According to the present invention, there is also provided a unit for diagnosing a jammed open condition of injectors of a diesel engine high-pressure common rail injection system, as defined in claim 6. A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a simplified diagram of a high-pressure injection system comprising a diagnostic unit in accordance with the present invention; Figure 2 shows a flow chart of the method according to the invention; Figures 3-6 show graphs of a number of quantities employed in the diagnostic method. Number 1 in Figure 1 indicates a high-pressure injection system for a diesel engine 2 comprising a block 3, cylinders 4, a drive shaft 5 (shown schematically), and a camshaft 6 (also shown schematically). Injection system 1 comprises a number of injectors 7 for supplying fuel to cylinders 4 of engine 2, and in turn supplied by a known "common rail" supply circuit 8. Supply circuit 8 comprises a fuel tank 9; a delivery pump 10 housed inside tank 9; a known common rail 11; a radial-piston pump 12 connected to delivery pump 10 by a low-pressure delivery line 13, and to common rail 11 by a high-pressure delivery line 14; and a fuel filter 15 located along low-pressure delivery line 13. Each of injectors 7 and radial-piston pump 12 are also connected to tank 9 by drain lines 16 for feeding part of the fuel, used during operation of the injectors and the pump, back into tank 9 in known manner and therefore not described in detail. Injection system 1 also comprises a diagnostic unit 17 for detecting malfunctioning of injection system 1. Diagnostic unit 17 comprises a first known position sensor 18 located on drive shaft 5 to generate a first position signal Φ 1 indicating the angular position of drive shaft 5 (drive angle A); a second known position sensor 19 located on camshaft 6 to generate a second position signal Φ 2 indicating the angular position of camshaft 6; a known acceleration sensor 20 located on block 3 of engine 2 to generate an acceleration signal S related to the intensity of vibration present on block 3 and caused by combustion of engine 2; and an electronic central control unit 21 receiving acceleration signal S and position signals Φ 1 and Φ 2 , and which implements the diagnostic operations described in detail later on with reference to Figure 2. The invention is based on the fact that, when one or more injectors are jammed in the open position, this results in abnormal combustion of engine 2, in turn resulting in far greater vibration as compared with correct combustion; and that such vibration is present even before the instant at which the injection start command is given. Such abnormal performance is clearly shown by way of comparison in Figures 3, 4, 5, and 6. More specifically, Figures 3 and 4 show graphs of acceleration signal S and the pressure P inside cylinder 4 as a function of drive angle A, and under correct operating conditions of injector 7; while Figures 5 and 6 show graphs of the same quantities with injector 7 jammed in the open position. As can be seen, an injector 7 jammed in the open position causes a pressure peak inside cylinder 4, and a considerable increase in the intensity of vibration on block 3 of engine 2. Moreover, as shown in Figures 3 and 5, when injector 7 is jammed in the open position, acceleration signal S begins oscillating well in advance with respect to correct operation of the injector, i.e. even before the instant at which the injection start command is given. As is known, fuel is injected in advance with respect to the top dead center position (zero drive angle A). Therefore, when the injector is operating correctly, ignition occurs roughly at the top dead center position, and acceleration signal S oscillates slightly, due to combustion, following the top dead center position. Conversely, when injector 7 is jammed in the open position, combustion occurs in advance, and the corresponding acceleration signal S (Figure 5) oscillates considerably and well in advance of the top dead center position. Therefore, by comparing the amplitude of acceleration signal S with a predetermined reference amplitude value S th , and by determining the drive angle (crossover angle) A o at which said amplitude exceeds reference value S th , it is possible to determine the presence of an injector 7 jammed in the open position. As shown in Figure 2, therefore, after acquiring acceleration signal S and position signals Φ 1 and Φ 2 (block 25), the measured value of the amplitude of acceleration signal S is compared with a predetermined reference amplitude value S th (block 26). If the measured value is greater than reference value S th (YES output of block 26), this means combustion is abnormal, and a fault indicator is generated. Conversely (NO output of block 26), combustion is normal and the diagnosis is terminated. Comparing the amplitude of acceleration signal S with predetermined reference amplitude value S th would be sufficient in itself to diagnose an injector 7 jammed in the open position and so generate a fault signal indicating malfunctioning of injector 7. For greater precision, however, and as shown in Figure 2, a further check is made of the phase of acceleration signal S. That is, the crossover angle A o at which acceleration signal S exceeds predetermined reference amplitude value S th is determined (block 27). Crossover angle A o is then compared with a predetermined reference angle value A th equal or related to the drive angle at which fuel is injected into each cylinder 4 under normal combustion conditions (block 28). If crossover angle A o is less than predetermined reference angle value A th (YES output of block 28), a jammed-open injector 7 is diagnosed, and a fault signal is generated (block 29) to indicate malfunctioning of an injector 7. Conversely (NO output of block 28), the diagnosis is terminated. Alternatively, the diagnosis performed in blocks 25-29 is repeated cyclically to continually monitor operation of injection system 1. The reference values S th and A th used in blocks 26 and 28 depend on the load and speed of engine 2, and are memorized in a map. By also checking the phase of acceleration signal S on the basis of second position signal Φ 2 supplied by second position sensor 19 on camshaft 6, it is possible to determine in which precise cylinder 4 combustion is occurring abnormally, by simply observing the phase of acceleration signal S with respect to the succession of explosion top dead center positions of individual cylinders 4. In this case, upon detecting an injector 7 jammed in the open position, a fault signal may be generated (block 29) to indicate malfunctioning of the injector 7 supplying the cylinder 4 in which combustion is occurring abnormally, and possibly disconnect the injector 7 to prevent damaging engine 2. The advantages of the present method are as follows. In particular, it provides for accurately determining the presence of an injector 7 jammed in the open position when both comparisons of acceleration signal S are made, and also for giving a reliable indication even in the event only the amplitude of the signal is compared. Moreover, it provides for accurately determining which injector 7 is jammed in the open position. Finally, the present method is straightforward, easy to implement, and requires only minor changes to injection system 1, i.e. the addition of a known acceleration sensor and a known device for processing the output signal of the sensor, in that the operations required may be performed directly by the electronic injection central control unit. Clearly, changes may be made to the method as described and illustrated herein without, however, departing from the scope of the present invention. For example, acceleration sensor 20 may be located on the cylinder head of the engine as opposed to block 3; or, as opposed to a single sensor 20, a number of acceleration sensors 20 may be located at different points of engine 2, in the event the amplitude of acceleration signal S generated by a single acceleration sensor 20 is not sufficient to determine malfunctioning of each cylinder 4.

Claims: A method of diagnosing a jammed open condition of injectors of a diesel engine high pressure common rail injection system, characterized by comprising the steps of: generating an acceleration signal (S) directly related to the intensity of vibration in said diesel engine; comparing said acceleration signal with reference values (Sth, Ath); and determining a jammed open condition in any injectors in the event of a predetermined relationship between said acceleration signal (S) and said reference values (Sth, Ath). A method as claimed in Claim 1, characterized in that said step of comparing said acceleration signal (S) with reference values (Sth, Ath) comprises the step of: comparing the amplitude of said acceleration signal (S) with a predetermined reference amplitude value (Sth). A method as claimed in Claim 2, characterized in that said step of determining a jammed open condition comprises the step of: generating a jammed open injector indicator (YES/NO) when the amplitude of said acceleration signal (S) exceeds said predetermined reference amplitude value (Sth). A method as claimed in Claim 3, characterized in that said step of comparing said acceleration signal (S) with reference values (Sth, Ath) also comprises the step of: determining a crossover drive angle value (Ao) upon the amplitude of said acceleration signal (S) exceeding said predetermined reference amplitude value (Sth); and comparing said crossover drive angle value (Ao) with a predetermined reference angle value (Ath). A method as claimed in Claim 4, characterized in that said step of determining a jammed open condition comprises the step of: generating a jammed open injector signal in the event said crossover drive angle value (Ao) is less than said predetermined reference angle value (Ath). A unit for diagnosing a jammed open condition of injectors of a diesel engine high pressure common rail injection system, characterized by comprising an acceleration sensor (20) generating an acceleration signal (S) related to the intensity of vibration in an engine (2); comparing means (26, 28) connected to said acceleration sensor (20) to compare said acceleration signal (S) with reference values (Sth, Ath); and jammed open injector detecting means (29) for determining a jammed open condition in any injectors in the event of a predetermined relationship between said acceleration signal (S) and said reference values (Sth, Ath). A unit as claimed in Claim 6, characterized in that said comparing means (26, 28) comprise an amplitude comparator (26) for comparing the amplitude of said acceleration signal (S) with a predetermined reference amplitude value (Sth), and for generating a jammed open injector indicator (YES/NO) when the amplitude of said acceleration signal (S) exceeds said predetermined reference amplitude value (Sth). A unit as claimed in Claim 7, characterized by comprising phase detecting means (27) for generating a crossover drive angle value (Ao) upon the amplitude of said acceleration signal (S) exceeding said predetermined reference amplitude value (Sth); and in that said comparing means (26, 28) comprise a phase comparator (28) for comparing said crossover drive angle value (Ao) with a predetermined reference angle value (Ath). A unit as claimed in Claim 8, characterized in that said fault detecting means (29) comprise generating means for generating a jammed open injector signal when said crossover drive angle value (Ao) is less than said predetermined reference angle value (Ath).

Inventors: BORRIONE STEFANO MARIA, BURATTI RICCARDO, BORRIONE,STEFANO MARIA, BURATTI,RICCARDO
Applicants: FIAT RICERCHE, C.R.F. SOCIETA CONSORTILE PER AZIONI
Application year: 1997
Main classification: F02D41
IPC codes: F02D41