Apparatus for determining malfunctioning of fuel injection control system

Abstract: A system for detecting malfunctions in an apparatus for controlling a fuel injection mechanism of a diesel engine (2) provided with a plurality of cylinders (C) is disclosed. Each cylinder (C) accommodates a piston (42) for producing rotation of a crankshaft (40) and a nozzle (4) for performing fuel injection during each reciprocation cycle of the piston (42). Injection amount of the fuel is altered based on a compensation value computed for each cylinder (C) so as to minimize a value indicating cyclic rotating speed fluctuation of the crankshaft (40) produced by each cylinder (C). The system is characterized by memory means for storing an initial data indicative of the compensation value of each cylinder (C) computed during an initial injection stage of each nozzle (4), comparing means for comparing a malfunction judgement value with a magnitude obtained by computing the difference or ratio between an actual compensation value and the initial data, and determining means for determining the malfunctioning of the apparatus when the computed magnitude exceeds the predetermined range.

Description: The present invention relates to a fuel injection control system employed in a diesel engine for injecting fuel into cylinders in accordance with the operating state of the engine. More particularly, the present invention pertains to an apparatus for determining malfunctioning of the fuel injection. A fuel injection control apparatus employed in a diesel engine is constituted by injection nozzles, fuel injection pumps, and other parts. There are a variety of existing apparatuses that determine malfunctioning in an injection system. For example, Japanese Unexamined Patent Publication 2-5736 describes a system for determining malfunctioning of a certain type of fuel injection control apparatus which compensates the amount of fuel injected in each cylinder. In this determining apparatus, malfunctions are confirmed by using a characteristic of the fuel injection control apparatus. The control system minimizes the difference in the amount of fuel injected in each cylinder. Dimensional differences, which are caused during production, and wear of various parts result in each nozzle having different injecting characteristics. As a result, the amount of injected fuel differs between each cylinder. This causes cyclic fluctuation of the engine speed and produces vibrations. In addition, the amount of injected fuel varies between cylinders and causes vibrations when the injecting characteristic of each cylinder is the same but the dimensions of the injection pump parts that are connected to each cylinder are different. To cope with such problems, the fuel injection control apparatus obtains the average value of the cyclic fluctuation of the crankshaft rotating speed produced by each cylinder. The apparatus also obtains the average value of the cyclic fluctuation of all of the cylinders. The control apparatus then reduces the deviation between the average values by compensating the amount of fuel injected in each cylinder. In other words, the difference of the injected fuel amount between each cylinder is absorbed by increasing or decreasing the amount of injected fuel therein based on a compensation value FCCB computed for each cylinder. Thus, the injecting characteristic of each cylinder may be estimated from its compensation value FCCB. Accordingly, the existence of malfunctioning parts in the injection system may be presumed, or detected, from such estimations. That is, the determining apparatus determines the existence of malfunctioning parts when the compensation value FCCB of a certain cylinder becomes larger than a predetermined reference value. However, the compensation value FCCB differs between cylinders. Therefore, erroneous determination of malfunctions may occur despite normal functioning of the injection system components when the value of the compensation value FCCB becomes large. Hence, it is necessary to provide a sufficient margin for the reference value so as to prevent such erroneous determinations. Accordingly, it is required that the reference value be set at a value larger than the anticipated maximum value of the compensation value FCCB under normal states. However, malfunctions are not detected when the value of the compensation value FCCB is small due to the large gap existing between the compensation value FCCB and the reference value. In such cases, the amount of fuel becomes abnormally high. This may lead to undesirable emissions from the engine. Thus, such a malfunctioning determining apparatus may not be useful when a high detecting accuracy is required to prevent degradation of the emission from the engine. Accordingly, the objective of the present invention is to provide a system for detecting malfunctioning of a fuel injection control apparatus with high accuracy. A further objective of the present invention is to provide a system for detecting malfunctioning of a fuel injection control apparatus when the compensation of injected fuel differs from one cylinder to another. To achieve the above objectives, the present invention provides a system for detecting malfunctions in an apparatus for controlling a fuel injection mechanism of a diesel engine provided with a plurality of cylinders is disclosed. Each cylinder accommodates a piston for producing rotation of a crankshaft and a nozzle for performing fuel injection during each reciprocation cycle of the piston. Injection amount of the fuel is altered based on a compensation value computed for each cylinder so as to minimize a value indicating cyclic rotating speed fluctuation of the crankshaft produced by each cylinder. The system is characterized by memory means for storing an initial data indicative of the compensation value of each cylinder computed during an initial injection stage of each nozzle, comparing means for comparing a malfunction judgement value with a magnitude obtained by computing the difference or ratio between an actual compensation value and the initial data, and determining means for determining the malfunctioning of the apparatus when the computed magnitude exceeds the predetermined range. The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: Fig. 1 is a diagrammatic drawing showing the structure of a diesel engine and fuel injection pump; Fig. 2 is a block diagram showing the electric structure of an electronic control unit; Fig. 3 is a flowchart illustrating a routine for computing compensation of each cylinder; Fig. 4 is a graph showing the relationship between the deviation and the cylinder compensation; Fig. 5 is a flowchart illustrating a routine for controlling injection of fuel; Fig. 6 is a flowchart illustrating a routine for storing the initial compensation; and Fig. 7 is a flowchart illustrating a routine for detecting malfunctioning. An embodiment according to the present invention will hereafter be described with reference to Figs. 1 through 7. As shown in Fig. 1, a diesel engine 2 and a fuel injection pump 1 are installed in a vehicle. The engine 2 is provided with a plurality of cylinders C. Each cylinder C is provided with an injection nozzle 4. The injection pump 1 is connected to each nozzle 4 to supply fuel to the cylinders C. A drive shaft 5 is rotatably coupled to the injection pump 1. A drive pulley 3 is secured to the distal end of the drive shaft 5 (left end as viewed in the drawing). The drive pulley 3 is connected to a crankshaft 40 of the engine 2 by a belt (not shown). The rotation of the crankshaft 40 is transmitted to the drive shaft 5 through the drive pulley 3 and the belt. A vane-type fuel feed pump 6 (shown in a state rotated 90 degrees in Fig. 1) is arranged on the drive shaft 5 in the injection pump 1. A disc-like pulser 7 is secured to the basal end of the drive shaft 5 (right end as viewed in Fig. 1). A plurality of teeth are provided along the periphery of the pulser 7. The teeth are missing at several positions (the number of positions coincides with the number of the cylinders provided in the engine 2). In other words, opened spaces are provided along the periphery of the pulser 7. The angular intervals between the opened spaces are equal. An equal number of teeth are provided between each pair of adjacent opened spaces. The basal end of the drive shaft 5 is coupled to a cam plate 8 by means of a coupling (not shown). A roller ring 9 is arranged between the pulser 7 and the cam plate 8. The cam plate 8 has a plurality of face cams Ba. The number of face cams 8a coincides with the number of the cylinders C. Cam rollers 10 are arranged along the periphery of the roller ring 9. The face cams 8a are opposed to the cam rollers 10. A spring 11 constantly urges the cam plate 8 toward the cam rollers 10. Thin causes constant engagement between the face cams 8a and the cam rollers 10. A fuel pressurizing plunger 12 is coupled to the cam plate 8. The cam plate B and the plunger 12 rotate integrally with the drive shaft 5. The rotating force of the drive shaft 5 is transmitted to the cam plate 8 by means of the coupling. This engages the cam plate 8 to the cam rollers 10 as it rotates. The engagement moves the cam plate 8 back and forth along the cam rollers 10. That is, the cam plate 8 reciprocates for a number of times equal to the number of face cams 8a, or the number of cylinders C. The reciprocating movement of the cam plate 8 simultaneously reciprocates the plunger 12 in a corresponding manner as it rotates. The plunger 12 is fitted into the cylinder 14 of a pump housing 13. A high pressure chamber 15 is defined between the distal end of the plunger 12 and the inner surface of the cylinder 14. Intake grooves 16 and distribution ports 17 are defined in the plunger 12 at its distal end. The number of both the intake grooves 15 and the distribution ports 17 are equal to the number of the cylinders C. Distribution passages 18, which correspond to the distribution ports 17, and intake ports 19, which correspond to the intake grooves 15, are provided in the pump housing 13. Rotation of the drive shaft 5 and actuation of the feed pump 6 sends the fuel, which is reserved in a fuel tank (not shown), to a fuel chamber 21 via a fuel supply port 20. When the plunger 12 moves in a direction corresponding to the suction stroke, the pressure chamber 15 is depressurized. In this state, communication between the intake grooves 16 and the suction ports 19 draws fuel into the pressure chamber 15 from the fuel chamber 21 via a fuel supply port 20. When the plunger 12 moves in a direction corresponding to the compression stroke, the pressure chamber 15 is pressurized. In this state, fuel is pressurized and sent to the injection nozzles 4 via the distribution passages 18. A fuel spill passage 22, which connects the pressure chamber 15 and the fuel chamber 21, is defined in the pump housing 13. An electromagnetic spill valve 23, which is normally opened, is provided in the spill passage 22. The spill valve 23 includes a coil 24 and a valve body 25. When the coil 24 is de-energized, the valve body 25 is opened. This allows fuel to spill into the fuel chamber 21. When the coil 24 ie energized, the valve body 25 is closed. This restricts the spilling of the fuel. Accordingly, the opening and closing of the spill valve 23 is controlled by altering its energized time. This, in turn, adjusts the spilling of fuel from the pressure chamber 15 to the fuel chamber 21. During the compression stroke of the plunger 12, the spill valve 23 is opened to depressurize the fuel in the fuel chamber 15 and stop the injection of fuel from the injection nozzles 4. In other words, regardless of the compression stroke, opening of the spill valve 23 prevents the fuel pressure from increasing and stops the injection of fuel from the injection nozzles 4. Therefore, during the compression stroke of the plunger 12, the timing to terminate the injection of fuel from the injection nozzles 4 is altered by controlling the opening and closing timing of the spill valve 23. This adjusts the amount of fuel injected from the nozzles 4. A timer 26 (shown in a state rotated 90 degrees in Fig. 1) is provided below the pump housing 13 to alter the timing of the fuel injection. The timer 26 alters the timing of engagement between the face cams 8a and the cam rollers 10, or the reciprocating timing of the cam plate 8 and the plunger 12 by varying the position of the roller ring 9 with respect to the rotating direction of the drive shaft 5. The timer 26 is driven by hydraulic pressure and includes a housing 27 and a piston 28 retained in the housing 27. A low pressure chamber 29 is defined in one aide (left side as viewed in Fig. 1) of the housing 27 while a pressurizing chamber 30 is defined in the other side (right side as viewed in Fig. 1) of the housing 27. A spring 31 urges the piston 28 toward the pressurizing chamber 30. The piston 28 is connected to the roller ring 9 by a slide pin 32. The fuel pressurized by the feed pump 6 is sent to the pressurizing chamber 30. The position of the piston 28 is determined by the balance between the fuel pressure and the urging force of the spring 31. This effects the position of the roller ring 9 and determines the reciprocating timing of the plunger 12. Fuel is used as the hydraulic source of the timer 26. Thus, the timer 26 is provided with a timing control valve (TCV) 33 to adjust the hydraulic pressure, or the fuel pressure. The TCV 33 is arranged in a communication passage 34, which connects the pressurizing chamber 30 to the low pressure chamber 29 in the housing 27. The TCV 33 is an electromagnetic valve, which is opened and closed by a duty controlled energizing signal. The opening of the TCV 33 is varied to adjust the fuel pressure in the pressurizing chamber 30. The adjustment of the fuel pressure alters the reciprocating timing of the plunger 12 and adjusts the fuel injection timing of the fuel nozzles 4. A rotating speed sensor 35 is provided integrally with the roller ring 9 and arranged to oppose the peripheral surface of the pulser 7. The speed sensor 35 is constituted by an electromagnetic pick-up coil and outputs timing signals as the sensor 35 passes over the projections that project from the peripheral surface of the pulser 7. That is, the speed sensor 35 outputs a pulse signal when the crankshaft 40 of the engine 2 is rotated for every predetermined crank angle (e.g., 11.25 degrees). Since the speed sensor 35 is integral with the roller ring 9, the sensor 35 is not influenced by the position of the ring 9, which is controlled by the timer 26, and outputs a constant reference signal in accordance with the movement of the plunger 12. The diesel engine 2 will now be described. A main combustion chamber 44 is defined in each cylinder C between a piston 42 and a cylinder head 43. A sub-combustion chamber 45 is provided for each cylinder C. The associated chambers 44, 45 are communicated with each other. Fuel is injected into each sub-combustion chamber 45 from the corresponding injection nozzle 4. A glow plug 46 is provided in each sub-combustion chamber 45 to assist the starting of the engine 2. A turbo charger 48 is provided for the engine 2. The turbo charger 48 includes a turbine 51 located in an exhaust passage 50, a compressor 49 located in an air intake passage 47, and a shaft connecting the turbine 51 and the compressor 50. A waste gate valve 52 is provided in the exhaust passage 50 to adjust the pressure of the exhaust gas boosted by the turbo charger 48. The exhaust and intake passages 50, 47 are connected to each other by a recirculation passage 54. This structure enables a portion of the exhaust gas in the exhaust passage 50 to be recirculated to the intake passage 47 by way of the recirculation passage 54. An exhaust gas recirculation (EGR) valve 55 is arranged in the recirculation passage 54 to adjust the flow rate of the recirculating gas. The negative pressure that is conveyed to the EGR valve 55 is regulated by a vacuum switching valve (VSV) 56. The VSV 56 is controlled by ON/OFF duty signals. More particularly, an increase in the duty ratio increases the value of the electric current flowing through the VSV 56 and raises the negative pressure conveyed to the EGR valve 55. This increases the transitional area of the recirculation passage 54. A throttle valve 58 is provided in the intake passage 47. The throttle valve 58 is opened and closed in cooperation with the lowering of an acceleration pedal 57. A bypass passage 59 is defined adjacent to the throttle valve 58 in the intake passage 47. A bypass restriction valve 60 is arranged in the bypass passage 59. The restriction valve 60 is opened and closed by an actuator 63, which is driven by two VSVs 61 and 62. The opening and closing of the restriction valve 60 is controlled in accordance with various operating conditions of the engine 2. For example, the restriction valve 60 is opened halfway during idling of the engine 2 to reduce noise and vibrations. The valve 60 is completely opened when the engine 2 is running in a normal state, and completely closed when the engine 2 is stopped. A warning lamp 65 is arranged in an instrument panel (not shown) of the vehicle to indicate malfunctioning of the injection nozzles 4 and warn the driver. The electromagnetic valve 23, the TCV 33, the glow plugs 46, and the VSVs 56, 61, 62, which are provided in the injection pump 1 and the diesel engine 2, and the warning lamp 65 are each connected to an electronic control unit (ECU) 71. The ECU 71 controls the operation timing of these members. In addition to the engine speed sensor 35, the following sensors are provided to detect the running condition of the engine 2. An intake air temperature sensor 72 is provided in the vicinity of an air cleaner 64, which is located near the inlet of the intake passage 47. The temperature sensor 72 detects the intake air temperature THA. An acceleration pedal angle sensor 73, which detects an acceleration pedal angle ACCP from the opened state of the throttle valve 58, is provided in the intake passage 47. An intake pressure sensor 74, which detects the intake pressure PiM of the gas boosted by the turbo charger 48, is provided in the vicinity of the intake port 53. Together with the engine speed sensor 35, the acceleration pedal angle sensor 73 and the intake pressure sensor 74 constitute an operating condition detecting means. The diesel engine is further provided with a coolant temperature sensor 75, which detects the coolant temperature THW, and a crank angle sensor 76, which detects a reference rotational position of the crankshaft 40 (e.g., the rotational position of the crankshaft 40 with respect to the top dead canter of the piston 42 in a designated cylinder C). A transmission (not shown) is provided with a vehicle speed sensor 77, which detects the vehicle speed SP. The speed sensor 77 includes a magnet 77a, which is rotated by the rotation of a gear provided in the transmission, and a reed switch 77b. The vehicle speed SP is detected by the activation and deactivation of the reed switch 77b during rotation of the magnet 77a. Each of the above sensors 35, 72-77 are connected to the ECU 71. The ECU 71 controls the electromagnetic spill valve 23, the TCV 33, the glow plugs 46, and the VSVs 56, 61, 62 in accordance with the signals sent from the sensors 35, 72-77. The structure of the ECU 71 will now be described with reference to the block drawing of Fig. 2. The ECU 71 includes a central processing unit (CPU) 81, a predetermined control program, a read only memory (ROM) 82, a random access memory (RAM) 83, and a backup RAM 84. The CPU 81, the ROM 82, the RAM 83, and the backup RAM 4 are each connected to an input interface 85 and an output interface 86 by a bus 87. The intake air pressure sensor 72, the acceleration pedal angle sensor 73, the intake pressure sensor 74, and the coolant temperature sensor 75 are connected to buffers 88, 89, 90, 91, respectively. The buffers 88-91 are each connected to a multiplexer 92. The multiplexer 82 is connected to an analog to digital (A/D) converter 93, which is connected to the input interface 85. The engine speed sensor 35, the crank angle sensor 76, and the vehicle speed sensor 77 are connected to the input interface 85 by way of a waveform shaping circuit 95. The CPU 85 reads the signals that are sent from the sensors 35, 72-77 through the input interface 85. The electromagnetic spill valve 23, the TCV 33, the glow plugs 46, the VSVs 56, 61, 62, and the warning lamp 65 are connected to drive circuits 96, 97, 98, 99, 100, 101, 102, respectively. The drive circuits 96-102 are each connected to the output interface 86. The CPU 81 optimally controls the electromagnetic spill valve 23, the TCV 33, the glow plugs 46, the VSVs 56, 61, 62, and the warning lamp 65 based on the detected values read through the input interface 85. Among the various routines carried out by the CPU 81, the flowchart of Fig. 3 illustrates a routine for computing a compensation value FCCB(p) (where p is an integer 1-4 corresponding to one of the four cylinders C) for each cylinder C. The flowchart of Fig. 5 illustrates a routine for controlling the fuel injection amount. The flowchart of Fig. 6 illustrates a routine for storing an initial compensation value BFCCB(p), which is the initial reading of the compensation value FCCB(p). The flowchart of Fig. 8 illustrates a routine for detecting malfunctioning of various parts in the fuel injection system, such as the injection nozzles 4 and the fuel injection pump 1. In the routine for computing the compensation of each cylinder C to reduce cyclic fluctuation, the CPU 81 first executes step 101 and measures time ΔT based on the pulses output from the engine speed sensor 35. Time ΔT is the time required for the drive shaft 5 (crankshaft 40) to rotate for a predetermined angle (e.g., 45 degrees). Based on the time ΔT, the CPU 81 computes a rotating speed (instantaneous rotating speed) NEi (where i is an integer corresponding to one of the four cylinders C) required for each piston 42 to rotate the drive shaft 6 by 45 degrees. In step 102, the CPU 81 computes the cyclic fluctuation of each cylinder C based on the instantaneous rotating speed NEi. For example, the CPU 81 computes the deviation, or cyclic fluctuation DNEp, between the maximum and minimum values of the instantaneous rotating speed NEi produced by a certain cylinder C. By performing this computation for each of the four cylinders C, four cyclic fluctuations DNE1, DNE2, DNE3, and DNE4 are obtained. In step 103, the CPU 81 computes an average value WNDLT of the cyclic fluctuation DNEp of every cylinder C. For example, the sum of the cyclic fluctuations DNE1, DNE2, DNE3, DNE4 is divided by four to obtain the average value WNDLT. In step 104, the CPU 81 computes a deviation value DDNEp between the average value WNDLT and the cyclic fluctuation DNEp of each cylinder C. In step 105, the CPU 81 refers to a map shown in Fig. 5 to obtain a compensation value FCCB(p) for each cylinder C in correspondence with the associated deviation value DDNEp. Each compensation value FCCB(p) is set as zero when the value of the deviation value DDNEp is included in a range indicated between 'a' and 'b' in the map. This range includes zero. If the deviation value DDNEp is smaller than 'a' or larger than 'b', the compensation value FCCB(p) is reduced as the deviation value DDNEp increases. That is, the compensation value FCCB (p) is set at zero when the cyclic fluctuation value DNEp is in the proximity of the average value WNDLT. The compensation value FCCB(p) becomes larger (FCCB(p)>0) as the cyclic fluctuation value DNEp becomes smaller than the average value WNDLT. Contrarily, the compensation value FCCB(p) becomes smaller (FCCB(p)<0) as the cyclic fluctuation value DNEp becomes larger than the average value WNDLT. The purpose of the map shown in Fig. 4 is to minimize the compensation value FCCB(p) and suppress cyclic fluctuation when the value of the rotation speed produced by a certain cylinder C is higher than the average value WNDLT. After obtaining the compensation value FCCB(p) in step 105, the CPU 81 terminates this routine. In the above cylinder compensation computing routine, the CPU 81 obtains the cyclic fluctuation DNEp of each cylinder C and the deviation value DDNEp between the value of the fluctuation DNEp and the average value WNDLT. The CPU 81 then obtains the compensation value FCCB(p) for minimizing the deviation value DDNEp so as to compensate the amount of fuel injection in each cylinder C. The fuel injection control routine illustrated in Fig. 5 will now be described. At step 201, the CPU 81 reads the values of the engine speed NE, the acceleration pedal angle ACCP, the intake pressure PiM, and the cylinder compensation value FCCB(p). The engine speed NE may be obtained from the average value of the instantaneous rotating speed NEi, which is computed in step 101 of the cylinder compensation computing routine, during a 180 degree rotation of the crankshaft 40. In this case, the sum of the instantaneous rotating speeds NE1, NE2, NE3, NE4 is divided by four to obtain the engine speed NE. At step 202, the CPU 81 refers to a map stored in the ROM 82 to compute a basic injection amount QBASE corresponding to the acceleration pedal angle ACCP, the engine speed NE, and other data. At step 203, the CPU 81 computes a maximum injection amount QFULL from the engine speed NE and the intake pressure PiM. The injection amount QFULL is the maximum value of the amount of injected fuel combusted by the intake air in the diesel engine. At step 204, the CPU 81 computes a compensation coefficient KS (0<K5≦1.0) that corresponds to the engine speed NE. The compensation coefficient K5 is used to prevent hunting when the engine speed NE is relatively high (1,000 rpm to 1,500 rpm) and is obtained by referring to a map stored in the ROM 82. At step 205, the CPU 81 computes the injection amount QBASE1 by adding the basic injection amount QBASE obtained in step 202 to the product of the compensation value FCCB(p) and the compensation coefficient K5. At step 206, the CPU 81 determines whether the injection amount QBASE1 is smaller than the maximum injection amount QFULL obtained in step 203. If it is determined that the injection amount QBASE1 is smaller than the maximum injection amount QFULL (QBASE1<QFULL), the CPU 81 proceeds to step 207 and sets the value of the injection amount QBASE1 as the terminal injection amount QFIN. When the injection amount QBASE1 is equal to or greater than the maximum injection amount QFULL (QBASE1≧ QFULL), the CPU 81 proceeds to step 208 and sets the value of the maximum injection amount QFULL as the terminal injection amount QFIN. In this manner, the CPU 81 selects the smaller value among the injection amounts QBASE1, QFULL to set the terminal injection amount QFIN. At step 209, the CPU 81 outputs an injection amount command value Vs that corresponds to the terminal injection amount QFIN. The electromagnetic spill valve 23 is controlled based on the injection amount command value Vs to adjust the amount of fuel supplied to the injection nozzles 4 from the fuel injection pump 1. The CPU 81 and the processing of step 202 in the fuel injection control routine correspond to a means for computing a basic injection amount. Furthermore, the CPU 81, the processing of steps 101 to 105 in the cylinder compensation control routine, and the processing of step 205 in the fuel injection control routine correspond to a means for compensating the injection amount. The initial compensation storing routine will now be described with reference to Fig. 6. This routine is executed periodically starting from when a key switch of the vehicle is turned on and ending when the key switch is turned off. This routine is carried out in correspondence with a counter and a flag FBFCC. The counter continues to add the elapsed time of the operation of the engine 2 by counting the executed cycles of the initial compensation storing routine. A count value IT is used to count the executed number of cycles. The count value IT corresponds to the cumulative operating time of the engine 2 and is stored in the backup RAM 84. The flag FBFCC is used to determine whether the initial value of the compensation value FCCB(p) of each cylinder C, or the initial compensation value BFCCB(p), is stored in the backup RAM 84. The flag FBFCC is set at zero when the engine 2 is started and switched to one when the count value IT reaches a predetermined judgement value STo. At step 301, the CPU 81 times the elapsed operating time of the engine 2. That is, when each cycle of the initial compensation storing routine is executed, one is added to the count value IT obtained during the previous cycle. The count value IT obtained in the current cycle is then stored in the backup RAM 84. At step 302, the CPU 81 determines whether the flag FBFCC is set at one. If the flag FBFCC is set at one (FBFCC=1), the CPU 81 determines that the initial compensation value BFCCB(p) of each cylinder C has been stored in the backup RAM 84 and terminates the routine. When the flag FBFCC is not set at one (FBFCC=0), the CPU 81 determines that the initial compensation value BFCCB(p) of each cylinder C has not yet been stored in the backup RAM 84 and proceeds to step 303. At step 303, the CPU 81 determines whether the count value IT is greater than the judgement value STo. The judgement value STo corresponds to the time required for sufficiently minimizing the differences between each cylinder compensation value FCCB(p). When the operation of a new engine 2 begins, the cylinder compensation value FCCB(p) corresponds to a value set when the vehicle is assembled in the factory. Thus, it is required for a certain length of time to elapse before each compensation value FCCB(p) is determined through learning. That is, each cylinder compensation value FCCB(p) is learned through repetitive execution of the cylinder compensation computing routine illustrated in Fig. 3. Repetitive execution of the routine takes into account the difference in the rotating speed produced by each cylinder C. Thus, the judgement value STo is referred to when judging whether a sufficient length of time required to minimize the differences between the values of each cylinder compensation value FCCB(p) has elapsed. When the count value IT is equal to or smaller than the judgement value STo, the difference between the cylinder compensation values FCCB(p) is still large. Thus, it is required to repeat further cycles of the cylinder compensation computing routine. Accordingly, at step 303, if it is determined that the count value IT is equal to or smaller than the judgement value STo (IT≦STo), the CPU 81 terminates the execution of the present cycle. When the count value IT becomes greater than the judgement value STo (IT>STo), a sufficient number of cycles of the cylinder compensation computing routine have been carried out. Therefore, the difference between the cylinder compensation values FCCB(p) is small. Accordingly, the CPU 81 stops further counting with the counter and proceeds to step 304. At step 304, the CPU 81 reads the compensation values FCCB(p) and stores them as the initial compensation values BFCCB(p) in the backup RAM 84. The CPU 81 then proceeds to step 305 and switches the flag FBFCC to one from zero. Afterwards, the CPU 81 terminates this routine. The CPU 81 and the processing of steps 301 to 305 in the initial compensation storing routine correspond to a means for reading the initial data. During an initial operating stage of the injection nozzles 4, the fuel injection pump 1, and other parts (i.e., when there is no wear in the parts constituting the fuel injection system), an initial compensation value FCCB(p) for each cylinder C is input in the backup RAM. The initial data corresponds to values indicating normal functioning of the injection system parts and injection of an optimal amount of fuel from the injection nozzles 4. The malfunction detecting routine of Fig. 7 will now be described. At step 401, the CPU 81 reads the current compensation value FCCB(p) and the initial compensation value BFCCB(p) of each cylinder C. At step 402, the CPU 81 computes a deviation value ΔFCCB(p) of the compensation values FCCB(p), BFCCB(p). The CPU 81 then judges whether the absolute value of the deviation value ΔFCCB(p) is greater than a predetermined malfunctioning judgement value ThFCCB. The absolute value |ΔFCCB(p)| corresponds to a change in the flow rate of the fuel injected from each injection nozzle 4. In other words, wear of the injection system parts increases the difference between the flow rate of the nozzles 4 during initial usage and the flow rate of the same nozzles 4 in the current state. This increases the absolute value |ΔFCCB(p)|. When the absolute value of the deviation value ΔFCCB(p) is greater than the predetermined malfunctioning judgement value ThFCCB (|ΔFCCB(p)|>ThFCCB), the CPU 81 determines that there is a malfunctioning part in the injection system. The CPU 81 then outputs a signal to light a warning lamp 65 and proceeds to step 404. If the absolute value of the deviation value ΔFCCB(p) is equal to or smaller than the predetermined malfunctioning judgement value ThFCCB (|ΔFCCB(p)|≦ThFCCB), the CPU 81 determines that the injection system is functioning normally and proceeds to step 404. At step 404, the CPU 81 determines whether the testing of each and every cylinder C has been carried out. If it is determined that the testing of each and every cylinder C has not yet been carried out, the CPU 81 repeats steps 401 to 403. When it is determined that the testing of each and every cylinder C has been carried out, the CPU 81 terminates this routine. The CPU 81 and the processing of steps 401 to 404 in the malfunction detecting routine correspond to a means for determining malfunctions. In the present invention, the initial compensation value BFCCB(p) of each cylinder C is used to confirm malfunctioning in the fuel injection system. The value of the initial compensation value BFCCB(p) for each cylinder C is taken during the initial stage of usage (normal functioning) of the injection system parts. The actual compensation value FCCB(p) of each cylinder is monitored to confirm the difference with respect to the corresponding initial compensation value BFCCB(p) and determine whether the fuel injection parts are functioning normally or abnormally. Malfunctioning is determined when the difference between the compensation value FCCB(p) and the corresponding initial compensation value BFCCB(p) is large. Since the initial compensation value BFCCB(p) of each cylinder C is employed as a reference value to detect malfunctions, the testing of the fuel injection system is accurate and highly reliable. Thus, erroneous detection of malfunctioning in the fuel injection system that is related to each cylinder C is avoided even when the value of the compensation value FCCB(p) of each cylinder C becomes maximum or minimum. In the prior art, a margin is provided for the malfunctioning judgement value ThFCCB to prevent erroneous detection of malfunctioning in cylinders for which the compensation value FCCB(p) becomes maximum. However, the present invention improves the detecting accuracy and eliminates the necessity to provide a margin of the malfunctioning judgement value ThFCCB. Therefore, erroneous detection of malfunctions caused by the judgement value ThFCCB being larger than the compensation value FCCB(p) of each cylinder C is avoided. In other words, in the prior art, if a large amount of fuel is injected due to a malfunction in the fuel injection system when the compensation value FCCB(p) of a certain cylinder C is small, the malfunction may not be detected. However, the present invention enables detection of malfunctions under such conditions. Accordingly, the present invention may be applied to a fuel injection control apparatus that requires high detecting accuracy to prevent degradation of the emissions from the engine 2. In addition to the meritorious features described above, the present invention also includes the features described below. (a) If the compensation value FCCB(p) of each cylinder C that is used as the initial compensation value BFCCB(p) is set when the operation of a new engine begins, or when the engine is assembled to the vehicle in the factory, the initial compensation value BFCCB(p) may be set when the compensation value FCCB(p) still requires adjustment. This lowers the malfunctioning detecting accuracy. However, in the present invention, the compensation value FCCB(p) obtained after a certain length of time elapses from the starting of the engine 2 is used as the initial compensation value BFCCB(p). That is, the compensation value FCCB(p) obtained after the count value IT exceeds the judgement value STo is used as the initial compensation value BFCCB(p). Accordingly, the accuracy of malfunctioning detection is improved by the present invention since the initial compensation value BFCCB(p) is set in accordance with the compensation value FCCB(p) that has been repetitively computed. (b) Testing of the fuel injection system is performed automatically when the engine 2 is operating. Furthermore, the initial compensation value BFCCB(p) used during the testing is set automatically. Accordingly, the driver is not required to undertake special procedures to perform the testing. (c) The driver is immediately informed of malfunctioning in the fuel injection system through the warning lamp. (d) The detection of malfunctions in the fuel injection system is applied to a fuel injection control system in which the amount of injected fuel is compensated for each cylinder of the engine. Therefore, exclusive sensors and separate testing mechanisms are not required. This enables the testing to be carried out through a simple structure. Although only one embodiment of the present invention have been described herein, it should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the scope of the appended claims. In particular, the present invention may also be embodied in the forms described below. (1) The present invention has been described as being used with a fuel injection system in which the amount of fuel injection is controlled by actuating the electromagnetic spill valve 23 of the fuel injection pump 1. However, the present invention may also be used in a fuel injection system in which the position of a spill ring fit onto the plunger is altered in accordance with the running condition of the engine to control the amount of injected fuel. (2) In the foregoing description, the warning lamp 65 is lit when it is determined that there is a malfunction in the fuel injection system. However, the warning lamp 65 may be eliminated. In this case, the detection of the malfunctioning is stored in the backup RAM 84 as diagnostic data and read out during maintenance of the vehicle. (3) The cumulative time length of the engine operation is timed to confirm the initial operating stage of the nozzles 4 in the described embodiment. However, the initial operating stage may be confirmed by measuring the cumulative running distance of the vehicle in which the diesel engine is installed. The running distance may be computed from the number of rotations of a transmission output shaft or the number of rotations of a vehicle wheel. Furthermore, instead of using the engine operating time, the sum of the rotations of the engine crankshaft or the total amount of injected fuel may be used. (4) The present invention may be applied to a fuel injection system in which the compensation value FCCB(p) of each cylinder C is obtained through a different method. In such system, the cyclic fluctuation is computed by first obtaining the instantaneous rotating speed NEi (i=1 to 4) corresponding to each cylinder C and then obtaining the deviation between successive instantaneous rotating speeds NEi-1, NEi ((NEi-1)-(NEi)). The compensation value FCCB(p) of each cylinder C is obtained so as to reduce the cyclic fluctuation of each cylinder C. Accordingly, when the value of the cyclic fluctuation is positive, the compensation value FCCB(p) reduces the amount of injected fuel. When the value of the cyclic fluctuation is negative, the compensation value FCCB(p) increases the amount of injected fuel. (5) The present invention may be applied to a fuel injection system in which the basic injection amount QBASE is compensated by reducing the ratio of the cyclic fluctuation in each cylinder C in correspondence with the instantaneous rotating speed NEi (i=1 to 4). (6) In the above description, malfunctioning of the fuel injection system is determined when the absolute value of the deviation between the initial compensation value BFCCB(p) and the cylinder compensation value FCCB(p) is greater than the malfunctioning judgement value ThFCCB. However, malfunctioning of the fuel injection system may be determined when the ratio between the initial compensation value BFCCB(p) and the cylinder compensation value FCCB(p) becomes greater than a predetermined judgement value. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims. A system for detecting malfunctions in an apparatus for controlling a fuel injection mechanism of a diesel engine (2) provided with a plurality of cylinders (C) is disclosed. Each cylinder (C) accommodates a piston (42) for producing rotation of a crankshaft (40) and a nozzle (4) for performing fuel injection during each reciprocation cycle of the piston (42). Injection amount of the fuel is altered based on a compensation value computed for each cylinder (C) so as to minimize a value indicating cyclic rotating speed fluctuation of the crankshaft (40) produced by each cylinder (C). The system is characterized by memory means for storing an initial data indicative of the compensation value of each cylinder (C) computed during an initial injection stage of each nozzle (4), comparing means for comparing a malfunction judgement value with a magnitude obtained by computing the difference or ratio between an actual compensation value and the initial data, and determining means for determining the malfunctioning of the apparatus when the computed magnitude exceeds the predetermined range.

Claims: A system for detecting malfunctions in an apparatus for controlling a fuel injection mechanism of a diesel engine provided with a plurality of cylinders, each cylinder accommodating a piston for producing rotation of a crankshaft and a nozzle for performing fuel injection during each reciprocation cycle of the piston, wherein an injection amount of the fuel is altered based on a compensation value computed for each cylinder so as to minimize a value indicating cyclic rotating speed fluctuation of the crankshaft produced by each cylinder, said system characterized by memory means for storing an initial data indicative of the compensation value of each cylinder computed during an initial injection stage of each nozzle, comparing means for comparing a malfunction judgement value with a magnitude obtained by computing the difference or ratio between an actual compensation value and the initial data, and determining means for determining the malfunctioning of the apparatus when the computed magnitude exceeds the predetermined range. The system as set forth in Claim 1, characterised by first detecting means for detecting an operating state of the diesel engine, first computing means for computing a basic injection amount of each nozzle, second detecting means for detecting rotation speed of the crankshaft driven by each of said pistons, compensating means for compensating the basic injection amount to minimize the cyclic fluctuation value of each cylinder, and actuating means for actuating each nozzle based on the compensated injection amount. The system as set forth in Claims 1 or 2, characterized by warning means for warning an operator of the malfunction of the apparatus in accordance with an instruction from the determining means. The system as set forth in any one of the preceding claims characterized by that said determining means determines the malfunctioning of the apparatus when an absolute value of the computed magnitude is out of a predetermined range defined between an upper limit and a lower limit. The system as set forth in Claim 4, characterized by that said compensation value is in inverse proportion to the cyclic fluctuation value of each cylinder, and that the compensation value is set at zero when the deviation value is included in a predetermined range including the value of zero. The system as set forth in any one of the preceding claims, characterized by that said first detecting means includes a first sensor for detecting an opening size of an accelerator and a second sensor for detecting pressure of intake airflow, and said second detecting means includes a sensor for detecting an engine speed. The system as set forth in Claim 6, characterized by that said basic injection amount is computed based on the opening size of the accelerator and the engine speed. The system as set forth in Claim 7, characterized by second computing means for computing a maximum injection fuel amount of the nozzle based on the engine speed and the pressure of intake airflow.

Inventors: HIDAKA SHIGEKI, ITO YOSHIYASU, IWAI AKIRA, HIDAKA, SHIGEKI, ITO, YOSHIYASU, IWAI, AKIRA
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1996
Main classification: F02D41
IPC codes: F02D45, F02D41, F02B3, F02D13