GB2226888A

GB2226888A - Abnormality detecting system for electric circuits

Info

Publication number: GB2226888A
Application number: GB8928696A
Authority: GB
Inventors: Kazuyuki Tazawa
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1988-12-21
Filing date: 1989-12-20
Publication date: 1990-07-11
Also published as: DE3942167C2; DE3942167A1; GB8928696D0

Description

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Abnormality Detecting System for Electric Circuits The present invention relates to a system for detecting abnormality in an electric circuit connected to an electronic control unit used in an electronic control system such as a control system for a motor vehicle.

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The electronic control unit provided on the motor vehicle has a plurality of operating circuits for operating various actuators such as fuel injectors. A recent electronic control unit has a self-diagnostic circuit for diagnosing operations of the operating circuits.

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Japanese Patent Application Laid-Open 63-27769 discloses a selfdiagnostic system for confirming operations of operating circuits in an electronic control system for a motor vehicle. In the self-diagnostic system, a shunt is provided in a bus for detecting current in the bus. The system has a detecting circuit comprising a window comparator and a logic product circuit for detecting the operation of each operating circuit.

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When the current is in the reference voltage range of the window comparator, the comparator produces a comparator signal. The comparator signal is applied to the logic product circuit. On the other hand, a control signal applied from the electronic control system to a corresponding operating circuit is also applied to the logic 2 s product circuit. The logic product circuit produces a confirmation signal in accordance with both the input signals.

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In the diagnostic system, since the detecting circuit is provided at every operating circuit, the system becomes complicated in composition, which causes increase of the manufacturing cost thereof, and reduction of reliability because of a large number of parts such as connector pins for connecting detecting circuits to a control unit of the electronic control system.

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The present invention seeks to provide an abnormality detecting system in which a current detecting sensor is provided for detecting varigu$ cyrrents in a plurality of operating circuits whereby faults in the circuits may be reliably detected.

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According to the present invention, there is provided an abnormality detecting system for an electric circuit having a plurality of operating circuits which are connected to a source through a bus, and a current sensor provided in the bus for detecting current flowing in the operating circuit, the system comprising first detector means associated with the current sensor for detecting an offset current of the current sensor at a time when no control signals are applied to the operating circuits, a memory for storing the offset current detected by the first detector means, second detector means associated with the current sensor for detecting the offset current at a time when a new control signal is not applied to one of the operating circuits to be diagnosed and no control signals are applied to the other operating circuits and for producing a new offset current, updating means for updating the offset current stored in the memory with the new offset current, third detector means associated with the current sensor for detecting current of a control signal applied to the operating circuit to be diagnose at a predetermined time after the application of the new control signal and for producing an output voltage corresponding to an operating current, calculator means for calculating the difference between the operating current and the new offset current and for producing a difference value, comparing means for comparing the difference value with a reference value and for producing the difference between the difference value and the reference value, and deciding means for deciding whether the difference is abnormal.

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The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

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BRIEF DESCRIPTION OF DRAWINGS .DTD:

Fig. I is a block diagram showing a circuit of an abnormality detecting system according to the present invention; I0 Fig. 2 is a block diagram formed in accordance with the function of the system; Fig. 3a is an illustration showing a current detecting sensor of the system; Fig. 3b shows a graph showing the characteristic of the sensor; Fig. 4 shows waveforms of injector drive pulse and injector current; Figs. 5a and 5b are flowcharts showing the operation of the system; Fig. 6 shows waveforms in a second embodiment of the present invention; and Figs. 7a to 7c are flowcharts showing the operation of the second embodiment.

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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS .DTD:

Referring to Fig. I, an electronic control unit (ECU) 1 is provided in an automobile for controlling an engine, a transmission, an air-conditioner and others. The electronic control unit 1 comprises a central processor unit (CPU) 2, a ROM 3, a RAM 4, a non-volatile RAM 4a, an output interface 5 and an input interface 6, which are connected to each other through a bus line 7. An oscillator 2a is connected to the CPU 2 for producing standard clock pulses which is divided and counted by a free- running counter. The count of the standard clock pulses is read out for determining I0 timings for performing various diagnoses. The R0M 3 stores various control programs for controlling various systems.

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The engine control system will be described hereinafter.

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The output interface 5 is connected to a base of each of transistors ii and 12 and an external transistor 13 through resistors 8, 9 and I0, respectively. Collectors of the transistors ii, 12 and 13 are connected to various actuators such as a coil 16a of fuel injector 16, a coil 17a of an idle speed control valve 17, and a coil 19a of an ignition coil 19, respectively. These coils are connected to a battery through a load current detecting sensor 22 and bus 21. The output interface 5 is further connected to a self-diagnosis lamp 14 for indicating abnormalities of the actuators. Thus, actuator operating circuits A are formed. The load current detecting sensor 22 is provided for detecting current IL flowing in each actuator operating circuit A.

The input interface 6 is applied with the power from a battery 20 and voltage from the load current detecting sensor 22 through an A/D converter 26. Further, output signals from various sensors 27 such as an intake-air quantity sensor, a crank angle sensor and 02 sensor are applied to the input interface 6.

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The ROM 3 stores fixed data and the RAM 4 is provided for storing data of output signals from sensors 27 and data I% I0 processed at the CPU 2. The non-volatile RAM 4a is provided to store trouble data of actuators 16, 17 and 19, sensors 27 and other. The RAM 4a is backed up by the battery 20 so as to maintain the stored data even if a key switch (not shown) is in off-state.

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The CPU 2 makes calculations of control data based on data stored in the RAM 4 in accordance with control programs stored in the ROM 3. The calculated control data are stored in the RAM 4 and applied to actuators 16, 17 and 19 through the output interface 5 at a predetermined timing. If an abnormality is detected, the CPU 2 produces a signal to emit the lamp 14 and the trouble data are stored in the RAM 4a.

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Fig. 3a shows the load current detecting sensor 22.

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The sensor 22 comprises a core 23 made of ferrite and having windings 15 wound around the core 23 to form transformers, a Hall element 24, and an amplifier 25. Windings 15 are connected to lines 18 of the actuator operating circuits A. When the power is applied to one of the actuator operating circuits A, a magnetic field is formed in the load current detecting sensor 22. The magnetic flux flows through the Hall element 24, so that a voltage produces in the Hall element 24, which is amplified by the amplifier 25. As shown in Fig. 3b, the load current detecting sensor 22 has a linear output characteristic. An offset voltage exists in the Haal element 24 and appears at the output terminal of the sensor 22 as an offset voltage VO.

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I0 Referring to Fig. 2, the electronic control unit 1 is provided with an input processing means 30 applied with output signals from sensors 27, battery 20 and current detecting sensor 22 for performing a waveform shaping process and an analog-digital conversion process. Processed data are applied to a calculator means 31 and stored in a memory means 32. The calculator means 31 is provided for calculating various control data based on the input signals in accordance with the control programs stored in the memory means 32.

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An output processing means 33 is provided for producing control signals for controlling the actuator operating circuits A.

An offset current memory means 34 is provided for storing an offset current.

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An offset current updating means 35 is provided for updating the offset current stored in the offset current memory means 34 with the output of the sensor 22 at a time when no control signals are applied to the circuits A.

A circuit current calculator means 36 is provided for calculating the load current IL flowing in one of the actuator operating circuits A in accordance with the output from the current detecting sensor 22 and the offset current.

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A circuit condition determining means 37 is provided \ for determining conditions of the actuator operating circuit a," The operation of the system is described hereinafter with reference to Figs. 1 to 4.

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The offset voltage VO of the sensor 22 varies with the temperature of the sensor, with time and others. Therefore, in order to detect the load current IL, the offset voltage VO is subtracted from the output voltage V of the sensor 22 as described below.

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The offset voltage VO of the sensor 22 is detected by the offset current updating means 35 when no control signals are applied to the actuator operating circuits A. The offset current corresponding to the detected offset voltage is stored in the offset current memory means 34 (RAM 4).

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!5 The current in one of the circuits A is detected when a control signal is applied thereto, and the current corresponding to the output voltage of the sensor 22 is applied to the circuit current calculating means 36. And then, the stored offset current is subtracted from the stored current.

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As an example, the diagnosis of the circuit of the fuel injector 16 is described hereinafter with reference to Fig. 4. The offset current ILTo at the time To' when the control signal Pi is produced or before the generation of the control signal Pi is obtained.

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Since the fuel injector 16 is an inductance load, a current Iinj of the fuel injector 16 delays with respect to the control signal Pi as shown in Fig. 4. The offset current may be obtained at the time To' when the control signal is generated. However, if the actuator is resistance load, capacitive load or lamp load, the current does not delay. Accordingly, the offset current must be obtained before the control signal.

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If another control signal P is applied to the other circuit as shown at a time To in Fig. 4, the voltage of the control signal P is added to the offset voltage VO. Accordingly, the offset voltage must be detected at the time when no control signals are applied to the operating circuits A.

More particularly, when the control signal Pi is applied to the fuel injector 16, it is determined whether other control signals are applied to other circuits. If no control signals are produced, a new offset current is detected at the generation of the control signal Pi to update the offset current stored in the RAM 4 at the last time. On the other hand, if another control signal is applied to another circuit, he offset current stored in the RAM at the last time is used for calculating the current IL.

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The obtained offset current ILTo is substracted from the current ILTI based on the output voltage of the sensor 22 at a time T1 to produce a current IL (IL = ILTI - ILTo).

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The circuit condition determining means 37 compares the current IL correspondent to operating voltage V with a I0 reference current IR for determining abnormality and produces a signal which is applied to a self-diagnosis means 38. The memory means 32 stores a plurality of reference current IR which are arranged in a table in accordance with the battery voltage BV as parameters. Namely, when the control signal Pi is applied to the fuel injector 16, the reference current IR is derived from the table.

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When the difference between the current IL and the reference current IR does not fall within a predetermined allowable range IR, abnormality of the injector operating circuit A is determined in the circuit condition determining means 37.

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When the circuit condition determining means 37 determines an abnormality of one of the actuator operating circuits A, an abnormality signal is applied from the means 37 to the self-diagnosis means 38. The selfdiagnosis means 38 operates to store the trouble data in the memory means 32 and to turn on the self-diagnosis lamp 14.

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The trouble data stored in the memory means 32 can be read by connecting another diagnostic device which is provided in an auto shop. Thus, an abnormal position in the system can be easily known at the auto shop.

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The operation of the control unit for the fuel injector 16 is described hereinafter with reference to the flowchart of Fig. 5 and to Fig. 4.

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A control signal (Pi of Fig. 4} for injecting fuel is applied to the fuel injector 16, so that an interrupt program for the time To starts. At a step $101 of Fig. 5a, a trigger signal for starting analog/digital (A/D) conversion operation is applied to the A/D converter 26 at the time To. Thus, current dependent on the output voltage signal of the current detecting sensor 22 is converted into a digital signal. At a step $I06, current ILT at the generation of the control signal Pi is stored in the RAM 4. The current ILT at the time To' is equal to the offset current ILTo.

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At a step SI02, output conditions of control signals applied from the output interface 5 to operating circuits A are read through addresses. At a step SI03, it is determined whether other control signals are applied to the other operating circuits or not. If no control signals are applied to the other operating circuits, the program goes to a step SI04. If at least one of the control signal is applied to one of the other circuits, the program goes to a step S105.

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At step SI04, the offset current ILTo at the time To is converted into a digital signal at the A/D converter 26 and the offset current stored in a predetermined address of the RAM 4 at the last routine is updated with the new offset current. At the step SI05, a terminating signal for stopping the A/D conversion operation is produced and a - restarting time for the A/D conversion operation is set to the time T1, so that the conversion operation stops until the time T1. Since the load of the fuel injector 16 has an inductance, the current Iinj varies with time until the maximum current.

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At the time T1, an interrupt program for the time T1 starts. At a step $201 of Fig. 5b, the conversion of the current dependent on the output voltage of the sensor 22 into a digital signal starts. At a step $202, the operation current ILTI at the time T1 is converted into a digital signal and the voltage BV of the battery 20 is also converted into a digital signal. These digital signals are stored in the respective addresses of the RAM 4.

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At a step $207, it is determined whether other control signals are applied to the other operating circuits. At a step $203, the offset current ILTo and the operating current ILTI are read from the RAM 4 for calculating a load current IL (IL = ILTI - ILTo). If another control signal is appled to the other circuit, the load current IL is obtained by subtracting the current ILT from the current ILTI (step $208). At a step $204, a reference current IR is derived from the ROM 3 in accordance with the battery voltage BV as parameter, and the difference IDIAG between the reference current IR and the current IL is calculated (IDIAG =IIL - IRI >.

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I0 At a step S205, it is determined whether the difference IDIAG is smaller than a predetermined allowable value AIR or not. If the difference IDIAG is smaller than the allowable value AIR, the program terminates the interrupt routine. If the difference IDIAG is larger than the allowable value AIR, the program goes to a step S206 where a trouble of the fuel injector 16 is determined. The self-diagnosis means 38 stores trouble data of the fuel injector 16 in the non-volatile RAM 18a and emits the lamp 24.

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If at least one of the other control signals is applied to the other operating circuit after the time To, the operating current IL becomes large. However, the system does not determine such a case as a trouble, so that misdiagnosis is avoided.

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Thus, circuit operating currents of a plurality of actuator operating circuits are precisely detected by the current detecting sensor 22. Further, disconnections of connectors in the actuator operating circuits and abnormalities of transistor{ Ii, 12 and 13 can also be detected.

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Referring to Figs. 6, 7a, 7b and 7c showing another embodiment of the present invention, structures and functions of the embodiment are the same as the first embodiment except for the offset current updating means 35.

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The current of the control signal in a certain operating circuit reduces gradually in accordance with the time constant of the operating circuit after the disappearance of the control signal Pi. Consequently, as shown in Fig. 6, when the control signal Pi to the operating circuit is turned off, the current does not become zero at the same time. Therefore, at a time Tol, remaining current is added to the offset current ILTo.

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In the offset current updating means 35 of this embodiment, the offset current ILTo is obtained at a time before a control signal for one of the operating circuits to be diagnosed is produced and when a predetermined time DTIME necessary for completely reducing the current has elapsed.

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For example, when the control signal Pi is applied to the fuel injector 16, it is determined whether the predetermined time DTIME has passed after the control signal to the other clrcuit is turned off or not. If the time DT!ME has passed, the offset current ILTo is newly detected at the time when the control-signal Pi is produced and the offset current ILTo stored in the RAM 4 at the last time is updated. On the other hand, if the time DTIME does not yet pass, the offset current ILTo stored in RAM at the last time is used for calculating the current IL.

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Since a faulty detection of the offset current is prevented, the load current IL is accurately calculated.

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The operation of the system of the second embodiment will be described with reference to flowcharts of Figs. 7a to 7c. Times Td, To and T1 in Fig. 6 are counted by a free-running counter.

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When the control signal P applied to the other circuit is turned off, an interrupt routine for time Td starts as shown in Fig. 7a. At a step $51, the time Td when the control signal P is turned off as shown in Fig. 6 is read from the free-running counter. At a step $52, the time Td is stored in the RAM 4 and the routine is terminated.

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When the control signal Pi is applied to the fuel injector 16, an interrupt routine for time To of Fig. 7b starts. At a step $401, the time To when the control signal Pi is produced is read from the free-running counter. At a step $402, the time To is stored in the RAM 4. At a step $403, the time Td and the time To stored in the RAM 4 are read to calculate the period- T representing the period until the control signal Pi is produced after the control signal P is turned off ( T = To - Td). At a step $404, it is determined whether the period T reaches the predetermined time DTIME or not. If the period AT does not reach the period DTIME, the program proceeds to a step $407. If the period A T reaches the time DTIME, the program proceeds to a step $405.

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At the step $405, a trigger signal for starting analog/digital (A/D) conversion operation is applied to the A/D converter 26 at the time To. Thus, the current based on the output voltage signal of the current detecting sensor 22 is converted into a digital signal.

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At a step $406, the offset current ILTo stored in a predetermined address of the RAM 4 at the last routine is updated with the new offset current ILTo. At the step $407, a terminating signal for stopping the A/D conversion operation is produced so that the conversion operation stops until TI.

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Further, at the step $407, a restarting time signal is set so that the A/D converter will start the conversion operation of the current at the time TI.

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At the time T1, an interrupt program for the time TI starts. The interrupt program for the time T1 shown in the flowchart of Fig. 7c is operated in the similar manner as the flowchart of Fig. 5b of the first embodiment. Therefore, the description of the operation is omitted.

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While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.

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Claims

CLAIMS i. An abnormality detecting system for one of a plurality of

operating circuits including respective actuators controlled by control signals from a control unit, the system comprising a current sensor for detecting current flowing in the operating circuits; updating means associated with the current sensor for updating an offset current of the current sensor with a first current detected at a time when no control signals are applied to the operating circuits; detector means associated with the current sensor for detecting a second current flowing in one of the operating circuits dependent on the control signal at a predetermined time after the application of the control signal; means for calculating the difference between the second current and the offset current; and means for comparing the current difference with a reference value to decide whether the current difference is abnormal.

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2. A system according to claim I, wherein:

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the updating means updates the offset current when the control signal is not applied to one of the operating circuits and a predetermined time has passed after the control signals of the other operating circuit are switched off, said predetermined time being the time necessary for the current flowing in the other operating circuit to fall to zero.

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3. A method for detecting abnormal operation in one of a plurality of operating circuits including respective actuators controlled by control signals from a control unit, having a current sensor for measuring current flowing in the operating circuits, the method comprising the steps of:

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measuring the offset current at a time when no control signals are applied to the operating circuits; storing the measured value of the offset current; measuring a second current flowing in one of the operating circuits dependent on the control signal at a predetermined time after the application of the control signal; calculating the difference between the second current and the offset current; and comparing the difference with a reference value to determine whether it is abnormal.

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4. An abnormality detecting system substantially as herein described with reference to the accompanying drawings.

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Publlshed 1990 at The Patent Oice. Sate Hcuse. 66 71 High Holborn. London WCI 1% 4TP. Further cople- rna.v be obtao e frc rr.. The Paent 0fneúSales Branch. St Man" Cra:/. Or:n'-n- Ken: BR5 31%D Printed b" Muluplex tecnuques ltd. St Mar/Crav. Kent. Con I 8T