GB2228153A - Detecting abnormality in electric circuit - Google Patents

Description

4 1 ABNORMALITY DETECTING SYSTEM FOR ELECTRIC CIRCUITS 1 The present

invention relates to a system for detecting an abnormality in an electric circuit. The circuit may be connected to an electronic control unit used in an electronic control systemr such as a control system for a motor vehicle.

An elec tronic control unit provided on a motor vehicle has a plurality of operating circuits for operating various actuators. such as fuel injectors. An electronic control unit is known which has a self diagnostic circuit for diagnosing operations of the operating circuits.

Figure 6a of the accompanying drawings shows a self-diagnostic circuit associated with a fuel injector driving circuit of an engine. The fuel injector driving circuit has a controller 52 supplied with a pulsed driving signal P from an electronic control unit, and a fuel injector driver 53 for exciting a coil 50 of a fuel injector in accordance with a signal from the controller 52. A shunt is provided for detecting current flowing in the coil 50. When a current flows in the coil 50, a current comparator 54 operates to compare the voltage at the shunt 51 with a reference voltage of the comparator. When the current reaches a peak current Ip (Figure 6b) corresponding to the reference voltage, the comparator t 2 54 produces a signal which is applied to the controller 52. The controller 52 acts to hold the current supplied to the fuel injector 50 at a predetermined holding current Ih.

As shown in Figure 6b, when the comparator 54 detects the peak current Ip. the controller 52 produces a discharge signal Pd which is applied to a discharge circuit 55. The discharge circuit 55 is provided for discharging a capacitor C of an integrating circuit consisting of a resistor R and the capacitor C. This operation is repeated at every pulse signal Pi and the voltage at the capacitor C varies as the waveform Ic of Figure 6b. The voltage Ic is applied to a noninverting input terminal of a comparator 56 and compared with a reference voltage Vref applied to an inverting input terminal thereof. When the voltage Ic is lower than the reference voltage Vref. the comparator 56 produces a low-level signal as a monitor signal Pm. Accordinglyr when the monitor signal Pm keeps a low level. it is determined that the fuel injector normally operates.

In the diagnostic circuiti the voltage at the capacitor C is dependent on the pulse repetition rate of the pulse signal P. Accordinglyr the level of the reference voltage Vref must be set at a high level corresponding to a maximum charged voltage. As a result. the circuit may fail to find a fault of the fuel injector driving circuit.

3 Japanese Patent Application Laid-Open No. 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.

When the current is in the reference voltage range of the win.dow comparatort 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 electric circuit is also applied to the logic product circuit. The logic circuit produces a confirmation signal in accordance with both the input signals.

In the diagnostic systemi 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.

Further. the diagnostic system cannot detect a fault in a transient state of the operation of an 11, 1 4 actuator. such as a fuel injector.

Figure 4 shows a fuel injector drive pulse Pi and a fuel injector current Iinj. The fuel injector current increases from an initial current Ito at a time To to a maximum current Iti at a time T1. When a movable member. such as a plunger, of the injector deteriorates with time and the sliding friction therein increases. the amount of injected fuel reduces. With such a fault. the current Iinj becomes small or changes irregularly. Howevert the maximum current Iti does not change. In other words. the fault occurs in the form of the change of transient current. Therefore. the above-described diagnostic system which detects a fault with the logic product circuit cannot diagnose such a fault.

An object of the present invention is to provide an abnormality detecting system which is simple in construction and may reliably detect various abnormalities of an electric circuit.

According to the present invention, there is provided an abnormality detecting system for an electric circuit having a load comprising a current sensor for detecting current flowing in the load; determining means for determining current detected by the current sensor at a predetermined interval of time after initiation of currrent flow in the load; and deciding means responsive to the determination of the determining means for deciding whether the determined A current is abnormal as a result of comparison with a reference current.

In an aspect of the inventiont the predetermined time is set at a time when the current reaches a maximum value in a normal state. and the reference current is set at the maximum value.

In order that the invention may be more readily understood. it will now be described. by way of example onlyi with reference to the accompanying drawings, in which:- Figure 1 is a block diagram showing a circuit of an abmormality detecting system according to the present invention; Figure 2 is a block diagram formed in accordance with the function of the system; Figure 3a is an illustration showing a load current detecting sensor of the system; Figure 3b shows a graph showing the characteristic of the sensor; Figure 4 shows waveforms of injector drive pulse and injector current; Figure 5 is a flowchart showing the operation of the system; Figure 6a is a block diagram showing a conventional self-diagnostic system; and Figure 6b shows waveforms at various points in the conventional system.

6 Referring to Fig. 1. 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 but line 7. The ROM 3 stores various control programs for controlling various systems.

The engine control system will be described hereinafter.

The output interface 5 is connected to a base of each of transistors 11 and 12 and an external transistor 13 through resistors 8, 9 and 10, respectively. Collectors of the transistors 11, 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 lga of an ignition coil 19, respectively. These coils are connected to a battery 20 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 voltage from the battery 20 and voltage from the load current detecting 7 7 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 0 2 sensor are applied to the input interface 6.

The ROM 3 stores fixed data and the RAM 4 is provided for storing data of output signals from sensors 27 and data processed at the CPU 2. The nonvolatile 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 offstate..

The CPU 2 makes calculations of control data based on data stored in the RAM 4 in accordance with control programs stored in the ROY, 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 activate the lamp 14.

Fig. 3a shows the load current detecting sensor 22. The sensor 22 comprises a core 23 made of ferrite and having windings 15a, 15b and 15c wound around the core 23 to form a transformer, a Hall element 24, and an amplifier 25. The windings 15a, 15b and 15c are connected to main line 21 and respective lines 18a, 18b and 18c of the actuator operating circuit A. When the power is applied to the actuator operating circuit A, a magnetic field is formed in the load k a current detecting sensor 22. The magnetic flux flows through the Hall element 24. so that a voltage produced in the Hall element 24, which is amplified by the amplifier 25. As shown in rig. 3b, the load current detecting sensor 22 has a linear output characteristic. Thus. the output voltage is proportional to the current.

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 load current detecting sensor 22 for performing a waveform shaping process and an analog-digital conversion process. Processed signals are applied to a control value calculator means 31 -and then stored in memory means 32. The calculator means 31 is provided for calculating various control value based on the input signals in accordance with the control programs stored in the memory means 32.

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

A load condition determining means 34 is provided for determining conditions of the actuator operating circuit A. The load condition determining means 34 receives the signal from the load current detecting sensor 22 via the input processing menas 30 after a predetermined time has passed since the output processing means 33 produces the control signal which is applied to the actuator operating circuits S W 9 1 A, and compa:es the load current IL in each actuator operating circuit A with a reference current IR for determining abnormality. The memory means 32 stores a plurality of reference currents IR'which are arranged in a table in accordance with the battery voltage BV as parameters. The actual load current IL is compared with the reference current IR and it is determined whether the difference between the currents IL and IR falls within a predetermined allowable range AIR or not. Unless the difference is within the allowable range AIR, abnormality of the actuator operating circuit A in a steady state and transient state is determined.

Namely, when the control signal is applied to the fuel injector 16, the reference current IR is derived from the table. The actual load current IL at a predetermined time Tl after the control signal is compared with the reference current IR. It is determined whether the difference between currents IL and IR falls within the allowable range AIR or not. For example, if the time Tl is set at a time when the load current reaches a maximum. value as shown in Fig. 4, abnormality in transient current caused by mechanical deterioration of movable parts of the fuel injector can be detected. More particularly, if the actual load current IL is smaller than the refernec ecurrent IR, it is determined that the moving speed of a movable part of the injector 1 reduces. Thus, trouble of the fuel injector can be detected.

A self-diagnosis means 35 operates to store the trouble data in the memory means J2 when the load condition determining means 34 determines an abnormality of the actuator operation circuit A and produces an abnormality signal whichis applied to the self-diagnosis lamp 14 to activate the lamp.

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.

At a step S100. the control signal (Pi of Fig. 4) for injecting fuel is applied to the fuel injector 16, so that fuel injection starts. At a step S101, a trigger signal for starting analog/digital (AID) conversion operation is applied to the AID converter 26 at the time To. Thus, the outpulb.. voltage signal of the load current detecting sensor 22 is converted into a digital signal.

At a step S102. the output of the sensor 22 corresponding to the current ito atthe time To is converted into a digital signal at the AID converter 26 and the digital signal is stored in a predetermined address of the RAM 4. At a step S103, a terminating signal for stopping the AID conversion operation is produced so that the conversion operation stops until T1. Since the load of the 1 -S- 11 fuel injector 16 has an inductance, the current linj varies with time until the maximum current is reached.

At the time T1, the conversion of the output voltage signal of the sensor 22 into a digital signal starts (step S104). At a step S105. the current Itl of the fuel injector 16 at the time Tl 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.

At a step S106, an increment AI of current ( AI = Itl - ItO) is calculated. The purpose of the- calculation of the current increment 6 1 is to eliminate the influence of drift on the output from the sensor 22. At a step S107. a reference current IR corresponding to a maximum current is derived from the ROM 3 in accordance with the battery voltage BV as paranete.r, and the difference IDIAG between the reference current IR and the current increment AI is calculated (1DIAG = AI - IR).

At a step S108, 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 returns to step S100 to repeat the routine. If the difference IDIAG is larger than the allowable value AIR, the program goes to a step S109 where a trouble of the fuel injector 16 is determined. The 12 self-diagnosis means 35 stores trouble data of the fuel injector in the non-volatile RAM 4a and lights the lamp 14.

Thus, the abnormality which comes out in the transient state of driving current can be detected. Further. disconnections of connectors in the actuator operating circuits and abnormalities of transistors 11, 12 and 13 can also be detected. Furthermore, according to the present invention, the detection of the abnormalities in the control circuits is easily and precisely performed without connecting many additional detecting devices and increasing cost, space and a number of connectors. And, loading conditions are also detected not only in the transient states but also in the normal conditions, so that partial mulfunction of moving parts can be detected, and deterioration of controllability is prevented beforehand.

While the presently preferred embodiment of the invention has been shown and described, it is to be understood that this disclosure is 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 (6)

Claims:

1. An abnormality detecting system for an electric circuit having a load comprising: a current sensor for detecting current flowing in the load; determining means for determining current detected by the current sensor at a predetermined interval of time after initiation of currrent flow in the load; and deciding means responsive to the determination of the determining means for deciding whether the determined current is abnormal as a result of comparison with a reference current.

2. The system as claimed in claim 1, wherein the reference current IR depends upon the voltage of a batterv connected to the circuit.

3. The system as claimed in claim 1 or 2. wherein the predetermined time is set at a time when the current reaches about maximum value and the reference current is set at about maximum value.

t 14

4. The system as claimed in claim ly wherein the deciding means compares the determined current A I and the reference current IR to produce a difference current IDIAG and compares the difference current with a reference value 6 IR and produces a fault signal when the difference current IDIAG is larger than the reference value A IR.

5. A method for detecting abnormality in an electric circuit having a load comprising the steps of detecting the current flowing in the load; determining the current Itl at a predetermined time T1 after initiation To of current flow in the load; comparing the determined current Itl with a reference current IR to produce a difference current IDIAG therebetween; and deciding whether the difference current IDIAG is abnormal in comparison with a reference value A IR.

6. An abnormality detecting system for an electric circuit having a load substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

Published 1990w The Patent Office. State liouse.66 71 Hig Holborr,.Londor.WC1R4TP.Furthe,- copies mkvbe obtained from The Patent Office Sales Branch. St Ma-y Crky. OrPington. Kent BR5 3RD Printed by Mult,.plex techraques ltd, St Mary Cray. Kent. Con. 167