GB2235996A

GB2235996A - Self-diagnostic system for a motor vehicle

Info

Publication number: GB2235996A
Application number: GB9014273A
Authority: GB
Inventors: Kunihiro Abe
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1989-06-29
Filing date: 1990-06-27
Publication date: 1991-03-20
Also published as: GB9014273D0; JP2987446B2; DE4019958A1; JPH0331041A

Abstract

Conventional self-diagnostic systems on board a motor vehicle may generate misleading diagnostic data because the data is stored in a volatile memory. Accordingly the present system is provided with a backup RAM 10 for storing fault data which is maintained by power supplied from a battery of the vehicle. Destruction of the stored data caused by a power failure is detected at 26 and the destruction of the stored data is indicated at 4.

Description

SELF-DIAGNOSTIC SYSTEM FOR A MOTOR VEHICLE The present invention relates

to a self- diagnostic system for a motor vehicle.

It is known to equip a motor vehicle with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving drivability, exhaust gas emission, fuel consumption, and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if amalfunction of the components or the sensors occurs, the engine does not operate properly.

However, because of the complexity of the electronic control system, it is difficult to immediately discern the malfunction. Accordingly, a selfdiagnostic device for easily checking the electronic control system should be provided in the motor vehicle.

Japanese Patent Application Laid Open 59-24270 discloses an electronic control system provided with a self-diagnostic system where signalling lamps provided on the vehicle are illuminated to indicate a fault code representing a defective part in the control system when an abnormality occurs in the sensors and actuators such as the injectors. Data on the fault is written in a backup random-access memory (RAM) at a predetermined address, which is provided in the electronic control system. A diagnostician in an auto shop reads out the fault code indicated by the lamps or display of a computer which is connected to the vehicle. Thus, the information on the fault is presented to the diagnostician so that anydefective part is appropriately repaired.

Japanese Patent Application Laid Open 61-98639 discloses a system in which engine operating condition monitoring means is provided to'detect abnormalities in components of the engine. The data on defective components is written in a non-volatile memory which is an electronically erasable programmable read only memory (EEPROM). However, the EEPROM requires special hardware and software for writing the data therein, causing an increase of cost. In addition, since the EEPROM is vulnerable to electric noise, miswriting data and destruction of stored data may occur. Therefore, the data stored in the memory is not reliable.

Japanese Patent Application Laid Open 62-74742 discloses a system having a non-voltatile memory which retains data even in the absence of power. The nonvolatile memory comprises a fuse or a temperature-sensitive coating. The data in the memory is held by melting the fuse or the discolouration of the coating. The nonvolatile memory may be a non- reversable electromagnetic ratchet means. However, in a non-volatile memory, the fuse, for example, must be changed at the auto shop after the vehicle is repaired. Thus, not only the number of the operational process increases, but also the fuse or the ratchet means for each diagnosing item must be provided in the shop. Hence the parts and the space for storing the parts must be increased.

In order to avoid such a disadvantage, a RAM backed up by an independent power supply is usually used as a non-volatile memory for storing the data. However, if the backup power applied to the RAM to retain the data is cut-off, for example by replacement of the battery before the diagnosis at the shop, the data is erased.

The object of the present invention is to provide a self-diagnostic system where it is easy to detect whether accurate data on faults is stored, thereby enabling precise repair of the vehicle.

According to the present invention there is provided a self-diagnostic system for a motor vehicle comprising means for detecting a fault and a memory for recording fault data which is maintained by power supplied from a battery of the vehicle; a detector for detecting the destruction of the recorded data when the power supply fails, and for producing a data destruction signal; and warning means responsive to the data destruction signal for warning of the destruction.

In an aspect of the invention, the detector means comprises means for comparing the data stored in the storing means with a reference data and for producing the data destruction signal when the stored data deviates from the reference data and the storing means is a backup RAM with a backup power supply.

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

Fig. 1 is a block diagram of a diagnosis system according to the present invention; Fig. 2 is a block diagram showing a main part of the system; Fig. 3 shows a flowchart showing operation of the system; and Fig. 4 is a diagram showing a table for storing fault codes and engine operating condition data.

An automobile is equipped with an electronic control system 1 for controlling various components of an engine.

-t Referring to rig. 1. the electronic control system 1 comprises a central processor unit (CPU) Si a random access memory (RAM) 9. a read only memory (ROM) 8. a backup random access memory (RAM) 10. an input interface 6 and an output interface 7. These CPU 5, RAM 9, RAM 100 ROM 8, input and output interfaces 6 and 7 are connected to each other through a bus line 11. Programs and data for controlling the engine and fixed data such as trouble.codes representing trouble data and trouble location are stored in the ROM 8.

The RAM 10 is to store trouble data codes and the trouble location codes and data on engine operating conditions at the occurrence of the trouble, at respective predetermined addresses. The backup RAM 10 is connected to a battery (not shown) so as to be applied with a backup supply voltage VBU through a constant voltage circuit for retaining the data.

The input interface 6 is applied with a coolant temperature signal Tw from a coolant temperature sensor 15, an air-fuel ratio feedback signal 1 from an 0 2 sensor 16, an intake-air quantity signal 0 from an intake manifold quantity sensor 12 and a crank angle signal from a crank angle sensor 13 for detecting crank angle e and engine speed N. The sensors 12, 13, 15 and 16 and other sensors and switches not shown construct an operating condition (engine parameter) detecting means 2. These signals from the 2-5 sensors and switches are temporarily stored in the RAM 9 after processing the data in the CPU 5. The CPU 5 produces 6 control signals, which are applied through the output interface 7 to an engine operating means 3. The engine operating means 3 comprises a driver 17 and fuel injectors 18 for controlling air-fuel ratioi and a power transistor and an ignition coil (not shown) for controlling ignition timing.

The CPU 5 further produces signal through the output interface 7 to a warning means 4 having a driver 19. and trouble code indicating lamps 20a and a warning lamp 20b. When an abnormality is detected in the system 1 by self-diagnosis function, a corresponding trouble code is read out from the RAM 10 so as to turn on or flash trouble code indicating lamps 20a, thereby indicating the trouble code. When it is detected that the data stored in the backup RAM 10 are erased or destroyed and the selfdiagnosis function is not working, the warning lamp 20b is turned on.

A diagnosis device 21 having a display 21a is detachably connected with the input interface 6 and the output interface 7 of the control system 1. The diagnosis device 21 is operated by a diagnostician so that the calculated data on engine operating conditions which are stored in the RAM 9 and the trouble codes stored in the backup RAM 10 are indicated on the display 21a.

The control system 1 is described more in detail with reference to Fig. 2. The control system 1 is provided with a self-diagnosis means 24, to which output signals of the 7 engine operating condition detecting mea=s 2 and output signals of a engine control data calculator 22 are applied. The calculator 22 calculates engine control data such as fuel injection pulse width and ignition timing in dependency on the operating conditions. A pulse width duty signal and an ignition signal dependent on a basic crank angle of each cylinder of the engine, each signal calc-ulated at the calculator 22, are applied to the engine operating means 3 through a control signal output means 23.

When an abnormality is detected in dependency on the output signals of the engine operating condition detecting means 2 and the calculator 22. a trouble data signal is applied to the ROM 8 from which a trouble code representing defective parts and conditions of the trouble are read out. The trouble,codes retrieved from the ROM 8 and data on operating conditions at the time when tL-- trouble occurred, which are temporarily stored in the RAM 9, are sequentially stored at predetermined addresses in the backup RAM 10 as shown in Fig. 4. Furthermore, the self-diagnosis means 24 applies a trouble code signal, dependent on the trouble code stored in the RAM 10 to the warning means 4 through a trouble code output means 25 so as to indicate the trouble code by flashing the trouble code indicating lamps 20a.

The control system further has a backup data destruction detecting means 26 to detect the destruction of the data stored in the backup RAM 10 caused by cutting off the power. The data in the RAM 10 is destroyed when the backup supply valtage VBU is cut off. The destroyed data are further deformed (or changed) when the voltage is supplied again. The destruction-of the data can be detected by comparing the data in the P-AM 10 with predetermined reference data stored in the ROM 8, or by detecting the shut off and resumption (again switch ON) of the supply voltage VBU and by initializing the RAM 10.

When the backup data destruction detecting means 26 determines that the data in the RAM is destroyed, a destruction signal is fed to the warning means 4 to light the warning lamp 20b when the self-diagnosis function is not yet'executed in the self-diagnosis means 24.

More particularly, when the battery is replaced with a new one, the supply of the voltage to the backup RAM 10 is cut off, so that the data stored at the addresses ADRO,, ADR1 as shown in Fig. 4 are erased. The new battery is installed so that the voltage is supplied again, thereby initializing the memory. The backup data destruction detecting means 26 determines whether the self-diagnosis is executed. When the self- diagnosis is not performed, the data destruction detecting means 26 applies the backup data destruction signal to the warning means 4.

9 When the outside diagnostic device 21 is connected to the control system 1 and a trouble data demand signal is applied thereto, the trouble code and the operating condition data stored in the backup RAM 10 are applied to the diagnostic device 21 through data output means 27 to alternately indicate the trouble code and the operating condition data on the display 21a.

The operation of the system is described hereinafter with reference to the flowchart of Fig. 3. While the engine is running, the control system performs a main routine of a control program for controlling air-fuel ratio and ignition timing. During the main routine, an interrupt request signal is applied to the self-diagnosis means 24 at every predetermined cycle, so that the following self-diagnostic program is performed.

At a step S101, the backup data stored in the backup RAM 10 is read out. AT a step 5102, it is determined whether the data was destroyed. When the RAM 19 is initialized or when the stored data are much different from the reference data stored in the ROM $, the destruction of the data is determined, and a self-diagnosis flag is cleared (FLAG = 0) at a step S103. At a step S104, the data necessary for the self-diagnosis is read out from the engine operating condition detecting means 2. If the destruction of the data is not detected at the step S102, the program goes directly to the step S104.

At a step S105. it is determined whether the conditions for carrying out the self-diagnosis are satisfied. When.the conditions are fulfilled, the program proceeds to a step S106 where the self-diagnosis flag is set (FLAG - 1)f thereafter executing the self-diagnosis at a step S107 dependent on the data read out at the step S104. At a step S108i it is determined whether there is an abnormality in the control system. When there is the abnormality, the program goes to a step S109 where a trouble code representing the defective parts which causes the abnormality in the control system 1 is retrieved from the ROM 8 and stored in the backup RAM 10. At a step 110. data on operating conditions, in which the trouble has occurred, is read out from the RAM 9 and also stored in the backup RAM 10. At a step S111. the trouble code is indicated by flashing the trouble code indicating lamp 20a.

Determining that the flag is set at step S112, the program goes to a step S114, where it is determined whether a trouble data demand signal is applied to the control system 1 from the outside diagnosis device 21. When the demand signal is not fed. the program returns to the main routine. On the other hand. when the demand signal is applied, the trouble code data and the operating condition data stored in the RAM 10 are fed to the diagnosis device 21 through the data output means 27 (step S115). The operating condition signal in the form of binary digit is converted into a decimal digit. Consequently. the trouble code and operating condition data are indicated on the display 21a in turn. Thus. the diagnostician confirms the defective part and the condition of the trouble corresponding to the indicated code in accordance with a instruction manual. At the same time. the trouble can be recurred in dependency on the operating condition data so that the control system 1 can be accurately repaired. When it is determined that there is no abnormality at the step S108, the program proceeds directly to the step S112.

To the contrary. when the conditions for the execution of the selfdiagnosis operation is not satisfied# the program jumps from the step S105 to the step S112. When the flag is cleared at the step S103, the program proceeds to a step S113 where the warning lamp 20b is turned on, thereby indicating that the data in the backup PAM 10 has been destroyed. Thereafter. the program goes to the step S114.

In accordance with the present invention, it is detected that at least one trouble has occurred and that the trouble data stored in the-backup RAM has been destroyed. Thus, an erroneous diagnosis can be avoided.

While the presently preferred embodiment of the present invention have 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

12 be made without departing from the scope of the invention as set forth in the appended claims.

Claims

CLAINS

A self-diagnostic system for a motor vehicle comprising means for detecting a fault and a memory for recording fault data which is maintained by power supplied from a battery of the vehicle; a detector for detecting the destruction of the recorded data when the power supply fails, and for producing a data destruction signal; and warning means responsive to the data destruction signal for warning of the destruction.
2. A system according to claim 1, wherein the detector comprises a comparator for comparing the data with reference data and for producing the data destruction signal when the stored data deviates from the reference data.
3. A system according to claim 1 or claim 2, wherein the memory is a random access memory.
4. A self-diagnostic system as herein described with reference to the accompanying drawings.

Published 1991 at Ihe Patent Offlee. State House. 66/71 High Holbom, LondonWC1R47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwrnfelinfach. Cross Keys. Newport NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.