Method and apparatus for self-diagnosis for an electronic control system for vehicles

In a vehicle control system having a main electronic control unit governing a plurality of subsidiary electronic control units, each of the subsidiary units includes an automatic continuous subsidiary unit self-diagnosis procedure which generates an interrupt signal causing the main electronic control unit to retrieve date and time data from the main unit clock. This subsidiary malfunction date and time data along with details of the subsidiary unit malfunction can be stored in either the main unit memory or the respective subsidiary unit memory for subsequent retrieval and display by an operator via the main control unit. Any malfunction of the main electronic control unit is similarly detected, stored and output by the main control unit for display.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to method and apparatus for self-diagnosis, suitable 
for improving the quality of service when a malfunction occurs in a 
vehicle electronic control system or unit (ECU) in which a main electronic 
control unit (main ECU) is connected via a communication line to plural 
subsidiary electronic control units (sub-ECUs). 
2. Related Art 
As electronic control systems for vehicles have developed, the ECU used in 
the vehicle has become a more complicated system and now typically 
includes plural sub-ECUs and a main ECU governing the sub-ECUs. A 
conventional diagnosis system executes a diagnosis procedure (diagnosis) 
to detect a malfunction of an ECU under the sole control of the main ECU, 
so that a malfunction of any of the sub-ECUs is detected only when the 
malfunctioning state occurs during the time that the main ECU calls for 
the ECUs to diagnose malfunctions (Self-Diagnosis). 
A system for conventional self-diagnosis of sub-ECUs is shown in FIG. 4. A 
main ECU 1 comprises a CPU 2 having a system check function and a 
diagnosis memory function, a memory 3 for storing diagnosis information, a 
clock IC 4 for generating date and time information on demand, to provide 
the date and time of the system check for recording in the memory, a 
battery 5 for back-up of the memory and the clock IC, and a communication 
interface 6 for data communication with sub-ECUs 10. 
Each Sub-ECU 10 (10A, 10B, . . . ) comprises a CPU 11 having a 
self-diagnosis function, a memory 12 for storing diagnosis results 
obtained by the sub-ECU, and a communication interface 13 for data 
communication with the main ECU 1. 
Referring to FIG. 5, when the system diagnoses itself, the main ECU starts 
a system check under direction of a service person or the like and then 
commands the respective sub-ECUs to start the self-diagnosis. After 
checking conditions of the communications with the respective sub-ECUs, 
the main ECU diagnoses itself. Meanwhile, each sub-ECU diagnoses itself 
and outputs the result of the self-diagnosis. The main ECU then 
sequentially receives the results of the self-diagnoses executed at the 
respective sub-ECUs. The main ECU displays the results of the system check 
done by the main ECU itself and by the respective sub-ECUs. These 
displayed results include those for self-diagnosis by the respective 
sub-ECUs and that of the main ECU and the results of the checks of the 
communications with the respective sub-ECUs. 
FIG. 6 shows processing steps of an automatic diagnosis procedure of the 
main ECU. During operation of this procedure, the main ECU checks the 
conditions of communications with the respective sub-ECUs and executes the 
self-diagnosis of the main ECU itself to monitor any malfunctions in the 
main ECU. When no current malfunction is detected, this process is 
repeated in a predetermined cycle. When malfunction is detected, the 
malfunction details and the date and time are written in the memory with a 
battery for each time the malfunction occurs. The main ECU then determines 
whether the display of the diagnosis memory has started. If it has not 
started, the process returns to the beginning, and the main ECU checks the 
conditions of the communications linking the respective sub-ECUs. If the 
display has started, the main ECU calls up the diagnosis information and 
the date and time of occurrence of the malfunction out of the memory and 
displays the diagnosis memory contents. The respective sub-ECUs do nothing 
during this diagnosis memory function. Such a diagnosis system for an ECU 
is disclosed in, for example, Japanese Patent Laid-Open No. 198733/1992. 
Although conventional systems can detect malfunction through the diagnoses 
of the respective ECUs while a current malfunction is occurring, the 
system cannot detect a malfunction when the malfunctioning is 
discontinuous, or when the malfunctioning occurs randomly. Thus, the 
conventional system does not have the capability of giving information of 
past (through the present) conditions of the respective sub-ECUs and the 
date and time at which a past malfunction occurred in the sub-ECUs. 
Because the conventional system does not provide the histories of 
transient malfunctions of respective sub-ECUs, it takes time to find 
malfunction causation and solution and the quality of servicing may 
suffer. Moreover, although simply applying a self-diagnosis function, such 
as executed by the main ECU, to the sub-ECUs will enable the sub-ECUs to 
achieve such a function, this expansion may create problems in that the 
apparatus will become bulky and costly. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and apparatus 
for self-diagnosis for an electronic control system for vehicles, without 
cost increase, with minimal requirement for additional parts, and with the 
capability of diagnosing events of a discontinuing nature, which occur at 
the respective ECUs. 
To accomplish the above object, according to a first aspect of the 
invention, there is provided a self-diagnosis method for a vehicle 
electronic control system in which a plurality of subsidiary electronic 
control units are connected by a communication line to a main electronic 
control unit for governing the respective subsidiary electronic control 
units, the method comprising the steps of: continuous self-diagnosing by 
each subsidiary electronic control unit to diagnose itself, signaling each 
malfunction, when detected, from the respective subsidiaries electronic 
control unit to the main electronic control unit; interrupting the main 
electronic control unit for retrieving the date and time of occurrence of 
the malfunction; and storing the date and time of occurrence of the 
malfunction, as well as malfunction details, in a memory means either in 
the main electronic control unit or in the said subsidiary electronic 
control unit. 
According to a second aspect of the invention, there is provided a 
self-diagnosis apparatus for a vehicle electronic control system that 
includes a main electronic control unit and a plurality of subsidiary 
electronic control units governed by the main electronic control unit, 
which apparatus performs a system check for diagnosing the main electronic 
control unit and has a diagnosis memory function for storing the results 
of the execution of the system check function and the results of 
individual self-diagnosis executed by each of the subsidiary electronic 
control units, as well as the corresponding date and time at which the 
malfunction occurred. The apparatus includes communicating means for, when 
any of said subsidiary electronic control units detects a malfunction by 
self-diagnosis, reporting the malfunction to the main electronic control 
unit; clock processing means provided in the main electronic control unit 
for, when receiving report of a malfunction from a subsidiary electronic 
unit, processing the date and time of occurrence of the malfunction; and 
memory control means for storing in the memory means details of a 
malfunction of any of the subsidiary electronic control units and the date 
and time of occurrence of the malfunction as the result of the 
self-diagnosis of the respective subsidiary electronic control units and 
for, retrieving and outputting diagnosis information out of said memory 
means, responsive to execution of the diagnosis memory function by the 
main electronic control unit. 
According to other aspects of the invention, there are also provided 
self-diagnosis systems further comprising one of the following features: 
(1) The memory means is within the main electronic control unit. 
(2) The memory means is within each subsidiary electronic control unit. 
(3) The memory means includes a non-volatile memory. 
(4) The non-volatile memory is a memory capable of electrically writing and 
electrically erasing information. 
According to the invention, each subsidiary electronic control unit 
continuously diagnoses itself and, when detecting a malfunction, requests 
interruption by means of communication to the main electronic control 
unit. If equipped with diagnosis information memory means, the subsidiary 
electronic control unit interrupts the main electronic control unit to 
request the present date and time based on the malfunction detection. As 
processed clock information is transmitted to the subsidiary electronic 
control unit, the subsidiary electronic control unit stores the date and 
time of occurrence of the malfunction and the malfunction details together 
as diagnosis information. In contrast, if not equipped with diagnosis 
information memorizing means, the subsidiary electronic control unit 
interrupts the main electronic control unit and transmits the malfunction 
details, upon detection, to the main electronic control unit. The main 
electronic control unit, when interrupted, executes an interrupt procedure 
for receiving the malfunction details from the subsidiary electronic 
control unit, receives the current date and time, and stores the 
malfunction details along with the date and time in the memory means of 
the main electronic control unit. 
According to the above-described self-diagnosis method of the invention, 
each time a malfunction is detected through the self-diagnosis executed at 
the respective subsidiary electronic control units, the date and time of 
occurrence and details of the malfunction are stored in the memory means 
by use of the clock function of the main electronic control unit. 
Therefore, the electronic control system can be diagnosed without any new 
additional clock function. The histories of diagnosis results of the 
respective subsidiary electronic control units can be displayed on user's 
demand, thereby facilitating finding malfunction causation and solution, 
and thereby improving the quality of service. 
According to the second aspect of the invention, the communicating means 
reports to the main electronic control unit when the automatic 
self-diagnosis of the respective subsidiary electronic control unit 
detects a malfunction. The main electronic control unit operates the clock 
processing means so as to output the date and time of the occurrence of 
the malfunction. The control means stores the date and time of the 
occurrence of the malfunction and malfunction details in the memory means 
in either the main electronic control unit or in the respective subsidiary 
electronic control units. Upon user's demand, the control means retrieves 
and displays the stored diagnosis information. According to the 
self-diagnosis apparatus of the invention, the respective subsidiary 
electronic control units constantly execute the self-diagnosis, and the 
detected details and date and time of occurrence of any malfunction are 
stored, so that the respective subsidiary electronic control units do not 
need to have a clock function, thereby simplifying the construction of the 
apparatus and achieving the same advantages as achieved by the 
above-described method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the invention will be described with reference 
to the attached drawings. To the extent the system shares in common 
details of construction as described with reference to FIG. 4, the 
description thereof will be omitted. 
Embodiments of a diagnosis memory function, a feature of the invention, 
will first be described. 
FIG. 1 shows a first embodiment of processing steps for effecting the 
diagnosis memory function. In this embodiment, details of the malfunction 
detected by self-diagnosis executed in the respective sub-ECUs 10 and the 
present date and time given by a main ECU 1 are written in the memory 12 
of the sub-ECU 10. 
The main ECU 1 has a procedure to fetch (retrieve) the respective sub-ECUs' 
diagnosis information from the sub-ECU and to display the system diagnosis 
information that the main ECU 1 obtains and stores by itself along with 
the diagnosis information that the respective sub-ECUs 10 obtain and 
store. The main ECU 1 constantly executes a system check of itself in the 
same manner as a conventional system and stores, when detecting a 
malfunction, malfunction details (diagnosis information) at the time that 
the malfunction occurs and the date and time of occurrence of the 
malfunction in the memory 3 with battery 5. The main ECU 1 fetches the 
diagnosis information obtained through the self-diagnosis function 
executed at the respective sub-ECUs. The main ECU 1 includes an interrupt 
routine initiated by a date-and-time request or signal from one of the 
respective sub-ECUs 10, either by a hardware interrupt of the CPU 2 or by 
monitoring a communication input from the sub-ECUs. 
When a sub-ECU 10A makes a time request, the interrupt routine in the CPU 2 
of the main ECU 1 calls the date and time out of a clock IC 4, transmits 
this date and time to the requesting sub-ECU 10A, and then terminates the 
interrupt routine. The corresponding sub-ECU 10A writes the received date 
and time into its memory 12 along with the malfunction details. 
When the main ECU 1 executes the diagnosis memory function and when the 
start of diagnosis memory is confirmed in step A, the main ECU 1 requests 
the sub-ECU 10A to transfer diagnosis information stored therein. The 
sub-ECU 10A reads the diagnosis information and the date and time of 
occurrence information out of the memory 12 in response to the transfer 
request and supplies the information to the main ECU 1. The information 
sent from the sub-ECU 10A is written in the memory 3 with battery 5. When 
the user requests a display of the contents of the diagnosis memory, the 
main ECU 1 calls up the diagnosis information of the main ECU 1 and the 
respective sub-ECUs 10 and the date and time of occurrences and displays 
them at a display unit. 
FIG. 2 shows a second embodiment of processing steps for effectuating a 
diagnosis memory function. In this embodiment, when any of the sub-ECUs 10 
detects a malfunction by the self-diagnosis executed therein, the sub-ECU 
10A sends the details of the malfunction to the main ECU 1, and the main 
ECU 1 writes the diagnosis information in the memory 3 with battery 5 and 
manages it. The main ECU 1 calls the date and time from the clock IC 4 
when the sub-ECU 10A generates a signal to interrupt the ECU 1 to call an 
interrupt procedure for receiving malfunction details. The main ECU 1 
writes the diagnosis information from the sub-ECU 10 and the date and time 
of occurrence of the malfunction in the memory 3 with battery 5. When the 
main ECU 1 executes the diagnosis memory function upon an instruction from 
a user, the diagnosis information of the main ECU 1 and the respective 
ECUs 10 and the date and time of occurrence data are called out of the 
memory 3 and displayed. 
FIG. 3 shows yet another embodiment of a system for effectuating the 
diagnosis memory function. In this system, each sub-ECU 10A is capable of 
researching malfunction history if the power is turned off. Each sub-ECU 
10A has a ROM (EEPROM) 14 capable of electrically writing and electrically 
erasing information, as a memory to store diagnosis information obtained 
through execution of the self-diagnosis function. The EEPROM 14 stores 
self-diagnosis results of the sub-ECU 1OA, as well as the date and time of 
occurrence of the malfunction. The diagnosis memory function of the main 
ECU 1 is the same as described with reference to FIG. 1. Upon time request 
of the present date and time from a sub-ECU 10A, the present date and time 
sent from the main ECU 1 and the malfunction details are written in the 
EEPROM 14. This diagnosis information is fetched by the execution of the 
diagnosis function of the main ECU 1 and is stored in the memory 3 with 
battery 5 in the main ECU 1. The diagnosis information is displayed upon 
an instruction from a user. 
Although in the above-described embodiment each sub-ECU has an EEPROM, the 
EEPROM may be replaced with a memory with battery.