JPH0678739B2 - Idle switch failure diagnosis method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of diagnosing a failure of an idle switch used in an engine of an automobile or the like.

[Prior Art] For a similar vehicle, for example, Japanese Patent Laid-Open No. 61-
As shown in Japanese Patent No. 175250, various sensors for detecting the operating state of the engine and vehicle such as an idle switch and a throttle sensor are mounted, and information from these sensors is input to an electronic control unit. Controlling the fuel system and ignition system of an engine is becoming popular.

However, it is important to prepare a system capable of easily diagnosing whether or not various sensors are out of order in a system provided with such a control system. The present invention relates to a method for diagnosing whether or not the idle switch has failed in the OFF state.

Conventionally, as a method to detect that the idle switch has failed at the OFF position, the idle switch is in the OFF condition,
When the output of the throttle sensor does not change continuously for a certain period of time (for example, 60 seconds), it is determined that the idle switch has a failure.

With this method, when the throttle valve is opened by artificial depression of the accelerator, unlike during idling, it is impossible that the opening will not change for 60 seconds. Based on the above, the idle switch is diagnosed as a failure when the impossible signal generation state occurs.

[Problems to be Solved by the Invention] By the way, the analog signal output from the above-described throttle sensor slightly changes due to engine vibration or the like. When the fluctuation region a includes a so-called threshold value b for A / D conversion as shown in FIG. 4, even if the fluctuation range of the analog signal is very small, the A / D
The output value after conversion will change. Therefore, when the idle switch OFF failure is diagnosed by the conventional method, the output after A / D conversion due to the slight fluctuations of the analog signal is generated even if the idle switch actually fails. May change and it may not be possible to make a determination to that effect.

Therefore, it is difficult to improve reliability of failure diagnosis.

The present invention aims to solve such problems.

[Means for Solving Problems] The present invention adopts the following configurations in order to achieve the above objects.

That is, the idle switch failure diagnosing method according to the present invention is set so that the output of the throttle sensor after A / D conversion changes stepwise every time a plurality of unit amounts change in the same direction and follows the output value. The following variable is provided, and if the following variable does not change for a certain period of time under the condition that the idle switch is OFF, it is determined that the idle switch is in the OFF state and has failed.

[Operation] An analog signal from the throttle sensor is A / D converted into a digital signal that increases / decreases by a predetermined unit amount and is input to a computer or the like. The tracking variable is updated and changes stepwise every time the A / D converted output of the throttle sensor increases or decreases by 2 units or 3 units or more, and follows the output of the throttle sensor.

When the idle switch is normal, the throttle valve is opened by depressing the accelerator or the like to turn off the idle switch. At this time, since the throttle valve is artificially opened, its opening degree changes variously, and it shows a fluctuation that is orders of magnitude larger than the unit amount of A / D conversion. Therefore, the tracking variable naturally changes.

If the idle switch fails in the OFF position, the OFF signal will continue to be output even when the throttle valve is held in the closed position. In that case, although the analog signal from the throttle sensor has a slight change due to the vibration of the engine, the change in the throttle opening corresponding to the multiple of the unit amount related to the A / D conversion does not occur. Therefore, the following variable remains held at a constant value and does not change. Therefore, the idle switch is OFF, and
The condition that the following variable has not changed for a certain period of time is satisfied, and it is determined that the idle switch has failed at the OFF position.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

In the figure, 1 is a carburetor of an engine for an automobile, 2 is a throttle valve thereof, and 3 is a throttle lever which rotates with opening and closing of the throttle valve 2. The throttle valve 2 is biased in the closing direction by a spring 4,
It is adapted to be opened by depressing an accelerator pedal (not shown). Further, the throttle lever 3 is locked by a stopper 5 to hold the throttle valve 2 in the closed position. Then, the open / close position of the throttle valve 2 is detected by the throttle sensor 6, and whether or not the throttle valve 2 is held at the closed position is detected by the idle switch 7. The throttle sensor 6 is mainly composed of a potentiometer, and is adapted to convert the open position of the throttle valve 2 into an analog electric signal. On the other hand, the idle switch 7 is turned on only when the throttle lever 3 is locked by the stopper 5 and held in the closed position, and is turned off when the throttle valve 2 is open. Becomes

Then, the signal from the throttle sensor 6 is input to the central processing unit 12 of the microcomputer system 11 via the interface 8 and the A / D converter 9, and the idle switch 7 and the mode changeover switch 13 are turned on. , OFF signal is input to the central processing unit 12 through the interface 14. The microcomputer system 11 is for controlling a fuel system and an ignition system of an engine by using signals from the throttle sensor 6, the idle switch 7 and other sensors (not shown) as input information, and the central processing unit 12
A storage device 15 and an output interface 16 are connected to the.

In the A / D conversion by the A / D converter 9, as shown in FIG. 3, the output value VTA2 is changed by one unit amount (e.g., every time the analog signal from the throttle sensor 6 changes by 0.09 degrees). 1b
It) is set to step up or down.

The microcomputer system 11 also incorporates a failure diagnosis program for the idle switch 7 according to the present invention. As shown schematically in FIG. 2, this program first determines in step 51 whether or not the signal from the idle switch 7 is ON, and if ON, proceeds to step 52. If OFF, go directly to step 54. In step 52, the tracking variable VTA20 is set to the same value as the output value VTA2 of the throttle sensor 6 after A / D conversion, and the process proceeds to step 53. At step 53, the increment counter CDIAG is reset and the routine proceeds to step 54. In step 54, the absolute value of the difference between the output value VTA2 of the throttle sensor 6 and the tracking variable VTA20 is 2 units of A / D conversion (2 bits).
If it is determined that it is not exceeded, the process proceeds to step 55, and if it is determined that it is not exceeded, the process proceeds to step 57. In step 55, the tracking variable
The same value as the output value VTA2 of the throttle sensor 6 after A / D conversion is set in VTA20, and the routine proceeds to step 56. At step 56, the increment counter CDIAG is reset and the routine proceeds to step 57. In step 57, it is judged whether or not the increment counter CDIAG has counted up to 60 seconds, and only when it reaches 60 seconds, step 58
Go to. In step 58, it is determined that the idle switch 7 has failed at the OFF position, and the determination result is stored in the storage device 15. Then, when the microcomputer system 11 is switched to the failure diagnosis mode by the operation of the mode changeover switch 13, the diagnosis result is displayed by turning on the diagnostic lamp 17 or the like. The above procedure is repeatedly executed in minute time units.

With such a configuration, the idle switch 7
When the state is OFF and the tracking variable VTA20 does not change for 60 seconds or more, it is determined that the idle switch 7 has failed at the OFF position (steps 51 → 54 → 57 →
58). The follow-up variable VTA20 is updated only when the output value VTA2 of the throttle sensor 6 changes by more than two unit amounts in the same direction. Therefore, even if the analog signal output from the throttle sensor 6 has a slight fluctuation due to engine vibration, etc., and even if the fluctuation matches the above-mentioned threshold value, the A / D conversion is performed. The subsequent output value VTA2 repeats increasing and decreasing by one unit amount, and the following variable VTA20 does not change. Therefore, it is possible to surely solve the conventional problem that it is not possible to accurately determine the OFF fail of the throttle sensor 6 due to the improper fluctuation of the output value VTA2 of the throttle sensor 6.

It should be noted that the mode of updating the follow-up variable is not limited to the above-mentioned one. Various modifications are possible without departing from the scope.

EFFECTS OF THE INVENTION Since the present invention has the above-described configuration, it is possible to prevent the idle switch from failing at the OFF position without being adversely affected by the minute fluctuation of the analog signal output from the throttle sensor. It is possible to provide a failure diagnosis method for an idle switch that can be reliably detected.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a schematic system explanatory view, FIG. 2 is a flow chart for explaining a control procedure, and FIG. 3 is a throttle sensor. It is an operation explanatory view for explaining the relation between an output value and a following variable. FIG. 4 is an explanatory diagram for explaining a conventional example. 2 ... Throttle valve 6 ... Throttle sensor 7 ... Idle switch 9 ... A / D converter 11 ... Microcomputer system

Claims (1)

[Claims] 1. A tracking variable that is set so as to follow the output value by gradually changing each time the output of the throttle sensor after A / D conversion changes by a plurality of unit amounts in the same direction is provided. If the tracking variable does not change for a certain period of time when the switch is off, the idle switch is turned off.
A method for diagnosing a failure of an idle switch, which comprises determining that a failure has occurred in a state.