Method and Apparatus for Diagnosing Failure in Idle Switch for Internal Combustion Engines

The present invention relates generally to a method and apparatus for diagnosing failure in an idle switch installed in an internal combustion engine. The idle switch is provided to detect and indicate the fully closed state of a throttle valve installed in a throttle chamber in an intake passage of the internal combustion engine.

An activation signal derived from the idle switch indicative of the fully closed state of the throttle valve is an essential factor to indicate that the idling engine is and to determine the correct amount of fuel to be fed to the engine when it is idling or decelerating with the throttle valve closed.

Hence, when such failures as insufficient contact or a broken line in the idle switch occur, proper control of the fuel injection quantity becomes impossible and accordingly undesirable exhaust gas components increase. In addition, the driver of the vehicle in which the engine is mounted cannot easily notice such kinds of failure.

Recently, the demand for a self-diagnosis system by which self-diagnosis for such kinds of failures can be carried out to indicate presence of such failures or to store information indicating the presence of such failures in a memory so as to simplify inspection and repair has been felt.

A Japanese document titled "M-TEU engine service manual" published on January, 1984 by Toyota Jidosha kabushiki kaisha exemplifies the above described diagnosing apparatus.

In the above-identified Japanese document, a full open switch which turns to ON and generates an On signal when the throttle valve is in a fully open state is used and the idle switch diagnosing apparatus indicates that the idle switch has failed if both ON signals of the idle switch and full open switch are simultaneously received.

However, the above-described idle switch diagnosing apparatus cannot clearly distinguish the failure of the idle switch from that of the full open switch. In addition, it cannot diagnose the condition of the idle switch when the idle switch cannot generate the ON signal because it is not being operated or there is a broken line in the idle switch.

It is an object of the present invention to provide a method and apparatus for easily and quickly diagnosing failure of the idle switch.

It is another object of the present invention to provide an apparatus and method for accurately diagnosing failure in the idle switch when the idle switch cannot produce the ON signal due to nonoperation of or a broken line in the idle switch.

The above-described objects can be achieved by providing an apparatus, comprising: (a) first means for detecting whether an internal combustion engine has times the engine has started on the basis of the information obtained by the first means, the second means being cleared in response to an activation signal of an idle switch indicating that an engine speed adjusting mechanmism of the engine causes the engine in an idle state; (c) third means for comparing the counted value of the second means with a predetermined value; and (d) fourth means for determining whether the idle switch has failed on the basis of the result of the comparison by the third means.

The above-described objects can be achieved by providing an apparatus, comprising: (a) first means for detecting the state (open or closed) of a throttle valve installed in an intake passage of an internal combustion engine, and outputting an activation signal indicative thereof, the throttle valve being associated with an accelerator of a vehicle; (b) second means for detecting a start of the internal combustion engine, and outputting a signal indicative thereof; (c) third means for counting a number of times the engine has started from the number of signals derived from the second means, the third means being cleared in response to the activation signal outputted from the first means; (d) fourth means for determining if the first means has failed on the basis of a value counted by the third means.

The above-described objects can be achieved by providing a method for detecting failure of a component of a vehicular engine, comprising the steps of: (a) detecting whether the engine has started; (b) counting the number of times the engine has started as detected in step (a); (c) clearing the counted value counted in the step (b) when receiving a signal from an idle switch to indicate that a throttle valve of the engine is in a fully closed state; (d) determining whether the counted value counted in the step (b) reaches a value equal to a predetermined value; (e) producing an alarm indicating that the idle has switch failed upon determination in the step (d) that the counted value derived in the step (b) has reached as value equal to the predetermined value.

FIG. 1 is a circuit block diagram of a preferred embodiment of an appratus for diagnosing failure in an idle switch of an internal combustion engine according to the present invention.

FIG. 2 is a flowchart of a trouble diagnose routine executed in the preferred embodiment shown in FIG. 1.

Reference will hereinafter be made to the drawings in order to facilitate understanding of the present invention.

FIG. 1 shows a preferred embodiment of to the present invention.

An idle switch 14 is installed in connection with a throttle valve 13. The throttle valve 13 is installed in an intake passage 12 of an internal combustion engine generally designated by 11. The throttle valve 13 is used to adjust air flow rate of intake air sucked into a cylinder of the engine 11, and is preferably linked with an accelerator pedal of a vehicle in which the engine 11 is mounted. The idle switch 14 serves to detect when the throttle valve 13 is in a fully closed state and is activated to produce an ON signal when the throttle valve 13 is fully closed, e.g., when the associated accelerator pedal is released. The ON signal of the idle switch 14 is transmitted to a control unit 15. The control unit 15 receives an ignition ON signal form an ignition switch 16. The ignition switch 16 is a key switch operated by an operator. The control unit 15 also receives an engine revolution speed signal from a crank angle sensor 17.

The crank angle sensor 17 is exemplified by a U.S. Pat. No. 4,656,993 issued on Apr. 14, 1987, the disclosure of which is hereby incorporated by reference.

The control unit 15 furthermore receives an air flow rate signal from an air flow sensor 18. The control unit 15 outputs an alarm signal to an alarm unit such as alarm lamp 19 installed preferably on the driver's side of the vehicle when the unit 15 determines that the idle switch 14 has failed.

The control unit 15 also outputs an injection signal to a fuel injector 20 to control a quantity and injection timing of fuel supplied to the engine 11 via the fuel injector 20 and also outputs an ignition signal to a spark plug 21 installed in each of engine cylinders to control an ignition timing.

The control unit 15 comprises a microcomputer which executes injection quantity control, ignition timing control, and so on the basis of the signal output of the crank angle sensor 17 and air flow meter 18, and idle switch 14 and diagnoses failure of the idle switch 14 and turns on the alarm lamp 19 failure of the idle switch 14 is determined.

FIG. 2 shows a flowchart representing a diagnostic routine which the control unit 15 executes for detecting failure in the idle switch 14.

It is noted that the microcomputer constituting the control unit 15 includes a CPU (Central Processing Unit), I/O unit (Input/Output), ROM (Read Only Memory), and RAM (Random Access Memory).

In steps ST1 to ST4, the control unit 15 determines whether the engine 11 has been started on the basis of a switching of the ignition switch 16 from OFF to On state and engine revolution speed.

More specifically, in the step ST1, the control unit 15 detects if the signal outputted from the ignition switch 16 has changed from the OFF state to the ON state. If YES in step ST1, the routine goes to step ST2 in which a flag FIGON is set to "1" and then goes to step ST3 in which the control unit 15 determines whether the engine speed detected by the crank angle sensor 17 is equal to or more than 600 rpm. If YES in step ST3, the routine goes to step ST4 is which the control unit 15 determines whether the flag FIGON is set to "1". If YES in step ST4, the routine goes to step ST5 in which a counter CIDNG is advanced by one (CIDNG.rarw.CIDNG+1). Hence, whenever the engine 11 is started, the count valve of counter CIDNG is sequentially advanced. However, the count valve of counter CIDNG remains unchanged when mere repetition of ON and OFF of the ignition switch 16 is carried out with no complete start of the engine 11. In a step ST6, the control unit 15 resets the flag FIGON to "0". Next, in a step ST7, the control unit 15 determines whether the count valve of the counter CIDNG exceeds a predetermined valve C.sub.1 as will be described later. In a step ST8, the control unit 15 determines the presence or absence of the activation signal of the idle switch 14, to specifically determine whether the signal outputted from the idle switch 14 has changed from the OFF state to the ON state. When the throttle valve 13 is returned from its open state to its fully closed state, the change of the signal derived from the idle switch 14 from the OFF state to the ON state is detected provided that the idle switch 14 functions normally. If YES in the step ST8, the routine goes to a step ST10 in which the counter CIDGN is cleared. Hence, if the idle switch 14 functions normally, the value of the counter CIDNG is held at a value of "1" of "0" and may indicate at least "0" when the engine stops.

On the contrary, if the idle switch 14 fails, the counter CIDGN is advanced as the engine 11 each time the engine is started. Therefore, in the step ST7, the control unit 15 compares the counted value from the counter CIDGN with the predetermined value C.sub.1 (for example, three, four, or five). If CIDGN.gtoreq.C.sub.1 (YES) in the step ST7, the control unit 15 determines that the idle switch 14 has failed and stores a value of IDING which is set to "1" in a memory. Then, the control unit 15 outputs the signal to the alarm lamp 19 to turn on the alarm lamp 19. The stored content described above is not erased even if the ignition switch 16 is turned off (nonvolatile memory is used).

Although in the example shown in FIG. 3 the count value of the counter CIDNG is cleared when the signal derived from the idle switch 14 changes from the OFF state to the ON state, alternatively it may be cleared upon change thereof from the ON state to the OFF state. Alternatively, since there are many cases where the signal is continuously derived from the idle switch 14 due to a broken line in the idle switch 14, the counter CIDNG may be cleared when the ON signal from the idle switch 14 is detected.

As described hereinabove, since the idle switch failure diagnosing method and apparatus according to the present invention can accurately detect failure in the idle switch due to insufficient contact in the idle switch or a broken line thereof and can activate an alarm, deterioration the quality of exhaust gas composition and reduction of fuel economy due to the failure in the idle switch can be avoided.

It will clearly be appreciated from those skilled in the art that the foregoing description is made in terms of the preferred embodiment and various changes and modifications may be made without departing from the scope of the present invention which is to be defined by the appended claims.