JPH0396638A - Self-diagnostic device for on-vehicle equipment - Google Patents

Abstract

PURPOSE:To prevent leak current by applying voltage onto a charge and discharge circuit which is connected with a switching means in parallel via a diode, and thereby judging whether or not there exists abnormality in electric load based on the anode terminal voltage after a specified time has elapsed since the switching means has been turned off. CONSTITUTION:A battery A acting as a power source, electric load B and a switching means C are connected in series with one another. When the switching means C is turned on, a charge and discharge circuit D is connected with the switching means C in parallel in on-vehicle equipment energized with electric load B so that the cathode terminal of a diode E is thereby connected with the aforesaid charge and discharge circuit D. In addition, the anode terminal of the diode E is provided with a voltage applying circuit G applying voltage via a current limiting resistor F. In a second place, the anode terminal voltage of the diode E is detected by a voltage detection means H after a specified time has elapsed since the switching means C has been turned off, then, it is judged by a judging means I whether of not there exists abnormality in electric load B based on the detected anode terminal voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a self-diagnosis device for diagnosing the presence or absence of an abnormality in an electrical load such as a fuel injection valve mounted on a vehicle.

<Prior Art> A conventional example of this type of self-diagnosis device is shown in FIG.

That is, the solenoid of the fuel injection valve 1 is connected in series with a power transistor 2 built into the control unit. The power transistor 2 is turned on and off by the control device 3 via the current limiting resistor 2a, so that the solenoid of the fuel injection valve 1 is energized from the battery 4.

Further, first and second voltage dividing resistors 5.6 are connected in parallel to the power transistor 2, and the voltage between these voltage dividing resistors 5.6 is applied to the input port of the control device 3.

The control device 3 diagnoses whether or not there is an abnormality in the fuel injection valve 1 according to the voltage across the voltage dividing resistor 5.6.

For example, if the voltage is maintained at a low level even when the power transistor 2 is turned on and off, a diagnosis is made that the solenoid of the fuel injection valve l is disconnected, and even when the power transistor 2 is turned on and off, When the voltage is maintained at a high level, it is diagnosed that the solenoid of the fuel injection valve 1 is short-circuited.

The power transistor 2 also includes a time constant resistor 7.
and capacitor 8 are connected in parallel, and these circuits 7.8
This forms the surge absorption circuit of the fuel injection valve I.

Note that 9 is a power supply circuit for applying a constant voltage VCC to the control device 3, 10 is a Zener diode for absorbing large voltage, and 11 is an ignition switch.

<Problem to be Solved by the Invention> However, in such a conventional self-diagnosis device, even when the ignition switch 11 is off, in other words, when the power transistor 2 is off, there is no power from the battery 4 via the solenoid of the fuel injection valve 1. first and second voltage dividing resistors 5,
Since a leakage current flows between the battery 4 and the input port, there is a problem that the battery 4 deteriorates or deteriorates.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a self-diagnosis device that can self-diagnose whether there is an abnormality in an electrical load while preventing leakage current.

<Means for Solving the Problem> For this reason, the present invention, as shown in FIG. The electric load B is energized, and includes a charging/discharging circuit D connected in parallel to the switching means C, and a diode E having a cathode terminal connected to the charging/discharging circuit D.
a voltage supply circuit G that applies a voltage to the anode terminal of the diode E via a current limiting resistor F; and a voltage supply circuit G that detects the anode terminal voltage of the diode E after a predetermined period of time has elapsed since the switching means C was turned off. and a determination stage (2) for determining whether or not there is an abnormality in the electric load B based on the detected anode terminal voltage.

<Function> In this way, the charging voltage state of the charging/discharging circuit is detected from the cathode terminal voltage of the diode to determine whether there is an abnormality in the electrical load, and the diode prevents leakage current when the switch means is turned off. I made it.

<Example> An example of the present invention will be described below based on FIGS. 2 to 4. Incidentally, the same elements as those in the conventional example are given the same reference numerals as in FIG. 5, and the explanation thereof will be omitted.

In FIG. 2, a first diode 21 is connected to the collector terminal side of the power transistor 2 as a switching means.
The cathode terminal of the first diode 21 is connected to the anode terminal of the second diode 22 . The first and second diodes 21. 22
A constant voltage VCC is applied from a power supply circuit 9 serving as a voltage supply circuit to the anode terminal of the transistor 2 through a current limiting resistor 23. The power supply circuit 9 is configured to output a constant voltage vec when the ignition switch 11 is on.

The cathode terminal of the second diode 22 is grounded via a resistor 24 and connected to the human power port of the @control device 25. The control device 25 operates according to the flowchart shown in FIG. 3, and determines whether or not there is an abnormality in the solenoid of the fuel injection valve 1 based on the voltage at the cathode terminal of the second diode 22, in other words, the voltage at the anode terminal of the first diode 21. It is supposed to be diagnosed.

Here, the control device 25 constitutes a voltage detection means and a determination means. Further, the time constant resistor 7 and the capacitor 8, which constitute the surge absorption circuit, constitute a charging/discharging circuit.

Next, the operation will be explained according to the flowchart of FIG. 3 while referring to the signal waveform diagram of FIG. 4. The routine shown in the flowchart of FIG. 3 starts operating when the power transistor 2 is switched from on to off.

First, when the control device 25 outputs the pulse signal shown in FIG. 4a to the power transistor 2, the power transistor 2 is turned on and the collector voltage of the power transistor 2 is switched to the L level as shown in FIG. 4b. At this time, the first and second diodes 21 . A constant voltage VCC is applied to 22 via a current limiting resistor 23,
Since the cathode terminal of the first diode 21 is connected to the collector terminal of the power transistor 2, the anode terminal voltage of the first diode 21 and the cathode terminal voltage of the second diode 22 are similar to the collector terminal voltage of the power transistor 2. Varies with voltage level. This results in
The cathode terminal voltage of the second diode 22 is switched to the L level as shown in FIG. 4C.

When the power transistor 2 is turned on, the capacitor 8
is discharged via the time constant resistor 7 and the power transistor 2.

In this state, the control device 25 switches the power transistor 2 from on to off and starts executing the routine shown in the flowchart of FIG.

That is, in Sl, a predetermined time T4 (for example, 50 μ
sec) After the delay, the cathode terminal voltage of the second diode 22 is read in S2.

In S3, it is determined whether the read cathode terminal voltage is less than the reference voltage. If YES, the process proceeds to S4; if NO, the process proceeds to S5.

In S4, it is determined that there is an abnormality because the solenoid of the fuel injection valve 1 is disconnected.

On the other hand, in S5, it is determined that the solenoid of the fuel injection valve 1 is normal.

By the way, when the power transistor 2 is switched from on to off, a large voltage from the battery 4 is applied to the capacitor 8 via the solenoid of the fuel injection valve 1 when the solenoid of the fuel injection valve is normal.

As a result, the charging voltage of the capacitor 8 rises instantaneously, so that the collector voltage of the power transistor 2 also rises rapidly to the H level as shown by the solid line in FIG. 4B. Therefore, the anode terminal voltage of the first diode 2l is also constant voltage V
cc, the cathode terminal voltage of the second diode 22 also instantaneously switches to the H level as shown by the solid line in FIG. 4C.

Therefore, after the predetermined time Td has elapsed since the power transistor 2 was switched from on to off, the cathode terminal voltage exceeds the reference voltage, so that it can be determined that the fuel injection valve 1 is normal.

On the other hand, when the solenoid of the fuel injection valve l is disconnected, only the constant voltage VCC is applied to the capacitor 8 via the first diode 2l, so the charging voltage of the capacitor 8 rises relatively slowly. power transistor 2
The collector voltage also rises gradually as shown by the chain line in FIG. 4b. Therefore, the anode terminal voltage of the first diode 2l also rises slowly, and accordingly, the cathode terminal voltage of the second diode also rises gradually as shown by the broken line in FIG. 4C. Since the cathode terminal voltage is maintained below the reference voltage, it can be determined that the solenoid of the fuel injection valve 1 is disconnected. Note that it may be determined that the solenoid of the fuel injection valve 1 is short-circuited when the cathode terminal voltage of the second diode 22 rises more rapidly than in a normal state.

In this way, it is possible to determine whether there is an abnormality in the solenoid of the fuel injection valve l, and when the power transistor 2 is turned off, in other words, when the ignition switch l1 is turned off,
The first diode 21 can prevent leakage current from flowing from the battery 4 through the solenoid of the fuel injection valve i to the input port of the control device 25 and the resistor 24, thereby preventing the battery 4 from deteriorating or dying.

Effects of the Invention> As explained above, the present invention connects a charging/discharging circuit in parallel to a switching means for operating an electric load, applies voltage to the charging/discharging circuit via a diode and a current limiting resistor, Since the presence or absence of an abnormality in the electrical load is determined based on the anode terminal voltage of the diode after a predetermined period of time has elapsed since the switch was turned off, it is possible to diagnose the presence or absence of an abnormality in the electrical load while also reducing leakage current by the diode. This can prevent battery deterioration or battery drain.

[Brief explanation of drawings]

Fig. 1 is a claim correspondence diagram of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a flowchart of the same as above,
FIG. 4 is a signal waveform diagram of each part of FIG. 2, and FIG. 5 is a circuit diagram showing a conventional example of a self-diagnosis device. 1...Fuel injection valve 2...Power transistor 4
...Battery 7...Resistance for time constant 8...
Capacitor 9... Power supply circuit 21... First diode 22... Second diode 23... Current limiting resistor 25... Control device

Claims (1)

[Claims] A vehicle-mounted device in which a battery power source, an electric load, and a switching means are connected in series, and the electric load is energized by turning on the switching means,
a charging/discharging circuit connected in parallel to the switching means; a diode having a cathode terminal connected to the charging/discharging circuit; a voltage supply circuit applying a voltage to the anode terminal of the diode via a current limiting resistor; Voltage detection means for detecting the anode terminal voltage of the diode after a predetermined period of time has elapsed since the switching means was turned off;
A self-diagnosis device for vehicle-mounted equipment, comprising: determination means for determining whether or not there is an abnormality in the electrical load based on the detected anode terminal voltage.