JP2001119854A - Fault-detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fault-detecting circuit which enables fail/safe operation which does not cause reliability to be lowered, by quickly detecting the fault of a drive circuit for an on/off apparatus for a relay, a solenoid valve, etc. SOLUTION: This fault-detecting circuit is composed of an on/off apparatus for a relay, a solenoid valve, etc., a plurality of semiconductor switches which turn them on and off by control signals, being connected in series to this on/off apparatus, and a voltage-detecting circuit which detected the voltage across the on/off apparatus, being connected in parallel with the above on/off apparatus, and one which decides whether the on/off apparatus drive circuit is out of order, by periodically superposing the OFF pulse signals with proper time widths each with different phases to the on control signal of the semiconductor switch, and monitoring the output of the voltage-detecting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure detection circuit for an ON / OFF device driving circuit for controlling ON / OFF of a load such as a relay or an electromagnetic valve.

[0002]

2. Description of the Related Art Conventionally, when an important load is controlled by an on / off device such as a relay or an electromagnetic valve, a failure of a drive circuit may have a fatal effect on a system. From the viewpoint, the driving circuit may be a double system. FIG. 5 is a circuit block diagram showing a conventional example of a drive circuit of a relay as an example of the on / off device. In FIG. 5, semiconductor switches 12 and 13 are connected in series to a relay 11 to form a double system. However, this conventional example is an example of a system in which a failure in a state where a relay is turned off is fail-safe. In the drawings, transistors are used as examples of the semiconductor switches 12 and 13, and components not related to the present invention are omitted in the drawings.

The operation will be described below with reference to FIG. In such a drive circuit, when an ON control signal is given to the semiconductor switches 12 and 13, the semiconductor switches 12 and 13 are turned on, the coil 111 of the relay 11 is excited, and the contact 112 of the relay 11 is turned on after the operation delay time Ton of the relay. Turn on. When an off control signal is given to the semiconductor switches 12, 13, the semiconductor switches 12, 13 are turned off, and the relay 11 is turned off.
Coil 111 is demagnetized, and the relay operation delay time To
After ff, the contact 112 of the relay is turned off. If the semiconductor switch is short-circuited, the contact 112 of the relay 11 is turned on in a single system using only one semiconductor switch, which may have a fatal effect on the system. Since the system is a system, the contact 112 can be turned off by turning off the normal semiconductor switch.

[0004]

The method of detecting a failure of a normal drive circuit is based on a comparison between the control signals of the semiconductor switches 12 and 13 and the state of the contact 112, and the control signal is turned on and the contact 1 is detected.
If the switch 12 is off, or if the control signal is off but the contact 112 is on, it is detected as a failure. Here, considering the case where the semiconductor switch 12 is short-circuited, the semiconductor switch 12 is turned on regardless of the control signal of the semiconductor switch 12. However, since the contact 112 operates normally due to the operation of the semiconductor switch 13, the contact 112 looks apparently normal, and it cannot be detected that a failure has occurred. Therefore, after a short-circuit failure of the semiconductor switch 12, the drive circuit becomes a single system driven only by the semiconductor switch 13, and there is a problem that reliability is reduced.

Further, if the semiconductor switch 13 also fails, the failure can be detected. However, if it is a short-circuit failure, the contact 112 is turned on, which may have a fatal effect on the system, and fail-safe. There was a problem in the point. The present invention has been made in view of the above points, and aims to solve these problems.
An object of the present invention is to provide a failure detection circuit that can quickly detect a failure in a drive circuit of an ON / OFF device such as a relay or a solenoid valve and that enables a fail-safe without reducing reliability.

[0006]

Means for achieving the object are as follows: (1) In claim 1, an on / off device such as a relay or a solenoid valve, and a control signal connected in series with the on / off device. A plurality of semiconductor switches that are turned on and off by a voltage detection circuit that detects a voltage between both ends of an on-off device connected in parallel with the on-off device, and outputs an off-pulse signal having an appropriate time width to an on-control signal of the semiconductor switch. It superimposes periodically in different phases, and monitors the output of the voltage detection circuit to judge whether or not the ON / OFF device drive circuit has failed.

(2) In claim 2, an on / off device such as a relay or a solenoid valve, a plurality of semiconductor switches which are turned on / off by a control signal connected in series with the on / off device, and are connected in parallel with the on / off device. A voltage detection circuit for detecting a voltage between both ends of the on / off device, and superimposing periodically on-pulse signals of an appropriate time width with different phases on the off-control signal of the semiconductor switch to monitor the output of the voltage detection circuit. By doing so, it is determined whether or not the ON / OFF device drive circuit has failed.

(3) In the third aspect, the above (1) and (2) are used in a failure detection circuit of a vehicle door control circuit. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0009]

FIG. 1 is a circuit block diagram showing first and second embodiments of a failure detection circuit according to the present invention, wherein a relay is used as an example of an on / off device. FIG. 2 shows the first
FIG. 6 is a waveform chart for explaining the operation of the example. In FIG. 1, 11 is a relay comprising a coil 111 and a contact 112, 12 and 13 are semiconductor switches which are turned on and off by a control signal, and 14 outputs "H" when voltage is present at both ends of the coil 111, and when there is no voltage, This is a voltage detection circuit that outputs “L”. However, this embodiment is an example of a system in which a failure in a state where the relay is off is fail-safe. In the embodiment, a transistor is used as a semiconductor switch, and components not related to the present invention are omitted in the drawings.

Failure detection in a state where both the semiconductor switches 12 and 13 are on and the contact 112 of the relay 11 is on will be described below with reference to FIGS. An off signal having a time width t1 as shown in FIG. 2 is superimposed on the control signal of the semiconductor switch 12 every period T. The semiconductor switch 13
The control signal is also superimposed with an off signal having a time width t1 with a phase shifted from that applied to the semiconductor switch 12. However, the time width t1 of the OFF signal is set sufficiently shorter than the operation delay time Toff of the relay described in the conventional example. Therefore, the contact 112 is not turned off by this off signal,
The load driven by the contact 112 is not affected. The average voltage at both ends of the coil 111 is reduced by adding the off signal, but the period T is set so that the average voltage does not affect the operation of the relay 11.

When the semiconductor switches 12 and 13 are both on, a voltage is applied to both ends of the coil 111. When either of them is turned off, no voltage is applied to both ends of the coil 111.
Therefore, when the semiconductor switches 12 and 13 are normal, the output of the voltage detection circuit 14 is a pulse having an average period T / 2 as shown in FIG. Considering the case where the semiconductor switch 12 has a short-circuit fault at the time shown in FIG. 2, the semiconductor switch 12 is turned on regardless of the control signal, and the output of the voltage detection circuit 14 after the fault is cycled as shown in FIG. It becomes a T pulse.

Considering the case where the semiconductor switch 12 has an open fault at the time shown in FIG.
Is turned off irrespective of the control signal, the output of the voltage detection circuit 14 after the failure is fixed at "L" as shown in FIG. As described above, the output of the voltage detection circuit 14 becomes a pulse having the average period T / 2 only when both the semiconductor switches 12 and 13 are normal. Therefore, if the output of the voltage detection circuit 14 is monitored, even if only one semiconductor switch has failed, the failure can be promptly detected, so that the reliability is not reduced. If the semiconductor switch 13 is turned off after the failure is detected, the contact 112 is turned off, so that there is no problem in terms of fail-safe. Further, in order to detect a failure by the output pulse signal of the voltage detection circuit 14, the voltage detection circuit 1
4 can be detected as a failure even when the output fails and the output is fixed.

FIG. 3 is a waveform chart for explaining the operation of the second embodiment. Hereinafter, according to FIGS. 1 and 3, when the semiconductor switches 12 and 13 are both off, the contact 11 of the relay 11
A description will be given of the failure detection in a state where 2 is off.
The time width t as shown in FIG.
One ON signal is superimposed every period T. The control signal of the semiconductor switch 13 is also superimposed with the ON signal of the time width t1 with a phase shifted from that applied to the semiconductor switch 12.
However, the time width t1 of the ON signal is set to be sufficiently shorter than the operation delay time Ton of the relay described in the conventional example. Therefore, the contact 112 is not turned on by this ON signal, and the load driven by the contact 112 is not affected. Also, by adding this ON signal, the coil 111
The period T is set so that the average voltage at both ends increases without affecting the operation of the relay 11. When the semiconductor switches 12, 13 are normal, the semiconductor switches 12, 1
3 are not turned on at the same time, the voltage detection circuit 14
Is fixed at "L" as shown in FIG.

Considering that the semiconductor switch 12 is short-circuited at the time shown in FIG. 3, since the semiconductor switch 12 is turned on regardless of the control signal, the output of the voltage detection circuit 14 after the failure is as shown in FIG. Thus, a pulse having a period T is obtained. Considering the case where the semiconductor switch 12 has an open failure at the time shown in FIG. 3, the semiconductor switch 12 is turned off regardless of the control signal, so that the output of the voltage detection circuit 14 after the failure is as shown in FIG. "L" is fixed.

As described above, the output of the voltage detection circuit 14 becomes a pulse having a period T only when the semiconductor switch 12 has a short-circuit fault. Therefore, if the output of the voltage detection circuit 14 is monitored, a short-circuit fault, which is a failure mode that is not fail-safe, can be promptly detected, so that reliability is not reduced. Further, since the output of the voltage detection circuit 14 has the same waveform in a normal state and in an open fault, an open fault cannot be detected when the contact 112 is off, but the open fault is a fail-safe failure mode, so that There is no problem even if a failure is detected when the contact 112 is turned on in advance.

A door control circuit used in a train or the like sometimes opens and closes a door by turning on and off an electromagnetic valve. However, since the door must not be opened during traveling, the solenoid valve is not controlled. Drive circuits require reliability and fail-safe. FIG. 4 is a circuit block diagram showing an embodiment in which the failure detection circuit according to the present invention is applied to an electromagnetic valve drive circuit for door control. In FIG. 4, reference numeral 41 denotes a solenoid valve. By turning on and off the semiconductor switches 12 and 13, the electromagnetic valve 41 is turned on and off to open and close the door. Components having the same symbols as those in FIG. 1 are the same as those in FIG. Components not related to the present invention are omitted in the drawings.

However, this embodiment is an example of a system in which a failure in a state where the solenoid valve is turned off is fail-safe. In this case as well, as described above, the semiconductor switch 1
A fault can be detected by superimposing the ON or OFF signal of the time width t1 on the control signals 2 and 13 with the phase shifted for each cycle T. At this time, similarly to the above, the time width t1 needs to be set sufficiently shorter than the operation delay times Ton and Toff of the solenoid valve so that the solenoid valve does not actually operate, but the solenoid valve controls air and the like. Therefore, since the operation delay time is usually longer than that of the relay, there is a feature that the failure detection can be performed more easily.

In the above embodiment, the case where two semiconductor switches are used is described. However, the same effect can be obtained when three or more semiconductor switches are used. Further, the case where a transistor is used for a semiconductor switch and a relay and an electromagnetic valve are used for an on / off device has been described, but the present invention is not limited to this. In the above-described embodiment, the system in which the failure when the on-off device is off is fail-safe is described. However, in the case of the system in which the failure when the on-off device is on is fail-safe, the semiconductor switch 12 is used. , 13 are connected in parallel instead of in series, so that a fault can be detected by a method applying the above embodiment.

[0019]

As described above, according to the failure detection circuit of the present invention, when a failure in a failure mode that has a fatal effect on the system occurs in one semiconductor switch, the failure can be reliably and promptly detected. Since detection is possible, fail-safe protection of a drive circuit of an ON / OFF device such as a relay or a solenoid valve can be performed, and an operation time in a single system that reduces reliability can be shortened. It is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing first and second embodiments of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a waveform chart for explaining the operation of the second embodiment of the present invention.

FIG. 4 is a circuit block diagram showing a third embodiment of the present invention.

FIG. 5 is a circuit block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Relay 12, 13 Semiconductor switch 14 Voltage detection circuit 41 Solenoid valve 111 Coil 112 Contact

Claims (3)

[Claims] 1. A failure detection circuit for an on / off device driving circuit for driving a load on / off, comprising: an on / off device such as a relay or a solenoid valve; and a plurality of semiconductor switches that are turned on / off by a control signal connected in series with the on / off device. A voltage detection circuit that detects a voltage between both ends of the on / off device connected in parallel with the on / off device, and periodically outputs off pulse signals of a predetermined time width at different phases to the on control signals of the plurality of semiconductor switches. A failure detection circuit configured to superimpose and monitor an output of the voltage detection circuit to determine whether an ON / OFF device and an ON / OFF device drive circuit including a plurality of semiconductors are faulty. 2. The fault detection circuit according to claim 1, wherein an on-pulse signal having a predetermined time width is periodically superimposed on an off-control signal of said plurality of semiconductor switches at different phases. 3. The failure detection circuit according to claim 1, wherein the failure detection circuit is applied to a failure detection circuit of a vehicle door control circuit.