JP2001053595A - Drive device for inductive load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely interrupt a load current, even if an arc-extinguishing circuit for absorbing a flyback voltage fails and the short-circuit fault of a switching element for energizing occurs. SOLUTION: Two transistors Tr1 and Tr2 are provided on energizing route to a coil L1 and the arc-extinguishing circuits 14 and 16 are provided on routes on both sides of the transistor Tr1 respectively. In the circuits, the arc- extinguishing circuit 14 normally absorbs the flyback voltage, however, when the open fault of the arc-extinguishing circuit 14 occurs, the arc-extinguishing circuit 16 absorbs the flyback voltage by making a current flow through the transistor Tr2 to the coil L1. Also, even it the short-circuit fault of the transistor Tr2 is caused by the operation of the arc-extinguishing circuit 16, since the transistor Tr1 is protected from the flyback voltage by the arc-extinguishing circuit 16, energizing to the coil L1 can be interrupted by the transistor Tr1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for an inductive load which drives an inductive load by turning on / off a switching element provided on a current supply path from a DC power supply to the inductive load.

[0002]

2. Description of the Related Art Conventionally, in a driving device for driving an inductive load such as a coil of a relay or a solenoid of an electromagnetic valve, a switching element such as a bipolar transistor or a MOSFET is provided on an energizing path from a DC power supply to the inductive load. And turning it on and off to switch between energization and non-energization of the inductive load.

In this type of driving device, when the switching element is turned off to cut off the current supply to the inductive load, a high voltage (so-called flyback voltage) having a polarity opposite to that of the current flowing through the inductive load is applied. ) Occurs. Then, when this flyback voltage is applied to the switching element as it is,
The switching element is deteriorated or destroyed.

[0004] For this reason, in this type of driving device, usually,
An arc-extinguishing circuit is provided in parallel with the inductive load, and the arc-extinguishing circuit clamps the flyback voltage generated when the current to the inductive load is cut off to a predetermined voltage or less set according to the withstand voltage of the switching element. Thus, the switching element is protected from the flyback voltage.

[0005]

However, in the prior art, the flyback voltage is absorbed by using one arc-extinguishing circuit provided in parallel with the inductive load.
If the arc-extinguishing circuit is deteriorated and becomes an open state, a voltage exceeding the withstand voltage is applied to the switching element when the current supply to the inductive load is cut off, and the switching element is immediately broken down.

[0006] When the switching element fails in this way, when the switching element fails in the open state, it is only impossible to supply current to the inductive load. If current can be supplied, driving of the inductive load can be continued, but when the switching element fails due to short-circuit,
It becomes impossible to cut off the current supply to the inductive load,
Current continues to flow through the inductive load, which in turn causes failure of the inductive load itself.

The present invention has been made in view of such a problem, and a drive device for an inductive load that drives an inductive load by turning on / off a switching element provided on a current supply path to the inductive load. In the above, the current flowing through the inductive load can be cut off even if the switching element is short-circuited due to the failure of the arc-extinguishing circuit for flyback voltage absorption provided in parallel with the inductive load. With the goal.

[0008]

According to a first aspect of the present invention, there is provided a driving apparatus for an inductive load.
Two switching elements (first switching element) connected in series on a power supply path for supplying power from a DC power supply to an inductive load.
(A switching element, a second switching element), and one end is connected to an energizing path between the first switching element and the inductive load on the inductive load side and an energizing path between the first switching element and the second switching element, respectively. And two arc extinguishing circuits (a first arc extinguishing circuit and a second arc extinguishing circuit) whose other ends are connected to an energizing path on the opposite side of the inductive load from the first switching element.

For this reason, when energizing the inductive load, it is only necessary to turn on the two switching elements in response to a command from the outside. Conversely, when energizing the inductive load is interrupted, externally, In this case, at least one of the switching elements may be turned off in response to the command. When the power supply to the inductive load is cut off, a flyback voltage is generated by the energy stored in the inductive load at the time of power supply. However, since the flyback voltage is absorbed by the first arc extinguishing circuit, It is possible to prevent the switching element, which has been turned off when the power supply to the load is cut off, from being deteriorated or destroyed by the flyback voltage.

Further, if the first arc extinguishing circuit fails for some reason (for example, a current flowing at the time of voltage clamping) and becomes open, the flyback voltage cannot be absorbed by the first arc extinguishing circuit. In the present invention, since the arc-extinguishing circuit (second arc-extinguishing circuit) is also provided in the energizing path between the first switching element and the second switching element, the flyback voltage is reduced by the second arc-extinguishing circuit. Can be absorbed. Therefore, even when the second switching element is turned off when the power supply to the inductive load is cut off, it is possible to prevent the second switching element from being deteriorated or destroyed by the flyback voltage.

On the other hand, since the second arc extinguishing circuit is connected in parallel to the energizing path from the first switching element to the inductive load, when the first arc extinguishing circuit fails and becomes open. By flowing a current to the inductive load via the first switching element, the flyback voltage is absorbed. For this reason, when all the switching elements are turned off when the power supply to the inductive load is cut off, the second arc extinguishing circuit forces the current to flow through the first switching element. One switching element may be degraded.

As described above, even if the first switching element is deteriorated and short-circuited, the second switching element is protected from the flyback voltage by the operation of the second arc extinguishing circuit. The first switching element and the second switching element are not short-circuited, and the inductive load is not continuously energized, so that energization to the inductive load can be reliably cut off.

Therefore, according to the inductive load driving device of the present invention, the inductive load can be continuously driven even when the first arc extinguishing circuit is in the open state. Even if the first switching element is short-circuited due to a circuit failure, the energization to the inductive load is cut off to prevent the inductive load itself from being broken by continuous energization to the inductive load. Can be.

Here, as the two switching elements (first switching element and second switching element), any switching element used to switch between energization and non-energization to an inductive load may be used. And may be a MOSFET or a bipolar transistor. And among them, MOSFET is
On-resistance is smaller than that of bipolar transistors,
It is possible to reduce the power loss when the inductive load is energized.

However, in the present invention, if a MOSFET is used for each of the switching elements, for example, immediately after the main power switch is turned on and the DC power supply is connected to the current supply path to the inductive load, the MOSFET is temporarily turned off. In some cases, the inductive state is turned on and current flows to the inductive load. This is because the on / off state of the MOSFET is not stable immediately after the power supply is connected until the charge is accumulated in the parasitic capacitance, and the MOSFET cannot be reliably kept in the off state.

Therefore, as the two switching elements, a MOSFET may be used for one switching element and a bipolar transistor may be used for the other switching element.

That is, according to this configuration, even if the switching element formed of the MOSFET is turned on immediately after the DC power supply is connected to the current supply path to the inductive load,
With the other switching element composed of a bipolar transistor, the current supply path to the inductive load can be reliably cut off, and current can be prevented from flowing to the inductive load when power is supplied to the drive device. Become.

According to the second aspect of the present invention, the power loss when the inductive load is energized is minimized while preventing the current from flowing to the inductive load when power is supplied to the driving device. You can do it.

Next, the inductive load driving device according to claim 3 is different from the driving device according to claim 1 or 2 in that
Detecting means for detecting a potential of an energizing path between the first switching element and the inductive load and a potential of an energizing path between the second switching element and the first switching element are provided. At the time of energization start, the control means turns on the second switching element and the first switching element in sequence at a predetermined time interval, and at the time of cutoff of current supply to the inductive load, the control means sets the second switching element and the first switching element. Are turned off, and when the control means sequentially turns on each switching element at the start of energization to the inductive load, the failure determination means determines each switching element from the potential of each energization path detected by the detection means. Is determined.

Therefore, according to the present invention (claim 3), the inductive load can be continuously driven when the first arc extinguishing circuit fails and is opened, and the first arc extinguishing circuit fails. As a result, even if the first switching element is short-circuited, not only can the current to the inductive load be cut off, but also the failure of the first or second switching element can be determined when the current to the inductive load starts. When the first or second switching element fails, the user is immediately notified of the failure and prompts the user for inspection and repair, or when the first or second switching element fails, the inductive load is reduced. It is possible to prohibit the energization and to more reliably prevent the inductive load from being energized continuously.

The reason why the failure determination means can determine the failure of each switching element from the potential of each energizing path detected by the detection means is as follows.

That is, first, before the control means turns on the second switching element, if each switching element is normal, the potential of each of the above-mentioned energizing paths is set to the level of the energized state connected through each arc extinguishing circuit. Path (the conducting path on the opposite side of the inductive load from the first transistor) has the same potential,
If the second transistor has already been short-circuited, the potential of the current path between the second switching element and the first switching element is reduced by the potential of the power supply connected to the second switching element on the side opposite to the first switching element. Potential. For this reason, before turning on the second switching element, the control means can determine the short-circuit failure of the second switching element from the potential of each of the energizing paths.

Next, when the control means turns on the second switching element in a state where it is determined that the second switching element is not short-circuited, if each switching element is normal, the second switching element is turned off. Only the potential of the conduction path between the element and the first switching element changes, and the potential of the conduction path between the first switching element and the inductive load does not change. However, at this time, if the second switching element has an open failure, the second switching element and the first
The potential of the current path between the switching element and the switching element does not change,
Conversely, if the first switching element has a short-circuit fault, the potential of the current path between the first switching element and the inductive load changes. Therefore, when the control means turns on the second switching element, the open failure of the second switching element and the short-circuit failure of the first switching element can be determined from the potential of each of the energizing paths.

Next, when it is determined that the second switching element is normal and the first switching element is not short-circuited, the control means turns on the first switching element. If the first switching element does not have an open failure, the potential of the conduction path between the first switching element and the inductive load changes, but if the first switching element has an open failure, the first switching element and the inductive load will not change. The potential of the current path between the load and the conductive load does not change. Therefore, when the control unit turns on the first switching element, it is possible to determine the open failure of the first switching element from the potential of each of the energizing paths.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an electric circuit diagram showing the configuration of an automatic starting device 10 for automatically starting an automobile engine, independently of a key operation of an ignition key by a driver.

The automatic starter 10 according to the present embodiment is mounted on a commercial manual transmission vehicle such as a bus or a taxi. After the engine control device (not shown) automatically stops the engine during idling operation of the engine, the driver starts the operation. Predetermined starting operation (for example, depressing a clutch pedal, etc.)
Is executed to automatically start the engine.

For this reason, the automatic starter 10 is provided with a coil (inductive load) L1 for conducting / cutting off a contact SW1 of a starter relay 8 provided on a current supply path from the battery 2 to the starter motor 6. From the battery 2 through the starter position ST in the key box 4, the coil L
An energization path for flowing a current through a path different from the energization path leading to No. 1 is formed.

That is, the contact SW1 of the starter relay 8
Is provided on an energization path from the positive electrode side of the battery 2 to the starter motor 6 as in a general vehicle, and energization to the coil L1 for driving the starter relay 8 is also performed.
When the driver inserts the ignition key into the key box 4 in the vehicle compartment and manually switches the switch in the key box 4 to the starter position ST so that the driver can perform the key operation as in a general vehicle. And coil L
1 is directly connected to the positive electrode side of the battery 2 via the key box 4 so that a current flows through the coil L1. In the present embodiment, the switch in the key box 4 is further set to the ignition position IG. In order to enable the automatic starter 10 to automatically energize the coil L1 even when the automatic starter 10 is switched to the state shown in FIG. An energizing path is formed in which power is supplied from the key box 4 and current flows through the coil 1 when the switching is being performed.

In the automatic starter 10, the power supply path to the coil L 1 is a P-channel MO whose source is connected to the positive electrode side of the battery 2 via the key box 4.
An SFET (hereinafter simply referred to as a transistor) Tr1, a PNP-type bipolar transistor (hereinafter simply referred to as a transistor) Tr2 having an emitter connected to the drain of the transistor Tr1, a diode D1 having a cathode connected to the coil L1, and a collector of the transistor Tr2 And a resistor R1 connecting the anode of the diode D1.

Note that the transistor Tr1 corresponds to the second switching element of the present invention, and the transistor Tr2 corresponds to the first switching element of the present invention. The resistance R1
When the output terminal connecting the automatic starter 10 and the coil L1 is erroneously grounded, the transistors Tr1 and T1
r2, the current flowing through each transistor Tr1,
The diode D1 is for protecting Tr2 from overcurrent, and is for enabling detection of engine start by manual operation of the driver.

On the other hand, the negative electrode side of the battery 2 is grounded to the ground line, and a terminal opposite to the starter relay 8 of the starter motor 6 and a terminal opposite to the key box 4 and the automatic starter 10 of the coil L1. , Respectively, are grounded to a ground line.

For this reason, the switch in the key box 4 is manually operated to the starter position ST, or the switch in the key box 4 is set to the ignition position IG.
Each transistor Tr in the automatic starter 10 in the state
1, when Tr2 is turned on, an energization path from the battery 2 to the coil L1 is formed, a current flows through the coil L1, and the contact SW1 of the starter relay 8 is turned on. When the contact SW1 of the starter relay 8 is turned on, an energization path from the battery 2 to the starter motor 6 is formed, a current flows through the starter motor 6, the starter motor 6 rotates, and an engine (not shown) is started. Will be.

By supplying a current to the coil L1 of the starter relay 8, the starter motor 6 can be rotated to start the engine. However, after the engine is started, the starter motor 6 is stopped. The switch in the key box 4 is manually operated by the driver to change the start position ST to the ignition position IG.
Or the respective transistors Tr1 and Tr2 in the automatic starter 10 are switched from on to off, a flyback voltage (a negative voltage lower than the ground potential) as indicated by a dotted line in FIG. High voltage).

FIG. 2 shows a state in which the transistors Tr1 and Tr2 in the automatic starter 10 are turned on and the coil L1 is energized.
3 shows a potential change at a point C on the cathode side of the diode D1 when the current supply to 1 is cut off.

When the flyback voltage is applied to the collector of the transistor Tr2 as it is, an overvoltage is applied to the transistors Tr1 and Tr2 in the automatic starter 10, and the two transistors Tr1 and Tr2 are deteriorated or destroyed. become.

Therefore, in order to absorb the flyback voltage, an energizing path between the collector of the transistor Tr2 and the resistor R1 in the automatic starter 10 and a path between the drain of the transistor Tr1 and the emitter of the transistor Tr2 are used. Arc extinguishing circuits 14 and 16 each composed of a diode having one end grounded to a ground line and a Zener diode are connected to the energization paths.

That is, each of the arc-extinguishing circuits 14 and 16 includes Zener diodes ZDc and ZDe whose drains are respectively connected to the collector and emitter of the transistor Tr2, an anode connected to the ground line, and a cathode connected to the Zener diodes ZDc and ZDe. And diodes Dc and De respectively connected to the cathode.

Each of these arc extinguishing circuits 14 and 16
As shown by the solid line in FIG. 2, when the power supply to the coil L1 is cut off, the flyback voltage applied to the collector or the emitter of the transistor Tr1 is reduced by the Zener diode ZDc,
It is clamped below a predetermined voltage determined by the breakdown voltage of ZDe and the forward voltage (so-called VF: about 0.7 V) of the diodes Dc and De.

Incidentally, Zener diodes ZDc, ZD which determine the clamp voltage by these arc extinguishing circuits 14, 16 respectively.
The breakdown voltage of e is set in consideration of the breakdown voltage between the collector and the emitter of each of the transistors Tr1 and Tr2 so that the transistors Tr1 and Tr2 are not deteriorated by the flyback voltage.

As described above, in this embodiment, the arc extinguishing circuits 14 and 16 are provided on the collector side and the emitter side of the transistor Tr2, respectively.
Normally, when no failure occurs in the transistor T16, the flyback voltage generated when the power supply to the coil L1 is cut off is the transistor T
It is absorbed by an arc-extinguishing circuit 14 (corresponding to a first arc-extinguishing circuit of the present invention) comprising a diode Dc and a Zener diode ZDc provided on the collector side of r2 (that is, on the coil L1 side). When the diode Dc or the Zener diode ZDc constituting the arc extinguishing circuit 14 fails and the arc extinguishing circuit 14 is opened, the transistor Tr
An arc-extinguishing circuit 16 (corresponding to a second arc-extinguishing circuit of the present invention) including a diode De and a Zener diode ZDe provided on the emitter side of the second transistor 2 supplies a current to the coil L1 via the transistor Tr2, thereby providing a flywheel. Absorb the back voltage.

Therefore, in the automatic starting device 10 of the present embodiment, one of the arc extinguishing circuits 14 that absorbs the flyback voltage generated when the power supply to the coil L1 is cut off has an open fault, and the flyback voltage cannot be absorbed. Even if the other arc extinguishing circuit 16 operates, the flyback voltage can be absorbed, and each transistor Tr
1, Tr2 can be protected from the flyback voltage generated when the power supply to the coil L1 is cut off.

The arc extinguishing circuit 16 which operates when one of the arc extinguishing circuits 14 has an open fault has a transistor Tr.
Since the flyback voltage is absorbed by flowing a current through the coil L1 through the coil 2, the operation of the arc extinguishing circuit 16 may deteriorate the transistor Tr2 and cause a short circuit. Even if it becomes the state, the flyback voltage can be absorbed by the arc extinguishing circuit 16, so that the transistor Tr1
Is not deteriorated by the flyback voltage.

For this reason, in the automatic starting device 10 of this embodiment, when the arc extinguishing circuit 14 fails, the transistors Tr1 and Tr2 are simultaneously short-circuited, and the coil L1 is continuously energized. The problem that the starter motor 6 keeps rotating does not occur, and even if one of the two transistors Tr1 and Tr2 fails and becomes short-circuited, the other transistor supplies power to the coil L1. It can be stopped reliably.

Next, the automatic starter 10 of the present embodiment includes:
A drive circuit 12 for turning on / off each of the transistors Tr1 and Tr2, and a well-known CPU, RAM, ROM and the like for controlling the on / off state of each of the transistors Tr1 and Tr2 via the drive circuit 12 Microcomputer (hereinafter simply referred to as CPU) 20;
A buffer circuit 18 is provided as detection means for inputting, into the CPU 20, a potential on an energization path to the coil L1 formed in the automatic starter 10.

The buffer circuit 18 includes a transistor T
An energizing path between the drain of r1 and the emitter of the transistor Tr2 (point a), an energizing path between the resistor R1 and the anode of the diode D1 (point b), and a diode D1
The potential of an energizing path (point c) between the cathode and the coil L1 is set as monitor signals Sa, Sb, Sc, respectively, by the CPU.
20 is composed of three buffer circuits Ba, Bb, and Bc.

During operation of the engine, the CPU 20 monitors the engine state through communication with the engine control device, and monitors the running state of the vehicle based on detection signals from various sensors mounted on the vehicle. From the running state of the vehicle, the running history of the vehicle, and the like, whether or not engine stop conditions are satisfied, such as the engine is currently in an idle state after warm-up, and the vehicle is expected to stop for a predetermined time or more. By performing an engine stop condition determination process, if it is determined in this determination process that the engine stop condition is satisfied, by outputting an engine stop permission signal to the engine control device,
The control of fuel injection to the engine on the engine control device side is prohibited, and the engine is stopped.

When the CPU 20 causes the engine control device to stop the engine, the driver
For example, it is determined whether or not an engine start command has been input by depressing a clutch pedal. When it is determined that an engine start command has been input, the monitor signals Sa, input from the buffer circuits Ba, Bb, Bc are determined. S
Based on b and Sc, the transistors Tr1, Tr2 and the diode D1 on the current supply path to the coil L1 are determined to be faulty, and the transistors Tr1 and Tr2 are turned on in order, so that a current flows through the coil L1 and the starter motor 6 is turned on. Drive and execute an engine start control process. Hereinafter, the engine start control process will be described with reference to the flowchart shown in FIG.

The engine start control process is executed when a driver starts inputting an engine start command.
That the potential at point C on the cathode side is at the low level (ground potential) (in other words, the current has already flowed through the coil L1 by the key operation by the driver, and the starter motor 6 is not rotating). Is a process executed on condition that

In the engine start control process,
As shown in FIG. 3, first, the transistors Tr1 and Tr2
Before turning on, the monitor signals Sa to Sc input from the buffer circuits Ba to Bc are checked in S110 (S represents a step), and in S120, the monitor signals Sa to Sc are Determine whether it is normal.

That is, as shown in FIG. 4, in a state where both the transistors Tr1 and Tr2 are turned off (failure determination section A), if the transistors Tr1 and Tr2 are normal, the monitor signals Sa to Sc become: When the transistors Tr1 and Tr1 are all at the Low level and the transistor Tr1 is short-circuited, the monitor signal Sa becomes the High level (battery voltage).
Before turning on Tr2, in S120, monitor signal Sa
It is determined whether or not the transistor Tr1 has a short-circuit failure by determining whether or not all the signals Sc are at the low level.

Then, in S120, the monitor signals Sa to
When it is determined that all Sc are normal, in the next S130, the driving signal of the transistor Tr1 is output to the driving circuit 12 to turn on the transistor Tr1,
Move to S140.

In S140, as in S110, the monitor signals Sa to S input from the respective buffer circuits Ba to Bc are used.
c is checked, and in S150, it is determined whether each of the monitor signals Sa to Sc is normal.

That is, as shown in FIG. 4, in a state where only the transistor Tr1 is turned on and the transistor Tr2 is held in the off state (failure determination section B), if the transistors Tr1 and Tr2 are normal, the monitor signal Sa Only the high level (battery voltage) and the other monitor signals Sb and Sc at the low level. At this time, if the transistor Tr2 has a short circuit fault, the monitor signals Sb and S
c also becomes High level, and conversely, the transistor T
If r1 has an open fault, all monitor signals
Therefore, in the engine start control process, even when only the transistor Tr1 is driven to the ON state, the monitor signals Sa to Sc are checked, and all the monitor signals Sa to Sc are normal (Sa: High, Sb, S
c: Low) to determine whether the transistor Tr2 has a short-circuit fault or the transistor Tr1 has an open fault.

Then, in S150, the monitor signals Sa to
When it is determined that all Sc are normal, in the next S160, a drive signal for the transistor Tr2 is output to the drive circuit 12 to turn on the transistor Tr2.
The process moves to S170.

In S170, monitor signals Sa to Sc input from the buffer circuits Ba to Bc are checked, as in S110 and S140, and in S180, whether these monitor signals Sa to Sc are normal or not is checked. Judge.

That is, as shown in FIG. 4, when both the transistor Tr1 and the transistor Tr2 are turned on (failure determination section C), each of the transistors Tr1 and Tr2 is turned off.
2 is normally turned on, and if a current flows through the coil L1 via the resistor R1 and the diode D1, the monitor signals Sa to Sc all go to the high level (battery voltage). If D1 has a short-circuit fault, only the monitor signal Sc is held at the low level, and if the transistor Tr2 has an open fault, both the monitor signals Sb and Sc are held at the low level.
In the engine start control process, the transistors Tr1, Tr
2 are both turned on, the monitor signal Sa
To Sc, and all monitor signals Sa to Sc
By judging whether it is High level,
It is checked whether the diode D1 has a short-circuit fault or the transistor Tr2 has an open fault.

Then, also in S180, each monitor signal Sa
When it is determined that all of Sc are normal, in S190, driving of the transistors Tr1 and Tr2 (in other words, energization of the coil L1) is continued to drive the starter motor 6 until the engine is started. When the engine is started, the driving of each of the transistors Tr1 and Tr2 is stopped.
Then, the energization control for the coil L1 is executed, and the process ends. In step S190, not only the energization of the coil L1 is continued until the engine is started, but also a start permission signal is output to the engine control device to restart the fuel injection control on the engine control device side. .

On the other hand, if it is determined in S120, S150, or S180 that the monitor signals Sa to Sc are abnormal, the process proceeds to S200, where the transistors Tr1, T
r2 is turned off, the control of energizing the coil L1 is stopped, and the details of the failure of the transistor Tr1, Tr2 or the diode D1 determined in S120, S150, or S180 are notified to the driver, and the process ends.

In this embodiment, in the above-described engine start control processing, the transistors Tr1 and Tr2 are turned on to energize the coil L1.
The processes of steps S60 and S190 function as the control means of the present invention (claim 3), and determine the failure of the transistors Tr1 and Tr2 based on the monitor signals Sa to Sc. S executed to
110, S120, S140, S150, S170, S
The processing of S180 and S200 functions as a failure determination unit of the present invention (claim 3).

As described above, in the automatic starter 10 of the present embodiment, the energization / de-energization of the coil L1 which is an inductive load is controlled on the energization path formed for automatically controlling the energization using the CPU 20. , A pair of transistors Tr1 and Tr comprising a MOSFET and a bipolar transistor
2 and the transistor Tr2 on the coil L1 side.
Each current path connected to the collector and emitter of
Arc extinguishing circuits 14 and 16 for absorbing a flyback voltage generated when the power supply to the coil L1 is cut off are provided.

Therefore, according to the present embodiment, even if one of the arc-extinguishing circuits 14 that normally operates fails, the flyback voltage can be absorbed by the other arc-extinguishing circuit 16, so that the coil L1 is energized. The control can be continued and the operation of the arc extinguishing circuit 16 allows the transistor Tr
2 can protect the transistor Tr1 from flyback voltage even if a short-circuit fault occurs in the transistor T2.
The power supply to the coil L1 can be reliably shut off via r1, and the problem that the coil L1 is continuously energized and the starter motor 6 continues to rotate can be prevented.

Further, the CPU 20 starts the operation when the engine is started.
In addition to turning on the transistors Tr1 and Tr2 to energize the coil L1, at the time of energization, the above-described engine start control process is performed to thereby control the transistors Tr1 and Tr2 and the diode provided on the energization path to the coil L1. The failure of D1 is determined, and when the failure is determined, energization of the coil L1 is prohibited, and the driver is notified of the fact.

For this reason, by continuing the energization control (engine start control) for the coil L1 in a state where some elements on the energization path to the coil L1 are faulty, other non-faulty ones do not fail. It is also possible to prevent the element from malfunctioning and the coil L1 from being continuously energized. Therefore, according to the present embodiment, a failure such as the starter motor 6 continuing to rotate can be reliably prevented by continuous energization of the coil L1, and vehicle safety can be ensured.

In this embodiment, a PNP-type bipolar transistor is used as the transistor Tr2 as the first switching element, and a P-channel MOSFET having a small on-resistance is used as the transistor Tr1 as the second switching element. Therefore, as described above, even if the transistor Tr1 formed of a MOSFET is temporarily turned on immediately after the power is turned on from the battery 2 to the automatic starter 10, the transistor Tr
2 is turned off to prevent a current from flowing through the coil L1. For this reason, according to the present embodiment, one of the two switching elements (transistors) is a MOSFET.
By using this, it is possible to prevent the starter motor 6 from malfunctioning immediately after the power is supplied to the automatic starter 10 while suppressing the power loss that occurs when the coil L1 is energized.

As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and can take various forms.

For example, in the above embodiment, each arc extinguishing circuit 1
Each of the arc extinguishing circuits 14 and 16 is composed of a Zener diode and a diode, respectively.
For example, as shown in FIG. 5 (a-1), the anode may be connected to the ground line, and the cathode may be constituted only by the diode D0 connected to the current supply path to the coil L0. As shown in 1), it can be configured by a series circuit of a resistor R0 and a capacitor C0.
When the arc extinguishing circuits 14 and 16 are composed of only the diode D0, as shown in FIG.
The flyback voltage generated when the power is cut off is clamped below the forward voltage VF of the diode D0, and the arc extinguishing circuits 14 and 16 are connected to the resistor R0 and the capacitor C0.
5B-2, the flyback voltage generated when the current to the coil L0 is cut off is the current i flowing through the resistor R0 due to the flyback voltage and the resistance value of the resistor R0. Is clamped below the voltage (iR0) determined by

Further, in the above embodiment, the CPU 20 sets the transistors Tr1 and Tr2 at the start of energizing the coil L1.
Although it has been described that when the failure of the coil L1 is determined, the energization to the coil L1 is prohibited. If the driving device for the inductive load does not include such a separate driving system, the two switching elements are used when the power supply to the inductive load (coil L1) is started. When it is determined that one of the transistors (Tr1, Tr2) has failed, the failure is notified to a user such as a driver to urge inspection and repair of the driving device. What is necessary is just to continue as it is.

Further, in the above embodiment, the case where the present invention is applied to the automatic starting device for automatically starting the vehicle-mounted engine has been described. However, according to the present invention, it occurs when the power supply to the inductive load is cut off. When the arc-extinguishing circuit that absorbs the flyback voltage fails, the inductive load can be reliably prevented from being continuously energized and safety can be improved. Then, the present invention can be applied to any device to improve the reliability of the device.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram illustrating a configuration of an entire automatic starting device according to an embodiment.

FIG. 2 is an explanatory diagram illustrating an operation of the arc extinguishing circuit according to the embodiment.

FIG. 3 is a flowchart illustrating an engine start control process executed by a CPU according to the embodiment.

FIG. 4 is an explanatory diagram showing a voltage change of each part of a current supply path to a coil caused by the engine start control process shown in FIG. 3;

FIG. 5 is an explanatory diagram illustrating another configuration example and operation of the arc extinguishing circuit.

[Explanation of symbols]

L1 coil (inductive load), 2 battery (DC power supply), 4 key box, 6 starter motor, 8 starter relay, 10 automatic starter, 12 drive circuit,
14, 16: arc extinguishing circuit, 18: buffer circuit, Tr1 ...
Transistor (MOSFET: second switching element), Tr2 ... Transistor (bipolar transistor: first switching element).

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) GX04

Claims (3)

[Claims] A first switching element provided on an energization path from a DC power supply to an inductive load, for conducting / cutting off the energization path in response to an external command, one end of which is connected to the first switching element; The other end is connected to an energizing path between the inductive load and the first switching element of the inductive load, and the other end is connected to an energizing path between the paths when the inductive load is cut off. And a first arc extinguishing circuit that absorbs the generated flyback voltage. A driving apparatus for an inductive load, comprising: A second switching element that conducts and shuts off in response to a command from the second switching element, and an energizing path between the second switching element and the first switching element, and the first switching element of the inductive load, A second arc extinguishing circuit for absorbing a flyback voltage generated between the paths when the power supply to the inductive load is interrupted, between the opposite side of the inductive load and a driving path of the inductive load. . 2. The inductive load driving device according to claim 1, wherein one of the first and second switching elements comprises a MOSFET, and the other comprises a bipolar transistor. 3. A potential of a current path between the first switching element and the inductive load and a potential of a current path between the second switching element and the first switching element are detected. Detecting means for turning on the second switching element and the first switching element in order at a predetermined time interval at the start of energization to the inductive load, and turning off the second switching element at energization cutoff to the inductive load; And control means for turning off the first switching element; and when the control means sequentially turns on the switching elements at the start of energization to the inductive load, the potential of each energization path detected by the detection means 3. The inductive load drive according to claim 1, further comprising: a failure determining unit that determines a failure of each of the switching elements. apparatus.