JP3314922B2 - Load drive system and fault detection method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load drive system and a failure detection method thereof. The present invention relates to a load drive system provided in a control unit (ECU) and a failure detection method thereof.

[0002]

2. Description of the Related Art Conventionally, for example, in a vehicle such as an automobile, an electromagnetic device having a semiconductor switching element or the like built therein,
Generally, driving of a load such as a motor and a lamp is performed by an electronic control unit (ECU) installed at a position physically separated from the load on the vehicle.

When a load is driven in a system having such a configuration, a drive circuit element for turning on / off the load may be incorporated in the ECU. There arises a problem that the wire diameter and the connector size of the electric wire connecting the ECU and the load increase. In addition, when driving the load is controlled by a general PWM (pulse width modulation), a load current intermittently flows at a high frequency on a wire harness connecting the ECU and the load. There is a problem that electromagnetic field noise is generated from the harness and adversely affects on-vehicle devices around the harness.

Therefore, conventionally, for such a load having a large load current, the load and the drive circuit element are integrally formed, and the load having the integrated drive circuit element is connected to the ECU by a wire harness. Then, the ECU outputs only the operation control signal of the load and does not supply power for driving, thereby suppressing the amount of current flowing through the wire harness itself, thereby generating from the wire harness. It is common to prevent electromagnetic field noise from occurring.

[0005] However, in-vehicle equipment provided in a vehicle is generally required to have a fail-safe function such as detecting a failure state and issuing an alarm. Therefore, as described above, the load and the drive circuit element are integrated. In the case of an in-vehicle device configured as described above, a failure diagnosis circuit is provided in the in-vehicle device,
It is necessary that the occurrence of a failure can be recognized by the ECU.

FIG. 11 is a diagram showing a circuit configuration in a conventional load drive system in which a load and a drive circuit for driving the load are provided separately.

As shown in FIG. 1, the ECU 10 and the in-vehicle device 20 have independent power supply lines, and include a control unit 101 built in the ECU 10 and a switching element 203 built in the in-vehicle device 20. Is
The connection is made via a wire harness 102. A failure diagnosis circuit 201 built in the on-vehicle device 20 is connected to the switching element 203 and a load 202 such as a motor, and outputs a signal representing the result of the failure diagnosis for the switching element 203 or the load 202 to a wire. A circuit configuration that can be transmitted to the control unit 101 of the ECU 10 via the harness 204 is provided, thereby realizing a fail-safe function against occurrence of a failure.

[0008]

However, FIG.
In the conventional circuit configuration shown in FIG. 1, the load 20 needs to include the failure diagnosis circuit 201 and the wire harness 204 for transmitting the output signal of the failure diagnosis circuit 201 to the ECU 10 is required. Since the number of electronic components and the number of wire harnesses that need to be built in the device 20 increase, it becomes an obstacle in reducing costs. Further, the failure diagnosis circuit 201 and the wire harness 2
Since the circuit 04 itself is added as a cause of failure, it is not a preferable circuit configuration from the viewpoint of improving the reliability of the entire system.

Accordingly, an object of the present invention is to provide a low-cost and highly reliable load drive system and a method for detecting a failure thereof.

[0010]

To achieve the above object, a load drive system and a failure detection method according to the present invention have the following features.

That is, in a load drive system including a load unit and a control unit for controlling the load unit, the load unit is connected to an input side of a load drive element (such as a switching element) for driving a load such as a motor. An inverting circuit for inverting the logical level of the electric signal is provided, a feedback resistor is connected between the output side of the load driving element and the input side of the inverting circuit, and further, the output side of the load driving element,
A pull-down resistor is connected to the ground side. The control unit provides a control signal for controlling the driving of the load to a signal line connecting the input side of the inverting circuit and the control unit (ECU). It is characterized by detecting.

According to this configuration, the voltage level of the control signal on the signal line can be set to a value related to the terminal voltage on the output side of the load driving element. By monitoring, failure diagnosis of the load, the load driving element, and the signal line becomes possible.

According to such a load driving system, there is no need to provide a dedicated circuit for failure diagnosis required in the conventional circuit configuration described above, and the number of wire harnesses connecting the control unit and the load unit is reduced. Therefore, a reduction in member cost and a reduction in the failure rate due to a reduction in the number of members are realized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a load drive system according to the present invention will be described in detail with reference to the drawings as an embodiment applied to a typical automobile.

[First Embodiment] FIG. 1 is a diagram showing a circuit configuration of a load drive system according to a first embodiment.

The load drive system shown in FIG. 1 is a vehicle-mounted electronic control unit (ECU) such as an engine control module.
10 and a load unit 20 including a cooling fan motor 214 as a load as an example of on-vehicle equipment driven by the ECU 10.

In the ECU 10, a control unit 110
Is connected to a battery (not shown) and converts the supply voltage VB of the battery to a predetermined voltage and then drives the drive unit 20.
And a controller (not shown) for controlling the operation of the drive unit 20 and the like. The output terminal T1 of the control unit 110 Is connected to the load unit 20 via a resistor 111 and a wire harness 112.

Here, the control operation of the control unit 110 will be briefly described.
V) is output from the output terminal T1 so as to start the load unit 20 by outputting a low voltage close to V) and to stop the load unit 20 when outputting a predetermined power supply voltage close to the battery voltage VB (V). ON / OF whose output voltage can be changed between VB and battery voltage VB (V)
Outputs F signal.

Inside the ECU 10, the resistance 111 is connected to the wire harness 112 side and the control unit 11
0 is connected to an input terminal T2 of an analog / digital (A / D) converter (not shown) provided inside the control unit 110.
The voltage on the side of one wire harness 112 can be measured.

On the other hand, inside the load unit 20,
The load 214 has one terminal connected to the battery (not shown) and the other terminal connected to the output terminal of the switching element 212. The switching element 212 forms a well-known common-emitter transistor switching circuit by a pull-down resistor 213 that connects between the output terminal T3 of the switching element and the ground potential.

An inverting circuit 210 for inverting a control signal transmitted by the wire harness 112 is connected to an input terminal of the switching element 212, and a connection between an output terminal of the switching element 212 and an input terminal of the inverting circuit 210. The feedback resistor 211 is connected between them.

In the above circuit configuration, the inverting circuit 210
The input threshold voltage of the battery voltage VB (V)
Was set to の. In the present embodiment, the state of the output terminal T1 of the control unit 110, the switching element 2
The resistance values of the resistor 111, the feedback resistor 211, and the pull-down resistor 213 are appropriately set such that the voltage VT2 detected at the terminal T2 changes by a predetermined voltage in accordance with the ON / OFF state of the load 12 and the failure state of the load 214. Set. As a specific setting, in the present embodiment, the resistance values of these resistors are R111, R211 and R213, respectively, and
1, the feedback resistor 211, the pull-down resistor 213, and the impedance ZL of the load 214 are represented by R111
+ Α = R211 = R213 >> ZL (α is a constant of about R111 × 1.1).

The detailed operation of the load driving system of FIG. 1 having the above configuration will be described below.

FIGS. 2 to 8 are time charts showing voltage waveforms at terminals T1 to T3 (hereinafter, referred to as a plurality of points) of the load drive system according to the first embodiment.

FIG. 2 shows the state of the voltage waveforms at the plurality of locations when the ECU 10 instructs the load unit 20 to start the load 214.

<Starting of the Load 214> First, the state of the switching element 212 is “OFF” and the voltage of the terminal T3 is the battery voltage VB (V).
A case where a voltage of 0 V is output from the output terminal T1 of the control unit 110 in a state where the control unit 4 is stopped will be described. In this case, the input voltage of the inverting circuit 210 is divided by the resistor 111 and the resistor 211 having the above-described resistance value relationship, so that the battery voltage VB
(V) is slightly lower than 1/2. Therefore, 1/2
The output of the inversion circuit 210 having a threshold voltage near VB becomes “HI”, and as a result, the switching element 212 is turned “ON”, so that the voltage at the terminal T3 becomes 0V. As a result, the load 214 starts operating and the input terminal T on the control unit 110 side.
The voltage of 2 becomes 0V.

<Stopping of the Load 214> FIG.
Shows the states of the voltage waveforms at the plurality of places when the load unit 20 instructs the load unit 20 to stop the load 214.

When the load 214 is to be stopped in the start (operation) state of the load 214 described with reference to FIG. 2, the voltage value of the battery voltage VB (V) is output from the output terminal T1 of the control unit 110. By outputting
The input voltage of the inverting circuit 210 includes a resistor 111 and a resistor 211.
１ ／ of the battery voltage VB (V)
Slightly higher. Therefore, the output of the inverting circuit 210 becomes “LOW”, and as a result, the switching element 212 becomes “OFF”, so that the terminal T3 becomes the battery voltage VB (V). As a result, the load 214
Stops, and the input terminal T2 of the control unit 110 becomes the battery voltage VB (V).

By such an operation, the control unit 11
With 0, the load 214 can be started and stopped.

<Speed Adjustment of Load 214> Next, by performing general PWM control on the load unit 20, the cooling fan motor (load) 2 in the operating state is operated.
The case of adjusting the operation speed of No. 14 will be described.

FIG. 4 shows the state of the voltage waveforms at the plurality of locations when the ECU 10 performs the PWM control on the load unit 20. The output terminal T of the control unit 110 is shown in FIG.
When a rectangular wave signal having an arbitrary duty ratio (FIG. 4 shows a case where the duty ratio is 50%) is transmitted from 1 by pulse width modulation, the voltage waveform of the output terminal T1 becomes 0-V
A rectangular wave signal of B is obtained.

In the load unit 20 to which this rectangular wave signal is input, the input voltage of the inverting circuit 210 when the rectangular wave signal is in the “H (= VB)” state is obtained by the resistors 111 and 2
11 and the battery voltage VB
(V) is slightly higher than 1/2. Therefore, the output of the inverting circuit 210 becomes “LOW”, and the switching element 212 becomes “OFF”. In this state, the terminal T3 is at the battery voltage VB (V), the driving of the load 214 is interrupted, and the input terminal T2 of the control unit 110 is at the battery voltage VB (V), as in the case of stopping the load 214 described above. ).

On the other hand, the input voltage of the inverting circuit 210 when the rectangular wave signal is “L (= 0)” is
The battery voltage VB (V) applied to the resistor 111
And the resistance 211, the voltage is slightly lower than バ ッ テ リ of the battery voltage VB (V). Therefore, the output of the inverting circuit 210 becomes “HI”, and the switching element 212 turns “ON”. In this state, the terminal T3 is at 0 V, the load 214 is driven and the input terminal T2 of the control unit 110 is at 0 V, as in the case of starting the load 214 described above.

Accordingly, the waveform of the rectangular wave signal output from the output terminal T1 as a control signal, the switching element 212
(= Terminal waveform of the load 214) and the waveform of the input terminal T2 have substantially the same shape.

<Detection of Short-Circuit of Switching Element 212> Subsequently, a case where the switching element 212 has a short-circuit failure, that is, a case where a failure in which the load 214 operates at 100% irrespective of the control PWM signal will be described.

FIG. 5 shows the state of the voltage waveforms at the plurality of locations when the switching element 212 has a short-circuit fault when the ECU 10 performs the PWM control on the load unit 20.

As shown in the figure, in this case, the output terminal T3 of the switching element 212 is output although a predetermined PWM signal is output from the output terminal T1 as in FIG.
Is 0V. However, when the voltage of the input terminal T2 is "0V", the voltage of the input terminal T2 is 0V, and the voltage of the output terminal T1 is "0V".
In the case of VB ", the voltage is divided by the resistor 111 and the resistor 211 and rises to a voltage slightly higher than 1/2 VB. Therefore, in the control unit 110 of the ECU 10, the voltage of the output terminal T1 is normally changed to the battery voltage VB (V ), The voltage of the input terminal T2 is the battery voltage VB (V), and as shown in FIG.
When it is detected that the voltage of No. 2 is near 1/2 VB, it is possible to detect that the switching element 212 of the load unit 20 has a short-circuit fault.

<Detection of disconnection of switching element 212, detection of short-circuit of load 214> Further, when the switching element 212 is disconnected or a short-circuit failure of the load 214 occurs,
That is, a case will be described in which a failure occurs in which the load operates at 0% irrespective of the control PWM signal.

FIG. 6 shows the state of voltage waveforms at a plurality of locations when the switching element 212 has a disconnection failure or a short-circuit failure of the load 214 when the ECU 10 performs PWM control on the load unit 20. Is shown.

As shown in the figure, in this case, the voltage at the terminal T3 is changed to the battery voltage VB even though a predetermined PWM signal is output from the output terminal T1 as in FIG.
(V), the voltage at the input terminal T2 is slightly lower than 1/2 VB when the voltage at the output terminal T1 is 0 V, while the voltage at the output terminal T1 is V
At the time of B, the voltage of the input terminal T2 becomes VB.

As described above, when the short-circuit failure of the switching element 212 occurs (FIG. 5), the switching element 2
12 and the short-circuit failure of the load 214 (FIG. 6).
2 is different from that in the normal state (FIG. 4),
By detecting these abnormal input voltages on the ECU 10 side, the failure state can be determined.

<Detection of Disconnection of Load 214 and Detection of Abnormal Load Resistance Value> A description will be given of a case where the load 214 has a disconnection failure or a failure in which the load resistance value of the load becomes abnormally large.

FIG. 7 shows a failure of the load 214 or a failure in which the load resistance value of the load becomes abnormally large (that is, a disconnection of the load 214) when the ECU 10 performs the PWM control on the load unit 20. (A state close to the above) is shown in FIG.

As shown in the figure, in this case, when the voltage of the output terminal T1 is the battery VB, the output of the inverting circuit 210 becomes "LOW" and the switching element 212 is turned off.
In the F state, the voltage of the terminal T3 is a voltage divided by the load resistance of the load 214 and the resistance 213 when the voltage of the terminal T3 is the battery voltage VB (V) in a normal state. That is, when a failure occurs in which the load resistance value becomes abnormally large, the battery voltage VB (V) when the voltage at the input terminal T2 is normal during the period when the voltage at the output terminal T1 is the battery voltage VB (V). And the voltage value is lower according to the load resistance, and when the load 214 is completely disconnected, the voltage at the input terminal T2 is about ／ VB. Accordingly, by detecting these abnormal input voltages on the ECU 10 side, it is possible to detect a disconnection failure of the load 214 or a failure in which the load resistance value of the load becomes abnormally large.

As described above, according to the present embodiment, the load 2
And a switching element 212 constituting a common-emitter transistor switching circuit for driving
Is provided with an inverting circuit 210 at the input stage and a simple circuit configuration in which a feedback resistor 211 is added from the output terminal T3 of the switching element to the input side of the inverting circuit 210. Without having
The control unit 110 can determine and detect the disconnection of the load 214 (including the case where the load resistance is abnormally large) and the occurrence of the short-circuit failure and the disconnection and short-circuit failure of the switching element 212. Further, the operation control signal of the load 214 and the detection signal of each of the above-described failure states can be shared by one wire harness 112. For this reason, according to the load drive system according to the present embodiment, since a complicated circuit configuration and a wire harness for transmitting the result of the failure diagnosis to the ECU are not required as in the related art, the number of parts is reduced. The cost can be reduced by reduction, and the failure rate can be reduced by reducing the number of parts.

[Second Embodiment] Next, a second embodiment based on the load drive system according to the first embodiment will be described. In the following description, the same configuration as that of the first embodiment will not be described repeatedly, and will be described focusing on the characteristic portions of the present embodiment.

In the present embodiment, the case where the load 214 is a DC motor in the configuration of the load unit 20 shown in FIG. 1 will be described.

FIG. 8 shows the ECU according to the second embodiment.
10 shows the state of the voltage waveform at the plurality of locations when PWM control is performed on the load unit 20.

In the figure, the period up to point a is
As in the first embodiment, an arbitrary duty PWM is output from the output terminal T1 of the control unit 110 in the ECU 10.
It is assumed that the control signal is generated to control the operation speed of the load 214.

Next, at the timing indicated by the point a, the battery voltage VB is output from the output terminal T1 of the control unit 110.
It is assumed that the stop of the load 214 is instructed by continuously outputting (V). At this time, the load 214, which is a DC motor, applies the flyback voltage of the inductance to a general hula wheel circuit (not shown) provided for the load 214 during a period t1 during which the current stored in the internal inductance is released. (Shown). Therefore, the voltage of the terminal T3 during the clamp period becomes the battery voltage VB (V). Then, when the release of the energy stored in the inductance is completed, the voltage of the terminal T3 becomes VM. Here, the voltage value VM
Is a voltage value smaller than the battery voltage VB (V) by an induced electromotive voltage generated by the inertial rotation of the DC motor of the load 214, and the value of the VM is substantially proportional to the rotation speed of the motor.

Therefore, in the control unit 110, the terminal T
3, a voltage corresponding to the voltage drop VM is measured at an input terminal T2 to which a voltage waveform substantially similar to the voltage waveform is input. By the proportional calculation based on the rotation speed, the rotation speed of the DC motor (load) 214 at the time when the stop command is output from the control unit 110 (the timing at point a in FIG. 8) can be detected.

Accordingly, the ECU 10 can determine, in addition to the various abnormality detections described in the first embodiment, the rotation operation abnormality caused by a failure, a foreign substance attached to the mechanical portion of the load 214 as the DC motor, and the like. .

In the control unit 110, the rotation speed information of the load 214 detected by measuring the voltage of the input terminal T2 as described above is fed back to the rectangular wave signal output from the output terminal T1 by PWM control. Thus, accurate rotation control of the load 214 may be performed.

[Third Embodiment] Next, a third embodiment based on the load drive system according to the above-described first embodiment will be described. In the following description, the same configuration as that of the first embodiment will not be described repeatedly, and will be described focusing on the characteristic portions of the present embodiment.

FIG. 9 is a diagram showing the circuit configuration of the load driving system according to the third embodiment. FIG. 9 shows the output stage of the inverting circuit 210 and the input stage of the switching element 212 in FIG. And that a delay circuit 215 is added.

The delay circuit 215 receives a change such as a rise and a fall of the output signal of the inverting circuit 210,
This is a general delay circuit that outputs a signal having the same polarity as the input signal to the delay circuit to the switching element 212 after a predetermined delay time.

FIG. 10 shows the state of the voltage waveform at the plurality of points in the load drive system according to the third embodiment.

From the output terminal T1 of the control unit 110,
When an arbitrary PWM signal is output, the switching element 21
2 has a predetermined delay phase. Therefore, the voltage waveform of the input terminal T2 has a stepped shape as shown in FIG. 10, and the control unit 110 converts the stepped voltage waveform input from the input terminal T2 into 1/3 VB and 2/3.
The waveform is shaped by a hysteresis comparator (not shown) having a slice level with VB to obtain a detection signal SCP shown in FIG.

Therefore, if the wire harness 112 connecting the ECU 10 and the load unit 20 is normally connected and the internal circuit of the load unit 20 is operating normally, the output from the output terminal T1 of the control unit 110 The detected square wave signal and the detection signal SCP have a predetermined phase difference. However, when the wire harness 112 is disconnected, the voltage waveform input from the input terminal T2 is the rectangular wave signal itself output from the output terminal T1 by the control unit 110. In this case, the rectangular wave signal and the detection signal The phase difference from the SCP is “0”.

When the wire harness 112 is grounded or short-circuited to a battery power source, the voltage waveform input from the input terminal T2 and the detection signal are independent of the rectangular wave signal output from the output terminal T1. SCP becomes battery voltage VB (V) or ground potential.

Therefore, by adding the delay circuit 215 to the load unit 20 as in the present embodiment, the control unit 110 can detect the various abnormalities described in the first embodiment, and can connect the ECU 10 and the load unit 20 with each other. It is possible to detect disconnection and ground fault of the wire harness 112 that connects them, and short-circuit to the battery power supply.

In each of the above embodiments, the load 214
A semiconductor switching element is employed as the drive circuit element 212 for driving the semiconductor element, and a common-emitter transistor switching circuit is configured and the inverting circuit 210 is used. However, the present invention is not limited to this.
It may be realized by various general electronic circuit devices such as a MOSFET and a C-MOS_IC.

Further, according to each of the above-described embodiments, the number of circuit elements provided in the load unit 20 for failure diagnosis can be extremely reduced, so that the circuit element and the drive circuit element 213 are integrally formed. It is also suitable for a one-chip IC.

Further, in each of the above-described embodiments, the load drive system according to the present invention is provided with an electronic control unit (EC
U) The present invention is applied to the control circuit including the load unit 20 and the load unit 20 disposed in the vicinity of the load 214 which is disposed remotely from the ECU. However, the present invention is not limited to this.
The present invention can be applied to various fields including applications between ECUs or between sensors and sensors, and applications other than ECUs mounted on vehicles.

[0065]

As described above, according to the present invention,
It is possible to provide a low-cost and highly reliable load drive system and a failure detection method thereof.

That is, according to the first and eighth aspects of the present invention, for example, the voltage fluctuation occurring in the voltage dividing resistor detected by the voltage detection circuit and the voltage fluctuation of the control signal output from the pulse width modulation circuit are detected. (Claims 2 and 9), there is no need to provide a dedicated circuit for failure diagnosis, and the number of wire harnesses connecting the ECU and the load can be reduced. Therefore, a reduction in member cost and a reduction in the failure rate due to a reduction in the number of members are realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a circuit configuration of a load driving system according to a first embodiment.

FIG. 2 is a time chart showing voltage waveforms at a plurality of points in the load drive system according to the first embodiment (at the time of starting the load).

FIG. 3 is a time chart showing voltage waveforms at a plurality of points in the load drive system according to the first embodiment (when the load is stopped).

FIG. 4 is a time chart showing voltage waveforms at a plurality of points in the load drive system according to the first embodiment (P
At the time of WM control).

FIG. 5 is a time chart showing voltage waveforms at a plurality of points in the load driving system according to the first embodiment (when a switching element is short-circuited).

FIG. 6 is a time chart showing voltage waveforms at a plurality of points in the load drive system according to the first embodiment (when a switching element is disconnected or a load is short-circuited).

FIG. 7 is a time chart showing voltage waveforms at a plurality of locations in the load drive system according to the first embodiment (when the load is disconnected).

FIG. 8 is a diagram illustrating a state of voltage waveforms at a plurality of locations when the ECU performs PWM control on a load unit in the second embodiment.

FIG. 9 is a diagram illustrating a circuit configuration of a load driving system according to a third embodiment.

FIG. 10 is a diagram illustrating states of voltage waveforms at the plurality of locations in the load driving system according to the third embodiment.

FIG. 11 is a diagram showing a circuit configuration in a conventional load drive system in which a load and a drive circuit for driving the load are provided separately.

[Explanation of symbols]

 10: ECU, 20: load unit, 101, 110: control unit, 102, 112, 204: wire harness, 111, 211, 213: resistance, 201: failure detection circuit, 202, 214: load, 203, 213: switching Element, 210: inverting circuit, 215: delay circuit,

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G05B 23/02 302 B60R 16/02 650 H02P 5/17 G01R 31/02

Claims (9)

(57) [Claims] 1. A control unit comprising: a control unit; and a load unit for controlling an operation of a load device in accordance with a control signal output from the control unit. And a power supply system for individually supplying power to the units, wherein the load unit is disposed integrally with or close to the load device so as to interrupt current flowing to the load device. A load driving element, an inverting circuit connected to an input side of the load driving element for inverting a logic level of a control signal input from the control unit via the signal line, and an input side of the inverting circuit. And a feedback resistor connected between the output side of the load driving element and a pull-down connected between the output side of the load driving element and the ground side. A pulse width modulation circuit that outputs a control signal having an arbitrary duty ratio to the input side of the inverting circuit via the signal line, and detects a voltage of the signal line. A voltage detecting circuit, based on the voltage fluctuation detected by the voltage detecting circuit,
A load drive system comprising: the load device, the load drive element, and a determination unit configured to determine a failure related to an electrical conduction state generated in the signal line. 2. The control unit further includes a voltage dividing resistor connected in series between the signal line and the pulse width modulation circuit, wherein the load unit has a resistance value of the feedback resistor and a resistance value of the pull-down resistor. A resistance value substantially coincident with the resistance value, and the determination unit compares a voltage change generated in the voltage dividing resistor detected by the voltage detection circuit with a voltage change of a control signal output from the pulse width modulation circuit. 2. The load drive system according to claim 1, wherein a failure relating to the electrical conduction state is determined by the following. 3. The load driving device according to claim 2, wherein the determination unit determines, as the failure related to the electrical conduction state, a disconnection and a short circuit of the load device and a disconnection and a short circuit of the load driving element. system. 4. The load unit further includes a delay circuit between the inverting circuit and the load driving element, wherein the determining unit detects a waveform of a control signal output from the pulse width modulation circuit and detects a waveform of the control signal. 3. The load drive system according to claim 2, further comprising determining a disconnection of the signal line, a ground fault, and a short circuit to a power supply based on a phase difference between the detected voltage signal and the waveform of the voltage signal. 5. The load device is a DC motor, and the determination means is based on a voltage detected by the voltage detection means and corresponding to a back electromotive force generated when the DC motor stops. 2. The load drive system according to claim 1, further comprising means for detecting a rotation speed of said DC motor. 6. An electric slice level for an input signal of the inverting circuit is substantially equal to a power supply voltage of the load device side.
The load drive system according to claim 1, wherein the load drive system is set to / 2. 7. The load drive system according to claim 1, wherein the load drive system is a drive system for a cooling fan mounted on a vehicle. 8. A control unit, and a load unit for controlling operation of a load device in accordance with a control signal output from the control unit, wherein the control unit and the load unit are connected by a signal line and separated from each other. And a load drive system for individually supplying power to the units, wherein the load unit includes a load drive element that interrupts a current supplied to the load device.
An inverting circuit connected to an input side of the load driving element so as to be integrated with or close to the load device and to invert a logical level of a control signal input from the control unit via the signal line; A feedback resistor is connected between an input side of the load driving element and an output side of the load driving element; a pull-down resistor is connected between an output side of the load driving element and a ground side; A control signal having an arbitrary duty ratio is output from the pulse width modulation circuit to the input side of the inverting circuit via the signal line, and as a result, based on a voltage change occurring in the signal line, the load device, A failure detection method for a load drive system, comprising: determining a failure relating to a load drive element and an electrical conduction state generated in the signal line. 9. The control unit, wherein a voltage dividing resistor is connected in series between the signal line and the pulse width modulation circuit, and a resistance value of the feedback resistor and a resistance value of the pull-down resistor in the load unit. Are set to be approximately the same,
By comparing the voltage fluctuation generated in the voltage dividing resistor by outputting the control signal with the voltage fluctuation of the control signal output from the pulse width modulation circuit, determining a failure related to the electrical conduction state. 9. The method for detecting a failure of a load drive system according to claim 8, wherein: