JP2019097022A - Load drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diagnose whether or not a cut-off switch element can normally switch between conduction and cut-off without passing a current through a load. A diagnostic voltage source 9 is connected to the load 2 side of the breaking switch element 6. The central processing unit 8 performs a failure diagnosis of the breaking switch element 6 based on the element end voltage Ve of the breaking switch element 6 on the load 2 side. At this time, the central processing unit 8 outputs the conduction / cutoff control signal S2 for turning on the cutoff switch element 6 in a state where the load drive power source 3 and the load 2 are cut off by the drive control signal S1. Based on the section voltage Ve and the element end voltage Ve when the conduction / cutoff control signal S2 for shutting off the cutoff switch element 6 is output, it is determined whether the cutoff switch element 6 is normal or abnormal. [Selection diagram]

Description

  The present invention relates to a load drive device suitable for application to automobiles, construction machines, industrial machines and the like.

  Automobiles, construction machines, industrial machines, etc. have movable loads such as solenoid valves. A switch element is connected in series to such a movable load, and the amount of current flowing to the load is controlled by controlling conduction and interruption of the switch element. Since the failure of the switch element has an important effect on the operation of the machine, a failure diagnosis method of the switch element is important. Patent Literatures 1 and 2 disclose methods for diagnosing such a failure of the switch element. In the methods described in Patent Documents 1 and 2, a failure of the switch element is diagnosed while supplying a current of a certain level or more to the load.

JP, 2010-146841, A Patent No. 5203859

  By the way, various configuration examples can be considered as a circuit for driving a load. As an example, a circuit configuration in which a load drive switch element is provided between a load drive power supply and a load, and a cutoff switch element is provided downstream of the load can be considered. In this configuration, the load driving switch element supplies the load current by ON / OFF control or PWM control, and the interrupting switch element is normally conducted. When an abnormality occurs in the load, the load current is cut off by interrupting both the load driving switch element and the interrupting switch element to stop the load.

  In particular, when a failure occurs in which the terminal on the upstream side of the load is short-circuited with the load drive power supply (power supply fault), a short circuit current flows in the load regardless of conduction and interruption of the load drive switch element. At this time, the policy for interrupting the load current is only the interrupting switch element provided downstream of the load. Therefore, it is necessary to properly diagnose the blocking switch element which is the protective function to improve the reliability.

  In addition, in a machine that repeats start and stop every predetermined time period, it is preferable to secure the normality of the protection function before the start of work. For this reason, it is preferable that the protective function of the interrupting switch element or the like be diagnosed in advance before the electronic control unit drives the load immediately after startup.

  When the failure diagnosis method disclosed in Patent Documents 1 and 2 is applied to such a switch device for shutoff of a load drive device, for example, when diagnosis of the shutoff switch device is performed when the electronic control unit is started, It is necessary to supply current to the load. However, when the start-up diagnosis is performed, problems may occur when the load current flows, for example, a minute operation or vibration of the load occurs to cause noise. As described above, there is a problem that the failure diagnosis method described in Patent Documents 1 and 2 can not be applied when there is a disadvantage that a load current flows in the startup diagnosis.

  The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to diagnose whether or not the interrupting switch element can normally switch between conduction and interrupt without flowing current to the load. It is an object of the present invention to provide a load driving device capable of

  In order to solve the problems described above, the present invention is provided between a load driving switch element provided between a load and a load driving power supply and controlled by a load driving control unit, and between the load and the ground. An interrupting switch element and a drive control signal to the load drive control unit are outputted, and a conduction / cutoff control signal for conducting or interrupting the interrupting switch element is outputted, and an element on the load side among the interrupting switch elements A load drive device comprising: a central processing unit that determines whether the cutoff switch element is normal or abnormal based on an end voltage; and a determination result output unit that outputs a determination result by the central processing unit. The diagnostic voltage source is connected to the load side of the interrupting switch element, and the central processing unit interrupts the load drive power supply and the load by the drive control signal. When the conduction / cutoff control signal is outputted when the conduction / cutoff control signal is made to conduct the shutoff switch element in a state where the shutoff switch element is made conductive and when the conduction / cutoff control signal is made to shut off the shutoff switch element It is characterized in that whether the interrupting switch element is normal or abnormal is judged based on the element end voltage.

  According to the present invention, it is possible to diagnose whether or not the interrupting switch element can be normally switched between conduction and disconnection without flowing current to the load.

FIG. 1 is a block diagram showing a load driving device according to a first embodiment of the present invention. It is a flowchart which shows the failure diagnostic process which the central processing part in FIG. 1 performs. FIG. 7 is a characteristic diagram showing temporal changes of the on / off control signal and the element end voltage when the shutoff switch element is normal. FIG. 7 is a characteristic diagram showing temporal changes in the on / off control signal and the element end voltage when the breaking switch element has an open failure; FIG. 7 is a characteristic diagram showing the time change of the conduction / cutoff control signal and the element end voltage when the shutoff switch element has a short circuit failure. FIG. 7 is a characteristic diagram showing temporal changes in the on / off control signal and the element end voltage when the switching element has a switching failure. It is explanatory drawing which shows the relationship between the area | region of a conduction * interruption | blocking control signal and an element end part voltage. It is a circuit diagram which shows the structure of the load side backflow prevention element in FIG. It is a circuit diagram showing the composition of the load side backflow prevention element by the 1st modification. FIG. 6 is a block diagram showing a load driving device according to a second embodiment of the present invention. It is a circuit diagram which shows the structure of the diagnosis side backflow prevention element in FIG. It is a circuit diagram showing composition of a diagnosis side backflow prevention element by the 2nd modification. It is a block diagram showing a load drive by a 3rd embodiment of the present invention. It is a circuit diagram which shows the load current detection part in FIG. It is a flowchart which shows the failure-diagnosis process which the central processing part in FIG. 13 performs. FIG. 7 is a characteristic diagram showing temporal changes of the on / off control signal, the element end voltage, the input voltage of the comparator, the output voltage of the comparator, and the output voltage of the amplifier circuit when the shutoff switch element is normal. FIG. 7 is a characteristic diagram showing temporal changes of the on / off control signal, the element end voltage, the input voltage of the comparator, the output voltage of the comparator, and the output voltage of the amplifier circuit when the breaking switch element has an open failure. FIG. 7 is a characteristic diagram showing temporal changes of the on / off control signal, the element end voltage, the input voltage of the comparator, the output voltage of the comparator, and the output voltage of the amplifier circuit when the shutoff switch element has a short circuit failure. FIG. 7 is a characteristic diagram showing temporal changes of the on / off control signal, the element end voltage, the input voltage of the comparator, the output voltage of the comparator, and the output voltage of the amplifier circuit when the blocking switch element fails in switching.

  Hereinafter, a load drive device according to an embodiment of the present invention will be described in detail with reference to the attached drawings.

  FIG. 1 shows a load driving device 1 according to a first embodiment. The load driving device 1 includes a load driving switch element 4, a cutoff switch element 6, a central processing unit 8, a display device 11 and the like. In the following, in consideration of the current flowing from the load drive power supply 3 to the ground, the load drive power supply 3 side is the upstream side, and the ground side is the downstream side.

  The load 2 constitutes, for example, a solenoid valve. The load 2 is electrically connected to a load drive power supply 3 consisting of a DC power supply. The load drive power supply 3 applies a DC drive voltage V 0 to the load 2. The load 2 performs an operation such as opening, closing, switching direction, etc. of the solenoid valve, for example, by power supply from the load drive power supply 3. The load 2 includes, for example, a coil SC such as a solenoid of a solenoid valve, and a free wheeling diode FD connected in parallel to the coil SC (see FIG. 14).

  The load 2 is not limited to the solenoid valve, and may be, for example, a buzzer or a lamp. Therefore, the load 2 is not limited to an inductive load such as a solenoid of a solenoid valve, and may be a resistive load. Also, depending on the specific configuration of the load, the freewheeling diode may be omitted.

  As shown in FIG. 1, the load drive switch element 4 is provided between the load 2 and the load drive power supply 3, and is controlled by the load drive control unit 5. That is, the load driving switch element 4 is disposed downstream of the load driving power supply 3 and upstream of the load 2. The load driving switch element 4 is formed of, for example, a semiconductor switch element such as a field effect transistor (FET). Therefore, a drive signal such as a gate voltage is input from the load drive control unit 5 to the load drive switch element 4, and ON and OFF are controlled according to the drive signal. As a result, the load drive switch element 4 is, for example, ON / OFF controlled or PWM controlled by the load drive controller 5 to control the current supplied to the load 2. At this time, the load drive control unit 5 outputs a drive signal for driving the load drive switch element 4 based on the drive control signal S1 from the central processing unit 8.

  The load drive switch element 4 is not limited to the FET, and may be, for example, a bipolar transistor. Further, the load drive switch element 4 is a relay (relay) if it performs control only to switch the connection state between the load 2 and the load drive power supply 3 between ON and OFF, that is, ON / OFF control. May be

  The cutoff switch element 6 is provided between the load 2 and the ground. That is, the cutoff switch element 6 is disposed on the downstream side (ground side) of the load 2. Therefore, the upper end 6A of the both ends of the cutoff switch element 6 is connected to the load 2, and the lower end 6B is connected to the ground. The shutoff switch element 6 urgently shuts off the load current IL when the load is abnormal. At this time, a path from the load drive power supply 3 to the ground connected to the downstream side of the cutoff switch element 6 via the load 2 forms a load current path.

  The cutoff switch element 6 is formed of, for example, a semiconductor switch element such as a field effect transistor (FET). Therefore, the on / off control signal S2 such as the gate voltage is input from the central processing unit 8 to the blocking switch element 6, and ON and OFF are controlled in accordance with the on / off control signal S2. The cutoff switch element 6 is not limited to the FET, and may be, for example, a relay.

  The voltage detection unit 7 is connected to the load 2 side of the cutoff switch element 6 and detects an element end voltage Ve of the cutoff switch element 6 on the load 2 side. Specifically, the voltage detection unit 7 detects an element end voltage Ve of the upper end portion 6 </ b> A of both ends of the cutoff switch element 6. The voltage detection unit 7 outputs a signal corresponding to the element end voltage Ve to the central processing unit 8. The voltage detection unit 7 may be capable of detecting the element end voltage Ve, may be connected to the upper end 6A of the cutoff switch element 6, or may be connected to the lower end of the load 2. It may be connected to the middle of the line between them.

  The central processing unit 8 transmits (outputs) the drive control signal S1 to the load drive control unit 5. In addition to this, the central processing unit 8 controls conduction and interruption of the interruption switch element 6. Therefore, the central processing unit 8 outputs the conduction / cutoff control signal S2 for controlling the shutoff switch element 6 to the shutoff switch element 6.

  The central processing unit 8 is configured by, for example, a microcomputer. The central processing unit 8 executes a failure diagnosis processing program shown in FIG. 2 stored in a memory (not shown). Thus, the central processing unit 8 diagnoses whether or not the shutoff switch element 6 is properly shut off.

  The diagnostic voltage source 9 outputs a diagnostic voltage Vd (Vd <V0) lower than the drive voltage V0 of the load drive power supply 3. As an example, when the drive voltage V0 is about 20 to 30 V, the diagnostic voltage Vd is about 4 to 5 V. For this reason, the diagnostic voltage source 9 is constituted by, for example, a DC step-down circuit that steps down the DC drive voltage V0 like a step-down chopper. The output side of the diagnostic voltage source 9 is connected to the upper end 6 A of the cutoff switch element 6. When the cutoff switch element 6 is in the cutoff state (OFF), the diagnostic voltage source 9 maintains the voltage of the upper end 6A at a constant value (diagnostic voltage Vd). The voltage source 9 for diagnosis is a pull-up resistor so that the element end voltage Ve of the upper end 6A of the cutoff switch element 6 is switched according to conduction (ON) and cutoff (OFF) of the cutoff switch element 6. (Not shown) is provided.

  The diagnostic voltage source 9 may always output the diagnostic voltage Vd. The diagnostic voltage source 9 may output the diagnostic voltage Vd only during failure diagnosis of the cutoff switch element 6 in order to reduce power consumption. In this case, the operation of the diagnostic voltage source 9 may be controlled by the central processing unit 8.

  The central processing unit 8 reads the element end voltage Ve of the upper end 6A of the cutoff switch element 6 via the voltage detection unit 7. Thus, the central processing unit 8 diagnoses that the cutoff switch element 6 is properly blocked based on the element end voltage Ve detected by the voltage detection unit 7. As described above, the diagnosis voltage source 9 can diagnose the cutoff switch element 6 without flowing a current to the load 2.

  The load side backflow prevention element 10 prevents current from flowing from the diagnostic voltage source 9 to the load drive switch element 4 via the load 2 when diagnosing the cutoff switch element 6. When there is a portion connected to the ground or the like inside the load driving switch element 4, the load-side backflow prevention element 10 is required. As a result, the voltage of the upper end portion 6A of the cutoff switch element 6 can be accurately detected. For example, in the case where there is no place connected to the ground or the like inside the load drive switch element 4, the load 2 may be directly connected to the load drive switch element 4. That is, the load driving device 1 may not have the load-side backflow prevention element 10. A specific example of the load-side backflow prevention element 10 is shown in FIG. FIG. 8 shows an example in which the load-side reverse flow prevention element 10 is configured using a single diode D.

  The display device 11 constitutes a judgment result output unit that outputs the judgment result of the failure diagnosis by the central processing unit 8. The display device 11 is configured of, for example, a liquid crystal monitor, and displays various types of information. The input side of the display device 11 is connected to the central processing unit 8. The central processing unit 8 outputs a signal corresponding to the diagnosis result to the display device 11 when the failure diagnosis process of the cutoff switch element 6 is executed. Thereby, the display device 11 displays the determination result of the failure diagnosis by the central processing unit 8 and notifies the operator.

  The judgment result output means is not limited to the display device 11. The determination result output means may be any means capable of notifying the operator of the result of the failure diagnosis, and may be, for example, a lamp, a buzzer or the like.

  Further, the load drive switch element 4, the cutoff switch element 6, the central processing unit 8 and the like constitute a load drive circuit 12 for driving the load 2. The load drive circuit 12 is connected to the load 2 and the display device 11.

  Next, a failure diagnosis processing program executed by the central processing unit 8 of the load driving device 1 according to the first embodiment will be described with reference to FIG.

  When the failure diagnosis processing of the cutoff switch element 6 is started, the central processing unit 8 outputs a drive control signal S1 to the load drive control unit 5 so as to disconnect the load drive power supply 3 from the load 2. Thereby, the load drive switch element 4 is switched to OFF.

  Thereafter, in step S1, the central processing unit 8 outputs a conduction / cutoff control signal S2 for turning off the shutoff switch element 6 (cutoff state) to the shutoff switch element 6. In the subsequent step S2, it is determined which of the regions (A), (B) and (C) the range of the element end voltage Ve (the voltage of the upper end 6A) detected by the voltage detection unit 7 is.

  At this time, the area (A) is an area where the element end voltage Ve is in the vicinity of the diagnostic voltage Vd from the diagnostic voltage source 9. Therefore, the central processing unit 8 determines whether the element end voltage Ve is equal to or higher than a first threshold value VH (eg, VH = 0.7 × Vd) higher than half of the diagnostic voltage Vd. It is determined whether the element end voltage Ve is within the range of the area (A).

  The area (C) is an area where the element end voltage Ve is near the ground potential. Therefore, the central processing unit 8 determines whether or not the element end voltage Ve is equal to or lower than a second threshold value VL (eg, VL = 0.3 × Vd) lower than half of the diagnostic voltage Vd. It is determined whether or not the end voltage Ve is within the range of the region (C).

  The area (B) is an area at an intermediate level between the area (A) and the area (C). Therefore, the central processing unit 8 determines whether the element end voltage Ve is in a range lower than the first threshold VH and higher than the second threshold VL (VH> Ve> VL). It is determined whether the element end voltage Ve is within the range of the region (B).

  If it is determined in step S2 that the element end voltage Ve is within the range of the area (A), the process proceeds to step S3. In step S3, the central processing unit 8 outputs a conduction / cutoff control signal S2 for turning the shutoff switch element 6 ON (connected state) to the shutoff switch element 6. In the subsequent step S4, as in step S2, it is determined which of the regions (A), (B), and (C) the element end voltage Ve (voltage of the upper end 6A) detected by the voltage detection unit 7 has. Do.

  If it is determined in step S4 that the element end voltage Ve is within the range of region (C), the process proceeds to step S5. In step S5, it is determined that the interrupting switch element 6 is normal, and the process ends.

  On the other hand, when it is determined in step S2 that the element end voltage Ve is within the range of the region (C), the process proceeds to step S6. In step S6, it is determined that a complete short circuit fault has occurred in the interrupting switch element 6. After that, the process proceeds to step 10, the display device 11 is displayed on the display device 11 that the complete short circuit failure has occurred as the content of the abnormality generated in the cutoff switch element 6, the operator is notified, and the processing is ended.

  If it is determined in step S2 that the element end voltage Ve is within the range of region (B), the process proceeds to step S7. In step S7, it is determined that a switching failure has occurred in the cutoff switch element 6. After that, the process proceeds to step 10, the display device 11 is displayed on the display device 11 that the switching failure has occurred as the content of the abnormality generated in the cutoff switch element 6, the operator is notified, and the processing is ended.

  If it is determined in step S4 that the element end voltage Ve is within the range of area (A), the process proceeds to step S8. In step S6, it is determined that a complete open failure has occurred in the interrupting switch element 6. After that, the process proceeds to step 10, the fact that the complete opening failure has occurred is displayed on the display unit 11 as the content of the abnormality generated in the shutoff switch element 6, the operator is notified, and the processing is ended.

  If it is determined in step S4 that the element end voltage Ve is within the range of region (B), the process proceeds to step S9. In step S9, it is determined that a switching failure has occurred in the cutoff switch element 6. After that, the process proceeds to step 10, the display device 11 is displayed on the display device 11 that the switching failure has occurred as the content of the abnormality generated in the cutoff switch element 6, the operator is notified, and the processing is ended.

  Next, failure diagnosis operation of the load driving device 1 according to the first embodiment will be described with reference to FIGS. 3 to 6.

  When the load driving device 1 starts up, the central processing unit 8 executes a failure diagnosis processing program shown in FIG. At this time, central processing unit 8 outputs drive control signal S 1 to load drive control unit 5 so that load drive power supply 3 is disconnected from load 2 at the time of diagnosis at startup, and load drive is performed through load drive control unit 5. Control switch element 4;

  First, an example of the operation when the shutoff switch element 6 is normal will be described with reference to FIG.

  As shown in FIG. 3, the central processing unit 8 switches ON / OFF of the conduction / cutoff control signal S2 output to the cut-off switch element 6 at a constant cycle. The element end voltage Ve of the upper end 6 A of the cutoff switch element 6 is detected by the voltage detection unit 7 and is output to the central processing unit 8.

  When the cut-off switch element 6 is appropriately cut off (OFF) with respect to the conduction / cut-off control signal S2 output from the central processing unit 8, the resistance value of the cut-off switch element 6 becomes a very high value. Therefore, the element end voltage Ve of the upper end 6A has the same value as the diagnostic voltage Vd output from the diagnostic voltage source 9. By reading and judging this by the central processing unit 8, it can be diagnosed that the shutoff switch element 6 is properly shut off.

  Further, if the cutoff switch element 6 is properly conducted (ON), the conduction resistance at that time becomes a sufficiently small value. For this reason, the element end voltage Ve of the upper end 6A is a voltage (zero voltage) that is almost the same as the ground potential. As described above, when the interrupting switch element 6 is normal, the element end voltage Ve of the upper end 6A of the interrupting switch element 6 has the diagnostic voltage Vd and the zero voltage according to the conduction / cutoff control signal S2. Switch between and. Therefore, the central processing unit 8 can detect the failure of the cutoff switch element 6 by evaluating the value of the element end voltage Ve.

  Next, the case where the disconnection switch element 6 has an open failure will be described with reference to FIG.

  In the case of the open failure, when the conduction / cutoff control signal S2 is OFF, the element end voltage Ve of the upper end 6A of the cut-off switch element 6 is the output voltage of the diagnostic voltage source 9 (diagnostic voltage Vd) It becomes the same value as. This point is the same as when the shutoff switch element 6 is normal. However, since the blocking switch element 6 is in the open failure state, the blocking switch element 6 is in the blocking state (OFF) regardless of the conduction / cutoff control signal S2. That is, when the conduction / cutoff control signal S2 is ON, the element end voltage Ve is not interlocked with the conduction / cutoff control signal S2, and the diagnostic voltage Vd is maintained. In such a case, the central processing unit 8 determines that an open failure has occurred in the cutoff switch element 6 and that it is in an abnormal state.

  Next, the case where a short circuit failure occurs in the cutoff switch element 6 will be described with reference to FIG.

  In the case of a short circuit failure, the interrupting switch element 6 is always in a conducting state. Therefore, the element end voltage Ve of the upper end 6A of the cutoff switch element 6 is always a low voltage (zero voltage) having the same potential as the ground regardless of the conduction / cutoff control signal S2. In such a case, the central processing unit 8 determines that a short circuit failure occurs in the interrupting switch element 6 and that the state is abnormal.

  Furthermore, a failure such as switching of the interrupting switch element 6 with an incomplete resistance value due to a switching failure rather than a complete open or short circuit is also conceivable. The operation in that case will be described with reference to FIG.

  In this case, when the conduction / cutoff control signal S2 is OFF, the element end voltage Ve does not have a value near the diagnostic voltage Vd. In addition, when the conduction / cutoff control signal S2 is ON, the element end voltage Ve does not reach the ground potential. From this, the central processing unit 8 determines that the cutoff switch element 6 is abnormal.

  As a method of determining whether or not an appropriate element end voltage Ve is detected, not only a method in which central processing unit 8 determines based on an analog value, but also a method in which a comparator is provided outside central processing unit 8 is considered. Be When conduction / cutoff control signal S2 is OFF, element end voltage Ve exceeds a predetermined threshold (eg, first threshold VH) near diagnostic voltage Vd, and conduction / cutoff control signal S2 When the device end voltage Ve is lower than another predetermined threshold value (for example, the second threshold value VL) near the ground potential when it is ON, it is determined that the cutoff switch element 6 is normal. Is possible.

  The waveform of the element end voltage Ve or the like shown in FIG. 6 is an example of a switching failure, and the form thereof is not determined uniquely. However, the central processing unit 8 diagnoses whether or not the element end voltage Ve to be measured appears properly when the ON / OFF of the conduction / cutoff control signal S2 is switched. Therefore, the present method makes it possible to detect various forms of switching failures, and is expected to improve the reliability. Further, the waveform of the conduction / cutoff control signal S2 shown in FIGS. 3 to 6 is an example, and the diagnosis does not necessarily have to be performed with the waveform of the illustrated pattern.

  Thus, according to the first embodiment, the diagnostic voltage source 9 is connected to the load 2 side of the cutoff switch element 6, and the central processing unit 8 receives the load drive power supply 3 by the drive control signal S 1. The element end voltage Ve when the on / off control signal S2 for making the blocking switch element 6 conductive (ON) in a state of blocking the load 2 is cut off, and the blocking switch element 6 to be blocked (OFF) Whether the interrupting switch element 6 is normal or abnormal is determined based on the element end voltage Ve when the conduction / cutoff control signal S2 is output.

  Therefore, when the central processing unit 8 outputs, for example, the ON / OFF control signal S2, and the element end voltage Ve has a value similar to that of the diagnostic voltage Vd, the open switch failure of the shutoff switch element 6 occurs. Can be determined to have occurred. Further, for example, when the central processing unit 8 outputs the ON / OFF control signal S2 of OFF and the element end voltage Ve has a value substantially equal to the ground potential of the voltage source 9 for diagnosis, the switch element for shutoff It can be determined that a short circuit failure has occurred in 6. Furthermore, when the central processing unit 8 outputs the ON / OFF control signal S2 of OFF, for example, the element end voltage Ve does not become a value near the diagnostic voltage Vd, and the ON / OFF control signal In the state where S2 is output, when the element end voltage Ve does not become the ground potential, it can be determined that a switching failure has occurred in the cutoff switch element 6. As a result, the central processing unit 8 determines whether the interrupting switch element 6 is normal or abnormal based on the relationship between the output state (ON and OFF) of the conduction / cutoff control signal S2 and the element end voltage Ve. be able to.

  The load driving device 1 further includes a voltage detection unit 7 connected to the load 2 side (upper end 6A) of the cutoff switch element 6, which detects the element end voltage Ve and outputs it to the central processing unit 8. There is. Therefore, the voltage detection unit 7 can directly detect the element end voltage Ve of the upper end portion 6A of the cutoff switch element 6.

  In addition, between the load 2 and the load driving switch element 4, a load-side backflow preventing element 10 is provided that prevents current flow from the diagnostic voltage source 9 toward the load 2. Thereby, even when there is a portion connected to the ground or the like inside the load driving switch element 4, for example, the current from the diagnostic voltage source 9 to the load 2 can be prevented.

  The central processing unit 8 according to the first embodiment detects the abnormal state of the interrupting switch element 6 by dividing it into three states of a complete open fault, a complete short circuit fault, and a switching fault. It shall be output. The present invention is not limited to this, and the central processing unit 8 may determine, for example, only the normality and the abnormality of the cutoff switch element 6 and output the result to the display device 11.

  Further, the load-side reverse flow prevention element 10 is not limited to one provided between the load 2 and the load driving switch element 4. For example, as indicated by a broken line in FIG. 1, instead of the load side backflow prevention element 10, it is connected to the upstream side (load 2 side) than the diagnostic voltage source 9 and between the load 2 and the cutoff switch element 6 The load side backflow prevention element 13 may be provided on the Moreover, both the load side backflow prevention elements 10 and 13 may be provided.

  Moreover, the load side backflow prevention element 10 is not limited to the one using the diode D. As in the first modified example shown in FIG. 9, the load side backflow preventing element 14 may be configured using a field effect transistor (FET). In this case, it is possible to prevent the current flowing upstream of the load 2 by the built-in diode D of the FET.

  Next, FIG. 10 shows a load driving device according to a second embodiment of the present invention. A feature of the second embodiment is that between the diagnostic voltage source and the cutoff switch element, a diagnostic side backflow prevention element is provided that prevents current from flowing from the load toward the diagnostic voltage source. It is to In the present embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The load driving device 21 according to the second embodiment is configured substantially the same as the load driving device 1 according to the first embodiment. For this reason, the load driving device 21 includes a load driving switch element 4, a cutoff switch element 6, a central processing unit 8, a display device 11 and the like. In addition to this, the load drive device 21 is provided with a diagnosis side backflow prevention element 22 provided between the diagnosis voltage source 9 and the cutoff switch element 6.

  The diagnosis side backflow prevention element 22 is connected between the output end of the diagnosis voltage source 9 and the upper end 6 A of the cutoff switch element 6. That is, the diagnosis side backflow prevention element 22 is connected between the diagnostic voltage source 9 and the load 2. Specifically, the diagnosis side backflow prevention element 22 is connected between the output end of the diagnosis voltage source 9 and the connection point between the diagnosis voltage source 9 and the cutoff switch element 6. The diagnosis side backflow prevention element 22 prevents mutual interference between the load current path and the diagnostic voltage source 9 when the load 2 is driven.

  The diagnosis side backflow prevention element 22 is configured substantially the same as the load side backflow prevention element 10. Therefore, the diagnosis side backflow prevention element 22 is configured using, for example, a single diode D (see FIG. 11).

  The load drive circuit 23 includes a diagnosis-side backflow prevention element 22 in addition to the load drive switch element 4, the cutoff switch element 6, the central processing unit 8 and the like. The load drive circuit 23 is connected to the load 2 and the display device 11.

  The load driving device 21 according to the second embodiment has the configuration as described above. Also in the second embodiment configured as described above, the same effects as those of the first embodiment described above can be obtained.

  Also, when the interrupting switch element 6 is disconnected from the state where the load 2 is being driven, and the timing of the interrupt between the interrupting switch element 6 and the load drive switch element 4 deviates, or The inductive energy of the solenoid valve serving as the load 2 may be released. In such a case, a large voltage may be instantaneously applied to the diagnostic voltage source 9, which may damage the circuit of the diagnostic voltage source 9.

  On the other hand, in the second embodiment, the diagnosis side backflow prevention element 22 is provided between the diagnosis voltage source 9 and the cutoff switch element 6. Therefore, the diagnosis side backflow prevention element 22 can prevent mutual interference between the load current path and the diagnostic voltage source 9 when the load 2 is driven.

  In the second embodiment, the diagnosis side backflow prevention element 22 is constituted by the diode D. The present invention is not limited to this, and as in a second modified example shown in FIG. 12, the diagnosis-side backflow prevention element 24 may be configured using the switch element 24A.

  For example, in the case of driving the normally-off load 2, when an open failure occurs in the cutoff switch element 6, it is impossible to drive the load 2 itself. For this reason, an open failure of the cutoff switch element 6 may be considered as a failure on the safety side. As described above, when it is only necessary to detect a short circuit failure of the interrupting switch element 6, it may be diagnosed whether the interrupting of the interrupting switch element 6 can be appropriately performed. At this time, the diagnosis side backflow prevention element 24 applies the output voltage (diagnosis voltage Vd) of the diagnosis voltage source 9 to the upper end 6A of the shutoff switch element 6 only when the shutoff switch element 6 is shut off.

  The diagnosis side backflow prevention element 24 shown in FIG. 12 includes a switch element 24A for connecting or blocking between the diagnosis voltage source 9 and the cutoff switch element 6. Conduction and interruption of the switch element 24A are interlocked and switched in a reverse logic relationship with ON / OFF of the conduction / cutoff control signal S2 for switching the shutoff switch element 6. Therefore, the on / off control signal S2 is input as a control signal (switching signal) of the switch element 24A via the logic element 24B formed of the NOT circuit.

  Therefore, when the cutoff switch element 6 is shut off, the switch element 24A conducts. Therefore, if the cut-off switch element 6 is normal, the voltage detection unit 7 detects the same voltage as the output voltage (diagnosis voltage Vd) of the diagnosis voltage source 9 and outputs it to the central processing unit 8. If the element end voltage Ve is clearly lower than the original output voltage (diagnosis voltage Vd) of the diagnostic voltage source 9, the central processing unit 8 shorts the shutoff switch element 6 Determine that a failure has occurred. When the start-up diagnosis is finished and the load 2 is driven, the switch element 24A is cut off by making the cut-off switch element 6 conductive. Therefore, no current flow from the load current path to the diagnostic voltage source 9 occurs, and mutual interference between the load current path and the diagnostic voltage source 9 can be prevented during load driving.

  Next, FIG. 13 shows a load driving device according to a third embodiment of the present invention. The feature of the third embodiment is that the load current detection unit, the diagnosis side backflow prevention element, and the comparator are provided. In the present embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The load driving device 31 according to the third embodiment is configured substantially the same as the load driving device 1 according to the first embodiment. For this reason, the load driving device 31 includes the load driving switch element 4, the interrupting switch element 6, the central processing unit 38, the display device 11 and the like. However, in the load drive device 31, the voltage detection unit 7 according to the first embodiment is omitted. On the other hand, the load drive device 31 includes a load current detection unit 32, a diagnosis side backflow prevention element 37, and a comparator 36.

  As shown in FIGS. 13 and 14, the load current detection unit 32 is connected to the downstream side of the load 2. The load current detection unit 32 includes a current / voltage conversion element 33 that generates a potential difference ΔV according to the load current IL flowing through the load 2, and an amplification circuit 34 that amplifies a signal according to the difference between the reference voltage Vref and the potential difference ΔV. ,have.

  The current / voltage conversion element 33 is constituted by, for example, a resistance element R, and is connected between the load 2 and the upper end 6A of the cutoff switch element 6. That is, the upper end portion 33A of the current / voltage conversion element 33 is connected to the load 2, and the lower end portion 33B of the current / voltage conversion element 33 is connected to the cutoff switch element 6. At this time, the lower end portion 6B of the cutoff switch element 6 is connected to the ground. Therefore, a path from the load drive power supply 3 to the ground connected to the downstream side of the cutoff switch element 6 via the load 2 forms a load current path. The current / voltage conversion element 33 is connected in the middle of the load current path.

  The current / voltage conversion element 33 generates a potential difference ΔV, which is proportional to the current flowing inside, between the two terminals. At this time, the same current as the load current IL flows in the current-voltage conversion element 33. Therefore, the current / voltage conversion element 33 generates a potential difference ΔV according to the load current IL. The current / voltage conversion element 33 outputs the potential of each of the two terminals to the amplification circuit 34.

  The amplification circuit 34 amplifies a signal corresponding to the difference between the reference voltage Vref and the potential difference ΔV, and outputs the amplified signal to the central processing unit 38. Therefore, the amplifier circuit 34 acquires a potential difference ΔV between two terminals of the current / voltage conversion element 33 (between the upper end 33A and the lower end 33B). Further, the reference voltage Vref is input to the amplification circuit 34 from the diagnostic voltage source 35 which is different from the potential difference ΔV. Therefore, the amplifier circuit 34 outputs a voltage value obtained by subtracting a value proportional to the potential difference ΔV from the reference voltage Vref to the central processing unit 38.

  The amplifier circuit 34 is configured of, for example, a differential amplifier circuit including an operational amplifier OPA. In this case, the potential of the upper end 33A of the current / voltage conversion element 33 is input to the inverting input terminal of the operational amplifier OPA. The potential of the lower end portion 33B of the current / voltage conversion element 33 is input to the non-inversion input terminal of the operational amplifier OPA. In addition to this, the noninverting input terminal of the operational amplifier OPA is a reference voltage input unit 34A. Therefore, the reference voltage Vref is input to the non-inverting input terminal of the operational amplifier OPA via the comparator 36.

  Therefore, when load current IL does not flow and potential difference ΔV does not occur between the two terminals of current / voltage conversion element 33, amplification circuit 34 receives the voltage input to the non-inverting input terminal of operational amplifier OPA. (Reference voltage Vref) is output as it is.

  The diagnostic voltage source 35 is configured substantially the same as the diagnostic voltage source 9 according to the first embodiment. Therefore, the diagnostic voltage source 35 outputs the reference voltage Vref lower than the drive voltage V0 as the diagnostic voltage. The output side of the diagnostic voltage source 35 is connected to the upper end 6 A of the cutoff switch element 6.

  As shown in FIG. 14, the diagnostic voltage source 35 is configured of, for example, a constant voltage source that outputs the same voltage as the reference voltage Vref of the amplifier circuit 34. In the diagnostic voltage source 35, when the cutoff switch element 6 is conductive, the voltage (input voltage Vi) on the input side of the comparator 36 is equal to the element end voltage Ve of the upper end 6A of the cutoff switch element 6. Is provided with a pull-up resistor PUR so that it can follow. That is, the diagnostic voltage source 35 shown in FIG. 14 doubles as a voltage source for failure diagnosis and a reference voltage source for the amplifier circuit 34 and the comparator 36. The diagnostic voltage source 35 may output a diagnostic voltage having a voltage value different from that of the reference voltage Vref. That is, the diagnostic voltage source 35 may be provided separately from the reference voltage source such as the amplifier circuit 34.

  The comparator 36 is connected to a connection point P between the diagnostic voltage source 35 and the diagnosis side backflow prevention element 37, and the element end voltage Ve input via the diagnosis side backflow prevention element 37 has a predetermined threshold value. When the voltage is lower than the value, the reference voltage Vref is output to the input side of the amplifier circuit. The comparator 36 is constituted by, for example, a Schmitt trigger inverter STI. The comparator 36 outputs the reference voltage Vref when the input voltage Vi exceeds a high potential threshold (for example, the first threshold Vth1) near the reference voltage Vref. The comparator 36 outputs the voltage (zero voltage) of the ground potential when the input voltage Vi falls below the low potential threshold (for example, the second threshold Vth2) near the ground potential.

  The comparator 36 is an output voltage according to the interruption and conduction of the interruption switch element 6 based on the voltage (input voltage Vi) of the input terminal interlocked with the element end voltage Ve of the upper end 6A of the interruption switch element 6 The signal Vo is output to the non-inverted input terminal of the operational amplifier OPA as the reference voltage input unit 34A of the amplifier circuit 34. Specifically, the comparator 36 outputs the voltage (zero voltage) of the ground potential as the output voltage Vo if the cutoff switch element 6 is disconnected (OFF). The comparator 36 outputs the reference voltage Vref of the amplifier circuit 34 as the output voltage Vo if the cutoff switch element 6 is turned on (ON). The amplification circuit 34 outputs the output voltage Vo of the comparator 36 as it is to the central processing unit 38 as it is by means of the operation of the amplification circuit 34 in the failure diagnosis at startup.

  At this time, the amplifier circuit 34 and the comparator 36 function as elements corresponding to the voltage detection unit 7 according to the first embodiment. For this reason, the central processing unit 38 operates the switching switch element 6 based on whether or not the output voltage Va from the amplifier circuit 34 is properly switched with respect to the on / off control signal S2 to the switching switch element 6. To diagnose

  The diagnosis side backflow prevention element 37 is provided between the diagnosis voltage source 35 and the cutoff switch element 6. That is, the diagnosis side backflow prevention element 37 is connected between the diagnostic voltage source 35 and the load 2. The diagnosis side backflow prevention element 37 is configured substantially the same as the diagnosis side backflow prevention element 22 according to the second embodiment. The diagnosis side backflow prevention element 37 prevents mutual interference between the load current path and the diagnostic voltage source 9 when the load 2 is driven.

  In the diagnosis side backflow prevention element 37, the input voltage Vi of the comparator 36 connected to the diagnostic voltage source 35 changes following the element end voltage Ve of the upper end 6A of the cutoff switch element 6. It must be of the nature. Therefore, the diagnosis side backflow prevention element 37 is configured of, for example, a diode D in which the direction from the diagnosis voltage source 35 toward the cutoff switch element 6 is a forward direction.

  When the load 2 is driven, the central processing unit 38 receives an output voltage Va from the amplification circuit 34 according to the load current IL. At this time, the central processing unit 38 outputs the drive control signal S1 to the load drive control unit 5 according to the load current IL. The load drive control unit 5 controls ON and OFF of the load drive switch element 4 according to the drive control signal S1. Thus, the central processing unit 38 can perform feedback control of the load current IL.

  The central processing unit 38 is configured by, for example, a microcomputer. The central processing unit 38 executes a failure diagnosis processing program shown in FIG. 15 stored in a memory (not shown). Here, when the load 2 is stopped, an output voltage Va corresponding to conduction or cutoff of the cutoff switch element 6 is input from the amplification circuit 34. Therefore, the central processing unit 38 diagnoses, based on the output voltage Va from the amplification circuit 34, whether or not the cutoff switch element 6 is properly blocked.

  Further, the load drive switch element 4 for switching the load, the switch element 6 for cutoff, the load current detection unit 32, the comparator 36, the diagnosis side backflow prevention element 37, the central processing unit 38, etc. Are configured. The load drive circuit 39 is connected to the load 2 and the display device 11.

  Next, a failure diagnosis processing program executed by the central processing unit 38 of the load driving device 31 according to the third embodiment will be described with reference to FIG.

  When the process for diagnosing the failure of the cutoff switch element 6 is started, the central processing unit 38 outputs a drive control signal S1 for turning off the load drive switch element 4 and cuts off the load drive power supply 3 from the load 2.

  Thereafter, in step S21, the central processing unit 38 outputs a conduction / cutoff control signal S2 for turning off the shutoff switch element 6 (cutoff state) to the shutoff switch element 6. In the subsequent step S22, the output voltage Va of the amplifier circuit 34 determines either the reference voltage Vref or the zero voltage (ground potential).

  If it is determined in step S22 that the output voltage Va is a zero voltage, the process proceeds to step S23. In step S23, the central processing unit 38 outputs a conduction / cutoff control signal S2 for turning the shutoff switch element 6 ON (connected state) to the shutoff switch element 6. In the subsequent step S24, as in step S22, the output voltage Va of the amplifier circuit 34 determines either the reference voltage Vref or the zero voltage.

  When it is determined in step S24 that the output voltage Va is the reference voltage Vref, the process proceeds to step S25. In step S25, it is determined that the interrupting switch element 6 is normal, and the process ends.

  On the other hand, when it is determined in step S22 that the output voltage Va is the reference voltage Vref, the process proceeds to step S26. In step S26, it is determined that a short circuit failure has occurred in the interrupting switch element 6. Thereafter, the process proceeds to step 28, and as the content of the abnormality occurring in the cutoff switch element 6, the fact that a short circuit failure has occurred is displayed on the display device 11, notified to the operator, and the processing is ended.

  If it is determined in step S24 that the output voltage Va is a zero voltage, the process proceeds to step S27. In step S27, it is determined that an open circuit failure or a switching failure has occurred in the interrupting switch element 6. Thereafter, the process proceeds to step 28, and as the contents of the abnormality occurring in the shutoff switch element 6, the fact that the open failure or the switching failure has occurred is displayed on the display device 11, notified to the operator, and the process is ended.

  Next, failure diagnosis operation of the load driving device 31 according to the third embodiment will be described with reference to FIGS. 16 to 19.

  When the load driving device 31 starts up, the central processing unit 38 executes a failure diagnosis processing program shown in FIG. At this time, central processing unit 38 outputs drive control signal S 1 to load drive control unit 5 so that load drive power supply 3 is disconnected from load 2 at the time of failure diagnosis at start-up. The drive switch element 4 is controlled.

  First, an example of the operation when the shutoff switch element 6 is normal will be described with reference to FIG.

  As shown in FIG. 16, the central processing unit 38 switches ON / OFF of the conduction / cutoff control signal S2 output to the shutoff switch element 6 at a constant cycle. When the cut-off switch element 6 is appropriately cut off (OFF) with respect to the conduction / cut-off control signal S2 output from the central processing unit 38, the resistance value of the cut-off switch element 6 becomes a very high value. Therefore, the element end voltage Ve of the upper end 6A has the same value as the reference voltage Vref output from the diagnostic voltage source 9. When the interrupting switch element 6 is properly conducted (ON) with respect to the on / off control signal S2 output from the central processing unit 38, the resistance value of the interrupting switch element 6 is set to a very low value. Become. For this reason, the element end voltage Ve of the upper end 6A is a voltage (zero voltage) that is almost the same potential as the ground potential. As described above, the element end voltage Ve of the upper end 6A of the interrupting switch element 6 is switched in conjunction with the conduction / cutoff control signal S2 output from the central processing unit 38.

  Here, the element end voltage Ve of the upper end 6A of the cutoff switch element 6 is input to the comparator 36 as the input voltage Vi. When the input voltage Vi is larger than the first threshold Vth1 on the high potential side, the comparator 36 considers that the cutoff switch element 6 is blocked, and outputs a voltage (zero voltage) of the ground potential. Further, when the input voltage Vi is lower than the second threshold Vth2 on the low potential side, it is considered that the cutoff switch element 6 is conductive, and the reference voltage Vref is output.

  The output voltage Vo of the comparator 36 is input to the reference voltage input section 34A of the amplifier circuit 34 separately from the input from the current / voltage conversion element 33. In the failure diagnosis at the time of startup, since the load current IL does not flow to the load 2, no potential difference ΔV occurs between both terminals of the current / voltage conversion element 33. Therefore, the amplifier circuit 34 outputs the voltage input to the reference voltage input unit 34A as it is to the central processing unit 38. That is, in the failure diagnosis at startup, the output voltage Va of the amplifier circuit 34 has the same value as the output voltage Vo of the comparator 36.

  Next, the case where the disconnection switch element 6 has an open failure will be described with reference to FIG.

  In the case of the open failure, when the conduction / cutoff control signal S2 is OFF, the element end voltage Ve of the upper end 6A of the cut-off switch element 6 is the output voltage (reference voltage Vref) of the diagnostic voltage source 9 It becomes the same value. This point is the same as when the shutoff switch element 6 is normal. However, since the cutoff switch element 6 is in the open failure state, the cutoff switch element 6 is in the cutoff state (OFF) regardless of the on / off control signal S2. That is, when the conduction / cutoff control signal S2 is ON, the element end voltage Ve is not interlocked with the conduction / cutoff control signal S2, and the reference voltage Vref is maintained. Therefore, the output voltage Vo of the comparator 36 received by the central processing unit 38 becomes the voltage (zero voltage) of the ground potential regardless of the on / off control signal S2. In such a case, the central processing unit 38 determines that an open failure occurs in the shutoff switch element 6 and that the state is an abnormal state.

  Next, the case where a short circuit failure occurs in the cutoff switch element 6 will be described with reference to FIG.

  In the case of a short circuit failure, the on state is always on, and the element end voltage Ve of the upper end 6A of the cutoff switch element 6 is always the same low voltage as the ground potential regardless of the on / off switching of the on / off control signal S2. (Zero voltage). Therefore, the output voltage Vo of the comparator 36 received by the central processing unit 38 becomes the reference voltage Vref regardless of the on / off control signal S2. In such a case, the central processing unit 38 determines that a short circuit failure occurs in the interrupting switch element 6 and that the state is abnormal.

  Furthermore, a failure such as switching of the interrupting switch element 6 with an incomplete resistance value due to a switching failure rather than a complete open or short circuit is also conceivable. The operation in that case will be described with reference to FIG.

  In this case, when the conduction / cutoff control signal S2 is OFF, the element end voltage Ve of the upper end 6A of the cut-off switch element 6 does not have a value near the reference voltage Vref. When the conduction / cutoff control signal S2 is ON, the element end voltage Ve of the upper end 6A of the cut-off switch element 6 does not become the ground potential. The element end voltage Ve of the upper end 6A of the cutoff switch element 6 becomes the input voltage Vi of the comparator 36. In this switching failure example, when the conduction / cutoff control signal S2 is ON, the input voltage Vi of the comparator 36 is slightly lower than the second threshold value Vth2. However, when the on / off control signal S2 is OFF, the input voltage Vi of the comparator 36 does not exceed the first threshold value Vth1. For this reason, the output voltage Va of the amplification circuit 34 maintains the voltage (zero voltage) of the ground potential regardless of the switching between ON and OFF of the conduction / cutoff control signal S2. Also in such a case, the central processing unit 38 determines that the cutoff switch element 6 is abnormal.

  The waveform of the element end voltage Ve or the like of the upper end 6A of the cutoff switch element 6 shown in FIG. 19 is an example of a switching failure, and the form thereof is not determined uniquely. However, central processing unit 38 conducts conduction of cutoff switch element 6 based on output voltage Va of amplification circuit 34 corresponding to element end voltage Ve when the conduction / cutoff control signal S2 is switched ON / OFF. And diagnose if the blockade switches properly. Therefore, the present method makes it possible to detect various forms of switching failure, and is expected to improve the reliability. The waveforms of the on / off control signal S2 shown in FIGS. 16 to 19 are merely examples, and the diagnosis does not necessarily have to be performed using the waveforms of the illustrated patterns.

  Further, after the driving of the load 2 is started, the cutoff switch element 6 is turned on (ON). At this time, the comparator 36 outputs the reference voltage Vref to the amplifier circuit 34. Therefore, the amplification circuit 34 outputs a value obtained by subtracting a voltage proportional to the potential difference ΔV between the terminals acquired from the current / voltage conversion element 33 from the reference voltage Vref. That is, in order to perform current feedback control, the amplifier circuit 34 outputs a signal (output voltage Va) according to the load current IL. Thus, the load current detection unit 32 performs a normal operation of detecting the load current IL. The load drive device 31 according to the third embodiment has a simple configuration without the addition of an input terminal to the central processing unit 38 for diagnosis at start-up, and the failure diagnosis at start-up of the switching switch element 6 is performed. It is possible.

  The load driving device 31 according to the third embodiment has the configuration as described above. Also in the third embodiment configured as described above, the same effects as those of the above-described first embodiment can be obtained.

  In the load drive device 31 according to the third embodiment, the diagnostic voltage source 35 is connected to the load 2 side of the cutoff switch element 6, and the potential difference ΔV corresponding to the load current IL flowing through the load 2 is A load that has a current / voltage conversion element 33 to be generated and an amplification circuit 34 that amplifies a signal corresponding to the difference between the reference voltage Vref and the potential difference ΔV and outputs the signal to the central processing unit 38 and detects the load current IL. A diagnosis side backflow prevention element provided between the current detection unit 32 and the diagnostic voltage source 35 and the cutoff switch element 6 for preventing current from flowing from the cutoff switch element 6 toward the diagnostic voltage source 35 An element end voltage Ve which is connected to a connection point P between the diagnostic voltage source 35 and the diagnosis side backflow prevention element 37 and is input via the diagnosis side backflow prevention element 37 has a predetermined threshold value ( For example, the second threshold value Vth2) And a comparator 36 which outputs the reference voltage Vref to the input side (reference voltage input unit 34A) of the amplifier circuit 34 when the voltage is low.

  Here, if the voltage drop due to the diagnosis side backflow prevention element 37 is ignored, the input voltage Vi having the same value as the element end voltage Ve is input to the comparator 36. Therefore, the output voltage Vo of the comparator 36 changes in accordance with the element end voltage Ve. Specifically, when the element end voltage Ve is higher than the first threshold Vth1 on the high potential side, the comparator 36 outputs the output voltage Vo which has become the ground potential. On the other hand, when the element end voltage Ve is lower than the second threshold Vth2 on the low potential side, the comparator 36 outputs the output voltage Vo that has become the reference voltage Vref.

  On the other hand, when the load drive power supply 3 is disconnected from the load 2, the load current IL does not flow. At this time, the amplifier circuit 34 outputs the output voltage Vo of the comparator 36 as it is. Therefore, the central processing unit 38 receives the output voltage Va from the amplification circuit 34 according to the element end voltage Ve.

  At this time, central processing unit 38 conducts conduction / cutoff control signal S2 (control signal) to conduct (turn on) switching switch element 6 in a state in which load drive power supply 3 and load 2 are cut off by drive control signal S1. The interrupting switch element 6 is based on the element end voltage Ve at the time of outputting the signal and the element end voltage Ve at the time of outputting the conduction / cutoff control signal S2 for interrupting the interrupting switch element 6. Determine if it is normal or abnormal. That is, the central processing unit 38 can determine whether the cutoff switch element 6 is normal or abnormal based on the output voltage Va of the amplifier circuit 34 which changes in accordance with the element end voltage Ve.

  Further, after the driving of the load 2 is started, the cutoff switch element 6 is turned on (ON). At this time, the amplification circuit 34 subtracts a voltage proportional to the potential difference ΔV between the terminals acquired from the current / voltage conversion element 33 from the reference voltage Vref which is the output voltage Vo of the comparator 36 and responds to the subtraction value. Output the output voltage Va. That is, when driving the load 2, the amplifier circuit 34 outputs a signal (output voltage Va) according to the load current IL. Thereby, the load current detection unit 32 can detect the load current IL and can input the output signal Va corresponding to the load current IL to the central processing unit 38.

  Therefore, when the load 2 is driven, the load current detection unit 32 can be used to detect the load current IL. In addition to this, the load current detection unit 32 can be used to output a signal (output voltage Va) according to the element end voltage Ve when the load 2 and the load drive power supply 3 are disconnected.

  As a result, the load driving device 31 according to the third embodiment can input a signal (output voltage Va) according to the element end voltage Ve to the central processing unit 38 using the load current detection unit 32. . Therefore, there is no need to add an input terminal to the central processing unit 38 in order to perform failure diagnosis on the shutoff switch device 6, and failure diagnosis on startup of the shutoff switch device 6 can be performed with a simple configuration. it can.

  In addition, the central processing unit 38 according to the third embodiment detects a case where the interrupting switch element 6 is abnormal divided into two states of an open failure and a short circuit failure or a switching failure, and the display device 11 It shall be output. The present invention is not limited to this, and the central processing unit 38 may determine, for example, only normality and abnormality of the cutoff switch element 6 and output the result to the display device 11.

  Further, in the third embodiment, the load-side backflow prevention element 10 is provided between the load 2 and the load drive switch element 4. The present invention is not limited to this, and may be connected upstream of the diagnostic voltage source, and a load-side backflow prevention element may be provided between the load and the cutoff switch element. Moreover, you may provide not only a single load side backflow prevention element but several load side backflow prevention elements.

  In the first to third embodiments, a single load 2 is connected in series to a single interrupting switch element 6. The present invention is not limited to this. A single interrupting switch element 6 may be connected in series to a plurality of loads 2 connected in series with each other, and for a plurality of loads 2 connected in parallel with each other, A single blocking switch may be connected in series.

  It is needless to say that each of the above embodiments is an exemplification, and partial replacement or combination of the configurations shown in the different embodiments is possible.

1, 21, 31 load drive device 2 load 3 load drive power supply 4 load drive switch element 5 load drive control unit 6 cut-off switch element 7 voltage detection unit 8, 38 central processing unit 9 diagnostic voltage source 10, 13, 14 load Side-backflow prevention element 11 Display device 22, 24 and 37 Diagnosis-side backflow prevention element 32 Load current detection unit 33 Current-to-voltage conversion element 34 Amplifier circuit 35 Diagnostic voltage source 36 Comparator

Claims (5)

A load drive switch element provided between the load and the load drive power supply and controlled by the load drive control unit;
A breaking switch element provided between the load and the ground;
A drive control signal to the load drive control unit is output, and a conduction / cutoff control signal to conduct or block the shutoff switch element is output, and based on an element end voltage on the load side of the shutoff switch element. A central processing unit that determines whether the shutoff switch element is normal or abnormal;
A load driving device including: a judgment result output unit for outputting the judgment result by the central processing unit;
A voltage source for diagnosis is connected to the load side of the interrupting switch element,
The central processing unit outputs the conduction / cutoff control signal that causes the cut-off switch element to conduct while the load drive power supply and the load are cut off by the drive control signal. It is characterized by judging whether the interruption switch element is normal or abnormal based on the element end voltage when the interruption / switching control signal for interrupting the interruption switch element is output. Load drive device.   The load driving device according to claim 1, further comprising: a voltage detection unit connected to the load side among the blocking switch elements, detecting a voltage at the element end and outputting the voltage to the central processing unit. .   Load-side reverse current that prevents current from flowing from the diagnostic voltage source toward the load between the load and the load drive switch element or between the load and the cut-off switch element 2. A load drive as claimed in claim 1, characterized in that a protection element is provided.   Between the diagnostic voltage source and the cutoff switch element, a diagnostic side backflow prevention element for preventing current from flowing from the load toward the diagnostic voltage source is provided. The load drive device according to claim 1. The current-voltage conversion element generates a potential difference according to a load current flowing through the load, and an amplification circuit amplifies a signal according to a difference between a reference voltage and the potential difference and outputs the amplified signal to the central processing unit. A load current detection unit that detects the load current;
A diagnosis side backflow prevention element provided between the diagnostic voltage source and the cutoff switch element, for preventing current from flowing from the load toward the diagnostic voltage source;
When it is connected to a connection point between the diagnostic voltage source and the diagnosis side backflow prevention element, and the element end voltage inputted via the diagnosis side backflow prevention element is lower than a predetermined threshold value The load drive device according to claim 1, further comprising: a comparator that outputs the reference voltage to an input side of the amplification circuit.

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