JP2014162423A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of promoting realization of smaller size and assurance of reliability.SOLUTION: On an electrification path from a power source (DC power source B) to a motor drive part 13, a power supply relay 17 for electrical conduction/shielding of the electrification path is provided. The power supply relay 17 is arranged in back to back arrangement in which two MOSFETs 17a, 17b are connected in series, to allow shielding of currents in both directions. A thermistor T1 is arranged near the MOSFET17b, for detecting temperature t1 near the MOSFET17b. Then, when the temperature t1 is equal to a preset reference temperature ta or higher, it is determined that heating abnormality is occurring at the MOSFET17b.

Description

  The present invention relates to an electric power steering apparatus including a power relay that controls conduction / cutoff of an energization line.

2. Description of the Related Art Conventionally, as a steering device, an electric power steering device that gives a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque with which a driver steers a steering wheel has been widespread.
As such an electric power steering device, for example, there is a technique described in Patent Document 1. In this technology, the open / close state of the electric motor and the energization line of its drive circuit is controlled by a power relay such as an electromagnetic relay. Here, the temperature of the electromagnetic relay is sequentially estimated, and when the estimated temperature value exceeds a predetermined value, the upper limit of the target current value of the electric motor is decreased stepwise.

JP 2001-206236 A

However, in the technique described in Patent Document 1, a so-called mechanical relay such as an electromagnetic relay is adopted as a power relay. However, since the mechanical relay has a large structural volume, an electric power steering apparatus that is desired to be downsized is desired. It is a problem.
Therefore, an object of the present invention is to provide an electric power steering device that can achieve downsizing and ensure the reliability of a power supply relay.

  In order to solve the above problems, one aspect of the present invention is an electric power steering apparatus including an electric motor that applies a steering assist force to a steering mechanism of a vehicle, and a motor driving unit that drives the electric motor. A power supply for supplying a power supply voltage to the motor drive unit, a first MOSFET provided in a current-carrying path from the power supply to the motor drive unit, which conducts / cuts off the current-carrying path, and a drain of the first MOSFET A first parasitic diode having an anode connected to the motor driving unit side and a cathode connected to the DC power source side between the sources, and the motor driving unit side than the first MOSFET of the energization path is provided. The second MOSFET for conducting / cutting off the energization path and the drain and source of the second MOSFET, the anode on the DC power supply side, A power relay having a second parasitic diode connected to the motor driving unit side of the sword, a temperature detecting unit for detecting a temperature at least in the vicinity of the second parasitic diode, and detected by the temperature detecting unit And an abnormality detection unit that detects an abnormality of the power supply relay based on temperature.

  Thus, by adopting a semiconductor relay with two MOSFETs arranged in series back-to-back as the power relay, the power relay can be reduced in size, and as a result, the entire electric power steering control device can be reduced in size. can do. Further, since the temperature in the vicinity of the latter MOSFET (second MOSFET) is detected among the two MOSFETs arranged in the energization path from the power source to the motor drive unit, abnormal heat generation of the power relay can be detected. As a situation where abnormal heat generation of the power relay occurs, there is a case where a conduction abnormality occurs only in the subsequent MOSFET. In this case, since power is supplied from the power supply to the motor drive section through the front-stage MOSFET and further through the parasitic diode of the rear-stage MOSFET, a larger current than normal flows through the parasitic diode of the rear-stage MOSFET, causing an abnormality. A fever occurs. Therefore, the abnormal heat generation can be appropriately detected by monitoring the temperature in the vicinity of the MOSFET in the subsequent stage.

In the above, the abnormality detection unit has an abnormality in the power relay when a temperature in the vicinity of the second parasitic diode detected by the temperature detection unit is equal to or higher than a preset reference temperature. It is preferable to judge that.
In this way, the temperature in the vicinity of the subsequent MOSFET is compared with a preset reference temperature. If the reference temperature is set to the steady heat generation temperature of the rear-stage MOSFET, abnormal heat generation of the rear-stage MOSFET can be easily detected.

Further, in the above, the temperature detection unit detects a temperature at a position away from the power relay on the first temperature detection unit that detects a temperature in the vicinity of the second parasitic diode and a mounting board of the power relay. A second reference temperature detector, wherein the abnormality detector has a preset absolute value of the difference between the temperature detected by the first temperature detector and the temperature detected by the second temperature detector. When the temperature is equal to or higher than the temperature, it is preferable to determine that an abnormality has occurred in the power supply relay.
In this way, the temperature in the vicinity of the MOSFET in the subsequent stage is compared with the temperature at a position away from the power supply relay. Therefore, it is possible to appropriately detect abnormal heat generation of the MOSFET in the subsequent stage. Further, when the temperature at a position away from the power supply relay is higher than the temperature in the vicinity of the MOSFET at the subsequent stage, it is possible to detect that a heat generation abnormality has occurred other than the power supply relay.

Further, in the above, when the abnormality detection unit detects an abnormality of the power supply relay, the current command value of the electric motor is limited compared to when the abnormality detection unit detects no abnormality of the power supply relay. It is preferable to include a current limiting unit.
Thus, when an abnormality occurs in the power supply relay, the power consumption of the power module can be reduced by limiting the current command value of the electric motor. Therefore, it is possible to prevent a problem from occurring in each element due to accumulation of heat generation.

  In the electric power steering apparatus of the present invention, a semiconductor relay in which two MOSFETs are arranged back-to-back is adopted as the power relay, so that the power relay can be reduced in size. Further, since the temperature in the vicinity of the power relay is monitored, when an abnormality occurs in the power relay, this can be detected appropriately. Therefore, when an abnormality occurs, appropriate measures can be taken and reliability can be ensured.

It is a figure which shows the basic structure of the electric power steering apparatus which concerns on this invention. It is a block diagram which shows the control system of a controller. It is a disassembled perspective view of the controller containing a semiconductor module. It is a top view of a semiconductor module. It is a flowchart which shows the temperature determination processing procedure performed with a temperature determination circuit. It is a block diagram which shows the structure of MCU. It is a block diagram which shows the control system of the controller in 2nd Embodiment. It is a top view of the semiconductor module in a 2nd embodiment. It is a flowchart which shows the temperature determination processing procedure performed with the temperature determination circuit in 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing a basic structure of an electric power steering apparatus according to the present invention.
In the electric power steering apparatus of FIG. 1, the column shaft 2 of the steering handle 1 is connected to a tight rod 6 of a steering wheel via a reduction gear 3, universal joints 4 </ b> A and 4 </ b> B, and a pinion rack mechanism 5. The column shaft 2 is provided with a torque sensor 7 that detects the steering torque of the steering handle 1, and an electric motor 8 that assists the steering force of the steering handle 1 is connected to the column shaft 2 via the reduction gear 3. Has been.

  The controller 10 that controls the electric power steering apparatus is supplied with electric power from a battery (not shown), and also receives an ignition key signal via an ignition key (not shown). The controller 10 calculates a steering assist command value serving as an assist (steering assist) command based on the steering torque Ts detected by the torque sensor 7 and the vehicle speed V detected by the vehicle speed sensor 9, and the calculated steering is performed. The current supplied to the electric motor 8 is controlled based on the auxiliary command value.

FIG. 2 is a block diagram showing a control system of the controller 10.
The controller 10 includes a microcomputer (MCU) 11, a bridge gate drive circuit 12, and a motor drive unit 13 having a FET bridge configuration.
The MCU 11 inputs a steering torque signal (steering torque Ts), a steering angle signal (steering angle θ), and a vehicle speed signal (vehicle speed V) via the input I / F circuit 14. The MCU 11 calculates a current command value based on these, and inputs the calculated current command value to the bridge gate drive circuit 12.

  The bridge gate drive circuit 12 forms a gate drive signal based on the input current command value and the like, and inputs it to the motor drive unit 13. The motor drive unit 13 drives an electric motor 8 constituted by a three-phase brushless motor. The current of the electric motor 8 is detected by the current detector 15, and the detected current signal is input as a feedback current to the MCU 11 via the A / D conversion circuit 16.

  Further, the circuit configuration of the motor driving unit 13 will be described. FETTr1 and Tr2, FETTr3 and Tr4, and FETTr5 and Tr6 connected in series are connected in parallel to the power supply line. Further, FETTr1 and Tr2, FETTr3 and Tr4, and FETTr5 and Tr6 connected in parallel to the power supply line are connected to the ground line. This constitutes an inverter.

  Here, the FET Tr1 and Tr2 constitute, for example, a c-phase arm of a three-phase motor by connecting the source electrode of the FET Tr1 and the drain electrode of the FET Tr2 in series. In addition, the FETTr3 and Tr4 constitute, for example, an a-phase arm of a three-phase motor by connecting the source electrode of the FETTr3 and the drain electrode of the FETTr4 in series. Further, the FETs Tr5 and Tr6 have a source electrode of the FET Tr5 and a drain electrode of the FET Tr6 connected in series to constitute, for example, a b-phase arm of a three-phase motor.

  Reference numeral 17 denotes a power supply relay that controls switching of the DC power supply B to be turned on. The power relay 17 is a semiconductor relay that includes two n-channel MOSFETs 17a and 17b and a resistor 17c. The MOSFETs 17a and 17b have a so-called back-to-back arrangement connected in series in the opposite direction. A parasitic diode (protective diode) is formed between the drain and source terminals of these two MOSFETs 17a and 17b so that current flows from the drain to the source.

  MOSFETs 17a and 17b are power switches for switching whether to connect the electrolytic capacitor C and the motor drive unit 13 to the DC power source B. Here, the MOSFET 17a is provided for circuit interruption for conducting / interrupting the power supply from the direct current power supply B, and the MOSFET 17b is provided for circuit protection for interrupting the power supply when the DC power supply B is reversely connected. In other words, the MOSFET 17a cuts off the forward current (right direction in FIG. 2) and the MOSFET 17b cuts off the reverse current (left direction in FIG. 2), thereby forming a power cutoff circuit that can cut off the bidirectional current. ing.

The MOSFETs 17a and 17b are on / off controlled by a switch drive circuit (gate driver) 18 so that the MOSFET 17a and 17b are in an on state (conducting state) when the electric power steering apparatus is in operation and are in an off state (non-conducting state) when stopped.
Further, a thermistor T1 is disposed in the vicinity of the MOSFET 17b. The temperature t1 detected by the thermistor T1 is input to the temperature determination circuit 19, and a temperature determination process for detecting abnormal heat generation of the power supply relay 17 is executed by the temperature determination circuit 19. This temperature determination process will be described later.

  3 is an exploded perspective view of the controller 10 including the semiconductor module of the electric power steering apparatus shown in FIG. 1. The controller 10 includes a case 20, a semiconductor module 30 as a power module including the motor drive unit 13, and heat dissipation. Sheet 39, control circuit board 40 including control arithmetic device 11 and gate drive circuit 12, power and signal connector 50, three-phase output connector 60, and cover 70.

  Here, the case 20 is formed in a substantially rectangular shape, and is provided on the flat-plate-shaped semiconductor module mounting portion 21 for mounting the semiconductor module 30 and the longitudinal end portion of the semiconductor module mounting portion 21. Three-phase for mounting a power and signal connector mounting portion 22 for mounting the power and signal connector 50 and a three-phase output connector 60 provided at the end in the width direction of the semiconductor module mounting portion 21 And an output connector mounting portion 23.

  A plurality of screw holes 21 a into which mounting screws 38 for mounting the semiconductor module 30 are screwed are formed in the semiconductor module mounting portion 21. A plurality of mounting posts 24 for mounting the control circuit board 40 are erected on the semiconductor module mounting portion 21 and the power and signal connector mounting portion 22, and the control circuit board 40 is mounted on each mounting post 24. A screw hole 24a into which a mounting screw 41 for mounting is screwed is formed. Further, the three-phase output connector mounting portion 23 is formed with a plurality of screw holes 23a into which mounting screws 61 for attaching the three-phase output connector 60 are screwed.

  The semiconductor module 30 has the circuit configuration of the motor drive unit 13 described above. As shown in FIG. 4, the substrate 31 has six FETs Tr <b> 1 to Tr <b> 6, a positive terminal 81 a connected to the power supply line 81, and A negative terminal 82a connected to the ground line is mounted. The substrate 31 is connected to an a-phase output terminal 92a connected to the a-phase output line 91a of the three-phase motor, a b-phase output terminal 92b connected to the b-phase output line 91b, and a c-phase output line 91c. A three-phase output unit 90 including a c-phase output terminal 92c is mounted. On the substrate 31, other surface mount components 37 including a capacitor are mounted. Further, the substrate 31 of the semiconductor module 30 is provided with a plurality of through holes 31a through which mounting screws 38 for mounting the semiconductor module 30 are inserted.

As shown in FIG. 3, the semiconductor module 30 configured as described above is attached to the semiconductor module mounting portion 21 of the case 20 by a plurality of mounting screws 38.
When mounting the semiconductor module 30 on the semiconductor module mounting portion 21, the heat dissipation sheet 39 is mounted on the semiconductor module mounting portion 21, and the semiconductor module 30 is mounted on the heat dissipation sheet 39. The heat generated by the semiconductor module 30 is radiated to the case 20 through the heat dissipation sheet 39 by the heat dissipation sheet 39. The heat radiating sheet 39 may be a heat radiating member such as heat radiating grease.

  The control circuit board 40 constitutes a control circuit including the control arithmetic device 11 and the gate drive circuit 12 by mounting a plurality of electronic components on the board. After the semiconductor module 30 is mounted on the semiconductor module mounting portion 21, the control circuit board 40 has a plurality of standing uprights on the semiconductor module mounting portion 21 and the power and signal connector mounting portion 22 from above the semiconductor module 30. A plurality of mounting screws 41 are mounted on the mounting post 24. The control circuit board 40 has a plurality of through holes 40a through which the mounting screws 41 are inserted.

  Further, the power and signal connector 50 is used to input a DC power source from a battery (not shown) to the semiconductor module 30 and various signals including signals from the torque sensor 12 and the vehicle speed sensor 9 to the control circuit board 40. Used. The power and signal connector 50 is attached to the power and signal connector mounting portion 22 provided on the semiconductor module mounting portion 21 with a plurality of mounting screws 51.

The three-phase output connector 60 is used to output current from the a-phase output terminal 92a, the b-phase output terminal 92b, and the c-phase output terminal 92c. The three-phase output connector 60 is attached to the three-phase output connector mounting portion 23 provided at the end in the width direction of the semiconductor module mounting portion 21 by a plurality of mounting screws 61. The three-phase output connector 60 is formed with a plurality of through holes 60a through which the mounting screws 61 are inserted.
Further, the cover 70 covers the case 20 to which the semiconductor module 30, the control circuit board 40, the power and signal connector 50, and the three-phase output connector 60 are attached from above the control circuit board 40. It is attached to cover.

Next, the temperature determination process executed by the temperature determination circuit 19 of FIG. 2 will be specifically described.
FIG. 5 is a flowchart showing a temperature determination processing procedure executed by the temperature determination circuit 19.
First, in step S1, the temperature determination circuit 19 acquires the temperature t1 detected by the thermistor T1, and proceeds to step S2.
In step S2, the temperature determination circuit 19 compares the thermistor temperature t1 acquired in step S1 with a preset reference temperature ta. Here, the reference temperature ta is set to the steady heat generation temperature of the parasitic diode of the MOSFET 17b. If it is determined that the thermistor temperature t1 is lower than the reference temperature ta, the process proceeds to step S3. If it is determined that the thermistor temperature t1 is equal to or higher than the reference temperature ta, the process proceeds to step S5 described later.

In step S3, the temperature determination circuit 19 determines that the thermistor T1 is normal, proceeds to step S4, sets the current limit flag FLG to “0” indicating that no current limit is performed, and then determines the temperature. The process ends.
On the other hand, in step S5, the temperature determination circuit 19 determines that a temperature abnormality has occurred in the thermistor T1, moves to step S6, and sets the current limit flag FLG to “1” indicating that current limit is performed. Then, the temperature determination process is terminated.

Next, a specific configuration of the MCU 11 will be described.
FIG. 6 is a block diagram showing the configuration of the MCU 11.
The current command value calculation unit 111 inputs the steering torque T and the vehicle speed V, and calculates the current command value Iref1 based on these.
The command value compensation unit 112 calculates a compensation value CM for compensating the current command value Iref1 calculated by the current command value calculation unit 111. The command value compensation unit 112 adds the self-aligning torque (SAT) estimated by the SAT estimation feedback unit 112a and the inertia compensation value calculated by the inertia compensation value calculation unit 112b by the addition unit 112c and the convergence property. A result obtained by adding the convergence compensation value calculated by the compensation value calculation unit 112d and the addition unit 112e is calculated as a compensation value CM. Here, the inertia compensation value is for compensating for the torque equivalent generated by the inertia of the electric motor 8 to prevent deterioration of the feeling of inertia or control response, and the convergence compensation value is the convergence property of the yaw rate. Is to compensate.

The compensation value CM calculated by the compensation value calculation unit 112 is added to the current command value Iref1 calculated by the current command value calculation unit 111 by the addition unit 113. The addition result of the adding unit 113 is input to the current limiting unit 114 as a current command value Iref2.
The current limiter 114 receives the current limit flag FLG that is the determination result of the temperature determination circuit 19 described above. When the current limit flag FLG = 1, the current command value Iref2 is limited to 20%, for example. The current command value Iref3 is output. On the other hand, when the current limit flag FLG = 0, the current command value Iref2 is output as it is (100%) as the current command value Iref3.

The subtraction unit 115 subtracts the motor current Im detected by the motor current detector 118a from the current command value Iref3 after the limiting process by the current limiting unit 114, and outputs the current deviation Iref4 to the current control unit 116.
The current control unit 116 performs PI control on the input current deviation and calculates a voltage command value E. The PWM control unit 117 calculates the duty ratio of the PWM signal that drives the semiconductor switching element (FET) of the inverter 118 (motor drive unit 13) based on the current control value E, and outputs this to the inverter 118.

  As described above, the power supply relay 17 that conducts / cuts off the energization path from the DC power supply B to the motor driving unit 13 is a semiconductor relay in which two switching elements (n-channel MOSFETs 17a and 17b) are arranged in series in a back-to-back manner. Therefore, as compared with a case where a so-called mechanical relay having a large structural volume such as an electromagnetic relay is employed as a power relay provided in an energization path from a power source, the power relay can be reduced in size. Therefore, it is suitable for an electric power steering apparatus that is desired to be downsized.

Of the two switching elements of the power relay 17, the temperature of the switching element (MOSFET 17b) that cuts off the current from the motor drive unit 13 side to the DC power source B side is detected, and based on the detected temperature, the power relay 17 Diagnose the abnormality.
Here, of the two switching elements, the MOSFET 17a arranged on the DC power supply B side (previous stage) of the energization path has a current in the reverse direction (from the motor drive unit 13 side to the DC power supply B side). It is an element that flows. On the other hand, the MOSFET 17b arranged on the motor drive unit 13 side (rear stage) of the energization path is an element in which a parasitic diode of the own current flows in a reverse direction (from the motor drive unit 13 side to the DC power supply B side).

Therefore, when an abnormality occurs only in the gate of the MOSFET 17a, the MOSFET 17a becomes non-conductive even if the switch drive circuit 18 outputs a signal for controlling the MOSFETs 17a and 17b to turn on the energization path. Therefore, abnormal heat generation does not occur.
However, when an abnormality occurs only in the gate of the MOSFET 17b, the MOSFET 17a becomes conductive and the MOSFET 17b becomes non-conductive. Then, the electric power supplied from the DC power supply B passes through the MOSFET 17a and further passes through the parasitic diode of the MOSFET 17b and is accumulated in the electrolytic capacitor C. At this time, a larger current than normal flows through the parasitic diode of the MOSFET 17b, and abnormal heat generation occurs.

Accordingly, the thermistor T1 is disposed in the vicinity of the MOSFET 17b, and the temperature t1 detected by the thermistor T1 is compared with the reference temperature ta which is the steady heat generation temperature, whereby the temperature abnormality of the thermistor T1, that is, the power supply relay 17 (MOSFET 17b) is abnormal. Occurrence can be detected.
Further, when a heat generation abnormality of the power supply relay 17 is detected, the motor current, which is the power consumption of the power module, is limited as compared with the normal time, so that it is possible to prevent the MOSFET 17b from being damaged due to abnormal heat generation of the parasitic diode. it can. Furthermore, since the current command value is limited when an abnormality occurs in the power supply relay 17, the steering assist force is reduced as compared with the normal time, but the EPS control itself can be continued. That is, when an abnormality occurs in the power relay 17, it is possible to continue the steering assist control that generates a steering assist force smaller than that in the normal state, and to continue the light steering while suppressing the heat generation.

As described above, when the temperature of the vicinity of the MOSFET 17b is monitored by the thermistor T1 and an unexpected sudden temperature rise is detected, the power consumed by the power module is reduced until the temperature at which each element does not fail. Failure due to overheating of the element can be prevented and the reliability of the system can be improved.
In the above description, the MOSFET 17a corresponds to the first MOSFET, the MOSFET 17b corresponds to the second MOSFET, the thermistor T1 corresponds to the temperature detection unit, and the temperature determination circuit 19 corresponds to the abnormality detection unit.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.
In the second embodiment, abnormal heat generation is detected by comparing the temperature t1 of the thermistor T1 with a preset reference temperature ta in the first embodiment, whereas the temperature t1 of the thermistor T1. Is compared with the thermistor temperature placed at some other location.
FIG. 7 is a block diagram showing a control system of the controller 10 in the present embodiment.

The controller 10 of this embodiment has the same configuration as the controller 10 shown in FIG. 2 except that the thermistor T2 is arranged in the controller 10 shown in FIG. Therefore, here, the description will focus on the different parts.
As shown in FIG. 8, the thermistor T2 is disposed on the substrate 31 of the semiconductor module 30 at a position away from the thermistor T1. The position where the thermistor T2 is disposed can be set as appropriate as long as a large current does not flow nearby on the substrate 31. The thermistor T <b> 2 inputs the detected temperature t <b> 2 to the temperature determination circuit 19.

FIG. 9 is a flowchart showing a temperature determination processing procedure executed by the temperature determination circuit 19 of the present embodiment.
First, in step S11, the temperature determination circuit 19 acquires the temperature t1 detected by the thermistor T1, and proceeds to step S12.
In step S12, the temperature determination circuit 19 acquires the temperature t2 detected by the thermistor T2, and proceeds to step S13.

  In step S13, the temperature determination circuit 19 calculates the absolute value (| t1-t2 |) of the difference between the thermistor temperature t1 acquired in step S11 and the thermistor temperature t2 acquired in step S12. Then, it is determined whether or not the absolute value of the thermistor temperature difference is lower than a preset reference temperature tb. Here, the reference temperature tb is set in consideration of the steady heat generation temperature of the parasitic diode of the MOSFET 17b and the steady heat generation temperature of the substrate 31 of the semiconductor module 30.

When it is determined that the absolute value of the thermistor temperature difference is lower than the reference temperature tb, the process proceeds to step S14. When it is determined that the absolute value of the thermistor temperature difference is equal to or higher than the reference temperature tb, The process proceeds to step S16.
In step S14, the temperature determination circuit 19 determines that the thermistors T1 and T2 are normal, proceeds to step S15, and sets the current limit flag FLG to “0” indicating that current limit is not performed. The temperature determination process ends.

  On the other hand, in step S16, the temperature determination circuit 19 determines that a temperature abnormality has occurred in the thermistor T1 or T2, and proceeds to step S17. At this time, if the thermistor temperature t1 is higher than the thermistor temperature t2, it is determined that the parasitic diode of the MOSFET 17b is overheated or the temperature detection of the thermistor T1 is defective. Further, when the thermistor temperature t1 is lower than the thermistor temperature t2, it is determined that the temperature detection of the thermistor T2 is poor or the element near the thermistor T2 is overheated abnormally.

In step S17, the temperature determination circuit 19 sets the current limit flag FLG to “1” indicating that current limit is performed, and then ends the temperature determination process.
As described above, the thermistor T1 is disposed in the vicinity of the MOSFET 17b, the thermistor T2 is disposed at a position away from the thermistor T1, and the temperature t1 detected by the thermistor T1 is compared with the temperature t2 detected by the thermistor T2. The temperature abnormality of the thermistor T1, that is, the occurrence of abnormality of the power supply relay 17 (MOSFET 17b) can be detected. Furthermore, it is possible to detect a temperature abnormality around the thermistor T2.

Therefore, the motor current can be limited not only when the heat generation abnormality occurs in the power supply relay 17 but also when the heat generation abnormality occurs in the elements around the thermistor T2, and the safety of the semiconductor module 30 is improved. Can be increased.
In the above description, the thermistor T1 corresponds to the first temperature detector, and the thermistor T2 corresponds to the second temperature detector.

  DESCRIPTION OF SYMBOLS 1 ... Steering handle, 2 ... Column shaft, 3 ... Reduction gear, 4A, 4B ... Universal joint, 5 ... Pinion rack mechanism, 6 ... Tight rod, 7 ... Torque sensor, 8 ... Electric motor, 9 ... Vehicle speed sensor, 10 DESCRIPTION OF SYMBOLS ... Controller, 11 ... MCU, 12 ... Bridge gate drive circuit, 13 ... Motor drive part, 14 ... Input I / F circuit, 15 ... Current detector, 16 ... A / D conversion circuit, 17 ... Power supply relay, 17a, 17b ... n-channel MOSFET, 18 ... switch drive circuit, 19 ... temperature determination circuit, 20 ... case, 21 ... semiconductor module mounting part, 21a ... screw hole, 22 ... power and signal connector mounting part, 23 ... three-phase output Connector mounting portion, 23a ... screw hole, 24 ... mounting post, 24a ... screw hole, 30 ... semiconductor module, 31 ... substrate, 31a ... through hole, 37 ... table Mounting parts 38 ... Mounting screw 39 ... Heat dissipation sheet 40 ... Control circuit board 40a ... Through hole 41 ... Mounting screw 50 ... Power and signal connector 51 ... Mounting screw 60 ... 3-phase output connector , 60a ... through hole, 61 ... mounting screw, 70 ... cover, 81 ... power supply line, 81a ... positive electrode terminal, 82a ... negative electrode terminal, 90 ... three phase output section, 91a ... a phase output line, 91b ... b phase output line 91c ... c-phase output line, G ... gate electrode (electrode), S ... source electrode (electrode), T1, T2 ... thermistor

Claims (4)

An electric power steering apparatus comprising: an electric motor that applies a steering assist force to a steering mechanism of a vehicle; and a motor drive unit that drives the electric motor,
A power supply for supplying a power supply voltage to the motor drive unit;
Provided in the energization path from the power source to the motor drive unit, the first MOSFET that conducts / cuts off the energization path, and the anode on the motor drive unit side between the drain and source of the first MOSFET, A first parasitic diode having a cathode connected to the DC power supply side, and a second MOSFET that is provided closer to the motor drive unit than the first MOSFET in the energization path and that conducts / cuts off the energization path; A power relay having a second parasitic diode having an anode connected to the DC power supply side and a cathode connected to the motor drive unit side between the drain and source of the second MOSFET;
A temperature detection unit for detecting a temperature in the vicinity of at least the second parasitic diode;
An electric power steering apparatus comprising: an abnormality detection unit that detects an abnormality of the power relay based on the temperature detected by the temperature detection unit.   The abnormality detection unit determines that an abnormality has occurred in the power relay when a temperature in the vicinity of the second parasitic diode detected by the temperature detection unit is equal to or higher than a preset reference temperature. The electric power steering apparatus according to claim 1, wherein The temperature detector is
A first temperature detector for detecting a temperature in the vicinity of the second parasitic diode;
A second temperature detection unit that detects a temperature at a position away from the power supply relay on the power supply relay mounting board; and
The abnormality detection unit
When the absolute value of the difference between the temperature detected by the first temperature detector and the temperature detected by the second temperature detector is equal to or higher than a preset reference temperature, an abnormality has occurred in the power relay. The electric power steering apparatus according to claim 1, wherein the determination is made.   A current limiter configured to limit the current command value of the electric motor when the abnormality detection unit detects an abnormality of the power supply relay as compared to when the abnormality detection unit detects no abnormality of the power supply relay; The electric power steering apparatus according to any one of claims 1 to 3, further comprising:

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