JP2018011385A - Motor controller and electrically-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor controller capable of preventing control from being limited by a failure of a thermistor in the motor controller in which the thermistor is mounted on each of a substrate on which switching elements are mounted, and a substrate on which an electronic component for generating a control signal to the switching element is mounted, and an electrically-driven power steering device.SOLUTION: In a controller 4, a control part 42 configured to generate a control signal to switching elements 411-414 comprises: first temperature estimation means for estimating a temperature of a metal substrate 43 based on a temperature detected by a second thermistor 46 and an integration value of a drive current when a failure in a first thermistor 45 mounted on the metal substrate 43 is detected; and second temperature estimation means for estimating a temperature of a printed circuit board 44 based on a temperature detected by the first thermistor 45 and an integration value of a drive current when a failure of the second thermistor 46 mounted on the printed circuit board 44 is detected.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a motor control device that supplies a drive current to an electric motor, and an electric power steering device including the motor control device.

  Conventionally, a motor control device that supplies a drive current to an electric motor generates a plurality of switching elements that output a drive current by switching the voltage of a DC voltage source, and a control signal that turns on / off the plurality of switching elements. There is a control unit including a plurality of electronic components, and a plurality of switching elements and electronic components of the control unit are mounted on different substrates (for example, see Patent Document 1).

  In the motor control device described in Patent Document 1, a plurality of switching elements are mounted on a metal substrate, and an electronic component such as a microcomputer for controlling the switching elements is mounted on the control substrate. The metal substrate and the control substrate are fixed to a housing that functions as a heat sink and face each other. The thermistor is mounted on the metal substrate, and when the temperature detected by the thermistor increases, the control unit limits the current supplied to the electric motor and prevents damage to the switching element due to overheating.

JP 2004-336975 A

  In the motor control device configured as described above, when the temperature of the switching element rises, the temperature of the electronic components mounted on the control board may also rise due to the influence. Some of these electronic components may have an operation-guaranteed temperature lower than that of the switching element. To prevent damage to the electronic components due to heat, a thermistor is placed not only on the metal board but also on the control board. When the temperature detected by the thermistor rises above a predetermined temperature, it is necessary to perform control to limit the current supplied to the electric motor.

However, the thermistor is known as a component having a higher failure rate than, for example, a resistor, a capacitor, or a diode. In general, the failure rate of resistors and capacitors is 0.0027 to 0.0074 / 10 ⁶ hours, whereas the failure rate of the thermistor is, for example, 0.32 / 10 ⁶ hours. Causes of the thermistor failure include moisture reacting with the internal electrode material and vibration. From the viewpoint of controlling the electric motor on the safe side, the current supplied to the electric motor is limited even if the temperature does not actually increase so that the switching element or microcomputer will not be damaged if the thermistor fails. Will have to do.

  The present invention has been made in view of the above circumstances, and its purpose is to provide a thermistor on each of a board on which a switching element is mounted and a board on which an electronic component for generating a control signal to the switching element is mounted. An object of the present invention is to provide a motor control device capable of suppressing the control of the electric motor caused by the failure of the thermistor in the mounted motor control device, and an electric power steering device including the motor control device.

  In order to achieve the above object, the present invention provides a motor control device that supplies a drive current to an electric motor, wherein the switching element that switches the voltage of a DC voltage source and outputs the drive current; and A first substrate mounted; a control unit including a plurality of electronic components that generate control signals to the switching element; a second substrate on which the plurality of electronic components are mounted; and the first substrate. A first thermistor mounted on the second substrate; and a second thermistor mounted on the second substrate, and the controller detects the failure of the first thermistor by the second thermistor. First temperature estimating means for estimating the temperature of the first substrate based on the detected temperature and the integrated value of the drive current output by the switching element; and the second thermistor Second temperature estimating means for estimating the temperature of the second substrate based on the temperature detected by the first thermistor and the integrated value of the driving current output by the switching element when a failure is detected. A motor control device is provided.

  In order to achieve the above object, the present invention provides a steering mechanism for turning steered wheels by a steering operation of a steering member of a vehicle, a torque sensor for detecting a steering torque applied to the steering member, and the steering An electric motor for generating a steering assist torque for assisting the steering operation of the member, and a control device for supplying a drive current to the electric motor in accordance with the steering torque detected by the torque sensor. An electric power steering device that is a motor control device is provided.

  According to the motor control device and the electric power steering device according to the present invention, it is possible to suppress the restriction on the control of the electric motor due to the failure of the thermistor.

It is a mimetic diagram showing an example of composition of an electric power steering device concerning an embodiment of the invention. It is an external view which shows an electric motor, a gear housing, a sensor housing, a controller housing, and a column housing. It is a block diagram which shows the structure of a gear mechanism and a gear housing while showing the inside of an electric motor and a controller housing in the cross section along the axial direction of an electric motor. It is a circuit block diagram which shows the structural example of the outline of a controller. It is a block diagram which shows the function structure of a controller. It is a graph which shows an example of the relationship information memorize | stored in memory. It is a graph which shows the modification of related information.

[Embodiment]
Embodiments of the present invention will be described with reference to FIGS. In addition, although embodiment described below is shown as a suitable specific example in implementing this invention, although there are some parts which have illustrated various technical matters that are technically preferable. The technical scope of the present invention is not limited to this specific embodiment.

(Configuration of electric power steering device)
FIG. 1 is a schematic diagram showing a configuration example of an electric power steering apparatus according to an embodiment of the present invention.

  The electric power steering apparatus 1 includes a steering mechanism 10, an electric motor 2, a gear mechanism 3 that transmits the rotational force of the electric motor 2 to the steering mechanism 10 as a steering assist force, and a controller 4 that controls the electric motor 2. doing. The controller 4 is an aspect of the “motor control device” of the present invention.

  The steering mechanism 10 includes a steering wheel 11 as a steering member rotated by a driver, a steering shaft 12 coupled to the steering wheel 11, and a rack shaft 13 extending in the vehicle width direction of the vehicle. The left and right steered wheels 19 are steered by the steering operation of the steering wheel 11.

  The steering shaft 12 includes a column shaft 121 to which the steering wheel 11 is fixed at one end, a pinion shaft 123 having pinion teeth 123 a that mesh with the rack teeth 13 a of the rack shaft 13, and the column shaft 121 and the pinion shaft 123. And an intermediate shaft 122 interposed. The column shaft 121 and the intermediate shaft 122 are connected by a universal joint 124, and the intermediate shaft 122 and the pinion shaft 123 are connected by a universal joint 125.

  The column shaft 121 includes an upper shaft 121a and a lower shaft 121b, and the upper shaft 121a and the lower shaft 121b are connected by a torsion bar 140 of the torque sensor 14. The torque sensor 14 detects the steering torque applied to the steering wheel 11 by the driver based on the twist of the torsion bar 140.

  The rack shaft 13 is accommodated in a cylindrical rack housing 15 so as to be movable in the axial direction. The rack shaft 13 is formed with rack teeth 13 a made of oblique teeth along the axial direction thereof, and the rack teeth 13 a mesh with the pinion teeth 123 a of the pinion shaft 123. Ball joint sockets 16 are fixed to both ends of the rack shaft 13, and tie rods 17 connected to these ball joint sockets 16 are connected to the left and right steered wheels 19 through knuckle arms (not shown). A bellows 18 made of bellows-like rubber or resin is disposed on the outer peripheral side of the ball joint socket 16.

  When the steering wheel 11 is rotated, the pinion shaft 123 connected to the steering wheel 11 via the column shaft 121 and the intermediate shaft 122 rotates, and the rack shaft 13 is rotated by the engagement of the pinion teeth 123a and the rack teeth 13a. Move linearly in the axial direction. Due to the linear motion of the rack shaft 13, the left and right steered wheels 19 are steered through the tie rods 17.

  The gear mechanism 3 is a worm gear mechanism including a worm 31 connected to the output rotation shaft of the electric motor 2 and a worm wheel 32 that rotates integrally with the lower shaft 121b. The controller 4 supplies a drive current to the electric motor 2 based on the vehicle speed and the steering torque detected by the torque sensor 14 to control the electric motor 2. The electric motor 2 generates a steering assist torque that assists the steering operation of the steering wheel 11.

  FIG. 2 shows an electric motor 2, a gear housing 51 that houses the gear mechanism 3, a sensor housing 52 that houses the torque sensor 14, a bottomed cylindrical controller housing 53 that houses the controller 4, and a column that houses the column shaft 121. FIG. 6 is an external view showing a housing 54. FIG. 3 is a configuration diagram showing the inside of the electric motor 2 and the controller housing 53 in a cross section along the axial direction of the electric motor 2 and the configuration of the gear mechanism 3 and the gear housing 51.

  The electric motor 2 includes a bottomed cylindrical motor housing 20, a shaft 21 that is an output rotation shaft, a rotor 22 that rotates integrally with the shaft 21, and a stator 23 that is fixed to the motor housing 20. . The stator 23 includes a cylindrical stator core 230, an insulator 231 inserted into the stator core 230, and a coil 232 wound around the insulator 231. The rotor 22 is provided with a plurality of segment magnets 221. The shaft 21 is rotatably supported by a first bearing 211 having an outer ring fixed to the motor housing 20 and a second bearing 212 having an outer ring fixed to the controller housing 53, and penetrates the central portion of the bottom of the controller housing 53. ing.

  The rotational speed of the electric motor 2 is detected by the resolver 24. The resolver 24 has a resolver rotor 241 fixed to the shaft 21 and a resolver stator 242 fixed to the controller housing 53. The detection signal of the resolver 24 is sent to the controller 4.

  The controller housing 53 is disposed between the motor housing 20 and the gear housing 51. The controller housing 53 and the motor housing 20 are fastened by a plurality of bolts 56, and the controller housing 53 and the gear housing 51 are fastened by a plurality of bolts 57. The gear housing 51 and the sensor housing 52 are fastened by a plurality of bolts 58.

  The controller housing 53 holds a power connector 531, a signal line connector 532, and a communication connector 533. The power connector 531 is connected to the battery via a power line, and power consumed by the electric motor 2 and the controller 4 is supplied from the battery via the power connector 531. A signal line (not shown) derived from the sensor housing 52 is connected to the signal line connector 532, and a detection signal of the torque sensor 14 is output to the controller 4 via the signal line connector 532. The communication connector 533 is connected to a CAN (Controller Area Network) communication line that performs communication between a plurality of devices mounted on the vehicle. The controller 4 can acquire various information such as the vehicle speed and the outside temperature via the communication line.

  The column housing 54 includes an outer tube 541 and an inner tube 542, and the outer tube 541 is relatively movable along the axial direction of the inner tube 542. A bearing 543 that rotatably supports the column shaft 121 is disposed between the inner peripheral surface of the inner tube 542 and the outer peripheral surface of the upper shaft 121a.

  The outer tube 541 is supported by a vehicle body (not shown) via a bracket 55. The bracket 55 has a locked state in which the outer tube 541 is locked (fixed in position) with respect to the vehicle body by a cam mechanism that is actuated by the operation of the operation lever 551 by the driver, and the outer tube 541 is movable in the vertical direction and the inner tube 542 In this unlocked state, tilt adjustment and telescopic adjustment of the steering wheel 11 can be performed.

  The shaft 21 and the worm 31 of the electric motor 2, and the lower shaft 121 b and the worm wheel 32 are connected to each other in a non-rotatable manner in the gear housing 51. When the shaft 21 of the electric motor 2 is rotated, the worm 31 is rotated together with the shaft 21, the rotational force is decelerated and transmitted to the worm wheel 32, and is applied to the lower shaft 121b as a steering assist force.

(Configuration of controller)
FIG. 4 is a circuit configuration diagram illustrating a schematic configuration example of the controller 4. The controller 4 includes an inverter circuit 41 including free-wheeling diodes 415 to 418 provided corresponding to the first to fourth switching elements 411 to 414 and the first to fourth switching elements 411 to 414, respectively. A control board 42 that generates a control signal for turning on or off the first to fourth switching elements 411 to 414, and a first substrate on which the first to fourth switching elements 411 to 414 and the free wheel diodes 415 to 418 are mounted. A metal substrate 43 (shown in FIG. 3), a printed circuit board 44 (shown in FIG. 3) as a second substrate on which a plurality of electronic components of the control unit 42 are mounted, and a first substrate mounted on the metal substrate 43. One thermistor 45 and a second thermistor 46 mounted on the printed circuit board 44 are provided.

  The metal substrate 43 is made of a metal having excellent thermal conductivity such as aluminum, and is fixed to the controller housing 53 by bolts (not shown). The metal substrate 43 dissipates heat generated in the inverter circuit 41 to the controller housing 53 and the like. The printed board 44 is a wiring board in which a wiring pattern made of copper foil is formed on the surface of a plate-like base material made of a dielectric such as glass epoxy.

  The metal board 43 and the printed board 44 are arranged in parallel to each other in the controller housing 53. A through hole is formed in the center of the metal substrate 43 and the printed circuit board 44, and the shaft 21 of the electric motor 2 is inserted into the through hole. The metal board 43 and the printed board 44 face each other in the axial direction of the shaft 21 and are electrically connected by inter-board connectors 431 and 441. A drive current is supplied to the electric motor 2 from the inverter circuit 41 via a cable 25 including a pair of electric wires 251 and 252 connected to a terminal 432 provided on the metal substrate 43.

  The first to fourth switching elements 411 to 414 are composed of power transistors such as IGBTs (gate bipolar transistors), for example, and switch the DC voltage supplied from the battery 100 as the DC voltage source via the power connector 531. The drive current to the electric motor 2 is output. In the circuit example shown in FIG. 4, the first switching element 411 and the third switching element 413 are connected in series between the positive electrode 531 a and the negative electrode 531 b of the power connector 531, and in parallel with the second switching element 411. The switching element 412 and the fourth switching element 414 are connected in series between the positive electrode 531 a and the negative electrode 531 b of the power connector 531. The drive current supplied to the electric motor 2 is detected by a current sensor 47 made of, for example, a Hall IC.

  One electric wire 251 of the cable 25 is connected between the first switching element 411 and the third switching element 413, and the other electric wire 252 is connected between the second switching element 412 and the fourth switching element 414. Connected between. When the first switching element 411 and the fourth switching element 414 are turned on by the control signal output from the control unit 42, the driving current in the forward direction (the direction of arrow A shown in FIG. 4) is supplied to the electric motor 2. Then, when the second switching element 412 and the third switching element 413 are turned on, a driving current in the reverse direction (direction of arrow B shown in FIG. 4) is supplied to the electric motor 2.

  When all of the first to fourth switching elements 411 to 414 are turned off during the rotation of the electric motor 2, current is regenerated through the return diodes 415 to 418. The drive current supplied to the electric motor 2 is a ratio of time during which the first switching element 411 and the fourth switching element 414 are turned on or the second switching element 412 and the third switching element 413 are turned on (duty The higher the ratio, the larger the ratio.

  The control unit 42 includes a plurality of electronic components, and the plurality of electronic components includes a CPU (Central Processing Unit) 421 and a memory 422 as a nonvolatile storage element. The memory 422 includes, for example, a ROM or a flash memory, and stores a program 422a for the operation of the CPU 421 and relationship information 422b described later.

  The CPU 421 can acquire detection signals from the first thermistor 45, the second thermistor 46, and the current sensor 47. In addition to the CPU 421 and the memory 422, the control unit 42 includes a passive element such as a resistor and a capacitor (not shown), and electronic components such as an AD converter and various gate ICs.

(Controller function)
FIG. 5 is a block diagram showing a functional configuration of the controller 4. The CPU 421 of the control unit 42 functions as the normal control means 60, the first temperature estimation means 61, the second temperature estimation means 62, and the overheat suppression control means 63 by executing the program 422a.

  The normal control means 60 is means for controlling the electric motor 2 in a normal state where both the inverter circuit 41 and the control unit 42 are not in a high temperature state. As the normal control means 60, the CPU 421 controls the electric motor 2 so that a larger steering assist torque is generated as the steering torque detected by the torque sensor 14 is larger and the vehicle speed is lower.

  The first temperature estimating means 61 is based on the temperature detected by the second thermistor 46 and the integrated value of the drive current detected by the current sensor 47 when a failure of the first thermistor 45 is detected. The temperature of the metal substrate 43 is estimated. The second temperature estimating means 62 is based on the integrated value of the temperature detected by the first thermistor 45 and the drive current detected by the current sensor 47 when a failure of the second thermistor 46 is detected. Thus, the temperature of the printed circuit board 44 is estimated.

  The failure of the first thermistor 45 may be caused by the fact that the temperature detected by the first thermistor 45 does not change for a predetermined time or more even though the temperature detected by the second thermistor 46 has changed. The temperature detected by 45 is a clear abnormal value (abnormally low or high temperature, or the difference from the temperature detected by the second thermistor 46 is extremely large). The failure of the second thermistor 46 is also detected in the same manner as the first thermistor 45. The failure of the first thermistor 45 and the second thermistor 46 may be detected by the processing of the CPU 421 of the control unit 42 or may be detected by receiving a signal indicating an abnormality output from an external device. Good.

  The CPU 421 acquires the detection signal of the current sensor 47 every predetermined control cycle (for example, 0.1 second), and integrates the drive current based on the detection signal over a predetermined time (for example, 10 minutes to 1 hour). In the present embodiment, the temperatures of the metal substrate 43 and the printed circuit board 44 are estimated based on the average value of the drive currents obtained by dividing the integration calculation result (integrated value) by the integrated time. This average value of the drive current is a moving average value of the drive current in the past predetermined time.

FIG. 6 is a graph illustrating an example of the relationship information 422b stored in the memory 422. This relationship information 422b is the difference _(T 1 -T ₂₎ is a differential temperature ([Delta] T) between the temperature of the temperature _{(T 1)} and the printed circuit board 44 of the metal substrate 43 _{(T 2),} the integrated value of the driving current, That is, it is information indicating the relationship with the average value (T _AVR ) of the drive current. The relation information 422b is defined based on the experimental result and stored in the memory 422 in advance. The memory 422 corresponds to the “storage unit” of the present invention. In the memory 422, the relationship information 422b is stored in a map format, for example.

  As shown in FIG. 6, when the average value of the drive current is low, the temperature of the metal substrate 43 is lower than the temperature of the printed circuit board 44, and when the average value of the drive current is high, the temperature print of the metal substrate 43 is performed. The temperature of the substrate 44 is higher. This is because the control unit 42 always performs an operation for obtaining a drive current to be supplied to the electric motor 2 regardless of the duty ratio of the inverter circuit 41, and the CPU 421 and the like generate heat by this operation process, whereas the temperature of the inverter circuit 41 This is because it largely depends on the duty ratio. In addition, since a larger current flows through the inverter circuit 41 than the control unit 42, the temperature of the metal substrate 43 is generally higher than the temperature of the printed circuit board 44.

Based on the temperature detected by the second thermistor 46 and the integrated value of the drive current (more specifically, the average value of the drive current (T _AVR )), the first temperature estimation means 61 obtains the relationship information 422b. The temperature of the metal substrate 43 is estimated with reference. That is, by referring to the relationship information 422b, the difference temperature between the metal substrate 43 and the printed circuit board 44 corresponding to the integrated value (average value) of the drive current can be obtained, and the print detected by the second thermistor 46 can be obtained. The temperature of the metal substrate 43 is estimated by adding this differential temperature to the temperature of the substrate 44.

Similarly, the second temperature estimating means 62 is based on the temperature detected by the first thermistor 45 and the integrated value of the drive current (more specifically, the average value (T _AVR ) of the drive current). The temperature of the printed circuit board 44 is estimated with reference to the information 422b. That is, the difference temperature between the metal substrate 43 and the printed circuit board 44 corresponding to the integrated value (average value) of the drive current obtained by referring to the relationship information 422b is the difference between the temperature of the metal substrate 43 detected by the first thermistor 45. By subtracting from the temperature, the temperature of the printed circuit board 44 is estimated.

  The overheat suppression control means 63 suppresses the drive current supplied to the electric motor 2 when the higher one of the temperature of the metal substrate 43 and the temperature of the printed circuit board 44 exceeds a predetermined value (for example, 80 ° C.). Specifically, the duty ratio of the inverter circuit 41 is reduced to about half compared to the case where the electric motor 2 is controlled by the normal control means 60. Thereby, the temperature of the metal substrate 43 is lowered by suppressing the heat generation of the first to fourth switching elements 411 to 414, and the influence of the heat generation of the first to fourth switching elements 411 to 414 and the electric motor 2 is affected. The temperature of the receiving printed circuit board 44 also decreases.

  When the failure of the first thermistor 45 is not detected, the overheat suppression control means 63 uses the temperature detected by the first thermistor 45 as the “temperature of the metal substrate 43”. When a failure is detected, the temperature estimated by the first temperature estimating means 61 is used as the “temperature of the metal substrate 43”. The overheat suppression control means 63 uses the temperature detected by the second thermistor 46 as the “temperature of the printed circuit board 44” when the failure of the second thermistor 46 is not detected. When a failure of 46 is detected, the temperature estimated by the second temperature estimating means 62 is used as the “temperature of the printed circuit board 44”.

  As a result, the overheat suppression control means 63 continues to execute control to suppress overheating of the inverter circuit 41 and the control unit 42 even when either the first thermistor 45 or the second thermistor 46 fails. be able to.

(Modification)
FIG. 7 is a graph showing a modification of the relationship information 422b. In the graph of FIG. 4, the case where the relationship between the difference temperature between the metal substrate 43 and the printed circuit board 44 and the average value of the drive current is shown by a single curve has been described, but in the modification shown in FIG. In addition, a case where a plurality of pieces of related information according to the outside air temperature are stored is illustrated. Moreover, in FIG. 7, the relationship information which should be referred in the case of outside temperature 0 degreeC, 20 degreeC, and 40 degreeC is shown as the example with the dashed-dotted line, the continuous line, and the broken line, respectively. In addition, the information on outside temperature can be acquired from CAN which is a communication network in a vehicle as described above.

  In this case, the first temperature estimation unit 61 estimates the temperature of the metal substrate 43 with reference to the relationship information corresponding to the outside air temperature among the plurality of relationship information, and the second temperature estimation unit 62 determines the plurality of the relationship information. The temperature of the printed circuit board 44 is estimated with reference to the relationship information corresponding to the outside air temperature. Note that the first temperature estimation unit 61 and the second temperature estimation unit 62 may select and refer to one relationship information closest to the acquired outside air temperature from among a plurality of relationship information. Information may be interpolated for reference.

(Effect of embodiment)
According to the embodiment described above, even when the first thermistor 45 fails, the temperature of the metal substrate 43 can be estimated by the first temperature estimating means 61, and when the second thermistor 46 fails. In addition, the temperature of the printed circuit board 44 can be estimated by the second temperature estimating means 62. As a result, it is possible to suppress the control of the electric motor due to the failure of the thermistor while arranging the thermistor not only on the metal substrate 43 but also on the printed circuit board 44 and monitoring the temperature of the control unit 42. It becomes.

  Further, according to the embodiment, the first temperature estimating means 61 refers to the relationship information 422b according to the temperature of the printed circuit board 44 detected by the second thermistor 46 and the integrated value of the drive current, and the metal The temperature of the substrate 43 is estimated. The second temperature estimating means 62 estimates the temperature of the printed circuit board 44 by referring to the temperature information of the metal substrate 43 detected by the second thermistor 45 and the relationship information 422b corresponding to the integrated value of the drive current. . Thereby, the accuracy of temperature estimation can be increased.

(Appendix)
As mentioned above, although this invention was demonstrated based on embodiment, each embodiment described above does not limit the invention based on a claim. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

  Further, the present invention can be appropriately modified and implemented without departing from the spirit of the present invention. For example, in the above embodiment, the case where the motor control device of the present invention is applied to electric power steering has been described. However, the present invention is not limited to this, and the motor control device of the present invention is applied to various devices using an electric motor as a drive source. It is possible to apply.

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus 10 ... Steering mechanism 11 ... Steering wheel (steering member) 14 ... Torque sensor 2 ... Electric motor 4 ... Controller (control apparatus)
411 to 414... First to fourth switching elements 42... Controller 422... Memory 422 b .. related information 43 .. metal substrate (first substrate) 44 .. printed circuit board (second substrate)
45 ... first thermistor 46 ... second thermistor 61 ... first temperature estimating means 62 ... second temperature estimating means 63 ... overheating suppression control means

Claims (5)

A motor control device for supplying a drive current to an electric motor,
A switching element that switches the voltage of a DC voltage source and outputs the drive current;
A first substrate on which the switching element is mounted;
A control unit comprising a plurality of electronic components for generating a control signal to the switching element;
A second substrate on which the plurality of electronic components are mounted;
A first thermistor mounted on the first substrate;
A second thermistor mounted on the second substrate;
The controller is
When a failure of the first thermistor is detected, the temperature of the first substrate is estimated based on the temperature detected by the second thermistor and the integrated value of the drive current output by the switching element. First temperature estimating means;
When a failure of the second thermistor is detected, the temperature of the second substrate is estimated based on the temperature detected by the first thermistor and the integrated value of the drive current output by the switching element. Second temperature estimating means,
Motor control device. The control unit further includes storage means for storing relationship information indicating a relationship between a differential temperature, which is a difference between the temperature of the first substrate and the temperature of the second substrate, and an integrated value of the drive current. ,
The first temperature estimating means estimates the temperature of the first substrate with reference to the relation information based on an integrated value of the driving current,
The second temperature estimating means estimates the temperature of the second substrate by referring to the relation information based on an integrated value of the driving current;
The motor control device according to claim 1. The control unit further includes an overheat suppression control unit that suppresses the driving current when a higher one of the temperature of the first substrate and the temperature of the second substrate exceeds a predetermined value,
When the failure of the first thermistor is detected, the overheat suppression control means uses the temperature estimated by the first temperature estimation means as the temperature of the first substrate, and the failure of the second thermistor is detected. When detected, the temperature estimated by the second temperature estimating means is used as the temperature of the second substrate.
The motor control device according to claim 1 or 2. A steering mechanism for turning the steered wheels by a steering operation of a steering member of the vehicle;
A torque sensor for detecting a steering torque applied to the steering member;
An electric motor for generating a steering assist torque for assisting a steering operation of the steering member;
A control device for supplying a drive current to the electric motor according to a steering torque detected by the torque sensor;
The control device is the motor control device according to any one of claims 1 to 3.
Electric power steering device. A steering mechanism for turning the steered wheels by a steering operation of a steering member of the vehicle;
A torque sensor for detecting a steering torque applied to the steering member;
An electric motor for generating a steering assist torque for assisting a steering operation of the steering member;
A control device for supplying a drive current to the electric motor according to a steering torque detected by the torque sensor;
The control device is the motor control device according to claim 2,
The storage means stores a plurality of the relationship information according to outside air temperature,
The first temperature estimation means estimates the temperature of the first substrate with reference to the relationship information according to the outside air temperature among the plurality of relationship information,
The second temperature estimation means estimates the temperature of the second substrate with reference to the relationship information according to an outside temperature among the plurality of relationship information.
Electric power steering device.

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