Motor control device and electric power steering device

Abstract

This motor control device is provided with: a motor case (20a); a bracket (60) that is fastened to the motor case (20a) using first bracket fixing screws (67s, 68s); a cover (61) that is fixed to the bracket (60); and a motor control circuit board (62) that is fastened to the bracket (60) using board fixing screws (70s-73s) and is accommodated in a space surrounded by the bracket (60) and the cover (61). The cover (61) is formed so as to be near the heads of the first bracket fixing screws (67s, 68s) and the heads of the board fixing screws (70s-73s).

Description

Motor control device and electric power steering device

[0001] The present invention relates to a motor control device and an electric power steering device.

[0002] The following Patent Document 1 describes a motor control device that includes a case having a case body and a cover that covers the case body, and a circuit board for motor control that is housed in the case and fastened to the case body using board fixing screws.

[0003] Japanese Patent Application Laid-Open No. 2022-130025

[0004] A configuration in which an electronic circuit device that controls a motor is integrated with the motor is known. Such a configuration is used, for example, in an electric power steering device. The present invention aims to prevent the screws from falling out in a configuration in which a circuit board for controlling a motor is fastened to a bracket with screws, and the bracket is fastened to the motor with screws.

[0005] To achieve the above object, one aspect of the present invention provides a motor control device comprising: a motor case that houses a stator and a rotor of a motor; a bracket fastened to the motor case with a first bracket fixing screw; a cover fixed to the bracket; and a motor control circuit board that is fastened to the bracket with a board fixing screw and housed in a space surrounded by the bracket and the cover. The cover is formed so that a portion facing the head of the first bracket fixing screw is close to the head of the first bracket fixing screw in the axial direction of the first bracket fixing screw, and a portion facing the head of the board fixing screw is close to the head of the board fixing screw in the axial direction of the board fixing screw.

[0006] An electric power steering device according to another aspect of the present invention includes the motor control device described above and a motor controlled by the motor control device, and applies a steering assist force to a steering system of a vehicle by the motor.

[0007] According to the present invention, in a configuration in which a circuit board for motor control is fastened to a bracket with screws, and the bracket is fastened to a motor with screws, it is possible to prevent these screws from falling off.

[0008] 5 is a configuration diagram showing an overview of an example of an electric power steering device of an embodiment. FIG. 6 is a configuration diagram showing an overview of an example of an electronic control unit (ECU) of an embodiment. FIG. 7 is a block diagram of an example of the functional configuration of a control arithmetic device. FIG. 8 is a perspective view illustrating attachment of an ECU to a motor. FIG. 9 is a plan view of a bracket. FIG. 10 is a cross-sectional view of the motor and ECU taken along line A-A in FIG. 5. FIG. 11 is a cross-sectional view of the motor and ECU taken along line B-B in FIG. 5. FIG. 12 is a cross-sectional view of the motor and ECU taken along line CC in FIG. 11. FIG. 13 is a configuration diagram showing an overview of a first modified example of an electric power steering device. FIG. 14 is a configuration diagram showing an overview of a second modified example of an electric power steering device. FIG. 15 is a configuration diagram showing an overview of a third modified example of an electric power steering device.

[0009] Embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments of the present invention shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the configuration, arrangement, etc. of component parts to those described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims.

[0010] In the following description, the present invention is applied to a motor control device for an electric motor that generates a steering assist force for an electric power steering system, but the present invention is not limited to application to electric power steering systems and can be widely applied to a variety of uses. For example, the present invention may be applied to a current control device that supplies a drive current to an actuator that drives the joints of a robot.

[0011] 1 is a diagram showing an outline of an example of an electric power steering (EPS) device according to an embodiment. A steering shaft (steering shaft, handle shaft) 2 of a steering wheel (steering handle) 1 is connected to steered wheels 8L, 8R via reduction gears (worm gears) 3, universal joints 4a and 4b, a pinion-rack mechanism 5, tie rods 6a, 6b, and hub units 7a, 7b, which constitute a reduction mechanism.

[0012] The pinion-rack mechanism 5 has a pinion 5a connected to a pinion shaft to which steering force is transmitted from the universal joint 4b, and a rack 5b meshing with the pinion 5a. The rotational motion transmitted to the pinion 5a is converted into linear motion in the vehicle width direction by the rack 5b. The steering shaft 2 is provided with a torque sensor 10 that detects steering torque Th. The steering shaft 2 includes an input shaft 2i and an output shaft 2o. The input shaft 2i and the output shaft 2o are connected by a torsion bar (not shown) that twists due to a difference in rotation angle between the input shaft 2i and the output shaft 2o. The torque sensor 10 electromagnetically measures the torsion angle of the torsion bar as the steering torque Th of the steering wheel 1. The steering shaft 2 is also provided with a steering angle sensor 14 that detects the steering angle θh of the steering wheel 1.

[0013] Furthermore, a motor 20 that assists the steering force of the steering wheel 1 is connected to the steering shaft 2 via a reduction gear 3. The motor 20 may be, for example, a polyphase motor. In the following description, an example of a three-phase motor having double windings in which first and second system coils are wound within the same motor housing and a common rotor is rotated by the coils of the two systems will be described, but the motor 20 may be a motor other than a double winding motor, and the number of phases of the motor 20 does not have to be three. A plurality of motors 20 that assist the steering force of the steering wheel 1 may be connected to the same steering shaft 2.

[0014] An electronic control unit (ECU) 30 that controls the electric power steering device receives power from a battery 13 and receives an ignition key signal via an ignition switch 11. The ECU 30 calculates a current command value for an assist control command based on a steering torque Th detected by a torque sensor 10, a vehicle speed Vh detected by a vehicle speed sensor 12, and a steering angle θh detected by a steering angle sensor 14, and controls the currents (A-phase current I1a, B-phase current I1b, and C-phase current I1c of the first system coils and A-phase current I2a, B-phase current I2b, and C-phase current I2c of the second system coils) to be supplied to the motor 20 using a voltage control command value obtained by performing compensation on the current command value. The ECU 30 is an example of a "motor control device" as defined in the claims.

[0015] The steering angle sensor 14 is not essential, and the steering angle θh may be calculated by adding the torsion angle of the torsion bar to the product of the motor rotation angle θm obtained from a rotation angle sensor 23a that detects the rotation angle of the rotary shaft of the motor 20 and the gear ratio of the reduction gear 3. The rotation angle sensor 23a may be, for example, a resolver that detects the rotation position of the motor, or a magnetic sensor that detects the magnetic field of a magnet attached to the rotary shaft of the motor 20. Furthermore, the steering angle of the steered wheels 8L, 8R may be used instead of the steering angle θh. For example, the steering angle may be detected by detecting the displacement of the rack 5b.

[0016] The ECU 30 includes a computer including, for example, a processor and peripheral components such as a storage device. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device may include any of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device may include memories such as a register, a cache memory, and a ROM (Read Only Memory) and a RAM (Random Access Memory) used as a main storage device. The functions of the ECU 30 described below are realized, for example, by the processor of the ECU 30 executing a computer program stored in the storage device.

[0017] The ECU 30 may be formed of dedicated hardware for executing the various information processes described below. For example, the ECU 30 may include a functional logic circuit configured in a general-purpose semiconductor integrated circuit. For example, the ECU 30 may have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0018] 2 is a schematic diagram illustrating an example of an ECU 30 according to an embodiment. The ECU 30 includes a motor rotation angle detection circuit 23, control and arithmetic units 31a and 31b, a first motor current interruption circuit 33A, a second motor current interruption circuit 33B, a first gate drive circuit 41A, a second gate drive circuit 41B, a first power conversion circuit 42A, a second power conversion circuit 42B, a first power supply interruption circuit 44A, and a second power supply interruption circuit 44B. A power wiring PWa that transmits power from the battery 13 is connected to the ECU 30 via a connector CNT. A positive power line Lpa of the power wiring PWa passes through a noise filter circuit, such as an EMC (Electro Magnetic Compatibility) filter formed by a choke coil La and ceramic capacitors Ca1 and Ca2, and then branches at a branch point Pb. One of the positive power supply lines Lpa branched at the branch point Pb is connected to the control arithmetic device 31a and the first power supply cutoff circuit 44A, and the other is connected to the control arithmetic device 31b and the second power supply cutoff circuit 44B.

[0019] One end of the choke coil La is connected to the positive power supply line Lpa and one end of the ceramic capacitor Ca1, the other end of the choke coil La is connected to one end of the ceramic capacitor Ca2 and the branch point Pb, and the other ends of the ceramic capacitors Ca1 and Ca2 are grounded. Meanwhile, the negative line of the power wiring PWa is connected to the ground line of the ECU 30.

[0020] Signals representing the steering torque Th detected by the torque sensor 10, the vehicle speed Vh detected by the vehicle speed sensor 12, and the steering angle θh detected by the steering angle sensor 14 are transmitted to the control arithmetic units 31a and 31b via the connector CNT. The control arithmetic unit 31a calculates a current command value, which is a control target value for the drive current of the motor 20, based on at least the steering torque Th, and outputs voltage control command values ​​V1a, V1b, and V1c obtained by applying compensation and the like to the current command value to the first gate drive circuit 41A. The voltage control command values ​​V1a, V1b, and V1c are the A-phase voltage control command value, B-phase voltage command value, and C-phase voltage command value for the first system coil, respectively.

[0021] The control and arithmetic device 31b calculates a current command value, which is a control target value of the drive current of the motor 20, based on at least the steering torque Th, and outputs voltage control command values ​​V2a, V2b, and V2c obtained by performing compensation on the current command value to the second gate drive circuit 41B. The voltage control command values ​​V2a, V2b, and V2c are the A-phase voltage control command value, B-phase voltage command value, and C-phase voltage command value of the second system coil, respectively. Note that the control and arithmetic devices 31a and 31b may be integrated into a single control and arithmetic device.

[0022] The first power supply interruption circuit 44A has a series circuit configuration in which two power supply interruption field effect transistors (FETs) QC1 and QC2 have their sources connected to each other, forming parasitic diodes in opposite directions. The first power supply interruption circuit 44A connects or disconnects the positive power supply line Lpa and the first power conversion circuit 42A. The drain of the power supply interruption FET QC1 is connected to the positive power supply line Lpa, and the drain of the power supply interruption FET QC2 is connected to the drains of the high-side FETs Q1, Q3, and Q5 of the first power conversion circuit 42A. The control and arithmetic device 31a outputs control signals SsA and SpA to the first gate drive circuit 41A, which respectively control the conduction and interruption of the power supply interruption FETs QC1 and QC2. The first gate drive circuit 41A outputs gate signals for the power supply interruption FETs QC1 and QC2 in response to the control signals SsA and SpA, thereby controlling the on / off of the power supply interruption FETs QC1 and QC2.

[0023] The second power supply interruption circuit 44B has a series circuit configuration in which the sources of two power supply interruption FETs QD1 and QD2 are connected to each other, forming parasitic diodes in opposite directions, and connects or disconnects the positive power supply line Lpa from the second power conversion circuit 42B. The drain of the power supply interruption FET QD1 is connected to the positive power supply line Lpa, and the drain of the power supply interruption FET QD2 is connected to the drains of the high-side FETs Q1, Q3, and Q5 of the second power conversion circuit 42B. The control and arithmetic device 31b outputs control signals SsB and SpB to the second gate drive circuit 41B, which respectively control the conduction and interruption of the power supply interruption FETs QD1 and QD2. The second gate drive circuit 41B outputs gate signals for the power supply interruption FETs QD1 and QD2 in response to the control signals SsB and SpB, thereby controlling the on / off of the power supply interruption FETs QD1 and QD2.

[0024] When the first gate drive circuit 41A receives voltage control command values ​​V1a, V1b, and V1c from the control and arithmetic device 31a, it generates six gate signals that are pulse-width modulated (PWM) based on these voltage control command values ​​V1a, V1b, and V1c and a triangular wave carrier signal. It then outputs these gate signals to the first power conversion circuit 42A. When the second gate drive circuit 41B receives voltage control command values ​​V2a, V2b, and V2c from the control and arithmetic device 31b, it generates six gate signals that are pulse-width modulated based on these voltage control command values ​​V2a, V2b, and V2c and a triangular wave carrier signal. It then outputs these gate signals to the second power conversion circuit 42B.

[0025] The first power conversion circuit 42A includes an inverter having three switching arms SWAa, SWAb, and SWAc configured by field-effect transistors (FETs) as switching elements, and electrolytic capacitors CA1 and CA2. The switching arms SWAa, SWAb, and SWAc are connected in parallel with one another. The A-phase switching arm SWAa includes a high-side FET Q1 and a low-side FET Q2 connected in series, the B-phase switching arm SWAb includes a high-side FET Q3 and a low-side FET Q4 connected in series, and the C-phase switching arm SWAc includes a high-side FET Q5 and a low-side FET Q6 connected in series.

[0026] A gate signal output from the first gate drive circuit 41A is input to the gate of each FET Q1 to Q6, and this gate signal causes A-phase current I1a, B-phase current I1b, and C-phase current I1c to flow from the connection points between the FETs of each switching arm SWAa, SWAb, and SWAc to the A-phase winding, B-phase winding, and C-phase winding of the first system coil of the motor 20 via the first motor current interruption circuit 33A. The electrolytic capacitors CA1 and CA2 have a noise removal function and a power supply auxiliary function for the first power conversion circuit 42A. The electrolytic capacitors CA1 and CA2 may be hybrid capacitors that use an electrolyte that combines a conductive polymer and an electrolytic solution, for example.

[0027] The second power conversion circuit 42B includes an inverter having three switching arms SWBa, SWBb, and SWBc configured by FETs (switching elements), and electrolytic capacitors CB1 and CB2. The switching arms SWBa, SWBb, and SWBc are connected in parallel with one another. The A-phase switching arm SWBa includes a high-side FET Q1 and a low-side FET Q2 connected in series, the B-phase switching arm SWBb includes a high-side FET Q3 and a low-side FET Q4 connected in series, and the C-phase switching arm SWBc includes a high-side FET Q5 and a low-side FET Q6 connected in series.

[0028] A gate signal output from the second gate drive circuit 41B is input to the gates of each FET Q1 to Q6, and this gate signal causes A-phase current I2a, B-phase current I2b, and C-phase current I2c to flow from the connection points between the FETs of each switching arm SWBa, SWBb, and SWBc through the second motor current cutoff circuit 33B to the A-phase winding, B-phase winding, and C-phase winding of the second system coil of the motor 20. Electrolytic capacitors CB1 and CB2 have a noise removal function and a power supply auxiliary function for the second power conversion circuit 42B. Electrolytic capacitors CB1 and CB2 may be, for example, hybrid capacitors.

[0029] The first power conversion circuit 42A and the second power conversion circuit 42B may be power conversion circuits that supply three-phase current to two different motors that respectively generate steering assist forces that assist the steering of the steering wheel 1. For example, these two different motors may be connected to the same steering shaft 2 via reduction gears.

[0030] Current detection circuits 39A1, 39B1, and 39C1 are provided on the source sides of low-side FETs Q2, Q4, and Q6, which form the lower arms of switching arms SWAa, SWAb, and SWAc of the first power conversion circuit 42A. The current detection circuits 39A1, 39B1, and 39C1 include shunt resistors through which downstream currents of the switching arms SWAa, SWAb, and SWAc flow, respectively. The current detection circuits 39A1, 39B1, and 39C1 detect the A-phase current, B-phase current, and C-phase current of the first system coil based on the voltage drop across the shunt resistors, and output the detected values ​​I1ad, I1bd, and I1cd.

[0031] Current detection circuits 39A2, 39B2, and 39C2 are provided on the source sides of low-side FETs Q2, Q4, and Q6, which form the lower arms of switching arms SWBa, SWBb, and SWBc of the second power conversion circuit 42B. The current detection circuits 39A2, 39B2, and 39C2 include shunt resistors through which downstream currents of the switching arms SWBa, SWBb, and SWBc, respectively, flow. The current detection circuits 39A2, 39B2, and 39C2 detect the A-phase current, B-phase current, and C-phase current of the second system coil based on the voltage drop across the shunt resistors, and output the detected values ​​I2ad, I2bd, and I2cd.

[0032] The first motor current interruption circuit 33A has three phase interruption FETs QA1, QA2, and QA3 for interrupting the phase current of the motor. The source of the phase interruption FET QA1 is connected to the junction of the FETs Q1 and Q2 of the switching arm SWAa of the first power conversion circuit 42A, and its drain is connected to the A-phase winding of the first system coil of the motor 20. The source of the phase interruption FET QA2 is connected to the junction of the FETs Q3 and Q4 of the switching arm SWAb, and its drain is connected to the B-phase winding of the first system coil. The source of the phase interruption FET QA3 is connected to the junction of the FETs Q5 and Q6 of the switching arm SWAc, and its drain is connected to the C-phase winding of the first system coil.

[0033] The control calculation device 31a outputs a control signal SmA that controls the conduction and cutoff of the first motor current cutoff circuit 33A to the first gate drive circuit 41A. The first gate drive circuit 41A outputs gate signals for the phase cutoff FETs QA1 to QA3 in response to the control signal SmA, and causes the A-phase current I1a, B-phase current I1b, and C-phase current I1c to flow or be cut off from the first power conversion circuit 42A to the motor 20.

[0034] The second motor current interruption circuit 33B has three phase interruption FETs QB1, QB2, and QB3 for interrupting the phase current of the motor. The source of the phase interruption FET QB1 is connected to the junction of the FETs Q1 and Q2 of the switching arm SWBa of the second power conversion circuit 42B, and its drain is connected to the A-phase winding of the second system coil of the motor 20. The source of the phase interruption FET QB2 is connected to the junction of the FETs Q3 and Q4 of the switching arm SWBb, and its drain is connected to the B-phase winding of the second system coil. The source of the phase interruption FET QB3 is connected to the junction of the FETs Q5 and Q6 of the switching arm SWBc, and its drain is connected to the C-phase winding of the second system coil.

[0035] The control calculation device 31b outputs a control signal SmB to the second gate drive circuit 41B, which controls the conduction and cutoff of the second motor current cutoff circuit 33B. The second gate drive circuit 41B outputs gate signals to the phase cutoff FETs QB1 to QB3 in response to the control signal SmB, and causes the A-phase current I2a, B-phase current I2b, and C-phase current I2c to flow or be cut off from the second power conversion circuit 42B to the motor 20.

[0036] The motor rotation angle detection circuit 23 obtains a detection value from the rotation angle sensor 23a and detects a motor rotation angle θm, which is the rotation angle of the rotary shaft of the motor 20. The motor rotation angle detection circuit 23 outputs the motor rotation angle θm to the control and arithmetic units 31a and 31b. The control and arithmetic unit 31a obtains detection values ​​I1ad, I1bd, and I1cd of the A-phase current, B-phase current, and C-phase current of the first system coil via an A / D conversion unit (not shown). The control and arithmetic unit 31b obtains detection values ​​I2ad, I2bd, and I2cd of the A-phase current, B-phase current, and C-phase current of the second system coil via an A / D conversion unit (not shown).

[0037] 3 is a block diagram showing an example of the functional configuration of the control arithmetic device 31a. While only the functional configuration for driving the coils of the first system of the motor 20 is shown in FIG. 3, the functional configuration for driving the coils of the second system has a similar configuration. The control arithmetic device 31a includes a current command value calculation unit 50, subtractors 52 and 53, a current limiting unit 54, a proportional-integral (PI) control unit 55, a two-phase / three-phase conversion unit 56, a three-phase / two-phase conversion unit 57, and an angular velocity conversion unit 58, and drives the motor 20 using vector control.

[0038] A current command value calculation unit 50 calculates a q-axis current command value Iq and a d-axis current command value Id to be passed through the motor 20 based on the steering torque Th, vehicle speed Vh, motor rotation angle θm of the motor 20, and rotation angular velocity ω of the motor 20. Meanwhile, detected values ​​I1ad, I1bd, and I1cd of the A-phase current, B-phase current, and C-phase current of the first system coil of the motor 20, detected by current detection circuits 39A1, 39B1, and 39C1, are converted into d-q2-axis currents id and iq by a three-phase / two-phase conversion unit 57. Subtractors 52 and 53 subtract the fed-back currents iq and id from the q-axis current command value Iq and the d-axis current command value Id, respectively, to calculate a q-axis deviation current Δq0 and a d-axis deviation current Δd0.

[0039] A current limiting unit 54 limits the upper limits of the q-axis deviation current Δq0 and the d-axis deviation current Δd0. The limited q-axis deviation current Δq and d-axis deviation current Δd are input to a PI control unit 55. The PI control unit 55 calculates voltage command values ​​vq and vd that set the q-axis deviation current Δq and the d-axis deviation current Δd to zero, respectively. A two-phase / three-phase conversion unit 56 converts the voltage command values ​​vd and vq into an A-phase voltage control command value V1a, a B-phase voltage command value V1b, and a C-phase voltage command value V1c for the first system of the motor 20, respectively, and outputs them to the first gate drive circuit 41A. An angular velocity conversion unit 58 calculates a rotational angular velocity ω of the motor 20 based on a temporal change in the motor rotational angle θm. The motor rotational angle θm and rotational angular velocity ω are input to a current command value calculation unit 50 and used for vector control.

[0040] Please refer to Figure 1. As shown by the dashed line, the ECU 30 of this embodiment is integral with the motor 20, and the ECU 30 is fixed to the motor 20 using screws. Figure 4 is a perspective view illustrating the attachment of the ECU 30 to the motor 20. The ECU 30 includes a bracket 60 fixed to the motor case 20a of the motor 20, a cover 61 fixed to the bracket 60, and a circuit board 62 on which the control circuit shown in Figure 2 is mounted.

[0041] The bracket 60 is fastened to the motor case 20a using bracket fixing screws 67s, 68s, and 69s (described below). The bracket fixing screws 67s and 68s are an example of a "first bracket fixing screw" as defined in the claims. The bracket fixing screw 69s is an example of a "second bracket fixing screw" as defined in the claims.

[0042] The cover 61 is fastened to the bracket 60 using cover fixing screws 64s, 65s, and 66s. Bosses 64b, 65b, and 66b are formed on the bracket 60, and screw holes 64t, 65t, and 66t are formed on the top surfaces of the bosses 64b, 65b, and 66b, respectively. Furthermore, mounting holes 64h, 65h, and 66h are formed in the cover 61 that penetrate the cover 61. The cover fixing screw 64s threads into the screw hole 64t through the mounting hole 64h, the cover fixing screw 65s threads into the screw hole 65t through the mounting hole 65h, and the cover fixing screw 66s threads into the screw hole 66t through the mounting hole 66h. Thus, the cover 61 is fastened to the bracket 60 using the cover fixing screws 64s, 65s, and 66s.

[0043] The circuit board 62 is fastened to the bracket 60 using board fixing screws 70s, 71s, 72s, and 73s, and is housed in a space surrounded by the bracket 60 and the cover 61. The circuit board 62 includes a connector 63 for connecting to a harness or a cable. The connector 63 is fastened to the circuit board 62 using connector fixing screws 74s and 75s.

[0044] Fig. 5 is a plan view of the bracket 60, and Figs. 6, 7, and 8 are cross-sectional views of the motor and ECU taken along lines A-A, B-B, and C-C, respectively, in Fig. 5. The cross-sectional views in Fig. 6, 7, and 8 show cross sections in a state in which the cover 61 and the circuit board 62 are fixed (attached) to the bracket 60 and the bracket 60 is fastened to the motor case 20a.

[0045] The motor 20 includes a motor case 20a, a motor rotating shaft 20b, a stator 20c fixed to the motor case 20a, a rotor 20d fixed to the motor rotating shaft 20b, and motor bearings 20e and 20f. The motor bearing 20e is held by a bracket 60, and the motor bearing 20f is held by the motor case 20a, rotatably supporting the motor rotating shaft 20b relative to the motor case 20a. The bracket 60 serves as a heat sink that dissipates heat generated from a circuit board 62 and also serves as a bearing holder that supports the motor bearing 20e. The motor case 20a houses the motor rotating shaft 20b, the stator 20c, the rotor 20d, and the motor bearing 20f, and also serves as a motor bearing holder that supports the motor bearing 20f.

[0046] The bracket 60 has screw holes 70t, 71t, 72t, and 73t formed therein for fastening the circuit board 62 to the bracket 60 using board fixing screws 70s, 71s, 72s, and 73s. The board fixing screws 70s to 73s are threaded into the screw holes 70t to 73t, respectively, through attachment holes formed in the circuit board 62. This fastens the circuit board 62 to the bracket 60.

[0047] The bracket 60 also has mounting holes 67h, 68h, and 69h that penetrate the bracket 60. The mounting holes 67h, 68h, and 69h are used to fasten the bracket 60 to the motor case 20a using bracket fixing screws 67s, 68s, and 69s. The bracket fixing screw 68s threads into a screw hole 68t formed in the motor case 20a through the mounting hole 68h. The bracket fixing screw 69s threads into a screw hole 69t formed in the motor case 20a through the mounting hole 69h. The bracket fixing screw 67s threads into a screw hole (not shown) formed in the motor case 20a through the mounting hole 67h. This fastens the bracket 60 to the motor case 20a.

[0048] 6 , the cover 61 is formed so that, when the cover 61 is fixed (attached) to the bracket 60, the inner surface of the portion facing the head of the bracket fixing screw 68s is close to the head of the bracket fixing screw 68s in the axial direction of the bracket fixing screw 68s. That is, the cover 61 has a shape such that the inner surface of the portion facing the head of the bracket fixing screw 68s is close to the head of the bracket fixing screw 68s in the axial direction of the bracket fixing screw 68s. For example, the cover 61 may be formed so that, at the portion facing the head of the bracket fixing screw 68s, an axial distance DC2 between the bearing surface of the bracket fixing screw 68s and the inner surface of the cover 61 is shorter than the length DL2 of the bracket fixing screw 68s.

[0049] For example, the cover 61 may be formed so that the axial distance DC2 between the inner surface of the cover 61 closest to the head of the bracket fixing screw 68s and the bearing surface of the bracket fixing screw 68s is shorter than the length DL2 of the bracket fixing screw 68s (see Fig. 7). Similarly, for the other bracket fixing screws 67s, the cover 61 is formed so that the inner surface of the portion facing the head of the bracket fixing screw 67s is close to the head of the bracket fixing screw 67s in the axial direction of the bracket fixing screw 67s.

[0050] The cover 61 is formed so that the inner surface of the portion facing the head of the board fixing screw 70s is close to the head of the board fixing screw 70s in the axial direction of the board fixing screw 70s when the cover 61 is fixed (attached) to the bracket 60. In other words, the cover 61 has a shape such that the inner surface of the portion facing the head of the board fixing screw 70s is close to the head of the board fixing screw 70s in the axial direction of the board fixing screw 70s.

[0051] For example, the cover 61 may be formed so that, at a portion facing the head of the substrate fixing screw 70s, the axial distance DC1 between the bearing surface of the substrate fixing screw 70s and the inner surface of the cover 61 is smaller than the length DL1 of the substrate fixing screw 70s. For example, the cover 61 may be formed so that the axial distance DC1 between the inner surface of the cover 61 closest to the head of the substrate fixing screw 70s and the bearing surface of the substrate fixing screw 70s is smaller than the length DL1 of the substrate fixing screw 70s.

[0052] Similarly, for the other board fixing screws 71s to 73s, the cover 61 is formed so that the inner surface of the portion facing the head of board fixing screw 71s is close to the head of board fixing screw 71s in the axial direction of board fixing screw 71s, the inner surface of the portion facing the head of board fixing screw 72s is close to the head of board fixing screw 72s in the axial direction of board fixing screw 72s, and the inner surface of the portion facing the head of board fixing screw 73s is close to the head of board fixing screw 73s in the axial direction of board fixing screw 73s.

[0053] See Figure 8. The connector 63 is sandwiched between the cover 61 and the bracket 60, and displacement is restricted. By being sandwiched between the cover 61 and the bracket 60, displacement of the connector 63 in the axial direction of, for example, the bracket fixing screw 69s is restricted. In this embodiment, the axial directions of the bracket fixing screws 67s to 69s and the board fixing screws 70s to 73s coincide with the axial direction of the motor rotary shaft 20b.

[0054] The connector 63 is disposed so as to be close to the head of the bracket fixing screw 69s in the axial direction of the bracket fixing screw 69s. For example, the connector 63 may be disposed so that, at a portion facing the head of the heat sink fixing screw 69s, the axial distance DC3 between the bearing surface of the bracket fixing screw 69s and the connector 63 is smaller than the length DL3 of the bracket fixing screw 69s. For example, the connector 63 may be disposed so that the axial distance DC3 between the portion of the connector 63 closest to the head of the bracket fixing screw 69s and the bearing surface of the bracket fixing screw 69s is smaller than the length DL3 of the bracket fixing screw 69s.

[0055] (Modifications) (1) In the above explanation, an example was described in which the motor control device of the present invention is applied to a column assist type electric power steering device, also known as an upstream assist type, but the motor control device of the present invention may also be applied to a downstream assist type electric power steering device. Below, configuration examples in which the motor control device of the present invention is applied to single pinion assist type, rack assist type, and dual pinion assist type electric power steering devices, as examples of downstream assist type electric power steering devices, will be explained.

[0056] 9 shows an example of a configuration in which the motor control device of the present invention is applied to a single-pinion assist electric power steering device. A steering wheel 1 is connected to one universal joint 4a of an intermediate shaft via a steering shaft 2. An input shaft 4c of a torsion bar (not shown) is connected to the other universal joint 4b. A pinion-rack mechanism 5 includes a pinion gear (pinion) 5a, a rack bar (rack) 5b, and a pinion shaft 5c. The input shaft 4c and the pinion-rack mechanism 5 are connected by a torsion bar (not shown) that twists due to a difference in rotation angle between the input shaft 4c and the pinion-rack mechanism 5. A torque sensor 10 electromagnetically measures the torsion angle of the torsion bar as the steering torque Th of the steering wheel 1. A motor 20 that assists the steering force of the steering wheel 1 is connected to the pinion shaft 5c via a reduction gear 3, and a rotation angle sensor 23a calculates rotation angle information of the motor rotation shaft of the motor 20.

[0057] (2) Figure 10 shows a configuration example in which the motor control device of the present invention is applied to a rack-assist type electric power steering device. A spiral groove (not shown) is formed on the outer peripheral surface of the rack bar 5b, and a similar lead spiral groove (not shown) is also formed on the inner peripheral surface of the nut 81. A ball screw is formed by arranging multiple rolling elements in the rolling path formed by these spiral grooves. A belt 84 is wound around a drive pulley 82 connected to a motor rotating shaft 20b of a motor 20 that assists the steering force of the steering wheel 1, and a driven pulley 83 connected to the nut 81, and the rotational motion of the motor rotating shaft 20b is converted into linear motion of the rack bar 5b. A rotation angle sensor 23a calculates rotation angle information of the motor rotating shaft of the motor 20.

[0058] (3) Figure 11 shows an example of a configuration in which the motor control device of the present invention is applied to a dual pinion assist type electric power steering device. The dual pinion assist type electric power steering device has a second pinion shaft 85 and a second pinion gear 86 in addition to a pinion shaft 5c and a pinion gear 5a, and a rack bar 5b has first rack teeth (not shown) that mesh with the pinion gear 5a and second rack teeth (not shown) that mesh with the second pinion gear 86. A motor 20 that assists the steering force of the steering wheel 1 is connected to the second pinion shaft 85 via a reduction gear 3, and a rotation angle sensor 23a calculates rotation angle information of the motor rotation shaft of the motor 20.

[0059] (Effects of the Embodiment) (1) The motor 20 includes a motor case 20a that houses a stator 20c and a rotor 20d of the motor 20, a bracket 60 that is fastened to the motor case 20a using bracket fixing screws 67s and 68s, a cover 61 that is fixed to the bracket 60, and a motor control circuit board 62 that is fastened to the bracket 60 using board fixing screws 70s to 73s and housed in a space surrounded by the bracket 60 and the cover 61. The cover 61 is formed so that portions of the cover 61 that face the heads of the bracket fixing screws 67s and 68s are close to the heads of the bracket fixing screws 67s and 68s in the axial direction of the bracket fixing screws 67s and 68s, and portions of the cover 61 that face the heads of the board fixing screws 70s to 73s are close to the heads of the board fixing screws 70s to 73s in the axial direction of the board fixing screws 70s to 73s. As a result, even if the board fixing screws 70s to 73s as well as the bracket fixing screws 67s and 68s become loose, the cover 61 can prevent these screws from falling off from their mounting positions.

[0060] (2) The cover 61 may be formed so that the distance between the bearing surfaces of the bracket fixing screws 67s, 68s at the portions facing the heads of the bracket fixing screws 67s, 68s is shorter than the length of the bracket fixing screws 67s, 68s, and the distance between the bearing surfaces of the board fixing screws 70s to 73s at the portions facing the heads of the board fixing screws 70s to 73s is shorter than the length of the board fixing screws 70s to 73s. This allows the cover 61 to prevent not only the board fixing screws 70s to 73s but also the bracket fixing screws 67s, 68s from falling out of their attachment positions even if they become loose.

[0061] (3) The bracket 60 may be fastened to the motor case 20a using bracket fixing screws 67s, 68s and a bracket fixing screw 69s, and the circuit board 62 may include a connector 63 for connecting to a harness or a cable. The connector 63 may be disposed adjacent to the head of the bracket fixing screw 69s in the axial direction of the bracket fixing screw 69s. This allows the connector 63 to prevent the screws from falling out of their mounting positions even if the bracket fixing screw 69s becomes loose.

[0062] (4) The connector 63 may be sandwiched between the cover 61 and the bracket 60 to restrict displacement. This restricts displacement of the connector 63 in the axial direction of the bracket fixing screw 69s, thereby more reliably preventing the bracket fixing screw 69s from falling off by the connector 63. In addition, it is possible to prevent the circuit board 62 from being bent due to external forces applied to the harness or cables.

[0063] 1...Steering wheel, 2...Steering shaft, 3...Reduction gear, 4a, 4b...Universal joint, 4c...Input side shaft, 5...Pinion rack mechanism, 5a...Pinion gear (pinion), 5b...Rack bar (rack), 5c...Pinion shaft, 6a, 6b...Tie rod, 7a, 7b...Hub unit, 8L, 8R...Steered wheels, 10...Torque sensor, 11...Ignition switch, 12...Vehicle speed sensor, 13...Battery, 14...Steering angle sensor, 20...Motor, 20a...Motor case, 20b...Motor rotating shaft, 20c...Stator, 20d...Rotor, 20e, 20f...Motor Motor bearing, 23...motor rotation angle detection circuit, 23a...rotation angle sensor, 30...electronic control unit (ECU), 31a, 31b...control calculation device, 33A...first motor current cut-off circuit, 33B...second motor current cut-off circuit, 39A1, 39A2, 39B1, 39B2, 39C1, 39C2...current detection circuit, 41A...first gate drive circuit, 41B...second gate drive circuit, 42A...first power conversion circuit, 42B...second power conversion circuit, 44A...first power supply cut-off circuit, 44B...second power supply cut-off circuit, 50...current command value calculation unit, 52, 53...subtractor, 54...current limiting unit, 55...proportional integral (P I) Control unit, 56... 2-phase / 3-phase conversion unit, 57... 3-phase / 2-phase conversion unit, 58... Angular velocity conversion unit, 60... Bracket, 61... Cover, 62... Circuit board, 63... Connector, 64b, 65b, 66b... Bosses, 64h, 65h, 66h, 67h, 68h, 69h... Mounting holes, 64s, 65s, 66s... Cover fixing screws, 64t, 65t, 66t, 68t, 69t, 70t, 71t, 72t, 73t... Screw holes, 67s, 68s, 69s... Bracket fixing screws, 70s, 71s, 72s, 73s... Board fixing screws, 74s, 75s... Connector fixing screws, 81... Nut , 82... driving pulley, 83... driven pulley, 84... belt, 85... second pinion shaft, 86... second pinion gear, Ca1, Ca2... ceramic capacitor, CA1, CA2, CB1, CB2... electrolytic capacitor, CNT... connector, Q1, Q3, Q5... high side FET, Q2, Q4, Q6... low side FET, QA1, QA2, QA3, QB1, QB2, QB3... phase cutoff FET, QC1, QC2, QD1, QD2... power cutoff FET, La... choke coil, Lpa... positive side power line, PWa... power wiring, SWAa, SWAb, SWAc, SWBa, SWBb,SWBc...switching arm,

Claims

1. A motor control device comprising: a motor case that houses a stator and rotor of a motor; a bracket fastened to the motor case using a first bracket fixing screw; a cover fixed to the bracket; and a circuit board for motor control that is fastened to the bracket using a board fixing screw and housed in a space enclosed by the bracket and the cover, wherein the cover is formed so that a portion facing the head of the first bracket fixing screw is close to the head of the first bracket fixing screw in the axial direction of the first bracket fixing screw, and a portion facing the head of the board fixing screw is close to the head of the board fixing screw in the axial direction of the board fixing screw.

2. The motor control device as described in claim 1, characterized in that the cover is formed so that the distance between the seat of the first bracket fixing screw at the portion facing the head of the first bracket fixing screw is smaller than the length of the first bracket fixing screw, and the distance between the seat of the board fixing screw at the portion facing the head of the board fixing screw is smaller than the length of the board fixing screw.

3. A motor control device as described in claim 1, characterized in that the bracket is fastened to the motor case using the first bracket fixing screw and the second bracket fixing screw, the circuit board is provided with a connector for connecting to a harness or cable, and the connector is positioned so as to be adjacent to the head of the second bracket fixing screw in the axial direction of the second bracket fixing screw.

4. The motor control device according to claim 3, wherein the connector is sandwiched between the cover and the bracket so that displacement of the connector is restricted.

5. An electric power steering device comprising: a motor control device according to any one of claims 1 to 4; and a motor controlled by said motor control device, said electric power steering device providing a steering assist force to a steering system of a vehicle by said motor.

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