Motor control device and electric power steering device

Abstract

To provide a motor control device capable of preventing cost increase while suppressing steering angle fluctuations for a few seconds after an event of an anomaly.SOLUTION: An abnormality-time control unit 45 performs abnormality-time drive control by switching between a short-circuit mode and a charging mode according to the magnitude of the voltage of a capacitor 37 during hands-off control when an abnormality is detected in an electronic control unit 200. In the short-circuit mode, either all of the upper FETs Qah, Qbh, and Qch of the inverter 21 are turned off and all of the lower FETs Qal, Qbl, and Qcl are turned on, or all of the upper FETs Qah, Qbh, and Qch are turned on and all of the lower FETs Qal, Qbl, and Qcl are turned off. In the charging mode, all of the upper FETs Qah, Qbh, and Qch and all of the lower FETs Qal, Qbl, and Qcl are turned off. Furthermore, during the execution of the abnormality-time drive control, when it is detected that the steering wheel has been gripped, the abnormality-time control unit 45 terminates the abnormality-time drive control and turns off all of the upper FETs Qah, Qbh, and Qch as well as all of the lower FETs Qal, Qbl, and Qcl.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Conventionally, Level 1 autonomous driving involves hands-on driving assistance (such as steering assistance) that requires the driver to hold the steering wheel. For this reason, if an abnormality such as a device failure or power loss occurs in the electric power steering device, the steering assistance is terminated and steering is handed over to the driver (handover) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-35979 Summary of the Invention [Problem to be solved by the invention]

[0004] In contrast, in autonomous driving at level 2 or higher, hands-off driving assistance (such as automatic steering) is provided, which does not require the driver to hold the steering wheel. Therefore, if an abnormality occurs in the electric power steering device, for example, it takes several seconds for the driver to notice the abnormality and hold the steering wheel. Therefore, it is required that the steering assistance is terminated several seconds after the abnormality occurs, and that the steering angle is not suddenly changed during that waiting time. However, in order to prevent a sudden change in the steering angle, it is necessary to control the electric motor using the electric power steering device in which the abnormality occurred. Here, for example, it is conceivable to configure the electric motor with a dual system for the circuit and the electric motor and a backup power supply, and to control the electric motor by switching to the dual system or the backup power supply when an abnormality occurs. However, configuring the dual system or the backup power supply can increase costs. An object of the present invention is to provide a motor control device and an electric power steering device that can suppress fluctuations in the steering angle for several seconds after an abnormality occurs while suppressing increases in costs. [Means for solving the problem]

[0005] In order to achieve the above object, one aspect of the present invention provides a motor control device (a) for an electric power steering device that controls an electric motor that applies a steering assist force to a steering system of a vehicle, and (b) includes a normal state control unit that PWM drives the electric motor via an inverter, (c) the normal state control unit is capable of executing hands-off control that PWM drives the electric motor so as to apply a steering assist force for hands-off automatic steering to the steering system, (d) further includes an abnormality detection unit that detects that an abnormality has occurred in the motor control device, (e) a grip detection unit that detects whether a driver is gripping a steering operation unit of the vehicle, (f) a capacitor connected in parallel to the inverter, (g) a voltage detection unit that detects the voltage of the capacitor, and (h) a hand and an abnormality control unit that performs abnormality drive control by switching between a short-circuit mode in which all upper FETs of the inverter are turned off and all lower FETs are turned on, or all upper FETs of the inverter are turned on and all lower FETs are turned off, and a charge mode in which all upper FETs and lower FETs of the inverter are turned off, depending on the magnitude of the voltage of the capacitor, when the abnormality detection unit detects the occurrence of an abnormality in the motor control unit during execution of the short-circuit control, and (i) when the grip detection unit detects that the steering operation unit has been gripped during execution of the abnormality drive control, the abnormality control unit terminates the abnormality drive control and turns off all upper FETs and lower FETs of the inverter.

[0006] Another aspect of the present invention provides a motor control device that (a) is a motor control device for an electric power steering device that controls an electric motor that applies a steering assist force to a steering system of a vehicle, and (b) includes a normal state control unit that PWM drives the electric motor via an inverter, (c) the normal state control unit is capable of executing hands-off control that PWM drives the electric motor so as to apply a steering assist force for hands-off automatic steering to the steering system, (d) further includes an abnormality detection unit that detects that an abnormality has occurred in the motor control device, and (e) a grip detection unit that detects whether a driver is gripping a steering operation unit of the vehicle. (f) a motor shutoff FET interposed between the inverter and the windings of the electric motor; and (g) an abnormality control unit that performs abnormality drive control by turning off all of the upper FETs of the inverter and turning on all of the lower FETs, or by turning on all of the upper FETs of the inverter and turning off all of the lower FETs, when the abnormality detection unit detects that an abnormality has occurred in the motor control device while hands-off control is being executed, and (h) the abnormality control unit terminates the abnormality drive control and turns off the motor shutoff FET when the grip detection unit detects that the steering operation unit has been gripped while the abnormality drive control is being executed.

[0007] Another aspect of the present invention is an electric power steering device that includes (a) the motor control device described above, and (b) an electric motor controlled by the motor control device, and (c) applies a steering assist force to the steering system of the vehicle by the electric motor. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a motor control device and an electric power steering device that can suppress fluctuations in the steering angle when an abnormality occurs, while suppressing increases in costs. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the overall configuration of an electric power steering device according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the internal configuration of an electronic control unit in detail. [Figure 3] FIG. 2 is a diagram illustrating functions of an electronic control unit realized by a processor. [Figure 4] FIG. 10 is a flowchart illustrating an abnormality control process. [Figure 5] FIG. 2 is a diagram illustrating a first period and a second period. [Figure 6] FIG. 10 is a flowchart illustrating an abnormality drive control process. [Figure 7] FIG. 10 illustrates the operation of the electronic control unit while performing a charging mode. [Figure 8] FIG. 10 illustrates the operation of the electronic control unit while implementing a short circuit mode. [Figure 9] FIG. 10 illustrates the operation of the electronic control unit while implementing a short circuit mode. [Figure 10] FIG. 10 is a diagram showing the overall configuration of an electric power steering device according to a modified example. [Figure 11] FIG. 10 is a diagram illustrating the operation of the electronic control unit at the end of abnormality drive control. [Figure 12] FIG. 10 is a diagram showing the functions of an electronic control unit realized by a processor in an electric power steering device according to a modified example. [Figure 13] FIG. 10 is a diagram showing in detail the internal configuration of a modified electronic control unit. [Figure 14] FIG. 10 is a flowchart illustrating a modified example of an abnormality control process. DETAILED DESCRIPTION OF THE INVENTION

[0010] The inventors discovered the following problem in the process of studying a motor control device that can suppress fluctuations in the steering angle for several seconds after an abnormality occurs. In such a motor control device, if an abnormality (e.g., loss of power) occurs in the motor control device of an electric power steering device, it is conceivable that power stored in a capacitor such as a smoothing capacitor would be supplied to a processor, inverter, etc. to suppress fluctuations in the steering angle. However, if the processor, inverter, etc. consume a lot of power, the power stored in the capacitor may run out, rendering the processor, inverter, etc. inoperable, and making it impossible to continue suppressing fluctuations in the steering angle.

[0011] An example of a motor control device and an electric power steering device according to an embodiment of the present invention will be described below with reference to the drawings. Note that the embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the configuration and arrangement of components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims. The following description will be given of a case in which the present invention is applied to an electric power steering device that applies a steering force to a steering system of a vehicle. The application of the steering force is performed by acquiring a steering assist command from a device (hereinafter also referred to as a "steering assist command device") separate from the electric power steering device, and PWM-driving an electric motor (a multi-phase motor) based on the acquired steering assist command. The vehicle is capable of switching between two steering modes: a hands-on mode that provides hands-on driving assistance requiring gripping of the steering wheel, and a hands-off mode that provides hands-off driving assistance not requiring gripping of the steering wheel. The steering assist command device outputs a steering assist command (hands-on steering assist command, hands-off steering assist command) according to the steering mode. The embodiments of the present invention will be described in the following order. 1. First embodiment 1-1 Overall configuration of electric power steering device 1-2 Control process in case of abnormality 1-3 Variations

[0012] 1. First Embodiment [1-1 Overall configuration of electric power steering device] Fig. 1 is a diagram showing the overall configuration of an electric power steering device 100 according to a first embodiment. As shown in Fig. 1, a steering shaft 2 of a steering wheel 1 (or more broadly, a "steering operation portion") is connected to steered wheels 8L, 8R via hub units 7a, 7b via a reduction gear 3, universal joints 4a, 4b, a pinion-rack mechanism 5, and tie rods 6a, 6b that constitute a reduction mechanism. The pinion-rack mechanism 5 has a pinion 5a to which steering force is transmitted from the universal joint 4b, and a rack 5b that meshes with the pinion 5a, and converts the steering force transmitted to the pinion 5a into linear motion in the vehicle width direction by the rack 5b. Further, the steering shaft 2 is provided with a torque sensor 9 for detecting the steering torque Th of the driver and a steering angle sensor 10 for detecting the steering angle θh of the steering wheel 1. An electric motor 11 that applies a steering assist force to the steering system is connected to the steering shaft 2 via a reduction gear 3. As the electric motor 11, for example, a three-phase motor can be used.

[0013] An electronic control unit 200 (broadly speaking, a "motor control device") that controls the electric power steering device 100 is supplied with power from the power supply 12 via a power cutoff relay 41 and a power supply line 35 shown in FIG. 2, and also receives an ignition key signal from an ignition switch. The power supply 12 does not have a backup power supply. If an abnormality occurs in the power supply 12, power is supplied from a capacitor 37 shown in FIG. 2.

[0014] The electronic control unit 200 is also connected to a vehicle CAN (Controller Area Network) 15, and receives various types of vehicle information from the vehicle CAN 15. For example, the electronic control unit 200 receives from the vehicle CAN 15 information on the vehicle speed Vh of the vehicle detected by a vehicle speed sensor (not shown) and information on the vehicle's steering mode (steering assist on / off information indicating whether the mode is hands-on or hands-off and whether steering assist is on (started / executing) or off (ended)). The vehicle CAN 15 is also connected to a steering assist command device 300 that outputs a steering assist command, and the electronic control unit 200 receives the steering assist command from the steering assist command device 300 via the vehicle CAN 15. Examples of the steering assist command include a hands-on steering assist command for providing hands-on driving assistance to the vehicle and a hands-off steering assist command for providing hands-off driving assistance. The hands-on steering assist command and the hands-off steering assist command may be, for example, a target steering angle θh* and a target steering torque Th* that enable the vehicle to travel hands-on or hands-off. In the first embodiment, a case where the target steering angle θh* is used will be described. The electronic control unit 200 then performs PWM (Pulse Width Modulation) control of the electric motor 11 via the inverter 21 based on the steering torque Th detected by the torque sensor 9, the steering angle θh detected by the steering angle sensor 10, and the vehicle speed Vh, steering mode, and steering assist command received from the vehicle CAN 15.

[0015] The steering angle sensor 10 is not essential, and the steering angle θh may be calculated by dividing the motor rotation angle θm obtained from a rotation angle sensor 16 that detects the rotation angle of the rotating shaft of the electric motor 11 by the gear ratio of the reduction gear 3 and adding the torsion angle of the torsion bar of the torque sensor 9. As the rotation angle sensor 16, for example, a resolver that detects the rotation position of the electric motor 11, or a magnetic sensor that detects the magnetic field of a magnet attached to the rotating shaft of the electric motor 11 may be used. Also, instead of the steering angle θh, the steering angle of the steered wheels 8L, 8R may be used. As a method for detecting the steering angle, for example, a method based on the displacement amount of the rack 5b may be used.

[0016] The electronic control unit 200 includes a computer having, for example, a processor 17 and peripheral components such as a storage unit 18. The processor 17 may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage unit 18 may be, for example, a semiconductor storage unit, a magnetic storage unit, or an optical storage unit. Examples of such memories include a register, a cache memory, and a ROM or RAM used as a main storage unit. Each function of the electronic control unit 200 described below is realized, for example, by the processor 17 of the electronic control unit 200 executing a computer program stored in the storage unit 18. The storage unit 18 also stores various data required for executing the computer program, such as a predetermined time (for example, 2 to 3 seconds) used in the abnormality control process described below. The computer may be configured with dedicated hardware for executing the information processing described below. For example, the dedicated hardware may be a functional logic circuit configured in a general-purpose semiconductor integrated circuit. Examples of such dedicated hardware include programmable logic devices (PLDs) such as field-programmable gate arrays (FPGAs).

[0017] Fig. 2 is a diagram showing in detail the internal configuration of the electronic control unit 200. As shown in Fig. 2, the electronic control unit 200 has a normal state control section 19, an FET drive circuit 20, an inverter 21, a current detection circuit 22, and a motor rotation angle detection circuit 23. The normal state control unit 19 PWM-drives the electric motor 11 via the FET drive circuit 20 and the inverter 21. When the steering mode is the hands-on mode, the normal state control unit 19 is capable of executing hands-on control, which PWM-drives the electric motor 11 so as to apply a steering assist force for hands-on driving assistance to the steering system. When the steering mode is the hands-off mode, the normal state control unit 19 is capable of executing hands-off control, which PWM-drives the electric motor 11 so as to apply a steering assist force for hands-off driving assistance to the steering system. Specifically, as shown in FIG. 3 , the normal state control unit 19 has a manual assist control unit 24, a first gain setting unit 25, a multiplier 26, a steering angle feedback control unit 27, a second gain setting unit 28, a multiplier 29, an adder 30, a command value setting unit 31, a current feedback control unit 32, and a PWM control unit 33. Each of the manual assist control unit 24 to the PWM control unit 33 is realized by the processor 17 executing a computer program stored in the storage unit 18.

[0018] The manual assist control unit 24 calculates a manual assist torque Tma based on the steering torque Th output from the torque sensor 9, the vehicle speed Vh received from the vehicle CAN 15, the steering angle θh output from the steering angle sensor 10, and the steering angular velocity ωh calculated from the steering angle θh. The manual assist torque Tma is a steering assist torque that assists the driver in steering the steering wheel 1. The manual assist torque Tma is input to a multiplier 26. The first gain setting unit 25 sets the value of the first steering assist gain based on the steering mode information received from the vehicle CAN 15. For example, when the steering assist on-off information is on, the value of the first steering assist gain is gradually changed to "0" over time, and when the steering assist on-off information is off, the value is gradually changed to "1" over time. In addition, the multiplier 26 multiplies the value of the first steering assist gain set by the first gain setting unit 25 by the manual assist torque Tma to calculate a post-multiplication manual assist torque Tma'. As a result, when the steering assist on-off information switches from on to off, Tma' gradually changes from 0 to Tma, and when the steering assist on-off information switches from off to on, Tma' gradually changes from Tma to 0. The post-multiplication manual assist torque Tma' is output to the adder 30.

[0019] The steering angle FB control unit 27 calculates the steering angle FB torque Tsfb based on the steering torque Th output from the torque sensor 9, the vehicle speed Vh and the target steering angle θh* received from the vehicle CAN 15, the steering angle θh output from the steering angle sensor 10, and the steering angular velocity ωh calculated from the steering angle θh. The steering angle FB torque Tsfb is a steering assist torque that causes the actual steering angle θh to follow the target steering angle θh*. The steering angle FB torque Tsfb is output to the multiplier 29. The second gain setting unit 28 sets the value of the second steering assist gain based on the steering mode information received from the vehicle CAN 15. For example, when the steering assist on-off information is off, the value of the second steering assist gain gradually changes to "0" over time, and when the steering assist on-off information is on, the value gradually changes to "1" over time. In addition, the multiplier 29 multiplies the value of the second steering assist gain set by the second gain setting unit 28 by the steering angle feedback torque Tsfb to calculate a post-multiplication steering angle feedback torque Tsfb'. As a result, when the steering assist on-off information switches from on to off, Tsfb' gradually changes from Tsfb'=Tsfb to 0, and when the steering assist on-off information switches from off to on, Tsfb' gradually changes from 0 to Tsfb. The post-multiplication steering angle feedback torque Tsfb' is output to the adder 30.

[0020] Adder 30 calculates the target steering torque (Tma'+Tsfb') by adding post-multiplication manual assist torque Tma' and post-multiplication steering angle FB torque Tsfb'. As a result, when the steering assist on-off information switches from on to off, the post-multiplication manual assist torque Tma' and the post-multiplication steering angle FB torque Tsfb' each gradually change, and the target steering torque gradually changes from 100% steering torque corresponding to the steering assist command (hands-on steering assist command) to 100% steering torque corresponding to the driver's steering torque Th. Also, when the steering assist on-off information switches from off to on, the post-multiplication manual assist torque Tma' and the post-multiplication steering angle FB torque Tsfb' each gradually change, and the target steering torque gradually changes from 100% steering torque corresponding to the driver's steering torque Th to 100% steering torque corresponding to the steering assist command (hands-off steering assist command). The command value setting unit 31 converts the target steering torque into a current command value Ir0 and sets the target current command value Ir by limiting the upper limit of the current command value Ir0. As the target current command value Ir, for example, a q-axis current command value or a d-axis current command value can be used. The target current command value Ir is output to the current FB control unit 32.

[0021] The current FB control unit 32 generates a voltage control command value Vref by feedback control such as PI (proportional-integral) control based on the deviation between the fed-back current value Im of the electric motor 11 and the target current command value Ir. As the current value Im, for example, a q-axis current iq and a d-axis current id obtained by converting the phase currents ia, ib, and ic of the electric motor 11 for the respective phases A, B, and C can be used. Furthermore, as the voltage control command value Vref, for example, voltage command values va1, vb1, and vc1 of the respective phases A, B, and C can be used. The voltage control command value Vref is output to the PWM control unit 33. The PWM control unit 33 generates gate signals (PWM signals) for driving the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qc1 of the inverter 21 based on the voltage control command value Vref. The PWM control unit 33 also acquires a control signal output from the abnormality detection unit 43, and if the acquired control signal is a signal that permits the output of a PWM signal, outputs the generated PWM signal to the inverter 21 via the FET drive circuit 20. On the other hand, if the acquired control signal is a signal that prohibits the output of a PWM signal, the output of the PWM signal is stopped. The FET drive circuit 20 performs amplification processing and level conversion of the PWM signal.

[0022] The inverter 21 is driven by a PWM signal output from the processor 17 (FET drive circuit 20) and supplies to the electric motor 11 a current for zeroing the deviation between the current value Im of the electric motor 11 and the target current command value Ir. Specifically, as shown in FIG. 2, the inverter 21 includes a bridge circuit 34 configured by connecting in parallel phase circuits Ca, Cb, and Cc formed corresponding to the phases A, B, and C of the electric motor 11. The bridge circuit 34 is connected between a power supply line 35, which is connected to the positive side (high potential side) of the power supply 12 and receives power, and a ground line 36. Each phase circuit Ca, Cb, Cc of the bridge circuit 34 has, in series, upper-stage FETs Qah, Qbh, Qch arranged on the power supply line 35 side (high potential side), lower-stage FETs Qal, Qbl, Qcl arranged closer to the ground line 36 side (low potential side) than the upper-stage FETs Qah, Qbh, Qch, and shunt resistors Ra, Rb, Rc arranged closer to the ground line 36 side (low potential side) than the lower-stage FETs Qal, Qbl, Qcl. For example, MOSFETs (metal-oxide-semiconductor field effect transistors) having parasitic diodes whose forward direction is from the ground line 36 toward the power supply line 35 can be used as the upper-stage FETs Qah, Qbh, Qch and the lower-stage FETs Qal, Qbl, Qcl.

[0023] Specifically, the drains of the upper-stage FETs Qah, Qbh, and Qch are connected to a power supply line 35. The sources of the upper-stage FETs Qah, Qbh, and Qch are connected to the drains of the lower-stage FETs Qal, Qbl, and Qcl. The sources of the lower-stage FETs Qal, Qbl, and Qcl are connected to a ground line 36 via shunt resistors Ra, Rb, and Rc. The upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl each receive a gate signal (PWM signal) output from the processor 17 (FET drive circuit 20) at their gates, turning the source-drain connections on and off. The junctions between the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl are electrically connected to the windings of phases A, B, and C of the electric motor 11 via motor breaker FETs Qam, Qbm, and Qcm, described later. The shunt resistors Ra, Rb, Rc are arranged closer to the ground line 36 (lower potential side) than the lower-stage FETs Qal, Qbl, Qcl, and the phase currents ia, ib, ic supplied from the bridge circuit 34 to the phases A, B, C of the electric motor 11 flow through the shunt resistors Ra, Rb, Rc. The connection points between the lower-stage FETs Qal, Qbl, Qcl and the shunt resistors Ra, Rb, Rc are electrically connected to a current detection circuit 22. The voltage drops va, vb, vc of the shunt resistors Ra, Rb, Rc are input to the current detection circuit 22.

[0024] The current detection circuit 22 detects the phase currents i, ib, and ic flowing through the shunt resistors Ra, Rb, and Rc based on the voltage drops va, vb, and vc across the shunt resistors Ra, Rb, and Rc. The phase currents i, ib, and ic can be detected, for example, by an estimation method using Kirchhoff's law. The phase currents i, ib, and ic are output to the processor 17. The current detection circuit 22 can be implemented, for example, by an AD (Analog-to-Digital) converter. The motor rotation angle detection circuit 23 detects the motor rotation angle θm based on the detection value output from the rotation angle sensor 16. The motor rotation angle θm is output to the processor 17.

[0025] The electronic control unit 200 further has a capacitor 37, a first voltage detection circuit 38 (broadly speaking, a "voltage detection section"), a second voltage detection circuit 39, motor cutoff FETs Qam, Qbm, and Qcm, a motor cutoff circuit 40, a power cutoff relay 41, and a control section 42. The control section 42 has an abnormality detection section 43, a grip detection section 44, and an abnormality control section 45. Capacitor 37 is inserted between power supply line 35 and ground line 36, and is connected in parallel to inverter 21. Capacitor 37 functions as a smoothing capacitor that smoothes the power supplied from power supply 12 to power supply line 35 (processor 17, inverter 21). Capacitor 37 also stores (charges) the power supplied to power supply line 35. The first voltage detection circuit 38 detects the voltage (high-potential-side voltage VR, which will be described later) of the capacitor 37. The second voltage detection circuit 39 detects the power supply voltage Vbat supplied from the power supply 12. The detection results of the high-potential-side voltage VR and the power supply voltage Vbat are output to the processor 17.

[0026] The motor shutoff FETs Qam, Qbm, and Qcm are interposed between the inverter 21 and the windings of the electric motor 11. Specifically, the source of the motor shutoff FET Qam is connected to the connection point between the upper-stage FET Qah and the lower-stage FET Qal of the inverter 21, and the drain is connected to the phase A winding of the electric motor 11. The source of the motor shutoff FET Qbm is connected to the connection point between the upper-stage FET Qbh and the lower-stage FET Qbl of the inverter 21, and the drain is connected to the phase B winding of the electric motor 11. The source of the motor shutoff FET Qcm is connected to the connection point between the upper-stage FET Qch and the lower-stage FET Qcl of the inverter 21, and the drain is connected to the phase C winding of the electric motor 11. A gate signal output from the processor 17 (abnormality control unit 45) is input to the gate of each of the motor shutoff FETs Qam, Qbm, and Qcm via the motor shutoff circuit 40, turning the source-drain on and off. The motor shutoff circuit 40 amplifies and converts the level of the gate signal output from the processor 17. The motor cutoff FETs Qam, Qbm, and Qcm are configured as FETs having parasitic diodes whose forward direction is from the inverter 21 toward the windings of the electric motor 11.

[0027] The power cutoff relay 41 is interposed between the power line 35 and the power supply 12, and connects or disconnects the power line 35 and the power supply 12 in response to a control signal output from the processor 17. The processor 17, the inverter 21, and the capacitor 37 are connected to the power line 35. Therefore, when the power line 35 and the power supply 12 are disconnected, the supply of power from the power supply 12 to the processor 17, the inverter 21, and the capacitor 37 is cut off. When an ignition key signal is input, the abnormality detection unit 43, the grip detection unit 44, and the abnormality control unit 45 execute the abnormality control process shown in Fig. 4. In parallel with the abnormality control process, the normality control unit 19 (manual assist control unit 24 to PWM control unit 33 in Fig. 3) repeatedly generates and outputs PWM signals. Fig. 4 is a diagram showing a flowchart of the abnormality control process. Each of the abnormality detection unit 43 to the abnormality control unit 45 (control unit 42) is realized when the processor 17 executes a computer program stored in the storage unit 18.

[0028] [1-2 Control process in case of abnormality] Next, we will explain the abnormality control process executed by the abnormality detection unit 43, the grip detection unit 44, and the abnormality control unit 45 (processor 17). In the initial state at the start of the abnormality control process, the power cutoff relay 41 and the motor cutoff FETs Qam, Qbm, and Qcm are on. 4, when the abnormality control process is executed, first, in step S101, the abnormality detection unit 43 acquires a steering state amount and steering assist information. Examples of the steering amount information include the steering torque Th output from the torque sensor 9, the steering angle θh output from the steering angle sensor 10, and the motor rotation angle θm output from the rotation angle sensor 16 (motor rotation angle detection circuit 23). Examples of the steering assist information include a steering assist command (target steering angle θh*) and steering mode information (hands-on mode, hands-off mode) output from the steering assist command device 300 via the vehicle CAN 15. Next, the process proceeds to step S102, where the abnormality detection unit 43 determines whether or not there is a hands-off steering assist request. As an example, a determination method can be adopted in which if the steering mode information acquired in step S101 indicates "hands-off mode," it is determined that there is a hands-off steering assist request, and if the steering mode information indicates "hands-on mode," it is determined that there is no hands-off steering assist request. Then, if the abnormality detection unit 43 determines that there is a hands-off steering assist request (YES), it proceeds to step S103. On the other hand, if it determines that there is no hands-off steering assist request (NO), it proceeds to step S112.

[0029] In step S103, the abnormality detection unit 43 detects that an abnormality has occurred in the electronic control unit 200 (abnormality detection). Methods of abnormality detection include, for example, diagnosing an abnormality in signals such as the steering torque Th, the steering angle θh, and the motor rotation angle θm, and diagnosing a fault in the inverter 21. As a method of diagnosing a fault in the inverter 21, for example, a method can be adopted in which it is determined whether the upper-stage FETs Qah, Qbh, and Qch or the lower-stage FETs Qal, Qbl, and Qcl have a short-circuit fault or an open-circuit fault based on the measured values (detected values) of the phase currents ia, ib, and ic flowing through the shunt resistors Ra, Rb, and Rc. Specifically, as shown in FIG. 5, during a period (first period T) during which a gate signal that turns on the upper-stage FET Qah and turns off the lower-stage FET Qal is output from the FET drive circuit 20, a1 If an overcurrent is detected as the phase current ia during the first period T a1 If the phase current ia detected in the first period T is substantially "0", it is determined that an open fault has occurred in the upper-stage FET Qah. b1 If an overcurrent is detected as the phase current ib during the first period T b1 If the phase current ib detected in the first period T is substantially "0", it is determined that an open fault has occurred in the upper-stage FET Qbh. c1 If an overcurrent is detected as the phase current ic during the first period T c1 If the phase current ic detected in step 1 is approximately "0", it is determined that an open fault has occurred in the upper stage FET Qch.

[0030] Similarly, in the fault diagnosis of the inverter 21, as shown in FIG. 5, a period during which the FET drive circuit 20 outputs a gate signal that turns off the upper-stage FET Qah and turns on the lower-stage FET Qal (a second period Ta2 If an overcurrent is detected as the phase current ia during the second period T a2 If the phase current ia detected in the second period T is substantially "0", it is determined that an open fault has occurred in the lower-stage FET Qal. b2 If an overcurrent is detected as the phase current ib during the second period T b2 If the phase current ib detected in the second period T is approximately "0", it is determined that an open fault has occurred in the lower-stage FET Qbl. Also, during the period T during which the FET drive circuit 20 outputs a gate signal that turns off the upper-stage FET Qch and turns on the lower-stage FET Qcl, c2 If an overcurrent is detected as the phase current ic during the second period T c2 If the phase current ic detected in step 1 is substantially "0", it is determined that an open fault has occurred in the lower stage FET Qc1. Another method of detecting an abnormality is to determine whether an abnormality has occurred in the electronic control unit 200 when, for example, the power supply voltage Vbat supplied from the power supply 12 is lost or when the power supply voltage Vbat becomes lower than the assistable voltage (for example, 6 to 7 V).

[0031] Next, the process proceeds to step S104, where the abnormality detection unit 43 determines whether or not an abnormality has occurred in the electronic control unit 200 in the abnormality detection of step S103. If it is determined that an abnormality has not occurred in the electronic control unit 200 (normal), the electronic control unit 200 is determined to be normal, and the process proceeds to step S105. On the other hand, if it is determined that an abnormality has occurred (abnormal), the process proceeds to step S106. In step S105, the abnormality detection unit 43 outputs a control signal permitting output of a PWM signal to the PWM control unit 33 of the normal-state control unit 19, and then the process proceeds to step S101. In parallel with this abnormal-state control process, in the normal-state control unit 19, the manual assist control unit 24 to the command value setting unit 31 calculate a target current command value Ir corresponding to the hands-off steering assist command. Furthermore, the current FB control unit 32 and the PWM control unit 33 perform feedback control based on the deviation between the calculated target current command value Ir and the current value Im of the electric motor 11 to generate a PWM signal. Upon receiving the control signal, the normal-state control unit 19 outputs the generated PWM signal to the inverter 21 via the FET drive circuit 20. That is, when it is determined in step S102 that there is a hands-off steering assist request, that is, when the steering mode is the hands-off mode, and it is determined in step S104 that the electronic control unit 200 is normal, the above-described hands-off control is performed. Furthermore, by moving to step S101, the flow of steps S101 to S104 is repeated, and step S105 is executed again, so that hands-off driving assistance (automatic steering) is continuously performed. Note that if abnormality drive control, which will be described later, is being executed, the abnormality drive control is terminated, and the power cutoff relay 41 is switched from off to on and maintained on.

[0032] Meanwhile, in step S106, the abnormality control unit 45 executes an abnormality drive control process to perform abnormality drive control by switching between a short circuit mode and a charge mode depending on the voltage (high-potential-side voltage VR) of the capacitor 37. The short circuit mode is a mode in which the terminals of the windings of the electric motor 11 for each phase A, B, and C are short-circuited to brake the electric motor 11 with a short brake (electromagnetic brake). The charge mode is a mode in which power is charged to the capacitor 37. In the abnormality drive control process, as shown in FIG. 6 , first, in step S201, the abnormality control unit 45 causes a notification unit (not shown) to notify that an abnormality has occurred in the electronic control unit 200. For example, a warning lamp provided on the dashboard can be used as the notification unit. The abnormality control unit 45 also switches the power cutoff relay 41 from on to off and keeps the power cutoff relay 41 off. That is, the power cutoff relay 41 is turned off while the abnormality drive control is being executed. This cuts off the connection between the power line 35 and the power supply 12, thereby cutting off the power supply from the power supply 12 to the processor 17, the inverter 21, and the capacitor 37. Therefore, the voltage (high-potential-side voltage VR) at the high-potential side end of the upper-stage FETs Qah, Qbh, and Qch of the inverter 21 becomes equal to the voltage of the capacitor 37 and varies depending on the amount of power stored in the capacitor 37. Furthermore, turning off the power cutoff relay 41 causes the power stored in the capacitor 37 to be supplied to the inverter 21 and the processor 17.

[0033] Next, the process proceeds to step S202, where the abnormality control unit 45 determines whether the high-potential-side voltage VR is smaller than a first threshold value th1. As the first threshold value th1, for example, a value (e.g., 3 V) slightly larger than the lower limit of the voltage at which the processor 17 can operate (hereinafter also referred to as the "reset voltage") can be adopted. If it is determined that the high-potential-side voltage VR is smaller than the first threshold value th1 (YES), it is determined that the processor 17 may stop and that charging of the capacitor 37 is necessary, and the process proceeds to step S203. On the other hand, if it is determined that the high-potential-side voltage VR is equal to or greater than the first threshold value th1 (NO), the process proceeds to step S204. In step S203, the abnormality control unit 45 outputs a control signal prohibiting the output of a PWM signal to the PWM control unit 33 of the normality control unit 19. Next, the abnormality control unit 45 turns off all of the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qc1, and switches to a charge mode in which these FETs are kept off (or, if the charge mode is already in, "maintains" the mode). As a result, if the short-circuit mode was active, the short-circuit mode is terminated, the short circuit between the terminals of the electric motor 11 is released, braking of the rotation of the electric motor 11 by the short brake (electromagnetic brake) is terminated, and the electric motor 11 becomes rotatable by an external force such as self-aligning torque. Then, as shown in FIG. 7, this rotation causes the electric motor 11 to generate power, which is stored (charged) in the capacitor 37 and further supplied to the processor 17, allowing the processor 17 to continue operating. FIG. 7 illustrates a case in which the terminal of the phase A winding of the electric motor 11 is at a high potential, causing current to flow from the electric motor 11 to the capacitor 37 through the parasitic diode of the upper-stage FET Qah, and the terminals of the phases B and C windings of the electric motor 11 are at a low potential, causing current to flow from the ground line 36 to the electric motor 11 through the parasitic diodes of the lower-stage FETs Qbl and Qcl. The abnormality control unit 45 then sets the value of a charging flag F, which indicates whether the capacitor 37 is being charged, to "1," terminates the abnormality drive control process, and returns to step S107. A charging flag F of "1" indicates that the capacitor 37 needs to be charged, and a charging flag F of "0" indicates that charging is not required. By returning to step S107, if the high-potential-side voltage VR is below the voltage at which the short-circuit mode can be entered, charging of the capacitor 37 continues via steps S107, S108, S109, S103, S104, and S106.

[0034] In step S204, the abnormality control unit 45 determines whether the value of the charging flag F is "1." If it is determined that the value of the charging flag F is "1" (YES), it determines that charging of the capacitor 37 is necessary, and the process proceeds to step S205. On the other hand, if it is determined that the value of the charging flag F is "0" (NO), the process proceeds to step S207. In step S205, the abnormal-time control unit 45 determines whether the high-potential side voltage VR is greater than the second threshold value th2. As the second threshold value th2, for example, a value greater than the first threshold value th1 (for example, 12V) can be adopted. And when the abnormal-time control unit 45 determines that the high-potential side voltage VR is less than or equal to the second threshold value th2 (NO), it ends this abnormal-time drive control process and returns to step S107. Thereby, even after the high-potential side voltage VR≥th1, when VR<th2 continues, the charging mode in which all of the upper FETs Qah, Qbh, Qch and the lower FETs Qal, Qbl, Qcl started in step S203 are turned off is continued, and the charging of the capacitor 37 is continued. On the other hand, when the abnormal-time control unit 45 determines that the high-potential side voltage VR is greater than the second threshold value th2 (YES), it proceeds to step S206. Thereby, when the charging of the capacitor 37 progresses and the charge amount of the capacitor 37 is sufficiently large and sufficient power can be supplied to the inverter 21 and the processor 17, it can proceed to steps S207 to S212 and can be switched to the short-circuit mode. Therefore, by this step S205, it is possible to switch and execute the charging mode and the short-circuit mode according to the magnitude of the high-potential side voltage VR (that is, the voltage of the capacitor 37).

[0035] In step S206, the abnormal-time control unit 45 sets the value of the charging flag F to "0". Thereby, the determination in step S204 becomes "NO" and it proceeds to step S207, and the determination in step S205 does not need to be performed. Therefore, when the capacitor 37 is charged and VR>th2 and the charging mode is shifted to the short-circuit mode, it does not switch to the charging mode until power is consumed and VR≤th1, and the short-circuit mode is maintained even when VR≤th2. Next, the process proceeds to step S207, where the abnormality control unit 45 determines whether a short circuit failure has been detected in any of the lower-stage FETs Qal, Qbl, and Qcl in the abnormality detection of step S103. That is, the process determines whether the lower-stage FETs Qal, Qbl, and Qcl cannot be turned off due to a short circuit failure. If the abnormality control unit 45 determines that a short circuit failure has been detected (YES), the process proceeds to step S209. On the other hand, if the abnormality control unit 45 determines that a short circuit failure has not been detected (NO), the process proceeds to step S208. In step S208, the abnormality control unit 45 determines whether an open circuit failure has been detected in any of the upper-stage FETs Qah, Qbh, and Qch in the abnormality detection in step S103. That is, it determines whether the upper-stage FETs Qah, Qbh, and Qch cannot be turned on due to an open circuit failure. If the abnormality control unit 45 determines that an open circuit failure has been detected (YES), the process proceeds to step S209. On the other hand, if the abnormality control unit 45 determines that an open circuit failure has not been detected (NO), the process proceeds to step S210.

[0036] In step S209, the abnormality control unit 45 outputs a control signal prohibiting output of a PWM signal to the PWM control unit 33 of the normal-state control unit 19. Next, as shown in FIG. 8 , the abnormality control unit 45 turns off all of the upper-stage FETs Qah, Qbh, and Qch of the inverter 21, turns on all of the lower-stage FETs Qal, Qbl, and Qc1, and switches to a short-circuit mode in which these FETs are maintained in their off-on states (or, if the short-circuit mode is already in, switches to "maintain"). Then, the abnormality control unit 45 proceeds to step S107. That is, if a short-circuit fault has occurred in any of the lower-stage FETs Qal, Qbl, or Qc1, or if an open-circuit fault has occurred in any of the upper-stage FETs Qah, Qbh, or Qc1, the abnormality control unit 45 turns off all of the upper-stage FETs Qah, Qbh, and Qch and turns on all of the lower-stage FETs Qal, Qbl, and Qc1. This short-circuits the terminals of the windings of each of the phases A, B, and C of the electric motor 11, and the rotation of the electric motor 11 is braked by a short brake (electromagnetic brake). Therefore, for example, when a failure (abnormality) occurs in the electronic control unit 200, it is possible to prevent the steering angle θh from suddenly changing between the time when the driver notices the abnormality in the electronic control unit 200 and the time when the driver grips the steering wheel 1. Also, even when the lower-stage FETs Qal, Qbl, and Qcl cannot be turned off or when the upper-stage FETs Qah, Qbh, and Qch cannot be turned on, short braking can be performed appropriately.

[0037] In step S210, the abnormality control unit 45 determines whether a short circuit failure has been detected in any of the upper-stage FETs Qah, Qbh, and Qch in the abnormality detection in step S103. That is, it determines whether a state exists in which the upper-stage FETs Qah, Qbh, and Qch cannot be turned off due to a short circuit failure. If the abnormality control unit 45 determines that a short circuit failure has been detected (YES), it proceeds to step S212. On the other hand, if it determines that a short circuit failure has not been detected (NO), it proceeds to step S211. In step S211, the abnormality control unit 45 determines whether an open circuit failure has occurred in any of the lower-stage FETs Qal, Qbl, and Qcl in the abnormality detection in step S103. That is, it determines whether the lower-stage FETs Qal, Qbl, and Qcl cannot be turned on due to an open circuit failure. If the abnormality control unit 45 determines that an open circuit failure has occurred (YES), it proceeds to step S212. On the other hand, if it determines that an open circuit failure has not been detected (NO), it determines that an abnormality other than a failure of the electronic control unit 200 (for example, a power loss) has occurred, and proceeds to step S209. Note that the abnormality control unit 45 may be configured to proceed to step S212 instead of step S209.

[0038] In step S212, the abnormality control unit 45 outputs a control signal prohibiting output of a PWM signal to the PWM control unit 33 of the normal-state control unit 19. Next, as shown in FIG. 9 , the abnormality control unit 45 turns on all of the upper-stage FETs Qah, Qbh, and Qch of the inverter 21 and turns off all of the lower-stage FETs Qal, Qbl, and Qcl, and switches to a short-circuit mode in which these FETs are maintained off and on (or, if the short-circuit mode is already in, switches to "maintain"). Then, the abnormality control unit 45 proceeds to step S107. That is, if a short-circuit fault has occurred in any of the upper-stage FETs Qah, Qbh, and Qch, or if an open-circuit fault has occurred in any of the lower-stage FETs Qal, Qbl, and Qcl, all of the upper-stage FETs Qah, Qbh, and Qch are turned on and all of the lower-stage FETs Qal, Qbl, and Qcl are turned off. This short-circuits the terminals of the windings of each of the phases A, B, and C of the electric motor 11, and the rotation of the electric motor 11 is braked by a short brake (electromagnetic brake). Therefore, for example, when a failure (abnormality) occurs in the electronic control unit 200, it is possible to prevent a sudden change in the steering angle θh between the time when the driver notices the abnormality in the electronic control unit 200 and the time when the driver grips the steering wheel 1. Also, even when the lower-stage FETs Qal, Qbl, and Qcl cannot be turned on or when the upper-stage FETs Qah, Qbh, and Qch cannot be turned off, it is possible to appropriately execute a short brake (electromagnetic brake).

[0039] Next, the process proceeds to step S107, where the abnormality control unit 45 determines whether the duration of the abnormality drive control is equal to or longer than a predetermined time. For example, if the abnormality drive control is executed again in step S107 while the abnormality drive control is being executed, the duration of the abnormality drive control can be the time elapsed since the initial execution of the abnormality drive control was started. Furthermore, the predetermined time can be, for example, the time it takes for the driver to notice the abnormality and grasp the steering wheel 1 when an abnormality occurs in the electronic control unit 200 while the steering mode is hands-off mode. For example, a time between two and three seconds can be used. If the abnormality control unit 45 determines that the duration of the abnormality drive control is shorter than the predetermined time (NO), the process proceeds to step S108. On the other hand, if the abnormality drive control is determined to be equal to or longer than the predetermined time (YES), the process proceeds to step S111.

[0040] In step S108, the grip detection unit 44 performs a hands-on / off determination to determine (detect) whether the driver is in a hands-on state where the driver grips the steering wheel 1 or in a hands-off state where the driver is not gripping the steering wheel 1. As a method for the hands-on / off determination, for example, a method of detecting whether the driver is gripping the steering wheel 1 according to the magnitude of the detection result of the torque sensor 9 can be adopted. For example, a method can be used in which the magnitude of the steering torque Th is compared with a predetermined threshold, and if the magnitude (i.e., absolute value) of the steering torque Th is equal to or greater than the threshold, it is determined that the driver is gripping the steering wheel 1, and if the magnitude is less than the threshold, it is determined that the driver is not gripping the steering wheel 1. Also, for example, instead of comparing the steering torque Th with the threshold, a comparison of the notch-filtered steering torque Th with the threshold may be used. Also, for example, as shown in FIG. 10, the vehicle may be configured to include a contact sensor 46 (broadly speaking, a "contact detection unit") that detects whether the driver is in contact with the steering wheel 1, and a grip detection unit 44 may detect whether the driver is gripping the steering wheel 1 according to the detection result of the contact sensor 46. For example, a method may be used in which, if the driver is in contact with the steering wheel 1, it is determined that the driver is gripping the steering wheel 1, and, if not in contact, it is determined that the driver is not gripping the steering wheel 1. Also, for example, the determination methods described in Japanese Patent No. 6950859, Japanese Patent Laid-Open No. 2022-118891, and Japanese Patent No. 6590090 may be used.

[0041] Next, the process proceeds to step S109, where the abnormality control unit 45 determines whether a hands-on state has been detected in the hands-on / off determination of step S108. If it is determined that a hands-off state has been detected (off), it is determined that the driver has not yet noticed the abnormality, or has noticed the abnormality but is not yet gripping the steering wheel 1, and the process returns to step S103. As a result, after step S103, in step S104, it is determined again whether an abnormality has occurred in the electronic control unit 200. If the abnormality continues, the process returns to step S103 again via steps S106 → S107 → S108 → S109. On the other hand, if the abnormality has been resolved and the vehicle has returned to normal, in step S105, the abnormality drive control is terminated, the hands-off control is started, and hands-off driving assistance (automatic steering) is performed. That is, if the duration of the abnormality drive control is less than a predetermined time while the abnormality drive control is being executed, and the abnormality detection unit 43 no longer detects an abnormality, the abnormality control unit 45 ends the abnormality drive control and causes the normality control unit 19 to perform hands-off control. On the other hand, if the abnormality control unit 45 determines that a hands-on state has been detected (ON), it determines that the driver has noticed the abnormality and has gripped the steering wheel 1, and proceeds to step S110.

[0042] In step S110, the abnormality control unit 45 outputs a control signal prohibiting the output of a PWM signal to the PWM control unit 33 of the normal-state control unit 19. Next, as shown in FIG. 11 , the abnormality control unit 45 turns off all of the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl via the FET drive circuit 20. That is, when the abnormality control unit 45 detects that the steering wheel 1 is gripped during the abnormality control, it terminates the abnormality control, which maintains these OFF states, and turns off all of the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl. This releases the short circuit between the terminals of the windings of the phases A, B, and C of the electric motor 11, and terminates braking of the rotation of the electric motor 11 by the short brake (electromagnetic brake). Therefore, for example, when a driver who notices an abnormality grips the steering wheel 1, braking of the rotation of the steering wheel 1 can be suppressed, preventing the driver from interfering with the steering operation. Next, the motor shutoff FETs Qam, Qbm, and Qcm are turned off via the motor shutoff circuit 40 and maintained in the off state, terminating the abnormality control process. That is, when the abnormality control unit 45 terminates the abnormality drive control, if the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl are all turned off, the motor shutoff FETs Qam, Qbm, and Qcm are turned off. This disconnects the inverter 21 from the electric motor 11, and the supply of power (current) from the inverter 21 to the windings of the electric motor 11 is interrupted.

[0043] Meanwhile, in step S111, the abnormality control unit 45 outputs a control signal prohibiting the output of a PWM signal to the PWM control unit 33 of the normality control unit 19. Next, as shown in FIG. 11 , the abnormality control unit 45 turns off all of the upper-stage FETs Qah, Qbh, and Qch and all of the lower-stage FETs Qal, Qbl, and Qcl via the FET drive circuit 20, and turns off the motor cutoff FETs Qam, Qbm, and Qcm via the motor cutoff circuit 40, and keeps these off, thereby terminating the abnormality control process. That is, if the duration of the abnormality drive control during execution of the abnormality drive control exceeds a predetermined time (2 to 3 seconds), the abnormality drive control is terminated, and all of the upper-stage FETs Qah, Qbh, and Qch and all of the lower-stage FETs Qal, Qbl, and Qcl are turned off. This terminates the abnormality drive control, releases the short circuit between the terminals of the windings of each phase A, B, and C of the electric motor 11, and terminates braking of the rotation of the electric motor 11 by the short brake (electromagnetic brake). Consider a case where, for example, the driver notices an abnormality and grips the steering wheel 1 before the duration of the abnormality drive control exceeds a predetermined time, but a hands-on state is not detected in step S108, resulting in an undetectable state. When this occurs, the abnormality drive control continues, the short brake (electromagnetic brake) continues, and the driver's steering operation is hindered. In contrast, when the duration of the abnormality drive control exceeds a predetermined time (2 to 3 seconds), the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl are all turned off. This prevents braking of the steering wheel 1 and prevents the driver from steering even if the undetectable state occurs. Furthermore, turning off the motor cutoff FETs Qam, Qbm, and Qcm disconnects the inverter 21 from the electric motor 11, cutting off the supply of power (current) from the inverter 21 to the windings of the electric motor 11.

[0044] On the other hand, in step S112, the abnormality detection unit 43 detects that an abnormality has occurred in the electronic control unit 200 (abnormality detection). As a method for abnormality detection, for example, the same method as the method for detecting an abnormality in the electronic control unit 200 mentioned in step S103 can be adopted. Next, the process proceeds to step S113, where the abnormality detection unit 43 determines whether or not an abnormality has occurred in the electronic control unit 200 in the abnormality detection of step S112. If it is determined that an abnormality has not occurred in the electronic control unit 200 (normal), the electronic control unit 200 is determined to be normal, and the process proceeds to step S114. On the other hand, if it is determined that an abnormality has occurred (abnormal), the process proceeds to step S115.

[0045] In step S114, the abnormality detection unit 43 outputs a control signal permitting output of a PWM signal to the PWM control unit 33 of the normal-state control unit 19, and then the process proceeds to step S101. In parallel with this abnormal-state control process, the manual assist control unit 24 to the command value setting unit 31 in the normal-state control unit 19 calculate a target current command value Ir corresponding to the hands-on steering assist command. The current FB control unit 32 and the PWM control unit 33 perform feedback control based on the deviation between the calculated target current command value Ir and the current value Im of the electric motor 11 to generate a PWM signal. Upon receiving the control signal, the normal-state control unit 19 outputs the generated PWM signal to the inverter 21 via the FET drive circuit 20. That is, when it is determined in step S102 that there is no hands-off steering assist request, that is, when the steering mode is the hands-on mode, and it is determined in step S113 that the electronic control unit 200 is normal, hands-on control is performed. In hands-on control, immediately after the steering assist on / off information switches from on to off, the PWM signal gradually changes from a 100% PWM signal corresponding to the steering assist command (hands-on steering assist command) to a 100% PWM signal corresponding to the driver's steering torque Th. Also, by moving to step S101, the flow is repeated, passing through steps S101 to S113, and then step S114 is executed again, and hands-on driving assist (steering assist) is continuously performed.

[0046] Meanwhile, in step S115, the abnormality control unit 45 causes a notifying unit (not shown) to notify that an abnormality has occurred in the electronic control unit 200. The notifying unit may be, for example, a warning lamp provided on the dashboard. The abnormality control unit 45 also turns off the power cutoff relay 41, turns off the motor cutoff FETs Qam, Qbm, and Qcm via the motor cutoff circuit 40, and turns off all of the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl via the FET drive circuit 20 and maintains these turned off. This allows for a handover of steering to the driver, enabling the driver to perform manual operation. The abnormality control unit 45 also outputs a control signal to the PWM control unit 33 to prohibit output of a PWM signal. This causes the PWM control unit 33 to stop outputting the PWM signal, and execution of hands-on control by the normality control unit 19 is terminated.

[0047] As described above, in the electronic control unit 200 according to the first embodiment, when the abnormality detection unit 43 detects an abnormality in the electronic control unit 200 during hands-off control, the abnormality control unit 45 performs a short-circuit mode (abnormality drive control) in which all of the upper-stage FETs Qah, Qbh, and Qch are turned off and all of the lower-stage FETs Qal, Qbl, and Qcl are turned on, as shown in FIG. 8 , or in which all of the upper-stage FETs Qah, Qbh, and Qch are turned on and all of the lower-stage FETs Qal, Qbl, and Qcl are turned off, as shown in FIG. 9 . As a result, as shown in FIGS. 8 and 9 , the terminals of the windings of the phases A, B, and C of the electric motor 11 are short-circuited, and the rotation of the electric motor 11 is braked by a short brake (electromagnetic brake). Therefore, for example, when an abnormality such as a failure or power loss occurs in the electronic control unit 200, fluctuations in the steering angle θh can be suppressed for several seconds after the abnormality occurs. This can suppress a sudden change in the steering angle θh for several seconds until the driver notices the abnormality and grips the steering wheel 1. Furthermore, compared to a configuration including, for example, a dual system of each circuit of the inverter 21 and the electric motor 11, an increase in cost can be suppressed.

[0048] Here, for example, if an abnormality (such as a power loss) occurs in the electronic control unit 200, the only power supplied to the processor 17 and the inverter 21 will be the power stored in the capacitor 37. Therefore, for example, if the power consumption of the processor 17 and the inverter 21 is large, the power stored in the capacitor 37 may run out, causing the processor 17 and the inverter 21 to become inoperable, and it may become impossible to continue the short-circuit mode (short brake). In contrast, the electronic control unit 200 according to the first embodiment is configured to execute, as abnormality drive control, a charge mode in which the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl are all turned off in addition to the short-circuit mode. This ends the processing in the short-circuit mode of abnormality drive control, releases the short circuit between the terminals of the electric motor 11, terminates braking of the rotation of the electric motor 11 by the short brake (electromagnetic brake), and enables the electric motor 11 to rotate by an external force such as self-aligning torque. Then, as shown in FIG. 7 , this rotation causes the electric motor 11 to generate power, and the generated power is stored (charged) in the capacitor 37. Furthermore, in the electronic control unit 200 according to the first embodiment, the abnormality control section 45 is configured to perform abnormality drive control by switching between the short circuit mode and the charge mode depending on the magnitude of the voltage of the capacitor 37. This makes it possible to prevent the power stored in the capacitor 37 from running out, and to continue the short circuit mode (short brake) intermittently.

[0049] Furthermore, in the electronic control unit 200 according to the first embodiment, when the grip detection unit 44 detects that the steering wheel 1 is gripped while the abnormality control unit 45 is executing the abnormality drive control, the abnormality control unit 45 terminates the abnormality drive control and turns off all of the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl, as shown in FIG. 11 . This releases the short circuit between the terminals of the windings of the phases A, B, and C of the electric motor 11, and terminates braking of the rotation of the electric motor 11 by the electromagnetic brake. Therefore, for example, when a driver who notices an abnormality grips the steering wheel 1, braking of the rotation of the steering wheel 1 can be suppressed, and the driver's steering operation is not hindered.

[0050] Furthermore, the electronic control unit 200 according to the first embodiment is configured to turn off the power cutoff relay 41 when abnormality control is being executed. Here, for example, if a short circuit occurs in any of the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl that are turned off during abnormality control, a through current will flow through the upper and lower FETs. In response to this, turning off the power cutoff relay 41 will cut off the connection between the inverter 21 (power supply line 35) and the power supply 12, thereby reducing the through current through the upper and lower FETs. In the abnormality-condition drive control process, the presence or absence of a short-circuit fault in the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qc1 is determined immediately before the abnormality-condition drive control is executed (step S103 in FIG. 4). Therefore, it is unlikely that a short-circuit fault will occur in an FET determined to be free of a short-circuit fault before the abnormality-condition drive control is executed during the abnormality-condition drive control. Therefore, the power cut-off relay 41 may not be turned off when the abnormality-condition drive control is executed.

[0051] [1-3 Variations] (1) In the first embodiment, as shown in Fig. 3, an example has been shown in which the steering angle FB control unit 27 of the electronic control unit 200 (normal state control unit 19) calculates the steering angle FB torque Tsfb from the target steering angle θh* and inputs the calculated steering angle FB torque Tsfb to the multiplier 29, but other configurations may also be employed. For example, in the case where the steering assist command device 300 calculates the steering angle FB torque Tsfb in the same way as the steering angle FB control unit 27 shown in Fig. 3 and outputs the calculated steering angle FB torque Tsfb to the electronic control unit 200 as the target steering torque Th*, the electronic control unit 200 (normal state control unit 19) may be configured to input the target steering torque Th* to the multiplier 29 without the steering angle FB control unit 27 (see Fig. 3) as shown in Fig. 12.

[0052] (2) Although the first embodiment has been described as an example in which a backup power supply is not provided to deal with abnormalities in the power supply 12, other configurations may also be employed. For example, as shown in FIG. 13 , the power supply 12 may have a main power supply 13 and a secondary power supply 14 (backup power supply) separate from the main power supply 13, and the main power supply 13 may supply power when the main power supply 13 is normal, and the secondary power supply 14 may supply power when an abnormality occurs in the main power supply 13. In this case, during the period when the power supply is switched from the main power supply 13 to the secondary power supply 14, power is supplied from the capacitor 37 to the processor 17 and the inverter 21. Furthermore, when power is supplied from the capacitor 37 to the processor 17 and the inverter 21, abnormality drive control (short-circuit mode, charge mode) is executed.

[0053] (3) In the first embodiment, when the abnormality control unit 45 detects that the steering wheel 1 is gripped during the abnormality drive control, the abnormality drive control is terminated, and the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl of the inverter 21 are turned off, and the motor shutoff FETs Qam, Qbm, and Qcm are turned off. However, other configurations may be adopted. For example, as shown in steps S301 and S302 of FIG. 14, the upper-stage FETs Qah, Qbh, and Qch and the lower-stage FETs Qal, Qbl, and Qcl may not be turned on or off, and only the motor shutoff FETs Qam, Qbm, and Qcm may be turned off. FIG. 14 is a flowchart of the abnormality control process, in which steps S110 and S111 of FIG. 4 are replaced with steps S301 and S302. Here, for example, when the rotation speed of the electric motor 11 is high, turning off the motor cutoff FETs Qam, Qbm, and Qcm may induce a malfunction. In contrast, in the first embodiment, because abnormality-time drive control (short brake) is being executed and the rotation speed of the electric motor 11 is low, turning off the motor cutoff FETs Qam, Qbm, and Qcm can prevent a malfunction from being induced. [Explanation of symbols]

[0054] 1...steering wheel, 2...steering shaft, 3...reduction gear, 4a...universal joint, 4b...universal joint, 5...pinion rack mechanism, 5a...pinion, 5b...rack, 6a...tie rod, 6b...tie rod, 7a...hub unit, 7b...hub unit, 8L...steered wheel, 8R...steered wheel, 9...torque sensor, 10...steering angle sensor, 11...electric motor, 12...power supply, 13...main power supply, 14...auxiliary power supply, 15...vehicle CAN, 16...rotation angle sensor, 17...processor, 18...storage unit, 19...normal state control unit, 20...FET drive circuit, 21...inverter, 22...current detection circuit, 23...motor rotation angle detection circuit path, 24... manual assist control unit, 25... first gain setting unit, 26... multiplier, 27... steering angle feedback control unit, 28... second gain setting unit, 29... multiplier, 30... adder, 31... command value setting unit, 32... current feedback control unit, 33... PWM control unit, 34... bridge circuit, 35... power supply line, 36... ground line, 37... capacitor, 38... first voltage detection circuit, 39... second voltage detection circuit, 40... motor cutoff circuit, 41... power cutoff relay, 42... control unit, 43... abnormality detection unit, 44... grip detection unit, 45... abnormality control unit, 46... contact sensor, 100... electric power steering device, 200... electronic control unit, 300... steering assist command device

Claims

1. A motor control device for an electric power steering device that controls an electric motor that applies a steering assist force to a steering system of a vehicle, a normal state control unit that PWM-drives the electric motor via an inverter; the normal state control unit is capable of executing hands-off control for PWM driving the electric motor so as to apply a steering assist force for hands-off automatic steering to the steering system, Furthermore, an abnormality detection unit that detects that an abnormality has occurred in the motor control device; a grip detection unit that detects whether a driver is gripping a steering operation unit of the vehicle; a capacitor connected in parallel to the inverter; a voltage detection unit that detects the voltage of the capacitor; an abnormality control unit that performs abnormality drive control by switching between a short-circuit mode in which all upper stage FETs of the inverter are turned off and all lower stage FETs are turned on, or all upper stage FETs of the inverter are turned on and all lower stage FETs are turned off, and a charge mode in which all upper stage FETs and all lower stage FETs of the inverter are turned off, depending on the magnitude of the voltage of the capacitor, when the abnormality detection unit detects the occurrence of an abnormality in the motor control unit during execution of the hands-off control; When the grip detection unit detects that the steering operation unit is gripped during execution of the abnormality drive control, the abnormality control unit terminates the abnormality drive control and turns off all of the upper stage FETs and the lower stage FETs of the inverter. Motor control device.

2. If the duration of the abnormality drive control is less than a predetermined time during execution of the abnormality drive control, and the abnormality detection unit no longer detects an abnormality, the abnormality control unit terminates the abnormality drive control and causes the normality control unit to perform the hands-off control. The motor control device according to claim 1 .

3. When the duration of the abnormality-state drive control reaches or exceeds the predetermined time during execution of the abnormality-state drive control, the abnormality-state control unit terminates the abnormality-state drive control and turns off all of the upper-stage FETs and the lower-stage FETs of the inverter. The motor control device according to claim 2 .

4. The grip detection unit detects whether the driver is gripping the steering operation unit in accordance with the magnitude of a detection result of a torque sensor that detects a steering torque applied to the steering system. The motor control device according to claim 1 .

5. The grip detection unit detects whether the driver is gripping the steering operation unit in accordance with a detection result of a contact detection unit that detects whether the driver is in contact with the steering operation unit. The motor control device according to claim 1 .

6. The predetermined time is between 2 seconds and 3 seconds. The motor control device according to claim 3 .

7. a power cutoff relay interposed between the inverter and a power source; The abnormality control unit turns on the power cutoff relay while the hands-off control is being executed, and turns off the power cutoff relay while the abnormality drive control is being executed. The motor control device according to claim 1 .

8. The abnormality control unit turns off all of the upper stage FETs of the inverter and turns on all of the lower stage FETs when a short circuit failure occurs in any of the lower stage FETs or when an open circuit failure occurs in any of the upper stage FETs. The motor control device according to claim 1 .

9. The abnormality control unit turns on all of the upper stage FETs of the inverter and turns off all of the lower stage FETs when a short circuit failure occurs in any of the upper stage FETs or when an open circuit failure occurs in any of the lower stage FETs. The motor control device according to claim 1 .

10. a motor cutoff FET interposed between the inverter and a winding of the electric motor; the motor cutoff FET is configured as an FET having a parasitic diode whose forward direction is from the inverter toward the winding, When the abnormality control unit terminates the abnormality drive control, if the upper stage FET and the lower stage FET of the inverter are all turned off, the abnormality control unit turns off the motor cutoff FET. The motor control device according to claim 1 .

11. A motor control device for an electric power steering device that controls an electric motor that applies a steering assist force to a steering system of a vehicle, a normal state control unit that PWM-drives the electric motor via an inverter; the normal state control unit is capable of executing hands-off control for PWM driving the electric motor so as to apply a steering assist force for hands-off automatic steering to the steering system, Furthermore, an abnormality detection unit that detects that an abnormality has occurred in the motor control device; a grip detection unit that detects whether a driver is gripping a steering operation unit of the vehicle; a capacitor connected in parallel to the inverter; a voltage detection unit that detects the voltage of the capacitor; a motor cutoff FET interposed between the inverter and a winding of the electric motor; an abnormality control unit that performs abnormality drive control by switching between a short-circuit mode in which all upper stage FETs of the inverter are turned off and all lower stage FETs are turned on, or all upper stage FETs of the inverter are turned on and all lower stage FETs are turned off, and a charge mode in which all upper stage FETs and all lower stage FETs of the inverter are turned off, depending on the magnitude of the voltage of the capacitor, when the abnormality detection unit detects the occurrence of an abnormality in the motor control unit during execution of the hands-off control; When the grip detection unit detects that the steering operation unit is gripped during execution of the abnormality drive control, the abnormality control unit ends the abnormality drive control and turns off the motor cutoff FET. Motor control device.

12. A motor control device according to any one of claims 1 to 11; an electric motor controlled by the motor control device, The electric motor applies a steering assist force to the steering system of the vehicle. Electric power steering device.

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