Steering control device

Abstract

This invention discloses a steering control device. In this steering control device, multiple control systems are configured to: switch the drive mode to a cooperative drive mode when the command values ​​calculated by the control units of the control systems are identical, and switch the drive mode to an independent drive mode when the command values ​​calculated by the control units of the control systems are different. The control system is configured to: gradually limit the command values ​​calculated individually by the control units of the control systems when the vehicle's start switch has been turned off. The control system is configured to: switch the drive mode to an independent drive mode when the start switch has been turned off while the vehicle is in motion, regardless of whether the command values ​​calculated by the control units of the control systems are different.

Description

Technical Field

[0001] This invention relates to a steering control device. Background Technology

[0002] Japanese Unexamined Patent Application Publication No. 2018-130007 (JP 2018-130007 A) discloses a steering control device that uses two control systems, including a main control system and a slave control system, to control the power supply to a motor. In the steering control device, a main control unit in the main control system calculates a current command value, and a slave control unit in the slave control system calculates a current command value. Under normal conditions, i.e., when it is determined that no anomaly has occurred where the current command values ​​of the control systems differ, the steering control device executes control in a cooperative drive mode; and when it is determined that an anomaly has occurred where the current command values ​​of the control systems differ, it executes control in an independent drive mode. In the cooperative drive mode, the steering control device uses the current command value calculated by the main control unit to control the power supply to both the main and slave control systems. In the independent drive mode, the steering control device uses the current command value calculated by the main control unit to control the power supply to the main control system, and uses the current command value calculated by the slave control unit to control the power supply to the slave control system.

[0003] Japanese Unexamined Patent Application Publication No. 2001-10514 (JP 2001-10514 A) discloses a controller as a steering control device that limits a calculated current command value in ignition off control when the ignition switch is turned off. The steering control device gradually limits the current command value for a predetermined time. After the predetermined time has elapsed, the steering control device limits the current command value to zero and disconnects itself by switching the power relay to the off state. Summary of the Invention

[0004] The ignition switch can be turned off while the vehicle is in motion. In the steering control unit, a signal indicating that the ignition switch has been turned off while the vehicle is in motion is input to each control system in the control system, and each control system in the control system executes the ignition off control while the vehicle is in motion. For example, due to the difference between the timing of the power relay in the main control system being switched to the off state and the timing of the power relay in the slave control system being switched to the off state, one control system in the main control system and the slave control system can switch to the ignition off control while in motion (i.e., the control executed when the ignition switch has been turned off while the vehicle is in motion) earlier than the other control system. Therefore, in the control system that has switched to the ignition off control while in motion earlier, the current command value calculated by the control unit of the control system is limited.

[0005] For example, when the primary control system transitions to ignition disconnect control while driving earlier than the secondary control system, the current command value calculated by the primary control unit is limited, while the current command value calculated by the secondary control unit is unrestricted. When the driver performs steering maneuvers under ignition disconnect control while driving, both the primary and secondary control units calculate current command values ​​corresponding to the steering maneuvers. In this case, since the current command value calculated by the primary control unit is limited and the current command value calculated by the secondary control unit is unrestricted, the current command values ​​calculated by the primary control unit and the current command values ​​calculated by the secondary control unit are different from each other. Therefore, in the secondary control system, the limited current command value calculated by the primary control unit and the unrestricted current command value calculated by the secondary control unit are determined to be different, and the drive mode is switched from cooperative drive mode to independent drive mode. The control for the power supply to the secondary control system switches from control using the limited current command value calculated by the primary control unit to control using the unrestricted current command value calculated by the secondary control unit. Therefore, the torque output from the secondary motor may fluctuate.

[0006] A steering control device according to one aspect of the invention includes a plurality of control systems configured to control the drive of a motor by switching between a plurality of drive modes, including a cooperative drive mode and an independent drive mode. Each control system includes a control unit configured to calculate a command value for controlling the motor. The control system is configured to control the motor drive based on the command value calculated by the control unit of one of the control systems when the cooperative drive mode is executed. The control system is configured to control the motor drive based on command values ​​calculated separately by the control units of the control systems when the independent drive mode is executed. The control system is configured to switch the drive mode to the cooperative drive mode when the command values ​​calculated by the control units of the control systems are identical, and to switch the drive mode to the independent drive mode when the command values ​​calculated by the control units of the control systems are different. The control system is configured to gradually limit the command values ​​calculated separately by the control units of the control systems when the vehicle's start switch has been turned off. The control system is configured to switch the drive mode to the independent drive mode when the start switch has been turned off while the vehicle is in motion, regardless of whether the command values ​​calculated by the control units of the control systems are different.

[0007] When the start switch is turned off while the vehicle is in motion, the timing of the transition to the control that should be executed when the start switch is turned off while the vehicle is in motion may differ among multiple control systems. Control systems that have already transitioned to the control that should be executed when the start switch is turned off while the vehicle is in motion gradually limit the command values ​​calculated by their control units, while other control systems that have not yet transitioned to the control that should be executed when the start switch is turned off while the vehicle is in motion do not limit the command values ​​calculated by their control units. With this configuration, when the start switch is turned off while the vehicle is in motion, the drive mode switches from cooperative drive mode to independent drive mode regardless of whether the command values ​​calculated by the control units of the control systems are different. Therefore, compared to the case where the drive mode switches from cooperative drive mode to independent drive mode after the command values ​​calculated by the control units of the control systems have become different, the control system can switch to independent drive mode earlier. Therefore, even when the command value in the control executed when the start switch is turned off while the vehicle is in motion is calculated by the control unit of the control system, fluctuations in the power supply to the control system can be suppressed. Therefore, when the start switch is turned off while the vehicle is in motion, fluctuations in the torque output from the motor can be suppressed.

[0008] In the steering control device according to this aspect, the control system can be configured to determine whether the start switch has been turned off while the vehicle is in motion. Each control system in the control system can be configured to send information about the drive mode of the control system to each of the other control systems in the control system, and to receive information about the drive mode of each of the other control systems in the control system. If one control system in the control system switches the drive mode to an independent drive mode due to the turn switch being turned off while the vehicle is in motion, that one control system can send information about the drive mode indicating that it has been switched to an independent drive mode to each of the other control systems in the control system, and each of the other control systems in the control system can receive information about the drive mode from that one control system and can switch its drive mode to an independent drive mode based on the information about the drive mode received from that one control system.

[0009] Because multiple control systems independently determine whether the starter switch has been turned off while the vehicle is in motion, the timing of the transition to the control that should be executed when the starter switch is turned off while the vehicle is in motion may differ among the multiple control systems, and the timing of switching to independent drive mode may also differ among the multiple control systems. Each of the remaining control systems in the control system switches the drive mode to independent drive mode based on information about the drive mode received from one control system. Therefore, compared to the case where each of the remaining control systems in the control system switches the drive mode to independent drive mode after it is individually determined that the starter switch has been turned off while the vehicle is in motion, the timing of switching to independent drive mode across multiple control systems can be matched. Therefore, the torque output from the motor can be stabilized.

[0010] In the steering control device according to this aspect, the control system can be configured to: maintain the independent drive mode when the start switch is turned on during a period when the drive mode is an independent drive mode due to the opening of the start switch while the vehicle is in motion, in a situation where the torque fluctuation of the motor caused by the switch of drive mode may cause the steering wheel to vibrate, and switch the drive mode to a cooperative drive mode when the torque fluctuation of the motor caused by the switch of drive mode is unlikely to cause the steering wheel to vibrate.

[0011] Using this configuration, even when the start switch is turned on during control operations performed while the vehicle is in motion (when the start switch has been turned off), and the torque fluctuations of the motor due to the drive mode switching might cause steering wheel vibration, the multiple control systems maintain independent drive modes. In this case, since the multiple control systems do not switch drive modes, torque fluctuations from the motor output can be suppressed. Therefore, the possibility of torque fluctuations causing steering wheel vibration affecting the driver's steering feel related to the steering wheel can be reduced. When the start switch is turned on during control operations performed while the vehicle is in motion (when the start switch has been turned off), and the torque fluctuations of the motor due to the drive mode switching are unlikely to cause steering wheel vibration, the multiple control systems switch to a cooperative drive mode. In this case, the multiple control systems can switch to the cooperative drive mode while suppressing torque fluctuations from the motor output.

[0012] In the steering control device according to this aspect, the control system can be configured to: when the steering wheel is being steered, determine that fluctuations in the motor torque caused by the switching of the drive mode may cause the steering wheel to vibrate, and maintain an independent drive mode. The control system can also be configured to: when the steering wheel is not being steered, determine that fluctuations in the motor torque caused by the switching of the drive mode are unlikely to cause the steering wheel to vibrate, and switch the drive mode to a cooperative drive mode.

[0013] In this configuration, the situation where the steering wheel is being steered is determined when the command value may fluctuate during drive mode switching, and when fluctuations in the torque output from the motor may cause steering wheel vibration. The situation where the steering wheel is not being steered is determined when the command value is unlikely to fluctuate during drive mode switching, and when fluctuations in the torque output from the motor are unlikely to cause steering wheel vibration. In this way, by switching the drive mode based on whether the steering wheel is being steered, the drive mode can be switched appropriately.

[0014] By utilizing the steering control device according to this aspect of the invention, fluctuations in torque output from the motor can be suppressed when the start switch has been turned off while the vehicle is in motion. Attached Figure Description

[0015] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein similar reference numerals denote similar elements, and in the drawings:

[0016] Figure 1 This is a schematic diagram showing the configuration of a steering system equipped with a steering control device according to an embodiment;

[0017] Figure 2 This is a block diagram schematically illustrating the configuration of the steering control unit;

[0018] Figure 3 It is a block diagram schematically showing the configuration of the first microcomputer and the second microcomputer;

[0019] Figure 4 It is a graph showing the time-dependent changes of the first and second gains calculated by the gain calculation unit when the ignition disconnect signal is input during driving;

[0020] Figure 5 This is a flowchart illustrating a routine for handling drive mode switching from a control system;

[0021] Figure 6 This is a timing diagram showing the flow of drive mode switching processing in the main control system when it is determined that the ignition switch has been disconnected earlier from the control system.

[0022] Figure 7 This is a flowchart illustrating a routine for handling drive mode switching from a control system;

[0023] Figure 8 This is a timing diagram showing the internal states during the switch from cooperative drive mode to independent drive mode due to the ignition switch being turned off while the vehicle is in motion; and

[0024] Figure 9 This is a timing diagram showing the internal state when the switch from cooperative drive mode to independent drive mode is not executed in the comparative example due to the ignition switch being turned off while the vehicle is in motion. Detailed Implementation

[0025] In the following description, an embodiment of applying the steering control device to an electric power steering system (hereinafter referred to as "EPS") will be described with reference to the accompanying drawings. Figure 1 As shown, EPS 1 includes a steering control mechanism 2 that turns the steering wheel 15 based on the driver's operation of the steering wheel 10, an auxiliary mechanism 3 that assists the driver in steering operation, and a steering control device 30 that controls the auxiliary mechanism 3.

[0026] The steering mechanism 2 includes a steering shaft 11 and a rack shaft 12. The steering shaft 11 has one end fixed to the steering wheel 10 and the other end having a pinion formed thereon. The rack shaft 12 has a rack formed thereon and meshing with the pinion. The rack and pinion mechanism 13 consists of a pinion and a rack. The steering shaft 11 includes a column shaft 11a connected to the steering wheel 10, an intermediate shaft 11b connected to the lower end of the column shaft 11a, and a pinion shaft 11c connected to the lower end of the intermediate shaft 11b. The pinion is formed at the lower end of the pinion shaft 11c. The rotational motion of the steering shaft 11 is converted into reciprocating linear motion along the axial direction of the rack shaft 12 by the rack and pinion mechanism 13. The reciprocating linear motion of the rack shaft 12 is transmitted to the left and right steering wheels 15 via tie rods 14 connected to both ends of the rack shaft 12, thereby changing the steering angle of the steering wheels 15 and changing the driving direction of the vehicle.

[0027] The auxiliary mechanism 3 includes a motor 20 and a reduction mechanism 22. The motor 20 includes a rotating shaft 21. The rotating shaft 21 of the motor 20 is connected to the column shaft 11a via the reduction mechanism 22. The reduction mechanism 22 reduces the rotational speed of the motor 20 and transmits rotational force to the column shaft 11a after the rotational speed is reduced. That is, the driver's steering operation is assisted by applying the torque of the motor 20 to the steering control shaft 11. For example, a three-phase brushless motor is used as the motor 20. For example, a worm gear mechanism is used as the reduction mechanism 22.

[0028] like Figure 2 As shown, the motor 20 includes a rotor 23 that rotates about a rotation axis 21 and a stator 24 disposed outside the rotor 23. Permanent magnets are fixed to the surface of the rotor 23. Different polarities (N pole and S pole) are alternately arranged in the circumferential direction of the rotor 23 within the permanent magnets. The permanent magnets generate a magnetic field as the motor 20 rotates. Three-phase coils 25, having U-phase, V-phase, and W-phase, are arranged in a ring within the stator 24. The coils 25 include a first coil 25a and a second coil 25b. Each coil in the first coil 25a and the second coil 25b includes a U-phase coil, a V-phase coil, and a W-phase coil connected in a star configuration. A steering control device 30, serving as a control unit configured to control the drive of the motor 20, is connected to the motor 20.

[0029] like Figure 1As shown, various sensors installed in the vehicle are connected to the steering control device 30. Among these sensors are a first torque sensor 40a, a second torque sensor 40b, a first rotation angle sensor 41a, a second rotation angle sensor 41b, and a vehicle speed sensor 42. The first torque sensor 40a and the second torque sensor 40b are mounted on the column shaft 11a. The first rotation angle sensor 41a and the second rotation angle sensor 41b are mounted in the motor 20. The first torque sensor 40a detects a first steering torque Th1 applied to the steering shaft 11 due to the driver's steering operation. The second torque sensor 40b detects a second steering torque Th2 applied to the steering shaft 11 due to the driver's steering operation. The first rotation angle sensor 41a detects a first rotation angle θ1 of the rotation shaft 21 of the motor 20. The second rotation angle sensor 41b detects a second rotation angle θ2 of the rotation shaft 21 of the motor 20. The vehicle speed sensor 42 detects the vehicle speed SPD, which is the vehicle's travel speed. The motor 20 is the controlled object of the steering control device 30, and the steering control device 30 controls the drive of the motor 20. Specifically, the steering control device 30 sets a target torque applied to the motor 20 of the steering mechanism 2 based on detection values ​​from various sensors, and controls the current supplied to the motor 20 so that the actual torque reaches the target torque. An ignition switch 43, which serves as the starter switch configured to start the vehicle, is connected to the steering control device 30. An ignition signal Sig indicating the on / off state of the ignition switch 43 is input to the steering control device 30. The ignition switch 43 outputs an ignition signal Sig corresponding to the driver's operation of the ignition switch 43.

[0030] The configuration of the steering control device 30 will be described below. For example... Figure 2 As shown, the steering control device 30 includes a main control system 50 having a first electronic control unit (hereinafter referred to as "first ECU 51") that controls the current supplied to the first coil 25a of the motor 20, and a slave control system 60 having a second electronic control unit (hereinafter referred to as "second ECU 61") that controls the current supplied to the second coil 25b of the motor 20.

[0031] The main control system 50 and the slave control system 60 control the drive of the motor 20 by switching the drive mode between a cooperative drive mode and an independent drive mode. In the cooperative drive mode, the power supply to both the main control system 50 and the slave control system 60 is controlled based on the command value calculated by the first ECU 51 of the main control system 50. On the other hand, in the independent drive mode, the power supply to the main control system 50 is controlled based on the command value calculated by the first ECU 51 of the main control system 50, and the power supply to the slave control system 60 is controlled based on the command value calculated by the second ECU 61 of the slave control system 60. In this embodiment, it is assumed that the functions of the main control system 50 and the slave control system 60 do not exchange. That is, in the cooperative drive mode, the power supply to both the main control system 50 and the slave control system 60 is not based on the command value calculated by the second ECU 61 of the slave control system 60.

[0032] The first ECU 51 of the main control system 50 includes a first microcomputer 52 as a control unit, a first drive circuit 53, a first drive relay 54, a first power relay 55, a first voltage sensor 56, a first capacitor 57, and a first current sensor 58. The second ECU 61 of the slave control system 60 includes a second microcomputer 62 as a control unit, a second drive circuit 63, a second drive relay 64, a second power relay 65, a second voltage sensor 66, a second capacitor 67, and a second current sensor 68. The first drive circuit 53 and the second drive circuit 63 have identical configurations. The first drive relay 54 and the second drive relay 64 have identical configurations. The first power relay 55 and the second power relay 65 have identical configurations. The first voltage sensor 56 and the second voltage sensor 66 have identical configurations. The first capacitor 57 and the second capacitor 67 have identical configurations. The first current sensor 58 and the second current sensor 68 have identical configurations. The first microcomputer 52 and the second microcomputer 62 have identical configurations except for the command value calculation unit, which will be described later. This identical configuration means that they have the same functions and the same performance under the same design concept.

[0033] A first power supply 70, serving as the source of current supplied to the first coil 25a, is connected to the first ECU 51. The high-potential side of the first drive circuit 53 and the high-potential side of the first power supply 70 are connected to each other via a first power line L1. The low-potential side of the first drive circuit 53 and the low-potential side of the first power supply 70 are connected to each other via a first power ground line GL1. The first power ground line GL1 is connected to a first power ground FG1. A first drive relay 54 is disposed in the first power line L1. The first drive relay 54 is switched on and off based on a first relay signal Srl1 from the first microcomputer 52, causing the first power line L1 to switch between a connected state and a disconnected state. When the first power line L1 is in the connected state, power from the first power supply 70 is supplied to the first drive circuit 53 via the first power line L1. When the first power line L1 is in the disconnected state, power from the first power supply 70 is not supplied to the first drive circuit 53 via the first power line L1.

[0034] The high-potential side of the first microcomputer 52 and the high-potential side of the first power supply 70 are connected to each other via a third power line L3. The low-potential side of the first microcomputer 52 is connected to a first internal ground SG1. A first power relay 55 is provided in the third power line L3, which is switched on and off according to the ignition signal Sig output from the vehicle's ignition switch 43. The first power relay 55 switches the third power line L3 between a connected state and a disconnected state according to the ignition signal Sig. When the ignition signal Sig indicating that the ignition switch 43 is on is input to the first power relay 55, the first power relay 55 is on and the third power line L3 is switched to the connected state. When the third power line L3 is in the connected state, power from the first power supply 70 is supplied to the first microcomputer 52 via the third power line L3. When the ignition signal Sig indicating that the ignition switch 43 is off is input to the first power relay 55, the first power relay 55 is off and the third power line L3 is switched to the disconnected state. When the third power line L3 is disconnected, power from the first power supply 70 is not supplied to the first microcomputer 52 via the third power line L3. A first voltage sensor 56 is disposed in the third power line L3. The first voltage sensor 56 detects the voltage generated in the third power line L3 from the first power supply 70 as the first ignition voltage Vg1.

[0035] A first capacitor 57 is disposed between a portion of the first power line L1 and the first power ground line GL1, the portion of the first power line L1 being located between the first drive relay 54 and the first drive circuit 53. The first capacitor 57 smooths the voltage from the first power supply 70.

[0036] The first drive circuit 53 is a three-phase drive circuit corresponding to the first coil 25a of the three phases. The first drive circuit 53 is configured as a known three-phase drive circuit, in which each three-phase drive circuit includes three switching arms of a pair of switching elements connected in series and then connected in parallel. For example, a metal-oxide-semiconductor field-effect transistor (MOS-FET) is used as each switching element. The upstream switching element of each pair of switching elements is connected to and disconnected from the high-potential side of the first power supply 70 and the first coil 25a. The downstream switching element of each pair of switching elements is connected to and disconnected from the low-potential side of the first power supply 70 and the first coil 25a.

[0037] The first current sensor 58 detects a first actual current value I1, which is the value of the phase current flowing in the power supply path between the first drive circuit 53 and the first coil 25a. The first microcomputer 52 uses power supplied from the first power source 70 via the third power line L3 to output a first motor control signal Sm1 for controlling the drive of the first drive circuit 53, and also outputs a first relay signal Srl1 for controlling the first drive relay 54. The first microcomputer 52 generates a PWM signal as the first motor control signal Sm1 to specify the on / off state of the switching elements in the first drive circuit 53.

[0038] The second power supply 80, which serves as the source of current supplied to the second coil 25b, is connected to the second ECU 61. The high-potential side of the second drive circuit 63 and the high-potential side of the second power supply 80 are connected to each other via the second power line L2. The low-potential side of the second drive circuit 63 and the low-potential side of the second power supply 80 are connected to each other via the second power ground line GL2. The second power ground line GL2 is connected to the second power ground FG2. A second drive relay 64 is disposed in the second power line L2. The second drive relay 64 is switched on and off based on the second relay signal Srl2 from the second microcomputer 62, causing the second power line L2 to switch between a connected state and a disconnected state. When the second power line L2 is in the connected state, power from the second power supply 80 is supplied to the second drive circuit 63 via the second power line L2. When the second power line L2 is in the disconnected state, power from the second power supply 80 is not supplied to the second drive circuit 63 via the second power line L2.

[0039] The high-potential side of the second microcomputer 62 and the high-potential side of the second power supply 80 are connected to each other via a fourth power line L4. The low-potential side of the second microcomputer 62 is connected to the second internal ground SG2. A second power relay 65 is provided in the fourth power line L4, which is turned on and off according to the ignition signal Sig output from the vehicle's ignition switch 43. The second power relay 65 switches the fourth power line L4 between a connected state and a disconnected state according to the ignition signal Sig. When the ignition signal Sig indicating that the ignition switch 43 is on is input to the second power relay 65, the second power relay 65 is turned on and the fourth power line L4 is switched to the connected state. When the fourth power line L4 is in the connected state, power from the second power supply 80 is supplied to the second microcomputer 62 via the fourth power line L4. When the ignition signal Sig indicating that the ignition switch 43 is off is input to the second power relay 65, the second power relay 65 is turned off and the fourth power line L4 is switched to the disconnected state. When the fourth power line L4 is disconnected, power from the second power supply 80 is not supplied to the second microcomputer 62 via the fourth power line L4. A second voltage sensor 66 is disposed in the fourth power line L4. The second voltage sensor 66 detects the voltage generated in the fourth power line L4 from the second power supply 80 as the second ignition voltage Vg2.

[0040] A second capacitor 67 is disposed between a portion of the second power line L2 and the second power ground line GL2, the portion of the second power line L2 being located between the second drive relay 64 and the second drive circuit 63. The second capacitor 67 smooths the voltage from the second power supply 80.

[0041] Each of the first power ground FG1 and the second power ground FG2 is a portion having a potential almost equal to that of a ground. In this embodiment, the first power ground FG1 and the second power ground FG2 are located in the vehicle body on which the steering control device 30 is mounted. Each of the first internal ground SG1 and the second internal ground SG2 is a portion that serves as a voltage reference in the circuit of the corresponding ECU. The first internal ground SG1 and the second internal ground SG2 are disposed on the plate on which the steering control device 30 is mounted.

[0042] In this way, different power supplies are connected to the first ECU 51 and the second ECU 61 via different power lines and different power ground lines. Therefore, in this embodiment, the control system configured to control the drive of the motor 20 is redundant, and the power supply configuration is redundant.

[0043] The second drive circuit 63 is a three-phase drive circuit corresponding to the three-phase second coil 25b. The second drive circuit 63 is configured as a known three-phase drive circuit, in which each three-phase drive circuit includes three switching arms of a pair of switching elements connected in series and then connected in parallel. The upstream switching element of each pair of switching elements is connected to and disconnected from the high-potential side of the second power supply 80 and the second coil 25b. The downstream switching element of each pair of switching elements is connected to and disconnected from the low-potential side of the second power supply 80 and the second coil 25b.

[0044] The second current sensor 68 detects a second actual current value I2, which is the value of the phase current flowing in the power supply path between the second drive circuit 63 and the second coil 25b. The second microcomputer 62 uses power supplied from the second power source 80 via the fourth power line L4 to output a second motor control signal Sm2 for controlling the drive of the second drive circuit 63, and also outputs a second relay signal Srl2 for controlling the second drive relay 64. The second microcomputer 62 generates a PWM signal as the second motor control signal Sm2 to specify the on / off state of the switching elements in the second drive circuit 63.

[0045] The functions of the first microcomputer 52 and the second microcomputer 62 will be described below. Figure 3 As shown, the first microcomputer 52 includes a first command value calculation unit 90, a first current feedback control unit 91, a first ignition determination unit 92, a first state holding unit 93, and a first transceiver unit 94. The second microcomputer 62 includes a second command value calculation unit 100, a second current feedback control unit 101, a second ignition determination unit 102, a second state holding unit 103, and a second transceiver unit 104. The first current feedback control unit 91 and the second current feedback control unit 101 have the same configuration. The first ignition determination unit 92 and the second ignition determination unit 102 have the same configuration. The first state holding unit 93 and the second state holding unit 103 have the same configuration. The first transceiver unit 94 and the second transceiver unit 104 have the same configuration. The difference in configuration between the first command value calculation unit 90 and the second command value calculation unit 100 is that the second command value calculation unit 100 includes a command value difference determination unit 109, which will be described later, but the first command value calculation unit 90 does not include the command value difference determination unit 109.

[0046] The first command value calculation unit 90 acquires the first steering torque Th1 detected by the first torque sensor 40a, the vehicle speed SPD detected by the vehicle speed sensor 42, and the signal generated by the first ignition determination unit 92. Based on the first steering torque Th1, the vehicle speed SPD, and the signal generated by the first ignition determination unit 92, the first command value calculation unit 90 calculates a first final current command value I1*, which is the target value of the first actual current value I1.

[0047] The first current feedback control unit 91 acquires the first final current command value I1* calculated by the first command value calculation unit 90, the first rotation angle θ1 detected by the first rotation angle sensor 41a, and the first actual current value I1 detected by the first current sensor 58. Based on the first actual current value I1 and the first rotation angle θ1, the first current feedback control unit 91 performs current feedback control based on the difference between the first final current command value I1* and the first actual current value I1 to make the first actual current value I1 consistent with the first final current command value I1*, thereby generating the first motor control signal Sm1.

[0048] The first ignition determination unit 92 acquires the first ignition voltage Vg1 detected by the first voltage sensor 56 and the vehicle speed SPD detected by the vehicle speed sensor 42. The first ignition determination unit 92 determines the state of the vehicle's ignition switch 43 based on the first ignition voltage Vg1 and the vehicle speed SPD. Specifically, when the first ignition voltage Vg1 is higher than a voltage threshold V0, the first ignition determination unit 92 determines that the ignition switch 43 has been turned on and generates a first ignition on signal Son1. The voltage threshold V0 is set to be the voltage generated when the ignition switch 43 is turned on, transmitted from the first power supply 70 via... Figure 2 The minimum value of the first ignition voltage Vg1 supplied by the third power line L3 shown. If the first ignition voltage Vg1 remains below the voltage threshold V0 for a predetermined time tg, the first ignition determination unit 92 determines that the ignition switch 43 has been turned off and generates a first ignition off signal Soff1. When the vehicle is in motion while the first ignition off signal Soff1 is generated, the first ignition determination unit 92 generates a first in-motion ignition off signal Soff1a. That is, if the vehicle speed SPD remains above the vehicle speed threshold SPD0 for a predetermined time tg and the first ignition voltage Vg1 remains below the voltage threshold V0 for a predetermined time tg, the first ignition determination unit 92 determines that the ignition switch 43 has been turned off while the vehicle is in motion and generates a first in-motion ignition off signal Soff1a. The vehicle speed threshold SPD0 is set to a vehicle speed SPD at which the vehicle is in motion can be determined.

[0049] The first state holding unit 93 holds the drive mode of the main control system 50. That is, the first state holding unit 93 holds information about the drive mode that instructs the main control system 50 to control the drive of the motor 20 in a cooperative drive mode, or information about the drive mode that instructs the main control system 50 to control the drive of the motor 20 in an independent drive mode. The first state holding unit 93 determines the drive mode of the main control system 50, for example, based on a signal generated by the first ignition determining unit 92 or information received from the first transceiver unit 94.

[0050] The first transceiver unit 94 sends information to and receives information from the second transceiver unit 104 of the second microcomputer 62 (described later). The second command value calculation unit 100 acquires the second steering torque Th2 detected by the second torque sensor 40b, the vehicle speed SPD detected by the vehicle speed sensor 42, and the signal generated by the second ignition determination unit 102. The second command value calculation unit 100 calculates a second final current command value I2* as the target value of the second actual current value I2 based on the second steering torque Th2, the vehicle speed SPD, and the signal generated by the second ignition determination unit 102.

[0051] The second current feedback control unit 101 acquires the second final current command value I2* calculated by the second command value calculation unit 100, the second rotation angle θ2 detected by the second rotation angle sensor 41b, and the second actual current value I2 detected by the second current sensor 68. Based on the second actual current value I2 and the second rotation angle θ2, the second current feedback control unit 101 performs current feedback control based on the difference between the second final current command value I2* and the second actual current value I2 to make the second actual current value I2 consistent with the second final current command value I2*, thereby generating the second motor control signal Sm2.

[0052] The second ignition determination unit 102 acquires the second ignition voltage Vg2 detected by the second voltage sensor 66 and the vehicle speed SPD detected by the vehicle speed sensor 42. The second ignition determination unit 102 determines the state of the vehicle's ignition switch 43 based on the second ignition voltage Vg2 and the vehicle speed SPD. The method by which the second ignition determination unit 102 determines the state of the vehicle's ignition switch 43 is the same as the method performed by the first ignition determination unit 92. Therefore, the second ignition determination unit 102 generates a second ignition on signal Son2, a second ignition off signal Soff2, and a second ignition off signal Soff2a during driving.

[0053] The second state holding unit 103 holds the drive mode of the control system 60. That is, the second state holding unit 103 holds information about the drive mode that instructs the control system 60 to control the drive of the motor 20 in a cooperative drive mode, or information about the drive mode that instructs the control system 60 to control the drive of the motor 20 in an independent drive mode.

[0054] The second transceiver unit 104 sends information to the first transceiver unit 94 of the first microcomputer 52 and receives information from the first transceiver unit 94 of the first microcomputer 52. The functions of the first command value calculation unit 90 and the second command value calculation unit 100 will be described below.

[0055] like Figure 3 As shown, the first command value calculation unit 90 includes a first basic command value calculation unit 95, a first gain output unit 96, a multiplier 97, and a first protection processing unit 98. The second command value calculation unit 100 includes a second basic command value calculation unit 105, a second gain output unit 106, a multiplier 107, a second protection processing unit 108, and a command value difference determination unit 109. The first basic command value calculation unit 95 and the second basic command value calculation unit 105 have the same configuration. The first gain output unit 96 and the second gain output unit 106 have the same configuration. The multiplier 97 and the multiplier 107 have the same configuration. The first protection processing unit 98 and the second protection processing unit 108 have the same configuration.

[0056] The vehicle speed SPD and the first steering torque Th1 are input to the first basic command value calculation unit 95. The first basic command value calculation unit 95 calculates a first basic current command value Iq1*, which is the current command value on the q-axis in the dq coordinate system, based on the vehicle speed SPD and the first steering torque Th1. The first basic command value calculation unit 95 calculates the first basic current command value Iq1* such that the absolute value of the first basic current command value Iq1* increases as the absolute value of the first steering torque Th1 increases and as the vehicle speed SPD decreases. The first basic command value calculation unit 95 sets the current command value on the d-axis in the dq coordinate system to "0".

[0057] The signal generated by the first ignition determination unit 92 is input to the first gain output unit 96. The first gain output unit 96 outputs a first gain G1 within the range of 0 to 1 based on the signal generated by the first ignition determination unit 92. When a first ignition on signal Son1 or a first ignition off signal Soff1 is input from the first ignition determination unit 92, the first gain output unit 96 outputs "1" as the first gain G1. When a first driving ignition off signal Soff1a is input from the first ignition determination unit 92, the first gain output unit 96 outputs a value equal to or less than "1" as the first gain G1 in the driving ignition off control.

[0058] Figure 4 This illustrates the time-dependent variation of the first gain G1 output from the first gain output unit 96 when a first driving ignition disconnect signal Soff1a is input from the first ignition determination unit 92. Figure 4 In this context, time "0" indicates the time elapsed since the ignition disconnect signal Soff1a was input from the first ignition determination unit 92 to the first gain output unit 96 during the first driving phase, after which the assistance duration D1 for assisting the driver's steering operation (i.e., the steering operation that should be assisted) has elapsed. The assistance duration D1 is a predetermined period for assisting the driver's steering operation because there is a high probability that the driver's steering operation will be performed immediately after the ignition switch 43 has been turned off. Figure 4 As shown, the first gain output unit 96 outputs a first gain G1, such that the absolute value of the first gain G1 decreases over time after the auxiliary duration D1 has elapsed. That is, the first gain output unit 96 gradually decreases the absolute value of the first gain G1 after the auxiliary duration D1 has elapsed. The absolute value of the first gain G1 decreases exponentially after the auxiliary duration D1 has elapsed. When a predetermined time has elapsed after the auxiliary duration D1, the first gain output unit 96 outputs the first gain G1 as "0".

[0059] The first basic current command value Iq1* calculated by the first basic command value calculation unit 95 and the first gain G1 output from the first gain output unit 96 are input to the multiplier 97. The multiplier 97 calculates a first adjusted current command value Iq1a*, which is obtained by multiplying the first basic current command value Iq1* by the first gain G1. When the first ignition determination unit 92 generates the first ignition on signal Son1 or the first ignition off signal Soff1, the first basic current command value Iq1* and the first adjusted current command value Iq1a* become the same. On the other hand, when the first ignition determination unit 92 generates the first driving ignition off signal Soff1a, the absolute value of the first adjusted current command value Iq1a* is equal to or less than the absolute value of the first basic current command value Iq1*. That is, when the first ignition determination unit 92 generates the first driving ignition off signal Soff1a, the absolute value of the first adjusted current command value Iq1a* is gradually limited.

[0060] The first adjusted current command value Iq1a* calculated by multiplier 97 and the signal generated by first ignition determination unit 92 are input to first protection processing unit 98. First protection processing unit 98 calculates a first final current command value I1* by limiting the first adjusted current command value Iq1a* to a first current limit value Ilim1 by performing various protection processes on the first adjusted current command value Iq1a*. These various protection processes include, for example, performing control to limit the first adjusted current command value Iq1a* when ignition switch 43 is off, or control to limit the first adjusted current command value Iq1a* to prevent overheating of main control system 50. The first current limit value Ilim1 is set according to various protection processes and is set to a minimum value at all times. For example, when the first ignition off signal Soff1 is input from first ignition determination unit 92, first protection processing unit 98 sets the first current limit value Ilim1 to essentially zero after a period of time for assisting the driver's steering operation has elapsed since the first ignition off signal Soff1 was input. In this case, the period for assisting the driver's steering operation is a predetermined period because the probability of performing the driver's steering operation immediately after the ignition switch 43 has been turned off is high, and it is set to be longer than the assistance duration D1. The absolute value of the first current limit value Ilim1 is set to gradually decrease after the period for assisting the driver's steering operation has elapsed.

[0061] The first transceiver unit 94 acquires the first adjusted current command value Iq1a* calculated by the multiplier 97, the first current limit value Ilim1 used by the first protection processing unit 98, and information about the drive mode of the main control system 50 held in the first state holding unit 93. Each predetermined control cycle, the first transceiver unit 94 transmits the first adjusted current command value Iq1a*, the first current limit value Ilim1, and the information about the drive mode of the main control system 50 to the second transceiver unit 104 of the slave control system 60.

[0062] Vehicle speed SPD and second steering torque Th2 are input to the second basic command value calculation unit 105. The second basic command value calculation unit 105 calculates a second basic current command value Iq2* as the current command value on the q-axis in the dq coordinate system based on vehicle speed SPD and second steering torque Th2. The second basic command value calculation unit 105 calculates the second basic current command value Iq2* such that the absolute value of the second basic current command value Iq2* increases as the absolute value of the second steering torque Th2 increases and as vehicle speed SPD decreases. The second basic command value calculation unit 105 sets the current command value on the d-axis in the dq coordinate system to "0".

[0063] The signal generated by the second ignition determination unit 102 is input to the second gain output unit 106. When the second ignition on signal Son2 or the second ignition off signal Soff2 is input from the second ignition determination unit 102, the second gain output unit 106 outputs "1" as the second gain G2. When the second driving ignition off signal Soff2a is input, the second gain output unit 106 outputs a value equal to or less than "1" as the second gain G2 in the driving ignition off control. Figure 4 As shown, the second gain output unit 106 outputs a second gain G2, such that the absolute value of the second gain G2 decreases over time after the auxiliary duration D1 has elapsed. That is, the second gain output unit 106 gradually decreases the absolute value of the second gain G2 after the auxiliary duration D1 has elapsed. After a predetermined time has elapsed after the auxiliary duration D1 has elapsed, the second gain output unit 106 outputs the second gain G2 as "0".

[0064] The second basic current command value Iq2* calculated by the second basic command value calculation unit 105 and the second gain G2 output from the second gain output unit 106 are input to the multiplier 107. The multiplier 107 calculates a second adjusted current command value Iq2a*, which is obtained by multiplying the second basic current command value Iq2* by the second gain G2. When the second ignition determination unit 102 generates the second ignition on signal Son2 or the second ignition off signal Soff2, the second basic current command value Iq2* and the second adjusted current command value Iq2a* become the same. On the other hand, when the second ignition determination unit 102 generates the second driving ignition off signal Soff2a, the absolute value of the second adjusted current command value Iq2a* is equal to or less than the absolute value of the second basic current command value Iq2*. That is, when the second ignition determination unit 102 generates the second driving ignition off signal Soff2a, the absolute value of the second adjusted current command value Iq2a* is gradually limited.

[0065] The second adjusted current command value Iq2a* calculated by multiplier 107, the first adjusted current command value Iq1a* received by second transceiver unit 104 from first transceiver unit 94, the drive mode of main control system 50, and the second steering torque Th2 detected by second torque sensor 40b are input to command value difference determination unit 109. Command value difference determination unit 109 determines whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are different from each other based on the result of determining whether the command value difference ΔI* between the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* is greater than the difference determination threshold ΔI0. The difference determination threshold ΔI0 is set to a value at which the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* can be considered to match each other, and is set to a value at which the command value difference ΔI* is not greater than (i.e., does not exceed) the difference determination threshold ΔI0 when the main control system 50 and the slave control system 60 are normal.

[0066] When the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are not different from each other, that is, when there is no abnormality between the main control system 50 and the slave control system 60 where the adjusted current command values ​​are different, the command value difference determination unit 109 executes the cooperative drive mode. When executing the cooperative drive mode, the command value difference determination unit 109 outputs the first adjusted current command value Iq1a* to the second protection processing unit 108. When executing the cooperative drive mode, the command value difference determination unit 109 outputs a signal indicating the execution of the cooperative drive mode to the second state holding unit 103.

[0067] When the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are different from each other, i.e., when an anomaly occurs between the main control system 50 and the slave control system 60 where the adjusted current command values ​​are different, the command value difference determination unit 109 executes the independent drive mode. When executing the independent drive mode, the command value difference determination unit 109 outputs the second adjusted current command value Iq2a* to the second protection processing unit 108. When executing the independent drive mode, the command value difference determination unit 109 outputs a signal indicating the execution of the independent drive mode to the second state holding unit 103. Based on the determination result regarding the difference between the adjusted current command values, the command value difference determination unit 109 switches the drive mode of the slave control system 60 by changing the adjusted current command value output to the second protection processing unit 108. During the period when the independent drive mode is executed as ignition disconnection control during driving, the command value difference determination unit 109 is unsure whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are different from each other.

[0068] The first adjusted current command value Iq1a* or the second adjusted current command value Iq2a* output from the command value difference determination unit 109 and the signal generated by the second ignition determination unit 102 are input to the second protection processing unit 108. The second protection processing unit 108 calculates a second final current command value I2* that limits the first adjusted current command value Iq1a* or the second adjusted current command value Iq2a* to a second current limit value Ilim2 by performing various protection processes on the first adjusted current command value Iq1a* or the second adjusted current command value Iq2a*. As various protection processes, for example, control is performed to limit the second adjusted current command value Iq2a* when the ignition switch 43 is turned off, or control is performed to limit the second adjusted current command value Iq2a* to prevent overheating from the control system 60. The second current limit value Ilim2 is set according to various protection processes and is set to a minimum value at all times. For example, when the second ignition disconnect signal Soff2 is input from the second ignition determination unit 102, the second protection processing unit 108 sets the second current limit value Ilim2 to essentially zero after a period of time for assisting the driver's steering operation has elapsed following the input of the second ignition disconnect signal Soff2. In this case, the period of time for assisting the driver's steering operation is a predetermined period of time for assisting the driver's steering operation because the probability of performing the driver's steering operation immediately after the ignition switch 43 has been turned off is high, and it is set to be a period longer than the assistance duration D1. The absolute value of the second current limit value Ilim2 is set to gradually decrease after the period of time for assisting the driver's steering operation has elapsed.

[0069] The signal generated by the second ignition determination unit 102 is input to the command value difference determination unit 109. When the second driving ignition disconnect signal Soff2a is input from the second ignition determination unit 102, regardless of whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are different from each other, the command value difference determination unit 109 switches the drive mode of the control system 60 from the cooperative drive mode to the independent drive mode. That is, the command value difference determination unit 109 outputs the second adjusted current command value Iq2a* to the second protection processing unit 108, so that the drive mode of the control system 60 is switched from the cooperative drive mode to the independent drive mode.

[0070] The following will refer to Figure 5 The process of switching the drive mode of the slave control system 60 is described. This description is based on the premise that a cooperative drive mode is being executed in the slave control system 60. The slave control system 60 repeatedly performs the following drive mode switching process. For the purpose of simplification, the description of determining the difference between the adjusted current command values ​​in the command value difference determination unit 109 will be omitted.

[0071] like Figure 5 As shown, when the second ignition determination unit 102 of the control system 60 is executing the cooperative drive mode (step S1), it determines whether the ignition switch 43 has been turned off while the vehicle is in motion (step S2). If the vehicle speed SPD is greater than the vehicle speed threshold SPD0 for a predetermined time tg and the second ignition voltage vg2 is not greater than the voltage threshold V0 for a predetermined time tg, the second ignition determination unit 102 determines that the ignition switch 43 has been turned off while the vehicle is in motion, and generates a second in-motion ignition off signal Soff2a.

[0072] If the ignition switch 43 is not turned off while the vehicle is in motion (No in step S2), the command value difference determination unit 109 of the control system 60 executes the cooperative drive mode (step S3) and ends the drive mode switching process. When executing the cooperative drive mode, the command value difference determination unit 109 outputs the first adjusted current command value Iq1a* to the second protection processing unit 108 and outputs a signal indicating the execution of the cooperative drive mode to the second state holding unit 103.

[0073] If the ignition switch 43 has been turned off while the vehicle is in motion ("Yes" in step S2), the command value difference determination unit 109 of the control system 60 executes the independent drive mode (step S4) and ends the drive mode switching process. When executing the independent drive mode, the command value difference determination unit 109 outputs the second adjusted current command value Iq2a* to the second protection processing unit 108 and outputs a signal indicating the execution of the independent drive mode to the second state holding unit 103.

[0074] like Figure 3 As shown, the second transceiver unit 104 acquires the second adjusted current command value Iq2a* calculated by the multiplier 107, the second current limit value Ilim2 used in the second protection processing unit 108, and information about the drive mode of the slave control system 60 held in the second state holding unit 103. Each predetermined control cycle, the second transceiver unit 104 sends the second adjusted current command value Iq2a*, the second current limit value Ilim2, and the information about the drive mode of the slave control system 60 to the first transceiver unit 94 of the main control system 50. Each predetermined control cycle, the second transceiver unit 104 receives the first adjusted current command value Iq1a*, the first current limit value Ilim1, and the information about the drive mode of the main control system 50. Each predetermined control cycle, the first transceiver unit 94 receives the second adjusted current command value Iq2a*, the second current limit value Ilim2, and the information about the drive mode of the slave control system 60.

[0075] When the first transceiver unit 94 receives a signal indicating an independent drive mode from the second transceiver unit 104, the main control system 50 switches its own drive mode to the independent drive mode. In this embodiment, the main control system 50 outputs a first adjusted current command value Iq1a* to the first protection processing unit 98, and does not change any control result in either the cooperative drive mode or the independent drive mode. Here, the main control system 50 can change various controls of the main control system 50 based on information obtained from the slave control system 60.

[0076] The following will refer to Figure 6 The description describes the drive mode switching process in which the ignition switch 43 is turned off earlier in the slave control system 60 than in the master control system 50, when the ignition switch 43 is turned off while the vehicle is in motion.

[0077] like Figure 6As shown in the timing diagram, when it is determined that the ignition switch 43 has been turned off while the vehicle is in motion (step S11), the command value difference determination unit 109 of the control system 60 switches the drive mode of the control system 60 from the cooperative drive mode to the independent drive mode (step S12). On the other hand, it has not yet been determined in the main control system 50 that the ignition switch 43 has been turned off while the vehicle is in motion. The second driving ignition off signal Soff2a generated by the second ignition determination unit 102 and the information about the drive mode of the main control system 50 received by the second transceiver unit 104 from the first transceiver unit 94, which instructs the main control system 50 to execute the cooperative drive mode, are input to the command value difference determination unit 109 of the control system 60. The command value difference determination unit 109 ignores the information indicating that it has not yet been determined in the main control system 50 that the ignition switch 43 has been turned off while the vehicle is in motion, prioritizes the information indicating that it has been determined in the corresponding control system that the ignition switch 43 has been turned off while the vehicle is in motion, and switches the drive mode of the control system 60 from the cooperative drive mode to the independent drive mode.

[0078] The second transceiver unit 104 of the control system 60 sends information about the drive mode of the sub-control system 60 to the first transceiver unit 94 of the main control system 50 (step S13). Based on the information about the drive mode of the sub-control system 60 received by the first transceiver unit 94 from the second transceiver unit 104, the main control system 50 switches its own drive mode to an independent drive mode (step S14). In the main control system 50, it has not yet been determined that the ignition switch 43 has been turned off while the vehicle is in motion. On the other hand, information about the drive mode of the sub-control system 60 received by the first transceiver unit 94 from the second transceiver unit 104 and instructing the sub-control system 60 to execute the independent drive mode is input to the main control system 50. The first state holding unit 93 of the main control system 50 ignores the information indicating that it has not yet determined that the ignition switch 43 has been turned off in its own control system, prioritizes the information indicating that it has determined in the sub-control system 60 that the ignition switch 43 has been turned off while the vehicle is in motion, and holds the information about the drive mode instructing the main control system 50 to control the drive of the motor 20 in the independent drive mode.

[0079] The drive mode switching process is determined earlier in the main control system 50 when the ignition switch 43 has been turned off while the vehicle is in motion, compared to the slave control system 60. Figure 6The processing is the same as shown. Upon determining that the ignition switch 43 has been turned off while the vehicle is in motion, the main control system 50 switches its drive mode from cooperative drive mode to independent drive mode. The first transceiver unit 94 of the main control system 50 sends information about the drive mode of the main control system 50 to the second transceiver unit 104 of the slave control system 60. The command value difference determination unit 109 of the slave control system 60 ignores information indicating that the ignition switch 43 has not yet been determined to be turned off in its own control system, prioritizes information indicating that the ignition switch 43 has been determined to be turned off while the vehicle is in motion in the main control system 50, and switches the drive mode to the independent drive mode that outputs the second adjusted current command value Iq2a*. The second state holding unit 103 of the slave control system 60 ignores information indicating that the ignition switch 43 has not yet been determined to be turned off in its own control system, prioritizes information indicating that the ignition switch 43 has been determined to be turned off while the vehicle is in motion in the main control system 50, and holds information about the drive mode instructing the slave control system 60 to control the drive of the motor 20 in independent drive mode.

[0080] like Figure 3 As shown, during the period when the adjusted current command value is gradually limited based on the input of the second driving ignition disconnect signal Soff2a—that is, during the period when an independent drive mode is being executed due to the ignition switch 43 being turned off while the vehicle is in motion—if it is determined that the ignition switch 43 has been turned on, the command value difference determination unit 109 determines whether a steering operation is being performed. The command value difference determination unit 109 determines whether a steering operation is being performed based on the result of determining whether the second steering torque Th2 is greater than the torque threshold Th0, and switches the drive mode from the control system 60 based on the result of determining whether a steering operation is being performed. The torque threshold Th0 is set to the value of the second steering torque Th2 that determines whether a steering operation is being performed.

[0081] The following will refer to Figure 7 Describe the process of switching the drive mode from the control system 60. Assume that an independent drive mode is being executed in the control system 60 due to the ignition switch 43 being turned off while the vehicle is in motion. The control system 60 repeatedly executes the following drive mode switching process during the period when the independent drive mode is being executed due to the ignition switch 43 being turned off while the vehicle is in motion.

[0082] The second ignition determination unit 102 of the control system 60 determines whether the ignition switch 43 was turned on during the period when the independent drive mode was being executed due to the ignition switch 43 being turned off while the vehicle was in motion (step S22). When the second ignition voltage Vg2 is greater than the voltage threshold V0, the second ignition determination unit 102 determines that the ignition switch 43 has been turned on and generates a first ignition on signal Son1.

[0083] When it is determined in step S22 that the ignition switch 43 is not turned on (No in step S22), the command value difference determination unit 109 of the control system 60 maintains the independent drive mode and ends the drive mode switching process.

[0084] When it is determined in step S22 that the ignition switch 43 has been turned on ("Yes" in step S22), the command value difference determination unit 109 of the control system 60 determines whether a steering operation is not being performed (step S23). The command value difference determination unit 109 determines whether a steering operation is being performed based on the result of determining whether the second steering torque Th2 is greater than the torque threshold Th0.

[0085] When it is determined in step S23 that a steering operation is being performed (No in step S23), the command value difference determination unit 109 of the control system 60 maintains the independent drive mode and ends the drive mode switching process. When the second steering torque Th2 is greater than the torque threshold Th0, the command value difference determination unit 109 determines that a steering operation is being performed and maintains the independent drive mode by outputting the second adjusted current command value Iq2a* to the second protection processing unit 108. Situations where a steering operation is determined to be being performed include situations where large fluctuations in the adjusted current command value may occur during drive mode switching, i.e., situations where fluctuations in the torque output from the motor 20 during drive mode switching may cause the steering wheel 10 to vibrate. When the steering wheel 10 vibrates due to torque fluctuations, it may affect the driver's steering feel associated with the steering wheel 10.

[0086] When it is determined in step S23 that no steering operation is being performed (i.e., no steering operation is being performed) ("Yes" in step S23), the command value difference determination unit 109 of the control system 60 switches the drive mode from independent drive mode to cooperative drive mode (step S24), and then ends the drive mode switching process. When the second steering torque Th2 is not greater than the torque threshold Th0, the command value difference determination unit 109 determines that no steering operation is being performed, and switches the drive mode from independent drive mode to cooperative drive mode by outputting the first adjusted current command value Iq1a* to the second protection processing unit 108. The situation in which no steering operation is being performed includes situations where large fluctuations in the adjusted current command value are unlikely to occur when switching drive modes, that is, situations where fluctuations in the torque output from the motor 20 are unlikely to cause vibration of the steering wheel 10 when switching drive modes.

[0087] In this way, when the ignition switch 43 is turned on during a period when the independent drive mode is being executed due to the ignition switch 43 being turned off while the vehicle is in motion, the independent drive mode is maintained when a steering operation is being performed, and the drive mode is switched from the independent drive mode to the cooperative drive mode when a steering operation is not being performed.

[0088] like Figure 3 As shown, when switching the drive mode from independent drive mode to cooperative drive mode, the command value difference determination unit 109 outputs the first adjusted current command value Iq1a* to the second protection processing unit 108, and outputs a signal indicating the execution of cooperative drive mode to the second state holding unit 103. The second transceiver unit 104 of the slave control system 60 sends information about the drive mode of the slave control system 60 to the first transceiver unit 94 of the master control system 50. Based on the information about the drive mode of the slave control system 60 received by the first transceiver unit 94 from the second transceiver unit 104, the master control system 50 switches its own drive mode to cooperative drive mode.

[0089] The operation of this embodiment will now be described. When the ignition switch 43 is turned off while the vehicle is in motion, the timing of the transition from the main control system 50 to the in-motion ignition off control by the slave control system 60 can be different from each other. This is because the timing of the generation of the first in-motion ignition off signal Soff1a by the first ignition determination unit 92 and the timing of the generation of the second in-motion ignition off signal Soff2a by the second ignition determination unit 102 are different from each other. One reason is that, for example, the timing of switching the third power line L3 to a disconnected state by disconnecting the first power relay 55 provided in the main control system 50 is different from the timing of switching the fourth power line L4 to a disconnected state by disconnecting the second power relay 65 provided in the slave control system 60. Another reason is that the first ignition voltage Vg1 and the second ignition voltage Vg2 are different from each other due to noise, etc. For these reasons, since the timing of determining that the ignition switch 43 has been turned off is different from each other, one control system of the main control system 50 and the slave control system 60 can transition to in-motion ignition off control earlier than the other control system. Reference will now be made to... Figure 8 This describes a situation where the main control system 50 switches to ignition disconnect control during driving earlier than the secondary control system 60.

[0090] Figure 8 Time T1 indicates the time when the ignition switch 43 is turned off by the driver. Time T2 indicates the time when both the main control system 50 and the secondary control system 60 transition to driving ignition off control. Time T3 indicates the time when the gradual limitation of the calculated adjusted current command value has begun after the auxiliary duration D1 has elapsed. At time T3, it is assumed that the driver performs a steering operation. Time T4 indicates the time when the command value difference determination unit 109 determines that the command value difference ΔI* is greater than the difference determination threshold ΔI0.

[0091] like Figure 8As shown, during the time period up to time T1, the main control system 50 and the slave control system 60 execute a cooperative drive mode. The first ignition voltage Vg1 and the second ignition voltage Vg2 are greater than the voltage threshold V0. Each of the first current limit values ​​Ilim1 and the second current limit value Ilim2 is set to, for example, the maximum value. The first gain G1 and the second gain G2 are set to "1". The first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are output as the same as the first basic current command value Iq1* and the second basic current command value Iq2*. For the purpose of simplification, it is assumed that the driver does not perform any steering operation, i.e., the first steering torque Th1 and the second steering torque Th2 are "0". Therefore, both the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are "0". Both the first final current command value I1* and the second final current command value I2* are "0". Since the cooperative drive mode is being executed, the first final current command value I1* and the second final current command value I2* are calculated based on the first adjusted current command value Iq1a*.

[0092] At time T1, the ignition switch 43 is turned off by the driver. Here, it is assumed that the first ignition voltage Vg1 of the main control system 50 becomes equal to or less than the voltage threshold V0 earlier than the second ignition voltage Vg2 of the slave control system 60. At this time, it is assumed that the vehicle speed SPD is greater than the vehicle speed threshold SPD0. If the condition that the vehicle speed SPD is greater than the vehicle speed threshold SPD0 remains for a predetermined time tg and the condition that the first ignition voltage Vg1 is not greater than (i.e., the first ignition voltage Vg1 is equal to or less than) the voltage threshold V0 remains for a predetermined time tg, the first ignition determination unit 92 of the main control system 50 determines that the ignition switch 43 has been turned off while the vehicle is in motion. Therefore, the main control system 50 switches its drive mode to independent drive mode. The slave control system 60 switches its drive mode to independent drive mode based on the information about the drive mode of the main control system 50 received from the first transceiver unit 94 of the main control system 50. Therefore, at time T2, both the main control system 50 and the slave control system 60 switch their drive modes to independent drive mode. Since the slave control system 60 enters the state where the second ignition voltage Vg2 does not exceed the voltage threshold V0 later than the main control system 50, the slave control system 60 determines later that the ignition switch 43 has been turned off while the vehicle is in motion.

[0093] The period from time T2 to time T3 is the auxiliary duration D1. During the auxiliary duration D1, since the steering wheel may be turned by the driver, the first gain G1 is kept at "1". The second gain G2 is also "1".

[0094] At time T3, due to the driver's steering operation, the absolute values ​​of the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are greater than "0". At time T3, the auxiliary duration D1 has elapsed. After time T3, the absolute value of the first gain G1 gradually decreases. After a predetermined time has elapsed following the auxiliary duration D1, the absolute value of the first gain G1 becomes "0". The first adjusted current command value Iq1a* is gradually limited as the absolute value of the first gain G1 gradually decreases. After a predetermined time has elapsed following the auxiliary duration D1, the first adjusted current command value Iq1a* becomes "0". On the other hand, the second gain G2 remains "1". Since the second gain G2 remains "1", the second adjusted current command value Iq2a* is still not limited. Because the independent drive mode is executed, the first final current command value I1* is the same as the first adjusted current command value Iq1a*, and the second final current command value I2* is the same as the second adjusted current command value Iq2a*.

[0095] At time T4, the command value difference ΔI* becomes greater than the difference determination threshold ΔI0. However, since the main control system 50 and the slave control system 60 switched their drive modes to independent drive modes at time T2, no drive mode switching is performed at time T4. For example, after time T4, a predetermined time has elapsed after the auxiliary duration D1 has elapsed. In this case, after time T4, the absolute value of the second gain G2 gradually decreases, and the second adjusted current command value Iq2a* and the second final current command value I2* are gradually limited as the absolute value of the second gain G2 gradually decreases. After time T4, the absolute values ​​of the first current limit value Ilim1 and the second current limit value Ilim2 gradually decrease and are set to their minimum values.

[0096] In this way, when it is determined that the ignition switch 43 has been turned off while the vehicle is in motion, the drive mode is switched from cooperative drive mode to independent drive mode regardless of whether the adjusted current command values ​​calculated by the microcomputer of the main control system 50 and the microcomputer of the slave control system 60 are different from each other. That is, compared to the case where the drive mode is switched from cooperative drive mode to independent drive mode after the adjusted current command values ​​calculated by the microcomputer of the main control system 50 and the microcomputer of the slave control system 60 have become different from each other, the main control system 50 and the slave control system 60 can switch their drive modes to independent drive mode earlier. Therefore, even when the ignition disconnection control (i.e., the control executed due to the ignition switch being turned off) calculates the command value based on the driver's steering operation separately by the control unit of the control system, it is possible to prevent the control for supplying power to each control system from fluctuating between control using restricted command values ​​and control using unrestricted command values.

[0097] On the other hand, the following will describe as follows: Figure 9 As a comparative example, the driving mode is not switched from cooperative driving mode to independent driving mode even when it is determined that the ignition switch 43 has been turned off while the vehicle is in motion.

[0098] The time period up to time T1 is the same as in this embodiment. Time T1 is the same as in this embodiment. At time T2, if the vehicle speed SPD is greater than the vehicle speed threshold SPD0 for a predetermined time tg and the first ignition voltage Vg1 is not greater than the voltage threshold V0 for a predetermined time tg, the first ignition determination unit 92 of the main control system 50 detects that the ignition switch 43 has been turned off while the vehicle is in motion. However, in the comparative example, at time T2, the main control system 50 does not switch its drive mode to independent drive mode. At time T2, the slave control system 60 also does not switch its drive mode to independent drive mode. Except that the main control system 50 and the slave control system 60 remain in cooperative drive mode, the time period from time T2 to time T3 is the same as in this embodiment. At time T3, since the driver has performed a steering operation, the absolute values ​​of the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are greater than "0". The first adjusted current command value Iq1a* is gradually restricted as the first gain G1 gradually decreases. On the other hand, since the second gain G2 is kept at "1", the second adjusted current command value Iq2a* is not yet restricted. Therefore, at time T4, the command value difference ΔI* becomes greater than the difference determination threshold ΔI0. Then, based on the determination result from the command value difference determination unit 109 that the command value difference ΔI* is greater than the difference determination threshold ΔI0, the main control system 50 and the slave control system 60 switch their drive modes to independent drive modes. At this point, before and after the drive mode is switched to independent drive mode, the control for supplying power to the main control system 50 is not changed from the control using the restricted first adjusted current command value Iq1a* calculated by the main control system 50. That is, before and after the drive mode is switched to independent drive mode, the adjusted current command value input to the first protection processing unit 98 is not changed from the first adjusted current command value Iq1a*. On the other hand, before and after the drive mode is switched to independent drive mode, the control for supplying power to the slave control system 60 changes from control using a limited first adjusted current command value Iq1a* calculated by the master control system 50 to control using a limited second adjusted current command value Iq2a* calculated by the slave control system 60. That is, before and after the drive mode is switched to independent drive mode, the adjusted current command value input to the second protection processing unit 108 changes from the first adjusted current command value Iq1a* to the second adjusted current command value Iq2a*. Therefore, the second motor control signal Sm2 may change and the torque output from the motor 20 may fluctuate.

[0099] The advantages of this implementation will be described below. (1) When the ignition switch 43 is turned off while the vehicle is in motion, the drive mode is switched from cooperative drive mode to independent drive mode regardless of whether the adjusted current command values ​​calculated by the microcomputer of the control system are different from each other. Therefore, when the ignition switch 43 is turned off while the vehicle is in motion, fluctuations in the torque output from the motor 20 can be suppressed.

[0100] (2) Since the main control system 50 and the slave control system 60 independently determine whether the ignition switch 43 has been turned off while the vehicle is in motion, the timing of the transition from ignition off control during driving to driving control may differ between the main control system 50 and the slave control system 60. Therefore, the timing of the main control system 50 and the slave control system 60 switching their drive modes from cooperative drive mode to independent drive mode may differ between them. The main control system 50 switches its drive mode from cooperative drive mode to independent drive mode based on information about the drive mode received from the slave control system 60. The slave control system 60 switches its drive mode from cooperative drive mode to independent drive mode based on information about the drive mode received from the main control system 50. Therefore, compared to the case where the control system independently determines whether the ignition switch 43 has been turned off while the vehicle is in motion and then independently switches the drive mode of the control system to independent drive mode, the timing of switching the drive mode to independent drive mode in the control system can be matched. Therefore, the torque output from the slave motor 20 can be stabilized.

[0101] (3) Even when the ignition switch 43 is turned on during the period when ignition disconnection control is being executed, if the torque fluctuation of the motor 20 caused by the switching of drive modes may cause the steering wheel 10 to vibrate, the main control system 50 and the slave control system 60 maintain independent drive modes. In this case, since the main control system 50 and the slave control system 60 do not switch their drive modes, the torque fluctuation output from the motor 20 can be suppressed. Therefore, the possibility that torque fluctuations may affect the driver's steering feel related to the steering wheel 10 by causing the steering wheel 10 to vibrate can be reduced. When the ignition switch 43 is turned on during the period when ignition disconnection control is being executed, if the torque fluctuation from the motor 20 caused by the switching of drive modes is unlikely to cause the steering wheel 10 to vibrate, the main control system 50 and the slave control system 60 switch their drive modes to a cooperative drive mode. In this case, the main control system 50 and the slave control system 60 can switch the drive mode to the cooperative drive mode while suppressing the torque fluctuation output from the motor 20.

[0102] (4) The situation where the steering wheel 10 is being steered is one where fluctuations in the adjusted current command value may occur when switching drive modes, i.e., fluctuations in the torque output from the motor 20 may cause the steering wheel 10 to vibrate. The situation where the steering wheel 10 is not being steered is one where fluctuations in the adjusted current command value are unlikely to occur when switching drive modes, i.e., fluctuations in the torque output from the motor 20 are unlikely to cause the steering wheel 10 to vibrate. In this way, by switching drive modes based on whether the steering wheel 10 is being steered, the drive mode can be switched appropriately.

[0103] The aforementioned implementation can be modified as follows. Unless there is a technical conflict, the following modification examples can be combined. The functions of the main control system 50 and the slave control system 60 can be interchanged. That is, when the first adjusted current command value Iq1a* of the main control system 50 is abnormal, the slave control system 60 can act as the main control system, while the main control system 50 can act as the slave control system. In this case, in the cooperative drive mode, the power supply to both the main control system 50 and the slave control system 60 can be performed based on the current command value calculated by the slave control system 60.

[0104] In the aforementioned embodiments, the command value difference determination unit 109 is only located in the slave control system 60. However, in addition to the slave control system 60, the command value difference determination unit can also be located in the master control system 50. Each control system in the control system can switch its drive mode based on the determination result from the command value difference determination unit of the control system. In this case, one control system may not need to send its drive mode to another control system.

[0105] The method for determining the state of the ignition switch 43, performed by the first ignition determination unit 92 and the second ignition determination unit 102, can be appropriately modified. For example, the first ignition determination unit 92 can use a determination condition regarding whether communication with another device has been cut off, instead of a determination condition regarding whether the first ignition voltage Vg1 is greater than the voltage threshold V0. The first ignition determination unit 92 determines the state of the ignition switch 43 if the determination condition is continuously met or not met for a predetermined time tg, but it can also determine the state of the ignition switch 43 immediately after the determination condition is met or not met.

[0106] The main control system 50 and the slave control system 60 can switch their drive modes to another drive mode besides the cooperative drive mode and the independent drive mode. For example, in this other drive mode, when an anomaly has occurred in one of the control systems of the main control system 50 and the slave control system 60, the motor 20 is driven only by the other normal control system of the main control system 50 and the slave control system 60.

[0107] The first microcomputer 52 obtains the voltage of the first power supply 70 as the first ignition voltage Vg1 via the first voltage sensor 56, but it can also obtain the voltage directly from the first power supply 70. The second microcomputer 62 obtains the voltage of the second power supply 80 as the second ignition voltage Vg2 via the second voltage sensor 66, but it can also obtain the voltage directly from the second power supply 80.

[0108] After the auxiliary duration D1 has elapsed, the first gain output unit 96 causes the absolute value of the first gain G1 to decrease exponentially. However, the method by which the absolute value of the first gain G1 is gradually decreased can be appropriately modified. For example, the first gain output unit 96 can decrease the absolute value of the first gain G1 proportionally to the time period after the auxiliary duration D1 has elapsed, or it can decrease the absolute value of the first gain G1 in stages according to the time period after the auxiliary duration D1 has elapsed. That is, compared to the case where the first gain G1 changes abruptly from "1" to "0" after the auxiliary duration D1 has elapsed, the first gain output unit 96 can decrease the absolute value more gradually. Similarly, the mode of calculating the second gain G2 performed by the second gain output unit 106 can also be appropriately modified, similar to the first gain output unit 96.

[0109] The first gain output unit 96 performs a gradual decrease in the absolute value of the first gain G1 after the auxiliary duration D1 has elapsed, but the present invention is not limited thereto. The first gain output unit 96 can also perform a gradual decrease in the absolute value of the first gain G1 when the first driving ignition disconnect signal Soff1a is input. That is, the auxiliary duration D1 may not be set. Similar to the case of the first gain output unit 96, the present invention is not limited to the configuration of gradually decreasing the absolute value of the second gain G2 output from the second gain output unit 106 after the auxiliary duration D1 has elapsed.

[0110] The first gain output unit 96 performs a gradual decrease in the absolute value of the first gain G1 only when the first driving ignition disconnect signal Soff1a is input, but it can also perform a gradual decrease when the first ignition disconnect signal Soff1 is input. Similar to the case of the first gain output unit 96, the gradual decrease in the absolute value of the second gain G2 output from the second gain output unit 106 can be performed when the first ignition disconnect signal Soff1 is input.

[0111] The power supply path to the main control system 50 can be appropriately changed. The power supply path to the slave control system 60 can also be appropriately changed. For example, the first power source 70 connected to the first ECU 51 and the second power source 80 connected to the second ECU 61 are different power sources, but they can be shared power sources.

[0112] The command value difference determination unit 109 determines whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are different from each other, but the present invention is not limited thereto. The command value difference determination unit 109 may perform the determination of the difference based on other command values, such as voltage command values.

[0113] If it is determined that the ignition switch 43 has been turned on during the period when the independent drive mode is executed due to the ignition switch 43 being turned off while the vehicle is in motion, the command value difference determination unit 109 determines whether to switch the drive mode of the slave control system 60 based on the second steering torque Th2, but the present invention is not limited thereto. For example, the command value difference determination unit 109 may determine whether to switch the drive mode of the slave control system 60 based on the first steering torque Th1, the rotational speed as the rate of change of the first rotation angle θ1 or the second rotation angle θ2, or the command value difference ΔI*. That is, the command value difference determination unit 109 may perform the determination based on any of the following state quantities, as long as said any state quantity is a state quantity that can determine whether the difference between the command value used in the independent drive mode and the command value used in the cooperative drive mode is small.

[0114] For example, the command value difference determination unit 109 can determine whether to switch the drive mode from the control system 60 based on the result that the difference between the command value used in independent drive mode and the command value used in cooperative drive mode is less than a predetermined value. The predetermined value is set as the difference that determines whether the adjusted current command value used in independent drive mode matches the adjusted current command value used in cooperative drive mode. In the absence of driver steering operation, since the first steering torque Th1 and the second steering torque Th2 are essentially zero, it is assumed that the command value difference ΔI* between the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* is essentially zero.

[0115] If it is determined that the ignition switch 43 has been turned on during the period when the independent drive mode is in effect due to the ignition switch 43 being turned off while the vehicle is in motion, the command value difference determination unit 109 performs a switch to the cooperative drive mode based on the condition that no steering operation has been performed, but the present invention is not limited thereto. For example, the command value difference determination unit 109 may perform a switch to the cooperative drive mode based on the condition that the difference between the command value used in the independent drive mode (i.e., the command value from the slave control system 60) and the command value used in the cooperative drive mode (i.e., the command value from the master control system 50) is less than a predetermined value. The predetermined value may be set to a value within a range that has little impact on the steering wheel 10, and this range is obtained experimentally.

[0116] The mechanical configuration of the motor 20 may include a system. For example, the coil 25 may include only one of the first coil 25a and the second coil 25b, and the main control system 50 and the slave control system 60 may control the current supplied to the same coil.

[0117] In the foregoing embodiment, the EPS 1 using the steering control device 30 is configured to apply the torque of the motor 20 to the steering shaft 11 via the reduction mechanism 22, but the invention is not limited thereto. The EPS 1 can be configured, for example, to apply the torque of the motor 20 to the rack shaft 12 via a ball screw mechanism. The steering control device 30 is not limited to a steering control device applied to an EPS, but can be applied to a linkage-based steer-by-wire system that can use a clutch to allow or cut off the power transmission between the steering control side and the steering side, or can be applied to a linkageless steer-by-wire system that cuts off the power transmission between the steering control side and the steering side.

Claims

1. A steering control device characterized by comprising: Comprising: a plurality of control systems configured to control driving of the electric motor (20) by switching between a plurality of drive modes including a cooperative drive mode and an independent drive mode, wherein each of the control systems includes a control unit configured to calculate a command value for controlling the electric motor (20), wherein the control systems are configured to, in a case where the cooperative drive mode is executed, control driving of the electric motor (20) based on the command value calculated by the control unit of one of the control systems, wherein the control systems are configured to, in a case where the independent drive mode is executed, control driving of the electric motor (20) based on the command values respectively calculated by the control units of the control systems, wherein the control systems are configured to, in a case where the command values calculated by the control units of the control systems are not different from each other, switch the drive mode to the cooperative drive mode, and in a case where the command values calculated by the control units of the control systems are different from each other, switch the drive mode to the independent drive mode, wherein the control systems are configured to, in a case where the start switch of the vehicle has been turned off, determine in each of the control systems that the start switch has been turned off, and gradually limit the command values respectively calculated by the control units of the control systems from a timing at which it has been determined in each of the control systems that the start switch has been turned off as a starting point, and wherein the control systems are configured to, in a case where the vehicle is running and at least one of the control systems has determined that the start switch has been turned off, switch the drive mode to the independent drive mode even if it has not been determined in the remaining control systems that the start switch has been turned off, regardless of whether the command values calculated by the control units of the control systems are different from each other or not.

2. The steering control device according to claim 1, characterized in that: each of the control systems is configured to transmit information on the drive mode of that control system to each of the remaining control systems, and receive information on the drive mode of each of the remaining control systems; and in a case where one of the control systems switches the drive mode to the independent drive mode due to turning off of the start switch while the vehicle is running, that one of the control systems transmits information on the drive mode indicating that that one of the control systems has been switched to the independent drive mode to each of the remaining control systems, and each of the remaining control systems receives the information on the drive mode from that one of the control systems, and switches the drive mode to the independent drive mode based on the information on the drive mode received from that one of the control systems even if it has not been determined in the remaining control systems that the start switch has been turned off.

3. The steering control device according to claim 1 or 2, characterized by The control system is configured to, in a case where the start switch is turned on during a period in which the drive mode is independent drive mode due to the start switch being turned off while the vehicle is running, maintain the independent drive mode in a case where a fluctuation in torque of the electric machine (20) due to a switch of drive mode is likely to vibrate the steering wheel (10), and switch the drive mode to the cooperative drive mode in a case where the fluctuation in torque of the electric machine (20) due to the switch of drive mode is unlikely to vibrate the steering wheel (10).

4. The steering control device according to claim 3, characterized in that: The control system is configured to, in a case where the start switch is turned on during a period in which the drive mode is independent drive mode due to the start switch being turned off while the vehicle is running, maintain the independent drive mode in a case where a fluctuation in torque of the electric machine (20) due to a switch of drive mode is likely to vibrate the steering wheel (10), and switch the drive mode to the cooperative drive mode in a case where the fluctuation in torque of the electric machine (20) due to the switch of drive mode is unlikely to vibrate the steering wheel (10). and The control system is configured to, in a case where the start switch is turned on during a period in which the drive mode is independent drive mode due to the start switch being turned off while the vehicle is running, maintain the independent drive mode in a case where a fluctuation in torque of the electric machine (20) due to a switch of drive mode is likely to vibrate the steering wheel (10), and switch the drive mode to the cooperative drive mode in a case where the fluctuation in torque of the electric machine (20) due to the switch of drive mode is unlikely to vibrate the steering wheel (10).

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