Steering control device

Abstract

To provide a steering control device capable of suppressing a change in torque output by a motor when an ignition switch is turned off while a vehicle is running.SOLUTION: A master control system 50 and a slave control system 60 control the drive of a motor 20 on the basis of a current command value calculated by the master control system 50 when a cooperative drive mode is executed, and control the drive of the motor 20 on the basis of a current command value calculated by the own control system when an independent drive mode is executed. The master control system 50 and the slave control system 60 are changed from the cooperative drive mode to the independent drive mode when the respective current command values are different from each other. The master control system 50 and the slave control system 60 are changed from the cooperative drive mode to the independent drive mode regardless of the fact that whether the respective current command values are different from each other or not when an ignition switch is turned off while a vehicle is running.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a steering control device. [Background technology]

[0002] Patent Document 1 discloses a steering control device that controls energization to a motor by two control systems, a master side and a slave side. The steering control device calculates a current command value in a master control unit provided in the master side control system, and calculates a current command value in a slave control unit provided in the slave side control system. The steering control device executes a cooperative drive mode in a normal state, that is, when it is determined that no abnormality occurs in which the current command values ​​diverge between the control systems, and executes an independent drive mode when it is determined that an abnormality occurs in which the current command values ​​diverge between the control systems. When executing the cooperative drive mode, the steering control device controls energization of both the master side and slave side control systems using a current command value calculated by the master control unit. When executing the independent drive mode, the steering control device controls energization of the master side control system using a current command value calculated by the master control unit, and controls energization of the slave side control system using a current command value calculated by the slave control unit.

[0003] Patent Document 2 discloses a controller as a steering control device that, when an ignition switch is turned off, limits a calculated current command value as a control when the ignition is off. The steering control device gradually limits the current command value over a certain period of time. After the certain period of time has elapsed, the steering control device limits the current command value to zero and turns itself off by cutting off a power supply relay. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-130007 A [Patent Document 2] JP 2001-10514 A Summary of the Invention [Problem to be solved by the invention]

[0005] The ignition switch may be turned off while the vehicle is traveling. In the steering control device, a signal indicating that the ignition switch has been turned off while the vehicle is traveling is input to each control system, and each control system executes control when the ignition is off while the vehicle is traveling. However, due to a difference between the timing at which the power supply relay provided in the master control system is turned off and the timing at which the power supply relay provided in the slave control system is turned off, one of the master control system and the slave control system may shift to control when the ignition is off while the vehicle is traveling before the other control system. As a result, in the control system that shifts to control when the ignition is off while the vehicle is traveling first, the current command value calculated by the control unit of that control system is current-limited.

[0006] For example, when the master control system shifts to the control when the ignition is off while the vehicle is traveling before the slave control system, the current command value calculated by the master control unit is limited, while the current command value calculated by the slave control unit is not limited. When the driver steers during the control when the ignition is off while the vehicle is traveling, the master control unit and the slave control unit calculate a current command value according to the steering. In this case, the current command value calculated by the master control unit is current-limited, while the current command value calculated by the slave control unit is not current-limited, so that a deviation occurs between the current command value calculated by the master control unit and the current command value calculated by the slave control unit. For this reason, the slave control system determines that a deviation occurs in the current command value between the current-limited current command value calculated by the master control unit and the current command value not limited by the slave control unit, and switches from the cooperative drive mode to the independent drive mode. The power supply to the slave control system changes from the control using the current-limited current command value calculated by the master control unit to the control using the current-unlimited current command value calculated by the slave control unit. This may cause the torque output from the motor to fluctuate. [Means for solving the problem]

[0007] A steering control device that solves the above problem includes a plurality of control systems that control the driving of a motor by switching between a plurality of driving states including a cooperative driving mode and an independent driving mode, and the plurality of control systems each have a control unit that calculates a command value for controlling the motor, and when executing the cooperative driving mode, the plurality of control systems each control the driving of the motor based on the command value calculated by the control unit of any one of the plurality of control systems, and when executing the independent driving mode, the plurality of control systems each control the driving of the motor based on the command value calculated by the control unit of its own control system. the plurality of control systems are switched to the cooperative drive mode when command values ​​calculated by the control units of the respective control systems do not deviate from each other, and are switched to the independent drive mode when the command values ​​calculated by the control units of the respective control systems deviate from each other; when a start switch of the vehicle is turned off, the plurality of control systems gradually limit the command values ​​calculated by the control units of their own control systems; and when the start switch is turned off while the vehicle is traveling, the plurality of control systems are switched to the independent drive mode regardless of whether the command values ​​calculated by the control units of the respective control systems deviate from each other or not.

[0008] When the start switch is turned off while the vehicle is running, the timing of transition to the control when the start switch is turned off while the vehicle is running may vary among the multiple control systems. The control system that has first transitioned to the control when the start switch is turned off while the vehicle is running gradually limits the command value calculated by the control unit of the control system, while the control system that has not yet transitioned to the control when the start switch is turned off while the vehicle is running does not limit the command value calculated by the control unit of the control system. In the above configuration, when the start switch is turned off while the vehicle is running, the cooperative drive mode is switched to the independent drive mode regardless of whether the command values ​​calculated by the control units of the respective control systems are deviated from each other. Therefore, each control system can be switched to the independent drive mode before the cooperative drive mode is switched to the independent drive mode after the command values ​​calculated by the control units of the respective control systems deviate from each other. Therefore, even if the command values ​​are calculated by the control units of each control system during the control when the start switch is turned off while the vehicle is running, it is possible to suppress fluctuations in the energization of each control system. As a result, it is possible to suppress fluctuations in the torque output from the motor when the start switch is turned off while the vehicle is running.

[0009] In the above steering control device, it is preferable that each of the multiple control systems determines whether the start switch is turned off while the vehicle is traveling, and that each of the multiple control systems transmits information about the drive mode of its own control system to the other control systems and receives information about the drive mode of the other control systems, and when any one of the multiple control systems switches to the independent drive mode due to the start switch being turned off while the vehicle is traveling, it transmits drive mode information indicating that its own control system has switched to the independent drive mode to the other control systems, and that the other control systems of the multiple control systems receive drive mode information from any one of the multiple control systems and switch to the independent drive mode based on the received drive mode information.

[0010] Since the multiple control systems each determine whether the start switch is turned off while the vehicle is running, the timing of transition to control when the start switch is turned off while the vehicle is running varies among the multiple control systems, and the timing of switching to the independent drive mode may also vary. The other control systems among the multiple control systems switch to the independent drive mode based on drive mode information received from any one of the multiple control systems. This makes it possible to synchronize the timing of switching to the independent drive mode among the multiple control systems, compared to when the other control systems separately determine that the start switch is turned off while the vehicle is running and then switch to the independent drive mode. This makes it possible to stabilize the torque output from the motor.

[0011] In the above-mentioned steering control device, during a period in which the independent drive mode has been switched on as a result of the start switch being turned off while the vehicle is traveling, it is preferable that when the start switch is turned on, the multiple control systems maintain the independent drive mode in a situation in which fluctuations in torque of the motor caused by switching the drive mode are likely to cause the steering wheel to vibrate, and switch to the cooperative drive mode in a situation in which fluctuations in torque of the motor caused by switching the drive mode are unlikely to cause the steering wheel to vibrate.

[0012] In the above configuration, the multiple control systems maintain the independent drive mode even when the start switch is turned on during a period in which control is being performed when the start switch is turned off while the vehicle is traveling, in a situation in which the torque fluctuation of the motor caused by switching the drive mode is highly likely to vibrate the steering wheel. In such a case, the multiple control systems can suppress the torque output from the motor from fluctuating by not switching the drive mode. This can suppress the torque fluctuation from vibrating the steering wheel and affecting the steering feel of the steering wheel by the driver. In addition, the multiple control systems switch to the cooperative drive mode during a period in which control is being performed when the start switch is turned off while the vehicle is traveling, in a situation in which the torque fluctuation of the motor caused by switching the drive mode is low likely to vibrate the steering wheel when the start switch is turned on. In such a case, the multiple control systems can switch the drive mode to the cooperative drive mode while suppressing the torque fluctuation from being output from the motor.

[0013] In the above-mentioned steering control device, it is preferable that when the steering wheel is being steered, the multiple control systems maintain the independent drive mode, as this is a situation in which fluctuations in torque of the motor caused by switching the drive mode are likely to cause the steering wheel to vibrate, and when the steering wheel is not being steered, they switch to the cooperative drive mode, as this is a situation in which fluctuations in torque of the motor caused by switching the drive mode are unlikely to cause the steering wheel to vibrate.

[0014] In the above configuration, when it is determined that the steering wheel is being steered, it is a situation in which it is assumed that the command value is likely to fluctuate when the drive mode is switched, and it is a situation in which it is assumed that the fluctuation in the torque output from the motor is likely to vibrate the steering wheel.When it is determined that the steering wheel is not being steered, it is a situation in which it is assumed that the command value is unlikely to fluctuate when the drive mode is switched, and it is assumed that the fluctuation in the torque output from the motor is unlikely to vibrate the steering wheel.In this way, by switching the drive mode based on whether the steering wheel is being steered, it is possible to preferably switch the drive mode. Effect of the Invention

[0015] According to the steering control device of the present invention, when the ignition switch is turned off while the vehicle is running, it is possible to suppress fluctuations in the torque output from the motor. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing a schematic configuration of a steering device equipped with a steering control device; [Diagram 2] FIG. 2 is a block diagram showing a schematic configuration of a steering control device. [Diagram 3] FIG. 2 is a block diagram showing a schematic configuration of a first microcomputer and a second microcomputer. [Figure 4] 5 is a graph showing changes over time in a first gain and a second gain calculated by a gain calculation unit when an ignition-off signal is input while the vehicle is running. [Diagram 5] 5 is a flowchart showing a procedure for switching the drive mode of a slave control system. [Figure 6] 6 is a sequence chart showing the flow of a drive mode switching process in the master control system when it is determined first in the slave control system that the ignition switch has been turned off during driving. [Figure 7]5 is a flowchart showing a procedure for switching the drive mode of a slave control system. [Figure 8] 5 is a timing chart showing an internal state when switching from the cooperative drive mode to the independent drive mode is executed due to the ignition switch being turned off while driving. [Figure 9] 6 is a timing chart showing, as a comparative example, the internal state in a case where switching from the cooperative drive mode to the independent drive mode is not executed due to the ignition switch being turned off while driving. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment in which the steering control device is applied to an electric power steering device (hereinafter referred to as "EPS") will be described with reference to the drawings. As shown in FIG. 1, the EPS 1 includes a steering mechanism 2 that steers steered wheels 15 based on the operation of a steering wheel 10 by a driver, an assist mechanism 3 that assists the steering operation of the driver, and a steering control device 30 that controls the assist mechanism 3.

[0018] The steering mechanism 2 includes a steering shaft 11 having a steering wheel 10 fixed to one end and a pinion gear formed at the other end, and a rack shaft 12 having a rack gear formed to mesh with the pinion gear. The pinion gear and the rack gear form a rack-and-pinion mechanism 13. The steering shaft 11 has 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. A pinion gear is formed at the lower end of the pinion shaft 11c. The rotational motion of the steering shaft 11 is converted into a reciprocating linear motion in the axial direction of the rack shaft 12 via the rack-and-pinion mechanism 13. The reciprocating linear motion of the rack shaft 12 is transmitted to left and right steered wheels 15 via tie rods 14 connected to both ends of the rack shaft 12, respectively, thereby changing the steering angle of the steered wheels 15 and changing the traveling direction of the vehicle.

[0019] The assist mechanism 3 includes a motor 20 having a rotating shaft 21, and a reduction mechanism 22. 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 speed of the rotation of the motor 20 and transmits the reduced rotational force to the column shaft 11a. That is, the torque of the motor 20 is applied to the steering shaft 11, thereby assisting the steering operation of the driver. 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.

[0020] As shown in FIG. 2, the motor 20 includes a rotor 23 that rotates around a rotating shaft 21, and a stator 24 that is disposed on the outer periphery of the rotor 23. A permanent magnet is fixed to the surface of the rotor 23. The permanent magnets are arranged with different polarities (N pole, S pole) alternately arranged in the circumferential direction of the rotor 23. These permanent magnets form a magnetic field when the motor 20 rotates. The stator 24 has three-phase coils 25, U-phase, V-phase, and W-phase, that are disposed in an annular shape. The coils 25 include a first coil 25a and a second coil 25b. The first coil 25a and the second coil 25b each include a U-phase, a V-phase, and a W-phase coil that are star-connected. A steering control device 30, which is a control unit that controls the driving of the motor 20, is connected to the motor 20.

[0021] As shown in FIG. 1, various sensors provided on the vehicle are connected to the steering control device 30. As various sensors, 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 are provided on the vehicle. The first torque sensor 40a and the second torque sensor 40b are provided on the column shaft 11a. The first rotation angle sensor 41a and the second rotation angle sensor 41b are provided on the motor 20. The first torque sensor 40a detects a first steering torque Th1 applied to the steering shaft 11 in association with the driver's steering operation. The second torque sensor 40b detects a second steering torque Th2 applied to the steering shaft 11 in association with the driver's steering operation. The first rotation angle sensor 41a detects a first rotation angle θ1 of the rotating shaft 21 of the motor 20. The second rotation angle sensor 41b detects a second rotation angle θ2 of the rotating shaft 21 of the motor 20. The vehicle speed sensor 42 detects the vehicle speed SPD, which is the traveling speed of the vehicle. The steering control device 30 controls the motor 20 as a control target and controls the driving of the motor 20. In detail, the steering control device 30 sets a target torque of the motor 20 to be applied to the steering mechanism 2 based on the detection values ​​of various sensors, and controls the current supplied to the motor 20 so that the actual torque becomes the target torque. The steering control device 30 is connected to an ignition switch 43 as a start switch for starting the drive source of the vehicle. A start signal Sig indicating the on / off of the ignition switch 43 is input to the steering control device 30. The ignition switch 43 outputs the start signal Sig in response to the operation of the ignition switch 43 by the driver.

[0022] The configuration of the steering control device 30 will be described. As shown in FIG. 2, the steering control device 30 includes a master side control system 50 having a first electronic control device (hereinafter referred to as "first ECU 51") that controls the current supplied to the first coil 25a of the motor 20, and a slave side control system 60 having a second electronic control device (hereinafter referred to as "second ECU 61") that controls the current supplied to the second coil 25b.

[0023] The master side control system 50 and the slave side control system 60 control the driving of the motor 20 by switching between a cooperative drive mode and an independent drive mode. In the cooperative drive mode, the energization of both the master side control system 50 and the slave side control system 60 is controlled based on a command value calculated by the first ECU 51 of the master side control system 50. On the other hand, in the independent drive mode, the energization of the master side control system 50 is controlled based on a command value calculated by the first ECU 51 of the master side control system 50, and the energization of the slave side control system 60 is controlled based on a command value calculated by the second ECU 61 of the slave side control system 60. In this embodiment, the function of the master side control system 50 and the function of the slave side control system 60 are not interchanged. That is, in the cooperative drive mode, the energization of both the master side control system 50 and the slave side control system 60 is not performed based on a command value calculated by the second ECU 61 of the slave side control system 60.

[0024] The first ECU 51 of the master side control system 50 has a first microcomputer 52 as a control unit, a first drive circuit 53, a first drive relay 54, a first power supply relay 55, a first voltage sensor 56, a first capacitor 57, and a first current sensor 58. The second ECU 61 of the slave side control system 60 has a second microcomputer 62 as a control unit, a second drive circuit 63, a second drive relay 64, a second power supply 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 the same configuration. The first drive relay 54 and the second drive relay 64 have the same configuration. The first power supply relay 55 and the second power supply relay 65 have the same configuration. The first voltage sensor 56 and the second voltage sensor 66 have the same configuration. The first capacitor 57 and the second capacitor 67 have the same configuration. The first current sensor 58 and the second current sensor 68 have the same configuration. The first microcomputer 52 and the second microcomputer 62 have the same configuration except for a command value calculation unit described later. The same configuration means having the same functions and performance within the same design concept.

[0025] A first power supply 70, which is a power source of a current supplied to the first coil 25a, is connected to the first ECU 51. The first drive circuit 53 and the high potential side of the first power supply 70 are connected via a first power supply line L1. The first drive circuit 53 and the low potential side of the first power supply 70 are connected via a first power supply ground line GL1. The first power supply ground line GL1 is connected to a first power supply ground FG1. A first drive relay 54 is provided on the first power supply line L1. The first drive relay 54 switches the first power supply line L1 between a conductive state and a cut-off state by being turned on and off based on a first relay signal Srl1 from the first microcomputer 52. When the first power supply line L1 is in a conductive state, the power of the first power supply 70 is supplied to the first drive circuit 53 via the first power supply line L1. When the first power supply line L1 is in a cut-off state, the power of the first power supply 70 is not supplied to the first drive circuit 53 via the first power supply line L1.

[0026] The first microcomputer 52 and the high potential side of the first power supply 70 are connected via a third power supply line L3. The low potential side of the first microcomputer 52 is connected to a first internal ground SG1. The third power supply line L3 is provided with a first power supply relay 55 that is turned on and off in response to a start signal Sig output from an ignition switch 43 of the vehicle. The first power supply relay 55 switches the third power supply line L3 between a conductive state and a cut-off state in response to the start signal Sig. When a start signal Sig indicating that the ignition switch 43 is on is input to the first power supply relay 55, the first power supply relay 55 is turned on and the third power supply line L3 is in a conductive state. When the third power supply line L3 is in a conductive state, the power of the first power supply 70 is supplied to the first microcomputer 52 via the third power supply line L3. When a start signal Sig indicating that the ignition switch 43 is off is input to the first power supply relay 55, the first power supply relay 55 is turned off and the third power supply line L3 is in a cut-off state. When the third power supply line L3 is in an interrupted state, power from the first power supply 70 is not supplied to the first microcomputer 52 via the third power supply line L3. A first voltage sensor 56 is provided on the third power supply line L3. The first voltage sensor 56 detects the voltage generated on the third power supply line L3 from the first power supply 70 as a first ignition voltage Vg1.

[0027] The first capacitor 57 is provided between a portion of the first power supply line L1 between the first drive relay 54 and the first drive circuit 53, and the first power supply ground line GL1. The first capacitor 57 smoothes the voltage from the first power supply 70.

[0028] The first drive circuit 53 is a three-phase drive circuit corresponding to the three-phase first coil 25a. The first drive circuit 53 is configured as a well-known three-phase drive circuit in which three switching arms, each of which is a pair of switching elements connected in series, are connected in parallel. For example, a MOS-FET (metal-oxide-semiconductor field-effect-transistor) is used as the switching element. The upstream switching element of the pair of switching elements opens and closes between the high potential side of the first power supply 70 and the first coil 25a. The downstream switching element of the pair of switching elements opens and closes between the low potential side of the first power supply 70 and the first coil 25a.

[0029] The first current sensor 58 detects a first actual current value I1 which is a current value of each phase flowing through a 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, as the first motor control signal Sm1, a PWM signal that specifies the on / off of a switching element constituting the first drive circuit 53.

[0030] The second ECU 61 is connected to a second power source 80 which is a power source of a current supplied to the second coil 25b. The second drive circuit 63 and the high potential side of the second power source 80 are connected via a second power line L2. The second drive circuit 63 and the low potential side of the second power source 80 are connected via a second power ground line GL2. The second power ground line GL2 is connected to a second power ground FG2. A second drive relay 64 is provided on the second power source line L2. The second drive relay 64 switches the second power source line L2 between a conductive state and a cut-off state by being turned on and off based on a second relay signal Srl2 from the second microcomputer 62. When the second power source line L2 is in a conductive state, the power of the second power source 80 is supplied to the second drive circuit 63 via the second power line L2. When the second power source line L2 is in a cut-off state, the power of the second power source 80 is not supplied to the second drive circuit 63 via the second power line L2.

[0031] The second microcomputer 62 and the high potential side of the second power supply 80 are connected via a fourth power supply line L4. The low potential side of the second microcomputer 62 is connected to the second internal ground SG2. The fourth power supply line L4 is provided with a second power supply relay 65 that is turned on and off in response to a start signal Sig output from an ignition switch 43 of the vehicle. The second power supply relay 65 switches the fourth power supply line L4 between a conductive state and a cut-off state in response to the start signal Sig. When a start signal Sig indicating that the ignition switch 43 is on is input to the second power supply relay 65, the second power supply relay 65 is turned on and the fourth power supply line L4 is in a conductive state. When the fourth power supply line L4 is in a conductive state, the power of the second power supply 80 is supplied to the second microcomputer 62 via the fourth power supply line L4. When a start signal Sig indicating that the ignition switch 43 is off is input to the first power supply relay 55, the first power supply relay 55 is turned off and the third power supply line L3 is in a cut-off state. When the third power supply line L3 is in an interrupted state, the power of the first power supply 70 is not supplied to the first microcomputer 52 via the third power supply line L3. A second voltage sensor 66 is provided on the fourth power supply line L4. The second voltage sensor 66 detects the voltage from the second power supply 80 generated on the fourth power supply line L4 as a second ignition voltage Vg2.

[0032] The second capacitor 67 is provided between a portion of the second power supply line L2 between the second drive relay 64 and the second drive circuit 63, and the second power supply ground line GL2. The second capacitor 67 smoothes the voltage from the second power supply 80.

[0033] The first power supply ground FG1 and the second power supply ground FG2 are portions whose potential is approximately equal to that of the earth. In this embodiment, the first power supply ground FG1 and the second power supply ground FG2 are the body of the vehicle on which the steering control device 30 is mounted. The first internal ground SG1 and the second internal ground SG2 are portions that serve as references for the voltages on the electric circuits in each ECU. The first internal ground SG1 and the second internal ground SG2 are provided on a board on which the steering control device 30 is mounted.

[0034] In this manner, separate power supplies are connected via separate power supply lines and power supply ground lines to the first ECU 51 and the second ECU 61. As a result, in this embodiment, the control system that controls the drive of the motor 20 is made redundant, and the power supply configuration is also made redundant.

[0035] 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 well-known three-phase drive circuit in which three switching arms, each of which is a pair of switching elements connected in series, are connected in parallel. The upstream switching element of the pair of switching elements opens and closes between the high potential side of the second power source 80 and the second coil 25b. The downstream switching element of the pair of switching elements opens and closes between the low potential side of the second power source 80 and the second coil 25b.

[0036] The second current sensor 68 detects a second actual current value I2 which is a current value of each phase flowing through a 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, as the second motor control signal Sm2, a PWM signal that specifies the on / off of a switching element constituting the second drive circuit 63.

[0037] The functions of the first microcomputer 52 and the second microcomputer 62 will be described. As shown in Fig. 3, the first microcomputer 52 has a first command value calculation unit 90, a first current feedback control unit 91, a first ignition determination unit 92, a first status holding unit 93, and a first transmission / reception unit 94. The second microcomputer 62 has a second command value calculation unit 100, a second current feedback control unit 101, a second ignition determination unit 102, a second status holding unit 103, and a second transmission / reception 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 status holding unit 93 and the second status holding unit 103 have the same configuration. The first transmission / reception unit 94 and the second transmission / reception unit 104 have the same configuration. The first command value calculation unit 90 and the second command value calculation unit 100 have different configurations in that the second command value calculation unit 100 has a command value deviation determination unit 109 described below, while the first command value calculation unit 90 does not have the command value deviation determination unit 109.

[0038] 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 a signal generated by a first ignition determination unit 92. The first command value calculation unit 90 calculates a first final current command value I1*, which is a target value of the first actual current value I1, based on the first steering torque Th1, the vehicle speed SPD, and the signal generated by the first ignition determination unit 92.

[0039] 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 executes current feedback control based on the deviation between the first final current command value I1* and the first actual current value I1 so as to make the first actual current value I1 follow the first final current command value I1*, thereby generating a first motor control signal Sm1.

[0040] 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 ignition switch 43 of the vehicle based on the first ignition voltage Vg1 and the vehicle speed SPD. Specifically, when the first ignition voltage Vg1 exceeds a voltage threshold V0, the first ignition determination unit 92 determines that the ignition switch 43 is turned on, and generates a first ignition-on signal Son1. The voltage threshold V0 is set to the minimum value of the first ignition voltage Vg1 supplied from the first power source 70 via the third power source line L3 shown in FIG. 2 when the ignition switch 43 is on. When the state in which the first ignition voltage Vg1 does not exceed the voltage threshold V0 continues for a predetermined time tg, the first ignition determination unit 92 determines that the ignition switch 43 has been turned off, and generates the first ignition-off signal Soff1. Furthermore, the first ignition determination unit 92 generates the first running ignition-off signal Soff1a when the vehicle is running among the states in which the first ignition-off signal Soff1 is generated. That is, when the state in which the vehicle speed SPD exceeds the vehicle speed threshold SPD0 continues for a predetermined time tg and the state in which the first ignition voltage Vg1 does not exceed the voltage threshold V0 continues 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 running, and generates the first running ignition-off signal Soff1a. The vehicle speed threshold SPD0 is set to a vehicle speed SPD at which it can be said that the vehicle is running.

[0041] The first status holding unit 93 holds the drive mode of the master-side control system 50. That is, the first status holding unit 93 holds drive mode information that the master-side control system 50 is controlling the drive of the motor 20 in the cooperative drive mode, or drive mode information that the master-side control system 50 is controlling the drive of the motor 20 in the independent drive mode. The first status holding unit 93 grasps the drive mode of the master-side control system 50 based on, for example, a signal generated by the first ignition determination unit 92 or information received from the first transmission / reception unit 94.

[0042] The first transmitting / receiving unit 94 transmits and receives information to and from a second transmitting / receiving unit 104 of the second microcomputer 62, which will be 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 a signal generated by the second ignition determination unit 102. The second command value calculation unit 100 calculates a second final current command value I2*, which is a 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.

[0043] 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 executes current feedback control based on the deviation between the second final current command value I2* and the second actual current value I2 so that the second actual current value I2 follows the second final current command value I2*, thereby generating a second motor control signal Sm2.

[0044] 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 of determining the state of the vehicle's ignition switch 43 in the second ignition determination unit 102 is the same as the determination method in the first ignition determination unit 92. As a result, the second ignition determination unit 102 generates a second ignition-on signal Son2, a second ignition-off signal Soff2, and a second running ignition-off signal Soff2a.

[0045] The second status storage unit 103 stores the drive mode of the slave-side control system 60. That is, the second status storage unit 103 stores drive mode information that the slave-side control system 60 is controlling the drive of the motor 20 in the cooperative drive mode, or drive mode information that the slave-side control system 60 is controlling the drive of the motor 20 in the independent drive mode.

[0046] The second transmitting / receiving unit 104 transmits and receives information to and from the first transmitting / receiving unit 94 of the first microcomputer 52 . The functions of the first command value calculation section 90 and the second command value calculation section 100 will be described.

[0047] As shown in Fig. 3, the first command value calculation unit 90 has a first basic command value calculation unit 95, a first gain output unit 96, a multiplier 97, and a first guard processing unit 98. The second command value calculation unit 100 has a second basic command value calculation unit 105, a second gain output unit 106, a multiplier 107, a second guard processing unit 108, and a command value deviation 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 guard processing unit 98 and the second guard processing unit 108 have the same configuration.

[0048] 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 a current command value on the q-axis in the d / q coordinate system, based on the vehicle speed SPD and the first steering torque Th1. The first basic command value calculation unit 95 calculates a first basic current command value Iq1* that has a larger absolute value as the absolute value of the first steering torque Th1 is larger and as the vehicle speed SPD is smaller. The first basic command value calculation unit 95 sets the current command value on the d-axis in the d / q coordinate system to "0".

[0049] The first gain output unit 96 receives a signal generated by the first ignition determination unit 92. The first gain output unit 96 outputs a first gain G1 in the range of 0 to 1 based on the signal generated by the first ignition determination unit 92. When the first ignition-on signal Son1 or the 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 the first running 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 as control when the running ignition is off.

[0050] FIG. 4 shows a time change of the first gain G1 output from the first gain output unit 96 when the first running ignition-off signal Soff1a is input from the first ignition determination unit 92. The time "0" in FIG. 4 indicates the time when the assistance continuation period D1 during which the steering operation of the driver should be assisted has elapsed since the first running ignition-off signal Soff1a is input from the first ignition determination unit 92 to the first gain output unit 96. The assistance continuation period D1 is a predetermined period during which the steering operation of the driver can be assisted because there is a high possibility that the driver will still steer the vehicle immediately after the ignition switch 43 is turned off. As shown in FIG. 4, the first gain output unit 96 outputs the first gain G1 with a smaller absolute value as the time passes after the assistance continuation period D1. That is, the first gain output unit 96 gradually decreases the absolute value of the first gain G1 after the assistance continuation period D1 has elapsed. The absolute value of the first gain G1 exponentially decreases after the auxiliary continuation period D1 has elapsed. When a predetermined time has elapsed after the auxiliary continuation period D1 has elapsed, the first gain output section 96 outputs the first gain G1 as “0”.

[0051] The multiplier 97 receives the first basic current command value Iq1* calculated by the first basic command value calculation unit 95 and the first gain G1 output by the first gain output unit 96. The multiplier 97 calculates a first adjusted current command value Iq1a*, which is a multiplication value obtained by multiplying the first basic current command value Iq1* and the first gain G1. When the first ignition-on signal Son1 or the first ignition-off signal Soff1 is generated in the first ignition determination unit 92, the first basic current command value Iq1* and the first adjusted current command value Iq1a* are equal to each other. On the other hand, when the first running ignition-off signal Soff1a is generated in the first ignition determination unit 92, 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 running ignition-off signal Soff1a is generated in the first ignition determination unit 92, the absolute value of the first adjusted current command value Iq1a* is gradually limited.

[0052] The first guard processing unit 98 receives the first adjusted current command value Iq1a* calculated by the multiplier 97 and a signal generated by the first ignition determination unit 92. The first guard processing unit 98 applies various guard processes to the first adjusted current command value Iq1a* to calculate a first final current command value I1* that limits the first adjusted current command value Iq1a* to a first current limit value Ilim1. As various guard processes, for example, control to limit the first adjusted current command value Iq1a* when the ignition switch 43 is turned off, and control to limit the current command value of the first adjusted current command value Iq1a* to protect the master side control system 50 from overheating are executed. The first current limit value Ilim1 is set according to various guard processes, and is set to a minimum value at each time. As an example, when the first ignition-off signal Soff1 is input by the first ignition determination unit 92, the first guard processing unit 98 sets the first current limit value Ilim1 to approximately zero after a period during which the driver's steering operation should be assisted has elapsed since the first ignition-off signal Soff1 was input. The period during which the steering operation should be assisted in this case is a predetermined period during which the driver's steering operation can be assisted because there is still a high possibility that the driver will steer the vehicle immediately after the ignition switch 43 is turned off, and is a period set longer than the assistance continuation period D1. The absolute value of the first current limit value Ilim1 is set to gradually decrease after the period during which the steering operation should be assisted has elapsed.

[0053] The first transmitter / receiver 94 acquires the first adjusted current command value Iq1a* calculated by the multiplier 97, the first current limit value Ilim1 used in the first guard processing unit 98, and information on the drive mode of the master-side control system 50 held by the first status holding unit 93. The first transmitter / receiver 94 transmits the first adjusted current command value Iq1a*, the first current limit value Ilim1, and information on the drive mode of the master-side control system 50 to the second transmitter / receiver 104 of the slave-side control system 60 at a predetermined control period.

[0054] The second basic command value calculation unit 105 receives the vehicle speed SPD and the second steering torque Th2 as inputs. The second basic command value calculation unit 105 calculates a second basic current command value Iq2*, which is a current command value on the q-axis in the d / q coordinate system, based on the vehicle speed SPD and the second steering torque Th2. The second basic command value calculation unit 105 calculates a second basic current command value Iq2* whose absolute value becomes larger as the absolute value of the second steering torque Th2 becomes larger and as the vehicle speed SPD becomes smaller. The second basic command value calculation unit 105 sets the current command value on the d-axis in the d / q coordinate system to "0".

[0055] The second gain output unit 106 receives a signal generated by the second ignition determination unit 102. 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 running 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 as control when the running ignition is off. As shown in FIG. 4, the second gain output unit 106 outputs the second gain G2 with a smaller absolute value as the time elapses after the assistance continuation period D1 has elapsed. That is, the second gain output unit 106 gradually reduces the absolute value of the second gain G2 after the assistance continuation period D1 has elapsed. When a predetermined time has elapsed since the auxiliary continuation period D1 has elapsed, the second gain output section 106 outputs the second gain G2 as "0."

[0056] The multiplier 107 receives the second basic current command value Iq2* calculated by the second basic command value calculation unit 105 and the second gain G2 output by the second gain output unit 106. The multiplier 107 calculates a second adjusted current command value Iq2a*, which is a multiplication value obtained by multiplying the second basic current command value Iq2* and the second gain G2. When the second ignition-on signal Son2 or the second ignition-off signal Soff2 is generated in the second ignition determination unit 102, the second basic current command value Iq2* and the second adjusted current command value Iq2a* are equal to each other. On the other hand, when the second running ignition-off signal Soff2a is generated in the second ignition determination unit 102, 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 running ignition-off signal Soff2a is generated in the second ignition determination unit 102, the absolute value of the second adjusted current command value Iq2a* is gradually limited.

[0057] The command value deviation determination unit 109 receives the second adjusted current command value Iq2a* calculated by the multiplier 107, the first adjusted current command value Iq1a* received by the second transceiver 104 from the first transceiver 94, the drive mode of the master side control system 50, and the second steering torque Th2 detected by the second torque sensor 40b. The command value deviation determination unit 109 determines whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* deviate from each other based on whether the command value deviation ΔI* between the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* exceeds a deviation determination threshold ΔI0. The deviation judgment 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 be the same, and is set to a value such that the command value deviation ΔI* does not exceed the deviation judgment threshold ΔI0 if the master side control system 50 and the slave side control system 60 are normal.

[0058] The command value deviation determination unit 109 executes the cooperative drive mode when the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* do not deviate from each other, that is, when no abnormality occurs in which the adjusted current command values ​​deviate between the master side control system 50 and the slave side control system 60. When executing the cooperative drive mode, the command value deviation determination unit 109 outputs the first adjusted current command value Iq1a* to the second guard processing unit 108. Furthermore, when executing the cooperative drive mode, the command value deviation determination unit 109 outputs a signal indicating that to the second status holding unit 103.

[0059] The command value deviation determination unit 109 executes the independent drive mode when the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* deviate from each other, that is, when an abnormality occurs in which the adjusted current command values ​​deviate between the master side control system 50 and the slave side control system 60. When executing the independent drive mode, the command value deviation determination unit 109 outputs the second adjusted current command value Iq2a* to the second guard processing unit 108. When executing the independent drive mode, the command value deviation determination unit 109 outputs a signal indicating that to the second status holding unit 103. The command value deviation determination unit 109 changes the adjusted current command value output to the second guard processing unit 108 based on the determination result of the deviation of the adjusted current command value, thereby switching the drive mode of the slave side control system 60. In addition, the command value deviation judgment unit 109 does not judge whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* deviate from each other during the period in which the independent drive mode is executed as control when the ignition is off while driving.

[0060] The second guard processing unit 108 receives the first adjusted current command value Iq1a* or the second adjusted current command value Iq2a* output from the command value deviation determination unit 109, and a signal generated by the second ignition determination unit 102. The second guard processing unit 108 applies various guard processes to the first adjusted current command value Iq1a* or the second adjusted current command value Iq2a* to calculate 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 the second current limit value Ilim2. As various guard processes, for example, control to limit the second adjusted current command value Iq2a* when the ignition switch 43 is turned off, and control to limit the current command value of the second adjusted current command value Iq2a* to protect the slave side control system 60 from overheating are executed. The second current limit value Ilim2 is set according to various guard processes, and a minimum value is set at each time. As an example, when the second ignition-off signal Soff2 is input by the second ignition determination unit 102, the second guard processing unit 108 sets the second current limit value Ilim2 to approximately zero after a period during which the driver's steering operation should be assisted has elapsed since the second ignition-off signal Soff2 was input. The period during which the steering operation should be assisted in this case is a predetermined period during which the driver's steering operation can be assisted because there is still a high possibility that the driver will steer the vehicle immediately after the ignition switch 43 is turned off, and is a period set longer than the assistance continuation period D1. The absolute value of the second current limit value Ilim2 is set to gradually decrease after the period during which the steering operation should be assisted has elapsed.

[0061] The command value deviation determination unit 109 receives a signal generated by the second ignition determination unit 102. When the second traveling ignition off signal Soff2a is received from the second ignition determination unit 102, the command value deviation determination unit 109 switches the drive mode of the slave-side control system 60 from the cooperative drive mode to the independent drive mode, regardless of whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* deviate from each other. That is, the command value deviation determination unit 109 outputs the second adjusted current command value Iq2a* to the second guard processing unit 108 in order to switch the drive mode of the slave-side control system 60 from the cooperative drive mode to the independent drive mode.

[0062] The drive mode switching process of the slave side control system 60 will be described with reference to Fig. 5. It is assumed that the cooperative drive mode is being executed in the slave side control system 60. The slave side control system 60 repeatedly executes the following drive mode switching process. For the sake of simplicity, the description of the determination of deviation of the adjusted current command value by the command value deviation determination unit 109 is omitted.

[0063] 5, when the cooperative drive mode is being executed (step S1), the second ignition determination unit 102 of the slave side control system 60 determines whether or not the ignition switch 43 has been turned off while the vehicle is traveling (step S2). When the vehicle speed SPD continues to exceed the vehicle speed threshold SPD0 for a predetermined time tg and the second ignition voltage Vg2 does not exceed the voltage threshold V0 for the predetermined time tg, the second ignition determination unit 102 determines that the ignition switch 43 has been turned off while the vehicle is traveling, and generates a second traveling ignition-off signal Soff2a.

[0064] If the ignition switch 43 is not turned off during driving (NO in step S2), the command value deviation determination unit 109 of the slave side control system 60 executes the cooperative driving mode (step S3) and ends the driving mode switching process. When executing the cooperative driving mode, the command value deviation determination unit 109 outputs the first adjusted current command value Iq1a* to the second guard processing unit 108 and outputs a signal indicating that the cooperative driving mode is to be executed to the second status holding unit 103.

[0065] When the ignition switch 43 is turned off during driving (YES in step S2), the command value deviation determination unit 109 of the slave side 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 deviation determination unit 109 outputs the second adjusted current command value Iq2a* to the second guard processing unit 108 and outputs a signal indicating that the independent drive mode is to be executed to the second status holding unit 103.

[0066] As shown in FIG. 3, the second transmitter / receiver 104 acquires the second adjusted current command value Iq2a* calculated by the multiplier 107, the second current limit value Ilim2 used in the second guard processing unit 108, and information on the drive mode of the slave-side control system 60 held by the second status holding unit 103. The second transmitter / receiver 104 transmits the second adjusted current command value Iq2a*, the second current limit value Ilim2, and information on the drive mode of the slave-side control system 60 to the first transmitter / receiver 94 of the master-side control system 50 at a predetermined control period. The second transmitter / receiver 104 also receives the first adjusted current command value Iq1a*, the first current limit value Ilim1, and information on the drive mode of the master-side control system 50 at a predetermined control period. The first transmitter / receiver 94 also receives the second adjusted current command value Iq2a*, the second current limit value Ilim2, and information on the drive mode of the slave-side control system 60 at a predetermined control period.

[0067] When the first transceiver 94 receives a signal indicating that the driving mode is the independent driving mode from the second transceiver 104, the master-side control system 50 switches its own driving mode to the independent driving mode. In this embodiment, the master-side control system 50 only needs to output the first adjusted current command value Iq1a* to the first guard processing unit 98 in both the cooperative driving mode and the independent driving mode, and no change is made as a control result. However, by acquiring information of the slave-side control system 60, the master-side control system 50 becomes able to change various controls of the master-side control system 50 based on the information of the slave-side control system 60.

[0068] The drive mode switching process when the slave control system 60 determines that the ignition switch 43 has been turned off during driving before the master control system 50 determines that the ignition switch 43 has been turned off will be described with reference to FIG.

[0069] As shown in the sequence chart of Fig. 6, when it is determined that the ignition switch 43 has been turned off during driving (step S11), the command value deviation determination unit 109 of the slave side control system 60 switches the drive mode of the slave side control system 60 from the cooperative drive mode to the independent drive mode (step S12). On the other hand, the master side control system 50 has not yet determined that the ignition switch 43 has been turned off during driving. The command value deviation determination unit 109 of the slave side control system 60 receives the second ignition-off signal Soff2a during driving generated by the second ignition determination unit 102 and information on the drive mode of the master side control system 50, which indicates that the master side control system 50 is executing the cooperative drive mode and which is received by the second transmission / reception unit 104 from the first transmission / reception unit 94. The command value deviation determination unit 109 ignores the fact that the master side control system 50 has not yet determined that the ignition switch 43 has been turned off while the vehicle is traveling, and gives priority to the fact that its own control system has determined that the ignition switch 43 has been turned off while the vehicle is traveling, and switches the drive mode of the slave side control system 60 from the cooperative drive mode to the independent drive mode.

[0070] The second transceiver 104 of the slave control system 60 transmits information about the drive mode of the slave control system 60 to the first transceiver 94 of the master control system 50 (step S13). The master side control system 50 switches its own drive mode to the independent drive mode based on the drive mode information of the slave side control system 60 received by the first transmission / reception unit 94 from the second transmission / reception unit 104 (step S14). In the master side control system 50, it has not yet been determined that the ignition switch 43 has been turned off during driving. Meanwhile, the master side control system 50 receives drive mode information of the slave side control system 60, which indicates that the slave side control system 60 is executing the independent drive mode, received by the first transmission / reception unit 94 from the second transmission / reception unit 104. The first status holding unit 93 of the master side control system 50 ignores the fact that it has not yet been determined that the ignition switch 43 has been turned off in its own control system, and prioritizes the fact that the slave side control system 60 has been determined that the ignition switch 43 has been turned off during driving, and holds the drive mode information that the master side control system 50 is controlling the drive of the motor 20 in the independent drive mode.

[0071] The drive mode switching process when the master side control system 50 determines that the ignition switch 43 has been turned off while driving before the slave side control system 60 does is similar to the process shown in FIG. 6. When the master side control system 50 determines that the ignition switch 43 has been turned off while driving, the master side control system 50 switches the drive mode of the master side control system 50 from the cooperative drive mode to the independent drive mode. The first transceiver 94 of the master side control system 50 transmits information on the drive mode of the master side control system 50 to the second transceiver 104 of the slave side control system 60. The command value deviation determination unit 109 of the slave side control system 60 ignores the fact that the ignition switch 43 has not yet been turned off in its own control system, and prioritizes the fact that the master side control system 50 has determined that the ignition switch 43 has been turned off while driving, and switches to the independent drive mode in which the second adjusted current command value Iq2a* is output. In addition, the second status holding unit 103 of the slave side control system 60 ignores the fact that its own control system has not yet determined that the ignition switch 43 has been turned off, and prioritizes the fact that the master side control system 50 has determined that the ignition switch 43 has been turned off while driving, and holds the drive mode information that the slave side control system 60 is controlling the drive of the motor 20 in the independent drive mode.

[0072] As shown in Fig. 3, when it is determined that the ignition switch 43 is turned on during a period in which the adjusted current command value is gradually limited based on the input of the second running ignition-off signal Soff2a, that is, during a period in which the independent drive mode is executed due to the ignition switch 43 being turned off during running, the command value deviation determination unit 109 determines whether or not a steering operation is being performed based on whether or not the second steering torque Th2 exceeds a torque threshold value Th0, and switches the drive mode of the slave-side control system 60 based on whether or not a steering operation is being performed. The torque threshold value Th0 is set to a value of the second steering torque Th2 that is sufficient to determine that a steering operation is being performed.

[0073] The drive mode switching process of the slave-side control system 60 will be described with reference to Fig. 7. It is assumed that the slave-side control system 60 is in the independent drive mode due to the ignition switch 43 being turned off while the vehicle is traveling. The slave-side control system 60 repeatedly executes the following drive mode switching process while the independent drive mode is being executed due to the ignition switch 43 being turned off while the vehicle is traveling.

[0074] The second ignition determination unit 102 of the slave side control system 60 determines whether or not the ignition switch 43 is turned on (step S22) during a period in which the independent drive mode is being executed due to the ignition switch 43 being turned off while traveling. When the second ignition voltage Vg2 exceeds the voltage threshold value V0, the second ignition determination unit 102 determines that the ignition switch 43 is turned on, and generates a first ignition on signal Son1.

[0075] If it is determined in step S22 that the ignition switch 43 is not turned on (NO in step S22), the command value deviation determination unit 109 of the slave side control system 60 maintains the independent drive mode and ends the drive mode switching process.

[0076] If it is determined in step S22 that the ignition switch 43 is turned on (YES in step S22), the command value deviation determination unit 109 of the slave side control system 60 determines whether or not a steering operation is being performed (step S23). The command value deviation determination unit 109 determines whether or not a steering operation is being performed based on whether or not the second steering torque Th2 exceeds the torque threshold value Th0.

[0077] When it is determined in step S23 that a steering operation is being performed (NO in step S23), the command value deviation determination unit 109 of the slave side control system 60 maintains the independent drive mode and ends the drive mode switching process. When the second steering torque Th2 exceeds the torque threshold value Th0, the command value deviation determination unit 109 determines that a steering operation is being performed and outputs the second adjusted current command value Iq2a* to the second guard processing unit 108 to maintain the independent drive mode. Note that a case where it is determined that a steering operation is being performed is a situation in which it is assumed that a large fluctuation in the adjusted current command value is likely to occur when the drive mode is switched, and it is a situation in which it is assumed that the fluctuation in torque output from the motor 20 when the drive mode is switched is likely to vibrate the steering wheel 10. If the steering wheel 10 vibrates due to the fluctuation in torque, this may affect the steering feeling of the steering wheel 10 by the driver.

[0078] When it is determined in step S23 that no steering operation has been performed (YES in step S23), the command value deviation determination unit 109 of the slave side control system 60 switches from the independent drive mode to the cooperative drive mode (step S24) and ends the drive mode switching process. When the second steering torque Th2 does not exceed the torque threshold value Th0, the command value deviation determination unit 109 determines that no steering operation has been performed and outputs the first adjusted current command value Iq1a* to the second guard processing unit 108 to switch from the independent drive mode to the cooperative drive mode. Note that the case where it is determined that no steering operation has been performed is a situation in which it is assumed that a large fluctuation in the adjusted current command value is unlikely to occur when the drive mode is switched, and it is a situation in which it is assumed that a fluctuation in the torque output from the motor 20 when the drive mode is switched is unlikely to vibrate the steering wheel 10.

[0079] In this way, if the ignition switch 43 is turned on during driving while the vehicle is in the independent drive mode due to the ignition switch 43 being turned off, the independent drive mode is maintained if steering is performed, and is switched from the independent drive mode to the cooperative drive mode if steering is not performed.

[0080] 3, when switching from the independent drive mode to the cooperative drive mode, the command value deviation determination unit 109 outputs the first adjusted current command value Iq1a* to the second guard processing unit 108 and outputs a signal indicating that the cooperative drive mode is to be executed to the second status holding unit 103. The second transceiver unit 104 of the slave-side control system 60 transmits information on the drive mode of the slave-side control system 60 to the first transceiver unit 94 of the master-side control system 50. The master-side control system 50 switches its own drive mode to the cooperative drive mode based on the information on the drive mode of the slave-side control system 60 received by the first transceiver unit 94 from the second transceiver unit 104.

[0081] The operation of this embodiment will now be described. When the ignition switch 43 is turned off while the vehicle is running, the timing of transition to the control when the ignition is turned off while the vehicle is running may vary between the master side control system 50 and the slave side control system 60. This is due to the difference between the timing at which the first ignition determination unit 92 generates the first ignition-off signal Soff1a while the vehicle is running and the timing at which the second ignition determination unit 102 generates the second ignition-off signal Soff2a while the vehicle is running. As a cause of this, for example, there is a difference between the timing at which the first power supply relay 55 provided in the master side control system 50 is turned off to cut off the third power supply line L3 and the timing at which the second power supply relay 65 provided in the slave side control system 60 is turned off to cut off the fourth power supply line L4. In addition, there is also a difference between the first ignition voltage Vg1 and the second ignition voltage Vg2 due to noise, etc. Due to the above factors, the timing at which the ignition switch 43 is determined to be off differs, and one of the master side control system 50 and the slave side control system 60 may shift to control when the ignition is off while driving before the other control system. Below, a case where the master side control system 50 shifts to control when the ignition is off while driving before the slave side control system 60 will be described with reference to FIG. 8.

[0082] Time T1 in Fig. 8 indicates the time when the driver turns off the ignition switch 43. Time T2 indicates the time when both the master side control system 50 and the slave side control system 60 transition to the control when the ignition is off while driving. Time T3 indicates the time when the auxiliary continuation period D1 elapses and the calculated adjusted current command value starts to be gradually limited. Time T3 also indicates the case where the driver performs a steering operation. Time T4 also indicates the time when the command value deviation judgment unit 109 judges that the command value deviation ΔI* exceeds the deviation judgment threshold ΔI0.

[0083] As shown in FIG. 8, in the period until time T1, the master side control system 50 and the slave side control system 60 execute the cooperative drive mode. The first ignition voltage Vg1 and the second ignition voltage Vg2 are in a state of exceeding the voltage threshold value V0. The first current limit value Ilim1 and the second current limit value Ilim2 are set to, for example, maximum values. The first gain G1 and the second gain G2 are "1". The first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* are outputted as the same as the first basic current command value Iq1* and the second basic current command value Iq2*. Here, in order to simplify the explanation, it is assumed that the driver does not perform a steering operation, that is, 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". Moreover, the first final current command value I1* and the second final current command value I2* are both 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 values ​​calculated based on the first adjusted current command value Iq1a*.

[0084] 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 master side control system 50 does not exceed the voltage threshold V0 before the second ignition voltage Vg2 of the slave side control system 60. At this time, it is assumed that the vehicle speed SPD exceeds the vehicle speed threshold SPD0. The first ignition determination unit 92 of the master side control system 50 determines that the ignition switch 43 has been turned off during driving when the vehicle speed SPD exceeds the vehicle speed threshold SPD0 for a predetermined time tg and the first ignition voltage Vg1 does not exceed the voltage threshold V0 for a predetermined time tg. As a result, the master side control system 50 is switched to the independent drive mode. Moreover, the slave side control system 60 switches its own drive mode to the independent drive mode based on the information on the drive mode of the master side control system 50 received from the first transmission / reception unit 94 of the master side control system 50. Therefore, at time T2, the master side control system 50 and the slave side control system 60 are switched to the independent drive mode. Note that the slave side control system 60 is slower in determining that the ignition switch 43 has been turned off during driving because the slave side control system 60 is slower in determining that the second ignition voltage Vg2 does not exceed the voltage threshold value V0 than the master side control system 50.

[0085] The period from time T2 to time T3 is the assistance duration D1. During the assistance duration D1, since there is still a high possibility that the driver will steer the vehicle, the first gain G1 is maintained at "1". The second gain G2 is also "1".

[0086] At time T3, the driver performs a steering operation, and therefore 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 continuation period D1 has elapsed. After time T3, the absolute value of the first gain G1 is gradually decreased. When a predetermined time has elapsed since the auxiliary continuation period D1 has elapsed, 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. When a predetermined time has elapsed since the auxiliary continuation period D1 has elapsed, the first adjusted current command value Iq1a* becomes "0". On the other hand, the second gain G2 is still maintained at "1". The second adjusted current command value Iq2a* is not yet limited because the second gain G2 is maintained at "1". Furthermore, since the independent drive mode is being 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*.

[0087] At time T4, the command value deviation ΔI* exceeds the deviation determination threshold ΔI0. However, since the master side control system 50 and the slave side control system 60 are switched to the independent drive mode at time T2, the drive mode is not switched at time T4. As an example, after time T4, a predetermined time has passed since the auxiliary continuation period D1 has passed. In this case, after time T4, the absolute value of the second gain G2 is gradually reduced, 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. In addition, after time T4, the absolute values ​​of the first current limit value Ilim1 and the second current limit value Ilim2 are gradually reduced and set to minimum values.

[0088] In this way, when it is determined that the ignition switch 43 has been turned off during driving, the cooperative drive mode is switched to the independent drive mode regardless of whether the adjusted current command values ​​calculated by the microcomputers of the master side control system 50 and the slave side control system 60 deviate from each other. That is, the master side control system 50 and the slave side control system 60 can be switched to the independent drive mode before the cooperative drive mode is switched to the independent drive mode after the adjusted current command values ​​calculated by the microcomputers of the master side control system 50 and the slave side control system 60 deviate from each other. This makes it possible to suppress the current supply to each control system from fluctuating between control using a limited command value and control using an unlimited command value, even if a command value corresponding to the steering by the driver is calculated by the control unit of each control system during control when the ignition is off.

[0089] On the other hand, as shown in FIG. 9, a comparative example will be described in which the cooperative drive mode is not switched to the independent drive mode even when it is determined that the ignition switch 43 has been turned off during driving.

[0090] The time up to time T1 is the same as in this embodiment. Time T1 is also the same as in this embodiment. At time T2, the first ignition determination unit 92 of the master side control system 50 detects that the ignition switch 43 has been turned off during driving when the vehicle speed SPD exceeds the vehicle speed threshold SPD0 for a predetermined time tg and the first ignition voltage Vg1 does not exceed the voltage threshold V0 for a predetermined time tg. However, in the case of the comparative example, the master side control system 50 is not switched to the independent drive mode at time T2. Furthermore, the slave side control system 60 is not switched to the independent drive mode at time T2. The period from time T2 to time T3 is the same as in this embodiment, except that the master side control system 50 and the slave side control system 60 are maintained in the cooperative drive mode. At time T3, the driver performs a steering operation, so the absolute values ​​of the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* become greater than "0". The first adjusted current command value Iq1a* is gradually limited as the first gain G1 gradually decreases. On the other hand, the second adjusted current command value Iq2a* is not yet limited because the second gain G2 is still maintained at "1". Therefore, at time T4, the command value deviation ΔI* exceeds the deviation judgment threshold ΔI0. Then, the command value deviation judgment unit 109 switches the master side control system 50 and the slave side control system 60 to the independent drive mode based on the command value deviation ΔI* exceeding the deviation judgment threshold ΔI0. In this regard, the current supply to the master side control system 50 remains unchanged as it is controlled using the current-limited first adjusted current command value Iq1a* calculated by the master side control system 50 before and after switching to the independent drive mode. That is, the adjusted current command value input to the first guard processing unit 98 does not change from the first adjusted current command value Iq1a* before and after switching to the independent drive mode. On the other hand, the current supply to the slave side control system 60 changes before and after switching to the independent drive mode from control using the first adjusted current command value Iq1a* that is current-limited and calculated by the master side control system 50 to control using the second adjusted current command value Iq2a* that is current-limited and calculated by the slave side control system 60.That is, the adjusted current command value input to the second guard processing unit 108 changes from the first adjusted current command value Iq1a* to the second adjusted current command value Iq2a* before and after switching to the independent drive mode. This causes a change in the second motor control signal Sm2, which may cause the torque output from the motor 20 to fluctuate.

[0091] The effects of this embodiment will be described. (1) When the ignition switch 43 is turned off while the vehicle is running, the cooperative drive mode is switched to the independent drive mode regardless of whether the adjusted current command values ​​calculated by the microcomputers of the control systems deviate from each other. This makes it possible to suppress fluctuations in the torque output from the motor 20 when the ignition switch 43 is turned off while the vehicle is running.

[0092] (2) The master side control system 50 and the slave side control system 60 each determine whether the ignition switch 43 is turned off while the vehicle is traveling, and therefore the timing of transition to the control when the ignition is turned off while the vehicle is traveling may vary between the master side control system 50 and the slave side control system 60. This may cause the timing of switching from the cooperative drive mode to the independent drive mode to vary between the master side control system 50 and the slave side control system 60. The master side control system 50 switches from the cooperative drive mode to the independent drive mode based on the drive mode information received from the slave side control system 60. Also, the slave side control system 60 switches from the cooperative drive mode to the independent drive mode based on the drive mode information received from the master side control system 50. This makes it possible to synchronize the timing of switching to the independent drive mode in each control system, compared to a case where each control system separately determines that the ignition switch 43 is turned off while the vehicle is traveling and then separately switches to the independent drive mode. This makes it possible to stabilize the torque output from the motor 20.

[0093] (3) Even if the ignition switch 43 is turned on during the period when the control when the ignition is off during driving is executed, the master side control system 50 and the slave side control system 60 maintain the independent drive mode in a situation where the torque fluctuation of the motor 20 caused by switching the drive mode is highly likely to vibrate the steering wheel 10. In such a case, the master side control system 50 and the slave side control system 60 can suppress the torque output from the motor 20 from fluctuating by not switching the drive mode. This can suppress the torque fluctuation from vibrating the steering wheel 10 and affecting the steering feeling of the steering wheel 10 by the driver. In addition, the master side control system 50 and the slave side control system 60 switch to the cooperative drive mode during the period when the control when the ignition is off during driving is executed in a situation where the torque fluctuation of the motor 20 caused by switching the drive mode is unlikely to vibrate the steering wheel 10 when the ignition switch 43 is turned on. In such a case, the master control system 50 and the slave control system 60 can switch the drive mode to the cooperative drive mode while suppressing fluctuations in the torque output from the motor 20.

[0094] (4) A case where it is determined that the steering wheel 10 is being steered is a situation where it is assumed that a variation in the adjusted current command value is likely to occur when the drive mode is switched, and it is likely that a variation in the torque output from the motor 20 will cause the steering wheel 10 to vibrate. A case where it is determined that the steering wheel 10 is not being steered is a situation where it is assumed that a variation in the adjusted current command value is unlikely to occur when the drive mode is switched, and it is likely that a variation in the torque output from the motor 20 will cause the steering wheel 10 to vibrate. In this way, by switching the drive mode based on whether the steering wheel 10 is being steered, it is possible to suitably switch the drive mode.

[0095] The above embodiment may be modified as follows. In addition, the following other embodiments may be combined with each other to the extent that there is no technical contradiction. The functions of the master-side control system 50 and the slave-side control system 60 may be switched. That is, when the first adjusted current command value Iq1a* of the master-side control system 50 is abnormal, the slave-side control system 60 may function as the master-side control system, and the master-side control system 50 may function as the slave-side control system. In this case, in the cooperative drive mode, energization of both the master-side control system 50 and the slave-side control system 60 may be performed based on the current command value calculated by the slave-side control system 60.

[0096] In this embodiment, the command value deviation judgment unit 109 is provided only on the slave side control system 60 side, but a command value deviation judgment unit may be provided not only on the slave side control system 60 but also on the master side control system 50. Each control system may switch the drive mode of its own control system based on the judgment result of the command value deviation judgment unit of its own control system. In this case, the drive mode of its own control system may not be transmitted to the other control systems.

[0097] The method of determining the state of the ignition switch 43 by the first ignition determination unit 92 and the second ignition determination unit 102 can be changed as appropriate. For example, the first ignition determination unit 92 may use a determination condition of whether communication with other devices has been interrupted, instead of a determination condition of whether the first ignition voltage Vg1 exceeds the voltage threshold V0. Also, the first ignition determination unit 92 determines the state of the ignition switch 43 when each determination condition is satisfied or not satisfied for a predetermined time tg, but may immediately determine the state of the ignition switch 43 when each determination condition is satisfied or not satisfied.

[0098] The master side control system 50 and the slave side control system 60 may be switched not only to the cooperative drive mode and the independent drive mode, but also to another drive mode in which, for example, if an abnormality occurs in either the master side control system 50 or the slave side control system 60, the motor 20 is driven only by the remaining normal system.

[0099] Although the first microcomputer 52 obtains the voltage from the first power supply 70 via the first voltage sensor 56 as the first ignition voltage Vg1, it may be arranged to obtain the voltage from the first power supply 70 directly. Furthermore, the second microcomputer 62 obtains the voltage from the second power supply 80 via the second voltage sensor 66 as the second ignition voltage Vg2, it may be arranged to obtain the voltage from the second power supply 80 directly.

[0100] The first gain output unit 96 exponentially reduces the absolute value of the first gain G1 after the auxiliary duration period D1 has elapsed, but the manner in which the absolute value of the first gain G1 is gradually reduced can be changed as appropriate. For example, the first gain output unit 96 may reduce the absolute value of the first gain G1 in proportion to the time after the auxiliary duration period D1 has elapsed, or may reduce the absolute value of the first gain G1 in a step-like manner according to the time after the auxiliary duration period D1 has elapsed. That is, the first gain output unit 96 may reduce the absolute value of the first gain G1 gradually compared to the case in which the first gain G1 is suddenly changed from "1" to "0" after the auxiliary duration period D1 has elapsed. In addition, the calculation of the second gain G2 by the second gain output unit 106 can also be changed as appropriate, similar to the first gain output unit 96.

[0101] The first gain output unit 96 gradually reduces the absolute value of the first gain G1 after the assistance duration period D1 has elapsed, but this is not limited to the above. The first gain output unit 96 may gradually reduce the absolute value of the first gain G1 when the first running ignition-off signal Soff1a is input. In other words, the assistance duration period D1 may not be provided. Similarly to the first gain output unit 96, gradually reducing the absolute value of the second gain G2 output by the second gain output unit 106 is not limited to being performed after the assistance duration period D1 has elapsed.

[0102] The first gain output unit 96 gradually decreases the absolute value of the first gain G1 only when the first running ignition-off signal Soff1a is input, but may also do so when the first ignition-off signal Soff1 is input. Similarly to the first gain output unit 96, the absolute value of the second gain G2 output by the second gain output unit 106 may also be gradually decreased when the first ignition-off signal Soff1 is input.

[0103] The power supply path to the master-side control system 50 can be changed as appropriate. Also, the power supply path to the slave-side control system 60 can be changed as appropriate. 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 separate power sources, but they may be a common power source.

[0104] The command value deviation determination unit 109 determines whether the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* deviate from each other, but this is not limiting. The command value deviation determination unit 109 may determine the deviation based on other command values ​​such as a voltage command value.

[0105] When it is determined that the ignition switch 43 is turned on during the period in which the independent drive mode is being executed due to the ignition switch 43 being turned off while the vehicle is traveling, the command value deviation determination unit 109 determines whether or not to switch the drive mode of the slave-side control system 60 based on the second steering torque Th2, but this is not limited thereto. For example, the command value deviation determination unit 109 may determine whether or not to switch the drive mode of the slave-side control system 60 based on the first steering torque Th1, based on the rotation speed which is the amount of change in the first rotation angle θ1 or the second rotation angle θ2, or based on the command value deviation ΔI*. In other words, the command value deviation determination unit 109 may execute the determination based on any state quantity as long as it is capable of determining that the deviation between the command value used in the independent drive mode and the command value used in the cooperative drive mode is small.

[0106] For example, the command value deviation determination unit 109 may determine whether or not to switch the drive mode of the slave-side control system 60 based on the deviation between the command value used in the independent drive mode and the command value used in the cooperative drive mode being smaller than a predetermined value. This predetermined value is set to a deviation that can be said to be the same as the adjusted current command value used in the independent drive mode and the adjusted current command value used in the cooperative drive mode. In a situation where the driver is not performing a steering operation, the first steering torque Th1 and the second steering torque Th2 are almost zero, so it is assumed that the command value deviation ΔI* between the first adjusted current command value Iq1a* and the second adjusted current command value Iq2a* will be almost zero.

[0107] The command value deviation determination unit 109 executes the switch to the cooperative drive mode when it is determined that the ignition switch 43 is turned on during the period in which the independent drive mode is being executed due to the ignition switch 43 being turned off while the vehicle is running, on the condition that no steering operation is performed, but this is not limited to the above. For example, the command value deviation determination unit 109 may execute the switch to the cooperative drive mode on the condition that the deviation between the command value used in the independent drive mode, i.e., the command value of the slave side control system 60, and the command value used in the cooperative drive mode, i.e., the command value of the master side control system 50, is smaller than a predetermined value. The predetermined value is set to a value range experimentally determined to have a small effect on the steering wheel 10.

[0108] The motor 20 may have a single mechanical configuration. For example, the coil 25 may have only one of the first coil 25a and the second coil 25b, and both the master control system 50 and the slave control system 60 may control the current supplied to the same coil.

[0109] In this embodiment, the EPS 1 to which the steering control device 30 is applied is configured as an EPS that applies the torque of the motor 20 to the steering shaft 11 via the reduction gear mechanism 22, but the present invention is not limited to this, and may be configured as an EPS that applies the torque of the motor 20 to the rack shaft 12 via a ball screw nut, for example. Also, the steering control device 30 is not limited to being applied to an EPS, and may be applied to a steer-by-wire device with a link that can connect and disconnect the power transmission between the steering side and the turning side by a clutch, or a linkless steer-by-wire device in which the power transmission between the steering side and the turning side is separated. [Explanation of symbols]

[0110] 1...EPS 10. Steering wheel 20…Motor 30...Steering control device 43…Ignition switch 50…Master control system 60…Slave control system 51,61…1st, 2nd ECU 52,62…1st and 2nd microcomputers 90, 100...1st and 2nd command value calculation units 109...Command value deviation judgment unit Iq1a*, Iq2a*: 1st and 2nd adjusted current command values

Claims

1. A plurality of control systems are provided for controlling the driving of the motors by switching between a plurality of driving states including a cooperative driving mode and an independent driving mode, The plurality of control systems each have a control unit that calculates a command value for controlling the motor, When the cooperative drive mode is executed, each of the plurality of control systems controls driving of the motor based on a command value calculated by the control unit of any one of the plurality of control systems; When the independent drive mode is executed, each of the plurality of control systems controls the drive of the motor based on a command value calculated by the control unit of the respective control system; the plurality of control systems are switched to the cooperative drive mode when the command values ​​calculated by the control units of the respective control systems do not deviate from each other, and are switched to the independent drive mode when the command values ​​calculated by the control units of the respective control systems deviate from each other; The plurality of control systems are configured to determine that the start switch has been turned off in each of the plurality of control systems when a start switch of the vehicle is turned off, and the command value calculated by the control unit of each of the plurality of control systems is gradually limited from the timing at which it is determined that the start switch has been turned off in each of the plurality of control systems, A steering control device that switches to the independent drive mode when at least one of the multiple control systems determines that the start switch has been turned off while the vehicle is traveling, regardless of whether the command values ​​calculated by the control units of each control system deviate from each other, even if the control system itself has not yet determined that the start switch has been turned off.

2. The plurality of control systems transmit information on a drive mode of the respective control systems to the other control systems and receive information on the drive modes of the other control systems, When one of the plurality of control systems switches to the independent drive mode due to the start switch being turned off during driving, the control system transmits drive mode information indicating that the control system has switched to the independent drive mode to the other control systems, 2. The steering control device according to claim 1, wherein the other control systems among the plurality of control systems receive drive mode information from any one of the plurality of control systems, and switch to the independent drive mode based on the received drive mode information even when it has not yet been determined in the other control system that the start switch has been turned off.

3. The plurality of control systems include When the start switch is turned on during a period in which the vehicle is switched to the independent drive mode due to the start switch being turned off while the vehicle is running, In a situation where a torque fluctuation of the motor caused by switching the drive mode is likely to cause a vibration of the steering wheel, the independent drive mode is maintained, 3. The steering control device according to claim 1, wherein the driving mode is switched to the cooperative driving mode in a situation where a fluctuation in torque of the motor caused by switching the driving mode is unlikely to cause vibration of the steering wheel.

4. The plurality of control systems include If the steering wheel is being steered, the independent drive mode is maintained because it is highly likely that a torque fluctuation of the motor caused by switching the drive mode will cause the steering wheel to vibrate.

4. The steering control device according to claim 3, wherein when the steering wheel is not being steered, the steering control device switches to the cooperative drive mode because it is considered that fluctuations in torque of the motor caused by switching drive modes are unlikely to cause vibrations in the steering wheel.

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