Steering control device

Abstract

A steering control device configured to control a steering system, the steering system including a turning mechanism, the turning mechanism including a motor configured to generate a motor torque, the motor torque serving as a motive power for moving a turning shaft (14) to turn a turning wheel (16) of a vehicle. The steering control device includes a control unit configured to control a target control value, the target control value serving as a target of a control value for controlling the motor torque of the motor. The control unit is configured to perform compensation on the target control value; acquire an offset value; and change the target control value such that the acquired offset value gradually decreases.

Description

TECHNICAL FIELD

[0001] The present application relates to a steering control device. BACKGROUND

[0002] A steering system for a vehicle includes a steering mechanism that enables a steering wheel to be operated, and a turning mechanism that turns a turning wheel of the vehicle by moving a turning shaft using a motor torque, which is an output of a motor, as a power. Japanese Unexamined Patent Application Publication No. 2019-131072 (JP 2019-131072 A) discloses an example of a steering system having a structure in which a power transmission path between the steering mechanism and the turning mechanism is cut off, that is, a steer-by-wire steering system.

[0003] JP 2019-131072 A discloses detecting a steering angle, which is an angle to which the steering wheel is operated, as a state of the steering mechanism. The detected steering angle is used to calculate a target control value that serves as a target of a control value for controlling an output of the motor provided in the turning mechanism. SUMMARY

[0004] In the foregoing steering system, a plurality of control states in which the target control value of the turning mechanism is controlled can be prepared. The desired function in the steering system can be maintained at the time of switching the control state among the plurality of control states. For example, the control state can be switched to a backup control state for controlling the target control value so that the target control value can be controlled even when any abnormality occurs.

[0005] However, in the foregoing case, a difference in the target control value can occur between before and after the control state is switched. In this case, the turning mechanism can perform an operation that is not expected by the driver. This gives the driver a sense of discomfort.

[0006] Here, the target control value of the turning mechanism is calculated as a control value based on a steering angle detected by the steering mechanism. However, for example, when the steering angle is suddenly changed, a control value that exceeds an output limit of the motor can be calculated as the target control value. In this case, the motor can cause vibration or noise due to the output that exceeds the output limit.

[0007] In a steer-by-wire steering system, even if the steering wheel is turned when the ignition switch is in an off state, the turning wheel is not turned, and when the steering wheel is turned, a positional relationship between the steering wheel and the turning wheel deviates from a predetermined correspondence relationship. In this case, after the ignition switch is switched from the off state to an on state, the turning wheel can be suddenly operated to reach a position corresponding to a steering angle. This gives the driver a sense of discomfort.

[0008] The present application provides a steering control device capable of suppressing discomfort given to a driver.

[0009] The present application also provides a steering control device capable of suppressing generation of vibration or noise in a motor.

[0010] One aspect of the present application relates to a steering control device configured to control a steering system, the steering mechanism including a turning mechanism including a motor configured to generate a motor torque used as a power for moving a turning shaft to turn a turning wheel of a vehicle. The steering control device includes a control unit configured to control a target control value used as a target of a control value for controlling the motor torque of the motor. The control unit is configured to perform compensation on the target control value; acquire an offset value; and change the target control value so that the acquired offset value gradually decreases.

[0011] In this aspect, the control unit can be configured to be capable of switching between a plurality of control states including a first control state in which a first target control value acquired under a predetermined condition is controlled and a second control state in which a second target control value acquired under a condition different from the predetermined condition of the first target control value is controlled; and to perform the compensation so that, after switching the control state, a post-switching target control value controlled in a post-switching control state moves toward a pre-switching target control value controlled in a pre-switching control state. The control unit can be configured to acquire, as the offset value, a difference in the target control value between before and after the control state is switched when the control state is switched, the offset value being an amount by which the target control value moves through the compensation.

[0012] With this configuration, when the control state is switched, the post-switching target control value moves toward the pre-switching target control value so that the difference from the pre-switching target control value is eliminated by the compensation using the offset value. In particular, at the time of switching the control state, the compensation is performed so that the post-switching target control value almost (substantially) matches the pre-switching target control value. Thereafter, since the offset value gradually decreases, the post-switching target control value approaches the original target control value acquired by calculation in the post-switching control state, and eventually reaches the original target control value. Therefore, even when there is a difference in the target control value between before and after the switching of the control state, it is possible to prevent the difference from being expressed as a movement of the turning mechanism that is not expected by the driver. Thus, it is possible to suppress discomfort given to the driver.

[0013] As described above, by adopting the configuration of switching the control state, a control state prepared for backup is considered to cope with a possible abnormality and to maintain a desired function in the steering system when such an abnormality occurs.

[0014] In this aspect, the first target control value can be calculated using a condition in which a first state variable detected by a first detection device is used; the second target control value can be calculated using a condition in which a second state variable detected by a second detection device is used; and the first detection device and the second detection device can be redundant detection devices that respectively detect independent state variables of the same detection target.

[0015] With this configuration, when an abnormality occurs in the first detection device, it is possible to switch the control state to the second control state as a backup to calculate the target control value based on the detection result from the redundant second detection device. This is to avoid calculating the target control value based on the detection result from the first detection device. In this case, even when there is a difference in the state variable between before and after the control state is switched, it is possible to prevent the target control value after the control state is switched from having a difference from the target control value before the switch. Therefore, even when the control state is switched to the control state for backup due to an abnormality in the first detection device, it is possible to suppress movement of the turning mechanism that is not expected by the driver.

[0016] In this aspect, the control unit can be configured to, when a target control value exceeding the output limit is calculated, perform compensation so that the target control value moves into the output limit of the motor; and the control unit can be configured to, when a target control value exceeding the output limit is calculated, acquire an excess control value as an offset value, the excess control value being a control value corresponding to an excess value exceeding the output limit of the motor, the offset value being an amount by which the target control value is moved by the compensation.

[0017] With this configuration, when a target control value exceeding the output limit of the motor is calculated, the target control value is moved into the output limit of the motor by compensation using the offset value. Thereafter, as the offset value gradually decreases, the target control value approaches the original target control value and eventually reaches the original target control value. Therefore, even when a target control value exceeding the output limit of the motor is calculated, it is possible to make it difficult to cause a situation in which the motor output power is greater than the output limit (i.e., a situation in which it is less likely to cause the motor output power to be greater than the output limit). Therefore, it is possible to suppress generation of vibration or noise in the motor.

[0018] In this aspect, the output limit can be a value associated with the angular velocity of the motor that is acquired in accordance with a relationship with the motor torque of the motor; the target control value can be a value associated with a state variable that can be converted into the angular velocity of the motor; and the control unit can be configured to, when a target control value exceeding the output limit is calculated, acquire an excess control value obtained from a difference between the output limit of the motor and a change amount of the target control value as an offset value.

[0019] With this configuration, it is possible to appropriately make it difficult to cause a situation in which the motor output power is greater than the output limit.

[0020] In this aspect, the control unit can be configured to perform compensation such that, when the vehicle power source is switched from the off state to the on state, the target control value is moved to reduce the motor torque of the motor, and the control unit can be configured to acquire, as the offset value, a control value corresponding to the turning amount of the turning wheel in a first period after the vehicle power source is switched from the off state to the on state when the vehicle power source is switched from the off state to the on state, the offset value being an amount by which the target control value is moved by the compensation.

[0021] With this configuration, when the target control value is calculated in a case where the turning wheel is to be turned (i.e., should be turned) in a first period after the vehicle power source is switched from the off state to the on state, the target control value is moved to reduce the motor torque of the motor by the compensation using the offset value, so that the turning wheel is not suddenly moved. Thereafter, as the offset value gradually decreases, the target control value approaches the original target control value, and eventually reaches the original target control value. Therefore, even when the target control value is calculated in a case where the turning wheel is to be turned (i.e., should be turned) in a first period after the vehicle power source is switched from the off state to the on state, sudden movement of the turning wheel in the first period after the switch can be suppressed. Thus, discomfort given to the driver can be suppressed.

[0022] In this aspect, the steering system can further include a steering shaft configured to cut off a power transmission path between the steering shaft and the turning wheel, the steering shaft being configured to rotate in accordance with an operation of a steering wheel. The target control value can be a target angle calculated as a value of a turning-related angle related to a turning angle of the turning wheel when a positional relationship with a steering angle satisfies a predetermined correspondence relationship, the steering angle being a rotation angle of the steering shaft. The control unit can be configured to acquire, as the offset value, a start movement value that is a difference between a value of the turning-related angle that satisfies the predetermined correspondence relationship acquired on the basis of the steering angle and a value of the turning-related angle acquired on the basis of an actual turning angle in a first period after the vehicle power source is switched from the off state to the on state.

[0023] For example, in a case where the turning system further includes a steering shaft, the steering shaft is configured such that a power transmission path between the steering shaft and the turning wheel is cut off, and the steering shaft is configured to rotate in accordance with an operation of the steering wheel, in a state where the vehicle power source is in the off state and the steering wheel is turned, a positional relationship between the steering angle and the turning angle deviates from a predetermined correspondence relationship. On the other hand, with the aforementioned configuration, even in a state where the positional relationship between the steering angle and the turning angle deviates from the predetermined correspondence relationship, when the vehicle power source is switched from the off state to the on state, it is possible to reduce the possibility that the turning wheel suddenly moves such that the turning angle reaches a position corresponding to the steering angle in a first period after the switching.

[0024] In this aspect, the predetermined correspondence relationship can be a steering angle ratio, the steering angle ratio being a ratio of the turning angle to the steering angle, and the predetermined correspondence relationship can vary based on a running state of the vehicle.

[0025] When a configuration for changing the steering angle ratio is provided as in the aforementioned configuration, it is particularly effective to acquire, as the offset value, a difference between a value of the turning-related angle that satisfies the predetermined correspondence relationship, which is acquired based on the steering angle, and a value of the turning-related angle that is acquired based on the actual turning angle, in a first period after the vehicle power source is switched from the off state to the on state.

[0026] Here, since the offset value is acquired in order to forcibly move the post-switch target control value, it is preferable to eliminate the offset value as soon as possible, but when a reduction value of the offset value is set to be excessively large, eventually, a movement of the turning mechanism that is not expected by the driver occurs.

[0027] Therefore, in this aspect, the control unit can be configured to change the reduction value for reducing the offset value based on at least one of a running state of the vehicle and a turning state of the turning mechanism.

[0028] For example, in a running state where the vehicle runs at a relatively high speed or in a turning state where the turning mechanism is performing a turn, even if the reduction value for reducing the offset value is set to a large value, and thus a movement of the turning mechanism that is not expected by the driver occurs, the driver is less likely to have a sense of discomfort. Therefore, with the aforementioned configuration, by taking into account the running state of the vehicle or the turning state of the turning mechanism, it is possible to eliminate the offset value as soon as possible and effectively while suppressing the sense of discomfort given to the driver.

[0029] In this aspect, when the offset value is present, the control unit can be configured to reduce the offset value by at least a minimum value regardless of the running state of the vehicle and the turning state of the turning mechanism.

[0030] With this configuration, it is possible to prevent the offset value from being continuously left, and it is possible to effectively reduce the offset value.

[0031] With the steering control device according to an aspect of the present application, discomfort given to the driver can be suppressed. With the steering device according to an aspect of the present application, generation of vibration or noise in the motor can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0032] Features, advantages, and technical and industrial significance of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, wherein the same reference numerals in different drawings denote the same element, and wherein:

[0033] Figure 1 is a diagram schematically showing a configuration of a steering system according to the first embodiment;

[0034] Figure 2 is a block diagram showing functions of a steering control device according to the first embodiment;

[0035] Figure 3 is a block diagram showing functions of an offset compensation and calculation unit according to the first embodiment;

[0036] Figure 4 is a block diagram showing functions of an offset value gradual change processing unit according to the first embodiment;

[0037] Figure 5 part (a) in FIG. 8 is a diagram schematically showing a change pattern of a target pinion angle according to the first embodiment, Figure 5 part (b) in FIG. 8 is a diagram schematically showing a change pattern of an offset value according to the first embodiment, and Figure 5 part (c) in FIG. 8 is a diagram schematically showing a change pattern of a state flag FLG according to the first embodiment;

[0038] Figure 6 is a diagram schematically showing a configuration of a steering system according to the second embodiment;

[0039] Figure 7 is a block diagram showing functions of a steering control device according to the second embodiment;

[0040] Figure 8 is a block diagram showing functions of an offset compensation and calculation unit according to the second embodiment;

[0041] Figure 9 is a block diagram showing functions of an offset value gradual change processing unit according to the second embodiment;

[0042] Figure 10 is a block diagram showing functions of an offset value acquisition processing unit according to the second embodiment;

[0043] Figure 11Part (a) in FIG. 6 is a graph schematically showing a case where the output limit of the turning motor according to the second embodiment is changed, Figure 11 Part (b) in FIG. 6 is a graph schematically showing a change pattern of the target pinion angle according to the second embodiment, and Figure 11 Part (c) in FIG. 6 is a graph schematically showing a change pattern of the offset value according to the second embodiment.

[0044] Figure 12 FIG. 7 is a graph schematically showing a configuration of a steering system according to the third embodiment;

[0045] Figure 13 FIG. 8 is a block diagram showing a function of a steering control device according to the third embodiment;

[0046] Figure 14 FIG. 9 is a block diagram showing a function of an offset compensation and calculation unit according to the third embodiment;

[0047] Figure 15 FIG. 10 is a block diagram showing a function of an offset value gradual change processing unit according to the third embodiment; and

[0048] Figure 16 Part (a) in FIG. 6 is a graph schematically showing a case where the output limit of the turning motor according to the second embodiment is changed, Figure 16 Part (b) in FIG. 6 is a graph schematically showing a change pattern of the target pinion angle according to the second embodiment, and Figure 16 Part (c) in FIG. 6 is a graph schematically showing a change pattern of the offset value according to the second embodiment. DETAILED DESCRIPTION

[0049] First Embodiment

[0050] Hereinafter, a first embodiment in which a steering control device is applied to a steer-by-wire steering system will be described with reference to the drawings. As shown in FIG. 1, a steering system 10 of a vehicle is a steer-by-wire steering system. The steering system 10 includes a steering control device 50 that controls an operation of the steering system 10. The steering system 10 includes a steering mechanism SK that is manipulated by a driver via a steering wheel 11 and a turning mechanism TK that turns a turning wheel 16 in accordance with a manipulation of the steering mechanism SK by the driver. The steering system 10 according to the present embodiment has a structure in which a power transmission path between the steering mechanism SK and the turning mechanism TK is generally mechanically cut off. Figure 1

[0051] The steering mechanism SK includes a steering shaft 12 that is connected to the steering wheel 11. The turning mechanism TK includes a turning motor 13 that turns the turning wheel 16 in accordance with a manipulation of the steering mechanism SK by the driver. The steering system 10 according to the present embodiment has a structure in which a power transmission path between the steering mechanism SK and the turning mechanism TK is generally mechanically cut off. Figure 1 ​The left and right turning wheels 16 are connected to both ends of the turning shaft 14 extending in the left-right direction via the tie rods 15, respectively. When the turning shaft 14 moves linearly, the turning angle θw, which is the turning angle of the turning wheels 16, changes.

[0052] The steering mechanism SK includes a reaction force motor 31, a reduction gear mechanism 32, a first rotation angle sensor 331, a second rotation angle sensor 332, and a torque sensor 34 as a configuration for generating a steering reaction force. The steering reaction force is a force acting in a direction opposite to the direction of the operation of the driver on the steering wheel 11. By applying the steering reaction force to the steering wheel 11, the driver can be given a proper sense of response.

[0053] The reaction force motor 31 is a source of the steering reaction force. For example, a three-phase brushless motor is employed as the reaction force motor 31. The reaction force motor 31, to be exact, its rotation shaft, is connected to the steering shaft 12 via the reduction gear mechanism 32. The torque of the reaction force motor 31 is applied to the steering shaft 12 as the steering reaction force.

[0054] The rotation angle sensors 331 and 332 are provided in the reaction force motor 31. The first rotation angle sensor 331 detects the rotation angle θal of the reaction force motor 31. The second rotation angle sensor 332 detects the rotation angle θa2 of the reaction force motor 31. The rotation angle sensors 331 and 332 are redundant rotation angle sensors that detect independent rotation angles with the rotation angle of the same reaction force motor 31 as a detection target. In other words, the rotation angle sensors 331 and 332 detect independent state variables of the same detection target, respectively. The steering angle θs is calculated using the rotation angles θal and θa2 of the reaction force motor 31. The reaction force motor 31 and the steering shaft 12 are cooperatively operated via the reduction gear mechanism 32. Therefore, the rotation angles θal and θa2 of the reaction force motor 31 and the rotation angle of the steering shaft 12, that is, the steering angle θs as the rotation angle of the steering wheel 11, have a correlation. Therefore, the steering angle θs can be calculated based on the rotation angles θal and θa2 of the reaction force motor 31. The first rotation angle sensor 331 is an example of a first detection device and the rotation angle θal detected thereby is an example of a first state variable. The second rotation angle sensor 332 is an example of a second detection device and the rotation angle θa2 detected thereby is an example of a second state variable.

[0055] The torque sensor 34 detects the steering torque Th applied to the steering shaft 12 by the operation of rotating the steering wheel 11. The torque sensor 34 is provided in the steering shaft 12 at a position closer to the steering wheel 11 than the reduction gear mechanism 32.

[0056] The turning mechanism TK includes a turning motor 41, a reduction gear mechanism 42, and a rotation angle sensor 43 as a configuration for generating a turning force that is a power for turning the turning wheel 16. The turning motor 41 is a source of the turning force. For example, a three-phase brushless motor is employed as the turning motor 41. A rotation shaft of the turning motor 41 is connected to a pinion shaft 44 via the reduction gear mechanism 42. Pinion teeth 44a of the pinion shaft 44 are engaged with rack teeth 14b of the turning shaft 14. A torque of the turning motor 41 is applied to the turning shaft 14 as the turning force via the pinion shaft 44. With rotation of the turning motor 41, the turning shaft 14 moves in the left-right direction in the vehicle width direction, that is, Figure 1

[0057] The rotation angle sensor 43 is provided in the turning motor 41. The rotation angle sensor 43 detects a rotation angle Θb of the turning motor 41. The steering system 10 includes a pinion shaft 13. The pinion shaft 13 is provided across the turning shaft 14. Pinion teeth 13a of the pinion shaft 13 are engaged with rack teeth 14a of the turning shaft 14. The reason for providing the pinion shaft 13 is that the turning shaft 14 is supported in a housing, not shown, together with the pinion shaft 44. That is, the turning shaft 14 is supported so as to be movable in the axial direction thereof and pressed against the pinion shafts 13 and 44 by a support mechanism (not shown) provided in the steering system 10. Thus, the turning shaft 14 is supported in the housing. Another support mechanism that supports the turning shaft 14 in the housing without using the pinion shaft 13 can be provided.

[0058] As shown in Figure 1 , a steering control device 50 that controls driving of the motors 31 and 41 is connected to the reaction force motor 31 and the turning motor 41. The steering control device 50 controls driving of the motors 31 and 41 by controlling supply of a current as a control value of the motors 31 and 41 on the basis of detection results from various sensors. Examples of the various sensors include a vehicle speed sensor 501, the torque sensor 34, the rotation angle sensors 331 and 332, and the rotation angle sensor 43. The vehicle speed sensor 501 detects a vehicle speed V that is a running speed of the vehicle.

[0059] The configuration of the steering control device 50 will be described below. The steering control device 50 includes a central processing unit (CPU), not shown, and a memory, and the CPU executes a program stored in the memory at intervals of a predetermined operation cycle. Thus, various processes are executed.

[0060] Some of the processes executed by the steering control device 50 are shown in Figure 2 .The processes shown in Figure 2 are some of the processes implemented by causing the CPU to execute the program stored in the memory for each of the processes implemented.

[0061] The steering control device 50 includes a steering-side control unit 50a that controls electric power supply to the reaction force motor 31. The steering-side control unit 50a includes a steering-side current sensor 55. The steering-side current sensor 55 detects a steering-side actual current value Ia that is acquired from a phase current value of the reaction force motor 31 that flows in a connection line between the steering-side control unit 50a and a phase motor coil of the reaction force motor 31. The steering-side current sensor 55 acquires a voltage drop of a shunt resistor connected to a source of a switching element in an inverter (not shown) that is provided corresponding to the reaction force motor 31 as a current. In Figure 2 In the following description, a phase connection line and a phase current sensor are collectively shown as a single one for convenience of description.

[0062] The steering control device 50 includes a steering-side control unit 50a that controls electric power supply to the reaction force motor 31. The steering-side control unit 50a includes a steering-side current sensor 55. The steering-side current sensor 55 detects a steering-side actual current value Ia that is acquired from a phase current value of the reaction force motor 31 that flows in a connection line between the steering-side control unit 50a and a phase motor coil of the reaction force motor 31. The steering-side current sensor 55 acquires a voltage drop of a shunt resistor connected to a source of a switching element in an inverter (not shown) that is provided corresponding to the reaction force motor 31 as a current. In Figure 2 In the following description, a phase connection line and a phase current sensor are collectively shown as a single one for convenience of description.

[0063] The function of the steering-side control unit 50a will be described below. The steering torque Th, the vehicle speed V, the rotation angles θal and θa2, the steering-side actual current value Ib that will be described later, and the pinion angle θp that will be described later are input to the steering-side control unit 50a. The steering-side control unit 50a controls electric power supply to the reaction force motor 31 based on the steering torque Th, the vehicle speed V, the rotation angles θal and θa2, the steering-side actual current value Ib that will be described later, and the pinion angle θp that will be described later. The pinion angle θp is calculated based on the steering-side rotation angle θb.

[0064] The turn side control unit 50a includes an abnormality detection unit 51, a steering angle calculation unit 52, a steering reaction force command value calculation unit 53, and a power supply control unit 54. The rotation angles θal and θa2 are input to the abnormality detection unit 51. The abnormality detection unit 51 detects an abnormality of the rotation angle sensors 331 and 332 on the basis of the rotation angles θal and θa2. The abnormality detection unit 51 detects an abnormality of the rotation angle sensors 331 and 332 on the basis of a comparison result of previous values of the rotation angles θal and θa2 and on the basis of whether the rotation angles θal and θa2 are input at predetermined periodic intervals. For example, when no rotation angle θal is input, the abnormality detection unit 51 detects an abnormality of the first rotation angle sensor 331. In this case, when a rotation angle θal is input, the abnormality detection unit 51 detects that the first rotation angle sensor 331 has returned to normal. When it is detected that the first rotation angle sensor 331 is normal and it is detected that the second rotation angle sensor 332 is normal, the abnormality detection unit 51 generates a state flag FLG1 indicating that the sensors are normal. On the other hand, when it is detected that the first rotation angle sensor 331 is abnormal and it is detected that the second rotation angle sensor 332 is normal, the abnormality detection unit 51 generates a state flag FLG2 indicating that the sensors are abnormal. These state flags FLG1 and FLG2 are output to the steering angle calculation unit 52, the power supply control unit 54, and the turn side control unit 50b.

[0065] The state flag FLG and the rotation angles θal and θa2 are input to the steering angle calculation unit 52. The steering angle calculation unit 52 converts the rotation angles θal and θa2 to a total angle including a range exceeding 360°, for example, by counting the number of rotations of the reaction force motor 31 from a neutral steering position, that is, the position of the steering wheel 11 when the vehicle is traveling straight ahead. The steering angle calculation unit 52 calculates a steering angle θs by multiplying the total angle obtained by the conversion by a conversion factor based on the rotation speed ratio of the reduction gear mechanism 32. For example, the steering angle θs is set to be positive when it is an angle on the right side with respect to the neutral steering position, and is set to be negative when it is an angle on the left side with respect to the neutral steering position. When the state flag FLG1 is input, the steering angle calculation unit 52 calculates the steering angle θs using the first rotation angle sensor 331. On the other hand, when the state flag FLG2 is input, the steering angle calculation unit 52 calculates the steering angle θs using the second rotation angle sensor 332. The calculated steering angle θs is output to the turn side control unit 50b.

[0066] The steering torque Th, the vehicle speed V, the turning side actual current value Ib, and the pinion angle θp are input to the steering reaction force command value calculation unit 53. The steering reaction force command value calculation unit 53 calculates a steering reaction force command value T* that is a target control value serving as a target of the steering reaction force, on the basis of the steering torque Th, the vehicle speed V, the turning side actual current value Ib, and the pinion angle θp. The calculated steering reaction force command value T* is output to the electric power supply control unit 54.

[0067] The state flag FLG, the steering reaction force command value T*, the rotation angles θal and θa2, and the steering side actual current value la are input to the electric power supply control unit 54. The electric power supply control unit 54 calculates a current command value for the reaction force motor 31 on the basis of the steering reaction force command value T*. The electric power supply control unit 54 calculates a difference between the current command value and a current value in a d-q coordinate system acquired by converting the steering side actual current value la detected by the steering side current sensor 55 on the basis of the rotation angles θal and θa2, and controls electric power supply to the reaction force motor 31 so that the difference is eliminated. In this case, when the state flag FLG1 is input, the electric power supply control unit 54 uses the current value in the d-q coordinate system acquired by converting the steering side actual current value la detected by the steering side current sensor 55 on the basis of the rotation angle θal. On the other hand, when the state flag FLG2 is input, the electric power supply control unit 54 uses the current value in the d-q coordinate system acquired by converting the steering side actual current value la detected by the steering side current sensor 55 on the basis of the rotation angle θa2. Thus, the reaction force motor 31 generates a torque on the basis of the steering reaction force command value T*. The driver can be given an appropriate sense of response on the basis of the road reaction force.

[0068] The function of the turning side control unit 50b will be described below. The vehicle speed V, the state flag FLG, the rotation angle θb, and the steering angle θs are input to the turning side control unit 50b. The turning side control unit 50b controls electric power supply to the turning motor 41 on the basis of the vehicle speed V, the state flag FLG, the rotation angle θb, and the steering angle θs.

[0069] The turning side control unit 50b includes a pinion angle calculation unit 61, a target pinion angle calculation unit 62, a pinion angle feedback control unit (pinion angle F / B control unit in the figure) 63, and an electric power supply control unit 64.

[0070] The rotation angle θb is input to a pinion angle calculation unit 61. The pinion angle calculation unit 61 converts the rotation angle θb into a total angle including a range exceeding 360°, for example, by counting the number of rotations of the turning motor 41 from a neutral rack position, that is, the position of the turning shaft 14 when the vehicle is traveling straight ahead. The pinion angle calculation unit 61 calculates a pinion angle θp, which is the actual rotation angle of the pinion shaft 44, by multiplying the total angle obtained through the conversion by a conversion factor based on the rotation speed ratio of the reduction gear mechanism 42. The pinion angle θp is set to positive when it is an angle to the right of the neutral rack position, and is set to negative when it is an angle to the left of the neutral rack position, for example. The turning motor 41 and the pinion shaft 44 operate in cooperation with each other via the reduction gear mechanism 42. Therefore, there is a correlation between the rotation angle θb of the turning motor 41 and the pinion angle θp. The pinion angle θp can be calculated from the rotation angle θb of the turning motor 41 using this correlation. The pinion shaft 44 is engaged with the turning shaft 14. Therefore, there is a correlation between the pinion angle θp and the amount of movement of the turning shaft 14. That is, the pinion angle θp is a value that reflects the turning angle θw of the turning wheel 16. The calculated pinion angle θp is output to a pinion angle F / B control unit 63 and a steering reaction force command value calculation unit 53.

[0071] The vehicle speed V, the state flag FLG, and the steering angle θs are input to a target pinion angle calculation unit 62. The target pinion angle calculation unit 62 calculates a target pinion angle θp*, which is a target control value serving as the pinion angle θp, based on the vehicle speed V, the state flag FLG, and the steering angle θs.

[0072] Specifically, the target pinion angle calculation unit 62 includes a steering angle ratio change and calculation unit 67 and an offset compensation and calculation unit 68. The vehicle speed V and the steering angle θs are input to the steering angle ratio change and calculation unit 67. The steering angle ratio change and calculation unit 67 calculates a converted angle θvg by adding an adjustment value Δθa to the steering angle θs. The steering angle ratio change and calculation unit 67 changes the adjustment value Δθa in accordance with the vehicle speed V to change a steering angle ratio that is a ratio of the converted angle θvg to the steering angle θs. For example, the adjustment value Δθa is changed so that a change in the converted angle θvg with respect to a change in the steering angle θs is larger when the vehicle speed V is low than when the vehicle speed V is high. The acquired converted angle θvg is output to the offset compensation and calculation unit 68 and the subtracter 69, and a converted angular velocity ωvg acquired by differentiating the converted angle θvg is output to the offset compensation and calculation unit 68 from the differentiator 66. The converted angle θvg is an angle that is used as a basis of the target pinion angle θp*. The pinion angle θp is controlled on the basis of the target pinion angle θp*. Accordingly, there is a correlation between the converted angle θvg and the pinion angle θp. That is, the converted angular velocity ωvg acquired on the basis of the converted angle θvg is a value that reflects the turning angle θw of the turning wheel 16 as a turning state of the turning mechanism TK.

[0073] The vehicle speed V, the state flag FLG, the converted angle θvg, the converted angular velocity ωvg, and the target pinion angle θp* are input to the offset compensation and calculation unit 68. The offset compensation and calculation unit 68 calculates an offset value θofst that is a compensation value at the time of calculating the target pinion angle θp* on the basis of the vehicle speed V, the state flag FLG, the converted angle θvg, the converted angular velocity ωvg, and the target pinion angle θp*. The offset value θofst will be described in detail later. A value obtained by subtracting the acquired offset value θofst from the converted angle θvg is output to the pinion angle F / B control unit 63 as the target pinion angle θp* acquired from the subtracter 69.

[0074] The target pinion angle θp* and the pinion angle θp are input to the pinion angle F / B control unit 63. The pinion angle F / B control unit 63 calculates a turning force command value Tp* that is a target control value used as a target of a turning force in feedback control of the pinion angle θp so that the pinion angle θp coincides with the target pinion angle θp*. The acquired turning force command value Tp* is output to the electric power supply control unit 64.

[0075] The turn force command value Tp*, the rotation angle θb, and the turn side actual current value Ib are input to the electric power supply control unit 64. The electric power supply control unit 64 calculates a current command value for the turn motor 41 based on the turn force command value Tp*. Then, the electric power supply control unit 54 calculates a difference between the current command value and a current value in the d-q coordinate system acquired by converting the turn side actual current value Ib detected by the turn side current sensor 65 based on the rotation angle θb, and controls the electric power supply to the turn motor 41 so that the difference is eliminated. Accordingly, the turn motor 41 rotates by an angle corresponding to the turn force command value Tp*.

[0076] The steering control device 50 includes a plurality of control states including a first control state and a second control state. In the first control state, a target pinion angle θp*(1) is controlled, which is calculated based on a converted angle θvg(1) corresponding to a steering angle θs(1) acquired from a rotation angle θal detected by the first rotation angle sensor 331. In the second control state, a target pinion angle θp*(2) is controlled, which is calculated based on a converted angle θvg(2) corresponding to a steering angle θs(2) acquired from a rotation angle θa2 detected by the second rotation angle sensor 332. The steering control device 50 switches between the first control state and the second control state based on a detection result from the abnormality detection unit 51 regarding an abnormality in the rotation angle sensors 331 and 332.

[0077] Specifically, the steering control device 50 basically switches to the first control state based on the state flag FLG1, and switches to the second control state upon determining that the first control state cannot be maintained. The determination indicating that the first control state cannot be maintained is related to detection of an abnormality in the first rotation angle sensor 331, i.e., the state flag FLG2. Thus, the second control state serves as a control state for backing up the first control state. The steering control device 50 switches to the second control state on a backup basis based on the state flag FLG2, and switches to the first control state when it is determined that it is possible to return to the first control state. The determination indicating that the first control state is restored is related to detection that the first rotation angle sensor 331 has returned to normal, i.e., the state flag FLG1.

[0078] When there is a difference between the steering angle θs(1) and the steering angle θs(2), the difference appears as a difference between the target pinion angle θp*(1) and the target pinion angle θp*(2). That is, there can be a difference in the target pinion angle θp* before and after the control state is switched. To cope with this situation, the steering control device 50, i.e., the turn side control unit 50b, has the function of the offset compensation and calculation unit 68.

[0079] The function of the offset compensation and calculation unit 68 will be described in more detail below. As shown in Fig. 6, the offset compensation and calculation unit 68 includes an offset value acquisition processing unit 71, a calculation value switching unit 72, and an offset value gradual change processing unit 73. Figure 3

[0080] The converted angle θvg and the target pinion angle θp* are input to the offset value acquisition processing unit 71. The offset value acquisition processing unit 71 calculates a difference value Δθvg acquired by subtracting the target pinion angle θp* from the converted angle θvg by the subtracter 74. The target pinion angle θp* input to the offset value acquisition processing unit 71 is a previous target pinion angle θp* used when the turn motor 41 was controlled in the previous cycle (one cycle before). The previous target pinion angle θp* is a value calculated based on the previous converted angle θvg in the previous cycle (one cycle before), and is a value reflecting the previous converted angle θvg. That is, the difference value Δθvg can also be said to be a difference value of the converted angle θvg acquired by subtracting the previous converted angle θvg from the current converted angle θvg. The acquired difference value Δθvg is output to the calculation value switching unit 72.

[0081] The state flag FLG, the difference value Δθvg, and the previous offset value θofst(-) are input to the calculation value switching unit 72, and the previous offset value θofst(-) is a value held in the previous value holding unit 75 in the previous cycle (one cycle before). The difference value Δθvg is input to a first input terminal N1 of the calculation value switching unit 72, and the offset value θofst(-) is input to a second input terminal N2 of the calculation value switching unit 72.

[0082] When the state flag FLG different from the previous state flag FLG in the previous cycle (one cycle before) is input, the calculation value switching unit 72 controls the selection state so that the difference value Δθvg input to the first input terminal N1 is output as an offset base value θofstb that is a base value of the offset value θofst. The selection state in which the difference value Δθvg is output as the offset base value θofstb occurs immediately when the state flag FLG1 is switched to the state flag FLG2. The time when the state flag FLG1 is switched to the state flag FLG2 is the time when the first control state is switched to the second control state. The same applies to the time when the second control state is switched to the first control state, that is, the time when the state flag FLG2 is switched to the state flag FLG1.

[0083] ​On the other hand, when the same state flag FLG as the value in the previous cycle (one cycle before) is input, the calculation value switching unit 72 controls the selection state so that the offset value θofst(-) input to the second input terminal N2 is output as the offset base value θofstb. The selection state in which the offset value θofst(-) is output as the offset base value θofstb is continuously held in the time period in which the input of the state flag FLG1 is held or in the time period in which the input of the state flag FLG2 is held. The time period in which the input of the state flag FLG1 is held is the time period in which the first control state is held. The time period in which the input of the state flag FLG2 is held is the time period in which the second control state is held.

[0084] As the offset base value θofstb selected in this way, the difference value Δθvg calculated by the offset value acquisition processing unit 71 at the time of switching from the state flag FLG1 to the state flag FLG2 is output to the offset value taper processing unit 73. As the offset base value θofstb at the time of holding the state flag FLG, the offset value θofst(-) that is the previous value of the offset value taper processing unit 73 is output to the offset value taper processing unit 73.

[0085] At the time of control state switching, when there is a difference between the steering angle θs(1) and the steering angle θs(2), the difference value Δθvg has a non-zero value. On the other hand, the calculation value switching unit 72 operates so that the difference value Δθvg generated due to the switching of the control state can be reflected in the offset base value θofstb by the difference value Δθvg output input to the first input terminal N1 at the time of control state switching.

[0086] On the other hand, even at times other than the time of control state switching, when there is a difference between the steering angle θs(1) and the steering angle θs(2), the difference value Δθvg has a non-zero value. On the other hand, since the difference value Δθvg output input to the first input terminal N1 is only at the time of control state switching, the calculation value switching unit 72 operates so that the difference value Δθvg generated at times other than the time of control state switching is not reflected in the offset base value θofstb.

[0087] The vehicle speed V, the converted angular velocity ωvg, and the offset base value θofstb are input to the offset value taper processing unit 73. Specifically, as shown in FIG. 8, the offset value taper processing unit 73 includes a decrease gain map calculation unit 81, a decrease value map calculation unit 82, a storage unit 83, a lower limit protection processing unit 84, and a sign processing unit 85. Figure 4

[0088] ​The vehicle speed V is input to the reduction gain map calculation unit 81. The reduction gain map calculation unit 81 includes a map in which a relationship between the vehicle speed V and the reduction gain G is defined, and calculates the reduction gain G using the map and using the vehicle speed V as an input. The reduction gain G is a gain for gradually reducing the offset value θofst so that the target pinion angle θp* does not suddenly change as the offset value θofst decreases. In this case, the reduction gain G is calculated so that its absolute value increases as the vehicle speed V increases, in consideration of the running state of the vehicle. The calculated reduction gain G is output to the multiplier 86.

[0089] The converted angular velocity ωvg is input to the reduction value map calculation unit 82. The reduction value map calculation unit 82 includes a map in which a relationship between the converted angular velocity ωvg and a reduction base value θdb that is a base value of the reduction value θd is defined, and calculates the reduction base value θdb using the map and using the converted angular velocity ωvg as an input. The reduction base value θdb is a component for gradually reducing the offset value θofst so that the target pinion angle θp* does not suddenly change as the offset value θofst decreases. In this case, the reduction base value θdb is calculated so that its absolute value increases as the converted angular velocity ωvg (i.e., the rate of change of the turning angle θw of the turning wheel 16) increases, in consideration of the turning state of the turning mechanism TK. A value obtained by multiplying the calculated reduction base value θdb by the reduction gain G is output to the lower limit protection processing unit 84 as the reduction value θd acquired from the multiplier 86.

[0090] The storage unit 83 is a predetermined storage area of a memory (not shown) in which a minimum value θdmin of the reduction value θd is stored. The minimum value θdmin is a component for reducing the offset value θofst so that the offset value θofst does not remain constant. Even when the reduction value θd output from the multiplier 86 is smaller than the minimum value θdmin, the minimum value θdmin is set to a value within a range experimentally acquired as an index for securing the minimum value of the reduction value θd. The acquired minimum value θdmin is output to the lower limit protection processing unit 84.

[0091] The reduction value θd output from the multiplier 86 and the minimum value θdmin output from the storage unit 83 are input to the lower limit protection processing unit 84. The reduction value θd is input to a first input terminal Ml of the lower limit protection processing unit 84, and the minimum value θdmin is input to a second input terminal M2 of the lower limit protection processing unit 84. The lower limit protection processing unit 84 is configured to switch its selection state so that one of the reduction value θd and the minimum value θdmin is output as the reduction value θd.

[0092] Specifically, the lower limit protection processing unit 84 determines whether the reduction value θd input to the first input terminal Ml is equal to or greater than the minimum value θdmin. When the reduction value θd input to the first input terminal Ml is equal to or greater than the minimum value θdmin, the lower limit protection processing unit 84 controls the selection state of the lower limit protection processing unit 84 so that the reduction value θd input to the first input terminal Ml is output as the final reduction value θd. On the other hand, when the reduction value θd input to the first input terminal Ml is less than the minimum value θdmin, the lower limit protection processing unit 84 controls the selection state of the lower limit protection processing unit 84 so that the minimum value θdmin is output as the final reduction value θd. That is, the lower limit protection processing unit 84 operates to reduce the offset value θofst by at least the minimum value θdmin so that the offset value θofst does not remain constant all the time. In this way, the reduction value θd selected as an appropriate value is output to the multiplier 87.

[0093] The offset base value θofstb is input to the sign processing unit 85. The sign processing unit 85 determines the sign of the offset base value θofstb and calculates one of "1" and "-1" as a value corresponding to the sign. The sign processing unit 85 calculates "1" when the offset base value θofstb is positive, and calculates "-1" when the offset base value θofstb is negative. The value obtained by multiplying the reduction value θd by the calculated value "1" or "-1" is output to the subtractor 88 as the final reduction value θd acquired from the multiplier 87. Then, the value obtained by subtracting the final reduction value θd from the offset base value θofstb is output to the subtractor 69 as the offset value θofst acquired from the subtractor 88.

[0094] When the offset value θofst is a non-zero value, the offset value gradual change processing unit 73 operates so that the reduction value θd output from the lower limit protection processing unit 84 is reflected in the offset value θofst. On the other hand, when the offset value θofst is zero, the offset value gradual change processing unit 73 operates so that the reduction value θd output from the lower limit protection processing unit 84 is not reflected in the offset value θofst. The offset value gradual change processing unit 73 operates so that the sign of the offset base value θofstb is not reversed as a result of the reflection of the reduction value θd. That is, when the absolute value of the offset base value θofstb is less than the absolute value of the reduction value θd, the offset value gradual change processing unit 73 operates so that the absolute value of the reduction value θd is the same as the absolute value of the offset base value θofstb.

[0095] The operation of the present embodiment will be described below. Figure 5Parts (a) to (c) in FIG. 7 show various change patterns in an example in which the state flag FLG is switched from the state flag FLG1 indicating normality of the sensor to the state flag FLG2 indicating abnormality of the sensor at the time of time tl. The following description is based on the assumption that the offset value θofst at time "0" is zero, the steering angle θs(l) corresponding to the rotation angle θal and the steering angle θs(2) corresponding to the rotation angle θa2 are constantly changing by a predetermined angle difference a, and the vehicle speed V is constant.

[0096] As shown in part (a) in FIG. 7, the converted angle θvg(l) indicated by the long-short alternate broken line in the lower part of the figure and the converted angle θvg(2) indicated by the long-two-short alternate broken line in the upper part of the figure are changing by the angle difference a. This can be understood as a change in the target pinion angle θp*(l) calculated based on the converted angle θvg(l) and a change in the target pinion angle θp*(2) calculated based on the converted angle θvg(2). At the time of time tl, the offset value acquisition processing unit 71 operates to calculate the angle difference a as the difference value Δθvg. Figure 5 As shown in part (b) in FIG. 7, the calculated value switching unit 72 operates to calculate an offset base value θofstb indicating the angle difference a, which is calculated as the offset value θofst. After time tl, the offset value gradual change processing unit 73 operates to gradually decrease the offset value θofst. The offset value θofst is gradually decreased until time t2 at which the offset value θofst is zero. The offset value θofst changed in this way is reflected to perform compensation on the target pinion angle θp* by subtracting it from the converted angle θvg at that time by the function of the offset compensation and calculation unit 68.

[0097] Figure 5 In this case, as shown in part (b) in FIG. 7, the calculated value switching unit 72 operates to calculate an offset base value θofstb indicating the angle difference a, which is calculated as the offset value θofst. After time tl, the offset value gradual change processing unit 73 operates to gradually decrease the offset value θofst. The offset value θofst is gradually decreased until time t2 at which the offset value θofst is zero. The offset value θofst changed in this way is reflected to perform compensation on the target pinion angle θp* by subtracting it from the converted angle θvg at that time by the function of the offset compensation and calculation unit 68.

[0098] Accordingly, when the control state is switched as indicated by the solid line in part (a) in FIG. 7, the target pinion angle θp* as the post-switching target control value after time tl is moved to the target pinion angle θp*(l) as the pre-switching target control value before time tl by compensation using the offset value θofst. In particular, at the instant of the switch, compensation is performed so that the target pinion angle θp* almost (substantially) matches the target pinion angle θp*(l). Figure 5 Thereafter, as indicated by the solid line in the figure, as the offset value θofst is gradually decreased, the target pinion angle θp* approaches the original target pinion angle θp*(2). The target pinion angle θp* changes to reach the original target pinion angle θp*(2) at time t2 at which the offset value θofst is zero.

[0099] In this case, as shown in part (b) in FIG. 7, the calculated value switching unit 72 operates to calculate an offset base value θofstb indicating the angle difference a, which is calculated as the offset value θofst. After time tl, the offset value gradual change processing unit 73 operates to gradually decrease the offset value θofst. The offset value θofst is gradually decreased until time t2 at which the offset value θofst is zero. The offset value θofst changed in this way is reflected to perform compensation on the target pinion angle θp* by subtracting it from the converted angle θvg at that time by the function of the offset compensation and calculation unit 68.​

[0100] The advantages of the present embodiment will be described below. In the present embodiment, as indicated by the solid line of part (a) in FIG. 10, even when there is a difference between the target pinion angle θp*(l) before the control state is switched and the target pinion angle θp*(2) after the control state is switched, this difference can be prevented from being expressed as a change in the target pinion angle θp* for actual control. That is, the occurrence of the driver-unintended movement of the turning mechanism TK can be suppressed. Therefore, the driver's discomfort can be suppressed. Figure 5

[0101] According to the present embodiment, when the first rotation angle sensor 331 becomes abnormal, the control state can be switched to the second control state for backup for calculating the target pinion angle θp* using the detection result from the redundant second rotation angle sensor 332. This is to avoid calculating the target pinion angle θp* based on the detection result from the first rotation angle sensor 331. In this case, even when there is a difference between the turning angle θs(l) before the control state is switched and the turning angle θs(2) after the control state is switched, the target pinion angle θp* after the control state is switched can be prevented from being different from the target pinion angle θp* before the switch. Therefore, even when the control state is switched to the control state for backup due to the first rotation angle sensor 331 becoming abnormal, the occurrence of the driver-unintended movement of the turning mechanism TK can be suppressed.

[0102] Here, since the offset value θofst is used to forcibly move the original target pinion angle θp*(2) after the switch, it is necessary to eliminate the offset value θofst as soon as possible, but when the reduction value of the offset value is set too large, the driver-unintended movement of the turning mechanism TK eventually occurs.

[0103] Therefore, the offset value gradual processing unit 73 has the function of the reduction gain map calculation unit 81 that takes into account the running state of the vehicle and the reduction value map calculation unit 82 that takes into account the turning state of the turning mechanism TK. Therefore, the reduction value θd for reducing the offset value θofst increases as the vehicle speed V increases and as the amount of change in the turning angle θw of the turning wheel 16 increases. Therefore, the driver's discomfort can be suppressed and the offset value θofst can be eliminated as soon as possible.

[0104] The offset value gradual processing unit 73 has the function of the lower limit protection processing unit 84 that takes into account the minimum value θdmin. Therefore, it is possible to prevent the offset value θofst from remaining all the time and effectively reduce the offset value θofst.

[0105] ​This embodiment can be modified as follows. The following modification examples can be combined with each other unless there is a technical conflict. The offset value gradual change processing unit 73 can not have the function of the lower limit protection processing unit 84 when there is no problem in a case where the offset value θofst is not decreased. In addition, the offset value gradual change processing unit 73 can have a function of substantially decreasing the offset value θofst by a minimum value θdmin. In this case, the decrease gain map calculation unit 81 and the decrease value map calculation unit 82 can be omitted. The offset value gradual change processing unit 73 can decrease the offset value θofst by multiplying the offset base value θofstb by a gain. The gain in this case can be considered to be the same in the decrease gain map calculation unit 81 and the decrease value map calculation unit 82.

[0106] In addition to the decrease gain map calculation unit 81 and the decrease value map calculation unit 82, the offset value gradual change processing unit 73 can include a calculation unit that takes another state into account. The offset value gradual change processing unit 73 can include only one of the decrease gain map calculation unit 81 and the decrease value map calculation unit 82, or can include a calculation unit that takes another state into account instead of both of them. As the other state, for example, the current value of the offset value θofst, that is, the residual value can be taken into account. In this case, as the residual value becomes smaller, the change rate of the decrease can be made smaller.

[0107] In the decrease gain map calculation unit 81, the change pattern of the decrease gain G can be changed as appropriate. For example, the vehicle speed V can be classified into low speed, medium speed, high speed, and the like, and the decrease gain G can be kept constant at the low speed. In this way, the change pattern of the decrease gain G can be changed according to the classification.

[0108] In the decrease value map calculation unit 82, the change pattern of the decrease base value θdb can be changed as appropriate. For example, the converted angular velocity ωvg can be classified into low angular velocity, medium angular velocity, high angular velocity, and the like, and the decrease base value θdb can be kept constant at the low angular velocity. In this way, the change pattern of the decrease base value θdb can be changed according to the classification.

[0109] In the decrease value map calculation unit 82, the pinion angular velocity obtained by differentiating the pinion angle θp can be used instead of the converted angular velocity ωvg. In addition, the decrease value map calculation unit 82 can calculate the decrease base value θdb corresponding to the angle at that time using the steering angle θs or the pinion angle θp.

[0110] The control state for backup can be a control state that copes with torque sensor abnormality by making the torque sensor 34 redundant, a control state that copes with electric power supply structure abnormality of the steering system 10 by making the electric power supply structure of the steering system 10 redundant, or a control state that copes with turn-side control unit abnormality by making the turn-side control unit 50b redundant. When the turn-side control unit 50b becomes redundant, the turn-side control unit 50b includes, for example, a first turn-side control unit and a second turn-side control unit. In this case, the wiring of the turn motor 41 becomes redundant, and the first turn-side control unit and the second turn-side control unit cooperatively control the drive of the turn motor 41 with each other. The first turn-side control unit receives a component based on the detection result from the first rotation angle sensor 331 as input, the second turn-side control unit receives a component based on the detection result from the second rotation angle sensor 332 as input, and each turn-side control unit independently calculates the target pinion angle θp*. The first turn-side control unit and the second turn-side control unit employ, for example, a master-slave control system. In this case, in a first control state in which the first rotation angle sensor 331 is normal, the first turn-side control unit is set as a master control unit, and the turn-side control units cooperatively control the drive of the turn motor 41 with each other using the target pinion angle θp* calculated by the first turn-side control unit. On the other hand, in a second control state in which the first rotation angle sensor 331 is abnormal, the function of the first turn-side control unit is stopped, and the drive of the turn motor 41 is controlled only by the second turn-side control using the target pinion angle θp* calculated by the second turn-side control unit. In this case, similarly to the foregoing embodiment, there is a possibility that the target pinion angle θp* will move before or after the control state switching. Similarly to the foregoing embodiment, this can also be addressed by employing the offset compensation and calculation unit 68 according to the foregoing embodiment.

[0111] The control state for backup can be a control state for coping with functional abnormality of the steering angle ratio change and calculation unit 67 that changes the steering angle ratio. In this case, the steering angle ratio change and calculation unit 67 can switch a first control state in which the steering angle ratio is variable when the vehicle speed sensor 501, that is, the vehicle speed V is normal, to a second control state in which the steering angle ratio is fixed when the vehicle speed sensor 501, that is, the vehicle speed V is abnormal. In this case, similarly to the foregoing embodiment, there is a possibility that the target pinion angle θp* will move before and after the control state switching. Similarly to the foregoing embodiment, this can also be addressed by employing the offset compensation and calculation unit 68 according to the foregoing embodiment.

[0112] The sensor that detects the rotation angle can detect the independent rotation angle of different detection targets, and the rotation angle is a state variable used to calculate the target pinion angle θp* of each control state. For example, the steering system 10 can include a steering angle sensor that directly detects the steering angle θs of the steering shaft 12. In this case, the first rotation angle sensor 331 and the steering angle sensor are connected to the steering-side control unit 50a. The turning-side control unit 50b can switch the first control state in which the target pinion angle θp* is calculated using the rotation angle θa detected by the first rotation angle sensor 331 to the second control state in which the target pinion angle θp* is calculated using the rotation angle detected by the steering angle sensor when the first rotation angle sensor 331 is abnormal. In this case, similarly to the foregoing embodiment, there is a possibility that the target pinion angle θp* will move before and after the control state is switched. Similarly to the foregoing embodiment, this can also be addressed by employing the offset compensation and calculation unit 68 according to the foregoing embodiment.

[0113] The offset base value θofstb can not be acquired from the difference value Δθvg, but can be acquired from the difference with respect to the rotation angle θa1 and the rotation angle θa2 before and after the control state is switched, or can be acquired from the difference with respect to the target pinion angle θp* before and after the control state is switched. The offset base value θofstb can be acquired from the difference with respect to the converted angle θvg before and after the control state is switched.

[0114] The offset compensation and calculation unit 68 according to the foregoing embodiment can be added as a function of the steering-side control unit 50a. This is effective when the steering reaction force command value T* is calculated based on the rotation angles θa1 and θa2, i.e., the steering angle θs. This modification example is effective when the control state for which a backup is prepared is a control state for coping with an abnormality of the torque sensor by making the torque sensor 34 redundant.

[0115] When the offset base value θofstb is zero, the sign processing unit 85 can calculate and output "0 (zero)". In this case, when the offset base value θofstb is zero, the reduction value θd is zero. That is, in this modification example, the offset value fade processing unit 73 can operate such that the reduction value θd output from the lower limit protection processing unit 84 is not reflected in the offset value θofst when the offset value θofst is zero.

[0116] The steering angle ratio changing and calculating unit 67 can change the steering angle ratio, for example, in accordance with a yaw rate detected by a yaw rate sensor of the vehicle in addition to the vehicle speed V. In this case, the steering angle ratio changing and calculating unit 67 can switch the control state in which the steering angle ratio is variable when the yaw rate sensor, i.e., the yaw rate is normal to a second control state in which the steering angle ratio is fixed or variable based on only the vehicle speed V when the yaw rate sensor, i.e., the yaw rate is abnormal. In this case, similarly to the foregoing embodiment, there is a possibility that the target pinion angle θp* will move before and after the control state is switched. Similarly to the foregoing embodiment, this can also be addressed by employing the offset compensation and calculating unit 68 according to the foregoing embodiment. This modification example can also be applied to a case in which the steering angle ratio is variable in accordance with a lateral acceleration output from a lateral acceleration sensor of the vehicle in addition to the vehicle speed V.

[0117] The pinion angle F / B control unit 63 can change the F / B gain, for example, in accordance with a yaw rate detected by a yaw rate sensor of the vehicle. In this case, the pinion angle F / B control unit 63 can switch a first control state in which the F / B gain is variable when the yaw rate sensor, i.e., the yaw rate is normal to a second control state in which the F / B gain is fixed when the yaw rate sensor, i.e., the yaw rate is abnormal. In this case, similarly to the foregoing embodiment, there is a possibility that the target pinion angle θp* will move before and after the control state is switched. Similarly to the foregoing embodiment, this can also be addressed by employing the offset compensation and calculating unit 68 according to the foregoing embodiment. This modification example can also be applied to a case in which the F / B gain is variable in accordance with another state variable.

[0118] The steering reaction force command value calculating unit 53 needs to use at least the steering torque Th to calculate the steering reaction force command value T* and can not use the vehicle speed V or can use a combination thereof with another element.

[0119] In the foregoing embodiment, the steering angle ratio can be fixed. In this case, the steering angle ratio changing and calculating unit 67 can be omitted. In the foregoing embodiment, the turning motor 41 can employ, for example, a structure in which the turning motor 41 is disposed coaxially with the turning shaft 14 or a structure in which the turning motor 41 is connected to the turning shaft 14 via a belt reduction gear using a ball screw mechanism.

[0120] In the foregoing embodiment, the CPU configuring the steering control device 50 can be realized as one or more processors executing a computer program, one or more dedicated hardware circuits, for example, an application specific integrated circuit executing at least some of various processes, or a circuit including a combination of a processor and a dedicated hardware circuit. The memory can be configured using all available media that can be accessed by a general-purpose or a dedicated computer.

[0121] In the foregoing embodiment, the steering system 10 adopts a linkageless structure in which the steering mechanism SK and the turning mechanism TK are generally mechanically disconnected from each other, but the present application is not limited to this, and a structure in which the steering mechanism SK and the turning mechanism TK can be mechanically disconnected by the clutch 21 can be adopted, as indicated by the long and short alternate dashed lines in Figure 1 The steering system 10 can be an electric power steering system that applies an assist force, which is a force for assisting the steering of the steering wheel 11. In this case, the steering wheel 11 is mechanically connected to the pinion shaft 13 via the steering shaft 12.

[0122] Second Embodiment

[0123] The second embodiment will be described below. Figure 6 A steering system 10 of a vehicle according to the second embodiment is shown. The same elements as in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

[0124] As Figure 6 indicated, the steering mechanism SK includes a reaction force motor 31, a reduction gear mechanism 32, a rotation angle sensor 33, and a torque sensor 34 as a configuration for generating a steering reaction force. A steering control device 50 that controls the drive of the motors 31 and 41 is connected to the reaction force motor 31 and the turning motor 41. The steering control device 50 controls the drive of the motors 31 and 41 by controlling the supply of current as a control value of the motors 31 and 41 based on the detection results from various sensors. Examples of the various sensors include a vehicle speed sensor 501, the torque sensor 34, the rotation angle sensor 33, and the rotation angle sensor 43. The vehicle speed sensor 501 detects a vehicle speed V as a vehicle travel speed.

[0125] The configuration of the steering control device 50 will be described below. The steering control device 50 includes a central processing unit (CPU) and a memory, which are not shown, and the CPU executes a program stored in the memory at intervals of a predetermined operation cycle. Thus, various processes are executed.

[0126] Some of the processes executed by the steering control device 50 are shown in Figure 7 . Figure 7 The processes shown are some of the processes implemented by causing the CPU to execute the program stored in the memory for each of the processes implemented.

[0127] The steering control device 50 includes a steering-side control unit 50a that controls electric power supply to the reaction force motor 31. The steering-side control unit 50a includes a steering-side current sensor 55. The steering-side current sensor 55 detects a steering-side actual current value Ia that is acquired from a phase current value of the reaction force motor 31 that flows in a connection line between the steering-side control unit 50a and a phase motor coil of the reaction force motor 31. The steering-side current sensor 55 acquires a voltage drop of a shunt resistor that is connected to a source stage of a switching element in an inverter (not shown) that is provided corresponding to the reaction force motor 31 as a current. In Figure 7 In the steering-side control unit 50a, for the purpose of facilitating description, a phase connection line and a phase current sensor are collectively shown as a single.

[0128] The steering control device 50 includes a steering-side control unit 50a that controls electric power supply to the reaction force motor 31. The steering-side control unit 50a includes a steering-side current sensor 55. The steering-side current sensor 55 detects a steering-side actual current value Ia that is acquired from a phase current value of the reaction force motor 31 that flows in a connection line between the steering-side control unit 50a and a phase motor coil of the reaction force motor 31. The steering-side current sensor 55 acquires a voltage drop of a shunt resistor that is connected to a source stage of a switching element in an inverter (not shown) that is provided corresponding to the reaction force motor 31 as a current. In Figure 7 In the steering-side control unit 50a, for the purpose of facilitating description, a phase connection line and a phase current sensor are collectively shown as a single.

[0129] The function of the steering-side control unit 50a will be described below. The steering torque Th, the vehicle speed V, the rotation angle θa, the turning-side actual current value Ib that will be described later, and the pinion angle θp that will be described later are input to the steering-side control device 50a. The steering-side control unit 50a controls electric power supply to the reaction force motor 31 on the basis of the steering torque Th, the vehicle speed V, the rotation angle θa, the turning-side actual current value Ib that will be described later, and the pinion angle θp that will be described later. The pinion angle θp is calculated on the basis of the rotation angle θb of the turning motor 41.

[0130] The turn side control unit 50a includes a steering angle calculation unit 52, a steering reaction force command value calculation unit 53, and a power supply control unit 54. The rotation angle θa is input to the steering angle calculation unit 52. The steering angle calculation unit 52 converts the rotation angle θa to a total angle including a range exceeding 360°, for example, by counting the number of rotations of the reaction force motor 31 from the steering neutral position, that is, the position of the steering wheel 11 when the vehicle is traveling straight ahead. The steering angle calculation unit 52 calculates the steering angle θs by multiplying the total angle obtained by the conversion by a conversion factor based on the rotation speed ratio of the reduction gear mechanism 32. For example, the steering angle θs is set to positive when it is an angle on the right side with respect to the steering neutral position, and is set to negative when it is an angle on the left side with respect to the steering neutral position. The calculated steering angle θs is output to the turn side control unit 50b.

[0131] The steering torque Th, the vehicle speed V, the turn side actual current value Ib, and the pinion angle θp are input to the steering reaction force command value calculation unit 53. The steering reaction force command value calculation unit 53 calculates a steering reaction force command value T* based on the steering torque Th, the vehicle speed V, the turn side actual current value Ib, and the pinion angle θp, the steering reaction force command value T* being a target control value that serves as a target of the steering reaction force. The calculated steering reaction force command value T* is output to the power supply control unit 54.

[0132] The steering reaction force command value T*, the rotation angle θa, and the steering side actual current value Ia are input to the power supply control unit 54. The power supply control unit 54 calculates a current command value Ia* for the reaction force motor 31 based on the steering reaction force command value T*. The power supply control unit 54 calculates a difference between the current command value Ia* and a current value in the d-q coordinate system obtained by converting the steering side actual current value Ia detected by the steering side current sensor 55 based on the rotation angle θa, and controls the power supply to the reaction force motor 31 so that the difference is eliminated. Thus, the reaction force motor 31 generates a torque based on the steering reaction force command value T*. The driver can be given an appropriate response feeling based on the road reaction force.

[0133] The function of the turn side control unit 50b will be described below. The vehicle speed V, the rotation angle θb, and the steering angle θs are input to the turn side control unit 50b. The turn side control unit 50b controls the power supply to the turn motor 41 based on the vehicle speed V, the rotation angle θb, and the steering angle θs.

[0134] The turn-side control unit 50b includes a pinion angle calculation unit 61, a target pinion angle calculation unit 62, a pinion angle feedback control unit (pinion angle F / B control unit in the figure) 63, and a power supply control unit 64.

[0135] The rotation angle θb is input to the pinion angle calculation unit 61. The pinion angle calculation unit 61 converts the rotation angle θb into a total angle including a range exceeding 360°, for example, by counting the number of rotations of the turn motor 41 from the neutral rack position, that is, the position of the turn shaft 14 when the vehicle is traveling straight ahead. The pinion angle calculation unit 61 calculates the pinion angle θp, which is the actual rotation angle of the pinion shaft 44, by multiplying the total angle obtained by the conversion by a conversion factor based on the rotation speed ratio of the reduction gear mechanism 42. The pinion angle θp is set to positive when it is an angle on the right side with respect to the neutral rack position, for example, and is set to negative when it is an angle on the left side with respect to the neutral rack position. The turn motor 41 and the pinion shaft 44 operate in conjunction with each other via the reduction gear mechanism 42. Therefore, there is a correlation between the rotation angle θb of the turn motor 41 and the pinion angle θp. This correlation can be used to calculate the pinion angle θp from the rotation angle θb of the turn motor 41. The pinion shaft 44 is engaged with the turn shaft 14. Therefore, there is a correlation between the pinion angle θp and the amount of movement of the turn shaft 14. That is, the pinion angle θp is a value that reflects the turn angle θw of the turn wheel 16. The calculated pinion angle θp is output to the pinion angle F / B control unit 63 and the steering reaction force command value calculation unit 53.

[0136] The vehicle speed V and the steering angle θs are input to the target pinion angle calculation unit 62. The target pinion angle calculation unit 62 calculates a target pinion angle θp* that is a target control value serving as a target angle of the pinion angle θp, based on the vehicle speed V and the steering angle θs.

[0137] Specifically, the target pinion angle calculation unit 62 includes a steering angle ratio change and calculation unit 67 and an offset compensation and calculation unit 68. The vehicle speed V and the steering angle θs are input to the steering angle ratio change and calculation unit 67. The steering angle ratio change and calculation unit 67 calculates a converted angle θvg by adding an adjustment value Δθa to the steering angle θs. The steering angle ratio change and calculation unit 67 changes the adjustment value Δθa according to the vehicle speed V, the steering angle ratio being a ratio of the converted angle θvg to the steering angle θs. For example, the adjustment value Δθa is changed so that the change in the converted angle θvg relative to the change in the steering angle θs is larger when the vehicle speed V is low than when the vehicle speed V is high. The obtained converted angle θvg is output to the offset compensation and calculation unit 68, and a converted angular velocity ωvg obtained from the differentiator 66 by differentiating the converted angle θvg is output to the offset compensation and calculation unit 68. The converted angle θvg is an angle that serves as a basis for the target pinion angle θp*. The pinion angle θp is controlled on the basis of the target pinion angle θp*. Therefore, there is a correlation between the converted angle θvg and the pinion angle θp. That is, the converted angular velocity ωvg obtained on the basis of the converted angle θvg is a value in which the turning angle θw of the turning wheel 16 is reflected as a turning state of the turning mechanism TK.

[0138] The vehicle speed V, the converted angle θvg, the converted angular velocity ωvg, and a current command value Ib* that will be described later are input to the offset compensation and calculation unit 68. The offset compensation and calculation unit 68 calculates the target pinion angle θp* on the basis of the vehicle speed V, the converted angle θvg, the converted angular velocity ωvg, and the current command value Ib* that will be described later. The offset compensation and calculation unit 68 has a function of calculating an offset value θofst, which is a compensation value for the target pinion angle θp* and is obtained in the process of calculating the target pinion angle θp*. The offset value θofst will be described in detail later. The obtained target pinion angle θp* is output to the pinion angle F / B control unit 63.

[0139] The target pinion angle θp* and the pinion angle θp are input to the pinion angle F / B control unit 63. The pinion angle F / B control unit 63 calculates a turning force command value Tp*, which is a target control value serving as a target of the turning force in feedback control of the pinion angle θp, so that the pinion angle θp follows the target pinion angle θp*. The obtained turning force command value Tp* is output to the electric power supply control unit 64.

[0140] The turn force command value Tp*, the rotation angle θb, and the turn side actual current value Ib are input to the electric power supply control unit 64. The electric power supply control unit 64 calculates a current command value Ib* for the turn motor 41 based on the turn force command value Tp*. Then, the electric power supply control unit 64 calculates a difference between the current command value Ib* and a current value in the d-q coordinate system obtained by converting the turn side actual current value Ib detected by the turn side current sensor 65 based on the rotation angle θb, and controls the electric power supply to the turn motor 41 so that the difference is eliminated. Thus, the turn motor 41 rotates by an angle corresponding to the turn force command value Tp*. The current command value Ib* obtained in the process of controlling the electric power supply to the turn motor 41 is output to the target pinion angle calculation unit 62.

[0141] The target pinion angle θp* is calculated as a control value based on the converted angle θvg obtained from the steering angle θs. However, when a control value exceeding the output limit of the turn motor 41 is calculated as the target pinion angle θp*, the turn motor 41 needs to output an output power exceeding its limit, for example, due to a sudden change in the steering angle θs. For the purpose of handling such a case, the steering control device 50, i.e., the turn side control unit 50b, has the function of an offset compensation and calculation unit 68.

[0142] The function of the offset compensation and calculation unit 68 will be described in more detail below. As shown in Fig. 8, the offset compensation and calculation unit 68 includes an offset value gradual change processing unit 73, a limit value calculation unit 720, and an offset value acquisition processing unit 71. Figure 8

[0143] ​The vehicle speed V, the converted angular velocity ωvg, and the previous offset value θofst(-) are input to the offset value gradual processing unit 73. The previous offset value θofst(-) is the value of the offset value θofst held in the previous cycle (one cycle prior), and the offset value θofst is the compensation value for the target pinion angle θp*. The offset value gradual processing unit 73 calculates the reduction value θd and the offset residual value θofstc based on the vehicle speed V, the converted angular velocity ωvg, and the offset value θofst(-). The reduction value θd is the component used to gradually reduce the offset value θofst so that the target pinion angle θp* does not change abruptly as the offset value θofst decreases. The offset residual value θofstc is the component indicating the residual of the offset value θofst obtained by subtracting the reduction value θd from the offset value θofst(-). The reduction value θd and the offset residual value θofstc will be described in detail later. The acquired reduction value θd is output to the offset value acquisition processing unit 71. The value obtained by subtracting the offset residual θofstc from the transformed angle θvg is output as the target pinion angle base value θpb* to subtractor 750. The target pinion angle base value θpb* is the base value of the target pinion angle θp* obtained from subtractor 74. The offset residual value θofstc is output to adder 76.

[0144] The current command value Ib* is input to the limit value calculation unit 720. The limit value calculation unit 720 calculates the angular velocity limit value ωpth based on the current command value Ib*. Specifically, the limit value calculation unit 720 calculates the angular velocity limit value ωpth, which is a limit value for the angular velocity ωp of the turning motor 41 obtained based on its relationship with the motor torque of the turning motor 41. The angular velocity limit value ωpth is, for example, using... Figure 11 The I-ω characteristics shown in part (a) were obtained. Figure 11 Part (a) shows the relationship between the absolute value of the actual current value Ib corresponding to the motor torque of the turning motor 41 and the absolute value of the angular velocity ωp. The I-ω characteristic is obtained based on the known NT characteristic, which is the relationship between the motor torque and the motor speed of the turning motor 41. Regarding the angular velocity limit value ωpth, the absolute value of the angular velocity ωp obtained based on the absolute value of the current command value Ib* is acquired as the angular velocity limit value ωpth. The acquired angular velocity limit value ωpth is output to the offset value acquisition and processing unit 71.

[0145] The converted angle θvg, the reduction value θd, and the angular velocity limit value ωpth are input to the offset value acquisition processing unit 71. The offset value acquisition processing unit 71 calculates an excess control value θacc on the basis of the converted angle θvg, the reduction value θd, and the angular velocity limit value ωpth. The excess control value θacc is a component corresponding to an excess value that exceeds the output limit of the turning motor 41. The excess control value θacc will be described later in detail. A value obtained by subtracting the excess control value θacc from the target pinion angle base value θpb* is output as the target pinion angle θp* acquired from the subtracter 750 to the pinion angle feedback (F / B) control unit 63. A value obtained by adding the excess control value θacc to the offset residual value θofstc is output as the offset value θofst acquired from the adder 76 to the previous value holding unit 77, and then output as the previous offset value θofst(-) to the offset value gradual change processing unit 73, which is a value in the previous cycle (one cycle ago).

[0146] The function of the offset value gradual change processing unit 73 will be described in detail below. The function identical to that of the offset value gradual change processing unit 73 according to the first embodiment will be omitted.

[0147] The converted angular velocity ωvg is input to Figure 9 The reduction value mapping calculation unit 82 illustrated in Fig. 8. The reduction value mapping calculation unit 82 includes a map in which a relationship between the absolute value of the converted angular velocity ωvg and a reduction base value θdb that is a base value of the reduction value θd is defined, and calculates the reduction base value θdb using the map and using the absolute value of the converted angular velocity ωvg as an input. The reduction base value θdb is a component for gradually reducing the offset value θofst so that the target pinion angle θp* does not suddenly change as the offset value θofst is reduced. In this case, the reduction base value θdb is calculated so that its absolute value increases as the converted angular velocity ωvg (i.e., the rate of change of the turning angle θw of the turning wheel 16) increases, in consideration of the turning state of the turning mechanism TK. A value obtained by multiplying the calculated reduction base value θdb by a reduction gain G is output as the reduction value θd acquired from the multiplier 86 to the lower limit protection processing unit 84.

[0148] The offset value θofst(-) is input to the sign processing unit 85. The sign processing unit 85 determines the sign of the offset value θofst(-) and calculates one of "1" or "-1" as the value corresponding to the sign. The sign processing unit 85 calculates "1" when the offset value θofst(-) is positive, and calculates "-1" when the offset value θofst(-) is negative. The value obtained by multiplying the reduction value θd by the calculated value of "1" or "-1" is output as the final reduction value θd obtained from the multiplier 87 to the subtractor 88. Then, the value obtained by subtracting the final reduction value θd from the offset value θofst(-) is output as the offset residual value θofstc obtained from the subtractor 88 to the subtractor 74 and the adder 76.

[0149] When the offset value θofst(-) is non-zero, the offset value gradation processing unit 73 operates such that the decrease in value θd output from the lower limit protection processing unit 84 is reflected in the offset value θofst(-). The offset value gradation processing unit 73 operates such that the sign of the offset value θofst(-) is not reversed due to the reflection of the decrease in value θd. That is, when the absolute value of the offset value θofst(-) is less than the absolute value of the decrease in value θd, the offset value gradation processing unit 73 operates such that the absolute value of the decrease in value θd is the same as the absolute value of the offset value θofst(-).

[0150] The function of the offset value acquisition and processing unit 71 will be described in detail below. Figure 10 As shown, the offset value acquisition and processing unit 71 includes a difference calculation unit 91, an absolute value processing unit 92, and a sign processing unit 93.

[0151] The converted angle θvg and the reduction value θd are input to the difference calculation unit 91. The difference calculation unit 91 calculates the difference base value Δθvgb obtained from the subtractor 95. The difference base value Δθvgb is obtained by subtracting the previous converted angle θvg(-) from the converted angle θvg, where the previous converted angle θvg(-) is the value held in the previous value holding unit 94 in the previous cycle (one cycle ago). The difference base value Δθvgb is the base value of the difference between the converted angle θvg in the current cycle and the previous cycle, without considering the reduction value θd for the offset value θofst. The value obtained by adding the reduction value θd to the obtained difference base value Δθvgb is output as the difference value Δθvg obtained from the adder 96 to the absolute value processing unit 92 and the sign processing unit 93. The difference Δθvg is the total difference between the current period and the previous period, taking into account the reduction θd for the offset θofst. When the offset θofst is zero, the difference base Δθvgb and the difference Δθvg have the same value.

[0152] The difference value Δθvg is input to an absolute value processing unit 92. The absolute value processing unit 92 calculates the absolute value of the difference value Δθvg. A value obtained by subtracting the angular velocity limit value ωpth from the absolute value of the acquired difference value Δθvg is output to a multiplier 98 as an excess value Δθvgx obtained from a subtracter 97. The excess value Δθvgx is a component corresponding to an excess value that exceeds the output limit of the turning motor 41, and indicates the absolute value of a component corresponding to an excess value by which the difference value Δθvg exceeds the angular velocity limit value ωpth. That is, the excess value Δθvgx is positive when the limit state is reached, and is negative when the limit state is not reached.

[0153] The difference value Δθvg is input to a sign processing unit 93. The sign processing unit 93 determines the sign of the difference value Δθvg and calculates one of "1" and "-1" as a value corresponding to the sign. The sign processing unit 93 calculates "1" when the difference value Δθvg is positive, and calculates "-1" when the difference value Δθvg is negative. A value obtained by multiplying the excess value Δθvgx by the calculated value of "1" or "-1" is output to a subtracter 750 and an adder 76 as an excess control value θacc obtained from the multiplier 98.

[0154] When the excess value Δθvgx is a positive value other than zero, the offset value acquisition processing unit 71 operates such that the excess value Δθvgx is reflected in the excess control value θacc. The state in which the excess value Δθvgx is positive is a state corresponding to a state in which the difference value Δθvg exceeds the angular velocity limit value ωpth based on the current command value Ib* at that time, that is, a target pinion angle θp* exceeding the output limit of the turning motor 41 is calculated (hereinafter, referred to as a "limit state").

[0155] When the excess value Δθvgx is zero or negative, the offset value acquisition processing unit 71 operates such that the excess value Δθvgx is not reflected in the excess control value θacc. That is, when the excess value Δθvgx is zero or negative, the offset value acquisition processing unit 71 operates such that the excess value Δθvgx is zero. The state in which the excess value Δθvgx is zero or negative is a state not corresponding to the limit state in which the difference value Δθvg does not exceed the angular velocity limit value ωpth based on the current command value Ib* at that time, that is, a target pinion angle θp* with a margin with respect to the output limit of the turning motor 41 is calculated.

[0156] The operation of this embodiment will be described below. Figure 11 Parts (a) to (c) of FIG. 12 show various change patterns in an example in which the excess value Δθvgx is positive, that is, the limit state has been reached at the time of time tl. The following description is based on the premise that the offset value θofst at time "0" is zero, and the vehicle speed V is constant. In the example shown in FIG. 12, the vehicle speed V is constant, and the current command value Ib* is constant. The angular velocity limit value ωpth is also constant. Figure 11In part (a) of FIG. 8, the horizontal axis represents the absolute value of the angular velocity ωp, and the vertical axis represents the absolute value of the actual current value Ib.

[0157] As shown in part (a) of FIG. 8, at the time t1, the excess value a of the difference value Δθvg exceeds the angular velocity limit value ωpth obtained from the current command value Ib* at that time, and the limit state is reached. Figure 11

[0158] This means that, as shown in part (b) of FIG. 8, a sudden change in the converted angle θvg indicated by the alternate long and short dashed lines in the figure is caused. At the time t1, the offset value acquisition processing unit 71 operates so that the excess value a is calculated as the excess control value θacc. By the function of the offset compensation and calculation unit 68, the excess control value θacc thus calculated is subtracted from the target pinion angle base value θpb* at that time to perform compensation on the target pinion angle θp*. Figure 11

[0159] In this case, as shown in part (c) of FIG. 8, the offset value acquisition processing unit 71 operates so that the offset value θofst representing the excess value a is calculated. After the time t1, the offset value fade processing unit 73 operates so that the offset value θofst, that is, the offset residual value θofstc, is changed to gradually decrease. The offset value θofst is changed to gradually decrease until it becomes zero at the time t2. By the function of the offset compensation and calculation unit 68, the offset value θofst thus acquired is used as the offset residual value θofstc, and the offset value θofst is subtracted from the converted angle θvg at that time to perform compensation on the target pinion angle θp*. Figure 11

[0160] Therefore, as indicated by the solid line of part (b) of FIG. 8, when the state corresponding to the limit state is reached, the target pinion angle θp* as the target control value after the time t1 is moved to the output limit of the turning motor 41 by using the compensation of the excess control value θacc. In particular, at the instant at which the limit state is reached, the compensation is performed so that the target pinion angle θp* is moved to the output limit of the turning motor 41. Figure 11 Thereafter, as indicated by the solid line in the figure, as the offset residual value θofstc gradually decreases, the target pinion angle θp* approaches the actually calculated converted angle θvg, that is, the original target pinion angle θp*. At the time t2 at which the offset residual value θofstc is zero, the target pinion angle θp* is changed to reach the actually calculated converted angle θvg, that is, the original target pinion angle θp*.

[0161]

[0162] ​​​​The advantages of this embodiment will be described below. In the present embodiment, as indicated by the solid line of the middle part (b), it is made difficult to cause a state in which the turning motor 41 needs to output power exceeding the limit even when the limit state is reached. Thus, generation of vibration or noise in the turning motor 41 can be suppressed. Figure 11

[0163] According to the present embodiment, the excess control value θacc, which is the difference between the angular velocity limit value ωpthand the difference Δθvg, is reflected in the offset value θofst. Thus, it can be appropriately made difficult to cause the limit state.

[0164] Here, since the offset value θofstforcibly moves the converted angle θvg, which is the original target pinion angle θp*, it is necessary to eliminate the offset value θofstas soon as possible, but an excessive reduction value of the offset value θofstis expressed as a movement of the turning mechanism TK that is not expected by the driver.

[0165] Thus, the offset value gradual change processing unit 73 has the function of the reduction gain map calculation unit 81 that takes into account the running state of the vehicle and the reduction value map calculation unit 82 that takes into account the turning state of the turning mechanism TK. Thus, as the vehicle speed V increases and the amount of change in the turning angle θwof the turning wheel 16 increases, the reduction value θdfor reducing the offset value θofstincreases. Thus, the feeling of discomfort of the driver can be suppressed and the offset value θofstcan be eliminated as soon as possible.

[0166] The difference base value Δθvgbmay be acquired from the difference between the target pinion angle θp* acquired on the basis of the converted angle θvgat that time and its previous value, or from the difference between the steering angle θsat that time and its previous value.

[0167] The offset compensation and calculation unit 68 according to the present embodiment can be added as a function of the steering side control unit 50a. This is effective when the steering reaction force command value T* is calculated to conform to the pinion angle θp.

[0168] Control of the turning motor 41 can be performed on the basis of the directly detected amount of movement of the turning shaft 14 instead of the pinion angle θp. In this case, in the foregoing embodiment, the control values and the like associated with the pinion angle θpare replaced by control values associated with the amount of movement of the turning shaft 14.

[0169] ​When the offset value θofst(-) is zero, the sign processing unit 85 can calculate and output "0 (zero)". In this case, when the offset value θofst(-) is zero, the reduction value θd is zero. That is, in this modified example, the offset value gradual change processing unit 73 can operate so that the reduction value θd output from the lower limit protection processing unit 84 is not reflected in the offset residual value θofstc when the offset value θofst(-) is zero.

[0170] When the difference Δθvg is zero, the sign processing unit 93 can calculate and output "0 (zero)". In this case, when the difference Δθvg is zero, the excess control value θacc is zero. That is, in this modified example, the offset value acquisition processing unit 71 can operate so that the excess value Δθvgx is not reflected in the excess control value θacc when the difference Δθvg is zero.

[0171] The steering angle ratio change and calculation unit 67 can change the steering angle ratio, for example, in accordance with a yaw rate detected by a yaw rate sensor of the vehicle other than the vehicle speed V. In this case, similarly to the foregoing embodiment, there is a state corresponding to the limit state. This can also be addressed by employing the offset compensation and calculation unit 68 according to the foregoing embodiment, similarly to the foregoing embodiment. This modified example can also be applied to a case in which the steering angle ratio is variable in accordance with a lateral acceleration output from a lateral acceleration sensor of the vehicle other than the vehicle speed V.

[0172] The steering reaction force command value calculation unit 53 needs to use at least the steering torque Th to calculate the steering reaction force command value T* and can not use the vehicle speed V or can use a combination thereof with another element.

[0173] In the foregoing embodiment, the steering angle ratio can be fixed. In this case, the steering angle ratio change and calculation unit 67 can be omitted. In the foregoing embodiment, the turning motor 41 can employ, for example, a structure in which the turning motor 41 is disposed coaxially with the turning shaft 14 or a structure in which the turning motor 41 is connected to the turning shaft 14 via a belt reduction gear using a ball screw mechanism.

[0174] In the foregoing embodiment, the CPU constituting the steering control device 50 can be realized as one or more processors executing a computer program, one or more dedicated hardware circuits such as an application specific integrated circuit executing at least some of the various processes, or a circuit including a combination of a processor and a dedicated hardware circuit. The memory can be constituted using all available media that can be accessed by a general-purpose or a special-purpose computer.

[0175] In the foregoing embodiment, the steering system 10 adopts a linkless structure in which the steering mechanism SK and the turning mechanism TK are generally mechanically disconnected from each other, but the present application is not limited to this, and a structure in which the steering mechanism SK and the turning mechanism TK can be mechanically disconnected by the clutch 21 can be adopted, as indicated by the alternate long and short dashed lines in FIG. 1. The steering system 10 can be an electric power steering system that applies an assist force, which is a force for assisting the steering of the steering wheel 11. In this case, the steering wheel 11 is mechanically connected to the pinion shaft 13 via the steering shaft 12. Figure 6

[0176] Third Embodiment

[0177] The third embodiment will be described below. Figure 12 A steering system 10 of a vehicle according to the third embodiment is shown. The same elements as in the first embodiment or the second embodiment will be indicated by the same reference numerals and the description thereof will be omitted.

[0178] The steering mechanism SK includes a reaction force motor 31, a reduction gear mechanism 32, a rotation angle sensor 33, and a torque sensor 34 as a configuration for generating a steering reaction force. The steering reaction force is a force that acts in a direction opposite to the direction of the operation of the steering wheel 11 by the driver. By applying the steering reaction force to the steering wheel 11, an appropriate response feeling can be given to the driver.

[0179] The reaction force motor 31 is a source of the steering reaction force. For example, a three-phase brushless motor is adopted as the reaction force motor 31. The reaction force motor 31, to be exact, its rotary shaft, is connected to the steering shaft 12 via the reduction gear mechanism 32. The torque of the reaction force motor 31 is applied to the steering shaft 12 as the steering reaction force.

[0180] The rotation angle sensor 33 is provided in the reaction force motor 31. The rotation angle sensor 33 detects the rotation angle θa of the reaction force motor 31. The rotation angle θa of the reaction force motor 31 is used to calculate the steering angle θs. The reaction force motor 31 and the steering shaft 12 are in combined operation with each other via the reduction gear mechanism 32. Therefore, the rotation angle θa of the reaction force motor 31 and the rotation angle of the steering shaft 12, that is, the steering angle θs as the rotation angle of the steering wheel 11, have a correlation. Therefore, the steering angle θs can be calculated on the basis of the rotation angle θa of the reaction force motor 31.

[0181] A vehicle power supply 502, which is a start switch of the vehicle such as an ignition switch, is connected to the steering control device 50. The vehicle power supply 502 detects the on / off state of the start switch of the vehicle and outputs a start signal Sig when the on state is detected.

[0182] ​The configuration of the steering control device 50 will be described below. The steering control device 50 includes a central processing unit (CPU) and a memory not shown, and the CPU executes a program stored in the memory at intervals of a predetermined operation cycle. Thus, various processes are executed.

[0183] Some processes are executed by the steering control device 50 shown in FIG. 1. Figure 13 The processes shown in FIG. 2 are some processes that are implemented by causing the CPU to execute the program stored in the memory for each of the processes implemented. Figure 13

[0184] The function of the steering-side control unit 50a will be described below. The steering torque Th, the vehicle speed V, the rotation angle θa, the turning-side actual current value Ib to be described later, and the pinion angle θp to be described later are input to the steering-side control unit 50a. The steering-side control unit 50a controls the electric power supply to the reaction force motor 31 based on the steering torque Th, the vehicle speed V, the rotation angle θa, the turning-side actual current value Ib to be described later, and the pinion angle θp to be described later. The pinion angle θp is calculated based on the rotation angle θb of the turning motor 41.

[0185] The steering-side control unit 50a includes a steering angle calculation unit 52, a steering reaction force command value calculation unit 53, and an electric power supply control unit 54. The rotation angle θa is input to the steering angle calculation unit 52. The steering angle calculation unit 52 converts the rotation angle θa to a total angle including a range exceeding 360°, for example, by counting the number of rotations of the reaction force motor 31 from a steering neutral position, which is the position of the steering wheel 11 when the vehicle is traveling straight ahead. The steering angle calculation unit 52 calculates a steering angle θs by multiplying the total angle obtained by the conversion by a conversion factor based on the rotation speed ratio of the reduction gear mechanism 32. For example, when the steering angle θs is a right side angle with respect to the steering neutral position θso, the steering angle θs is set to be positive, and when the steering angle θs is a left side angle with respect to the steering neutral position, the steering angle θs is set to be negative. The calculated steering angle θs is output to the steering-side control unit 50b.

[0186] The steering torque Th, the vehicle speed V, the turning-side actual current value Ib, and the pinion angle θp are input to the steering reaction force command value calculation unit 53. The steering reaction force command value calculation unit 53 calculates a steering reaction force command value T* that serves as a target control value of a target of the steering reaction force, based on the steering torque Th, the vehicle speed V, the turning-side actual current value Ib, and the pinion angle θp. The calculated steering reaction force command value T* is output to the electric power supply control unit 54.

[0187] ​The steering reaction force command value T*, the rotation angle θa, and the steering side actual current value Ia are input to the electric power supply control unit 54. The electric power supply control unit 54 calculates a current command value Ia* for the reaction force motor 31 based on the steering reaction force command value T*. The electric power supply control unit 54 calculates a difference between the current command value Ia* and a current value in the dq coordinate system obtained by converting the steering side actual current value Ia detected by the steering side current sensor 55 based on the rotation angle θa, and controls electric power supply to the reaction force motor 31 such that the difference is eliminated. Thus, the reaction force motor 31 generates a torque based on the steering reaction force command value T*. The driver can be given an appropriate sense of response based on the road reaction force.

[0188] The function of the turning side control unit 50b will be described below. The vehicle speed V, the rotation angle θb, and the steering angle θs are input to the turning side control unit 50b. The turning side control unit 50b controls electric power supply to the turning motor 41 based on the vehicle speed V, the rotation angle θb, the steering angle θs, and a start signal Sig to be described later.

[0189] The turning side control unit 50b includes a pinion angle calculation unit 61, a target pinion angle calculation unit 62, a pinion angle feedback control unit (pinion angle F / B control unit in the drawing) 63, and an electric power supply control unit 64.

[0190] The rotation angle θb is input to the pinion angle calculation unit 61. The pinion angle calculation unit 61 converts the rotation angle θb to a total angle including more than 360° range, for example, by counting the number of rotations of the turning motor 41 from a neutral rack position, which is the position of the turning shaft 14 when the vehicle is traveling straight forward. The pinion angle calculation unit 61 calculates a pinion angle θp, which is the actual rotation angle of the pinion shaft 44, by multiplying the total angle obtained by the conversion by a conversion factor based on the rotation speed ratio of the reduction gear mechanism 42. For example, when the pinion angle θp is a right side angle with respect to the midpoint θpo of the neutral rack position, the pinion angle θp is set to positive, and when the pinion angle θp is a left side angle with respect to the neutral rack position, the pinion angle θp is set to negative. The turning motor 41 and the pinion shaft 44 are operated in conjunction with each other via the reduction gear mechanism 42. Therefore, there is a correlation between the rotation angle θb of the turning motor 41 and the pinion angle θp. The correlation can be used to calculate the pinion angle θp from the rotation angle θb of the turning motor 41. The pinion shaft 44 is engaged with the turning shaft 14. Therefore, there is a correlation between the pinion angle θp and the amount of movement of the turning shaft 14. That is, the pinion angle θp is a value in which the turning angle θw of the turning wheel 16 is reflected, and is an example of a turning related angle. The calculated pinion angle θp is output to the target pinion angle calculation unit 62, the pinion angle F / B control unit 63, and the steering reaction force command value calculation unit 53.

[0191] The vehicle speed V, the steering angle θs, the pinion angle θp, and the start signal Sig are input to the target pinion angle calculation unit 62. The target pinion angle calculation unit 62 calculates a target pinion angle θp* that is a target angle of the pinion angle θp, which is a target control value, based on the vehicle speed V, the steering angle θs, the pinion angle θp, and the start signal Sig.

[0192] Specifically, the target pinion angle calculation unit 62 includes a steering angle ratio change and calculation unit 67 and an offset compensation and calculation unit 68. The vehicle speed V and the steering angle θs are input to the steering angle ratio change and calculation unit 67. The steering angle ratio change and calculation unit 67 calculates a converted angle θvg by adding an adjustment value Δθa to the steering angle θs. The steering angle ratio change and calculation unit 67 changes the adjustment value Δθa for changing a ratio of the converted angle θvg to the steering angle θs in accordance with the vehicle speed V. For example, the adjustment value Δθa is changed so that a change in a change of the converted angle θvg with respect to the steering angle θs when the vehicle speed V is low is larger than a change in a change of the converted angle θvg with respect to the steering angle θs when the vehicle speed V is high. The obtained converted angle θvg is output to the offset compensation and calculation unit 68 and the subtracter 69, and a converted angular velocity ωvg obtained by differentiating the converted angle θvg is output to the offset compensation and calculation unit 68 from the differentiator 66. The converted angle θvg is an angle that is used as a basis of the target pinion angle θp*. The pinion angle θp is controlled on the basis of the target pinion angle θp*. Therefore, there is a correlation between the converted angle θvg and the pinion angle θp. That is, the converted angular velocity ωvg obtained on the basis of the converted angle θvg is a value in which the turning angle θw of the turning wheel 16 is reflected as a turning state of the turning mechanism TK. The converted angle θvg is a value in which the turning angle θw of the turning wheel 16 is reflected. Therefore, the steering angle ratio is an example of a predetermined correspondence relationship between the steering angle θs and the turning angle θw of the turning wheel 16.

[0193] The vehicle speed V, the pinion angle θp, the converted angle θvg, the converted angular velocity ωvg, and the start signal Sig are input to the offset compensation and calculation unit 68. The offset compensation and calculation unit 68 calculates an offset value θofst as a compensation value at the time of calculating the target pinion angle θp* on the basis of the vehicle speed V, the pinion angle θp, the converted angle θvg, the converted angular velocity ωvg, and the start signal Sig. The offset value θofst will be described in detail later. A value obtained by subtracting the obtained offset value θofst from the converted angle θvg is output to the pinion angle F / B control unit 63 as the target pinion angle θp* obtained from the subtracter 69.

[0194] The target pinion angle θp* and the pinion angle θp are input to the pinion angle F / B control unit 63. The pinion angle F / B control unit 63 calculates the turning force command value Tp*, which is the target control value used as the target for the turning force in the feedback control of the pinion angle θp, so that the pinion angle θp conforms to the target pinion angle θp*. The obtained turning force command value Tp* is output to the power supply control unit 64.

[0195] The turning force command value Tp*, the rotation angle θb, and the actual turning side current value Ib are input to the power supply control unit 64. The power supply control unit 64 calculates the current command value Ib* for the turning motor 41 based on the turning force command value Tp*. Then, the power supply control unit 64 calculates the difference between the current command value Ib* and the current value in the dq coordinate system obtained by converting the actual turning side current value Ib detected by the turning side current sensor 65, based on the rotation angle θb, and controls the power supply to the turning motor 41 to eliminate this difference. Therefore, the turning motor 41 rotates by an angle corresponding to the turning force command value Tp*.

[0196] In the steering system 10, when the vehicle's start switch is off, the reaction force motor 31 and the steering motor 41 are not powered by the power supply control units 54 and 64. That is, even when the vehicle's start switch is off and the steering wheel 11 is turned, the steering wheel 16 does not turn. When the steering wheel 11 is manipulated in this state, the positional relationship between the steering wheel 11 and the steering wheel 16 deviates from a predetermined correspondence based on the steering angle ratio. To address this, the steering control device 50, i.e., the cornering side control unit 50b, has the function of an offset compensation and calculation unit 68.

[0197] The function of offset compensation and calculation unit 68 will be described in more detail below. For example... Figure 14 As shown, the offset compensation and calculation unit 68 includes an offset value acquisition and processing unit 71, a calculated value switching unit 72, and an offset value gradation processing unit 73.

[0198] The converted angle θvg and the pinion angle θp are input to the offset value acquisition and processing unit 71. The offset value acquisition and processing unit 71 calculates the starting shift value Δθvg_p obtained from the subtractor 74 by subtracting the pinion angle θp from the converted angle θvg. The obtained starting shift value Δθvg_p is output to the calculation value switching unit 72.

[0199] The start signal Sig, the start moving value Δθvg_p, and the preceding offset value θofst(-) held as a value held in the preceding value holding unit 75 in the preceding cycle (one cycle ago) are input to the calculated value switching unit 72. The start moving value Δθvg_p is input to the first input Nl of the calculated value switching unit 72, and the offset value θofst(-) is input to the second input N2 of the calculated value switching unit 72.

[0200] When the start signal Sig is input, the calculated value switching unit 72 controls the selection state so that the start moving value Δθvg_p input to the first input Nl is output as an offset base value θofstb, which is a base value of the offset value θofst. The selection state in which the start moving value Δθvg_p is output as the offset base value θofstb is instantaneously present when the start signal Sig is input. When the start signal Sig is input, it is determined that the start switch of the vehicle is switched from the off state to the on state at the start.

[0201] On the other hand, when the start signal Sig is not input, the calculated value switching unit 72 controls the selection state so that the offset value θofst(-) input to the second input N2 is output as the offset base value θofstb. The selection state in which the offset value θofst(-) is output as the offset base value θofstb is continuously held for a period in which the start signal Sig is not input. The period in which the start signal Sig is not input is a period in which it is determined that it is not the start time. The period in which it is not the start time is a period in which the start switch of the vehicle is in the on or off state, or a period in which the start switch is switched from the on state to the off state.

[0202] As the offset base value θofstb selected as a suitable value in this way, the start moving value Δθvg_p calculated by the offset value acquisition processing unit 71 at the time when the start signal Sig is input is output to the offset value gradual change processing unit 73. As the offset base value θofstb, the offset value θofst(-) that is the preceding value of the offset value gradual change processing unit 73 is output to the offset value gradual change processing unit 73 for a period in which the start signal Sig is not input.

[0203] The start moving value Δθvg_p is a non-zero value when the positional relationship between the steering wheel 11 and the cornering wheel 16 deviates from the predetermined correspondence based on the steering angle ratio. On the other hand, when it is determined that it is the start time, the calculated value switching unit 72 outputs the start moving value Δθvg_p input to the first input Nl thereof. That is, the start moving value Δθvg_p is a control value corresponding to the amount by which the cornering wheel 16 needs to turn in the first period immediately after the start. The calculated value switching unit 72 operates so that, when the start switch of the vehicle is in the off state, the amount by which the positional relationship between the steering wheel 11 and the cornering wheel 16 deviates from the predetermined correspondence based on the steering angle ratio due to the steering of the steering wheel 11 is reflected in the offset base value θofstb using the start moving value Δθvg_p.

[0204] On the other hand, even when it is determined that it is not the start time, the start moving value Δθvg_p has a non-zero value. In this regard, since the start moving value Δθvg_p input to the first input Nl is not output when it is determined that it is not the start time, the calculated value switching unit 72 operates so that the start moving value Δθvg_p generated at a time other than the time when it is determined that it is the start time is not reflected in the offset base value θofstb.

[0205] The vehicle speed V, the converted angular velocity ωvg, and the offset base value θofstb are input to the offset value tapering processing unit 73. Specifically, as shown in FIG. 8, the offset value tapering processing unit 73 includes a reduction gain map calculation unit 81, a reduction value map calculation unit 82, a storage unit 83, a lower limit protection processing unit 84, and a sign processing unit 85. Figure 15

[0206] The vehicle speed V is input to the reduction gain map calculation unit 81. The reduction gain map calculation unit 81 includes a map in which the relationship between the vehicle speed V and the reduction gain G is defined, and calculates the reduction gain G using the map and using the vehicle speed V as input. The reduction gain G is a gain for gradually reducing the offset value θofstso that the target pinion angle θp* does not suddenly change as the offset value θofstis reduced. In this case, the reduction gain G is calculated so that its absolute value increases as the vehicle speed V increases, taking into account the running state of the vehicle. The calculated reduction gain G is output to a multiplier 86.

[0207] ​The converted angular velocity ωvg is input to a reduction value mapping calculation unit 82. The reduction value mapping calculation unit 82 includes a mapping in which a relationship between an absolute value of the converted angular velocity ωvg and a reduction base value θdb that is a base value of the reduction value θd is defined, and calculates the reduction base value θdb using the mapping and using the absolute value of the converted angular velocity ωvg as an input. The reduction base value θdb is a component for gradually reducing the offset value θofst so that the target pinion angle θp* does not suddenly change as the offset value θofst decreases. In this case, the reduction base value θdb is calculated so that its absolute value increases as the converted angular velocity ωvg, that is, a rate of change of the turning angle θw of the turning wheel 16, increases, in consideration of a turning state of the turning mechanism TK. A value obtained by multiplying the calculated reduction base value θdb by a reduction gain G is output to the lower limit protection processing unit 84 as the reduction value θd obtained from the multiplier 86.

[0208] The storage unit 83 is a predetermined storage area of a memory (not shown) in which a minimum value θdmin of the reduction value θd is stored. The minimum value θdmin is a component for reducing the offset value θofst so that the offset value θofst does not persist. The minimum value θdmin is set to a value within a range experimentally obtained as an index for securing a minimum value of the reduction value θd even when the reduction value θd output from the multiplier 86 is smaller than the minimum value θdmin. The obtained minimum value θdmin is output to the lower limit protection processing unit 84.

[0209] The reduction value θd output from the multiplier 86 and the minimum value θdmin output from the storage unit 83 are input to the lower limit protection processing unit 84. The reduction value θd is input to a first input M1 of the lower limit protection processing unit 84, and the minimum value θdmin is input to a second input M2 of the lower limit protection processing unit 84. The lower limit protection processing unit 84 is configured to switch its selection state so that one of the reduction value θd and the minimum value θdmin is output as the reduction value θd.

[0210] Specifically, the lower limit protection processing unit 84 determines whether the reduction value θd input to the first input Ml is equal to or greater than the minimum value θdmin. When the reduction value θd input to the first input Ml is equal to or greater than the minimum value θdmin, the lower limit protection processing unit 84 controls the selection state of the lower limit protection processing unit 84 so that the reduction value θd input to the first input Ml is output as the final reduction value θd. On the other hand, when the reduction value θd input to the first input Ml is less than the minimum value θdmin, the lower limit protection processing unit 84 controls the selection state of the lower limit protection processing unit 84 so that the minimum value θdmin is output as the final reduction value θd. That is, the lower limit protection processing unit 84 operates to reduce the offset value θofst by at least the minimum value θdmin so that the offset value θofst does not persist. In this way, the reduction value θd selected as an appropriate value is output to the multiplier 87.

[0211] The offset base value θofstb is input to the sign processing unit 85. The sign processing unit 85 determines the sign of the offset base value θofstb and calculates one of "1" and "-1" as a value corresponding to the sign. The sign processing unit 85 calculates "1" when the offset base value θofstb is positive, and calculates "-1" when the offset base value θofstb is negative. The value obtained by multiplying the reduction value θd by the calculated value "1" or "-1" is output to the subtractor 88 as the final reduction value θd obtained from the multiplier 87. Then, the value obtained by subtracting the final reduction value θd from the offset base value θofstb is output to the subtractor 69 as the offset value θofst obtained from the subtractor 88.

[0212] When the offset value θofst is a non-zero value, the offset value ramp processing unit 73 operates so that the reduction value θd output from the lower limit protection processing unit 84 is reflected in the offset value θofst. On the other hand, when the offset value θofst is zero, the offset value ramp processing unit 73 operates so that the reduction value θd output from the lower limit protection processing unit 84 is not reflected in the offset value θofst. The offset value ramp processing unit 73 operates so that the sign of the offset base value θofstb is not reversed as a result of the reflection of the reduction value θd. That is, when the absolute value of the offset base value θofstb is less than the absolute value of the reduction value θd, the offset value ramp processing unit 73 operates so that the absolute value of the reduction value θd is the same as the absolute value of the offset base value θofstb.

[0213] The operation of this embodiment will be described below. Figure 16 Parts (a) to (c) of FIG. 12 show various change patterns in an example in which it is determined at the time t1 that it is the start time. The following description is based on the premise that the offset value θofst is zero at time "0" and the vehicle speed V is constant.

[0214] Figure 16 Part (a) shows the positional relationship between the steering wheel 11 and the turning angle θw of the turning wheel 16 at time "0". The state shown is when the turning angle θw of the turning wheel 16 corresponds to the midpoint θw0 of the neutral rack position and the vehicle's start switch is off. Due to the steering wheel 11 turning to the right by a predetermined angle, the positional relationship between the steering wheel 11 and the turning wheel 16 deviates from a predetermined correspondence based on the steering angle ratio. That is, the state shown is a state where the converted angle θvg obtained based on the steering angle θs does not match the pinion angle θp obtained based on the pinion shaft 44, which is "θvg≠θp".

[0215] At the timing of time tl, the vehicle's start switch is switched to the on state, and then the offset value acquisition and processing unit 71 operates to calculate the difference between the converted angle θvg and the pinion angle θp as the initial movement value Δθvg_p.

[0216] In this case, such as Figure 16 As shown in part (c), the calculation value switching unit 72 operates to calculate the offset base value θofstb representing the initial movement value Δθvg_p, and calculates it as the offset value θofst. After time t1, due to the function of the offset value gradual processing unit 73, the offset value θofst changes to gradually decrease. The offset value θofst changes to gradually decrease until it becomes zero at time t2. The converted angle θvg at this time is subtracted from the offset value θofst that has changed in this way to perform compensation on the target pinion angle θp* through the function of the offset compensation and calculation unit 68.

[0217] Therefore, as from Figure 16 As indicated by the alternating long and short dashed lines in part (b) of the diagram, when the start-up time is determined, the target pinion angle θp* that the turning wheel 16 needs to turn in the first cycle after start-up is inherently calculated based on the converted angle θvg at that time. On the other hand, as indicated by the solid lines in the attached diagram, after the time t1 when the start-up time is determined, the target pinion angle θp* moves in the direction of decreasing motor torque of the turning motor 41 by using compensation of the offset value θofst, so that the turning wheel 16 does not turn suddenly. At the timing point where the start-up time is determined, compensation is performed on the target pinion angle θp* (i.e., the control target pinion angle θp*) so that the motor torque of the turning motor 41 is zero.

[0218] Thereafter, as indicated by the solid line in the drawing, as the offset value θofst is gradually reduced, the target pinion angle θp* approaches the actually calculated converted angle θvg, and it is indicated by the alternate long and short dashed line in the drawing, that is, the original target pinion angle θp*. At the timing of the time t2 at which the offset value θofst is zero, the target pinion angle θp* changes to reach the actually calculated converted angle θvg, that is, the original target pinion angle θp*.

[0219] The advantages of this embodiment will be described below. In this embodiment, as indicated by the solid line in part (b) in the drawing, when it is determined that it is the start time, even if the target pinion angle θp* at which the cornering wheel 16 is required to turn in the first period after the start can be initially calculated on the basis of the converted angle θvg at that time, sudden turning of the cornering wheel 16 in the first period after the start can be suppressed. Thus, discomfort given to the driver can be suppressed. Figure 16

[0220] In this embodiment, the start movement value Δθvg_p is acquired as the offset value θofst. Thus, even when the positional relationship between the steering angle θs and the cornering angle θw, that is, the pinion angle θp deviates from the predetermined correspondence relationship based on the steering angle ratio, sudden turning of the cornering wheel 16 to a position corresponding to the steering angle θs in the first period after the start can be suppressed.

[0221] When a configuration for changing the steering angle ratio is provided as in this embodiment, it is particularly effective to acquire, as the offset value θofst, the start movement value Δθvg_p, which is the difference between the converted angle θvg and the pinion angle θp in the first period after the start.

[0222] Here, since the offset value θofst forcibly moves the actually calculated converted angle θvg, that is, the original target pinion angle θp*, it is required to eliminate the offset value θofst as soon as possible, but an excessive reduction value of the offset value θofst appears as a movement of the cornering mechanism TK that is not expected by the driver.

[0223] Thus, the offset value gradual change processing unit 73 has the functions of a reduction gain map calculation unit 81 that takes into account the running state of the vehicle and a reduction value map calculation unit 82 that takes into account the cornering state of the cornering mechanism TK. Thus, as the vehicle speed V increases and the amount of change in the cornering angle θw of the cornering wheel 16 increases, the reduction value θd for reducing the offset value θofst increases. Thus, discomfort of the driver can be suppressed and the offset value θofst can be eliminated as soon as possible.

[0224] ​The offset value gradual change processing unit 73 has a function of the lower limit protection processing unit 84 that takes into account the minimum value θdmin. Therefore, it is possible to prevent the offset value θofst from remaining continuously and it is possible to reduce the offset value θofst effectively.

[0225] In the reduction value map calculation unit 82, the pinion angle velocity obtained by differentiating the pinion angle θp can be used instead of the converted angular velocity ωvg. In addition, the reduction value map calculation unit 82 can calculate the reduction base value θdb corresponding to the angle at that time using the steering angle θs or the pinion angle θp.

[0226] The offset value θofst can not be obtained from the initial movement value Δθvg_p, but can be obtained from the difference between the steering angle θs and the converted pinion angle obtained by inverse transforming the pinion angle θp based on the steering angle ratio, or can be obtained from the difference between the value obtained by converting the steering angle θs to the movement amount of the turning shaft 14 and the actual movement amount of the turning shaft 14. In addition, the offset value θofst can be obtained from the difference between the steering angle θs immediately before the vehicle start switch is turned off and the steering angle θs at the time of start. In this case, the converted difference obtained by converting the difference based on the steering angle ratio can be used.

[0227] When the target control value for performing compensation is the turning force command value Tp* or the current command value Ib*, the offset value θofst can be obtained, for example, from the difference between the target pinion angle θp* and the pinion angle θp.

[0228] The offset compensation and calculation unit 68 according to this embodiment can be added as a function of the steering side control unit 50a. This is effective when the turning reaction force command value T* is calculated to conform to the pinion angle θp.

[0229] Instead of controlling the pinion angle θp, the control of the turning motor 41 can be performed based on the movement amount of the turning shaft 14 directly detected. In this case, in the foregoing embodiment, the control value and the like associated with the pinion angle θp are replaced with the control value associated with the movement amount of the turning shaft 14.

[0230] When the offset base value θofstb is zero, the sign processing unit 85 can calculate and output "0 (zero)". In this case, when the offset base value θofstb is zero, the reduction value θd is zero. That is, in this modified example, the offset value gradual change processing unit 73 can operate so that the reduction value θd output from the lower limit protection processing unit 84 is not reflected in the offset value θofst when the offset value θofst is zero.

[0231] The steering angle ratio changing and calculation unit 67 can, for example, change the steering angle ratio based on the yaw rate detected by the vehicle's yaw rate sensor, in addition to the vehicle speed V. In this case, similar to the aforementioned embodiment, when the vehicle's start switch is off, due to the steering of the steering wheel 11, the positional relationship between the steering wheel 11 and the turning wheel 16 deviates from a predetermined correspondence based on the steering angle ratio. Similar to the aforementioned embodiment, this can also be addressed by employing the offset compensation and calculation unit 68 according to the aforementioned embodiment. This modified example can also be applied to cases where the steering angle ratio is variable based on the lateral acceleration output from the vehicle's lateral acceleration sensor, in addition to the vehicle speed V.

[0232] The steering reaction force command value calculation unit 53 requires at least the steering torque Th to calculate the steering reaction force command value T*, and may not use the vehicle speed V or may use a combination of it with other elements.

[0233] In the aforementioned embodiments, the steering angle ratio can be fixed. In this case, the steering angle ratio changing and calculation unit 67 can be omitted. The steering motor 41 can be, for example, in a structure in which the steering motor 41 is coaxially arranged with the steering shaft 14 or in a structure in which the steering motor 41 is connected to the steering shaft 14 via a belt reduction gear using a ball screw mechanism.

[0234] In the foregoing embodiments, the CPU constituting the steering control device 50 can be implemented as one or more processors executing computer programs, one or more dedicated hardware circuits such as application-specific integrated circuits (ASICs) performing at least some of various processes, or a circuit comprising a combination of processors and dedicated hardware circuits. The memory can be constructed using any available media accessible by a general-purpose or special-purpose computer.

[0235] In the foregoing embodiments, the steering system 10 employs a linkageless structure, in which the steering mechanism SK and the turning mechanism TK are typically mechanically disconnected from each other. However, the present invention is not limited to this, and a structure in which the steering mechanism SK and the turning mechanism TK can be mechanically disconnected via a clutch 21 can also be used, such as by... Figure 12 The alternating long and two short dashed lines indicate this. The steering system 10 can be an electric power steering system that applies an auxiliary force, which is a force used to assist the steering of the steering wheel 11. In this case, the steering wheel 11 is mechanically connected to the pinion shaft 13 via the steering shaft 12.

Claims

1. A steering control device configured to control a steering system including a turning mechanism including a motor configured to generate a motor torque serving as a power to move a turning shaft (14) to turn a turning wheel (16) of a vehicle, the steering control device characterized by comprising: a control unit configured to control a target control value serving as a target of a control value that controls the motor torque of the motor, wherein the control unit is configured to: perform compensation on the target control value; acquire an offset value; and change the target control value so that the acquired offset value gradually decreases, the control unit is configured to be able to switch between a plurality of control states including a first control state in which a first target control value acquired under a predetermined condition is controlled and a second control state in which a second target control value acquired under a condition different from the predetermined condition of the first target control value is controlled, and to be able to perform the compensation so that, after a control state is switched, a post-switch target control value controlled in a post-switch control state moves toward a pre-switch target control value controlled in a pre-switch control state; and the control unit is configured to acquire, as the offset value, a difference between the target control value before and after the control state is switched when the control state is switched, the offset value being an amount by which the target control value moves through the compensation.

2. The steering control device according to claim 1, characterized in that: the first target control value is calculated in a condition in which a first state variable detected by a first detection device is used; the second target control value is calculated in a condition in which a second state variable detected by a second detection device is used; and the first detection device and the second detection device are redundant detection devices that respectively detect independent state variables of the same detection target.

3. A steering control device configured to control a steering system including a turning mechanism including a motor configured to generate a motor torque serving as a power to move a turning shaft (14) to turn a turning wheel (16) of a vehicle, the steering control device characterized by comprising: a control unit configured to control a target control value serving as a target of a control value that controls the motor torque of the motor, wherein the control unit is configured to: perform compensation on the target control value; acquire an offset value; and change the target control value so that the acquired offset value gradually decreases, the control unit is configured to, when a vehicle power supply is switched from an off state to an on state, perform the compensation so that the target control value is moved to decrease the motor torque of the motor; and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The control unit is configured to acquire, as the offset value, a control value corresponding to a turning amount of the turning wheel (16) to be turned in a first period after the vehicle power supply is switched from the off state to the on state, when the vehicle power supply is switched from the off state to the on state, the offset value being an amount by which the target control value is moved by the compensation, The steering system further includes a steering shaft (12) configured to be cut off from a power transmission path between the steering shaft (12) and the turning wheel (16), the steering shaft (12) being configured to be rotated in accordance with an operation of a steering wheel (11); The target control value is a target angle calculated as a value of a turning-related angle having relevance to a turning angle of the turning wheel (16) when a positional relationship with a steering angle satisfies a predetermined correspondence relationship, the steering angle being a rotation angle of the steering shaft (12); and The control unit is configured to acquire, as the offset value, a start movement value that is a difference between a value of the turning-related angle satisfying the predetermined correspondence relationship acquired on the basis of the steering angle and a value of the turning-related angle acquired on the basis of an actual turning angle in a first period after the vehicle power supply is switched from the off state to the on state.

4. The steering control device according to claim 3, characterized by The predetermined correspondence relationship is a steering angle ratio that is a ratio of the turning angle to the steering angle, and the predetermined correspondence relationship varies on the basis of a running state of the vehicle.

5. The turning control device according to any one of claims 1 to 4, characterized by, The control unit is configured to change a reduction value for reducing the offset value on the basis of at least one of a running state of the vehicle and a turning state of the turning mechanism.

6. The steering control device according to claim 5, characterized by The control unit is configured to reduce the offset value by at least a minimum value regardless of the running state of the vehicle and the turning state of the turning mechanism when the offset value is present.

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