Steering control device

Abstract

The present invention discloses a steering control device. The steering control device includes an electronic control unit, which is configured to: calculate a target reaction torque as a target value of a steering reaction force, which is a force opposing a steering input to a steering unit (4); and control the operation of a steering-side motor (13) provided in the steering unit (4) so as to generate a motor torque corresponding to the target reaction torque. The electronic control unit is configured to calculate an angular axial force as an axial component based on an axial force acting on a rotating shaft operated to rotate a rotating wheel (5), the angular axial force being an axial force in which road surface information is not reflected, and the angular axial force being determined based on an angle that can be converted into a rotation angle of the rotating wheel (5). The electronic control unit is configured to perform a protection process so that the angular axial force is not excessive.

Description

Technical Field

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

[0002] In the related art, a steer-by-wire system in which the power transmission path between a steering unit, which is steered by the driver, and a rotation unit, which rotates the steering wheels in response to the driver's steering, is disconnected, is known as a steering system. In this steering system, road surface information, such as the road surface reaction force applied to the steering wheels, is not mechanically transmitted to the steering wheel. Therefore, a steering control device that controls this steering system transmits road surface information to the driver by causing a steering-side actuator to apply a steering reaction force determined based on the road surface information to the steering wheel.

[0003] For example, Japanese Unexamined Patent Application Publication No. 2017-165219 (JP 2017-165219 A) discloses a steering control device that focuses on an axial force acting on a rotating shaft connected to a rotating wheel and determines a steering reaction force based on the following distributed axial force: The distributed axial force is obtained by distributing an angular axial force calculated based on a target steering angle obtained based on a steering angle of a steering wheel and a current axial force calculated based on a driving current for a rotating-side motor as a driving source of a rotating-side actuator at a predetermined distribution ratio. The angular axial force is calculated to increase as the absolute value of the target rotation angle increases. Summary of the Invention

[0004] While a vehicle is driving, it may find itself in a situation where, as the driver's steering wheel causes the vehicle to turn, the centrifugal force becomes greater than the friction between the rear wheels and the road surface. This situation is particularly likely to occur on low-friction roads, such as icy roads. In this situation, the vehicle is in an oversteer state, where the vehicle's rotation exceeds the driver's steering. In this oversteer state, the driver can perform what's known as countersteer, turning the steering wheel to the side opposite to the vehicle's direction of rotation, in order to restore the vehicle's attitude.

[0005] Here, the angular axial force is based on the target rotation angle obtained from the steering wheel's steering angle. Therefore, when countersteering is performed, the angular axial force increases as the steering wheel's steering angle increases, and the steering reaction force may become excessive. Consequently, when countersteering is performed, the driver may feel a sense of heaviness while steering the steering wheel, and the steering feel may become worse.

[0006] The present invention provides a steering control device capable of preventing a steering feeling from becoming worse in a case where reverse steering is performed.

[0007] A steering control device according to one aspect of the present invention is configured to control a steering system having a structure in which a power transmission path between a steering unit and a rotating unit that rotates a rotating wheel according to a steering input to the steering unit is cut off. The steering control device includes an electronic control unit configured to: calculate a target reaction torque as a target value of a steering reaction force, which is a force that opposes the steering input to the steering unit; and control the operation of a steering-side motor provided in the steering unit so as to generate a motor torque corresponding to the target reaction torque. The electronic control unit is configured to calculate an angular axial force as an axial component based on an axial force acting on a rotating shaft that operates to rotate the rotating wheel, the angular axial force being an axial force in which road surface information is not reflected, and the angular axial force is determined based on an angle that can be converted into a rotation angle of the rotating wheel. The electronic control unit is configured to perform a protection process so that the angular axial force is not excessive.

[0008] With this configuration, when calculating the axial component, a safeguard is implemented to prevent excessive angular axial force. Consequently, even in situations where reverse steering is being performed, excessive steering reaction force can be suppressed. Consequently, in situations where reverse steering is being performed, the driver is less likely to feel a sense of heaviness while steering the steering wheel (i.e., during steering wheel operation), and a worsening of steering feel can be prevented.

[0009] The electronic control unit can be configured to limit the absolute value of the angular axial force so that the absolute value of the angular axial force is equal to or less than the limit value at which the angular axial force is not excessive. By this configuration, the angular axial force can be appropriately limited to the desired limit value.

[0010] In the steering control device, the electronic control unit may be configured to store an angular axial force adjustment map for performing adjustments so that the angular axial force is not excessive. This configuration simplifies the configuration associated with the protection process because the angular axial force adjustment map can be used to perform adjustments so that the angular axial force is not excessive.

[0011] In a steering control device, the limit value can be adjusted based on vehicle speed. For example, when a vehicle is traveling at high speed, the axial force acting on the rotating shaft increases. Therefore, the angular axial force can be set to increase in consideration of the road surface reaction force. This also applies to situations where countersteering is being performed. In this regard, with this configuration, since the limit value is adjusted based on vehicle speed, it is possible to apply an appropriate steering reaction force while suppressing excessive steering reaction force in situations where countersteering is being performed.

[0012] With the steering control device according to an aspect of the present invention, it is possible to prevent the steering feeling from becoming worse in a case where reverse steering is performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like numerals represent like elements, and in which:

[0014] Figure 1 is a diagram schematically showing the configuration of a steering system;

[0015] Figure 2 is a block diagram showing a steering control device;

[0016] Figure 3 is a block diagram showing a target reaction torque calculation unit;

[0017] Figure 4 is a block diagram showing a reaction component calculation unit;

[0018] Figure 5 is a graph showing an example of an angular axial force adjustment map. DETAILED DESCRIPTION

[0019] The following will describe a steering control device according to an embodiment of the present invention with reference to the accompanying drawings. Figure 1 As shown, the steering system 2 controlled by the steering control device 1 according to the embodiment is configured as a steer-by-wire system. The steering system 2 includes a steering unit 4 steered by the driver via a steering wheel 3 and a turning unit 6 that turns a turning wheel 5 according to the steering of the steering unit 4 by the driver.

[0020] The steering unit 4 includes a steering shaft 11 to which the steering wheel 3 is fixed, and a steering actuator 12 that applies a steering reaction force to the steering shaft 11. The steering actuator 12 includes a steering motor 13 serving as a drive source, and a steering speed reducer 14 that reduces the rotation of the steering motor 13 and transmits the reduced rotation to the steering shaft 11. For example, a three-phase brushless motor can be employed as the steering motor 13 according to this embodiment.

[0021] The rotating unit 6 includes: a pinion shaft 21; a rack shaft 22 serving as a rotating shaft connected to the pinion shaft 21; a rack housing 23 that accommodates the rack shaft 22 so that the rack shaft 22 can reciprocate; and a rack and pinion mechanism 24 including the pinion shaft 21 and the rack shaft 22. The pinion shaft 21 and the rack shaft 22 are arranged to have a predetermined crossing angle. The pinion teeth 21a formed in the pinion shaft 21 and the rack teeth 22a formed in the rack shaft 22 are engaged with each other to constitute the rack and pinion mechanism 24. The pull rod 26 is connected to both ends of the rack shaft 22 via rack ends 25, each of which is formed of a spherical joint. The ends of the pull rod 26 are connected to the steering knuckles (not shown) to which the right and left turning wheels 5 and 5 are assembled.

[0022] The pinion shaft 21 is provided because the rack shaft 22 is supported in a housing (not shown). Specifically, the rack shaft 22 is supported so as to be movable in its axial direction and is pressed against the pinion shaft 21 by a support mechanism (not shown) provided in the steering system 2. Therefore, the rack shaft 22 is supported in the housing. Alternatively, a separate support mechanism supporting the rack shaft 22 can be provided in the housing, rather than using another support mechanism for the pinion shaft 21.

[0023] The rotating unit 6 includes a rotating actuator 31 that applies a rotational force to the rack shaft 22 for rotating the rotating wheel 5. The rotating actuator 31 includes a rotating motor 32 serving as a drive source, a transmission mechanism 33, and a conversion mechanism 34. The rotating actuator 31 applies a rotational force to the rotating unit 6 by transmitting the rotation of the rotating motor 32 to the conversion mechanism 34 via the transmission mechanism 33, and causing the conversion mechanism 34 to convert the rotation into reciprocating motion of the rack shaft 22. In this embodiment, a three-phase brushless motor, for example, is used as the rotating motor 32, a belt mechanism, for example, is used as the transmission mechanism 33, and a ball screw mechanism, for example, is used as the conversion mechanism 34.

[0024] In the steering system 2 having the aforementioned configuration, the rotation angle of the turning wheel 5 is changed by applying a turning force from the turning-side actuator 31 to the rack shaft 22 according to the driver's steering operation. At this time, a steering reaction force opposing the driver's steering is applied from the turning-side actuator 12 to the steering wheel 3.

[0025] The electrical configuration of this embodiment will be described below. The steering control device 1 is connected to the steering-side motor 13 and the turning-side motor 32, and controls the operation of the steering-side motor 13 and the turning-side motor 32. The steering control device 1 includes a central processing unit (CPU) and memory (not shown), and the CPU executes a program stored in the memory at intervals according to a predetermined operating cycle. Thus, various controls are performed. In other words, the steering control device 1 includes an electronic control unit (ECU) containing the CPU and memory.

[0026] Connected to the steering control device 1 are a vehicle speed sensor 41 that detects the vehicle speed V, which is the vehicle's traveling speed, and a torque sensor 42 that detects the steering torque Th applied to the steering shaft 11. The torque sensor 42 is located on the steering shaft 11 at a position closer to the steering wheel 3 than the connection to the steering-side speed reducer 14. The torque sensor 42 detects the steering torque Th based on the torsion of the torsion bar 43. A steering-side rotational angle sensor 44 detects the rotational angle θs of the steering-side motor 13, i.e., a relative angle within a range of 360° (360 degrees), as a detection value indicating the steering amount of the steering unit 4. A turning-side rotational angle sensor 45 detects the rotational angle θt of the turning-side motor 32, i.e., a relative angle, as a detection value indicating the rotation amount of the turning unit 6. Both the steering-side rotational angle sensor 44 and the turning-side rotational angle sensor 45 are connected to the steering control device 1. For example, the steering torque Th and the rotational angles θs and θt are detected as positive values when the steering wheel is turned right, and as negative values when the steering wheel is turned left. The steering control device 1 controls the operations of the steering-side motor 13 and the turning-side motor 32 based on various state quantities.

[0027] The configuration of the steering control device 1 will be described below. Figure 2 As shown, the steering control device 1 includes a steering control unit 51 that outputs a steering motor control signal Ms and a steering drive circuit 52 that supplies drive power to the steering motor 13 based on the steering motor control signal Ms. A current sensor 54 detects phase current values Ius, Ivs, and Iws of the phase current of the steering motor 13, which flows in a connecting line 53 between the steering drive circuit 52 and the phase motor coil of the steering motor 13. The current sensor 54 is connected to the steering control unit 51. Figure 2 , for convenience of description, the connection line 53 for the phase and the current sensor 54 for the phase are generally shown as a single one.

[0028] The steering control device 1 includes a rotation-side control unit 56 that outputs a rotation-side motor control signal Mt and a rotation-side drive circuit 57 that supplies drive power to the rotation-side motor 32 based on the rotation-side motor control signal Mt. A current sensor 59 detects phase current values Iut, Ivt, and Iwt of the phase current of the rotation-side motor 32, which flow in a connection 58 between the rotation-side drive circuit 57 and the phase motor coils of the rotation-side motor 32. The current sensor 59 is connected to the rotation-side control unit 56. Figure 2For ease of description, the phase connection lines 58 and the phase current sensors 59 are collectively shown as a single unit. For example, a known PWM inverter including multiple switching elements, such as FETs, is employed in each of the steering drive circuit 52 and the rotation drive circuit 57 according to this embodiment. The steering motor control signal Ms and the rotation motor control signal Mt are gate on / off signals that specify the on / off states of the switching elements.

[0029] The steering-side control unit 51 and the turning-side control unit 56 supply driving power from the vehicle-mounted power supply B to the steering-side motor 13 and the turning-side motor 32 by outputting the steering-side motor control signal Ms and the turning-side motor control signal Mt to the steering-side drive circuit 52 and the turning-side drive circuit 57. Thus, the steering-side control unit 51 and the turning-side control unit 56 control the operation of the steering-side motor 13 and the turning-side motor 32.

[0030] The following describes the configuration of the steering control unit 51. The steering control unit 51 generates a steering motor control signal Ms by executing the operation procedures indicated by the following control blocks at intervals according to a predetermined operation cycle. The steering control unit 51 receives inputs such as the vehicle speed V, steering torque Th, rotation angle θs, phase current values Ius, Ivs, and Iws, the q-axis current value Iqt serving as the drive current for the turning motor 32, and a rotation corresponding angle θp (described later). The steering control unit 51 then generates the steering motor control signal Ms based on these state quantities and outputs the generated steering motor control signal Ms.

[0031] Specifically, the steering side control unit 51 includes: a steering angle calculation unit 61 that calculates the steering angle θh of the steering wheel 3; a target reaction torque calculation unit 62 that calculates the target reaction torque Ts* as the target value of the steering reaction force; and a steering side motor control signal calculation unit 63 that outputs a steering side motor control signal Ms.

[0032] The rotation angle θs of the steering-side motor 13 is input to the steering angle calculation unit 61. The steering angle calculation unit 61 converts the rotation angle θs into a total angle encompassing a range exceeding 360°, for example, by counting the number of revolutions of the steering-side motor 13 from the steering neutral position, and then obtains this total angle. The steering angle calculation unit 61 calculates the steering angle θh by multiplying the converted total angle by a conversion factor based on the rotation speed ratio of the steering-side speed reducer 14. The calculated steering angle θh is output to the target reaction torque calculation unit 62.

[0033] The vehicle speed V, steering torque Th, steering angle θh, q-axis current value Iqt, and rotation correspondence angle θp are input to the target reaction torque calculation unit 62. As will be described later, the target reaction torque calculation unit 62 calculates a target reaction torque Ts* based on the state quantity and outputs the calculated target reaction torque Ts* to the steering-side motor control signal calculation unit 63. The target reaction torque calculation unit 62 outputs a target steering angle θh*, which is a target value of the steering angle θh of the steering wheel 3, obtained during the calculation of the target reaction torque Ts*, to the turning-side control unit 56.

[0034] In addition to the target reaction torque Ts*, the rotation angle θs and the phase current values Ius, Ivs, and Iws are input to the steering motor control signal calculation unit 63. According to this embodiment, the steering motor control signal calculation unit 63 calculates a d-axis target current value Ids* on the d-axis and a q-axis target current value Iqs* on the q-axis in the d / q coordinate system based on the target reaction torque Ts*. The d-axis target current value Ids* represents the target current value on the d-axis in the d / q coordinate system. The q-axis target current value Iqs* represents the target current value on the q-axis in the d / q coordinate system. The steering motor control signal calculation unit 63 calculates the q-axis target current value Iqs* so that its absolute value increases as the absolute value of the target reaction torque Ts* increases. In this embodiment, the d-axis target current value Ids* is set to substantially zero. The steering motor control signal calculation unit 63 generates the steering motor control signal Ms, which is output to the steering drive circuit 52, by performing current feedback control in the d / q coordinate system.

[0035] Specifically, the steering motor control signal calculation unit 63 calculates the d-axis current value Ids and the q-axis current value Iqs by mapping the phase current values Ius, Ivs, and Iws onto the d / q coordinate system based on the rotation angle θs. The d-axis current value Ids and the q-axis current value Iqs are the actual current values of the steering motor 13 in the d / q coordinate system. The steering motor control signal calculation unit 63 calculates target voltage values based on the current difference between the d-axis and the q-axis so that the d-axis current value Ids conforms to the d-axis target current value Ids* and the q-axis current value Iqs conforms to the q-axis target current value Iqs*, and calculates the steering motor control signal Ms having a duty ratio (duty cycle) based on the target voltage values.

[0036] The calculated steering motor control signal Ms is output to the steering drive circuit 52. Consequently, drive power corresponding to the steering motor control signal Ms is supplied from the steering drive circuit 52 to the steering motor 13. A steering reaction force indicated by the target reaction torque Ts* is applied from the steering motor 13 to the steering wheel 3.

[0037] The following describes the configuration of the turning-side control unit 56. The turning-side control unit 56 generates the turning-side motor control signal Mt by executing the operation process indicated by the following control blocks at intervals according to a predetermined operation cycle. The turning-side control unit 56 receives inputs such as the rotation angle θt, the target steering angle θh*, and the phase current values Iut, Ivt, and Iwt of the steering-side motor 32. The turning-side control unit 56 then generates the turning-side motor control signal Mt based on the state quantity and outputs the generated turning-side motor control signal Mt.

[0038] Specifically, the turning control unit 56 includes a turning corresponding angle calculation unit 71 that calculates a turning corresponding angle θp, which is the rotation angle of the pinion shaft 21. The turning control unit 56 also includes a target turning torque calculation unit 72 that calculates a target turning torque Tt*, which is a target value of the turning force, and a turning motor control signal calculation unit 73 that outputs a turning motor control signal Mt. In the steering system 2 according to this embodiment, the steering angle ratio, i.e., the ratio between the steering angle θh and the turning corresponding angle θp, is set to a fixed ratio of 1:1, and the target turning corresponding angle, which is the target value of the turning corresponding angle θp, is set to be the same as the target steering angle θh*.

[0039] The rotation angle θt of the steering-side motor 32 is input to the rotation-corresponding angle calculation unit 71. The rotation-corresponding angle calculation unit 71 converts the input rotation angle θt into a total angle by, for example, counting the number of revolutions of the steering-side motor 32 from a neutral position where the vehicle is moving straight forward, and obtains the total angle. The rotation-corresponding angle calculation unit 71 calculates the rotation-corresponding angle θp by multiplying the rotation angle converted into the total angle by a conversion factor based on the reduction ratio of the transmission mechanism 33, the lead of the conversion mechanism 34, and the speed ratio of the rack and pinion mechanism 24. That is, when it is assumed that the pinion shaft 21 is connected to the steering shaft 11, the rotation-corresponding angle θp corresponds to the steering angle θh of the steering wheel 3. The calculated rotation-corresponding angle θp is output to the subtractor 74 and the target reaction torque calculation unit 62. In addition to the rotation-corresponding angle θp, the target steering angle θh* is input to the subtractor 74.

[0040] The angular difference Δθp obtained from the subtractor 74 by subtracting the rotation corresponding angle θp from the target steering angle θh*, i.e., the target rotation corresponding angle, is input to the target rotation torque calculation unit 72. Based on the angular difference Δθp, the target rotation torque calculation unit 72 calculates the target rotation torque Tt*, which is the target value of the rotational force applied by the rotation-side motor 32, as a control value for bringing the rotation corresponding angle θp into conformity with the target steering angle θh*. Specifically, the target rotation torque calculation unit 72 calculates the target rotation torque Tt* by summing the output values of the proportional element, the integral element, and the differential element, and the angular difference Δθp used as input. That is, the target rotation torque calculation unit 72 calculates the target rotation torque Tt* based on the execution of the rotation angle feedback control so that the actual rotation corresponding angle θp conforms to the target steering angle θh*, i.e., the target rotation corresponding angle.

[0041] In addition to the target rotational torque Tt*, the rotation angle θt and the phase current values Iut, Ivt, and Iwt are input to the rotating-side motor control signal calculation unit 73. Based on the target rotational torque Tt*, the rotating-side motor control signal calculation unit 73 calculates the q-axis target current value Iqt* on the q-axis in the d / q coordinate system. The rotating-side motor control signal calculation unit 73 calculates the q-axis target current value Iqt* so that its absolute value increases as the absolute value of the target rotational torque Tt* increases. In this embodiment, the d-axis target current value Idt* on the d-axis is substantially set to zero. Similar to the steering-side motor control signal calculation unit 63, the rotating-side motor control signal calculation unit 73 generates the rotating-side motor control signal Mt, which is output to the rotating-side drive circuit 57, by performing current feedback control in the d / q coordinate system. The q-axis current value Iqt calculated during the calculation of the rotating-side motor control signal Mt is output to the target reaction torque calculation unit 62.

[0042] The calculated rotation-side motor control signal Mt is output to the rotation-side drive circuit 57. Consequently, the drive power corresponding to the rotation-side motor control signal Mt is supplied from the rotation-side drive circuit 57 to the rotation-side motor 32. The rotation-side motor 32 then applies a rotational force indicated by the target rotational torque Tt* to the rotating wheel 5.

[0043] The configuration of the target reaction torque calculation unit 62 will be described below. Figure 3As shown, the target reaction torque calculation unit 62 includes an input torque base component calculation unit 81 that calculates an input torque base component Tb*, which is a force used to rotate the steering wheel 3 in the direction of the driver's steering. The target reaction torque calculation unit 62 also includes a reaction component calculation unit 82 that calculates a reaction component Fir, which is a force resisting the rotation of the steering wheel 3 based on the driver's steering. The target reaction torque calculation unit 62 includes a target steering angle calculation unit 83 that calculates a target steering angle θh*, which is a target value for the steering angle θh; and a steering angle feedback control unit (hereinafter referred to as a "steering angle F / B control unit") 84 that calculates a steering angle feedback component (hereinafter referred to as a "steering angle F / B component") Tfbh by performing a steering angle feedback operation.

[0044] The steering torque Th is input to the input torque base component calculation unit 81. The input torque base component calculation unit 81 calculates the input torque base component Tb* so that its absolute value increases as the absolute value of the steering torque Th increases. The calculated input torque base component Tb* is input to the target steering angle calculation unit 83 and the adder 85.

[0045] The vehicle speed V, the steering angle θh, the q-axis current value Iqt of the steering-side motor 32, the rotation corresponding angle θp, and the target steering angle θh* are input to the reaction component calculation unit 82. The reaction component calculation unit 82 calculates a reaction component Fir corresponding to the axial force acting on the rack shaft 22 as will be described later based on the state quantity, and outputs the calculated reaction component to the target steering angle calculation unit 83.

[0046] The vehicle speed V, the steering torque Th, the input torque base component Tb*, and the reaction component Fir are input to the target steering angle calculation unit 83. The target steering angle calculation unit 83 calculates the target steering angle θh* using a model expression for relating the target steering angle θh* to the input torque Tin*, which is a value obtained by adding the steering torque Th to the input torque base component Tb* and subtracting the reaction component Fir therefrom.

[0047] Tin*=C·θh*'+J·θh*”…(1)

[0048] This model expression defines and expresses the relationship between the torque and rotation angle of a rotary shaft that rotates with the rotation of the steering wheel 3 in a configuration in which the steering wheel 3 and the turning wheel 5 are mechanically connected, that is, in which the steering unit 4 and the turning unit 6 are mechanically connected. This model expression is expressed using the viscosity coefficient C obtained by modeling the friction of the steering system 2 and the inertia coefficient J obtained by modeling the inertia of the steering system 2. The viscosity coefficient C and the inertia coefficient J are set to vary according to the vehicle speed V. The target steering angle θh* calculated using the model expression is output to the reaction component calculation unit 82 in addition to the subtractor 86 and the turning-side control unit 56.

[0049] The angular difference Δθs obtained from subtractor 86 by subtracting the steering angle θh from the target steering angle θh* is input to steering angle F / B control unit 84. Based on the angular difference Δθs, steering angle F / B control unit 84 then calculates a steering angle F / B component Tfbh, which serves as the basis for the steering reaction force applied by the steering-side motor 13. This component serves as a control value for controlling the steering angle θh to the target steering angle θh* through feedback. Specifically, steering angle F / B control unit 84 calculates the sum of the output values of the proportional element, the integral element, and the differential element, along with the angular difference Δθs used as input, as the basic reaction torque. The calculated steering angle F / B component Tfbh is output to adder 85.

[0050] The target reaction torque calculation unit 62 calculates, as a target reaction torque Ts*, a value obtained by adding the steering angle F / B component Tfbh to the input torque base component Tb* in the adder 85. The configuration of the reaction component calculation unit 82 will be described below.

[0051] like Figure 4As shown, the reaction component calculation unit 82 includes an allocated axial force calculation unit 91, an end reaction force calculation unit 92, and an obstacle contact reaction force calculation unit 93. The allocated axial force calculation unit 91 calculates the allocated axial force Fd as the axial component corresponding to the axial force acting on the rack shaft 22 that is operated to rotate the turning wheel 5. The end reaction force calculation unit 92 calculates the end reaction force Fie, which is a reaction force used to limit additional steering when the absolute value of the steering angle θh of the steering wheel 3 approaches the limit steering angle. The obstacle contact reaction force calculation unit 93 calculates the obstacle contact reaction force Fo, which is a reaction force used to limit steering so that the turning wheel 5 rotates toward an obstacle such as a curb when the turning wheel 5 contacts the obstacle during rotation. The reaction component calculation unit 82 calculates the reaction component Fir by adding the allocated axial force Fd to the larger absolute value of the end reaction force Fie or the obstacle contact reaction force Fo. Then, the reaction component calculation unit 82 outputs the reaction component Fir.

[0052] Specifically, the allocated axial force calculation unit 91 includes: a current axial force calculation unit 101 that calculates the current axial force Fer; and an angular axial force calculation unit 102 that calculates the angular axial force Fib. The current axial force Fer and the angular axial force Fib are calculated in the same dimension (N·m) as the torque. The allocated axial force calculation unit 91 includes a distribution processing unit 103 that calculates the allocated axial force Fd corresponding to the calculated axial force, which is an estimated axial force acting on the rack shaft 22 obtained by distributing the angular axial force Fib and the current axial force Fer in a predetermined ratio so that the axial force acting on the rack shaft 22 via the rotating wheel 5 is appropriately reflected.

[0053] The q-axis current value Iqt for the rotating-side motor 32 is input to the current axial force calculation unit 101. Based on the q-axis current value Iqt, the current axial force calculation unit 101 calculates the current axial force Fer. The current axial force Fer is the axial force actually acting on the rack shaft 22 that operates to rotate the rotating wheel 5, that is, an estimate of the axial force actually transmitted to the rack shaft 22. The current axial force Fer is calculated as an axial force that reflects road surface information. Examples of road surface information include information about subtle irregularities that do not affect the vehicle's lateral behavior and information about stepped portions that do affect the vehicle's lateral behavior. Specifically, the current axial force calculation unit 101 calculates the current axial force Fer so that its absolute value increases as the absolute value of the q-axis current value Iqt increases, assuming that the torque applied to the rack shaft 22 by the rotating-side motor 32 is balanced with the torque corresponding to the force applied to the rack shaft 22 via the rotating wheel 5. The calculated current axial force Fer is output to the multiplier 105.

[0054] The target steering angle θh* and the vehicle speed V, which are the target rotation corresponding angles, are input to the angular axial force calculation unit 102. The angular axial force calculation unit 102 calculates the angular axial force Fib based on the target steering angle θh* and the vehicle speed V. The angular axial force Fib is an ideal value of the axial force defined by a model of an appropriately set vehicle. The angular axial force Fib is calculated as an axial force in which road surface information is not reflected. Specifically, the angular axial force calculation unit 102 calculates the angular axial force Fib so that its absolute value increases as the absolute value of the target steering angle θh* increases. The angular axial force calculation unit 102 calculates the angular axial force Fib so that its absolute value increases as the vehicle speed V increases. The calculated angular axial force Fib is output to the protection processing unit 200.

[0055] The angular axial force Fib and the vehicle speed V are input to the protection processing unit 200. The protection processing unit 200 includes an angular axial force adjustment map in which the relationship between the angular axial force Fib and the vehicle speed V and the adjusted angular axial force Fib' is defined, and calculates the adjusted angular axial force Fib' using the map and the angular axial force Fib and the vehicle speed V as inputs. The angular axial force adjustment map is a map used to perform the protection process so that the angular axial force Fib is not excessive (i.e., so that the angular axial force Fib is not too large).

[0056] like Figure 5 As shown, the angular axial force Fib adjustment map is set so that when the absolute value of the angular axial force Fib is divided into three areas including a small area, a middle area and a large area, the adjusted angular axial force Fib' in the small area and the middle area increases linearly as the angular axial force Fib increases. The angular axial force adjustment map is set so that in the area where the absolute value of the angular axial force Fib is large, the absolute value of the adjusted angular axial force Fib' is limited to a predetermined limit value Flim. As the vehicle speed V becomes higher, the limit value Flim is set to have a larger value. Based on experiments, simulations, etc., the limit value Flim is set to a value within a range in which the reaction component Fir, i.e., the target reaction force Ts*, calculated based on the adjusted angular axial force Fib' is not excessive. The protection processing unit 200 adjusts the angular axial force Fib corresponding to the vehicle speed V by using the mapping calculation of the angular axial force adjustment map. The calculated adjusted angular axial force Fib' is output to the multiplier 106.

[0057] In addition to the vehicle speed V, the current axial force Fer and the adjusted angular axial force Fib' are input to the distribution processing unit 103. The distribution processing unit 103 includes a distribution gain calculation unit 107, which calculates distribution gains Ger and Gib as the distribution ratios for distributing the current axial force Fer and the angular axial force Fib' based on the vehicle speed V. The distribution gain calculation unit 107 according to this embodiment includes a distribution gain map that defines the relationship between the vehicle speed V and the distribution gains Ger and Gib, and calculates the distribution gains Ger and Gib using this map and the vehicle speed V as input. The distribution gain Gib has a smaller value when the vehicle speed V is high than when the vehicle speed V is low, and the distribution gain Ger has a larger value when the vehicle speed V is high than when the vehicle speed V is high. In other words, the distribution ratio of the angular axial force Fib along the distributed axial force Fd decreases as the vehicle speed V increases, and the distribution ratio of the current axial force Fer along the distributed axial force Fd increases as the vehicle speed V increases.

[0058] In particular, when the vehicle speed V is a low speed including a stop, the distribution gain Ger is zero. In this case, the current axial force Fer indicates that its distribution ratio is zero, that is, the current axial force is not distributed to the distributed axial force Fd. When the vehicle speed V is a high speed sufficiently higher than the low speed, the distribution gain Gib is zero. In this case, the angular axial force Fib indicates that its distribution ratio is zero, that is, the angular axial force is not distributed to the distributed axial force Fd. That is, the distribution ratio in this embodiment includes the concept of zero value, in which only one of the current axial force Fer and the angular axial force Fib is distributed to the distributed axial force Fd. The distribution gains Ger and Gib are calculated so that their sum is "1". The calculated distribution gain Ger is output to the multiplier 105, and the calculated distribution gain Gib is output to the multiplier 106.

[0059] The distribution processing unit 103 calculates the distributed axial force Fd by causing the adder 108 to add the value obtained by causing the multiplier 105 to multiply the current axial force Fer by the distribution gain Ger and the value obtained by causing the multiplier 106 to multiply the angle axial force Fib by the distribution gain Gib. The calculated distributed axial force Fd is output to the adder 94.

[0060] The target steering angle θh*, which is the target rotation corresponding angle, is input to the end reaction force calculation unit 92. The end reaction force calculation unit 92 includes an end reaction force map that defines the relationship between the target steering angle θh* and the end reaction force Fie, and uses this map and the target steering angle θh* as input to calculate the end reaction force Fie. The end reaction force map is configured so that when the absolute value of the target steering angle θh* is equal to or less than the threshold angle θie, a value of zero is calculated as the end reaction force Fie, and when the target steering angle θh* is greater than the threshold angle θie, a value greater than zero is calculated as the end reaction force Fie.

[0061] The end reaction force Fie is set so that when the target steering angle θh* increases sufficiently above the threshold angle θie, its absolute value becomes so large that human power steering is no longer possible. This end reaction force Fie is a high-gradient axial force whose value suddenly increases in proportion to the target steering angle θh* when the target steering angle θh* increases sufficiently above the threshold angle θie. The threshold angle θie is set to a value corresponding to the rotation angle θp at a virtual rack end position closer to neutral than the mechanical rack end position, where the rack end 25 contacts the rack housing 23 and axial movement of the rack shaft 22 is restricted. The calculated end reaction force Fie is output to the reaction force selection unit 95.

[0062] In addition to the q-axis current value Iqt, the angular difference Δθx obtained from the subtractor 96 by subtracting the rotation corresponding angle θp from the steering angle θh, and the rotation speed ωt obtained by differentiating the rotation corresponding angle θp, are input to the obstacle contact reaction force calculation unit 93. The obstacle contact reaction force calculation unit 93 according to the present embodiment calculates an obstacle contact gain Go based on the state quantity, indicating the degree of approximation to the situation in which the obstacle contact reaction force Fo would be applied. The obstacle contact reaction force calculation unit 93 includes an obstacle contact reaction force map in which the relationship between the obstacle contact gain Go and the obstacle contact reaction force Fo is defined, and calculates the obstacle contact reaction force Fo using this map and the obstacle contact gain Go as input.

[0063] The obstacle contact reaction force map is configured so that the obstacle contact reaction force Fo is zero when the obstacle contact gain Go is zero and gradually increases in proportion to the obstacle contact gain. When the obstacle contact gain Go exceeds the gain threshold Gth, the obstacle contact reaction force Fo suddenly increases in proportion to the obstacle contact gain Go. The gain threshold Gth is a value within the range within which it is possible to determine that the rotating wheel 5 will contact an obstacle through rotation and is set based on experiments, simulations, and other factors. The obstacle contact reaction force Fo is configured so that when the obstacle contact gain Go is sufficiently greater than the gain threshold Gth, its absolute value becomes so large that human steering is no longer possible. The obstacle contact reaction force Fo is a high-gradient axial force whose value suddenly increases in proportion to the obstacle contact gain Go when the obstacle contact gain Go exceeds the gain threshold Gth. Therefore, in the region where the obstacle contact gain Go is equal to or less than the gain threshold Gth, the obstacle contact reaction force Fo represents the reaction when only the tire portion of the rotating wheel 5 contacts the obstacle. This reaction force depends on the characteristics of the elastic component of the rubber of the rotating wheel 5 and the characteristics of the elastic component of the suspension of the vehicle connected to the rotating wheel 5, and can be calculated through experiments. In the area where the obstacle contact gain Go is greater than the gain threshold Gth, the reaction force when the wheel portion of the rotating wheel 5 contacts the obstacle is reproduced by the obstacle contact reaction force Fo. The calculated obstacle contact reaction force Fo is output to the reaction force selection unit 95.

[0064] In addition to the end reaction force Fie and the obstacle contact reaction force Fo, the steering speed ωh obtained by differentiating the steering angle θh is input to the reaction force selection unit 95. The reaction force selection unit 95 selects the reaction force with the larger absolute value between the end reaction force Fie and the obstacle contact reaction force Fo. The reaction force selection unit 95 then outputs the selected reaction force Fsl to the adder 94. The selected reaction force Fsl is a value obtained by setting the sign of the selected reaction force, that is, the direction of the selected reaction force, to the sign indicated by the steering speed ωh.

[0065] Then, the reaction component calculation unit 82 outputs the reaction component Fir to the target steering angle calculation unit 83. The reaction component Fir is a value obtained by causing the adder 94 to add the selected reaction force Fsl to the distributed axial force Fd. The operation of this embodiment will be described below.

[0066] While the vehicle is driving, it may find itself in a situation where, as the driver's steering of the steering wheel 3 causes the vehicle to turn, the centrifugal force becomes greater than the friction between the rear wheels and the road surface. This situation is particularly likely to occur on low-friction roads, such as icy roads. In this situation, the vehicle is in an oversteer state, where the vehicle's rotation exceeds the driver's steering of the steering wheel 3. In this oversteer state, the driver performs so-called countersteering to turn the steering wheel 3 to the side opposite to the vehicle's turning direction, thereby restoring the vehicle's posture. Here, the angular axial force Fib is based on the target turning angle θh* obtained based on the steering angle θh of the steering wheel 3. Therefore, when the steering angle θh of the steering wheel 3 reaches a large angle close to end contact due to countersteering, the angular axial force Fib becomes excessive, and the reaction component Fir calculated based on the angular axial force Fib increases. When the target reaction torque Ts* is calculated based on the reaction component Fir, the steering reaction force applied to the steering wheel 3 may become excessive.

[0067] In this regard, in the present embodiment, the protection process is performed by the protection processing unit 200 so that the angular axial force Fib is not excessive (i.e., so that the angular axial force Fib is not too large). That is, the angular axial force Fib' that has undergone adjustment through the protection process of the protection processing unit 200 is reflected in the reaction component Fir instead of the angular axial force Fib obtained by the angular axial force calculation unit 102. Therefore, even in a case where reverse steering is performed, the reaction component Fir and the target reaction torque Ts* calculated based on the reaction component Fir are unlikely to be excessive. Therefore, it is possible to suppress an excessive increase in the steering reaction force applied to the steering wheel 3.

[0068] Advantages of the present embodiment will be described below. (1) Since the protection process is performed by the protection processing unit 200 so that the angular axial force Fib is not excessive, the driver is less likely to feel heavy during steering of the steering wheel 3 in a case where reverse steering is being performed, and the steering feel can be prevented from becoming worse.

[0069] (2) Since the protection processing unit 200 can set the limit value Flim for the protection process, the angular axial force Fib can be appropriately limited to the desired limit value. (3) In this embodiment, since the angular axial force adjustment map can be used to perform adjustment so that the angular axial force Fib is not excessive, the configuration associated with the protection process can be simplified.

[0070] (4) In the present embodiment, since the angular axial force Fib is adjusted using the angular axial force adjustment map, the optimum steering reaction force based on the vehicle specifications can be easily achieved by changing the shape of the map.

[0071] (5) For example, when the vehicle is traveling at high speed, the axial force acting on the rack shaft 22 increases, so the angular axial force Fib can be set to increase in consideration of the road surface reaction force. This also applies to situations where countersteering is being performed. In this regard, in this embodiment, since the limit value Flim is adjusted based on the vehicle speed V, it is possible to apply an appropriate steering reaction force while suppressing excessive steering reaction force in situations where countersteering is being performed.

[0072] This embodiment may be modified as follows. Unless a technical conflict occurs, this embodiment and the following modified examples may be combined. The protection processing unit 200 may have a function of selecting a value to be output by comparing the absolute value of the angular axial force Fib with the limit value Flim, instead of a mapping calculation function that adjusts the mapping using the angular axial force. In this case, the protection processing unit 200 is in a selection state in which the angular axial force Fib obtained by the angular axial force calculation unit 102 is output when the absolute value of the angular axial force Fib is equal to or less than the limit value Flim. On the other hand, the protection processing unit 200 is in a selection state in which the angular axial force Fib set to the limit value Flim is output when the absolute value of the angular axial force Fib is greater than the limit value Flim. The protection processing unit 200 may have a function of making the absolute value of the angular axial force Fib equal to or less than the limit value Flim by offsetting the angular axial force Fib by a predetermined offset value to reduce the absolute value of the angular axial force Fib. In this case, the protection processing unit 200 is in a state in which, when the absolute value of the angular axial force Fib is equal to or less than the limit value Flim, the angular axial force Fib acquired by the angular axial force calculation unit 102 is output. On the other hand, the protection processing unit 200 is in a state in which, when the absolute value of the angular axial force Fib is greater than the limit value Flim, the angular axial force Fib offset by a predetermined offset value is output.

[0073] The limit value Flim may not be changed according to the vehicle speed V. The limit value Flim may be changed according to another parameter such as the lateral acceleration or the yaw rate, for example. In this case, the vehicle speed V may be added to the parameters.

[0074] In controlling the steering-side motor 13, the target reaction torque Ts* can be calculated using the input torque base component Tb*, obtained by executing torque feedback control to bring the steering torque Th into conformity with the target steering torque calculated based on the steering torque Th and the reaction component Fir. Alternatively, in controlling the steering-side motor 13, so-called feedforward control can be implemented rather than steering angle F / B control. In this case, the target reaction torque Ts* can be calculated based on the assist component calculated from the steering torque Th and the reaction component Fir.

[0075] The distribution processing unit 103 may change the distribution ratio of the current axial force Fer and the angular axial force Fib according to parameters other than the vehicle speed V. For example, a driving mode indicating a state in which a control mode of an onboard engine or the like is set may be used as such a parameter.

[0076] The obstacle contact reaction force calculation unit 93 may determine whether to apply the obstacle contact reaction force Fo based on, for example, a result of comparison between the q-axis current value Iqt, the angle difference Δθx and the rotation speed ωt and their corresponding thresholds.

[0077] The angular axial force calculation unit 102 may calculate the angular axial force Fib based on the steering angle θh or the rotation corresponding angle θp, or may calculate the angular axial force Fib using another method that considers other parameters such as the steering torque Th or the vehicle speed V.

[0078] In addition to the current axial force Fer and the angle axial force Fib, an axial force based on another parameter may be assigned to the assigned axial force Fd. For example, an axial force based on a vehicle state quantity calculated based on the yaw rate and lateral acceleration, an axial force based on the detection value of an axial force sensor detecting the axial force of the rack shaft 22, or an axial force based on the tire force acting on the rotating wheel 5 may be used as the axial force based on another parameter.

[0079] The reaction component calculation unit 82 can reflect at least the angular axial force Fib in the reaction component Fir. When the reaction component calculation unit 82 only reflects the angular axial force Fib in the reaction component Fir, the current axial force calculation unit 101 and the distribution processing unit 103 can be omitted.

[0080] The reaction component calculation unit 82 can calculate one of the end reaction force Fie and the obstacle contact reaction force Fo as the reaction component for limiting steering. The reaction component calculation unit 82 can set the reaction component for limiting steering to a reaction force that occurs in situations or conditions different from those in which the end reaction force Fie and the obstacle contact reaction force Fo occur, instead of or in addition to the end reaction force Fie and the obstacle contact reaction force Fo. For example, the reaction force that occurs when the voltage of the vehicle-mounted power supply B decreases and the rotation-side motor 32 cannot apply sufficient rotational force can be used as the reaction force that occurs in situations or conditions different from those in which the end reaction force Fie and the obstacle contact reaction force Fo occur.

[0081] In the aforementioned expression (1), the target steering angle θh* can be calculated using a model expression that is additionally modeled using a so-called spring constant (eg, spring coefficient K) determined based on the specifications of the suspension or wheel alignment of the vehicle.

[0082] In the aforementioned embodiment, as the controlled steering system 2, a steering system having a structure in which the power transmission path between the steering unit 4 and the rotating unit 6 can be cut off by a clutch can be controlled. In the above embodiment, the steering control device 1 can be composed of a processing circuit, which includes: 1) one or more processors operating according to a computer program (software), 2) one or more dedicated hardware circuits, such as application-specific integrated circuits (ASICs) that execute at least some of the various processes, or 3) a combination thereof. The processor includes a CPU and memories such as RAM and ROM. The memory stores program codes or instructions for the CPU to execute processes. The memory, i.e., non-transitory computer-readable media, includes all available media that can be accessed by a general-purpose or special-purpose computer.

Claims

1. A steering control device configured to control a steering system having a structure in which a power transmission path between a steering unit (4) and a rotation unit (6) that rotates a rotation wheel (5) according to a steering input to the steering unit (4) is cut off, the steering control device being characterized by comprising: an electronic control unit configured to calculate a target reaction torque as a target value of a steering reaction force, the steering reaction force being a force opposing the steering input to the steering unit (4); and controlling the operation of a steering-side motor (13) provided in the steering unit (4) so as to generate a motor torque corresponding to the target reaction torque, wherein the electronic control unit is configured to calculate an angular axial force as an axial component based on an axial force acting on a rotating shaft that operates to rotate the rotating wheel (5), the angular axial force being an axial force in which road surface information is not reflected, and the angular axial force being determined based on an angle that can be converted into a rotation angle of the rotating wheel (5), and Wherein, the electronic control unit is configured to perform a protection process so that the angular axial force is not excessive.

2. The steering control device according to claim 1, characterized in that: The electronic control unit is configured to limit an absolute value of the angular axial force so that the absolute value of the angular axial force is equal to or less than a limit value at which the angular axial force is not excessive.

3. The steering control device according to claim 2, characterized in that: The electronic control unit is configured to store an angular axial force adjustment map for performing adjustment so that the angular axial force is not excessive.

4. The steering control device according to claim 2 or 3, characterized in that: The limit value is adjusted based on vehicle speed.

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