Steering control device

Abstract

To provide a steering control device that is able to suppress deterioration of steering feeling in a situation where counter steering is performed.SOLUTION: A target reaction torque calculation unit calculates target reaction torque to be a target value of a steering reaction force that is a force against a steering unit that is input to the steering unit. The target reaction torque calculation unit includes a reaction component calculation unit 82 that calculates a reaction component Fir that is a force against a rotation of the steering wheel made by the steering of a driver. The reaction component calculation unit 82 includes an angular axial force calculation unit 102 that calculates an angular axial force Fib that is determined according to a target steering angle θh* and is an axial force whose road surface information is not reflected, as an axial force component corresponding to an axial force acting on a rack shaft that operates in order to turn a turning wheel. Further, the reaction force component calculation unit 82 includes a guard processing unit 200 that performs guard processing so as not to excessively increase the angular axial force Fib.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] Conventionally, as one type of steering device, there is a steer-by-wire type steering device in which a power transmission path between a steering section steered by a driver and a steering section that steers the steered wheels in response to the driver's steering is separated. In this type of steering device, road surface information such as a road surface reaction force received by the steered wheels is not mechanically transmitted to the steering wheel. Therefore, some steering control devices that control this type of steering device apply a steering reaction force that takes into account the road surface information to the steering wheel by a steering side actuator, thereby transmitting the road surface information to the driver.

[0003] For example, Patent Document 1 discloses a steering control device that focuses on the axial force acting on a steering shaft connected to a steered wheel and determines a steering reaction force based on a distributed axial force obtained by distributing, at a predetermined distribution ratio, an angle axial force calculated from a target steering angle obtained based on the steering angle of the steering wheel and a current axial force calculated from a drive current of a steering-side motor that is a drive source of a steering-side actuator. Note that the angle axial force is calculated to be a larger axial force as the absolute value of the target steering angle becomes larger. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-165219 A Summary of the Invention [Problem to be solved by the invention]

[0005] When a vehicle is traveling, the centrifugal force may become greater than the frictional force between the rear wheels and the road surface while the driver is turning the steering wheel. This condition is particularly likely to occur on low-friction roads such as icy roads. In this case, the vehicle becomes oversteered, turning toward the side in which the vehicle is turning more than the driver has turned the steering wheel. In this oversteered state, the driver may steer the steering wheel in the direction opposite to the direction in which the vehicle is turning, which is called counter-steering, in order to correct the vehicle's position.

[0006] Here, the angular axial force corresponds to a target steering angle obtained based on the steering angle of the steering wheel. Therefore, when counter-steering is performed, the angular axial force increases as the steering angle of the steering wheel increases, and the steering reaction force may become excessive. As a result, when counter-steering is performed, the driver may feel that the steering of the steering wheel is heavy, and the steering feeling may deteriorate.

[0007] An object of the present invention is to provide a steering control device that can suppress deterioration of steering feeling when counter-steering is performed. [Means for solving the problem]

[0008] A steering control device that solves the above problem is a steering control device that controls a steering device having a structure in which a power transmission path between a steering unit and a steering unit that steers the steered wheels in accordance with steering input to the steering unit is separated, and is equipped with a target reaction torque calculation unit that calculates a target reaction torque that is a target value of a steering reaction force, which is a force that resists the steering input to the steering unit, and controls 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, wherein the target reaction torque calculation unit includes an angle axial force calculation unit that calculates an angular axial force, which is an axial force that is determined in accordance with an angle that can be converted into a steering angle of the steered wheels and does not reflect road surface information, as an axial force component corresponding to an axial force acting on a steering shaft that operates to steer the steered wheels, and the target reaction torque calculation unit includes a guard processing unit that performs guard processing to prevent the angular axial force from becoming excessive.

[0009] According to the above configuration, in the calculation of the axial force component, a guard process is performed so that the angular axial force does not become excessive. This prevents the steering reaction force from becoming excessive even in a situation where counter steering is performed. Therefore, in a situation where counter steering is performed, the driver is less likely to feel the steering of the steering wheel as being heavy, and deterioration of the steering feeling can be suppressed.

[0010] Specifically, the guard processing unit can achieve this by limiting the absolute value of the angular axial force to a limit value or less so that the angular axial force does not become excessive. According to the above configuration, the angular axial force can be appropriately limited to a desired value.

[0011] In the above steering control device, it is preferable that the guard processing unit includes an angle axial force adjustment map for making an adjustment so that the angle axial force does not become excessive. According to the above configuration, since the angular axial force can be adjusted by the angular axial force adjustment map so that the angular axial force does not become excessive, the configuration relating to the guard process can be simplified.

[0012] In the above steering control device, it is preferable that the limit value is adjusted based on the vehicle speed. For example, when a vehicle is traveling at high speed, the axial force acting on the steering shaft becomes large, and therefore, taking into consideration the road surface reaction force, it is preferable to set the angular axial force to be large. This is also true in a situation where counter-steering is performed. In consideration of this, in the above configuration, the limit value is adjusted based on the vehicle speed, so that an appropriate steering reaction force can be applied while preventing the steering reaction force from becoming excessive in a situation where counter-steering is performed. Effect of the Invention

[0013] According to the steering control device of the present invention, it is possible to suppress deterioration of steering feeling in a situation where counter steering is performed. [Brief description of the drawings]

[0014] [Figure 1] FIG. [Diagram 2] FIG. [Diagram 3] FIG. 4 is a block diagram of a target reaction torque calculation unit. [Figure 4] FIG. 4 is a block diagram of a reaction force component calculation unit. [Diagram 5] 13 is a graph showing an example of an angle axial force adjustment map. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of a steering control device will be described with reference to the drawings. As shown in Fig. 1, the steering device 2 to be controlled by the steering control device 1 of this embodiment is configured as a steer-by-wire type steering device. The steering device 2 includes a steering unit 4 that is steered by a driver via a steering wheel 3, and a turning unit 6 that steers steered wheels 5 in response to steering of the steering unit 4 by the driver.

[0016] The steering section 4 includes a steering shaft 11 to which the steering wheel 3 is fixed, and a steering side actuator 12 capable of applying a steering reaction force to the steering shaft 11. The steering side actuator 12 includes a steering side motor 13 serving as a drive source, and a steering side reducer 14 that reduces the rotation of the steering side motor 13 and transmits it to the steering shaft 11. Note that a three-phase brushless motor, for example, is used as the steering side motor 13 in this embodiment.

[0017] The steered portion 6 includes a pinion shaft 21, a rack shaft 22 as a steered shaft connected to the pinion shaft 21, a rack housing 23 that accommodates the rack shaft 22 so that it can reciprocate, and a rack-and-pinion mechanism 24 consisting of the pinion shaft 21 and the rack shaft 22. The pinion shaft 21 and the rack shaft 22 are disposed at a predetermined cross angle, and the rack-and-pinion mechanism 24 is formed by meshing pinion teeth 21a formed on the pinion shaft 21 with rack teeth 22a formed on the rack shaft 22. Tie rods 26 are connected to both ends of the rack shaft 22 via rack ends 25 consisting of ball joints, and the ends of the tie rods 26 are connected to knuckles (not shown) to which the left and right steered wheels 5 are respectively assembled.

[0018] The pinion shaft 21 is provided in order to support the rack shaft 22 inside a housing (not shown). In other words, the rack shaft 22 is supported movably along its axial direction and is pressed toward the pinion shaft 21 by a support mechanism (not shown) provided in the steering device 2. In this way, the rack shaft 22 is supported inside the housing. However, another support mechanism for supporting the rack shaft 22 in the housing may be provided without using the pinion shaft 21.

[0019] The steering unit 6 includes a steering-side actuator 31 that applies a steering force to the rack shaft 22 to steer the steered wheels 5. The steering-side actuator 31 includes a steering-side motor 32 that serves as a drive source, a transmission mechanism 33, and a conversion mechanism 34. The steering-side actuator 31 transmits the rotation of the steering-side motor 32 to the conversion mechanism 34 via the transmission mechanism 33, and converts it into reciprocating motion of the rack shaft 22 in the conversion mechanism 34, thereby applying a steering force to the steering unit 6. Note that in this embodiment, for example, a three-phase brushless motor is used for the steering-side motor 32, for example, a belt mechanism is used for the transmission mechanism 33, and for example, a ball screw mechanism is used for the conversion mechanism 34.

[0020] In the steering device 2 configured in this manner, a steering force is applied from the steering-side actuator 31 to the rack shaft 22 in response to a steering operation by the driver, thereby changing the steering angle of the steered wheels 5. At this time, a steering reaction force that resists the steering by the driver is applied to the steering wheel 3 from the steering-side actuator 12.

[0021] The electrical configuration of this embodiment will be described. The steering control device 1 is connected to the steering side motor 13 and the steered side motor 32, and controls the operation of these. The steering control device 1 is equipped with a central processing unit (CPU) and memory (not shown), and the CPU executes a program stored in the memory at each predetermined calculation cycle. This allows various controls to be performed.

[0022] The steering control device 1 is connected to a vehicle speed sensor 41 that detects a vehicle speed V, which is the traveling speed of the vehicle, and a torque sensor 42 that detects a steering torque Th applied to the steering shaft 11. The torque sensor 42 is provided on the steering wheel 3 side of the steering shaft 11 relative to the connecting portion with the steering side reduction gear 14, and detects the steering torque Th based on the twist of a torsion bar 43. The steering control device 1 is also connected to a steering side rotation sensor 44 that detects a rotation angle θs of the steering side motor 13 as a relative angle within a range of 360 degrees as a detection value indicating the steering amount of the steering unit 4, and a turning side rotation sensor 45 that detects a rotation angle θt of the turning side motor 32 as a relative angle as a detection value indicating the steering amount of the turning unit 6. The steering torque Th and the rotation angles θs, θt are detected as positive values ​​when the vehicle is steered to the right, and as negative values ​​when the vehicle is steered to the left, for example. The steering control device 1 then controls the operation of the steering-side motor 13 and the steered-side motor 32 based on these various state quantities.

[0023] The configuration of the steering control device 1 will be described in detail. As shown in Fig. 2, the steering control device 1 includes a steering side control unit 51 that outputs a steering side motor control signal Ms, and a steering side drive circuit 52 that supplies drive power to the steering side motor 13 based on the steering side motor control signal Ms. A current sensor 54 is connected to the steering side control unit 51 to detect each phase current value Ius, Ivs, Iws of the steering side motor 13 flowing through a connection line 53 between the steering side drive circuit 52 and a motor coil of each phase of the steering side motor 13. Note that in Fig. 2, for convenience of explanation, the connection lines 53 of each phase and the current sensors 54 of each phase are illustrated as one each.

[0024] The steering control device 1 includes a steering side control unit 56 that outputs a steering side motor control signal Mt, and a steering side drive circuit 57 that supplies drive power to the steering side motor 32 based on the steering side motor control signal Mt. A current sensor 59 is connected to the steering side control unit 56 to detect each phase current value Iut, Ivt, Iwt of the steering side motor 32 flowing through a connection line 58 between the steering side drive circuit 57 and the motor coil of each phase of the steering side motor 32. For convenience of explanation, in FIG. 2, the connection lines 58 of each phase and the current sensors 59 of each phase are illustrated as one. The steering side drive circuit 52 and the steering side drive circuit 57 of this embodiment each employ a well-known PWM inverter having a plurality of switching elements such as FETs. Also, the steering side motor control signal Ms and the steering side motor control signal Mt are gate on / off signals that define the on / off state of each switching element.

[0025] The steering side control unit 51 and the turning side control unit 56 then output 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, thereby supplying drive power from the on-board power source B to the steering side motor 13 and the turning side motor 32, respectively. In this way, 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.

[0026] The configuration of the steering side control unit 51 will be described. The steering-side control unit 51 executes each calculation process shown in each control block below at each predetermined calculation cycle to generate the steering-side motor control signal Ms. The steering-side control unit 51 receives the vehicle speed V, steering torque Th, rotation angle θs, each phase current value Ius, Ivs, Iws, q-axis current value Iqt which is the drive current of the turning-side motor 32, and a turning corresponding angle θp described later. The steering-side control unit 51 generates and outputs the steering-side motor control signal Ms based on each of these state quantities.

[0027] In detail, 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 a target reaction torque Ts* which is a 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.

[0028] The steering angle calculation unit 61 receives the rotation angle θs of the steering-side motor 13. The steering angle calculation unit 61 converts the rotation angle θs into an integrated angle including a range exceeding 360 degrees, for example, by counting the number of rotations of the steering-side motor 13 from the steering neutral position, and obtains the angle. The steering angle calculation unit 61 then multiplies the rotation angle converted into the integrated angle by a conversion coefficient based on the rotation speed ratio of the steering-side reduction gear 14 to calculate the steering angle θh. The steering angle θh calculated in this manner is output to the target reaction force torque calculation unit 62.

[0029] The vehicle speed V, steering torque Th, steering angle θh, q-axis current value Iqt, and steering corresponding angle θp are input to the target reaction torque calculation unit 62. The target reaction torque calculation unit 62 calculates a target reaction torque Ts* based on these state quantities as described below, and outputs the target reaction torque Ts* to the steering-side motor control signal calculation unit 63. The target reaction torque calculation unit 62 also outputs to the steering-side control unit 56 the target steering angle θh*, which is a target value of the steering angle θh of the steering wheel 3 obtained in the process of calculating the target reaction torque Ts*.

[0030] 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 side motor control signal calculation unit 63. The steering side motor control signal calculation unit 63 of this embodiment 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* indicates the target current value on the d-axis in the d / q coordinate system, and the q-axis target current value Iqs* indicates the target current value on the q-axis. The steering side motor control signal calculation unit 63 calculates a q-axis target current value Iqs* having a larger absolute value as the absolute value of the target reaction torque Ts* increases. In this embodiment, the d-axis target current value Ids* is basically set to zero. The steering side motor control signal calculation unit 63 generates a steering side motor control signal Ms to be output to the steering side drive circuit 52 by executing current feedback control in the d / q coordinate system.

[0031] Specifically, the steering-side motor control signal calculation unit 63 calculates the d-axis current value Ids and the q-axis current value Iqs, which are the actual current values ​​of the steering-side motor 13 in the d / q coordinate system, by mapping the phase current values ​​Ius, Ivs, Iws onto the d / q coordinates based on the rotation angle θs. Then, the steering-side motor control signal calculation unit 63 calculates target voltage values ​​based on each current deviation on the d-axis and q-axis so that the d-axis current value Ids follows the d-axis target current value Ids* and the q-axis current value Iqs follows the q-axis target current value Iqs*, and generates a steering-side motor control signal Ms having a duty ratio based on the target voltage values.

[0032] The steering side motor control signal Ms calculated in this manner is output to the steering side drive circuit 52. As a result, the steering side motor 13 is supplied with drive power according to the steering side motor control signal Ms from the steering side drive circuit 52. Then, the steering side motor 13 applies a steering reaction force indicated by the target reaction torque Ts* to the steering wheel 3.

[0033] The steering side control section 56 will now be described. The turning side control unit 56 executes each calculation process shown in each control block below at each predetermined calculation cycle to generate the turning side motor control signal Mt. The turning side control unit 56 receives the rotation angle θt, target steering angle θh*, and each phase current value Iut, Ivt, Iwt of the turning side motor 32. The turning side control unit 56 then generates and outputs the turning side motor control signal Mt based on each of these state quantities.

[0034] In detail, the turning side control unit 56 is provided with a steering corresponding angle calculation unit 71 which calculates a steering corresponding angle θp which is a rotation angle of the pinion shaft 21. The turning side control unit 56 also includes a target turning torque calculation unit 72 which calculates a target turning torque Tt* which is a target value of the above-mentioned steering force, and a turning side motor control signal calculation unit 73 which outputs a turning side motor control signal Mt. Note that in the steering device 2 of this embodiment, the steering angle ratio which is the ratio between the steering angle θh and the turning corresponding angle θp is set constant at a ratio of 1:1, and the target turning corresponding angle which is a target value of the turning corresponding angle θp is equal to the target steering angle θh*.

[0035] The turning-corresponding angle calculation unit 71 receives the rotation angle θt of the turning-side motor 32. The turning-corresponding angle calculation unit 71 converts the input rotation angle θt into an integrated angle by, for example, counting the number of rotations of the turning-side motor 32 from a neutral position where the vehicle travels straight, and obtains the angle. The turning-corresponding angle calculation unit 71 then multiplies the rotation angle converted into the integrated angle by a conversion coefficient based on the reduction ratio of the transmission mechanism 33, the lead of the conversion mechanism 34, and the rotation speed ratio of the rack-and-pinion mechanism 24 to calculate the turning-corresponding angle θp. In other words, the turning-corresponding angle θp corresponds to the steering angle θh of the steering wheel 3 when it is assumed that the pinion shaft 21 is connected to the steering shaft 11. The turning-corresponding angle θp calculated in this manner is output to the subtractor 74 and the target reaction torque calculation unit 62. The subtractor 74 receives the target steering angle θh* in addition to the turning-corresponding angle θp.

[0036] Target turning torque calculation section 72 receives target steering angle θh*, i.e., angle deviation Δθp obtained by subtracting steering corresponding angle θp from target steering corresponding angle, via subtractor 74. Then, based on angle deviation Δθp, target turning torque calculation section 72 calculates target turning torque Tt*, which is a target value of the steering force applied by steering-side motor 32, as a control amount for making steering corresponding angle θp follow target steering angle θh*. Specifically, target turning torque calculation section 72 calculates, as target turning torque Tt*, the sum of output values ​​of a proportional element, an integral element and a derivative element which have angle deviation Δθp as input. In other words, target turning torque calculation section 72 calculates target turning torque Tt* based on execution of steering angle feedback control for making actual turning corresponding angle θp follow target steering angle θh*, which is the target turning corresponding angle.

[0037] In addition to the target turning torque Tt*, the rotation angle θt and the phase current values ​​Iut, Ivt, and Iwt are input to the turning-side motor control signal calculation unit 73. The turning-side motor control signal calculation unit 73 calculates a q-axis target current value Iqt* on the q-axis in the d / q coordinate system based on the target turning torque Tt*. The turning-side motor control signal calculation unit 73 calculates a q-axis target current value Iqt* having a larger absolute value as the absolute value of the target turning torque Tt* increases. In this embodiment, the d-axis target current value Idt* on the d-axis is basically set to zero. Then, like the steering-side motor control signal calculation unit 63, the turning-side motor control signal calculation unit 73 generates the turning-side motor control signal Mt to be output to the turning-side drive circuit 57 by executing current feedback control in the d / q coordinate system. The q-axis current value Iqt calculated in the process of generating the turning-side motor control signal Mt is output to the target reaction torque calculation unit 62.

[0038] The turning side motor control signal Mt calculated in this manner is output to the turning side drive circuit 57. As a result, the turning side motor 32 is supplied with drive power according to the turning side motor control signal Mt from the turning side drive circuit 57. Then, the turning side motor 32 imparts to the steered wheels 5 a turning force indicated by the target turning torque Tt*.

[0039] Here, the target reaction torque calculation unit 62 will be described. As shown in Fig. 3, the target reaction torque calculation unit 62 includes an input torque basic component calculation unit 81 that calculates an input torque basic component Tb*, which is a force that rotates the steering wheel 3 in the steering direction of the driver. 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 that resists the rotation of the steering wheel 3 caused by the steering of the driver. The target reaction torque calculation unit 62 also includes a target steering angle calculation unit 83 that calculates a target steering angle θh*, which is a target value of 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 executing a steering angle feedback calculation.

[0040] The steering torque Th is input to the input torque base component calculation unit 81. The input torque base component calculation unit 81 calculates an input torque base component Tb* having a larger absolute value as the absolute value of the steering torque Th increases. The input torque base component Tb* is input to a target steering angle calculation unit 83 and an adder 85.

[0041] The vehicle speed V, the steering angle θh, the q-axis current value Iqt of the steered-side motor 32, the steering corresponding angle θp, and the target steering angle θh* are input to the reaction force component calculation unit 82. Based on these state quantities, the reaction force component calculation unit 82 calculates a reaction force component Fir corresponding to the axial force acting on the rack shaft 22, as will be described later, and outputs the reaction force component Fir to a target steering angle calculation unit 83.

[0042] The vehicle speed V, steering torque Th, input torque base component Tb*, and reaction force 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 equation that relates 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 force component Fir, to the target steering angle θh*.

[0043] Tin*=C・θh*'+J・θh*'' …(1) This model formula defines and expresses the relationship between the torque and rotation angle of the rotation shaft that rotates with the rotation of the steering wheel 3 in a system in which the steering wheel 3 and the steered wheels 5 are mechanically connected, i.e., in a system in which the steering unit 4 and the steered unit 6 are mechanically connected. This model formula is expressed using a viscosity coefficient C that models the friction and the like of the steering device 2, and an inertia coefficient J that models the inertia of the steering device 2. The viscosity coefficient C and the inertia coefficient J are variably set according to the vehicle speed V. The target steering angle θh* calculated using the model formula in this manner is output to the reaction force component calculation unit 82 in addition to the subtractor 86 and the steered side control unit 56.

[0044] The steering angle F / B control unit 84 receives an angle deviation Δθs obtained by subtracting the steering angle θh from the target steering angle θh* in a subtractor 86. Then, based on the angle deviation Δθs, the steering angle F / B control unit 84 calculates a steering angle F / B component Tfbh that is the basis of the steering reaction force applied by the steering-side motor 13 as a control amount for feedback-controlling the steering angle θh to the target steering angle θh*. Specifically, the steering angle F / B control unit 84 calculates, as the basic reaction force torque, the sum of the output values ​​of a proportional element, an integral element, and a derivative element that receive the angle deviation Δθs as an input. The steering angle F / B component Tfbh calculated in this manner is output to an adder 85.

[0045] Then, the target reaction torque calculation unit 62 calculates a value obtained by adding the steering angle F / B component Tfbh to the input torque basic component Tb* in an adder 85 as the target reaction torque Ts*. Next, the configuration of the reaction force component calculation unit 82 will be described.

[0046] As shown in Fig. 4, the reaction force component calculation unit 82 includes a distribution axial force calculation unit 91, an end reaction force calculation unit 92, and an obstacle hitting reaction force calculation unit 93. The distribution axial force calculation unit 91 calculates a distribution axial force Fd as an axial force component corresponding to the axial force acting on the rack shaft 22 that operates to steer the steered wheels 5. The end reaction force calculation unit 92 calculates an end reaction force Fie which is a reaction force for restricting further turning steering when the absolute value of the steering angle θh of the steering wheel 3 approaches the limit steering angle. The obstacle hitting reaction force calculation unit 93 calculates an obstacle hitting reaction force Fo which is a reaction force for restricting steering that steers the steered wheels 5 toward an obstacle when the steered wheels 5 hit an obstacle such as a curb due to steering. Then, the reaction force component calculation unit 82 adds the reaction force having the larger absolute value out of the end reaction force Fie and the obstacle hitting reaction force Fo to the distributed axial force Fd, and calculates and outputs the reaction force component Fir.

[0047] In detail, the distribution axial force calculation unit 91 includes a current axial force calculation unit 101 that calculates the current axial force Fer, and an angle axial force calculation unit 102 that calculates the angle axial force Fib. The current axial force Fer and the angle axial force Fib are calculated in the dimension of torque (N·m). The distribution axial force calculation unit 91 also includes a distribution processing unit 103 that calculates a distribution axial force Fd corresponding to a calculated axial force that is an estimated axial force acting on the rack shaft 22 obtained by distributing the angle axial force Fib and the current axial force Fer at a predetermined ratio so that the axial force acting on the rack shaft 22 through the steered wheels 5 is suitably reflected.

[0048] The current axial force calculation unit 101 receives the q-axis current value Iqt of the steered-side motor 32. The current axial force calculation unit 101 calculates the current axial force Fer based on the q-axis current value Iqt. The current axial force Fer is an estimated value of the axial force that actually acts on the rack shaft 22 that operates to steer the steered wheels 5, that is, the axial force that is actually transmitted to the rack shaft 22. The current axial force Fer is calculated as an axial force that reflects road surface information such as minute irregularities that do not affect the lateral behavior of the vehicle and steps that affect the lateral behavior of the vehicle. Specifically, the current axial force calculation unit 101 calculates the current axial force Fer so that the absolute value of the q-axis current value Iqt becomes larger as the absolute value of the current axial force Fer becomes larger, assuming that the torque applied to the rack shaft 22 by the steered-side motor 32 and the torque corresponding to the force applied to the rack shaft 22 through the steered wheels 5 are balanced. The current axial force Fer calculated in this manner is output to the multiplier 105.

[0049] The angle axial force calculation unit 102 receives the target steering angle θh*, which is the target steering corresponding angle, and the vehicle speed V. The angle axial force calculation unit 102 calculates the angle axial force Fib based on the target steering angle θh* and the vehicle speed V. The angle axial force Fib is an ideal value of the axial force defined by an arbitrarily set vehicle model. The angle axial force Fib is calculated as an axial force that does not reflect the above road surface information. Specifically, the angle axial force calculation unit 102 calculates the angle axial force Fib so that the absolute value of the angle axial force Fib increases as the absolute value of the target steering angle θh* increases. Furthermore, the angle axial force calculation unit 102 calculates the angle axial force Fib so that the absolute value of the angle axial force Fib increases as the vehicle speed V increases. The angle axial force Fib calculated in this manner is output to the guard processing unit 200.

[0050] The guard processing unit 200 receives the angular axial force Fib and the vehicle speed V. The guard processing unit 200 is provided with an angular axial force adjustment map that defines the relationship between the angular axial force Fib, the vehicle speed V, and the adjusted angular axial force Fib', and receives the angular axial force Fib and the vehicle speed V as inputs and performs map calculations to obtain the adjusted angular axial force Fib'. The angular axial force adjustment map is a map that functions to perform guard processing so that the angular axial force Fib does not become excessive.

[0051] As shown in FIG. 5, the angle axial force adjustment map is set so that, when the absolute value of the angle axial force Fib is classified into three regions, a small region, a medium region, and a large region, the larger the angle axial force Fib is, the larger the adjusted angle axial force Fib' becomes linearly larger in the small region and the medium region. Also, the angle axial force adjustment map is set so that the absolute value of the adjusted angle axial force Fib' is maintained at a predetermined limit value Flim in a region where the absolute value of the angle axial force Fib is large. The limit value Flim is set so that the larger the vehicle speed V is, the larger the value of the reaction force component Fir calculated based on the adjusted angle axial force Fib', that is, the value of the target reaction force torque Ts*, is set based on tests, simulations, etc. as a value within a range in which the value of the reaction force component Fir, i.e., the value of the target reaction force torque Ts*, is not excessive. Then, the guard processing unit 200 adjusts the angle axial force Fib according to the vehicle speed V through map calculation using the angle axial force adjustment map. The adjusted angle axial force Fib' calculated in this way is output to the multiplier 106.

[0052] 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 that calculates distribution gains Ger, Gib, which are 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 of this embodiment includes a distribution gain map that defines the relationship between the vehicle speed V and the distribution gains Ger, Gib, and calculates the distribution gains Ger, Gib using the map with the vehicle speed V as an input. The distribution gain Gib has a smaller value when the vehicle speed V is large than when it is small, and the distribution gain Ger has a larger value when the vehicle speed V is large than when it is small. In other words, the distribution ratio of the angular axial force Fib in the distribution axial force Fd becomes smaller as the vehicle speed V increases, and the distribution ratio of the current axial force Fer in the distribution axial force Fd becomes larger as the vehicle speed V increases.

[0053] In particular, the distribution gain Ger is zero when the vehicle speed V is low, including when the vehicle is stopped. In this case, the current axial force Fer indicates that the distribution ratio is zero, i.e., the distribution gain Gib is zero when the vehicle speed is high enough relative to the low vehicle speed. In this case, the angle axial force Fib indicates that the distribution ratio is zero, i.e., the distribution gain Gib is zero. In other words, the distribution ratio in this embodiment includes the concept of a zero value in which only either the current axial force Fer or the angle axial force Fib is distributed to the distribution axial force Fd. The distribution gains Ger and Gib are calculated so that their sum is "1". The distribution gain Ger calculated in this manner is output to the multiplier 105, and the distribution gain Gib is output to the multiplier 106.

[0054] The distribution processing unit 103 calculates a distribution axial force Fd by adding, in an adder 108, a value obtained by multiplying the current axial force Fer by the distribution gain Ger in a multiplier 105 and a value obtained by multiplying the angle axial force Fib by the distribution gain Gib in a multiplier 106. The distribution axial force Fd thus calculated is output to the adder 94.

[0055] A target steering angle θh*, which is a target steering-corresponding angle, is input to the end reaction force calculation unit 92. The end reaction force calculation unit 92 is provided with an end reaction force map that defines the relationship between the target steering angle θh* and the end reaction force Fie, and calculates the end reaction force Fie from the map using the target steering angle θh* as an input. The end reaction force map calculates a zero value as the end reaction force Fie when the absolute value of the target steering angle θh* is equal to or smaller than the threshold angle θie, and calculates a value whose absolute value is greater than zero as the end reaction force Fie when the target steering angle θh* exceeds the threshold angle θie.

[0056] The end reaction force Fie is set to have such a large absolute value that the human cannot steer any further when the target steering angle θh* exceeds the threshold angle θie to a certain extent. The end reaction force Fie is a high-gradient axial force whose value increases rapidly in proportion to the target steering angle θh* when the target steering angle θh* exceeds the threshold angle θie to a certain extent. The threshold angle θie is set to the value of the steering-corresponding angle θp at a virtual rack end position provided on the neutral position side of the mechanical rack end position where the axial movement of the rack shaft 22 is restricted by the rack end 25 abutting against the rack housing 23. The end reaction force Fie calculated in this manner is output to the reaction force selection unit 95.

[0057] In addition to the q-axis current value Iqt, an angle deviation Δθx obtained by subtracting the steering corresponding angle θp from the steering angle θh in a subtractor 96, and a steering speed ωt obtained by differentiating the steering corresponding angle θp are input to the obstacle hit reaction force calculation unit 93. The obstacle hit reaction force calculation unit 93 of this embodiment calculates an obstacle hit gain Go indicating the degree of approximation to a situation in which an obstacle hit reaction force Fo should be applied, based on these state quantities. The obstacle hit reaction force calculation unit 93 is provided with an obstacle hit reaction force map that defines the relationship between the obstacle hit gain Go and the obstacle hit reaction force Fo, and uses the obstacle hit gain Go as an input to perform map calculation of the obstacle hit reaction force Fo.

[0058] In the obstacle hitting reaction force map, when the obstacle hitting gain Go is zero, the obstacle hitting reaction force Fo becomes zero, and the obstacle hitting reaction force Fo gradually increases in proportion to the obstacle hitting gain Go. When the obstacle hitting gain Go becomes larger than the gain threshold Gth, the obstacle hitting reaction force Fo suddenly increases in proportion to the obstacle hitting gain Go. The gain threshold Gth is a value within a range where it is acceptable to determine that the steered wheels 5 are hitting an obstacle due to steering, and is set based on tests, simulations, and the like. In addition, the obstacle hitting reaction force Fo is set to have such a large absolute value that further steering cannot be performed by human force when the obstacle hitting gain Go exceeds the gain threshold Gth to a certain extent. The obstacle hitting reaction force Fo is a high gradient axial force whose value suddenly increases in proportion to the obstacle hitting gain Go when the obstacle hitting gain Go becomes larger than the gain threshold Gth. As a result, in a region where the obstacle hit gain Go is equal to or less than the gain threshold Gth, the obstacle hit reaction force Fo reproduces the reaction force when only the tire portion of the steered wheel 5 hits an obstacle. This reaction force depends on characteristics based on the elastic component of the rubber of the steered wheel 5 and characteristics based on the elastic component of the suspension of the vehicle to which the steered wheel 5 is connected, and can be obtained experimentally. Also, in a region where the obstacle hit gain Go is greater than the gain threshold Gth, the obstacle hit reaction force Fo reproduces the reaction force when the wheel portion of the steered wheel 5 hits an obstacle. The obstacle hit reaction force Fo calculated in this manner is output to the reaction force selection unit 95.

[0059] In addition to the end reaction force Fie and the obstacle hit 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 a reaction force having a larger absolute value from the end reaction force Fie and the obstacle hit reaction force Fo, and outputs a value obtained by converting the sign of the reaction force, i.e., the direction, into the sign indicated by the steering speed ωh, to the adder 94 as a selected reaction force Fsl.

[0060] Then, the reaction force component calculation section 82 outputs a value obtained by adding the selected reaction force Fsl to the distributed axial force Fd in an adder 94 to the target steering angle calculation section 83 as a reaction force component Fir. The operation of this embodiment will now be described.

[0061] When the vehicle is traveling, the centrifugal force may become larger than the frictional force between the rear wheels and the road surface while the driver is turning the steering wheel 3. This condition is particularly likely to occur on low-friction roads such as icy roads. In this case, the vehicle becomes in an oversteer state in which the vehicle turns toward the side where the vehicle turns more than the driver has steered the steering wheel 3. In such an oversteer state, the driver steers the steering wheel 3 toward the side opposite to the side where the vehicle turns, that is, performs a so-called countersteer, in order to correct the vehicle's attitude. Here, the angular axial force Fib corresponds to the target steering angle θh* obtained based on the steering angle θh of the steering wheel 3. For this reason, when the steering angle θh of the steering wheel 3 becomes a large angle close to the end contact by performing countersteer, the angular axial force Fib becomes excessive, and the reaction force component Fir calculated by reflecting the angular axial force Fib becomes large. If the target reaction torque Ts* is calculated based on this reaction component Fir, the steering reaction force applied to the steering wheel 3 may become excessive.

[0062] In this regard, in this embodiment, the guard processing unit 200 performs guard processing so that the angular axial force Fib does not become excessive. In other words, the reaction force component Fir reflects the adjusted angular axial force Fib' that has been guarded by the guard processing unit 200, rather than the angular axial force Fib obtained through the angular axial force calculation unit 102. As a result, even in a situation where counter steering is performed, the reaction force component Fir and the target reaction force torque Ts* calculated based on the reaction force component Fir are unlikely to become excessive. Therefore, the steering reaction force applied to the steering wheel 3 is prevented from becoming excessive.

[0063] The effects of this embodiment will be described. (1) Since the guard processing unit 200 performs guard processing to prevent the angular axial force Fib from becoming excessive, in a situation where counter steering is being performed, the driver is less likely to feel that the steering of the steering wheel 3 is heavy, and deterioration of the steering feeling can be suppressed.

[0064] (2) In the guard processing unit 200, since it is only necessary to set the limit value Flim in order to perform the guard processing, it is possible to appropriately limit the angular axial force Fib to a desired value. (3) In this embodiment, since the angular axial force Fib can be adjusted so as not to become excessively large by the angular axial force adjustment map, the configuration related to the guard process can be simplified.

[0065] (4) In the present embodiment, the angular axial force Fib is adjusted by the angular axial force adjustment map. Therefore, by changing the shape of the map, it is possible to easily realize an optimal steering reaction force according to the vehicle specifications, etc.

[0066] (5) For example, when the vehicle is traveling at high speed, the axial force acting on the rack shaft 22 becomes large, and therefore, taking into consideration the road surface reaction force, it is preferable to set the angular axial force Fib to be large. This is also true in a situation where counter-steering is performed. In consideration of this, in this embodiment, the limit value Flim is adjusted based on the vehicle speed V, so that an appropriate steering reaction force can be applied while preventing the steering reaction force from becoming excessive in a situation where counter-steering is performed.

[0067] The above embodiment may be modified as follows. In addition, the following other embodiments may be combined with each other to the extent that there is no technical contradiction. The guard processing unit 200 may have a function of selecting a value to be output through a comparison between the absolute value of the angle axial force Fib and the limit value Flim, instead of the function of map calculation using the angle axial force adjustment map. In this case, the guard processing unit 200 is in a selection state of outputting the angle axial force Fib obtained through the angle axial force calculation unit 102 when the absolute value of the angle axial force Fib is equal to or less than the limit value Flim. On the other hand, the guard processing unit 200 is in a selection state of outputting the angle axial force Fib set to the limit value Flim when the absolute value of the angle axial force Fib is greater than the limit value Flim. The guard processing unit 200 may also have a function of setting the absolute value of the angle axial force Fib to a value equal to or less than the limit value Flim by offsetting the absolute value of the angle axial force Fib by a predetermined offset amount to the side that reduces the absolute value of the angle axial force Fib. In this case, the guard processing unit 200 is in a state of outputting the angle axial force Fib obtained through the angle axial force calculation unit 102 when the absolute value of the angle axial force Fib is equal to or less than the limit value Flim. On the other hand, when the absolute value of the angular axial force Fib is larger than the limit value Flim, the guard processing unit 200 outputs the angular axial force Fib offset by a predetermined offset amount.

[0068] The limit value Flim does not have to be changed in response to the vehicle speed V. In addition, the limit value Flim may be changed in response to other parameters, such as the lateral acceleration, the yaw rate, etc., in which case the vehicle speed V may be added to the parameters.

[0069] In the control of the steering-side motor 13, the target reaction torque Ts* may be calculated using, as the input torque base component Tb*, a value calculated by executing torque feedback control that makes the steering torque Th follow a target steering torque calculated based on the steering torque Th and the reaction component Fir. Alternatively, the control of the steering-side motor 13 may be realized by so-called feedforward control without executing steering angle F / B control. In this case, the target reaction torque Ts* may be calculated based on the assist component calculated based on the steering torque Th and the reaction component Fir.

[0070] The distribution processing unit 103 may change the distribution ratio of the current axial force Fer and the angle axial force Fib in accordance with a parameter other than the vehicle speed V. As such a parameter, for example, a drive mode indicating a setting state of a control pattern of an on-board engine or the like can be used.

[0071] The obstacle hitting reaction force calculation unit 93 may alternatively determine whether or not it is a situation in which the obstacle hitting reaction force Fo should be applied based on, for example, a comparison of the magnitudes of the q-axis current value Iqt, the angle deviation Δθx, and the steering speed ωt with their corresponding threshold values.

[0072] The angle axial force calculation unit 102 may calculate the angle axial force Fib based on the steering angle θh and the steering corresponding angle θp, or may calculate the angle axial force Fib by another method, for example, by taking into account other parameters such as the steering torque Th and the vehicle speed V.

[0073] The distributed axial force Fd may be an axial force based on other parameters in addition to the current axial force Fer and the angular axial force Fib. Examples of the axial force based on other parameters include a vehicle state quantity axial force calculated based on the yaw rate and lateral acceleration, an axial force based on a detection value of an axial force sensor that detects the axial force of the rack shaft 22, or an axial force based on a tire force acting on the steered wheels 5.

[0074] The reaction force component calculation unit 82 is only required to reflect at least the angular axial force Fib in the reaction force component Fir. When the reaction force component calculation unit 82 reflects only the angular axial force Fib in the reaction force component Fir, the current axial force calculation unit 101 and the distribution processing unit 103 can be omitted.

[0075] The reaction force component calculation unit 82 may calculate either the end reaction force Fie or the obstacle hit reaction force Fo as the reaction force component that restricts steering. The reaction force component calculation unit 82 may set a reaction force that occurs in a situation or under different conditions instead of the end reaction force Fie and the obstacle hit reaction force Fo, or may set a reaction force in addition to the end reaction force Fie and the obstacle hit reaction force Fo as the reaction force component that restricts steering. As such a reaction force that occurs in a situation or under different conditions, for example, a reaction force that is applied when the voltage of the on-board power source B drops and sufficient steering force cannot be applied by the steering-side motor 32 can be used.

[0076] In the above formula (1), the target steering angle θh* can also be calculated using a model formula that adds a so-called spring term using a spring coefficient K that is determined by the specifications of the vehicle suspension, wheel alignment, etc.

[0077] In the above embodiment, the steering device 2 to be controlled may be a steering device having a structure in which the power transmission path between the steering unit 4 and the steered unit 6 can be separated by a clutch. In the above embodiment, the steering control device 1 can be configured by a processing circuit including: 1) one or more processors that operate according to a computer program (software); 2) one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC) that executes at least some of various processes; or 3) a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program codes or instructions configured to cause the CPU to execute processes. The memory, i.e., the non-transitory computer-readable medium, includes any available medium that can be accessed by a general-purpose or special-purpose computer. [Explanation of symbols]

[0078] 1...Steering control device 2...Steering gear 3. Steering wheel 4…Steering section 5…Steering wheel 6…Steering section 22…Rack shaft 62...Target reaction torque calculation unit 102...Angle axial force calculation section 200: Guard processing section Flim...Limit value Fib…Angle axial force Fir: Reaction component Ts*: Target reaction torque

Claims

1. A steering device having a structure in which a power transmission path between a steering unit and a steering unit that steers steered wheels in response to a steering input to the steering unit is separated, A steering control device comprising: a target reaction torque calculation unit that calculates a target reaction torque that is a target value of a steering reaction force that is a force resisting the steering input to the steering unit; and controls 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 target reaction force torque calculation unit includes a distribution axial force calculation unit that calculates a distribution axial force as an axial force component corresponding to an axial force acting on a turning shaft that operates to turn the steered wheels, The distribution axial force calculation unit is a current axial force calculation unit that calculates a current axial force which is determined according to an output of a steering-side motor provided in the steering unit and which reflects road surface information; an angle axial force calculation unit that calculates an angle axial force that is determined according to an angle that can be converted into a steering angle of the steered wheels and that does not reflect the road surface information; a distribution processing unit that calculates the distributed axial force obtained by distributing the current axial force and the angle axial force at a predetermined ratio, The steering control device includes a guard processing unit that performs guard processing between the current axial force before being allocated to the distributed axial force and the angle axial force before being allocated to the distributed axial force so that the angle axial force before being allocated to the distributed axial force does not become excessive.

2. 2. The steering control device according to claim 1, wherein the guard processing unit limits an absolute value of the angular axial force before the allocation to a limit value or less so that the angular axial force before the allocation does not become excessive.

3. 3. The steering control device according to claim 2, wherein the guard processing unit includes an angle axial force adjustment map for performing an adjustment so that the angle axial force before the distribution does not become excessive.

4. The steering control device according to claim 2 or 3, wherein the limit value is adjusted based on a vehicle speed.

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