Steering gear

Abstract

To provide a steering device that is able to prevent instability of a vehicle when the vehicle enters an area having a large road surface friction coefficient from an area having a small road surface friction coefficient.SOLUTION: A steering device includes a road surface friction coefficient estimating unit that estimates a road surface friction coefficient that is a coefficient of friction of a road surface on which a vehicle is traveling; a filter unit that moderates a temporal change of the road surface friction coefficient estimated by the road surface friction coefficient estimating unit; a limit tire slip angle estimating unit that, using the road surface friction coefficient after a filter process by the filter unit, estimates a limit tire slip angle that is a tire slip angle at which tire cornering force of a turning wheel becomes maximum; and a tire slip angle limiting unit that limits a tire slip angle of the turning wheel so as to prevent the tire slip angle of the turning wheel from exceeding the limit tire slip angle.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Patent Document 1 discloses the following technology. That is, the tire slip angle at which the tire cornering force generated in the wheel is maximized is stored as the target slip angle. When it is determined that the vehicle may come into contact with an obstacle ahead, a steering angle at which the tire slip angle becomes equal to the target slip angle is calculated as the target steering angle. Then, the steering actuator is driven and controlled so that the actual steering angle becomes the target steering angle. As a result, the steering angle of the wheel is controlled so that the steering angle of the wheel becomes equal to the steering angle at which the tire cornering force becomes maximum, improving the ability to avoid contact with the obstacle ahead. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-168698 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to provide a steering device that can prevent the tire slip angle of the steered wheels from exceeding the tire slip angle at which the tire cornering force is maximized, and can prevent the vehicle from becoming unstable when the vehicle enters from a region where the road surface friction coefficient is small to a region where the road surface friction coefficient is large. [Means for solving the problem]

[0005] One embodiment of the present invention provides a steering device including a road surface friction coefficient estimation unit that estimates a road surface friction coefficient, which is the friction coefficient of the road surface on which a vehicle is traveling; a filter unit that smooths out changes over time in the road surface friction coefficient estimated by the road surface friction coefficient estimation unit; a limit tire slip angle estimation unit that uses the road surface friction coefficient after filtering by the filter unit to estimate a limit tire slip angle, which is the tire slip angle at which the tire cornering force of the steered wheel is maximized; and a tire slip angle limiting unit that limits the tire slip angle of the steered wheel so as to prevent the tire slip angle of the steered wheel from exceeding the limit tire slip angle.

[0006] This configuration can prevent the tire slip angle of the steered wheels from exceeding the tire slip angle at which the tire cornering force is maximized, and also prevents the vehicle from becoming unstable when the vehicle enters an area with a high road friction coefficient from an area with a low road friction coefficient. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering system to which a steering device according to one embodiment of the present invention is applied. [Diagram 2] FIG. 2 is a block diagram showing the electrical configuration of the motor control ECU, and is used to explain the electrical configuration related to the operation in the automatic steering mode. [Diagram 3] FIG. 3 is a block diagram showing the configuration of the first steering envelope control unit. [Figure 4] FIG. 4 is a block diagram showing the configuration of the road surface friction estimating unit. [Diagram 5] FIG. 5 is a block diagram showing the configuration of the angle control unit. [Figure 6] FIG. 6 is a block diagram showing the configuration of the torque control unit. [Figure 7A] FIG. 7A is a graph for explaining the operation of the comparative example when the vehicle enters from the high μ region to the low μ region. [Figure 7B]FIG. 7B is a graph for explaining the operation of the comparative example when the vehicle enters from the low μ region to the high μ region. [Figure 8A] FIG. 8A is a schematic diagram showing that in a comparative example, when a vehicle enters from a low μ region to a high μ region, the vehicle state tends to become unstable. [Figure 8B] FIG. 8B is a schematic diagram showing that in this embodiment, when the vehicle enters from the low μ region to the high μ region, the vehicle state is unlikely to become unstable. [Figure 9A] FIG. 9A is a time chart showing a change in the road surface friction coefficient μ input to the limit tire slip angle estimating section when the vehicle enters from a low μ region to a high μ region. [Figure 9B] FIG. 9B is a time chart showing the change over time in the steering angle limit value θsl calculated by the steering angle limit value calculation unit when the vehicle enters from the low μ region to the high μ region. [Figure 9C] FIG. 9C is a time chart showing the change over time in the target steering angle θSEC after the limiting process calculated by the limiting section when the vehicle enters from the low μ region into the high μ region. [Figure 10] FIG. 10 is a block diagram showing the electrical configuration of the motor control ECU, and is used to explain the electrical configuration related to the operation in the manual steering mode. [Figure 11] FIG. 11 is a block diagram showing the configuration of the second steering envelope control unit. [Figure 12] FIG. 12 is a graph showing an example of setting the target assist torque Tat relative to the steering torque Td. [Figure 13] FIG. 13 is a flowchart for explaining a modified example of the filter section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Description of the embodiment of the present invention] One embodiment of the present invention provides a steering device including a road surface friction coefficient estimation unit that estimates a road surface friction coefficient, which is the friction coefficient of the road surface on which a vehicle is traveling; a filter unit that smooths out changes over time in the road surface friction coefficient estimated by the road surface friction coefficient estimation unit; a limit tire slip angle estimation unit that uses the road surface friction coefficient after filtering by the filter unit to estimate a limit tire slip angle, which is the tire slip angle at which the tire cornering force of the steered wheel is maximized; and a tire slip angle limiting unit that limits the tire slip angle of the steered wheel so as to prevent the tire slip angle of the steered wheel from exceeding the limit tire slip angle.

[0009] This configuration can prevent the tire slip angle of the steered wheels from exceeding the tire slip angle at which the tire cornering force is maximized, and also prevents the vehicle from becoming unstable when the vehicle enters an area with a high road friction coefficient from an area with a low road friction coefficient. In one embodiment of the present invention, the filter unit is configured to smooth out the change over time in the road surface friction coefficient estimated by the road surface friction coefficient estimation unit only when the road surface friction coefficient estimated by the road surface friction coefficient estimation unit changes from a small road surface friction coefficient to a large road surface friction coefficient.

[0010] In one embodiment of the present invention, the tire slip angle limiting section is configured to limit the turning angle of the steered wheels so that the tire slip angle of the steered wheels does not exceed the limit tire slip angle. In one embodiment of the present invention, the tire slip angle limiting unit includes a tire slip angle calculation unit that calculates a tire slip angle of the steered wheel, a steering angle limit value calculation unit that calculates a steering angle limit value for limiting the steering angle using the tire slip angle and the limit tire slip angle, and a limiting unit that limits a target steering angle for automatic steering using the steering angle limit value.

[0011] In one embodiment of the present invention, the tire slip angle limiting unit includes an electric motor for generating assist torque, a target assist torque setting unit for setting a target assist torque, and a motor control unit for controlling the electric motor, and the tire slip angle limiting unit includes a tire slip angle calculation unit for calculating a tire slip angle of the steered wheel, a steering angle limit value calculation unit for calculating a steering angle limit value for limiting the steering angle using the tire slip angle and the limit tire slip angle, and a steering angle limiting torque calculation unit for calculating a steering angle limiting torque for limiting the steering angle using the steering angle limit value and the steering angle, and the motor control unit is configured to control the torque of the electric motor using the target assist torque and the steering angle limiting torque. Detailed Description of the Embodiments of the Invention Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. [1] Overview of electric power steering system FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering system to which a steering device according to one embodiment of the present invention is applied.

[0012] The electric power steering system 1 includes a steering wheel (handle) 2 as a steering member for steering a vehicle, a steering mechanism 4 for steering steered wheels 3 in conjunction with the rotation of the steering wheel 2, and a steering assist mechanism 5 for assisting the driver in steering. The steering wheel 2 and the steering mechanism 4 are mechanically connected via a steering shaft 6 and an intermediate shaft 7.

[0013] The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be capable of relative rotation. A torque sensor 12 is disposed near the torsion bar 10. The torque sensor 12 detects the steering torque (torsion bar torque) T applied to the steering wheel 2 based on the amount of relative rotational displacement between the input shaft 8 and the output shaft 9. dIn this embodiment, the steering torque T d For example, the torque for steering leftward is detected as a positive value, and the torque for steering rightward is detected as a negative value. The larger the absolute value of the torque, the greater the steering torque T d The magnitude of is assumed to be large.

[0014] The steering mechanism 4 is composed of a rack-and-pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steering shaft. The steered wheels 3 are connected to each end of the rack shaft 14 via tie rods 15 and knuckle arms (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13.

[0015] The rack shaft 14 extends linearly in the left-right direction of the vehicle. A rack 17 that meshes with the pinion 16 is formed in the middle of the rack shaft 14 in the axial direction. The pinion 16 and the rack 17 convert the rotation of the pinion shaft 13 into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

[0016] When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is then converted into axial movement of the rack shaft 14 by the pinion 16 and the rack 17. As a result, the steered wheels 3 are steered. The steering assist mechanism 5 includes an electric motor 18 for generating a steering assist force (assist torque), and a reducer 19 for amplifying the output torque of the electric motor 18 and transmitting it to the steering mechanism 4. The reducer 19 is made up of a worm gear mechanism including a worm gear 20 and a worm wheel 21 meshing with the worm gear 20. The reducer 19 is accommodated in a gear housing 22 serving as a transmission mechanism housing. In the following, the reduction ratio (gear ratio) of the reducer 19 is referred to as i decReduction ratio i dec is the rotation angle θ of the worm wheel 21 ww Rotation angle θ of the worm gear 20 relative to wg The ratio θ wg / θ ww It is defined as:

[0017] The worm gear 20 is rotationally driven by the electric motor 18. In addition, the worm wheel 21 is connected to the output shaft 9 so as to be integrally rotatable therewith. When the worm gear 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven, and motor torque is applied to the steering shaft 6, causing the steering shaft 6 (output shaft 9) to rotate. The rotation of the steering shaft 6 is then transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into axial movement of the rack shaft 14. This causes the steered wheels 3 to be turned. In other words, by rotating the worm gear 20 by the electric motor 18, steering assistance by the electric motor 18 and steering of the steered wheels 3 become possible. The electric motor 18 is provided with a rotation angle sensor 23 for detecting the rotation angle of the rotor of the electric motor 18.

[0018] The vehicle is equipped with a CCD (Charge Coupled Device) camera 25 that photographs the road ahead of the vehicle in the direction of travel, a GPS (Global Positioning System) 26 for detecting the vehicle's position, a radar 27 for detecting road shapes and obstacles, and a map information memory 28 that stores map information. The vehicle is further equipped with a vehicle speed sensor 29, a yaw rate sensor 30, a lateral acceleration sensor 31, a first mode switch 33, and a second mode switch 34. The vehicle speed sensor 29 is a sensor for detecting a vehicle speed V. The yaw rate sensor 30 is a sensor for detecting a yaw rate γ. The yaw rate γ is a rotational angular velocity around a vertical axis passing through the center of gravity of the vehicle.

[0019] The lateral acceleration sensor 31 detects the lateral acceleration A yThis is a sensor for detecting lateral acceleration A y is the acceleration acting in the y-axis direction, which is the width direction of the vehicle. The first mode switch 33 is a switch for setting the steering mode to the manual steering mode. The second mode switch 34 is a switch for setting the steering mode to the automatic steering mode. The CCD camera 25, GPS 26, radar 27, map information memory 28, vehicle speed sensor 29, yaw rate sensor 30, lateral acceleration sensor 31, first mode switch 33 and second mode switch 34 are connected to a host ECU (Electronic Control Unit) 201 for performing driving assistance control and automatic driving control. The host ECU 201 recognizes the surrounding environment, estimates the vehicle's position, plans a route, etc., based on the information obtained by the CCD camera 25, GPS 26 and radar 27 and map information, and determines control target values ​​for steering and drive actuators.

[0020] In this embodiment, the host ECU 201 controls the target steering angle θ auto In this embodiment, the automatic steering control is, for example, a control for making the vehicle travel along a target trajectory. auto is a target value of the steering angle for automatically driving the vehicle along the target trajectory. auto The process of setting is well known, so a detailed description will be omitted here.

[0021] In addition, the host ECU 201 outputs a mode signal S indicating the manual steering mode or the automatic steering mode based on the output signals of the first mode switch 33 and the second mode switch 34. mode Generate. The target steering angle θ set by the host ECU 201 auto , mode signal S mode , a vehicle speed V detected by a vehicle speed sensor 29, a yaw rate γ detected by a yaw rate sensor 30, and a lateral acceleration A detected by a lateral acceleration sensor 31. yis provided to the motor control ECU 202 via the in-vehicle network. d An output signal of the rotation angle sensor 23 is input to the motor control ECU 202. The motor control ECU 202 controls the electric motor 18 based on these input signals and information provided by the host ECU 201.

[0022] The motor control ECU 202 outputs the mode signal S mode is a signal indicating the automatic steering mode, the electric motor 18 is controlled by performing the operation in the automatic steering mode, and the mode signal S mode is a signal indicating the manual steering mode, the electric motor 18 is controlled by performing an operation in the manual steering mode. [2] Electrical configuration of motor control ECU 202 in automatic steering mode [2.1] Overall structure FIG. 2 is a block diagram showing the electrical configuration of motor control ECU 202, and is used to explain the electrical configuration related to the operation in the automatic steering mode.

[0023] The motor control ECU 202 includes a microcomputer 50, a drive circuit (inverter circuit) 41 controlled by the microcomputer 50 to supply power to the electric motor 18, and a current flowing through the electric motor 18 (hereinafter, “motor current I m The power supply 41 is provided with a current detection circuit 42 for detecting a current that is generated by the power supply 41 and a current detection circuit 42 for detecting a current that is generated by the power supply 41. The microcomputer 50 includes a CPU and memory (ROM, RAM, non-volatile memory, etc.), and functions as a plurality of functional processing units by executing a predetermined program. The plurality of functional processing units include a rotation angle calculation unit 51, a rack axial force estimation unit 52, a first steering envelope control unit 53, an angle control unit 54, a torque control unit (current control unit) 55, and a tire angle calculation unit 59, which are related to the automatic steering mode. [2.2] Rotation angle calculation unit 51 and tire angle calculation unit 59 The rotation angle calculation unit 51 calculates the rotor rotation angle θ of the electric motor 18 based on the output signal of the rotation angle sensor 23. m Calculate the following.

[0024] The tire angle calculation unit 59 calculates the rotor rotation angle θ m Reduction ratio i dec The value divided by is the overall gear ratio i oagr By dividing by θ, the steering angle of the steered wheels 3 (hereinafter referred to as the tire angle θ t ") is calculated. Overall gear ratio i oagr is the tire angle θ of the steered wheel 3 t The steering angle of the steering wheel 2 relative to the rotation angle θ of the output shaft 9 s ) and is preset. [2.3] Rack axial force estimation section 52 The rack axial force estimation unit 52 estimates the motor current I m and the rotor rotation angle θ calculated by the rotation angle calculation unit 51. m and steering torque T d Based on the above, the rack axial force F acting on the rack 17 is rack Estimate the rack axial force F rack The estimate of rack As the rack axial force estimating unit 52, for example, the rack axial force estimating unit disclosed in Japanese Patent Application Laid-Open No. 2021-949 may be used. [2.4] First steering envelope control section 53 The first steering envelope control unit 53 controls the tire slip angle of the steered wheels 3 to be equal to or smaller than the tire grip limit tire slip angle α sl The target steering angle θ after the limiting process to prevent the steering angle from exceeding SEC Calculate the tire slip angle α at the tire grip limit. sl is the tire slip angle at which the cornering force of the steered wheels 3 is maximum.

[0025] FIG. 3 is a block diagram showing the configuration of the first steering envelope control unit 53. As shown in FIG. The first steering envelope control unit 53 includes a road surface friction estimating unit 61, a filter unit 62, a limit tire slip angle estimating unit 63, a tire slip angle estimating unit 64, a steering angle limit value calculating unit 65, and a limiting unit 66. The steering angle limit value calculating unit 65 is an example of the "steering angle limit value calculating unit" in the present invention.

[0026] FIG. 4 is a block diagram showing the configuration of the road surface friction estimating unit 61. As shown in FIG. The road friction estimation unit 61 estimates the rack axial force estimated value ^F calculated by the rack axial force estimation unit 52. rack , yaw rate γ, and lateral acceleration A y and tire angle θ t The road friction coefficient μ, vehicle body slip angle β, and yaw rate γ are estimated based on the vehicle speed V. The estimated values ​​of the road friction coefficient μ, vehicle body slip angle β, and yaw rate γ are represented by ^μ, ^β, and ^γ, respectively. t Instead, the rotor rotation angle θ calculated by the rotation angle calculation unit 51 m may also be used.

[0027] The road surface friction estimating unit 61 includes an observed value calculating unit 71 , an estimated value calculating unit 72 , a subtraction unit 73 , and a gain calculating unit 74 . The observation value calculation unit 71 calculates an observation quantity y required to calculate a state quantity estimated value ^x including the road surface friction coefficient estimated value ^μ as a state variable. The estimate value calculation unit 72 calculates the state quantity estimated value ^x and also calculates an observation quantity estimated value ^y which is an estimate value ^y of the observation quantity y. The subtraction unit 73 calculates an observation deviation Δy which is a deviation between the observation quantity y and the observation quantity estimated value ^y. The gain calculation unit 74 calculates a Kalman gain K for correcting the state quantity estimated value ^x based on the observation deviation Δy.

[0028] Specifically, the observation value calculation unit 71 receives the lateral acceleration Ay, the yaw rate γ, and the rack shaft estimated value ^F rack The observed value calculation unit 71 receives the rack shaft estimated value ^F rack Based on this, the tire force acting on the steered wheels 3 is the kingpin torque T kpaSpecifically, the observed value calculation unit 71 calculates the rack shaft estimated value ^F which is approximated to the tie rod force acting in the axial direction of the tie rod 15. rack The kingpin torque T as an observed value is calculated by multiplying it by the knuckle arm length determined by the vehicle specifications. kpa Calculate the following.

[0029] Observed kingpin torque T kpa It is known that the lateral acceleration A can be approximated by the product of the tire cornering force and the caster trail plus the tire alignment torque. y , yaw rate γ and kingpin torque T kpa The third-order observable y[A y ,γ,T kpa ] (3×1 matrix). The observation amount y thus obtained is provided to the subtraction unit 73.

[0030] The estimated value calculation unit 72 receives the tire angle θ t , the vehicle speed V, and the Kalman gain K. The tire angle θ t and vehicle speed V as input quantities u, and a state quantity estimated value ^x and an observation quantity estimated value ^y are calculated based on, for example, a two-wheeled, two-degree-of-freedom planar vehicle model as a dynamics model of the road surface friction coefficient. Specifically, the estimate calculation unit 72 calculates a third-order state quantity estimate ^x[^β,^γ,^μ] (3×1 matrix) including an estimate ^β of vehicle body slip angle β, an estimate ^γ of yaw rate γ, and an estimate ^μ of road surface friction coefficient μ. The vehicle body slip angle β is the angle about a vertical axis passing through the center of gravity of the vehicle between the front-rear direction of the vehicle body and the vehicle traveling direction.

[0031] In addition, the estimated value calculation unit 72 calculates the lateral acceleration A y Estimate of ^A y , the estimated yaw rate γ^γ and the kingpin torque T kpa The estimate of ^T kpa The third-order observation estimate ^y[^A y ,^γ,^T kpa] (3×1 matrix). The observation quantity estimate value ^y obtained in this way is provided to the subtraction unit 73. The subtraction unit 73 subtracts the observation quantity estimate value ^y from the observation quantity y to calculate the observation deviation Δy. This observation deviation Δy is provided to the gain calculation unit 74. The gain calculation unit 74 calculates a Kalman gain K for correcting the state quantity estimate value ^x so as to reduce the observation deviation Δy, based on the observation deviation Δy. The estimate value calculation unit 72 corrects the state quantity estimate value ^x, based on the Kalman gain K.

[0032] In this embodiment, the observed value calculation unit 71, the estimated value calculation unit 72, and the gain calculation unit 74 constitute an extended Kalman filter EKF, which is a type of nonlinear Kalman filter. The road surface friction estimation unit 61 constitutes an estimation observer that uses the extended Kalman filter EKF. For ease of explanation, hereinafter, the estimated value ^μ of the road surface friction coefficient μ calculated by the road surface friction estimation unit 61 will be referred to as the "road surface friction coefficient μ," and the estimated value ^β of the vehicle body slip angle β calculated by the road surface friction estimation unit 61 will be referred to as the "vehicle body slip angle β." The "road surface friction coefficient μ" estimated by the road surface friction estimation unit 61 is provided to a filter unit 62. The "vehicle body slip angle β" estimated by the road surface friction estimation unit 61 is provided to a tire slip angle estimation unit 64.

[0033] Returning to FIG. 3 , the filter unit 62 includes a filter 62A for smoothing the change over time in the road surface friction coefficient μ estimated by the road surface friction estimation unit 61. The filter 62A may be a low-pass filter. In this embodiment, the filter unit 62 performs filtering processing on the road surface friction coefficient μ provided by the road surface friction estimation unit 61 using the filter 62A. The filtered road surface friction coefficient μ output from the filter unit 62 is provided to the limit tire slip angle estimation unit 63.

[0034] The tire slip angle estimation unit 64 estimates the vehicle body slip angle β given by the road surface friction estimation unit 61, the vehicle speed V, the yaw rate γ, and the front wheelbase l, which is the distance in the front-rear direction of the vehicle from the center of gravity of the vehicle to the axle of the front wheels. fand tire angle θ t Based on this, the tire slip angle α of the steered wheel 3 is calculated. f (Hereinafter, simply referred to as "tire slip angle α.") Specifically, the tire slip angle estimator 64 calculates the tire slip angle α based on the following equation (1).

[0035]

number

[0036] The limit tire slip angle estimation unit 63 calculates the sign of the tire slip angle α estimated by the tire slip angle estimation unit 64, the road surface friction coefficient μ output from the filter unit 62, and the wheel load F of the steered wheels 3. z and cornering stiffness C α Based on this, the tire slip angle at the tire grip limit (hereinafter referred to as the limit tire slip angle α sl ") is calculated. Cornering stiffness C α is the tire cornering force F of the steered wheel 3 in the range where the tire slip angle α is very small. y The tire cornering force F of the steered wheels 3 is a rising gradient with respect to the tire slip angle α and is set in advance. y is the force acting on the tire of the steered wheel 3 from the road surface in a direction perpendicular to the tire traveling direction.

[0037] Specifically, the limit tire slip angle estimator 63 calculates the limit tire slip angle α sl Calculate the following.

[0038]

number

[0039] The steering angle limit value calculation unit 65 calculates the overall gear ratio i oagr a tire slip angle α estimated by the tire slip angle estimating unit 64, a vehicle speed V, a yaw rate γ, and a front wheel base l fand the road surface friction coefficient μ output from the filter unit 62 and the wheel load F of the steered wheels 3. z and cornering stiffness C α Based on this, the steering angle at the tire grip limit is set to the steering angle limit value θ sl The steering angle limit value calculation unit 65 is an example of the "steering angle limit value calculation unit" in the present invention.

[0040] Specifically, the steering angle limit value calculation unit 65 calculates the steering angle limit value θ based on the following equation (3). sl Calculate the following.

[0041]

number

[0042] The limiting unit 66 limits the target steering angle θ auto and the steering angle limit value θ calculated by the steering angle limit value calculation unit 65. sl Based on this, the target steering angle θ after the limiting process is SEC Calculate the following. Specifically, the limiting unit 66 calculates the target steering angle θ after the limiting process based on the following equations (4a) and (4b). SEC Calculate the following.

[0043]

number

[0044] In formulas (4a) and (4b), G α is the adjustment gain, 0 <G α In this embodiment, G α is G α =1. G α = 1, the absolute value of the tire slip angle α |α| is the limit tire slip angle α sl Absolute value of |α sl If the target steering angle θ auto The target steering angle θ after the limiting process is SECTherefore, in this case, the target steering angle θ auto is not restricted.

[0045] On the other hand, the absolute value of the tire slip angle α |α| is the limit tire slip angle α sl Absolute value of |α sl In the above case, the steering angle limit value θ sl is the target steering angle θ after the limiting process SEC Therefore, in this case, the target steering angle θ auto is the steering angle limit value θ sl can be replaced by. The tire slip angle estimating section 64, the steering angle limit value calculating section 65 and the limiting section 66 in FIG. 3 are an example of the "tire slip angle limiting section" in the present invention. [2.5] Configuration of angle control unit 54 The angle control unit 54 determines the target steering angle θ after the limiting process. SEC Based on this, a target motor torque T mt Calculate the following.

[0046] FIG. 5 is a block diagram showing the configuration of the angle control unit 54. The angle control unit 54 includes a feedback control unit 101 , a feedforward control unit 102 , a torque addition unit 103 , a first reduction ratio division unit 104 , and a second reduction ratio division unit 105 . The first reduction ratio division unit 104 divides the rotor rotation angle θ m Reduction ratio i dec By dividing by this, the rotor rotation angle θ m The rotation angle (actual steering angle) θ of the output shaft 9 (steering shaft 6) s Convert to.

[0047] The feedback control unit 101 detects the actual steering angle θ s The target steering angle θ after the limiting process SEC The feedback control unit 101 includes an angle deviation calculation unit 101A and a PD control unit 101B. The angle deviation calculation unit 101A calculates a target steering angle θSEC and the actual steering angle θ s Deviation Δθ(=θ SEC -θ s ) is calculated. The PD control unit 101B performs a PD calculation (proportional differential calculation) on the angle deviation Δθ calculated by the angle deviation calculation unit 101A, thereby obtaining a feedback control torque T fb Calculate the feedback control torque T fb is provided to the torque addition unit 103.

[0048] The feedforward control unit 102 is provided to compensate for a delay in response due to the inertia of the electric power steering system 1, thereby improving the response of the control. The feedforward control unit 102 includes an angular acceleration calculation unit 102A and an inertia multiplication unit 102B. The angular acceleration calculation unit 102A calculates the target steering angle θ after the limiting process. SEC By differentiating it twice, the target angular acceleration d 2 θ SEC / dt 2 Calculate the following.

[0049] The inertia multiplication unit 102B multiplies the target angular acceleration d calculated by the angular acceleration calculation unit 102A by 2 θ SEC / dt 2 is multiplied by the inertia J of the electric power steering system 1 to obtain the feedforward control torque T ff (=J d 2 θ SEC / dt 2 The inertia J is calculated, for example, from a physical model (not shown) of the electric power steering system 1. The feedforward control torque T ff is given to the torque addition unit 103 as an inertia compensation value.

[0050] The torque addition unit 103 calculates the feedback control torque T fb to the feedforward control torque T ff By adding the above, the target torque for the output shaft 9, that is, the target steering torque T st (=T fb +Tff ) is calculated. Target steering torque T st is provided to a second reduction ratio division unit 105. The second reduction ratio division unit 105 calculates the target steering torque T st Reduction ratio i dec By dividing by mt This target motor torque T mt is applied to the torque control section 55 (see FIG. 2). [2.6] Configuration of torque control unit 55 The torque control unit 55 determines whether the motor torque of the electric motor 18 is equal to or smaller than the target motor torque T mt That is, the torque control unit 55 controls the torque of the electric motor 18 (torque feedback control).

[0051] FIG. 6 is a block diagram showing the configuration of the torque control unit 55. The torque control unit 55 includes a target motor current calculation unit 111 , a current deviation calculation unit 112 , a PI control unit 113 , and a PWM (Pulse Width Modulation) control unit 114 . The target motor current calculation unit 111 calculates the target motor torque T mt The torque constant K of the electric motor 18 t The target motor current I mt Calculate the following.

[0052] The current deviation calculation unit 112 calculates the target motor current I obtained by the target motor current calculation unit 111. mt and the motor current I detected by the current detection circuit 42. m Deviation ΔI (=I mt -I m ) is calculated. The PI control unit 113 performs a PI calculation (proportional integral calculation) on the current deviation ΔI calculated by the current deviation calculation unit 112 to obtain a motor current I m The target motor current I mtThe PWM control unit 114 generates a PWM control signal having a duty ratio corresponding to the drive command value, and supplies the PWM control signal to the drive circuit 41. As a result, power corresponding to the drive command value is supplied to the electric motor 18. [2.7] Effects of the embodiment in automatic steering mode In the above embodiment, for example, G α = 1, the absolute value of the tire slip angle α |α| is the limit tire slip angle α sl Absolute value of |α sl In this case, the steering angle limit value θ sl is the target steering angle θ after the limiting process SEC (see equation (4b)). As a result, the steering angle θ is calculated based on the steering angle limit value θ sl (steering angle at tire grip limit). As a result, the tire slip angle α of the steered wheels 3 is prevented from becoming larger than the limit slip angle α sl (Tire cornering force F y This prevents the vehicle from exceeding the tire slip angle at which the slip angle is maximized, thereby preventing the vehicle state from becoming unstable.

[0053] In addition, G α If is set to a value less than 1, |α| sl Before reaching the steering angle limit value θ sl is the target steering angle θ after the limiting process SEC Since |α| is calculated as |α sl Before reaching the steering angle θ s This will allow you to limit the amount of data that can be used. In addition, in the above-described embodiment, the first steering envelope control unit 53 includes a filter unit 62 for smoothing the change over time in the road surface friction coefficient μ, thereby preventing the vehicle from becoming unstable when the vehicle enters from a region where the road surface friction coefficient is low (hereinafter referred to as the "low μ region") to a region where the road surface friction coefficient is high (hereinafter referred to as the "high μ region").

[0054] In the following, a configuration that is substantially the same as the above-described embodiment, but in which the first steering envelope control unit 53 does not include the filter unit 62, will be referred to as a comparative example. Using Figures 7A and 7B, it will be explained that when a vehicle enters from a low μ region to a high μ region, the vehicle state is more likely to become unstable than when the vehicle enters from a high μ region to a low μ region.

[0055] In FIG. 7A and FIG. 7B, a curve S1 represents the tire cornering force (tire grip force) F with respect to the tire slip angle α when the vehicle is traveling in the low μ region. y A curve S2 is a graph showing the relationship between the tire cornering force F and the tire slip angle α when the vehicle is traveling in a high μ region. y 4 is a graph showing the relationship between the target steering angle θ auto Target tire slip angle α according to tar are shown respectively.

[0056] FIG. 7A is a graph for explaining the operation of the comparative example when the vehicle enters from the high μ region to the low μ region. When the vehicle is traveling in a high μ region, the target tire slip angle α tar When the road surface friction coefficient μ (curve S2) is used, the tire slip angle α increases as shown by the arrow a1. slH The tire slip angle α is limited by this.

[0057] Target tire slip angle α tar When the vehicle enters the low μ region from the high μ region while maintaining the above, the tire cornering force F y In addition, the comparatively large limit tire slip angle α slH As shown by the arrow b1, the comparatively small limit tire slip angle α calculated using the comparatively small road friction coefficient μ (curve S1) slL As a result, the tire slip angle α changes to a relatively small limit tire slip angle α slLThis limits the steering angle limit value θ sl is set to a relatively small value, and as shown by the arrow a3, the tire slip angle α decreases and the tire cornering force F y Since there is almost no change in the vehicle condition, the vehicle is less likely to become unstable.

[0058] FIG. 7B is a graph for explaining the operation of the comparative example when the vehicle enters from the low μ region to the high μ region. When the vehicle is traveling in a low μ region, the target tire slip angle α tar When the road surface friction coefficient μ (curve S1) is used, the tire slip angle α increases as shown by the arrow a1. slL The tire slip angle α is limited by this.

[0059] Target tire slip angle α tar When the vehicle enters the high μ region from the low μ region while maintaining the above, the tire cornering force F y In addition, the limit tire slip angle α sl As shown by the arrow b1, the comparatively large limit tire slip angle α calculated using the comparatively large road friction coefficient μ (curve S2) slH changes rapidly to. As a result, the steering angle limit value θ sl is set to a relatively large value, and as shown by the arrow a3, the tire slip angle α increases and the tire cornering force F y Since the vehicle condition is likely to become unstable as shown in FIG. 8A, the vehicle condition is likely to become unstable as shown in FIG. 8A. L is the low μ region, and the region E indicated by the hatching extending diagonally downward to the right H is the high μ region (the same applies to FIG. 8B described later).

[0060] In this embodiment, the first steering envelope control unit 53 includes a filter unit 62 for gradualizing the change over time of the road surface friction coefficient μ. As a result, even when the vehicle enters a high μ region from a low μ region, the limit tire slip angle α sl This suppresses the sudden increase in the tire cornering force F y and steering angle limit value θ sl This can prevent the vehicle state from becoming unstable even when the vehicle enters the high μ region from the low μ region, as shown in FIG. 8B.

[0061] 9A is a time chart showing the change in road surface friction coefficient μ input to limit tire slip angle estimator 63 when the vehicle enters from a low μ region to a high μ region. In Fig. 9A, the dashed line shows the change in road surface friction coefficient μ in a comparative example, and the solid line shows the change in road surface friction coefficient μ in this embodiment. FIG. 9B shows the steering angle limit value θ calculated by the steering angle limit value calculation unit 65 when the vehicle enters the high μ region from the low μ region. sl 9B is a time chart showing the change over time of the steering angle limit value θ sl The solid line indicates the change in the steering angle limit value θ sl This shows the change in

[0062] FIG. 9C shows the target steering angle θ after the limiting process calculated by the limiting unit 66 when the vehicle enters the high μ region from the low μ region. SEC 9C is a time chart showing the change over time of the target steering angle θ auto The dashed line indicates the target steering angle θ after the limiting process in the comparative example. SEC The solid line indicates the change in the target steering angle θ after the limiting process in this embodiment. SEC This shows the change in

[0063] In the comparative example, at time t1 when the vehicle enters the high μ region from the low μ region, the road friction coefficient μ increases abruptly (see FIG. 9A), and the steering angle limit value θ slincreases rapidly (see FIG. 9B), and the target steering angle θ SEC increases rapidly (see Figure 9C). In contrast, in this embodiment, at time t1 when the vehicle enters the high μ region from the low μ region, the road surface friction coefficient μ increases gradually (see FIG. 9A), and the steering angle limit value θ sl increases gradually (see FIG. 9B), and the target steering angle θ SEC increases gradually (see FIG. 9C). This makes it possible to prevent the vehicle state from becoming unstable when the vehicle enters the high μ region from the low μ region. [3] Electrical configuration of motor control ECU 202 in manual steering mode [3.1] Overall structure FIG. 10 is a block diagram showing the electrical configuration of motor control ECU 202, and is used to explain the electrical configuration related to the operation in the manual steering mode.

[0064] The motor control ECU 202 includes a microcomputer 50, a drive circuit 41 that is controlled by the microcomputer 50 and supplies power to the electric motor 18, and a current (motor current I m ) and a current detection circuit 42 for detecting the current. The microcomputer 50 includes a CPU and a memory, and functions as a plurality of functional processing units by executing a predetermined program. The plurality of functional processing units include a rotation angle calculation unit 51, a rack axial force estimation unit 52, a second steering envelope control unit 56, a target assist torque setting unit 57, a torque addition unit 58, a torque control unit 55, and a tire angle calculation unit 59, which are related to the manual mode. The torque control unit 55 is an example of the "motor control unit" in the present invention.

[0065] Since the rotation angle calculation unit 51, the tire angle calculation unit 59, the rack axial force estimating unit 52, and the torque control unit 55 are the same as the rotation angle calculation unit 51, the tire angle calculation unit 59, the rack axial force estimating unit 52, and the torque control unit 55 in FIG. 2, respectively, the description thereof will be omitted. [3.2] Second steering envelope control section 56 The second steering envelope control unit 56 determines whether the tire slip angle α is equal to the limit tire slip angle α sl The envelope control torque (torque for limiting steering angle) T SEC Calculate the following.

[0066] FIG. 11 is a block diagram showing the configuration of the second steering envelope control unit 56. As shown in FIG. The second steering envelope control unit 56 includes a road surface friction estimator 61, a filter unit 62, a limit tire slip angle estimator 63, a tire slip angle estimator 64, a steering angle limit value calculator 65, a steering angle calculator 67, and an envelope control torque calculator 68. The steering angle limit value calculator 65 is an example of the "steering angle limit value calculator" in the present invention. The envelope control torque calculator 68 is an example of the "steering angle limiting torque calculator" in the present invention.

[0067] Road surface friction estimator 61, filter unit 62, limit tire slip angle estimator 63, tire slip angle estimator 64 and steering angle limit value calculation unit 65 are the same as road surface friction estimator 61, filter unit 62, limit tire slip angle estimator 63, tire slip angle estimator 64 and steering angle limit value calculation unit 65 in FIG. 3, respectively, and therefore their description will be omitted. The steering angle calculation unit 67 calculates the tire angle θ t Overall gear ratio i oagr By multiplying this, the actual steering angle (the rotation angle of the output shaft 9) θ s The steering angle calculation unit 67 calculates the rotor rotation angle θ m Reduction ratio i dec By dividing by , the actual steering angle θ s may be calculated.

[0068] The envelope control torque calculation unit 68 calculates the actual steering angle θ s and the limit tire slip angle α estimated by the limit tire slip angle estimating unit 63. sl Based on this, the envelope control torque (torque for limiting the steering angle) T SECSpecifically, the envelope control torque calculation unit 68 calculates the envelope control torque T SEC Calculate the following.

[0069]

number

[0070] In (5a) and (5b), G α is the adjustment gain, 0 <G α In this embodiment, G α is G α = 1. In the formula (5b), k is a virtual spring constant and is set in advance, and c is a virtual viscous damping coefficient and is set in advance. The tire slip angle estimating section 64, the steering angle limiting value calculating section 65 and the envelope control torque calculating section 68 in FIG. 11 are an example of the "tire slip angle limiting section" of the present invention. [3.3] Target assist torque setting unit 57 Returning to FIG. 10, the target assist torque setting unit 57 sets the target assist torque T at The target assist torque setting unit 57 sets the steering torque T d Based on this, the target assist torque T at Set the steering torque T d Target assist torque T at An example of the setting is shown in FIG.

[0071] Target assist torque T at is set to a positive value when the electric motor 18 is to generate a steering assist force for steering in the left direction, and is set to a negative value when the electric motor 18 is to generate a steering assist force for steering in the right direction. at is the steering torque T d For positive values ​​of , the steering torque T d For negative values ​​of , it is negative. And, the target assist torque Tat is the steering torque T d The larger the absolute value of is, the larger the absolute value is set.

[0072] The target assist torque setting unit 57 determines the steering torque T d The target assist torque T at may be calculated. [3.4] Torque adder 58 The torque addition unit 58 calculates the target assist torque T at The envelope control torque T calculated by the envelope control torque calculation unit 68 SEC By adding mt Calculate the following.

[0073] Target motor torque T mt is given to the torque control unit 55. The torque control unit 55 controls the motor torque T m is the target motor torque T mt The drive circuit 41 is controlled so that the output voltage Vp approaches the reference voltage Vp. [3.5] Effects of the embodiment in manual steering mode In the above embodiment, for example, G α = 1, the absolute value of the tire slip angle α |α| is the limit tire slip angle α sl Absolute value of |α sl If less than |, the envelope control torque T SEC Since the target assist torque T at is the target motor torque T mt (see equation (5a)). Therefore, in this case, normal manual steering is performed.

[0074] |α| is |α sl | or more, the envelope control torque T calculated by equation (5b) SEC The target assist torque T at By adding to the target motor torque T mtIn this case, the steering angle θ s Absolute value of |θ s | is the steering angle limit value θ sl Absolute value of |θ sl | is larger than the envelope control torque T SEC Since the target motor torque T mt is the target assist torque T at will be smaller than

[0075] And the steering angle θ s Absolute value of |θ s | is the steering angle limit value θ sl Absolute value of |θ sl The larger the target motor torque T mt As a result, the driver feels that the steering wheel is heavy compared to normal manual steering. This makes it difficult for the driver to steer, so the steering angle θ becomes smaller than the steering angle limit value θ sl (steering angle at tire grip limit). As a result, the tire slip angle α of the steered wheels 3 is prevented from becoming larger than the limit slip angle α sl (Tire cornering force F y This prevents the vehicle from exceeding the tire slip angle at which the slip angle is maximized, thereby preventing the vehicle state from becoming unstable.

[0076] G α If is set to a value less than 1, |α| sl Before reaching the envelope control torque T SEC is calculated based on equation (5b), so |α| sl Before reaching the steering angle θ s This will allow you to limit the amount of data that can be used. In addition, in the above-described embodiment, the first steering envelope control unit 53 includes a filter unit 62 for smoothing the change over time in the road surface friction coefficient μ, thereby preventing the vehicle state from becoming unstable when the vehicle enters a high μ region from a low μ region. [3.6] Modification of the envelope control torque calculation unit 68 The envelope control torque calculation unit 68 calculates the envelope control torque T SEC The following may be calculated.

[0077]

number

[0078] G α is the adjustment gain, 0 <G α It is set to a value in the range ≦1. For example, G α = 1, the absolute value of the tire slip angle α |α| is the limit tire slip angle α sl Absolute value of |α sl If less than |, the envelope control torque T SEC Since the target assist torque T at is the target motor torque T mt (see equation (6a)). Therefore, in this case, normal manual steering is performed.

[0079] |α| is |α sl | or more, the envelope control torque T calculated by equation (6b) SEC The target assist torque T at By adding to the target motor torque T mt In this case, the steering angle θ s Absolute value of |θ s | is the steering angle limit value θ sl Absolute value of |θ sl | is larger than the envelope control torque T SEC Since the target motor torque T mt is the target assist torque T at will be greater than.

[0080] And the steering angle θ s Absolute value of |θ s | is the steering angle limit value θ sl Absolute value of |θ sl The larger the target motor torque Tmt As a result, the driver feels that the steering wheel is lighter than during normal manual steering. This gives the driver a feeling of slipping, and he or she tries to return the steering wheel to its original position. As a result, the steering angle θ becomes larger than the steering angle limit value θ sl (steering angle at tire grip limit). As a result, the tire slip angle α of the steered wheels 3 is prevented from becoming larger than the limit slip angle α sl (Tire cornering force F y This prevents the vehicle from exceeding the tire slip angle at which the slip angle is maximized, thereby preventing the vehicle state from becoming unstable.

[0081] G α If is set to a value less than 1, |α| sl Before reaching the envelope control torque T SEC is calculated based on equation (6b), so |α| sl Before reaching the steering angle θ s This will allow you to limit the amount of data that can be used. [4] Other variations Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms. For example, in the above-described embodiment, the filter unit 62 makes the time change of the road surface friction coefficient μ gentle regardless of the change mode of the road surface friction coefficient μ provided by the road surface friction estimation unit 61. However, the time change of the road surface friction coefficient μ may be made gentle only when the road surface friction coefficient μ provided by the road surface friction estimation unit 61 changes from a small value to a large value. For example, the filter unit 62 may perform an operation as shown in FIG. 13.

[0082] That is, the filter unit 62 first calculates the current value μ of the road surface friction coefficient μ given by the road surface friction estimation unit 61. k and the previous value μ k-1 Difference with (μ k -μ k-1 ) (step S1). Next, the filter unit 62 calculates the difference (μ k -μ k-1 ) is a given threshold A th (However, Ath >0) (step S2). (μ k -μ k-1 ) th If so (step S2: NO), the filter unit 62 returns to step S1.

[0083] In step S2, (μ k -μ k-1 )≧A th If it is determined that the road surface friction coefficient μ is 1 (step S2: YES), the filter unit 62 performs a filter process on the road surface friction coefficient μ using the filter 62A (step S3), and then the process returns to step S1. In the above embodiment, the angle control unit 54 (see FIG. 2) includes the feedforward control unit 102, but the feedforward control unit 102 may be omitted. In this case, the feedback control torque T fb is the target steering torque T st It becomes.

[0084] In the above embodiment, the tire slip angle α of the steered wheels 3 is equal to the limit tire slip angle α sl The steering angle θ s (Tire angle θ of steered wheel 3 t However, the tire slip angle α is limited by the tire angle θ as shown in equation (1). t Since the tire slip angle α of the steered wheels 3 is a function of the vehicle speed V, the tire slip angle α of the steered wheels 3 is equal to the limit tire slip angle α sl The vehicle speed V may be limited so as not to exceed

[0085] In this case, the vehicle speed V is limited by, for example, braking control. However, in the case of braking control, it takes time to decelerate the vehicle due to the moment of inertia of the vehicle. Therefore, the steering angle θ s (Tire angle θ t ) has the advantage of being more responsive than the method of limiting the vehicle speed V. ​In the above embodiment, the first steering envelope control unit 53 and the second steering envelope control unit 56 are provided in the motor control ECU 202, but they may be provided in the host ECU 201.

[0086] In the above embodiment, the present invention is applied to a column-type EPS, but the present invention can be applied to EPS other than the column type. The present invention can also be applied to a steer-by-wire system. Although the embodiments of the present invention have been described in detail, these are merely examples used to clarify the technical content of the present invention, and the present invention should not be interpreted as being limited to these examples, and the scope of the present invention is limited only by the appended claims. [Explanation of symbols]

[0087] 1... electric power steering system, 3... steered wheel, 4... steering mechanism, 18... electric motor, 51... rotation angle calculation section, 52... rack axial force estimation section, 53... first steering envelope control section, 54... angle control section, 55... torque control section, 56... second steering envelope control section, 57... target assist torque setting section, 58... torque addition section, 61... road surface friction estimation section, 62... filter section, 63... limit tire slip angle estimation section, 64... tire slip angle estimation section, 65... steering angle limit value calculation section, 66... ​​limit section, 67... steering angle calculation section, 68... envelope control torque calculation section

Claims

1. a road surface friction coefficient estimation unit that estimates a road surface friction coefficient, which is a friction coefficient of a road surface on which a vehicle is traveling; a filter unit for smoothing a change over time in the road surface friction coefficient estimated by the road surface friction coefficient estimation unit; a limit tire slip angle estimating unit that estimates a limit tire slip angle, which is a tire slip angle at which a tire cornering force of a steered wheel becomes maximum, using the road surface friction coefficient after filtering by the filter unit; a tire slip angle limiting unit that limits the tire slip angle of the steered wheel so as to prevent the tire slip angle of the steered wheel from exceeding the limit tire slip angle, The filter unit is configured to smooth out the change over time in the road surface friction coefficient estimated by the road surface friction coefficient estimation unit only when the road surface friction coefficient estimated by the road surface friction coefficient estimation unit changes from a small road surface friction coefficient to a large road surface friction coefficient.

2. 2. The steering device according to claim 1, wherein the tire slip angle limiting unit is configured to limit the turning angle of the steered wheels so that the tire slip angle of the steered wheels does not exceed the limit tire slip angle.

3. The tire slip angle limiting portion is a tire slip angle calculation unit that calculates a tire slip angle of the steered wheels; a steering angle limit value calculation unit that calculates a steering angle limit value for limiting the steering angle by using the tire slip angle and the limit tire slip angle; The steering device according to claim 2 , further comprising: a limiting unit that limits a target steering angle for automatic steering by using the steering angle limit value.

4. an electric motor for generating an assist torque; A target assist torque setting unit that sets a target assist torque; a motor control unit that controls the electric motor, The tire slip angle limiting portion is a tire slip angle calculation unit that calculates a tire slip angle of the steered wheels; a steering angle limit value calculation unit that calculates a steering angle limit value for limiting the steering angle by using the tire slip angle and the limit tire slip angle; a steering angle limiting torque calculation unit that calculates a steering angle limiting torque for limiting the steering angle by using the steering angle limit value and the steering angle, The motor control unit uses the target assist torque and the steering angle limiting torque. The steering apparatus according to claim 2 , wherein the electric motor is configured to be torque controlled.

5. A road surface friction coefficient estimation unit that estimates a road surface friction coefficient, which is the friction coefficient of the road surface on which the vehicle is traveling; a filter unit for smoothing a change over time in the road surface friction coefficient estimated by the road surface friction coefficient estimation unit; a limit tire slip angle estimating unit that estimates a limit tire slip angle, which is a tire slip angle at which a tire cornering force of a steered wheel becomes maximum, using the road surface friction coefficient after filtering by the filter unit; a tire slip angle limiting unit that limits a turning angle of the steered wheels so that the tire slip angle of the steered wheels does not exceed the limit tire slip angle; an electric motor for generating an assist torque; A target assist torque setting unit that sets a target assist torque; a motor control unit that controls the electric motor, The tire slip angle limiting portion is a tire slip angle calculation unit that calculates a tire slip angle of the steered wheels; a steering angle limit value calculation unit that calculates a steering angle limit value for limiting the steering angle by using the tire slip angle and the limit tire slip angle; a steering angle limiting torque calculation unit that calculates a steering angle limiting torque for limiting the steering angle by using the steering angle limit value and the steering angle, The motor control unit uses the target assist torque and the steering angle limiting torque. A steering device configured to torque control the electric motor.

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