Vehicle control device, vehicle control method, vehicle control program, and rear wheel steering device

Abstract

In one aspect of a vehicle control device, a vehicle control method, a vehicle control program, and a rear wheel steering device according to the present invention, a target control amount, which is a control amount that is a target of a rear wheel steering actuator provided in a vehicle, is acquired so that a vehicle body slip angle becomes zero on the basis of a vehicle speed, a steering angle of a front wheel, and vehicle specifications, and the target control amount is corrected so that an estimated vehicle body slip angle obtained by adding a vehicle body slip angle caused by a roll rate becomes zero on the basis of a physical quantity related to the roll state of the vehicle. Thus, the accuracy of vehicle control based on the estimated value of the vehicle body slip angle can be improved.

Description

Vehicle control device, vehicle control method, vehicle control program, and rear wheel steering device

[0001] The present invention relates to a vehicle control device, a vehicle control method, a vehicle control program, and a rear wheel steering device.

[0002] The turning behavior control device of Patent Document 1 sets a target turning radius R, a revolution reference point Le, and a target center of rotation Lo, sets a target sideslip angle β and a target yaw rate γ in accordance with the target turning radius R, revolution reference point Le, and target center of rotation Lo, calculates target steering angles δf(s) and δr(s) for the front and rear wheels in accordance with the target sideslip angle β and target yaw rate γ, and drives and controls the steering mechanism so that the target steering angles δf(s) and δr(s) are achieved.

[0003] Japanese Patent Application Laid-Open No. 2009-018756

[0004] However, when the vehicle slip angle, which is the angle between the orientation of the vehicle and the direction of travel of the vehicle, is estimated using information on the vehicle speed and steering input, the cornering force (in other words, the yaw moment) generated by the roll behavior of the vehicle is not taken into consideration, and the accuracy of estimating the vehicle slip angle when the roll behavior is occurring decreases. As a result, when the roll behavior is occurring, vehicle control based on the estimated value of the vehicle slip angle cannot be performed with high accuracy, and there are cases where the effects of the vehicle control on improving maneuverability and ride comfort are reduced.

[0005] The present invention has been made in consideration of the conventional situation, and an object of the present invention is to provide a vehicle control device, a vehicle control method, a vehicle control program, and a rear wheel steering device that can improve the accuracy of vehicle control based on an estimated value of a vehicle body slip angle.

[0006] Therefore, in one aspect, a vehicle control device, a vehicle control method, and a vehicle control program according to the present invention acquire a plurality of physical quantities that indicate a driving state of the vehicle, including a first physical quantity related to a vehicle speed of the vehicle, a second physical quantity related to a steering angle of front wheels of the vehicle, and a third physical quantity related to a roll state of the vehicle, and acquire a target control quantity that is a control quantity to be a target for an actuator provided on the vehicle, based on at least the first physical quantity and the second physical quantity of the plurality of physical quantities and predetermined vehicle specifications of the vehicle, so that a vehicle body slip angle, which is the angle between the orientation of the vehicle and the direction of travel of the vehicle, becomes zero, and acquire an actual control quantity to be given to the actuator by correcting the target control quantity based on at least some of the plurality of physical quantities including the third physical quantity, so that an estimated vehicle body slip angle that takes into account a vehicle body slip angle caused by a roll rate becomes zero, and output a signal corresponding to the actual control quantity. In one aspect of the rear wheel steering device according to the present invention, the actuator is a rear wheel steering actuator provided in the rear wheel steering device for applying a steering angle to the rear wheels of a vehicle.

[0007] According to the present invention, it is possible to improve the accuracy of vehicle control based on an estimated value of the vehicle body slip angle.

[0008] 1 is a block diagram showing a vehicle control system; FIG. 2 is a diagram showing an overview of a vehicle body slip angle estimation method; FIG. 3 is a block diagram showing the logic of a vehicle body slip angle estimation method; FIG. 4 is a block diagram showing a first embodiment of control logic for front wheel steering angle and rear wheel steering angle; FIG. 5 is a Bode plot showing the frequency characteristics of vehicle body slip angle; FIG. 6 is a block diagram showing a second embodiment of control logic for front wheel steering angle and rear wheel steering angle; FIG. 7 is a Bode plot showing the frequency characteristics of lateral acceleration and vehicle body slip angle; FIG. 8 is a block diagram showing the basic control theory of an H-infinity control unit; FIG. 9 is a block diagram showing the detailed control theory of an H-infinity control unit.

[0009] Hereinafter, embodiments of a vehicle control device, a vehicle control method, a vehicle control program, and a rear wheel steering device according to the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing a vehicle control system 200 mounted on a vehicle 100. The vehicle 100 is a four-wheeled automobile equipped with a pair of left and right front wheels 101, 102 and a pair of left and right rear wheels 103, 104.

[0010] As will be described in detail later, the vehicle control system 200 is a system having a function of estimating a vehicle body slip angle β [rad], which is the angle between the orientation of the vehicle 100 and the traveling direction of the vehicle 100, and controlling the traveling actuators of the vehicle 100 based on the estimated value of the vehicle body slip angle β (in other words, the vehicle body sideslip angle). The vehicle control system 200 includes an external environment recognition unit 300, a vehicle state acquisition unit 400, a vehicle control device 500, and an actuator unit 600.

[0011] The external environment recognition unit 300 acquires external environment information of the vehicle 100, in other words, information about the driving environment of the road on which the vehicle 100 is traveling. In one aspect, the external environment recognition unit 300 includes a GPS (Global Positioning System) receiving unit 310, a map database 320, a wireless communication device 330, a camera 340, a radar 350, and a LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) 360.

[0012] The GPS receiver 310 receives signals from GPS satellites to measure the latitude and longitude of the position of the vehicle 100. The map database 320 is created in a storage device mounted on the vehicle 100. The map information in the map database 320 includes information such as road positions, road shapes, and intersection positions.

[0013] The wireless communication device 330 is a device for performing road-to-vehicle communication and / or vehicle-to-vehicle communication. In the case of road-to-vehicle communication, the wireless communication device 330 transmits information about the vehicle 100 to a roadside device and receives road traffic information, such as curves and intersections, from the roadside device. In the case of vehicle-to-vehicle communication, the wireless communication device 330 acquires road traffic information and behavior information of the other vehicle from another vehicle and transmits the behavior information and road traffic information of the vehicle 100 to the other vehicle.

[0014] The camera 340 is a stereo camera, a monocular camera, a 360° camera, or the like, and captures images of the surroundings of the vehicle 100 to obtain image information of the surroundings of the vehicle 100. The radar 350 and the LiDAR 360 detect moving and stationary objects around the vehicle 100 and output information about the detected objects.

[0015] The vehicle state acquisition unit 400 acquires information regarding the motion state of the vehicle 100. In one aspect, the vehicle state acquisition unit 400 includes a wheel speed sensor 410, an acceleration sensor 420, a gyro sensor 430, a front wheel steering angle sensor 440, and a rear wheel steering angle sensor 450. The wheel speed sensor 410 is a sensor that detects the rotational speed of each of the four wheels 101-104 of the vehicle 100. The vehicle control device 500 acquires signals of the rotational speed of each of the four wheels 101-104 detected by the wheel speed sensor 410, and calculates the vehicle speed V [m / s], which is the traveling speed of the vehicle 100.

[0016] The acceleration sensor 420 is a sensor that detects acceleration in the vehicle behavior, and detects the longitudinal acceleration αx [m / s 2 ] and lateral acceleration αy [m / s 2 The gyro sensor 430 is a sensor that detects the angular velocity [rad / s] of the vehicle behavior, and detects the yaw rate, roll rate, and pitch rate of the vehicle 100. The vehicle 100 may be equipped with a multi-axis inertial sensor that integrates the acceleration sensor 420 and the gyro sensor 430.

[0017] Furthermore, the front wheel steering angle sensor 440 detects a front wheel steering angle δf [rad], which is the steering angle (in other words, tire angle) of the front wheels 101, 102 that is varied by the front wheel steering device 630. Here, instead of directly detecting the steering angle of the front wheels 101, 102, the front wheel steering angle sensor 440 can obtain a physical quantity related to the operation angle (steering operation amount) of the steering wheel 631 as a physical quantity (second physical quantity) related to the steering angle of the front wheels 101, 102. Furthermore, the rear wheel steering angle sensor 450 detects a rear wheel steering angle δr [rad], which is the steering angle of the rear wheels 103, 104 that is varied by the rear wheel steering device 640.

[0018] The actuator unit 600 is configured to include a plurality of travel actuators of the vehicle 100, specifically, a drive unit 610, a brake unit 620, and the aforementioned front wheel steering unit 630 and rear wheel steering unit 640. The drive unit 610 is an internal combustion engine or a motor that applies drive force to the front wheels 101, 102 and / or rear wheels 103, 104 of the vehicle 100. The brake unit 620 is a device that applies braking force, such as friction braking force or regenerative braking force, to each of the wheels 101-104 of the vehicle 100. The drive unit 610 and the brake unit 620 are equipped with actuators that can electronically control the drive force and braking force as control variables using electric signals.

[0019] Front wheel steering device 630 is, for example, a steer-by-wire type steering device, and includes a steering wheel 631 as a steering input device that is operated by the driver to indicate the traveling direction of vehicle 100, in other words, that accepts steering operations by the driver, and a front wheel steering actuator 632 that applies a steering force to front wheels 101, 102. Front wheel steering device 630 varies the front wheel steering angle δf by controlling front wheel steering actuator 632 based on a signal of the operation angle (in other words, the operation amount) of steering wheel 631.

[0020] The rear wheel steering device 640 includes a rear wheel steering actuator 641 that applies a steering force to the rear wheels 103, 104, and varies the rear wheel steering angle δr by controlling the rear wheel steering actuator 641 based on a rear wheel steering angle command. Note that the front wheel steering actuator 632 and the rear wheel steering actuator 641 are driven by, for example, a motor.

[0021] The vehicle control device 500 includes a microcomputer 510 as a control unit that performs calculations based on input information and outputs the calculation results. The microcomputer 510 includes an MPU (Micro Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. (not shown), and realizes various control functions by, for example, running programs stored in the ROM as a storage unit using the MPU. The microcomputer 510 can also be referred to as an MCU (Micro Controller Unit), processor, processing device, arithmetic device, etc.

[0022] The microcomputer 510 acquires information about the driving environment of the road on which the vehicle 100 is traveling, including position information of the vehicle 100, road shape information, road surface information, and information about objects around the vehicle 100, from the external environment recognition unit 300. The microcomputer 510 also acquires information about the motion and driving state of the vehicle 100, such as the vehicle speed V, longitudinal acceleration αx, lateral acceleration αy, angular velocities including yaw rate r, front wheel steering angle δf, and rear wheel steering angle δr, from the vehicle state acquisition unit 400. The microcomputer 510 then generates a control command for controlling the motion of the vehicle 100 based on the various acquired information, and controls the operation of the actuator unit 600 by outputting the generated control command to the actuator unit 600.

[0023] Here, the microcomputer 510 performs automatic driving control as motion control of the vehicle 100. In the automatic driving control, the microcomputer 510 generates a target trajectory and a target vehicle speed for the vehicle 100 as a driving plan based on external information about the vehicle 100, and outputs a control command to the actuator unit 600 to drive the vehicle 100 along the target trajectory and the target vehicle speed.

[0024] In detail, the microcomputer 510 includes, as software, the functional units of the surrounding situation recognition unit 511, the driving plan generation unit 512, the vehicle control unit 513, and the vehicle body slip angle estimation unit 514. In other words, a vehicle control program provided by a non-volatile memory such as a ROM causes the microcomputer 510 to function as the surrounding situation recognition unit 511, the driving plan generation unit 512, the vehicle control unit 513, and the vehicle body slip angle estimation unit 514.

[0025] The surrounding situation recognition unit 511 recognizes the situation around the vehicle 100, including the position information of the vehicle 100, the road shape, and information about obstacles, based on the external environment information acquired from the external environment recognition unit 300. The driving plan generation unit 512 generates a target trajectory and a target vehicle speed for the vehicle 100 as a driving plan, based on the situation around the vehicle 100 recognized by the surrounding situation recognition unit 511. Then, the vehicle control unit 513 outputs a control command to the actuator unit 600 to drive the vehicle 100 along the driving plan, specifically, along the target trajectory and the target vehicle speed, based on the target trajectory and the target vehicle speed information based on the driving plan by the driving plan generation unit 512 and the motion state of the vehicle 100 acquired by the vehicle state acquisition unit 400.

[0026] Vehicle body slip angle estimation unit 514 estimates vehicle body slip angle β using a vehicle equation of motion (in other words, a vehicle model) based on the motion state of vehicle 100 acquired by vehicle state acquisition unit 400. In other words, the vehicle control program provided by a non-volatile memory such as a ROM includes a vehicle body slip angle estimation program, and microcomputer 510 functions as vehicle body slip angle estimation unit 514 by executing the vehicle body slip angle estimation program.

[0027] Vehicle control unit 513 then acquires a signal of vehicle body slip angle β estimated by vehicle body slip angle estimation unit 514, calculates a control command so that the estimated value of vehicle body slip angle β approaches a target value, and outputs the calculated control command to actuator unit 600. Note that the target value of vehicle body slip angle β is, for example, vehicle body slip angle = 0 [rad] or within a predetermined range near zero.

[0028] By controlling the vehicle body slip angle β (hereinafter also referred to as "zeroing control"), the vehicle control unit 513 aims to stabilize driving, such as by preventing spins, and to improve the ability to follow the target trajectory. In this way, the vehicle control program provided by the ROM or the like causes the microcomputer 510 to function as a vehicle body slip angle estimation unit 514 that estimates the vehicle body slip angle β, and as the vehicle control unit 513 that outputs a control command based on the vehicle body slip angle β to the actuator unit 600.

[0029] The following describes in detail the process of estimating the vehicle body slip angle β using the vehicle equation of motion, which is performed by the vehicle body slip angle estimator 514. The basic equation of motion of the vehicle 100 can be expressed as Equation 1 and Equation 2.

[0030] In Equation 1 and Equation 2, m [kg] is the vehicle mass, V [m / s] is the vehicle speed (in other words, the first physical quantity related to the vehicle speed of the vehicle 100), r [rad / s] is the yaw rate, Ff [N] is the lateral force generated by the front wheels, Fr [N] is the lateral force generated by the rear wheels, and Iz [kgm 2 ] is the moment of inertia, Lf [m] is the front wheel base which is the distance from the center of gravity to the front wheel axle, and Lr [m] is the rear wheel base which is the distance from the center of gravity to the rear wheel axle. Here, the vehicle mass m, the moment of inertia Iz, the front wheel base Lf, and the rear wheel base Lr are physical quantities related to the vehicle specifications of the vehicle 100 that are given in advance, that is, stored in advance as constants in memory.

[0031] Furthermore, the lateral forces Ff and Fr are expressed by Equations 3 and 4.

[0032] In Equation 3 and Equation 4, αf [rad] is the front wheel slip angle, αr [rad] is the rear wheel slip angle, Kf [N / rad] is the cornering stiffness of the front wheels 101, 102, and Kr [N / rad] is the cornering stiffness of the rear wheels 103, 104. The front wheel slip angle αf and the rear wheel slip angle αr are the angles between the direction of the center plane of the wheel and the direction of travel of the wheel when viewed from above.

[0033] In the vehicle body slip angle estimation method executed by the vehicle body slip angle estimation unit 514, the front wheel slip angle αf is approximated as shown in Equation 5, and the rear wheel slip angle αr is approximated as shown in Equation 6.

[0034] In Equation 5 and Equation 6, δf [rad] is the front wheel steering angle (a second physical quantity related to the steering angle of the front wheels 101, 102), δr [rad] is the rear wheel steering angle, h [m] is the center of gravity height as a vehicle specification (more specifically, the distance from the roll center to the center of gravity), and φ [rad] is the roll angle (in other words, a third physical quantity related to the roll state of the vehicle 100).

[0035] When the front wheel slip angle αf and the rear wheel slip angle αr are approximated as in Equations 5 and 6, the lateral forces Ff and Fr of Equations 3 and 4 can be expressed as in Equations 7 and 8.

[0036] The vehicle body slip angle estimator 514 acquires a plurality of physical quantities indicating the traveling conditions of the vehicle 100, including the vehicle speed V, the front wheel steering angle δf, and the roll angle φ, and estimates the vehicle body slip angle β based on the acquired plurality of physical quantities and the vehicle specifications, using the equations of motion of the vehicle model shown in the above-mentioned Formula 7 and Formula 8. Here, Formulas 5 and 6, which approximate the front wheel slip angle αf and the rear wheel slip angle αr, include the term "center of gravity height h / vehicle speed V*roll rate," which is the term for the vehicle body slip angle caused by the roll rate φ (dot), as described above.

[0037] That is, the vehicle body slip angle estimator 514 (microcomputer 510) has a function of calculating the roll rate φ (dots) from the roll angle φ as a third physical quantity related to the roll state of the vehicle 100, and estimating the vehicle body slip angle (roll rate slip angle) caused by the roll rate φ (dots) among the vehicle body slip angles. Therefore, even if a cornering force (in other words, a yaw moment) occurs in association with the roll behavior of the vehicle 100, the vehicle body slip angle estimator 514 can prevent a decrease in the estimation accuracy of the vehicle body slip angle β.

[0038] For example, when a force is applied in the roll direction of the vehicle 100 due to the alignment of the vehicle 100, the wheels themselves may be angled or tilted, resulting in a turning force similar to that of a two-wheeled vehicle. Therefore, when the vehicle body slip angle estimator 514 estimates the vehicle body slip angle β from the steering angles δf and δr of the front and rear wheels and the vehicle speed V without taking roll behavior into consideration, if a cornering force is generated in conjunction with the roll behavior of the vehicle 100, an error will occur in the estimated value of the vehicle body slip angle β.

[0039] Therefore, the vehicle body slip angle estimator 514 takes into account vehicle motion in the roll direction and introduces a correction term based on the roll rate φ (dots) in estimating the vehicle body slip angle β, thereby realizing estimation processing of the vehicle body slip angle β that takes into account turning movements and transient changes other than simple steering. As a result, even if a cornering force is generated due to the roll behavior of the vehicle 100, a decrease in the estimation accuracy of the vehicle body slip angle β is suppressed, and the stability and control accuracy of vehicle control using the estimated value of the vehicle body slip angle β can be improved.

[0040] An outline of the process for estimating vehicle body slip angle β that introduces a correction term based on roll rate φ (dots) will be described below. Figure 2 is a diagram showing vehicle body slip angle β, slip angle βf1 at the front wheelset point due to yaw rate r, slip angle βf2 at the front wheelset point due to roll rate φ (dots), and various parameters related to these slip angles in a two-wheel model in which the two left and right wheels of vehicle 100 are grouped together in the center.

[0041] The aforementioned equation 5 for calculating the slip angle αf of the front wheels can be rewritten as equation 9 if the slip angle at the front wheel axle point is βf.

[0042] Similarly, Equation 6 for calculating the slip angle αr of the rear wheels can be rewritten as Equation 10, where βr is the slip angle at the rear wheel axle point, βr1 is the slip angle at the rear wheel axle point due to the yaw rate r, and βr2 is the slip angle at the rear wheel axle point due to the roll rate φ (dot).

[0043] When the vehicle 100 rolls and a roll angle φ occurs, a slip angle βf2, which is a slip component that depends on the roll rate φ (dots), the height of the center of gravity h, and the vehicle speed V, occurs at the front wheel axle point. Similarly, when the vehicle 100 rolls and a roll angle φ occurs, a slip angle βr2, which is a slip component that depends on the roll rate φ (dots), the height of the center of gravity h, and the vehicle speed V, occurs at the rear wheel axle point. Here, βf2 = βr2 = roll rate φ (dots) × h / V.

[0044] Therefore, the vehicle body slip angle estimator 514 introduces a correction term based on the roll rate φ (dot) into the vehicle equation of motion so that the vehicle body slip angle β is estimated taking into account the vehicle body slip angle βf2 caused by the roll rate φ (dot). By constructing estimation logic for the vehicle body slip angle β in this way, it is possible to prevent the estimation accuracy of the vehicle body slip angle β from being reduced due to roll behavior.

[0045] 3 is a block diagram showing an example of the estimation logic for vehicle body slip angle β in vehicle body slip angle estimator 514, in other words, a processing procedure by a vehicle body slip angle estimation program. Vehicle body slip angle estimator 514 has the following functional units: a tire model 701, a front and rear wheel slip angle estimator 702, a two-wheel model 703, a Kalman filter 704, an optimization regulator (LQR: Linear Quadratic Regulator) 705, a lateral acceleration estimator 706, a roll rate estimator 707, a roll rate slip angle calculator 708, a first correction unit 709, and a second correction unit 710.

[0046] Tire model 701 acquires information on longitudinal acceleration αx and lateral acceleration αy detected by acceleration sensor 420, and also acquires information on front wheel slip angle αf (hat) and rear wheel slip angle αr (hat) estimated by front / rear wheel slip angle estimator 702. Tire model 701 then determines front wheel cornering stiffness Kf [N / rad] and rear wheel cornering stiffness Kr [N / rad] based on the information on longitudinal acceleration αx, lateral acceleration αy, front wheel slip angle αf (hat), and rear wheel slip angle αr (hat), and outputs the information on cornering stiffness Kf, Kr to two-wheel model 703 represented by a vehicle equation of motion.

[0047] The tire model 701 includes a vertical load calculation unit 701a and a cornering stiffness calculation unit 701b. The vertical load calculation unit 701a calculates the vertical load Fz of the wheel based on the equation of motion for pitch (Equation 11) and the equation of motion for roll (Equation 12).

[0048] In Equation 11, My is the pitch moment of the entire vehicle, θ is the pitch angle, Iy is the pitch moment of inertia, Cy is the pitch damping force coefficient, and Ky is the pitch stiffness. Also, in Equation 12, Mx is the roll moment of the entire vehicle, φ is the roll angle, Ix is the roll moment of inertia, Cx is the roll damping force coefficient, and Kx is the roll stiffness.

[0049] Here, the pitch moment My of the entire vehicle and the roll moment Mx of the entire vehicle are composed of moments based on the longitudinal acceleration αx and the lateral acceleration αy, and a moment due to the anti-dive force. The vertical load calculation unit 701a calculates the anti-dive force based on the equation of motion for pitch and the equation of motion for roll, and calculates the vertical load Fz on the wheel from the anti-dive force, the longitudinal acceleration αx (hat), and the lateral acceleration αy (hat). In this application, the symbol "hat" indicates an estimated value.

[0050] The cornering stiffness calculation unit 701b acquires information on the front wheel slip angle αf (hat) and rear wheel slip angle αr (hat) estimated by the front / rear wheel slip angle estimator 702, and information on the vertical load Fz calculated by the vertical load calculation unit 701a. The cornering stiffness calculation unit 701b then calculates the front wheel cornering stiffness Kf and the rear wheel cornering stiffness Kr based on the front / rear wheel slip angles αf (hat), αr (hat) and the vertical load Fz.

[0051] The front / rear wheel slip angle estimator 702 acquires information on the estimated yaw rate r (hat) and the estimated vehicle body slip angle β (hat) output by the Kalman filter 704. The front / rear wheel slip angle estimator 702 then calculates the front wheel slip angle αf (hat) according to Equation 5, and calculates the rear wheel slip angle αr (hat) according to Equation 6.

[0052] On the other hand, the lateral acceleration estimating unit 706 acquires information on the estimated yaw rate r (hat) and the estimated vehicle body slip angle β (hat) output by the Kalman filter 704, and calculates the lateral acceleration αy (hat) using the estimated vehicle body slip angular velocity β (hat, with a dot) according to Equation 13. The estimated yaw rate r (hat) is a physical quantity related to the yaw angle (fourth physical quantity).

[0053] Furthermore, roll rate estimator 707 acquires information about the lateral acceleration αy (hat) estimated by lateral acceleration estimator 706, and calculates roll rate φ (dot), which is a physical quantity related to the roll state of vehicle 100, based on the equation of motion related to roll, which is Equation 12. That is, roll rate estimator 707 estimates roll rate φ (dot), which is a physical quantity related to the roll state, using a pre-given vehicle model based on steering angles δf and δr of the front and rear wheels, vehicle speed V, yaw rate r (hat) and vehicle body slip angle β (hat) estimated from vehicle specifications, and further based on vehicle speed V. Roll rate slip angle calculator 708 then calculates slip angle βf2 of the front wheels due to the roll rate φ (dot), using Equation 14, based on the roll rate φ (dot) estimated by roll rate estimator 707, vehicle speed V, and center of gravity height h.

[0054] The first correction unit 709 corrects the front wheel steering angle δf with the slip angle βf2 and outputs the result as information on the front wheel steering angle δf to be used in the two-wheel model 703, and also corrects the rear wheel steering angle δr with the slip angle βf2 and outputs the result as information on the rear wheel steering angle δr to be used in the two-wheel model 703. In other words, the roll rate slip angle calculation unit 708 determines the lateral force based on the roll rate φ (dot) of the vehicle 100 based on the previous estimated value of the vehicle body slip angle β, and feeds back the determined lateral force based on the roll rate φ (dot) of the vehicle 100 to the vehicle equation of motion in the two-wheel model 703.

[0055] The calculation process in the first correction unit 709 is expressed by Equation 15, where δfh is the front wheel steering angle output by the first correction unit 709. In other words, calculating the front wheel slip angle αf according to Equation 14 based on the front wheel steering angle δfh output by the first correction unit 709 means calculating the front wheel slip angle αf taking into account the vehicle body slip angle βf2 caused by the roll rate φ (dot).

[0056] The two-wheel model 703 acquires information on the front wheel cornering stiffness Kf and rear wheel cornering stiffness Kr determined by the tire model 701, the front wheel steering angle δf and rear wheel steering angle δr corrected by the first correction unit 709, and the detected value of the vehicle speed V, and estimates the vehicle body slip angle β based on the equation of motion of the vehicle model. Here, the information on the front wheel steering angle δf and rear wheel steering angle δr acquired by the two-wheel model 703 is a value corrected by the first correction unit 709 with the front wheel slip angle βf2 due to the roll rate φ (dot), in other words, information that takes into account the vehicle body slip angle βf2 caused by the roll rate φ (dot).

[0057] Therefore, the two-wheel model 703 uses an equation of motion that does not include a term based on the roll rate φ (dot) in the estimation calculation of the vehicle body slip angle β based on the equation of motion of the vehicle model, as shown in Equation 16. In Equation 16, I z is the yaw moment of inertia [kgm 2 ].

[0058] Furthermore, each term in the determinant of Equation 16 is defined as shown in Equation 17.

[0059] The two-wheel model 703 integrates the differential value of the yaw rate and the differential value of the vehicle body slip angle β calculated according to Equation 15, respectively, to calculate an estimated value of the yaw rate r and an estimated value of the vehicle body slip angle β. Here, as described above, information on the cornering stiffnesses Kf and Kr calculated by the tire model 701 is introduced into the equation of motion of the two-wheel model 703. Therefore, the equation of motion of the two-wheel model 703 can express the small roll of the transient motion of the vehicle 100 and the difference in grip force generated by the front and rear wheels during rotational motion, improving the accuracy of estimating the vehicle body slip angle β.

[0060] The Kalman filter 704 removes errors (in other words, noise) from the yaw rate r (hat) and vehicle body slip angle β (hat) estimated by the two-wheel model 703, and outputs the results as final estimated values ​​of the yaw rate r and vehicle body slip angle β. The vehicle control unit 513 acquires information on the yaw rate r (hat) and vehicle body slip angle β (hat) output by the Kalman filter 704, and uses the information for vehicle control, which will be described in detail later.

[0061] Furthermore, the information on the yaw rate r (hat) and vehicle body slip angle β (hat) output by the Kalman filter 704 is used to estimate a front wheel slip angle αf and a rear wheel slip angle αr in the front / rear wheel slip angle estimator 702. Furthermore, the information on the yaw rate r (hat) and vehicle body slip angle β (hat) output by the Kalman filter 704 is used to estimate a lateral acceleration αy in the lateral acceleration estimator 706.

[0062] Furthermore, the optimizing regulator 705 is a feedback controller that determines an optimal control input by state feedback so as to minimize the evaluation function, and controls the control input of the two-wheel model 703 in cooperation with the second corrector 710. Here, the combination of the Kalman filter 704 and the optimizing regulator 705 is expressed by Equation 18.

[0063] In Equation 18, F is the gain of the optimizing regulator 705, K is the gain of the Kalman filter 704, and r se indicates the actual measurement value (detection value) of the yaw rate detected by the gyro sensor 430.

[0064] By combining the Kalman filter 704 and the optimizing regulator 705, the Kalman filter 704 corrects the error, and the optimizing regulator 705 determines an optimal control gain by taking into consideration the magnitude of the control input and the convergence of the state quantity. Therefore, by providing the vehicle body slip angle estimator 514 with a feedback control system that combines the Kalman filter 704 and the optimizing regulator 705, the estimation accuracy of the vehicle body slip angle β that takes into consideration the lateral force generated by the roll rate φ (dot) can be improved.

[0065] Next, a description will be given of details of the vehicle control that the vehicle control unit 513 performs based on the estimated value of the vehicle body slip angle β estimated by the vehicle body slip angle estimation unit 514. Fig. 4 is a block diagram showing one aspect of the vehicle control program (vehicle control method) executed by the vehicle control unit 513, and shows the control logic for the front wheel steering angle δf and the rear wheel steering angle δr.

[0066] The vehicle control unit 513 includes a steering gear ratio control unit 810 that controls the front wheel steering angle δf based on the operation angle of the steering wheel 631. The steering gear ratio control unit 810, for example, acquires a signal of the operation angle of the steering wheel 631 and a signal of the vehicle speed V, and converts the operation angle of the steering wheel 631 into a target value of the front wheel steering angle δf based on a steering gear ratio that is variable according to the vehicle speed V. The steering gear ratio control unit 810 then outputs a signal of the target value of the front wheel steering angle δf as a signal of an actual control amount to be given to the front wheel steering actuator 632. In this application, the steering gear ratio is the ratio of the operation angle of the steering wheel 631 to the front wheel steering angle δf.

[0067] Vehicle control unit 513 also includes a rear wheel control unit 820 that controls rear wheel steering angle δr based on an estimated value of vehicle body slip angle β. In other words, a rear wheel steering device is configured including rear wheel steering actuator 641 and rear wheel control unit 820 as a control device for rear wheel steering actuator 641. Rear wheel control unit 820 acquires vehicle body slip angle β and roll rate φ (dot) estimated in vehicle body slip angle estimator 514 using a vehicle model (Equation 15) based on front wheel steering angle δf, rear wheel steering angle δr, longitudinal acceleration αx, lateral acceleration αy, vehicle speed V, etc.

[0068] The rear wheel control unit 820 has the following functional units: a slip angle generation amount calculation unit 821, a first correction unit 822, a feedforward control unit 823, a second correction unit 824, a deviation calculation unit 825, a feedback control amount calculation unit 826 (in other words, a PID controller), and a third correction unit 827. The slip angle generation amount calculation unit 821 calculates a vehicle body slip angle βf2 caused by the roll rate φ (dots). The first correction unit 822 subtracts the vehicle body slip angle βf2 calculated by the slip angle generation amount calculation unit 821 from the front wheel steering angle δf output from the steering gear ratio control unit 810, and outputs a front wheel steering angle δfh corrected for the influence of front wheel lateral slip due to roll.

[0069] Then, based on the signal of the front wheel steering angle δfh output from the first correction unit 822 and a predetermined transfer function, the feedforward control unit 823 calculates a target rear wheel steering angle δrtg1 at which the vehicle body slip angle β becomes zero under the condition of the front wheel steering angle δfh. Furthermore, the second correction unit 824 acquires the signal of the target rear wheel steering angle δrtg1 output from the feedforward control unit 823, adds the vehicle body slip angle calculated by the slip angle generation amount calculation unit 821 to the target rear wheel steering angle δrtg1, and outputs a target rear wheel steering angle δrtg2 corrected for the influence of the vehicle body slip angle caused by roll.

[0070] The following provides a more detailed explanation of the functions of the slip angle generation amount calculation unit 821, first correction unit 822, feedforward control unit 823, and second correction unit 824. The transfer function β(s) of vehicle body slip angle β with respect to vehicle body slip angle βf2 generated by front wheel steering angle δf, rear wheel steering angle δr, and roll rate φ (dot) is given by Equation 18.

[0071] Here, if we expand Equation 19 by always assuming β(s)=0 and find an equation for rear wheel steering control relative to the front wheel steering angle and roll rate, we obtain Equation 20.

[0072] Furthermore, formula 20 is expanded, and the transfer function in the feedforward controller for zeroing the vehicle body slip angle is defined as formula 21, with the input being the front wheel steering angle δf and the output being the rear wheel steering angle δr. On the other hand, the first correction unit 822 sets the front wheel steering angle δfh input to the feedforward control unit 823 to the front wheel steering angle δfh = δf - βf2, and further, the second correction unit 824 adds the vehicle slip angle βf2 to the target rear wheel steering angle δrtg1 output from the feedforward control unit 823, thereby enabling the rear wheel steering angle δr to be calculated based on the front wheel steering angle δf in accordance with the mathematical model of Equation 20.

[0073] Furthermore, a deviation calculation unit 825 calculates the deviation (deviation = target vehicle body slip angle βtg - estimated value of vehicle body slip angle β) between the vehicle body slip angle β, which is calculated by the vehicle body slip angle estimation unit 514 and includes the vehicle body slip angle caused by the roll rate φ (dots), and a target vehicle body slip angle βtg, which is a target value of the vehicle body slip angle β, as a control deviation Δβ in feedback control. Here, the target vehicle body slip angle βtg is set to 0 rad.

[0074] The feedback control amount calculation unit 826 acquires the signal of the control deviation Δβ calculated by the deviation calculation unit 825, and calculates a feedback control amount (feedback correction amount for the rear wheel steering angle) by feedback control such as PID control so that the control deviation Δβ approaches zero, in other words, so that the actual vehicle body slip angle β approaches a target value. In other words, since the target vehicle body slip angle βtg is set to 0 rad, the feedback control amount calculation unit 826 calculates a feedback control amount so that the vehicle body slip angle β, which includes the vehicle body slip angle caused by the roll rate φ (dot), becomes 0 rad. Note that when PID control is used, the feedback control amount calculation unit 826 can calculate the feedback control amount (in other words, the feedback correction amount for the rear wheel steering angle) from the control deviation Δβ by using a P operation (proportional operation) of the PID alone or a combination of PID operations (for example, a PI operation, a PD operation, or a PID operation).

[0075] The third correction unit 827 acquires the target rear-wheel steering angle δrtg2 output by the second correction unit 824 and the feedback control amount output by the feedback control amount calculation unit 826. Then, the third correction unit 827 adds the target rear-wheel steering angle δrtg2 output by the second correction unit 824 to the feedback control amount output by the feedback control amount calculation unit 826, and outputs the result as the final target rear-wheel steering angle δrtg.

[0076] As described above, the feedback control amount calculation unit 826 and the third correction unit 827 correct the target control amount so that the estimated vehicle body slip angle β, which takes into account the vehicle body slip angle caused by the roll rate φ (dots), becomes zero, obtains the actual control amount to be applied to the rear wheel steering actuator 641, and outputs a signal corresponding to the actual control amount. If the vehicle body slip angle β approaches zero by controlling the rear wheel steering angle δr, the maneuverability and ride comfort of the vehicle 100 improve. Furthermore, because the vehicle body slip angle β is estimated taking into account the vehicle body slip angle caused by the roll rate φ (dots), the effect of improving the maneuverability and ride comfort of the vehicle 100 due to the control to zero the vehicle body slip angle is prevented from decreasing even when a roll behavior is occurring.

[0077] Fig. 5 is a Bode diagram (gain diagram) showing the frequency characteristics of vehicle body slip angle β with respect to front wheel steering angle δf. Here, the dotted line in Fig. 5 shows the frequency characteristics when rear wheel steering angle control that sets vehicle body slip angle β to zero (in other words, control to set vehicle body slip angle to zero) is performed in accordance with the control logic shown in Fig. 4, and the solid line in Fig. 5 shows the frequency characteristics when rear wheel steering angle control that sets estimated vehicle body slip angle β to zero is not performed (in other words, when the rear wheel steering angle is fixed at the neutral position). Fig. 5 shows that vehicle body slip angle β can be set to zero with high accuracy by performing rear wheel steering angle control that sets estimated vehicle body slip angle β to zero in accordance with the control logic shown in Fig. 4.

[0078] However, the Bode diagram of Figure 5 shows that although the vehicle body slip angle β can be set to zero with high accuracy in the low frequency range, the gain tends to increase in the high frequency range. A control logic that can suppress this tendency for the gain to increase in the high frequency range will be described below as a second embodiment.

[0079] Figure 6 is a block diagram showing a second embodiment of vehicle control by a vehicle control program executed by a vehicle control unit 513. In Figure 6, blocks having the same functions as those in Figure 4 are designated by the same reference numerals, and detailed description thereof will be omitted. Similar to the vehicle control unit 513 shown in Figure 4, the vehicle control unit 513 in Figure 6 includes a steering gear ratio control unit 810 and a rear wheel control unit 820, but the functional units constituting the rear wheel control unit 820 are different.

[0080] 4 includes a first correction unit 822, a feedforward control unit 823, a second correction unit 824, a deviation calculation unit 825, a feedback control amount calculation unit 826, and a third correction unit 827, whereas the rear wheel control unit 820 shown in Fig. 6 includes a feedforward control unit 823, an H-infinity control unit 828 (H∞ control unit 828), and a correction unit 829. Here, the feedforward control unit 823 uses the transfer function shown in Equation 21 to determine the target rear wheel steering angle δrtg1 based on the front wheel steering angle δf output from the steering gear ratio control unit 810, and outputs the determined target rear wheel steering angle δrtg1.

[0081] On the other hand, H-infinity control unit 828 acquires information on estimated lateral acceleration αy (hat) and estimated vehicle body slip angle β (hat), calculates and outputs a feedback correction amount. Correction unit 829 adds the feedback correction amount output by H-infinity control unit 828 to target rear-wheel steering angle δrtg1 output by feedforward control unit 823, and determines and outputs the final target rear-wheel steering angle δrtg.

[0082] 7 is a Bode diagram (gain diagram) showing the frequency characteristics of lateral acceleration αy with respect to front wheel steering angle δf and the frequency characteristics of vehicle body slip angle β with respect to front wheel steering angle δf. The solid line in FIG. 7 shows the frequency characteristics when rear wheel control unit 820 does not include H-infinity control unit 828 and controls rear wheel steering angle δr only by feedforward control unit 823. FIG. 7 shows that when rear wheel control unit 820 does not include H-infinity control unit 828 and controls rear wheel steering angle δr only by feedforward control unit 823, the lateral acceleration αy and vehicle body slip angle β tend to become unstable in the high frequency range due to the influence of the vehicle body slip angle caused by roll rate φ (dots).

[0083] Therefore, rear wheel control unit 820 includes feedforward control unit 823 and H-infinity control unit 828 that determines the feedback correction amount by H-infinity control, which can specify the frequency response of a closed-loop system. Correction unit 829 then adds the feedback correction amount output by H-infinity control unit 828 to the target rear wheel steering angle δrtg1 output by feedforward control unit 823, and outputs the result as the final target rear wheel steering angle δrtg.

[0084] The dotted line in Figure 7 indicates the target frequency characteristic in H-infinity control. As the dotted line in Figure 7 indicates, H-infinity control unit 828 is designed to stabilize lateral acceleration αy in the high frequency range and to suppress the gain of vehicle slip angle β relative to front wheel steering angle even in the high frequency range. Furthermore, the dashed-dotted line in Figure 7 indicates the actual frequency characteristic when H-infinity control is implemented, and by obtaining frequency characteristics that approximately match the target, it is possible to stabilize lateral acceleration αy in the high frequency range and suppress the gain of vehicle slip angle β relative to front wheel steering angle δf even in the high frequency range.

[0085] 8 is a block diagram showing the basic control theory of the H-infinity control unit 828, which has a generalized plant P and a controller K. The generalized plant P is a control model having four inputs and outputs: a manipulated variable (control input) u, an external input (disturbance input) w, an observed output (control output) y, and a controlled variable (evaluation output) z. The controller K is represented by a transfer function from the observed output y to the manipulated variable u, and a feedback rule of u = Ky is applied.

[0086] 9 is a block diagram showing in more detail the control theory of H-infinity control unit 828. Generalized plant P includes vehicle model M. Vehicle model M includes each of the calculation units shown in FIG. 3 : tire model 701, front and rear wheel slip angle estimator 702, two-wheel model 703, Kalman filter 704, lateral acceleration estimator 706, roll rate estimator 707, roll rate slip angle calculator 708, and first correction unit 709.

[0087] The vehicle model M then calculates and outputs an estimated yaw rate r (hat), an estimated lateral acceleration αy (hat), and an estimated vehicle body slip angle β (hat) based on the longitudinal acceleration αx, lateral acceleration αy, vehicle speed V, front wheel steering angle δf, and rear wheel steering angle δr. Here, the estimated vehicle body slip angle β (hat) output by the vehicle model M is a value that takes into account the vehicle body slip angle caused by the roll rate. Note that the respective calculation units of the vehicle model M have been described in detail above, so description thereof will be omitted here.

[0088] The estimated yaw rate r (hat) estimated by the vehicle model M is output as a controlled variable z of the generalized plant P. Furthermore, the estimated lateral acceleration αy (hat) and estimated vehicle body slip angle β (hat) estimated by the vehicle model M are output as an observed output y of the generalized plant P. Then, the controller K acquires the estimated lateral acceleration αy (hat) and estimated vehicle body slip angle β (hat), which are the observed output y of the generalized plant P, determines an operated variable u in accordance with a set transfer function, and outputs a signal of the operated variable u to the generalized plant P.

[0089] The generalized plant P receives a signal of the manipulated variable u from the controller K, and also receives a signal of the actual front wheel steering angle δf as an external input w. The signal of the actual front wheel steering angle δf is provided to the vehicle model M and the feedforward control unit 823. The feedforward control unit 823 calculates the target rear wheel steering angle δrtg1 for making the vehicle slip angle β zero under the condition of the actual front wheel steering angle δf, based on a predetermined transfer function.

[0090] The correction unit 829 then adds the operation amount u (feedback correction amount) output by the controller K (H-infinity control unit 828) to the target rear-wheel steering angle δrtg1 output by the feedforward control unit 823, and outputs the result as the final target rear-wheel steering angle δrtg. The signal for the target rear-wheel steering angle δrtg is used to estimate the yaw rate r, lateral acceleration αy, and vehicle body slip angle β in the vehicle model M, and is further used to control the rear-wheel steering device 640.

[0091] In this way, the rear wheel control unit 820 of the second embodiment corrects the target control variable (more specifically, the target rear wheel steering angle δrtg1) using H-infinity control so that the estimated vehicle body slip angle β, which takes into account the vehicle body slip angle caused by the roll rate φ (dot), becomes zero, and obtains the actual control variable to be applied to the rear wheel steering actuator 641. The vehicle control device 500 of the second embodiment is also configured to obtain physical quantities related to the roll state using a vehicle model based on the vehicle speed V, the front wheel steering angle δf, and vehicle specifications, estimate the vehicle body slip angle β and the lateral acceleration αy using the vehicle model, and obtain corrections for obtaining the actual control variable using H-infinity control based on the vehicle body slip angle β and the lateral acceleration αy. As shown in FIG. 7 , compared to controlling the rear wheel steering angle using only the feedforward control unit 823, stabilization of the lateral acceleration αy can be achieved in the high-frequency range, and the gain of the vehicle body slip angle β relative to the front wheel steering angle can be suppressed even in the high-frequency range.

[0092] The manipulated variable u (feedback correction amount) output by the controller K is calculated based on the vehicle body slip angle β, which reflects the influence of the vehicle body slip angle caused by the roll rate, and the lateral acceleration αy, and the manipulated variable u (feedback correction amount) includes the correction due to the roll rate. Therefore, in the second embodiment using H-infinity control (see FIG. 6), the correction by the correction units 822 and 824 in the first embodiment using PID control (see FIG. 4) is omitted. On the other hand, in the first embodiment using PID control, although the vehicle body slip angle β used in the PID control includes the influence of the roll rate, correction by the roll rate is performed by the correction units 822 and 824 in the upstream and downstream of the feedforward control unit 823 to improve the effect of the feedback control (to improve robustness).

[0093] Incidentally, in a vehicle to which the vehicle control device, vehicle control method, vehicle control program, and rear-wheel steering device according to the present invention are applied, rear-wheel steering can be performed by outputting a control command to the rear-wheel steering actuator 641 even in driving situations in which only a vehicle body slip angle due to roll rate occurs, such as when traveling straight on an uneven road surface. Therefore, rear-wheel steering in driving situations in which only a vehicle body slip angle due to roll rate occurs can be considered to be the implementation of rear-wheel steering control based on the vehicle body slip angle that takes into account the vehicle body slip angle caused by the roll rate.

[0094] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0095] For example, the tire model 701 may include a correction term based on tire deterioration and a correction term based on the friction coefficient of the road surface. Here, the microcomputer 510 can estimate tire deterioration based on the travel distance of the vehicle 100. The microcomputer 510 can also acquire, via the in-vehicle network, information on the friction coefficient of the road surface estimated by a control unit that controls the braking device of the vehicle 100, for example.

[0096] Furthermore, the traveling actuators of the vehicle 100 that the vehicle control device 500 controls based on the estimated vehicle body slip angle are not limited to the steering actuator, but may include the drive device 610 (drive actuator) and / or the braking device 620 (brake actuator). In other words, the vehicle control device 500 can control at least one of the steering actuator, the drive actuator, and the brake actuator so that the estimated vehicle body slip angle that takes into account the vehicle body slip angle caused by the roll rate becomes zero. Here, the control of the drive actuator and the brake actuator based on the estimated vehicle body slip angle includes distribution control of the drive force and the braking force to four wheels or the front and rear wheels.

[0097] Furthermore, the vehicle control system 200 may include a first microcomputer (first vehicle control device) that executes a vehicle body slip angle estimation program, and a second microcomputer (second vehicle control device) that executes a vehicle control program that outputs a control signal to a traveling actuator based on the estimated vehicle body slip angle. Also, the system may include a microcomputer included in the rear wheel steering device 640 or the like that constitutes the actuator unit 600 that executes the vehicle control program.

[0098] Furthermore, vehicle body slip angle estimator 514 can determine the vehicle body slip angle caused by the roll rate based on the roll rate detected by gyro sensor 430. In other words, when estimating the roll rate using a vehicle body model, the physical quantity related to the roll state of the vehicle (third physical quantity) is acquired using a pre-given vehicle model based on the first physical quantity related to the vehicle speed, the second physical quantity related to the steering angle of the front wheels, and at least some of the third physical quantities related to the roll state of the vehicle excluding the third physical quantity, as well as vehicle specifications. On the other hand, when detecting the roll angle or roll rate using a sensor, the physical quantity related to the roll state of the vehicle (third physical quantity) is a value of the roll angle or roll rate directly detected by the sensor.

[0099] 100...vehicle, 101-104...wheels, 200...vehicle control system, 500...vehicle control device, 510...microcomputer, 513...vehicle control unit, 514...vehicle body slip angle estimation unit, 810...steering gear ratio control unit, 820...rear wheel control unit, 821...slip angle generation amount calculation unit, 823...feedforward control unit, 825...deviation calculation unit, 826...feedback control amount calculation unit, 828...H-infinity control unit

Claims

1. A vehicle control device for controlling an actuator provided in a vehicle, comprising: acquiring a plurality of physical quantities indicating a driving condition of the vehicle including a first physical quantity related to a speed of the vehicle, a second physical quantity related to a steering angle of the front wheels of the vehicle, and a third physical quantity related to a roll state of the vehicle; acquiring a target control quantity which is a control quantity to be a target of the actuator based on at least the first physical quantity and the second physical quantity of the plurality of physical quantities and predetermined vehicle specifications of the vehicle, so that a vehicle body slip angle, which is the angle between the orientation of the vehicle and the traveling direction of the vehicle, becomes zero; acquiring an actual control quantity to be given to the actuator by correcting the target control quantity based on at least some of the plurality of physical quantities including the third physical quantity, so that an estimated vehicle body slip angle taking into account a vehicle body slip angle generated by a roll rate becomes zero; and outputting a signal corresponding to the actual control quantity.

2. A vehicle control device as claimed in claim 1, wherein the actuator is a rear wheel steering actuator provided in a rear wheel steering device for applying a steering angle to the rear wheels of the vehicle, and the vehicle control device outputs a signal corresponding to the actual control amount to be applied to the rear wheel steering actuator.

3. A vehicle control device as described in claim 2, wherein obtaining the actual control amount includes a process of determining a roll rate of the vehicle based on the third physical amount, estimating a vehicle body slip angle caused by the roll rate from among the vehicle body slip angles, and correcting the target control amount so as to cancel out the vehicle body slip angle caused by the estimated roll rate, thereby obtaining the actual control amount.

4. A vehicle control device as described in claim 3, wherein the plurality of physical quantities includes a fourth physical quantity related to a yaw angle of the vehicle, and the third physical quantity is obtained using a pre-given vehicle model based on at least a portion of the plurality of physical quantities other than the third physical quantity and the vehicle specifications.

5. A vehicle control device as claimed in claim 4, wherein obtaining the actual control amount includes a process of estimating the vehicle body slip angle, including a vehicle body slip angle caused by the roll rate, using the vehicle model, and correcting the target control amount to obtain the actual control amount so that the estimated vehicle body slip angle, including the vehicle body slip angle caused by the roll rate, becomes zero.

6. A vehicle control device according to claim 2, wherein the vehicle is provided with a steering input device that accepts steering operations by a driver, and the second physical quantity is a physical quantity related to the amount of steering operation of the steering input device.

7. A vehicle control device as described in claim 2, wherein the plurality of physical quantities includes a fourth physical quantity related to a yaw angle of the vehicle, and acquiring the actual control quantity includes a process of acquiring the third physical quantity using a pre-given vehicle model based on at least a part of the plurality of physical quantities other than the third physical quantity and the vehicle specifications, and further acquiring the estimated vehicle body slip angle and a lateral acceleration applied to the vehicle using the vehicle model, and acquiring a correction for obtaining the actual control quantity based on the estimated vehicle body slip angle and the lateral acceleration.

8. A vehicle control device according to claim 7, wherein a correction for obtaining the actual control amount is obtained using H-infinity control.

9. A vehicle control method executed by a vehicle control device provided in a vehicle, comprising: acquiring a plurality of physical quantities indicating a driving condition of the vehicle including a first physical quantity related to a vehicle speed of the vehicle, a second physical quantity related to a steering angle of front wheels of the vehicle, and a third physical quantity related to a roll state of the vehicle; acquiring a target control quantity that is a control quantity to be a target for an actuator provided in the vehicle based on at least the first physical quantity and the second physical quantity of the plurality of physical quantities and predetermined vehicle specifications of the vehicle, so that a vehicle body slip angle, which is an angle between the orientation of the vehicle and the traveling direction of the vehicle, becomes zero; acquiring an actual control quantity to be given to the actuator by correcting the target control quantity based on at least a portion of the plurality of physical quantities including the third physical quantity, so that an estimated vehicle body slip angle taking into account a vehicle body slip angle generated by a roll rate becomes zero; and outputting a signal corresponding to the actual control quantity.

10. A vehicle control program executed by a vehicle control device provided in a vehicle, comprising: acquiring a plurality of physical quantities indicating a driving condition of the vehicle, including a first physical quantity related to a vehicle speed of the vehicle, a second physical quantity related to a steering angle of the front wheels of the vehicle, and a third physical quantity related to a roll state of the vehicle; acquiring a target control quantity that is a control quantity to be a target for an actuator provided in the vehicle, based on at least the first physical quantity and the second physical quantity of the plurality of physical quantities and predetermined vehicle specifications of the vehicle, so that a vehicle body slip angle, which is the angle between the orientation of the vehicle and the traveling direction of the vehicle, becomes zero; acquiring an actual control quantity to be given to the actuator by correcting the target control quantity, based on at least a portion of the plurality of physical quantities including the third physical quantity, so that an estimated vehicle body slip angle taking into account a vehicle body slip angle generated by a roll rate becomes zero; and outputting a signal corresponding to the actual control quantity.

11. A rear-wheel steering device comprising: a rear-wheel steering actuator that applies a steering angle to the rear wheels of a vehicle; and a control device that outputs a signal corresponding to an actual control amount to be given to the rear-wheel steering actuator, the control device acquiring a plurality of physical quantities that indicate the driving conditions of the vehicle including a first physical quantity related to the vehicle speed of the vehicle, a second physical quantity related to the steering angle of the front wheels of the vehicle, and a third physical quantity related to the roll state of the vehicle; acquiring a target control amount that is a control amount to be targeted for the rear-wheel steering actuator based on at least the first physical quantity and the second physical quantity of the plurality of physical quantities and predetermined vehicle specifications of the vehicle, so that a vehicle body slip angle, which is the angle between the orientation of the vehicle and the traveling direction of the vehicle, becomes zero; and acquiring an actual control amount to be given to the rear-wheel steering actuator by correcting the target control amount based on at least some of the plurality of physical quantities including the third physical quantity, so that an estimated vehicle body slip angle taking into account the vehicle body slip angle caused by a roll rate becomes zero.

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