JP2006123611A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device for a vehicle capable of enhancing turning performance at braking. <P>SOLUTION: The steering device for the vehicle is provided with a steering control controller 3 for controlling steering angles of front wheels 11, 11 and rear wheels 14, 14 according to a steering angle of a steering wheel 10. The device is provided with a tire front/rear force presumption part 4 for presuming tire front/rear force of the front wheels 11, 11 and the rear wheels 14, 14; and a steering angle correction means for correcting a front wheel steering angle θ and a rear wheel steering angle δ at initial stage of steering in a direction that a yaw rate of the vehicle is increased when the presumed tire front/rear force F<SB>X</SB>is increased in a speed reduction direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of a vehicle steering apparatus that includes a steering control unit that controls a steering angle of a steered wheel according to a traveling state.

In a conventional vehicle steering system equipped with a rear wheel steering mechanism, when the brake pedal is depressed during high-speed driving, the rear wheel steering angle is decelerated from high speed to low speed by fixing it to the same phase as the front wheel steering angle. In this case, the rear wheel steering angle is prevented from being controlled to the opposite phase side, and the vehicle behavior is stabilized (see, for example, Patent Document 1).
Japanese Utility Model Publication No. 3-6548

  However, in the above prior art, the rear wheel steering angle is fixed depending on whether or not the brake is stepped on regardless of the amount of braking force generated. There has been a problem that turning performance during braking is reduced due to a decrease in tire lateral force.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a vehicle steering apparatus capable of improving turning performance during braking.

In order to achieve the above object, in the present invention,
In a vehicle steering apparatus including a steering control unit that controls a steering angle of a steered wheel according to a steering angle of a steering operation unit,
Tire longitudinal force estimating means for estimating the tire longitudinal force of the steering wheel;
When the tire longitudinal force increases in the deceleration direction, the turning angle correction means for correcting the turning angle in the initial stage of steering in the direction in which the yaw rate of the vehicle increases;
It is characterized by providing.

  In the present invention, since the turning angle at the initial stage of steering is corrected from the tire longitudinal force in the direction in which the yaw rate increases, the turning performance can be improved during braking in which the tire lateral force decreases and the yaw rate decreases. it can.

  Hereinafter, the best mode for carrying out the present invention will be described based on Examples 1 and 2.

First, the configuration will be described.
FIG. 1 is an overall system diagram of the vehicle steering apparatus according to the first embodiment. The vehicle steering apparatus according to the first embodiment includes a front wheel steering mechanism 12 and a rear wheel steering mechanism 15, and independently controls the angles of the front and rear wheels. It is a possible steering device.

  A steering angle sensor (steering angle detection means) 1 and a front wheel steering actuator 7 are connected to a column shaft 13 that connects a steering wheel (steering operation means) 10 and a front wheel steering mechanism 12 that steers the front wheels (steering wheels) 11 and 11. Is provided.

  The front wheel steering actuator 7 is constituted by, for example, a motor and a speed reducer, and the output shaft of the motor is connected to the column shaft 13 via the speed reducer. This front-wheel steering actuator 7 is for decelerating the rotation input via the column shaft 13 by the variable gear ratio according to the steering angle command value from the front-wheel steering controller 5 and outputting it to the steering gear of the front-wheel steering mechanism 12. As a result, the steering gear ratio, which is the ratio of the steering angle of the steering wheel 10 to the steering angle of the front wheels 11, 11, is variably controlled.

  The rear wheel steering actuator 8 includes a motor and a speed reducer, like the front wheel steering actuator 7, and a speed reducer is mounted on the rack shaft of the rear wheel steering mechanism 15 that steers the rear wheels (steering wheels) 14 and 14. The output shaft of the motor is connected through this. The rear wheel steering actuator 8 variably controls the steering angles of the rear wheels 14 and 14 according to the steering angle command value from the rear wheel steering controller 6.

  The front wheel steering controller 5 is a rudder that eliminates the deviation between the target front wheel steering angle generated by the steering control controller (steering control means) 3 and the actual front wheel steering angle value detected by the front wheel actual steering angle sensor 16. An angle command value is calculated, and the calculated steering angle command value is output to the front wheel steering actuator 7.

  The rear wheel steering controller 6 controls the steering angle command so as to eliminate the deviation between the target rear wheel steering angle generated by the steering control controller 3 and the actual rear wheel steering angle value detected by the rear wheel actual steering angle sensor 17. The value is calculated, and the calculated steering angle command value is output to the rear wheel steering actuator 8.

  The steering angle sensor 1 detects the steering angle of the steering wheel 10 using a pulse encoder or the like. The vehicle speed sensor 2 detects the vehicle speed from the average value of the wheel speeds. Further, the tire longitudinal force estimating unit (tire longitudinal force estimating means) 4 calculates the generated tire longitudinal force based on the brake fluid pressure. The lateral G sensor (lateral acceleration detecting means) 18 detects lateral acceleration (lateral G) acting in the lateral direction of the vehicle. A roll angle sensor (roll angle detection means) 19 detects a roll angle, which is a rotation angle around the longitudinal axis of the vehicle, from a suspension stroke or the like.

  The steering controller 3 detects the steering angle detected by the steering angle sensor 1, the vehicle body speed detected by the vehicle speed sensor 2, the tire longitudinal force estimated by the tire longitudinal force estimation unit 4, and the lateral G sensor 18. A target front wheel rudder angle and a target rear wheel rudder angle are generated according to the lateral G and the roll angle detected by the roll angle sensor 19, and the target front wheel rudder angle is output to the front wheel steering controller 5, The rear wheel steering angle is output to the rear wheel steering controller 6.

  The steering control controller 3 reduces the steering gear ratio and turns the rear wheels 14 and 14 to the opposite side to the front wheels 11 and 11 in the low vehicle speed range, and increases the steering gear ratio and the rear wheel in the high vehicle speed range. Wheels 14 and 14 are steered to the same phase as front wheels 11 and 11. This achieves both improvement in steady turning performance at low speed and securing of running stability at high speed.

  FIG. 2 is a control block diagram of the steering control controller 3, and the steering control controller 3 includes a target value generation unit (target yaw rate calculation means) 31 and a target output generation unit 32.

  The target value generation unit 31 generates a target yaw rate and a target lateral speed based on the steering angle, the vehicle speed, the tire longitudinal force, the lateral G, and the roll angle. The generated target yaw rate and target lateral velocity are output to the target output generator 32.

  The target output generation unit 32 generates a target front wheel steering angle and a target rear wheel steering angle based on the target yaw rate and the target lateral speed from the target value generation unit 31.

  FIG. 3 is a control block diagram of the target value generation unit 31, and the target value generation unit 31 includes a vehicle model calculation unit 311 and a target value calculation unit 312. The vehicle model calculation unit 311 calculates vehicle parameters using a two-wheel model based on the steering angle and the vehicle body speed. The calculated vehicle parameter is output to the target value calculation unit 312.

  The target value calculation unit 312 includes a target characteristic parameter calculation unit 3121, a target characteristic parameter correction unit 3122, a target yaw rate calculation unit 3123, and a target lateral velocity calculation unit 3124.

  The target characteristic parameter calculation unit 3121 calculates a target characteristic parameter of the vehicle from the vehicle speed and the vehicle parameter. The calculated target characteristic parameter is output to the target characteristic parameter correction unit 3122.

  The target characteristic parameter correction unit 3122 corrects the target characteristic after correction based on the target characteristic parameter, the estimated tire longitudinal force estimated by the tire longitudinal force estimation unit 4, the vehicle characteristic (lateral G, roll angle) when the tire longitudinal force is generated, and the like. Calculate the parameters. The calculated target characteristic parameter after correction is output to the target yaw rate calculation unit 3123 and the target lateral velocity calculation unit 3124.

  The target yaw rate calculation unit 3123 calculates the target yaw rate of the vehicle from the steering angle and the corrected target characteristic parameter. The calculated target yaw rate is output to the target output value generation unit 32. The target lateral speed calculation unit 3124 calculates the target lateral speed of the vehicle from the steering angle and the corrected target characteristic parameter. The calculated target lateral velocity is output to the target output value generation unit 32.

  FIG. 4 is a control block diagram of the target output generation unit 32, and the target output generation unit 32 includes a target front / rear steering angle calculation unit 321 and a target rear wheel steering angle calculation unit 322. The target front wheel steering angle calculation unit 321 determines the target front wheel steering angle from the target yaw rate and the target lateral speed. The target rear wheel steering angle calculation unit 322 determines a target rear wheel steering angle from the target yaw rate and the target lateral speed.

Next, the operation will be described.
[Vehicle model calculation]
The vehicle model calculation unit 311 calculates vehicle parameters using the vehicle model shown below.

In general, assuming a two-wheel model, the yaw rate and lateral speed of the vehicle can be expressed by the following equation (1).

である。 here,

It is.

When the transfer functions of the yaw rate and lateral velocity for the front wheel steering are obtained from the state equation, the following equations (3) and (4) are obtained.

ここで、

である。 The yaw rate transfer function is expressed by the following equation (5) from equation (3).

here,

It is.

ここで、

である。 Similarly, the lateral velocity transfer function is expressed by the following equation (7) from equation (4).

here,

It is.

が求められる。 From the above, vehicle parameters

Is required.

[Target value calculation]
A target characteristic parameter calculation unit 3121 of the target value calculation unit 312 obtains a target yaw rate ψ ′ ^* and a target lateral velocity V _y ^* from the vehicle body speed V, the vehicle parameter, and a target value parameter described later.

The target yaw rate ψ ′ ^* is expressed by the following equation (9) from equation (5).

The target lateral velocity V _y ^* is expressed by the following equation (10) from equation (7).

ただし、yrate_gain_map（ヨーレート定常ゲイン），yrate_omegn_map（ヨーレート応答（固有振動数）），yrate_zeta_map（ヨーレート減衰率），yrate_zero_map（ヨーレート進み要素）はチューニングパラメータである。 Here, the parameter of the target yaw rate ψ ′ ^* is expressed by the following equation (11).

However, yrate_gain_map (yaw rate steady gain), yrate_omegn_map (yaw rate response (natural frequency)), yrate_zeta_map (yaw rate decay rate), and yrate_zero_map (yaw rate advance element) are tuning parameters.

ただし、vy_gain_map（横速度定常ゲイン），vy_omegn_map（横速度応答（固有振動数）），vy_zeta_map（横速度減衰率），vy_zero_map（横速度進み要素）はチューニングパラメータである。 Further, the parameter of the target lateral speed V _y ^* is expressed by the following equation (12).

However, vy_gain_map (transverse velocity steady gain), vy_omegn_map (lateral velocity response (natural frequency)), vy_zeta_map (lateral velocity damping factor), and vy_zero_map (lateral velocity advance element) are tuning parameters.

[Target value correction calculation]
The target characteristic parameter correction unit 3122 uses the estimated tire longitudinal force F _x calculated by the tire longitudinal force estimation unit 4 to change the yaw rate response characteristic when a tire longitudinal force is generated during braking or the like. The yaw rate response ω _{ψ '*} (V) is corrected.

In Example 1, the estimated tire longitudinal force F _x, determined from the brake pressure of the front wheel 11, 11. The relationship between the brake pressure and the estimated tire longitudinal force F _x, since may be determined in advance by experiment or the like, in Example 1, obtaining an estimated tire longitudinal force F _x by using the map shown in FIG.

The target yaw rate response ω _{ψ ′ *} (V) at the normal time (without correction) can be obtained from the following equation (13) from the equation (11).
ω _{ψ '*} (V) = ω _ψ' (V) × yrate_omegn_map… (13)
If α is the target yaw rate response correction coefficient, the corrected target yaw rate response ω _{dψ ′ *} (V) is obtained from the estimated tire longitudinal force F _x as shown in the following equation (14).
ω _{dψ '*} (V) = ω _ψ' (V) × yrate_omegn_map × α (F _x )… (14)

The target yaw rate response correction coefficient α is stored as a map as shown in FIG. 6 that is predicted in advance using an equation based on the estimated tire longitudinal force F _x , an experiment, or the like, and is referred to by the estimated tire longitudinal force F _x . May be. As shown in FIG. 6, the target yaw rate response correction coefficient α is set so as to increase as the estimated tire longitudinal force F _x increases toward the braking force, that is, as the tire longitudinal force increases in the deceleration direction. Also, the target yaw rate response correction coefficient alpha, when the estimated tire longitudinal force F _x is greater zero or in driving force, i.e., when the estimated tire longitudinal force F _x is zero or acceleration direction, set to be 1 Has been. Thereby, when the brake pressure is not generated, the corrected target yaw rate response ω _{dψ ′ *} (V) remains the target yaw rate response ω _{ψ ′ *} (V) before correction.

Further, the target yaw rate response correction coefficient α is set so as to increase as the lateral acceleration (lateral G) or roll angle increases when the estimated tire longitudinal force F _x acts on the braking force side. That is, when the lateral G and the roll angle are generated, the response of the vehicle is inferior to that of the normal time. Therefore, the target yaw rate response correction coefficient α is further increased according to the amount of the lateral G and the roll angle generated. Thus, by adding correction to the yaw rate response that decreases due to factors other than braking force, it is possible to suppress a decrease in turning performance.

となる。 Thus, the target yaw rate during braking is

It becomes.

から、

[Target front wheel rudder angle calculation]
The target front wheel steering angle calculation unit 321 of the target output value generation unit 32 calculates the target front wheel steering angle θ ^* from the corrected target yaw rate, ψ _d ′ ^*, and the target lateral speed V _y ^* .

From

Therefore, the target front wheel steering angle θ ^* is expressed by the following equation (18).

ただし、一般に後輪舵角には角度に制限があるため、補正後目標後輪舵角を
δ_lim ^*＝sign(δ^*)×min(|δ^*|,δ_max ^*) …(20)
とする。ここで、δ_max ^*は、後輪最大舵角とする。 [Target rear wheel rudder angle calculation]
Similarly, the target rear wheel steering angle calculation unit 322 calculates the target rear wheel steering angle δ ^* from the corrected target yaw rate, ψ _d ′ ^*, and the target lateral velocity V _y ^* .
The target rear wheel steering angle δ ^* is expressed by the following equation (19).

However, since the angle of the rear wheel rudder angle is generally limited, the corrected target rear wheel rudder angle is set to δ _lim ^* = sign (δ ^* ) × min (| δ ^* |, δ _max ^* ) (20)
And Here, δ _max ^* is the rear wheel maximum steering angle.

The target front wheel steering angle θ ^* and the corrected target rear wheel steering angle δ ^* are set so that the convergence time is shorter than the convergence time of the front wheel steering angle θ and the rear wheel steering angle δ without correction. . As a method of shortening the convergence time, for example, it can be realized by changing yrate_zeta_map (yaw rate attenuation rate) which is one of the tuning parameters.

[Correction control end judgment]
The timing to terminate the correction control, and when the output from the longitudinal force estimating unit 4 tires longitudinal force tire (braking force) F generation amount of _x becomes zero. As a result, the control can be continued during braking, and even if F _x = 0 during braking, etc., only the correction of the transient rudder angle will change. Since there is no change to “None”, there is no effect from the control change.

Further, even when the vehicle is stopped (vehicle speed = 0), the correction control is terminated, and the control can be released when the brake is continuously depressed, that is, when the vehicle is stopped with F _x ≠ 0. At this time, the next correction control is started on the condition that F _x = 0 and the vehicle speed is increased.

[Target yaw rate response correction control]
FIG. 7 is a flowchart showing the flow of the target yaw rate response correction control process executed by the target characteristic parameter correction unit 3122 of the steering controller 3, and each step will be described below.

  In step S1, it is determined whether the vehicle speed detected by the vehicle speed sensor 2 is zero. If YES, the process proceeds to step S2, and if NO, the process proceeds to step S5.

In step S2, a determination is made as to whether the estimated tire longitudinal force F _x is not zero. If YES, the process proceeds to step S4. If NO, the process proceeds to step S3.

In step S3, the target yaw rate response correction coefficient α of the target yaw rate response ω _{ψ ′ *} (V) is set to 1, and the process proceeds to step S6.

In step S4, the target yaw rate response correction coefficient α of the target yaw rate response ω _{ψ ′ *} (V) is obtained with reference to the estimated tire longitudinal force F _x and the map shown in FIG. 6, and the process proceeds to step S6.

In step S5, the target yaw rate response correction coefficient α of the target yaw rate response ω _{ψ ′ *} (V) is set to 1, and the process proceeds to step S6.

In step S6, the corrected target yaw rate response ω _{dψ ′ *} (V) is obtained based on the target yaw rate response correction coefficient α obtained in any of steps S3 to S5, and the _{process proceeds} to return (turning angle correction). Equivalent to means).

[Target yaw rate response correction control operation]
When the driver does not step on the brake while traveling, the flow proceeds from step S1 to step S2 to step S3 to step S6 in the flowchart of FIG. 7. In step S3, the target yaw rate response correction coefficient α is 1. _Therefore , in step S6, the corrected target yaw rate response ω _{dψ ′ *} (V) is set to the target yaw rate response ω _{ψ ′ *} (V) before correction.

When stepping on the driver braking during traveling, in the flowchart of FIG. 7, it will flow from step S1 → step S2 → step S4 → step S6, in step S4, in accordance with the estimated tire longitudinal force F _x The target yaw rate response correction coefficient α is set, and in step S6, the corrected target yaw rate response ω _{dψ ′ *} (V) is calculated _using the target yaw rate response correction coefficient α set in step S4.

At this time, as the braking force increases, the target yaw rate response correction coefficient α is set to a larger value (α> 1), and the corrected target yaw rate response ω _{dψ ′ *} (V) is the target yaw rate response ω _{ψ ′ *} before correction _. Since it becomes larger than (V), the phase of the target yaw rate ψ ′ ^* is advanced, and the transient steering angle of the front wheels and the rear wheels, that is, the front and rear wheel steering angles at the initial stage of steering can be increased. As a result, the target steady-state value can be made the same as the normal time (the steering gear ratio is the same as the normal time) while the yaw rate ψ ′ rises quickly, so that the driver does not feel uncomfortable and can easily perform the corrective steering.

Further, the larger the lateral G and the roll angle, the larger the target yaw rate response correction coefficient α is set, and the corrected target yaw rate response ω _{dψ ′ *} (V) becomes the target yaw rate response ω _{ψ ′ *} (V) before correction. Therefore, the turning performance can be improved with respect to the yaw rate response that decreases due to a factor other than the braking force when the lateral G or roll is generated, which is further inferior to the straight running performance.

[Problems of conventional technology]
In a vehicle steering system that performs steering gear ratio variable control and rear wheel steering angle control according to the state of the vehicle, in order to improve maneuverability and stability, the front and rear wheel steering angles are changed according to the vehicle speed (at high speed: front wheels). Steering response slow / rear wheel in-phase control, low speed: front wheel steering response quick / rear wheel reverse phase control). However, even during sudden deceleration, the steering gear ratio and the rear wheel rudder angle change according to the vehicle speed, which may result in vehicle behavior unintended by the driver.

  In response to the above problem, Japanese Utility Model Publication No. 3-6548 discloses a technique for ensuring the stability of the vehicle behavior during braking by making the rear wheel steering angle constant by depressing the brake pedal. Japanese Patent Application Laid-Open No. 11-301506 describes a technique for securing the stability of the vehicle behavior during braking by fixing the steering gear ratio of the front wheels during ABS operation.

  However, in the former of the above prior arts, the steering angle ratio is fixed even in slow braking because the rear wheel steering angle is fixed depending on whether or not the brake is depressed regardless of the amount of braking force generated. Therefore, the steering in a state where the brake pedal is smoothly changed from the high speed to the low speed remains in the same phase, so that the maneuverability cannot be improved. Also, when applied to front wheel or front and rear wheel control, at high-speed emergency avoidance (rapid braking → steering), the front wheel steering response slow / rear wheel in-phase (or neutral) control is fixed and tire force is applied during sudden braking. Since the cornering force is reduced, the vehicle responsiveness is lowered, and the steering is difficult to work. → It is difficult to turn (avoidance performance is lowered).

  In the latter case, since the steering gear ratio is fixed at a slow speed by detecting the presence or absence of ABS operation, the steering characteristics change from normal (usually a quick steering response) to match the target line for the driver. There was a problem that it was difficult (eg, the amount of operation intended by the driver was insufficient / too difficult to correct from too much).

[Target yaw rate response correction]
On the other hand, in Example 1, when the generation amount of the tire longitudinal force (braking force) F _x is output by the tire longitudinal force estimating unit 4, the target yaw rate response ω _{ψ ′ *} (V) is _expressed by the equation (14). (Α> 1). As a result, the rise of the target yaw rate ψ ′ ^* is accelerated, and when the steering angles of the front and rear wheels are calculated by the equations (18) and (19), the transient steering angle increases.

  As shown in FIG. 8, the front wheel rudder angle with the correction of the target yaw rate response is larger than that without the correction, so that a transient yaw is generated. Further, as shown in FIG. 9, the rear wheel steering angle with correction has a larger transient steering angle than that without correction, and thus the increase in lateral speed is suppressed.

  Furthermore, in the first embodiment, the convergence point of the front wheel steering angle θ and the rear wheel steering angle δ is a point earlier than the case without correction. That is, since the convergence time of the front wheel steering angle θ and the rear wheel steering angle δ is shorter than that without correction, it is possible to achieve early stabilization of the vehicle behavior while increasing the transient steering angle.

  By increasing the transient response, the vehicle yaw rate response can be accelerated as shown in FIG. 10, and the steady value of the rudder angle is the same as the value without correction, so that the driver can easily perform correction steering. It becomes. Incidentally, in FIG. 10, the “difference due to deceleration” is a decrease in the necessary yaw rate accompanying deceleration.

  In the first embodiment, the above control logic can increase the transient yaw rate even when, for example, steering for obstacle avoidance during deceleration, the travel line according to the steering amount, That is, it can be brought closer to the target line intended by the driver (see FIG. 11).

Next, the effect will be described.
In the vehicle steering apparatus according to the first embodiment, the following effects can be obtained.

(1) In a vehicle steering apparatus including a steering control controller 3 that controls the turning angles of the front wheels 11 and 11 and the rear wheels 14 and 14 according to the steering angle of the steering wheel 10, the front wheels 11 and 11 and the rear wheels 14 , the tire longitudinal force estimating unit 4 for estimating a tire longitudinal force of 14, when the estimated tire longitudinal force F _x is increased to deceleration direction, the front wheel steering angle θ and a rear wheel steering angle δ in the initial steering stage, the yaw rate of the vehicle Since turning angle correcting means (step S6 in FIG. 7) for correcting in an increasing direction is provided, turning performance can be improved during braking in which the yaw rate ψ ′ decreases with a decrease in tire lateral force.

(2) a vehicle speed sensor 2 that detects the vehicle speed, a steering angle sensor 1 that detects the steering angle of the steering wheel 10, a target value generation unit 31 that calculates a target yaw rate ψ ' ^* according to the vehicle speed and the steering angle, The steering control controller 3 sets the target front wheel steering angle θ ^* and the target rear wheel steering angle δ ^* based on the target yaw rate, and the turning angle correction means is based on the estimated tire longitudinal force F _x . The target yaw rate response ω _{ψ ′ *} (V) at the initial stage of steering is corrected. That is, at the time of braking, in order to increase the yaw rate response ω _{ψ ′ *} (V) at the initial turn necessary for emergency avoidance or the like, only the phase of the target yaw rate ψ ′ ^* is advanced, so that the front wheels 11 and 11 and the rear wheel 14 , 14 can be increased. As a result, the target steady-state value can be made the same as normal while the rise of the yaw rate ψ ′ is accelerated, so that the driver feels less uncomfortable and can easily perform corrective steering.

(3) The turning angle correction means sets the target yaw rate correction coefficient α to a larger value (α> 1) as the estimated tire longitudinal force F _x increases in the deceleration direction, and sets the target yaw rate response ω _{ψ ′ *} (V) To increase the braking force, the lateral force of the tire decreases as the braking force increases. On the other hand, by increasing the transient steering angle, the traveling line can be brought closer to the target line intended by the driver.

  (4) The turning angle correction means corrects the turning angle so that the convergence time of the turning angle after correction is shorter than the convergence time of the turning angle without correction. It is possible to achieve early stabilization of the vehicle behavior while increasing the turning performance by increasing the transient steering angle.

(5) longitudinal force estimating unit 4 tires, based on the brake pressure of the front wheels 11 and 11, for obtaining the estimated tire longitudinal force F _x, can be estimated braking force of the tire by using a simpler method. In the first embodiment, since the estimation of the tire driving force is unnecessary, the method of estimating the braking force from the brake pressure is the simplest method.

(6) A lateral G sensor 18 for detecting the lateral G of the vehicle is provided, and the turning angle correction means sets the target yaw rate correction coefficient α to a larger value (α> 1) as the lateral G increases, and the target yaw rate response Since ω _{ψ ′ *} (V) is increased, the yaw rate response that decreases due to the occurrence of the lateral G can be corrected, and the decrease in turning performance can be suppressed.

(7) A roll angle sensor 19 for detecting the roll angle of the vehicle is provided, and the turning angle correction means sets the target yaw rate correction coefficient α to a larger value (α> 1) as the roll angle increases, and the target yaw rate response Since ω _{ψ ′ *} (V) is increased, the yaw rate response that decreases due to the occurrence of rolls can be corrected, and the decrease in turning performance can be suppressed.

(8) When the estimated tire longitudinal force F _x is zero or in the acceleration direction, the turning angle correction means sets the target yaw rate correction coefficient α to 1 and terminates the correction of the turning angle. Even when the estimated tire longitudinal force _Fx becomes zero due to the above or the like, only the correction of the transient steering angle changes, and the target steady-state value does not change.

In the second embodiment, the tire longitudinal force estimation unit 4 calculates the longitudinal load movement estimated value ΔW _X and the lateral load movement estimated value ΔW _Y from the longitudinal acceleration G _x and the lateral acceleration G _y , and estimates the estimated tire from these deviations. Find the longitudinal force F _x . In addition, about the structure of Example 2, since it is the same as the structure of Example 1 shown in FIGS. 1-4, description is abbreviate | omitted.

First, longitudinal acceleration G _x , lateral acceleration G _y , front axis to center of gravity distance L _f , center of gravity to rear axis distance L _r , front axis width d _f , rear axis width _dr , front roll axis height h _f , rear From the roll axis height h _r , the center of gravity height to the vehicle roll axis height h _s , the center of gravity height H _G , the front roll rigidity R _f , the rear roll rigidity R _r, and the vehicle weight W, the longitudinal load movement estimation value ΔW _X , lateral load The movement amount ΔW _Y is obtained as in the following formulas (21) and (22).

Subsequently, the estimated tire longitudinal force F _x is obtained from the deviation ΔW _X −ΔW _Y. As a method for obtaining the estimated tire longitudinal force F _x , the one in which the horizontal axis is replaced with the deviation ΔW _X −ΔW _Y from the brake pressure with respect to the estimated tire longitudinal force calculation map of Example 1 shown in FIG. 5 is used. be able to.

  Note that the target yaw rate response correcting action of the second embodiment is the same as that of the first embodiment, and thus the description thereof is omitted.

Next, the effect will be described.
In the vehicle steering system of the second embodiment, the following effects are obtained in addition to the effects (1) to (4) and (6) to (9) of the first embodiment.

(9) The tire longitudinal force estimation unit 4 calculates the longitudinal load movement estimated value ΔW _X and the lateral load movement estimated value ΔW _Y from the longitudinal acceleration G _x and the lateral acceleration G _y , and estimates the estimated tire longitudinal force from these deviations. Find F _x . That is, since the estimated tire longitudinal force F _x is calculated based on the vehicle behavior (longitudinal acceleration G _x , lateral acceleration G _y ), compared with the method of the first embodiment in which the tire longitudinal force is estimated from the brake pressure, The force F _x can be estimated more accurately.

(Other examples)
The best mode for carrying out the present invention has been described based on the first embodiment. However, the specific configuration of the present invention is not limited to the first embodiment and does not depart from the gist of the present invention. Any change in the design of the range is included in the present invention.

  For example, in the embodiment, the variable gear ratio mechanism is used for the steering angle control of the front wheels, but the present invention can also be applied to a so-called steer-by-wire system in which the steering wheel and the front wheels are mechanically separated. .

  In the embodiment, the front wheel steering control and the rear wheel steering control are used, but the present invention can also be applied to a configuration of only the front wheel steering control or only the rear wheel steering control. Moreover, the estimation method of the tire longitudinal force is arbitrary, and may be estimated using parameters such as a tire slip ratio and road surface μ, without being limited to the brake fluid pressure and the wheel load.

1 is an overall system diagram of a vehicle steering apparatus according to a first embodiment. 4 is a control block diagram of a steering control controller 3. FIG. 3 is a control block diagram of a target value generation unit 31. FIG. 4 is a control block diagram of a target output generation unit 32. FIG. 3 is an estimated tire longitudinal force F _x calculation map according to brake pressure. 3 is a target yaw rate response correction coefficient α setting map corresponding to an estimated tire longitudinal force F _x . 7 is a flowchart showing a flow of a target yaw rate response correction control process executed by a target characteristic parameter correction unit 3122 of the steering control controller 3. It is a figure which shows the front-wheel steering angle change with respect to the step input of Example 1. FIG. It is a figure which shows the rear-wheel steering angle change with respect to the step input of Example 1. FIG. It is a figure which shows the yaw rate change with respect to the step input of Example 1. FIG. It is a figure which shows the driving | running | working locus change of the vehicle with respect to the step input of Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering angle sensor 2 Vehicle speed sensor 3 Steering control controller 31 Target value production | generation part 311 Vehicle model calculating part 312 Target value calculating part 3121 Target characteristic parameter calculating part 3122 Target characteristic parameter correction | amendment part 3123 Target yaw rate calculating part 3124 Target lateral speed calculating part 32 Target output generation unit 321 Target front wheel steering angle calculation unit 322 Target rear wheel steering angle calculation unit 323 Gain calculation unit 4 Tire longitudinal force estimation unit 5 Front wheel steering controller 6 Rear wheel steering controller 7 Front wheel steering actuator 8 Rear wheel steering actuator 10 Steering wheel 11, 11 Front wheel 12 Front wheel steering mechanism 13 Column shaft 14, 14 Rear wheel 15 Rear wheel steering mechanism 16 Front wheel actual steering angle sensor 17 Rear wheel actual steering angle sensor

Claims (9)

In a vehicle steering apparatus including a steering control unit that controls a steering angle of a steered wheel according to a steering angle of a steering operation unit,
Tire longitudinal force estimating means for estimating the tire longitudinal force of the steering wheel;
When the tire longitudinal force increases in the deceleration direction, the turning angle correction means for correcting the turning angle in the initial stage of steering in the direction in which the yaw rate of the vehicle increases;
A vehicle steering apparatus comprising: The vehicle steering apparatus according to claim 1,
Vehicle speed detection means for detecting the vehicle speed;
Steering angle detection means for detecting a steering angle of the steering operation means;
Target yaw rate calculating means for calculating a target yaw rate based on the vehicle speed and the steering angle;
With
The steering control means sets a target steering angle of the steered wheel according to the target yaw rate,
The steering angle correction means corrects the target yaw rate at the initial stage of steering. The vehicle steering apparatus according to claim 1 or 2,
The steering angle correction means increases the amount of correction of the turning angle as the tire longitudinal force increases in the deceleration direction. The vehicle steering apparatus according to any one of claims 1 to 3,
The turning angle correcting means corrects the turning angle so that the turning time of the turning angle is shorter than the turning time of the turning angle without correction. Vehicle steering system. The vehicle steering apparatus according to any one of claims 1 to 4, wherein:
The vehicle steering device according to claim 1, wherein the tire longitudinal force estimating means estimates the tire longitudinal force based on a brake pressure of the steering wheel. The vehicle steering apparatus according to any one of claims 1 to 5,
The vehicle steering apparatus according to claim 1, wherein the tire longitudinal force estimating means estimates the tire longitudinal force based on a wheel load of the steered wheels. The vehicle steering apparatus according to any one of claims 1 to 6, wherein:
A lateral acceleration detecting means for detecting the lateral acceleration of the vehicle;
The vehicle steering apparatus according to claim 1, wherein the turning angle correction means increases the correction amount of the turning angle as the lateral acceleration increases. The vehicle steering apparatus according to any one of claims 1 to 7,
Roll angle detection means for detecting the roll angle of the vehicle,
The steering apparatus for a vehicle, wherein the turning angle correction means increases the amount of correction of the turning angle as the roll angle increases. The vehicle steering apparatus according to any one of claims 1 to 8,
The steering angle correction means ends the correction of the steering angle when the tire longitudinal force becomes zero or in an acceleration direction.

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