JPH06340266A - Control of rear wheel steering gear - Google Patents

Abstract

PURPOSE:To cooperatively keep a vehicle to the stable side under the small behavior condition always in the control of ABS or the like by judging whether or not a control signal of the ABS control or the like is inputted to change over the inputted control signal to a proportional gain as a steering wheel angle factor gradually reducing as time goes on. CONSTITUTION:While the same phase side yaw rate factor Kgamma is gradually reduced as the vehicle speed V is reduced in the reduction of vehicle speed by ABS control, the inverse phase side temporary proportional gain Ktheta' is a function of time and reduces more largely than the yaw rate factor Kgamma. A desired rear wheel steering angle ET is calculated from a value Ktheta'.theta of the steering wheel angle theta multiplied by temporary proportional gain Ktheta' and a value Kgamma.gamma of the yaw rate gamma multiplied by the yaw rate factor Kgamma to control the rear wheel steering. Thus, even if a driver turns the wheel provisionally on a slippery road surface the value of Ktheta'.theta will have very small effect leaving only the value of Kgamma.gamma so that the rear wheels 11 are steered to keep the vehicle to the stable side under the condition of small change of behavior.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a rear wheel steering system for electronically steering a rear wheel in a four-wheel steering system (4WS) for a vehicle such as an automobile.
Related to cooperative control with control and the like.

[0002]

2. Description of the Related Art Generally, rear wheel steering control is a vehicle speed sensitive type, in which a rear wheel is reverse-phase steered in a low speed range to improve a small turning performance, and a rear wheel is in-phase steered in a medium and high speed range to obtain a vehicle speed. Accordingly, it is fundamental to variably control the steering ratio to achieve vehicle stability. By the way, the vehicle causes a yawing motion (rotational motion) around the vertical axis of the vehicle body due to a road surface condition, a difference in driving force between left and right rear wheels and a grip force, and a disturbance such as a side wind. It is known that these disturbances change the behavior of the vehicle regardless of the driver's skill and impair the stability.

By the way, in recent years, a yaw rate sensor for directly detecting the yaw rate (rotational angular velocity) of the yawing motion of the vehicle with high accuracy has been developed. According to this yaw rate sensor, not only in the case of front wheel steering,
Changes in the behavior of the vehicle due to disturbances such as cross winds can also be detected quickly. Therefore, the yaw rate is actively used,
A control method has been proposed in which the rear wheels are steered so as to ensure the stability of the vehicle against various disturbances.

Here, in the rear wheel steering control using the yaw rate of the yaw rate sensor, the proportional gain of the steering wheel angle is set in the opposite phase direction in consideration of maneuverability, and the proportional gain of the yaw rate is considered in stability in the in-phase direction. It is conceivable that the target rear wheel steering angle is calculated by both of them and the rear wheel steering is performed by the anti-phase steering angle proportional control and the yaw rate feedback control. By the way, in recent years, some vehicles are equipped with a device for ABS control or torque distribution control, and are controlled so as to prevent wheel locking or slipping when braking or accelerating on a low μ road. Therefore, for example, when the ABS control is performed, the slippery road surface state can be determined from the signal, and if the state of the antiphase steering angle proportional control is maintained at this time, the behavior of the vehicle is rather changed by the antiphase steering. May become unstable. Therefore, when the control such as the ABS is performed, it is desired that the rear wheel steering control is coordinated so as to be maintained on the stable side.

Conventionally, as for the rear wheel steering control during the ABS control, there is a prior art disclosed in, for example, Japanese Patent Laid-Open No. 2-262471. In this prior art, when the anti-skid brake is operated, the first steering angle coefficient is switched to the second steering angle coefficient which is set to a larger value, and the first yaw rate coefficient is set to a larger second yaw rate. It is shown that the target rear wheel steering angle is calculated using the second steering angle coefficient and the second yaw rate coefficient for steering control.

[0006]

By the way, the above prior art is a control method in which both the steering angle coefficient and the yaw rate coefficient are changed to those having different characteristics when the antiskid brake is actuated. Therefore, especially when the vehicle speed is low, there is a problem that the change of the coefficient at the time of switching is large and the behavior of the vehicle is greatly changed.

In view of such a point, the present invention stabilizes the vehicle in a state in which the behavior of the vehicle is always small during the control such as ABS in the rear wheel steering control by the antiphase steering angle proportional control and the yaw rate feedback control. The aim is to cooperate to keep on the side.

[0008]

To achieve this object, the present invention is directed to a yaw rate coefficient set in the in-phase direction as a function of yaw rate and vehicle speed, a steering wheel angle, and a steering wheel angle set in the opposite phase direction as a function of vehicle speed. The target rear wheel steering angle is calculated from the coefficient, and in the rear wheel steering device that automatically steers the rear wheels based on the target rear wheel steering angle, it is determined whether or not a control signal such as ABS control is input, When a control signal is input, the steering wheel angle coefficient is switched to a proportional gain that gradually decreases over time.

[0009]

In the present invention based on the above control method, the target rear wheel steering angle is calculated by the yaw rate, the yaw rate coefficient, the steering wheel angle, and the steering wheel angle coefficient when the vehicle is traveling, and the rear wheel steering device is operated based on this target rear wheel steering angle. . Therefore, the yaw rate when the vehicle behavior changes due to disturbances such as vehicle speed, steering wheel angle, or crosswind, the rear wheels are automatically steered in-phase or in anti-phase to obtain the desired steering angle, etc. Turnability and stability at high speed and against disturbance are improved. on the other hand,
For example, when ABS control is performed and its control signal is input, the steering angle coefficient is switched to a proportional gain that gradually decreases as a function of time, so that the yaw rate feedback control smoothly shifts to a strong direction under any running condition. Therefore, reverse phase steering is not performed in the low speed range, and sudden changes in vehicle behavior are reliably prevented even in slippery road conditions.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, an outline of the vehicle drive system and the four-wheel steering system will be described. First, in the vehicle 1, the engine 2 is connected to the clutch 3 and the transmission 4, and the output side of the transmission 4 is configured to be transmitted to the front wheels 7 via the front differential 5, the axle 6, and the like. The output side of the transmission 4 is also configured to be transmitted to the rear wheel 11 via the propeller shaft 8, the rear differential 9, the axle 10, and the like.
Four-wheel drive runs. Further, it has a front wheel steering device 20 and a rear wheel steering device 30 as a four-wheel steering system.

In the front wheel steering device 20, a steering shaft 22 having a steering wheel 21 has a hydraulic control valve 2
3 is connected to the front wheels 7 via the power cylinder 24, the rod 25, and the knuckle arm 26, and the front wheels 7 are manually steered by operating the steering wheel. Rear wheel steering device 3
Reference numeral 0 denotes an electric motor 31, which is connected to an eccentric shaft 33 via a worm gear 32 for reduction, and which is connected to the eccentric shaft 33 via a link 34, a lever 35, a knuckle arm 36, and the like. It is connected to the wheels 11 and is configured to automatically steer the rear wheels 11 by driving a motor. In addition, when the motor power is turned off during an abnormality, the worm gear 32
Due to the non-reciprocity, the rear wheel 11 is maintained in a predetermined steering angle state with respect to the road surface external force.

The control system includes a steering wheel angle sensor 40 for detecting the steering wheel angle θ, a steering wheel angular velocity sensor 41 for detecting the steering wheel angular velocity dθ, a rear wheel steering angle sensor 42 for detecting the rear wheel steering angle Er, and a rear wheel steering angular velocity ωr. It has a rear wheel steering angular velocity sensor 43 for detecting. Further, it has a yaw rate sensor 44 for detecting a yaw rate γ of a rotational angular velocity according to the turning state of the vehicle. Further, in order to calculate the control vehicle speed V, a front left wheel speed sensor 45 for detecting the front left wheel speed Nfr and a rear right wheel speed sensor 46 for detecting the rear right wheel speed Nrl are provided, and these sensor signals are used as the control unit 50. Is input to the motor 31 to be electrically processed, and a motor signal corresponding to the steering direction of the rear wheels, the steering angle, and the steering angular velocity is output to the motor 31.

The control unit 50 has a vehicle speed calculation unit 51 to which the front left wheel speed Nfr and the rear right wheel speed Nrl are input, and calculates the control vehicle speed V by V = (Nfr + Nrl) / 2. The vehicle speed V is input to the steering wheel angle coefficient setting unit 52, the steering wheel angle coefficient Kθ is set as a function of the vehicle speed V, and simultaneously input to the yaw rate coefficient setting unit 53, and the yaw rate coefficient Kγ is similarly set as a function of the vehicle speed V. To do. The steering wheel angle coefficient Kθ has a reverse phase over the entire vehicle speed as shown in the steering angle gain map of FIG. 3A, and has a characteristic that the absolute value of the value decreases and decreases as the vehicle speed V decreases in the low and medium speed range. The yaw rate coefficient Kγ is in-phase throughout the vehicle speed as shown in the yaw rate gain map in the same figure, and has a characteristic that it gradually increases as the vehicle speed V increases. Therefore, both coefficients Kθ and Kγ are set with reference to this map.

The steering wheel angle θ and the steering wheel angle coefficient Kθ are input to the multiplication unit 54 to calculate a multiplication value Kθ · θ of both, and the yaw rate γ and the yaw rate coefficient Kγ are also input to the multiplication unit 55 to calculate both multiplication values Kγ · θ. Calculate γ. These two multiplication values Kθ · θ and Kγ · γ are input to the target rear wheel steering angle calculation unit 56, and the target rear wheel steering angle ET is calculated by ET = Kγ · γ + Kθ · θ. Therefore, the term of Kγ · γ is a stabilizing element that keeps the vehicle on the stable side, and the term of Kθ · θ is a turning element that promotes turning.

Here, the yaw rate γ is generated according to the turning state of the vehicle due to turning or disturbance over the entire vehicle speed, and this coefficient Kγ is a characteristic of an increasing function of the vehicle speed V. Therefore, the higher the vehicle speed V, the more the value of Kγ · γ becomes. growing. The steering wheel angle θ is generally very small in the medium-high speed range, and therefore the value of Kθ · θ becomes close to zero even if the coefficient Kθ is small in the opposite phase direction. Therefore, when the yaw rate γ is detected in the medium-high speed range, the target rear wheel steering angle ET is in the in-phase direction due to the value of Kγ · γ, and stability-oriented control is performed. In the low speed range where the steering wheel angle θ is large, the turning property is controlled with emphasis on the value of Kθ · θ in the opposite phase direction, and at this time, the yaw rate γ is corrected to the stable side by the value of Kγ · γ in the in-phase direction.

The target rear wheel steering angle ET and the rear wheel steering angle Er are input to the deviation calculating section 57 to calculate the deviation ED by ED = ET-Er. This deviation ED is the target rear wheel turning speed setting unit 5
8, and the target rear wheel turning speed ωo corresponding to the deviation ED is set by the map of FIG. 3 (b). Further, the target rear wheel turning speed ωo and the rear wheel steering angular speed ωr are input to the speed difference calculation unit 59, and the speed difference ωd is calculated by ωd = ωo−ωr. Then, the speed difference ωd is input to the control amount setting unit 60,
The control amount Kp of the proportional component is set according to the speed difference ωd, and the driving unit 61 supplies the forward or reverse motor current I according to the control amount Kp to the motor 31.

Coordinated control when ABS control or the like is performed in the above control system will be described. First, it has a temporary proportional gain calculating section 62 to which the steering wheel angle coefficient Kθ and the ABS control signal are input. When the ABS control signal is input, it switches to the temporary proportional gain Kθ ′ and outputs it to the multiplying section 54.
The temporary proportional gain Kθ ′ is calculated by multiplying the steering wheel angle coefficient Kθn immediately before the input of the ABS control signal by the reduction constant G.
The decrease constant G gradually decreases as a function of time, for example, is a temporary delay constant, and is set by G = Ts / (1 + Ts) by the time constant T and the Laplace operator s. Therefore, the temporary proportional gain Kθ ′ is configured to be calculated and output by Kθ ′ = G · Kθn, G = Ts / (1 + Ts).

Next, the operation of this embodiment will be described. First, the engine 2 is operated, and the transmission power of the transmission 4 is transmitted to the front wheels 7 and the rear wheels 11 by the drive system, so that the vehicle 1 moves
Drive with wheel drive. At this time, when the driver operates the steering wheel 21, the front wheels 7 are steered and manually steered by the front wheel steering device 20. Further, the flowchart of FIG. 6 is executed every predetermined time, and the rear wheel steering control is performed depending on the conditions such as traveling, steering wheel operation, and turning of the vehicle.

That is, in step S1, the steering wheel angle θ, the yaw rate γ, the rear wheel steering angle Er, and the rear wheel steering angular velocity ωr are read,
The vehicle speed V is calculated in step S2. And step S3
It is determined whether or not the ABS control signal is input, and if not input, the process proceeds to step S4 to clear the flag. After that, the process proceeds to step S5, where the steering wheel angle coefficient K is determined according to the vehicle speed V.
θ and the yaw rate coefficient Kγ are set, and in step S6 the target rear wheel steering angle ET is calculated from the steering wheel angle θ and its coefficient Kθ, and the yaw rate γ and its coefficient Kγ. Then step S
The deviation ED between the target rear wheel steering angle ET and the rear wheel steering angle Er is calculated in 7 and the target rear wheel turning speed ωo is set in step S8.
In step S9, the target rear wheel steering speed ωo and the rear wheel steering angular speed ω
The speed difference ωd from r is calculated, and the speed difference ωd is calculated in step S10.
The control amount Kp corresponding to d is determined, and the motor current I of the control amount Kp is output in step S11 to drive the motor 31.

Therefore, in the rear wheel steering system 30, the motor 3
1, the worm gear 32 and the eccentric shaft 33 rotate, the link 34 and the lever 35 swing left and right, and the rear wheel 11 is automatically steered. In this case, the rear wheels 11 are in-phase or anti-phase, and are subjected to anti-phase steering angle proportional control and yaw rate feedback control so as to obtain a desired steering angle or steering angular velocity.

Therefore, when the steering wheel 21 is greatly turned at a low speed such as starting, the target rear wheel steering angle ET becomes negative due to the value of Kθ · θ, and the rear wheel 11 is steered in a small turn by reverse-phase steering.
At this time, if the vehicle makes a sharp turn or the yaw rate γ increases due to the vehicle turning due to the road surface μ, the value of Kγ · γ causes the rear wheel 1
The reverse-phase steering of 1 is reduced and corrected, and the behavior of the vehicle is stabilized. When turning at medium and high speeds, the target rear wheel steering angle ET is mainly K
The value of γ · γ becomes positive and the rear wheels 11 are steered in phase,
Therefore, the stability of the vehicle when turning is improved. The relationship among the steering wheel angle θ, the yaw rate γ, the coefficients Kθ and Kγ, and the target rear wheel steering angle ET in this case is shown in FIG. Further, when the vehicle rapidly turns to the left or right due to a disturbance such as a side wind, the yaw rate γ changes greatly, and this behavior change of the vehicle 1 is quickly detected. Then, the rear wheel 11 is steered so as to maintain the in-phase state regardless of the turning of the vehicle 1 by the value of Kγ · γ. For this reason, the vehicle 1 stably assumes an opposite posture so as not to be swept away by a side wind, and smoothly returns to the original course.

On the other hand, when the vehicle speed V sharply decreases as shown by the alternate long and short dash line in FIG. 6 when the brake is operated while traveling on a low μ road such as a snowy road, the vehicle speed V is gradually decreased by ABS control. Is corrected to prevent wheel lock. By inputting the control signal at this time, the process proceeds from step S3 to step S12 to check the flag,
First, at step S13, the steering wheel angle coefficient Kθn immediately before the ABS control is read out, and at step S14, the steering wheel angle coefficient Kθn and the reduction constant G are used to make a temporary proportional gain K.
Calculate θ ′. Then, in step S15, the temporary proportional gain Kθ 'is compared with the set value a near zero, and if it is larger than the set value a, the process proceeds to step S5, and the temporary proportional gain Kθ' is switched instead of the steering wheel angle coefficient. Therefore, after the ABS control is started, the temporary proportional gain Kθ ′ on the opposite phase side always has a characteristic that it smoothly decreases with a temporary delay with the passage of time regardless of the vehicle speed V and its change, as shown in FIG.

Therefore, when the vehicle speed is reduced by the ABS control,
The yaw rate coefficient Kγ on the in-phase side gradually decreases as the vehicle speed V decreases as shown in FIG. 6 due to the characteristics of FIG. 3A, but the temporary proportional gain Kθ ′ on the anti-phase side is a yaw rate as a function of time. It is greatly reduced from the coefficient Kγ. Then, the target rear wheel steering angle ET is calculated from the multiplied value Kθ ′ · θ of the steering wheel angle θ and the temporary proportional gain Kθ ′ and the multiplied value Kγ · γ of the yaw rate γ and its coefficient Kγ, and the rear wheel steering control is performed. Therefore, even if the driver turns the steering wheel on this slippery road surface, the value of Kθ ′ · θ becomes very small and has no effect, and the behavior of the rear wheel 11 changes the vehicle behavior mainly by the value of Kγ · γ. The yaw rate feedback control is strengthened by steering so as to maintain the stable side in a small state. Therefore, when ABS control is performed during braking on a slippery road surface,
Further, the rear wheel steering control cooperates to maintain the behavior of the vehicle 1 in a stable state, thereby preventing a sudden change in the vehicle behavior during braking.

Then, in step S15, the temporary proportional gain K
When it is determined that θ ′ has become zero, the process proceeds to step S16, the flag is set, and the above control is ended. When the ABS control is released, steps S3 to S
Then, the control is returned to the original rear wheel steering control.

Although the embodiments of the present invention have been described above, the present invention can be similarly applied to the case where the torque distribution of the front and rear wheels is controlled to prevent slippage on a slippery road surface. It can also be temporarily adopted when the yaw rate sensor fails, in which case it is possible to effectively prevent sudden changes in the behavior of the vehicle immediately after the failure. Furthermore, the temporary proportional gain may be reduced not only as a function of time but also as a function of vehicle speed.

[0026]

As described above, according to the present invention,
In a rear wheel steering system that automatically steers the rear wheels by reverse phase steering angle proportional control and yaw rate feedback control,
When performing control such as S, the proportional gain on the opposite phase side of the steering wheel angle is controlled so as to gradually decrease, so the yaw rate feedback control is strengthened and the vehicle behavior on a slippery road surface is effectively stabilized. Can be kept. ABS
When the control of etc. is started, the steering wheel angle coefficient at that time is switched to a temporary proportional gain that decreases as a function of time.
The proportional gain on the opposite phase side can be reliably reduced under any running condition. Further, since the proportional gain at the time of switching always changes smoothly, the behavior of the vehicle does not change.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system suitable for a control method for a rear wheel steering system according to the present invention.

FIG. 2 is a configuration diagram showing an outline of a vehicle drive system and a four-wheel steering system.

FIG. 3 is a diagram showing a map of a steering wheel angle coefficient, a yaw rate coefficient, and a target rear wheel turning speed.

FIG. 4 is a flowchart showing rear wheel steering control during normal and ABS control.

FIG. 5 is a diagram showing a state of rear wheel steering when turning left and right.

FIG. 6 is a diagram showing a state of vehicle speed and proportional gain in the case of ABS control.

[Explanation of symbols]

 30 rear wheel steering device 31 electric motor 40 steering wheel angle sensor 44 yaw rate sensor 50 control unit 52 steering wheel angle coefficient setting unit 53 yaw rate coefficient setting unit 56 target rear wheel steering angle calculation unit 62 temporary proportional gain calculation unit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 117: 00 137: 00

Claims (2)

[Claims] 1. A target rear wheel steering angle is calculated from a yaw rate coefficient set in the in-phase direction by a function of yaw rate and vehicle speed, and a steering wheel angle coefficient set in a reverse phase direction by a function of vehicle speed, and the target rear wheel steering angle is calculated. In a rear wheel steering system that automatically steers the rear wheels based on the wheel steering angle, it is determined whether a control signal such as ABS control is input, and if a control signal is input, the steering wheel angle coefficient changes as time elapses. A control method for a rear wheel steering system, characterized by switching to a proportional gain that gradually decreases. 2. The proportional gain is gradually reduced with a temporary delay from a value when a control signal is input.
A method for controlling the rear wheel steering device described.