JPH072130A - Method for controlling rear wheel steering device - Google Patents

Abstract

PURPOSE:To surely prevent the spin or the like of a vehicle in turning and braking operation by making the increased correction of the yaw rate coefficient by the acceleration coefficient to be set according to the negative longitudinal acceleration in the braking operation and the jerk coefficient to be set not more than the set value of the differentiated value of the negative longitudinal acceleration. CONSTITUTION:When a sudden brake is applied during the turning operation, the negative longitudinal acceleration (-a) becomes a constant small value until a vehicle is stopped, and its differentiated value (-j) is rapidly reduced in the beginning of the braking. Thus, the acceleration coefficient Ka and the jerk coefficient Kj become positive large values in the beginning of the braking, and the yaw rate coefficient kgamma is corrected to be increased. Though the rear wheel steering angle Er is largely steered instantaneously in the direction of the same phase irrespective of the reduction of the vehicle speed, and the cornering force of the rear wheels is reinforced. This constitution suppresses the swing-out of the rear wheels and prevents the roll-in of the vehicle and the rapid change of the spin behavior even if a large turning moment caused by the inertia force in the rapid braking during the turning operation is applied to the vehicle.

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. Concerning measures to prevent crowding and spin.

[0002]

2. Description of the Related Art In recent years, a yaw rate sensor for directly detecting a yaw rate (rotational angular velocity) of a yawing motion of a vehicle with high accuracy has been developed. With this yaw rate sensor, not only in the case of steering the front wheels, but also changes in the behavior of the vehicle due to disturbances such as road surface conditions and side winds can be promptly detected. Therefore, it has been proposed that the yaw rate of a yaw rate sensor be positively used in a four-wheel steering system to steer the rear wheels by anti-phase steering angle proportional control and yaw rate feedback control.

Conventionally, as for the rear wheel steering control, there is a prior art disclosed in, for example, Japanese Patent Laid-Open No. 2-262471. In this prior art, the steering angle coefficient is set in the opposite phase direction and the yaw rate coefficient is set in the same phase direction as a function of the vehicle speed, and the multiplication value of the front wheel steering angle and the steering angle coefficient and the multiplication value of the yaw rate coefficient and the yaw rate are added. Then, the target rear wheel steering angle is calculated.
Then, it is shown that a control signal of a deviation between the target rear wheel steering angle and the rear wheel steering angle is output, and the rear wheel steering control is performed by the anti-phase steering angle proportional control and the yaw rate feedback control.

[0004]

By the way, in the above-mentioned prior art, since the control is performed only by the anti-phase steering angle and the in-phase yaw rate, the following problems occur. That is, at the time of turning at medium and high speeds, the rear wheels are steered in phase by the yaw rate and the yaw rate coefficient, and the stability of the vehicle is ensured. When the driver operates the brakes in this state to perform braking, the yaw rate coefficient decreases as the vehicle speed decreases, and the rear wheels are quickly steered back in the neutral direction as indicated by the alternate long and short dash line in FIG. In this case, in the slow braking, the turning inertial force of the vehicle is small, and the cornering force of the rear wheels is relatively large even if the steering wheel is turned back and steered, so that the vehicle is stably held. However, during sudden braking, the turning inertial force of the vehicle increases, and on the rear wheels the cornering force is greatly reduced due to the increase of the braking force and the steering back, and due to these relationships, an over moment is applied to the vehicle and winding or spin occurs. Sometimes.

In view of such a point, the present invention corrects the reverse wheel steering control by the anti-phase steering angle proportional control and the yaw rate feedback control so as to surely prevent the vehicle from spinning during turning braking. To aim.

[0006]

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. In the rear wheel steering system that calculates the target rear wheel steering angle by the coefficient and automatically steers the rear wheels based on this target rear wheel steering angle, the acceleration coefficient set according to the negative longitudinal acceleration during braking. , And a jerk coefficient which is set below a set value of the differential value of the negative longitudinal acceleration, and the yaw rate coefficient is increased and corrected by these acceleration coefficient and jerk coefficient during braking.

[0007]

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 actuator such as the motor is operated based on the target rear wheel steering angle. . Then, depending on the yaw rate when turning due to disturbance such as vehicle speed, steering wheel angle, side wind, etc., the rear wheels are automatically steered in the same phase or opposite phase to obtain the desired steering angle etc. Improves stability against disturbance. On the other hand, when the vehicle is suddenly braked especially during medium-to-high speed turning, the longitudinal acceleration and its differential value change in the negative direction, and the yaw rate coefficient is increased and corrected by the acceleration coefficient and jerk coefficient at the initial stage of braking, and the rear wheel momentarily increases in the in-phase direction. Steered to enhance cornering force. Therefore, the vehicle is prevented from being caught or spun by the cornering force, and the vehicle stability at the time of sudden turning braking is improved.

[0008]

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 system 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 calculator 51 for inputting the front left wheel speed Nfl and the rear right wheel speed Nrr, and calculates the control vehicle speed V by V = (Nfl + Nrr) / 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 in accordance with the turning state of the vehicle due to turning or disturbance over the entire vehicle speed, and this coefficient Kγ is a characteristic of the increasing function of the vehicle speed V. Therefore, the value of Kγ · γ becomes larger as the vehicle speed V increases. 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.

In the control system described above, measures for preventing vehicle spin during turning braking will be described. First, braking can be judged by the change in the negative direction of the longitudinal acceleration, and at the initial stage of braking when an over moment occurs, it can be judged by the change in the differential value of the longitudinal acceleration in the negative direction, and sudden braking can be judged by providing a dead zone. Further, since the turning performance of the vehicle spin during turning braking depends on the yaw rate coefficient, the yaw rate coefficient may be increased and corrected by the longitudinal acceleration and its differential value.

Therefore, a front / rear G sensor 47 for detecting the front / rear acceleration a is provided. The longitudinal acceleration a is input to the acceleration coefficient setting unit 62 to set the acceleration coefficient Ka (Ka ≦ 1) according to the negative longitudinal acceleration −a, and is input to the jerk coefficient setting unit 63 to determine the negative longitudinal acceleration. A jerk coefficient Kj (Kj ≦ 1) corresponding to the differential value −j is set. Acceleration coefficient K
As shown in FIG. 3C, a is a characteristic in which the smaller the negative longitudinal acceleration −a is, the more it gradually increases. The jerk coefficient Kj is, as shown in FIG. 7D, a characteristic that the smaller the differential value −j of the negative longitudinal acceleration is equal to or less than the set value −js, the more the characteristics gradually increase.

These acceleration coefficient Ka and jerk coefficient Kj
Is input to the target rear wheel steering angle calculation unit 56, and the yaw rate coefficient K
γ is increased and corrected. That is, the overall target rear wheel steering angle ET including these coefficients Ka and Kj is configured to be calculated by ET = Kγ · γ (1 + Ka · Kj) + Kθ · θ.

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. 4 is executed at predetermined time intervals to perform rear wheel steering control.

That is, the steering wheel angle θ, the yaw rate γ, the rear wheel steering angle Er, the rear wheel steering angular velocity ωr, and the longitudinal acceleration a are read in step S1, and the vehicle speed V is calculated in step S2. After that, the process proceeds to step S3, 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 S4, the acceleration coefficient Ka is set according to the negative longitudinal acceleration −a, and the jerk coefficient Kj is set according to the differential value −j of the negative longitudinal acceleration. Then, in step S5, the steering wheel angle θ, its coefficient Kθ, yaw rate γ, its coefficient Kγ, acceleration coefficient Ka,
The target rear wheel steering angle ET is calculated by the above equation using the jerk coefficient Kj. Therefore, under steady and accelerated traveling conditions, Ka = 0 and Kj = 0, and the yaw rate coefficient Kγ
Is not corrected.

Further, the deviation ED between the target rear wheel steering angle ET and the rear wheel steering angle Er is calculated in step S6, the target rear wheel turning speed ωo is set in accordance with the deviation ED in step S7, and the target rear wheel steering speed ωo is set in step S8. A speed difference ωd between the wheel turning speed ωo and the rear wheel steering angular speed ωr is calculated. After that, in step S9, the speed difference ωd
The control amount Kp is determined according to the
The motor current I of p is output 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 low speed under steady and accelerated traveling conditions, the target rear wheel steering angle ET becomes K.
The value becomes negative depending on the values of θ and θ, and the rear wheel 11 is steered in a small turn by reverse-phase steering. At this time, if the yaw rate γ increases due to a sharp turn or the vehicle turning due to the road surface μ, Kγ · γ
By the value of, the reverse-phase steering of the rear wheels 11 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 becomes positive mainly due to the value of Kγ · γ, and the rear wheel 1
1 is in-phase steered. Therefore, the cornering force Fcr of the rear wheel 11 increases and the front and rear wheels 7,
The cornering forces Fcf and Fcr of 11 are balanced with a margin. Therefore, the vehicle can travel on a predetermined turning circle in a stable posture, and the turning stability is improved. FIG. 5 shows 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.
become that way.

When the vehicle suddenly turns to the left or right due to a disturbance such as a crosswind, 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 rear wheels 11 are steered in the same phase at the time of medium- and high-speed turning to control the vehicle 1 so as to keep it on the stable side, when braking is performed by the brake operation, a negative longitudinal acceleration -a corresponding to the braking state is obtained. And its differential value −j. Therefore, in the case of gentle braking, Ka> 0 in the map of FIG. 3C, but since the differential value −j is larger than the set value −js, Kj = 0 in the map of (d), which is the same as above. To K
No correction is made for γ. Therefore, the yaw rate coefficient Kγ decreases as the vehicle speed V decreases, the rear wheels 11 are swiftly switched back in the neutral direction, and the cornering force F of the rear wheels 11 decreases as the centrifugal force Fg decreases.
cr is also reduced.

Further, when the vehicle is suddenly braked during the above-mentioned turning, the negative longitudinal acceleration -a becomes a constant small value until the vehicle stops as shown in FIG. 6, and its differential value -j is at the initial stage of braking as shown in FIG. It rapidly decreases and changes. Therefore, Ka · Kj becomes a large positive value in the initial stage of braking, and the yaw rate coefficient Kγ is increased and corrected. Therefore, the rear wheels 11 are momentarily steered further in the in-phase direction as shown in FIG. 6 regardless of the decrease in the vehicle speed V, and the cornering force Fcr of the rear wheels 11 is strengthened. Therefore, even if a large turning moment acts on the vehicle 1 due to the inertial force at the time of sudden turning braking, the outward cornering force of the rear wheel 11 is suppressed by the enhanced cornering force Fcr, and thus the rolling or spinning of the vehicle 1 is prevented. The sudden change of the behavior of is prevented.

When Kj = 0 immediately after braking, the target rear wheel steering angle ET gradually decreases thereafter by the yaw rate coefficient Kγ which is a function of the acceleration coefficient Ka and the vehicle speed V. Therefore, the rear wheels 11 are smoothly steered back in the neutral direction as shown in FIG. 6 in a state where there is little change in the behavior of the vehicle.

The embodiment of the present invention has been described above, but the present invention is not limited to this.

[0028]

As described above, according to the present invention,
In a rear wheel steering system that automatically steers the rear wheels by anti-phase steering angle proportional control and yaw rate feedback control, the yaw rate coefficient is increased and corrected by the coefficient of negative longitudinal acceleration and its differential value at the beginning of sudden braking, so At the time of sudden braking, the cornering force of the rear wheels can be strengthened to effectively prevent the vehicle from being caught or spun, and the vehicle stability at the time of sudden turning braking is improved. After the initial braking, the rear wheels are smoothly steered back to the neutral direction, so there is little change in vehicle behavior. By the negative longitudinal acceleration and its differential value, the initial braking and the subsequent control can be smoothly performed. Since the acceleration coefficient and the jerk coefficient are linear characteristics, it is possible to appropriately prevent the vehicle from spinning and the like depending on the braking state.

[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, a target rear wheel turning speed, an acceleration coefficient, and a jerk coefficient.

FIG. 4 is a flowchart showing rear wheel steering control.

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

FIG. 6 is a time chart showing a state such as rear wheel steering during sudden braking.

[Explanation of symbols]

 30 rear wheel steering device 31 electric motor 40 steering wheel angle sensor 44 yaw rate sensor 47 front-rear G 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 acceleration coefficient setting unit 63 jerk coefficient setting Department

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B62D 113: 00 117: 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, the acceleration coefficient is set according to the negative longitudinal acceleration during braking, and the differential coefficient of the negative longitudinal acceleration is set below the set value. A method for controlling a rear wheel steering system, wherein the yaw rate coefficient is increased and corrected by the acceleration coefficient and the jerk coefficient during braking. 2. The control method for a rear wheel steering system according to claim 1, wherein both the acceleration coefficient and the jerk coefficient are set to have larger characteristics as the negative longitudinal acceleration or the derivative thereof is smaller.