JPH0891238A - Control method for rear wheel steering device - Google Patents

Abstract

PURPOSE: To safely facilitate taking a vehicle in and out of a garage and parking a vehicle in a longitudinal line by driving a motor with a right and a left disconnection switch operated regardless of a target steering angle when a low speed mode is selected with a mode change-over switch operated, and thereby arbitrarily steering each rear wheel manually. CONSTITUTION: A control unit 50 operates a target rear wheel snaking 56 based on both a yaw rate factor 53 which is at least a function of vehicle speeds 45 and 4 and is set to a identical phase direction, and a handle angle factor 52 which is set to a reverse phase direction, and drives an electric motor 31 in response to the aforesaid snaking for automatically steering each rear wheel. In this case, a normal mode where each rear wheel is steered in response to the steered angle of each front wheel, is switched over to a manual mode for rear wheel steering by a mode change-over switch 47. Besides, when a change-over to a manual mode is made, the rear wheels are steered to the right and left directions by a light and a left disconnection switch 49 and 48. Furthermore, when a low speed mode is selected at the time of low vehicle speeds, the electric motor 31 is driven by operating the right and left disconnection switches 49 and 48 regardless of a target rear wheel steering angle, and each rear wheel is thereby arbitrarily steered manually.

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 rear wheel steering control by manual operation.

[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. In recent years, a yaw rate sensor has been developed which directly detects the yaw rate (rotational angular velocity) of the yawing motion of the vehicle with high accuracy. 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, there is a tendency that the steering angle and the yaw rate are further added to the coefficients in the anti-phase direction and the in-phase direction according to the vehicle speed, and the rear wheel steering control is performed by the anti-phase steering angle proportional control and the yaw rate feedback control.

Therefore, when the steering wheel is turned at an extremely low speed, the rear wheels are steered in the opposite phase to improve the small turning ability, which is convenient when making a tight turn or making a U-turn. However, the reverse-phase steering of the rear wheels is not always preferable in the case where the garage has a sufficient space in the width direction of the vehicle, or when the vehicle is parked in parallel on a narrow road.

That is, the turning center at an extremely low speed is set at the intersections of the lines perpendicular to the front wheels 7 and the rear wheels 11, as shown in FIG. For this reason, when the rear wheels 11 are steered in reverse phase with respect to the front wheels 7, the turning center P1 is set close to the inside of the vehicle, and the small turning performance is improved.
Largely jumps to the side like the locus S1. When the rear wheels 11 are the same as the two-wheel steering without steering, the turning center P
2 is set on the rear wheel 11, and the turning radius becomes large,
The protrusion of the rear end corner portion A of the vehicle is reduced like a trajectory S2. When the rear wheels 11 are steered in phase, the turning center P3 is set further rearward, and the vehicle rear end corner portion A does not project laterally like the locus S3.

For this reason, when the rear wheels are steered in reverse phase when the vehicle is parked, the corners of the front and rear ends of the vehicle tend to protrude laterally and come into contact with the walls of the garage, making it difficult to operate the steering wheel. . Therefore, when turning such as entering a garage, other modes are set instead of the normal mode of the anti-phase steering angle proportional control.
It is desired to manually steer the rear wheels so that the turning ability and turning posture of the vehicle can be arbitrarily adjusted according to the judgment of the driver.

[0006] Conventionally, as for the one for setting a special mode in the above-mentioned rear wheel steering control, for example, Japanese Patent Laid-Open No. 61-24
There is a prior art of 1276 publication. In this prior art, in the case of a slippery low μ road, the rear wheel steering control is performed by switching to a special mode in which the rear wheel antiphase steering range is zero or extremely small, and spin when the vehicle suddenly changes direction, etc. Has been shown to avoid the danger of.

[0007]

By the way, in the above-mentioned prior art, since it is a method of significantly limiting the reverse-phase steering of the rear wheels in the special mode, a small turning property is required in the case of garage parking. Is sacrificed, which is not desirable.

In view of such a point, an object of the present invention is to facilitate manual rear wheel steering control at extremely low speeds to facilitate garage parking, parallel parking, and the like.

[0009]

To achieve this object, the present invention is directed to a yaw rate coefficient which is set in the in-phase direction as a function of at least the yaw rate and vehicle speed, a steering wheel which is set in the opposite phase direction as a function of the steering wheel angle and the vehicle speed. In the rear wheel steering device that calculates the target rear wheel steering angle by the angle coefficient and automatically drives the rear wheels by driving the motor based on the target rear wheel steering angle,
A normal mode in which the rear wheels are steered according to the front wheel steering angle is switched to a manual mode in which the rear wheels are steered manually by the driver, and the rear wheels are switched when the mode switch is switched to the manual mode. A right cut switch that steers to the right and a left cut switch that steers the rear wheels to the left are provided, and when the low speed mode is determined by operating the mode changeover switch when the vehicle speed is low, the right cut switch or the left cut switch is operated. Thus, the motor is driven irrespective of the target rear wheel steering angle, and the rear wheels are arbitrarily manually steered.

[0010]

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,
When moving the vehicle in and out of the garage at extremely low speeds, the mode changeover switch is operated to switch to the low speed mode.At this time, for example, when making a right turn, if the driver operates the left cut switch, the rear wheels will move to the left. Arbitrarily reverse phase steering,
The vehicle makes a sharp turn. When the right-turn switch is operated, the rear wheels are steered to the right in the same phase to linearize the turning posture, and the manual steering allows the vehicle to be safely and easily put in and out of a narrow garage from a narrow road.

[0011]

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, a yaw rate sensor 44 for detecting a yaw rate γ of a rotational angular velocity according to a turning state of the vehicle, a front left wheel speed sensor 45 for detecting a front left wheel speed Nfr for calculating a control vehicle speed V, and a rear right wheel speed Nrl are detected. The rear right wheel speed sensor 46 is provided.

Further, a mode changeover switch 47 for changing over the normal mode in which the rear wheels are steered in accordance with the steered angle of the front wheels to the manual mode in which the driver manually operates the rear wheels by changing over the mode changeover switch 47. A right-turn switch 48 for turning to the right and a left-turn switch 4 for turning to the left
Have 9. These sensor and switch signals are input to the control unit 50 and electrically processed, and a motor signal corresponding to the steering direction, the steering angle, and the steering angular velocity of the rear wheels is output to the motor 31.

The control unit 50 has a vehicle speed calculating section 51 to which the front left wheel speed Nfr and the rear right wheel speed Nrl are inputted, 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

[Equation 1] Calculate by The term Kγ · γ is a stabilizing element that keeps the vehicle on the stable side, and the term 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 the characteristic of the increasing function of the vehicle speed V, the higher the vehicle speed V, the larger the value of Kγ · γ. 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 input to the turning speed conversion unit 58 and converted into the turning speed ωo according to the deviation ED by the map of FIG.

Next, the steering wheel angle and the speed component of the yaw rate will be described. The steering wheel angular speed dθ and the steering wheel angle coefficient Kθ are input to the multiplication unit 60, and the product value Kθ ·
Calculate dθ. The yaw rate γ is input to the differentiating unit 61 and the yaw rate γ is time differentiated to obtain the yaw rate differential value d.
γ is calculated, and the yaw rate differential value dγ and the yaw rate coefficient Kγ are input to the multiplication unit 62 and the product of the two, Kγ · dγ
To calculate. These two multiplication values Kθ · dθ, Kγ · d
γ is input to the target rear wheel steering angular velocity calculation unit 63, and the target rear wheel steering angular velocity dET is

[Equation 2] Calculate by This target rear wheel steering angular speed dET is input to the additional steering speed setting unit 64, and the additional steering speed ω1 corresponding to the target rear wheel steering angular speed dET is set according to the map of FIG. Then, the turning speed ωo and the additional turning speed ω1 are input to the target turning speed calculation unit 65, and the target turning speed ωT is

[Equation 3] Calculate by In this way, by adding the additional turning speed ω1, it becomes possible to control with good response to the state of the steering wheel operation or the change in the vehicle behavior.

The target turning speed ωT and the rear wheel steering angular speed ωr as an actual value are input to the control amount setting section 66, first the deviation ωd between them is obtained, and then the proportional and integral control amounts corresponding to the deviation ωd. Determine Kc. Then, the drive circuit 67 is configured to supply the forward or reverse motor current I corresponding to the control amount Kc to the motor 31.

In the normal mode control system, a manual rear wheel steering control system at extremely low speed will be described. First, there is a low speed mode control unit 70 to which the vehicle speed V and the signals from the mode changeover switch 47, the right cut switch 48 and the left cut switch 49 are input, and the mode changeover switch 47 is operated at an extremely low speed below the set vehicle speed of 10 km / h, for example. When turned on,
Determine low speed mode. When the right-turn or left-turn switches 48 and 49 are turned on, the rear wheel steering angle ER is checked, and the motor 31 is rotated in the left and right steering directions depending on the operation time regardless of the steering wheel operation, yaw rate, etc. Manually steer the rear wheels. In addition, mode switch 4
When 7 is turned off, the normal mode is restored immediately. On the other hand, when the vehicle speed becomes equal to or higher than the set vehicle speed, the target rear wheel steering angle in the normal mode is gradually restored to prevent instability due to a sudden change in vehicle behavior.

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.

When the vehicle is traveling by operating the steering wheel, the steering wheel angle θ, the steering wheel angular velocity dθ, the yaw rate γ, the rear wheel steering angle ER, and the rear wheel steering angular velocity ωr are detected, and the vehicle speed V and the yaw rate differential value dγ are calculated. In the control unit 50, the steering wheel angle coefficient Kθ and the yaw rate coefficient Kγ are set according to the vehicle speed V, and the target rear wheel steering angle is determined by these coefficients Kθ, Kγ, the steering wheel angle θ, the yaw rate γ, and their speeds dθ, dγ. ET and the rear wheel steering angular velocity dET are calculated, and the target steering speed ωT is calculated based on the steering speed ωo and the additional steering speed ω1. Then, the control amount Kc is determined by the target turning speed ωT and the rear wheel steering angular speed ωr, and the mode current I corresponding to the control amount Kc is output to output the motor 31.
Is driven. Therefore, in the rear wheel steering device 30, the worm gear 32 and the eccentric shaft 33 are rotated by the motor 31, and the link 34 and the lever 35 are swung left and right. And the rear wheel 1
1 is automatically steered by the anti-phase steering angle proportional control and the yaw rate feedback control so as to obtain a desired steering angle or steering angle speed in the same phase or in the opposite phase.

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 reverse-phase steered to make a small turn.
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. If the vehicle suddenly turns left or right due to a disturbance such as a crosswind, the yaw rate γ
Is greatly increased or decreased, and the behavior change of the vehicle 1 is quickly detected. The rear wheel 11 is driven by the vehicle 1 depending on the value of Kγ · γ.
Is steered so as to maintain the in-phase state despite the fact that the vehicle has turned, so that the vehicle 1 has a stable posture so as not to be swept by the side wind, and smoothly returns to the original course.

Next, the control for entering the garage at an extremely low speed will be described with reference to the flowchart of FIG. First, in step S1, the vehicle speed V and the target rear wheel steering angle ETO in the normal mode are set.
Is read, and the vehicle speed V is checked in step S2, and 10
In the case of an extremely low speed of km / h or less, the process proceeds to step S3. Then, the operation of the mode changeover switch 47 is checked, and if the switch is ON, the process proceeds to step S4 to determine the low speed mode. Therefore, first, the operation of the right-turn switch 48 is checked. If the switch is ON, the process proceeds to step S5. If the switch is OFF, the process proceeds to step S8 to check the operation of the left-turn switch 49.

Here, for example, as shown in FIG. 5, when the vehicle 1 located at a substantially right angle on the narrow road 72 in front of the garage 71 is right-turned forward to enter the garage, the left-turn switch 49 is turned on.
N Then, the process proceeds from step S8 to step S9, the rear wheel steering angle ER is compared with the maximum value -2 deg, and if it is less than the maximum value, the target rear wheel steering speed ωT is set in step S10, and the motor 31 is kept constant in step S11. Turn to the left at the speed. Then, when the finger is released from the switch 49, the process proceeds from step S8 to step S12, the motor is stopped, and a predetermined rear wheel steering angle ER is manually steered to the left. Also when the rear wheel steering angle ER reaches the maximum value, step S9
To Step S12, the motor is stopped, and in Step S13, the rear wheel steering angle ER in this case is set as the parameter ER1 when the low speed mode is released. Therefore, when the vehicle is traveling to the right, the rear wheels 11 are steered in reverse phase, the vehicle 1 makes a sharp turn effectively in the narrow road 72 in a state where the turning radius is small, and becomes substantially the same direction as the garage 71. enter.

After the front of the vehicle 1 has entered the garage 71 in this way, the right-turn switch 48 is turned on. Then, from step S4 to step S5, the maximum value of 2 deg is reached.
If it is less than the maximum value, the process proceeds to step S6 and the target rear wheel turning speed ωT is similarly set.
Turn 1 at a constant speed in the right steering direction. And switch 48
When the finger is released from, the process proceeds from step S4 to step S8 to step S12, the motor is stopped, and the steering wheel is manually steered to the right by a predetermined rear wheel steering angle ER.
Then, the rear wheel steering angle ER in this case is set as the parameter ER1 when the low speed mode is released. Therefore, the rear wheels 11 are steered in-phase this time, the turning radius of the vehicle 1 becomes very large, the turning posture becomes linear, and the vehicle 1 is prevented from coming into contact with the side wall of the garage 71 having a narrow rear end corner. In this way, when the vehicle 1 is put into the narrow garage 71 from the narrow road 72, it is possible to safely and easily put the vehicle 1 in the garage by avoiding the turning of the handle and the contact of the vehicle 1 with the garage wall.

When the vehicle 1 is to be taken out of the garage 71, the vehicle may be operated while operating the switches in the opposite manner to the above. When the mode changeover switch 47 is turned off after the vehicle 1 is exited, the process proceeds from step S3 to step S14, where the target rear wheel steering angle ETO in the normal mode is set to the target rear wheel steering angle ET and the low speed mode is immediately returned to the normal mode. Step S15
Go to and control normally. Therefore, when the steering wheel 21 is turned back, the rear wheels 11 are also returned to their original positions.

If the vehicle speed V rises to 10 km / h or more when the vehicle 1 is taken out of the garage 71, the process proceeds from step S2 to step S16 to check the elapsed time, for example, within 0.1 second. Advances to step S18, and the target rear wheel steering angle ET is set to the target rear wheel steering angle ET in the normal mode.
The parameter ER1 for canceling the low speed mode is added to O and set, and normal control is performed in step S15. When 0.1 second has elapsed, the process proceeds from step S16 to step S17, and the parameter ER1 at the time of releasing the low speed mode is decreased at a predetermined rate. Thus, in this case as well, the normal mode is restored, but by gradually returning to the target rear wheel steering angle ET in the normal mode while the vehicle is traveling, sudden changes in vehicle behavior are prevented.

In addition, when entering the garage by turning left or back,
Also in the case of parallel parking or the like, the manual rear wheel steering control can be similarly performed by operating the switch.

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

[0032]

As described above, according to the present invention,
In the rear wheel steering system that automatically steers the rear wheels by the anti-phase steering angle proportional control and the yaw rate feedback control, if the low speed mode is judged by operating the mode changeover switch at extremely low speed, the right cut switch or the left cut switch is operated. Motors are driven regardless of the target steering angle of the rear wheels, and the rear wheels can be manually steered arbitrarily, so the turning ability and turning posture of the vehicle can be adjusted, which allows for narrow garage access and parallel parking in narrow roads. It can be done safely and easily. Since only the mode change switch, the right cut switch and the left cut switch are added, the structure is simplified.

Further, if the function of the small turning property of the rear wheel steering is carried out by the manual operation in the low speed mode, the steering wheel angle and its angular velocity sensor become unnecessary. Therefore, the cost of the system can be significantly reduced.

[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 for setting a steering wheel angle coefficient and a yaw rate coefficient, a map for converting to a steering speed, and a map for setting an additional steering speed.

FIG. 4 is a flowchart showing manual rear wheel steering control in a low speed mode.

FIG. 5 is a diagram showing a garage entry state.

FIG. 6 is an explanatory diagram showing a turning center for rear wheel steering at an extremely low speed.

[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 70 low speed mode control unit

Claims (2)

[Claims] 1. A target rear wheel steering angle is calculated by at least a yaw rate coefficient set in the in-phase direction by a function of yaw rate and vehicle speed, a steering wheel angle coefficient set in a reverse phase direction by a function of vehicle speed, and this target is calculated. In the rear-wheel steering system that automatically steers the rear wheels by driving the motor based on the rear-wheel steering angle, the normal mode in which the rear wheels are steered according to the front-wheel steering angle There is a mode selector switch that switches to the manual mode, and a right-turn switch that steers the rear wheels to the right when the mode selector switch is switched to the manual mode, and a left-turn switch that steers the rear wheels to the left. If the low speed mode is determined by operating the mode selection switch when the vehicle speed is low, operating the right or left switch will cause the motor to move regardless of the target rear wheel steering angle. Driven to,
A method for controlling a rear wheel steering device, which comprises manually steering the rear wheels arbitrarily. 2. In the low speed mode, the mode is immediately returned to the normal mode by operating the mode changeover switch, and when the vehicle speed increases, the mode is returned to the normal mode while gradually returning to the target rear wheel steering angle of the normal mode. Item 2. A method for controlling a rear wheel steering system according to Item 1.