JPH02234881A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve the turning property and running stability in the early stage of rotation by detecting the steering angle acceleration of a steering handle, and correcting the steering quantity calculated by a control means with a correction quantity based on the steering angle acceleration. CONSTITUTION:A rear wheel steering device 4 has a driving means 24 for moving a relay rod 23 connected to left and right rear wheels on the both end parts in the axial direction, and the driving means 24 moves the relay rod 23 in the vehicle width direction by the positive rotation or reverse rotation of a step motor 27 controlled by a controller 25, when a clutch 29 is in the connected, state. The controller 25 calculates the rear wheel steering quantity with a determined steering ratio to the front wheel steering quantity. In this case, the steering angel acceleration of a steering handle is detected from the output of a handle steering angle sensor 31, and the above rear wheel steering quantity is corrected by a correction quantity according to the steering angle acceleration, and the step motor 27 is duty-controlled on the basis of the corrected rear wheel steering quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a four-wheel steered vehicle that steers the rear wheels in accordance with the steering of the front wheels.

(Prior art) Conventionally, as a rear wheel steering device of a vehicle, for example,
As disclosed in Publication No. 7-44568, etc., a drive means for steering the rear wheels, and a detection means for detecting the steering angle of the steering wheel or the lateral acceleration or yaw rate (angular velocity around the vertical axis of the vehicle) of the vehicle. and a control means that receives a signal from the detection means and controls the operation of the drive means is known.

Such rear wheel steering devices include those that only steer the rear wheels in the same phase as the front wheels, or ones that steer the rear wheels in the opposite phase to the front wheels at low vehicle speeds, and those that steer the rear wheels in the same phase as the front wheels at high vehicle speeds. There is something to steer. Such in-phase steering is usually proportional control in which the rear wheels are steered at the same time as the front wheels are steered, and while this in-phase proportional control can improve the running stability of the vehicle, it does not generate yaw rate. There is a problem that it becomes difficult and the ability to turn the head decreases.

Therefore, in order to solve this problem of reduced turning performance, we created a non-following state in which the rear wheels are not made to follow the front wheels at the beginning of a turn, that is, the rear wheels are not steered in the same phase direction as the front wheels. Delay control and phase reversal control have been proposed in which the rear wheels follow the front wheels and are steered in the same phase after the end of the steering.

The above delay control is described in, for example, Japanese Patent Application Laid-Open No. 58-1644.
As disclosed in Publication No. 77, the rear wheels are not steered for a predetermined period of time (delay time) from when the front wheels start steering, and are kept in a non-following state, and after the delay time has elapsed, the rear wheels are made to follow the front wheels and are steered to the same phase. By creating a non-following state in which only the front wheels are steered at the beginning of a turn, the necessary yaw rate is generated.

In addition, the phase reversal control described above puts the rear wheels in a non-following state in which the rear wheels are steered in an opposite phase to the front wheels for a predetermined period of time from the start of steering of the front wheels, and after the predetermined period of time has elapsed, the rear wheels are made to follow the front wheels and return to the same phase. In this way, the necessary yaw rate is generated by creating a non-following state in which the rear wheels are steered in an opposite phase to the front wheels at the beginning of a turn.

(Problems to be Solved by the Invention) When the driver turns the vehicle by operating the steering wheel, there are times when the driver wants to make the turn quickly and times when he wants to make the turn slowly. However, both the delay control and phase reversal control simply create a non-following state at the beginning of a turn to uniformly arouse the yaw rate.
This cannot be said to be an effective way to achieve harmony between turning performance and driving stability according to the driver's intention.

The present invention has been made in view of the above points, and its purpose is to focus on the fact that the driver's intention during turning as described above is most noticeable in the steering angle acceleration of the steering wheel, and to The present invention aims to provide a rear wheel steering device that controls the steering of the rear wheels based on this steering angle acceleration and can effectively balance turning performance and driving stability according to the driver's intention. .

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a rear wheel steering device for a vehicle that steers the rear wheels at least in the same phase as the front wheels in response to the steering of the front wheels. A control means for calculating a steering amount of the rear wheels using a predetermined steering ratio with respect to the steering amount, and controlling the steering of the rear wheels according to the steering amount; and a steering angle acceleration detection means for determining the steering angle acceleration of the steering wheel. ,
and a correction means for receiving a signal from the steering angle acceleration detection means and correcting the steering amount calculated by the control means by subtracting a value corresponding to the steering angle acceleration in an opposite phase direction. be.

(Function) With the above configuration, in the present invention, when the vehicle turns, the steering angle acceleration of the steering wheel that occurs at the initial stage is detected by the detection means, and the correction means receiving the signal from the detection means performs control. The steering amount is corrected by subtracting a value corresponding to the steering angle acceleration in an opposite phase direction from the steering amount calculated by the means, and the steering of the rear wheels is controlled by the control means in accordance with the corrected steering amount. . Here, the steering angle acceleration has a large value when the driver operates the steering wheel in a hurry, and a small value when the driver operates the steering wheel slowly. Therefore, at the beginning of a turn, the rear wheels are steered in a phase opposite to the front wheels to a degree that corresponds to the driver's intention, and a yaw rate is generated, thereby effectively improving turning performance.

On the other hand, after the initial stage of turning, the above-mentioned steering angular acceleration becomes zero or a negative value, so the control means maintains the steering amount calculated using the predetermined steering ratio, or changes it to the steering amount corrected in the same phase direction. The rear wheel steering is controlled accordingly. This ensures that the rear wheels are steered in the same phase as the front wheels, ensuring driving stability.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the overall configuration of a four-wheel steering vehicle according to an embodiment of the present invention. A rear wheel steering device 4 is provided.

The front wheel steering device 2 extends in the vehicle width direction, and has tie rods IIL, IIR and a knuckle arm 1 at both ends.
A relay rod 13 connected to the left and right front wheels IL and IR via 2L and 12R, a steering shaft 15 having a steering handle 14 at one end, and a U-turn of the steering shaft 15 in the axial direction of the relay rod 13. (that is, in the vehicle width direction), and is configured to steer the front wheels IL and IR by displacing the relay rod 13 in the vehicle width direction by operating the steering handle 14.

The rear wheel steering device 4 also includes a relay rod 23 extending in the vehicle width direction and having both ends connected to the left and right rear wheels 3L, 3R via tie rods 21L, 21R and knuckle arms 22L, 22R, respectively. , a driving means 24 for moving the relay rod 23 in its axial direction (that is, in the vehicle width direction).
and a controller 25 as a control means for controlling the operation of the driving means 24, and when the driving means 24 or the controller 25 is in operation, the relay rod 23 is moved to a neutral position (
In other words, the position where the rear wheels 3L and 3R are in a straight-line state with zero steering angle)
A neutral position return means 26 made of a spring or the like is provided for holding the neutral position.

The driving means 24 is a step motor 2 that can rotate in forward and reverse directions.
7, and the rotational force of the step motor 27 is transferred to the relay rod 2.
3 and the power transmission mechanism 28
and a clutch 29 interposed therein. Then, when the clutch 29 is in the connected state, the step motor 2
7, the relay rod 23 is moved left and right in the vehicle width direction to steer the rear wheels 3L and 3R.

The controller 25 controls the steering of the rear wheels 3L and 3R by controlling the operation of the step motor 27 and the switching of the clutch 29 on and off.
A steering angle sensor 31 detects the steering angle of the vehicle (hereinafter referred to as the steering angle), a vehicle speed sensor 32 detects the vehicle speed, and an encoder 33 detects the rotational position of the step motor 27.
, a pair of front and rear G sensors 3 each detecting the lateral acceleration of the vehicle body.
4a. Detection signals from rear wheel steering angle sensors 35 and the like that detect the steering angles of the rear wheels 3L and 3R from the position of the relay rod 34bs and the relay rod 23 in the vehicle width direction are manually input.

FIG. 2 is a block diagram of the controller 25. As shown in FIG. In the figure, 41 is a first control section that performs feedforward control based on signals from the steering wheel angle sensor 31 and vehicle speed sensor 32 as driving operation information, and based on the output signal from this control section 41. This controls the steering of the rear wheels.

The result of this control is detected by a detection unit 42 consisting of a sensor such as an encoder 33, and noise is removed by a filter 43. The control results after noise removal are stored in the storage unit 44.
The reference model ζ of rear wheel steering stored in the reference model ζ of rear wheel steering is compared, and if the two are different, feedback control is performed by the second control unit 45.

The feedforward control of the first control section 41 is performed by ff
This is carried out according to the flowchart shown in Figure i3. That is, first, in step S1, the vehicle speed V and the steering wheel steering angle θ are determined.
After reading F, a steering ratio K, which is the ratio of the amount of steering of the rear wheels to the amount of steering of the front wheels, is calculated in step S2. The above-mentioned steering ratio K is determined based on a pre-stored map as shown in FIG. This steering ratio K is set so that at low vehicle speeds, the rear wheels are steered in a negative direction, that is, in the opposite phase to the front wheels, and at high vehicle speeds, the rear wheels are steered in a positive direction, that is, in the same phase as the front wheels. .

Subsequently, in step S3, the rear wheel steering amount θRl(-K・
θF), and in step S4, the steering angle θF is set to 1.
The steering wheel angular velocity θF is calculated by step-level differentiation, and the steering wheel steering angular acceleration υF is calculated by second-order differentiation. Above step S
Although not shown, the calculation section 4 is composed of a differential circuit or the like, and a steering angle acceleration detection means 51 detects the steering wheel steering angle acceleration υF using this calculation section and the steering wheel steering angle sensor 31. It is configured.

Next, in step S5, a rear wheel steering correction amount θR2 is calculated. This steering correction amount θR2 is determined by the following formula.

θR2−DI −υp +D2 ・θF ・
...(1) However, DI and D2 are positive coefficients.

Then, in step S6, the steering correction amount θR2 is calculated from the rear wheel steering amount θR1 calculated in the step S3.
The steering amount θRO of the rear wheels is calculated by subtracting . That is,
The rear wheel steering amount θ1−0 after this correction is θI? 0-θR
l-θR2 - θRl-Dl - yv -D2 -θF- (2). The arithmetic unit in steps S5 and S6 receives the signal from the steering angle acceleration detection stage 51 and determines the amount of rear wheel steering θ#? A correction means 52 is configured to subtract the steering correction amount θR2 from 1 to obtain the rear wheel steering amount θ1?0.

After that, in step S7, a rear wheel steering amount signal is output,
Return.

Therefore, when the steering of the rear wheels 3L and 3R is controlled according to such flowchart 1, the steering amount (steering angle) θRO of the rear wheels when the vehicle turns is determined by the above ('2J
As shown in the formula, values corresponding to the steering wheel angular acceleration υF and the steering wheel angular velocity θF are subtracted in the opposite phase direction from the steering amount θRl calculated using a predetermined I·ν steering ratio. FIG. 5 shows the steering amount θRO of the rear wheels and the steering wheel steering under such control, especially when turning at high speed (that is, when the steering ratio K is on the same phase side in FIG. 4 in a steady turning state). Fig. 3 shows curves of changes over time of angular velocity θF and steering wheel angular acceleration υF. In addition, in FIG. 5, the amount of steering of the rear wheels (the amount of actual steering) θRO
In addition to showing the change curve A of
? 1 change curve B is shown by a broken line, and for reference, the value obtained by subtracting only the value corresponding to the steering wheel angular velocity θF from the above-mentioned steering amount θR1 in the opposite phase direction (-θl?1-D2 ・θ
F) variation song 1i! C is shown by a phantom line.

As can be seen from Figure 5, when turning while driving at high speed, the rear wheels 3L and 3R are steered in the opposite phase to the front wheels IL and IR at the beginning of the turn, which generates a yaw rate and improves turning performance. On the other hand, after the initial stage of turning when a certain amount of yaw rate occurs, the rear wheels 3L and 3R are steered in the same phase as the rear wheels IL and IR, thereby improving running stability.

Moreover, the amount of steering of the rear wheels 3L and 3R in the opposite phase direction at the beginning of the turn is 〇l? 0 increases when the driver operates the steering wheel 14 rapidly (that is, when the steering wheel angular acceleration υF is large), and when the driver operates the steering wheel 15 slowly (that is, when the steering wheel angular acceleration υF is small). ), the yaw rate at the beginning of the turn is set to a value that corresponds to the driver's intention, and it is possible to improve turning performance and driving stability in an H effect.

Furthermore, when turning a vehicle (steering wheel operation), it is normal to turn the steering leg handle 14 in one direction and then return it in the opposite direction.When starting this return operation, the vehicle becomes unstable, but this implementation In the case of the example, the steering amount θRO of the rear wheels at the start of the return operation is larger in the same phase direction than the steering amount θR1 before correction, so an unstable state can be effectively prevented. Can be done.

In addition, in the case of the above embodiment, in particular, a value corresponding to the steering wheel steering angular velocity θF is also subtracted in the opposite phase direction from the steering amount θRl calculated using a predetermined steering ratio to obtain the rear wheel steering amount θRO.
By calculating , the rear wheels 3L and 3R are steered with a predetermined time delay from the start of operation of the steering wheel 14 or the start of steering of the front wheels IL and IR, so that so-called delay control is performed at the same time. It is possible to further improve the turning performance and running stability of the vehicle.

It should be noted that the present invention is not limited to the above embodiments, but includes various other modifications.

For example, in the embodiment described above, the correction means 52 subtracts values corresponding to the steering wheel angular acceleration υF and the steering wheel angular velocity θF from the steering amount θR1 calculated using a predetermined steering ratio in opposite phase directions, and However, in the present invention, the rear wheel steering amount θRO may be calculated by subtracting only a value corresponding to the steering wheel angular acceleration υF in the opposite phase direction.

Further, in the above embodiment, the present invention is applied to the rear wheel 3L at low vehicle speed.
, 3R are steered in the opposite phase to the front wheels IL, IR, and the rear wheels 3L, 3R are steered in the same phase as the front wheels IL, IR at high vehicle speeds. Of course, it can also be applied to cases where the friction coefficient is detected and the rear wheels are steered to the same or opposite phase as the front wheels depending on the magnitude, or when the rear wheels are steered only to the same phase as the front wheels. It is.

(Effects of the Invention) As described above, according to the rear wheel steering device of the present invention, the steering angle acceleration of the steering wheel is detected, and the steering angle acceleration is subtracted from the steering amount calculated by a at a predetermined steering ratio. By controlling the steering of the rear wheels, the rear wheels are steered in the opposite phase to the front wheels, especially at the beginning of a turn, with a magnitude that corresponds to the driver's intention, improving maneuverability and driving stability. It is possible to significantly improve the performance.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and therefore, Fig. 1 is an overall configuration diagram of a four-wheel steering vehicle, Fig. 2 is a block diagram of a controller, Fig. 3 is a flowchart of rear wheel steering control, and Fig. FIG. 4 is a map diagram for setting the steering ratio, and FIG. 5 is a characteristic diagram showing the change characteristics of the steering amount of the rear wheels, the steering wheel steering angular velocity, and the steering wheel steering angular acceleration when the vehicle turns. IL, IR...front wheel, 3L, 3R...rear wheel, 4...rear wheel steering device, 14...steering handle, 25...controller (control means), 51...studder angle acceleration Detection means, 52... Correction means. 1L, IR... Front wheels 3L, 3R... Rear wheels 4... Rear wheel steering device 14... Steering handle 25... Controller (control means) 51... Steering angle acceleration detection means 52...・Correction method number one! il diagram diagram

Claims (1)

[Claims] (1) A rear wheel steering device for a vehicle that steers the rear wheels at least in the same phase as the front wheels in response to the steering of the front wheels, which calculates the amount of steering of the rear wheels using a predetermined steering ratio with respect to the amount of steering of the front wheels. ,
a control means for controlling the steering of the rear wheels according to the amount of steering;
A steering angle acceleration detection means for detecting the steering angle acceleration of the steering wheel; and upon receiving a signal from the steering angle acceleration detection means, the steering amount calculated by the control means is converted into a value corresponding to the steering angle acceleration in an opposite phase direction. A rear wheel steering device for a vehicle, comprising a correction means for subtracting and correcting.