JP3003716B2 - Vehicle rear wheel steering system - Google Patents

Abstract

PURPOSE:To provide a rear wheel steering mechanism capable of attaining both driving stability and direction changing characteristic during slip control by employing a second compensation means for compensating the rear wheel steering characteristic in the opposite phase direction so that the compensation amount in the same phase direction decreases with the increase in the steering wheel operation angle. CONSTITUTION:A control unit U1 changes the setting of steering ratio characteristic of the rear wheels 2RL and 2RR relative to the front wheels 2FL and 2FR according to the ABS operating conditions and control conditions of brake mechanism 23 working on each wheel. Steering ratio is compensated in the opposite phase direction by a compensation value KC and a compensation value KD to improve danger avoiding property by improving direction changing characteristic during the operation of the ABS. The compensation value KC is set so that its negative value increases with the increase in the steering angle QH. The compensation value KD is set so that its negative value increases with the increase in the steering angle operating speed dQH/dt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a four-wheel steering vehicle, and more particularly, to an anti-skid brake control system for preventing skid or locking of wheels during vehicle braking, or a vehicle. A slip control device such as a traction control system for preventing idling of the drive wheels at the time of starting and sudden acceleration is provided, and the rear wheel steering characteristics are corrected in accordance with the operation of the slip control device. The present invention relates to a rear-wheel steering device capable of achieving both running stability and turning performance during the slip control in a four-wheel steering vehicle.

[0002]

2. Description of the Related Art Conventionally, a front wheel steering mechanism for steering a front wheel and a rear wheel steering mechanism for steering a rear wheel have been provided, and the steering angle of the rear wheel is determined according to the steering angle of the front wheel and the vehicle speed. In low-speed running, the rear wheels are steered in the opposite phase with respect to the front wheels to improve small turning performance. Speed-sensitive type 4 that prevents side skidding and improves running stability
Wheel steered vehicles are known.

[0003] In addition, an operating oil pressure (brake fluid pressure) for a brake device of each wheel is detected so as to secure a maximum frictional force between each wheel and a road surface by detecting a state in which the rotational speed of each wheel drops during braking. An anti-skid brake control system (hereinafter abbreviated as "ABS") is known which is configured to control skid or lock of a wheel caused by sudden braking or braking on a low μ road. I have.

Further, by detecting a slip state of the drive wheel at the time of starting or sudden acceleration, a throttle opening of the engine and a brake device for the drive wheel are ensured so that the maximum frictional force between the drive wheel and the road surface can be secured. There is known a traction control system (hereinafter abbreviated as "TRC") configured to control the operating oil pressure for the vehicle and thereby secure the road surface grip force of the drive wheels at the time of starting or sudden acceleration.

Further, in a four-wheel steering vehicle equipped with an ABS, the rear wheel steering characteristics are changed based on the operation or non-operation of the ABS in order to improve the steerability of the vehicle during sudden braking. That perform cooperative control between an ABS and a rear wheel steering device. Such a rear-wheel steering device of a four-wheel steering vehicle corrects a predetermined rear-wheel steering characteristic during normal running determined as a function of vehicle speed or the like in an in-phase direction at the time of operating the ABS, so that a sudden braking operation is performed. This prevents the vehicle from swinging ass. (For example, JP-A-62-2
No. 12471).

[0006]

By the way, in a conventional four-wheel steering vehicle in which the above-described cooperative control of the rear wheel steering device and the slip control device is performed, for example, ABS of the ABS is required to improve running stability. Since the rear wheel steering characteristics are corrected in the same phase direction with the operation, AB
In order to avoid danger during the S operation, there is a possibility that the turning performance of the vehicle may be insufficient even if the steering wheel is largely operated. Also,
In a speed-sensitive four-wheel-steering vehicle, the rear wheels are steered in the same phase direction with respect to the front wheels during high-speed running. Therefore, when the vehicle spins due to braking during high-speed running, the vehicle steers away from the spin by counter-steering operation. However, there is a problem that the counter steer operation is not effective.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a rear wheel steering system for a vehicle in which danger avoidance by operating a steering wheel and anti-spin performance by counter steering are improved while running stability during slip control is ensured. And

[0008]

According to the first aspect of the present invention, there is provided means for correcting the rear wheel turning characteristics in the same phase direction in accordance with the operation of the slip control device.
The object is achieved by providing a means for correcting the rear wheel turning characteristics in the in-phase direction so that the correction amount in the in-phase direction increases as the steering wheel speed increases.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an overall configuration diagram schematically showing a rear wheel steering device according to an embodiment of the present invention. In FIG. 1, left and right front wheels 2FL and 2FR of a vehicle 1 are linked by a front wheel steering mechanism A, and left and right rear wheels 2RL and 2RR are linked by a rear wheel steering mechanism B.

The front wheel steering mechanism A is composed of a pair of knuckle arms 3FL, 3FR and tie rods 4FL, 4FR, and a relay rod 5F connecting the tie rods 4FL, 4FR to each other. Front wheel steering mechanism A
The rack (not shown) connected to the relay rod 5F and the pinion 6 connected to the steering shaft 7
A front and rear steering mechanism A displaces the relay rod 5F in the left and right direction in accordance with the amount of operation displacement of the steering wheel 8, that is, the steering angle of the steering wheel. Front wheel 2FL, 2F
It is configured to steer R.

The rear wheel steering mechanism B steers a pair of knuckle arms 3RL, 3RR and tie rods 4RL, 4RR, a relay rod 5R connecting these tie rods 4RL, 4RR to each other, and left and right rear wheels 2RL, 2RR. A servo motor 10 serving as a drive source for causing the servo motor 10 to transmit the driving force of the servo motor 10 to the relay rod 5R. The left and right rear wheels 2RL and 2RR are steered by displacing the relay rod 5R in the left and right direction via the relay 11.

The rear wheel steering mechanism B includes a clutch 12 interposed in the link mechanism 11 for releasing the link between the servo motor 10 and the relay rod 5R, and a relay rod 5R.
And a neutral holding means 9 comprising a spring 9a interposed between the motor and the vehicle body to constantly urge the relay rod 5R in the neutral direction. In case of failure, clutch 1
2 is released and the relay rod 5R is
Is forcibly held in the neutral position, whereby the vehicle can be operated as a normal front-wheel steering vehicle.

The vehicle 1 includes a steering angle sensor 13 for detecting a steering wheel steering angle, a vehicle speed sensor 14 for detecting a vehicle speed, an encoder 17 for detecting a rotational position of the servomotor 10, A rear wheel steering angle sensor 18 for detecting the displacement of the relay rod 5R is provided.
Further, there is provided a control unit U1 to which the detection results of the steering angle sensor 13, the vehicle speed sensor 14, the encoder 17 and the rear wheel steering angle sensor 18 are input, and the control unit U1 controls the servo motor 10 based on the detection results of the sensors. The rotation is controlled.

That is, the control unit U1
It incorporates a vehicle speed sensitive rear wheel turning control device, and the rear wheel turning control device controls the front wheels 2F based on a predetermined turning ratio characteristic.
The steering ratio of the rear wheels 2RL and 2RR to the steering wheel ratio L and 2FR is set with a predetermined steering ratio characteristic as a function of the vehicle speed V detected by the vehicle speed sensor 14, and the set rear wheel steering ratio K = θ _R The target rear wheel turning angle is set based on / θ _F (θ _F is the front wheel turning angle, θ _R is the rear wheel turning angle) and the steering angle θ _H detected by the steering angle sensor 13.

The control unit U1 operates the servomotor 10 via the servomotor driving circuit based on the target rear wheel turning angle set in this way, and controls the rotational position of the servomotor 10 detected by the encoder 17 and The rear wheels 2RL and 2RR are steered while the displacement of the relay rod 5R detected by the rear wheel steering angle sensor 18 is monitored by the rear wheel steering control device.

FIG. 2 is an overall configuration diagram showing an outline of an anti-skid brake control system mounted on the vehicle shown in FIG.

In FIG. 2, the left and right front wheels 2F of the vehicle 1 are shown.
L, 2FR and the left and right rear wheels 2RL, 2RR, a disk rotor 23a that rotates integrally with each wheel, and a caliber that brakes the rotation of each disk rotor 23a when brake hydraulic pressure (brake fluid pressure) is supplied. 23b are arranged respectively.

The vehicle 1 is, during braking operation, i.e., when the depression brake pedal, braking for each braking device 23
An ABS configured to individually and variably adjust the dynamic oil pressure is provided. The ABS is provided on each wheel, and an acceleration sensor 24 for detecting the deceleration of the vehicle 1. Wheel speed sensor 25 for detecting each
A control unit U2 to which the detection results of these sensors 24 and 25 are input, and a control unit U
2 based on the control signal output from
Control valve 26 for variably controlling the braking hydraulic pressure supplied to the hydraulic control valve 3
And a hydraulic unit (not shown) for supplying brake fluid set at a predetermined pressure to the hydraulic control valve 26.

The control unit U2 controls each wheel 2FL, 2FR, 2
A predetermined slip with respect to the vehicle speed V such that the wheels and the road surface generate an optimal braking force based on the rotation speed of a predetermined wheel among the rotation speeds of RL and 2RR, for example, the rotation speed of the fastest wheel. Setting a reference rotation speed with a rate,
The reference rotational speed is compared with the rotational speed of each wheel detected by each wheel speed sensor 25, and the hydraulic pressure control valve 26 controls the brake fluid pressure for each wheel so as to prevent skid or lock of each wheel. I do.

On the other hand, the ABS control unit U2
As shown in FIG. 1 and FIG. 2, a signal S indicating the ABS operation state and the road surface μ state is output to the control unit U1 of the rear wheel steering device, and the control unit U1 AB of brake device 23
The front wheels 2FL, 2F according to the S operation state and the control state
The steering ratio characteristics of the rear wheels 2RL and 2RR with respect to R are configured to be changed.

FIG. 3 is a diagram showing a turning ratio characteristic set by a rear wheel turning control device incorporated in control unit U1. In FIG. 3, a curve I shows a normal steering ratio characteristic set based on the vehicle speed V when the ABS is not operating, and a curve II shows a normal steering ratio K being a constant value due to the ABS operation. The state corrected by the correction value K _A is shown. Note that this correction value K _A is a positive value in a rear-wheel drive vehicle (FR vehicle), and therefore the curve II is corrected to the same phase as the steering ratio K of the curve I as shown in FIG. However, in a front-wheel drive vehicle (FF vehicle), the correction value K _A
Is corrected to the negative phase side of the steering ratio K of the curve I.

Furthermore curve III of FIG. 3, the correction value K _B is changed in accordance with the road surface condition during the ABS is active,
This shows a state in which the steering ratio has been corrected to the same phase as the curve II. The correction value K _B, as shown in FIG. 4, are set as a function of the road surface μ is determined by the control unit U2 on the basis of the fall state of the wheel speed during ABS operation. Thus the correction value of the steering ratio with the ABS operation is a ± K _A + K _B, since the absolute value of K _A in the normal state is set to a value smaller than the value of K _B, the actuation of the ABS As a result, the steering ratio is corrected in the same phase direction.

Further, in this embodiment, a correction is made to improve the turning performance when the steering wheel is operated during the ABS operation and to improve the danger avoidance. In this case, the negative value increases as the correction value K _C set to increase the negative value as the steering wheel angle θ _H increases and / or the steering wheel speed dθ _H / dt increases. the set correction value K _D as the steering ratio is corrected in the opposite phase direction than the curve III in FIG. That is, A
The correction amount of the steering ratio corrected in the same phase direction with the operation of the BS is a correction value K _C that is a function of the steering wheel angle θ _H and / or a K _D that is a function of the steering wheel speed dθ _H / dt.
Will decrease.

Further, in this embodiment, when the steering wheel is turned back, that is, when the polarity of the steering wheel angle θ _H does not match the polarity of the steering wheel speed dθ _H / dt, θ _H and d
Since the product of θ _H / dt becomes negative, it is determined that the steering wheel is being turned back, and the correction value K _E that increases as the steering wheel turning speed increases increases.
As the steering wheel return speed increases, the turning ratio is corrected to be larger in the same phase direction, thereby improving the anti-spin performance by counter-steering. Therefore, if the thus corrected steering angle ratio K _T is off the _{handle, K T = ± K A +} K B -K C -
K _D, and when switching back the handle, K _T = ± K _A +
The _{K B -K C -K D + K} E.

Next, a routine for correcting the rear wheel steering characteristics by the control unit U1 will be described with reference to the flowcharts of FIGS.

In FIG. 5, first, at step S1, the vehicle speed V is read from the output of the vehicle speed sensor 14, and at the next step S1.
In step 2, the rear wheel turning ratio K corresponding to the vehicle speed V is set based on the curve I in the figure. In the next step S3, it is checked whether or not the ABS has been operated. If the ABS has not been operated, the process directly proceeds to step S12 in FIG. 6, and the calculation is executed with the steering ratio K _T = K. Next, when it is determined in step S3 that the ABS has been activated, a constant correction value K _A is set in step S4, and the road surface μ is read in step S5,
In step S6 the map of FIG. 4 sets the correction value K _B as a function of mu. Next, referring to FIG. 6, the steering wheel angle θ _H is read in step S7, and the steering wheel speed dθ _H / dt is calculated in step S8. In the next step S9, it is checked whether or not the product of the steering angle θ _H and the steering speed dθ _H / dt is negative, that is, whether or not the steering wheel is turned back. Step S10
To set a correction value -K _C at which the negative value increases as the steering wheel angle θ _H increases, and further increases the negative value as the absolute value of the steering wheel speed dθ _H / dt increases at step S11. and setting the correction value -K _D to, for calculating a steering angle ratio K _T after correction in step S12 from the equation _{K T = ± K a + K} B -K C -K D.

On the other hand, when it is determined in step S9 that the value of θ _H × dθ _H / dt is negative, that is, when the steering wheel is turned back, the process proceeds to step S13, where the absolute value of the steering wheel speed dθ _H / dt is calculated. set the correction value K _E which increases according to an increase, by setting the correction value -K _D in the next step S11, wherein K _T = ± a steering angle ratio K _T after correction in step S12
Computed from _{K A + K B -K D +} K E.

The above is the correction control routine of the rear wheel turning ratio associated with the operation of the ABS in the four-wheel steering vehicle equipped with the ABS. The steering angle θ _H and the steering speed dθ _H /
AB by correcting the rear wheel turning characteristics according to dt.
It is possible to improve running stability during S control, danger avoidance by steering wheel operation, and spin prevention by counter steer. In a four-wheel steering vehicle equipped with a TRC, the same effect can be obtained by performing the same correction.

[0030]

According to the first aspect of the present invention, as the steering wheel turning speed at the time of turning back the steering wheel is increased, the rear wheel turning characteristic is corrected in the same phase direction, so that the anti-spin performance by counter steering is improved. be able to.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram schematically showing a rear wheel steering device of a vehicle according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing an outline of an anti-skid brake control system mounted on the vehicle shown in FIG.

FIG. 3 is a diagram showing a turning ratio characteristic set in the rear wheel steering device shown in FIG. 1;

FIG. 4 is a map showing a steering ratio correction value corresponding to a road surface μ;

FIG. 5 is a flowchart showing a part of a correction control routine of a rear wheel turning characteristic associated with the operation of the ABS.

FIG. 6 is a flowchart showing the remaining part of the flowchart of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Vehicle 2FL Left front wheel 2FR Right front wheel 2RL Left rear wheel 2RR Right rear wheel 9 Neutral holding means 10 Servo motor 13 Handle steering angle sensor 14 Vehicle speed sensor 18 Rear wheel steering angle sensor 23 Brake device 24 Acceleration sensor 25 Wheel speed sensor

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 117: 00 (72) Inventor Ken Murai 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Hiroyuki Noda 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (56) References JP-A-62-238171 (JP, A) JP-A-62-18368 (JP, A) JP-A 63 −112284 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00

Claims (1)

(57) [Claims] 1. A four-wheel steering vehicle having a slip control device such as an anti-skid brake control system for preventing skid or locking of a wheel during braking of a vehicle. A first correcting means for correcting the rear wheel steering characteristic in the same phase direction; and, when turning back the steering wheel, the rear wheel rotation so that the correction amount in the same phase direction increases with an increase in the steering wheel angular velocity. A four-wheel steering device for a vehicle, comprising: a second correction unit that corrects steering characteristics in the same phase direction.