JP2619656B2 - Control method of four-wheel steering device for automobile - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a four-wheel steering device for an automobile.

2. Description of the Related Art In a vehicle, a four-wheel steering system in which a rear wheel is steered in a direction opposite to the front wheel steering direction (reverse phase steering) or in the same direction (in-phase steering) in response to front wheel steering by a steering wheel operation. Various devices have been developed and known in the past. In such a four-wheel steering device, a deceleration state during turning is detected, and when braking and deceleration is performed during turning, the steering angle of the rear wheels in the same phase turning direction is increased. Japanese Patent Application Laid-Open No. Sho 60-135370 discloses a vehicle in which the vehicle body is prevented from swinging while turning.

Problems to be Solved by the Invention However, in the braking deceleration state during turning, the vehicle behavior greatly differs depending on which wheel is in a locked state or a state close to the locked state. Control to increase the steering angle of
In some cases, steering stability may be impaired.

The present invention has as its main object to address the conventional problems as described above.

Means for Solving the Problems The present invention relates to a four-wheel steering system for an automobile in which a rear wheel is automatically steered in accordance with steering of a front wheel. Provide a sensor,
At the time of braking operation during turning of the car, the slip rate of each wheel is obtained from the rotation speed information of each wheel detected by the wheel speed sensor, and the slip rate of the turning inner wheel of the front wheel is larger than the slip rate of other wheels to some extent. If there is, control is performed to reduce the amount of steering of the rear wheels in the in-phase turning direction.

In an automobile, when braking only during turning, when the turning inner wheel of the front wheel is locked, a strong understeer characteristic is exhibited. However, as described above, the slip ratio of the turning inner wheel of the front wheel is more than a certain degree more than the slip ratio of other wheels (for example, 1.2). When it is large, it is determined that only the turning inner wheel of the front wheel is approaching the locked state, and control for decreasing the steering amount of the rear wheel in the in-phase turning direction is performed in advance, so that the strong understeer is obtained. The characteristics can be canceled beforehand and the steering stability can be improved.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a steering wheel, 2 denotes a front wheel, and a known front wheel steering system extending from the steering wheel 1 to the front wheel 2 includes a control valve 3 that operates according to the steering torque of the steering wheel 1; There is provided a known hydraulic power steering device including a power cylinder 5 having left and right oil chambers into which the discharge hydraulic pressure of the hydraulic pump 4 is introduced into one of the right and left by operation.

Reference numerals 6a and 6b denote left and right oil pressure sensors for detecting the oil pressures of the left and right oil chambers of the power cylinder 5. Left and right oil pressure signals detected by the oil pressure sensors 6a and 6b are input to the operational amplifier 7, and the left and right oil pressure signals are detected. The oil pressure difference is calculated, and a signal corresponding to the oil pressure difference is input to the control unit 9.

In the above description, the hydraulic power steering device generates a hydraulic assisting force in accordance with the steering torque of the steering wheel 1, and thus the hydraulic pressure difference corresponds to the steering torque of the steering wheel 1. The signal input to 9 is a steering force signal corresponding to the front wheel steering force.

Reference numeral 8 denotes a vehicle speed sensor that emits a vehicle speed signal according to the vehicle speed. The vehicle speed signal is also input to the control unit 9.

The control unit 9 determines a rear wheel steering angle target value from the input steering force signal and the vehicle speed signal based on a vehicle speed-steering force-rear wheel steering angle characteristic set in advance, and based on the determined value, a motor or the like is used. An output signal is issued to the rear wheel steering actuator 10, and the rear wheel 13 is steered via an electromagnetic clutch 11, for example, a rear wheel steering mechanism 12 including a link mechanism, and the rear wheel detects the rear wheel steering angle. By the feedback control based on the rear wheel steering angle signal of the wheel steering angle sensor 14, the steering is turned to the steering angle according to the target value.

15L, 15R and 16L, 16R are wheel speed sensors for detecting the rotational speeds of the left and right front wheels and the left and right rear wheels, respectively, and wheel speed signals ω _FL , ω _FR and ω _{RL of} these wheel speed sensors.
ω _RR is input to the control unit 9.

In FIG. 1, reference numeral 17 denotes a motor rotation speed sensor.
When a motor is used as the rear wheel steering actuator 10 as shown in the figure, the motor speed is controlled by the signal of the motor rotation speed sensor 17. A brake switch 18 detects a braking operation.

In the above description, when the front wheels are steered by operating the steering wheel during traveling at a certain vehicle speed, the oil pressure difference detected by the oil pressure sensors 6a, 6b, that is, the steering force signal is input to the control unit 9, and the control unit 9, for example, Assuming that the hydraulic pressure difference (steering force) -rear wheel steering angle setting characteristic shown in FIG. 3 is indicated by the solid line a in FIG. 3, the rear wheel steering angle target value is determined based on the setting characteristic a. An output is generated, and the rear wheels are steered according to the target value determined above.

When the control unit 9 detects that a braking operation has been performed during the above-mentioned turning, for example, by a signal such as an ON operation of a brake switch 18, the control unit 9 detects a slip state of the wheel by a method as shown in FIG. The control for changing the wheel steering amount is performed.

That is, when braking during turning, first, each wheel speed sensor
15L, 15R, 16L, 16R, the signals from the wheels are used to detect the rotational speed of each wheel, respectively, and the slowest rotational speed ωa, the second slowest rotational speed ωb, and the fastest rotational speed ωc are determined. It is determined whether or not the wheel having the rotation speed ωa is the front turning inner wheel.

If the rotational speed of the front inner wheel is ωa, the slip rates Sa and Sb of ωa and ωb are calculated based on the fastest rotational speed ωc. When Sa ≧ Sb · K (where K is a constant and K is set to about 1.2), it is determined that only the inner turning front wheel is in the wheel locked state. Then, the hydraulic pressure difference (steering force) -rear wheel steering angle characteristic is changed from the characteristic in the standard state (initial setting function) as shown by the solid line a in FIG. 3 to the characteristic as shown by the dotted line b. Then, the rear wheel steering angle target value is determined by the characteristic indicated by the dotted line b, and the rear wheel is steered according to the determined value, whereby the steering amount of the rear wheel in the understeer direction (in-phase turning direction) is greatly reduced. The strong understeer characteristics caused by the turning inner wheel lock of the front wheels are canceled beforehand, and stable running can be performed.
The steering stability can be improved.

In an automobile equipped with a hydraulic power steering apparatus as shown in FIG. 1, it is easiest to detect the steering force from the hydraulic pressure difference of the power cylinder as shown in the figure. However, the steering assist is performed by rotating the electric motor. In the case of the vehicle equipped with an electric power steering device, the steering force can be detected by the motor torque obtained from the current value flowing through the electric motor. In the case of the vehicle without the power steering device, for example, the steering shaft is used. The steering force may be detected from the torque acting on the vehicle or the cornering force of the front wheels, and the front wheel steering angle may be detected instead of the steering force, and the rear wheel steering angle target value may be detected from the front wheel steering angle and the vehicle speed. The present invention is also applicable to a rear wheel steering device that determines the following.

The actuator 10, the rear wheel steering mechanism 12, and the like are not limited to the illustrated embodiment, and any conventionally known one can be used.

As described above, according to the present invention, in the four-wheel steering system, the slip state of the wheels during braking during turning is detected, and the amount of steering of the rear wheels in the same phase turning direction is determined by which of the wheels is locked. The change control is finely controlled depending on whether the vehicle is under control, which prevents the strong understeer characteristics caused by the lock of the front inner wheel turning and improves the steering stability, and is practical in terms of ensuring safe driving. It can have a great effect.

[Brief description of the drawings]

FIG. 1 is an explanatory plan view showing an embodiment of the present invention, FIG. 2 is a flowchart showing a control mode according to the present invention, and FIG. 3 is a diagram showing an example of a steering force-rear wheel steering angle characteristic. 1 ... handle, 2 ... front wheel, 5 ... power cylinder, 6
a, 6b: hydraulic pressure sensor, 7: operational amplifier, 8: vehicle speed sensor, 9: control unit, 10: rear wheel steering actuator, 13: rear wheel, 14: rear wheel steering angle sensor , 15L, 15R, 16L, 16R ... wheel speed sensor, 18 ... brake switch.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B62D 113: 00

Claims (1)

(57) [Claims] 1. A four-wheel steering system for an automobile in which a rear wheel is automatically steered in accordance with steering of a front wheel, a wheel speed sensor for detecting rotation speeds of front, rear, left and right wheels is provided. At the time of braking operation during turning, the slip ratio of each wheel is obtained from each signal of the wheel speed sensor, and when the slip ratio of the inner wheel of the front wheel is larger than the slip ratio of the other wheels to some extent, the front wheel of the rear wheel A control method for a four-wheel steering apparatus for an automobile, wherein control is performed to reduce a steering amount in the same direction as a steering direction.