JPH0715817Y2 - Four-wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a four-wheel steering device that steers rear wheels in response to steering of front wheels.

(Prior Art) In this type of four-wheel steering system, a power cylinder that steers the rear wheels is operated by a servo valve that is operated by a servomotor controlled by a control device, and the rear wheels are set to the steering angle and vehicle speed of the front wheels. Relatedly, at high speeds, there is one that steers in-phase with the front wheels.

(Problems to be Solved by the Invention) It is not preferable to steer the vehicle body in a direction opposite to the lateral inclination direction in a state where the vehicle body is inclined laterally, because running stability is deteriorated particularly at a high speed. In the above-mentioned prior art, since the rear wheel steering is performed by the control device in association with the front wheel steering angle and the vehicle speed, when the lateral inclination occurs due to the centrifugal force during the curved traveling, the turning radius of the vehicle increases. It is also possible to correct the rear wheel steering angle so as to prevent the driving stability from being deteriorated. However, when lateral inclination occurs due to the state of the load or the inclination of the road surface, it cannot be detected to prevent the traveling stability from deteriorating. An object of the present invention is to detect the lateral inclination of a vehicle body directly, and thereby to steer the vehicle in a direction opposite to the lateral inclination direction at a high speed so that the running stability of the vehicle is not deteriorated.

For this purpose, the four-wheel steering system according to the present invention is operated by the rear wheel power cylinder 24 for steering the rear wheels 26a, 26b and the servomotor 46, as illustrated in the accompanying drawings. The servo valve 21 for controlling the supply and discharge of the working fluid from the supply pump 30b to and from the working chambers of the rear wheel power cylinder 24, and the front wheels 16a, 16
Four-wheel steering consisting of a control device 40 that operates the servo motor 46 according to the steering angle and vehicle speed of b to steer the rear wheels in phase with the front wheels at high speed via the servo valve 21 and the rear wheel power cylinder 24. In the device, suspension spring devices 17a, 17b, 27a, 27b respectively provided between each wheel and the vehicle body 19, and at least one displacement sensor 50a, 50b, 51a for detecting the contraction amount of the left and right suspension spring devices, respectively. , 51b, the control device 40, if the difference in the amount of contraction detected by the left and right displacement sensors 50a, 50b, 51a, 51b increases, the ratio of the rear wheel steering angle to the front wheel steering angle at high speed, When the lateral inclination direction of the vehicle body 19 and the steering direction of the front wheels 16a and 16b, which are given by the positive and negative differences in the amount of contraction, are the same direction, the difference in the amount of contraction is reduced as compared to the case where it is 0, and it is increased in the opposite direction. As said servo motor
It is characterized by activating 46.

(Operation) Left and right displacement sensors 50a, 50b, 51a, 51 with a slight lateral inclination of the vehicle body
When the difference in the amount of contraction detected by b is small, the rear wheels are steered in the same phase as the front wheels at high speed as in the conventional four-wheel steering system, so transient turning performance at high speed is improved. . If the lateral inclination of the vehicle body increases and the difference in the amount of contraction increases, the control device 40 changes the steering angle of the rear wheels in phase with the front wheels at high speeds to the lateral inclination direction of the vehicle body 19 and the front wheels 16a, 16b.
When the steering direction is in the same direction, the amount of contraction is reduced as compared with the case where it is 0, and when it is in the opposite direction, the amount of contraction is increased. This allows
When the vehicle is in the same direction in which the vehicle is leaning laterally and the steering direction is the same as the steering direction, turning of the steering wheel is easier, and when the direction of lateral leaning and the steering direction are opposite, the turning radius of the vehicle is It is prevented that the traveling stability at the time of turning in the reverse direction is deteriorated due to the increase in the lateral inclination of the vehicle body.

(Effects of the Invention) As described above, according to the present invention, particularly at high speed, the advantage of the four-wheel steering device is exhibited when the lateral inclination of the vehicle body is small, and when the lateral inclination is increased, the lateral inclination direction is increased. It is possible to prevent the steering wheel from being cut off when the steering direction is the same direction and to prevent the traveling stability during turning from being deteriorated when the lateral inclination direction and the steering direction are opposite. Further, according to the present invention, since the displacement sensor directly detects the lateral inclination of the vehicle body to control the rear wheel steering angle, even when the vehicle body laterally leans due to the state of load or the inclination of the road surface, the vehicle turns at high speed. It is possible to prevent a decrease in running stability at the time.

(Embodiment) The present invention will be described below with reference to an embodiment shown in the accompanying drawings.

As shown in FIG. 1, the vehicle body 19 and the left and right front wheels 16a, 16
Between the b and the rear wheels 26a, 26b, a suspension spring device 17a,
17b, 27a, 27b are provided, and each suspension spring device 17a, 17b, 27a, 2
Displacement sensors 50a, 50b, 51a, 51b for detecting the amount of contraction of 7b are provided. Each displacement sensor uses, for example, a differential transformer, and detects the quasi-static contraction amount of each suspension spring device 50a, 50b, 51a, 51b excluding fine fluctuations due to unevenness of the ground.

As shown in FIG. 1, a tandem type supply pump 30 driven by an automobile engine includes a front wheel side pump 30a and a rear wheel side pump 30b, and the hydraulic oil discharged from each pump 30a, 30b is a front wheel power steering device. It is supplied to the servo valve 11 of 10 and the servo valve 21 of the rear wheel power steering device 20. The front wheel power steering device 10 includes a steering shaft 15 provided with a steering handle 15a.
Front wheel servo valve 11 provided in the middle of transmitting to the rack and pinion mechanism 12 that converts the rotation of the wheel into a reciprocating motion of the front wheel operating rod 13.
The front wheel power cylinder 14 provided on the front wheel operating rod 13 is a main constituent member. Front wheel servo valve 11 is steering shaft 15
It operates according to the steering wheel torque input from the front wheel side pump 30a with respect to both working chambers of the front wheel power cylinder 14.
Control the supply and discharge of the hydraulic oil supplied from, the steering force amplified by this is output to the front wheel operating rod 13, steer the front wheels 16a, 16b via a known tie rod and knuckle arm, etc. The hydraulic oil is discharged to the reservoir 31. A front wheel steering angle sensor 18 for detecting the steering angle and the steering direction of the front wheels 16a, 16b is provided in the middle of the steering shaft 15.

The rear wheel power steering device 20 includes a rear wheel servo valve 21 in which a return shaft 21b is connected to a rear wheel operating rod 23 by a rack and pinion mechanism 22, and a rear wheel power cylinder provided in the rear wheel operating rod 23.
24 is the main component. The rear wheel servo valve 21 is an input shaft 21a rotated by a stepping motor 46 described later.
And the return shaft 21b are actuated in response to relative rotation of the return shaft 21b to control the supply and discharge of hydraulic oil supplied from the rear wheel side pump 30b to both working chambers of the rear wheel power cylinder 24.
The rear wheel actuating rod 23 is moved according to the turning angle of a, and the rear wheels 26a, 26b are passed through known tie rods, nuckle arms, etc.
Is used to discharge the used hydraulic oil to the reservoir 31. The rear wheel power cylinder 24 is provided with a pair of return springs 25 that bias the rear wheel operating rod 23 toward the steering neutral position when the rear wheel power cylinder 24 is not operating.

The pulse generator 45, which distributes a pulse to the stepping motor 46 and operates it, is controlled by the electronic control unit 40. As shown in FIG. 1, the electronic control unit 40 has a microprocessor (hereinafter referred to as CPU) 41, a read-only memory (hereinafter referred to as ROM) 42, and a writable memory (hereinafter referred to as RAM) 43 as main constituent elements. The front wheel steering angle sensor 18, the vehicle speed sensor 44 for detecting the vehicle speed, and a lateral inclination detector 47 described later are connected to the CPU 41 via an interface not shown, and the pulse generator 45 is also connected via an interface not shown. It is connected.

The lateral inclination detector 47 is composed of first and second adders 48a and 48b and a subtractor 49, as shown in FIG. The front and rear displacement sensors 50a, 50b on the right side are connected to the first adder 48a, and the quasi-static contraction amounts of the front and rear suspension spring devices 17a, 27a are added. Similarly, the second adder 48b operates on the left side. The quasi-static contraction amounts of the front and rear suspension springs 17b and 27b are added. Subtractor 49
Calculates the difference between the added values of the left and right shrinkage amounts added by the first and second adders 48a and 48b. This difference is the front wheels 16a, 16
The lateral inclination angle of the vehicle body with respect to the ground is divided by the sum of the wheel treads of b and the rear wheels 26a, 26b. If the difference is large, the lateral inclination angle is large. Also, depending on whether this difference is positive or negative,
You can know the direction of 19 lateral inclinations.

The ROM 42 stores a map in which the change characteristics of the rear wheel steering angle with respect to the front wheel steering angle are programmed. This characteristic map is composed of a plurality of control patterns according to the difference between the vehicle speed and the added value of the amount of contraction, as schematically shown by the solid line in FIG. In the example shown in the figure, in the low speed range, the rear wheel steering angle increases in reverse phase as the front wheel steering angle increases when the front wheel steering angle becomes larger than a certain value, and the front wheel steering angle increases when the vehicle speed increases. The ratio of the rear steering angle to the rear wheel is programmed to be reduced. In the high speed range, the rear wheel steering angle increases in phase to the predetermined steering angle in accordance with the increase in the front wheel steering angle, and when the lateral inclination direction of the vehicle body 19 and the steering directions of the front wheels 16a, 16b are in the same direction, the vehicle speed and the aforesaid The difference is programmed so that the ratio of the rear wheel steering angle to the front wheel steering angle is increased when the vehicle speed and the sum of the differences are increased when the lateral inclination direction and the steering direction are opposite directions. In the example shown by the solid line in FIG. 2, the maximum value of the rear wheel steering angle in the high speed range is constant, but as shown by the two-dot chain line, when the ratio is large, the maximum value of the rear wheel steering angle is also large. May be

Next, the operation of this embodiment will be described with reference to the flowchart shown in FIG.

The front wheel rudder angle and steering direction detected by the front wheel rudder angle sensor 18, the vehicle speed detected by the vehicle speed sensor 44, and the difference between the amount of contraction calculated by the lateral tilt detector 47 and the positive and negative signs indicating the lateral tilt direction. Is stored in a predetermined register of the RAM 43. Then, every time an interrupt signal is given every predetermined unit time, the CPU 41 executes the control operation according to the flowchart of FIG. First, in step 100, the CPU 41 reads the vehicle speed stored in the register to determine the vehicle speed range, and in the case of a low speed range, in step 101, a plurality of control patterns in the low speed range stored in the ROM 42 are used to determine the required speed according to the vehicle speed. Is read out, and the rear wheel steering angle is searched based on the front wheel steering angle stored in the register in step 102. Next, the CPU 41 calculates the output pulse number for giving the rear wheel steering angle to the rear wheels 26a, 26b in step 105, and outputs this output pulse number to the pulse generator 45 via an interface not shown in step 106. To do.

If the vehicle speed is in the high speed range, step 100 to step 103
Then, the CPU 41 reads out a required control pattern according to the vehicle speed, the difference in the amount of contraction, the front wheel steering direction and the lateral inclination direction by the plurality of control patterns in the high speed range stored in the ROM 42.
In step 104, the rear wheel steering angle is searched based on the front wheel steering angle. Next, in the steps 105 and 106, the CPU 41 calculates the number of output pulses for giving the rear wheel steering angle and outputs it to the pulse generator 45 in the same manner as described above. When the vehicle speed range is the medium speed range, the CPU 41 does not output the number of output pulses to the pulse generator 45 except for the transient state. The ROM 42 stores a control program for the CPU 41 to perform such control operation.

The pulse generator 45 outputs the number of pulses input from the CPU 41 to the stepping motor 46,
Rotate 46 by a predetermined angle. As a result, the rear wheel servo valve 21 is activated, and the rear wheel power steering device 20 causes the rear wheels 26a and 26b to
The vehicle is steered by an angle according to the vehicle speed, the difference between the contraction amounts of the left and right suspension spring devices 17a, 17b, 27a, 27b and the sign thereof, and the front wheel steering angle and the steering direction.

If the lateral inclination of the vehicle body is slight and the difference in the amount of contraction between the suspension spring devices 17a, 27a on the right side and the suspension spring devices 17a, 27b on the left side is small, the vehicle speed changes from each control pattern in FIG. The corresponding control pattern is selected. As a result, the rear wheel steering characteristics are similar to those of the conventional four-wheel steering system, the rear wheels are largely reversed-phase steered at low speeds to improve small turning performance, and the rear wheels are small in-phase steered at high speeds to provide transient turning performance. improves.

If the lateral inclination angle of the vehicle speed with respect to the road surface increases due to the deviation of the load, the inclination of the road surface, the rapid turn, etc., the difference in the amount of contraction increases. In this state, in the low speed range, the same control pattern as in the case where the difference in the contraction amount is small is selected, but in the high speed range, the contraction is performed when the front wheel steering is performed in the same direction as the lateral inclination direction of the vehicle body 19. A control pattern is selected in which the rear wheel steering angle is smaller than when the amount is small, and when the front wheel steering is performed in the direction opposite to the lateral tilt direction, the rear wheel steering angle is larger than when the amount of contraction is small. Is selected.
As a result, in the low speed range, there is no particular difference from the conventional four-wheel steering system, but in the high speed range, when the front wheels are steered in the same direction as the lateral inclination direction, the turning radius of the vehicle is reduced and the steering wheel is cut off. When the front wheels are steered in the direction opposite to the lateral inclination direction, the turning radius is prevented from increasing and the running stability during turning is prevented from being lowered.

In the above embodiment, the input shaft 21a of the rotary type rear wheel servo valve 21 is connected to the stepping servo motor 46.
However, the input member of the rear wheel servo valve of another type may be operated by the servo valve of another type. Further, it is not necessary to provide the displacement sensor in all suspension spring devices, but only in the left and right front wheel suspension spring devices or only in the left and right rear wheel suspension spring devices, and the lateral inclination of the vehicle body is detected by the difference between the left and right contraction amounts. You may do it.

[Brief description of drawings]

The attached drawings show an embodiment of a four-wheel steering system according to the present invention. Fig. 1 is a schematic diagram showing the whole, Fig. 2 is a diagram showing characteristics of a rear wheel steering angle with respect to a front wheel steering angle, and Fig. 3 is a control. It is a flowchart of a program. Explanation of sign 16a, 16b ... front wheel, 17a, 17b ... suspension spring device, 21 ... servo valve (rear wheel servo valve), 24 ... rear wheel power cylinder, 26a, 26b
Rear wheel, 27a, 27b ... Suspension spring device, 30b ... Supply pump (rear wheel side pump), 40 ... Control device (electronic control device), 46 ... Stepping motor, 50a, 50b, 51a, 51b ... Displacement sensor.

Claims (1)

[Scope of utility model registration request] 1. A rear wheel power cylinder for steering a rear wheel, a servo valve which is operated by a servo motor to control supply and discharge of a working fluid from a supply pump to and from both working chambers of the rear wheel power cylinder, and a front wheel. In a four-wheel steering system including a control unit that operates the servomotor according to the steering angle and the vehicle speed to steer the rear wheels in phase with the front wheels at high speed via the servo valve and the rear wheel power cylinder, A suspension spring device provided between the vehicle bodies and at least one displacement sensor for each of the left and right suspension spring devices for detecting the amount of contraction of the left and right suspension spring devices are provided, and the controller controls the amount of contraction detected by the left and right displacement sensors. If the difference increases, the ratio of the rear wheel rudder angle to the front wheel rudder angle at high speed is determined by the lateral tilt direction of the vehicle body and the front wheel steering direction, which are given by the positive and negative of the difference in the contraction amount. Serial contraction amount of the difference was that the reduction small than zero, four-wheel steering system, characterized in that when the reverse actuating the servo motor to increase.