JPH0525710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle, and particularly to a four-wheel steering system for a vehicle in which a steering ratio is changed according to the loaded weight of the vehicle.

(Prior Art) It is generally known that when the loaded weight of a vehicle increases, the running stability of the vehicle decreases. This is because when the loaded weight increases, the ground load of the rear wheels increases, and the cornering power increases more than that of the front wheels, and as a result, the steering characteristics change in the direction of oversteering. Particularly in front-engine vehicles, which have a light rear weight when empty, running stability is significantly reduced as the loaded weight increases. The decrease in running stability of the vehicle due to the increase in the loaded weight of the vehicle
Naturally, this problem also occurs in vehicles that employ a four-wheel steering system as described in Japanese Patent Application Laid-open No. 55-91458. This four-wheel steering system is a steering system that steers both the front wheels and the rear wheels. Normally, at high vehicle speeds, the rear wheels are steered in the same phase direction as the front wheels. It is possible to change lanes on the road extremely smoothly with good running stability. Furthermore, in a low vehicle speed range, the rear wheels are steered in the opposite phase direction to the front wheels, making it possible to reduce the turning radius, and this four-wheel steering system is attracting attention as an excellent steering system.

(Object of the Invention) An object of the present invention is to provide a four-wheel steering system for a vehicle in which running stability is not impaired even when the loaded weight of the vehicle increases.

(Structure of the Invention) A four-wheel steering device for a vehicle according to the present invention includes a steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels, and a ratio of the steering angle of the rear wheels to the steering angle of the front wheels depending on the vehicle speed. In a four-wheel steering system for a vehicle comprising a control device that controls a rear wheel steering device so that the rear wheels are steered based on a steering ratio that is changed based on a steering ratio that is changed, a loaded weight input means for inputting information regarding a loaded weight of the vehicle is provided. The controller is configured to correct the steering ratio, which is predetermined according to the vehicle speed, in the same phase direction as the loaded weight increases, based on the output signal of the loaded weight input means. It is characterized by controlling the rear wheel steering device. Therefore, it is possible to suppress an increase in the cornering power of the rear wheels caused by an increase in the loaded weight.

(Example) Examples of the present invention will be described in detail below. 1st
The figure is a schematic plan view illustrating a first embodiment of the present invention. The steering mechanism 2 that steers the left and right front wheels 1L and 1R includes a steering wheel 3, a rack 4a and a pinion 4b that convert rotational motion of the steering wheel 3 into linear reciprocating motion.
Left and right tie rods 5, 5' have base ends connected to each end of the rack 4a, and one end connects to each tie rod 5, 5'.
5', the other ends are connected to the left and right front wheels 1L, 1R, respectively, and the knuckle arms 6, 6' move the left and right tie rods 5, 5' back and forth in the vehicle width direction in response to the steering of the steering wheel 3. It is configured to move and steer the left and right front wheels 1L and 1R left and right.

On the other hand, the rear wheel steering device 8 that steers the left and right rear wheels 9R, 9L includes a rear wheel operating rod 7 held on the vehicle body so as to be slidable in the left and right direction, and tie rods 10, 10 at both left and right ends of the rod 7, respectively. The rear wheels 9L and 9R are steered by movement of the operating rod 7 in the width direction of the vehicle body. A rack 12 is formed in a part of the operating rod 7, and this rack 12
The pinion 13 meshing with the rear wheels 9L, 9 is rotated by the pulse motor 14 via the pair of bevel gears 15, 16 and the pinion shaft 17, so that the rear wheels 9L, 9 are rotated in accordance with the direction and amount of rotation of the pulse motor 14.
Turn R.

Further, the rear wheel operating rod 7 passes through the power cylinder 18, and a piston 19 that partitions the inside of the cylinder 18 into left and right hydraulic chambers 18a, 18b is fixed to the operating rod 7.
Hydraulic passages 21a and 21b led from a control valve 20 provided around the pinion shaft 17 are connected to the a and 18b, respectively, and a pump 23 driven by the control valve 20 and a motor 22 is connected to the a and 18b, respectively. A hydraulic pressure supply passage 24 and a return passage 25 are provided between them. here,
The control valve 20 is connected to the pulse motor 1
4, the hydraulic pressure supplied from the pump 23 via the hydraulic pressure supply passage 24 is applied to one of the hydraulic chambers 18 of the power cylinder 18 according to the direction of the rotational force.
a or 18b, and acts to return the hydraulic oil in the other hydraulic chamber 18b or 18a to the pump 23 via the return passage 25. Therefore,
By the pulse motor 14, the bevel gears 15, 1
6, pinion shaft 17, pinion 13 and rack 1
When the operating rod 7 is moved in the axial direction via the piston 2, the hydraulic pressure introduced into the power cylinder 18 assists the movement of the operating rod 7 via the piston 19.

The pulse motor 14 is controlled by a controller 26, which receives a vehicle speed signal A output from a vehicle speed sensor 27 and a front wheel steering angle signal B from a front wheel steering angle sensor 28 that detects the front wheel steering angle. and a loaded weight signal C are input from loaded weight input means 29 that inputs information regarding the loaded weight of the vehicle. This controller 26 outputs signals D and E based on these input signal values. Pulse motor 14 and pump drive motor 2
2 are driven by signals D and E, respectively.
The target rear wheel steering angle calculated by the controller 26 has a steering ratio characteristic as shown in FIG. 2, for example. That is, at low speeds, the rear wheels are steered in opposite phases, and at medium and high speeds, the rear wheels are steered in the same phase. If the loaded weight input by the loaded weight input means 29 is small, the rear wheel steering angle is calculated using the steering ratio shown by the solid line in FIG.
A rear wheel steering angle signal D corresponding to the calculated rear wheel steering angle is input to the pulse motor 14. The pulse motor rotates by a number of degrees corresponding to the target rear wheel steering angle, and moves the rear wheel operating rod 17 in the vehicle width direction via the bevel gears 15, 16, pinion shaft 17, pinion 13, and rack 12. As a result, the rear wheels 9L and 9R are steered, and at this time the power cylinder 18 is activated to assist the movement of the steering rod 7. When it is detected by the loaded weight input means 29 that a loaded weight is added to the vehicle, the rear wheel steering angle is calculated so that the larger the loaded weight is, the closer the steering ratio is to 1 in the same phase direction. be done. For example, when three people are on board, the rear wheel steering angle is calculated using the steering ratio of curve b in FIG. 2, and when five people are on board, the rear wheel steering angle is calculated using the steering ratio of curve C. Therefore, an increase in the cornering power of the rear wheels caused by an increase in the loaded weight is suppressed. The loaded weight input means 26 includes a weight sensor that detects the loaded weight itself, a vehicle height sensor that indirectly detects the loaded weight by detecting the ups and downs of the vehicle height, or inputs the loaded state according to the number of passengers and loaded luggage. It is possible to adopt a manual changeover switch or the like.

Next, a second embodiment of the present invention will be described. FIG. 3 is a schematic diagram illustrating the second embodiment. Steering mechanism 2 that steers the left and right front wheels 1L and 1R
is almost the same as the first embodiment, but rack 4a
A pinion 30 is meshed with the rack 4a to extract the movement of the rack 4a in the vehicle width direction as rotational movement.
The rotary movement taken up by pinion 30 is transmitted by shaft 31 to mechanical rear wheel steering drive 32 . The mechanical rear wheel steering drive device 32 is controlled by the controller 26, converts the input rotation of the shaft 31, and moves the rack 33 of the controller 26 in the width direction of the vehicle body. A pinion 34 is engaged with the rack 33, and when the pinion 34 rotates as the rack 33 moves, the shaft 35 rotates and rotates the pinion 13 provided at the other end of the shaft 35. Rear wheel steering device 8
has almost the same configuration as the first embodiment, and the pinion 13 rotates, the operating rod 7 moves in the width direction of the vehicle body, and the rear wheels 9L and 9R are steered.
Also, as in the first embodiment, when the rear wheels 9L, 9R are steered, the power cylinder 18 is operated to assist the movement of the steering rod 7. This steering device 3 serves as the mechanical rear wheel steering drive device 32.
dead zone setting/amplification/inversion means for amplifying the rotational force of the input shaft of No. 2 at a predetermined ratio and reversing the rotation direction to transmit only a predetermined rotation angle range of the input shaft to the output shaft. There is something.

This rear wheel steering drive device 32 is a controller 26
This controller 26 receives a vehicle speed signal A output from a vehicle speed sensor 27.
and a loaded weight signal C from loaded weight input means 29 that detects the loaded weight of the vehicle. The controller 26 calculates a steering ratio as shown in FIG. 2 from the input vehicle speed signal A and loaded weight signal C, and a steering ratio signal D corresponding to the calculated steering ratio is sent to the rear wheel steering drive system. 32, the transmission mechanism within the device 32 is thereby operated, and the rear wheels 9L, 9R are steered at the optimum steering angle.

(Effects of the Invention) The four-wheel steering system for a vehicle according to the present invention is designed to make the steering ratio closer to 1 in the same phase direction when the loaded weight of the vehicle is larger. Also, the increase in cornering power of the rear wheels can be suppressed, and the running stability of the vehicle will not be impaired by an increase in the loaded weight.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of a first embodiment of the present invention, FIG. 2 is a diagram for explaining steering ratio control in the present invention, and FIG. 3 is a schematic plan view of a second embodiment of the present invention. 1L, 1R...Front wheel, 2...Steering mechanism, 8...Rear wheel steering device, 9R, 9L...Rear wheel,
26... Controller, 27... Speed sensor, 2
8... Front wheel steering angle sensor, 29... Load weight input means, 32... Mechanical rear wheel steering drive device.

Claims (1)

[Claims] 1. A steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels, and a steering ratio that changes the ratio of the steering angle of the rear wheels to the steering angle of the front wheels in accordance with the vehicle speed. A four-wheel steering system for a vehicle, comprising a control device for controlling a rear wheel steering device, wherein the control device is provided with a loaded weight input means for inputting information regarding the loaded weight of the vehicle, and the control device is configured to control the rear wheel steering device. In response to the output signal of the loaded weight input means, the rear wheel steering device is controlled so as to correct a steering ratio predetermined according to the vehicle speed in the same phase direction as the loaded weight increases. A four-wheel steering system for vehicles.