JPH0330220Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a four-wheel steering system for a four-wheel drive vehicle, and in particular, the present invention relates to a four-wheel steering system for a four-wheel drive vehicle, and in particular, the invention relates to a four-wheel steering system for a four-wheel drive vehicle, in particular, in which rear wheel steering is performed by an actuator operated by hydraulic fluid supplied from a hydraulic pump. This invention relates to a four-wheel steering system for a modern four-wheel drive vehicle.

Conventional technology Four-wheel drive vehicles can be broadly divided into part-time systems that can switch between two-wheel drive and four-wheel drive, and full-time systems that have a center differential between the front and rear wheels and are constantly in four-wheel drive. do. In the latter full-time system, for example, there is a conventional system as shown in "Motor Fan" No. 10 (Sanei Shobo), published on October 1, 1981, page 105. This inputs the engine power output from the transmission into the gear case of the center differential, drives the rear differential with one side gear of the center differential, and drives the front differential with the other side gear. . Therefore, in this full-time system, torque is constantly applied to the front and rear wheels via the center differential. In recent years, limited slip differentials, viscose couplings, etc. have come into use as the center differential.

On the other hand, in recent years, some vehicles have been designed in which the rear wheels are steered and the compliance steering of the rear wheels is controlled to be optimal using lateral forces that act during cornering. For example, JP-A-58-
214470, a hydraulic actuator is provided on the lateral rod of the rear wheel, and by operating this hydraulic actuator with hydraulic fluid supplied from a hydraulic pump, the length of the lateral rod is changed, and the length of the rear wheel is changed. Compliance steer is coming under control.

By the way, the hydraulic pump is usually driven by the output shaft of the engine via a belt or the like, so that the pump discharge amount is proportional to the engine speed.

In recent years, four-wheel drive vehicles have been proposed that employ the above-mentioned four-wheel steering device. Therefore, even in the four-wheel steering system of this four-wheel drive vehicle, the hydraulic pump that operates the actuator for steering the rear wheels is driven by the output shaft of the engine.

Problems to be Solved by the Invention However, in the conventional four-wheel steering system for four-wheel drive vehicles, lateral force acts on the wheels during cornering, and this lateral force changes the compliance steering of the rear wheels. , this compliance steering change causes the lateral force to increase as the vehicle speed increases, so hydraulic fluid is supplied to the actuator for rear wheel steering in accordance with the vehicle speed, and a large lateral force requires a large actuator operating force. It is desirable to counter this with

However, since the hydraulic pump of the actuator is operated by engine rotation as described above, it becomes difficult to obtain a discharge amount proportional to the vehicle speed. That is, since the vehicle speed is determined by the rotation of the engine after it is shifted by the transmission, it is necessary to control the discharge amount of the hydraulic pump in consideration of the gear position of the transmission, which requires unnecessary control. equipment is required,
Since it is necessary to set the discharge capacity of the hydraulic pump to a large value, there is a problem in that the size of the device and the cost increase significantly. Furthermore, as shown in Japanese Patent Application Laid-Open No. 60-92956, for example, a pump that supplies pressurized fluid to a rear wheel steering system can be driven by an electric motor, and this electric motor is controlled according to the vehicle speed. There is a device. However, even in the case of the device disclosed in the above-mentioned publication, an electric motor and a special control device for controlling the electric motor are required, making the structure complicated and expensive.

Therefore, the present invention uses the engine power that has passed through gear shifting elements such as the transmission and center differential to drive the hydraulic pump for rear wheel steering, making it easy to adjust the discharge amount of the hydraulic pump according to the vehicle speed. It is an object of the present invention to provide a four-wheel steering device for a four-wheel drive vehicle that has become available.

Means and Effects for Solving the Problems In order to achieve the above object, the present invention is provided in a four-wheel drive vehicle using a center differential, and uses an actuator operated by hydraulic fluid supplied from a hydraulic pump. In a four-wheel steering system in which the rear wheels are now steered, at least a hydraulic pump that operates an actuator for rear wheel steering is connected to the front wheel drive shaft or the rear wheel drive shaft connected to the center differential. Since the rear wheel drive shaft and the front wheel drive shaft always rotate in proportion to the wheel rotation, the amount of liquid discharged by the hydraulic pump is proportional to the wheel rotation, that is, the vehicle speed. Therefore, the ideal actuator operating force for rear wheel steering can be easily obtained.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

That is, the figure shows a four-wheel steering device 2 used in a four-wheel drive vehicle 1 showing one embodiment of the present invention, in which front wheels 3, 3a
It includes a power cylinder 4 for steering and an actuator 6 for steering rear wheels 5, 5a. The power cylinder 4 has a function of providing an auxiliary steering force to the steering force of the steering wheel 7, and is operated by hydraulic fluid discharged from a hydraulic pump for steering the front wheels (not shown). ing. On the other hand, the actuator 6 is configured to steer the rear wheels 5, 5a only by its operating force, and is operated by hydraulic fluid discharged from a hydraulic pump for steering the rear wheels. ing. That is, the actuator 6 is constituted by piston rods 6c and 6d protruding from both sides of a piston 6b in a cylinder 6a, respectively.
are connected to knuckle arms 8, 8a protruding from the rear wheels 5, 5a via joints 9, 9a, and when the piston rods 6c, 6d are moved left and right in conjunction with the piston 6b, the rear The wheels 5 and 5a are steered.

The four-wheel drive system of this embodiment employs a full-time system, and a viscose coupling 10 is used as a center differential. This viscose coupling 10 is a unit that transmits force between disks by friction of viscous fluid, and includes a pair of disks 12 and 12 that are opposed to each other with a viscous medium interposed in an outer case 11.
One of these disks 12, 12a is connected to the outer case 11, and the other is interlocked with the outer case 11 via a planetary gear 13. The engine 15 is transmitted to the output shaft 14a of the transmission 14.
The power is input to the pinion gear of the planetary gear 13 via a pair of gears 16, 16a. Furthermore, the viscose coupling ring 1
One of the disks 12 of the 0 is connected to a first shaft 17, and this first shaft 17 is connected to a rear differential 19 via a bevel gear 18 so as to be interlocked with a rear drive shaft 20. The power transmission path from the first shaft 17 to the rear drive shaft 20 constitutes a rear wheel drive shaft 21. Further, the other disk 12a of the viscose coupling 10 is connected to the second shaft 22, and the second disk 12a is connected to the second shaft 22.
The shaft 22 is connected via a bevel gear 23 to a propeller shaft 24 for front wheel drive. The propeller shaft 24 is connected to a front differential (not shown) and drives a front drive shaft (not shown). and,
From the second shaft 22 to the propeller shaft 24
A front wheel drive shaft 25 is configured by a power transmission path that reaches the front drive shaft via the front drive shaft.

In this embodiment, the front wheel drive shaft 25
A first shaft for power extraction is attached to the second shaft 22 constituting the
A gear 30 is provided, and a pump drive shaft 32 is connected via a second gear 31 meshed with the first gear 30.
The pump drive shaft 32 drives the hydraulic pump 33 for steering the rear wheels. However, the pump drive shaft 32 is provided with a one-way clutch 34 that is engaged with the front wheel drive shaft 25 when the vehicle rotates in the forward direction of the vehicle, and becomes free to rotate when the vehicle rotates in the backward direction.

The steering shaft 7a is provided with a front control valve 40 for steering the front wheels and a rear control valve 41 for steering the rear wheels.
The hydraulic fluid from the hydraulic pump for steering the front wheels is supplied to the power cylinder 4 via the front control valve 40, and the hydraulic fluid from the hydraulic pump 33 for steering the rear wheels is supplied via the rear control valve 41. The actuator 6 is supplied with the following information.

The operation of this embodiment with the above configuration will be described below.

That is, the engine power output from the transmission 14 is distributed to the front wheel drive shaft 25 and the rear wheel drive shaft 21 via the viscose coupling 10, and the front wheels 3, 3a and the rear wheels 5, 5a are driven. It now has four-wheel drive capability.

Next, in the four-wheel steering, the power cylinder 4 is operated by hydraulic fluid from a front wheel steering hydraulic pump (not shown) driven by the engine 15, and the steering assist force for the front wheels 3, 3a is obtained. The actuator 6 is operated by the hydraulic fluid from the hydraulic pump 33 for wheel steering.
is operated, and the rear wheels 5, 5a are steered by this actuator 6. By the way, the latter rear wheel steering, for example, at high speed, the front wheels 3,
By steering in the same phase as 3a, understeer is achieved to stabilize the vehicle during cornering, and at low speeds, by steering in the opposite phase to front wheels 3 and 3a, turning performance and agility are improved. It is operated so that the On the other hand, apart from the rear wheel steering function, lateral force acts on the rear wheels 5, 5a during cornering. Then, this lateral force acts on the actuator 6 via the knuckle arms 8, 8a, and the piston 6b is moved against the hydraulic pressure of the actuator 6, causing a compliance steer change in the rear wheels 5, 5a. . The lateral force increases as the vehicle speed increases, and accordingly, the change in compliance steering of the rear wheels 5, 5a also increases as the speed increases.

In this embodiment, the hydraulic pump 33 for steering the rear wheels is driven by the front wheel drive shaft 25 via the first and second gears 30 and 31. This 25 rotations of the front wheel drive shaft is the front wheel 3,
3a It is always proportional to the rotation and proportional to the vehicle speed. Therefore, the hydraulic pressure discharge amount of the hydraulic pump 33 is increased in proportion to the vehicle speed, and the actuator 6
The hydraulic pressure increases as the speed is shifted from a low speed state to a high speed state. In other words, this increase in hydraulic pressure is opposed to the increase in the lateral force, suppressing fluctuations in the actuator 6 in response to the lateral force in the entire vehicle speed range, and preventing compliance steering changes in the rear wheels 5, 5a. It can be significantly reduced.

In this embodiment, since a one-way clutch 34 is provided on the pump drive shaft 32, the hydraulic pump 33 is prevented from being reversed when the vehicle is moving backward.

By the way, the pump drive shaft 32 has first and second shafts.
Although the pump drive shaft 32 and the front wheel drive shaft 25 are interlocked with the front wheel drive shaft 25 through gears 30 and 31, the interlocking between the pump drive shaft 32 and the front wheel drive shaft 25 is not through gears but through other interlocking mechanisms such as pulleys and belts. Power may also be transmitted by In addition, a hydraulic pump 33 for rear wheel steering
In addition to the front wheel drive shaft 25, the rear wheel drive shaft 21 is also rotated in proportion to the vehicle speed, so even if the hydraulic pump 33 is driven by the rear wheel drive shaft 21, the same result as in the above embodiment is achieved. can perform the functions of Furthermore, although the viscose coupling 10 is used as a four-wheel drive center differential, the present invention is not limited to this, and a general differential, a limited differential, or a fluid coupling may be used. Further, when an actuator for auxiliary steering of the front wheels is provided, a hydraulic pump for driving this actuator may be driven by a front wheel drive shaft or a rear wheel drive shaft.

Effects of the Invention As explained above, in the four-wheel steering system of the four-wheel drive vehicle of the present invention, the hydraulic pump that drives the actuator for rear wheel steering is connected to the front wheels connected to the center differential of the four-wheel drive. Since it was driven by a front wheel drive shaft or a rear wheel drive shaft, the rotation speed of these front and rear wheel drive shafts is always proportional to the wheel.
The amount of hydraulic fluid discharged by the hydraulic pump is increased in proportion to the vehicle speed, and the hydraulic pressure of the actuator can also be increased in proportion to this. Therefore, the operating force of the actuator can be made to counteract the wheel lateral force that increases with vehicle speed, and the compliance steer change of the rear wheels caused by the lateral force can be prevented or significantly reduced, thereby stabilizing the vehicle. be able to. Furthermore, by driving the hydraulic pump with the front wheel drive shaft or the rear wheel drive shaft, the discharge amount can be easily controlled in proportion to the vehicle speed without the need for a special control device, and the device can be made more compact. It also has the excellent effect of achieving significant cost reductions.

[Brief explanation of the drawing]

The figure is a schematic configuration diagram showing a four-wheel steering system for a four-wheel drive vehicle, which is an embodiment of the present invention. 1... Four-wheel drive vehicle, 2... Four-wheel steering device, 3,
3a...front wheel, 5,5a...rear wheel, 6...actuator, 10...viscose coupling (center differential), 14...transmission, 1
5...Engine, 21...Rear wheel drive shaft, 25...
...Front wheel drive shaft.

Claims (1)

[Scope of utility model registration request] In a four-wheel steering system that is installed in four-wheel drive vehicles that use a center differential, the rear wheels are now steered via an actuator operated by hydraulic fluid supplied from a hydraulic pump. A four-wheel steering system for a four-wheel drive vehicle, characterized in that a hydraulic pump for operating an actuator for a four-wheel drive vehicle is driven by a front wheel drive shaft or a rear wheel drive shaft connected to the center differential.