Four-wheel driven vehicle

Details Four-wheel driven vehicle Four-wheel driven vehicle

1998-11-20

2001-03-13

Johnson, Brian L. (Department: 3618)

Motor vehicles

Having four wheels driven

C180S247000, C180S248000, C074S015400, C192S083000

Reexamination Certificate

active

06199653

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a four-wheel driven vehicle provided with a front wheel driving system. One of three (3) modes may be selected. A two-wheel drive (2WD) mode in which on only rear wheels are driven, a first four-wheel drive (F4WD) mode in which the front wheels are driven together with the rear wheels at a peripheral speed substantially identical with that of the rear wheels, and second four-wheel drive (S4WD) mode in which the front wheels are driven together with the rear wheels at a peripheral speed higher than that of the rear wheels.
2. Related Art
A conventional agricultural tractor serving as a four-wheel driven vehicle, whose front and rear wheels rotate at a nearly equal peripheral speed are described in U.S. Pat. Nos. 4,669,559, 4,696,365, 4,723,623, 4,856,611, 4,862,988, and 5,293,956. Such a conventional tractor has the problem that, when hard cornering at the end of field during work such as cultivation, the rotation of its front wheels is too slow to follow the turning of the tractor, whereby the front wheels slip and damage the field. Recently, to avoid such damage to the field, a front wheel speed-up system has been employed by the four-wheel driven vehicle to increase the rotational speed of the front wheels and enable them to follow the turning of the vehicle without slip during hard cornering.
The conventional front wheel speed-up system is provided with a speedup clutch whose engagement makes the rotational speed of front wheels higher. The speed-up clutch is mechanically made to engage by the rotational force of a steering wheel when being steered beyond a predetermined angle. Alternatively, the speed-up clutch is engaged by an actuator when a sensor disposed at the steering wheel or on linkage between the steering wheel and the front wheels detects steering beyond the predetermined angle. The latter speed-up clutch consists of two hydraulic clutches; one of them adapted to engage for driving the front wheels at a nearly identical peripheral speed with that of rear wheels and the other adapted to engage for driving them at a higher peripheral speed. When each of the hydraulic clutches is operated to engage, a hydraulic pressure is applied to the clutch so as to make it engage. When it is operated to disengage, pressure oil is drained so as to release the hydraulic pressure and the biasing force of a spring makes the clutch disengage.
The mechanical speed-up clutch requires a large force for steering due to its mechanical structure. The latter speed-up clutch, which is switchable according to detection of steering angle by the sensor, has the fault that, when the electric or hydraulic system for the clutches malfunctions, both the clutches disengage and the vehicle is goes into 2WD mode, thereby lacking traction power. Also, it requires a large capacity for transmitting power into the front wheels, thereby requiring relatively large clutches which increases the space required for the clutches.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a new and improved four-wheel driven vehicle, which has a pair of rear wheels driven all the time and are operable to be put into one of three driving modes: a two-wheel drive (2WD) mode in which only the rear wheels are driven; a first four-wheel drive (F4WD) mode in which the front wheels are driven at a peripheral speed substantially identical with that of the rear wheels; and a second four-wheels drive (S4WD) mode in which the front wheels are driven at a peripheral speed higher than that of the rear wheels, wherein an operator can select between 2WD and F4WD modes, the driving mode can be automatically changed into F4WD mode on the operation of braking both the rear wheels even if it is in 2WD mode, and the driving can automatically be changed into S4WD mode upon steering beyond a predetermined angle while it is in F4WD mode, and wherein the driving mode changing means is compact.
To achieve the object, a rear-wheel driving system branches at the intermediate thereof into a front-wheel driving system comprising a first transmission for driving the front wheels at a peripheral speed substantially identical with that of the rear wheels and a second transmission for driving the front wheels at a peripheral speed higher than that of the rear wheels.
A hydraulically operable first friction clutch is provided for connecting and separating the first transmission with the rear-wheel driving system. A hydraulically double-acting first piston is provided to engage and disengage the first friction clutch. The first piston is provided with a first fluid chamber at one side for the clutch-engaging action thereof and a second fluid chamber at the other side for the clutch-disengaging action thereof. A biasing member for biasing the first friction clutch to engage is disposed in the first chamber.
A hydraulically operable second friction clutch is provided for connecting and separating the second transmission with the rear-wheel driving system. A hydraulically single-acting second piston is provided to engage the second friction clutch. The second piston is provided with a third fluid chamber at one side for the clutch-engaging action thereof.
The front-wheel driving system further comprises a directional control valve which is operable to be put into one of three positions: a first position for supplying fluid to the first chamber; a second position for supplying fluid to the second chamber; and a third position for supplying fluid the third chamber.
The directional control valve is shifted to the first position for F4WD mode, so that the pressure of the fluid from the directional control valve is generated in the first chamber in addition to the biasing force of the biasing member therein, whereby the first piston acts to make the first friction clutch engage. The directional control valve is shifted to the second position for 2WD mode, so that the pressure of the fluid from the directional control valve is generated in the second chamber and applied to the first piston against the biasing force of the biasing member so as to make the first friction clutch disengage. The directional control valve is shifted to the third position for S4WD mode, so that the pressures of the fluid from the directional control valve are generated in the second and third chambers, whereby the hydraulic pressure in the second chamber is applied to the first piston so as to make the first friction clutch disengage and the hydraulic pressure in the third chamber is applied to the second piston so as to make the second friction clutch engage.
When both left and right rear wheels are braked in 2WD mode, the directional control valve is changed from the second position to the first position, thereby changing the driving mode into F4WD.
Also, when the vehicle is steered beyond the predetermined angle in F4WD mode, the directional control valve is changed from the first position to the third position, thereby changing the driving mode into S4WD.
Furthermore, the directional control valve is provided with a first solenoid and a second solenoid. When the first solenoid is energized, the directional control valve is put to the second position. When the second solenoid is energized, it is put to the third position. When neither the first solenoid nor the second solenoid is energized, it is put to the first position.
Due to the above mentioned construction, the first friction clutch engages for F4WD by the hydraulic pressure force and the biasing force of the biasing member together generated in the first chamber, so that the capacity of the first friction clutch can be reduced and the construction of the device including the first friction clutch can be compacted so as to reduce the space required for it.
Also, even if the hydraulic or electric system for controlling the driving of the front wheels malfunctions, the directional control valve stays in the first position for F4WD mode, so that the first friction clutch engages by the biasing force of the biasing membe

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