Working vehicle

Details Working vehicle Working vehicle

1999-06-24

2001-03-27

Johnson, Brian L. (Department: 3618)

Motor vehicles

Having four wheels driven

With means for braking either structure transmitting drive...

C180S247000, C180S250000, C074S66500G, C192S048500, C192S083000, C192S083000

Reexamination Certificate

active

06206128

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to working vehicles, and more particularly to an improvement in a working vehicle having a front wheel change speed device for transmitting drive from an engine to front wheels in an equal speed mode for driving the front wheels and rear wheels at a substantially equal peripheral speed, and in an accelerating mode for driving the front wheels at a substantially faster peripheral speed than the rear wheels.
2. Description of the Related Art
A working vehicle having the above construction is disclosed in Japanese Patent Laying-Open Publication H5-162654, for example. This conventional vehicle has an equal speed clutch for transmitting substantially the same drive speed to front wheels as a peripheral speed of rear wheels, and an accelerating clutch for transmitting a faster drive speed to the front wheels than the peripheral speed of the rear wheels. When a steering angle of the front wheels is less than a predetermined value, the equal speed clutch remains engaged under the biasing force of a spring. When the steering angle of the front wheels reaches the predetermined value, a hydraulic selector valve is operated in response to the steering operation to engage the accelerating clutch by means of hydraulic drive to transmit high-speed drive to the front wheels.
This type of working vehicle is constructed to reduce a turning radius by increasing drive speed of the front wheels automatically when the front wheels are steered by a large degree as when the vehicle makes a turn near a ridge during a farming operation. However, where, as in the conventional working vehicle, the equal speed clutch is maintained engaged by the biasing force of a spring, the spring used is relatively strong to secure the engaged state reliably. In order to accelerate the front wheels, an operation to engage the accelerating clutch must be executed against the biasing force of the spring. This operation requires strong drive, which has been a cause of an enlarged hydraulic system.
SUMMARY OF THE INVENTION
The object of this invention is to provide a working vehicle having an improved construction for operating clutches to switch front wheel driving modes.
The above object is fulfilled, according to this invention, by a working vehicle comprising a front wheel change speed device having an equal speed clutch for transmitting drive to the front wheels in an equal speed drive state, an accelerating clutch disposed on a common axis with the equal speed clutch for transmitting drive to the front wheels in an accelerating state, a shift member shiftable along the axis to three positions for selectively operating the equal speed clutch and the accelerating clutch, and an actuator for shifting the shift member along the axis to the three positions.
With this construction, the actuator drives the shift member for selectively engaging the equal speed clutch and accelerating clutch. Thus, the front wheel change speed device has a simple construction for operating the two clutches.
In a preferred embodiment of this invention, the accelerating clutch is in the form of a friction type clutch. Thus, when drive is transmitted in acceleration to the front wheels, a sudden speed increase is checked to suppress shock. Further, the equal speed clutch is in the form of a claw type clutch operable to maintain a reliable, strong tractive force without slippage.
Other features and advantages of this invention will be apparent from the following description of an embodiment to be taken with reference to the drawings.


REFERENCES:
patent: 4648493 (1987-03-01), Schilling et al.
patent: 4723622 (1988-02-01), Toshikuni et al.
patent: 4862988 (1989-09-01), Umemoto
patent: 5038885 (1991-08-01), Sato et al.
patent: 5383531 (1995-01-01), Yoshioka et al.
patent: 2032022 (1980-04-01), None
patent: 35858 (1978-04-01), None
patent: 5162654 (1993-06-01), None
patent: 9072309 (1997-03-01), None

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