Motor vehicles – Having four wheels driven – Including pump and fluid motor – or generator and electric...
Reexamination Certificate
1999-04-15
2001-02-20
Johnson, Brian L. (Department: 3618)
Motor vehicles
Having four wheels driven
Including pump and fluid motor, or generator and electric...
C180S244000, C180S248000, C180S006200
Reexamination Certificate
active
06189641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a four-wheel hydraulic drive system for a working vehicle including a hydraulic pump, a first hydraulic motor fluidly connected therewith so as to drive first driving wheels, and a second hydraulic motor for driving second driving wheels, wherein a braking force applied on the first driving wheels by braking devices can extend to the second driving wheels.
2. Related Art
There has been a conventional four-wheel drive working vehicle provided with a hydraulic transmission including a hydraulic pump driven by an engine and a hydraulic motor fluidly connected with the pump for driving either pair of front or rear wheels (usually, rear wheels). Such a conventional four-wheel drive vehicle has been provided under the bottom of the midsection thereof with a transmission shaft for transmitting power from the hydraulic transmission to the other pair of wheels (usually, front wheels).
As compared to a two-wheel drive vehicle, the four-wheel drive vehicle easily creates a stronger propelling force so as to be effective in climbing a hill or working in a paddy field.
In the conventional construction, the peripheral speed of the front wheels is normally set higher than that of the rear wheels so as to minimize the cornering radius of the vehicle in field. The problem has arisen that the front wheels tend to be dragged during a small radius cornering so as to prevent the vehicle from smooth cornering.
During usual travel on a flat road, such as asphalt pavement or the like, the same problem arises that the difference of peripheral speed between the front wheels and the rear wheels causes the front wheels to slip or be dragged and to wear, even if the vehicle travels in a substantially straight direction. The tendency that the front wheels are dragged is increased in proportion to the travelling speed of the vehicle. Furthermore, driving of four wheels wastes power. Therefore, a typical driver on a flat road has shut-off power transmission to the front wheels, so as to drive only the rear wheels. In other words, the driver has caused the vehicle to travel in the two-wheel drive mode during usual travel on a road. However, when the rear wheels are braked in the two-wheel drive mode, frictional resistance is only generated between the rear wheels and the road, such that the problem has arisen that the braking distance becomes longer than that in the four-wheel drive mode; wherein the braking force to the rear wheels extends to the front wheels such that frictional resistance is generated between all four wheels and the road.
Additionally, there has been the problem that a working machine of a type equipped on the bottom of the midsection of the vehicle body must be designed to avoid the intervention with the above-mentioned transmission shaft disposed under the same.
SUMMARY OF THE INVENTION
A four-wheel hydraulic drive system for a working vehicle having a pair of first driving wheels (such as rear wheels) and a pair of second driving wheels (such as front wheels), which includes a hydraulic pump and a hydraulic motor (a first hydraulic motor) fluidly connected with the pump for driving the first driving wheels, is further provided with another hydraulic motor (a second hydraulic motor) fluidly connected with the same pump for driving the second driving wheels according to the present invention, thereby omitting the conventional transmission shaft for the second driving wheels and expanding the space under the bottom of midsection of the vehicle body so as to enable a working machine to be equipped in the space.
Presupposing that the peripheral speed of the second driving wheels is set higher than that of the first driving wheels during travel in regular four-wheel drive, the four-wheel hydraulic drive system can be switched between a first four-wheel drive mode and a second four-wheel drive mode. In the first four-wheel drive mode, the torque of the second hydraulic motor is substantially identical to that of the first hydraulic motor, such that the vehicle can travel with a strong propelling force. In the second four-wheel drive mode, the torque of the second hydraulic motor is smaller than that of the first hydraulic motor, such that the vehicle can travel on a flat road at high speed without dragging and wearing of the second driving wheels. When braking devices for first driving wheels are actuated during travelling in the second four-wheel drive mode, the braking force extends to the second driving wheels so as to reduce the braking distance because the second hydraulic motor is smaller torque act as dynamic brake.
Alternatively, the four-wheel hydraulic drive system of the present invention is further provided with means which reduces the hydraulic pressure for driving the second hydraulic motor as the steering degree of the steerable second driving wheels is increased. The resultant vehicle can turn in a small cornering radius smoothly without dragging of the second driving wheels.
Besides, the four-wheel hydraulic drive system of the present invention is further provided with means which reduces the hydraulic pressure for driving the second hydraulic motor as the vehicle speed is increased. The resultant vehicle can travel on a road at high speed without dragging of the second driving wheels causing the wearing thereof while saving the cost of fuel.
Furthermore, according to the present invention, a vehicle employing the four-wheel drive system including such means for reducing the hydraulic pressure for driving the second hydraulic motor, may also include a braking device for braking the first driving wheels. In such a situation, if the braking device is actuated when the means for reducing hydraulic pressure is actuated such that hydraulic pressure to the second hydraulic motor is reduced, the hydraulic pressure to the second hydraulic motor is automatically increased. The resultant vehicle can travel at high speed with low cost of fuel as the above-mentioned, and also, when the first driving wheels are braked by the braking device, the braking force extends to the second driving wheels through the second hydraulic motor such that all four wheels are braked, thereby reducing the braking distance.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed several exemplary embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.
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Fischmann Bryan
Johnson Brian L.
Kanzaki Kokyukoki Mfg. Co. Ltd.
Sterne Kessler Goldstein & Fox P.L.L.C.
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