Motor vehicles – Having four wheels driven – Including pump and fluid motor – or generator and electric...
Patent
1995-05-23
1996-10-15
Hurley, Kevin
Motor vehicles
Having four wheels driven
Including pump and fluid motor, or generator and electric...
180197, B60K 2816
Patent
active
055645194
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a four-wheel traveling system for a tipper such as a large construction dump truck and so forth. More specifically, the invention relates to a drive system for a tipper, in which rear wheels are driven by a driving force developed by an internal combustion engine and front wheels are driven by a variable hydraulic motor driven by hydraulic pressure supplied from a hydraulic pressure source driven by output torque of the internal combustion engine.
BACKGROUND ART
A large constructing dump truck as one form of a tipper has steerable fronts wheel and driving rear wheels mounted on a vehicle body, and also has a tiltable rear body. A typical known traveling system for such a dump truck mechanically drives the driving rear wheels by transmitting an output of an internal combustion engine, such as a diesel engine (hereinafter simple referred to as "engine") via a power transmission.
As a traveling system of a normal on-the-road vehicle, Japanese Unexamined Patent Publication (Kokai) NO. Showa 63-258223, for example, discloses a mechanical and hydraulic type four-wheel drive traveling system, in which an output torque of the engine is mechanically transmitted to the rear wheels via the power transmission, a variable hydraulic pump is driven by the output torque of the engine, and the front wheels are driven by a variable hydraulic motor driven by the discharged pressurized fluid of the hydraulic pump. Similarly, Japanese Unexamined Patent Publication No. Showa 61-191429 also proposes a four-wheel drive system for a vehicle, in which one of the front and rear wheels are driven by a hydraulic drive system.
In the traveling system having a drive system exclusively employing the mechanical drive system, a traction force can be lowered when slippage is caused on the driving rear wheels. Therefore, such drive system has low performance in traveling ability in a muddy area or in hill-climbing.
Conversely, with the four-wheel drive traveling system, in which the mechanical drive system and a hydraulic drive system are combined, traveling ability in muddy areas and hill-climbing performance can be improved. However, in such system, it becomes necessary to synchronize the rear wheels and front wheels. In the prior art, in detecting wheel slippage at the rear wheels, the displacement of the variable hydraulic pump and the capacity of the variable hydraulic motor are set at zero so as not to drive the front wheel, while no slippage is caused on the rear wheels, and the displacement of the variable hydraulic pump and the capacity of the variable hydraulic motor are varied to adjust the hydraulic force to a reference value to transmit the driving force to the front wheel.
Therefore, the displacement of the hydraulic pump and the capacity of the hydraulic motors are increased from zero after occurrence of wheel slippage on the rear wheels and varied against the certain hydraulic force as a reference value, to drive the front wheels. This causes time lag from occurrence of wheel slippage on the rear wheels to driving of the front wheels to make smooth traveling impossible.
This difficulty in providing smooth traveling is particularly significant in the case of a tipper having several of tens tons of movable load.
On the other hand, as set forth above, in the four-wheel traveling system, the wheel rotation speed on the front wheels is determined by the discharge amount of the variable hydraulic pump and the capacity of the variable hydraulic motor. Here, provided that the pump displacement is constant, the discharge amount of the hydraulic pump is determined by the engine revolution speed. Accordingly, the wheel rotation speed of the front wheels is variable depending upon the engine revolution speed. On the other hand, the wheel rotation speed of the rear wheels is determined by the engine revolution speed and a speed ratio of the power transmission. Therefore, provided that the engine revolution speed is constant, the wheel rotation speeds of the front wheels and the rear whe
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Ando Hiroyuki
Hasegawa Nobuki
Katoh Masaya
Ogawa Satoshi
Oka Koichi
Hurley Kevin
Kabushiki Kaisha Komatsu Seisakusho
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