Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Reexamination Certificate
1999-11-02
2001-11-27
Vanaman, Frank (Department: 3611)
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
C180S053400
Reexamination Certificate
active
06321867
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to four wheel drive articulated tractors and, more particularly, to improvements to the drive system for hydrostatically driven tractors.
It is desirable to integrate all the drives for the input driven components of an articulated four wheel drive tractor into a single gearbox affixed to the rear axle housing of the tractor. Such a mechanism would place the hydrostatic pump for powering the traction drive of the tractor, the hydraulic pump for the tractor hydraulic system, the drive for the power-takeoff (PTO) system, and any auxiliary hydraulic pumps to be driven off the same gearbox device with the output driver components, including the hydrostatic motor, speed reduction gears and output drive shafts.
Lubrication of a gear set is a consideration in the design of a gearbox device for transferring rotational power through gear sets arranged and configured to provide the proper rotational speed to a component driven from the engine of the tractor. Commonizing lubrication sumps can minimize the number of lubrication systems that need to be provided as well as provide more effective lubrication of the gear sets and the cooling of the lubrication fluid.
Conventional tractor drive mechanisms include a mechanical transmission to provide different output speeds for a given engine input speed. Even hydraulically driven tractors have utilized a three speed mechanical transmission between the hydrostatic motor and the final drive to provide desired different output speeds to the operation of the final drive for powering the movement of the tractor. It would be desirable to replace the three speed mechanical transmission on hydrostatically driven tractors to minimize cost and to enhance operation of the tractor.
Obtaining maximum drawbar pull and maximum road speed capability in a hydrostatically driven tractor requires the variable hydrostatic motor be operated at close to it's maximum rated operating speed when in road gear. Since there is little margin then remaining for overspeeding under conditions where the tractor is moving downhill, some overspeed control must be provided.
When the hydrostatic drive is used with a high torque rise engine, the available charge pump flow drops as the engine speed drops until the point of not being able to maintain servo pressure is reached, resulting in a hydrostatic stall. Under these conditions, the engine will continue to run, while the hydraulic fluid is being sent over relief creating heat.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a hydrostatically driven tractor utilizing a variable hydrostatic motor to provide operative power to the drive wheels of the tractor.
It is a feature of this invention that an electronic control of the hydrostatic drive mechanism is provided.
It is another feature of this invention that the overspeed control for the hydrostatic motor is provided electronically.
It is an advantage of this invention that the displacement of the hydrostatic motor is automatically increased to reduce output speed whenever the tractor overspeeds by traveling downhill.
It is another advantage of this invention that the displacement of the hydrostatic motor is automatically corrected in response to a comparison of the detected output speed of the motor with the desired output speed.
It is another object of this invention to provide an overspeed control for a hydrostatically driven tractor.
It is still another object of this invention to provide remote cooling of the hydraulic fluid used for lubricating a remote drop box for a tractor power-takeoff.
It is still another feature of this invention that the oil is taken for a remote drop box from the oil cooler outlet into a hydraulic motor/pump combination.
It is still another advantage of this invention that the pump displacement for the remote drop box is slightly larger than the motor so that the remote drop box will not overfill.
It is still another object of this invention to provide a supplemental charge pressure and flow to prevent hydrostatic stall conditions.
It is yet another feature of this invention that a supplemental charge flow is provided with a circuit that includes a reducing valve to provide adequate charge pressure and flow to the hydrostatic pump to maintain servo pressure even when engine speed drops off.
It is yet another advantage of this invention that the hydrostatic stall condition can be avoided when engine speed drops from encountering a high draft load.
It is yet another object of this invention to provide a hydrostatically driven, four wheel drive tractor which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use.
These and other objects, features and advantages can be found in the instant invention in which a system is provided for lubricating and cooling a remote drop box for a hydrostatically drive four wheel drive tractor. The hydrostatic motor is operated very close to its maximum rated operating speed during roading in order to maximize drawbar pull and road speed capability for a variable hydrostatic motor, leaving very little margin for overspeeding that occurs when the tractor is roading downhill. An electronic overspeed control is provided to provide dynamic engine braking. When the hydrostatic drive is used with a high torque engine, the available charge pump flow drops as the engine speed drops, and eventually reaches a point where the required servo pressure to maintain the hydraulic pump in stroke cannot be maintained. Such a condition is alleviated by the supplemental charge flow system. Stabilization of the hydraulic load sensing system, which is subject to rhythmic flow pulsations or surging, particularly when flow compensators in valving interact with the flow compensator of the hydraulic pump, is accomplished with an attenuator/hose assembly.
REFERENCES:
patent: 3655004 (1972-04-01), Hoashi
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patent: 3978937 (1976-09-01), Chichester et al.
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patent: 4530416 (1985-07-01), Kassai
patent: 4546847 (1985-10-01), Abels
patent: 4554991 (1985-11-01), Eden
patent: 5919243 (1999-07-01), Huh
patent: 5937646 (1999-08-01), Zakula
patent: 1555661 (1970-01-01), None
patent: 1505645 (1970-10-01), None
patent: 57-44533 (1982-03-01), None
Miller Larry W.
New Holland North America Inc.
Stader John William
Vanaman Frank
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