Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Reexamination Certificate
2000-05-17
2001-08-28
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
C060S454000, C060S464000, C060S488000
Reexamination Certificate
active
06279317
ABSTRACT:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improving the performance of a hydrostatic drive, especially a hydrostatic drive for a vehicle, by means of a regeneration circuit.
2. Background Information
Hemostatic drives are popular in applications where it is desirable to have good speed control under varying loads. They are also popular in hazardous, dirty, and nasty environments, such as coal mines, quarries, food processing plants, and on construction sites. Much effort has been expended in trying to increase the efficiency and performance ranges of hydrostatic drives. Hydrostatic drives are typically called, in the trade, closed loop systems, and comprise a fixed or variable displacement pump supplied with fluid by means of a charge pump.
Existing ways of obtaining a broader range of speed and torque in a hydrostatic drive with a given pump, motors, and engine combination comprise:
a) using a mechanical transmission with a variety of gearing arrangements in conjunction with one or more hydraulic motors, and
b) valving to switch the hydraulic motors from a parallel circuit to a series circuit, and back again, as required.
Regeneration circuits are common to the trade on industrial equipment such as hydraulic presses. Regeneration circuits using rotary dividers are in the public domain for industrial equipment such as hydraulic presses. A publication illustrating gerotor rotary flow dividers in regeneration circuits is the American Society of Agricultural Engineers Paper No. 911596 “Gerotor Rotary Flow Divider” by George Morgan, P. E., Sales Manager, White Hydraulics, Inc. presented at the 1991 International Winter Meeting sponsored by the American Society of Agricultural Engineers at the Hyatt Regency Chicago, Chicago, Ill., December, 1991 which is hereby incorporated by reference. The American Society of Agricultural Engineers is located at 2950 Niles Road, St. Joseph, Mich., 49085-9659, USA, Ph. (616) 429-0300, Fax: (616) 429-3852.
Hydra-Pneu Consulting, Inc., 726 Outer Gray Drive, Newburgh, Ind. 47630-1517, Ph. (812) 853-3234, conducted a course in “Advanced Fluid Power” in 1991, where the instructor, Bud Trinkel, discussed the use of a rotary flow divider in an open loop press circuit. One of his previous students had developed it, and brought it to his class. Applicant then introduced it to his employer at the time, White Hydraulics, Hopkinsville, Ky. The engineers doubted it would work. It did.
The state of the art uses flow dividers in regeneration circuits for open loop, fixed displacement circuits. Neither regeneration circuits, nor regeneration circuits with rotary flow dividers, nor regeneration circuits with gerotor rotary flow dividers have ever been used with closed loop hydrostatic drives, especially vehicle closed loop hydrostatic drives.
With existing state-of-the-art hydrostatic drives with bi-directional pumps, approaches to proper filtration and cooling are limited. High pressure filtration arrangements are expensive, so typically are not used on mobile equipment. Similarly, for coolers to withstand the high pressures of the hydrostatic closed loop system flows, the designs would be heavy and expensive. Consequently, choices for filtration and cooling, practically, are limited to case drain flow or inlet charge pump flow, or hot oil shuttle arrangements where a small amount of flow is cooled and filtered at a time. This means that the bulk of the flow is not properly filtered or cooled, and this results in componentry wear which reduces componentry life.
As will be seen from the subsequent description, the preferred embodiments of the present invention broadens the performance range of a closed loop hydrostatic drive in a novel manner and overcomes exisiting limitations of closed loop hydrostatic drives.
SUMMARY OF THE INVENTION
The present invention is an improvement to a closed loop hydrostatic drive which broadens the performance range of said hydrostatic drive with a given prime mover, hydraulic pump, and hydraulic motor combination. Said improvement comprises a rotary flow divider in conjunction with appropriate valving as required to isolate said flow divider from the closed loop hydrostatic drive. In the preferred embodiment of the present invention, a three way, two position, solenoid operated, spring return valve receives exhaust hydraulic flow from at least one hydraulic motor. In normal, or low speed operation, the exhaust flow is the low pressure supply to the hydrostatic drive pump. For the high speed, or regeneration, cycle, the solenoid valve is actuated, and the exhaust hydraulic flow from the at least one hydraulic motor outlet is diverted to a rotary flow divider. In the preferred embodiment of the present invention, for a 20 gallon per minute variable displacement pump in a closed loop hydrostatic drive, it would be a four section White ROLLERSTATOR (Reg. U.S. Trademark) gerotor flow divider. Fluid flow from half of the rotary flow divider sections is returned to a low pressure section of the closed loop hydrostatic drive for return to the pump, while the fluid flow from the other half of the rotary flow divider is routed to a high pressure section of the closed loop hydrostatic drive between the pump and the at least one hydraulic motor. The effect of this arrangement is, for a rotary flow divider with sections of equal fluid displacement per revolution, that the fluid flow into the at least one hydrualic motor becomes approximately double the output fluid flow of the hydraulic pump. The preferred embodiment of the present invention further comprises a filter and an oil cooler and a one-way check valve through which the fluid flow from the half of the rotary flow divider sections is returned to the low pressure section of the closed loop hydrostatic drive is routed after said fluid flow leaves the rotary flow divider and prior to entering into the low pressure side of the closed loop hydrostatic drive. The purpose of the one-way check valve is to prevent reverse fluid flow back through the oil cooler, the filter, and the rotary flow divider. When regeneration is to be used only in one direction, such as forward, an appropriate interlock can be used so the solenoid operated valve is not actuated. Then, when the hydrostatic drive pump is reversed, and what was the low pressure side of the closed loop becomes the high pressure side, said interlock in conjunction with the solenoid operated valve in the at rest position in conjunction with the one-way check valve protects the oil cooler, the filter, and the rotary flow divider from reverse fluid flow.
A low pressure relief valve, normally incorporated in a charge pump supplying fluid to the low pressure side of the hydrostatic drive, precludes excessive pressure building up in said low pressure side of the hydrostatic drive from fluid flow from either of the rotary flow divider or the charge pump.
REFERENCES:
patent: 4002028 (1977-01-01), Budzich
patent: 4503928 (1985-03-01), Mallen-Herrero et al.
patent: 4649705 (1987-03-01), Williamson
patent: 5511368 (1996-04-01), Kocher
patent: 5794438 (1998-08-01), Lisniansky
patent: 6145287 (2000-11-01), Rosskopf
American Society of Agricultural Engineers, paper #911596 Gerotor Rotary Flow Divider by George H. Morgan, P.E.
Camoriano Theresa F.
Leslie Michael
Look Edward K.
Manley Mark A.
Price Gary K.
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