Rotary expansible chamber devices – With changeable working chamber magnitude – Intermeshing rotary members
Reexamination Certificate
1998-11-13
2001-06-12
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
With changeable working chamber magnitude
Intermeshing rotary members
C418S171000
Reexamination Certificate
active
06244839
ABSTRACT:
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION
The present invention relates generally to variable displacement gear pumps. More particularly, the present invention relates to a variable displacement internal gear pump with pressure compensation.
As will be appreciated by those skilled in the art, fixed displacement gear pumps are widely used because they are simple, rugged, compact, and relatively inexpensive. However, constant pressure systems that use such pumps waste energy by exhausting excess flow at system pressure through relief valves. If gear pumps can be economically made into variable displacement forms, they can be used to make constant pressure systems more efficient.
Gear pumps are made in both external and internal configurations. Internal gear pumps are of two types, internal spur gear or gerotor. Internal spur gear pumps use a crescent shaped member in the space in between the inner and outer gear teeth while gerotor pumps have a tooth profile which does not require a crescent member. The gerotor mechanism is made up of inner and outer toothed elements. The internal toothed element has one less tooth than does the outer element and the outer element uses a conjugate tooth profile. As a result, the inner and outer tooth profiles maintain continuous fluid tight contact during operation.
Designing a pressure compensated variable displacement gear pump is a challenging problem that several engineers have attempted to solve. Most designs involve internal gear arrangements. During the last twenty years, several patents have been issued on such concepts. For example, U.S. Pat. No. 5,476,374, issued to Langeck on Dec. 19, 1995, describes an axially-ported variable volume gerotor pump configuration. In that invention, variable flow control is achieved by returning part of the output flow to the pump inlet. U.S. Pat. No. 4,492,539, issued to Specht on Jan. 8, 1985, shows a variable displacement gerotor pump. The described design varies the eccentric position of an outer member relative to an inner member by rotating position control members. Another patent by Specht, U.S. Pat. No. 4,413,960, issued Nov. 8, 1983, describes a position controlled device for a variable delivery pump. In this patent, the pump body can be rotated through an infinite range of angles relative to the pump housing to regulate the eccentric position of pumping elements. This action controls the volume output of the pump.
Another internal gear pump is shown in U.S. Pat. No. 4,097,204, issued to Palmer on Jun. 27, 1978. The Palmer patent shows a variable displacement gear pump which uses a radial movement of the external gear axis to form an eccentric with the internal gear to vary the volume of fluid displaced by the pump.
While the known art shows variable displacement pump forms that may be physically realized, their complexities make practical commercialization unrealistic. Thus, known art fails to address the need for an improved pressure compensated variable displacement internal gear pump. In particular, the known art fails to provide an internal gear pump using variable displacement that is fast-acting. An improved internal gear pump should quickly respond to changing displacement requirements to improve overall pump efficiency.
SUMMARY OF THE INVENTION
The present invention addresses the problems associated with the known art. The present invention is based upon research begun by Dr. Cole concerning internal gear pump design that has been continued and broadened to include pressure compensation for variably displacing the internal gear pump. The resulting variable displacement gerotor pump has a fixed gear axis eccentricity and varies displacement by moving controlling elements linearly along the drive shaft. The improved pump is very responsive to changing displacement requirements.
In an exemplary embodiment, the internal gear pump includes a housing accepting fluids to be pumped and emitting pumped fluids. The housing is penetrated by an elongated drive shaft that is preferably driven by an associated motor or the like. The drive shaft extends into the housing where it rotates internal elements to pump the fluids into and out of the housing.
In the exemplary embodiment, the gear pump includes several internal components that slide along the longitudinal axis of the drive shaft to vary the fluid displacement of the pump. The axially-moving element assembly includes the drive shaft, inner gerotor element, port plug, thrust bearing and retainer sleeve. The inner gerotor element is keyed to the drive shaft and, except for the port plug, the axially-moving element assembly rotates as a unit. Of course, this assembly is driven by the drive shaft.
A coupling with a hexagonal cross-section or other shape of male spline is formed at the driven end of the drive shaft with a corresponding coupling formed in the end of the prime mover shaft from the motor. This allows torque to be transmitted to the drive shaft while facilitating simultaneous axial motion of the drive shaft with respect to the drive coupling. Minimum engagement length in the coupling assures that torque can be continuously transmitted when the drive shaft slides axially in response to pressure deviations, as will be discussed in detail hereinafter.
The driven end of the shaft includes an integral flanged piston disposed inside the pump housing that also serves to axially retain the internal gerotor element and port plug. The outside diameter of the piston is only slightly smaller than the inside diameter of the bore in which it slides. The outward face of the piston is in contact with fluid that is nominally at system pressure.
The internal gerotor element and port plug are retained by a thrust bearing that slides over the drive shaft and is held in place by a retainer sleeve that securely attaches to one end of the drive shaft. The inner face of the thrust bearing contacts the inner periphery of the rear face of the port plug and overlaps the bore of the plug. As mentioned previously, when the drive shaft is rotating, the port plug rotates independently (and slower) than the thrust washer. Similar relative motion occurs at the front end of the port plug where it contacts the rear face of the inner gerotor element.
The port plug has the same number of teeth as an outer gerotor element does. There is only a small clearance between the outermost edge of the teeth of the port plug and the innermost edge of the conjugate teeth of the outer gerotor. This allows the port plug to act as a piston that can slide axially inside the outer gerotor. The outer rear face of the plug is in contact with fluid that is nominally at system pressure. The area of this face is the same as the area of the piston that is integral with the drive shaft (making these two areas equal is an important concept, because it allows the pump to behave dynamically like a double-rod-end equal-piston-area hydraulic cylinder with a spring mass load, as later described.). Thus, the outward piston face and rear face of the port can push the assembly in the housing.
The inner gerotor and port plug slide inside the outer gerotor. The outer gerotor member is driven by the inner gerotor member. The outer gerotor and the port plug rotate together at a slower speed than the inner gerotor. However, eccentricity between the inner and outer gerotor members is fixed.
In an exemplary embodiment, the variable displacement gear pump is displaced by a pressure compensator. In one embodiment, the pressure compensator senses the system pressure and then displaces the pump to meet the desired flow required by the system. The pressure compensator acts like a 3-position, 4-way, closed-center valve controlled by pressure operating against a return spring. As system pressure gets above or below the spring load pressure, it will displace the spool to a certain position, allowing a corresponding amount of flow into the pump. As the system pressure rises, the corresponding pressure upon the spring load will cause the spool to open until the spring load pressure equals the system pressur
Cole Jack H.
Tay Yong Fong
Head Johnson & Kachigian
University of Arkansas
Vrablik John J.
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