Gerotor pump with variable tolerance housing

Information

  • Patent Grant
  • 6688866
  • Patent Number
    6,688,866
  • Date Filed
    Thursday, November 15, 2001
    22 years ago
  • Date Issued
    Tuesday, February 10, 2004
    20 years ago
Abstract
A gerotor pump is provided that includes a pump housing having a pump cover and a pump end plate. The pump cover defines an open end, an axial bore, and a bottom end. The pump end plate engages the open end of the pump cover thereby enclosing the axial bore of the pump cover and creating an inner cylindrical chamber in the pump housing. A wear plate and a gerotor gear set assembly are operatively disposed within the inner cylindrical chamber such that the gerotor gear set assembly is operatively disposed between the wear plate and the pump end plate. A biasing member is disposed between the bottom end of the pump cover and the wear plate, and is adapted to operatively bias the wear plate against the gerotor gear set assembly and the pump end to create an axial zero tolerance condition between the pump elements.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The subject invention relates, generally, to gerotor pumps, more specifically to a gerotor pump having a housing that allows for variations in its internal axial tolerances.




2. Description of the Related Art




Gerotor pumps are commonly employed in the automotive industry for pumping oil to lubricate and cool various components of a typical automotive power train. For example, pumps of this type are often employed in transfer cases of automotive transmission assemblies. Gerotor pumps typically include a gerotor set having an externally toothed inner gear rotor intermeshed with an internally toothed outer gear rotor, wherein each rotor is disposed about respective eccentric axes. Other rotor pump sets are known that employ smooth surfaced rotors, one disposed within another and placed about respective eccentric axes. Regardless of the structure of the rotor set, the pumping action is accomplished by the rotational opening and closing of voids, or volumes, formed by the offset of the inner to the outer rotor during their rotation within a pump housing.




The gerotor set is typically seated in a cylindrical inner chamber of a pump housing and enclosed by an outer cover plate fixedly secured to the pump housing. A drive shaft rotates the inner rotor against the outer rotor to pump fluid between the intermeshed teeth from an inlet to an outlet in the housing.




The efficiency of the pump depends greatly upon the axial sealing of the gerotor set seated in the inner chamber between the pump housing on one axial side of the gerotor set and the outer cover plate on the other axial side of the gerotor set. The axial sealing of the gerotor set between the pump housing and the cover plate requires close manufacturing tolerances of the axial depth of the inner chamber housing the gerotor set. Such close manufacturing tolerances results in increase labor and expensive machining costs of the pump. The close tolerances also require a high torque input to initiate the rotation and pumping action of the pump elements. Additionally, in operation, when constructed with the necessary close tolerances for efficient pumping, the pump can easily exceed the desired design output pressure requiring supplemental structure for pressure relief.




Lastly, current manufacturing practices often call for the use of different materials for the pump elements and the pump housing to save weight. The use of different materials results in the undesirable effect of variations in the axial clearances as a function of temperature changes within the pump due to differing material coefficients of expansion. These temperature related changes in axial clearances, or tolerances, cause wide variations in pump performance.




Accordingly, it is desirable to provide a gerotor pump having a housing for enclosing the gerotor set which not only reduces the need for the close, exacting tolerances of prior art pumps, but also allows for variations in the thermal expansion of the pump elements while lowering the rotational torque input required to start the pump. Therefore, it is desirable to provide a gerotor pump having a variable tolerance housing.




SUMMARY OF THE INVENTION




The deficiencies in the related art are overcome by the present invention in a gerotor pump for pumping pressurized fluid between an inlet port and an outlet port. The gerotor pump includes a pump housing defined by a pump cover and a pump end plate. The pump cover defines an open end, an axial bore, a bottom end, and a central opening in the bottom end. The pump end plate is adapted to matingly engage the open end of the pump cover thereby enclosing the axial bore of the pump cover and creating an inner cylindrical chamber in the pump housing. A wear plate having a central opening is operatively disposed within the inner cylindrical chamber of the pump housing. Also, a gerotor gear set assembly having an inner and an outer rotor is disposed within the inner cylindrical chamber of the pump housing such that the gerotor gear set assembly is operatively set between the wear plate and the pump end plate. A shaft is received through the pump cover and the wear plate through the central openings and is operatively connected to the gerotor gear set assembly for rotating the gerotor gear set assembly within the inner cylindrical chamber of the pump housing. A biasing member is operatively disposed between the bottom end of the pump cover and the wear plate. The biasing member is adapted to bias the wear plate against the gerotor gear set assembly and the pump end to create an axial zero tolerance condition.




The present invention thereby overcomes the disadvantages and drawbacks of the current art by reducing the need for the close, exacting tolerances of prior art pumps, and also allows for variations in the thermal expansion of the pump elements while lowering the rotational torque input required to start the pump. This is accomplished by the variable tolerance characteristics of the pump housing that are available due to the use of the biasing member within the housing that causes the gerotor assembly to be held in zero tolerance to the other pump elements.











BRIEF DESCRIPTION OF THE DRAWINGS




Other advantages of the invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:





FIG. 1

is a top view of one embodiment of the gerotor pump of the present invention;





FIG. 2

is an exploded perspective view of one embodiment of the gerotor pump of the present invention;





FIG. 3

is a cross-sectional view of one embodiment of the gerotor pump of the present invention taken along line


3





3


of

FIG. 1

;





FIG. 4

is a partial cross-sectional view of one embodiment of a gerotor pump of the present invention depicting a partial section across the inlet port taken along line


4





4


of

FIG. 1

;





FIG. 5

is a top view of a gerotor pump and flexible cover plate according to an alternate embodiment of the present invention;





FIG. 6

is a cross-sectional view taken along line


6





6


of

FIG. 5

;





FIG. 7

is a partially exploded perspective view of the gerotor pump and flexible cover plate of the embodiment of

FIG. 5

;





FIG. 8

is a cross-sectional view taken along line


8





8


of

FIG. 5

; and





FIG. 9

is cross-sectional side view of a gerotor pump and flexible cover plate according to an additional embodiment of the present invention.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)




Referring to the drawings, wherein like reference numbers represent like or corresponding parts throughout the several views, a gerotor pump according to one embodiment of the present invention is generally indicated at


10


in FIG.


1


. The pump


10


is employed for pumping a fluid media, such as oil, from an inlet port


12


at a lower pressure, out through a corresponding outlet port


14


at a higher pressure. As shown in

FIG. 2

, the gerotor pump


10


is of a generally cylindrical disc-shaped configuration and includes a pump housing


16


, a wear plate


18


, a gerotor gear assembly set


20


, and a biasing member


26


. The pump housing


16


is defined by a pump cover


22


and a pump end plate


24


.




The pump cover


22


of the pump housing


16


defines an open end


28


, an axial bore


30


, a bottom end


32


, and a central opening


34


in the bottom end


32


. The pump end plate


24


fits within, and is disposed in a mating manner against, the open end


28


, thereby enclosing the axial bore


30


and creating an inner cylindrical chamber


36


within the pump housing


16


. In turn, the open end


28


further defines a lower seating surface


38


, an inwardly sloping sealing surface


40


, and an upper seating surface


42


that concomitantly receive mating surfaces


44


,


46


, and


48


, respectively, of the pump end plate


24


, which are of similar dimensions. The axial bore


30


of the pump cover


22


also includes a plurality of retaining grooves


50


disposed axially about its circumference. When assembled, the wear plate


18


, gerotor gear assembly set


20


, and a biasing member


26


are disposed within the inner cylindrical chamber


36


of the pump cover


22


.




The wear plate


18


has an annular groove


52


, a central opening


54


, and a plurality of retaining tabs


56


that extend axially along its outer circumference. The plurality of retaining tabs


56


are disposed upon the wear plate


18


in such an manner as to correspondingly engage the plurality of retaining grooves


50


in the axial wall


30


of the pump cover


22


. The retaining tabs


56


and their corresponding retaining grooves


50


prevent the wear plate


18


from rotating within the inner cylindrical chamber


36


, yet allow for longitudinal movement of the wear plate


18


axially within the pump housing


16


.




The preferred embodiment of the present invention employs a gerotor gear set assembly


20


, as is commonly known in the art. The gerotor gear set assembly


20


includes an inner toothed gear rotor


58


having a central opening


60


disposed within an outer toothed gear rotor


62


. As in a typical gerotor design, the inner-toothed gear rotor


58


has one less tooth than the outer-toothed gear rotor


62


, and is offset from the central axis upon which the outer-toothed rotor


62


is disposed. Thereby, the inner toothed rotor


58


, in meshing relationship with the outer toothed rotor


62


, forms expanding and contracting volumes or chambers between the teeth, which act as pumping chambers for the fluid media as the gerotor gear set assembly


20


is rotated. The outer-toothed gear rotor


62


is seated within the inner cylindrical chamber


36


on top of the wear plate


18


such that it is encompassed by the axial wall


30


. Thus, the gerotor gear set assembly


20


is disposed between, and operatively supported by, the wear plate


18


and the pump end plate


24


within the inner cylindrical chamber


36


.




The pump end plate


24


includes a flat planar surface


64


having an inlet channel


66


and an outlet channel


68


machined in a known manner therethrough. In addition, the end plate


24


further includes a central opening


70


, and inlet and outlet ports


12


and


14


, respectively. When the pump end plate


24


is matingly engaged to the pump cover


22


, the flat planar surface


64


is seated against the gerotor gear set assembly


20


. In this manner, the inlet channel


66


and the outlet channel


68


are in fluid communication with both the gerotor gear set assembly


20


and the inlet and outlet ports


12


and


14


, respectively, for routing fluid media into the gerotor pump


10


at a lower pressure and out at a higher pressure.




The central openings


34


,


54


, and


70


of the pump cover


22


, the wear plate


18


, and the pump end plate


24


, respectively, concomitantly allow for receiving an axial extending, cylindrical drive shaft


72


therethrough for connection to the central opening


60


of the inner rotor


58


of the gerotor gear set assembly


20


. The drive shaft


72


is operatively connected in a manner commonly known in the art, using splines or the like, to the inner rotor


58


at


74


.




As best shown in

FIG. 1

, the center axis of the pump is indicated at “A”. The open end


28


and axial bore


30


of the pump cover


22


are coaxial to the center axis “A”. However, the central openings


34


,


54


, and


70


are coaxially offset to an axis “B” which is eccentric to the center axis “A” of the pump housing


16


, so that the inner rotor


58


of the gerotor gear set assembly


20


is offset relative to the outer rotor


62


. This offset between the inner rotor


58


and outer rotor


62


of the gerotor pump


10


provides the desired pumping action, as described above.




The drive shaft


72


is thereby used to rotate the gerotor gear set assembly


20


within the inner cylindrical chamber


36


of the pump housing


16


to pump the fluid media from the inlet


12


to the outlet


14


of the pump end plate


24


. It should be appreciated that the inlet


12


and the outlet


14


are further connected, in a known manner, in fluid communication with the next higher assembly in which the gerotor pump


10


is installed, such as a transfer case, for example.




The biasing member


26


is disposed within the annular groove


52


of the wear plate


18


such that, when the gerotor pump


10


is assembled, the biasing member


26


is in contact with both the wear plate


18


and the bottom surface


32


. The annular groove


52


of the wearplate


18


retains the biasing member


26


in a coaxial position relative to the inner cylindrical chamber


36


. It should be appreciated that the annular groove


52


may be disposed within either the wear plate


18


, the bottom surface


32


, or both to allow the biasing member


26


to be maintained in position yet contact both surfaces.




The biasing member


26


, within the pump housing


16


, causes the wear plate


18


to slide along the retaining grooves


50


, and press the gerotor gear set assembly


20


axially against the pump end plate


24


. This closes any clearances, or tolerances, between the pump elements and provides a “zero” axial tolerance condition. In the preferred embodiment, the biasing member


26


is an o-ring, manufactured of any of a group of known materials capable of maintaining high resiliency and crush resistance within a heat intensive and oil laden environment including fluorocarbon rubber or highly-saturated nitrile, for example. In another non-limiting embodiment, the biasing member


26


may be formed as a flat annular ring as shown in FIG.


4


. It should additionally be appreciated by those of ordinary skill in the art that the biasing member


26


may be formed in other various cross-sectional shapes without departing from the scope or spirit of the present invention.




In operation, in an initial, static state, the biasing member


26


presses against the wear plate


18


forcing the wear plate


18


and the gerotor gear set assembly


20


against the pump end plate


24


, thereby removing any axial gaps between these pump elements and holding the gerotor gear set assembly


20


to an axial “zero” clearance, or tolerance, between the wear plate


18


and the pump end plate


24


. The low physical rotational drag of this configuration allows for a low torque start with high prime characteristics. In its operating capacity, the resiliency and compression characteristics of the material of the biasing member


26


may be selected to provide a specific maximum pressure capability of the gerotor pump


10


. This is possible due to the fact that, as the pump pressure reaches the compression limits of the biasing member


26


, the biasing member


26


will allow the wear plate


18


to slightly move away from the gerotor gear set assembly


20


. As the wear plate


18


moves away from the gerotor gear set assembly


20


, the axial tolerances open and the output pressure is lowered due to cross-bleeding of the gerotor gear set assembly


20


. As the pressure drops, the biasing member


26


will recover and the axial tolerances will again be zeroed.




Another embodiment of the present invention is generally indicated at


110


, in

FIG. 5

, wherein like reference numbers are increased by a factor of


100


are used to designate like structure with respect to the embodiment illustrated in

FIGS. 1-4

. The gerotor pump


110


is used for pumping pressurized fluid between an inlet


112


and an outlet


114


. The gerotor pump


110


has a generally cylindrical disc-shaped configuration and includes a pump housing


116


having a cylindrical pump housing opening


128


as shown in FIG.


6


. The pump housing


116


further includes an axial wall


130


defining an inner cylindrical chamber


136


and a bottom surface


132


.




A gerotor gear set assembly


120


including an inner toothed gear rotor


158


and an outer toothed gear rotor


162


, as is commonly known in the art, is seated within the inner cylindrical chamber


136


, encompassed by the axial wall


130


, and axially supported by the bottom surface


132


. A longitudinal, cylindrical drive shaft


172


is operatively connected in a manner commonly known in the art to the gerotor gear set assembly


120


for rotating the gerotor gear set assembly


120


within the inner chamber


136


to pump the fluid entering the chamber


136


from the inlet


112


to the outlet


114


.




The gerotor pump


110


further includes a cylindrical cover plate


124


recessed within and against the axial wall


130


and seated against the gerotor gear set assembly


120


for closing the pump housing opening


128


. The cover plate


124


includes a generally flat planar surface


164


in mating engagement with the gerotor gear set assembly


120


and a center bore


160


for receiving the drive shaft


172


therethrough for connection to and rotation of the gerotor gear set assembly


120


. The cover plate


124


also includes a peripheral lip


176


extending axially from the planar surface


164


which abuts and is in sealing and mating engagement with the axial wall


130


of the pump housing


116


for sealing and closing the pump housing opening


128


.




The gerotor pump


110


further includes a spring bias member generally indicated at


126


interconnected between the pump housing


116


and the cover plate


124


for continuously biasing the cover plate


124


axially against the gerotor gear set assembly


120


. The spring bias member


126


maintains axial bearing pressure between the cover plate


124


and the gerotor gear set assembly


120


to reduce the manufacturing tolerance typically required for proper sealing between the cover plate


124


, gerotor gear set assembly


120


and axial wall


130


forming the inner chamber


136


of the pump housing


116


.




Referring to

FIGS. 5 through 8

, the spring member


126


includes a plurality of flexible locking tabs


178


spaced circumferentially about the circumference of the cover plate


124


for engaging an outer portion of the pump housing


116


to bias the cover plate


124


against the gerotor gear set assembly


120


. Each flexible locking tab


178


includes a generally U-shaped base portion


180


formed integrally with the peripheral lip


176


and extending radially outwardly therefrom as shown in FIG.


7


. Each flexible locking tab


178


further includes a generally L-shaped snap lock portion


182


extending axially downwardly from the base portion


180


for engaging the outer portion of the pump housing


116


. Referring to

FIGS. 7 and 8

, the snap lock portion


182


includes a flat contact end


184


spaced from and planar to the planar surface


164


of the cover plate


124


. A U-shaped torsion bar portion


188


extends between the lock portion


182


and the contact end


184


for biasing the cover plate


124


against the gerotor gear set assembly


120


in the inner chamber


136


. The cover plate


124


and flexible locking tabs


178


may be an integral stamped steel solid body or solid molded plastic body.




The pump housing


116


includes a plurality of anti-rotation arms


186


formed integrally with and extending radially outwardly from the outer portion of the housing


116


for releasably locking with the respective flexible locking tabs


178


to spring bias the cover plate


124


against the gerotor gear set assembly


120


. More specifically, the contact end


184


of the snap lock portion


182


engages the surface of the anti-rotation arm


186


of the pump housing


116


to releasably lock the flexible locking tabs


178


to the pump housing


116


.




In assembly, the gerotor gear set assembly


120


is seated within the inner chamber


136


with the outer periphery of the gear set assembly


120


in mating engagement with a portion of the axial wall


130


of the pump housing


116


and supported by the bottom surface


132


as shown in FIG.


6


. The cover plate


124


is then recessed within the pump housing opening


128


such that the peripheral lip


176


matingly engages the remaining portion of the axial wall


130


to close the opening


128


and seal the gerotor gear set assembly


120


between the bottom surface


132


, axial wall


130


and planar surface


164


of the cover plate


124


. The cover plate


124


is initially aligned with the pump housing


116


with each of the flexible locking tabs


178


positioned between an adjacent pair of the anti-rotation arms


186


. The cover plate


124


is then rotated counterclockwise about the pump housing


116


until the contact ends


184


and torsion bar portions


188


extend over the surfaces of the anti-rotation arms


186


abutting against the leg portions


182


as shown in FIG.


8


. The flexible locking tabs


178


maintain a biasing force, or tension, and sealing engagement between the cover plate


124


and the gerotor gear set assembly


120


to prevent leakage of fluid during normal operating pressures. The flexible locking tabs


178


and cover plate


124


also afford increase prime-ability of the pump


110


due to the zero tolerance between the cover plate


124


, gerotor gear set assembly


120


and pump housing


116


. Still further, the flexible locking tabs


178


allow the cover plate to flex or move away from the gerotor gear set assembly


120


in response to an increased fluid pressure to allow leakage across the face of the gear set assembly


120


to regulate the output pressure of the pump


110


.




Referring to

FIG. 9

, an additional alternative embodiment of the present invention is shown wherein the spring bias member


126


includes a plurality of separate torsion bars


190


circumferentially spaced about the gerotor pump


110


and operatively connected between the pump housing


116


and the cover plate


124


. The torsion bars


190


include a thin metal plate having a first end


192


fixedly secured to the pump housing


116


by a fastener


194


and a second end


196


in mating engagement with the cover plate


124


for urging the cover plate


124


against the gerotor gear set assembly


120


in a manner similar to the embodiment shown in

FIGS. 5 through 8

.




The invention has been described in an illustrative manner. It is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.



Claims
  • 1. A gerotor pump for pumping pressurized fluid between an inlet port and an outlet port, said gerotor pump including:a pump housing defined by a pump cover and a pump end plate, said pump cover defining an open end, an axial bore, a bottom end, and a central opening in said bottom end, said pump end plate adapted to matingly engage said open end of said pump cover thereby enclosing said axial bore of said pump cover and creating an inner cylindrical chamber within said pump housing; a wear plate having a central opening and operatively disposed within said inner cylindrical chamber of said pump housing; a gerotor gear set assembly disposed within said inner cylindrical chamber of said pump housing such that said gerotor gear set assembly is operatively supported between said wear plate and said pump end plate; a shaft operatively connected to said gerotor gear set assembly for rotating said gerotor gear set assembly within said inner cylindrical chamber of said pump housing; a biasing member formed as a resilient annular ring that is operatively disposed between said bottom end of said pump cover and said wear plate, only said resilient annular ring adapted to operatively bias said wear plate against said gerotor gear set assembly and said pump end plate to create an axial zero tolerance condition between said wear plate, said gerotor gear set assembly, and said pump end plate.
  • 2. A gerotor pump as set forth in claim 1 wherein said wear plate includes an annular groove disposed in its bottom surface, said biasing member adapted to be received within said annular groove.
  • 3. A gerotor pump as set forth in claim 1 wherein said bottom surface of said pump cover includes an annular groove, said biasing member adapted to be received within said annular groove.
  • 4. A gerotor pump as set forth in claim 1 wherein said biasing member is made from at least one of a group comprising fluorocarbon rubber or highly-saturated nitrile compounds.
  • 5. A gerotor pump as set forth in claim 1 wherein said annular ring is further defined as an o-ring.
  • 6. A gerotor pump as set forth in claim 1 wherein said wear plate includes a plurality of retaining tabs extending outward from the circumference of said wear plate and parallel to its central axis, and said pump cover includes a plurality of retaining grooves disposed axially along said inner bore, said retaining tabs adapted to slidingly engage said retaining grooves such that said wear plate is free to move axially within said pump cover but is prevented from rotating.
  • 7. A gerotor pump as set forth in claim 1 wherein said gerotor gear set assembly includes an inner pumping gear element having external teeth interposed in meshing relationship with an outer pumping gear element having internal teeth, said inner pumping gear element operatively disposed on a central pump axis defined by center axis of said pump housing, said outer pumping gear element operatively disposed on an axis that is offset relative to said central pump axis so that rotation of said inner and outer pumping gear elements, relative to one another, creates gaps between said internal and external teeth which define expanding and contracting pumping volumes.
  • 8. A gerotor pump as set forth in claim 1 wherein said pump end plate includes a planar surface in contact engagement with said gerotor gear assembly, said planar surface including an inlet passage and an outlet passage in fluid communication with said pumping volumes of gerotor gear set assembly.
  • 9. A gerotor pump as set forth in claim 1 wherein said pump end plate includes an inlet port in fluid communication with said inlet port and an outlet port in fluid communication with said outlet passage such that said inlet port delivers fluid media at a lower pressure to said gerotor gear set assembly and said outlet port receives fluid media at a higher pressure from said gerotor gear set assembly.
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Number Name Date Kind
2405061 Shaw Jul 1946 A
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3299824 Gauthier Jan 1967 A
3632240 Dworak Jan 1972 A
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4976594 Bernstrom Dec 1990 A
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Number Date Country
57-76284 May 1982 JP