Abstract:
A pump assembly is provided that includes a gerotor pump and a manifold. An aspirating member is positioned between a pump inlet cavity in the manifold and a fluid reservoir. Fluid flow generated by operation of the pump is diverted by a flow control valve and accelerates as it passes between the aspirating member and the manifold. The resulting decrease in static pressure draws the fluid out of the reservoir where it mixes with the higher velocity fluid. As the combined fluid is slowed, the static pressure increases to “supercharge” the inlet cavity to improve the inlet fill and reduce cavitation. An inlet port in the gerotor pump corresponds to the inlet cavity in the manifold. The timing and geometry of an input port is optimized to prevent noise inducing pressure spikes while maintaining sufficient back pressure in the pump chambers to collapse entrapped vapor bubbles in the fluid.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a positive displacement fluid pump and more specifically to a gerotor pump assembly suitable for use in hydraulic systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    In a positive displacement fluid pump commonly referred to as a gerotor pump, a ring gear and a pinion gear inside of the ring gear are supported in a pump housing for rotation about parallel, laterally separated centerlines. The teeth on the respective gears cooperate to define a plurality of variable volume pumping chambers whereupon during rotation of the gear members, a pumping chamber increases in volume to a maximum volume and then decreases in volume. Fluid from the relatively low pressure inlet port of the pump is drawn into pumping chambers that are increasing in volume. Upon further rotation of the gerotor when the pumping chambers are decreasing in volume, the fluid is pushed out through the outlet port of the pump at a relatively higher pressure. The inlet and the outlet ports are separated angularly or “timed” to prevent the pump chambers from simultaneously overlapping both the inlet port and the outlet port.  
           [0003]    A common limitation exhibited by many gerotor pumps is excessive noise caused by cavitation (the rapid formation and collapse of bubbles in the pumped fluid). Cavitation in gerotor pumps is generally caused by the pump speed being greater than the time required to fill the pumping chambers. The incomplete charge of the pumping chambers entraps air or other vapor within the fluid. If not accounted for, the entrapped vapor bubbles collapse in the discharge port creating noise inducing pressure pulses that also decrease pump efficiency. The present invention provides a pump assembly with improved charging and timing conditions to reduce cavitation and resulting noise.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a new and improved positive displacement pump assembly with improved timing, porting geometry and inlet fluid mechanics to improve fill and reduce cavitation.  
           [0005]    In accordance with an embodiment of the present invention, a pump assembly is provided that includes a gerotor pump and a manifold. An aspirating member is positioned between an inlet cavity in the manifold and a fluid reservoir proximate the pump assembly. High pressure fluid diverted by a flow control valve accelerates as it passes between the aspirating member and the manifold. The resulting lower static pressure draws the fluid out of the reservoir where it mixes with the relatively higher velocity diverted fluid. As the combined fluid is slowed, the static pressure increases to “supercharge” the inlet cavity resulting in an improvement in the inlet fill and a reduction in cavitation.  
           [0006]    In accordance with another embodiment of this invention, a gerotor pump is provided with a plurality of pump chambers defined by the teeth of a ring gear and a pinion gear. The pumping chambers expand in an inlet half of a crescent-shaped cavity created between the ring gear and the pinion gear and collapse in a discharge half of the crescent-shaped cavity. An inlet port in a planar member faces the inlet half of the crescent-shaped cavity. A discharge port in the planar member faces the discharge half of the crescent-shaped cavity and is timed relative to the inlet port for pumping the fluid. The timing and geometry of the input port and output port are optimized to prevent noise inducing pressure spikes while maintaining sufficient back pressure in the pump chambers to collapse entrapped vapor bubbles in the fluid.  
           [0007]    Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description:  
         [0009]    [0009]FIG. 1 is an exploded perspective view of an embodiment of the present invention showing a manifold and gerotor pump.  
         [0010]    [0010]FIG. 2 is a partial sectional view of the manifold according to FIG. 1 showing an aspirating member according to a preferred embodiment.  
         [0011]    [0011]FIG. 3 is a cross-sectional view of the manifold and aspirating member along the line  3 - 3  in FIG. 2.  
         [0012]    [0012]FIG. 4 is a cross-sectional view of the manifold and aspirating member along the line  4 - 4  in FIG. 3.  
         [0013]    [0013]FIG. 5 is an enlarged cross-sectional view of the aspirating member according to FIG. 2.  
         [0014]    [0014]FIG. 6 is a view of the gerotor pump showing a pinion gear and a ring gear positioned within a housing.  
         [0015]    [0015]FIG. 7 is a view of a planar member showing an inlet port and a discharge port.  
         [0016]    [0016]FIG. 8 is a cross-sectional view of a second embodiment of the aspirating member.  
         [0017]    [0017]FIG. 9 is a cross-sectional view of the second embodiment of the aspirating member along the line  9 - 9  in FIG. 8. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    Referring now to the drawings, two preferred embodiments of the present invention are described in detail. Referring to FIG. 1, a preferred embodiment of the present invention is shown that includes a pump assembly  10 , preferably for use in supplying fluid to a wet clutch and more preferably for use with a wet clutch of a motor vehicle. Pump assembly  10  generally includes a manifold  12  and a gerotor pump  14 . Manifold  12  is placed in communication with a fluid reservoir (not illustrated) and is designed to route the flow of a fluid from the reservoir, through pump  14  and into a wet clutch (not illustrated).  
         [0019]    Referring to FIGS. 1, 2 and  3 , manifold  12  is preferably formed of a strong material, such as a steel or a high strength plastic, and generally includes a body  13  having a duct therethrough to allow passage of an input shaft (not illustrated) that transmits torque between a wet clutch and a transmission. Body  13  preferably includes a planar connecting structure  15  defining an inlet cavity  16  and an outlet cavity  18  therein. Manifold  12  further includes an intake port  20  that is preferably placed in direct communication with inlet cavity  16  and is designed to receive an aspirating member  22 . As shown in FIGS. 3 and 4, a first duct  24  is preferably provided within body  13  that terminates on one end in intake port  20  and on the other end at an orifice  26 . First duct  24  is preferably laterally offset to one side of a geometric center of aspirating member  22  to promote a vortex-like action in a fluid as the fluid flows from first duct  24  into intake port  20 . A second duct  28  is preferably provided within body  13  that terminates on one end into first duct  24  and on the other end at an orifice (not illustrated). A flow control valve (not illustrated) is provided in the orifice to redirect a portion of the total fluid output of pump  14  in order to maintain the useful fluid output of pump  14  within a predetermined range. Fluid that is redirected by the flow control valve will flow through second duct  28  and first duct  24  into intake port  20 .  
         [0020]    Referring to FIG. 5, in a preferred embodiment, aspirating member  22  includes a generally cylindrical body  30  defining a duct  32  therethrough to allow passage of a fluid. Body  30  includes a first outer surface  33  preferably having a first annular cavity  34  disposed therein to receive a locking member  35 , such as a rigid pin. A second outer surface  36  is provided having a diameter that is preferably smaller than first outer surface  33  and preferably includes a second annular cavity  37  disposed therein for receiving a sealing member  38 , such as an o-ring. A radially contracting conical surface  39  extends from second outer surface  36  to a third outer surface  40  having a diameter that is preferably smaller than second outer surface  36 . When aspirating member  22  is received in intake port  20 , sealing member  38  in second annular cavity  37  sealingly engages a corresponding wall in intake port  20 . Additionally, a first annular void  41  is created between conical surface  39  and a corresponding conical surface  42  in intake port  20 . Similarly, a second annular void  43  is created between third outer surface  40  and a corresponding surface  44  in intake port  20 . Voids  41  and  43  permit the free flow of fluid between aspirating member  22  and intake port  20  as the fluid enters intake  20  through first duct  24 . Referring to FIGS. 2 and 5, aspirating member  22  is preferably secured in intake port  20  by inserting locking member  35  into the area formed between cavities  34  and  44 . An inlet tube  50  is secured to manifold  12  proximate aspirating member  22  to provide communication between aspirating member  22  and a remote fluid reservoir. Inlet tube  50  is preferably attached to manifold  12  via a plurality of threaded fasteners (not illustrated). However, it is recognized that other methods of attachment known in the art, such as welding, may be utilized to secure inlet tube  50  to manifold  12 .  
         [0021]    Referring to FIGS. 1 and 6, pump  14  generally includes a housing  52  sandwiched between a flat inboard side  54  of a planar member  56  and a flat outboard side  58  of a cover  60 . Relative rotation between housing  52 , planar member  56  and cover  60  is prevented by a plurality of dowels  62  that are inserted through a plurality of commonly positioned apertures  63  in housing  52 , planar member  56  and cover  60 . A plurality of fasteners  64  positioned through cover  60 , housing  52  and planar member  56  secure pump  14  to manifold  12 . Pump  14  further includes a ring gear  66  having a cylindrical outside surface  68  that cooperates with a cylindrical inside surface  70  of housing  52  in supporting ring gear  66  for rotation about a first longitudinal centerline  72  parallel to and laterally separated from a second longitudinal centerline  73  of pump  14 , as shown in FIG. 6. A pinion gear  74  of pump  14  is disposed inside of ring gear  66  and coupled to an input device (not illustrated) for rotation as a unit with the input device about second longitudinal centerline  73 .  
         [0022]    Referring to FIG. 6, the lateral separation between the first and second longitudinal centerlines  72 ,  73  defines a crescent-shaped cavity  80  between ring gear  66  and pinion gear  74 . Cavity  80  is closed on opposite sides by flat inboard side  54  of planar member  56  and flat outboard side  58  of cover  60 , respectively. The wedge-shaped ends of the crescent shaped cavity  80  are separated from each other by a tooth  82  on pinion gear  74  in full mesh with a pair of teeth  83 A,  83 B on ring gear  66 . With counterclockwise rotation of ring gear  66  and pinion gear  74  as indicated by the directional arrows in FIG. 6, tooth  84  on pinion gear  74  cooperates with a tooth  85  on ring gear  66  in dividing the crescent-shaped cavity  80  into an inlet half  86  and a discharge half  88 . The gear teeth on pinion gear  74  and ring gear  66  cooperate in defining a plurality of pump chambers  90  that expand in inlet half  86  of crescent-shaped cavity  80  and collapse in discharge half  88  of crescent-shaped cavity  80 .  
         [0023]    Referring to FIG. 7, an inlet port  92  in planar member  56  is disposed therethrough and faces inlet half  86  of crescent-shaped cavity  80 . Upon assembly of pump  14 , inlet port  92  is designed to communicate with the aforesaid fluid reservoir through inlet cavity  16  of manifold  12 . Like crescent-shaped cavity  80 , inlet port  92  is preferably crescent-shaped and more preferably includes a relatively narrow upstream end  96  that expands into a relatively wider downstream end  98 . The expanding width of inlet port  92  is preferably sized to match the similarly expanding width of inlet half  86  of crescent-shaped cavity  80 . A discharge port  94  in planar member  56  is disposed therethrough and faces discharge half  88  of crescent-shaped cavity  80 . Discharge port  94  is preferably crescent-shaped and more preferably includes a relatively wide upstream end  96 ′ that contracts into a more narrow downstream end  98 ′. Like inlet port  92 , the narrowing width of discharge port  94  is preferably sized to match the similarly narrowing width of discharge half  88  of crescent-shaped cavity  80 . Matching the width of inlet port  92  and discharge port  94  to the width of inlet half  86  and discharge half  88 , respectively, maximizes the fill efficiency of pump  14 . Discharge port  94  communicates with the aforesaid clutch through outlet cavity  18  in manifold  12 . The timing between inlet port  92  and a top-dead-center  99  of pump  14  is characterized by an angle theta 1 . The timing between top-dead-center  99  of pump  14  and discharge port  94  is characterized by an angle theta 2  In a preferred embodiment, theta, is in the range of approximately 0° to 17° and more preferably approximately 7°. Theta 2  is preferably in the range of approximately 0° to 37° and more preferably approximately 37°. In this configuration, the time inlet half  86  of crescent-shaped cavity  80  spends in communication with inlet port  92  is maximized such that inlet half  86  completely fills with fluid to prevent cavitation within pumping chambers  90 .  
         [0024]    Referring to FIG. 1, cover  60  preferably includes an inlet groove  100  characterized by geometry substantially similar to inlet port  92 . Inlet groove  100  faces and therefore “shadows” inlet port  92  on the opposite side of crescent-shaped cavity  80  from inlet port  92 . Similarly, a discharge groove  102  characterized by geometry substantially similar to discharge port  94  is preferably disposed in cover  60  facing discharge port  94  on the opposite side of crescent-shaped cavity  80  from discharge port  94 . Grooves  100 ,  102  balance the pressure within crescent-shaped cavity  80  to reduce friction and prevent premature wear of the components.  
         [0025]    Referring to FIG. 8, a second embodiment of an aspirating member  22 ′ is provided having a generally cylindrical body  30 ′ that includes a duct  32 ′ therethrough to allow passage of a fluid from a fluid reservoir to inlet cavity  16  in manifold  12 . Aspirating member  22 ′ generally includes a first outer surface  33 ′ preferably having a first annular cavity  34 ′ disposed therein to receive a locking member  35 ′. Locking member  35 ′ is preferably substantially similar in form and function to locking member  35  in the preferred embodiment of aspirating member  22 . A second outer surface  36 ′ is provided having a diameter that is preferably smaller than first outer surface  33 ′ and more preferably includes a second annular cavity  37 ′ for receiving a sealing member  38 ′, such as an o-ring. An annular groove  104  extends from second outer surface  36 ′ to a third outer surface  40 ′ having a diameter that is preferably substantially similar to the diameter of second outer surface  36 ′. Third outer surface  40 ′ preferably includes a third annular cavity  106  designed to receive a sealing member  38 ′. When aspirating member  22 ′ is received in an intake port  20 ′, sealing members  38 ′ in cavities  37 ′ and  106  sealingly engage a corresponding wall  108  in intake port  20 ′. Additionally, an annular void  41 ′ is created between groove  104  and wall  108  in intake port  20 ′. Void  41 ′ permits the free flow of fluid between aspirating member  22 ′ and intake port  20 ′ as the fluid enters intake port  20 ′ through first duct  24 . The fluid entering from first duct  24  is accelerated through a plurality of ducts  110  exiting at a relatively high velocity. Additionally, as shown in FIG. 9, ducts  110  may be slightly angled when viewed axially to enhance the vortex-like action in the fluid. The operation of aspirating member  22 ′ is substantially similar in operation to the preferred embodiment of aspirating member  22 , as described in further detail below.  
         [0026]    Operation of the inventive pump assembly  10  will be described with reference to FIGS. 1, 3,  4 ,  5  and  6 . Rotation of the input device (not illustrated) causes the pinion gear  74  and ring gear  66  to rotate. High pressure fluid diverted by the flow control valve (not illustrated) travels through second duct  28  and first duct  24  until it encounters aspirating member  22 . The high pressure fluid is accelerated through voids  41  and  43  exiting at a relatively high velocity to create a relatively low static pressure at the outlet of aspirating member  22 . The low static pressure at the outlet of aspirating member  22  works as a suction to draw in fluid from the reservoir through duct  32 . Additionally, the offset of first duct  24  creates a vortex in the fluid as it passes through voids  41  and  43  to further amplify the pressure drop. The high velocity fluid mixes with the relatively lower velocity inlet fluid, thereby transferring the momentum of the high velocity fluid to the inlet fluid. The mix of fluid then enters inlet cavity  16  at a mean velocity that, when slowed in inlet cavity  16 , results in an increase in the static pressure at the pump inlet. Operation of aspirating member  22  transfers fluid from the reservoir to inlet cavity  16  of pump  14  at a moderate charging pressure to suppress cavitation at the expanding pump chambers  90  of pump  14  in the inlet half  86  of the crescent-shaped cavity  80 .  
         [0027]    Inlet half  86  of crescent-shaped cavity  80  expands as it passes inlet cavity  16  and the corresponding inlet port  92  in planar member  56 . The expanding pumping chambers  90  draw in the “supercharged” inlet flow as pumping chambers  90  traverse crescent-shaped cavity  80 . The extended timing of inlet port  92  and “supercharged” inlet flow cooperate to permit pumping chambers  90  to completely fill with fluid. The extended timing and “supercharged” inlet flow alone operate to improve the volumetric efficiency of pump  14 , even when no cavitation is present. Moreover, by removing upstream end  96 ′ of outlet port  94  an angle of theta 2  from top-dead-center  99  of pump  14 , the entering fluid is pre-compressed to reduce cavitation and resulting noise. As each of pumping chambers  90  traverses crescent-shaped cavity  80  from inlet half  86  to discharge half  88 , the fluid in pumping chambers  90  is momentarily completely trapped to assure separation between inlet cavity  16  and outlet cavity  18 . The fluid is expelled from the collapsing pump chambers  90  in discharge half  88  of crescent-shaped cavity  80  through discharge port  94  and into outlet cavity  18 .  
         [0028]    Although certain preferred embodiments of the present invention have been described, the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention. A person of ordinary skill in the art will realize that certain modifications and variations will come within the teachings of this invention and that such variations and modifications are within its spirit and the scope as defined by the claims.