Abstract:
A rotary type lubrication pump for a vehicle transfer case and a method of producing the lubrication pump, the lubrication pump having an inner gear and an outer gear produced by molding a synthetic polymer, and a pump body and a pump cover produced by stamping steel.

Description:
FIELD OF THE INVENTION 
     The invention relates to a lubrication pump and a method of producing the lubrication pump, and more particularly to a lubrication pump for a vehicle transfer case which pumps a lubricant through a passageway in an axial bore of a shaft. 
     BACKGROUND OF THE INVENTION 
     A four wheel drive vehicle includes a vehicle transfer case for distributing a driving force from a transmission connected to a prime mover such as an internal combustion engine to front and rear wheels through a vehicle drive train assembly. The transfer case is adapted to be secured to one end of the vehicle transmission. An input shaft is rotatably supported within the transfer case for coupling with an output shaft of the vehicle transmission. The input shaft of the transfer case is coupled to a speed change mechanism which is then coupled to an output shaft of the transfer case. The output shaft of the transfer case is then coupled with the vehicle drive train assembly. Lubrication of a plurality of bearings within the transfer case is accomplished by a pumping mechanism, such as a gerotor pump, which is mounted on the input shaft of the transfer case and pumps a lubricant through an axial bore of the input shaft. 
     Typically, pumping mechanisms have been constructed of cast aluminum which has been precision machined. Restriction of the total weight, durability, and temperature resistance of materials used to produce the pumps are a concern for design of the pumping mechanism. 
     It would be desirable to produce a lubrication pump for a vehicle transfer case in which weight is minimized and durability and temperature resistance are maximized. 
     SUMMARY OF THE INVENTION 
     Consistent and consonant with the present invention, a lubrication pump for a vehicle transfer case in which weight is minimized and durability and temperature resistance are maximized has surprisingly been discovered. The lubrication pump for a vehicle transfer case comprises: 
     a pump body having a generally hollow cylindrical shape and a central longitudinal axis, one end of the pump body having a radial wall with a centrally disposed aperture; 
     a synthetic polymer pump insert having a generally cylindrical main body with a central aperture, an inlet channel, and an outlet channel, the inlet channel in fluid communication with a source of lubricating fluid and the outlet channel in fluid communication with the central aperture of the main body, the pump insert inserted in the pump body; 
     a synthetic polymer outer gear, the outer gear being generally ring shaped with an inner surface forming an aperture, the inner surface having a generally sinusoidal shape which forms a plurality of peaks and valleys, the outer gear received in the pump body adjacent the pump insert; 
     a synthetic polymer inner gear, the inner gear being generally disc shaped with a central aperture formed by an inner surface, the inner surface having a shaft engaging portion to drivingly engage the inner gear with a shaft of a vehicle transfer case, an outer surface of the inner gear having a generally sinusoidal shape which forms a plurality of peaks and valleys, the number of peaks and valleys of the outer surface of the inner gear being at least one less than the number of peaks and valleys of the inner surface of the outer gear, the inner gear rotatingly received in the central aperture of the outer gear adjacent the pump insert; and 
     a generally disc shaped pump cover having a central aperture, the pump cover attached to the pump body to enclose the pump insert, the outer gear and the inner gear within the pump body and form a substantially liquid tight seal with the pump body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a lubrication pump for a vehicle transfer case incorporating the features of the invention; 
     FIG. 2 is a schematic view of the lubrication pump for a vehicle transfer case illustrated in FIG. 1; 
     FIG. 3 is a partial elevation view of the inner gear of the lubrication pump taken along line  3 — 3  of FIG. 1; and 
     FIG. 4 is a partial elevation view of the inner gear, the outer gear, the pump insert, and the inlet adapter of the lubrication pump taken along line  4 — 4  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, and particularly FIG. 1, there is shown generally at  10  a lubrication pump for a vehicle transfer case incorporating the features of the invention. The lubrication pump  10  includes a pump body  12 , a pump insert  14 , an outer gear  16 , an inner gear  18 , and a pump cover  20 . 
     The pump body  12  has a hollow cylindrical shape with an outer wall  22 . One end of the pump body  12  has a radial wall  24  surrounding a central aperture  26 . A lip  28  is formed at an inner edge of the radial wall  24  surrounding the central aperture  26 . An inlet aperture  30  is formed in the outer wall  22 . A radial ledge  32  extends radially outward from the end of the outer wall  22  opposite the radial wall  24 . The radial ledge  32  is ring shaped, having an inner portion of the ring attached to the outer wall  22 . An annular array of spaced apart extensions  34  are formed at an outer edge of the ring shaped radial ledge  32 . The extensions  34  extend in an axial direction from the outer edge of the radial ledge  32 . In the embodiment shown, the pump body  12  is produced from stamped steel. It is understood that other methods such as precision machining, for example, or other materials, such as a synthetic polymer, for example, could be used to produce the pump body  12 . 
     The pump insert  14  has a cylindrical main body  36  with a centrally disposed aperture  38 . An arcuate inlet channel  40  is disposed in the main body  36  and is in fluid communication with an inlet aperture  42 . The inlet aperture  42  is adapted to receive an inlet adapter  44  which is in fluid communication with a source of lubricating fluid  104 , as illustrated in FIG.  2 . An arcuate outlet channel  46  is disposed in the main body  36  radially opposite the inlet channel  40 . An outlet opening  48  facilitates fluid communication between the outlet channel  46  and the aperture  38 . An annular ridge  50  is disposed on the inner surface of the main body  36  which forms the aperture  38 . 
     The outer gear  16  consists of an annular ring having a generally sinusoidal inner surface  52  which forms an aperture  54 . A front face  56  and a rear face  58  contain a plurality of recessed portions  60  defined by the peaks  62  and the valleys  64  of the sinusoidal inner surface  52 . In the embodiment shown, there are fifteen peaks  62  and fifteen valleys  64  formed on the sinusoidal inner surface  52 . It is understood that an inner surface  52  having more or fewer peaks  62  and valleys  64  can be used without departing from the scope and spirit of the invention. 
     The inner gear  18  consists of a disc having a central aperture  66 . In the embodiment shown, the inner surface  68  of the inner gear  18  is serrated to receive a serrated portion  70  of a shaft  72 . It is understood that other engaging surfaces between the inner gear  18  and the shaft  72  can be used such as a single D or a double D, for example, without departing from the scope and spirit of the invention. A front face  74  of the inner gear  18  has an annular ring  76  surrounding the central aperture  66 . An outer surface  80  has a generally sinusoidal shape or annular array of lobes having a plurality of peaks  82  and valleys  84 . In the embodiment shown, there are fourteen peaks  82  and fourteen valleys  84  formed in the sinusoidal outer surface  80  of the inner gear  18 . It is understood that an outer surface  80  having more or fewer peaks  82  and valleys  84  can be used without departing from the scope and spirit of the invention. The number of peaks  82  and valleys  84  formed on the outer surface  80  will ideally be one less than the number of peaks  62  and valleys  64  formed on the inner surface  52  of the outer gear  16 . It is understood that the difference between the number of peaks  82  and valleys  84  formed on the outer surface  80  of the inner gear  18  and the number of peaks  62  and valleys  64  formed on the inner surface  52  of the outer gear  16  can be greater than one. As illustrated in FIG. 3, a rear face  78  has an annular ring  86  formed thereon adjacent and radially inward of the outer surface  80 . 
     In the embodiment shown, glass filled nylon is used to produce the pump insert  14 , the inlet adapter  44 , the outer gear  16 , and the inner gear  18 . Glass percentages up to 60 percent have been found to perform satisfactorily. A glass percentage of 35 percent has been found to provide optimal performance. Additionally, nylon without a glass filler has also been found to perform satisfactorily as a material of construction for the pump insert  14 , the inlet adapter  44 , the outer gear  16 , and the inner gear  18 . It is also understood that other synthetic polymers could be used without departing from the scope and spirit of the invention. 
     The pump cover  20  consists of a disc having a central aperture  88  formed in an annular ring  90  which is offset in the direction of a front face  92 . A plurality of protuberances  94  form an anti-rotation structure and extend radially from the pump cover  20 . It is understood that the anti-rotation structure could be formed on the pump body  12  as well. In the embodiment shown, the pump cover  20  is produced from stamped steel. It is understood that other methods such as precision machining, for example, or other materials, such as a synthetic polymer, for example, could be used to produce the pump cover  20 . 
     The shaft  72  includes an axial bore  96  as illustrated in FIG. 2. A radial aperture  98  which communicates with the axial bore  96  is disposed in one end of the shaft  72  adjacent the serrated portion  70 . A plurality of spaced apart lubrication apertures  100  are in fluid communication with the axial bore  96  and extend radially therefrom. 
     To assemble the lubrication pump  10 , the pump insert  14  is inserted into the hollow portion of the pump body  12  in the orientation shown in FIG.  1 . The inner gear  18  is mated to the outer gear  16  as illustrated in FIG.  4  and inserted into the pump body  12  adjacent the pump insert  14 . The pump cover  20  is mated to the pump body  12  such that the protuberances  94  are disposed between the extensions  34 . The extensions  34  of the pump body  12  are then hemmed to join the pump body  12  and the pump cover  20  to enclose the pump insert  14 , the outer gear  16 , and the inner gear  18  therein. The inlet adapter  44  is then inserted through the inlet aperture  30  of the pump body  12  and releasably fastened to the inlet aperture  42  of the pump insert  14 . Once the lubrication pump  10  is assembled, the lubrication pump  10  is placed on the shaft  72  by sliding the shaft  72  through the central aperture  88  of the pump cover  20 . The serrated portion  70  of the shaft  72  is mated with the inner surface  68  of the inner gear  18 . The radial aperture  98  of the shaft  72  is disposed adjacent the inner surface of the pump insert  14  to facilitate fluid communication with the outlet opening  48  of the outlet channel  46 . The end of the shaft  72  is then slid through the central aperture  26  of the pump body  12 . The shaft  72  forms a substantially liquid tight seal with the pump body  12  and the pump cover  20 . 
     In the embodiment shown, the inlet adapter  44  is releasably fastened to the inlet aperture  42  of the pump insert  14  by a screwed connection. It is understood that other connection methods could be used. A conduit  102  fluidly connects the inlet aperture  42  with a source of lubricating fluid  104 , as schematically illustrated in FIG. 2. A typical lubricating fluid used is automatic transmission fluid with or without additives, although it is understood that other lubricating fluids may be used. 
     In operation, the shaft  72  is caused to rotate in the clockwise direction, as depicted by the arrow  106  in FIG. 2, by connection to a driving mechanism such as a transmission of an automobile (not shown). In turn, the inner gear  18  is caused to rotate within the outer gear  16 . Since there are fewer peaks  82  and valleys  84  in the inner gear than there are peaks  62  and valleys  64  in the outer gear  16 , the inner gear  18  is permitted to rotate without causing the outer gear  16  to rotate. As the inner gear  18  rotates, lubrication fluid is caused to be pumped from the source of lubrication fluid  104 , through the conduit  102 , and into the lubrication pump  10 . Within the lubrication pump  10 , the fluid moves through the inlet aperture  42 , through the inlet channel  40 , through the outer gear  16  and the inner gear  18 , through the outlet channel  46  and the outlet opening  48 , through the radial aperture  98  and through the axial bore  96 . The lubrication fluid is then caused to flow through the plurality of lubrication apertures  100  to lubricate bearings (not shown). The protuberances  94  militate against rotation of the lubrication pump  10  with the shaft  72  by abutting surfaces of the vehicle transfer case (not shown) adapted to receive the protuberances  94 . 
     Since the lubrication pump  10  is typically hidden from view and not easily inspected, it is critical that the lubrication pump  10  be reliable in its operation. The nature of the design of the lubrication pump  10  is such that pump prime must be maintained, or insufficient lubrication fluid may be pumped to the bearings. The extent of the prime required for the lubrication pump  10  to operate efficiently is a function of the amount of clearance between the outer gear  16  and the inner gear  18  and the pump body  12  and pump cover  20 . Since the operating temperature of the lubrication pump  10  is typically approximately 250 degrees Fahrenheit, the thermal expansion of the lubrication pump  10  components becomes important. Nylon having 35 percent glass filler has an expansion coefficient of approximately 0.00008 inches per inches-degree Fahrenheit. Nylon with 60 percent glass filler has an expansion coefficient of approximately 0.00004 inches per inches-degree Fahrenheit. Due to the expansion characteristics of nylon and glass filled nylon versus that of steel, the efficiency of the lubrication pump  10  increases as the operating temperature increases. This is not true with pumps of the prior art using an aluminum pump body and cover with powdered metal gears. 
     By using molded parts produced from nylon and glass filled nylon, machining costs are minimized. No precision machining is required. Lubrication pumps having inner and outer gears produced from powdered metal typically require precision machining, adding to cost and complexity of production. 
     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.