Abstract:
An integrated speed reducer and gerotor pump is disclosed. The device comprises a motor, a speed reducer, and a gerotor pump. The motor provides torque at an elevated speed. The speed reducer is coupled with the motor and converts the torque at an elevated speed into torque at a reduced speed. The gerotor pump is coupled with the speed reducer and uses the torque at the reduced speed for pumping fluids.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to U.S. Provisional Patent Application No. 60/417,340 filed, Oct. 9, 2002, from which priority is claimed. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a speed reduction unit and a pump, in general, and, in particular, to an integrated speed reducer and pump assembly. 
   2. Description of Related Art 
   Oil pumps are widely used in vehicles of all types to provide pressurized oil flow for lubrication or for hydraulic actuation. Conventional oil pumps for vehicles are connected directly or indirectly through gears, chains or belts to the main shafts of engines for such vehicles. The rotational speeds of these pumps are in direct proportion to the engine speeds. Therefore, as engine speed increases under demanded power, the speed of a pump also increases, causing output oil pressure of the pump to increase. At higher engine speeds, the oil pressure may increase to undesirable levels. To overcome this situation, pressure relief valves are often provided in pump systems to relieve the pressure and direct the excess oil back to the pumps. However, energy is lost in this process. Thus, disconnecting an oil pump from the main drive shaft of an engine is highly desirable. 
   An attractive means to provide an independently powered oil pump is to electrify the pump, driving the pump independently with an electric motor. There are many advantages using electrified oil pump. For example, in an engine oil pump application an electric pump can provide lubricant to vital parts prior to engine start and/or after engine shutdown, thus extending engine life. In addition, it can adaptively regulate lubricant flow to suit various operating conditions and, as a result, improve engine performance. 
   However, to provide adequate power level to drive an oil pump, an electric motor usually has to run at elevated speeds to conserve motor size. Consequently, a separate speed reduction unit connecting the oil pump and electric motor is often necessary, acting as a torque multiplier. Unfortunately, the addition of a speed reduction unit requires additional space. Therefore, there is a need to integrate a speed reducer with an oil pump. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view showing the front of the preferred embodiment. 
       FIG. 2  is an exploded perspective view showing the back of the preferred embodiment. 
       FIG. 3  is a longitudinal sectional view of the preferred embodiment. 
       FIG. 4  is an exploded perspective view showing the carrier and sun roller assembly. 
       FIG. 5  is an exploded perspective view of the planet assembly. 
       FIG. 6A  is a rear perspective view of the housing. 
       FIG. 6B  is a front perspective view of the housing. 
       FIG. 7  is a front view of rotor engaging the ring gear. 
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a preferred embodiment of the integrated speed reducer and pump assembly  1  includes an electric motor  50 , a speed reducer  100 , and a gerotor pump  200 . The speed reducer  100  includes a carrier  110 , a sun roller assembly  130 , a planet assembly  140 , an outer ring  160 , and an output plate shaft  170 . 
   As shown in  FIG. 4 , the carrier  110  includes a rectangular plate  111 , a spindle  113 , two bearings  120  and  121 , and mounting holes  112 . The spindle  113  extends perpendicularly from the center of the plate  111  and defines a spindle hole  114 , a spindle slot  115 , and obround pin holes  116 . The spindle hole  114  is an annular hole extending the length of the spindle  113  and eccentric to the center axis of the spindle  113  and the plate  111 . The spindle slot  115  cuts across the spindle  113  parallel with the plate  111  exposing the spindle hole  114 . In addition, the obround pin holes  116  extend the length of the spindle  113  and are offset from and parallel with the spindle hole  114 . The two bearings  120  and  121  are affixed to an outer surface  117  of the spindle  113 . If desired, the bearings  120  and  121  may be additionally secured by inserting a snap ring  122  that fits into a channel  119  of the spindle  113 . While the preferred embodiment illustrates two bearings, any multitude of bearings may be used. Finally, the mounting holes  112  are positioned around the plate  111  of the carrier  110  for mounting to the gerotor pump  200 . 
   As shown in  FIG. 4 , the sun roller assembly  130  includes a sun roller  131  and two bearings  136  and  137 . The sun roller  131  is a shaft that includes an input end  132 , a first raceway  133 , channels  134  and shoulders  135 . The two bearings  136  and  137  are affixed along the sun roller  131  abutting the shoulders  135 , defining a first raceway  133  therebetween which rotates freely. As shown in  FIG. 3 , the sun roller assembly  130  resides within the spindle hole  114  of the spindle  113  so that the first raceway  133  is aligned with the spindle slot  115 . Snap rings  138  lock into the channels  134  of the sun roller  131 , thereby, axially fixing bearings  136  and  137  on the sun roller  131  In addition, snap rings  124  lock into channels  123  of the spindle hole  114 , thereby, axially fixing the sun roller assembly  130  within the spindle hole  114 . To power the sun roller assembly  130 , the input end  132  couples with the electric motor  50  using any appropriate mechanical means, such as keyways, splines, or integrated with the motor rotor shaft. 
   Referring to  FIG. 5 , the planet assembly  140  includes a planetary roller  141 , a support bearing  144 , an elastic insert  147 , and a pin shaft  150 . The elastic insert  147  is circularly shaped with an outer surface  148  and a center hole  149 . The support bearing  144  is a circular anti-friction bearing, such as a ball bearing, with an inner race  145  and an outer race  146 . The planetary roller  141  is also circularly shaped with an inner surface  142  and a second raceway  143 . When assembled as in  FIGS. 1 and 2 , the support bearing  144  attaches to the elastic insert  147  with its inner race  145  fitted tightly over the outer surface  148 . Then, the planetary roller  141  is fitted to the support bearing  144  with an interference fit between its inner race  142  and the outer race  146  of the support bearing  144  so that the planetary roller  141  can rotate freely. Next, the elastic insert  147  is attached to the pin shaft  150  by inserting the pin shaft  150  through the center hole  149  of the elastic insert  147 . Finally, the pin shaft  150  is inserted through the pin holes  116  in the spindle  113  so that the attached, elastic insert  147 , support bearing  144 , and planetary roller  141  are assembled within the spindle slot  115 . The obround shape of the pin holes  116  allow the pin shaft  150  to slide back and forth slightly. During operation, this allows the planetary roller  141  to automatically shift to an effective position for the second raceway  143  of the planetary roller  141  to engage in a convergent wedge between the first raceway  133  of the sun roller  131  and a third raceway  161  of the outer ring  160  allowing torque to be transferred between the sun roller  131  and the outer ring  160 . 
   As shown in  FIGS. 1 and 2 , the outer ring  160  is annularly shaped with a third raceway  161 , two bearing seats  162  and  163 , a front face  164 , and mounting holes  165 . The outer ring  160  engages with the carrier  110  so that the bearings  120  and  121  seat within the respective bearing seats  162  and  163 . In this position, the third raceway  161  engages the second raceway  143  of the planetary roller  141  allowing torque to be transferred. The mounting holes  165  are positioned equally around the front face  164  for attachment to the output plate shaft  170 . 
   The output plate shaft  170  includes a base plate  171 , a driving shaft  172 , a key slot  173 , openings  174 , and mounting holes  175 . The mounting holes  175  are positioned around an edge portion  176  of the base plate  171 . Accordingly, the base plate  171  attaches to the outer ring  160  using an appropriate mechanical means, such as bolts or rivets, by aligning the mounting holes  175  of the output plate shaft  170  to the respective mounting holes  165  of the outer ring  160 . The openings  174  are equally positioned around the base plate  171  and may be any appropriate shape, such as elliptical, to encourage the circulation of traction fluid, if used, around the speed reducer  100 . The driving shaft  172  extends perpendicularly from the center of the base plate  171  and includes the key slot  173  that is directed axially for coupling with the gerotor pump  200 . 
   The gerotor pump  200  includes a housing  210 , a bidirectional seal  260 , a rotor  230 , a ring gear  240 , and an end cover  250 . Referring to  FIGS. 1–2 , the speed reducer  100  and gerotor pump  200  both share a common housing  210 . As shown in  FIGS. 6A and 6B , the housing  210  defines a front face  211 , a back face  212 , a chamber  213 , a recessed seat  214 , a center hole  215 , a gear bore  216 , an outer surface  217 , fins  218 , a first plurality of mounting holes  219 , and a second plurality of mounting holes  220 . The gear bore  216  is eccentric to the center of the chamber  213 . The first plurality of mounting holes  219  is equally positioned around the back face  212 . Accordingly, the housing  210  attaches to the carrier  110  using an appropriate mechanical means, such as bolts or rivets, by aligning the first plurality of mounting holes  219  of the housing to the respective mounting holes  112  of the carrier  110 . Thus, the back face  212  attaches to the plate  111  of the carrier  110  so that the speed reducer  100  resides completely within the chamber  213 . In addition, the driving shaft  172  extends through the center hole  215  of the housing  215 . If desired, the chamber  213  may be filled with traction fluid to aid the transfer of power through the raceways  133 ,  143 , and  161  of the speed reducer  100 . The bidirectional seal  260  seats against the recessed seat  214  of the housing  210  and the driving shaft  172  of the output plate shaft  170  to prevent any transfer of fluids between the speed reducer  100  and the gerotor pump  200 . The fins  217  are equally spaced around the outer surface  217  of the housing  210  for the dual purpose of cooling and re-enforcement of the housing  210 . The second plurality of mounting holes  220  is equally positioned around the front face  211  of the housing for mounting of the end cover  250 . 
   Referring to  FIG. 7 , the rotor  230  and ring gear  240  are basically typical of those used in gerotor pumps. The rotor  230  includes external teeth  231 , a center hole  232 , and a key slot  233 . The ring gear  240  includes internal teeth  241 , and an outside surface  242 . The rotor  230  has one less external tooth  231  than the ring gear  240  has internal teeth  241 . The rotor  230  resides within the ring gear  240  so that the external teeth  231  mesh with the internal teeth  241  forming pumping chambers  300 A,  300 B,  300 C, and  300 D. The ring gear  240  seats within the gear bore  216  and the center hole  232  of the rotor  230  couples with the driving shaft  172  of the output plate shaft  170  by placing the key  173  within key slot  233  of the rotor and key slot  173  of the driving shaft  172 . While the preferred embodiment discloses a key  177 , those skilled in the art will recognize that the center hole  232  of the rotor  230  may be coupled with the driving shaft  172  using any appropriate mechanical means, such as a spline or coupling. 
   Referring to  FIGS. 1 and 2 , the end cover  250  includes an inlet port  251 , an outlet port  252 , an inlet chamber  253 , an outlet chamber  254 , a mounting face  255 , and mounting holes  256 . The mounting holes  256  are equally positioned around the mounting face  255 . Accordingly, the end cover  250  attaches to the housing  210  using an appropriate mechanical means, such as bolts or rivets, by aligning the mounting holes  256  of the end cover  250  with the respective second plurality of mounting holes  220  of the housing  220 . The inlet port  252  is frustum conically shaped and extends perpendicularly from the end cover  250 . The inlet port  251  receives fluid from a fluid source and communicates the fluid to the inlet chamber  253 . The outlet port  252  is frustum conically shaped and extends perpendicularly from the end cover  250 . The outlet port  252  receives fluid from the outlet chamber  254  and discharges the fluid. The inlet chamber  253  is arcuately shaped and communicates fluid from the inlet port  252  to the pumping chambers  300 A and  300 B. The outlet chamber  254  is arcuately shaped and communicates fluid from the pumping chambers  300 C and  300 D to the outlet port  252 . 
   In operation, the electric motor  50  supplies power in the form of torque at an elevated speed to the sun roller  131 . As the sun roller  131  rotates, torque is transferred from the sun roller  131  to the planetary roller  141  to the outer ring  160  via frictional contact between the first raceway  133  and second raceway  143  and between the second raceway  143  and third raceway  161 . During this transfer, the torque is converted from an elevated rotational speed at the sun roller  131  to a reduced rotational speed at the outer ring  160 . As a result, the attached driving shaft  172  rotates at a reduced speed, but the torque is multiplied. 
   The traction forces generated at the contacts between the first raceway  133  and the second raceway  143 , as well as between the second raceway  143  and the third raceway  161  push the planetary roller  141  into a converged wedge formed between the first raceway  133  and the third raceway  161 . Under steady state, equilibrium is established, leading to the following relationship: 
               K   S       K   R       =         μ   o     ⁢   sin   ⁢           ⁢   δ     -     2   ⁢           ⁢       sin   2     ⁡     (     δ   2     )                 
where
         K S =effective support stiffness of planetary roller   K R =effective contact stiffness between the planetary roller and the sun roller and between the planetary roller and the outer ring   μ o =operating traction coefficient   δ=wedge angle between the first raceway and third raceway       
   To prevent the speed reducer from excessive slip at the contacts, the following inequality must hold true 
               K   S       K   R       =           μ   o     ⁢   sin   ⁢           ⁢   δ     -     2   ⁢           ⁢       sin   2     ⁡     (     δ   2     )           ≤         μ   m     ⁢   sin   ⁢           ⁢   δ     -     2   ⁢           ⁢       sin   2     ⁡     (     δ   2     )                   
where
         μ m =maximum available traction coefficient.
 
The above equation may also be expressed as
       
   
     
       
         
           
             
               
                 K 
                 S 
               
               
                 
                   
                     K 
                     R 
                   
                   · 
                   sin 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 δ 
               
             
             + 
             
               tan 
               ⁢ 
               
                   
               
               ⁢ 
               
                 δ 
                 2 
               
             
           
           ≤ 
           
             μ 
             m 
           
         
       
     
   
   As shown in  FIG. 7 , the driving shaft  172  drives the rotor  230  at the reduced speed to rotate in the direction shown as “R”. As the rotor  230  rotates, it drives the ring gear  240  to rotate within the gear bore  216  around an axis eccentric to the rotor  23 . As a result, an area of lower pressure develops in the pumping chambers labeled  300 A and  300 B. With further rotation of rotor  230 , the pumping chambers  300 A and  300 B decrease in volume producing areas of higher pressure as shown by the pumping chambers labeled  300 C and  300 D. Consequently, the fluid is pumped from the pumping chambers  300 C and  300 D through outlet chamber  254  and discharged through the outlet port  252 .