Abstract:
An object of the invention is to provide an electric oil pump with greatly improved operation, increased endurance, and extended service life of an Oldham&#39;s coupling connecting a drive shaft that rotates a rotor in a pump housing and a motor output shaft in a motor housing. 
     The electric pump comprises a pump housing having a rotor and a drive shaft for rotatably supporting the rotor, and a motor housing connected to the pump housing and having an output shaft connected to the drive shaft via an Oldham&#39;s coupling. The pump housing is provided with a coupling chamber for accommodating the Oldham&#39;s coupling, and a linking channel for transporting the leaked oil from a rotor chamber accommodating the rotor of the pump housing to the coupling chamber.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electric oil pump that can greatly improve the operation, increase the endurance, and extend the service life of an Oldham&#39;s coupling connecting a drive shaft that rotates a rotor in a pump housing and a motor output shaft in a motor housing. 
   2. Description of the Related Art 
   Electric oil pumps comprising a combination of a pump housing having a drive shaft provided with a rotor of an inner contact gear type and a motor housing having a motor for rotating the drive shaft mounted on the rotor have been used as pumps in lubrication systems of automobiles or the like. A specific example of such electric oil pump is described in Japanese Patent Application Laid-open No. H11-173278. The essence of the invention disclosed in this application is that a hydraulic gear pump and a motor are connected via a bracket. A drive shaft on the side of the hydraulic gear pump and a rotor shaft on the side of the motor are connected via a coupling, and an Oldham&#39;s coupling is disclosed as an example of the coupling. 
   The construction of the Oldham&#39; coupling disclosed in Japanese Patent Application Laid-open No. H11-173278 enables the rotation transfer even when the input shaft and output shaft are not coaxial. A plate-shaped protrusion is formed on the distal end of the output shaft of the motor, and a groove for inserting the protrusion is formed on the input shaft side of the pump housing. The output shaft of the motor rotates and the rotor shaft rotates in a state where the plate shaped protrusion is inserted into the groove. In this case, the rotation is transferred even though the input shaft and output shaft are not coaxial, but the plate-shaped protrusion and the groove rub against each other and the surfaces thereof wear each other in long-term usage, thereby decreasing the strength of the coupling. It is an object of the present invention to increase the endurance and extend the service life of the Oldham&#39;s coupling connecting the output shaft and input shaft. 
   SUMMARY OF THE INVENTION 
   With the foregoing in view, the inventors have conducted a comprehensive study aimed at the resolution of the above-described problems, and the invention of claim  1  resolves the problems by providing an electric oil pump comprising a pump housing comprising a rotor and a drive shaft for rotatably supporting the rotor, and a motor housing connected to the pump housing and having an output shaft connected to the drive shaft via an Oldham&#39;s coupling, wherein a coupling chamber for accommodating the Oldham&#39;s coupling and a linking channel for transporting the leaked oil from a rotor chamber of the pump housing where a rotor is accommodated to the coupling chamber are provided in the pump housing. 
   The invention of claim  2  resolves the problems by providing an electric oil pump comprising a pump housing having a cover section having a bearing hole formed therein, a pump body section having a rotor chamber formed therein, and a base section having a shaft through hole and a coupling chamber connected to the shaft through hole and opened outwardly, a drive shaft rotatably supported by the bearing hole and shaft through hole and protruding into the coupling chamber, a rotor accommodated in the rotor chamber, and a motor housing comprising an output shaft connected by an Oldham&#39;s coupling to the drive shaft protruding into the coupling chamber, wherein an annular drain groove is formed between the cover section and the pump body section or between the pump body section and the base section, surrounding the rotor chamber; and a linking channel for linking the annular drain groove and the coupling chamber is formed in the pump body section and the base section. 
   Furthermore, the invention of claim  3  resolves the problems by providing the electric oil pump of the above-described configuration, wherein an annular drain groove surrounding the rotor chamber is formed between the cover section and pump body section and between the pump body section and base section. 
   The invention of claim  4  resolves the problems by providing the electric oil pump of the above-described configuration, comprising a discharge channel leading from the linking channel to an oil pan, wherein the position of the coupling chamber is below the position of a discharge section provided in the oil pan. The invention of claim  5  resolves the problems by providing the electric oil pump of the above-described configuration, wherein a linking channel is formed between the bearing hole and the annular drain groove in the cover section. 
   With the invention of claim  1 , a linking channel for transporting the leaked oil from a rotor chamber of the pump housing where a rotor is accommodated to the coupling chamber is provided in the Oldham&#39;s coupling. Therefore, the oil constantly spreads to the rubbing zone in the Oldham&#39;s coupling accommodated in the coupling chamber, good and stable rotation transfer is carried out from the output shaft of the motor housing to the drive shaft of the pump housing, and excellent endurance can be attained. 
   Furthermore, with the invention of claim  2 , because an annular drain groove surrounding the rotor chamber is formed between the cover section and the pump body section, the leaked oil from the rotor chamber can be reliably removed by the annular drain groove and the leaked oil can be effectively pumped, practically without any waste, to the coupling chamber. Other effects are almost identical to those of the invention of claim  1 . Furthermore, with the invention of claim  3 , forming annular drain grooves on both sides in the axial direction of the pump body section makes it possible to remove the leaked oil from both surfaces of the rotor chamber and to conduct rapid oil supply to the coupling chamber. 
   With the invention of claim  4 , providing a discharge channel leading from the linking channel to the oil pan makes it possible to pump the oil from the coupling chamber to the oil pan when the amount of leaked oil increases and pressure rises. Furthermore, because the coupling chamber is positioned below the discharge section provided in the oil pan, the coupling chamber can be maintained in a state where it is filled with oil. 
   With the invention of claim  5 , a linking channel is formed between the bearing hole and the annular drain groove. As a result, oil penetrates to the periphery of the shaft and lubrication can be ensured between the shaft and the bearing hole or the bearing, e.g., the shaft through hole. Furthermore, because the bearing holes in both end sections of the shaft and the coupling chamber are linked by the linking channel, they have the same pressure, the shaft is not displaced axially by the difference in pressure between the two end sections of the shaft, and stable rotation operation of the shaft can be ensured. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view with partial vertical cut-out illustrating the configuration of the present invention; 
       FIG. 2(A)  is a front view of the cover section, (B) is a sectional side view of (A); 
       FIG. 3(A)  is a front view of the pump body section, (B) is a sectional side view of (A); 
       FIG. 4(A)  is a front view of the base section, (B) is a sectional side view of (A), (C) is a cross-sectional view of the main portion of (A); 
       FIG. 5  is an exploded perspective view of an Oldham&#39;s coupling; 
       FIG. 6  is an exploded side view with a partial vertical section illustrating the present invention; 
       FIG. 7  illustrates schematically the operation in which an electric oil pump in accordance with the present invention is mounted on an oil pan and the leaked oil is discharged from the discharge section into the oil pan; 
       FIG. 8  is a graph comparing the performance of the pump in accordance with the present invention and the conventional pump. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described below based on the appended drawings. As shown in  FIG. 1  and  FIG. 6 , the electric oil pump in accordance with the present invention comprises a pump housing A, a motor housing B, a rotor  21 , and a drive shaft  22 . The rotor  21  and drive shaft  22  are mounted inside the pump housing A. The pump housing A comprises a cover section A 1 , a pump body section A 2 , and a base section A 3 , and those cover section A 1 , pump body section A 2 , and base section A 3  are joined via a fastener such as bolts and screws along the axial direction of the drive shaft  22  contained therein. 
   As shown in  FIG. 1  and  FIG. 6 , the cover section A 1  mainly comprises a cover body  1  and a bearing hole  2 . The bearing hole  2  is formed on the side of the surface of the cover body  1  where it is joined to the pump body section A 2 . The bearing hole  2  serves to support the drive shaft  22  inserted therein. Furthermore, as shown in  FIG. 2 , port recesses  3 ,  4  are formed around the bearing hole  2 . As shown in  FIG. 4(A) , the port recesses  3 ,  4  correspond to the positions of an intake port  15  and a discharge port  16  formed in the base section A 3  and have almost the same shape in the plane thereof as those intake port  15  and discharge port  16 . Furthermore, the port recesses  3 ,  4  are in the form of shallow grooves. 
   Furthermore, as shown in  FIG. 2 , an annular drain groove  5  is formed so as to surround the port recesses  3 ,  4 . Furthermore, a seal groove  6  is formed on the outside of the annular drain groove  5 . A drain hole section  7  is formed between the annular drain groove  5  and seal groove  6 . The annular drain groove  5  is formed to surround from the outside the region of a rotor chamber  10  formed in the pump body section A 2 , and makes it possible to remove the leaked oil. The drain hole section  7  is formed to be located specifically in the lower portion of the cover section A 1  and crosses the annular drain groove  5  on the lower side thereof. The leaked oil flowing in the annular drain groove  5  is collected in the drain hole section  7  (see  FIG. 2(B) ). As shown in  FIG. 1  and  FIG. 2 , this drain hole section  7  comprises a hole opening  7   a  and a feed guide recess  7   b . The leaked oil that flowed out from the hole opening  7   a  can be transferred in a stable state thereof along the feed guide recess  7   b  to the main oil hole section  11  of the below-described pump body section A 2 . 
   The drain hole section  7  and bearing hole  2  are linked together via a first linking channel  8 . The first linking channel  8  passes through inside the cover body  1  of the corner section A 1  and serves to pump out the oil that leaked to the bearing hole  2  into the drain hole section  7 . The linking location of the first linking channel  8  and the bearing hole  2  comprises an axial linking passage  8   a  with an inner diameter less than the bearing hole  2  and matching the linking location in the axial direction of the bearing hole  2  and a drain-side linking passage  8   b  linked to the drain hole section  7 , and the channel is formed by the intersection of the axial linking passage  8   a  and drain-side linking passage  8   b  (see  FIG. 2(B) ). 
   Furthermore, the pump body section A 2  is disposed between the cover section A 1  and base section A 3 , as shown in  FIG. 6 . The rotor chamber  10  in the form of a through hole accommodating the rotor  21  is formed in a body main unit  9 . The main oil hole section  11  is formed in the position corresponding to the drain hole section  7  on the side of the surface of the pump body section A 2  that is joined to the cover section A 1 , and a second linking channel  12  is formed so as to pass from the main oil hole section  11  toward the surface of the pump body section A 2  that is joined to the base section A 3 . 
   The inner diameter of the main oil hole section  11  is formed larger than the inner diameter of the second linking channel  12 . The main oil hole section  11  serves to receive the leaked oil from the drain hole section  7  of the cover section A 1  and feed the leaked oil to the second linking channel  12 . Thus, the second linking channel  12  is linked to the first linking channel  8  and annular drain groove  5  formed in the cover section A 1  via the drain hole section  7 , and this second linking channel  12  transfers the oil that flowed in from the annular drain groove  5  of the cover section A 1  and the first linking channel  8  to a coupling chamber  20  formed in the base section A 3 . 
   As shown in  FIG. 6 , in the base section A 3 , a shaft through hole  14  is formed in a base main unit  13 . Together with the bearing hole  2  formed in the cover section A 1 , the shaft through hole  14  serves as a bearing rotatably supporting the drive shaft  22 . As shown in  FIGS. 4(A)  and (C), the intake port  15  and discharge port  16  are formed around the shaft through hole  14  of the base main unit  13 . Those intake port  15  and discharge port  16  are formed to match the positions of the port recesses  3 ,  4  when the pump body section A 2  and base section A 3  are joined together (see  FIG. 1 ). The intake port  15  passes through to an oil pan  30  disposed on the outside of the pump housing A (see  FIG. 1  and  FIG. 7 ). 
   A third linking channel  17  is formed in the base main unit  13 . The third linking channel  17  is configured to be linked to the second linking channel  12  when the pump body section A 2  and base body A 3  are joined together. As shown in  FIG. 1(A)  and  FIG. 4(B) , the third linking channel  17  is linked to the shaft through hole  14 . More specifically, a drain opening section  17   a  is formed in the location where the shaft through hole  14  and the third linking channel  17  intersect. The drain opening section  17   a  is formed as a zone expanding radially in part of the shaft through hole  14  and makes it possible to pump out the sufficient amount of oil transported from the third linking channel  17  to the shaft through hole  14  in the drain opening section  17   a .    
   Furthermore, a discharge channel  18  linked to the oil pan  30  is formed in the third linking channel  17 . As shown in  FIG. 7 , the discharge channel  18  is linked to a discharge section  31  provided in the oil pan  30 . Furthermore, the position of the discharge section  31  provided in the oil pan  30  is set to be higher than the coupling chamber  20 . Owing to such a configuration, when the amount of leaked oil increased and pressure rises, the oil can be pumped out to the oil pan  30  via the discharge section  31  and also via the coupling chamber  20 . Furthermore, because the coupling chamber  20  is positioned below the discharge section  31  of the oil pan  30 , the coupling chamber  20  can be almost constantly maintained in a state in which it is filled with oil. A second annular drain groove  19  is formed in the surface of the base section A 3  where the base section is joined to the pump body section A 2 . The second annular drain groove  19  crosses the third linking channel  17 , and the oil present in the second annular drain groove  19  is caused to flow into the third linking channel  17 . Forming the two drain grooves makes it possible to remove the leaked oil from both surfaces of the rotor chamber and supply the rapidly flowing oil to the coupling chamber  20 . 
   Furthermore, as shown in  FIG. 4(B) , the coupling chamber  20  is formed in the base main unit  13  of the base section A 3  in the joint surface thereof with the motor housing B. The coupling chamber  20  is formed as an almost cylindrical receding zone in the joining outer wall surface of the base main unit  13 . The coupling chamber  20  is linked to the shaft through hole  14 . The coupling chamber  20  comprises a leaked oil pool section  20   a  with an inner diameter slightly larger than that of the shaft through hole  14  and a guide section  20   b  serving as a guide for joining to the motor housing B. The leaked oil is accumulated in the leaked oil pool section  20   a  and part of the guide section  20   b . The drive shaft  22  is disposed inside the coupling chamber  20  of the bump housing A. Furthermore, the drive shaft  22  is connected to an output shaft  26  of the monitor housing B via an Oldham&#39;s coupling  23 . 
   As shown in  FIG. 6 , in the above-described cover section A 1 , pump body section A 2 , and base section A 3 , a rotor  21  constituting a pump with internal contact gears such as torodial gears is contained in the rotor chamber  10  of the pump body section A 2 , and the drive shaft  22  is mounted on the rotor  21  on the drive side thereof via a key or the like. Rotational support is provided by the bearing hole  2  on the side of the cover section A 1  and the shaft through hole  14  on the side of the base section A 3 . More specifically, one end of the drive shaft  22  in the axial direction is the portion fixedly attached to the rotor  21  and supported in the bearing hole  2 . The other end side of the drive shaft  22  in the axial direction thereof becomes an input side and serves for connection to the output shaft  26  of the motor housing B. The end portion  22   a  on the input side of the drive shaft  22  is connected to the output shaft of the motor housing B via the Oldham&#39;s coupling  23 . A shaft seal  29  is provided on the motor section side in the coupling chamber  20  to seal the oil located inside the coupling chamber  20 . 
   In the motor housing B, the motor section is mounted inside a housing main unit  24 , and the output shaft  26  of the motor section. Furthermore, the output shaft  26  of the motor section is disposed inside a flange section  27 . The flange section  27  is connected to the base section A 3  of the pump housing A via a fastener such a screw or a bolt. A second coupling chamber  28  enabling the Oldham&#39;s coupling  23  to be inserted and disposed therein is also provided in the flange section  27 . 
   As shown in  FIG. 5 , the Oldham&#39;s coupling  23  comprises insertion groove sections  23   a  and insertion plate sections  23   b . The insertion plate sections  23   b  are formed in the end portion  22   a  on the input side of the drive shaft  22  and the distal end portion of the output shaft  26 , and the insertion groove sections  23   a  are formed on both sides in the axial direction of a joint member  23   c . The insertion plate sections  23   b  of the drive shaft  22  and output shaft  26  are configured to be inserted into respective insertion groove sections  23   a  formed in the joint member  23   c.    
   A configuration is also possible in which respective insertion grooves  23   a  are formed in the drive shaft  22  and output shaft  26 , and the insertion plate sections  23   b ,  23   b  are formed in both sides in the axial direction of the joint member  23   c . Furthermore, the joint members  23   c  are disposed in the coupling chamber  20  of the pump housing A and the second coupling chamber  28  of the motor housing B, the Oldham&#39;s coupling  23  of the drive shaft  22  and output shaft  26  is configured, while inserting the insertion plate sections  23   b  into the insertion grooves  23   a , and the pump housing A and motor housing B are joined. 
     FIG. 8  is a graph illustrating the amount of wear in the Oldham&#39;s coupling  23  with and without lubrication. The figure shows that feeding the leaked oil to the coupling chamber  20  in accordance with the present invention reduced the amount of wear in the rubbing zone of the Oldham&#39;s coupling  23 .