Patent Publication Number: US-9885356-B2

Title: Variable displacement pump

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable displacement pump that is used, for example, for supplying lubricating oil to an internal combustion engine or an automatic transmission. 
     As an oil pump that is used for an internal combustion engine or an automatic transmission, etc., Japanese Patent Application Publication No. 2010-164056 discloses a previously-proposed variable displacement pump including a swing-type outer rotor guide. In this technique, the outer rotor guide is swingably held inside a pump housing. Moreover, a cylindrical outer rotor is rotatably fitted into the outer rotor guide. Accordingly, the outer rotor rotates relative to the outer rotor guide, in response to rotation of an inner rotor coupled through a plurality of coupling plates with the outer rotor. 
     SUMMARY OF THE INVENTION 
     In the case of the pump as constructed above, a contact area between an inner circumferential surface of the outer rotor guide and an outer circumferential surface of the outer rotor is large. Because the outer rotor rotates while shearing oil film formed between the inner circumferential surface of the outer rotor guide and the outer circumferential surface of the outer rotor, a shearing resistance is high. Therefore, there is a problem that a torque necessary to drive the pump is large. In particular, this problem becomes prominent at the time of low temperature under which oil viscosity is high. 
     It is an object of the present invention to provide a variable displacement pump devised to solve or ease the above problem. 
     According to one aspect of the present invention, there is provided a variable displacement pump comprising: a housing including a pair of end wall surfaces through which a drive shaft passes, wherein a suction port and a discharge port are formed in at least one of the pair of end wall surfaces; an annular outer rotor guide swingably disposed between the pair of end wall surfaces such that both end surfaces of the outer rotor guide are in close contact with the pair of end wall surfaces, wherein the outer rotor guide includes an outer rotor supporting surface given in a cylinder-surface shape, the drive shaft passing radially inward of the outer rotor supporting surface; a cylindrical outer rotor including an outer circumferential surface given in a cylinder-surface shape, the outer rotor being rotatably fitted into the outer rotor supporting surface; an inner rotor provided radially inward of the outer rotor and configured to rotate integrally with the drive shaft at a location eccentric relative to the outer rotor; and a plurality of coupling plates coupling the inner rotor and the outer rotor such that rotational force is transmitted from the inner rotor to the outer rotor, wherein a space between the inner rotor and the outer rotor is partitioned into a plurality of chambers by the plurality of coupling plates, and a concave portion is formed in the outer rotor supporting surface such that the concave portion exists over an entire axial range between the both end surfaces of the outer rotor guide. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a variable displacement pump according to the present invention. 
         FIG. 2  is an oblique perspective view of the variable displacement pump according to the present invention. 
         FIG. 3  is a front view of a main region of the variable displacement pump according to the present invention. 
         FIG. 4  is a perspective view of the variable displacement pump according to the present invention. 
         FIG. 5  is a front view of a housing and an outer rotor guide of the variable displacement pump. 
         FIG. 6  is an oblique perspective view of the housing and the outer rotor guide. 
         FIG. 7  is a front view of the outer rotor guide. 
         FIG. 8  is an oblique perspective view of the outer rotor guide. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention. 
     An embodiment according to the present invention will be explained in detail referring to  FIGS. 1 to 8 . 
       FIG. 1  is a view showing a state where an end plate (not shown) has been detached from a variable displacement pump according to the present invention.  FIG. 2  is an oblique perspective view of the state shown by  FIG. 1 . The variable displacement pump  1  includes a housing  2 , an outer rotor guide  3 , an outer rotor  4 , an inner rotor  5 , and a plurality of pendulum-type coupling plates  6 . The outer rotor guide  3  is formed in an annular shape (circular-ring shape) and arranged inside the housing  2 . The outer rotor  4  is formed in a cylindrical shape (circular tube shape) and fitted into the outer rotor guide  3 . The inner rotor  5  is arranged radially inward of the outer rotor  4 . The plurality of pendulum-type coupling plates  6  couple (connect) the outer rotor  4  with the inner rotor  5 . 
     The housing  2  includes a body portion  2 A and the end plate (not shown). The body portion  2 A includes a peripheral wall surface  2   a  and an end wall surface  2   b  which is located at axially one end portion of the body portion  2 A. The body portion  2 A is formed with a concave portion  8  (see  FIG. 5 ) defined by the peripheral wall surface  2   a  and the end wall surface  2   b . The end plate covers the concave portion  8 . The end plate is integrally fastened to the body portion  2 A by bolts or the like. The end plate (not shown) includes an end wall surface (not shown) which is located at axially another end portion of the body portion  2 A. The end wall surface (not shown) of the end plate faces the end wall surface  2   b  of the concave portion  8 . In this embodiment, a suction port  11  and a discharge port  12  are formed in the end wall surface  2   b  of the body portion  2 A. The suction port  11  communicates with (i.e., is open to) an inlet  13  whereas the discharge port  12  communicates with (i.e., is open to) an outlet (not shown) formed in the end plate. The suction port  11  and the discharge port  12  are separated from each other and located away from each other by an appropriate angle (e.g. center portions thereof are away from each other by 180 degrees). Moreover, a drive shaft  15  is provided to the housing  2  such that the drive shaft  15  passes through the end wall surface  2   b  of the body portion  2 A and the end wall surface of the end plate. 
     The annular outer rotor guide  3  includes an outer rotor supporting surface  3   a , an outer circumferential surface  3   b , and a pair of end surfaces  3   c . The outer rotor supporting surface  3   a  is formed as a surface of axially-penetrating cylindrical hollow of the annular outer rotor guide  3 . The outer rotor guide  3  is disposed inside the housing  2  such that the pair of end surfaces  3   c  are respectively in intimate contact with the end wall surface  2   b  and the end wall surface of the end plate. The outer rotor guide  3  includes a bearing portion  16  at one side portion of the outer rotor guide  3  (with respect to a direction perpendicular to an axial direction of the pump), and an arm  17  at another side portion of the outer rotor guide  3  which is opposite to the one side portion of the outer rotor guide  3 . The bearing portion  16  is formed by depressing the one side portion of the outer rotor guide  3  in a half-cylindrical concave shape (i.e. in a half-round concave shape in cross section). The arm  17  is formed to protrude from the another side portion of the outer rotor guide  3 . The outer rotor guide  3  is swingably supported by the body portion  2 A through a shaft  18  which is engaging with the bearing portion  16 . A spring  19  is provided between the arm  17  and the body portion  2 A. A pressure control chamber  20  is separately formed between the outer circumferential surface  3   b  and the peripheral wall surface  2   a  of the body portion  2 A, on an opposite side of the outer rotor guide  3  from the spring  19 . The pressure control chamber  20  extends along a longitudinal direction of the outer rotor guide  3 . The spring  19  biases the outer rotor guide  3  in a direction that reduces a volume of the pressure control chamber  20 . The pressure control chamber  20  is sealed from the inlet  13  by a seal piece  21 . The seal piece  21  is provided near a tip portion of the arm  17 . 
     Six plate-retaining grooves  24  are formed in an inner circumferential surface  4   a  of the cylindrical outer rotor  4  at even intervals. Each of the six plate-retaining grooves  24  is formed in a circular shape in cross section as viewed in the axial direction of the variable displacement pump  1 . Alternatively, the six plate-retaining grooves  24  may be formed in the inner circumferential surface  4   a  at uneven intervals. Moreover, an outer circumferential surface  4   b  of the cylindrical outer rotor  4  is formed as a simple cylindrical surface. The outer circumferential surface  4   b  of the cylindrical outer rotor  4  is rotatably fitted into the outer rotor supporting surface  3   a . Strictly speaking, it is noted that a very minute gap in which oil film is formed exists between the outer circumferential surface  4   b  and the outer rotor supporting surface  3   a.    
     The inner rotor  5  which is rotatably provided radially inside the outer rotor  4  includes an outer circumferential surface  5   b  formed as a cylindrical surface. Moreover, the inner rotor  5  is formed with an attachment hole  5   c  which axially passes through a center of the inner rotor  5 . The drive shaft  15  is fixed into the attachment hole  5   c , i.e. fixed to the inner rotor  5 . The drive shaft  15  is eccentric relative to the outer rotor  4 . That is, an axis of the drive shaft  15  is deviated from a center (axis) of the outer rotor  4 . Hence, the inner rotor  5  rotates integrally with the drive shaft  15 , at a location eccentric relative to the outer rotor  4 . Since the inner rotor  5  is eccentric relative to the outer rotor  4 , a crescent-shaped space (as viewed in the axial direction) as a whole is formed between the inner rotor  5  and the outer rotor  4 . This crescent-shaped space communicates with (is open to) the suction port  11  and the discharge port  12 . Moreover, six slots  25  are formed in the outer circumferential surface  5   b  at even intervals such that each of the six slots  25  extends in a radial direction of the inner rotor  5 . 
     As shown in  FIG. 3 , each of the coupling plates  6  includes a radially inner end  6   a  and a radially outer end  6   b . The radially inner end  6   a  is substantially in the form of triangle which expands along a radially inner direction in cross section (as viewed in the axial direction). The radially outer end  6   b  is in the form of circle in cross section (as viewed in the axial direction). The radially outer end  6   b  is swingably fitted into the plate-retaining groove  24  of the outer rotor  4  whereas the radially inner end  6   a  is inserted into the slot  25  of the inner rotor  5  and is slidable in the slot  25 . Accordingly, rotational force of the inner rotor  5  is transmitted to the outer rotor  4 . The above-mentioned crescent-shaped space between the inner rotor  5  and the outer rotor  4  is separately partitioned into six chambers  26  by the six coupling plates  6 . 
     Each of the housing  2 , the outer rotor guide  3 , the outer rotor  4  and the inner rotor  5  is formed of a synthetic resin or a sintered metal. 
     In the variable displacement pump  1  constructed as above, when the inner rotor  5  rotates via the drive shaft  15  in a clockwise direction of  FIG. 1 , rotational force is transmitted through the coupling plates  6  to the outer rotor  4  so that the outer rotor  4  rotates in the same direction (the clockwise direction of  FIG. 1 ). A distance between the inner circumferential surface  4   a  of the cylindrical outer rotor  4  and the outer circumferential surface  5   b  of the inner rotor  5  varies according to rotational positions (circumferential positions) of the outer rotor  4  and the inner rotor  5  which are eccentric relative to each other. Hence, a volume of each chamber  26  also varies according to the rotational positions of the outer rotor  4  and the inner rotor  5 . The volume of each chamber  26  takes its minimum at a lower side of  FIG. 1 , and gradually increases with the clockwise rotation. Then, the volume of each chamber  26  takes its maximum at an upper side of  FIG. 1 , and then decreases with the clockwise rotation. By this volume variation of the chamber  26 , a pump function of pumping oil from the suction port  11  to the discharge port  12  can be attained. 
     A hydraulic pressure (oil pressure) in a main gallery of the engine or a control hydraulic pressure adjusted by a control solenoid is supplied to the pressure control chamber  20 . When hydraulic pressure of the pressure control chamber  20  is low, an eccentricity amount of the inner rotor  5  (relative to the outer rotor guide  3  and the outer rotor  4 ) is enlarged by the outer rotor guide  3  biased by the spring  19  in the direction that reduces the pressure control chamber  20 , as shown in  FIGS. 1 and 3 . As a result, a pump capacity becomes high. On the other hand, when the hydraulic pressure of the pressure control chamber  20  is high, the outer rotor guide  3  swings against biasing force of the spring  19  in a direction that enlarges the pressure control chamber  20  so that the eccentricity amount of the inner rotor  5  is reduced. As a result, the pump capacity becomes low. 
     Next, the outer rotor guide  3  will now be explained in detail referring to  FIGS. 5 to 8 . 
     As shown in  FIGS. 7 and 8 , the outer rotor supporting surface  3   a  of the outer rotor guide  3  is formed with two concave portions  30  each of which is continuous over an axially entire range between the pair of end surfaces  3   c . That is, each of the two concave portions  30  is formed in the outer rotor supporting surface  3   a  so as to penetrate the outer rotor guide  3  in the axial direction. A pad portion  29  is provided circumferentially between the two concave portions  30 . That is, the pad portion  29  is a part of the cylinder-surface-shaped outer rotor supporting surface  3   a  which remains between the two concave portions  30  after forming the two concave portions  30 . The pad portion  29  exists substantially at a location corresponding to a center of the suction port  11  which extends in an arc shape, as viewed in the axial direction. In other words, the pad portion  29  radially overlaps with a substantially center portion of the arc-shaped suction port  11 . The pad portion  29  functions to suppress a backlash of the outer rotor  4  disposed in the outer rotor guide  3 . As shown in  FIGS. 5 and 6 , the two concave portions  30  extend in a circumferential direction of the outer rotor guide  3  such that whole of the two concave portions  30  is within a region of the suction port  11 , i.e. within an angular range (circumferential range) of the arc-shaped suction port  11 . In other words, the two concave portions  30  completely overlap with a part of the circumferential range of the arc-shaped suction port  11 , with respect to the radial direction. Moreover, it is favorable that each of the concave portions  30  is located within the region of the suction port  11  even when the outer rotor guide  3  swings during a pump operation. According to the present invention, a depth of each concave portion  30  in the radial direction is not limited to any value, but is set such that a shearing force of oil film is sufficiently reduced. 
     Hydraulic pressure of each of the six chambers  26  becomes higher as the chamber  26  becomes closer to the discharge port  12  during the pump operation. That is, one of the six chambers  26  which is close to the discharge port  12  has a higher pressure than another of the six chambers  26  which is away from the discharge port  12 . Hence, the outer rotor  4  is pushed toward the discharge port  12 , inside of the outer rotor guide  3 . As a result, a high surface pressure is applied to a part of the outer rotor supporting surface  3   a  which is near the discharge port  12  and which is tightly in contact with the cylindrical outer rotor  4  whereas a low surface pressure is applied to a part of the outer rotor supporting surface  3   a  which is near the suction port  11 . Hence, a concern about local abrasion is not brought even if the concave portions  30  are formed in the outer rotor supporting surface  3   a  at the location corresponding to the circumferential region of the suction port  11 . Therefore, it is favorable that the concave portions  30  are formed in the outer rotor supporting surface  3   a  near the suction port  11 . In a case that the concave portions  30  are formed in the outer rotor supporting surface  3   a  at a location (radially) corresponding to a circumferential region of the discharge port  12 , a very high surface pressure is applied to the part of the outer rotor supporting surface  3   a  which is near the discharge port  12 . In consideration of this, any concave portion  30  is not formed in the part of the outer rotor supporting surface  3   a  which (radially) corresponds to the region of the discharge port  12 , in this embodiment. 
     Moreover, any concave portion  30  is not formed also in a part of the outer rotor supporting surface  3   a  which (radially) corresponds to a circumferential region between the suction port  11  and the discharge port  12 . This is because there is a risk that high-pressure oil becomes easy to leak through the concave portion  30  to a low-pressure side so as to cause a reduction of pump performance, in the case that the concave portion  30  is formed in the part of the outer rotor supporting surface  3   a  which corresponds to the region between the suction port  11  and the discharge port  12 . 
     According to the above-mentioned structures in this embodiment, a contact area between the outer rotor supporting surface  3   a  of the outer rotor guide  3  and the outer circumferential surface  4   b  of the outer rotor  4  is reduced by virtue of the concave portions  30 , without being associated with an excessive rise of surface pressure. 
     That is, because the two concave portions  30  each of which is formed continuously from one end surface  3   c  to another end surface  3   c  are provided in this embodiment, the contact area between the outer rotor supporting surface  3   a  of the outer rotor guide  3  and the outer circumferential surface  4   b  of the outer rotor  4  is reduced by that amount. Accordingly, a shearing resistance between the outer rotor supporting surface  3   a  and the outer circumferential surface  4   b  can be reduced. As a result, the torque necessary to drive the pump can be reduced. 
     Moreover, according to the embodiment, each of the concave portions  30  is continuously formed over the axially entire range between the both end surfaces  3   c  of the outer rotor guide  3 , as mentioned above. Hence, the outer rotor guide  3  including the concave portions  30  can be easily molded by use of a die at a low cost, when molding the outer rotor guide  3  by a sintering or a synthetic-resin molding. Alternatively, the concave portions  30  can be easily shaped by machine processing because axially both ends of the outer rotor guide  3  are open. 
     Moreover, in this embodiment, the high-pressure oil can be inhibited from leaking through the concave portions  30  to the low-pressure suction side as compared with a case that one circumferentially-continuous concave portion is formed. 
     Although the invention has been described above with reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. 
     For example, in the above embodiment, the two concave portions  30  are formed in the outer rotor supporting surface  3   a . However, the structure according to the present invention is not limited to this. According to the present invention, one concave portion  30  may be provided. Alternatively, three or more concave portions  30  may be provided. 
     For example, in this embodiment, the suction port  11  and the discharge port  12  are formed in the end wall surface  2   b  of the housing body portion  2 A. However, the structure according to the present invention is not limited to this. According to the present invention, each of the suction port  11  and the discharge port  12  may be formed in both of the end wall surface  2   b  and the end wall surface of the end plate. Alternatively, the suction port  11  and the discharge port  12  may be formed only in the end wall surface of the end plate. Further alternatively, one of the suction port  11  and the discharge port  12  may be formed in the end wall surface  2   b  while forming another of the suction port  11  and the discharge port  12  in the end wall surface of the end plate. 
     For example, in this embodiment, the six plate-retaining grooves  24  are provided in the inner circumferential surface  4   a  of the cylindrical outer rotor  4  at even circumferential intervals. However, according to the present invention, the number of plate-retaining grooves  24  is not limited to six. Moreover, according to the present invention, the plate-retaining grooves  24  may be provided in the inner circumferential surface  4   a  at uneven circumferential intervals. 
     This application is based on a prior Japanese Patent Application No. 2014-261445 filed on Dec. 25, 2014. The entire contents of this Application are hereby to incorporated by reference. 
     The scope of the invention is defined with reference to the following claims.