Patent Publication Number: US-10788024-B2

Title: Fluid pressure pump

Description:
TECHNICAL FIELD 
     The present invention is related to a fluid pressure pump, for example, an axial piston type fluid pressure pump. This application claims a priority based on Japanese Patent Application No. JP 2012-080136 filed on Mar. 30, 2012, the disclosure of which is incorporated herein by reference. 
     BACKGROUND ART 
     Patent Literature 1 discloses a conventional axial piston type hydraulic pump. The axial piston type hydraulic pump is composed of a cylinder block in which a plurality of cylinders are provided, a plurality of pistons arranged in the plurality of cylinders to be slidable, and a valve plate. A cylinder port is formed in the cylinder block to be connected with the cylinder and to have an opening on a sliding surface of the cylinder block. The valve plate has a sliding surface which faces the sliding surface of the cylinder block and a back surface opposite to the sliding surface. A suction port and a discharge port are provided in the valve plate. The discharge port branches to three discharge holes on the side of the back. 
     Citation List 
     [Patent Literature 1] Japanese Patent 3,547,900 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to reduce a pressure loss in a fluid pressure pump. 
     In an aspect of the present invention, a fluid pressure pump includes: a port plate having a first port and a second port, one of which functions as a suction port and the other of which functions as a discharge port; and a piston unit. The port plate and the piston unit are rotated relatively around a rotation axis. The piston unit includes a barrel in which a plurality of cylinders are formed; a plurality of pistons configured to carry out a reciprocating motion in the plurality of cylinders, respectively; and a valve plate in which a plurality of valve plate holes are formed to be respectively connected with the plurality of cylinders. The plurality of valve plate holes are arranged on a circumference around the rotation axis, and each of the first port and the second port is formed to have an arc shape around the rotation axis. The port plate includes a plurality of first bridges configured to divide the first port in a circumferential direction to provide a plurality of first port holes; and a plurality of second bridges configured to divide the second port in the circumferential direction to provide a plurality of second port holes. A summation of the number of first port holes and the number of second port holes is greater than the number of valve plate holes. 
     Because the summation of the number of first port holes and the number of second port holes is greater than the number of valve plate holes, the number of first bridges and the number of second bridges are great. Therefore, the width of the first bridge and the width of the second bridge can be made narrow. Thus, a pressure loss is reduced. 
     It is desirable that the number of first port holes and the number of second port holes are equal to each other. 
     In a second aspect of the present invention, a fluid pressure pump includes: a port plate having a first port and a second port, one of which functions as a suction port and the other of which functions as a discharge port; and a piston unit. The port plate and the piston unit rotate relatively around a rotation axis. The piston unit includes: a barrel having a plurality of cylinders; a plurality of pistons configured to carry out a reciprocating motion in the plurality of cylinders respectively; and a valve plate having a plurality of valve plate holes formed to be connected with the plurality of cylinders, respectively. The plurality of valve plate holes are arranged on a circumference around the rotation axis, and each of the first port and the second port is formed to have an arc shape around the rotation axis. The port plate includes: a plurality of first bridges configured to divide the first port in a circumferential direction to provide a plurality of first port holes; and a plurality of second bridges configured to divide the second port in the circumferential direction to provide a plurality of second port holes. An optional one of the plurality of valve plate holes is referred to as an optional valve plate hole. A first area as an area of the plurality of first bridges which overlaps with the optional valve plate hole changes based on the relative rotation of the piston unit and the port plate around the rotation axis in a view parallel to the rotation axis, and a second area as an area of the plurality of second bridges which overlaps with the optional valve plate hole changes based on the relative rotation. A quotient when a maximum value of the first area is divided by the area of the optional valve plate hole and a quotient when a maximum value of the second area divided by the area of the optional valve plate hole are both smaller than 0.65. 
     Because the quotient when the maximum value of the first area is divided by the area of the optional valve plate hole and the quotient when the maximum value of the second area divided by the area of the optional valve plate hole are small, the pressure loss is reduced. 
     It is desirable that the quotient when the maximum value of the first area is divided by the area of the optional valve plate hole and the quotient when the maximum value of the second area divided by the area of the optional valve plate hole are equal to each other. 
     According to the present invention, the pressure loss in the fluid pressure pump is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above object, the other objects, the effect, and the features of the present invention would become clearer from the description of the embodiments made in the conjunction with the attached drawings. 
         FIG. 1  is a diagram schematically showing a fluid pressure actuator having a fluid pressure pump according to a first embodiment of the present invention. 
         FIG. 2  is a diagram showing the outline of the fluid pressure pump in the first embodiment. 
         FIG. 3  is a sectional view showing a valve plate of the fluid pressure pump according to the first embodiment. 
         FIG. 4  is a sectional view showing a port plate of the fluid pressure pump according to the first embodiment. 
         FIG. 5  is a diagram schematically showing the overlapping state of the valve plate hole and the bridge. 
         FIG. 6  is a sectional view showing the port plate of a fluid pressure pump in a comparison example. 
         FIG. 7  is a diagram showing a relation between pressure loss and rotation angle in the fluid pressure pump according to the first embodiment and the fluid pressure pump according to the comparison example. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a fluid pressure pump according to the present invention will be described with reference to the attached drawings. 
     First Embodiment 
     Referring to  FIG. 1 , a fluid pressure actuator having a fluid pressure pump according to a first embodiment of the present invention will be described. For example, the fluid pressure actuator such as a fluid pressure actuator  100  is an EHA (Electro-Hydrostatic Actuator) which is used for a flight control system of an aircraft. The fluid pressure actuator  100  contains an electric motor  1 , a fluid pressure pump  2 , an output cylinder  3 , a return channel  6 , a first output cylinder passage  7  and a second output cylinder passage  8 . 
     The output cylinder  3  has a first output cylinder chamber  31 , a second output cylinder chamber  32  and an output piston  33  arranged between the first output cylinder chamber  31  and the second output cylinder chamber  32 . The output piston  33  moves to the right direction in the drawing when a working fluid is supplied to the first output cylinder chamber  31  and is discharged from the second output cylinder chamber  32 . The output piston  33  moves to the left direction in the drawing when the working fluid is supplied to the second output cylinder chamber  32  and is discharged from the first output cylinder chamber  31 . For example, the working fluid is hydraulic oil. 
     The fluid pressure pump  2  has a first port  11  and a second port  12 . The electric motor  1  drives the fluid pressure pump  2 . When the electric motor  1  rotates to a first direction, the fluid pressure pump  2  discharges from the first port  11 , the working fluid suctioned from the second port  12 . When the electric motor  1  rotates to a second direction opposite to the first direction, the fluid pressure pump  2  discharges from the second port  12 , the working fluid suctioned from the first port  11 . That is, one of the first port  11  and the second port  12  functions as a suction port and the other thereof functions as a discharge port. When the rotation direction of the electric motor  1  changes, the suction port and the discharge port are switched. 
     The first output cylinder passage  7  connects the first port  11  and the first output cylinder chamber  31 . The second output cylinder passage  8  connects the second port  12  and the second output cylinder chamber  32 . The working fluid leaked from the fluid pressure pump  2  is stored in an accumulator  4  connected with a return passage  6 . The working fluid stored in the accumulator  4  is returned to the first output cylinder passage  7  through a check valve  5  when the pressure of the return passage  6  exceeds the pressure of the first output cylinder passage  7 . The working fluid stored in the accumulator  4  is returned to the second output cylinder passage  8  through another check valve  5  when the pressure of the return passage  6  exceeds the pressure of the second output cylinder passage  8 . 
     Referring to  FIG. 2 , the fluid pressure pump  2  has a port plate  10  and a piston unit  20 . The port plate  10  is fixed and the piston unit  20  is supported to be rotatable. The first port  11  and the second port  12  are formed in the port plate  10 . The piston unit  20  has a barrel  21 , a plurality of pistons  23 , a valve plate  24 , a swash plate  27  and a shaft  28 . A plurality of cylinders  22  are formed in the barrel  21 . The plurality of cylinders  22  are arranged on a circumference around a rotation axis S in an equal interval. The plurality of pistons  23  are arranged to be reciprocatable in parallel to the rotation axis S in the plurality of cylinders  22 , respectively. The positions of the plurality of pistons  23  in the direction parallel to the rotation axis S are determined by the swash plate  27 . A plurality of valve plate holes  25  are formed in the valve plate  24  to be respectively connected with the plurality of cylinders  22 . The valve plate  24  is arranged to overlap with the port plate  10 . The shaft  28  is connected with the electric motor  1 . The electric motor  1  rotates the piston unit  20  around the rotation axis S with respect to the port plate  10 . When the swash plate  27  leans with respect to the rotation axis S, each of the plurality of pistons  23  carries out a reciprocating motion in a corresponding one of the plurality of cylinders  22  in synchronization with the rotation of the piston unit  20 . The capacity of cylinder  22  increases and decreased through the reciprocating motion of the piston  23 . When the electric motor  1  is rotating to the first direction, the first port  11  overlaps with the valve plate hole  25  connected with the cylinder  22  whose capacity is decreasing (i.e. which is discharging the working fluid), and the second port  12  overlaps with the valve plate hole  25  connected with the cylinder  22  whose capacity is increasing (i.e. which is suctioning the working fluid). When the electric motor  1  is rotating to the second direction, the first port  11  overlaps with the valve plate hole  25  connected with the cylinder  22  whose capacity is increasing (i.e. which is suctioning the working fluid), and the second port  12  overlaps with the valve plate hole  25  connected with the cylinder  22  whose capacity is decreasing (i.e. which is discharging the working fluid). When the inclination of the swash plate  27  is changed, a discharge capacity of the fluid pressure pump  2  changes. 
     Referring to  FIG. 3 , the plurality of valve plate holes  25  are formed in the valve plate  24  to be arranged on the circumference around the rotation axis S in an equal interval. In this embodiment, a case where the number of cylinders  22  and the number of pistons  23  are nine will be described. However, the numbers of the valve plate holes  25 , the cylinders  22  and the pistons  23  are not limited to nine. 
     Referring to  FIG. 4 , each of the first port  11  and the second port  12  which are formed in the port plate  10  is formed to have an arc shape around the rotation axis S. The first port  11  and the second port  12  are symmetrically formed with respect to a symmetry plane P which contains the rotation axis S. The first port  11  and the second port  12  are separated from each other so that one valve plate hole  25  does not overlap with the first port  11  and the second port  12  at the same time. The port plate  10  includes an inner portion  15   a  on an inner side of the first port  11 , an outer portion  15   b  on an outer side of the first port  11 , a plurality of bridges  13  which connect the inner portion  15   a  and the outer portion  15   b , an inner portion  16   a  on an inner side of the second port  12 , an outer portion  16   b  on an outer side of the second port  12 , and a plurality of bridges  14  which connects the inner portion  16   a  and the outer portion  16   b . The width of the bridge  13  in the circumferential direction is shown by a symbol W 13  and the width of the bridge  14  in the circumferential direction is shown by a symbol W 14 . The plurality of bridges  13  divide the first port  11  into the circumferential direction to form a plurality of first port holes  11   a . The plurality of bridges  14  divide the second port  12  into the circumferential direction to form a plurality of second port holes  12   a . It can be prevented by the plurality of bridges  13  that the distance between the inner portion  15   a  and the outer portion  15   b  is increased due to the pressure of the working fluid which passes the first port  11 . It can be prevented by the plurality of bridges  14  that the distance between the inner portion  16   a  and the outer portion  16   b  is increased due to the pressure of the working fluid which passes the second port  12 . 
     Note that in the present embodiment, a case where the number of brides  13  and the number of bridges  14  are both 5, and the number of first port holes  11   a  and the number of second port holes  12   a  are both 6 will be described. However, the number of bridges  13  and the number of bridges  14  are not limited to 5 and the number of first port holes  11   a  and the number of second port holes  12   a  are not limited to 6. 
     Referring to  FIG. 5 , the valve plate hole  25  and the bridge  13  overlap, depending on the rotation angle between the port plate  10  and the valve plate  24 . When the valve plate hole  25  and the bridge  13  overlap, the opening area between the port plate  10  and the valve plate  24  decreases. Therefore, the bridge  13  causes a pressure loss in the fluid pressure pump  2 . In the same way, the bridge  14  causes the pressure loss in the fluid pressure pump  2 . 
     In the present embodiment, the number of bridges  13  and the number of bridges  14  are determined such that a summation of the number of first port holes  11   a  and the number of second port holes  12   a  is more than the number of valve plate holes  25 . In a general axial piston type fluid pressure pump, because the number of valve plate holes often is seven or nine, it is desirable that each of the number of bridges  13  and the number of bridges  14  is equal to or more than three. Because the number of bridges  13  and the number of bridges  14  are more, the necessary strength of the port plate  10  is secured even if the width W 13  of bridge  13  and the width W 14  of bridge  14  are narrow. It can be prevented that the distance between the inner portion  15   a  and the outer portion  15   b  is increased due to the pressure of working fluid, and it can be prevented that the distance between the inner portion  16   a  and the outer portion  16   b  is increased due to the pressure of the working fluid. By narrowing the width W 13  and the width W 14 , the pressure loss in the fluid pressure pump  2  is reduced. 
     Here, it is supposed that an optional one of the plurality of valve plate holes  25  is referred to as an optional valve plate hole  25 . A first area as an area of the plurality of bridges  13  which overlaps with the optional valve plate hole  25  in a view parallel to the rotation axis S changes according to a relative rotation of the piston unit  20  and the port plate  10  around the rotation axis S. Also, a second area as an area of the plurality of bridges  14  which overlaps with the optional valve plate hole  25  changes according to the relative rotation. In the present embodiment, the quotient when the maximum value of the first area is divided by the area of the optional valve plate hole  25  and the quotient when the maximum value of the second area is divided by the area of the optional valve plate hole  25  are smaller than 0.65. Because the quotient when the maximum value of the first area or the second area is divided by the area of the optional valve plate hole  25  is small, the pressure loss in the fluid pressure pump  2  is reduced. 
     Hereinafter, the pressure loss in the fluid pressure pump  2  according to the present embodiment is compared with the pressure loss in the fluid pressure pump according to a comparison example, in order to explain the reduction effect of pressure loss in the present embodiment. 
     Referring to  FIG. 6 , the fluid pressure pump according to comparison example is configured in the same way as the fluid pressure pump  2  according to the present embodiment, except for the point that the port plate  10  is replaced by the port plate  50 . A first port  51  and a second port  52  which are respectively equivalent to the first port  11  and the second port  12  are formed in the port plate  50 . The first port  51  and the second port  52  are formed to have an arc shape around the rotation axis S. The port plate  50  includes a plurality of bridges  53  by which the first port  51  is divided into the circumferential direction to form a plurality of first port holes  51   a , and a plurality of bridges  54  by which the second port  52  is divided into the circumferential direction to form the plurality of second port holes  52   a . The width of the bridge  53  in the circumferential direction is shown by a symbol W 53  and the width of the bridge  54  in the circumferential direction is shown by a symbol W 54 . In this comparison example, the number of bridges  53  and the number of bridges  54  are two respectively, and the number of first port holes  51   a  and the number of second port holes  52   a  are three respectively. Because the number of bridges  53  and the number of bridges  54  are less than the number of bridges  13  and the number of bridges  14 , the width W 53  and the width W 54  need to be made wider than the width W 13  and the width W 14 . 
       FIG. 7  is a diagram showing a relation between the pressure loss of the fluid pressure pump according to the comparison example and the fluid pressure pump  2  according to the present embodiment and the rotation angle to the port plate  10  or  50  of the piston unit  20 . The vertical axis shows pressure loss and the horizontal axis shows rotation angle. The maximum value of the pressure loss in the fluid pressure pump  2  according to the present embodiment is small, as compared with the maximum value of the pressure loss in the fluid pressure pump according to comparison example. As shown in  FIG. 7 , in the fluid pressure pump  2  according to the present embodiment, the pressure loss is reduced. 
     Because the pressure loss is reduced in the fluid pressure pump  2 , it is not required to increase the discharge pressure of the fluid pressure pump  2  so as to make up the pressure loss. Therefore, it is possible to manufacture the fluid pressure pump  2  in a small size and it is possible to manufacture the fluid pressure actuator  100  having the fluid pressure pump  2 , in a small size. 
     Note that when the fluid pressure pump  2  is applied to EHA (Electro-Hydrostatic Actuator), it is desirable that the first port  11  and the second port  12  are symmetrically formed with respect to a symmetry plane P which contains the rotation axis S, in order to switch an suction port and a discharge port between the first port  11  and the second port  12 . That is, it is desirable that the number of first port holes  11   a  is equal to the number of second port holes  12   a . It is desirable that the quotient when the maximum value of the area of the plurality of bridges  13  which overlaps with the optional valve plate hole  25  is divided by the area of the optional valve plate hole  25  is equal to the quotient when the maximum value of the area of the plurality of bridges  14  which overlaps with the optional valve plate hole  25  is divided by the area of the optional valve plate hole  25 , in a view parallel to the rotation axis S. 
     As described above, the fluid pressure pump according to the present invention has been described with reference to the embodiments. However, the fluid pressure pump according to the present invention is not limited to the above embodiments. For example, a modification may be applied to the above embodiments and the above embodiments may be combined. For example, when one of the first port  11  and the second port  12  is fixedly used as the suction port and the other is fixedly used as the discharge port, the first port  11  and the second port  12  needs not to be symmetrically formed with respect to the symmetry plane P which contains the rotation axis S.