JP4124716B2 - Swash plate type hydraulic pump / motor - Google Patents

Description

  The present invention relates to an improvement of a swash plate type hydraulic pump / motor applicable to a hydrostatic transmission (hereinafter referred to as HST) as a continuously variable transmission for a traveling device of an agricultural machine, an industrial vehicle, or a construction machine, for example.

  The basic form of HST is a combination of a variable hydraulic pump and a fixed hydraulic motor. In the case of a piston type, the output of the hydraulic motor is changed by changing the tilt angle of the hydraulic pump to make the discharge amount 0 to ± maximum discharge amount. By changing the rotation speed, in the case of a vehicle, it is possible to continuously change the speed from the stop to the maximum forward / reverse speed.

  As a HST hydraulic pump or hydraulic motor, a conventional non-opposing piston motor that accommodates a piston only on one side of a cylinder block is generally used.

  However, if the speed required by the vehicle becomes high or the driving force becomes large, it is necessary to increase the capacity of the HST hydraulic pump and hydraulic motor. Disadvantageous.

  Therefore, it is conceivable to use, for example, an opposed swash plate type hydraulic pump / motor disclosed in Patent Document 1 as an HST hydraulic pump or hydraulic motor.

  As shown in FIG. 6, the opposed swash plate type hydraulic pump / motor 100 houses a plurality of sets of first and second pistons 101, 102 in a cylinder block 103, and as the cylinder block 103 rotates. Thus, the first and second pistons 101 and 102 reciprocate so as to face each other following the first and second swash plates 105 and 106, thereby expanding and contracting the volume chamber 104.

  The hydraulic oil is supplied and discharged through the through hole 110 of the first swash plate 105, the control ports 111 and 112 opened in the valve plate 108, the through hole 113 of the shoe 109, the through hole 114 of the first piston 101, and the like.

The opposed swash plate type hydraulic pump / motor 100 can increase the capacity without increasing the loss as compared with the conventional non-opposed piston pump / motor in which the piston is accommodated on one side of the cylinder block.
JP-A-50-115304

  However, the opposed swash plate type hydraulic pump / motor 100 has a structure in which the hydraulic oil is supplied and discharged through the first swash plate 105, the valve plate 108, and the shoe 109. There is a problem that it is difficult to change the structure to change the capacity by changing the angle.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a swash plate type hydraulic pump / motor that can take a large practical volume ratio while being small.

A first invention includes a cylinder block that houses a plurality of sets of first and second pistons to define a volume chamber, and the first and second pistons that expand and contract the volume chamber as the cylinder block rotates. First and second swash plates that reciprocate opposite to each other, first and second swash plate bearings that support the first and second swash plates in a tiltable manner, and first and second swash plates. A swash plate driving means for tilting, a valve body rotatably inserted into the cylinder block, a supply / discharge port that opens on the outer peripheral surface of the valve body, and an opening on the inner peripheral surface of the cylinder block that accompanies the rotation A cylinder port that communicates each volume chamber with the lever supply / discharge port, and includes a support hole into which the valve body is inserted, and a seal ring interposed between the valve body and the support hole. Has a gap with respect to the outer peripheral surface of the valve body, and the valve body is inserted into the support hole through a seal ring. A plurality of bearing ports that open in the axial direction with each supply / exhaust port on the outer peripheral surface of the valve body, and the supply / exhaust port and the bearing port that face each other across the rotation center axis of the cylinder block communicate with each other A plurality of dummy ports that open to the inner peripheral surface of the cylinder block and communicate with the bearing ports as the cylinder block rotates. The dummy port and the cylinder port face each other across the rotation center axis of the cylinder block. Was characterized.

The second invention is characterized in that, in the first invention, as the swash plate driving means, a pair of back surface drive pistons for pushing the first and second swash plates from the back are provided.

  According to the first invention, the working fluid is supplied to and discharged from each volume chamber through each supply / discharge port of the valve body and each cylinder port of the cylinder block.

  By changing the tilt angle of the first and second swash plates, the variable capacity ratio can be substantially doubled compared to a conventional piston motor or the like. Compared to conventional piston motors with the same maximum capacity, the cylinder block pitch circle diameter P.I. C. D can be halved and the size of the apparatus can be reduced.

  When comparing the device of the present invention with a conventional non-opposing piston motor that houses the piston only on one side of the cylinder block, the difference in the sliding part is that the shoe is in sliding contact with the first swash plate side. It is.

  However, in the operating state at the minimum capacity, the tilt angle of the first swash plate is 0 (neutral), the piston does not stroke against the first swash plate, and the shoe is also pressed statically. There is no relative movement with the first swash plate side.

  Therefore, the first swash plate is neutral and the second swash plate can be practically used efficiently up to about 1 / 2.5 of the capacity at the maximum tilt angle.

  On the other hand, in the apparatus of the present invention, at the maximum capacity, the tilt angle of the first swash plate becomes maximum, the piston slides, and the shoe slides slightly with respect to the first swash plate side.

  However, the device of the present invention has a cylinder block pitch circle diameter P.D. as compared with a conventional non-opposing piston motor having the same maximum capacity. C. Since D can be halved and the size of the sliding portion is approximately ½, the effect on efficiency due to the increase in the number of sliding portions is extremely small.

  The device according to the present invention has a practical capacity ratio that is approximately twice that of a conventional non-opposing piston motor, since the efficiency at both the minimum capacity and the maximum capacity is in the practical range.

The valve body is elastically supported via a seal ring with respect to the support hole, and the working fluid guided to the supply / discharge port forms a fluid film between the valve body and the cylinder block. By floatingly supporting the block, the cylinder block smoothly rotates.

Then , the pressure difference guided to each bearing port is opposed to the pressure difference guided to each supply / exhaust port, so that the valve body is suppressed from being pressed against one side, and the cylinder block is slid smoothly with respect to the valve body. be able to.

The force that presses the valve body against the cylinder block by the pressure guided to each cylinder port and each dummy port can be distributed symmetrically about the rotation center axis of the cylinder block, and is formed between the valve body and the cylinder block. The fluid film can be made uniform, and the cylinder block can be slid smoothly with respect to the valve body.

4. The tilt angle of the first and second swash plates can be switched by selectively increasing the drive pressure guided to each back drive piston.

  Embodiments in which the present invention is applied to an HST motor mounted on a work vehicle or the like will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, a piston motor 1 provided as a swash plate type hydraulic pump / motor has a housing chamber 24 formed by a case 25 and a port block 50, and the cylinder block 4 and the first, The second swash plate 30, 40 and the like are accommodated.

  The cylinder block 4 has a shaft 5 coupled coaxially. A base end portion of the shaft 5 is connected to the cylinder block 4 through a spline 29. The other end of the shaft 5 is supported by the case 25 via a bearing 28. The tip of the shaft 5 protrudes outward from the bottom of the case 25, and its rotation is transmitted to the left and right wheels via a differential gear through a reduction gear (not shown).

  The cylinder block 4 is supported by a case 25 so that two bearings 26 and 27 can rotate. That is, the rotating body of the cylinder block 4 and the shaft 5 is supported on the case 25 via the three bearings 26, 27, and 28. The bearing 27 sandwiched between the bearings 26 and 28 can be eliminated.

  A plurality of first and second cylinders 6, 7 are arranged on the cylinder block 4 so as to be substantially parallel to the rotation axis and opposed to each other, and are opened on both end faces of the cylinder block 4. The first and second cylinders 6 and 7 have pitch circles P.A. C. They are placed side by side with a certain distance on top.

  First and second pistons 8 and 9 are inserted into the first and second cylinders 6 and 7, respectively, and a volume chamber 10 is defined between them. One end sides of the first and second pistons 8 and 9 protrude from both end surfaces of the cylinder block 4 and are supported via shoes 21 and 22 in contact with the first and second swash plates 30 and 40. When the cylinder block 4 rotates, the first and second pistons 8 and 9 reciprocate in opposition to the first and second swash plates 30 and 40, and the volume chambers of the first and second cylinders 6 and 7. 10 is scaled.

  As urging means for pressing each shoe 21, 22 against the first and second swash plates 30, 40, a retainer plate 75 through which each shoe 21, 22 is inserted and slidably seated on the inner peripheral portion of the retainer plate 75. A retainer holder 73 and a plurality of center springs 74 that are compressed and interposed between the retainer holder 73 and the cylinder block 4 are provided.

  In order to make the displacement volume of the piston motor 1 variable, the back surfaces 31 and 41 of the first and second swash plates 30 and 40 are formed in a cylindrical surface shape and tilted via the first and second swash plate bearings 32 and 42. Supported to roll.

  As a mechanism for supplying and discharging hydraulic oil to and from each volume chamber 10, a columnar valve body 60 that is rotatably inserted into the cylinder block 4, and a pair of supply / discharge ports 61 that open to the outer peripheral surface of the valve body 60, The cylinder block 4 is provided with a cylinder port 11 that opens to the inner peripheral surface of the cylinder block 4 and communicates with the supply / discharge port 61 and the volume chamber 10 intermittently as the cylinder block 4 rotates.

  As shown in FIGS. 2A, 2 </ b> B, and 2 </ b> C, the port block 50 is formed with a support hole 55 into which the valve body 60 is inserted. The support hole 55 has a gap with respect to the outer peripheral surface of the valve body 60, and three seal rings 56 are interposed between the support hole 55 (see FIG. 1). Three annular grooves 57 are formed on the inner peripheral surface of the support hole 55, and seal rings 56 are respectively stored in the annular grooves 57.

  As shown in FIG. 1, two pins 58 are interposed between the port block 50 and the valve body 60, and both rotations are locked by the pins 58. The pin 58 is inserted between the port block 50 and the valve body 60 with a gap.

In this way, the valve body 60 is elastically supported by the support holes 55 via the seal rings 56, and the middle of the valve body 60 is fitted to the inner peripheral surface of the cylinder block 4 via the bush 70 (FIG. 3). 4), concentric accuracy with respect to the cylinder block 4 is ensured. Thereby, the cylinder block 4 can slide smoothly with respect to the valve body 60.

  Further, when the gap between the valve body 60 and the bush 70 is reduced due to production errors or the like, the seal ring 56 is elastically deformed because the valve body 60 is supported by the cylinder block 4 via the seal ring 56. Therefore, the dimensional error is absorbed and the valve body 60 is not strongly pressed against the bush 70, so that the efficiency is not reduced and the wear is not increased.

  As shown in FIG. 2C, the port block 50 is formed with a pair of entrances / exits 51. Each inlet / outlet 51 communicates with a high pressure side and a low pressure side of a hydraulic pressure source via a pipe (not shown).

  As shown in FIGS. 5A, 5B, 5C, and 5D, two annular grooves 62 and 63 are opened on the outer peripheral surface of the valve body 60 facing the port block 50. 62 and 63 open between the seal rings 56 (see FIG. 1), and communicate with the respective entrances / exits 51 (see FIG. 2) of the port block 50.

  A pair of supply / discharge ports 61 opens in an arc shape on the outer peripheral surface of the valve body 60 facing the inner peripheral surface of the cylinder block 4, and the supply / discharge ports 61 and the annular grooves 62, 63 communicate with each other inside the valve body 60. Thus, through holes 64 and 65 extending in the axial direction are formed.

  The hydraulic fluid guided from the hydraulic pressure source is, for example, one inlet / outlet port 51 (see FIG. 2) of the port block 50, the annular groove 62 of the valve body 60, the through hole 64, one supply / exhaust port 61, and each cylinder port of the cylinder block 4. 11 (see FIG. 1) is supplied to each volume chamber 10. At this time, the hydraulic oil flowing out from each volume chamber 10 as the cylinder block 4 rotates rotates from each cylinder port 11 of the cylinder block 4, the other supply / discharge port 61, the through hole 65 of the valve body 60, the annular shape. It is discharged to the tank through the groove 63 and the other inlet / outlet 51 of the port block 50. Accordingly, the first and second pistons 8 and 9 reciprocate the first and second cylinders 6 and 7 to rotate the cylinder block 4.

  As shown in FIGS. 5A, 5 </ b> B, and 5 </ b> E, two pairs of bearing ports 66 are formed on the outer peripheral surface of the valve body 60 and open in parallel with the supply / discharge ports 61. Each bearing port 66 extends in an arc shape so as to sandwich each supply / discharge port 61.

By the supply and discharge ports 61 and the hydraulic oil introduced into the bearing port 66 forms an oil film between the valve body 60 and the bush 70, the valve body 60 floating support with respect to the cylinder block 4, with respect to the valve body 60 Thus, the cylinder block 4 rotates smoothly.

  When the outer peripheral surface of the valve body 60 is divided into two regions in the circumferential direction, the supply / discharge port 61 and the bearing port 66 that open to the same region are communicated with different through holes 65. In other words, the supply / discharge port 61 and the bearing port 66 that face each other across the rotation center axis O of the cylinder block 4 communicate with each other through the through hole 65. Accordingly, the force for pressing the valve body 60 against the cylinder block 4 by the pressure guided to the bearing port 66 and the supply / exhaust port 61 in each region is substantially equally distributed in the circumferential direction.

  That is, the bearing port 66 that is symmetrical to the supply / discharge port 61 is formed so that the radial pressure balance between the valve body 60 and the cylinder block 4 is balanced in consideration of the pressure distribution in the vicinity of the opening.

  As shown in FIGS. 3A and 3B, the cylinder block 4 has a valve hole 12 into which the valve body 60 is inserted, and the cylinder port 11 communicates with each volume chamber 10 with respect to the valve hole 12. Are open radially.

  A cylindrical bush 70 is interposed in the valve hole 12 of the cylinder block 4. The bush 70 is fixed to the cylinder block 4 and constitutes an inner wall surface in sliding contact with the valve body 60.

  As shown in FIGS. 4A, 4 </ b> B, and 4 </ b> C, the bush 70 is formed with a hole that constitutes each cylinder port 11, and each cylinder is sandwiched by the rotation center axis O of the cylinder block 4. A dummy port 72 facing the port 11 is formed. Each cylinder port 11 and each dummy port 72 open with a certain interval in the circumferential direction of the bush 70. The number of each dummy port 72 is set to be twice that of each cylinder port 11, and each dummy port 72 opens in two rows in the axial direction so as to sandwich each cylinder port 11. Accordingly, the force for pressing the valve body 60 against the cylinder block 4 by the pressure guided to each cylinder port 11 and each dummy port 72 is distributed symmetrically about the rotation center axis O of the cylinder block 4.

  As a result, the valve body 60 is suppressed from being pressed against one side by the pressure difference guided to each supply / discharge port 61, the hydraulic oil film formed between the valve body 60 and the bush 70 is made uniform, and the cylinder block 4 is The body 60 can be slid smoothly.

  That is, in the high pressure region generated in the supply / exhaust port 61 of the valve body 60, the holes constituting the cylinder ports 11 intermittently face the bush 70 as the cylinder block 4 rotates, and the high pressure region expands or contracts. On the other hand, when the bearing port 66 is provided and the dummy port 72 is not provided, a large unbalance force is generated, and the cylinder block 4 is strongly pressed against the valve body 60. Therefore, by providing the bushing 70 with a dummy port 72 having an angle of 180 degrees with each cylinder port 11, when the cylinder port 11 is connected to the supply / discharge port 61 of the valve body 60, the dummy port 72 is connected to the bearing port 66. It is possible to avoid that both the high pressure areas are balanced by connecting and the cylinder block 4 is strongly pressed against the valve body 60.

  Note that the bush 70 may be eliminated and the dummy port 72 may be formed integrally with the cylinder block 4.

  As a swash plate driving means for tilting the first swash plate 30, the port block 50 is provided with a pair of rear drive pistons 33 and 34 that push the first swash plate 30 from behind. A tilt angle control valve (not shown) selectively increases the drive pressure guided to each of the rear drive pistons 33, 34, thereby switching the tilt angle of the first swash plate 30 in two stages. The first swash plate 30 is formed with receiving portions 39a and 39b that receive the driving force from the rear drive pistons 33 and 34.

  As a swash plate driving means for tilting the second swash plate 40, the case 25 is provided with a pair of rear drive pistons 43, 44 that push the second swash plate 40 from behind. The tilt angle control valve selectively increases the drive pressure guided to the rear drive pistons 43 and 44, so that the tilt angle of the second swash plate 40 can be switched in two stages. The second swash plate 40 is formed with receiving portions 49a and 49b for receiving the driving force from the rear driving pistons 43 and 44.

  The displacement of the piston motor 1 is changed in three stages by switching the driving pressure guided to the rear driving pistons 33 and 34 and the rear driving pistons 43 and 44 via the tilt angle control valve. FIG. 1 shows a position where the displacement of the piston motor 1 becomes an intermediate value. At this time, high pressure is guided to the back drive pistons 33 and 44 and low pressure is guided to the back drive pistons 34 and 43, whereby the inclination of the first swash plate 30 is minimized, and the receiving portion 39 b is connected to the port block 50. The second swash plate 40 has the largest inclination, and the receiving portion 49 a is in contact with the bottom surface 25 a of the case 25.

  Here, the piston motor 1 of the present invention will be compared with a conventional non-opposing piston motor that houses the piston only on one side of the cylinder block.

  The motor to be compared is a swash plate type variable motor and is composed of a cylinder block having the same pitch circle diameter and outer diameter as the piston motor 1 of the present invention, a piston having the same diameter, and a swash plate having the same maximum tilt angle.

  When the first swash plate 30 side of the piston motor 1 of the present invention is in the neutral state and the second swash plate 40 side is at the maximum inclination angle (state in FIG. 1), the displacement volume is ½ of the maximum displacement volume. When the motor is at the maximum inclination, the volumes are equal.

  When compared in this state, the conventional non-opposing piston motor has one end sliding between the shoe and the swash plate, and the other end sliding between the cylinder block and the valve plate. Further, the piston also slides between the cylinder block.

  On the other hand, the piston motor 1 of the present invention slides between the shoes 21 and 22 and the first and second swash plates 30 and 40 at both ends. In addition, the second piston 9 on the second swash plate 40 side and the cylinder block 4 slide, the first piston 8 on the first oblique root 30 side and the cylinder block 4 slide, and the valve body 60 inserted into the cylinder block 4. There is sliding between.

  Comparing the two motors, the sliding of the shoe 22 and the second swash plate 40 on the second swash plate 40 side of the piston motor 1 of the present invention is the same as that of the conventional non-opposing piston motor, and the two motors swing. Power loss is equal. Next, the sliding of the shoe 21 and the first swash plate 30 on the first swash plate 30 side of the piston motor 1 of the present invention and the sliding between the cylinder block and the valve plate of the conventional non-opposing piston motor will be compared. . Since the first swash plate 30 is in a neutral state and the pitch circle diameter of the shoe 21 on the first swash plate side is equal to the pitch circle diameter of the cylinder block of the conventional non-opposing piston motor and the valve plate, If the balance as a hydrostatic bearing is properly taken, both power losses can be made almost equal. Similarly, it can be said that the power loss due to the sliding between the second piston 9 and the cylinder block 4 on the second swash plate 40 side and the sliding of the same part of the conventional non-opposing piston motor is almost equal.

  Therefore, what remains is sliding between the cylinder block 4 and the inserted valve body 60, and this portion has room for extra loss in the piston motor 1 of the present invention. However, the cylinder block 4 and the valve body 60 are held in a gap state so that the pressure is balanced and a large radial force does not work. Furthermore, the diameter of the valve body 60 is also small due to the structure installed on the inner diameter portion of the cylinder block 4. Therefore, the power loss generated in this portion can be made extremely small with respect to the value generated in the shoe and valve plate of the conventional non-opposing piston motor.

  From this, when the first swash plate 30 side of the piston motor 1 of the present invention is in a neutral state, it is almost the same as a conventional non-opposing piston motor having a sliding capacity equal to 1/2 of the maximum displacement volume. Efficiency is obtained. This is because the conventional non-opposing piston motor can be practically used up to about 2.5 in capacity ratio (maximum capacity / minimum capacity), so that the piston motor 1 of the present invention is also ½ of the maximum displacement volume. This means that the volume ratio can be used up to about 2.5. This is 5 in capacity ratio with respect to the maximum volume of the piston motor 1 of the present invention.

  What about the efficiency at the maximum volume position of the piston motor 1 of the present invention? A comparison will be made with a conventional swash plate motor having the same capacity as the maximum capacity of the piston motor 1 of the present invention. Since the conventional non-opposing piston motor has half the number of pistons compared to the piston motor 1 of the present invention, both the pitch circle diameter and the outer diameter of the cylinder block 4 are large (piston diameter and maximum swash plate). If the tilt angles are equal, the pitch circle diameter is doubled).

  When the power loss by each sliding member is compared in the same manner as described above, the distance between the shoe and the swash plate and between the cylinder block and the valve plate (in the piston motor 1 of the present invention, the shoe 21 and the first swash plate 30 questions) are the same. The piston motor 1 is much less.

  On the other hand, when the first piston 8 on the first swash plate 30 side of the piston motor 1 of the present invention slides on the cylinder block 4, the first piston 8 strokes and moves relative to the cylinder block 4. Moreover, although it is small, there is also a loss between the cylinder block 4 and the inserted valve body 60, and the power loss increases in these portions as compared with the conventional non-opposing piston motor.

  When the advantages and disadvantages of the above power loss are summed, the efficiency at the maximum volume position of the piston motor 1 of the present invention can secure a value of substantially the same level as that of the conventional non-opposing piston motor.

  As described above, the piston motor 1 of the present invention can increase the practical range to about twice the conventional capacity by obtaining the same efficiency as the conventional non-opposing piston motor from the maximum capacity to the minimum capacity with the capacity ratio of 5. it can.

  In the case of HST using the piston motor 1 of the present invention, the vehicle speed can be controlled over the entire speed range according to the operation amount of the speed pedal. That is, by operating the speed lever, the speed lever signal changes the current of the proportional solenoid valve (SPPC valve), the pilot pressure output from the proportional solenoid valve changes in proportion to this current, and the tilt angle control valve can be switched. The swash plate angle of the piston motor 1 constituting the HST is switched in three stages. And the vehicle is changed to 0 to the maximum speed of each range by changing the discharge amount of the hydraulic pump which comprises HST to 0- ± max. The discharge amount of the hydraulic pump is normally operated with a foot pedal of the vehicle connected to the pump swash plate. As described above, by combining the switching by the speed lever and the pedal operation, the vehicle in the entire speed range can be controlled only by the HST.

  The rear drive pistons 33, 34 and 43, 44 are not limited to sequence control using a single proportional electromagnetic valve, but a single proportional electromagnetic valve is used to control the rear drive pistons 33, 34. Another proportional solenoid valve may be used to control the drive pistons 43 and 44.

  It is also possible to provide a potentiometer for detecting the tilt angle of each swash plate, and to perform feedback control to bring the tilt angle of each swash plate closer to the target value according to the signal.

  The present invention is not limited to the above-described embodiment, but can be applied to a piston pump as a swash plate type hydraulic pump / motor, and it is obvious that various modifications can be made within the scope of the technical idea. .

  The present invention can be applied to various swash plate type hydraulic pumps and motors including a hydraulic motor or a hydraulic pump constituting the HST.

Sectional drawing of the piston motor which shows embodiment of this invention. Similarly, (a) is a left front view of the port block, (b) is a right front view of the port block, and (c) is a cross-sectional view taken along line DD of the port block. Similarly, (a) is a cross-sectional view taken along line HH of the cylinder block, and (b) is a vertical cross-sectional view of the cylinder block. Similarly, (a) is a side view of the bush, (b) is a sectional view taken along the line FF of the bush, and (c) is a sectional view taken along the line GG of the bush. Similarly, (a) is a side view of the valve body, (b) is a cross-sectional view taken along line EE of the valve body, (c) is a left front view of the valve body, and (d) is a BB line of the valve body. Sectional drawing in alignment, (e) is sectional drawing in alignment with CC line of a valve body. Sectional drawing of the swash plate type hydraulic pump motor which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston motor 4 Cylinder block 5 Shaft 6 1st cylinder 7 2nd cylinder 8 1st piston 9 2nd piston 21, 22 Shoe 30 1st swash plate 40 2nd swash plate 56 Seal ring 60 Valve body 61 Supply / exhaust port 66 Bearing Port 72 dummy port

Claims (2)

A plurality of sets of first, a cylinder block defining a volume chamber is accommodated a second piston, the first to scaling the volume chamber in accordance with rotation of the cylinder block, the second piston opposite to each other the first reciprocating Te, a second swash plate, the first, first to support the second swash plate tiltably, and a second swash plate bearing, the first, the second swash plate, respectively tilt a swash plate driving means for a valve body which is rotatably inserted into the cylinder block, and a supply and discharge port that opens to the outer peripheral surface of the valve body, with the rotation of the opening perilla the inner peripheral surface of the cylinder block a cylinder port communicating the respective volume chambers to said supply and discharge ports, comprising: a support hole in which the valve body is inserted, and a seal ring interposed between the valve body and the supporting hole, the The support hole has a gap with respect to the outer peripheral surface of the valve body, and the support hole The valve body is supported via a seal ring, and a plurality of bearing ports are formed on the outer peripheral surface of the valve body so as to open in parallel with the supply / discharge ports, and sandwich the rotation center shaft of the cylinder block. A plurality of dummy ports that communicate with the bearing ports and that open to the inner peripheral surface of the cylinder block and communicate with each of the bearing ports as it rotates. A swash plate type hydraulic pump motor , wherein the ports are opposed to each other across the rotation center axis of the cylinder block . 2. The swash plate type hydraulic pump motor according to claim 1 , wherein the swash plate driving means includes a pair of rear drive pistons for pushing the first and second swash plates from the back.

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