JP4124715B2 - 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. 9, 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 shoe connected to the first piston, a port plate that slides on the shoe and the first swash plate and rotates together with the cylinder block, and a bearing that opens to the first swash plate bearing A through port, a supply / discharge port that opens in the first swash plate and communicates with the bearing through port, a valve port that opens in the port plate and communicates intermittently with the supply / discharge port, and a valve port that passes through the shoe and and a shoe port communicating with the volume chamber, The frictional force for the first swash plate Topureto was assumed, characterized in that the smaller than the frictional force with respect to the port plate of the shoe.

According to a second aspect of the present invention , there is provided centering support means for rotatably supporting the port plate with respect to the first swash plate.

According to a third aspect of the present invention , a retainer plate for inserting each shoe is provided, and the retainer plate is fixed to the port plate.

The fourth invention has assumed that comprising the center spring for pressing the first swash plate of each shoe through the port plate.

According to a fifth aspect of the present invention , a pair of rear drive pistons that push the first and second swash plates from behind are provided as swash plate driving means.

  According to the first invention, the working fluid includes a bearing through port that penetrates the first swash plate bearing, a supply / discharge port that opens to the first swash plate, a valve port that opens to the port plate, and a shoe port that penetrates the shoe. It passes through and is discharged into each volume chamber.

  The working fluid guided to the supply / discharge port forms a fluid film between the first swash plate and the port plate, and the port plate floats and supports the first swash plate, thereby smoothly rotating the port plate.

  When the apparatus of the present invention is compared with a conventional non-opposing piston motor in which the piston is accommodated only on one side of the cylinder block, the major difference in the sliding portion is the portion where the shoe is in sliding contact with the first swash plate side.

  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.

Further , the friction force of the port plate against the first swash plate is made smaller than the friction force of each shoe against the port plate, and the port plate slides smoothly with respect to the first swash plate due to the difference of the friction force. Rotate with. That is, even if the sliding range of the port plate and each shoe is not restricted by the retainer plate or the like, the port plate rotates together with the cylinder block and the shoe slides in the radial direction with respect to the port plate.

According to the second invention, the port plate is rotated in a predetermined path with respect to the first swash plate via the center ring support means, so that the supply / discharge timing of the working fluid to each volume chamber is maintained.

According to the third invention, even if the balance of the frictional forces acting on both surfaces of the port plate is lost, the port plate rotates together with the cylinder block via the retainer plate, and the operation of the piston motor can be maintained.

According to the fourth invention, the center spring presses each shoe against the first swash plate through the port plate, so that the port plate is prevented from being lifted from the first swash plate by the pressure rising at the start-up, and each shoe is Lifting from the port plate is suppressed, and the supply and discharge of the working fluid is maintained.

According to the fifth aspect of the invention, the tilt angles of the first and second swash plates are 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.

  A shaft 5 is coupled to the cylinder block 4. One end of the shaft 5 is supported by the port block 50 via the bearing 12, and the other end is supported by the case 25 via the bearing 11. The tip of the shaft 5 (side supported via the bearing 11) protrudes outward from the bottom of the case 25, and its rotation is transmitted to the left and right wheels via a differential gear via a reduction gear (not shown).

  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 opposite to each other between the first and second swash plates 30 and 40, and the volume of the first and second cylinders 6 and 7 is increased. The chamber 10 is expanded or contracted.

  In order to make the displacement volume per revolution 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 the first and second swash plate bearings 32 and 42 are formed. It is supported through tilting.

  As shown in FIGS. 7A and 7B, the first and second swash plate bearings 32 and 42 are provided with plain bearings 27, respectively. The plain bearing 27 has a pair of holes 28 and is fastened to the case 25 and the port block 50 through two screws that pass through the holes 28.

  As a mechanism for reciprocating each first piston 8 following the first swash plate 30, a sh-21 connected to the protruding end of each first piston 8, and the sh-21 and the first swash plate 30 And a port plate 60 that slides and rotates together with the cylinder block 4.

  As a mechanism for supplying and discharging the hydraulic oil to and from each volume chamber 10, a bearing through port 53 (see FIG. 3) that opens to the first swash plate bearing 32 and the first swash plate 30 that communicates with the bearing through port 53 and opens. A supply / exhaust port 37 (see FIG. 4), a valve port 64 that is intermittently connected to the supply / exhaust port 37 and opens to the port plate 60, and communicates through the shoe 21 through the valve port 64 and the volume chamber 10. The shoe port 19 is provided. The hydraulic oil guided from the hydraulic pressure source is supplied to each volume chamber 10 through one bearing through port 53, one supply / discharge port 37, valve port 64, shoe port 19, and the inside of the first piston 8. The hydraulic oil flowing out from each volume chamber 10 as the cylinder block 4 is rotated passes through the shoe port 19, the valve port 64, the other supply / discharge port 37, and the other bearing through port 53 and is discharged to the tank. Is done. Thereby, 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. 3A, 3 </ b> B, and 3 </ b> C, the port block 50 is formed with a pair of inlets / outlets 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).

  The port block 50 is formed with a bearing through port 53 that communicates each inlet / outlet 51 and the first swash plate bearing 32. In the plain bearing 27 (see FIG. 7), a long hole 29 communicating with each bearing through port 53 is formed. The elongated hole 29 (see FIG. 7) extends in the circumferential direction of the first swash plate bearing 32.

  As shown in FIGS. 4A, 4 </ b> B, 4 </ b> C, and 4 </ b> D, through holes 35 are formed in the cylindrical back surfaces 31 of the first swash plate 30. Communicates with the long hole 29 of the plain bearing 27.

  A pair of supply / discharge ports 37 are opened on the sliding surface 36 of the first swash plate 30. Each supply / discharge port 37 has a pitch circle P.D. C. And the hydraulic oil is supplied to and discharged from each volume chamber 10.

  As shown in FIGS. 5A, 5 </ b> B, and 5 </ b> C, the port plate 60 includes a sliding surface 61 that is in sliding contact with the sliding surface 36 (see FIG. 4) of the first swash plate 30, and the shoe 21. It is formed in a disk shape having a sliding surface 62 that is in sliding contact therewith. A long hole 63 extending in an arc shape is opened in the sliding surface 61, and the long hole 63 communicates with each supply / discharge port 37 (see FIG. 4). A valve port 64 is opened in the sliding surface 62, and the valve port 64 communicates with the shoe port 19 of each shoe 21.

  As centering support means for rotatably supporting the port plate 60 on the first swash plate 30, an annular guide sleeve 66 fitted to the inner peripheral portion 65 (see FIG. 4) of the port plate 60, and the first swash plate 30. The guide sleeve 66 is slidably fitted to the plain bearing 67.

  As shown in FIGS. 8A and 8B, an uneven portion 68 is formed on the outer peripheral portion of the guide sleeve 66, and the uneven portion 68 is fitted to the inner peripheral portion 65 of the port plate 60. The rotation with respect to the port plate 60 is locked. The port plate 60 is rotated in a predetermined orbit with respect to the first swash plate 30 via the guide sleeve 66, so that the supply / discharge timing of the hydraulic oil to each volume chamber 10 is maintained.

  As a restricting means for restricting the sliding range of the port plate 60 with respect to each shoe 21, a retainer plate 70 that is inserted into each shoe 21 and fixed to the port plate 60 is provided. A pin 79 is interposed between the port plate 60 and the retainer plate 70 to stop both rotations. The port plate 60 rotates together with the cylinder block 4 via the retainer plate 70.

  As shown in FIGS. 6A, 6 </ b> B, and 6 </ b> C, the disc-shaped retainer plate 70 is formed with holes 71 through which the shoes 21 are inserted. The opening diameter of the hole 71 is formed larger than the outer diameter of the shoe 21 engaged therewith, and each shoe 21 can slide with respect to the port plate 60 inside the hole 71.

  As an urging means for pressing each shoe 21 against the first swash plate 30 via the port plate 60, a retainer holder 73 slidably seated on the inner peripheral portion 72 of the retainer plate 70, and the retainer holder 73 and the cylinder block 4 and a plurality of center springs 74 that are compressed and interposed. The center spring 74 presses each shoe 21 against the first swash plate 30 via the port plate 60, thereby suppressing the port plate 60 from being lifted from the first swash plate 30 by the pressure rising at the time of start-up. It is possible to suppress the floating of the port plate 60 and maintain the supply and discharge of the hydraulic oil.

  As biasing means for pressing each shoe 22 against the second swash plate 40, a retainer plate 75 that engages with each shoe 22, a retainer 76 that is slidably seated on the inner periphery of the retainer plate 75, and the retainer And a plurality of center springs 77 interposed between the cylinder block 4 and the cylinder block 4 in a compressed manner.

  By arbitrarily setting the pressure receiving area and the like of each port plate 60 with respect to each supply / discharge port 37, the load pressing the port plate 60 against the first swash plate 30 is made smaller than the lifting load, and the port plate 60 is It does not float from the swash plate 30 and secures the sealability between them. As a result, the hydraulic oil guided to the supply / discharge port 37 forms an oil film between the first swash plate 30 and the port plate 60, and functions as a hydrostatic bearing that supports the port plate 60 in a floating manner with respect to the first swash plate 30. To do.

  By arbitrarily setting the pressure receiving area and the like of each shoe 21, the load for pressing each shoe 21 against the port plate 60 is made smaller than the load that lifts, so that each shoe 21 does not lift from the port plate 60. Ensure sealing performance between. Accordingly, the hydraulic oil guided to the supply / discharge port 37 forms an oil film between the port plate 60 and each shoe 21, and functions as a hydrostatic bearing that supports each shoe 21 in a floating manner with respect to the port plate 60.

  The shoe 21 on the first swash plate 30 side is pressed against the port plate 60 side by the pressure guided to each volume chamber 10, but an upward force is generated by the action of a static pressure bearing by a pocket formed on the bottom surface of the shoe 21. . For this reason, the shoe 21 is pressed against the port plate 60 by the difference between the pressing force and the lifting force.

  Similarly, the port plate 60 is also pressed against the first swash plate 30 by the difference between the pressing force applied to the front side of the port plate 60 and the pressing force generated on the back surface.

  In the present invention, when the pressing force / pushing force = the pressing ratio, the pressing ratio of the shoe 21 to the port plate 60 is set larger than the pressing ratio of the port plate 60 to the first swash plate 30, and the first swash plate of the port plate 60 is set. The friction force with respect to 30 is made smaller than the friction force with respect to the port plate 60 of each shoe 21.

  The radial component force generated in the first piston 8 on the first swash plate 30 side by the pressure guided to each volume chamber 10 as shown by the arrow in FIG. Therefore, the port plate 60 is rotated. At this time, since the pressing ratio of the shoe 21 is larger than that of the port plate 60, when the friction coefficient generated on each sliding surface is equal, no slip in the rotational direction occurs between the shoe 21 and the port plate 60. Slip occurs between the first swash plates 30.

  When the motor actually rotates, the lubricating state between the port plate 60 and the first swash plate 30 having a large relative speed is improved, and the friction coefficient is reduced. This tendency is further promoted.

  Therefore, in a normal operation state, the shoe 21 on the first swash plate 30 side can rotate the port plate 60 with frictional force.

  That is, the port plate 60 slides smoothly with respect to the first swash plate 30 due to the difference in frictional force acting on both surfaces of the port plate 60 and rotates together with the cylinder block 4. Thus, even if the sliding range of the port plate 60 and each shoe 21 is not restricted by the retainer plate 70, the port plate 60 rotates together with the cylinder block 4, while each shoe 21 has its radius with respect to the port plate 60. Slide in the direction.

  Even if the balance of the frictional force acting on both surfaces of the port plate 60 is lost, the port plate 60 rotates together with the cylinder block 4 via the retainer plate 70 and the operation of the piston motor 1 can be maintained.

  The force for rotating the port plate 60 by the shoe 21 is due to the frictional force between the shoe 21 and the port plate 60 in a normal operation state. However, when the motor starts up or changes greatly in rotation, pressure, etc. during operation, the pressing ratio of the shoe 21 decreases transiently, or the frictional force between the port plate 60 and the first swash plate 30 increases. By doing so, the rotation by the frictional force becomes impossible, and there is a possibility that the rotational direction shifts between the shoe 21 and the port plate 60.

  Under such circumstances, the shoe 21 slightly deviates in the rotational direction and hits the retainer plate 70 to rotate it. Since the retainer plate 70 is coupled to the port plate 60 by pins 79, it can be reliably rotated.

  However, since the port plate 60 is normally rotated by the frictional force between the shoe 21 and the contact portion between the shoe 21 and the retainer plate 70 and the frequency at which a force is applied to the pin 79 between the retainer plate 70 and the port plate 60. It is reduced and durability is secured.

  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 the rear drive pistons 33 and 34, whereby the tilt angle of the first swash plate 30 is switched 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 each of the rear drive pistons 43 and 44, whereby the tilt angle of the second swash plate 40 is switched in two stages. The first and second swash plates 30 and 40 are formed with receiving portions 49a and 49b that receive the driving force from the rear driving pistons 43 and 44, respectively.

  There are two main sliding portions of the piston motor 1, the sliding portion j of the port plate 60 with respect to the first swash plate 30 and the sliding portion k of the shoe 22 with respect to the second swash plate 40. This is the same as the conventional non-opposing piston motor at two locations, that is, the sliding portion of each shoe with respect to the swash plate and the sliding portion of the cylinder block with respect to the valve plate, and the friction does not increase. The piston motor 1 has a pitch circle diameter P.P. of the cylinder block 4 as compared with a conventional non-opposing piston motor having the same maximum capacity. C. D can be halved and the size can be reduced. Further, the size of the sliding portion j of the port plate 60 with respect to the first swash plate 30 and the sliding portion k of the shoe 22 with respect to the second swash plate 40 are also halved. become.

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

  The motor to be compared is a swash plate type variable motor, which 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 a neutral state and the second swash plate 40 is at the maximum inclination angle (state shown in FIG. 2B), the displacement volume is 1/2 of the maximum displacement volume. Yes, the volume is equal to the case where the conventional non-opposing piston motor to be compared is at the maximum inclination angle.

  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 has one end sliding between the shoe 22 and the second swash plate 40, the other end sliding between the port plate 60 and the first swash plate 30, and the other side of the second swash plate 40 side. There is sliding between the second piston 9 and the cylinder block 4, sliding between the first piston 8 and the cylinder block 4 on the first swash plate 30 side, and the shoe 21 and the port plate 60.

  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 equal to the swing of the conventional non-opposing piston motor, and the power loss is also small. equal. Next, the power loss due to the sliding between the port plate 60 and the first swash plate 30 and between the cylinder block and the valve plate of the conventional non-opposing piston motor is almost equal because both sliding members have the same size. It is thought that it can be done.

  Similarly, it can be said that the power loss due to the sliding of the second piston 9 on the second swash plate 40 side, the cylinder block 4 and the same part of the conventional non-opposing piston motor is almost equal.

  Therefore, the remaining is the sliding between the first piston 8 and the cylinder block 4 on the first swash plate 30 side, and the shoe 21 and the port plate 60. This portion is more lost in the piston motor 1 of the present invention. There is room to produce. However, since the first swash plate 30 side is in a neutral state, the first piston 8 on the first swash plate 30 side does not make a stroke and does not cause relative movement with the cylinder block 4. In addition, the shoe 21 remains pressed against the port plate 60, and no relative movement is generated during this time. Therefore, it can be said that the power loss at these parts is extremely small.

  Therefore, when the first swash plate 30 side is in a neutral state in the piston motor 1 of the present invention, it is almost the same as a conventional non-opposing piston motor having a sliding part size 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? The comparison will be made with a conventional non-opposing piston 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 as compared with that of the piston motor 1 of the present invention, both of the outer diameters of the cylinder blocks are large. (If the piston diameter is equal to the maximum swash plate inclination angle, the pitch circle diameter is doubled.)
When the power loss due to each sliding member is compared 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, between the port plate 60 and the first swash plate 30) are the same. The piston motor 1 of the invention is overwhelmingly less. On the other hand, when the first piston 8 and the cylinder block 4 on the first swash plate 30 side of the piston motor 1 of the present invention slide with the shoe 21 and the port plate 60, the first piston 8 strokes and the cylinder block 4 Since the relative movement occurs and the shoe 21 also performs a slight relative movement with respect to the port plate 60, 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.

  The piston motor 1 is configured as described above, and the variable capacity ratio can be substantially doubled compared to the conventional piston motor by switching the tilt angles of the first and second swash plates 30 and 40. Become. In the case of HST using this piston motor 1, it is possible to perform an automotive control that controls the vehicle speed over the entire speed range in accordance with the operation amount of the speed lever. 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 between the L, M, and H positions. Then, the vehicle is changed from 0 to the maximum speed of each range (L, M, H) by changing the discharge amount of the hydraulic pump constituting the HST from 0 to ± 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.

  As shown in FIGS. 2 (a), 2 (b), and 2 (c), the driving pressure guided to the rear driving pistons 33 and 34 and the rear driving pistons 43 and 44 is switched through the tilt angle control valve. The displacement per one revolution of the piston motor 1 changes in three stages.

  (A) of FIG. 2 shows the L position where the displacement volume of the piston motor 1 becomes the maximum value (for example, 60 cm 3 / rev). At this time, high pressure is guided to the back drive pistons 34, 44 and low pressure is guided to the back drive pistons 33, 43, whereby the inclination of the first and second swash plates 30, 40 is maximized, and the receiving portion 39a. 49a are in contact with the end surface 50a of the port block 50 and the bottom surface 25a of the case 25, respectively.

  FIG. 2B shows an M position where the displacement of the piston motor 1 becomes an intermediate value (for example, 30 cm 3 / rev). At this time, a high pressure is guided to each of the backside drive pistons 33, 44 and a low pressure is guided to each of the backside drive pistons 34, 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. While the second swash plate 40 is in contact with the end surface 50 a, the inclination of the second swash plate 40 is maximized, and the receiving portion 49 a is in contact with the bottom surface 25 a of the case 25.

  (C) of FIG. 2 shows the H position where the displacement volume of the piston motor 1 becomes the minimum value (for example, 12 cm 3 / rev). At this time, high pressure is guided to the back drive pistons 33, 43 and low pressure is guided to the back drive pistons 34, 44, whereby the inclination of the first and second swash plates 30, 40 is minimized, and the receiving portion 39b. 49b are in contact with the end face 50a of the port block 50 and the bottom face 25a of the case 25, respectively.

  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. (A), (b), (c) is sectional drawing which shows the operating state of a piston motor, respectively. 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 sectional view taken along line BB of the port block. Similarly, (a) is a right front view of the first swash plate, (b) is a side view of the first swash plate, (c) is a right front view of the first swash plate, and (d) is a D- Sectional drawing which follows a D line. Similarly, (a) is a left front view of the port plate, (b) is a sectional view taken along line EE of the port plate, and (c) is a right front view of the port plate. Similarly, (a) is a left front view of the retainer plate, (b) is a cross-sectional view taken along line EE of the retainer plate, and (c) is a right front view of the retainer plate. Similarly, (a) is a front view of a plain bearing, and (b) is a cross-sectional view along the line CC of the plain bearing. Similarly, (a) is a front view of the guide sleeve, and (b) is a cross-sectional view taken along line GG of the guide sleeve. Sectional drawing of the swash plate type hydraulic pump motor which shows a prior art example.

Explanation of symbols

Reference Signs List 1 piston motor 4 cylinder block 5 shaft 6 first cylinder 7 second cylinder 8 first piston 9 second piston 19 shoe port 21 shoe 30 first swash plate 32 first swash plate bearing 37 supply / discharge port 40 second swash plate 60 Port plate 64 Valve port 66 Guide sleeve 70 Retainer plate 74 Center spring

Claims (5)

A cylinder block that houses a plurality of first and second pistons to define a volume chamber;
First and second swash plates that reciprocate the first and second pistons so as to expand and contract the volume chamber as the cylinder block rotates,
First and second swash plate bearings that support the first and second swash plates in a tiltable manner;
Swash plate driving means for tilting the first and second swash plates,
A shoe coupled to the first piston;
A port plate that slides in contact with the shoe and the first swash plate and rotates together with the cylinder block;
A bearing through port opening in the first swash plate bearing;
A supply / discharge port that opens in the first swash plate and communicates with the bearing through port;
A valve port that opens into the port plate and communicates intermittently with this supply and discharge port;
With a shoe port that penetrates the shoe and communicates with this valve port and the volume chamber ,
A swash plate type hydraulic pump / motor characterized in that a friction force of the port plate with respect to the first swash plate is set to be smaller than a friction force with respect to the port plate of each shoe . 2. The swash plate type hydraulic pump motor according to claim 1, further comprising centering support means for rotatably supporting the port plate with respect to the first swash plate. 3. A swash plate type hydraulic pump motor according to claim 1 , further comprising a retainer plate through which each shoe is inserted, and the retainer plate is fixed to the port plate. 4. The swash plate type hydraulic pump motor according to claim 1 , further comprising a center spring that presses each shoe against the first swash plate through the port plate. 5. The swash plate type liquid according to claim 1 , wherein the swash plate driving means includes a pair of rear drive pistons that push the first and second swash plates from the back. Pressure pump / motor.

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