JP5777411B2 - Bi-directional rotary type axial piston pump - Google Patents

Description

  The present invention relates to a bidirectional rotary type axial piston pump.

  For example, a swash plate type variable displacement axial piston pump is conventionally used in a hydraulic power supply device that requires a relatively small capacity and high pressure hydraulic oil supply such as an actuator cylinder for driving a hydraulic boom of a heavy machine. There is. This is because a swash plate in which end shoes of a plurality of pistons housed in a cylinder chamber of a cylinder block that is rotated integrally with a rotating shaft in a pump unit is supported so as to be inclined with respect to the rotating shaft. As a pump that sucks and discharges pressure oil as each piston reciprocates with a stroke according to the swash plate angle as the rotary shaft is driven by a prime mover such as a servo motor. It works.

  Accordingly, the discharge amount determined by the piston pushing capacity of such an axial piston pump is determined by the swash plate angle, but this angle can be changed by control using hydraulic pressure. That is, in a hydraulic circuit including an axial piston pump, an electromagnetic switching valve is provided between a discharge flow path of the pump and a pressure receiving portion of a variable capacity mechanism for performing angular displacement of the swash plate, and the electromagnetic switching valve is turned on. In this state, a part of the self-discharge pressure of the pump is guided as a pilot pressure to the pressure receiving part, and the inclination angle is reduced by driving the pressure receiving part against the spring biasing force by driving the pressure receiving part. The discharge flow rate of the pump mechanism is displaced to the small capacity side. In addition, the introduction of pilot pressure oil is stopped when the electromagnetic switching valve is OFF, and the pressure receiving part connected to the low-pressure flow path communicating with the tank or the like reduces or releases the pressing action on the swash plate, and the swash plate angle is Increased by the spring biasing force, the pump discharge flow rate is displaced to the large capacity side.

  In the hydraulic drive device that drives the piston rod of the actuator cylinder forward and backward by hydraulic control, a variable displacement axial piston pump as described above is used as a bidirectional rotary pump. This bidirectional rotary pump includes two forward and reverse discharge ports, and the supply of hydraulic oil in the forward and reverse bidirectional directions is switched according to the rotational direction of the motor. This pump simply connects both ports directly to the piston head side and rod side of the actuator cylinder, and does not require a control valve. The pump is driven forward and backward by a simple hydraulic circuit consisting of a self-supply valve and a safety valve. be able to. If such a bi-directional rotary pump is used, a hydraulic supply device can be configured with a compact design without hydraulic piping with a simple hydraulic circuit that circulates hydraulic oil in a substantially closed system.

  However, in the configuration of the axial piston pump, sliding is performed between each member and between the bearing members, so that the sliding contact surface is likely to be rattled, causing vibration and noise. There is also the risk of adversely affecting stability.

  Therefore, conventionally, a lubricating film is formed by forcibly supplying a high-pressure fluid pressurized from outside the target portion as a lubricant to the gap between the target sliding contact surfaces, and the sliding contact surfaces are kept in a non-contact state. Many so-called hydrostatic bearings are used. For example, a static pressure pocket is provided on the sliding surface of the piston shoe with the swash plate to introduce lubricating oil into the pocket, or a lubricant is supplied between the bottom of the swash plate and the bearing (for example, Patent Documents 1, 2, and 3).

  In addition, in an axial piston pump that obtains a plurality of independent discharge flows from a plurality of discharge ports formed in the valve plate, an unbalance moment based on the hydraulic pressure difference between the discharge ports acts on the swash plate. There is a possibility that the swash plate may vibrate, but it is equipped with a mechanism that gives a complementary reverse moment to the swash plate by the hydraulic pressure led from each discharge port so as to cancel such an unbalance moment (For example, see Patent Document 4).

Japanese Patent Laid-Open No. 9-324749 Japanese Patent Laid-Open No. 10-77956 JP 2002-5006 A JP-A-9-88811

  However, looking at the entire swash plate of the axial piston pump, it is roughly divided into two areas, the area in which the piston in contact with the piston shoe is in the discharge mode and the area in the suction mode. There is a relatively large difference in the back pressure applied to the swash plate between the two, which may cause swash plate vibration and noise.

  Moreover, in the case of the bidirectional rotation type, when the rotation direction is reversed, the discharge area and the suction area of the swash plate are also switched. However, attention has been paid to the difference in back pressure between the discharge area and the suction area of the swash plate as described above, and means for canceling such a difference in back pressure even in the unidirectional rotation type. There was no one with.

  In view of the above problems, the object of the present invention is to compensate for the back pressure difference between the discharge area and the suction area of the swash plate corresponding to both forward and reverse rotations, and to maintain a stable and stable balance. An object of the present invention is to provide a bidirectional rotary type axial piston pump capable of obtaining a plate bearing state.

  The present invention relates to a rotating shaft driven by a prime mover, a cylinder block rotating integrally with the rotating shaft, and a plurality of cylinder blocks formed in parallel with the rotating shaft at equal angular intervals around the rotating shaft. Each of the cylinder chambers, a piston housed in each cylinder chamber, and a swash plate that is supported so as to be tiltable with respect to the rotation shaft and has an inclined surface with which an end shoe of each piston slides. In accordance with the rotational drive of the rotary shaft that can be switched between forward and reverse by the above, each piston reciprocates with a stroke corresponding to the angle of the swash plate, and the pressure oil is sucked and selectively specified by the rotational direction. A spring portion that tilts and biases the swash plate toward an inclination angle position that is a maximum discharge amount, and a pump discharge pressure as a pilot pressure. An operation piston portion that is operated by the action of the portion and presses the swash plate toward the minimum discharge amount position against the biasing force of the spring portion, and the operation piston portion according to the increase or decrease of the pilot pressure In a bidirectional rotary type axial piston pump having a variable capacity mechanism that changes a discharge capacity per unit rotation of the cylinder block by displacing a stroke distance of the piston by an inclination angle displacement of the swash plate accompanying a mechanical displacement. A bearing portion that receives a bottom surface of the swash plate that slides as the swash plate tilts, and the bearing portion is half of the inclined surface that the end shoe of the piston is in sliding contact with in the discharge mode or the suction mode. The first slidable contact surface facing the first swash plate bottom surface region corresponding to the region, and the end shoe of another piston in the suction mode or the discharge mode are in slidable contact And a second slidable contact surface facing the second swash plate bottom surface region corresponding to a half region of the first and second slidable contact surfaces on both sides of the penetrating region of the rotating shaft. In each of these, a part of the pump discharge pressure oil is introduced through an oil passage formed in the housing to form a lubricating oil film between the first and second swash plate bottom surface areas facing each other. A pair of concave pocket areas is provided, each pocket area having a relatively small opening area formed in the center of the sliding surface and a relatively opening area formed around the small pocket. The double swash plate has a large pocket with a large pocket, and the back pressure of the discharge mode piston is applied to the bottom surface area of the first swash plate depending on the rotation direction of the rotary shaft, and the bottom portion of the second swash plate Rotating drive with back pressure of piston in suction mode on surface area A first lubricating oil passage for guiding pump discharge pressure oil from one discharge port only to a large pocket of the first sliding contact surface and a small pocket of the second sliding contact surface in a moving state; and the first swash plate The small pocket of the first sliding contact surface and the small pocket of the first sliding contact surface in a rotationally driven state in which the back pressure of the suction mode piston is applied to the bottom surface region and the discharge mode piston back pressure is applied to the second swash plate bottom surface region A hydraulic circuit having a second lubricating oil passage for guiding pump discharge pressure oil from the other discharge port only to the large pocket of the second sliding contact surface is provided.

  That is, in the bidirectional rotary type axial piston pump of the present invention, a so-called hydrostatic bearing is formed by forming a lubricating film formed by introducing a part of the self-pressure oil of the pump discharge pressure between the bottom surface of the swash plate. The slidable contact surface of the bearing portion in which the concave pocket region is provided is connected to the first swash plate bottom surface region on the half region side where the end shoe of about half of the pistons in the discharge mode or the suction mode of the swash plate is slidably contacted. The second sliding surface facing the second swash plate bottom surface area on the other half area side where the first sliding contact surface and the end shoe of another piston in the suction mode or the discharging mode of the swash plate are in sliding contact with each other. Two contact pockets are set, and a pair of concave pocket areas provided on both sliding contact surfaces are formed in the central small pocket with a relatively small opening area and a large opening area with a relatively large opening area. Double pocket structure consisting of a pocket And a hydraulic circuit having two oil passages for introducing a part of the discharge pressure from one of the pump discharge ports to only one of the combinations by selectively combining one small pocket and the other large pocket. Therefore, a large pocket on one sliding contact surface on the side where a larger heavy load is applied due to the back pressure of the piston in the discharge mode and a sliding on the other side on which the smaller heavy load is applied due to the back pressure of the piston in the suction mode. Pump discharge pressure can be introduced into a small pocket on the contact surface.

  Therefore, in one sliding contact surface to which a greater load is applied from the swash plate, it opposes with a relatively strong hydraulic pressure over a wider region of the large pocket with respect to one swash plate bottom surface region on the facing side, At the same time, the other slidable contact surface with a small load from the swash plate is opposed to the other swash plate bottom surface region on the facing side by a relatively small hydraulic pressure only in a smaller region of the small pocket. Therefore, the difference in load applied to the bearing portion based on the back pressure difference between the swash plate region receiving the back pressure from the piston in the discharge mode and the swash plate region receiving the back pressure from the piston in the suction mode is The conventional rattling vibration and noise caused by the back pressure difference can be suppressed by offsetting the difference in hydraulic pressure against the bottom surface of the swash plate between the two sliding surfaces.

  In addition, even if the rotation drive direction of the pump is reversed and the region on the side receiving the strong back pressure of the piston in the discharge mode of the swash plate and the region on the side where the back pressure received by the piston in the suction mode is switched, In the two sliding contact surfaces on the bearing side, the oil passage in the hydraulic circuit is also switched, and the pockets into which the pump discharge pressure oil is introduced are interchanged between the large side and the small side. In any rotational drive state, the difference in load applied to the bearing portion based on the back pressure difference applied to the swash plate is canceled out, and it is possible to always achieve an appropriate load balance in the bearing portion.

  Further, the hydraulic circuit is configured such that a part of the pump discharge pressure oil is guided from one of the two discharge ports to the bearing portion through the first lubricating oil passage, and at the same time, one of the pump discharge pressure oils from the same discharge port. The first pilot oil passage that introduces the part as pilot pressure oil into the variable displacement mechanism, and a part of the pump discharge pressure oil from the other discharge port to the bearing portion through the second lubricating oil passage and simultaneously the same discharge port A second pilot oil passage that introduces a part of the pump discharge pressure oil from the pump to the variable displacement mechanism as pilot pressure oil, so that the rotation direction can be selected regardless of whether the pump is driven forward or backward. The pilot pressure oil is always satisfactorily introduced into the variable capacity mechanism even if the oil passage for introduction of the pump discharge pressure oil to a part of the bearing portion is switched along with the target switching.

  Further, when the swash plate is displaced to the large capacity side, the capacity variable mechanism forms a first circuit connection for lowering the pilot pressure by connecting the operation piston portion to the low pressure side flow path and the swash plate on the small capacity side. It is preferable that a switching valve for forming a second circuit connection for guiding the pump discharge pressure oil as pilot pressure oil to the operation piston portion is provided.

  That is, in a state where the first circuit connection is formed by this switching valve, the pilot pressure obtained by introducing a part of the self-pressure through the first pilot oil passage or the second pilot oil passage acts on the operation piston portion. In the state where the piston portion presses the swash plate to reduce the inclination angle, the pump discharge amount is switched to the small capacity side, and the second circuit connection is formed by the switching valve, the pilot pressure oil As the pilot pressure decreases, the action on the operating piston portion is reduced, the inclination angle increases while releasing the swash plate, and the pump discharge amount is switched to the large capacity side.

  With such a switching valve, it is possible to switch to a large capacity side during flow rate control so as to increase the flow rate, and during pressure control, it is possible to suppress the load torque applied to the motor to be small by switching to the small capacity side. Therefore, an efficient bi-directional rotary pump can be realized without increasing the size of the apparatus.

  In the variable displacement pump as described above, since the swash plate angle control is performed by the self-pressure of the pump, when the discharge pressure falls below the pump minimum adjustment pressure, the operation piston section is inclined. Since the pilot pressure for pushing the plate cannot be secured, it becomes difficult to maintain the swash plate angle in a small state, and there is a possibility that the swash plate may move uncontrolled. Therefore, each of the first and second pilot oil passages has a check valve that prevents the pressure oil from flowing out from the operation piston portion to the pump discharge port side and contains the pilot pressure acting on the operation piston portion. It is desirable to arrange them respectively.

  With these check valves, when the swash plate tilting position is switched to the small capacity side in the capacity variable mechanism, the enclosed pilot pressure acts on the operating piston even if the pump discharge pressure is less than the minimum adjustment pressure. Since it can be continued, a stable control state can be maintained even in a low pressure region.

  As described above, the present invention is a half of the inclined surface where the end shoe of the piston in the discharge mode or the suction mode is slidably contacted with the bearing portion that receives the bottom surface of the swash plate that slides as the swash plate tilts. The first slidable contact surface facing the first swash plate bottom surface region corresponding to the region, and the second oblique region corresponding to the other half region where the end shoe of another piston in the suction mode or the discharge mode is slidably contacted A second sliding contact surface facing the plate bottom surface area is provided at both side positions sandwiching the penetrating section area of the rotating shaft, and a part of the pump discharge pressure is applied to each of the first and second sliding contact surfaces. As a pair of concave pocket regions that form a lubricating oil film between the first and second swash plate bottom surface regions that are introduced through an oil passage formed in the housing and face each other, A small pocket having a relatively small opening area and the small pocket. It has a double pocket structure with a large pocket with a relatively large opening area formed around the lid, and a larger load is applied from the swash plate area where the back pressure from the piston in the discharge mode is applied. A piston that is in the suction mode at the same time that it is opposed to one of the sliding contact surfaces of the bearing portion by a relatively strong hydraulic pressure over a wider area of the large pocket with respect to one swash plate bottom surface area on the facing side. Relatively small hydraulic pressure only in the smaller area of the small pocket with respect to the other swash plate bottom surface area on the opposite side of the other slidable contact surface where the load from the swash plate area to which the back pressure is applied is small The difference in load applied to the bearing portion based on the back pressure difference between the swash plate region that receives the back pressure from the piston in the discharge mode and the swash plate region that receives the back pressure from the piston in the suction mode. The effect of offsetting the difference in oil pressure against the bottom surface of the swash plate between the two sliding contact surfaces of the bearing portion, and suppressing the conventional rattling vibration and noise caused by the back pressure difference. .

  In addition, even if the rotation drive direction of the pump is reversed and the region on the side receiving the strong back pressure of the piston in the discharge mode of the swash plate and the region on the side where the back pressure received by the piston in the suction mode is switched, In the two sliding contact surfaces on the bearing side, the oil passage in the hydraulic circuit is also switched, and the pockets into which the pump discharge pressure oil is introduced are interchanged between the large side and the small side. In any rotational drive state, the difference in load applied to the bearing portion based on the back pressure difference applied to the swash plate is canceled out, and it is possible to always achieve an appropriate load balance in the bearing portion.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram of the bidirectional | two-way rotation type axial piston pump by one embodiment of this invention, (a) is a sectional side view of this pump, (b) is a front view of this pump. In the pump of FIG. 1, a schematic diagram showing the pocket structure of each sliding contact surface of the bearing portion corresponding to the discharge port region and the suction port region of the cylinder block shown in the upper part, and oil for guiding a part of the pump discharge pressure to each pocket It is a hydraulic circuit diagram including a path, and shows a pump drive state in which the rotational directions are normal and reverse with each other in (a) and (b).

  1 and 2 show a bidirectional rotary axial piston pump according to an embodiment of the present invention. FIG. 1 is a schematic configuration diagram of the pump, in which (a) is a side sectional view and (b) is a front view. In this front view, the arrangement of the cylinder chamber of the cylinder block is indicated by a dotted line as a transparent portion. FIG. 2 is a schematic diagram showing a pocket configuration of each sliding contact surface of the bearing portion and a hydraulic circuit diagram including an oil passage for guiding a part of the pump discharge pressure to each pocket, and (a) and (b) The pump drive state in which the rotation direction is forward and reverse is shown. In addition, the schematic diagram which showed the discharge port area | region and suction port area | region of the cylinder block in the rotation drive state in each upper part of the bearing part was put in order.

  A bidirectional rotary type axial piston pump according to the present embodiment includes a rotary shaft 1 driven by a prime mover (not shown), a cylinder block 2 rotated integrally with the rotary shaft 1 in a housing 30, and a cylinder block 2, a plurality of cylinder chambers 3 formed in parallel with the rotation shaft 1 at equal angular intervals around the rotation shaft 1, pistons 4 accommodated in the cylinder chambers 3, and inclination with respect to the rotation shaft 1 The swash plate 6 is provided so as to be supported and provided with an inclined surface with which the end shoe 5 of each piston slides.

  Accordingly, each of the pistons 4 reciprocates in the cylinder chamber 3 with a stroke corresponding to the angle of the swash plate 1 in accordance with the rotational drive of the rotary shaft 1 that can be switched between the forward and reverse directions by the prime mover. A pumping action is obtained that sucks and discharges from either of the two discharge ports selectively specified by the rotation direction.

  Further, the axial piston pump according to the present embodiment is provided with a variable capacity mechanism for changing the discharge dose per unit rotation of the cylinder block 2. That is, the swash plate 6 is tilted and biased toward the tilt angle position where the maximum discharge amount is obtained by the spring portion 8, and the swash plate 6 is set to the minimum discharge amount against the biasing force by the spring portion 8. The operation piston part 9 which pushes toward the position which becomes is provided. The operation piston portion 9 is operated by the action of a pilot pressure that is a part of the pump discharge pressure, and the inclination angle of the swash plate 6 is displaced by a mechanical displacement corresponding to the increase or decrease of the pilot pressure. Along with this, the stroke distance of the piston 4 in the cylinder block 2 is displaced, and the pump discharge capacity is changed.

  Furthermore, in the variable capacity mechanism according to the present embodiment, when the swash plate 6 is displaced to the large capacity side, the operation piston portion 9 is connected to the low pressure side flow path to form a first circuit connection that lowers the pilot pressure. When the swash plate 6 is displaced to the small capacity side, an electromagnetic switching valve 10 is provided which forms a second circuit connection for guiding the pump discharge pressure to the operation piston unit 9 as a pilot pressure.

  In this axial piston pump, the port X of the first discharge side oil passage 11x and the port Y of the second discharge side oil passage 11y communicating with the two discharge ports respectively serve as a hydraulic cylinder for driving an actuator (not shown). Can be connected in series. This pump can supply pressure oil in both forward and reverse directions, and the discharge direction of the pressure oil is selected according to the forward and reverse rotation direction.

  The first pilot oil passage 12x and the second pilot oil passage 12y branched from the first and second discharge oil passages (11x, 11y), respectively, and a part of the hydraulic oil from each discharge port by these pilot oil passages. It is connected to the operation piston part 9 of the variable capacity mechanism through an electromagnetic switching valve 10 guided as a pilot pressure.

  In the state where the electromagnetic switching valve 10 forms the port PA connection (port B plug) as the second circuit connection, a part of the self-pressure is generated from the first discharge side oil passage 11x or the second discharge side oil passage 11y. The pilot pressure guided through the pilot oil passage 12x or the second pilot oil passage 12y acts on the operation piston portion 9, and the operation piston of the operation piston portion 9 is displaced to press the swash plate 6. By reducing the inclination angle, the pump discharge amount is switched to the small capacity side.

  Further, in the state where the electromagnetic switching valve 10 forms the port BT connection (port A plug) as the first circuit connection, the pilot pressure is reduced by stopping the introduction of the pilot pressure oil, and accordingly, the operation piston unit 9 is moved to. The pressure of the operation piston is released from the operation piston and the inclination angle is increased while the pump discharge amount is switched to the large capacity side.

  It should be noted that when the second circuit connection on the large capacity side is formed, operation is performed by preventing the flow of pressure oil from the operation piston portion 9 side to the first discharge side oil passage 11x or the second discharge side oil passage 11y. In order to contain the pilot pressure acting on the pilot section 9, check valves (Cx, Cy) are arranged in the first pilot oil passage 12x and the second pilot oil passage 12y, respectively.

  Therefore, when the pump discharge amount is switched to the small capacity side in the variable capacity mechanism, the pilot pressure confined by these check valves (Cx, Cy) is operated even if the pump discharge pressure is less than the minimum adjustment pressure. Since it can continue to act on the piston portion 9, a stable control state can be maintained even in a low pressure region.

  Further, the swash plate 6 has a semi-cylindrical bottom portion 7 and supports the swash plate 6 by receiving the bottom portion that slides as the swash plate tilts on a sliding contact surface having the same curvature as the curved surface of the bottom portion. The bearing portion 20 is fixed in the housing 30. Accordingly, the swash plate 6 is supported by the bearing portion 20 so as to be tiltable about the rotary shaft 1.

  This bearing portion 20 has a hydrostatic bearing structure in which a pump discharge pressure oil is guided through an oil passage 31 formed in the housing 30 on a sliding contact surface, and a lubricating film is formed between the bottom surface of the swash plate. It has become. The slidable contact surface of the bearing portion 20 is composed of two first and second slidable contact surfaces (23, 25) located on both sides of the central groove portion 22 including the rotation shaft through hole 21.

  Each piston 4 sucks hydraulic oil into the cylinder chamber 3 in the approximately half area on the inclined surface of the swash plate 6 slidably contacting the end shoe 5 as the cylinder block 2 rotates, and operates by sucking in the other half area. Discharge the oil. If the rotation direction of the cylinder block 2 is reversed, the discharge mode and the suction mode by the piston 4 in the bisection region on the inclined surface are interchanged. Therefore, the port X based on one region and the port Y based on the other region also replace each other as a discharge port and a suction port by switching the rotation direction.

  Further, the inclined surface of the swash plate 6 is such that the back pressure received from the piston 4 in the half region where the end shoe 5 of the piston 4 in the discharge mode is in sliding contact is the end shoe 5 of the other piston 4 in the suction mode. Is larger than the back pressure received from the piston 4 in the other half region where the slidable contact occurs.

  Therefore, the bottom surface of the swash plate 6 also corresponds to one half region (port X side) of the inclined surface as the first swash plate bottom surface region and corresponds to the other half region (port Y side). The region is set as the second swash plate bottom surface region, and the one that receives the sliding of the first swash plate bottom surface region on the bearing portion 20 side is defined as the first sliding contact surface 23, and the second swash plate bottom surface region The side that accepts sliding is configured to be the second sliding contact surface 25.

  A part of the pump discharge pressure is introduced into each of the first slidable contact surface 23 and the second slidable contact surface 25 via an oil passage 31 formed in the housing 30 and faces each other. A pair of concave pocket regions (24, 26) for forming a lubricating oil film is provided between the two swash plate bottom surface regions. Each pocket region (24, 26) has a small pocket (24S, 26S) formed at the center of the sliding surface and a relatively small opening area, and a relatively open area formed around the small pocket. It has a double pocket configuration with large large pockets (24L, 26L).

  And in the hydraulic circuit of this pump, it branches from the 1st discharge side oil path 11x, and the pump discharge pressure oil is made into the large pocket 24L of the 1st sliding contact surface 23, and the small pocket 26S of the 2nd sliding contact surface 25. Branched from the first lubricating oil passage 13x and the second discharge-side oil passage 11y, and the pump discharge pressure oil is divided into the small pocket 24S of the first sliding contact surface 23 and the large pocket 26L of the second sliding contact surface 25. And a second lubricating oil passage 13y that leads to the same.

  In the above configuration, in the operation process in which the hydraulic oil is discharged from the first discharge side flow passage 11x to the port X according to the rotation direction of the rotary shaft 1, on the swash plate on the port X side, as shown in FIG. The piston 4 is in the discharge mode and the rotational drive state in which the piston 4 is in the suction mode on the swash plate on the port Y side, and the first lubricating oil passage 13x branches from the first discharge-side oil passage 11x. Part of the pump discharge pressure oil is introduced into the large pocket 24L of the sliding contact surface 23 and the small pocket 26S of the second sliding contact surface 25.

  Therefore, in this operation process, a large back pressure by the discharge mode piston 4 applied to the swash plate half area on the port X side causes a large load on the first sliding contact surface 23 via the first swash plate bottom surface area. A small back pressure by the piston 4 in the suction mode applied to the swash plate half region on the port Y side causes a small load on the second slidable contact surface 25 via the second swash plate bottom surface region. The hydraulic pressure sent to the large pocket 24L counters a large load applied to the surface 23 over a relatively large area, and at the same time, the small pocket 26S against the small load applied to the second sliding contact surface 25. When the sent hydraulic pressure counteracts with a relatively small area, the back pressure region difference from the swash plate side is offset by the pocket hydraulic pressure difference between the first and second sliding contact surfaces.

  Further, such a canceling effect is also exhibited in the operation process in which the above is the pump forward rotation direction and the reverse rotation direction. That is, in the process of discharging the hydraulic oil from the 21st discharge side flow passage 11y to the port Y as shown in FIG. 2 (b), the piston 4 is sucked on the swash plate on the port X side, and the mode is set. The small pocket 24S of the first sliding contact surface 23 is in a rotational drive state in which the piston 4 is in the discharge mode on the side swash plate, and through the second lubricating oil passage 13y branched from the second discharge-side oil passage 11y. A part of the pump discharge hydraulic oil is introduced into the large pocket 26L of the second sliding contact surface 25.

  Therefore, in this operation process, a large back pressure by the piston 4 in the discharge mode applied to the swash plate half area on the port Y side generates a large load on the second sliding contact surface 25 via the second swash plate bottom surface area. A small back pressure by the piston 4 in the suction mode applied to the swash plate half area on the port X side causes a small load on the first slidable contact surface 23 via the first swash plate bottom surface area. The hydraulic pressure sent to the large pocket 26L counters a large load applied to the surface 25 over a relatively large area, and at the same time, a small load applied to the first sliding contact surface 23 is applied to the small pocket 24S. When the sent hydraulic pressure counteracts with a relatively small area, the back pressure region difference from the swash plate side is offset by the pocket hydraulic pressure difference between the first and second sliding contact surfaces.

  As described above, in the bidirectional rotary type axial piston pump according to the present embodiment, the difference in piston back pressure between the discharge port side and the suction port side is the same regardless of whether the pump is driven forward or backward. Since the first and second sliding contact surfaces cancel each other on the bearing portion 20 side, an appropriate balanced swash plate bearing state is always maintained, and the bearing portion 20 based on the back pressure difference during the rotation drive is maintained. There is no risk of rattling vibration or noise.

1: Rotating shaft 2: Cylinder block 3: Cylinder chamber 4: Piston 5: End shoe 6: Swash plate 7: Semi-cylindrical bottom portion 8: Spring portion 9: Operating piston portion 10: Electromagnetic switching valve 11x: First discharge side Oil passage 11y: second discharge side oil passage 12x: first pilot oil passage 12y: second pilot oil passage 13x: first lubricating oil passage 13y: second lubricating oil passage 20: bearing portion 21: through hole 22: central groove portion 23: 1st sliding contact surface 25: 2nd sliding contact surface 24, 26: Recessed pocket area | region 24L, 26L: Large pocket 24S, 26S: Small pocket 30: Housing 31: In-housing oil path Cx, Cy: Check valve

Claims (3)

A rotating shaft driven by a prime mover, a cylinder block rotating integrally with the rotating shaft, and a plurality of cylinder chambers formed in the cylinder block in parallel with the rotating shaft at equal angular intervals around the rotating shaft; A piston housed in each cylinder chamber, and a swash plate having an inclined surface supported so as to be inclined with respect to the rotating shaft and in contact with an end shoe of each piston, both forward and reverse by the prime mover In accordance with the rotational drive of the rotation shaft that can be switched in the direction, each piston reciprocates with a stroke corresponding to the angle of the swash plate, thereby sucking the pressure oil and selectively specifying the two discharges according to the rotational direction. Discharging from one of the outlets,
The swash plate is operated by the action of a part of the pump discharge pressure as the pilot pressure and the spring part that tilts and urges the swash plate toward the inclination angle position that becomes the maximum discharge amount, and resists the urging force of the spring part. An operation piston portion that presses the swash plate toward the minimum discharge amount position, and a stroke of the piston by an inclination angle displacement of the swash plate accompanying a mechanical displacement of the operation piston portion according to increase or decrease of the pilot pressure. In the bidirectional rotary type axial piston pump provided with a variable capacity mechanism for changing the discharge capacity per unit rotation of the cylinder block by displacing the distance,
A bearing portion that receives the bottom surface of the swash plate that slides as the swash plate tilts,
The bearing portion includes a first slidable contact surface facing a first swash plate bottom surface region corresponding to a half region of an inclined surface with which an end shoe of a piston in a discharge mode or a suction mode is slidably contacted, and a suction mode or The second sliding contact surface facing the second swash plate bottom surface area corresponding to the other half area with which the end shoe of the other piston in the discharge mode is in sliding contact is sandwiched between the penetrating area of the rotating shaft. On both sides,
The first and second swash plate bottom surfaces are respectively opposed to each of the first and second sliding contact surfaces by introducing a part of the pump discharge pressure oil through an oil passage formed in the housing. A pair of concave pocket regions that form a lubricating oil film is provided between the small pockets, each pocket region having a relatively small opening area formed at the center of the sliding contact surface, It has a double pocket configuration with a large pocket with a relatively large opening area formed around it,
Depending on the rotation direction of the rotary shaft, a discharge mode piston back pressure is applied to the first swash plate bottom surface area, and a suction mode piston back pressure is applied to the second swash plate bottom surface area. A first lubricating oil passage for guiding pump discharge pressure oil from one discharge port only to a large pocket of the first sliding contact surface and a small pocket of the second sliding contact surface; and the first swash plate bottom surface region In the rotational driving state where the back pressure of the piston in the suction mode is applied to the bottom surface area of the second swash plate and the back pressure of the piston in the discharge mode is applied to the second swash plate bottom surface area, the second pocket of the first sliding contact surface and the second A bidirectional rotary type axial piston pump comprising a hydraulic circuit having a second lubricating oil passage for guiding pump discharge pressure oil from the other discharge port only to a large pocket on the sliding contact surface. In the hydraulic circuit, a part of the pump discharge pressure oil is guided from one of the two discharge ports to the bearing portion through the first lubricating oil passage, and at the same time, one of the pump discharge pressure oils from the same discharge port. The first pilot oil passage that introduces the portion as pilot pressure oil into the variable displacement mechanism and the same as the part of the pump discharge pressure oil is guided from the other discharge port to the bearing portion via the second lubricating oil passage 2. The bidirectional rotary axial piston according to claim 1, further comprising a second pilot oil passage that introduces a part of pump discharge pressure oil from the discharge port as pilot pressure oil into the variable displacement mechanism. pump.   When the swash plate is displaced to the large capacity side, the variable capacity mechanism forms a first circuit connection for reducing the pilot pressure by connecting the operating piston portion to the low pressure side flow path, and reduces the swash plate. 3. A switching valve that forms a second circuit connection that guides pump discharge pressure oil to the operation piston portion as pilot pressure oil when displacing to the capacity side is provided. A counter-rotating axial piston pump.

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