Patent Application
20130327208
The present invention relates to a swash plate type hydraulic rotating machine suitably serving as, for example, a swash plate type hydraulic pump or swash plate type hydraulic motor.
Conventionally, there are known swash plate type hydraulic rotating machines such as swash plate type hydraulic pumps and swash plate type hydraulic motors (see Patent Literature 1).
In the swash plate type hydraulic pump having the above configuration, when the rotating shaft 3 rotates, the pistons 13 reciprocate within the respective cylinders 11 in accordance with the inclination of the swash plate 15. The swash plate type hydraulic pump utilizes the motion of the pistons 13 to suck a required amount of low-pressure working fluid and to discharge the working fluid to the high-pressure side. Swash plate type hydraulic motors are configured such that the rotation of the rotating shaft and the movement of the working fluid are opposite to those of the above swash plate type hydraulic pump.
In the above-described conventional swash plate type hydraulic pump 100, the keep plate 17, which is pushed toward the swash plate 15 side by the spring force of the set springs 20 and the hydraulic pressure in the cylinders 11, causes the shoes 14 to be in close contact with the sliding contact surface 15c of the swash plate 15. However, when the rotating shaft 3 and the cylinder block 9 rotate at high speed, the speed of the reciprocating motion of the pistons 13 within the cylinders 11 increases, which results in that the pistons 13 pull the shoes 14 toward the valve plate 4 side with greater force. In such a high-speed rotation state, if the hydraulic pressure in the cylinders 11 decreases due to, for example, a low-pressure operation, then the force pushing the shoes 14 against the swash plate 15 depends on the spring force of the set springs 20. As a result, the pulling force of the pistons 13 pulling the shoes 14 toward the valve plate 4 side becomes greater than the pushing force pushing the shoes 14, which pushing force is derived from the set springs 20 and the hydraulic pressure. Consequently, as shown in
In order to prevent the shoes from being lifted as above, the swash plate type hydraulic pump disclosed in Patent Literature 1 is configured such that the peripheral portion of the keep plate 17 pushing the shoes 14 against the swash plate 15 has a tapered structure. Accordingly, the rigidity of the keep plate 17 is improved and deformation of the keep plate 17 is prevented, and thereby the shoes 14 are prevented from being lifted.
Patent Literature 2 discloses an axial plunger type hydraulic system, in which the bearing surface of the shoes, the bearing surface contacting the swash plate, is formed of an aluminum-silicon alloy that is lighter than copper alloys and has excellent abrasion resistance, so that centrifugal force to be exerted on the shoes is reduced. In this manner, the shoes are prevented from being lifted from the swash plate.
Even though deformation of the keep plate 17 is prevented in the conventional swash plate type hydraulic pump 100 as disclosed in Patent Literature 1, if the set springs 20 shrink, then there is a risk that the keep plate 17 moves toward the valve plate 4 side, resulting in that the shoes 14 become lifted from the swash plate 15. Here, one conceivable method of preventing the shoes from being lifted as above is to increase the spring force of the set springs 20 pushing the keep plate 17 toward the swash plate 15 side. However, there is a limit of the spring force of the set springs 20. In addition, if the spring force is increased, then the friction force between the swash plate 15 and the shoes 14 increases, resulting in reduced efficiency and a risk of seizing. For these reasons, the conventional swash plate type hydraulic pump 100 cannot bear a significant increase in the rotational speed of the rotating shaft 3.
In the axial plunger type hydraulic system disclosed in Patent Literature 2, in order to fix the position of the shoes, not a keep plate but a frame is provided at the outer peripheral portion of the swash plate. The frame serves to hold the shoes such that the shoes are kept in contact with the swash plate. When the hydraulic system having this configuration operates, relative slip occurs between the frame of the swash plate and the shoes. Therefore, the axial plunger type hydraulic system disclosed in Patent Literature 2 cannot bear a significant increase in the rotational speed.
In view of the above, an object of the present invention is to provide a technique for preventing the shoes from being lifted from the swash plate in a swash plate type hydraulic rotating machine such as a swash plate type hydraulic pump or swash plate type hydraulic motor, and also to provide a structure capable of bearing further increase in the rotational speed of the swash plate type hydraulic rotating machine.
A swash plate type hydraulic rotating machine according to the present invention includes: a rotating shaft; a valve plate and a swash plate facing each other and away from each other in an axial direction of the rotating shaft; a cylinder block fitted to an outside of the rotating shaft between the valve plate and the swash plate, such that the cylinder block is slidingly in contact with the valve plate; a plurality of cylinders provided in the cylinder block; a plurality of pistons inserted in the respective cylinders, such that the pistons are movable in the axial direction in a reciprocating manner; a plurality of shoes each connected to a distal end of a respective one of the pistons such that each shoe is movable in a rocking manner, wherein the distal end of each piston protrudes from a respective one of the cylinders toward the swash plate side; an annular keep plate loosely fitted to the rotating shaft between the swash plate and the cylinder block, the keep plate holding the shoes; a plain bearing provided between the keep plate and the cylinder block, the plain bearing supporting the keep plate; and spring members provided between the plain bearing and the cylinder block, the spring members biasing the plain bearing to cause the plain bearing to push the keep plate toward the swash plate side. A gap in the axial direction between the plain bearing the cylinder block is 0 or a fine gap when the swash plate type hydraulic rotating machine is in an assembled state.
In the above swash plate type hydraulic rotating machine, the gap desirably has a size of 0, or has a size of more than 0 and equal to or less than 1.2 mm.
Alternatively, a swash plate type hydraulic rotating machine according to the present invention includes: a rotating shaft; a valve plate and a swash plate facing each other and away from each other in an axial direction of the rotating shaft; a cylinder block fitted to an outside of the rotating shaft between the valve plate and the swash plate, such that the cylinder block is slidingly in contact with the valve plate; a plurality of cylinders provided in the cylinder block; a plurality of pistons inserted in the respective cylinders, such that the pistons are movable in the axial direction in a reciprocating manner; a plurality of shoes each connected to a distal end of a respective one of the pistons such that each shoe is movable in a rocking manner, wherein the distal end of each piston protrudes from a respective one of the cylinders toward the swash plate side; an annular keep plate loosely fitted to the rotating shaft between the swash plate and the cylinder block, the keep plate holding the shoes; a plain bearing provided between the keep plate and the cylinder block, the plain bearing supporting the keep plate; spring members provided between the plain bearing and the cylinder block, the spring members biasing the plain bearing to cause the plain bearing to push the keep plate toward the swash plate side; and a filling member filling a gap in the axial direction between the plain bearing and the cylinder block.
The filling member may be at least one shim plate. A time-hardening or thermosetting filler may be provided between the filling member and one of the plain bearing and the cylinder block. Alternatively, the filling member may be a press-fit bushing.
According to the swash plate type hydraulic rotating machine having the above configuration, the gap between the cylinder block and the plain bearing is 0 or a fine gap. Accordingly, movement of the plain bearing toward the valve plate side is restricted as a result of the plain bearing contacting the cylinder block. That is, the keep plate, which pushes the shoes against the swash plate, is restricted from moving toward the valve plate side. Therefore, for example, even when the rotational speed of the rotating shaft increases and thereby inertial force that pulls the pistons toward the valve plate side, and centrifugal force moment that causes tipping of the shoes, become greater than the spring force of the set springs, the shoes do not become lifted from the swash plate or become tipped. As described above, in the swash plate type hydraulic rotating machine according to the present invention, the shoes are prevented from being lifted from the swash plate and from tipping. Therefore, the swash plate type hydraulic rotating machine according to the present invention can prevent the occurrence of, for example, decrease in operating efficiency, uneven wear of the swash plate and the shoes, galling phenomenon, and seizing, which are caused when the shoes slidingly rotate on the swash plate in a state where there is edge contact between the swash plate and the shoes. Since, as described above, the shoes do not become lifted from the swash plate even if the rotational speed of the rotating shaft is increased, the rotational speed of the rotating shaft can be further increased in the swash plate type hydraulic rotating machine.
According to the present invention, even if inertial force that pulls the pistons toward the valve plate side, and centrifugal force moment that causes tipping of the shoes, become greater than the spring force of the set springs, the movement of the keep plate toward the valve plate side is restricted as a result of the plain bearing contacting the cylinder block. This makes it possible to prevent the shoes from being lifted from the swash plate and from tipping.
One embodiment of the present invention is described below in detail with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same reference signs, and a repetition of the same description is avoided. Hereinafter, the description is given by taking a swash plate type hydraulic pump as an example of a swash plate type hydraulic rotating machine.
First, a schematic configuration of the swash plate type hydraulic pump is described with reference to
At one side of the cylinder block 9 (right side in
The cylinder block 9 integrally includes a guide portion 91 and a body 92. The guide portion 91 is inserted in a spherical plain bearing 80 which will be described below. The body 92 is provided with cylinders 11 in which pistons 13 are inserted. The body 92 has a diameter larger than that of the guide portion 91. The guide portion 91 protrudes from the body 92 toward the first side. Accordingly, the cylinder block 9 has two stepped end surfaces facing the first side. The end surface at the first step is a first end surface 95 positioned at the first side of the guide portion 91, and the end surface at the second step is a second end surface 96 positioned at the first side of the body 92. The cylinder block 9 has the aforementioned valve plate sliding contact surface 97 as an end surface facing the second side. A plurality of cylinders 11 (only two cylinders are shown in
An annular keep plate 17 is provided between the cylinder block 9 and the swash plate 15. A plurality of shoe bearing holes 17a are formed in the keep plate 17, such that the shoe bearing holes 17a are provided corresponding to the respective cylinders 11. Each shoe 14 is fitted in a respective one of the shoe bearing holes 17a. The outer periphery of the shoe 14 has a smaller diameter portion 14c and a larger diameter portion 14d. The smaller diameter portion 14c can be fitted into the shoe bearing hole 17a. The larger diameter portion 14d is positioned at the first side relative to the smaller diameter portion 14c, and the larger diameter portion 14d has a diameter larger than that of the shoe bearing hole 17a. A stepped surface between the smaller diameter portion 14c and the larger diameter portion 14d of the shoe 14, the stepped surface facing the second side, contacts a peripheral portion around the shoe bearing hole 17a. In this manner, movement of the shoe 14 toward the second side is restricted.
The keep plate 17 is supported by the rotating shaft 3 via the spherical plain bearing 80, such that the keep plate 17 can move in a rocking manner. The diameter of an outer peripheral surface 81 of the spherical plain bearing 80 gradually increases toward the second side. The outer peripheral surface 81 is formed as a smooth curved surface. A flange 82 is formed at the second-side end of the outer peripheral surface 81 of the spherical plain bearing 80. The spherical plain bearing 80 is inserted toward the first side within the inner periphery of the keep plate 17. The outer peripheral surface 81 of the spherical plain bearing 80 is in contact with the inner peripheral surface 17b of the keep plate 17. The keep plate 17 can move in a rocking manner around the rotating shaft 3 as a result that the inner peripheral surface 17b of the keep plate 17 slides on the outer peripheral surface 81 of the spherical plain bearing 80. A fitting portion 83 and a guide hole 84 are formed at the inner periphery of the spherical plain bearing 80. The fitting portion 83 is positioned at the first side relative to the guide hole 84. Splines extending in the axial direction L are formed at the fitting portion 83 of the spherical plain bearing 80. The splines are fitted to the splines formed at the outer periphery of the rotating shaft 3. As a result, the spherical plain bearing 80 can integrally rotate with the rotating shaft 3 and move in the axial direction L. The guide hole 84 of the spherical plain bearing 80 has an opening facing the second side, and is formed as hollow space into which the above-described guide portion 91 of the cylinder block 9 can be inserted toward the first side. In a state where the guide portion 91 of the cylinder block 9 is inserted in the guide hole 84 of the spherical plain bearing 80, the outer periphery of the guide portion 91 of the cylinder block 9 is in contact with the inner periphery of the guide hole 84 of the spherical plain bearing 80. The spherical plain bearing 80 is thus guided by the guide portion 91 of the cylinder block 9, and therefore, the spherical plain bearing 80 can move in the axial direction L without wobbling.
Set springs 20 are provided between the spherical plain bearing 80 and the cylinder block 9. The set springs 20 serve to bias the spherical plain bearing 80 and the cylinder block 9 toward the opposite sides in the axial direction L. Specifically, a plurality of spring accommodating holes 93, which are open facing the first side, are formed in the body 92 of the cylinder block 9. A set spring 20 which is a coil spring is fitted in each spring accommodating hole 93. The first side of the set spring 20 protrudes from the cylinder block 9, and the protruding end of the set spring 20 is in contact with the flange 82 of the spherical plain bearing 80. Due to the spring force of the set springs 20 and hydraulic pressure in the cylinders 11, the valve plate sliding contact surface 97 of the cylinder block 9 is pushed against the valve plate 4, so that the valve plate sliding contact surface 97 is in close contact with the valve plate 4. Also, the spherical plain bearing 80, which is pushed toward the first side by the spring force of the set springs 20 and the hydraulic pressure in the cylinders 11, pushes the keep plate 17 toward the first side. Further, the keep plate 17, which is pushed toward the first side, pushes the shoes 14 against the sliding contact surface 15c of the swash plate 15.
Hereinafter, operations of the swash plate type hydraulic pump 10 having the above configuration are described in relation to a case where, of the suction/discharge ports 5 and 6, one suction/discharge port 5 is used as a suction port and the other suction/discharge port 6 is used as a discharge port. First, when a driving unit such as an engine drives the rotating shaft 3 to rotate, the cylinder block 9 integrally rotates with the rotating shaft 3, and the valve plate sliding contact surface 9a of the cylinder block 9 rotates while slidingly contacting the valve plate 4. Also, the shoes 14 held by the keep plate 17 rotate with the cylinder block 9 and the pistons 13 while slidingly contacting the sliding contact surface 15c of the swash plate 15. As a result, the pistons 13 reciprocate within the respective cylinders 11 at a stroke corresponding to the maximum tilting angle of the swash plate 15. In a suction stroke where each piston 13 moves from the top dead center to the bottom dead center, pressure oil is sucked from the suction/discharge passage into the respective cylinder 11 through the suction port 5. In a discharge stroke where each piston 13 moves back from the bottom dead center to the top dead center, the pressure oil previously sucked into the respective cylinder 11 is discharged as high-pressure oil to the suction/discharge passage through the discharge port 6. When the maximum tilting angle of the swash plate 15 is adjusted by a tilting actuator (not shown), the stroke of the pistons 13 is changed, accordingly. In this manner, the discharge capacity from the cylinders 11 can be variably controlled.
The above swash plate type hydraulic pump 10 is configured such that, when in an assembled state, a gap in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 is 0 or a fine gap. The term “assembled state” herein refers to a fully assembled state of the swash plate type hydraulic pump 10. It should be noted that the term “assembled state” does not exclude an operating state of the swash plate type hydraulic pump 10. The gap in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 may be 0 or a fine gap when the swash plate type hydraulic pump 10 is in an operating state. The above expression, “the gap is 0”, means that the spherical plain bearing 80 and the cylinder block 9 are continuously arranged in the axial direction L and there is no vacant space therebetween. Therefore, the state where the gap in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 is 0 includes: a state where the cylinder block 9 and the spherical plain bearing 80 are in contact with each other in the axial direction L; and a state where there is space G (i.e., a gap) in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 and the space G is filled with a filling member F. In a case where the gap in the axial direction L between the spherical plain bearing 80 and the cylinder block 9 is 0, the spherical plain bearing 80 is unable to move toward the second side in the axial direction L since the spherical plain bearing 80 is in direct or indirect contact with the cylinder block 9.
The above expression, “the gap is a fine gap”, means that there is a fine gap ΔL in the axial direction L between the cylinder block 9 and the spherical plain bearing 80. If there is a fine gap ΔL in the axial direction L between the spherical plain bearing 80 and the cylinder block 9, then the spherical plain bearing 80 can move toward the second side in the axial direction L by the gap ΔL. However, the size of the gap ΔL is sufficiently small. The size of the gap ΔL is such that the amount of movement of the keep plate 17 toward the second side, which is caused when the spherical plain bearing 80 moves toward the second side, is in such a range as not to cause the shoes 14 to lose contact with the sliding contact surface 15c of the swash plate 15. Specifically, the size of the gap ΔL is more than 0 and equal to or less than 1.2 mm, and more desirably, more than 0 and equal to or less than 0.8 mm. For reference, in a conventional general swash plate type hydraulic motor, the gap in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 is designed to be approximately 3 to 5 mm.
In the swash plate type hydraulic pump 10 shown in
In the swash plate type hydraulic pump 10 having the above configuration, if the rotating shaft 3 rotates at high speed when the hydraulic pressure in the cylinders 11 has decreased due to, for example, a low-pressure operation, then inertial force that pulls the pistons 13 toward the second side, and centrifugal force moment that causes tipping of the shoes 14, may become greater than the spring force of the set springs 20. In this case, if the keep plate 17 is pulled by the pistons 13 and moved toward the second side, then the pushing force of the shoes 14 against the swash plate 15 decreases, which causes tipping of the shoes 14. In this respect, the swash plate type hydraulic pump 10 according to the present embodiment is configured such that when force that causes the keep plate 17 to move toward the second side occurs, the movement of the spherical plain bearing 80 toward the second side is restricted since the spherical plain bearing 80 directly or indirectly contacts the cylinder block 9, and the movement of the keep plate 17 toward the second side is restricted since the keep plate 17 contacts the spherical plain bearing 80. In this manner, the movement of the keep plate 17 toward the second side is restricted in the swash plate type hydraulic pump 10 according to the present embodiment. Therefore, even in the case described above, there is not a risk that the shoes 14 become lifted from the sliding contact surface 15c of the swash plate 15 or become tipped. As a result, the swash plate type hydraulic pump 10 according to the present embodiment prevents the occurrence of for example, pump efficiency decrease, uneven wear of components such as the swash plate 15 and the shoes 14, galling phenomenon, and seizing, which are caused when the shoes 14 slidingly rotate in a state where there is edge contact between the sliding contact surface 15c of the swash plate 15 and the shoes 14. In addition, in the swash plate type hydraulic pump 10 according to the present embodiment, the set springs 20 used therein may have spring force according to conventional specifications. Accordingly, there is not a risk that increased spring force causes an increase in the friction force between the swash plate 15 and the shoes 14, which causes efficiency decrease or seizing. Moreover, the number of components added to prevent the shoes 14 from being lifted from the sliding contact surface 15c of the swash plate 15 and to prevent the shoes 14 from tipping is small, and thus the structure is simple. When the gap G in the axial direction L is filled with the filling member F, the cylinder block 9 and the spherical plain bearing 80 rotate in synchronization with each other. For this reason, relative slip does not occur between the filling member F and the cylinder block 9, and between the filling member F and the spherical plain bearing 80. Accordingly, excessive friction does not occur between the cylinder block 9 and the filling member F, and between the spherical plain bearing 80 and the filling member F. Therefore, these components can bear further increase in the rotational speed of the swash plate type hydraulic pump 10.
Although one preferred embodiment of the present invention is as described above, the present invention is not limited to the above-described embodiment. Various design changes may be made to the above embodiment without departing from the scope of the claims.
For example, although the gap in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 is 0 in the swash plate type hydraulic pump 10 according to the above embodiment, the gap may alternatively be a fine gap.
It should be noted that the position of the gap ΔL in the axial direction L between the cylinder block 9 and the spherical plain bearing 80 is not limited to the position between the first end surface 95 of the cylinder block 9 and the hole bottom 85 of the guide hole 84 of the spherical plain bearing 80.
As another example, although the shim plates 30 are used as the filling member F in the swash plate type hydraulic pump 10 according to the above embodiment, the filling member F is not limited to the shim plates 30.
Further alternatively, a press-fit bushing may be used as the filling member F.
As yet another example, in the swash plate type hydraulic pump 10 according to the above embodiment, the position of the gap in the axial direction L between the cylinder block 9 and the spherical plain bearing 80, which gap is to be filled with the filling member F, is not limited to the position between the first end surface 95 of the cylinder block 9 and the hole bottom 85 of the guide hole 84 of the spherical plain bearing 80.
In the above examples shown in
The present invention is, when applied to a swash plate type hydraulic rotating machine such as a swash plate type hydraulic pump or swash plate type hydraulic motor, capable of preventing the shoes from being lifted from the swash plate even if the rotational speed of the rotating shaft is increased. Therefore, the present invention is widely applicable to swash plate type hydraulic rotating machines that include a swash plate with a variable maximum tilting angle, regardless of the structural details of such machines.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/007103 | 12/7/2010 | WO | 00 | 5/1/2013 |
