JPH1150952A - Axial piston pump or motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve mechanical efficiency and volumetric efficiency by balancing moment of force to act on a driving shaft, in an axial piston pump or a motor in which reaction from the piston is received by a flange of the driving shaft, and the flange is supported by a hydrostatic bearing. SOLUTION: A recessed part 21 is formed on the piston bottom dead center side of a sliding surface of a thrust plate 20 for constituting a hydrostatic bearing for supporting a driving shaft 8 in the thrust direction, the recessed part 21 is superposed on a recessed part 14 formed on a flange part 8b and to which high pressure is to be guided, the pressure receiving area on the piston bottom dead center side of the hydrostatic bearing is increased, recessed parts 22, 23 into which internal pressure of a casing 1 are formed on the top dead center side of the piston of the sliding surface, and the pressure receiving area of the hydrostatic baring is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial piston pump or motor in which a reaction force from a piston is received by a flange of a drive shaft and the flange is supported by a hydrostatic bearing. It relates to possible improvements.

[0002]

2. Description of the Related Art As an axial piston pump or motor, for example, there is one as shown in FIG.

As shown in the figure, a cylinder block 2 is rotatably accommodated in a casing 1 of the axial piston pump or motor about a rotation shaft 3.
A plurality of cylinders 4 are formed on a predetermined circumference centered on the rotation shaft 3 of the cylinder block 2 so as to be substantially parallel to the rotation shaft 3.
Are reciprocally accommodated in the axial direction.

[0004] A hollow portion 6 opens on the side of the piston 5 protruding from the cylinder 4, and a connecting rod 7 is accommodated in each of the hollow portions 6, and the spherical tip 7 a of the connecting rod 7 has It is fitted to the bottom of the hollow portion 6a with a spherical pair. Further, a flange portion 8b spreading laterally from an end portion of the shaft portion 8a of the drive shaft 8 is opposed to a base end portion 7b side of the connecting rod 7, and a spherical base end portion 7b is formed on the flange portion 8b. The spherical hole 10 is fitted in a spherical pair.

The drive shaft 8 is rotatably supported by the casing 1 via a cylindrical radial bearing 11 fitted on the outer periphery of the shaft portion 8a.

[0006] The drive shaft 8 has a through hole 1 through which the drive shaft 8 penetrates at the center on the surface of the flange 8 b opposite to the connecting rod 7 as shown in FIGS. 16 and 17.
Thrust plate 12 which is a disc-shaped member provided with
Through the receiving surface 13 of the casing 1.

As shown in FIG. 18, this flange portion 8b
On the surface opposite to the piston 5, the piston 5 is located just behind the proximal end 7 b of the connecting rod 7.
The same number of concave portions 14 are formed. Thrust plate 12
Of the land 16 around the recess 14
Are slidably contacted. The working fluid in the cylinder 4 passes through these recesses 14 through the fluid passages 5a and 7c penetrating on the central axes of the pistons 5 and the connecting rods 7 and the fluid passages 15 penetrating through the flange 8b. Is derived (see FIG. 15). Thus, a hydrostatic bearing is configured by the flange portion 8b and the thrust plate 12.

With the above configuration, in the axial piston pump, the rotation of the drive shaft 8 is transmitted to the cylinder block 2 via the connecting rod 7, and the cylinder block 2 rotates. At this time, since the shaft 8c of the drive shaft 8 and the shaft 3a of the rotary shaft 3 are inclined at a predetermined inclination angle, the piston 5 reciprocates in the cylinder 4 according to the rotation angle of the cylinder block 2. This allows
The working fluid is sucked into the cylinder from the port 4a during the stroke where the piston 5 extends, and the working fluid is discharged from the port 4a of the cylinder 4 during the stroke where the piston 5 contracts.

[0009]

In the compression stroke of the piston 5 in such an axial piston pump and motor, a piston as shown in FIG. 19 is connected from the base end 7b of each connecting rod 7 to the flange 8b. The reaction force F1 acts.

In this case, since the piston reaction force F1 is directed in the direction of the shaft 3a of the rotating shaft 3, in addition to the component force F2 in the direction of the shaft 8c of the drive shaft 8, a direction perpendicular to the shaft 8c (see FIG. (Upward). And this component F2
Is supported by a reaction force F4 in the direction of the shaft 8c by a hydrostatic bearing (fluid pressure guided to the concave portion 14 of the flange portion 8b), and a component force F3 is generated by the radial bearing 11 in a direction orthogonal to the bearing 8c ( It is supported by the reaction force F5 (downward in the figure), and the forces balance as a whole.

However, in this case, since the component force F3 and the reaction force F5 are different in the point at which the force acts, the drive shaft 8 is provided around the direction orthogonal to the axis 8c (the direction orthogonal to the plane of FIG. 19). The moment M1 acts.

This moment M1 is applied to the flange 8 at the bottom dead center side of the piston 5 (above the shaft 8c in FIG. 19).
b acts on the thrust plate 12,
Excessive solid contact between the flange portion 8b and the thrust plate 12 is caused, and the mechanical efficiency of the pump is reduced.

The moment M1 is determined by the piston 5
On the top dead center side (below the shaft 8c in FIG. 19), the flange portion 8b acts to separate the thrust plate 12 from the thrust plate 12, so that the amount of working fluid leaking from the concave portion 14 of the hydrostatic bearing becomes excessive. There is a possibility that the working fluid in the cylinder 4 leaks, which may reduce the volumetric efficiency of the pump. Leakage of working fluid from such a hydrostatic bearing
This is a problem especially when the axial piston motor is used for a device such as a crane that applies a rotational force to the drive shaft 3 from the outside when the motor is not driven. This may cause a so-called slip-down phenomenon in which the shaft 8 is rotated by an external rotational force.

The present invention has been made in view of such a problem. In an axial piston pump or motor in which a reaction force from a piston is received by a flange of a drive shaft and the flange is supported by a hydrostatic bearing. ,
It is an object of the present invention to provide an axial piston pump or motor capable of improving mechanical efficiency and volumetric efficiency by balancing moments of forces acting on a drive shaft.

[0015]

According to a first aspect of the present invention, there is provided a flange rotatably supported by a casing via a radial bearing and supporting a fluid pressure acting via a piston. A drive shaft supported via a hydrostatic bearing, a cylinder block supported by the casing so as to be rotatable around a rotation shaft inclined at a predetermined angle with respect to the drive shaft, and a rotation shaft of the cylinder block. An axial piston pump or motor comprising: a cylinder formed in parallel with the piston and reciprocatingly receiving the piston from the distal end side; and a rotational force transmitting mechanism for transmitting rotational force between the drive shaft and the cylinder block. The support force of the static pressure bearing at the bottom dead center side of the piston is made greater than the support force at the top dead center side of the piston It makes was balanced moments of force acting on the drive shaft.

According to a second aspect of the present invention, the rotational force transmitting mechanism synchronously rotates the drive shaft and the rotational shaft of the cylinder block, and further includes a shoe at a base end of the piston, and a flat base end surface of the piston and a flat base end surface of the piston. While the upper part of the shoe was brought into surface contact, the flange of the drive shaft and the lower part of the shoe were fitted in a spherical pair.

According to a third aspect of the present invention, in the hydrostatic bearing, a surface of the flange portion opposite to the piston is slidably contacted with the support portion fixed to a casing; A concave portion formed just behind the supporting position of the piston proximal end of the piston portion and receiving a high pressure from a cylinder in which the piston is accommodated, and the flange portion at the bottom dead center side of the piston of the supporting portion. The pressure receiving area of the hydrostatic bearing at the bottom dead center side of the piston was widened by forming a concave portion overlapping the concave portion.

According to a fourth aspect of the present invention, the concave portion formed at the bottom dead center side of the piston of the support portion of the hydrostatic bearing is formed symmetrically on the high pressure side and the low pressure side of the axial piston pump or motor.

According to a fifth aspect of the present invention, the recess formed at the bottom dead center side of the piston of the support portion of the hydrostatic bearing always overlaps at least one of the recesses formed in the flange portion.

According to a sixth aspect of the present invention, in the hydrostatic bearing, the flange portion has a surface opposite to the piston, a slidably contacting surface, and a supporting portion fixed to the casing. A recess formed just behind the supporting position of the piston base end of the flange and receiving a high pressure from a cylinder in which the piston is housed, while the casing has The pressure receiving area of the hydrostatic bearing at the top dead center side of the piston is reduced by forming a recess through which the low pressure is introduced.

According to a seventh aspect of the present invention, the concave portion into which the low pressure inside the casing is guided to the piston top dead center side of the support portion of the static pressure bearing is formed on an outer periphery of the thrust plate and a drive shaft formed on the thrust plate. It is formed along the inner periphery of the through hole for penetration.

According to an eighth aspect of the present invention, a concave portion is formed near a boundary between a high pressure side and a low pressure side of the support portion of the hydrostatic bearing, and when the concave portion overlaps the concave portion formed in the flange portion, the pressure of the hydrostatic bearing is reduced. The area was expanded.

In a ninth aspect, the support portion of the hydrostatic bearing is a thrust plate fixed to the casing.

According to a tenth aspect, the support portion of the hydrostatic bearing is formed on a part of the inner peripheral surface of the casing.

[0025]

According to the first aspect of the present invention, the piston in the cylinder expands and contracts with the rotation of the drive shaft and the cylinder block, but the drive shaft and the rotation axis of the cylinder block are inclined. The reaction force that the piston exerts on the flange portion of the drive shaft is directed obliquely to the drive shaft.As a result, the radial force of the drive shaft of this piston reaction force and the support force of the radial bearing that supports the drive shaft are: It has a moment to tilt the drive shaft so that the bottom dead center side of the piston is pushed down to the side opposite to the piston. On the other hand, in the hydrostatic bearing, the support force at the bottom dead center side of the piston is stronger than the support force at the top dead center side of the piston. The moments to be canceled out and the inclination of the drive shaft is prevented. As a result, the mechanical efficiency of the pump or the motor is maintained high, and liquid leakage from the hydrostatic bearing can be prevented, so that the volumetric efficiency of the pump or the motor does not decrease.

In the second invention, the upper portion of the shoe is brought into contact with the flat base end surface of the piston by surface contact, while the lower portion of the shoe is fitted on the flange portion of the drive shaft in a spherical pair, from the piston side. The force generated by the acting fluid pressure is supported by a reaction force in a direction substantially coincident with the axis of the piston, and the side of the piston, which is a major obstacle in improving the performance of the pump or motor, such as the maximum operating pressure and rotation speed, is In an axial piston pump or motor in which almost no force acts, the moment applied to the drive shaft is balanced to prevent the drive shaft from tilting. State) is maintained well, and a very high pressure and high speed pump or motor can be realized.

In the third aspect of the present invention, the high pressure of the pump or the motor flows into the concave portion formed on the piston bottom dead center side of the support portion of the hydrostatic bearing, so that the pressure receiving area of the hydrostatic bearing is reduced.
It spreads only on the bottom dead center side of the piston, and as a result, the moment of the force acting on the drive shaft is balanced, and the inclination of the drive shaft is prevented.

In the fourth aspect of the present invention, the high pressure of the pump or the motor is guided to the recess formed on the high pressure side of the recess formed on the piston bottom dead center side of the support portion of the hydrostatic bearing, and acts on the drive shaft. This concave part is formed symmetrically on the high pressure side and low pressure side, so even if the pump or motor reversely rotates and the high pressure side and low pressure side are switched, the hydrostatic bearings are exactly the same. And the moment of the force acting on the drive shaft can be balanced.

According to the fifth aspect of the present invention, the concave portion formed on the piston bottom dead center side of the support portion of the hydrostatic bearing always overlaps with at least one of the concave portions formed on the flange portion. In the meantime, the pressure receiving area of the hydrostatic bearing always increases on the bottom dead center side of the piston, and the moment of the force acting on the drive shaft continues to be balanced.

In the sixth and seventh inventions, the pressure receiving area on the piston top dead center side of the hydrostatic bearing is reduced by the recess formed on the piston top dead center side of the support portion of the static pressure bearing. As a result, the moment of the force acting on the drive shaft is balanced, and the inclination of the drive shaft is prevented.

In the first to seventh inventions, the supporting force is changed between the bottom dead center of the piston and the top dead center of the piston of the hydrostatic bearing. If the number of pistons arranged on the low pressure side changes periodically, if the number of pistons on the high pressure side is large, the floating force of the hydrostatic bearing will be relatively weaker than the reaction force of the piston, A variation in the number of pistons on the high pressure side causes a variation in the pressing ratio of the hydrostatic bearing. On the other hand, in the eighth invention,
A recess is formed near the boundary between the high-pressure side and the low-pressure side of the support portion of the hydrostatic bearing, so when the number of pistons arranged on the high-pressure side is large, the recess in the flange portion is near the boundary between the high-pressure side and the low-pressure side. The pressure receiving area of the hydrostatic bearing is expanded by overlapping with the concave portion formed near the boundary between the high pressure side and the low pressure side of the support portion, and the floating force of the hydrostatic bearing is increased by expanding the pressure receiving area. As a result, fluctuations in the pressing ratio due to fluctuations in the number of pistons on the high pressure side of the pump or the motor can be suppressed.

In the ninth aspect, since the supporting portion of the hydrostatic bearing is a thrust plate, machining of the concave portion can be easily performed.

In the tenth aspect, since the support portion of the hydrostatic bearing is the inner peripheral surface of the casing, the number of parts can be reduced.

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the overall configuration of an axial piston pump or motor according to the present embodiment.

As shown, the axial piston pump or motor shown in FIG. 1 has the same basic structure as the conventional example shown in FIG. 15, and only the structure of the thrust plate 12 is different. .

More specifically, a cylinder block 2 housed in a casing 1 of an axial piston pump or motor so as to be rotatable about a rotating shaft 3 is provided with a reciprocally movable piston 5 in a plurality of cylinders 4. A flange 8b of the drive shaft 8 is connected to the hollow portion 6 of the piston 5 via a connecting rod 7 which is tiltably accommodated.
Link with In this case, the distal end 7a of the connecting rod 7 is located at the bottom 6a of the hollow portion 6, and the proximal end 7b of the connecting rod 7 is located at the spherical hole 1 formed in the flange 8b.
0 are fitted via spherical pairs.

The drive shaft 8 is rotatably supported on the casing 1 via a radial bearing 11 on the outer periphery of the shaft portion 8a. The radial bearing 11 supports a component force in the radial direction (the vertical direction in the drawing) of the force acting from the piston 5 side.

The surface of the flange 8b of the drive shaft 8 opposite to the piston 5 is slidably in contact with the thrust plate 20 fixed to the receiving surface 13 of the casing 1.
The flange portion 8b and the thrust plate 20 form a hydrostatic bearing, which supports a thrust component of the force acting from the piston 5 side.

In this case, the configuration of the flange portion 8b is the same as that shown in FIG.
8 is the same as the configuration of the conventional example shown in FIG.
On the surface opposite to the piston 5, the piston 5 is located just behind the proximal end 7 b of the connecting rod 7.
The same number of circular recesses 14 are formed as
A land portion 16 is formed around the periphery. These recesses 14 have respective pistons 5 and connecting rods 7.
Passages 5a and 7c penetrating respectively on the central axes of
Through the fluid passage 15 passing through the flange portion 8b,
The working fluid in the cylinder 4 is led.

On the other hand, FIG.
As shown in FIG. 3, a configuration unique to the present invention is used.

As shown in the figure, the disk-shaped thrust plate 20 has a semicircle (a semicircle on the upper side in FIG. 2) corresponding to the bottom dead center of the piston 5 and a top dead center. The semi-circle (the lower semi-circle in FIG. 2), which is the part facing the side,
The configuration of the sliding surface 20a in contact with the flange portion 8b is different. That is, the recess 21 is formed symmetrically on the high pressure side (the left side in FIG. 2) and the low pressure side (the right side in FIG. 2) in the semicircle on the piston bottom dead center side of the sliding surface 20a. In this case, while the pump or the motor is operating and the flange 8b is rotating with respect to the thrust plate 20,
The flange portion 8b is formed with a sufficient length in the rotation direction of the flange portion 8b so as to always overlap with one of the concave portions 14 in the high pressure state of the flange portion 8b. The recess 21 is formed separately on the high pressure side and the low pressure side, and the recess 2 on the high pressure side is formed.
1 does not communicate with the recess 14 in the low pressure state.

As a result, high-pressure fluid pressure is always guided from the cylinder 4 to the high-pressure side recess 21, and high-pressure working fluid from the cylinder 4 flows into the thrust plate 20 at the piston bottom dead center side of the hydrostatic bearing. The area (pressure receiving area) acting between the flange portions 8b is increased, and the supporting force of the hydrostatic bearing for supporting the flange portions 8b at the piston bottom dead center side is increased. In addition, this concave part 21 is left-right symmetrical (symmetrical on the high pressure side and the low pressure side)
By rotating the pump or the motor in the reverse direction, it is possible to cope with the case where the high pressure side and the low pressure side are reversed. The recess 21 is formed in such a shape that the recess 21 on the low pressure side does not communicate with the recess 14 in the high pressure state.

On the other hand, in the semicircle on the top dead center side of the sliding surface 20a, a concave portion 22 is formed along the outer periphery, and a concave portion 23 is formed along the through hole 20b through which the drive shaft 8 passes. It is formed from the side (left side) to the low pressure side (right side).
These recesses 22 and 23 are adapted to always guide the low pressure in the casing 1.

Thus, on the piston top dead center side of the hydrostatic bearing, the area (pressure receiving area) where the high-pressure working fluid from the cylinder 4 acts between the thrust plate 20 and the flange portion 8b is reduced to the concave portions 22 and 23. The static pressure bearing weakens the supporting force for supporting the flange portion 8b on the bottom dead center side of the piston.

With such a configuration, as shown in FIG. 4, the force F6 at which the hydrostatic bearing supports the flange portion 8b at the bottom dead center side of the piston (upper side in the figure) is changed to the upper dead center side (lower side in the figure) of the piston. Side), the force F7 for supporting the flange portion 8b
Can be strengthened. Thereby, these forces F6, F7
Is the component force F in the thrust direction of the load F1 from the piston 5.
2 and the force F5 that the radial bearing 11 supports the shaft portion 8a balances the sum of the radial component F2 of the load F1 from the piston 5 and the force F1 (F2 and F3). ) And F5, F
6, the moment given to the drive shaft 8 by F7 is also just balanced. The recesses 21 and 2
The widths of 2, 23 are set such that the moments acting on the drive shaft 8 are just balanced.

Next, the operation will be described.

When the axial piston pump or the motor operates, the rotation of the drive shaft 8 causes the flange portion 8b and the thrust plate 20 to rotate relative to each other while sliding. At this time, the radial load acting on the drive shaft 8 from the piston 5 is supported by the radial bearing 11, and the thrust force is supported by the hydrostatic bearing formed between the flange portion 8b and the thrust plate 20. .

In this case, in the present invention, a recess 21 is formed on the thrust plate 20 at the bottom dead center side of the piston (upper side in the figure), and this recess 21 is formed at least in the recess 14 located on the bottom dead center side of the piston. It is designed to communicate with one. Therefore, as shown by pressure contours in FIG. 5, the range in which the supporting force by the working fluid guided to the piston bottom dead center side and the high pressure side (upper left in the figure) acts over a wide range of the thrust plate 20, As a result, the force with which the hydrostatic bearing supports the flange portion 8b at the piston bottom dead center side is the same as that of the conventional concave portion 21 as shown by pressure contours in FIG.
Can be strengthened compared to the case without.

In the thrust plate 20, recesses 22 and 23 are formed on the piston top dead center side (the lower side in the figure).
The low pressure inside the casing 1 is led to these concave portions 22 and 23. For this reason, as shown in FIG. 5, the range in which the supporting force by the working fluid guided to the piston bottom dead center side and the high pressure side (upper left in the figure) acts on these concave portions 22,
As a result, the force by which the hydrostatic bearing supports the flange portion 8b on the piston top dead center side is reduced as compared with the case where the concave portions 22, 23 shown in FIG. 6 are not provided.

As described above, in the present invention, the supporting force of the hydrostatic bearing is strong at the piston bottom dead center side and weak at the piston top dead center side. Is equal on the piston bottom dead center side and the piston top dead center side, the drive shaft 8 is twisted with respect to the shaft 8c (that is, the flange 8b is pressed against the thrust plate 20 on the piston bottom dead center side, The moments acting (to pull away from the thrust plate 20 on the piston top dead center side) are just canceled out and the moment acting on the drive shaft 8 is balanced as a whole. Therefore, the contact surface pressure between the flange portion 8b and the thrust plate 20 may be excessively large, and a gap may be formed between the flange portion 8b and the thrust plate 20 to cause leakage of the working fluid from the hydrostatic bearing. Nevertheless, the mechanical and volumetric efficiency of the axial piston pump or motor is kept high.

FIGS. 7 and 8 show another embodiment of the present invention.

As shown, recesses 22 and 23 like the thrust plate 20 shown in FIGS. 2 and 3 are formed on the sliding surface 25a of the thrust plate 25 of this embodiment. 21 are not formed. in this way,
The moment acting on the drive shaft 8 may be balanced as a whole only by reducing the supporting force of the hydrostatic bearing on the piston top dead center side by the recesses 22 and 23 alone.

FIGS. 9 to 11 show still another embodiment of the present invention.

In this embodiment, as shown in FIG.
The concave portion 26 formed in the flange portion 8b is formed in an arc shape and is arranged along the circumferential direction. Then, as shown in FIGS. 10 and 11, the sliding surface 30 of the thrust plate 30 is used.
In a, concave portions 31, 32, and 33 are formed corresponding to the shape of the concave portion 26 of the flange portion 8b.

More specifically, the thrust plate 30 is provided at the piston bottom dead center side of the thrust plate 30.
The recesses 31 extending along the inner periphery slightly from the outer periphery and constantly communicating with at least one of the recesses 26 are formed on the high-pressure side (left side in the figure) and the low-pressure side (right side in the figure), respectively, It is formed symmetrically. Also,
The concave portion 32 formed along the entire outer periphery of the thrust plate 30 is widened at the piston top dead center side, and along the through hole 30b through which the drive shaft 8 passes, the high pressure is formed at the piston top dead center side. Recesses 33 are formed at symmetrical positions on the low pressure side and the low pressure side, respectively. The low pressure inside the casing 1 is introduced into these recesses 32 and 33.

Even with such a configuration, the supporting force of the hydrostatic bearing is made stronger at the piston bottom dead center side than at the piston top dead center side, and the moment acting on the drive shaft 8 can be balanced as a whole. . In particular, in this embodiment, the concave portions 32, 33
Can be widened, and the supporting force of the hydrostatic bearing on the piston top dead center side can be reduced accordingly, so that the degree of freedom in adjusting the supporting force of the hydrostatic bearing can be increased.

Further, as shown in this embodiment, in the present invention, the shapes of the recesses formed in the flange portion 8b and the thrust plate are not particularly limited, and the supporting force on the bottom dead center side of the hydrostatic bearing is increased. The concave portions having an arbitrary shape can be selected and combined so that the supporting force on the top dead center side is weakened.

FIG. 12 shows still another embodiment of the present invention.

On the sliding surface 35a of the thrust plate 35 of this embodiment, recesses 31, 32, and 33 similar to those of the thrust plate 30 of FIGS. 10 and 11 are formed. Near the border with the side (right side)
A plurality of recesses 36 and 37 are provided on the piston bottom dead center side and the piston top dead center side, respectively. These recesses 36, 3
Each of the reference numerals 7 has a length that does not connect to the recesses 31, 32, and 33, extends in a notch shape in the radial direction of the thrust plate 35, and is formed along the rotation direction of the drive shaft 8. In these concave portions 36 and 37, a high pressure is introduced if the overlapping concave portion 26 on the flange portion 8b side is a high pressure side, and a low pressure is introduced if the concave portion 26 on the low pressure side.

By providing such recesses 36 and 37, as shown in FIG. 13, the pressing ratio obtained by dividing the thrust direction load (pressing force) from the piston 5 side by the floating force of the hydrostatic bearing is obtained. It can be kept almost constant.

More specifically, the number of the pistons 5 of the axial piston pump or the motor is an odd number n.
When the number of the pistons 5 on the high pressure side is (n + 1) / 2 (for example, four) and when the number of pistons 5 is (n-1) / 2 (for example, seven) due to the rotation of the cylinder block 2, However, in the present invention, since the floating force of the hydrostatic bearing on the top dead center side of the piston is weakened, the load from the piston 5 depends on the number of the pistons 5 on the high pressure side. And the balance of the floating force of the hydrostatic bearing is different. That is, the number of pistons 5 on the high pressure side is (n +
In the case of 1) / 2 (for example, in the case of four), the floating force of the hydrostatic bearing is weaker than the pressing force from the piston 5, while the number of the high pressure side pistons 5 is (n-1). In the case of / 2 (three), a sufficient floating force is given from the hydrostatic bearing to the pressing force of the piston 5, so that the number of the high pressure side pistons 5 is (n + 1) / 2 The pressing ratio is
The number of high-pressure side pistons 5 becomes larger than the case of (n-1) / 2, and as shown by the broken line in FIG. 13, at the moment when the number of high-pressure side pistons 5 is switched, the pressing ratio becomes It fluctuates rapidly.

On the other hand, if the concave portions 36 and 37 are provided as in the present embodiment, the piston 5 on the high pressure side can be provided.
Is (n + 1) / 2, the piston 5
Are located near the boundary between the low pressure side and the high pressure side,
7, the pressure receiving area of the hydrostatic bearing is expanded by the concave portions 36 and 37, so that the floating force of the hydrostatic bearing is increased, and the pressing ratio becomes smaller than when the concave portions 36 and 37 are not provided. On the other hand, the number of the high pressure side pistons 5 is (n−
In the case of 1) / 2 pistons, the piston 5 is disposed inside the boundary between the low pressure side and the high pressure side, and the overlap between the recesses 36 and 37 is small, so that the pressure receiving area of the hydrostatic bearing is particularly increased. However, the pressing ratio does not greatly change from the case where the concave portions 36 and 37 are not provided. As a result, a change in the pressing ratio due to switching of the number of the high-pressure-side pistons 5 can be suppressed to a small value, and the pressing ratio can be kept substantially constant during the operation of the axial piston pump or the motor.

In the above embodiment, the hydrostatic bearing is formed between the thrust plate and the flange portion 8b of the drive shaft 8. However, in the present invention, the thrust plate is not necessarily required. Instead of the requirement, for example, the moment applied to the drive shaft 8 may be balanced by directly supporting the flange portion 8b by the receiving portion 13 of the casing 1 and forming a concave portion in the receiving portion 13.

FIG. 14 shows still another embodiment of the present invention.

As shown in the figure, in this embodiment, the drive shaft 8 and the cylinder block 41 are connected via a rotation transmitting mechanism 42 different from the connecting rod, and The present invention is applied to an axial piston pump or motor in which the upper part of -44 is abutted by surface contact, and the lower part of this shoe -44 is fitted into a spherical hole 45 formed in the flange portion 8b of the drive shaft 8 by a spherical pair. Applied. This axial piston pump or motor has a piston 4
The force generated by the fluid pressure acting from the third side is supported by the reaction force in the direction substantially coincident with the axis of the piston 43, and a major obstacle to improving the performance of the pump or the motor such as the maximum operating pressure and the number of revolutions. The lateral force of the piston is hardly applied.

By forming the recess 47 in the thrust plate 46 of such an axial piston pump or motor, the sliding state (lubricating state) of all the sliding parts of the pump or motor is kept good. Very high pressure and high speed pumps or motors can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a front view showing the thrust plate.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an explanatory diagram showing a balance of forces acting on a drive shaft.

FIG. 5 is an explanatory diagram showing a distribution of pressure acting on a flange portion of a drive shaft from a hydrostatic bearing.

FIG. 6 is an explanatory diagram showing a distribution of pressure acting on a flange portion of a drive shaft from a hydrostatic bearing.

FIG. 7 is a front view showing a thrust plate according to another embodiment of the present invention.

8 is a sectional view taken along the line AA of FIG. 7;

FIG. 9 is a front view showing a flange portion of a drive shaft according to still another embodiment of the present invention.

FIG. 10 is a front view showing the thrust plate.

11 is a sectional view taken along the line AA of FIG. 10;

FIG. 12 is a front view showing a thrust plate according to still another embodiment of the present invention.

FIG. 13 is a characteristic diagram showing a change in the pressing ratio.

FIG. 14 is a sectional view showing still another embodiment of the present invention.

FIG. 15 is a sectional view showing a conventional axial piston pump or motor.

FIG. 16 is a front view showing the thrust plate.

FIG. 17 is a sectional view taken along the line AA of FIG. 16;

FIG. 18 is a front view showing a flange portion of the drive shaft.

FIG. 19 is an explanatory diagram showing a balance of forces acting on the drive shaft.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casing 2 Cylinder block 3 Rotating shaft 4 Cylinder 5 Piston 8 Drive shaft 8a Shaft part 8b Flange part 11 Radial bearing 14 Recess 20 Thrust plate 20a Sliding surface 21 Recess 22 Recess 23 Recess 25 Thrust plate 25a Sliding surface 26 Recess 30 Thrust Plate 30a Sliding surface 31 Recess 32 Recess 33 Recess 35 Thrust plate 35a Sliding surface 36 Recess 37 Recess 46 Thrust plate 47 Recess

Claims (10)

[Claims] 1. A casing has a flange portion rotatably supported via a radial bearing and supports a fluid pressure acting via a piston, and is supported by the casing via a hydrostatic bearing at the flange portion. A drive shaft; a cylinder block rotatably supported by the casing around a rotation axis inclined at a predetermined angle with respect to the drive shaft; and a piston formed in parallel with the rotation axis of the cylinder block, and An axial piston pump or a motor, comprising: a cylinder that reciprocates from a cylinder; and a rotational force transmitting mechanism that transmits rotational force between the drive shaft and the cylinder block. By increasing the supporting force at the bottom dead center side than the supporting force at the top dead center side of the piston, the drive shaft Axial piston pump or motor, characterized in that to balance the moment of force acting. 2. The rotating force transmitting mechanism synchronously rotates the driving shaft and the rotating shaft of the cylinder block, and has a shoe at a base end of the piston, and has a flat base end face of the piston and an upper part of the shoe. 2. The axial piston pump or motor according to claim 1, wherein a flange portion of the drive shaft and a lower portion of the shoe are fitted in a spherical pair while a surface contact is made. 3. The static pressure bearing includes: a surface of the flange portion opposite to the piston, a support portion that slidably contacts the surface and is fixed to a casing; A recess formed just behind the support position of the base end and receiving a high pressure from the cylinder in which the piston is housed, and overlapping the recess of the flange at the bottom dead center side of the piston of the support. The axial piston pump or motor according to claim 1 or 2, wherein a recess is formed to increase a pressure receiving area of the hydrostatic bearing on the piston bottom dead center side. 4. A concave portion formed at a bottom dead center side of said piston in a support portion of said static pressure bearing is formed symmetrically on a high pressure side and a low pressure side of said axial piston pump or motor. 4. The axial piston pump or motor according to 3. 5. A concave portion formed at a bottom dead center side of said piston in a support portion of said hydrostatic bearing always overlaps at least one of concave portions formed in said flange portion. Or an axial piston pump or a motor according to claim 4. 6. The static pressure bearing includes: a surface of the flange portion opposite to the piston, a support portion that is slidably in contact with the surface and fixed to the casing; A recess formed just behind the support position of the piston base end and receiving a high pressure from a cylinder in which the piston is accommodated, while a low pressure inside the casing is introduced to the piston at the top dead center side of the support portion. The axial piston pump or motor according to claim 1, wherein a pressure receiving area of the hydrostatic bearing on the side of the piston at the top dead center is reduced by forming a recessed portion. 7. A recess through which a low pressure inside the casing is guided to the piston top dead center side of the support portion of the static pressure bearing, a through hole for penetrating a drive shaft formed on the outer periphery of the thrust plate and the thrust plate. The axial piston pump or motor according to claim 6, wherein the axial piston pump or the motor is formed along an inner circumference of the hole. 8. A pressure receiving area of the hydrostatic bearing is enlarged when a concave portion is formed near a boundary between a high pressure side and a low pressure side of a support portion of the hydrostatic bearing, and when the concave portion overlaps a concave portion formed in the flange portion. The axial piston pump or the motor according to any one of claims 1 to 7, wherein the axial piston pump or the motor is configured to be configured as follows. 9. The axial piston pump or motor according to claim 1, wherein the support portion of the hydrostatic bearing is a thrust plate fixed to the casing. 10. The axial piston pump or motor according to claim 1, wherein a support portion of the hydrostatic bearing is formed on a part of an inner peripheral surface of the casing.