JPH05187350A - Cradle type variable fluid machine - Google Patents

Abstract

PURPOSE:To facilitate a return to neutrality, displacement and maintenance of stability in a cradle type variable oil-hydraulic motor and the like by constituting the motor to make a pin provided in a swash plate variable so that an arm length from the oscillating center becomes long according to the increase of thrust loading. CONSTITUTION:Pistons 10 are reciprocated corresponding to an inclination angle theta of a swash plate 7 with rotation of a cylinder block 6 driven by an engine and vary displacement in bores 6a to discharge a hydraulic oil. At this time, thrust loading from the pistons 10 acts on the swash plate 7 through a shoe 9, and discharge pressure is introduced to a pressure chamber through an inlet hole of the sliding surface 7b. Consequently, a spool is moved to a cradle guide 1a corresponding to the inclination angle theta, a distance from the oscillating center O is varied, an arm length L0 becomes the longest at the inclination angle theta=0, and an arm length L1 becomes short corresponding to the inclination angle Q=alpha. As a result, the moment acting on the swash plate 7 becomes maximum at the inclination angle theta=0, and a return to neutrality is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc-shaped cradle guide centering around a swing center such as a cradle type variable displacement axial piston pump, a cradle type variable hydraulic motor, a cradle type variable displacement compressor, and the like. , An improvement of a cradle type variable fluid machine having an arc surface cradle swingably supported by the cradle guide.

[0002]

2. Description of the Related Art As a conventional cradle type variable fluid machine, for example, a cradle type variable displacement axial piston pump (hereinafter referred to as a cradle type pump), it has been practically used.
Those disclosed in Japanese Patent Publication No. 49784, Japanese Utility Model Laid-Open No. 60-131679 and Japanese Utility Model Laid-Open No. 62-779 are known. As shown in FIG. 5, these cradle type pumps have an arc surface cradle 90 having a swing center O as a center.
a has a swash plate 90 provided in a protruding manner, and the swash plate 90 is swingably supported by an arc-shaped cradle guide recessed in a casing (not shown). This swash plate 90
A sliding surface 9 for rotating and sliding a shoe (not shown) on the back surface of the
0b is formed, and a thrust load is applied to the sliding surface 90b from a piston (not shown) moored to the shoe. In addition, the swash plate 90 has a pin 9 at a right angle to the swinging direction.
1 is fixed, and the pin 91 is anchored to a servo cylinder (not shown) so that the tilt angle θ of the swash plate 90 is controlled in the ± directions, whereby the discharge capacity and the discharge direction of the hydraulic oil are made variable. ing.

[0003]

However, the cradle type variable fluid machine in which the pin 91 is fixed to the swash plate 90 like the above-mentioned conventional cradle type pump is, for example, hydraulically driven (H).
ST = Hydrostatic Transmissi
on) when incorporated in a circuit, the following problems occur.

That is, for example, as shown in FIG. 6, a cradle type pump 80 as a cradle type variable fluid machine driven by an engine E / G is a charge pump 81.
Is incorporated in a tandem type, and this cradle type pump 80 is incorporated in an HST circuit together with a hydraulic motor 83 that drives an actuator 82.
When the pin 91 fixed to the swash plate 90 is anchored to the servo cylinder 85 controlled by the discharge pressure of the charge pump 81 via the direction control valve 84, the servo cylinder 8
5, control of the pin 91, that is, displacement from the neutral state of the tilt angle θ = 0 to the tilt angle θ = α (α is not 0 but an angle of ±. The same applies hereinafter) and is maintained at the tilt angle θ = α. Inclination θ = α
From the return to the neutral state, the discharge capacity and the discharge direction of the cradle type pump are determined. Here, the spring force x which changes the servo cylinder 85 depending on the position of the spool.
And a constant discharge pressure P from the charge pump 81, a pressure p acting on one of the spools is a discharge pressure P, a pressure p '= 0 acting on the other spool, or a pressure p = When 0 and pressure p ′ = discharge pressure P, displacement and maintenance are performed by discharge pressure P−spring force x, and when pressure p = pressure p ′ = discharge pressure P or pressure p = pressure p ′ = 0, The spring force x restores.

In this case, the inevitable frictional force acting on the sliding contact surface between the cradle 90a and the cradle guide resists the swing of the cradle 90a. Then, in the HST circuit, the thrust load composed of the discharge pressure Pd acting on the sliding surface 90b and the tilt angle θ of the swash plate 90 are controlled so as to have the relationship shown in FIG. 7 based on the inertial force. Therefore, the tilt angle θ =
In the vicinity of 0, the maximum thrust load acts on the swash plate 90, and the frictional force is maximized at this time. Therefore, at the time of startup, the cradle 9 does not stabilize in the neutral state where the tilt angle θ = 0.
0a is maintained at the inclination angle θ at the time of the previous stop, and the directional control valve 84
In order to avoid the worst situation in which the hydraulic oil is discharged in the opposite direction despite the operation of, the servo cylinder 85 with a large spring force x is conventionally used to reduce the pressures p, p ′ and the tilt angle θ. The relationship of is set as shown in FIG.
The swash plate 90 is easily returned to the neutral state.

However, in the conventional cradle type pump as described above, since the pin 91 is fixed to the swash plate 90, the arm length L between the pin 91 and the swing center O is always constant and constant. The swash plate 90 is always controlled by the moment resulting from the product of the arm length L and the control pressure by the servo cylinder 85. For this reason, in this cradle type pump, the large spring force x of the servo cylinder 85 resists and is unlikely to be displaced from the neutral state to the tilt angle θ = α. Further, in this cradle type pump, if the arm length L from the swing center O is kept long in order to increase the moment in order to avoid such difficulty of displacement, this time the tilt angle θ = α is maintained. Becomes unstable.

An object of the present invention is to make it easy to return to a neutral state without causing an increase in the restoring force of a servo cylinder, to be easily displaced, and to be stably maintained.

[0008]

In the cradle type pump of the present invention, in order to solve the above problems, the pin is changed so that the arm length from the swing center becomes longer according to the increase of the thrust load. It adopts a new means of configuring.

[0009]

When the cradle type variable fluid machine of the present invention is incorporated in the HST circuit, the thrust load is maximum in the vicinity of the tilt angle θ = 0, which inevitably acts on the sliding contact surface between the cradle and the cradle guide. The frictional force is maximized, but at this time, since the arm length of the pin becomes long, the moment that controls the swash plate is large, and the swash plate easily returns to the neutral state. Also, in this cradle type pump, since the swash plate easily returns to the neutral state, it is not necessary to employ a servo cylinder with a large restoring force, and the tilt angle θ = α from the neutral state.
Is also easily displaced. Further, in this cradle type pump, when the thrust load is small, the arm length of the pin is made small. Therefore, at this time, the moment for controlling the swash plate is small, and the maintenance at the inclination angle θ = α is also stable.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the cradle type variable fluid machine of the present invention is embodied in a cradle type pump will be described below with reference to the drawings. As shown in FIG. 1, this cradle type pump has a bearing 5a in a closed space 4 formed by a front casing 1, a middle casing 2 and an end cover 3.
The drive shaft 5 is supported via the above, and a cylinder block 6 having a plurality of bores 6a is fitted to the spline of the drive shaft 5 in parallel with the shaft center. In the front casing 1, a pair of cradle guides 1a symmetrically extends across the drive shaft 5 on the cylinder block 6 side in a direction perpendicular to the drive shaft 5 and has a swing center O (see FIG. 3) as a center. It is recessed in the shape of an arc. The swash plate 7 having an arc-shaped cradle 7a aligned with the cradle guide 1a is interposed between the end faces of the front casing 1 projecting from both ends of the cradle guide 1a, and is supported by these end faces.

In each bore 6a of the cylinder block 6,
A piston 10 is housed reciprocally according to the tilt angle of the swash plate 7 via a shoe 9 rotatably slidably attached to a sliding surface 7b of the swash plate 7. Further, a valve plate (not shown) having suction and discharge ports communicating with the bore 6a is fixed to the end cover 3 between the cylinder block 6 and the end cover 3, and the suction and discharge ports of this valve plate are excluded. The portion closes the bore opening end of the cylinder block 6.
These suction and discharge ports are formed symmetrically with respect to the axis of the drive shaft 5 in parallel with the extending direction of the cradle guide 1a, and are determined by the axis of the pin 72a and the axis of the drive shaft 5, which will be described later. The faces are also formed symmetrically. Thus, the discharge pressure from the discharge port acts on the swash plate 7 as a thrust load. The end cover 3 is formed with suction and discharge ports which communicate with the suction and discharge ports, respectively.

A compression spring is arranged in an annular space between the drive shaft 5 and the cylinder block 6 via a spacer and a circlip (not shown). The compression spring presses the pivot 11 along the axis through the spacer and the pin,
The pivot 11 is pivotally anchored to a shoe retainer 12 that anchors the shoe 9 so that it can slide in the radial direction. The compression spring presses the cylinder block 6 in the direction opposite to the swash plate 7 via the spacer and the circlip.

As shown in FIG. 2, the swash plate 7 has a through hole 7c for allowing the drive shaft 5 to pass therethrough, and a rear surface having a flat sliding surface 7b perpendicular to the axial direction. On the sliding surface 7b, the discharge pressure action area 9a by the discharge port is formed on the locus of the shoe 9.
And a suction pressure action area 9b by the suction port. These discharge pressure working area 9a and suction pressure working area 9b
Are mutually changed by ± of the inclination angle θ of the swash plate 7. Further, as shown in FIGS. 3 and 4, a spool chamber 70 having a line extending vertically from the swing center O to the sliding surface 7b as a central axis is provided through the swash plate 7, In the spool chamber 70, a spool 72 having a pin 72a extending at right angles to the swinging direction is mounted on the cradle guide 1a side via a spring 71. A long hole 73 is formed on the upper surface of the swash plate 7 so as to be closed by the spool 72 even when the spool 72 is located at the rear end on the cradle guide 1a side, and the pin 72a of the spool 72 is guided along the long hole 73. To be done. When the pin 72 a is located at the front end of the elongated hole 73 on the cylinder block 6 side, the pressure chamber 75 is maintained between the spool 72 and the blind lid 74. Further, in the swash plate 7, there are provided a pair of introduction holes 81, 82 which open above the discharge pressure working area 9a and the suction pressure working area 9b, respectively, and check valves 83, 8 respectively.
4 communicates with the pressure chamber 75. Also, the blind lid 7
An orifice 74a is provided at the position 4.

As shown in FIG. 1, the middle casing 2 is provided with a servo cylinder 13 extending at right angles to the swinging direction of the cradle guide 1a. In this servo cylinder 13, as shown in FIG. 2, a piston chamber 30 communicating with the openings 30a and 30b at both ends is formed in the middle casing 2, and a servo piston 31 is formed in the piston chamber 30.
Are slidably mounted by a rod 32. Springs 33 and 34 facing each other are built in the servo piston 31 by the spacers 35 to 38 and the circlips 39 and 40, and the spacers 3 located farther from each other.
Reference numerals 7 and 38 denote bulging portions 32a and 32 formed on the rod 32.
It can be separated from the circlips 39 and 40 by b. As the springs 33 and 34, relatively weak springs are adopted. Further, in the center of the servo piston 31,
A spacer 41 is loosely fitted in the rod 32 so as to be slidable in a direction perpendicular to the rod 32. The spacer 41 has a pin 72a of the swash plate 7.
Is loosely fitted.

Openings 30a and 30b of the servo cylinder 13
Is connected to a three-position directional control valve 51 controlled by a predetermined signal. The directional control valve 51 is tandemly connected to the drive shaft 5 of the cradle type pump and driven by the engine E / G. Charge pump 5
3 is connected. In such a cradle type pump,
When the drive shaft 5 is driven by the engine E / G, the cylinder block 6 rotates. As a result, the piston 10 reciprocates in the bore 6a in accordance with the inclination angle θ of the swash plate 7 to cause a change in volume of the bore 6a, and low-pressure hydraulic oil is introduced from the suction port to the volume expansion bore 6a. The high-pressure hydraulic oil is discharged from the discharge port through the discharge port from the bore 6a in the process of reducing the volume. At this time, thrust load acts on the swash plate 7 from the piston 10 via the shoes 9. With respect to this thrust load, the discharge pressure Pd is introduced into the pressure chamber 75 from one of the introduction holes 81 and 82 in the sliding surface 7b of the swash plate 7 shown in FIG.

For example, as shown in FIG. 7, the discharge pressure Pd, that is, the thrust load, is large in the vicinity of the tilt angle θ = 0. This large discharge pressure Pd is as shown in FIGS. 3 and 4.
It is introduced into the pressure chamber 75 from one of the introduction holes 81 and 82.
Therefore, the spool 72 moves toward the cradle guide 1a side against the biasing force of the spring 71, and the pin 72a is moved to the long hole 73.
Away from the center O of the swing. Therefore, the pin 72a
The arm length L ₀ between the rocking center O and the swing center O is the arm length L when the tilt angle θ = α.
Lengthened compared to ₁ . Therefore, the moment due to the product of the arm length L ₁ and the control pressure by the servo cylinder 13 is increased. Although the suction pressure Ps is introduced from the other of the introduction holes 81 and 82, the check valves 83 and 84 on the other side of the introduction holes 81 and 82 that introduce the suction pressure Ps are the introduction holes that introduce the discharge pressure Pd. Blocks backflow from one of 81 and 82.

Therefore, in this cradle type pump, the unavoidable frictional force acting on the sliding contact surface between the cradle 7a and the cradle guide 1a is maximized due to the maximum thrust load in the vicinity of the tilt angle θ = 0. However, at this time, that is, when the tilt angle θ = 0, the arm length L _{0 of the} pin 72a is
Is longer than the arm length L ₁ when the inclination angle θ = α, the swash plate 7
Is greater than the moment when the tilt angle θ = α, and the swash plate 7 easily returns to the neutral state. Also,
In this cradle type pump, since the swash plate 7 easily returns to the neutral state in this way, it is not necessary to employ a spring having a large spring force as the servo cylinder 13, and the displacement from the neutral state to the inclination angle θ = α is easy.

On the contrary, when the inclination angle θ = α, the discharge pressure Pd
That is, the thrust load is small, but this small discharge pressure P
d is introduced into the pressure chamber 75 from one of the introduction holes 81 and 82. Therefore, the spool 72 is returned to the cylinder block 6 side by the urging force of the spring 71, and the pin 72a is moved to the elongated hole 7.
The center of swing O is approached along 3. The hydraulic oil in the pressure chamber 70 is returned to the closed space 4 by the orifice 74a. Therefore, the arm length L ₁ between the pin 72a and the swing center O
Is shorter than the arm length L ₀ when the tilt angle θ = 0.
Therefore, the moment due to the product of the arm length L ₁ and the control pressure by the servo cylinder 13 is reduced.

Therefore, in this cradle type pump, the swash plate 7 can be stably maintained at the inclination angle θ = α. Therefore, in this cradle type pump, both excellent responsiveness and stable discharge capacity can be achieved. Although the present invention has been embodied as a cradle type pump in the above-described embodiments, it goes without saying that the present invention can be embodied as a variable hydraulic motor, a compressor, and the like.

[0020]

As described above in detail, in the cradle type variable fluid machine of the present invention, since the arm length from the swing center becomes longer as the thrust load increases, the pin is adopted.
It is possible to easily return to the neutral state, easily displace, and perform stable maintenance without increasing the restoring force of the servo cylinder.

Therefore, in this cradle type variable fluid machine, both excellent responsiveness and stable performance can be achieved.

[Brief description of drawings]

FIG. 1 is a partial vertical sectional view of a cradle type pump of an embodiment.

FIG. 2 is a sectional view of an essential part including a swash plate in the cradle type pump of the embodiment.

FIG. 3 is a top view of a swash plate in the cradle type pump of the embodiment.

FIG. 4 is a sectional view of a swash plate in the cradle type pump of the embodiment.

FIG. 5 is a top view of a swash plate in a conventional cradle type pump.

FIG. 6 is a circuit diagram in which a conventional cradle type pump is incorporated in an HST circuit.

FIG. 7 is a graph showing a relationship between a discharge pressure and a tilt angle of a cradle type pump in an HST circuit.

FIG. 8 is a graph showing the relationship between servo cylinder internal pressure and tilt angle in a conventional cradle type pump.

[Explanation of symbols]

1 ... Front casing 1a ... Cradle guide 7
… Swash plate 7a… Cradle 9… Shoe 1
0 ... Piston 11 ... Pivot 12 ... Shoe retainer O
… Swing center 7b… Sliding surface 72a… Pin 1
3 ... servo cylinder L _0, L ₁ ... arm length

Claims (1)

[Claims] 1. A casing having an arc-shaped cradle guide recessed about the center of rocking, and an arc-shaped cradle pivotably supported by the cradle guide, and rocking. A swash plate having a sliding surface on which a thrust load acts by rotating a shoe on the rear surface, and a servo cylinder for controlling the inclination angle of the swash plate through the pin. In the cradle type variable fluid machine including the cradle type variable fluid machine, the pin is variably configured such that an arm length from the swing center becomes longer according to an increase in the thrust load. Fluid machinery.