AXIAL PISTON PUMP OR MOTOR
United States Patent 3643549
An axial piston pump or motor comprises a cylinder barrel fixedly mounted on a rotating shaft, a plurality of cylindrical bores formed axially in the cylinder barrel, piston slidably fitted in the associated bores, a swashplate adjustably arranged at a desired inclination angle with respect to the axis of the shaft, slipper pads each engaged with an end of each piston and a retainer ring for keeping the slipper pads in contact with the swashplate. A spherical pressure member which externally engages a corresponding central bore of the retainer ring is internally slidably mounted on a cylindrical portion of an annular pusher having a flange portion which is in turn slidably mounted on the shaft. Between the spherical pressure member and the pusher is disposed a first spring while a second spring is disposed between the pusher and the cylinder barrel. As inclination angles below a predetermined valve of the swashplate, the retainer ring is urged toward the swashplate through engagement of the flange of the annular pusher with the spherical pressure member under the force of the second spring. At an inclination angles above the predetermined valve, the retainer ring is urged through engagement of the flange of the pusher therewith at a point.
US Patent References:
Power transmission
Reel - June 1957 - 2776628
Piston return mechanism
Reinke - September 1966 - 3274897
Swashplate pump
Hann et al. - January 1966 - 3230893
Power transmission
Reel - June 1957 - 2776628
Piston return mechanism
Reinke - September 1966 - 3274897
Swashplate pump
Hann et al. - January 1966 - 3230893
Application Number:
05/058464
Publication Date:
02/22/1972
Filing Date:
07/27/1970
View Patent Images:
Export Citation:
Assignee:
Mitsubishi Jukogyo Kabushiki Kaisha (Tokyo, JA)
Primary Class:
Other Classes:
91/507
International Classes:
F01B3/00; F04B1/12; F04B1/20
Field of Search:
91/504-507 92/12.2
Primary Examiner:
Freeh, William L.
Claims:
What is claimed is
1. A device for supporting the retainer ring of an axial piston pump or motor having a plurality of pistons slidably fitted in cylinders formed in a cylinder barrel fixedly mounted on a shaft, slipper pads engaged with the outer ends of the pistons, and a retainer ring for keeping the slipper pads in sliding contact with a swashplate disposed at a desired inclination angle with respect to the axis of the shaft, said pistons being adapted to reciprocate sequentially within the associated cylinders in the direction parallel to the axis of the shaft with rotation of the cylinder barrel, comprising an annular pusher axially slidably fitted on the shaft and pressed toward the swashplate by means of at least one elastic member, and a spherical pressure member axially slidably fitted on the pusher and engaged in a spherical seat in the center of the retainer ring by means of an auxiliary elastic member disposed between the spherical pressure member and the pusher, in such a manner that, when the angle of inclination of the swashplate has exceeded a certain value, the retainer ring comes into contact with the peripheral edges of the pusher at a point away from the center of rotation of the ring toward the slide where the pistons reach their top dead points.
2. A fluid-operated pump or motor device, comprising a rotatable shaft, a cylinder barrel affixed to said shaft for rotation therewith, a swashplate mounted adjacent said cylinder barrel for positioning at a desired operationable angle in respect to the axis of said shaft, said cylinder barrel having a plurality of angularly spaced fluid-handling cylinders and a piston movable in each cylinder, slipper pad means engaged with the outer ends of each piston and bearing against said swashplate, a retainer ring carrying said slipper pad means and having a central at least partially spherical sprocket, a pusher axially movable on said shaft, a pressure member movable axially on saId pusher and having at least a partially spherical exterior surface arranged around said shaft engaged in said socket of said retainer ring to permit tilting of said retainer ring on said pressure member, first spring means between said pusher and said pressure member urging said pressure member in a direction toward said retainer ring and said swashplate and second spring means between said cylinder barrel and said pusher urging said pusher toward said pressure member, said first and second spring means being sized and arranged so that they become selectively effective in accordance with the angle of said retainer ring in respect to said shaft.
3. A fluid-operated pump or motor device according to claim 2, wherein there are 9 of said cylinders distributed around said cylinder barrel and wherein said second spring means includes an axially movable plunger member, said cylinder barrel having a plurality of plunger bores arranged in equally spaced relationship around said barrel, and one of said plunger members being movable in said bores, and a compression spring for each plunger member urging said plunger member toward engagement with said pusher.
4. A fluid-operated pump or motor device according to claim 3, wherein there are 3 plunger members arranged in equally angularly spaced relationship in said cylinder barrel between said cylinders and said shaft.
1. A device for supporting the retainer ring of an axial piston pump or motor having a plurality of pistons slidably fitted in cylinders formed in a cylinder barrel fixedly mounted on a shaft, slipper pads engaged with the outer ends of the pistons, and a retainer ring for keeping the slipper pads in sliding contact with a swashplate disposed at a desired inclination angle with respect to the axis of the shaft, said pistons being adapted to reciprocate sequentially within the associated cylinders in the direction parallel to the axis of the shaft with rotation of the cylinder barrel, comprising an annular pusher axially slidably fitted on the shaft and pressed toward the swashplate by means of at least one elastic member, and a spherical pressure member axially slidably fitted on the pusher and engaged in a spherical seat in the center of the retainer ring by means of an auxiliary elastic member disposed between the spherical pressure member and the pusher, in such a manner that, when the angle of inclination of the swashplate has exceeded a certain value, the retainer ring comes into contact with the peripheral edges of the pusher at a point away from the center of rotation of the ring toward the slide where the pistons reach their top dead points.
2. A fluid-operated pump or motor device, comprising a rotatable shaft, a cylinder barrel affixed to said shaft for rotation therewith, a swashplate mounted adjacent said cylinder barrel for positioning at a desired operationable angle in respect to the axis of said shaft, said cylinder barrel having a plurality of angularly spaced fluid-handling cylinders and a piston movable in each cylinder, slipper pad means engaged with the outer ends of each piston and bearing against said swashplate, a retainer ring carrying said slipper pad means and having a central at least partially spherical sprocket, a pusher axially movable on said shaft, a pressure member movable axially on saId pusher and having at least a partially spherical exterior surface arranged around said shaft engaged in said socket of said retainer ring to permit tilting of said retainer ring on said pressure member, first spring means between said pusher and said pressure member urging said pressure member in a direction toward said retainer ring and said swashplate and second spring means between said cylinder barrel and said pusher urging said pusher toward said pressure member, said first and second spring means being sized and arranged so that they become selectively effective in accordance with the angle of said retainer ring in respect to said shaft.
3. A fluid-operated pump or motor device according to claim 2, wherein there are 9 of said cylinders distributed around said cylinder barrel and wherein said second spring means includes an axially movable plunger member, said cylinder barrel having a plurality of plunger bores arranged in equally spaced relationship around said barrel, and one of said plunger members being movable in said bores, and a compression spring for each plunger member urging said plunger member toward engagement with said pusher.
4. A fluid-operated pump or motor device according to claim 3, wherein there are 3 plunger members arranged in equally angularly spaced relationship in said cylinder barrel between said cylinders and said shaft.
Description:
BACKGROUND OF THE INVENTION
This invention relates to a device for supporting a retainer ring of an axial piston pump or motor, and is directed to the provision of an improved device for supporting a retainer ring of a pump or motor of variable delivery type, in which the stroke of the pistons is varied and hence the delivery is regulated in accordance with the angle of inclination of a swashplate.
A variable delivery axial piston pump or motor of the prior art, as shown in FIGS. 1 and 2, comprises a rotating shaft 01, a cylinder barrel 02 fixedly mounted on the shaft 01, and a swashplate 03 disposed in such a manner as to be positioned at a desired inclination angle with respect to the axis if the shaft 01, the cylinder barrel 02 being formed axially with a plurality of cylinders 04 at angular intervals around the shaft 01, with an equal number of pistons 05 slidably fitted in said cylinders.
Each piston 05 is engaged at the end close to the swashplate 03 with a slipper pad 07 via a ball joint 06, and each slipper pad 07 is slidably kept pressed against the surface of the swashplate 03 by means of a common retainer ring 08. Therefore, as the cylinder barrel 02 rotates, the pistons o5 within the respective cylinders 04 reciprocate to effect the suction and discharge of liquid to be delivered. The retainer ring 08 serves to keep the slipper pads 07 pressed against the swashplate 03, lest they should separate themselves from the swashplate due to the inertia force of the reciprocating pistons 05 and slipper pads 07 and the centrifugal force of the slipper pads 07 themselves.
A measure commonly in use to realize the above purpose is, as illustrated in FIGS. 1 and 2, to provide on the shaft 01 and axially slidable spherical pressure member 010 which mates with a spherical seat 09 in the center of the retainer ring 08 and is urged by a spring 011 toward the swashplate 03.
Since the spherical pressure member 010 and the retainer ring 08 rotate relative to the swashplate 03 which is stationary, the retainer ring 08, as is shown in FIG. 2, makes a swaying motion within the range of an angle twice the angle of inclination θ of the swashplate 03.
The conventional retainer ring supporting mechanism as described above has the following disadvantages:
When the rotational speed of the shaft 01 is constant, the inertia force of the pistons 05 and slipper pads 07 is proportional to the stroke of the pistons 05. In a variable delivery pump wherein the strokes of the pistons 05 are changed with change in the angle of inclination of the swashplate 03, therefore, the inertia force of the pistons 05 and slipper pads 07 is the greatest when the inclination angle of the swashplate is at its maximum. Accordingly, it is necessary to keep the retainer ring 08 pressed against the swashplate 03 with a force greater than the inertia force of the swashplate at its maximum. In case where such a variable delivery pump is installed for driving a steering system, it is often operated at an inclination angle of zero (where the pistons do not make a stroke). This means, however, that the retainer ring 08 is kept pressed against the swashplate 03 with a force corresponding to the force at the maximum angle of inclination (i.e., where the pistons reciprocate at the maximum stroke), thus having adverse effects upon the mechanical efficiency of the pump and the durability of the sliding parts.
For this reason, it is desirable that the force for urging the retainer ring toward the swashplate is automatically changed with the angle of inclination of the swashplate (or the stroke of the pistons).
It is also noted that the resultant force of the inertia force due to the reciprocating motion of the pistons 05 and the slipper pads 07 and the centrifugal force is due to the rotation of the slipper pads 07 acts on the swashplate 03, as shown in FIG. 3, as a separating force on the side where the individual pistons reach their top dead points and as a pressure-contacting force on the opposite side where the individual pistons reach their bottom dead points. Such forces for separation and pressure contact increase with an increase of the inclination angle of the swashplate. Consequently, the point of application of the force for separating the slipper pads away from the swashplate 03 shifts gradually toward the side where the pistons reach their top dead points with increase of the inclination angle of the swashplate.
As a result, in a conventional structure of the retainer ring supporting mechanism in which the retainer ring 08 is kept pressed through the central portion thereof against the swashplate irrespective of change in the inclination angle of the swashplate or the displacement of the point of application of the separating force, the center of application of the separating force and the point where the retainer ring is kept pressed against the swashplate (or the center point of the shaft) are widely apart from each other when the angle of inclination of the swashplate is large and, therefore, the pressing force of the retainer ring 08 must be considerably increased. This is not desirably for the life of the sliding parts of the retainer ring 08 and the spherical pressure member 010.
SUMMARY OF THE INVENTION
The principal object of the present invention is to provide a device for supporting the retainer ring of an axial piston pump or motor which is free from the disadvantages of the conventional mechanisms as described above and achieves a high mechanical efficiency with long service life.
In accordance with the invention, there are provided an annular pusher axially slidably fitted on the shaft and pressed toward the swashplate by means of at least one elastic member, and a spherical pressure member axially slidably fitted on the pusher and engaged in a spherical seat in the center of the retainer ring by means of an auxiliary elastic member disposed between the spherical pressure member and the pusher, in such a manner that, when the angle of inclination of the swashplate has exceeded a certain value, the retainer ring comes onto contact with the peripheral edge of the pusher at a point away from the center of rotation of the ring toward the side where the pistons reach their top dead points.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a longitudinal sectional view of the essential parts of an axial piston pump of the prior art having a conventional mechanism for supporting the retainer ring;
FIG. 2 is an enlarged view of the prior art retainer ring support assembly of FIG. 1;
FIG. 3 shows a curve of separating force versus pressure-contacting force of pistons and slipper pads against the surface of the swashplate;
FIG. 4 is a longitudinal sectional view of the essential parts of a variable delivery axial piston pump or motor provided with a retainer ring supporting device according to the invention;
FIG. 5 is an end view of the cylinder barrel viewed along the line V--V of FIG. 4;
FIGS. 6 to 8 are longitudinal sectional views of the retainer ring support assembly, taken along the line VI--VI of FIG. 5, showing the retainer ring and pusher at different angles of inclination of the swashplate;
FIG. 9 is a graph showing the relationship between the displacement of center of separating force and the supporting point of the retainer ring against the swashplate angle; and
FIG. 10 is a graph showing the relationship between the separating force or pressure-contacting force of the retainer ring and the inclination angle of the swashplate.
DESCRIPTION OF A PREFERRED EMBODIMENT
In FIGS. 4 to 8 throughout, reference numeral 1 designates a shaft which is driven by an electric motor or the like (not shown). Numeral 2 designates a cylinder barrel fixedly mounted on the shaft 1 by splining at 3. A plurality of cylinders 4 (nine in the embodiment) are axially formed in the barrel 2 at angular intervals around the shaft 1. In these cylinders 4 are slidably fitted pistons 5, respectively.
A tilting box 6 is held by a pump casing (not shown), and a swashplate 7 is held by the tilting box 6. By tilting the box 6 with respect to the axis of the shaft 1 the angle of inclination θ of the swashplate can be adjusted.
Numeral 8 indicates slipper pads, each of which is engaged with one of each piston 5 via a ball joint 9 and is kept in sliding contact with the swashplate 7 by means of a retainer ring 10. The pistons 5 are driven sequentially to reciprocate axially within the cylinders 4 with rotation of the cylinder barrel 2. An annular pusher 11 is slidably mounted on the shaft 1 and is urged toward the swashplate 7 by means of a pressure contact springs 12 disposed between it and the cylinder barrel 2. At the moment when the inclination angle θ of the swashplate 7 has exceeded a certain valve, the pusher 11 comes into contact with the retainer ring 10 at a point P of the peripheral edge 13 thereof and presses the retainer ring 10 toward the swashplate 7. In this case, the pusher 11 rotates together with the shaft 1, and the retainer ring 10 makes a swaying motion with an angle twice as the inclination angle θ of the swashplate while rotating at the same speed as the shaft 1 via the slipper pads 8. The retainer ring 10 rotates in contacting relationship with the peripheral edge 13 of the pusher 11 at a point P in a way similar to bevel gears in engagement, the point P moving circumferentially on the retainer ring 10 or the edge 13.
A spherical pressure member 14 is slidably fitted on the stem 15 of the pusher 11 and is pressed toward the swashplate 7 by means of an auxiliary spring 16 disposed between it and the pusher 11. This spherical pressure member 14 engages in a spherical seat 17 formed in the center of the retainer ring 10 and presses the retainer ring 10 toward the swashplate 7.
The auxiliary spring 16 is so dimensioned that the force urged on the spherical pressure member 14 by it is less than that urged on the pusher 11 by the pressure contact springs 12.
It is now assumed that the assembly is so designed that the greatest possible angle of inclination of the swashplate 7 is θmax and the retainer ring 10 comes into contact with the peripheral edge 13 of the pusher 11 at an inclination angle θ = 1/2 θmax of the swashplate. Then, in the range of θ < 1/2 θmax, the retainer ring 10 is supported at the center thereof by the spherical pressure member 14, as shown in FIG. 7 while the range of η > 1/2 θmax, it is supported by the pusher 11 at the point P on the side where one of pistons substantially reaches the top dead point, as shown in FIG. 8.
This has an advantage that the supporting point of the retainer ring 10 (i.e., the center at which the retainer ring is pressed against the swashplate) can be kept close to the center of the force for separating the pistons and slipper pads from the swashplate surface, since the center point of the separating force is shifted toward the side where the pistons reach their top dead points with increase of the inclination angle of the swashplate angle. Thus the pressure-contacting force of the retainer ring 10 may be advantageously reduced as compared with the conventional supporting system using only the spherical pressure member.
FIG, 9 shows graphically the relationship between the displacement of the center of separating force or the supporting point of the separating force and the inclination angle θ of the swashplate. The broken line (x) represents the displacement of the center of separating force, the full line (y) represents the supporting position of the retainer ring.
As can be seen from the graph, in the range of θ<1/2θmax the retainer ring is supported at its center with the spherical pressure member, while in the range of θ>1/2 θmax, it is supported by the pusher at a point on the side where the pistons reach their top dead points by the pusher. Thus the supporting point of the retainer ring is kept at a shorter distance from the center of separating force.
Another advantage of the device according to this invention is that, in the range of 1/2θmax to θmax in which the retainer ring 10 is supported by the pusher 11, the pressure contacting force for the retainer ring is automatically increased with increase of the inclination angle θ of the swashplate.
When the swashplate angle θ is in the range below 1/2θmax, the auxiliary spring 16 is compressed to the extreme and the pressure contact springs 12 are fully expanded so that the peripheral edge 13 of the pusher 11 is kept in contact with the rear end of the spherical pressure member 14. Thus, the retainer ring 10 is kept pressed against the swashplate surface with a relatively weak force by the pressure contact springs 12 in their most expanded state.
Once the angle θ has exceeded 1/2θmax, the side of the retainer ring 10 where the pistons reach their top dead points is brought into contact with the peripheral edge 13 of the pusher 11. With further increase of the inclination angle θ, the pusher 11 recedes and the pressure contact springs 12 for supporting the pusher 11 are compressed with the result that the pressure contacting force of the retainer ring 10 is proportionally increased. IN this case, the spherical pressure member 14 still presses the retainer ring 10 toward the swashplate with a weak force exerted by the expanding auxiliary spring 16. Here the spherical pressure member 14 serves as a radial bearing for the retainer ring 10 rather than as means for exerting a contacting pressure.
In FIG. 10 there is shown the relationship between the inclination angle θ of the swashplate and the pressure-contacting force or the separating force for the retainer ring. In the graph the full line a represents the pressure-contacting force and the broken line b represents the separating force. It can be seen from the graph that the pressure-contacting force of the retainer ring is small when the inclination angle θ is small so that the force for separating the pistons 5 and the slipper pads 8 from the surface of the swashplate 7 is relatively small. In the range of a larger inclination angle or of an increased separating force the pressure-contacting force of the retainer ring is correspondingly increased in a desirably manner. Since the retainer ring 10 and the pusher 11 remain in point contact without sliding on each other, both members are practically free from wear.
As will be seen from the foregoing, the device of the present invention has no danger of exerting any force more than required on the pressure-contacting part of the retainer ring and thus makes it possible to provide an axial piston pump of an improved mechanical efficiency and a great durability.
While in the embodiment the point where the made of supporting the retainer ring is changed from the one using the spherical pressure member to the one using the pusher is set at an inclination angle of 1/2θmax, the setting of the point may of course be selected according to the necessity.
It will also be apparent that other modifications may be made without departing from the spirit and scope of the invention.
This invention relates to a device for supporting a retainer ring of an axial piston pump or motor, and is directed to the provision of an improved device for supporting a retainer ring of a pump or motor of variable delivery type, in which the stroke of the pistons is varied and hence the delivery is regulated in accordance with the angle of inclination of a swashplate.
A variable delivery axial piston pump or motor of the prior art, as shown in FIGS. 1 and 2, comprises a rotating shaft 01, a cylinder barrel 02 fixedly mounted on the shaft 01, and a swashplate 03 disposed in such a manner as to be positioned at a desired inclination angle with respect to the axis if the shaft 01, the cylinder barrel 02 being formed axially with a plurality of cylinders 04 at angular intervals around the shaft 01, with an equal number of pistons 05 slidably fitted in said cylinders.
Each piston 05 is engaged at the end close to the swashplate 03 with a slipper pad 07 via a ball joint 06, and each slipper pad 07 is slidably kept pressed against the surface of the swashplate 03 by means of a common retainer ring 08. Therefore, as the cylinder barrel 02 rotates, the pistons o5 within the respective cylinders 04 reciprocate to effect the suction and discharge of liquid to be delivered. The retainer ring 08 serves to keep the slipper pads 07 pressed against the swashplate 03, lest they should separate themselves from the swashplate due to the inertia force of the reciprocating pistons 05 and slipper pads 07 and the centrifugal force of the slipper pads 07 themselves.
A measure commonly in use to realize the above purpose is, as illustrated in FIGS. 1 and 2, to provide on the shaft 01 and axially slidable spherical pressure member 010 which mates with a spherical seat 09 in the center of the retainer ring 08 and is urged by a spring 011 toward the swashplate 03.
Since the spherical pressure member 010 and the retainer ring 08 rotate relative to the swashplate 03 which is stationary, the retainer ring 08, as is shown in FIG. 2, makes a swaying motion within the range of an angle twice the angle of inclination θ of the swashplate 03.
The conventional retainer ring supporting mechanism as described above has the following disadvantages:
When the rotational speed of the shaft 01 is constant, the inertia force of the pistons 05 and slipper pads 07 is proportional to the stroke of the pistons 05. In a variable delivery pump wherein the strokes of the pistons 05 are changed with change in the angle of inclination of the swashplate 03, therefore, the inertia force of the pistons 05 and slipper pads 07 is the greatest when the inclination angle of the swashplate is at its maximum. Accordingly, it is necessary to keep the retainer ring 08 pressed against the swashplate 03 with a force greater than the inertia force of the swashplate at its maximum. In case where such a variable delivery pump is installed for driving a steering system, it is often operated at an inclination angle of zero (where the pistons do not make a stroke). This means, however, that the retainer ring 08 is kept pressed against the swashplate 03 with a force corresponding to the force at the maximum angle of inclination (i.e., where the pistons reciprocate at the maximum stroke), thus having adverse effects upon the mechanical efficiency of the pump and the durability of the sliding parts.
For this reason, it is desirable that the force for urging the retainer ring toward the swashplate is automatically changed with the angle of inclination of the swashplate (or the stroke of the pistons).
It is also noted that the resultant force of the inertia force due to the reciprocating motion of the pistons 05 and the slipper pads 07 and the centrifugal force is due to the rotation of the slipper pads 07 acts on the swashplate 03, as shown in FIG. 3, as a separating force on the side where the individual pistons reach their top dead points and as a pressure-contacting force on the opposite side where the individual pistons reach their bottom dead points. Such forces for separation and pressure contact increase with an increase of the inclination angle of the swashplate. Consequently, the point of application of the force for separating the slipper pads away from the swashplate 03 shifts gradually toward the side where the pistons reach their top dead points with increase of the inclination angle of the swashplate.
As a result, in a conventional structure of the retainer ring supporting mechanism in which the retainer ring 08 is kept pressed through the central portion thereof against the swashplate irrespective of change in the inclination angle of the swashplate or the displacement of the point of application of the separating force, the center of application of the separating force and the point where the retainer ring is kept pressed against the swashplate (or the center point of the shaft) are widely apart from each other when the angle of inclination of the swashplate is large and, therefore, the pressing force of the retainer ring 08 must be considerably increased. This is not desirably for the life of the sliding parts of the retainer ring 08 and the spherical pressure member 010.
SUMMARY OF THE INVENTION
The principal object of the present invention is to provide a device for supporting the retainer ring of an axial piston pump or motor which is free from the disadvantages of the conventional mechanisms as described above and achieves a high mechanical efficiency with long service life.
In accordance with the invention, there are provided an annular pusher axially slidably fitted on the shaft and pressed toward the swashplate by means of at least one elastic member, and a spherical pressure member axially slidably fitted on the pusher and engaged in a spherical seat in the center of the retainer ring by means of an auxiliary elastic member disposed between the spherical pressure member and the pusher, in such a manner that, when the angle of inclination of the swashplate has exceeded a certain value, the retainer ring comes onto contact with the peripheral edge of the pusher at a point away from the center of rotation of the ring toward the side where the pistons reach their top dead points.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a longitudinal sectional view of the essential parts of an axial piston pump of the prior art having a conventional mechanism for supporting the retainer ring;
FIG. 2 is an enlarged view of the prior art retainer ring support assembly of FIG. 1;
FIG. 3 shows a curve of separating force versus pressure-contacting force of pistons and slipper pads against the surface of the swashplate;
FIG. 4 is a longitudinal sectional view of the essential parts of a variable delivery axial piston pump or motor provided with a retainer ring supporting device according to the invention;
FIG. 5 is an end view of the cylinder barrel viewed along the line V--V of FIG. 4;
FIGS. 6 to 8 are longitudinal sectional views of the retainer ring support assembly, taken along the line VI--VI of FIG. 5, showing the retainer ring and pusher at different angles of inclination of the swashplate;
FIG. 9 is a graph showing the relationship between the displacement of center of separating force and the supporting point of the retainer ring against the swashplate angle; and
FIG. 10 is a graph showing the relationship between the separating force or pressure-contacting force of the retainer ring and the inclination angle of the swashplate.
DESCRIPTION OF A PREFERRED EMBODIMENT
In FIGS. 4 to 8 throughout, reference numeral 1 designates a shaft which is driven by an electric motor or the like (not shown). Numeral 2 designates a cylinder barrel fixedly mounted on the shaft 1 by splining at 3. A plurality of cylinders 4 (nine in the embodiment) are axially formed in the barrel 2 at angular intervals around the shaft 1. In these cylinders 4 are slidably fitted pistons 5, respectively.
A tilting box 6 is held by a pump casing (not shown), and a swashplate 7 is held by the tilting box 6. By tilting the box 6 with respect to the axis of the shaft 1 the angle of inclination θ of the swashplate can be adjusted.
Numeral 8 indicates slipper pads, each of which is engaged with one of each piston 5 via a ball joint 9 and is kept in sliding contact with the swashplate 7 by means of a retainer ring 10. The pistons 5 are driven sequentially to reciprocate axially within the cylinders 4 with rotation of the cylinder barrel 2. An annular pusher 11 is slidably mounted on the shaft 1 and is urged toward the swashplate 7 by means of a pressure contact springs 12 disposed between it and the cylinder barrel 2. At the moment when the inclination angle θ of the swashplate 7 has exceeded a certain valve, the pusher 11 comes into contact with the retainer ring 10 at a point P of the peripheral edge 13 thereof and presses the retainer ring 10 toward the swashplate 7. In this case, the pusher 11 rotates together with the shaft 1, and the retainer ring 10 makes a swaying motion with an angle twice as the inclination angle θ of the swashplate while rotating at the same speed as the shaft 1 via the slipper pads 8. The retainer ring 10 rotates in contacting relationship with the peripheral edge 13 of the pusher 11 at a point P in a way similar to bevel gears in engagement, the point P moving circumferentially on the retainer ring 10 or the edge 13.
A spherical pressure member 14 is slidably fitted on the stem 15 of the pusher 11 and is pressed toward the swashplate 7 by means of an auxiliary spring 16 disposed between it and the pusher 11. This spherical pressure member 14 engages in a spherical seat 17 formed in the center of the retainer ring 10 and presses the retainer ring 10 toward the swashplate 7.
The auxiliary spring 16 is so dimensioned that the force urged on the spherical pressure member 14 by it is less than that urged on the pusher 11 by the pressure contact springs 12.
It is now assumed that the assembly is so designed that the greatest possible angle of inclination of the swashplate 7 is θmax and the retainer ring 10 comes into contact with the peripheral edge 13 of the pusher 11 at an inclination angle θ = 1/2 θmax of the swashplate. Then, in the range of θ < 1/2 θmax, the retainer ring 10 is supported at the center thereof by the spherical pressure member 14, as shown in FIG. 7 while the range of η > 1/2 θmax, it is supported by the pusher 11 at the point P on the side where one of pistons substantially reaches the top dead point, as shown in FIG. 8.
This has an advantage that the supporting point of the retainer ring 10 (i.e., the center at which the retainer ring is pressed against the swashplate) can be kept close to the center of the force for separating the pistons and slipper pads from the swashplate surface, since the center point of the separating force is shifted toward the side where the pistons reach their top dead points with increase of the inclination angle of the swashplate angle. Thus the pressure-contacting force of the retainer ring 10 may be advantageously reduced as compared with the conventional supporting system using only the spherical pressure member.
FIG, 9 shows graphically the relationship between the displacement of the center of separating force or the supporting point of the separating force and the inclination angle θ of the swashplate. The broken line (x) represents the displacement of the center of separating force, the full line (y) represents the supporting position of the retainer ring.
As can be seen from the graph, in the range of θ<1/2θmax the retainer ring is supported at its center with the spherical pressure member, while in the range of θ>1/2 θmax, it is supported by the pusher at a point on the side where the pistons reach their top dead points by the pusher. Thus the supporting point of the retainer ring is kept at a shorter distance from the center of separating force.
Another advantage of the device according to this invention is that, in the range of 1/2θmax to θmax in which the retainer ring 10 is supported by the pusher 11, the pressure contacting force for the retainer ring is automatically increased with increase of the inclination angle θ of the swashplate.
When the swashplate angle θ is in the range below 1/2θmax, the auxiliary spring 16 is compressed to the extreme and the pressure contact springs 12 are fully expanded so that the peripheral edge 13 of the pusher 11 is kept in contact with the rear end of the spherical pressure member 14. Thus, the retainer ring 10 is kept pressed against the swashplate surface with a relatively weak force by the pressure contact springs 12 in their most expanded state.
Once the angle θ has exceeded 1/2θmax, the side of the retainer ring 10 where the pistons reach their top dead points is brought into contact with the peripheral edge 13 of the pusher 11. With further increase of the inclination angle θ, the pusher 11 recedes and the pressure contact springs 12 for supporting the pusher 11 are compressed with the result that the pressure contacting force of the retainer ring 10 is proportionally increased. IN this case, the spherical pressure member 14 still presses the retainer ring 10 toward the swashplate with a weak force exerted by the expanding auxiliary spring 16. Here the spherical pressure member 14 serves as a radial bearing for the retainer ring 10 rather than as means for exerting a contacting pressure.
In FIG. 10 there is shown the relationship between the inclination angle θ of the swashplate and the pressure-contacting force or the separating force for the retainer ring. In the graph the full line a represents the pressure-contacting force and the broken line b represents the separating force. It can be seen from the graph that the pressure-contacting force of the retainer ring is small when the inclination angle θ is small so that the force for separating the pistons 5 and the slipper pads 8 from the surface of the swashplate 7 is relatively small. In the range of a larger inclination angle or of an increased separating force the pressure-contacting force of the retainer ring is correspondingly increased in a desirably manner. Since the retainer ring 10 and the pusher 11 remain in point contact without sliding on each other, both members are practically free from wear.
As will be seen from the foregoing, the device of the present invention has no danger of exerting any force more than required on the pressure-contacting part of the retainer ring and thus makes it possible to provide an axial piston pump of an improved mechanical efficiency and a great durability.
While in the embodiment the point where the made of supporting the retainer ring is changed from the one using the spherical pressure member to the one using the pusher is set at an inclination angle of 1/2θmax, the setting of the point may of course be selected according to the necessity.
It will also be apparent that other modifications may be made without departing from the spirit and scope of the invention.