GB1569662A - Piston and slideshoe assembly - Google Patents

Description

(54) A PISTON AND SLIDESHOE ASSEMBLY (71) We, ROBERT BOSCH GmbH, a German company of Postfach 50, 7000 Stuttgart 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a piston and slide shoe assembly for use in hydrostatic machines.

In radial machines, for example, the piston and slide shoe are usually connected to one another by special connecting elements which are expensive to make and to assembly.

In the piston and slide shoe assembly in accordance with the invention, the piston is positively connected to the slide shoe with a spherically curved surface on the slide shoe in engagement with a corresponding spherically curved surface formed at one end of the piston, the assembly comprising a hammer-like extension at the spherically curved end of the piston, the extension being formed by a head and a shank, elongate in cross-section, connecting the head to the piston, an asymmetrical bore in the slide shoe large enough for the head to pass axially therethrough, and an elongate recess in the slide shoe in communication with the asymmetrical bore through a passage wide enough for the shank to pass laterally therethrough with the elongate axis of the shank in alignment with the direction of movement of the shank through the passage and at an angle to the elongate axis of the recess, the arrangement being such that, after passing the head axially through the asymmetrical bore and the shank laterally through the passage, rotation of the piston relatively to the slide shoe about the axis of the extension brings the elongate axis of the shank into alignment with the elongate axis of the recess and positively connects the piston and slide shoe together.

The advantages of such an assembly are that it is simple and cheap to produce and is extraordinarily simple to assembly.

Preferably, the head of the hammer-like extension is cylindrical and the shank is provided with parallel surfaces spaced apart by a distance which is no greater than the width of the passage.

If desired, a duct may be provided passing through the piston and terminating at the spherically curved surface on the piston in such a position that, when the assembly is arranged in a working machine, working pressure passing through the duct forms a pressure field between the engaging spherically curved surfaces.

In a preferred embodiment, the hammerlike extension passes through the slide shoe, a pair of spherically curved surfaces on the piston being formed one on each side of the extension and another pair of correspondingly spherically curved surfaces on the slide shoe being formed one on each side of the recess.

The invention also extends to an hydrostatic machine incorporating at least one piston and slide shoe assembly as set forth above, in which the or each piston is arranged in a rotor and the or each slide shoe is guided on the track surface of a stroke generating ring by means of a pair of axially elastic radially non-elastic or resilient guide rings arranged concentric with the stroke ring.

In order that the invention may be clearly understood and readily carried into effect, an embodiment thereof will now be described with reference to the accompanying drawings in which: Figure 1 is a partial section through a piston and slide shoe assembly in accordance with the invention, incorporated in a radial piston machine; Figure 2 is a section taken on the line Il-Il in Figure 1; Figure 3 is a view of the piston and slide shoe assembly of Figure 1 showing the outer or "track" surface of the slide shoe; and Figure 4 shows the piston and slide shoe assembly of Figure 1 to a larger scale.

As can be seen from the drawings, the radial piston machine, which is only partially illustrated in Figures 1 and 2, has a stroke generating ring 10, and a rotor 11 which is driven by a shaft (not illustrated).

A plurality of radial bores 12 are formed in the rotor 11, only one of which is shown.

A piston 13, made partially hollow, is arranged to slide sealingly in the bore 12 and is provided at its outer end with a spherical surface 14 in engagement with a spherical surface 15 of a slide shoe 16. The slide shoe slides on the inner wall 101 of the ring 10 by means of its cylindrically formed outer track surface 17.

The piston 13 and the slide shoe 16 are positively connected together by means of an assembly which comprises a hammerlike extension 18 arranged at the spherically curved end of the piston 13, an asymmetrical bore 27 and an elongate recess 29 in communication with the bore 27 through a passage 28. The bore 27, the recess 29 and the passage 28 are all in the slide shoe 16. The extension 18 consists of a cylindrical shank 19 and a cylindrical head 20 the diameter of which is greater than that of the shank 19. Two opposite segments are removed from the shank 19 whereby two parallel surfaces 21 and 22 are formed which are spaced apart by a distance B. The width of the shank between the surfaces 21 and 22 is substantially less than the original diameter of the cylindrical shank 19 so that, with the opposite segments removed, the shank 19 is elongate in cross-section.

A throttle bore 23 adjacent the inner wall of the piston 13 passes through the base of the piston 13. An annular groove 24 is formed in the spherical surface 14 of the piston 13, the annular groove 24 being in communication with the throttle bore 23 and a longitudinal groove 25 leading from the groove 24 to the elongate shank 19.

The asymmetrical bore 27, the diameter of which is somewhat greater than the diameter of the head 20 on the piston 13, passes through the slide shoe 16. The elongate axis of the elongate recess 29 extends in the direction of travel of the slide shoe on the stroke ring 10 and the axis of symmetry of the recess 29 coincides with the longitudinal axis of the piston 12. The length of the passage 28 from the bore 27 to the elongate recess 29, is somewhat greater than the width B (Figure 2) of the shank 19.

A groove 30, the contour of which extends parallel to that of the elongate recess 29, extends around the recess 29 facing the track surface 17 of the slide shoe. The width of the elongate recess 29 is slightly greater than the original diameter of the cylindrical shank 19. The width of the groove 30 is so calculated that the cylindrical head 20 is located therein with clearance. The base of the groove 30 and the inner surface of the head 20 sliding thereon are spherical surfaces. The length of the shank 19 and the thickness of the web 31 forming the base of the groove 30 are so calculated that the positive connection provided by the assembly is substantially clearance free axially of the extension 18.

In projection, the track surface of the slide shoe is rectangular in shape and on each side, in the direction of travel, it has a chamfer 32 or 33 which does not however extend over the entire width of the track surface. A line joining the centres of the bore 27 and of the elongate recess 29 and passing through the passage 28, extends transversely with respect to the direction of travel of the slide shoe which is represented in Figure 3 by an arrow. Nevertheless, the slide shoe 16 is suitable for both senses of rotation of the rotor 11.

On the outer sides of the slide shoe 16, shoulders 34 and 35 are formed against which axially resilient, but radially nonresilient, rings 36 and 37 are supported and which force the slide shoe against the inner wall 10t of the ring 10 when no fluid pressure prevails.

The piston-slide shoe assembly is assembled by slightly inclining the piston, pushing the head 20 through the bore 27 until the two spherical surfaces 14 and 15 engage one another. The piston is then rotated until the parallel surfaces 21 and 22 on the shank 19 come to rest in the passage 28. Then by straightening the piston, the shank 19 slides through the passage 28, with the elongate axis of the shank 19 at an angle, in this case about 90 , to the elongate axis of the recess 29. The piston is then rotated about the axis of the extension 18 through 90G so as to bring the surfaces 21 and 22 and the elongate axis of the shank into substantial alignment with the elongate axis of the elongate recess 29. The piston is thereby so positively connected with respect to the slide shoe but in such a manner that. during operation, it is pivotable relatively to the slide shoe. The slide shoes can also freely adjust axially relatively to the ring 10.

During the suction stroke of the pistons, the slide shoes are resiliently radially guided on the inner surface 101 of the ring 10 by the rings 36 and 37. The axial resilience of these rings, permits small axial deviations between pistons and slide shoes required as a matter of tolerance, without causing any disadvantage.

The piston-slide shoe assembly is substantially relieved hydrostatically and is therefore completely friction free. Thus, the track surface 17 of the slide shoe can be maintained short in the peripheral direction, which means a low mass of slide shoe and low friction losses between the slide shoe and the stroke ring.

Through the throttle bore 23, pressure oil arrives in the annular groove 24 whereby pressure fields are built up between the slide shoe and the piston and between the shoe and the stroke ring by means of which a complete hydraulic relief is achieved between the piston and the slide shoe.

WHAT WE CLAIM IS:- 1. A piston and slide shoe assembly for use in hydrostatic machines in which the piston is positively connected to the slide shoe with a spherically curved surface on the slide shoe in engagement with a corresponding spherically curved surface formed at one end of the piston, the assembly comprising a hammer-like extension at the spherically curved end of the piston, the extension being formed by a head and a shank, elongate in cross-section, connecting the head to the piston, an asymmetrical bore in the slide shoe large enough for the head to pass axially therethrough, and an elongate recess in the slide shoe in communication with the asymmetrical bore through a passage wide enough for the shank to pass laterally therethrough with the elongate axis of the shank in alignment with the direction of movement of the shank through the passage and at an angle to the elongate axis of the recess, the arrangement being such that, after passing the head axially through the asymmetrical bore and the shank laterally through the passage, rotation of the piston relatively to the slide shoe about the axis of the extension brings the elongate axis of the shank into alignment with the elongate axis of the recess and positively connects the piston and slide shoe together.

2. A piston and slide shoe assembly according to claim 1, in which the head is cylindrical and the shank is provided with parallel surfaces spaced apart by a distance which is no greater than the width of the passage.

3. A piston and slide shoe assembly according to claim 2, in which the shank is produced by removing segments from a cylindrical shank to form the parallel surfaces.

4. A piston and slide shoe assembly ao cording to any preceding claim, in which a duct passes through the piston and terminates at the spherically curved surface on the piston in such a position that, when the assembly is arranged in a working machine working pressure passing through the duct forms a pressure field between the engaging spherically curved surfaces.

5. A piston and slide shoe assembly according to any preceding claim, in which the hammer-like extension passes through the slide shoe, a pair of spherically curved surfaces on the piston being formed one on each side of the extension and another pair of correspondingly spherically curved surfaces on the slide shoe being formed one on each side of the recess.

6. A piston and slide shoe according to any preceding claim, in which the or each spherically curved surface on the slide shoe is guided substantially clearance-free on the or each spherically curved surface on the piston.

7. An hydrostatic machine incorporating at least one piston and slide shoe assembly according to any preceding claim, in which the or each piston is arranged in a rotor and the or each slide shoe is guided on the track surface of a stroke generating ring by means of a pair of axially elastic radially non-elastic or resilient guide rings arranged concentric with the stroke ring.

8. An hydrostatic machine according to claim 7, in which the guide rings are positively retained axially by the or each slide shoe.

9. An hydrostatic machine according to claim 7 or claim 8 in which the outer surface of the or each slide shoe is made cylindrical corresponding to the inner surface of the stroke generating ring.

10. A piston and slide shoe assembly for use in hydrostatic machines, substantially as herein described with reference to the accompanying drawings.

11. An hydrostatic machine incorporating a piston and slide shoe assembly according to claim 10.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. maintained short in the peripheral direction, which means a low mass of slide shoe and low friction losses between the slide shoe and the stroke ring. Through the throttle bore 23, pressure oil arrives in the annular groove 24 whereby pressure fields are built up between the slide shoe and the piston and between the shoe and the stroke ring by means of which a complete hydraulic relief is achieved between the piston and the slide shoe. WHAT WE CLAIM IS:-

1. A piston and slide shoe assembly for use in hydrostatic machines in which the piston is positively connected to the slide shoe with a spherically curved surface on the slide shoe in engagement with a corresponding spherically curved surface formed at one end of the piston, the assembly comprising a hammer-like extension at the spherically curved end of the piston, the extension being formed by a head and a shank, elongate in cross-section, connecting the head to the piston, an asymmetrical bore in the slide shoe large enough for the head to pass axially therethrough, and an elongate recess in the slide shoe in communication with the asymmetrical bore through a passage wide enough for the shank to pass laterally therethrough with the elongate axis of the shank in alignment with the direction of movement of the shank through the passage and at an angle to the elongate axis of the recess, the arrangement being such that, after passing the head axially through the asymmetrical bore and the shank laterally through the passage, rotation of the piston relatively to the slide shoe about the axis of the extension brings the elongate axis of the shank into alignment with the elongate axis of the recess and positively connects the piston and slide shoe together.

2. A piston and slide shoe assembly according to claim 1, in which the head is cylindrical and the shank is provided with parallel surfaces spaced apart by a distance which is no greater than the width of the passage.

3. A piston and slide shoe assembly according to claim 2, in which the shank is produced by removing segments from a cylindrical shank to form the parallel surfaces.

4. A piston and slide shoe assembly ao cording to any preceding claim, in which a duct passes through the piston and terminates at the spherically curved surface on the piston in such a position that, when the assembly is arranged in a working machine working pressure passing through the duct forms a pressure field between the engaging spherically curved surfaces.

5. A piston and slide shoe assembly according to any preceding claim, in which the hammer-like extension passes through the slide shoe, a pair of spherically curved surfaces on the piston being formed one on each side of the extension and another pair of correspondingly spherically curved surfaces on the slide shoe being formed one on each side of the recess.

6. A piston and slide shoe according to any preceding claim, in which the or each spherically curved surface on the slide shoe is guided substantially clearance-free on the or each spherically curved surface on the piston.

7. An hydrostatic machine incorporating at least one piston and slide shoe assembly according to any preceding claim, in which the or each piston is arranged in a rotor and the or each slide shoe is guided on the track surface of a stroke generating ring by means of a pair of axially elastic radially non-elastic or resilient guide rings arranged concentric with the stroke ring.

8. An hydrostatic machine according to claim 7, in which the guide rings are positively retained axially by the or each slide shoe.

9. An hydrostatic machine according to claim 7 or claim 8 in which the outer surface of the or each slide shoe is made cylindrical corresponding to the inner surface of the stroke generating ring.

10. A piston and slide shoe assembly for use in hydrostatic machines, substantially as herein described with reference to the accompanying drawings.

11. An hydrostatic machine incorporating a piston and slide shoe assembly according to claim 10.