Piston Assembly for Hydraulic Pump

This application claims the benefit of European Patent Application No. 24305724.7 filed May 10, 2024, the disclosure of which is incorporated herein by reference in its entirety.

The present invention relates to a method of assembling a piston and shoe of a hydraulic pump, and a piston and shoe assembly.

A piston pump typically comprises a barrel that has a number of bores for receiving pistons therein. The pistons are arranged such that axial displacement within the corresponding bore causes either compression or suction dependent on the stroke of the piston.

The pistons are held by shoes at one end that translate along the surface of an angle block, e.g. an inclined plate. Rotation of the barrel and shoes cause the pistons to move axially within the bores of the barrel as the shoes move axially inwards or outwards due to the inclination of the angle block.

To secure the piston to the shoe with a ball joint functionality, the pistons may have a piston sphere that is placed into an open socket of the shoe, which is then crimped about the piston sphere to secure the piston sphere in place. The crimped portions of the shoe can be a point of weakness that can fail in use.

According to a first aspect of the invention, there is provided a method of assembling a piston and shoe of a hydraulic pump, the method comprising: inserting a shaft of the piston through an aperture of the shoe such that it extends through to the other side until a piston head of the piston is seated in the shoe.

Optionally, the method comprises inserting a plug into the shoe such that the piston head is held between the shoe and the plug.

Optionally, the method comprises installing a piston sleeve onto the shaft of the piston.

Optionally, the method comprises installing a fixing into the piston and piston sleeve to secure the piston and piston sleeve together.

Optionally, the piston sleeve is a first piston sleeve and the method comprises: removing the fixing from the piston and first piston sleeve; removing the first piston sleeve from the shaft of the piston; and installing a second piston sleeve onto the shaft of the piston.

Optionally, the second piston sleeve is of a greater or smaller cross section than the first piston sleeve.

According to a second aspect of the invention, there is provided a method of disassembling a piston and shoe of a hydraulic pump, the method comprising: passing a shaft of the piston through an aperture of the shoe to thereby decouple a piston head of the piston from the shoe.

According to a third aspect of the invention, there is provided a piston and shoe assembly for a hydraulic pump, the assembly comprising: a piston comprising a piston shaft and a piston head; and a shoe comprising an aperture, wherein the piston shaft is sized such that it can pass through the shoe aperture and the piston head is sized such that it cannot pass through the shoe aperture.

Optionally, the piston and shoe assembly comprises a plug at least partially located within the shoe and arranged to hold the piston head in the shoe.

Optionally, the piston and shoe assembly comprises a piston sleeve along the piston shaft.

Optionally, the piston and shoe assembly comprises a fixing arranged to secure the piston sleeve to the piston shaft.

Optionally, the piston comprises a piston inner passageway and the plug comprises a plug inner passageway, the piston inner passageway and plug inner passageway arranged in fluid communication.

Optionally, the plug inner passageway comprises an enlarged opening for receiving fluid communication from the piston inner passageway.

Optionally, the piston head comprises a spherical portion, the piston shaft has a circular cross-section and the shoe aperture is of circular cross-section, and the diameter of the spherical portion of the piston head is greater than the diameter of the piston shaft and the shoe aperture has a diameter that is greater than the diameter of the piston shaft and smaller than the diameter of the piston head.

According to a fourth aspect of the invention, a hydraulic pump is provided comprising the piston and shoe assembly according to the third aspect.

As described herein, according to a first aspect, there is provided a method of assembling a piston and shoe of a hydraulic pump, the method comprising: inserting a shaft of the piston through an aperture of the shoe such that it extends through to the other side until a piston head of the piston is seated in the shoe.

Advantageously, the piston and shoe can be assembled without requiring deformation of the shoe such as crimping. The method may not comprise deforming, reshaping, bending or crimping the shoe to secure the piston head. Advantageously, a method of assembling a piston and shoe is provided that does not require deformation of the shoe, such as crimping of the shoe. The method can provide a piston and shoe assembly of enhanced strength, durability and wear resistance because the shoe can be formed of a material that does not need to be deformable. For example, the shoe may be formed of stainless steel for enhanced strength and the plug can be formed of copper alloy, such as bronze, for sliding and wear resistance properties, though any suitable material(s) may be used in practice. The method may also increase the ease with which the piston and shoe can be assembled and hence reduce assembly costs.

Inserting the shaft of the piston through the aperture of the shoe may comprise passing the length of the piston shaft through the aperture. For example, the piston may begin on a first side of the shoe aperture and be passed through the aperture of the shoe such that a majority of or the entirety of the piston shaft is on the second side of the aperture. In the example, the piston head may remain on the first side of the shoe aperture. In short, the shaft is passed through the shoe.

The piston head may be sized such that it cannot pass through the aperture. The seating of the piston head in the shoe may comprise the piston head abutting a shoulder of the shoe aperture. The piston as a whole therefore may pass partially through the shoe but not entirely through due to the piston head. The piston head and the shoe may therefore prevent relative axial displacement of the piston in at least one direction by the piston head being seated in the shoe.

The piston head and piston shaft may be linked by a piston neck. The piston neck may be narrower than the piston head and the piston shaft. The piston neck may transition from its most narrow at the piston head to its widest point at the piston shaft. The piston neck may taper from a narrow diameter at the piston head to a wider diameter at the piston shaft. The piston neck may be a connecting element between the piston shaft and the piston head, and may serve to delineate those two elements. Any suitable form of piston neck may be employed as required. The neck may pass through the aperture, at least partially.

The piston neck may be configured to enable sufficient rotation of the shaft relative to the shoe. The piston neck diameter and/or piston neck taper may be configured to position the piston shaft appropriately relative to the shoe in the event that the piston and shoe are assembled in a hydraulic pump, e.g. when aligned with or pressed against an angle block. The piston neck may be configured to ensure the correct angle of the shoe with respect to the piston in the event that the piston and shoe are adjacent or against an angle block, for example when the piston and shoe are assembled in a hydraulic pump.

The method may comprise assembling a plurality of pistons and shoes of a hydraulic pump. The method may comprise inserting a shaft of each of the plurality of pistons through respective apertures of the plurality of shoes until a piston head of each piston is seated in each shoe such that the pistons extend through to the other side of the shoes.

The method may comprise inserting a plug into the shoe such that the piston head is held between the shoe and the plug. The plug may allow the piston to be maintained in place and may limit backlash (e.g. axial movement of the piston head relative to the shoe) in use to ensure the correct stroke of the piston. The plug may limit or eliminate fluid leakage from inside of the piston assembly to the outside. Limiting backlash and/or leakage may increase the efficiency of a hydraulic pump.

The method may comprise adjusting the plug to reduce backlash of the piston. The method may comprise adjusting the plug to adjust pressure balancing and lubrication functions of the piston and shoe.

The method may therefore comprise securing the piston, via the piston head, to the shoe by restricting the piston head between the shoe aperture and the plug. Inserting the plug into the shoe may prevent the piston shaft from passing back through the aperture. The method may comprise securing the plug to the shoe e.g. by a press fit, a friction fit, or any suitable fixing means, to thereby ensure that piston—and specifically the piston head—is held securely within the shoe.

The method may comprise installing a piston sleeve onto the shaft of the piston.

The method may comprise increasing the working diameter of the piston shaft via the addition of the piston sleeve. Advantageously, the method may use a standard size piston for use with a number of differing bore diameters of different pumps by installing correspondingly sized piston sleeves onto the piston shaft. The resulting shaft assembly, e.g. the piston shaft and the piston sleeve, may have a cross section that cannot pass through the shoe aperture. Advantageously, different materials may be used for the piston shaft and piston sleeve. The properties of the sleeve can therefore be different to those of the shaft, and the shaft may therefore be e.g. less durable than the sleeve.

The method may comprise installing a fixing into the piston and piston sleeve to secure the piston and piston sleeve together.

The method may comprise joining the piston and piston sleeve together. Any suitable fixing may be used. The fixing may be a pin. The pin may be a stop pin. A plurality of fixings may be used. The piston and piston sleeve may comprise corresponding openings and the step of installing the fixing may comprise installing the fixing into the corresponding openings of the piston and piston sleeve. The opening in the piston may be in the piston shaft. The method may comprise inserting the fixing through the piston sleeve and piston shaft, to thereby fix the piston sleeve to the piston shaft.

The method may comprise inserting the shoe into a shoe holder.

The shoe may be configured to engage the shoe holder in an abutting arrangement. Inserting the shoe into the shoe holder may comprise first passing the piston shaft through the shoe holder. Inserting the shoe into the shoe holder may locate the shoe and piston relative to other shoes and pistons, already or to be, inserted into the shoe holder.

The method may comprise inserting the piston shaft into a barrel of a hydraulic pump.

The piston sleeve may be a first piston sleeve and the method may comprise: removing the fixing from the piston and first piston sleeve; removing the first piston sleeve from the shaft of the piston; and installing a second piston sleeve onto the shaft of the piston.

Advantageously, the method may provide a means of reconfiguring the piston without requiring disassembly of the piston from the shoe. For example, a damaged piston sleeve may be replaced without requiring disassembly of the piston from the shoe. Thus, the method may comprise changing the piston sleeve to a second piston sleeve different to the first piston sleeve. The method may therefore comprise re-sizing the working size of the piston of the hydraulic pump. The method may comprise repairing the pump by replacing the piston sleeve. The method may therefore be a method of repairing a hydraulic pump, and/or reconfiguring a hydraulic pump.

The plug may be replaced to repair the pump or reconfigure the balancing according to the piston sleeve cross section.

The second piston sleeve may be of a greater or smaller cross section than the first piston sleeve.

Advantageously, the method may provide a means of reconfiguring the piston and shoe for use in a hydraulic pump having a different bore diameter without requiring disassembly of the piston from the shoe.

The method may comprise assembling a hydraulic pump. The hydraulic pump may comprise an angle block that provides an inclined surface and the method may comprise positioning the shoe on the inclined surface of the angle block. The method may comprise lubricating the angle block with fluid supplied from within a barrel of the pump via fluid passageways within the piston, shoe and optionally the plug. The method may comprise separating the shoe from the angle block by providing pressure communication from within a barrel of the pump to a region between the angle block and shoe via the fluid passageways within the piston, shoe and optionally the plug. The separation may be by a layer (e.g. a very thin layer) of lubricant (e.g. oil) to lubricate the contact area.

The method according to the first aspect of the invention, and optionally and of the optional features of the first aspect described, may be repeated to assemble a plurality of pistons and shoes of a hydraulic pump.

According to a second aspect of the invention, there is provided a method of disassembling a piston and shoe of a hydraulic pump, the method comprising: passing a shaft of the piston through an aperture of the shoe to thereby decouple a piston head of the piston from the shoe.

Advantageously, the piston and shoe can be disassembled without requiring deformation of the shoe such as crimping. The method may not comprise deforming, reshaping, bending or crimping the shoe to decouple the piston head from the shoe. Advantageously, a method of disassembling a piston and shoe is provided that does not require deformation of the shoe, such as crimping of the shoe. Therefore, the method can provide a piston and shoe assembly of enhanced strength and durability because the shoe can be formed of a material that does not need to be deformable and is more resistant to wear. The method may also increase the ease with which the piston and shoe can be both assembled and disassembled and hence reduce the associated costs.

Passing the shaft of the piston through the aperture of the shoe may comprise passing the length of the piston shaft through the aperture. For example, the piston shaft may begin on a first side of the shoe aperture and be passed through the aperture of the shoe such that a majority of or the entirety of the piston shaft is on the second side of the aperture. In the example, the piston head may begin and remain on the second side of the shoe aperture.

The method of disassembling a piston and shoe of a hydraulic pump may comprise the reverse of the method of assembling a piston and shoe of a hydraulic pump described in relation to the first aspect. The disassembly may allow maintenance, repair, and/or cleaning of components of the hydraulic pump. The method may be a method of maintenance of the hydraulic pump comprising disassembling as described herein.

The method of disassembling the piston and shoe of a hydraulic pump may comprise removing a plug from the shoe such that the piston head can be removed from the shoe.

The method may comprise releasing the piston from the shoe by removing the restriction provided by the piston head being arranged between the shoe aperture and the plug. Removing the plug from the shoe may allow the piston shaft to pass through the aperture.