Piston of a hydraulic piston engine

Abstract

A piston (1) of a hydraulic piston machine is described, comprising a piston rod (2), a ball head (3) at one end of the piston rod (2), and a shoe (4) mounted to the ball head (3), wherein the ball head (3) comprises a through channel (5), the shoe (4) comprises a sliding surface (6) and a through hole (7) in communication with an end of the through channel (5), and a plastic material (8) is arranged in a gap between the shoe (4) and the ball head (3) and forms an inner coating (9) of the through hole (7). The production of such a piston should be facilitated. To this end, a sealing surface (14) is arranged at the end of the through channel (5), wherein the sealing surface (14) surrounds an opening of the through channel (5) into the through hole (7), and an inner diameter of the sealing surface (14) is smaller than an inner diameter of the inner coating (9) of the through hole (7).

Description

TECHNICAL FIELD

[0001] The invention relates to a piston of a hydraulic piston machine, the piston comprising a piston rod, a ball head at one end of the piston rod, and a shoe mounted to the ball head, wherein the ball head comprises a through channel, the shoe comprises a sliding surface end surface and a through hole in communication with the end of the through channel, and a plastic material is arranged in a gap between the shoe and the ball head and forms an inner coating of the through hole. BACKGROUND

[0002] Such a piston is known, for example, from US 2012 / 0148342 A1.

[0003] Such a piston can be used, in particular, in a water press. A water press uses water as a hydraulic fluid. In comparison with oil, water has no lubricating properties, so the friction between the sliding surfaces has to be reduced in another way. In the present case, the friction between the ball head and the shoe is reduced by the plastic material.

[0004] Such a piston is usually produced in such a way that the shoe and the ball head of the piston are assembled and the assembly is placed in a tool in which the plastic material is injected. In order to guide the plastic material into the gap between the shoe and the ball head, a pin is inserted into the piston rod and through the through channel until it reaches the opening of the through channel. The tip on the pin forms a flow guide for the molten plastic introduced through the through hole.

[0005] Such a method of manufacturing a piston is complex and requires very precise positioning of all components of the piston and the tool. SUMMARY

[0006] It is an object of the invention to facilitate the production of a piston of a hydraulic piston machine.

[0007] The solution to this object is that a sealing surface is arranged at the end of the through channel, wherein the sealing surface surrounds the opening of the through channel into the through hole and the inner diameter of the sealing surface is smaller than the inner diameter of the inner coating of the through hole.

[0008] In this way, the pin can be inserted from the side of the shoe opposite the ball head. The pin seals on the sealing surface, so the molten plastic material cannot enter the through channel. However, the molten plastic material can enter the gap between the shoe and the ball head and also form the inner coating of the through hole.

[0009] In an embodiment of the invention, the sealing surface is conically shaped. The conical shape makes it easy for the pin to be centered with respect to the through channel, so that the pin is automatically in the correct position. Furthermore, the conical shape of the sealing surface allows a better connection between the through channel and the through hole even when the shoe is tilted with respect to the piston rod.

[0010] In an embodiment of the application, the radial outer diameter of the sealing surface corresponds to the radial inner diameter of the inner coating. The radial inner diameter of the coating can be equal to or slightly smaller than the radial outer diameter of the sealing surface. This provides a good transition between the inner coating of the through hole and the plastic material in the gap between the shoe and the ball. To this end, the diameter of the pin is equal to or slightly larger than the diameter of the sealing surface.

[0011] In an embodiment of the application, the through channel comprises a first portion with a reduced inner diameter, wherein the sealing surface is located at the end of the first portion. The reduced inner diameter provides space for the sealing surface.

[0012] In an embodiment of the application, a second portion of the through channel has the same inner diameter as the through hole. More precisely, the inner diameter of the inner coating of the through hole is the same as the inner diameter of the second portion. Thus, the hydraulic fluid can pass through the through channel and through the through hole without substantial throttling, so that a hydraulic balance on the shoe can be achieved. The through hole can have more than two of the mentioned portions.

[0013] In an embodiment of the application, the through hole comprises a radial inner recess, and the inner coating extends into the radial inner recess. Thus, a positive interlock between the plastic material and the shoe can be achieved.

[0014] In an embodiment of the application, the radial inner recess is located at the sliding surface of the shoe. This makes it possible to form the radial inner recess in a simple manner.

[0015] In an embodiment of the application, the shoe comprises a body, wherein the plastic material extends from the gap to the outer circumference of the body. The plastic material is integral, with enhanced mechanical stability.

[0016] In an embodiment of the application, the plastic material covers the front surface or face of the body facing the piston rod. Thus, the connection between the plastic material in the gap between the shoe and the ball and the material outside the body is formed in an area that is not subjected to any frictional forces. Thus, the connection between these two parts of the plastic material is very stable and durable. The plastic material can be injected from the front surface or face.

[0017] In an embodiment of the application, the outer circumference of the body comprises an outer recess, and the plastic material extends into the outer recess. Thus, a second form fit between the plastic material and the body of the shoe is achieved.

[0018] In an embodiment of the application, the outer recess is located at a diameter of the body that is larger than the diameter of the ball. The larger the diameter of the body where the recess is located, the stronger the connection between the plastic material and the body.

[0019] In an embodiment of the application, the plastic material outside the body is processed at least on the face opposite the end surface. Thus, the thickness of the shoe between the end surface and the face opposite the end surface can be adjusted with high precision.

[0020] In an embodiment of the application, the end surface comprises a sliding element made of a ceramic material. The sliding element can be installed to the end surface before positioning the assembly of the shoe and the piston in the injection tool, or the ceramic element can be cemented in the end surface of the shoe.

[0021] In an embodiment of the application, the sliding element is in the form of a ring. Thus, the shoe can abut against the swash plate having a considerable surface.

[0022] In an embodiment of the application, the plastic material is rotatably fixed on the shoe. Thus, there is no movement between the plastic material and the shoe. BRIEF DESCRIPTION OF DRAWINGS

[0023] The application will now be described in more detail with reference to the drawings, in which

[0024] Figure 1 a first embodiment of a part of a piston is shown,

[0025] Figure 2 a part of a tool that can be used for producing a piston is shown schematically, and

[0026] Figure 3 a piston and other parts of a hydraulic machine are shown. DETAILED DESCRIPTION

[0027] Figure 1 A piston 1 of a hydraulic piston machine is shown schematically. The hydraulic piston machine can be, for example, an axial piston machine.

[0028] The piston 1 comprises a piston rod 2, a ball head 3 at one end of the piston rod 2, and a shoe 4 mounted to the ball head 3. The ball head 3 comprises a through passage 5. The shoe 4 comprises an end surface 6 and a through hole 7 in communication with one end of the through passage 5. A plastic material 8 is arranged in the gap between the shoe 4 and the ball head 3 and forms an inner coating 9 of the through hole 7.

[0029] During the operation of the hydraulic piston machine, the shoe 4 can be tilted in relation to the piston rod 2, for example, when the piston 1 is moved above a swash plate 21 Figure 3 ) in relation to the axis of the piston rod 2. Hydraulic fluid can be supplied through the through passage 5 and the through hole 7 to create a hydraulic pressure between the end surface 6 and the swash plate. The dimensions of the end surface 6 are determined so that the shoe 4 is loaded with balanced forces.

[0030] The shoe 4 comprises a body 10, for example made of steel or other similar material. The plastic material 8 has friction-reducing properties. A preferred material for the plastic material 8 is PEEK (polyether ether ketone). Other plastic materials can be chosen from the group of high-strength thermoplastic plastic materials based on polyaryletherketone, in particular polyether ether ketone, polyamide, polyacetal, polyarylether, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetherimide, polyamide-imide, polyacrylate, phenolic resins, such as novolak resins or similar substances, glass, graphite, polytetrafluoroethylene or carbon, in particular in the form of fibres, for use as a filler. When using these materials, water can be used as the hydraulic fluid.

[0031] The through channel 5 comprises a second portion 12 having the same inner diameter as the through hole 7, more precisely the inner coating 9 of the through hole 7, and a first portion 11 of reduced diameter. The first portion 11 is much shorter than the rest of the through channel 5 and much shorter than the second portion 12. The hydraulic fluid flowing through the through channel 5 and the through hole 7 is therefore substantially not subject to any throttling at this location, so that the hydraulic pressure on the end surface 6 can be maintained.

[0032] The body 10 comprises a radially inner recess 13. The plastic material of the inner coating 9 extends into the radially inner recess and forms a positive interlock with the body 10 of the shoe 4. The radially inner recess 13 is located at the end surface 6 of the shoe 4. This facilitates the manufacture of the radially inner recess 13 by machining. The radially inner recess 13 is accessible or accessible from the end surface 6.

[0033] A sealing surface 14 is formed at the end of the through channel 5. The sealing surface 14 surrounds the opening of the through channel 5 into the through hole 7, and the inner diameter of the sealing surface 14 is smaller than the inner diameter of the inner coating 9 of the through hole 7.

[0034] As Figure 1 can be seen, the sealing surface 14 is conically shaped. The radially outer diameter of the sealing surface 14 corresponds to the radially inner diameter of the inner coating 9.

[0035] The advantages of this construction will be explained with reference to Figure 2 .

[0036] When producing the shoe 4 with regard to Figure 1With the described type of piston 1, the body 10 of the shoe 4 is assembled to the ball head 3. This assembly is placed in the injection tool. The pin 15 is inserted through the metal tube 22 and through the bore 7 until it rests against the sealing surface 14. The diameter of the pin 15 is equal to or slightly larger than the outer diameter of the sealing surface 14. A gap is provided between the pin 15 and the body 10 so that the plastic material 8 can be injected around the pin 15 in the through bore 7. However, the plastic material 8 cannot enter the through channel 5 because the pin 15 and the sealing surface 14 together form a rod. The inner coating 9 ensures that there are no lateral forces on the pin 15 when the tube 22 is closed against the end surface 6 and closed. The through bore 7 does not have to be very precise to ensure the closure.

[0037] When the pin 15 has substantially the same outer diameter as the sealing surface 14, a smooth transition between the inner coating 9 and the plastic material 8 in the gap between the ball head 3 and the body 10 can be achieved.

[0038] The plastic material 8 extends from this gap to the outer circumference 16 of the body 10. The plastic material 8 covers the front surface or face 17 of the body facing the piston rod 2. The connection between the plastic material 8 in the gap between the body 10 and the ball head 3 and the plastic material 8 on the circumference of the body 10 is thus formed in an area that is free from any friction, so that this connection is very stable and does not wear. The tube 22 is in close proximity to the end surface 6. The plastic material 8 is injected from the front surface or face 17.

[0039] The body 10 comprises an outer recess 18 into which the plastic material 8 extends. The plastic material 8 forms a positive interlock or form fit with the body 10 at two locations, namely at the radially inner recess 13 and at the outer recess 18. The plastic material 8 is held non-rotatable with respect to the body 10 of the shoe 4.

[0040] The outer recess 18 is located at a diameter of the body 10 which is larger than the diameter of the ball head 3. The outer recess is thus located at a diameter which is positive for the holding force of the plastic material 8 with respect to the body 10 of the shoe 4.

[0041] The plastic material 8 outside the body 10 comprises a face 19 opposite the end surface 6. The end surface 6 can be provided with a sliding element 20 formed of a ceramic material. The sliding element 20 can be in the form of a ring. During operation of the hydraulic axial piston machine, a pressure plate 23 acts on this face 19. At least this face 19 is machined so that the thickness of the shoe 4 in this area, i.e. the distance between the sliding surface of the sliding element 20 and the face 19, can be adjusted with high precision. This makes it possible to exert a uniform pressure on the shoe 4.

[0042] As mentioned above, the piston rod 2 and the ball head 3 can be made of a metallic material, for example steel, or also of a ceramic material.

[0043] Figure 3 The piston 1 and other components of the hydraulic machine 24 are shown. Identical elements are denoted with identical reference numerals.

[0044] The hydraulic machine 24 comprises a housing 25 in which a cylinder barrel 26 is rotatably supported. The cylinder barrel 26 comprises a plurality of cylinder bodies 27. The piston 1 is arranged in each of the cylinder bodies 27.

[0045] The cylinder barrel 26 acts on the pressure plate 23 through a spring 28. The pressure plate 23 holds the shoe 4 of the piston 1 on the swash plate 21 which is inclined with respect to the axis of rotation of the cylinder barrel 26. The swash plate 21 is made of stainless steel and is provided on the side against which the shoe 4 abuts with a ceramic sheet 29 so that the sliding element 20 of the shoe 4 runs on the swash plate ceramic.

[0046] The piston 1 can be made of steel and the friction is reduced by the plastic material 8. However, the piston can be made of a ceramic material which is used together with the plastic material 8. However, when a ceramic material is used, the ceramic can slide on the ceramic.

Claims

1. A piston (1) of a hydraulic piston machine, comprising a piston rod (2), a ball head (3) located at one end of the piston rod (2), and a slipper (4) mounted to the ball head (3), wherein, The ball head (3) includes a through channel (5), the slipper (4) includes an end surface (6) and a through hole (7) communicating with the end of the through channel (5), and a plastic material (8) is disposed in the gap between the slipper (4) and the ball head (3) and forms an inner coating (9) of the through hole (7), characterized in that a sealing surface (14) is disposed at the end of the through channel (5), wherein the sealing surface (14) surrounds the opening of the through channel (5) into the through hole (7), and the inner diameter of the sealing surface (14) is smaller than the inner diameter of the inner coating (9) of the through hole (7) at the end of the through hole (7) adjacent to the sealing surface (14).

2. The piston according to claim 1, characterized in that, The sealing surface (14) is conical in shape.

3. The piston according to claim 1 or 2, characterized in that, The radial outer diameter of the sealing surface (14) corresponds at least to the radial inner diameter of the inner coating (9).

4. The piston according to claim 1 or 2, characterized in that, The through channel (5) includes a first portion (11) with a reduced inner diameter, wherein the sealing surface (14) is located at the end of the first portion (11).

5. The piston according to claim 4, characterized in that, The second part (12) of the through channel (5) has the same inner diameter as the through hole (7).

6. The piston according to claim 1 or 2, characterized in that, The through hole (7) includes a radial recess (13), and the inner coating (9) extends into the radial recess (13).

7. The piston according to claim 6, characterized in that, The radial recess (13) is located on the end surface (6) of the slipper (4).

8. The piston according to claim 1 or 2, characterized in that, The slipper (4) includes a body (10) wherein the plastic material (8) extends from the gap to the outer periphery (16) of the body (10).

9. The piston according to claim 8, characterized in that, The plastic material (8) covers the front surface or front face (17) of the body (10) facing the piston rod (2).

10. The piston according to claim 8, characterized in that, The outer periphery (16) of the body includes an outer recess (18), and the plastic material (8) extends into the outer recess (18).

11. The piston according to claim 10, characterized in that, The outer recess (18) is located at the diameter of the body (10), and the diameter is larger than the diameter of the ball head (3).

12. The piston according to claim 8, characterized in that, The plastic material (8) on the exterior of the body (10) is processed at least on the surface (19) opposite to the end surface (6).

13. The piston according to claim 1 or 2, characterized in that, The end surface (6) includes a sliding element (20) made of ceramic material.

14. The piston according to claim 13, characterized in that, The sliding element (20) is in the form of a ring.

15. The piston according to claim 1 or 2, characterized in that, The plastic material (8) can be rotatably fixed to the slipper (4).

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