Hydraulic drive device with a sinking piston

Abstract

The invention relates to a piston (1), in particular for receiving into a cylinder bore (2) of a hydraulic drive device, such as an axial piston machine, having a first piston section (1A) with a first peripheral surface, a second piston section (1B) with a second peripheral surface and an end surface (1C), wherein the second peripheral surface directly adjoins the first peripheral surface in the direction of a centre axis (3) of the piston (1) and directly adjoins the end surface (1C), wherein the first peripheral surface of the first piston section (1A) is cylindrically configured about the centre axis (3), and wherein the second piston section (1B) has a maximum diameter which is smaller than the diameter of the first piston section (1A). Furthermore, the invention relates to a cylinder bore (2) in a hydraulic drive device, which matches such a piston, and to a hydraulic drive device having such a piston (1) and cylinder bore (2).

Description

Technical Field

[0001] This invention relates to a piston for use in a hydraulic drive device. Furthermore, this invention relates to a drive device having such a piston and a method for manufacturing the piston. Background Technology

[0002] Hydraulic drives, such as axial piston machines, are well known in the prior art. In a swashplate-designed axial piston machine, there exists a cylinder, which typically contains multiple cylinder bores. Each cylinder bore within the cylinder can receive a piston, which can translate and rotate within the bore during operation.

[0003] For example, DE 10 2022 206 073 A1 describes such a cylinder bore in an axial piston machine. The bore has two axially spaced support regions on which the piston can slide. The first support region facing the slide of the axial piston machine has a larger axial length than the support region facing the pressure chamber. Thus, the first support region can withstand higher loads occurring in the corresponding region, and the shorter sealing length of the second support region improves lubrication. Furthermore, the overall axial support generated by the two support regions remains large, and excessive surface pressure, such as that caused by piston tilting, is avoided.

[0004] The inner surface of the cylinder bore is typically manufactured by reaming. Shape accuracy and quality are crucial for function, especially the piston's sealing and sliding ability within the bore. For this purpose, the bore is first formed with a small machining allowance. The bottom of the cylinder bore is usually cut flat in another step, by turning and milling, because drills typically produce a tapered tip. The machining allowance is then eliminated using a reamer. However, reamers, similar to drills, have a kerf with a diameter smaller than their rated diameter. At this kerf, the reamer cannot cut to the desired extent, leaving a small, unreamed portion at the end or bottom of the cylinder bore. Traditional reamers and their kerfs are known, for example, from the website https: / / www.lehrerfreund.de / technik / 1s / reiben / 3102. Modern reamers with kerfs are known, for example, from EP 2 895 289 B1.

[0005] To remove this excess portion, a hinterstich is used in the prior art. The hinterstich, often made as a backing, has a diameter slightly larger than the diameter of the reamed cylinder bore. Therefore, the piston can be pushed forward all the way to the bottom of the bore, but sealing inevitably ceases at the height of the hinterstich.

[0006] However, manufacturing such a groove is quite complicated. In addition, there is a risk that the surface that has already been reamed during the manufacturing of the groove may be damaged by the cutting tool during the introduction process, thereby compromising the seal between the cylinder bore and the piston. Summary of the Invention

[0007] Therefore, the objective of this invention is to simplify the manufacturing process and provide a hydraulic drive, particularly an axial piston machine, in which the aforementioned problems are avoided or mitigated.

[0008] This task is accomplished by a piston for a hydraulically driven device as claimed in claim 1, a cylinder bore matching such a piston as claimed in claim 4, a piston-cylinder unit as claimed in claim 7, and a method as claimed in claim 8. Advantageous improvements are the subject of the dependent claims.

[0009] In particular, the task is accomplished by a piston, especially for reception in a cylinder bore of a hydraulically driven device, having a first piston section having a first circumferential surface, a second piston section having a second circumferential surface, and an end face, wherein the second circumferential surface is directly adjacent to the first circumferential surface and directly adjacent to the end face along the direction of the central axis, wherein the first circumferential surface of the first piston section is cylindrical about the central axis, and wherein the maximum diameter of the second piston section is smaller than the diameter of the first piston section. In other words, a short, recessed second section with a smaller diameter than the first section is provided at the "front" end of the piston. This eliminates the need for the side-concave arrangement explained in the prior art or the cumbersome finishing of the bottom or outlet of the cylinder bore. Furthermore, this second section extends into the outlet of the cylinder bore as a recessed piston member, thereby reducing the dead-point volume between the piston and the cylinder bore.

[0010] Preferably, the second circumferential surface is cylindrical. The piston is manufactured, for example, by turning, in which the first section, in particular, can undergo further material removal, such as grinding, to produce the necessary dimensional accuracy and surface quality for hydraulic sealing within the cylinder bore. Therefore, the second circumferential surface can be easily manufactured in a clamping device having the first circumferential surface. However, because the surface quality of the second surface, separated from the inner surface of the cylinder bore, may be lower, simple manufacturing of the second circumferential surface, such as turning using a roughing tool, is sufficient. In this way, the second circumferential surface can be manufactured inexpensively without significant overhead.

[0011] Furthermore, the present invention provides a cylinder bore, specifically for receiving a piston in a hydraulically driven device such as an axial piston machine, having: a first bore section manufactured by reaming, the diameter and length of which are determined such that the first section of the piston, as explained above, can be received in the bore section of the cylinder bore in a hydraulically sealed and longitudinally movable manner; and a second bore section adjacent to the bottom of the cylinder bore and manufactured differently from the first bore section due to the cutting edge of the reamer used during reaming, particularly gradually becoming a truncated cone shape, wherein the length of the second bore section is less than or equal to the axial length of the second piston section.

[0012] The piston, as explained above, preferably works in conjunction with the cylinder bore, where the grooving process described above as prior art can be abandoned. Dead center volume is further reduced, especially since no additional space is provided in the cylinder through grooving. Furthermore, the lengths of the piston and bore can remain unchanged compared to previous designs, thus maintaining a structural series with corresponding piston and cylinder bores without power loss or significant redesign.

[0013] For such a cylinder bore, the initial hole is preferably formed cylindrically by turning and / or drilling. The cylinder bore can then be matched to the diameter of the first section of the piston by reaming the first drilled section. Conventionally, a hole is introduced into the workpiece that is undersized relative to the piston for which it is designed. The hole is then reamed by means of a reamer, that is, a smaller additional portion of the material is removed from the periphery by cutting to achieve the inner diameter of the cylinder bore that matches the piston diameter. If the hole is made with conventional tools, a cylindrical inner profile is created at least in the lower portion of the drilled hole by the rotation of the tool during drilling and reaming, in which the piston should later move.

[0014] Furthermore, it is preferable to perform heat treatment, particularly quenching, and preferably nitriding, on the cylinder bore after reaming. In this way, the quenched cylinder bore can better withstand the loads acting on it. In addition, the manufacture of the bore is more complicated than that of the piston to be installed in the bore, so it is suitable to design the bore primarily for wear resistance, because the piston can be manufactured more easily than the bore it belongs to, and thus more easily replaced.

[0015] According to the present invention, a piston-cylinder unit is provided having a piston and a cylinder bore as explained above, wherein the piston is mounted in the cylinder bore such that a second section of the piston does not contact the outer wall of the cylinder bore at any position of the piston within the cylinder bore. Hydraulic drives, such as axial piston machines, in particular have multiple such piston-cylinder units, which form the main part of the hydraulic drive.

[0016] Another embodiment of the invention is a method for manufacturing the aforementioned piston-cylinder unit, the method comprising the steps of: manufacturing an initial cylinder bore having an initial circumferential surface and a bottom, wherein the initial circumferential surface is cylindrical about a central axis and directly adjacent to the bottom; and manufacturing a completed circumferential surface of the cylinder bore, starting from the initial cylinder bore, by means of a reamer, the reamer having a tapered cut at its end side. According to the invention, the corresponding completed circumferential surface has first, second, and third sections, which are directly adjacent to each other in the given order along the direction of the central axis of the cylinder bore or piston-cylinder unit. The third section is directly adjacent to the bottom, wherein this third section is formed from the initial circumferential length not machined by the reamer. The tapered second section is formed by the cut of the reamer. The first section is cylindrical about a central axis, wherein its diameter is larger than the diameter of the initial circumferential surface.

[0017] In another step of this design, a piston is manufactured as explained above, wherein the first circumferential surface of the piston is matched with the first section of the cylinder bore for fluid sealing, and wherein the second circumferential surface is formed along the central axis to be equal to or longer than the sum of the second and third sections of the cylinder bore. The maximum diameter of the second circumferential surface is thus chosen to be smaller than the diameter of the first section, so that when the piston end face abuts against the bottom of the cylinder bore, the second circumferential surface has a gap relative to the second and third sections of the cylinder bore. Finally, the piston is installed into the cylinder bore thus formed.

[0018] This method avoids the problem of lateral recesses in the cylinder bore, which has traditionally been used to prevent parts of the bore that cannot be machined by reaming from contacting the piston, which could otherwise cause the piston to seize and potentially damage the hydraulic drive. Instead, the piston end is machined slightly narrower, making it impossible for it to contact the cylinder bore wall.

[0019] The original cylinder bore can preferably be manufactured by turning and / or drilling. Drilling can be performed after turning. Of course, other methods for manufacturing cylinder bores are also conceivable in principle, such as etching or additive methods such as sintering and 3D printing. However, such methods are significantly more expensive than the preferred method of turning and drilling in the current art.

[0020] Furthermore, it is preferable to form the original cylinder bore and the finished cylinder bore from a single, integrated cylinder block. Alternatively, an additional bushing, for example made of brass, can be fitted into the cylinder bore. The piston then runs on the brass bushing. Moreover, such a bushing avoids the lateral concavity described earlier in the prior art. However, a disadvantage of using a bushing is the need for another component, which is also costly to manufacture. Additionally, this other component must also be installed. In summary, a single, integrated cylinder block reduces costs.

[0021] The cylinder block is preferably the cylinder barrel of an axial piston machine, and this cylinder barrel is preferably constructed in a swashplate configuration. For other embodiments of swashplate machines that are hydraulically driven, a conical piston is typically used, which runs through a cylindrical cylinder bore via piston rings. Therefore, the present invention is almost irrelevant to such swashplate machines. Attached Figure Description

[0022] Figure 1 This is an illustration of a hydraulically driven device having a piston from the prior art, the piston having a relatively long groove formed in the cylinder bore; Figure 2 This is an illustration of a hydraulically driven device having a piston from the prior art, the piston having a short groove formed in the cylinder bore; Figure 3 It is an image of a cylinder bore with a shoulder caused by reaming; Figure 4 To illustrate the problem being addressed, a conventional piston in the cylinder bore of a hydraulic drive is shown, wherein in this figure not only the piston but also (as in...) Figure 1 and 2 (Similarly) the holes were not machined separately after reaming; and Figure 5 As shown in the previous figure, a sinking piston according to the invention is shown in the orifice of a hydraulic drive device. Detailed Implementation

[0023] The embodiments of this disclosure are described below, and prior art to date is also described based on the accompanying drawings for a better understanding of the invention.

[0024] Figure 1 A hydraulic drive device with a piston 10 from the prior art is shown, the piston having a relatively long groove 201 formed in a cylinder bore 20.

[0025] In an axial piston machine with a swashplate design, which serves as an example of a hydraulically driven device, there is a cylinder 5. One or more cylinder bores 20 in the cylinder 50 (only one cylinder bore 20 is shown here in a cut-off portion of the cylinder 50 for simplicity) are capable of receiving a piston 10, which can move translationally and rotationally, especially rotatably, within the cylinder 20 during operation.

[0026] At the end of this cylinder bore (whose circumferential surface is mostly machined by reaming, as its shape accuracy and quality are very important for function, especially sealing), there is usually a so-called groove 201 or backing. The diameter of this groove 201 or backing is larger than the diameter of the cylinder bore 20.

[0027] The shovel groove 201 has a background in both manufacturing technology and function.

[0028] In pump operation, long grooves are typically implemented to facilitate better sliding and pressure film formation between the outer peripheral surface 10A of the piston 10 and the cylinder bore 20, or simply the "cylinder". This results in less friction between the piston 10 and the cylinder bore 20, leading to better efficiency. Simultaneously, the piston end face 10B can be pushed all the way to the bottom of the cylinder bore 20, thus reducing the dead-point volume, because the groove 201 creates a flat end face 20C within the cylinder bore 20.

[0029] During the pressure rise (high pressure side), the piston moves into the cylinder and passes over a fixed edge (the beginning of the slot 201), whereby oil is drawn into the gap during operation to form a pressure pad that creates a lubricating film between the piston 10 and the cylinder bore 20.

[0030] For hydraulically driven devices or axial piston motors, or in their motor-driven operation, short grooves 201 are typically achieved because the piston direction is reversed during the pressure rise. This is evident from existing technologies. Figure 2 As shown in the diagram. In the case of a long groove 201, the oil will be sheared at the edges of the groove and will not form a suitable pressure pad. Therefore, the piston edge, which is then supported in the cylinder bore, is utilized here. Other features are as follows: Figure 1 There is no difference from existing technology.

[0031] In manufacturing, it's not possible to ream all the way to the bottom of the hole. This is due to the type of reamer used, which has a certain kerf. EP 2 895 289 B1 illustrates an example of such a reamer. Using such a reamer will always leave a shoulder in the cylinder bore without a notch. This is evident in... Figure 3 As shown in the figure, Figure 3 The cylinder bore 2 according to the invention is shown.

[0032] according to Figure 3 The cylinder bore 2 is first manufactured continuously with a small machining allowance, so that the cylinder bore 2 up to the bottom 2C first has a circumferential surface 2B. In the next step, this circumferential surface 2B is reamed to a circumferential surface 2A with a slightly larger diameter using a reamer. Because the reamer has a cutting edge as explained above, a section of cylinder bore 2 with the unreamed hole diameter and circumferential surface 2B is left near the bottom of the hole, as produced from the profile of the reamer, along with a short transition zone 2D from the reamed circumferential surface 2A to surface 2B, which is not further explained here.

[0033] Unlike existing technologies, according to the present invention, the cylinder bore 2 is only machined in such a way that... Figure 3As shown in the diagram, instead of grooving as explained earlier, the machining allowance of the circumferential surface 2B up to the bottom of the hole 2C is left in the cylinder bore 2.

[0034] If a traditional piston is inserted into such a machined hole, it will be as follows: Figure 4 The image shows a collision between piston 1 and cylinder bore 2. Specifically, the piston will... Figure 4 The piston is pressed against the circumferential surface 2B at face 1B and may be connected to it by friction welding or "piston biting". To avoid this, the piston could be shortened accordingly so that it no longer extends all the way to the unreamed face. However, this would not only reduce mechanical efficiency (i.e., draw greater friction from a smaller piston length through higher lateral forces) but also worsen hydraulic efficiency. That is, the piston end 1C is thus further away from the bore bottom 2C, thereby increasing the dead-point volume. Therefore, the manufacturing of the groove has so far generally been achieved as explained above, although it is very costly and has other known disadvantages (especially the risk of damage to the sealed reamed face). That is, this known design is as compact as possible and achieves high efficiency due to the small dead-point volume.

[0035] As in Figure 5 As shown, the present invention addresses the problem by employing a novel external profile of the piston 1. As in the prior art, starting from the first piston section 1A, a second piston section 1B with a second circumferential surface is formed on the front side of the piston 1 near the end face 1C. This second piston section directly abuts the end face 1C and transitions into the first piston section. This second piston section 1B has a maximum diameter smaller than the diameter of the first piston section 1A and, in particular, smaller than the diameter of the unreamed cylinder bore 2B. Furthermore, the second piston section 1B is slightly longer than the unreamed region 2B of the cylinder bore 2 (together with the transition region 2D). This avoids collisions between the piston 1 and the cylinder bore 2 that would occur without such machining. Simultaneously, the external machining of the piston 1 in the second piston section 1B, such as by turning and / or grinding, is significantly less expensive than the costly grooving machining of the prior art.

[0036] Furthermore, by maintaining an effective piston length, neither the dead center volume nor the lateral force (relative to existing technologies with short grooves) changes significantly. Ultimately, by being able to omit the groove and instead reduce the piston diameter in the second piston section 1B, even the dead center volume is slightly reduced, because with the same groove length and the piston section 1B being machined round, a (negligible) smaller volume is additionally generated due to the smaller diameter of the limiting surface.

[0037] While the turning of the second piston section was mentioned in the previous embodiment, the second piston section does not necessarily need to be turned round. The important thing is that its extension parallel to the central axis is at least slightly greater than the remaining overhangs 2B and 2C of the cylinder bore 2 after reaming. For example, the second piston section may also be provided with a polygonal or elliptical external shape, as long as this external shape cannot come into contact with the unreamed (or otherwise machined after drilling) sections 2C and 2D of the cylinder bore 2 after assembly.

Claims

1. A piston (1), particularly for receiving into a cylinder bore (2) of a hydraulically driven device, said piston having: -The first piston section (1A) with the first circumferential surface; -The second piston section (1B) with a second circumferential surface; and -End face (1C); -The second circumferential surface is directly adjacent to the first circumferential surface and directly adjacent to the end face (1C) along the direction of the central axis (3) of the piston (1). -The maximum diameter of the second piston section (1B) is smaller than the diameter of the first piston section (1A).

2. The piston (1) according to claim 1, characterized in that, The second circumferential surface is cylindrical.

3. The piston (1) according to claim 1 or 2, characterized in that, The piston (1) is hardened.

4. A cylinder bore (2) specifically designed for receiving a piston (1) according to any one of claims 1 to 3, particularly in a hydraulically driven device, comprising: - A first bore section (2A) manufactured by reaming, the diameter and length of which are determined such that the first piston section (1A) of the piston (1) to be received can be received in a hydraulically sealed and longitudinally movable manner in the first bore section (2A) of the cylinder bore (2). - The second hole section (2B), which is adjacent to the bottom (2C) of the cylinder bore (2) and is machined differently from the first hole section (2A) due to manufacturing reasons, especially not reamed and / or gradually becomes a truncated cone shape. -The length of the second hole section (2B) is less than or equal to the axial length of the second piston section (1B) of the piston (1) to be received.

5. The cylinder bore (2) according to claim 4, wherein the original bore is cylindrically formed by turning and / or drilling and the cylinder bore (2) is matched with the diameter of the first piston section (1A) of the piston (1) to be received by reaming the first bore section (2A).

6. The cylinder bore (2) according to claim 4 or 5, wherein the cylinder bore (2) is heat-treated, especially quenched and preferably nitrided.

7. A piston cylinder unit having a piston (1) according to any one of claims 1 to 3 and a cylinder bore (2) according to any one of claims 4 to 6, wherein the piston (1) is mounted in the cylinder bore (2) such that the second piston section (1B) does not contact the outer wall of the cylinder bore (2) in any position of the piston (1) while mounted in the cylinder bore (2).

8. A method for manufacturing a piston cylinder unit according to claim 7, comprising the following steps: - Manufacture an original cylinder bore with an original circumferential surface and a bottom (2C), wherein the original circumferential surface is formed cylindrically about the central axis (3) directly adjacent to the bottom (2C); - As a cylinder bore (2), the completed circumferential surface of the cylinder bore is manufactured by means of a reamer, starting from the original cylinder bore, wherein the corresponding completed circumferential surface has a first segment (2A), a second segment (2D) and a third segment (2B), which are directly adjacent to each other in the direction of the central axis (3) in the given order, wherein the third segment (2B) is directly adjacent to the bottom of the bore (2C), wherein the third segment (2B) is formed by the original circumferential surface that has not been processed by the reamer, wherein the tapered second segment (2D) is formed by the cut of the reamer, and wherein the first segment (2A) is cylindrical about the central axis (3) of the original cylinder bore, wherein its diameter is larger than the diameter of the original cylinder bore. - Manufacture a piston (1) according to any one of claims 1 to 3, wherein the circumferential surface of the first piston section (1A) of the piston (1) fluid-tightly matches the first section (2A) of the cylinder bore (2), wherein the circumferential surface of the second piston section (1B) of the piston (1) is formed along the direction of the central axis (3) to be equal to or longer than the sum of the second section (2D) and the third section (2B) of the cylinder bore (2), wherein the maximum diameter of the circumferential surface of the second piston section (1B) is selected to be smaller than the diameter of the first section (2A) of the cylinder bore (2), such that when the end face (1C) of the piston (1) abuts against the bottom of the cylinder bore (2), the circumferential surface of the second piston section (1B) has a gap relative to the second section (2D) and the third section (2B) of the cylinder bore (2), and - Install the piston (1) into the completed cylinder bore (2).

9. A method according to claim 8, wherein the original cylinder bore and the finished cylinder bore are formed by an integral cylinder block.

10. The method according to claim 8 or 9, wherein the cylinder body having the cylinder bore (2) and / or the piston (1) are subjected to heat treatment, particularly nitriding, after the final material removal of the cylinder bore (2) and the piston (1), especially after reaming of the cylinder bore (2).

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