GB2417990A

GB2417990A - Hydrostatic displacement unit

Info

Publication number: GB2417990A
Application number: GB0517094A
Authority: GB
Inventors: Harald Kuhn
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2004-09-14
Filing date: 2005-08-22
Publication date: 2006-03-15
Anticipated expiration: 2025-08-22
Also published as: DE102004044412B4; GB0517094D0; GB2417990B; DE102004044412A1; FR2875261A1; FR2875261B1

Abstract

The invention relates to a hydrostatic displacement unit (1) in a radial piston construction comprising at least one piston (4), which is arranged in a rotor (2) and is supported on a lifting cam ring (7) by means of a rolling element (6), the rolling element (6) being arranged in the piston (4) and a pressure relief chamber (9), which is connected to the pressure chamber (11) of the piston (4), being provided for the hydrostatic relief of the rolling element (6). In order to improve the hydrostatic relief of the rolling element (6), it is proposed, according to the invention, to provide a pressure transmission means (10) for the pressure relief chamber (9). According to one configuration of the invention, the pressure transmission means (10) is configured as a step piston (12) and arranged in the piston (4).

Description

24 1 7990 Hydrostatic displacement unit The invention relates to a

hydrostatic displacement unit in a radial piston construction comprising at least one piston, which is arranged in a rotor and is supported on a lifting ring by means of a rolling element, the rolling element being arranged in the piston and a pressure relief chamber, which is connected to the pressure chamber of the piston, being provided for the hydrostatic relief of the rolling element.

Displacement units of this type are used as radial piston motors or radial piston pumps. Single-stroke configurations, for example radial piston machines that are acted on internally, in which the pistons are supported on a substantially circular lifting ring, are known in this connection. Such displacement units may also be of multiple-stroke configuration, for example radial piston machines with external piston support, the pistons being supported on a lifting ring provided with a cam track.

In such cases, the piston is supported on the lifting ring via a rolling element, for example a ball or a cylinder roller, arranged in the piston. For the hydrostatic relief of the rolling element, it is already known to provide a pressure relief chamber, which is connected to the pressure chamber of the piston, between the piston and the rolling element. However, as a result of the arrangement of the rolling element in the piston (the rolling element thus being arranged within the contour of the piston), the surface of the pressure relief chamber is constructionally delimited and smaller than the piston surface, so merely a partial hydrostatic relief of the rolling element may be achieved. If a slide bearing is arranged between the rolling element and the piston, high frictional forces occur between the rolling element and the slide bearing as a result of the merely partial hydrostatic relief. This may result in increased wear to the slide bearing. Moreover, the high frictional forces occurring between the slide bearing and the rolling element result in a braking effect on the rolling element, which counteracts rolling of the rolling element on the lifting ring, as a result of which increased wear to the rolling element or the lifting ring may occur. Furthermore, the high frictional forces cause high shear forces between the rolling element and the lifting ring, as a result of which high loads are exerted on the rolling element and the lifting ring, which reduce the service life of these components and can lead to premature failure of these components.

The object of the present invention is to provide a hydrostatic displacement unit of the type mentioned at the outset, which is improved with respect to the hydrostatic relief of the rolling element.

According to the invention, this object is achieved in that a pressure transmission means is provided for the pressure relief chamber. According to the invention, for the hydrostatic relief of the rolling element, a pressure transmission means is associated with the pressure relief chamber, as a result of which the pressure in the pressure relief chamber is higher than that in the pressure chamber of the piston, increased hydrostatic relief of the rolling element thus being achieved. This allows the non-uniform surface ratio, caused by the delimited surface of the pressure relief chamber, between the surface of the piston and the surface of the pressure relief chamber to be compensated, in the case of a rolling element arranged within the piston contour, and an almost complete hydrostatic relief of the rolling element to be achieved. This increased hydrostatic relief of the rolling element results in decreased friction and more secure rolling of the rolling element on the lifting ring, as a result of which the lifting ring, the rolling element and optionally the slide bearing are subject to less wear, increased efficiency of the displacement unit thus being achieved. As a result of the reduced mechanical loads, owing to the reduced friction on the rolling element, the lifting ring and the slide bearing, the service life of these components is also increased. The hydrostatic relief according to the invention also allows an increased pressure load capacity and improved start-up behaviour of the displacement unit to be achieved.

Particular advantages are produced if, according to one embodiment of the invention, the pressure transmission means is arranged in the piston. If the pressure transmission means is integrated into the piston, overall complexity and overall space requirements are low.

According to a preferred embodiment of the invention, the pressure transmission means is configured as a step piston. With a step piston, a transmission between the pressure in the pressure chamber, which acts on the piston, and the pressure in the pressure relief chamber, which acts to hydrostatically relieve the rolling element, may be achieved in a simple manner.

The step piston expediently comprises a first control surface, which is connected to the pressure chamber, and a second control surface, which is connected to a pressure transmission chamber connected to the pressure relief chamber, the first control surface being larger than the second control surface. A suitable surface ratio of the first control surface to the second control surface allows a desired pressure transmission, and thus a desired hydrostatic relief, to be adjusted in a simple manner.

According to an advantageous development of the invention, the step piston is provided with a stop valve means, by means of which the pressure transmission chamber may be connected to a container. With a stop valve means, after-suction for the pressure transmission chamber may be achieved in a simple manner.

The stop valve means is expediently configured as a check valve, in particular a spring-loaded check valve, which is open toward the pressure transmission chamber.

If a connection line, which is connected to the pressure chamber, is connected to the pressure transmission chamber, the pressure transmission chamber, and thus the pressure relief chamber, may be supplied with pressure medium from the pressure chamber in a simple manner.

It is particularly advantageous if the connection of the connection line to the pressure transmission chamber may be activated by the step piston, wherein when the pressure chamber is discharged, the connection of the connection line to the pressure transmission chamber is open and when there is pressure in the pressure chamber, the connection of the connection line to the pressure transmission chamber is shut off. As a result of this activation of the connection of the pressure chamber to the pressure transmission chamber by the step piston, it may easily be achieved that when the pressure chamber is discharged, the pressure relief chamber is connected to the pressure chamber, for supplying pressure medium, and when there is pressure in the pressure chamber during operation of the displacement unit, this connection is shut off in order to generate in the pressure transmission chamber, and thus in the pressure relief chamber, increased pressure for the increased hydrostatic relief of the rolling element.

In a development of the invention, it is provided that the step piston is actively connected to a spring, which opposes the pressure on the first control surface. A spring of this type allows the step piston to be forced in a simple manner, when the pressure chamber is discharged, into a position in which the pressure transmission chamber is connected to the pressure chamber via the connection line.

A spring chamber receiving the spring is expediently discharged into a container.

The spring chamber may be discharged into the container in a simple manner if a connection line connecting the spring chamber to the housing interior of the displacement unit, which is discharged into the container, is configured in the piston.

A low overall complexity of the arrangement of the step piston within the piston may be achieved if the step piston, according to one embodiment of the invention, is arranged in a bore, which is guided from the pressure chamber to the pressure relief chamber, in the piston, the pressure transmission chamber and the spring chamber being configured between the step piston and the bore.

The stop valve means connecting the pressure transmission chamber to the container may be produced with low overall complexity if the stop valve means is arranged in a connection bore, which is guided from the second control surface to the spring chamber, in the step piston.

According to a preferred embodiment of the displacement unit, in which the rolling element is configured as a cylinder roller and a slide bearing is arranged between the piston and the rolling element, the pressure relief chamber may be formed in a simple manner by a recess in the slide bearing.

Further advantages and details of the invention will be described below in greater detail with reference to the embodiment illustrated in the schematic figures, in which: Figure 1 is a partial cross section through a displacement unit according to the invention; Figure 2 is a longitudinal section through Figure 1; Figure 3 is a plan view of the piston of Figure 1; and Figure 4 is an enlarged view of a longitudinal section according to Figure 2.

Figure 1 is a basic, partial cross section through a multiple-stroke displacement unit 1, which is configured as a radial piston machine with external piston support.

The displacement unit 1 comprises a rotor 2, which is configured as a cylinder block and is rotatably mounted about an axis of rotation (not shown in greater detail). The rotor 2 is provided with cylinder bores 3, which are arranged in a star-shaped configuration and in each of which a piston 4 is arranged. The piston 4 is supported by means of a rolling element 6, which is configured as a cylinder roller 5, on a lifting ring 7, which is provided with a cam track. The rolling element 6, as may be seen from Figures 1 to 3, is arranged within the circular contour of the piston 4. The piston 4, as shown in Figure 2, is provided with lateral webs 4a, 4b for axially securing and guiding the rolling element 6.

A slide bearing 8, which is provided in its central region with a pocketlike recess, which forms a pressure release chamber 9, which is connected to the pressure chamber 11, which is configured between the cylinder bore 3 and the piston 4, for the hydrostatic relief of the rolling element 6, is arranged between the piston 4 and the rolling element 6. As a result of the arrangement of the rolling element 6 within the contour of the piston 4 and the configuration of the pressure relief chamber 9 in the slide bearing 8, the pressure relief chamber 9, as may be seen from Figure 3, comprises a surface, which is smaller than the circular surface, which is acted on by the pressure, of the piston 4.

According to the invention, a pressure transmission means 10, by means of which a higher pressure may be generated in the pressure relief chamber 9 than in the pressure chamber 1 1 between the cylinder bore 3 and the piston 4, is arranged in the piston 4.

The pressure transmission means 10, as illustrated in Figure 4, is configured as a step piston 12, which is arranged in a stepped bore 13 in the piston 4. The bore 13 in the piston 4 extends from the pressure chamber 11, which is configured between the piston 4 and the cylinder bore 3, to the pocket-like recess formed in the slide bearing 8, and thus to the pressure relief chamber 9.

The step piston 12 comprises a first portion, on the end face of which a first control surface 14 is configured. The first control surface 14 is acted on by the pressure in the pressure chamber 1 1. A second control surface 15 is configured at the opposing end face of the step piston 12, the second control surface 15 being configured on a second portion of the step piston 12, which second portion has a smaller diameter than the first portion. The second control surface 15 is arranged in a pressure transmission chamber 16, which is configured between the step piston 12 and the bore 13 and is connected to the pressure relief chamber 9.

A spring chamber 17 containing a spring 18, which forces the step piston 12, counter to the pressure on the first control surface 14, into the illustrated position, in which the step piston 12 abuts a retaining means 20, for example a retaining ring, which is arranged in the bore 13, is configured between the bore 13 and the first portion of the step piston 12. The spring chamber 17 is connected to the housing interior of the displacement unit 1, which is discharged into a container, via a connection line 19, which is configured in the piston 4.

A stop valve means 22 is arranged in the step piston 12 for the aftersuction of pressure medium into the pressure transmission chamber 16. The stop valve means 22 is arranged in a connection bore 23, which is guided from the second control surface 15 to the spring chamber 17, and is configured as a spring-loaded check valve 24, which is open toward the pressure transmission chamber 16.

A connection line 21, which is configured in the piston 4 and is connected to the pressure chamber 11, is connected to the bore 13 in the region of the pressure transmission chamber 16. The opening of the connection line 21 into the pressure transmission chamber 16 is arranged on the bore 13 and may be activated by the step piston 12 such that, in the illustrated position of the step piston 12, the step piston 12 being held by the spring 18 in abutment against the retaining means 20, the opening is partially open and the pressure chamber 11 is thus connected to the pressure transmission chamber 16 via the connection line 21.

When there is pressure in the pressure chamber 11, and thus on the first control surface 14, the step piston 12 is forced, counter to the spring 18, in the downward direction as shown in Figure 4, the opening of the connection line 21 into the bore 13 being shut off by the step piston 12, and a pressure, which, in accordance with the surface ratio of the first control surface 14 to the second control surface 15 of the step piston, is higher than the pressure in the pressure chamber 11, thus being generated in the pressure transmission chamber 16, which is connected to the pressure relief chamber 9.

When there is pressure in the pressure chamber 11, an increased pressure may thus be generated in the pressure relief chamber 9 by the pressure transmission means 10 during operation of the displacement unit 1, so despite the surface of the pressure relief chamber 9, which is smaller than the surface of the piston 4, and thus the non-uniform surface ratio between the surface of the piston 4 and the surface of the pressure relief chamber 9, an almost complete hydrostatic relief of the rolling element 6 may be achieved in the case of a rolling element 6 arranged within the piston contour.

Claims

Claims 1. A hydrostatic displacement unit in a radial piston construction

comprising at least one piston, which is arranged in a rotor and is supported on a lifting ring by means of a rolling element, the rolling element being arranged in the piston and a pressure relief chamber, which is connected to the pressure chamber of the piston, being provided for the hydrostatic relief of the rolling element, characterized in that a pressure transmission means is provided for the pressure relief chamber.
2. A hydrostatic displacement unit according to claim 1, characterised in that the pressure transmission means is arranged in the piston.
3. A hydrostatic displacement unit according to either claim 1 or claim 2, characterized in that the pressure transmission means is configured as a step piston.
4. A hydrostatic displacement unit according to claim 3, characterized in that the step piston comprises a first control surface, which is connected to the pressure chamber, and a second control surface, which is connected to a pressure transmission chamber connected to the pressure relief chamber, the first control surface being larger than the second control surface.
5. A hydrostatic displacement unit according to either claim 3 or claim 4, characterized in that the step piston is provided with a stop valve means, by means of which the pressure transmission chamber may be connected to a container.
6. A hydrostatic displacement unit according to claim 5, characterized in that the stop valve means is configured as a check valve, in particular a spring-loaded check valve, which is open toward the pressure transmission chamber.
7. A hydrostatic displacement unit according to any one of claims 4 to 6, characterised in that a connection line, which is connected to the pressure chamber, is connected to the pressure transmission chamber.
8. A hydrostatic displacement unit according to claim 7, characterised in that the connection of the connection line to the pressure transmission chamber may be activated by the step piston, wherein when the pressure chamber is discharged, the connection of the connection line to the pressure transmission chamber is open and when there is pressure in the pressure chamber, the connection of the connection line to the pressure transmission chamber is shut off.
9. A hydrostatic displacement unit according to any one of claims 4 to 8, characterised in that the step piston is actively connected to a spring, which opposes the pressure on the first control surface.
10. A hydrostatic displacement unit according to claim 9, characterised in that a spring chamber receiving the spring is discharged into a container.
1 1. A hydrostatic displacement unit according to claim 10, characterised in that a connection line connecting the spring chamber to the housing interior of the displacement unit is configured in the piston.
12. A hydrostatic displacement unit according to any one of claims 3 to 11, characterised in that the step piston is arranged in a bore, which is guided from the pressure chamber to the pressure relief chamber, in the piston, the pressure transmission chamber and the spring chamber being configured between the step piston and the bore.
13. A hydrostatic displacement unit according to any one of claims 5 to 12, characterised in that the stop valve means is arranged in a connection bore, which is guided from the second control surface to the spring chamber, in the step piston.
14. A hydrostatic displacement unit according to any one of the preceding claims, characterised in that the rolling element is configured as a cylinder roller and a slide bearing is arranged between the piston and the rolling element, the pressure relief chamber being formed by a recess in the slide bearing.