WO2025061520A1 - Radial piston compressor - Google Patents

Abstract

The present invention relates to a radial piston compressor comprising a compressor unit (1) and a drive device (2) for driving the compressor unit (1), wherein: the compressor unit (1) comprises a plurality of combinations (13) of piston and working chamber, said combinations being disposed radially around an eccentric shaft (11, 12); the eccentric shaft (11, 12) is driven by the drive device (2); each combination (13) of piston and working chamber comprises a piston (132) having a piston axis (K) and having a center of mass (M); the compressor unit (1) comprises a piston guide ring (14); the pistons (132) are each equipped with a contact face (1321) for the piston guide ring (14); the piston guide ring (14) is in contact with the contact face (1321); the contact face (1321a) of the pistons (132) is oriented at an inclination toward the piston axis (K).

Description

Radial piston compressor

The present invention relates to a radial piston compressor according to the preamble of claim 1.

A radial piston compressor is a fluid power component. Unlike an axial piston compressor, this type of compressor has at least one piston-working chamber combination arranged radially and perpendicular to the drive shaft. A radial piston compressor can also be referred to as a compressor based on the radial piston principle.

The piston's displacement or reciprocating motion is usually driven by an eccentric. Therefore, the drive shaft with the eccentric can also be referred to as an eccentric shaft. Radial piston compressors typically comprise several piston-working chamber combinations that extend radially from the eccentric shaft in a star-shaped pattern.

A piston-working chamber combination essentially comprises a working chamber, also called a cylinder, and a piston that moves up and down within the working chamber. The piston has a central geometric piston axis that coincides with the piston's direction of travel. In a radial piston compressor with an eccentric shaft, the piston has a contact surface on its side facing the eccentric shaft, against which the eccentric disc impacts or rests during rotation of the eccentric shaft. The eccentric shaft has an axis of rotation about which the eccentric shaft is rotated. When the eccentric impacts the contact surface, the piston moves upwards, compressing a medium in the working chamber. The return movement of the piston can be achieved, for example, by piston guide rings that are in contact with the piston. In this way, the piston can be moved back to a lower low point until the eccentric disc hits the piston crown again.

Radial piston compressors are used, for example, to compress coolant in automotive air conditioning systems, especially in electrically powered vehicles. A coolant such as CO2 can be used as the compressed medium. However, other media or coolants are also conceivable. A radial piston compressor of the aforementioned type is known, for example, from DE 10 2020 211 680 A1 and from the patent application DE 10 2022 133 723 A1, which was unpublished at the time of this application.

For a radial piston compressor that uses an eccentric to move the piston to TDC (top dead center) and a piston guide ring for return to BDC (bottom dead center), the use of a single-sided piston guide ring may be necessary for certain space- or cost-related reasons. The return force (with asymmetric force application) leads to a tilting moment of the piston. This tilting leads to adverse effects in the piston drive.

Previous solutions rely on the piston guide ring on both sides with a rectangular cross-section, whereby the symmetrical force introduction eliminates the tilting.

Other solutions of a central piston guide ring (piston guide ring arranged in the center of the piston) are complicated and therefore more costly to manufacture and assemble.

This is where the present invention comes in and sets itself the task of proposing an improved radial piston compressor, in particular a radial piston compressor whose pistons are exposed to less tilting moment when using only one piston guide ring.

According to the invention, this object is achieved by a radial piston compressor having the characterizing features of claim 1. Due to the fact that the contact surface of the pistons is inclined in the direction of the piston axis, a contact surface for the piston guide ring is provided, which can contribute to reducing a tilting moment caused by a piston guide ring attached on one side.

In other words, by using a suitable contour in the contact area between the piston guide ring and the piston, the force causing a tilting moment is significantly reduced. In particular, the solution proposed here introduces the contact force in such a way that the majority of the force vector passes through the center of mass of the piston, thus preventing a tilting moment from being generated. If the use of a single, single-sided guide ring is necessary, for example, due to space constraints, cost requirements, etc., tilting can be significantly reduced. For example, a reduction in the tilting moment of approximately 10% is possible. The reduced tilting results in less wear, lower noise levels, and more harmonious dynamics.

Further advantageous embodiments of the proposed invention emerge in particular from the features of the subclaims. The subject matter and features of the various claims can, in principle, be combined with one another in any desired manner.

In an advantageous embodiment of the invention, a perpendicular to the contact surface can be provided to intersect the center of mass of the piston. In this case, it is expected that the retraction force, relative to its direction, will also intersect the center of mass of the piston, so that a tipping moment can be counteracted as effectively as possible.

In an advantageous embodiment of the invention, it can be provided that only one piston guide ring is arranged on one side of the piston or piston axis. Such a design can be advantageously realized with the inclined contact surface of the piston proposed by the invention. Installation space and costs can be saved. At the same time, the design-related, but undesirable, tilting moment of the piston can be reduced.

In a further advantageous embodiment of the invention, it can be provided that the contact surface of the pistons is inclined at an angle a in the direction of the piston axis, wherein the angle a is between 40° and 75°, in particular between 45° and 60°, preferably at an angle a = 55° to the piston axis.

With a piston-side contact surface aligned at an angle of 55° relative to the piston axis, a reduction in the tilting moment of the piston of about 10% can be achieved purely mathematically compared to a contact surface aligned perpendicular to the piston axis.

In a further advantageous embodiment of the invention, it can be provided that the piston guide ring has a rectangular cross-section, wherein one edge of the piston guide ring rests on the contact surface of the piston. In a further advantageous embodiment of the invention, the piston guide ring can be provided with a contact surface on its inner side that is in contact with the contact surfaces of the pistons. In such an embodiment, a surface is also provided on the inner ring side, which faces the contact surface of the respective piston and preferably bears against it in a form-fitting manner. Here, the contact surface of the inner ring can also be designed or aligned to correspond to the contact surface of the piston, so that a largely form-fitting contact can be achieved.

In a further advantageous embodiment of the invention, it can be provided that the contact surface of the piston guide ring has a shape corresponding to the contact surface of the piston. In this case, a surface-to-surface pairing is particularly conceivable, which preferably have the same orientation with regard to the piston axis. However, other surface designs are also conceivable in order to achieve the desired effect of reducing the tilting moment of the piston. In particular, in order to reduce the resulting tilting moment to a minimum, it is proposed that the surface on the ring pointing perpendicular to the return force (directed towards the piston) also be designed conically so that the contact point is as close as possible to the center of mass.

In a further advantageous embodiment of the invention, the contact surface of the piston can be provided as part of a dovetail-shaped recess in the piston. The inclined surface can be introduced into the piston in the form of a dovetail cutter.

In a further advantageous embodiment of the invention, the piston guide ring can have a conical cross-section, at least in sections. This configuration is particularly suitable when the contact surface of the piston is designed as part of a recess with a dovetail cross-section.

In a further advantageous embodiment of the invention, it can be provided that the contact surfaces of the piston guide ring and piston are designed exactly parallel or with a slight gap in the corresponding direction for shifting the contact point into a preferred position. In particular, with a ring with a conical design and an inclined contact surface parallel to the piston axis, the contact point is automatically set at the upper end of the ring. In contrast, with two parallel surfaces, the contact point can be depending on tolerances, parallelisms, inclinations due to assembly and/or dynamics during operation.

As outlined above, a gap can also be provided at the contact surface to influence the contact with the "dovetail." However, this is not a direct gap; instead, the angle a on the piston guide ring is slightly different, resulting in a point contact. With this displacement, it is preferable to check that the force component perpendicular to this surface also hits the center of mass.

The gap can be used to preferably influence the position of force O2 so that it has the smallest possible lever arm H1 relative to the center of mass. The contact surface of the piston guide ring with the surface of the piston parallel to the piston axis is preferably designed with an angular difference, i.e., it is also conical. This creates a linear contact instead of a flat contact.

Further features and advantages of the present invention will become clear from the following description of preferred embodiments with reference to the accompanying drawings.

The following reference symbols are used in the figures:

D axis of rotation

K Piston axis

M center of mass

R retraction force

V Tilting moment

S Perpendicular to the contact surface of the piston

01 Force component without tilting moment

02 Force component with reduced tilting moment

Hl lever arm / distance from the center of mass

1 compressor unit

2 drive device

11 Drive shaft 12 Eccentric disc

13 Piston-working chamber combination

14 Piston guide ring

15 cylinder cover

16 cylinder housings

17 Compressor housing cover

21 Drive housing

121 eccentric bearings

131 work space

132 pistons

133 transmission element

141 Inside of piston guide ring / contact surface

141a bevelled contact surface

1321 contact surface

1321a bevelled contact surface a Angle between piston axis and bevelled contact surface

Features and details described in connection with a method naturally also apply in connection with the device according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other. Furthermore, a method according to the invention that may be described can be carried out with the device according to the invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a" and "an" are intended to include the plural forms, unless the context clearly indicates otherwise. It will also be understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of recited features, integers, steps, operations, elements, and/or components, but not the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.

First, reference is made to Figs. 1 and 2.

A radial piston compressor essentially comprises a compressor unit 1 and a drive device 2. The radial piston compressor comprises a housing, which can be composed of individual housing components, such as, in the present exemplary embodiment, a drive housing 21, a cylinder housing 16 and a compressor housing cover 17. Other housing divisions are also conceivable.

The compressor unit 1 comprises a drive shaft 11 with an eccentric disc 12. The combination of drive shaft 11 and eccentric disc 12 can also be referred to as an eccentric shaft. The drive shaft 11 has a rotational axis D. The compressor unit comprises at least one piston-working chamber combination 13, preferably several piston-working chamber combinations 13, 13a, 13b... 13f, which are arranged radially around the drive shaft 11. The piston-working chamber combinations 13 can also be referred to as a star-shaped arrangement around the drive shaft 11. The piston-working chamber combination 13 comprises a working chamber 131 with a piston 132 displaceably arranged therein. The piston 132 has a piston axis K. The displacement direction of the piston 132 corresponds to the piston axis K. The working chamber 131 can also be referred to as a cylinder. The working chamber 131 is equipped with a cylinder cover 15 on the head side. The working chambers 131 of the piston-working chamber combinations 13 can be formed at least partially from the cylinder housing 16.

The drive shaft 11, in turn, can be rotated by the drive device 2, which can be designed, for example, as an electric machine. Due to the rotation of the drive shaft 11, the eccentric disc 12 strikes the piston 132 and displaces it in the working chamber 131, whereby the medium in the working chamber, for example a refrigerant, can be compressed. The return movement of the piston 132 can, for example, be carried out by a piston guide ring 14, which is in contact with the piston 132. In this way, the piston 132 can be displaced back to a BDC (bottom dead center) until the eccentric disc 12 again strikes the piston crown. The piston 132, in particular the Piston crown, can also be equipped with a transmission element 133 or a transmission element 133 can be arranged between the eccentric disc 12 and the piston 132. With the transmission element 133, the stroke of the eccentric disc 12 is transmitted to the piston 132 so that the latter can execute the compression movement in the direction of top dead center TDC. The transmission element 133 can, for example, be made of a different material than the piston 132 and the eccentric disc 12, in particular of sintered metal, bronze, brass, or plastic. This can, for example, reduce wear or achieve a certain degree of damping when the eccentric disc 12 impacts. The eccentric disc 12 can also be equipped with an eccentric bearing 121, in particular a needle bearing.

The further details and functionality of a radial piston compressor are well known to those skilled in the art. For further details, please refer, for example, to DE 10 2020 211 680 A1.

Reference is made below to Figs. 3 to 6, which show details of a radial piston compressor, in particular a piston with two piston guide rings according to the prior art.

In the following, particular reference is made to Fig. 3.

Here, a combination of two pistons, the eccentric shaft, and a piston guide ring is shown without any additional attachments for clarity. The main purpose of this illustration is to describe in more detail the position of the piston guide ring in relation to the pistons. To clarify the respective piston positions, the positions "bottom dead center" (BDC) and "top dead center" (TDC) are shown. It can also be seen that the piston guide ring, and in particular the inside of the piston guide ring, rests on the respective contact surface of the piston. It is clear that the upper piston is always pulled from TDC to BDC by the lower piston when the lower piston is moved from BDC to TDC.

In the following, particular reference is made to Fig. 4.

A cross-section AA according to Fig. 3 is shown. It can be seen that two piston guide rings 14, each with a rectangular cross-section, are provided. The piston guide rings are mounted on both sides of the piston or the piston axis. It can also be seen that the piston 132 has the corresponding contact surface 1321 for the piston guide ring 14. The inner side 141 of the piston guide ring 14 accordingly also forms a contact surface for resting on the contact surface 1321 of the piston 132. The contact surface 1321 is designed to correspond to the inner side 141 of the piston guide ring 14. In this case, the contact surface 1321, like the inner surface 141, has a flat surface, which is also aligned parallel to the axis of rotation of the eccentric shaft and perpendicular to the piston axis. To prevent the piston from tilting due to the retraction force, two piston guide rings are used as standard.

In the following, particular reference is made to Fig. 5.

A piston is shown in cross-section. Reference symbol M represents the center of mass of the piston. Reference symbol R represents the retraction force of the piston guide ring on the piston at the contact surface. It can be seen that with two force application points relative to the center of mass, no tilting moment V results.

In the following, particular reference is made to Fig. 6.

A piston is shown in cross-section. It should be noted that when only one piston guide ring is used, for example, due to space-related or economical considerations, a tilting moment V occurs with respect to the center of mass.

Reference is made below to Figs. 7 to 12. Figs. 7 to 12 illustrate embodiments of various components of a radial piston compressor according to the invention.

In the following, particular reference is made to Fig. 7.

A piston 132 is shown in cross-section with two contact surfaces 1321a. A beveled contact surface 1321a is provided, in particular such that the contact surface 1321a is tilted in the direction of the piston axis K, in particular in the direction of the center of mass M. An angle α is shown for orientation. A retraction force R is also shown, which is perpendicular to the contact surface 1321a. It can be seen that the retraction force R, or its force vector, intersects the center of mass M. This is preferably the case when a perpendicular S on the contact surface 1321a intersects the center of mass M. The retraction force R still acts parallel to the piston axis K, but when supported on this inclined surface 1321a, the force is divided in the direction parallel and orthogonal to the surface. One force component is shown. The production of a corresponding shape is possible, for example, with a dovetail milling cutter.

In the following, particular reference is made to Fig. 8.

A piston 132 is depicted in cross-section with two beveled contact surfaces 1321a. It can be seen that only a single piston guide ring 14 is provided. It can also be seen that a single piston guide ring 14 with a rectangular cross-section is received in the dovetail-shaped groove, with the contact surface 1321a being formed by a portion of the dovetail-shaped groove, in particular by the flank of the dovetail-shaped groove facing the rotational axis D.

In the following, particular reference is made to Fig. 9.

A piston 132 in cross-section with only one piston guide ring 14 with a conical cross-section with appropriate design of the angle of the contact surface 141a is provided so that the force vector passes through the center of mass M.

In the following, particular reference is made to Fig. 10.

A single piston guide ring 14 with a conical cross-section is shown in a sectional perspective view. It can be seen that the inner surface 141a of the piston guide ring 14 has a configuration corresponding to a beveled contact surface 1321 of the piston 132, in particular, it has a likewise beveled inner surface or contact surface 141a.

In the following, particular reference is made to Fig. 11. A detail of a piston 132 and a piston guide ring 14 is shown. To clarify some force vectors, a force component O1 without tilting moment, a force component O2 with reduced tilting moment, and the retraction force R are shown. This force component O2 would be applied to the flat support of the piston, in particular to the surface parallel to the piston axis K. Depending on the tolerance, the contact takes place at any point and accordingly leads to the influence of a tilting moment by the force component O2. This is particularly evident in the design according to Fig. 12. The contact is defined in the upper area, close to the center of mass M.

In the following, particular reference is made to Fig. 12.

A detail of a piston 132 and a piston guide ring 14 is shown. A piston guide ring 14 with an additional conical inner surface 141a for creating a specific favorable contact point can be seen. In the exemplary embodiment shown here, the contact surface 141a is aligned at an angle a of 55° with respect to the piston axis K. From this exemplary embodiment, with an assumed retraction force R of 1 Newton, a tilting moment V of 1.22 N * 3.87 mm (O2 * H1) = 4.72 Nmm results. The pressing force of the piston guide ring 14 on the beveled contact surface 1321a is accordingly 1.74 N. H1 is the distance to the center of mass M.

The original tilting moment, i.e. the tilting moment for a single piston guide ring with a contact surface or inner surface aligned parallel to the rotational axis D of the eccentric shaft or perpendicular to the piston axis K, would be 5.23 Nmm, i.e. 1N*5, 225mm, in this example, assuming a retraction force of IN. A reduction in the tilting moment of approximately 10% can be achieved in the example shown.

Claims

Claims 1. Radial piston compressor, comprising - a compressor unit (1) and a drive device (2) for driving the compressor unit (1), wherein - the compressor unit (1) comprises a plurality of piston-working chamber combinations (13) which are arranged radially around an eccentric shaft (11, 12), wherein - the eccentric shaft (11, 12) is driven by the drive device (2), whereby - each piston-working chamber combination (13) comprises a piston (132) with a piston axis (K) and a center of mass (M), wherein - the compressor unit (1) comprises a piston guide ring (14), wherein - the pistons (132) are each provided with a contact surface (1321) for the piston guide ring (14), wherein the piston guide ring (14) is in contact with the contact surface (1321), characterized in that the contact surface (1321a) of the pistons (132) is inclined in the direction of the piston axis (K). 2. Radial piston compressor according to claim 1, characterized in that a perpendicular (S) of the contact surface (1321a) intersects the center of mass (M) of the piston (132). 3. Radial piston compressor according to at least one of the preceding claims, characterized in that only one piston guide ring (14) is arranged on one side of the piston (132) or piston axis (K). 4. Radial piston compressor according to at least one of the preceding claims, characterized in that the contact surface (1321a) of the pistons (132) is inclined at an angle a in the direction of the piston axis (K), wherein the angle a is between 40° and 75°, in particular between 45° and 60°, preferably at an angle a = 55° to the piston axis. 5. Radial piston compressor according to at least one of the preceding claims, characterized in that the piston guide ring (14) has a rectangular cross-section wherein an edge of the piston guide ring (14) bears against the contact surface (1321a) of the piston (132). 6. Radial piston compressor according to at least one of the preceding claims, characterized in that the piston guide ring (14) is provided on its inner side with a contact surface (141a) which is in contact with the contact surfaces (1321a) of the pistons (132). 7. Radial piston compressor according to at least one of the preceding claims, characterized in that the contact surface (141a) of the piston guide ring (14) has a shape corresponding to the contact surface (1321a) of the piston (132). 8. Radial piston compressor according to at least one of the preceding claims, characterized in that the contact surface (1321a) of the piston (132) is part of a dovetail-shaped recess in the piston (132) in cross section. 9. Radial piston compressor according to at least one of the preceding claims, characterized in that the piston guide ring (14) has a conical shape in cross section at least in sections. 10. Radial piston compressor according to at least one of the preceding claims, characterized in that the contact surfaces (141a, 1321a) of the piston guide ring (14) and the piston (132) are designed to be exactly parallel or slightly with a gap in the corresponding direction for shifting the contact point into a preferred position.