Piston-cylinder assembly for a radial piston compressor and radial piston compressor

Abstract

The present invention relates to a piston-cylinder assembly for a radial piston compressor, the piston-cylinder assembly comprising a drive shaft (4) having a cylindrical eccentric (6) for guiding the movement of the piston to the top dead center and a cylindrical piston guide ring (13) for guiding the movement of the piston to the bottom dead center, wherein both the eccentric and the piston guide ring are connected to the piston by means of respective concave / convex contact surfaces for positive force transmission.

Description

Technical Field

[0001] The present invention relates to a piston-cylinder assembly for a radial piston compressor and to a radial piston compressor having a plurality of piston-cylinder assemblies arranged uniformly distributed in the circumferential direction. In particular, the present invention relates to a piston-cylinder assembly for a radial piston compressor for compressing a refrigerant, wherein CO 2 (refrigerant R744) is used as the refrigerant. The refrigerant is compressed to a pressure of 140 bar or higher in the high-pressure range, and thus the piston-cylinder assembly is subject to high mechanical loads. Background Art

[0002] Document EP 1 553 291 A2 relates to a reciprocating piston machine intended to be suitable as a compressor for a CO 2 vehicle air conditioning system. The reciprocating piston machine has: a radially oriented piston-cylinder unit arranged uniformly distributed in the circumference; and an eccentric shaft. The eccentric shaft extends through a housing enclosing the cylinder and uses its eccentricity to control the stroke of the piston, i.e., the radially outwardly oriented compression movement of the piston in the direction of the top dead center of the piston movement. The return movement of the piston is controlled by a common control ring engaged in a recess of the piston (see in particular Figure 3 of EP 1 553291 A2). Disadvantageously, the control ring controls the sliding contact with the piston via an internal control surface. This sliding contact can lead to wear and component failure. More disadvantageously, the piston body has a flat contact surface ("inner end surface 15") at its end facing the eccentric, through which the piston is in direct contact with the outer ring of a rolling contact bearing arranged on the eccentric. Thus, the piston body is exposed to high loads. The contact surface between the piston and the bearing outer ring also undergoes continuous changes.

[0003] Document DE 10 2012 005 297 A1 discloses a piston-cylinder assembly for a radial piston compressor intended to be suitable for compressing a refrigerant CO 2 (refrigerant R744). The stroke movement of the pistons arranged uniformly distributed in the circumferential direction in the cylinder bore is generated via an eccentric arranged on a drive shaft. The eccentric has a rolling contact bearing with an outer bearing ring. The transmission element is in the form of a connecting rod, which is supported on the outer shell surface of the bearing outer ring via a concave support surface. At the end of the connecting rod spaced apart from the support surface, a connecting rod eye is provided, through which the connecting rod is articulated to the piston by means of a piston pin. Thus, the piston has a receiving hole for the piston pin.

[0004] The disadvantages of the piston-cylinder assembly known from DE 10 2012 005 297 A1 are: the forces generated in the range of the piston's stroke / compression movement in the direction of top dead center (TDC) are relatively high; and the forces generated in the range of the piston's suction movement in the direction of bottom dead center (BDC) act on the connecting rod via the piston pin and on the piston. Especially in the case of a radial piston compressor for the refrigerant CO 2 in which high pressures occur in the compressor and thus large forces and surface pressures are generated, the piston pin and the receiving area for the piston pin on the connecting rod form a component area that bears critical loads. Especially in the case of a small-sized radial piston compressor, for example, for an air conditioning system of a motor vehicle, the piston has a small diameter and the piston pin can likewise only have a small diameter. Due to the piston-cylinder assembly of the radial piston compressor for the refrigerant CO 2 being exposed to high loads, in the case of the design known from DE 10 2012 005 297 A1, very high surface pressures occur, especially in the connection area of the piston pin / connecting rod eye. Therefore, there is a risk of wear of the piston pin and / or the connecting rod in the area of the connecting rod eye and premature component failure.

[0005] Due to the high loads generated in the area of the receiving hole of the piston pin, the piston itself is also exposed to high surface pressures. Therefore, wear and premature component failure can also occur in the case of the piston. Another disadvantage is that the receiving hole for the piston pin mechanically weakens the piston.

[0006] Furthermore, the disadvantages in the case of the piston-cylinder assembly known from document DE 10 2012 005 297 A1 are: the connecting rod occupies a large amount of structural space and has a relatively complex shape. The connecting rod extends a large length in the radial direction and has a connecting rod eye at its end facing the piston and an operating surface at its end facing the eccentric that interacts with a control ring having an L-shaped cross section. The return movement is transmitted to the piston via the control ring. Summary of the Invention

[0007] The present invention is based on the following object: to provide a robust and at the same time compact piston-cylinder assembly, i.e., one that occupies less structural space. It is intended that no mechanical weakening of the piston occurs even under high compression pressures and relatively low surface pressures do not occur either. The object of the present invention is also to provide a robust radial piston compressor that is suitable for the higher pressures and larger forces that occur during the compression of the refrigerant CO 2 This object is achieved by the piston-cylinder assembly of the present invention and by the radial piston compressor of the present invention. Advantageous developments result from the following description and the drawings.

[0008] ​

[0009] The piston-cylinder assembly for a radial piston compressor according to the present invention comprises: a piston; a cylinder bore in which the piston is arranged displaceably along the central axis of the cylinder bore; a drive shaft having a rotational axis and having a cylindrical eccentric, the center point of the eccentric being spaced apart from the rotational axis of the drive shaft, wherein during the rotational movement of the drive shaft, the piston can be moved radially outwards away from the drive shaft in the cylinder bore by means of the cylindrical eccentric until top dead center (TDC); and a transmission element which transmits the movement of the eccentric to the piston for generating an outward movement of the piston in the cylinder bore away from the drive shaft, wherein the transmission element has a first bearing surface on which the transmission element is supported on the cylindrical surface of the eccentric.

[0010] According to the present invention, the piston has a concave first operating surface facing the transmission element, and the transmission element has a convex second bearing surface facing the first operating surface, wherein the first operating surface and the second bearing surface form a form-fitting connection effective in the circumferential direction of the eccentric, and a cylindrical piston guide ring is provided, and the piston can move radially inwards towards the drive shaft in the cylinder bore from top dead center (TDC) until bottom dead center (BDC), wherein the piston has a convex second operating surface which faces the inner shell surface of the piston guide ring and together with the inner shell surface of the piston guide ring forms a form-fitting connection which is effective in the direction of the central axis of the cylinder bore.

[0011] Within the scope of the present invention, the stroke movement of the piston is thus transmitted by the eccentric via the first bearing surface to the transmission element, and the transmission element transmits the stroke movement via the convex second bearing surface of the transmission element and the concave first operating surface of the piston to the piston. At the same time, the convex second operating surface is formed on the piston and is operatively connected to the inner shell surface of the piston guide ring. The piston guide ring causes the piston to return from top dead center TDC to bottom dead center BDC.

[0012] In the case of the piston-cylinder assembly according to the present invention, even at high compression pressures, the surface pressure occurring at the contact surface between the convex second bearing surface of the transmission element and the concave first operating surface of the piston is significantly less than the surface pressure occurring in the region of the piston pin, the connecting rod eye and the receiving bore for the piston pin in the piston body in the case of the design known from document DE 10 2012 005 297A1. Due to the shape of the second bearing surface and the first operating surface, the contact surface between the convex second bearing surface of the transmission element and the concave first operating surface of the piston has such a large size that even in a radial piston compressor for refrigerant CO 2At the high compression pressures that occur, the surface pressure does not reach the critical value. Premature component wear is thus avoided, and the components achieve the required service life.

[0013] In the case of the design according to the invention, the drive element can be very compact and thus only occupies little structural space, since the drive element is not connected to the piston and no operating surface interacting with the control ring needs to be formed on the drive element, and the return movement is transmitted to the piston via this control ring. This is because, in order to transmit the return movement to the piston, according to the invention, the piston guide ring acts directly on the piston with its inner shell surface via a second operating surface formed on the piston body. Thus, the drive element can be very compact and, in terms of both its shape and material selection, can be particularly suitable for its task of transmitting the stroke movement of the compression stroke to the piston and at the same time occupying as little structural space as possible. During the compression stroke, the greatest mechanical loads occur during the operating cycle of the piston. Thus, it is advantageous that the design according to the invention enables the drive element to be designed such that it is optimally suitable for the task of transmitting the compression stroke movement.

[0014] The first bearing surface of the drive element can be designed as a flat surface, for example a flat surface in the form of a disc. In this case, the flat surface interacts with the cylindrical shell surface of the eccentric or with the cylindrical outer ring of a rolling contact bearing arranged on the shell surface of the eccentric.

[0015] According to one embodiment of the invention, the first bearing surface of the drive element is a flat surface or a concave cylindrical shell part having a first bearing surface radius that corresponds to the radius of the cylindrical shell surface of the eccentric. If the first bearing surface is designed as a flat surface, there is a linear contact between the first operating surface and the cylindrical shell surface of the eccentric. If the first bearing surface of the drive element is designed as a concave cylindrical shell part, a larger contact surface is achieved between the eccentric and the drive element compared to the embodiment with a flat first bearing surface, which results in a smaller surface pressure under a given mechanical load.

[0016] According to one embodiment of the invention, it is provided that the second bearing surface of the drive element is a cylindrical shell part having a second bearing surface radius and the first operating surface of the piston is a cylindrical shell part having a first operating surface radius, or wherein the second bearing surface of the drive element is a spherical surface part having a second bearing surface radius and the first operating surface of the piston is a spherical socket having a first operating surface radius, where the second bearing surface radius and the first operating surface radius are dimensionally the same.

[0017] If the second bearing surface of the transmission element and the first operating surface of the piston are designed as cylindrical shell portions with the same radius, the piston is fixed against rotation about its longitudinal axis. Such fixing of the piston against rotation can be convenient and advantageous if one is interested in a constant angular position of the piston relative to the cylinder bore and the housing in which the cylinder bore is arranged. For example, the piston can have a piston valve which has to interact with an inflow channel which is arranged in the housing and is for the fluid to be compressed.

[0018] In order to prevent the transmission element, which is designed as a cylindrical shell portion, from moving in the axial direction, axial fixing must be effected. This axial fixing can be formed, for example, by a thrust surface which projects in the radial direction and / or by a thrust ring, snap ring or similar element which is inserted into a groove in the piston body or the housing.

[0019] If the second bearing surface of the transmission element is designed as a spherical surface portion and the first operating surface of the piston is designed as a spherical socket with the same radius, the piston can rotate about its longitudinal axis. However, since the spherical-cap-shaped contact surface between the transmission element and the piston holds the transmission element in position in the axial direction, it is not necessary to prevent it from moving in the axial direction. The transmission element is automatically axially fixed / centered relative to the axis of the piston by the spherical surface portion and the spherical socket. Thus, no additional axial fixing of the transmission element is required.

[0020] According to an embodiment of the invention, it is provided that the second operating surface of the piston is a cylindrical shell portion with a second operating surface radius, wherein the second bearing surface radius of the transmission element and the second operating surface radius of the piston have the same center point, wherein the center point on the cylindrical surface of the eccentric is the point at which the center line of the cylinder bore penetrates the cylindrical surface of the eccentric, and wherein the sum of the radius of the eccentric and the second operating surface radius of the piston corresponds to the radius of the inner shell surface of the piston guide ring. The effect achieved hereby is that the piston guide ring in the form of a ring and its inner shell surface never, i.e. not in any angular position of the eccentric, lose contact with the second operating surface of the piston. The piston guide ring thus always remains in contact (without losing contact) with the respective piston. Thus, additional contact changes and sliding displacement movements between the piston guide ring and the piston are avoided, and this has advantages in terms of dynamics and wear. Acoustic advantages are also obtained, since no rattling noise is generated.

[0021] According to one embodiment of the present invention, the contact area between the second support surface of the transmission element and the first operating surface of the piston and / or between the cylindrical surface of the eccentric and the first support surface of the transmission element is slightly convex in a direction transverse to the radius of curvature of the said surfaces. This convex shape of the contact area is also referred to as a "spherical shape". The advantage of the convex or spherical shape of the contact area mentioned is that angular misalignment that may exist between the eccentric axis and the normal to the piston axis is compensated for. Thus, even if the eccentric axis is not exactly at right angles to the longitudinal axis of the piston, the force can be easily transmitted from the eccentric to the transmission element and from the transmission element to the piston. By means of the convex or spherical shape of the contact area, the piston-cylinder assembly according to the present invention is insensitive to manufacturing-induced deviations or deviations that occur during operation, with the value of the angular deviation between the eccentric rotation axis and the piston longitudinal axis being 90°.

[0022] The eccentric can be a cylindrical disc connected to the drive shaft. Alternatively, the eccentric can be integrally formed with the drive shaft and can be in one piece with the drive shaft.

[0023] The transmission element can basically be directly supported on the cylindrical shell surface of the eccentric with its first support surface. In this case, the cylindrical surface of the eccentric is the cylindrical shell surface of the eccentric itself.

[0024] According to one embodiment of the present invention, it is provided that the cylindrical surface of the eccentric is the cylindrical shell surface of the outer ring of a rolling contact bearing, and the rolling contact bearing is thus arranged on the eccentric. The rolling contact body of the rolling contact bearing can be in direct contact with the shell surface of the eccentric, or a bearing inner ring is arranged between the rolling contact body and the shell surface of the eccentric. Then, the shell surface of the bearing outer ring forms the cylindrical surface of the eccentric, and the said cylindrical surface thus interacts with the first support surface of the transmission element. By means of the rolling contact bearing, the friction between the eccentric and the transmission element is significantly reduced compared to the design in which the transmission element is directly supported on the shell surface of the eccentric with its first support surface.

[0025] According to one embodiment of the present invention, two piston guide rings are provided, which are arranged spaced apart from each other in the axial direction of the eccentric, wherein two second operating surfaces are formed on the piston, and in each case, one second operating surface is assigned to the inner shell surface of the piston guide ring. Thus, tilting of the piston about an axis extending perpendicular to its longitudinal axis due to the unilateral introduction of the return force into the piston can be avoided. Thus, the return force is symmetrically introduced into the piston on both sides of the piston center line. Thus, the piston does not tilt and can be better guided.

[0026] According to an embodiment of the present invention, at least a part of the second operating surface formed on the piston or a part of the second operating surface formed on the piston is offset outward in a direction perpendicular to the central axis of the piston with respect to the first operating surface of the piston that interacts with the transmission element, and is radially spaced apart in the direction of the central axis of the piston. In this way, the piston-cylinder assembly occupies a small structural space in the axial and radial directions of the eccentric member and is very compact.

[0027] According to an embodiment of the present invention, the transmission element is made of a metal or metal alloy having a small coefficient of sliding friction, in particular made of a copper, bronze or brass alloy. By virtue of the small surface pressure borne by the transmission element in the case of the design according to the present invention, the material of the transmission element can be selected such that the sliding friction between the transmission element and the cylindrical surface of the eccentric member or the first operating surface of the piston is minimized. In addition to the advantage of less sliding friction, favorable characteristics in terms of emergency operation and insufficient lubrication can also be achieved by selecting the material.

[0028] According to an embodiment of the present invention, the first support surface of the transmission element and / or the first operating surface of the piston has one or more recesses forming lubricant storage portions. Therefore, sufficient lubricant can always be ensured to be supplied to the contact surface. Description of the Drawings

[0029] The present invention will be described in more detail below with reference to the drawings, in which, in each case, it is schematic,

[0030] Figure 1 a first embodiment of the piston-cylinder assembly according to the present invention is shown in a radial half-section;

[0031] Figure 2 a second embodiment of the piston-cylinder assembly according to the present invention is shown in a radial half-section;

[0032] Figure 3 shows an enlarged view of the area D from Figure 2 ;

[0033] Figure 4 a third embodiment of the piston-cylinder assembly according to the present invention is shown in a radial half-section;

[0034] Figure 5 a fourth embodiment of the piston-cylinder assembly according to the present invention is shown in an exploded view;

[0035] Figure 6 the piston and the transmission element are shown in a three-dimensional view as separate components;

[0036] Figure 7Shows a radial piston compressor with a piston-cylinder assembly according to the present invention;

[0037] Figure 8 Shows a comparative juxtaposed view of the second and fourth embodiments of the present invention. Detailed Description

[0038] Figure 1 Shows, in a radial half-section, a first embodiment of a piston-cylinder assembly according to the present invention. The piston-cylinder assembly includes a drive shaft 4 not specifically illustrated in Figure 1 Only the axis of rotation 5 of the drive shaft 4 is indicated in. Figure 1 The pistons 1 are arranged circumferentially around the drive shaft 4. The center line 3 of the cylinder bores 2 intersects the axis of rotation 5 of the drive shaft 4. For the sake of clarity, the cylinder bores 2 are not illustrated in Figure 1 The tubular eccentric 6 is designed as an integral part of the drive shaft 4 or as a component connected to the drive shaft 4 to rotate therewith. The center point 7 of the eccentric 6 is arranged at a distance offset from the axis of rotation 5 of the drive shaft 4 to produce an eccentricity. The eccentric 6 has a tubular surface 10 as its shell surface, and the tubular surface 10 has a radius 17.

[0039] The piston-cylinder assembly according to the present invention further includes a tubular piston guide ring 13 having an inner shell surface 14.

[0040] A transmission element 8 is arranged between the eccentric 6 and the piston 1 of the piston-cylinder assembly. The transmission element 8 is used to transmit the stroke of the eccentric 6 to the piston 1 so that the piston 1 performs a compression movement in the direction of the top dead center TDC. In Figure 1 In the exemplary embodiment illustrated in, the transmission element 8 is directly supported on the tubular surface 10 of the eccentric 6 via a first support surface 9. In Figure 1 In the exemplary embodiment illustrated in, the first support surface 9 is designed as a concave arc-shaped cylindrical shell part surface having a first support surface radius 16. The first support surface radius 16 corresponds to the radius 17 of the tubular surface 10 here. The first support surface 9 and the tubular surface 10 are thus complementary to each other. In principle, the first support surface 9 can also have a concave shape different from the circular ring shape.

[0041] The transmission element 8 has a convex second support surface 12. In Figure 1In the exemplary embodiment illustrated in the figures, the second support surface 12 is designed as a cylindrical shell part surface having a second support surface radius 19. In principle, instead of the cylindrical shell part shape, the second support surface 12 can also have a convex shape different from the cylindrical shape. The piston 1 is supported on the second support surface 12 of the transmission element 8 via a first operating surface 11 formed on the piston 1. The first operating surface 11 of the piston 1 is of a concave shape. In the exemplary embodiment illustrated in the figures, the first operating surface 11 of the piston 1 is designed as a concave cylindrical shell part surface having a first operating surface radius 22, which first operating surface radius 22 corresponds to the second support surface radius 19. Thus, the first operating surface 11 of the piston 1 and the second support surface 12 of the transmission element 8 are formed in a complementary manner to each other. In principle, the first operating surface 11 of the piston 1 can also have a concave shape different from the cylindrical shape.

[0042] A second operating surface 15 of convex shape is formed on the piston 1. In the exemplary embodiment illustrated in the figures, the second operating surface 15 of the piston 1 is a cylindrical shell part surface having a second operating surface radius 20. The piston engages in a form-fitting manner with the inner shell surface 14 of the piston guide ring 13 via the second operating surface 15. This form-fitting is effective in the direction of the center line 3 of the cylinder bore 2. By means of the piston guide ring 13, the return movement is transmitted to the second operating surface 15 of the piston 1, i.e., the movement of the piston 1 from the top dead center TDC of the piston movement to the bottom dead center BDC.

[0043] In Figure 1 the exemplary embodiment illustrated in the figures, the second support surface radius 19 of the transmission element 8 and the second operating surface radius 22 of the piston 1 have the same center point 21. The center point 21 corresponds here to the point at which the center line 3 of the cylinder bore 2 penetrates the cylindrical surface 10 of the eccentric 6. The effect achieved by this design measure is that the sum of the radius 17 of the cylindrical surface 10 and the second operating surface radius 22 of the piston 1 corresponds to the radius 23 of the inner shell surface 14 of the piston guide ring 13. The effect achieved thereby is that the piston guide ring 13 and its inner shell surface 14 never lose contact with the second operating surface 15 of the piston 1, i.e., do not lose contact with the second operating surface 15 of the piston 1 at any angular position of the eccentric 6 or the drive shaft 4. The piston guide ring 13 thus always remains in contact (without losing contact) with the corresponding piston 1. Thus, additional contact changes and sliding displacement movements between the piston guide ring 13 and the piston 1 are avoided, and this has dynamic advantages in terms of the kinematics of the movement sequence and advantages in terms of wear. Acoustic advantages are thus also achieved, since no rattling noise or other annoying noises are generated.

[0044] The piston guide ring 13 guides the piston 1 on the eccentric 6 (or on the outer bearing ring 25, see the second exemplary embodiment, the third exemplary embodiment, and the fourth exemplary embodiment below), and prevents the piston 1 from "lifting" from the cylindrical surface 10 (or from the housing surface 24 of the outer ring 25 of the rolling contact bearing 26) during the downward movement / return movement of the piston 1. The piston guide ring 13 slides on the second operating surface 15, which is formed on the piston 1. The piston guide ring 13 keeps the piston 1 and the transmission element 8 in sliding contact with the eccentric 6 (or in sliding contact with the outer bearing ring 25 of the rolling contact bearing 26 arranged on the eccentric, according to the embodiments of the present invention described below).

[0045] Figure 2 A second embodiment of the piston-cylinder assembly according to the present invention is shown in a radial half-section. The difference between this second embodiment and Figure 1 the first embodiment shown is that the rolling contact bearing 26 is arranged on the eccentric 6 by means of the outer ring 25 and the rolling contact body 28. The transmission element 8 is not directly supported on the housing surface of the eccentric 6 as in the first embodiment, but on the housing surface 24 of the outer bearing ring 25. In the second embodiment of the present invention, the cylindrical housing surface 10 of the eccentric is thus formed by the housing surface 24 of the outer bearing ring 25 of the rolling contact bearing 26. In other respects, the description of the first exemplary embodiment also applies to the second exemplary embodiment.

[0046] The rolling contact bearing 26 is arranged on the eccentric 6. More precisely, in the illustrated exemplary embodiment, the rolling contact body 28 of the rolling contact bearing 26 rolls directly on the housing surface of the eccentric 6. In principle, it is also possible to provide an inner bearing ring on which the rolling contact body 28 rolls. In the illustrated exemplary embodiment, the rolling contact body 28 is held or guided by the cage 29. The rolling contact bearing 26 can be designed, for example, as a needle bearing or a cylindrical roller bearing.

[0047] Many advantages can be obtained by using the rolling contact bearing 26. First, the friction is significantly reduced compared to the first embodiment of the present invention. Second, the housing surface 24 of the outer bearing ring 25 can be hardened more simply than the housing surface of the eccentric 6. This is especially the case when the eccentric 6 and the drive shaft 4 ( Figure 2 not shown in the figure) are formed as a single piece. It may be advantageous to harden the surface on which the transmission element 8 is supported by its first support surface 9. Especially in the case of using the refrigerant CO 2In the case of a radial piston compressor, it may be necessary to harden the surface that the transmission element 8 contacts via its first bearing surface in order to avoid premature wear caused by the occurrence of high forces and surface pressures. Then, it is simpler to harden the separate outer ring of the rolling contact bearing 26 as a single component than to harden the shell surface of the eccentric 6 that is integrally formed with the drive shaft 4 and formed as a single piece.

[0048] Figure 3 shows Figure 2 An enlarged view of region D of a second exemplary embodiment. The radius 23 of the inner shell surface 14 of the piston guide ring 13 and the radius 17 of the cylindrical surface 10 are shown. The cylindrical surface 10 is formed by the outer shell surface 24 of the outer ring 25 of the rolling contact bearing 26. In addition, the first bearing surface radius 16 and the second operating surface radius 20 are shown.

[0049] Figure 4 A third embodiment of the piston-cylinder assembly according to the invention is shown in a radial half-section. The third embodiment basically corresponds to the second embodiment of the invention, the only difference being the design of the transmission element 8. In the case of the Figure 4 third embodiment of the invention, the first bearing surface 9 is designed as a flat circular surface or a surface in the shape of a disc, rather than being designed as a concave arc-shaped surface as in the case of the second exemplary embodiment. It can be seen that at each contact point between the flat bearing surface 9 and the outer shell surface 24 of the bearing outer ring 25, the transmission element 8 is inclined relative to the piston 1 due to the movement of the eccentric 6. The transmission element 8 slides with its convex second bearing surface 12 relative to the concave first operating surface 11 of the piston 1. The transmission element 8 also slides with its flat first bearing surface 9 relative to the outer shell surface 24 of the outer ring 25 of the rolling contact bearing 26.

[0050] Figure 5 A fourth embodiment of the piston-cylinder assembly according to the invention is shown in an exploded view. Exactly as in the case of the second and third embodiments, the transmission element 8 is supported on the outer ring 25 of the rolling contact bearing 26. In Figure 5 the eccentric 6 is not shown. The second operating surface 15 of the piston 1 is also formed in exactly the same way as in the case of the first to third embodiments and interacts with the inner shell surface 14 of the piston guide ring 13 in exactly the same way as in the case of the first to third embodiments. According to Figure 4 the fourth embodiment, the differences are: the design of the transmission element 8, which has a convex, spherical cap-shaped second bearing surface 12 and a flat first bearing surface 9; and the design of the piston 1, which has a concave first operating surface 11 (hidden in Figure 4In the ( ), the first operating surface 11 is in the shape of a spherical socket and interacts with the second supporting surface 12.

[0051] The basic functions correspond to the basic functions of the first to third embodiments of the present invention. The ball cap shape of the second supporting surface 12 of the transmission element 8 and the spherical socket shape of the first operating surface 11 of the piston 1 provide additional advantages:

[0052] The transmission element 8 is axially fixed in the spherical socket of the piston 1. In the case of the second supporting surface 12 designed as a spherical cap and the first operating surface 11 designed as a spherical socket, additional axial fixation can be omitted to prevent the transmission element 8 from moving axially (and such axial fixation is required in the case where the transmission element 8 has a cylindrical shell portion with the second supporting surface 12).

[0053] The drive shaft 4 ( Figure 4 not shown in the ) relative to the center line 3 of the cylinder bore 2 ( Figure 4 not shown in the ) can be compensated by the pairing of the spherical socket and the spherical section according to the fourth exemplary embodiment.

[0054] If, as Figure 5 shown in the, only a single piston guide ring 13 is provided, the guiding length between the piston 1 and the cylinder bore 2 on the opposite side of the piston guide ring 13 can be achieved up to the bottom of the piston. If the piston lengths are the same, better guiding of the piston 1 is thereby achieved.

[0055] Figure 6 The piston 1 and the transmission element 8 as separate components according to the fourth embodiment of the present invention are shown. The concave, ball cap-shaped first operating surface 11 of the piston 1 forms a spherical socket (or spherical hollow portion), and in the assembled state of the piston-cylinder assembly, the convex, ball cap-shaped second supporting surface 12 of the transmission element 8 is received in this spherical socket.

[0056] The lower side of the transmission element 8 facing the eccentric 6 ( Figure 6 not shown in the ) is planar, i.e., the first supporting surface 9 is planar. The effect achieved by the flat first supporting surface 9 is that the transmission element 8 can rotate freely relative to the piston 1 in the circumferential direction. By means of the linear contact with the housing surface 24 of the bearing outer ring 25 ( Figure 6 not shown in the ), the surface pressure on the transmission element 8 is indeed higher than in the case of the transmission element 8 designed according to the second embodiment of the present invention. However, if the transmission element 8 is formed, for example, from rolling contact bearing steel and hardened (e.g., 100Cr6 hardened steel), the transmission element 8 can withstand the increased surface pressure.

[0057] In the illustrated exemplary embodiment, the first bearing surface 9 of the transmission element 8 and the first operating surface 11 of the piston 1 have recesses 30 which form lubricant storage portions. A lubricant (such as lubricating oil) accumulates in the recesses 30. The lubricant storage portions ensure that there is always a sufficient amount of lubricant in the contact surfaces.

[0058] Figure 7 A radial piston compressor having a piston-cylinder assembly according to the invention is schematically shown. In the illustrated exemplary embodiment, the piston-cylinder assembly is designed by way of example according to the second embodiment of the invention, i.e., the transmission element 8 has a concave first bearing surface 9 in the shape of a cylindrical part, and the second bearing surface 12 of the transmission element 8 is in the shape of a cylindrical part and interacts with the first operating surface 11 of the piston 1 which is in the shape of a cylindrical part. It goes without saying that the piston-cylinder assembly can also be designed according to the first embodiment, the third embodiment or the fourth embodiment of the invention.

[0059] The cylinder bores 2 are arranged in the cylinder block 27. The individual pistons 1 are driven by an eccentric 6 via a single drive shaft 4. For a clearer implementation, Figure 7 no details of a complete radial piston compressor are shown. For example, all valve devices as well as the inflow and outflow channels for the refrigerant are omitted. Due to the piston-cylinder assembly according to the invention, the radial piston compressor according to Figure 7 is small both in the radial direction and in the axial direction, i.e., the radial piston compressor occupies little structural space in the two directions mentioned above.

[0060] Figure 8 The differences between the second embodiment and the fourth embodiment of the invention are again illustrated in a comparative juxtaposed manner. The illustration at A) on the left-hand side shows the second embodiment of the invention. The transmission element 8 has a first bearing surface 9 designed as a concave cylindrical shell part surface and a second bearing surface 12 designed as a convex cylindrical shell part surface. Correspondingly, the first operating surface 11 of the piston 1 is designed as a concave cylindrical shell part surface. The fourth embodiment of the invention is illustrated at B) on the right-hand side. The transmission element 8 has a flat first bearing surface 9 and a second bearing surface 12 designed as a spherical surface part or a spherical surface part. The first operating surface 11 of the piston 1 is correspondingly designed as a spherical socket.

[0061] If, in this patent, the discussion regarding a surface or a radius is that one surface corresponds to another surface, one surface is complementary to another surface, or one radius corresponds to another radius, this does not necessarily mean that the surfaces or radii must be formed exactly the same. In order to obtain a good contact surface and avoid a so-called "edge support" (i.e., an arrangement in which only a partial area of the contact surface bears the load), the radius 19 of the second support surface is, for example, always slightly smaller than the radius 22 of the first operating surface on the piston 1. For the same reason, the radius 9 of the first support surface on the transmission element 8, for example, is always slightly larger than the radius 17 of the cylindrical surface 10 or the radius of the housing surface 24 of the outer ring 25 of the rolling contact bearing 26.

[0062] List of Reference Numerals

[0063] 1 Piston

[0064] 2 Cylinder Bore

[0065] 3 Center Line of the Cylinder Bore

[0066] 4 Drive Shaft

[0067] 5 Axis of Rotation of the Drive Shaft

[0068] 6 Eccentric

[0069] 7 Center Point of the Eccentric

[0070] 8 Transmission Element

[0071] 9 First Support Surface of the Transmission Element

[0072] 10 Cylindrical Surface

[0073] 11 First Operating Surface of the Piston

[0074] 12 Second Support Surface of the Transmission Element

[0075] 13 Piston Guide Ring

[0076] 14 Inner Housing Surface of the Piston Guide Ring

[0077] 15 Second Operating Surface of the Piston

[0078] 16 First Support Surface Radius

[0079] 17 Radius of the Cylindrical Surface

[0080] 19 Second Support Surface Radius

[0081] 20 Second Operating Surface Radius

[0082] 21 Center Point

[0083] 22 First Operating Surface Radius

[0084] Radius of the inner shell surface of the 23 piston guide ring

[0085] 24 Outer shell surface

[0086] 25 Outer ring

[0087] 26 Rolling contact bearing

[0088] 27 Cylinder block

[0089] 28 Rolling contact body

[0090] 29 Cage

[0091] 30 Recess

Claims

1. A piston-cylinder assembly for a radial piston compressor, the piston-cylinder assembly comprising: a piston (1); a cylinder bore (2), in which the piston (1) is arranged displaceably along a center line (3) of the cylinder bore (2); a drive shaft (4) having a rotational axis (5) and having a cylindrical eccentric (6), a center point (7) of the eccentric (6) being spaced apart from the rotational axis (5) of the drive shaft (4), wherein, during a rotational movement of the drive shaft (4), the piston (1) can be moved radially outwards in the cylinder bore (2) away from the drive shaft (4) by the eccentric (6) until a top dead center (TDC); and a transmission element (8) that transfers the movement of the eccentric (6) to the piston (1) for generating an outward movement of the piston (1) in the cylinder bore (2) away from the drive shaft (4), wherein the transmission element (8) has a first bearing surface (9) and the transmission element (8) is supported on a cylindrical surface (10) of the eccentric (6) by means of the first bearing surface (9); characterized in that the piston (1) has a concave first operating surface (11) facing the transmission element (8), and the transmission element (8) has a convex second bearing surface (12) facing the first operating surface (11), wherein the first operating surface (11) and the second bearing surface (12) form a positively-locking connection effective in the circumferential direction of the eccentric (6), and a cylindrical piston guide ring (13) is provided, by means of which the piston (1) can be moved radially inwards in the cylinder bore (2) from the top dead center (TDC) towards the drive shaft (4) until a bottom dead center (BDC), wherein the piston (1) has a convex second operating surface (15) that faces an inner shell surface (14) of the piston guide ring (13) and, together with the inner shell surface (14) of the piston guide ring (13), forms a positively-locking connection effective in the direction of the center line (3) of the cylinder bore (2). Wherein, the second operating surface (15) of the piston (1) is a cylindrical shell portion having a second operating surface radius (20), and the first operating surface (11) of the piston (1) has a second bearing surface radius (19), wherein the second bearing surface radius (19) and the second operating surface radius (20) have the same center point (21), and this center point (21) corresponds to the point where the center line (3) of the cylinder bore (2) penetrates the cylindrical surface (10) of the eccentric member (6), and wherein the sum of the radius (17) of the cylindrical surface (10) of the eccentric member (6) and the second operating surface radius (20) of the piston (1) corresponds to the radius (23) of the inner shell surface (14) of the piston guide ring (13).

2. The piston-cylinder assembly according to claim 1, wherein, the first bearing surface (9) of the transmission element (8) is a flat surface or a concave cylindrical shell portion having a first bearing surface radius (16), and the first bearing surface radius (16) corresponds to the radius (17) of the cylindrical surface (10) of the eccentric member (6).

3. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, the second bearing surface (12) of the transmission element (8) and the first operating surface (11) of the piston (1) are cylindrical shell portions having a second bearing surface radius (19), or wherein the second bearing surface (12) of the transmission element (8) is a spherical surface portion, and the first operating surface (11) of the piston (1) is a spherical socket having a second bearing surface radius (19).

4. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, the contact area between the second bearing surface (12) of the transmission element (8) and the first operating surface (11) of the piston (1) and / or between the cylindrical surface (10) of the eccentric member (6) and the first bearing surface (9) of the transmission element (8) is slightly convex in a direction transverse to the radius of curvature of the surface.

5. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, the cylindrical surface (10) of the eccentric member (6) is the cylindrical outer shell surface (24) of the outer ring (25) of a rolling contact bearing (26), and the rolling contact bearing (26) is thus arranged on the eccentric member (6).

6. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, two piston guide rings (13) are provided, and the piston guide rings (13) are arranged to be spaced apart from each other in the axial direction of the eccentric member (6), wherein two second operating surfaces (15) are formed on the piston (1), and in each case, one second operating surface (15) is assigned to the inner shell surface (14) of the piston guide ring (13).

7. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, At least a part of the second operating surface (15) formed on the piston (1) or the part of the second operating surface (15) formed on the piston (1) is arranged to be offset outward in a direction perpendicular to the center line of the piston (1) with respect to the first operating surface (11) of the piston (1) that interacts with the transmission element (8), and is radially spaced apart in the direction of the center line of the piston (1).

8. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, the transmission element (8) is made of a metal or metal alloy with a low coefficient of sliding friction.

9. The piston-cylinder assembly according to claim 8 above, wherein, the transmission element (8) is made of copper.

10. The piston-cylinder assembly according to claim 8 above, wherein, the transmission element (8) is made of bronze.

11. The piston-cylinder assembly according to claim 8 above, wherein, the transmission element (8) is made of a brass alloy.

12. The piston-cylinder assembly according to any one of the preceding claims 1-2, wherein, the first support surface (9) of the transmission element (8) and / or the first operating surface (11) of the piston (1) have recesses (30) forming lubricant storage portions.

13. A radial piston compressor having a plurality of piston-cylinder assemblies according to any one of claims 1 to 12, the piston-cylinder assemblies being arranged to be evenly distributed in the circumferential direction, wherein, the cylinder bores (2) are provided in a cylinder block (27), and each piston (1) is driven by an eccentric member (6) via a single drive shaft (4).

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