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, comprising a drive shaft (4) with a cylindrical eccentric (6) for guiding the movement of the piston to a top dead center and with a cylindrical piston guide ring (13) for guiding the movement of the piston to a 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 the positive transmission of the forces.

Description

[0001] The invention relates to a piston-cylinder assembly for a radial piston compressor according to the preamble of claim 1, as well as to a radial piston compressor having a plurality of piston-cylinder assemblies evenly distributed in a circumferential direction. In particular, the invention relates to a piston-cylinder assembly for a radial piston compressor used to compress refrigerant, using CO2 (refrigerant R744) as the refrigerant. This refrigerant is compressed in the high-pressure range to pressures of 140 bar or higher, resulting in high mechanical loads on the piston-cylinder assembly.

[0002] The document EP 1 553 291 A2 deals with a reciprocating piston engine that is intended to be suitable as a compressor for a CO2 vehicle air conditioning system. The reciprocating piston engine has radially directed piston-cylinder units that are evenly distributed over the circumference and an eccentric shaft. The eccentric shaft extends through a housing body enclosing the cylinders and, by means of its eccentric, controls the stroke of the pistons, i.e. the radially outward compression movement of the piston towards the top dead center of the piston movement. The return movement of the pistons is controlled by a common control ring that engages in a recess in the pistons (cf. in particular Fig. 3 EP 1 553 291 A2). A disadvantage is that the control ring is in controlling sliding contact with the piston via an inner control surface. This sliding contact can lead to wear and component failure. Another disadvantage is that the piston body has a flat contact surface (the "inner end face 15") at its end facing the eccentric, with which the piston is in direct contact with the outer ring of a rolling bearing arranged on the eccentric. The piston body is therefore exposed to high loads. There is also a constant change in the contact surface between the piston and the bearing outer ring.

[0003] From the publication DE 10 2012 005 297 A1, a piston-cylinder assembly for a radial piston compressor is known, which is said to be suitable for compressing the refrigerant CO2 (refrigerant R744). The reciprocating movement of the pistons, which are arranged evenly distributed in the circumferential direction in cylinder bores, is generated by an eccentric mounted on a drive shaft. The eccentric has a rolling bearing with an outer bearing ring. A transmission element designed as a connecting rod is supported on the outer surface of the outer bearing ring via a concavely shaped support surface. At the end of the connecting rod spaced from the support surface, a connecting rod eye is provided, via which the connecting rod is articulated to the piston by means of a piston pin. The piston therefore has a receiving bore for the piston pin.

[0004] A disadvantage of the piston-cylinder assembly known from DE 10 2012 005 297 A1 is that both the high forces occurring during the stroke movement / compression movement of the piston towards top dead center (TDC) and the forces occurring during the intake movement of the piston towards bottom dead center (BDC) act on the connecting rod or the piston via the piston pin. Particularly in radial piston compressors for the refrigerant CO2, where high pressures and therefore large forces and surface pressures occur, the piston pin and the receiving areas for the piston pin on the connecting rod represent component areas that are subject to critical loads. Especially in small-sized radial piston compressors, e.g. for air conditioning systems in motor vehicles, the pistons have small diameters and the piston pins can also only have small diameters.Due to the high loads to which piston-cylinder assemblies of radial piston compressors for the refrigerant CO2 are exposed, the design known from DE 10 2012 005 297 A1 is subjected, particularly in the piston pin / connecting rod eye connection area. This poses a risk of wear and premature component failure of the piston pin and / or connecting rod in the connecting rod eye area.

[0005] The piston itself is also exposed to high surface pressures due to the high loads occurring in the area of ​​the piston pin mounting bore. This can also lead to wear and premature component failure.

[0006] Another disadvantage is that the bore for the piston pin mechanically weakens the piston.

[0007] Another disadvantage of the piston-cylinder assembly known from document DE 10 2012 005 297 A1 is that the connecting rod requires a large amount of space and has a relatively complex shape. The connecting rod extends radially over a considerable length and has connecting rod eyes at its end facing the piston and active surfaces at its end facing the eccentric. These surfaces interact with control rings with an L-shaped cross-section. The return movement is transmitted to the piston via the control rings.

[0008] WO 2014 / 087201 A1 discloses a piston-cylinder unit having the features of the preamble of claim 1. This piston-cylinder unit, intended for use in wind turbines, has a drive rod 20 with a very large longitudinal extension. The drive rod serves to transmit the movement of the piston to an eccentric cam. A large distance exists between the piston and the holding element 34, on which the retaining ring 41 engages. The arrangement therefore requires a large amount of installation space and is unsuitable for use in radial piston compressors.

[0009] The invention is based on the object of providing a piston-cylinder assembly that is robust yet compact, i.e., requires minimal installation space. The piston should not be mechanically weakened, and even at high compression pressures, relatively low surface pressures should occur. The object of the invention is also to provide a robust radial piston compressor that is suitable for the high pressures and large forces that occur during compression of the refrigerant CO2.

[0010] This object is achieved by a piston-cylinder assembly having the features of independent patent claim 1 and by a radial piston compressor having the features of patent claim 11. Advantageous further developments emerge from the subclaims, the following description and the drawings.

[0011] The piston-cylinder assembly according to the invention for a radial piston compressor comprises a piston, a cylinder bore in which the piston is arranged to be displaceable along a center line of the cylinder bore, a drive shaft with a rotational axis and with a cylindrical eccentric whose center point is spaced from the rotational axis of the drive shaft, wherein the piston can be moved by the cylindrical eccentric in the cylinder bore in a radial direction away from the drive shaft and outwards up to a top dead center (TDC) upon a rotational movement of the drive shaft, and a transmission element which transmits the movement of the eccentric to the piston to generate the movement of the piston in the cylinder bore outwards, away from the drive shaft, wherein the transmission element has a first support surface with which the transmission element is supported on a cylindrical surface of the eccentric.

[0012] According to the invention, the piston has a concavely shaped first active surface facing the transmission element and the transmission element has a convexly shaped second support surface facing the first active surface, wherein the first active surface and the second support surface form a positive connection effective in the circumferential direction of the eccentric, and a cylindrical piston guide ring is provided, by means of which the piston can be moved in the cylinder bore starting from the top dead center (TDC) in the radial direction towards the drive shaft inwards up to a bottom dead center (UT), wherein the piston has a convexly shaped second active surface facing an inner circumferential surface of the piston guide ring, which forms a positive connection with the inner circumferential surface of the piston guide ring effective in the direction of the center line of the cylinder bore.

[0013] Within the scope of the invention, the piston's stroke movement is transmitted from the eccentric via the first support surface to the transmission element, and the transmission element transmits the stroke movement to the piston via the convex-shaped second support surface of the transmission element and the concave-shaped first active surface of the piston. At the same time, a convex-shaped second active surface is formed on the piston, which is operatively connected to the inner circumferential surface of the piston guide ring. The piston guide ring causes the piston's return movement from top dead center (TDC) to bottom dead center (BDC).

[0014] In the piston-cylinder assembly according to the invention, the surface pressure that occurs in the contact surface between the convex second support surface of the transmission element and the concave first active surface of the piston is significantly lower, even at high compression pressures, than the surface pressures that occur in the area of ​​the piston pin, the connecting rod eye, and the receiving bore for the piston pin in the piston body in the design known from document DE 10 2012 005 297 A1. Due to the shape of the two surfaces, the contact surface between the convex second support surface of the transmission element and the concave first active surface of the piston is so large that even at the high compression pressures that occur in radial piston compressors for the refrigerant CO2, the surface pressures do not reach critical values. Premature wear of the components is thus avoided, and the components achieve the required service life.

[0015] With the design according to the invention, the transmission element can be made very compact, so that it only takes up a small installation space, because the transmission element is not connected to the piston and no active surfaces need to be formed on the transmission element that interact with a control ring via which the return movement is transmitted to the piston. In order to transmit the return movement to the piston, the piston guide ring acts directly on the piston with its inner circumferential surface via the second active surface formed on the piston body. The transmission element can therefore be made very compact and, both in terms of its shape and its choice of material, can be specifically adapted for its task of transmitting the reciprocating movement for the compression stroke to the piston while at the same time taking up as little installation space as possible.The greatest mechanical loads occur during the piston's working cycle during the compression stroke. Therefore, it is advantageous that the design according to the invention allows the transmission element to be configured in such a way that it is optimally adapted to the task of transmitting the compression stroke movement.

[0016] The first support surface of the transmission element can be designed as a flat surface, e.g., a flat circular disk-shaped surface. In this case, the flat surface interacts with the cylindrical outer surface of the eccentric or a cylindrical outer ring of a rolling bearing arranged on the outer surface of the eccentric.

[0017] According to one embodiment of the invention, the first support surface of the transmission element is a flat surface or a concavely shaped cylinder surface section with a first support surface radius, wherein the first support surface radius corresponds to the radius of the cylinder surface of the eccentric. If the first support surface is designed as a flat surface, there is linear contact between the first active surface and the cylinder surface of the eccentric. If the first support surface of the transmission element is designed as a concavely shaped cylinder surface section, a larger contact area is achieved between the eccentric and the transmission element compared to an embodiment with a flat first support surface, which leads to lower surface pressures for a given mechanical load.

[0018] According to one embodiment of the invention, it is provided that the second support surface of the transmission element is a cylinder jacket section with a second support surface radius and the first effective surface of the piston is a cylinder jacket section with a first effective surface radius, or wherein the second support surface of the transmission element is a spherical surface section with a second support surface radius and the first effective surface of the piston is a ball socket with a first effective surface radius, wherein the second support surface radius and the first effective surface radius are the same size.

[0019] If the second support surface of the transmission element and the first active surface of the piston are formed as cylinder jacket sections with the same radius, the piston is secured against rotation about its longitudinal axis. Such a rotation lock of the piston can be useful and advantageous if a constant angular position of the piston relative to the cylinder bore and the housing in which the cylinder bore is located is important. For example, the piston can have a piston valve, which must interact with an inflow channel arranged in the housing for the fluid to be compressed.

[0020] To prevent the transmission element, which is designed as a cylinder jacket section, from drifting in the axial direction, an axial lock must be provided. Such an axial lock can be formed, for example, by radially protruding thrust surfaces and / or by thrust rings, snap rings, or similar elements inserted into grooves in the piston body or housing.

[0021] If the second support surface of the transmission element is designed as a spherical surface section and the first active surface of the piston is designed as a ball socket with the same radius, the piston can rotate around its longitudinal axis. However, it does not need to be secured against axial displacement because the spherical cap-shaped contact surface between the transmission element and the piston holds the transmission element in place in the axial direction. The transmission element is automatically axially secured / centered to the piston axis by the spherical surface section and the ball socket. Additional axial securing of the transmission element is then unnecessary.

[0022] According to one embodiment of the invention, the second effective surface of the piston is a cylinder jacket section with a second effective surface radius, wherein the second support surface radius of the transmission element and the second effective 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 pierces the cylindrical surface of the eccentric, and wherein the sum of the radius of the eccentric and the second effective surface radius of the piston corresponds to the radius of the inner surface of the piston guide ring. This ensures that the piston guide ring, designed as a circular ring, never loses contact with the second effective surface of the piston with its inner surface, i.e. in no angular position of the eccentric. In this way, the piston guide ring is always in contact (without loss of contact) with the respective piston.This prevents additional contact changes and sliding movements between the piston guide ring and the piston, which offers dynamic and wear-reducing advantages. It also provides acoustic benefits because no rattling noises are generated.

[0023] According to one embodiment of the invention, a contact zone between the second support surface of the transmission element and the first active 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 the direction transverse to the radii of curvature of these surfaces. This convex shape of the contact zone is also referred to as a "spherical shape." One advantage of a convex or spherical shape of the aforementioned contact zones is that any angular misalignments between the eccentric axis and a piston axis normal are compensated. This allows the forces from the eccentric to the transmission element or from the transmission element to the piston to be transmitted smoothly, even if the eccentric axis is not exactly perpendicular to the longitudinal axis of the piston.Due to the convex or spherical shape of the contact zones, the piston-cylinder assembly according to the invention is insensitive to deviations of the angle between the eccentric rotation axis of the piston longitudinal axis from the value of 90° due to manufacturing or occurring during operation.

[0024] The eccentric may be a cylindrical disc connected to the drive shaft. Alternatively, the eccentric may be formed integrally and in one piece with the drive shaft.

[0025] The transmission element can, in principle, rest directly on the cylindrical surface of the eccentric with its first support surface. In this case, the cylindrical surface of the eccentric is the cylindrical surface of the eccentric itself.

[0026] According to one embodiment of the invention, the cylindrical surface of the eccentric is a cylindrical outer surface of an outer ring of a rolling bearing, wherein the rolling bearing is arranged on the eccentric. The rolling elements of the rolling bearing can be in direct contact with the outer surface of the eccentric, or an inner bearing ring can be arranged between the rolling elements and the outer surface of the eccentric. The outer surface of the bearing outer ring then forms the cylindrical surface of the eccentric, which interacts with the first support surface of the transmission element. The rolling bearing significantly reduces the friction between the eccentric and the transmission element compared to a design in which the transmission element is supported with its first support surface directly on the outer surface of the eccentric.

[0027] According to one embodiment of the invention, two piston guide rings are provided, which are arranged spaced apart from one another in the axial direction of the eccentric, wherein two second active surfaces are formed on the piston, each second active surface being assigned to an inner circumferential surface of a piston guide ring. This prevents the piston from tilting about an axis running perpendicular to its longitudinal axis due to a one-sided introduction of a restoring force into the piston. The restoring force is thus introduced symmetrically into the piston on both sides of the piston centerline. This prevents the piston from tilting and provides better guidance.

[0028] According to one embodiment of the invention, at least part of the second active surface formed on the piston, or parts of the second active surfaces formed on the piston, are offset outward relative to the first active surface of the piston, which interacts with the transmission element, in a direction perpendicular to the center line of the piston, and are spaced radially outward in the direction of the center line of the piston. In this way, the piston-cylinder assembly requires little installation space both in the axial direction of the eccentric and in the radial direction of the eccentric and is very compact.

[0029] According to one embodiment of the invention, the transmission element is made of a metal or a metal alloy with a low coefficient of sliding friction, in particular copper, bronze, or a brass alloy. Due to the low surface pressures to which the transmission element is exposed in the design according to the invention, the material for the transmission element can be selected such that the sliding friction between the transmission element and the cylindrical surface of the eccentric or the first active surface of the piston is minimized. In addition to the advantage of lower sliding friction, the material selection also achieves favorable properties with regard to emergency running and insufficient lubrication.

[0030] According to one embodiment of the invention, the first support surface of the transmission element and / or the first active surface of the piston has a recess forming a lubricant reservoir. This ensures a sufficient supply of lubricant to the contact surfaces at all times.

[0031] The invention is explained in more detail below with reference to the figures, each of which shows schematically Fig. 1 a first embodiment of a piston-cylinder assembly according to the invention in radial half-section; Fig. 2 a second embodiment of a piston-cylinder assembly according to the invention in radial half-section; Fig. 3 an enlarged view of area D from Fig. 2 ; Fig.4 a third embodiment of a piston-cylinder assembly according to the invention in radial half-section; Fig.5 a fourth embodiment of the piston-cylinder assembly according to the invention in an exploded view; Fig. 6 the piston and the transmission element as individual parts in a perspective view; Fig. 7 a radial piston compressor with piston-cylinder assemblies according to the invention. Fig. 8 a comparative comparison of the second and fourth embodiments of the invention.

[0032] Fig. 1 shows a first embodiment of a piston-cylinder assembly according to the invention in radial half-section. The piston-cylinder assembly comprises a Fig. 1 not shown drive shaft 4. In Fig. 1 Only the rotational axis 5 of the drive shaft 4 is indicated. Pistons 1 are arranged circumferentially around the drive shaft 4. The center lines 3 of the Fig.1 The cylinder bores 2, not shown for reasons of clarity, intersect at the rotational axis 5 of the drive shaft 4. The cylindrical eccentric 6 is designed as an integral component of the drive shaft 4 or as a component connected in a rotationally fixed manner to the drive shaft 4. The center point 7 of the eccentric 6 is arranged offset by a distance from the rotational axis 5 of the drive shaft 4 to generate the eccentricity. The eccentric 6 has a cylindrical surface 10 with a radius 17 as its outer surface.

[0033] The piston-cylinder assembly according to the invention further comprises a cylindrical piston guide ring 13 which has an inner circumferential surface 14.

[0034] A transmission element 8 is arranged between the eccentric 6 and the piston 1 of a piston-cylinder assembly. The transmission element 8 transmits the stroke of the eccentric 6 to the piston 1, so that the piston executes the compression movement towards top dead center (TDC). The transmission elements 8 are supported in the Fig. 1 illustrated embodiment via a first support surface 9 directly on the cylindrical surface 10 of the eccentric 6. In the Fig. 1 In the illustrated embodiment, the first support surface 9 is designed as a concavely curved cylinder surface section with a first support surface radius 16. The first support surface radius 16 corresponds to the radius 17 of the cylindrical surface 10. The first support surface 9 and the cylindrical surface 10 are thus complementary to one another. In principle, the first support surface 9 could also have a concave shape other than a circular ring.

[0035] The transmission element 8 has a convex shaped second support surface 12. In the Fig. 1 In the illustrated embodiment, the second support surface 12 is designed as a cylinder jacket section surface with a second support surface radius 19. In principle, the second support surface 12 could also have a convex shape deviating from the cylindrical shape instead of a cylinder jacket section shape. The piston 1 is supported on the second support surface 12 of the transmission element 8 via a first active surface 11 formed on the piston 1. The first active surface 11 of the piston 1 has a concave shape. In the illustrated embodiment, the first active surface 11 of the piston 1 is designed as a concave cylinder jacket section surface with a first active surface radius 22 that corresponds to the second support surface radius 19. The first active surface 11 of the piston 1 and the second support surface 12 of the transmission element 8 are thus complementary to one another.In principle, the first effective surface 11 of the piston 1 could also have a concave shape deviating from the cylindrical shape.

[0036] A convexly shaped second active surface 15 is formed on the piston 1. In the illustrated embodiment, the second active surface 15 of the piston 1 is a cylinder jacket section surface with a second active surface radius 20. Via the second active surface 15, the piston is in positive engagement with the inner jacket surface 14 of the piston guide ring 13. The positive engagement is effective in the direction of the center line 3 of the cylinder bore 2. The piston guide ring 13 transmits the return movement to the second active surface 15 of the piston 1, i.e. the movement with which the piston 1 is moved from the top dead center TDC to the bottom dead center BDC of the piston movement.

[0037] In the Fig. 1 In the illustrated embodiment, the second support surface radius 19 of the transmission element 8 and the second effective surface radius 22 of the piston 1 have the same center point 21. The center point 21 corresponds to the point at which the center line 3 of the cylinder bore 2 pierces the cylindrical surface 10 of the eccentric 6. This design measure ensures that the sum of the radius 17 of the cylindrical surface 10 and the second effective surface radius 22 of the piston 1 corresponds to the radius 23 of the inner circumferential surface 14 of the piston guide ring 13. This ensures that the piston guide ring 13 with its inner circumferential surface 14 never loses contact with the second effective surface 15 of the piston 1, i.e., in no angular position of the eccentric 6 or the drive shaft 4. In this way, the piston guide ring 13 is always in contact (without loss of contact) with the respective piston 1.This prevents additional contact changes and sliding movements between piston guide ring 13 and piston 1, which offers dynamic advantages in terms of the kinematics of the movement sequence and wear-related advantages. Acoustic advantages are also achieved because no rattling noises or other disturbing sounds are generated.

[0038] The piston guide ring 13 guides the pistons 1 on the eccentric 6 (or on the bearing outer ring 25, see the following embodiments two, three, and four) and prevents the pistons 1 from "lifting off" the cylinder surface 10 (or the outer surface 24 of the outer ring 25 of the rolling bearing 26) during a downward movement / return movement of the pistons 1. The piston guide ring 13 slides on the second active surface 15 formed on the piston 1. The piston guide ring 13 holds the pistons 1 and the transmission elements 8 in sliding contact with the eccentric 6 (or with an outer bearing ring 25 of a rolling bearing 26 arranged on the eccentric according to the embodiments of the invention described below).

[0039] Fig. 2 shows a second embodiment of a piston-cylinder assembly according to the invention in radial half-section. This second embodiment differs from the one shown in Fig. 1 The first embodiment shown is distinguished from the fact that a rolling bearing 26 with an outer ring 25 and rolling elements 28 is arranged on the eccentric 6. The transmission elements 8 are not supported directly on the outer surface of the eccentric 6, as in the first embodiment, but rather they are supported on the outer surface 24 of the bearing outer ring 25. In the second embodiment of the invention, the cylindrical surface 10 of the eccentric is thus formed by the outer surface 24 of the bearing outer ring 25 of the rolling bearing 26. Otherwise, the description of the first embodiment also applies to the second embodiment.

[0040] The rolling bearing 26 is arranged on the eccentric 6. More precisely, in the illustrated embodiment, the rolling elements 28 of the rolling bearing 26 roll directly on the outer surface of the eccentric 6. In principle, it would also be possible to provide an inner bearing ring on which the rolling elements 28 roll. In the illustrated embodiment, the rolling elements 28 are held by a cage 29 or are guided by it. The rolling bearing 26 can be designed, for example, as a needle bearing or a cylindrical roller bearing.

[0041] The use of the rolling bearing 26 provides several advantages. On the one hand, friction is significantly reduced compared to the first embodiment of the invention. On the other hand, the outer surface 24 of the bearing outer ring 25 can be hardened more easily than the surface of the eccentric 6. This is especially true when the eccentric 6 is integrally formed in one piece with the drive shaft 4 (in Fig. 2 (not shown). It may be advantageous to harden the surface on which the transmission elements 8 are supported with their first support surface 9. Particularly in radial piston compressors for the refrigerant CO2, hardening the surface with which the transmission elements 8 are in contact via their first support surface may be necessary to prevent premature wear due to the high forces and surface pressures that occur. It is then easier to harden a separate outer ring of the rolling bearing 26 as a single component than the outer surface of an eccentric 6 formed integrally and in one piece with the drive shaft 4.

[0042] Fig. 3 shows an enlarged view of the area D of the second embodiment from Fig. 2 . The radius 23 of the inner circumferential surface 14 of the piston guide ring 13 and the radius 17 of the cylindrical surface 10 are shown, with the cylindrical surface 10 being formed by the outer circumferential surface 24 of the outer ring 25 of the rolling bearing 26. Also shown are the first support surface radius 16 and the second effective surface radius 20.

[0043] Fig. 4 shows a third embodiment of a piston-cylinder assembly according to the invention in a radial half-section. This third embodiment corresponds essentially to the second embodiment of the invention, the only difference being the design of the transmission element 8. In the third embodiment of the invention according to Fig. 4 The first support surface 9 is designed as a flat circular or circular disk-shaped surface, not as a concavely curved surface as in the second embodiment. At the individual contact points between the flat support surfaces 9 and the outer surface 24 of the bearing outer ring 25, it can be seen that the transmission element 8 tilts relative to the piston 1 as a result of the movement of the eccentric 6. The transmission element 8 slides with its convexly shaped second support surface 12 relative to the concavely shaped first active surface 11 of the piston 1. The transmission element 8 also slides with its flat first support surface 9 relative to the outer surface 24 of the outer ring 25 of the rolling bearing 26.

[0044] Fig. 5 shows a fourth embodiment of the piston-cylinder assembly according to the invention in an exploded view. Just as in the second and third embodiments, the transmission elements 8 are supported on the outer ring 25 of the rolling bearing 26. The eccentric 6 is in Fig. 5 Not shown. The second active surface 15 of the piston 1 is also designed in the same way and interacts with the inner surface 14 of the piston guide ring 13 in the same way as in the first to third embodiments. The difference of the fourth embodiment according to Fig. 4 lies in the design of the transmission element 8, which has a convex spherical cap-shaped second support surface 12 and a flat first support surface 9, as well as in the design of the piston 1, which has a concave spherical socket-shaped first effective surface 11 (in Fig. 4 hidden) which interacts with the second support surface 12.

[0045] The basic functionality corresponds to that of the first to third embodiments of the invention. The spherical cap shape of the second support surface 12 of the transmission element 8 and the spherical socket shape of the first active surface 11 of the piston 1 offer additional advantages: The transmission element 8 is axially secured in the ball socket of the piston 1. An additional axial securing device to prevent axial displacement of the transmission element 8 (which is required for the transmission element 8 with the cylindrical shell section of the second support surface 12) can be dispensed with in the case of the second support surface 12 designed as a spherical cap and the first active surface 11 designed as a ball socket. A misalignment of the drive shaft 4 in ( Fig. 4 not shown) to the center lines 3 of the cylinder bores 2 (in Fig. 4 not shown) can be compensated by the ball socket-ball segment pairing according to the fourth embodiment. If - as in Fig. 5 If, as shown, only a single piston guide ring 13 is provided, the guide length between piston 1 and cylinder bore 2 can be extended to the piston base on the opposite side of the piston guide ring 13. This results in better guidance of piston 1 with the same piston length.

[0046] In Fig. 6 The piston 1 and the transmission element 8 according to the fourth embodiment of the invention are shown as individual components. The concave, spherical cap-shaped first active surface 11 of the piston 1 forms a ball socket (or spherical recess) in which the convex, spherical cap-shaped second support surface 12 of the transmission element 8 is received in the assembled state of the piston-cylinder assembly.

[0047] The eccentric 6 (in Fig. 6 The underside of the transmission element 8 facing the piston 1 (not shown) is flat, ie the first support surface 9 is a flat surface. The flat first support surface 9 ensures that the transmission element 8 can rotate freely in the circumferential direction relative to the piston 1. Due to the line contact with the outer surface 24 of the bearing outer ring 25 (in Fig. 6 (not shown), the surface pressures on the transmission element 8 are higher than on a transmission element 8 constructed according to the second embodiment of the invention. However, if the transmission element 8 is constructed, for example, from rolling bearing steel and hardened (e.g., 100Cr6 hardened), it can withstand the increased surface pressures.

[0048] In the illustrated embodiment, the first support surface 9 of the transmission element 8 and the first active surface 11 of the piston 1 have a recess 30 forming a lubricant reservoir. Lubricant (e.g., lubricating oil) accumulates in the recesses 30. These lubricant reservoirs ensure that a sufficient amount of lubricant is always present in the contact surfaces.

[0049] Fig. 7 schematically shows a radial piston compressor with piston-cylinder assemblies according to the invention. In the illustrated embodiment, the piston-cylinder assemblies are designed, by way of example, according to the second embodiment of the invention, i.e., the transmission elements 8 have concave first support surfaces 9 in the shape of a cylinder segment, and the second support surfaces 12 of the transmission elements 8 are designed in the shape of a cylinder segment and interact with the first active surfaces 11 of the pistons 1 in the shape of a cylinder segment. It is understood that the piston-cylinder assemblies could also be designed according to the first, third, or fourth embodiment of the invention.

[0050] The cylinder bores 2 are arranged in a cylinder block 27. The individual pistons 1 are driven by a single drive shaft 4 with an eccentric 6. To achieve a better overview, all details of a complete radial piston compressor have been shown in Fig. 7 not shown. For example, all valve arrangements and inflow and outflow channels for the refrigerant are missing. Due to the piston-cylinder assemblies according to the invention, the radial piston compressor according to Fig. 7 small in the radial direction and also in the axial direction, ie it requires little installation space in both directions.

[0051] In Fig. 8the differences between the second and fourth embodiments of the invention are shown again in a comparative comparison. The illustration for A) on the left shows the second embodiment of the invention. The transmission element 8 has a first support surface 9 designed as a concave cylinder jacket section surface and a second support surface 12 designed as a convex cylinder jacket section surface. The first active surface 11 of the piston 1 is accordingly designed as a concave cylinder jacket section surface. On the right-hand side under B) the fourth embodiment of the invention is shown. The transmission element 8 has a flat first support surface 9 and a second support surface 12 designed as a spherical surface section or spherical surface segment. The first active surface 11 of the piston 1 is accordingly designed as a ball socket.

[0052] Where the present patent claims or the present description refer to surfaces or radii as one surface corresponding to another, one surface being complementary to another surface, or one radius corresponding to another radius, this does not necessarily mean that the surfaces or radii must be exactly the same. To maintain a good contact surface and avoid the occurrence of so-called "edge supports" (i.e., arrangements in which only partial areas of the contact surfaces bear the loads), the second support surface radius 19, for example, should always be slightly smaller than the first effective surface radius 22 on the piston 1. For the same reason, the first support surface radius 9 on the transmission element 8, for example, should always be slightly larger than the radius 17 of the cylindrical surface 10 or the radius of the outer circumferential surface 24 of the outer ring 25 of the rolling bearing 26. List of reference symbols

[0053] 1 Piston 2 Cylinder bore 3 Centerline of the cylinder bore 4 Drive shaft 5 Rotational axis of the drive shaft 6 Eccentric 7 Center point of the eccentric 8 Transmission element 9 First support surface of the transmission element 10 Cylinder surface 11 First active surface of the piston 12 Second support surface of the transmission element 13 Piston guide ring 14 Inner surface of the piston guide ring 15 Second active surface of the piston 16 First support surface radius 17 Radius of the cylinder surface 19 Second support surface radius 20 Second active surface radius 21 Center point 22 First active surface radius 23 Radius of the inner surface of the piston guide ring 24 Outer surface 25 Outer ring 26 Rolling bearing 27 Cylinder block 28 Rolling element 29 Cage 30 Recess

Claims

1. A piston-cylinder assembly for a centrifugal piston compressor, 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) with an axis of rotation (5) and with a cylindrical eccentric (6), the center (7) of which is spaced from the axis of rotation (5) of the drive shaft (4), wherein the piston (1) can be moved by the cylindrical eccentric (6) during a rotary movement of the drive shaft (4) in the cylinder bore (2) in a radial direction away from the drive shaft (4) in an outward direction up to a top dead center (TDC); and a transmission element (8) which transmits the movement of the eccentric (6) to the piston (1) in order to generate the outward movement of the piston (1) in the cylinder bore (2) directed away from the drive shaft (4), the transmission element (8) having a first supporting surface (9) with which the transmission element (8) is supported on a cylindrical surface (10) of the eccentric (6); wherein the piston (1) has a concave-shaped first active surface (11) facing the transmission element (8) and the transmission element (8) has a convex-shaped second supporting surface (12) facing the first active surface (11), wherein the first active surface (11) and the second supporting surface (12) form a positive connection effective in the circumferential direction of the eccentric (6), and wherein a cylindrical piston guide ring (13) is provided, by means of which the piston (1) can be moved in the cylinder bore (2) starting from the top dead centre (TDC) in a radial direction inwards towards the drive shaft (4) up to a bottom dead centre (BDC), characterized in in that the piston (1) has a convexly shaped second active surface (15) which faces an inner surface (14) of the piston guide ring (13) and forms a positive connection with the inner surface (14) of the piston guide ring (13) which is effective in the direction of the center line (3) of the cylinder bore (2).

2. Piston-cylinder assembly according to claim 1, wherein the first supporting surface (9) of the transmission element (8) is a flat surface or a concavely shaped cylinder jacket section with a first supporting surface radius (16), wherein the first supporting surface radius (16) corresponds to the radius (17) of the cylinder surface (10) of the eccentric (6).

3. Piston-cylinder assembly according to one of the preceding claims, wherein the second supporting surface (12) of the transmission element (8) and the first effective surface (11) of the piston (1) are cylinder shell sections with a second supporting surface radius (19) or wherein the second supporting surface (12) of the transmission element (8) is a spherical surface section and the first effective surface (18) of the piston (1) is a spherical socket with a second supporting surface radius (19).

4. Piston-cylinder assembly according to one of the preceding claims, wherein the second effective surface (15) of the piston (1) is a cylinder skirt portion with a second effective surface radius (20), wherein the second supporting surface radius (19) and the second effective surface radius (20) have the same center point (21), wherein the center point (21) on the cylinder surface (10) of the eccentric (6) is the point at which the center line (3) of the cylinder bore (2) pierces the cylinder surface (10) of the eccentric (6), at which the center line (3) of the cylinder bore (2) pierces the cylindrical surface (10) of the eccentric (6), and wherein the sum of the radius (17) of the cylindrical surface (10) of the eccentric (6) and the second effective surface radius (20) of the piston (1) corresponds to the radius (23) of the inner surface (14) of the piston guide ring (13).

5. Piston-cylinder assembly according to one of the preceding claims, wherein a contact zone between the second supporting surface (12) of the transmission element (8) and the first active surface (11) of the piston (1) and / or between the cylindrical surface (10) of the eccentric (6) and the first supporting surface (9) of the transmission element (8) is slightly convex in the direction transverse to the radii of curvature of these surfaces.

6. Piston-cylinder assembly according to one of the preceding claims, wherein the cylindrical surface (10) of the eccentric (6) is a cylindrical outer surface (24) of an outer ring (25) of a rolling bearing (26), wherein the rolling bearing (26) is arranged on the eccentric (6).

7. Piston-cylinder assembly according to one of the preceding claims, wherein two piston guide rings (13) are provided, which are arranged spaced apart from one another in the axial direction of the eccentric (6), wherein two second active surfaces (15) are formed on the piston (1), wherein in each case a second active surface (15) is assigned to an inner surface (14) of a piston guide ring (13).

8. Piston-cylinder assembly according to one of the preceding claims, wherein at least a part of the second active surface (15) formed on the piston (1) or parts of the second active surfaces (15) formed on the piston (1) is or are arranged offset outwards relative to the first active surface (11) of the piston (1) cooperating with the transmission element (8) in the direction perpendicular to the centerline of the piston (1) and spaced radially outwards in the direction of the centerline of the piston (1).

9. Piston-cylinder assembly according to one of the preceding claims, wherein the transmission element (8) is made of a metal or a metal alloy with a low coefficient of sliding friction, in particular of copper, bronze or a brass alloy.

10. Piston-cylinder assembly according to one of the preceding claims, wherein the first supporting surface (9) of the transmission element (8) and / or the first active surface (11) of the piston (1) has or have a recess (30) forming a lubricant reservoir.

11. Radial piston compressor with a plurality of piston-cylinder assemblies arranged uniformly distributed in a circumferential direction according to one of claims 1 to 10, wherein the cylinder bores (2) are provided in a cylinder block (27) and the individual pistons (1) are driven via a single drive shaft (4) with an eccentric (6).

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