Piston compressor having eccentric lifting element

Abstract

A piston compressor has a piston guided in a compressor cylinder, wherein the piston and the compressor cylinder form a compressor chamber for compressing a fluid. A shaft is provided that rotates around its axis. A lifting element is arranged eccentrically to the axis of the shaft and is provided fixed to the shaft. The lifting element and the piston are configured in such way that the piston performs a movement between a maximum and a minimum lifting position when the shaft rotates around its axis.

Claims

1. A piston compressor, comprising: a piston guided in a compressor cylinder, wherein the piston and the compressor cylinder form a compressor chamber for compressing a fluid; a shaft provided so as to rotate around its axis; and a lifting element arranged eccentrically to the axis of the shaft and provided fixed to the shaft, wherein the lifting element and the piston are configured such that the piston performs a movement between a maximum and a minimum lifting position when the shaft rotates around its axis, the compressor further comprises at least one further piston guided in a further compressor cylinder, the at least one further piston connected, directly or via further intermediate elements, to a further lifting element for each at least one further piston arranged on the shaft such that the at least one further piston is configured to perform a movement between a maximum and a minimum lifting position when the shaft rotates around its axis, a space that provides cooling is provided between the lifting element and the further lifting elements, and the space houses a cooling fluid therewithin, the shaft has a cylindrical shape and the lifting element has a hollow cylindrical shape, an inner diameter of the hollow cylindrical shaped lifting element corresponds to an outer diameter of the shaft, and an outer diameter of the hollow cylindrical shaped lifting element corresponds to an inner diameter of bearings for coupling the lifting element with the intermediate elements and the further intermediate elements, and the lifting element and the further lifting element are arranged so as to abut each other in the axial direction of the shaft.

2. The compressor according to claim 1, wherein the lifting element and the piston are directly connected to each other or are connected via intermediate elements.

3. The compressor according to claim 1, wherein the compressor comprises at least two further pistons, each further piston being guided in a further compressor cylinder.

4. The compressor according to claim 3, wherein the compressor cylinder and the further compressor cylinders are arranged in an angular arrangement, an angle between axes of the compressor cylinders is between 60 and 120.

5. The compressor according to claim 1, wherein the compressor cylinder and the further compressor cylinder are arranged such that a distance between axes of the compressor cylinder and the further compressor cylinder in the direction of the axis of the shaft: (i) is smaller than a sum of outer radiuses of the compressor cylinder and the further compressor cylinder, and/or (ii) is larger than an extension of each intermediate element coupling the piston with the shaft.

6. The compressor according to claim 1, wherein the compressor cylinder and the further compressor cylinder are arranged in a row.

7. The compressor according to claim 1, wherein the at least one further piston is connected directly or via the further intermediate elements to the further lifting element such that the at least one further piston is configured to perform a movement between a maximum and a minimum lifting position when the shaft rotates around its axis, wherein an extension of the lifting element in a direction of the axis of the shaft is selected such that the piston and the at least one further piston are connectable to the lifting element and the further lifting element, wherein axes of the pistons are positioned spaced from each other in the direction of the axis of the shaft.

8. The compressor according to claim 7, wherein each lifting element and the shaft are configured as one piece, the shaft has a cylindrical shape, and/or the lifting element has a disc shape or a cylindrical shape.

9. The compressor according to claim 1, further comprising: a split crank case with two separate parts that are connectable with each other along a connecting surface, wherein, before connecting the separate parts with each other, a mounting opening that is delimited by the connecting surface is dimensioned such that a pre-assembled crank drive comprising the shaft, the lifting element and the piston, is insertable via the mounting opening into one of the two separate parts.

10. The compressor according to claim 9, wherein (i) the connecting surface extends parallel to the direction of the axis of the shaft, wherein at least one of the cylinders is coupled to one of the separate parts while the remaining cylinder/s are connected to the other part, or (ii) the connecting surface extends perpendicular to the axis of the shaft, wherein the connecting surface cuts each cylinder opening in the crank case of each cylinder into two parts.

11. The compressor according to claim 1, wherein each of the lifting element and the further lifting element are configured as a separate piece, the lifting elements and the shaft are connected with each other in a torque transmitting manner by a connecting force acting in the direction of the axis of the shaft, and the connecting force is provided by biasing the shaft and the lifting elements in the direction of the axis of the shaft against each other.

12. The compressor according to claim 11, wherein each of the lifting elements comprise a bore for receiving the shaft, the bores of each lifting element are aligned to each other in that that the shaft, being cylindrically shaped, is insertable in the direction of the axis of the shaft through the bores when each lifting element is already preassembled in a crank case of the compressor in that they are already coupled with the pistons, and further comprising an abutment surface protruding in a radial direction, with respect to the axis of the shaft, from the shaft to allow transmitting the connecting force from the shaft to the lifting elements.

13. The compressor according to claim 1, wherein the lifting elements are arranged eccentrically to the axis of the shaft, and are provided fixed to the shaft, the lifting elements are aligned with each other in that an angle between the symmetry axis of the lifting elements is less than 180.

14. The compressor according to claim 1, wherein the piston is connected to the lifting element via a connection rod, the lifting element comprises a circular disc, which is eccentrically provided to the shaft regarding its axis, a roller bearing or a slide bearing is provided between the lifting element and the piston, and/or the fluid is a gas or a liquid.

15. A vehicle, comprising: a compressor according to claim 1, and (i) wherein the compressor is configured to supply air to at least one of the following systems of the vehicle: a fuel cell, a pneumatic braking system, an air suspension, a compressed air reservoir, and/or (ii) wherein the vehicle is configured as a commercial vehicle, a truck, a trailer, a passenger car, and/or a combination of a towing vehicle and a trailer, and/or (iii) wherein the vehicle is configured as an electric, hybrid or conventional vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a shows a schematic drawing of a piston compressor according to an embodiment of the invention, wherein the piston is in its maximum lifting position,

(2) FIG. 1b shows the compressor of FIG. 1a, wherein the piston is in its minimum lifting position,

(3) FIG. 2a shows another embodiment of a shaft of a piston compressor according to the invention and a lifting element,

(4) FIG. 2b shows another embodiment of a shaft of a piston compressor according to the invention and a lifting element,

(5) FIG. 2c shows another embodiment of a shaft of a piston compressor according to the invention and two lifting elements,

(6) FIG. 2d shows a further embodiment of a shaft of a piston compressor according to the invention and two lifting elements,

(7) FIG. 2e shows another embodiment of a shaft of a piston compressor according to the invention and two lifting elements, and

(8) FIG. 2f shows another embodiment of a shaft of a piston compressor according to the invention and two lifting elements.

(9) FIG. 3 is a schematic side view of a compressor according to an embodiment of the invention;

(10) FIG. 4 is a schematic front view of a compressor according to an embodiment of the invention;

(11) FIG. 5 is a schematic side view of the compressor of FIG. 3 with crank case and air passages;

DETAILED DESCRIPTION OF THE DRAWINGS

(12) FIG. 1a and FIG. 1b are schematic drawings of a piston compressor, wherein the piston is in its maximum lifting position. (FIG. 1a) and minimum lifting position (FIG. 1b).

(13) A piston 1 is shown which is guided in a compressor cylinder 2. The compressor cylinder 2 extends in the drawing vertically upwards so that its axis 10 is oriented vertically. The piston 1 is movable in the compressor cylinder 2 along the axis 10 from a maximum lifting position as it is shown in FIG. 1a to a minimum lifting position as it is shown in FIG. 1b. The piston 1 and the compressor cylinder 2 form a compressor chamber 3, wherein a fluid is compressed by the movement of the piston 1.

(14) Further, a shaft 4 is shown extending perpendicularly out of the drawing plane. Consequently, the axis 5 of the shaft 4 extends perpendicularly out of the drawing plane as well. The shaft 4 is configured so as to rotate around its axis 5.

(15) A lifting element 6 is provided on the shaft 4. The lifting element 6 comprises a circular or cylindrical element. The axis of the circular or cylindrical element is oriented in parallel to the axis 5 of the shaft 4 but with an offset to this axis 5. Thus, the lifting element 6 is provided eccentrically to the shaft 4.

(16) When the shaft 4 rotates around its axis 5, the lifting element 6 rotates around this axis as well due to its fixed connection to the shaft 4.

(17) Around the lifting element 6, a connection element 7 is provided. The connection element 7 comprises a circular or cylindrical element coaxially provided to the lifting element 6. The lifting element 6 and the connection element 7 form a space 8 between both elements 6, 7.

(18) The space 8 can be configured in such way, that the lifting element 6 slides on the inner surface of the connection element 7 while the shaft 4 rotates around its axis 5. Therefore, a slide bearing is formed by the lifting element 6, the connection element 7 and the space 8. In this embodiment, a lubricant can be provided in the space 8 to reduce friction between the lifting element 6 and the connection element 7.

(19) In another embodiment, roller elements such as balls or needles, are provided in the space 8. Therefore, a roller bearing is formed by the lifting element 6, the connection element 7 and the space 8 comprising the roller elements. In this embodiment, a lubricant can be provided in the space 8 to reduce friction between the lifting element 6, the roller elements and the connection element 7.

(20) As the lifting element 6 is arranged eccentrically to the axis 5, the lifting element 6 and the connection element 7 perform a lifting movement when the shaft 4 rotates, in particular performs a full rotation, around its axis 5.

(21) To the connection element 7, an intermediate element 9 comprising a connection rod is pivotally attached with one end of the connection rod. The other end of the connection rod is pivotally attached to the piston 1. The intermediate element 9 is configured such that, when the shaft 4 rotates, in particular performs a full rotation, around its axis 5, the intermediate element 9 transmits the lifting movement of the connection element 7 to the piston 1.

(22) This lifting movement can be seen by comparing FIG. 1a and FIG. 1b showing the piston 1 in the maximum (FIG. 1a) and minimum (FIG. 1b) lifting position.

(23) Further components of the compressor, in particular ports or valves, are not shown to keep the drawing simple.

(24) The embodiment shown in FIG. 1a and FIG. 1b represents only one embodiment according to the invention. Further embodiments can be formed by providing more than just one piston. For example, two or more pistons can be arranged around the axis 5 of the shaft 4. Preferably, these pistons are arranged regularly spaced. For example, three or six pistons can be arranged around the shaft 4, in particular spaced by 120 or 60, respectively.

(25) In the following, several embodiments of a shaft and one or more lifting elements are shown.

(26) FIG. 2a shows an embodiment of a shaft of a piston compressor according to the invention and a lifting element.

(27) A shaft 4 with an axis 5 is shown extending from the left to the right. On the shaft 4 a lifting element 6 is provided, which is shown in a section view. The shaft 4 and the lifting element 6 are provided as two separate elements.

(28) The lifting element 6 is provided eccentrically to the axis 5 of the shaft 4 causing the lifting element 6 to perform a lifting movement when the shaft 4 rotates, in particular performs a full rotation, around its axis 5.

(29) Around the lifting element 6 one or more piston(s) can be arranged which are each guided in a compressor cylinder as described above. The pistons can be arranged in the same plane the axis 5 is oriented perpendicular to. That means, each axis of the compressor cylinders can be arranged in this plane.

(30) FIG. 2b shows another embodiment of a shaft of a piston compressor according to the invention and a lifting element.

(31) In contrast to the embodiment shown in FIG. 2a, the lifting element 6 comprises a bigger extension in the direction of the axis 5. This allows the arrangement of more pistons in the direction of the axis 5 which can be moved by the one lifting element 6. This allows providing compressor cylinders in a row, wherein the pistons of these cylinders are controlled by the same lifting element 6.

(32) FIG. 2c shows another embodiment of a shaft of a piston compressor according to the invention and two lifting elements.

(33) Basically, this embodiment corresponds to the embodiment of FIG. 2a, wherein a further lifting element 13 is provided on the shaft 4. Between both lifting elements 6, 13 a space 11 in the direction of the axis 5 is formed. As the lifting elements 6, 13 are connected to the connection element 7 of FIG. 1a and FIG. 1b, respectively forming a part of a roller or slide bearing, the space 11 is used for cooling the lifting elements 6, 13. In particular, cooling of a permanent lubricant can be ensured and flowing out of the lubricant from the bearings is avoided due to the lubricant getting too fluent.

(34) FIG. 2d shows a further embodiment of a shaft of a piston compressor according to the invention and two lifting elements.

(35) This embodiment corresponds to the embodiment shown in FIG. 2c, wherein the further lifting element 13 comprises a sleeve 12 the shaft 4 extends through. The sleeve 12 abuts to the lifting element 6. As the part of the further lifting element 13 is thinner than the part comprising the sleeve 12, a space 11 is formed between the lifting elements 6, 13. This space 11 is used for cooling in the same manner as described above with respect to FIG. 2c.

(36) FIG. 2e shows another embodiment of a shaft of a piston compressor according to the invention and two lifting elements.

(37) This embodiment corresponds to the embodiment shown in FIG. 2d, wherein the sleeve 12 is configured as a separate element. Therefore, manufacturing of the lifting elements 6, 13 and of the sleeve 12 gets easier because the geometry of each element 6, 12, 13 is simplified.

(38) FIG. 2f shows another embodiment of a shaft of a piston compressor according to the invention and two lifting elements.

(39) This embodiment essentially corresponds to the embodiment of FIG. 2c. In contrast, the lifting elements 6, 13 and the shaft 4 are configured as one piece. Advantageously, the lifting elements 6, 13 do not have to be mounted to the shaft 4 in a separate assembling step.

(40) The embodiments shown in FIG. 1a, FIG. 1b and FIGS. 2a to 2f are not limiting of the subject-matter of the invention. Instead, the intention of these drawings is to illustrate some aspects of the invention in more detail. Furthermore, more embodiments can be formed by combining some or all of the shown embodiments.

(41) In the following, FIGS. 3 to 5 will be described in detail, wherein different names might be used for the same parts. For instance, the connecting element 7 may at least partially be referred to as a connecting rod or conrod.

(42) FIG. 5 schematically illustrates the cross section of a compressor 14, in particular of an air compressor 14. The compressor 14 comprises a shaft 4 being rotatably mounted by roller bearings 15 around a rotation axis 17. The illustrated compressor 14 comprises three compressor units 19, each of which comprises a cylinder 23 and a piston 21. As can be seen by the front view of FIG. 4, the compressor units 19, in particular their pistons 21 and cylinders 23 are spaced from each other in the circumferential direction by 120. To simplify the illustration, FIG. 5 only shows one compressor unit 19.

(43) The compressor 14 further comprises three crank mechanisms 25 for transforming a rotational movement 27 of the shaft 4 into a reciprocating movement 29 of the piston 21. Each of the crank mechanisms 25 comprise a lifting element 31 in the form of an eccentric 31, in particular of a disc-shaped eccentric 31. Further, each crank mechanism comprises a conrod 33 being coupled with the shaft 4 by a roller bearing 36. The roller bearing 36 surrounds the shaft 4 (crank shaft 4). In particular, the roller bearing 36 is mounted on and surrounds the disc-shaped eccentric 31. The shaft 4 and the eccentrics 31 are surrounded by the roller bearing 36 in circumferential direction U. The axial direction A is indicated with A. The radial direction is indicated with R.

(44) As can best be seen in FIGS. 3 and 5, the shaft 4 is free of counterweights and flywheels 35 being mounted in axial direction A between the crank mechanisms 25, in particular between the disc-shaped lifting elements 31 and the conrods 33 being mounted on the lifting elements 31 by roller bearings 36. In particular, the crank mechanisms 25, in particular the lifting elements 31, are located in axial direction A directly next to each other. The lifting elements 31 are realized as eccentrics 31, in particular as disc-shaped eccentrics 31. In the illustrated case, the disc-shaped eccentrics 31 are produced as individual parts with respect to each other and with respect to the shaft. However, the lifting elements 31 are fixedly connected on the shaft 4 in that they rotate with the same rotation speed as the shaft. In the illustrated case, this is realized by a threaded nut 90 which engages a thread 92 on the shaft 4 to connect the lifting elements in a force fitting manner, namely by a compression force 94 acting in axial direction A. In the present case, the compression force 94 compresses the lifting elements 31, the flywheels 35 and a ring shaped shoulder 96 against each other. The ring shaped shoulder 96 provides an abutment surface protruding in radial direction from the shaft to allow transmitting the connecting force from the shaft 4 to the lifting elements 31, in particular from the threaded nut 90 via the ring shaped shoulder 96 through the flywheel 35 to the lifting elements 31. The ring shaped shoulder 96 can be connected to the shaft by any fitting method, in particular by press fitting. Alternatively, the lifting elements 31 and the shaft can be produced from one piece, for instance by casting. Alternatively, only the three lifting elements 31 can be produced as one single piece, in particular in the form of a perforated cylinder having a cylindric bore which is offset from the symmetry axis of the cylinder so that they can act as eccentric. Such perforated cylindrical eccentric 31 could be fixed on the shaft 4 for instance by press fitting.

(45) As can best be seen from FIGS. 3 and 5, the compressor units 19, in particular the middle axis of their pistons 21, and/or the crank mechanisms 25, in particular the lifting elements 31 and the conrods 33, are located in axial direction A between the roller bearings 15. In particular, the roller bearings 15 are spaced from each other in axial direction A to provide a space in between for the compressor units 19, in particular the middle axis of the pistons 21 and the crank mechanisms 25, in particular the lifting elements 31. As can further be seen in FIG. 5, the roller bearings 15 which rotatably mount the shaft 4 are preferably spaced in axial direction A to provide space for the crank mechanisms 25, the compressor units 19 and the flywheels 35 in between the roller bearings 15. In particular, the flywheels 35, the crank mechanisms 35 and the compressor units 19 are located in axial direction between the roller bearings 15 of the shaft 4.

(46) The compressor 14 further comprises two flywheels 35 being configured to counteract mass forces 37, 39, 41, in particular rotating mass forces 37 and alternating mass forces 39, 41, acting on the shaft 4. This is in particular realized by configuring the flywheel in that, in addition to its flywheel function (flattening the torque curve of a compressor), it provides a counterweight function. This is in particular realized by configuring the flywheels 35 in that their centers of gravity 43 are spaced in radial direction R from the rotation axis 17 and positioned in circumferential direction relative to the lifting elements 31, the conrods 33 and the pistons 21 in that the resulting rotating mass force 45 of the flywheels 35 counteract the mass forces 37, 39 and 41 of the lifting elements 31, the conrods 33 and/or the pistons 31. As can be seen in FIG. 3, the center of gravity 43 of the flywheels 35 are aligned with each other in circumferential direction U. In other words, the space of the centers of gravity 43 of the flywheels 35 in circumferential direction U is zero. Additionally, the center of gravity 43 of the flywheels 35 is spaced from the rotation axis 7 of the shaft 4 by the same distance.

(47) The flywheels 35 in FIGS. 3, 4 and 5 are configured to counteract rotating mass forces 37 of the eccentrics 31. This is in particular realized by configuring the flywheels 35 in that their center of gravity 43 is spaced in radial direction R from the rotation axis 17,55 of the shaft 4 and of the flywheel 35, wherein the center of gravity 77 of the eccentrics 31 is spaced from the center of gravity 43 of the flywheel 35 in circumferential direction U by 180. In other words, the center of gravity 77 of the eccentrics 31 are located in circumferential direction on opposite sides of the rotation axis 17, 55 of the shaft 4 and the flywheel 35. As the flywheel 35 and the eccentrics are coupled with the shaft 4 in that they rotate with the same rotation speed as the shaft, their relative position in circumferential direction U with respect to each other remains constant upon the rotation of the shaft 4. Therefore, the rotating mass forces 37 of the eccentrics 31 act in the opposite radial direction R as the rotating mass forces 45 of the flywheels 35, thereby counteracting each other.

(48) The flywheels 35 are further configured to counteract alternating mass forces 39, 41 of the pistons 21. As can be seen in FIG. 4, each piston 21 causes alternating mass forces 39 which act in a direction parallel to the movement 29 of the piston 21. The alternating mass forces 39 comprise a parallel force component 41 acting parallel to the rotating mass forces 37 of the lifting elements 31 and an orthogonal force component 40 acting orthogonal to the rotating mass forces 37 of the lifting elements 31. The circumferential position of the pistons 21 and of the lifting elements 31 are chosen with respect to each other in that the alternating mass forces 39, 40, 41 of the pistons 21 at least partially compensate each other, in particular in that the orthogonal components 40 at least partially compensate each other. In particular, their circumferential positions are chosen with each other in that the alternating mass forces 39, 40, 41 superimpose each other into a superimposed force 79 with varying amplitudes acting parallel to the rotating mass forces 37 of the lifting elements 31. This is in particular realized by circumferentially offsetting the pistons 21 from each other by 120 into a star arrangement, as shown in FIG. 4 in combination with aligning the centers of gravity 77 and/or the symmetry axis of the eccentrics 31 with each other, as shown in FIG. 4. Based on such superimposed alternating mass force 79, the center of gravity 43 of the flywheels 35 can be spaced from the rotation axis 7 of the shaft 13 in the opposite direction of the superimposed force 79. Thereby, the flywheels 35 can be used to compensate both, the rotating mass forces 37 of the lifting elements 31 and at least a part of the parallel force components 41 of the alternating mass forces 39 of the pistons 21.

(49) FIG. 5 illustrates a preferred embodiment of compressor 14 which sucks air from the inside of the crankcase 81. The crankcase 81 comprises a housing 83 in which the shaft 4, the lifting elements 31 and at least part of the conrods 33 are located. The shaft 4 is rotatably mounted via the roller bearings 15 against the housing 83 and a cover 91 of the crank case 81. The housing 83 comprises one bore 85 for each piston 21 through which the conrod 33 and the piston 21 can protrude out of the housing 83. The crankcase 81 further comprises a cylinder 23 for each piston 21. The cylinder 23 can be located in radial direction R over the bore 85.

(50) The crankcase housing 83 can further comprise a mounting opening 89 for inserting the shaft 4, in particular pre-mounted with the eccentrics 31, in axial direction A into the housing 83. The crankcase 81 further comprise a cover 91 for closing the mounting opening 89 after the shaft 4, and in particular the crank mechanisms and the compressor units are mounted. The shaft 4 can be supported in radial direction R by roller bearing 15 against the cover 91. The cover 91 and the housing 83 both comprise a bore with the same diameter and the same rotation axis, in particular the rotation axis 17 of the shaft, via which the roller bearings 15 are rotatably mounted at the housing 83 and the cover 91.

(51) The compressor 14 further comprise an air-filter 95 for filtering air before entering the crankcase 81. The air-filter 95 is mounted in axial direction A between the cover 91 and a filter cover 99. The air-filter 95 can be hollow cylindrically shaped. The air flow 97 through the compressor 14 is schematically illustrated by reference sign 97. From the left to the right, the air passes through (not shown) openings in the air-filter cover 99 into the inside of the hollow cylindrically shaped air-filter 95 through which the air 97 passes in radial direction R. After leaving the air-filter 95, the filtered air 97 enters the crankcase housing 83 via not shown openings in the cover 91. Subsequently, the air passes through openings (bores) 101 in the piston 21 into the air compression chamber delimited by the piston 21 and the cylinder 23. The cylinder 23 comprises openings (bores) 103 into a discharge-channel system 105. The discharge-channel system 105 comprises a ring shaped air collecting channel 107 in which compressed air from the three compressor units 19 is collected before being guided to an consume of compressed of air, such as a pneumatic braking system. The collecting channel 107 comprises cooling fins 108. The collecting channel 107 is fluidly connected with each of the compressor units 19 by individual discharge channels (lines) 109. The individual discharge channels 109 can be delimited, in radial direction on the inside, by the cylinder 23 and, in radial direction at the outside, by a cylinder cover 111. Further, in particular in the course of the individual discharge channels 109 in radial direction R, the discharge channel 109 can be realized by a bore through the cylinder 23 extending in axial direction of the shaft outside of the compression chamber. Further, the individual discharge channel 109 can and/or the collecting channel 107 can be integrated into the crankcase housing 83.

(52) FIG. 5 illustrates an embodiment of a compressor 14, in which the lifting element 31 and the further lifting element/s 31 are configured as a separate piece, wherein the lifting elements 31 and the shaft 4 are connected with each other in a torque transmitting manner by a connecting force 94 acting in the direction A of the axis 17 of the shaft 4. The force 94 is provided by biasing means 90, 92 biasing the shaft 4 and the lifting elements 31 in the direction A of the axis 17 of the shaft 4 against each other. The biasing means comprise a threaded nut 90 cooperating with a corresponding thread 92 on the shaft 4. Each of the lifting elements 31 are disc shaped and comprise a bore 114 a for receiving the shaft 4. The bores 114 of the lifting elements 31 are aligned to each other in that that the shaft 4 can be inserted in the direction of the axis of the shaft 4 through the bores 114. Thereby, each lifting element 31 can be previously preassembled in a crank case 81 of the compressor 14 in that they are already coupled with the pistons 21. The compressor further comprises a ring shaped shoulder 96 providing an abutment surface 116 protruding in radial direction, with respect to the axis of the shaft, from the shaft to allow transmitting the connecting force 94 from the shaft 4 to the lifting elements 31.

(53) Due to the fact that the lifting elements 31 are separate elements, they can be individually pre-assembled to the pistons 21 outside of the crank case 81 which allows a strong fitting, in particular press fitting, between the connecting rods 33 and the lifting elements 31, in particular via roller bearings 36 connecting the lifting elements 31 with the pistons via the connecting rod 33. Further, thanks to the lifting elements being separate parts, they can be inserted into the crank case via piston openings, in particular bores 85, in the crank case 81. This particularly allows to combine the advantages of pre-assembling the pistons 21 and the lifting elements 31 outside of the crank case 81 with a one-piece crank case 81. The torque transmission from a motor, in particular electric motor, to the shaft 4 can be provided by coupling, for instance by a clutch 118.

(54) In an alternative embodiment, the crank case can be a split crank case, which is illustrated by the cutting lines 120 and 122 in FIG. 5. Split line 120 illustrates an embodiment, in which the split line extends in axial direction A. Split line 122 illustrates an alternative embodiment, in which the split line extends in radial direction R. Along the split line 120, 122, the separate parts of the crank case can be connected with each other. By selecting the split lines for example as illustrated by the split lines 120 and 122, a pre-assembled crank drive comprising the shaft 4, the lifting elements 31, the connecting rods 33 and the pistons 21 can be inserted via a mounting opening into one of the separate parts of the crank case. This allows to preassemble the complete crank drive with multiple pistons 21 outside of the crank case 81 and/or to configure multiple lifting elements 31 in one peace while still enabling an easy assembling of the compressor 14.

(55) The features disclosed in the above description, the figures and the claims might be significant for the realization of the invention in its different embodiments individually as in any combination.

REFERENCE SIGNS

(56) 1 piston 2 compressor cylinder 3 compressor chamber 4 shaft 5 axis 6 lifting element 7 connection element 8 space 9 intermediate element 10 axle of compressor cylinder 11 space 12 sleeve 13 lifting element 14 compressor 15 roller bearings 17, 55 rotation axis 19 compressor unit 21 piston 23 cylinder 25 crank mechanism 27 rotational movement 29 reciprocating movement 31 eccentric 33 connecting rods/conrods 35 flywheel 36 roller bearing 37 rotating mass forces 39 alternating mass force of the piston 40 orthogonal force component 41 parallel force component 43 center of gravity of the flywheel 45 rotating mass forces 77 center of gravity of the eccentric 79 superimposed force 81 crank case 83 housing 85 bore 89 mounting opening 90 threaded nut 91 cover 92 thread 94 compression force 95 air filter 96 ring-shaped shoulder 97 air flow 99 filter cover 101, 103 openings (bores) 105 discharge-channel system 107 collecting channel 108 cooling fins 109 individual discharge channel 111 cylinder head (cover) 114 bore 116 abutment surface 118 clutch 120, 122 cutting lines R radial direction A axial direction U circumferential direction