Reciprocating Piston Machine, in Particular a Compressor for a Vehicle Air-Conditioning Unit
A reciprocating piston machine (100) is provided such as a CO2 compressor for a vehicle air-conditioning unit. The machine (100) comprises a plurality of pistons and a swivel disk (107) that is rotated by and can be positioned at an adjustable angle with respect to a drive shaft (104). The swivel disk (107) is mounted on the drive shaft (104) so as to be axially movable thereon. In addition, the swivel disk is connected in an articulated manner to at least one supporting element (109) which is disposed so that it is spaced apart from the drive shaft (104) but rotates therewith. Each of the pistons (106) comprises a joint arrangement (110) with which the swivel disk (107) is in sliding engagement. The connection (116) between the drive shaft (104) and the swivel disk (107) serves substantially only to transmit torque, whereas the supporting element (109) serves substantially only to provide axial support to the pistons (106) and/or to the swivel disk (107) and hence to absorb the force exerted by the gas.
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The invention relates to a reciprocating piston machine and, in particular to a CO2 compressor for a vehicle air-conditioning unit.
A reciprocating compressor of this kind is known, for example, from the German patent DE 197 49 727 A1. This compressor comprises a case within which is disposed a plurality of pistons arranged in a circle around a rotating drive shaft. The driving force is transmitted from the drive shaft to an annular swivel disk by way of a driver and, in turn, is transmitted from the disk to the pistons, the reciprocating movement of which is parallel to the drive shaft. The annular swivel disk is pivotally mounted on a sleeve that is mounted on the shaft so as to be slidable in the axial direction. Within this sleeve a slot is provided through which the driver engages the disk. The extent to which the sleeve can slide along the drive shaft is thus limited by the dimensions of the slot. The apparatus is assembled by installing the driver so that it projects through the slot. Drive shaft, driver, sliding sleeve and swivel disk are disposed in a so-called drive space where the pressure can vary. The volume displaced, and hence the transport efficiency of the compressor, depend on the relationship between the pressures on the suction side and the pressure side of the pistons or, correspondingly, on the pressures in the cylinders on the one hand and in the drive space on the other hand.
The driver serves to transmit torque between the drive shaft and the swivel disk as well as to provide axial support for the pistons, i.e. to absorb the force of the gas. The construction according to DE 197 49 727 A1 is based on an older construction, for instance according to DE 44 11 926 A1, in which the driver consists of two parts; a first driver part attached to the drive shaft is disposed next to the swivel disk, at a considerable distance therefrom, and a second driver part, in articulated engagement with the first part, constitutes a lateral projection from the swivel disk. This construction has the disadvantage that it is crucially involved in determining the minimal axial length of the compressor. Furthermore, the swivel disk with its thickened hub region has a relatively large moment of inertia because of its lateral projection, combined with a centre of gravity a considerable distance away from the drive axis, so that a sudden change in rotational velocity with corresponding inertia results in an undesired tilting of the swivel disk. Also, because the centre of gravity is far from the tilt axis, the drive mechanism is put out of balance because it can be balanced only for what is preferably a mean angle of swivel-disk tilt. Similar considerations apply to the construction according to EP 1 172 557 A2.
In comparison to these known constructions, the one proposed according to DE 197 49 727 is distinguished by being considerably more compact. Inertial forces are reduced to a minimum. Furthermore, this construction also ensures that the inner dead-point position of the pistons is maintained precisely; so-called exhaust spaces are prevented. A preferred embodiment according to DE 97 49 727 will now be described in detail with reference to
The head shape of the free driver end makes it possible to change the tilt angle of the annular disk 6, in that the driver head 15 forms a bearing body about which the disk 6 pivots, making a tilting movement that alters the stroke magnitude of the pistons 2. Another prerequisite for tilting of the disk 6 is that its bearing spindle 20 must be able to move along the drive shaft 5. For this purpose, as shown in
A disadvantage of the known construction is that because of the principle according to which the driver contacts the swivel disk, the deformation produced in the disk is not the same on both sides, and therefore the way in which the disk runs along the sliding blocks becomes unfavorable. In the vicinity of the cylindrical bore in the swivel disk within which the spherical end of the driver is supported, this construction leaves only a very thin wall remaining, so that this region becomes severely deformed. Hence the running properties of the sliding blocks along the swivel disk are correspondingly impaired. This problem has been recognized previously. A means of avoiding it is proposed, for example, in WO 02/38939 A1, namely a difference between the geometrical shapes of driver and associated bore.
FR 2 782 126 A1 discloses another swivel-disk drive mechanism in which a driver projects into a swivel disk. Unlike the state of the art according to DE 197 49 727 A1, however, this swivel disk is also coupled in the radial direction and therefore cannot be displaced radially. The advantage of this construction is that the associated joint can transmit forces over an area, and consequently enables a relatively compact construction.
In summary, however, it can be concluded that all of the known constructions suffer from the disadvantages discussed below, in particular because of the superposition of multiple functions:
-
- to transmit the driving force (by way of driver/torque support) and also
- to support the swivel disk in such a way that the top-dead-centre point of the piston remains unchanged.
This produces the following behaviour:
-
- both of these influences subject the head of the driver, which as a rule is spherical, to considerable surface pressure in two regions;
- this surface pressure also appears at the corresponding places on the swivel disk;
- as a result of these surface pressures deformations can easily occur, which can influence one another in an uncontrolled manner, depending on the circumstances.
Impinging on the known driver/torque support are both the torque and the reactive force exerted by the swivel disk to support resulting gas forces. Both force and bending moment are maximal in the region of the seating on the drive shaft. Hence the drive shaft must have correspondingly large dimensions, and of course this also applies to the dimensioning of both the driver and the swivel disk, especially in the region of the bore in which the driver is seated. The larger dimensions inevitably result in correspondingly higher masses and hence moments of inertia. These can unfavorably influence the regulatory behavior and must be compensated. Another result of the larger dimensions is that the joint arrangements associated with the pistons are larger or must be made larger. This applies to the sliding blocks as well as to the pistons themselves.
To remedy this situation, measures must be taken to reduce the impinging forces.
Hence, it is an object of the present invention to provide a reciprocating piston machine such as a compressor of the kind cited above that has a more lightweight construction without restricting its functional reliability.
According to the present invention there is provided a reciprocating piston machine, such as a CO2 compressor for vehicle air-conditioning units, comprising a plurality of pistons and a swivel disk, in particular annular in form, that is rotated by a drive shaft and that is positioned at an adjustable angle with respect to the drive shaft, the disk being mounted on the drive shaft so as to be axially movable thereon and being connected in an articulated manner to at least one supporting element so disposed that it is spaced apart from the drive shaft but rotates therewith, and each of the pistons comprising a joint arrangement with which the swivel disk is in sliding engagement; characterized in that the connection between the drive shaft and the swivel disk serves substantially only to transmit torque, and the supporting element serves substantially only to provide axial support to the pistons and/or to the swivel disk and hence to absorb the force exerted by the gas.
The aim of the present invention is thus to avoid the functional superposition present in the state of the art, namely
-
- to support the gas force, as well as
- to transmit torque
in the region between swivel disk and drive shaft. That is, these functions are uncoupled, so that the demands placed on the individual components for transmitting the said forces and moments are reduced and hence the components can be made smaller. In particular, it is also possible for tolerances between the individual components to be adjusted more precisely, and excessive surface pressures can be avoided. In accordance with the invention, therefore, the axial support of the pistons on one hand and the transmission of torques from the drive shaft to the swivel disk on the other hand are assigned to different components.
It has proved useful to transmit the torque by way of the swivel joint between disk and drive shaft, especially in view of the fact that as a rule two pin joints are provided for the purpose. The amount of play in this pin suspension can be precisely adjusted, and pressure points can be avoided. Hence, in accordance with the invention a superposition of circumferential and axial forces in the region between supporting element and swivel disk is prevented.
Preferred embodiments and structural details of the solution in accordance with the invention are described in the subordinate claims.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, wherein
The compressor 100 shown schematically in longitudinal section in
The swivel-disk mechanism 105 comprises an annular swivel disk 107 that is movably connected both to a sliding sleeve 108, which is mounted on the drive shaft 104 so as to be axially displaceable, and to a supporting element 109, which is disposed so that it is spaced apart from the drive shaft 104 but rotates therewith. Each of the pistons 106 comprises a joint arrangement 110 with which the annular swivel disk 107 is in sliding engagement. The joint arrangement 110 is constructed according to the state of the art and comprises two hemispherical sliding blocks 111, 112.
The sliding sleeve 108 is likewise constructed according to the state of the art, and is placed under axial tension by helical compression springs 113.
The supporting element 109 in the embodiments illustrated in
Because the transmission of torque is uncoupled from support against the force exerted by gas, it is possible to make the swivel disk relatively small and correspondingly lightweight in structure, without the occurrence of deformations. It is also simpler to construct the force-transmitting means without allowance for play, with the consequence that the compressor makes less noise during operation.
The tilting articulation 116 between drive shaft 104 and swivel disk 107 can be variously constructed. As can be seen in
In the embodiment according to
In the embodiment according to
The embodiment according to
In the embodiment shown in
The above-mentioned abutment 121 also ensures that the centre 122 of the spherical supporting element 109 coincides with the midpoint of the joint arrangement 110 associated with each piston, with no need for additional adjustments during assembly of the compressor. This installed position is preferred; however, it can also be advantageous to provide a slight “offset” amounting to as much as about 1/10 mm between the circle on which the centre of the supporting element 109 lies and the circle passing through the midpoints of the joint arrangements 110, so that the exhaust space will vary slightly depending on the tilt angle. Preferably the centre 122 of the supporting element 109 is situated on a circle that extends radially slightly beyond the circle on which the midpoints of the piston-joint arrangements 110 lie. This embodiment has the advantage that the swivel disk is at no time subjected to tilting forces that would tilt it in another, unintended direction.
At this juncture it should once again be mentioned that it is conceivable to provide two, so-called, gas-force supports or supporting elements 109, which provide support in axially opposite directions. By this means it is possible to avoid a so-called double fitting, with the problem of over-specification. The two supporting elements can also be asymmetrically disposed.
In the case of a single gas-force support, it could support the swivel disk shortly ahead of the upper top-dead-centre position, because in this position the force is maximal owing to opening of the valve. In such a variant, however, care must be taken that the centre of the supporting element continues to coincide with the midpoint of the piston-joint arrangement 110. It should also be noted that when the joint is positioned ahead of top dead centre, the swivel disk is somewhat thinner-walled on its most heavily loaded, pressure, side than on the opposite, pulling, side.
The swivel-disk mechanism 105 here is identical to that in
In the embodiment according to
This construction has the advantage of avoiding the need to construct a bore in the drive shaft 104 to serve as bearing for the rod-like force-transmission element 114. Accordingly, the diameter of the drive shaft 104 can be greatly reduced.
Reference will now be made to
In addition, the swivel disk 107 differs from those previously described in that the slot 115 does not extend all the way through the swivel disk 107 but is blind and forms a recess or pocket 130. It is only open from the inner side of the disk 107 and is produced at an angle by a tool that is inserted from one side into the inner region of the swivel disk 107 or that first passes through the opposite side of the disk 107 in the directions indicated by the arrows A and B respectively.
One advantage of a pocket-shaped recess 130 is that oil is retained in the recess because of the centrifugal force acting here. This promotes good lubrication in the regions where force is transmitted. Another advantage lies in the fact that deformations of the swivel disk 107 owing to force transmission in the region of the pocket are avoided because the disk 107 is stronger by virtue of the fact that less of it has been removed than when the recess is open through to the outer circumference of the disk 107.
In a modification, as shown in dashed lines in
A further development of the construction of swivel disk arrangement shown in
The force-transmission element 114 can be connected to the shaft 104 in a suitable manner, for example by press fitting. In the embodiment shown in
In order to ensure that the centre of mass of the force-transmission element 114 coincides with the shaft axis, the region labeled ‘m’ of the force-transmission element 114 is preferably weighted.
It will be appreciated that the swivel disk 107 can be guided on or in the region of the drive shaft 104 by a great variety of structures and that those described here are merely several examples out of many possible arrangements. However, in all cases the designs uncouple the functions of the transmission of torque from the support that acts against the forces exerted by the pistons in order that the demands placed on the individual components for transmitting these forces and moments are reduced.
Further, it will be appreciated that the swivel disc 107 is mounted on the drive shaft 104 by means of a sleeve or bolt to which it is connected in an articulated manner and which is actually movable within the said drive shaft. Of course, the drive shaft 104 comprises a hollow portion for accommodating the aforementioned inner sleeve or bolt. Further, the hollow portion of the drive shaft comprises two longitudinally extending holes diametrically opposed through which the bearing pins 118 extend.
LIST OF REFERENCE NUMERALS
Claims
1. A reciprocating piston machine (100) comprising a plurality of pistons and a swivel disk (107) that is rotated by a drive shaft (104) and that is positioned at an adjustable angle with respect to the drive shaft (104), the disk (107) being mounted on the drive shaft (104) so as to be axially movable thereon and being connected in an articulated manner to at least one supporting element (109) so disposed that it is spaced apart from the drive shaft (104) but rotates therewith, and each of the pistons (106) comprising a joint arrangement (110) with which the swivel disk (107) is in sliding engagement, characterized in that the connection (116) between the drive shaft (104) and the swivel disk (107) serves substantially only to transmit torque, and the supporting element (109) serves substantially only to provide axial support to the pistons (106) and/or to the swivel disk (107) and hence to absorb the force exerted by the gas.
2. A machine (100) as claimed in claim 1, characterized in that the disk (107) is mounted on the drive shaft (104) by means of a sleeve (108, 133) or corresponding element to which it is connected in an articulated manner.
3. A machine (100) as claimed in claim 2, characterized in that the sleeve (108) or corresponding element, such as a bolt, is axially movable along the drive shaft (104) either around or within the said drive shaft.
4. A machine (100) as claimed in claim 1, characterized in that the supporting element (109) is constructed with a spherical, cylindrical or barrel-shaped (129) profile.
5. A machine (100) as claimed in claim 4, characterized in that the supporting element has a barrel-shaped longitudinal profile and a substantially spoon-shaped transverse cross-sectional profile.
6. A machine as claimed in claim 1, characterized in that the swivel disk (107) comprises a recess (115, 130) that defines a space in which the supporting element (109) is engaged, the long axis of the recess being oriented radially while its longer cross-sectional axis extends in the circumferential direction.
7. A machine (100) as claimed in claim 6, characterized in that the recess (130) formed in the swivel disk (107) that does not extend all the way through the swivel disk and is blind.
8. A machine (100) as claimed in claim 1, characterized in that the swivel disk (107) comprises at least one axial extension (131) in one or both axial directions.
9. A machine (100) as claimed in claim 1, characterized in that the supporting element (109) is connected to the drive shaft (104) by means of a rod-like force-transmission element (114).
10. A machine as claimed in claim 9, characterized in that the force-transmission element (114) projects away from the drive shaft (104) at an angle, so that when the swivel disk (107) is tilted at an intermediate position, the rod-axis is oriented radially with respect to the swivel disk (107).
11. A machine as claimed in claim 9, characterized in that force-transmitting element (114) is weighted to ensure that its centre of mass coincides with the axis of the drive shaft (104).
12. A machine (100) as claimed in claim 1, characterized in that the supporting element (109) is disposed at the free end of an L-shaped forcetransmitting element (114), one limb (126) of which extends approximately parallel to the drive shaft (104) and is supported axially against a bearing plate (127) that is nonrotatably connected to the drive shaft (104).
13. A machine as claimed in claim 1, characterized in that the centre (122) of the supporting element (109) lies on a circular line that either coincides with the circle on which the midpoints of the piston-joint arrangements (110) lie or extends radially slightly beyond said circle.
14. A machine as claimed in claim 1, characterized in that two supporting elements (109) are provided, which provide support in axially opposite directions.
Type: Application
Filed: Oct 1, 2004
Publication Date: Mar 26, 2009
Applicant: ZEXEL VALEO COMPRESSOR EUROPE GMBH (Ludwigsburg)
Inventor: Otfried Schwarzkopf (Kuerten)
Application Number: 11/664,154
International Classification: F04B 27/18 (20060101); F04B 27/10 (20060101);