Abstract:
The invention concerns a linear compressor, particularly a refrigerant compressor, with a housing ( 2, 2 ′) and a compression unit, which comprises a compressor with a piston and a cylinder as well as a linear motor driving the piston in relation to the cylinder along a movement axis, the compression unit ( 30 ) being connected to the housing ( 2 ) via a spring arrangement ( 7 ). It is endeavoured to provide a space saving support of the compression unit ( 30 ) in the housing that enables good vibration suppression. For this purpose, the spring arrangement comprises a spring ( 6, 7 ), which is curved in the circumferential direction in relation to the movement axis ( 50 ), said spring surrounding the compression unit ( 3 - 5 ) on at least a share of its circumference.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicant hereby claims foreign priority benefits under U.S.C. §119 from German Patent Application No. 10 2005 038 780.2 filed on Aug. 17, 2005, the contents of which are incorporated by reference herein. This Application relates to German Patent Applications No. 10 2005 038 783.7 (Attorney Docket No. 6495-0168); No. 10 2005 038 784.5 (Attorney Docket No. 6495-0169); No. 10 2005 038 785.3 (Attorney Docket No. 6495-0170); No. 10 2005 038 781.0 (Attorney Docket No. 6495-0172), filed on the same date herewith. 
     FIELD OF THE INVENTION 
     The invention concerns a linear compressor, particularly a refrigerant compressor, with a housing and a compression unit, which comprises a compressor with a piston and a cylinder as well as a linear motor driving the piston in relation to the cylinder along a movement axis, the compression unit being connected to the housing via a spring arrangement. 
     BACKGROUND OF THE INVENTION 
     During operation, the reciprocating piston causes oscillations in the compression unit. It is desired to decouple these oscillations from the housing in order to keep the noise generation outside the housing small. 
     Therefore, it is known from U.S. Pat. No. 6,881,042 B2 to support the compression unit of a linear compressor on the bottom of the housing via several helical springs. The helical springs cause a decoupling with regard to oscillations between the compression unit and the housing, so that outside the housing the oscillations are detectable only to a very limited extent. 
     However, such helical springs require relatively much space between the housing and the compression unit, so that dimensions of the housing will inevitably be increased. When such a compressor is used as refrigerant compressor in a domestic refrigeration appliance, for example a refrigerator or a freezer, the space required for the housing will no longer be available volume for storing goods to be cooled. Further, the helical springs have the disadvantage that perpendicular to their screw axis they can only provide a relatively poor damping. This, however, is exactly the direction, in which the reciprocating piston causes oscillations. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the task of providing a space saving supporting of the compression unit in the housing, which ensures good vibration damping properties. 
     With a linear compressor as mentioned in the introduction, this task is solved in that the spring arrangement comprises a spring, which is curved in the circumferential direction in relation to the movement axis, said spring surrounding the compression unit on at least a share of its circumference. 
     In directions lying in the plane of its curve, the spring has a relatively large rigidity. These directions substantially correspond to the cross-section of the compression unit. Accordingly, the risk is small that the spring will be too heavily deformed in a direction, in which the compression unit could strike against the inside of the housing. Due to the rigidity of the spring, given forces will namely only cause very small deflections in this direction. In a perpendicular direction, which is parallel to the movement axis of the piston, the spring has, however, a very soft characteristic, that is, a low rigidity or a low spring constant, so that the oscillations of the compression unit can be well adopted without being transferred to the housing. This is, however, exactly the direction, in which also the oscillations are generated. The higher rigidity of the spring exists in the x-direction and the y-direction, these directions defining the cross-section of the compression unit, whereas the rigidity in the z-direction, that is, the direction of the movement axis, is small. Usually, such a linear compressor is driven in a horizontal orientation, that is, with a horizontal movement axis. In this case, the spring has a high rigidity in the vertical direction, that is, also against the gravitational force, but a low rigidity in the direction of the movement axis. 
     It is preferred that the spring is made as a plane annular spring. Such a spring is easily manufactured. It is cost effective and has sufficiently good properties. Here, the term “plane” is not to be understood in the strict geometrical sense. Particularly at its ends, the annular spring can be deformed somewhat in relation to its plane. 
     It is preferred that a first end of the spring is connected to the housing and a second end of the spring is connected to the compression unit. The spring can, for example, be connected to the housing and the compression unit by means of welding. Thus, the complete length of the spring is utilised. 
     It is advantageous that in relation to the movement axis the first end and the second end are radially offset in relation to each other. Thus, the two ends do not collide. Accordingly the spring permits an oscillation of the compression unit along the movement axis. It is also ensured that the compression unit has a sufficient distance to the housing. 
     It is advantageous, when the spring is made as a spiral with one winding. Thus, the spring surrounds the compression unit on practically its complete circumference. This has the advantage that the fixing points of the spring on the compression unit and the housing can practically be located on a radial beam. This gives a favourable design. 
     It is preferred that in the gravity direction the spring is connected to the top of the housing and the compression unit. Thus, the compression unit is suspended in the housing. In this direction, the spring has the largest rigidity. 
     Preferably, the spring is arranged on the compression unit in an area of a diameter reduction. This gives an even better utilisation of the space available inside the housing. The compression unit can have a smaller distance to the housing than would be possible, when the spring would have to fit in all positions between the compression unit and the housing. 
     In a preferred embodiment, it is ensured that the spring is fixed on a support ring, which is inserted in the housing. In this case, the mounting is simpler. The spring can be fixed on the support ring and on the compression unit, and then the compression unit, provided with the support ring, can be inserted in the housing. Then the support ring is connected with the housing. 
     It is preferred that the spring is fixed axially on the support ring and/or on the compression unit. In this case, it is expedient to deflect at least the end sections of the spring somewhat axially from the plane of the spring. When the width of the spring is larger than the thickness, a larger surface is available for the fixing. Axial forces can be applied during the fixing, which is particularly advantageous with a welded joint. 
     Preferably, the support ring has an axial projection, which bears on the inside of the housing. The axial projection increases the stability of the housing. 
     Preferably, the projection is made to be annular. In this case, the housing is stiffened on its complete circumference. 
     Preferably, the spring arrangement has at least two curved springs, which have an axial distance to each other in relation to the movement axis. In this case, the compression unit is even better supported. Thus, it cannot tilt around a horizontal axis. 
     It is preferred that the springs have opposite winding directions. This will suppress possibly occurring torsional movements. 
     Preferably, the spring has a rectangular cross-section, a ratio of the radial extension b to the axial extension t in relation to the movement axis being at least 2:1. It has turned out that the rigidity of such a spring in the vertical direction is large enough, however, in the axial direction small enough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described on the basis of a preferred embodiment in connection with the drawings, showing: 
         FIG. 1  is a schematic longitudinal section through a linear compressor; 
         FIG. 2  is a section II-II according to  FIG. 1 ; 
         FIG. 3  is a perspective view of a spring; 
         FIG. 4  is a schematic longitudinal section through a modified embodiment of a linear compressor; 
         FIG. 5  is a section  5 - 5  according to  FIG. 4 ; 
         FIG. 6  is a section  6 - 6  according to  FIG. 4 ; and 
         FIG. 7  is a perspective view of a modified embodiment of the spring. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a linear compressor  1 , which is located in a hermetically closed case  2 ,  2 ′. 
     The linear compressor  1  has a compression section  3 , a drive section  4  and a resonance spring arrangement  5 . The unit formed by compression section  3 , drive section  4  and resonance spring arrangement  5  is suspended in the case  2  by means of two plane annular springs  6 ,  7  each being formed as a spiral with one winding. The annular springs  6 ,  7  are fixed in the drive section  4 . 
     The compression section  3  has a cylinder  8 , whose one end is covered by a cylinder head  9 . The cylinder  8  and the cylinder head  9  are combined in a case  10  in the form of a cartridge. A suction muffler  11  and a pressure muffler  12  are fixed on the cylinder head  9 . The suction muffler  11  is connected to a suction opening  13  and the pressure muffler  12  is connected to a pressure opening  14  in the cylinder head. 
     The case  10  is inserted in an intermediary ring  15 , which is connected to the drive section  4 . During mounting, the case  10  and thus the cylinder  8  can be displaced within certain limits in the axial direction of the cylinder in relation to the intermediary ring  15 . When a predetermined position of the cylinder in relation to the drive section  4  has been reached, the case  10  is fixed in the intermediary ring  15 , for example by welding, soldering or gluing. 
     In the cylinder  8  is located a piston  16 , which borders a compression chamber  17  together with the cylinder  8  and the cylinder head  9 . 
     The drive section  4  has a linear motor  4 ′. The linear motor has an outer stator  18  with a recess  19  for a winding, not shown in detail, and an inner stator  20 . Between the outer stator  18  and the inner stator  20  is an annular gap  21 , in which an armature  22  is movable. The armature  22  has permanent magnets  23 , which are connected to each other by two rings  24 ,  25 . The rings  24 ,  24  can, for example, be made of plastic. The rings  24 ,  25  are connected to inner rings  26 ,  27  by way of arms, not shown in detail, which are guided through slots in the inner stator  20 . 
     The inner rings  26 ,  27  are connected to a piston rod  28 , which again is connected to the piston  16 . 
     The outer stator  18  and the inner stator  20  are connected to each other through motor covers  29 ,  30  that are clamped together by means of screw bolts  31 . The screw bolts are guided in parallel with the movement direction of the piston rod  28 . 
     The intermediary ring  15  is connected to the cylinder-side motor cover  30 , for example by means of welding, gluing or soldering. 
     The resonance spring arrangement  5 , which is located on an end of the drive section  4  being opposite to the compression section  3 , has a spring pack  32  of several plate springs  33 . The spring pack  32  is connected to the piston rod  28  in a central area  34 . Via bolts  36 , an outer section  35  of the spring pack  32  is connected to a stop housing  37  that forms a stop for the spring pack  32 . 
     On the end projecting from the spring pack  32 , the piston rod  28  is connected to an oil pump arrangement  38 , which immerses in an oil sump, not shown in detail that forms in the bottom part of the case  2 . 
     When the winding located in the recess  19  is energized, the armature  22  moves in one direction, taking the piston rod  28  along in this direction. When the direction of the current is reversed, the armature  22  with the piston rod  28  moves in the opposite direction, and accordingly moves the piston  16  in the opposite direction. Thus, the volume of the compression chamber  17  is periodically increased or reduced. The resonance spring arrangement  5  is adapted to the frequency of the current, so that the movable part of the linear compressor  1 , which is formed by the armature  22 , the piston rod  28 , the piston  16 , the oil pump arrangement  38  and the movable part of the resonance spring arrangement  5 , oscillates in resonance. 
     During operation, the piston  16  and the armature  22  move along a movement axis  50 . As a reaction to this, also the usually fixed part of the compression unit, namely the outer stator  18 , the inner stator  20 , the motor covers  29 ,  30 , the cylinder  8  with the case  10  and the two mufflers  11 ,  12 , will oscillate along the movement axis  50 . This oscillation has a smaller amplitude than the oscillation of the piston  16  and the armature  22 , as the mass of this part is larger than the mass of the moved parts with piston  16  and armature  22 . However, it is still perceptible. Accordingly, the oscillation along the movement axis  50  must be prevented from transferring to the housing  2 . In any case, oscillations along the movement axis  50  have to be severely damped. 
     In a direction perpendicular to the movement axis  50 , that is, in a direction  51 , and the plane defined by this, the risk of oscillations is substantially smaller. Here, it is endeavoured to arrange the compression unit with the smallest possible distance to the housing  2  to keep the dimensions of the housing  2  small. 
     In order, to meet these requirements, the two annular springs  6 ,  7 , which will be explained in detail by means of  FIGS. 2 and 3 , are used to suspend the compression unit in the housing  2 . The  FIGS. 2 and 3  show the annular spring  7 . The other annular spring  6  is made to be identical, however mounted with a different winding direction in the housing  2 . 
     Same elements have the same reference numbers as in  FIG. 1 . 
       FIG. 2  shows the mounting situation of the annular spring  7 , whose upper end is connected to the inner wall of the case  2  via a welded joint  52  and whose lower end is connected to the intermediary ring  15  via a welded joint  53 . The other annular spring  6 , however, is connected directly with the motor cover  29 , where the motor cover has a diameter, which is smaller than the outer diameter of the outer stator  18 . 
     The annular spring  7  is made as a spiral with one winding, which extends over an angle of somewhat more than 360°. The annular spring  7  is made of flat spring steel, whose thickness, that is, the extension t in the axial direction, is smaller than the width, that is, the extension b in the radial direction. The ratio b:t is 2:1. 
     Consequently, in the radial direction, for example in the vertical direction  51 , the annular spring  7  has a substantially larger rigidity than in the direction of the movement axis  50 . Accordingly, a displacement of the compression unit  3 ,  4 ,  5  along the movement axis  50  is possible; however a larger displacement in the radial direction  51  is reliably prevented by the annular springs  6 ,  7 . Thus, the compression unit  3 - 5  is prevented from striking on the inside of the housing  2 . As the compression unit  3 - 5  can oscillate in a relatively free manner along the movement axis  50 , without striking on the housing  2 , the oscillation will only be slightly trans-ferred to the housing  2 . 
     The compression unit  3 - 5  is connected by the two annular springs  6 ,  7  to the housing  2  at two positions located at a distance from each other along the movement axis  50 . The consequence of this is that the compression unit  3 - 5  cannot tilt in relation to the housing  2 . 
     The two annular springs  6 ,  7  are mounted in the housing  2  with opposite orientation or winding direction. This counteracts torsional torques, which could possibly occur in the compression unit  3 - 5 . 
     The compression unit  3 - 5  is so to speak suspended in the housing  2 , that is, the welded joint  52  is provided approximately at the uppermost position at the inner wall of the housing  2 . In a similar manner, the welded joint  53  is provided vertically upon the motor cover  29  or on the intermediary ring, respectively. 
     The two ends  54 ,  55  of the annular spring  7  are offset in relation to each other in the radial direction. This means that, even though they overlap somewhat in the circumferential direction, they do not collide when the compression unit  3 - 5  oscillates along the movement axis  50 . 
     Of course, it is also possible to use an annular spring  6 ,  7 , whose length amounts to more than 360o. A longer spiral gives an even softer characteristic along the movement axis  50 . However, additional space may be required in the vertical direction. 
     The cross-section of the annular spring  6 ,  7  can also be circular, square or have other shapes. 
     In an embodiment, in which the annular spring had one single winding and a rectangular cross-section with a width b=3 mm and a thickness t=1.5 mm and a largest diameter D=85 mm, a displacement of the compression unit  3 - 5  along the movement axis  50  of ±1 mm could be damped to a displacement of the housing of a few μm. Such oscillations are no longer noticeable in a disturbing manner. 
       FIG. 4  shows a modified embodiment of a linear compressor  1 , in which the same elements have the same reference numbers. 
     The housing now has a middle section  2   a , a case  2   b  surrounding the compression section  3  and a case  2   c  surrounding the resonance spring arrangement  5 . 
     As can be seen from  FIG. 7 , the annular springs  6 ,  7  are still substantially made to be flat. However, the first end section  54  is deformed slightly in one axial direction and the second section  55  is slightly deformed in the other axial direction. Thus, not only in the radial direction, but also in the axial direction the two end sections  54 ,  55  have a small distance to each other. 
     With this embodiment of the annular springs  6 ,  7  it is possible to fix the annular springs  6 ,  7  on support rings  56 ,  57  in the axial direction, that is, the axial end of each of the two end sections  54 ,  55  can be fixed on the support rings  56 ,  57  and on the motor covers  29 ,  30 . 
     Each support ring  56 ,  57  has a circumferential annular flange  58 ,  59 . Now, the annular springs  6 ,  7  can be fixed on the end of the drive section  4 , for example by welding. As, in the radial direction, the annular springs  6 ,  7  extend over the drive section  4 , the annular springs  6 ,  7  can subsequently be fixed on the support rings  56 ,  57  without problems, for example also by welding. Then the complete unit of compression section  3 , drive section  4  and resonance spring arrangement  5  together with the support rings  56 ,  57  can be pushed into the middle section  2   a  of the housing and be fixed there. The fixing can, for example, be made at the same time as the fixing of the two cases  2   b ,  2   c  on the middle section  2   a , for example by welding. Advantageously, the circumferential annular projections  58 ,  59  serve the purpose of increasing the overall stability of the housing. 
     Further, at the bottom of the housing  2  rubber elements  60  can be seen, with which the horizontally arranged linear compressor  1  can be placed on a base, not shown in detail. 
     While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.