Patent Publication Number: US-6213742-B1

Title: Scroll-type fluid mover having an eccentric shaft radially aligned with a volute portion

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to scroll-type fluid mover such as scroll-type vacuum pumps and compressors. 
     Scroll-type fluid mover, for example, scroll-type compressors have a movable scroll and a fixed scroll. Each scroll includes a base plate and a volute portion formed on the base plate. The volute portions cooperate to form a compression chamber. An eccentric shaft is formed on a drive shaft. The movable scroll is rotatably supported by the eccentric shaft. When the drive shaft rotates, the movable scroll orbits the axis of the drive shaft. Then, the compression chamber contracts from the periphery to the center of the volute portions, which compresses gas. 
     FIG. 6 shows a prior art structure for supporting a movable scroll with respect to the drive shaft. The structure of FIG. 6 is described as being prior art in Japanese Examined Publication No. 63-59032. In the apparatus of FIG. 6, an eccentric shaft  41  is formed on the drive shaft  42 . The axis of the eccentric shaft  42  is displaced with respect to the axis of the drive shaft  42  in the radial direction by a distance equal to the revolution radius of a movable scroll  44 . The drive shaft  42  is supported by a housing  48  of the compressor and a bearing  46 . The movable scroll  44  includes a base plate  44   a,  a volute portion  44   b  projecting from the base plate  44   a , a boss  43  formed on the opposite side of the base plate  44   a  from the volute portion  44   b.  The volute portion  44   b  cooperates with a volute portion  45   b  of a fixed scroll  45 , which forms a compression chamber  47  between the scrolls  44 ,  45 . The eccentric shaft  41  is inserted in the boss  43  and supports the movable scroll  44  through the boss  43 . Accordingly, the eccentric shaft  41  supports the movable scroll  44  at a position outside of a working region R, which includes the volute portion  44   b.  In other words, the movable scroll  44  is supported at a position that is axially spaced from the compression chamber  47 . 
     Centrifugal force is applied to the movable scroll  44  when it revolves. Also, compression reaction force generated by compressing gas in the compression chamber  47  is applied to the movable scroll  44 . A resultant radial working force K, which combines the centrifugal force and the compression reaction force, is especially high in the working region R. However, the eccentric shaft  41  supports the movable scroll  44  at a position axially spaced from the region R. For this reason, the working force K applies an inclination moment to the movable scroll  44  with the supporting position of the eccentric shaft  41  at the center. For example, when there is a measurement error between the eccentric shaft  41  and the boss or between the volute portions  44   b,    45   b,  the inclination moment inclines the movable scroll  44  with respect to the fixed scroll  45 . Thus parts of the movable scroll  44  apply concentrated, localized forces to the fixed scroll  45 . As a result, the smooth orbital movement of the movable scroll  44  is interrupted and the sealing of the compression chamber  47  between the scrolls  44 ,  45  deteriorates, thus causing rattling and gas leakage from the compression chamber  47 . 
     To solve this problem, Japanese Examined Publication No. 63-59032 reveals the construction shown in FIG. 7. A movable scroll  44  has a boss  43  projecting on both sides of a base plate  44   a . An eccentric shaft  41 , which passes through the boss  43 , is provided in the middle of a drive shaft  42 . Accordingly, the eccentric shaft  41  supports the movable shaft  44  in a working region R, which includes the volute portion  44   b.  The drive shaft  42  has a first portion  42   a  and a second portion  42   b,  which are at opposite ends of the eccentric shaft  41 . The first portion  42   a  is supported by bearings  46  and a compressor housing  48 . The second portion  42   b  is supported by bearings  46  and a fixed scroll  45 . Accordingly, the drive shaft  42  supports the movable scroll  44  at both sides of the working region R, or both sides of the compression chamber. 
     When a radial working force K based on centrifugal force and compression reaction force is applied to the movable scroll  44 , the force K is received by the portions  42   a,    42   b  of the drive shaft  42 , which are located at both ends of the eccentric shaft  41 . As a result, there is no inclination moment applied to the movable scroll  44 , and the movable scroll  44  does not incline with respect to the fixed scroll  45 . 
     To achieve smooth rotation of the drive shaft  42 , the axes of the portions  42   a,    42   b  of the drive shaft  42  must be precisely aligned and the axes of the bearings  46  must be precisely aligned. However, this increases the cost of production. 
     To insert the eccentric shaft  41 , which is in the middle of the drive shaft  42 , in the boss  43 , at least one of the portions  42   a,    42   b  of the drive shaft  42  must be separate from the eccentric shaft  41 . After the eccentric shaft  41  is inserted in the boss  43 , the separate part is fixed to the eccentric shaft  41 . However, in this procedure, the number of parts and steps increase and the assembly work is difficult, thus increasing the manufacturing costs. 
     SUMMARY OF THE INVENTION 
     The present invention is designed to solve the above problems. The objective of the present invention is to provide scroll-type fluid mover that prevents the movable scroll from inclining with respect to the fixed scroll and that is easily machined due to a simple construction. 
     To achieve the above objective, the scroll-type fluid mover according to the present invention includes a fixed scroll, which includes a base plate and a volute portion extending from the base plate, and a movable scroll, which includes a base plate and a volute portion extending from the base plate. The two volute portions cooperate to form a variable displacement fluid pocket between the two scrolls. A drive shaft is driven to rotate about its axis. An eccentric shaft is connected to the drive shaft. The axis of the eccentric shaft is offset from the axis of the drive shaft. The eccentric shaft has a proximal end and a distal end. The proximal end is fixed to the drive shaft and the distal end is radially unsupported. The eccentric shaft rotatably supports the movable scroll so that the movable scroll orbits the axis of the drive shaft without rotating about its own axis when the drive shaft rotates. Gas is introduced into and compressed in the fluid pocket in accordance with the orbital movement of the movable scroll. The eccentric shaft extends axially such that at least a part of the eccentric shaft is located in a location that is radially aligned with the volute portion of the movable scroll, whereby the eccentric shaft supports the movable scroll to prevent inclination of the movable scroll with respect to the fixed scroll. 
     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a diagrammatic cross sectional view showing a scroll-type vacuum pump of a first embodiment according to the present invention; 
     FIG. 2 is a partial sectional view taken on the line  2 — 2  of FIG. 1; 
     FIG. 3 is a diagrammatic view showing the structure for supporting a movable scroll according to the embodiment of FIG. 1; 
     FIG. 4 is a partial, diagrammatic sectional view showing a structure for supporting a movable scroll in a second embodiment of the present invention; 
     FIG. 5 is a partial, diagrammatic sectional view showing a structure for supporting a movable scroll in a third embodiment of the present invention; 
     FIG. 6 is a partial, diagrammatic sectional view showing a prior art structure for supporting a movable scroll from Japanese Examined publication No. 63-59032; and 
     FIG. 7 is a partial, diagrammatic sectional view showing a further prior art structure for supporting a movable scroll disclosed in Japanese Examined publication No. 63-59032. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A scroll-type vacuum pump according to a first embodiment of the present invention will now be explained in reference to FIGS. 1 to  3 . 
     As shown in FIG.  1  and FIG. 2, a front housing  11  is joined to a fixed scroll  12 , which also serves as a rear housing. A drive shaft  13  is rotatably supported in the front housing  11  through a bearing  15 . An eccentric shaft  14  is integrally formed on one end of the drive shaft  13  in a space between the front housing  11  and the fixed scroll  12 . The axis H of the eccentric shaft H is radially displaced with respect to the axis L of the drive shaft  13 . The drive shaft  13  and the eccentric shaft  14  are integrally formed, for example, by casting. 
     The movable scroll  16  is rotatably supported by the eccentric shaft  14  such that the shaft  14  rotates relative to the movable scroll  16 . In other words, the movable scroll  16  is supported by one end of the drive shaft  13  through the eccentric shaft  14 . A well known rotation control mechanism  17 , which includes a crank pin  17   a,  is provided between the movable scroll  16  and the front housing  11 . The control mechanism  17  prevents the movable scroll  16  from rotating about its axis H. Accordingly, when the drive shaft  13  rotates, the movable scroll  16  orbits the axis L of the drive shaft  13 . 
     The fixed scroll  12  includes a base plate  21 , which also serves as a housing of the pump, and a volute portion  22  projecting from the inner surface of the base plate  21  towards the front housing  11 . The movable scroll  16  includes a base plate  23  and a volute portion  24  projecting from one surface of the base plate  23  towards the fixed scroll  12 . The volute portions  22 ,  24  of both scrolls  12 ,  16  cooperate with each other. Compression chambers  25 , or fluid pockets, are formed by the volute portions  22 ,  24  and the base plate  21 ,  23 . Volute-shaped seals  31  are attached to ends  22   a,    24   a  of the volute portions  22 ,  24 . The seal  31  attached to the fixed scroll  12  contacts the surface of the base plate  23  of the movable scroll  16 . The seal  31  attached to the movable scroll  16  contacts the surface of the base plate  21  of the fixed scroll  12 . The seals  31  seal the compression chambers  25 . When the movable scroll  16  orbits the axis L of the drive shaft  13 , gas in each compression chamber  25  moves from the periphery of the volute portions  22 ,  24  to the center, while its volume is reduced. 
     A peripheral wall  26 , which also serves as the pump&#39;s housing, is formed integrally on the periphery of the base plate  21  of the fixed scroll  12  to surround the volute portions  22 ,  24 . The peripheral wall  26  has an end surface  26   a  that faces the base plate  23  of the movable scroll  16 . A space  27  for accommodating the volute portions  22 ,  24  is formed between the base plate  21 ,  23  and within the peripheral wall  26 . A dust seal  32  is attached to the end surface  26   a  to contact the base plate  23  of the movable scroll  16  and seal the space  27 . 
     An inlet  28 , which is connected to an air intake piping (not shown), is formed in the peripheral wall  26  and is connected to the compression chamber  25  through the accommodation space  27 . A discharge passage  29  is formed in the fixed scroll  12  and the movable scroll  16 . The discharge passage  29  includes a first passage  29   a  formed in the fixed scroll  12  and a second passage  29   b  formed in the movable scroll  16 . The first passage  29   a  is connected to a discharge piping (not shown). The second passage  29   b  is selectively connected or disconnected to the first passage  29   a  when the movable scroll  16  orbits. When the second passage  29   b  is connected to the first passage  29   a,  the compression chamber  25 , which is located near the center of the volute portions  22 ,  24 , is connected to the discharge piping through the discharge passage  29 . Accordingly, when the movable scroll  16  orbits, the gas drawn into the compression chamber  25  from the intake piping through the inlet  28  is compressed and then discharged from the compression chamber  25  to the discharge piping through the discharge passage  29 . 
     A structure for supporting the movable scroll  16  will now be described referring to FIGS. 1 to  3 . A first boss  36  projects from the center of the base plate  23  of the movable scroll  16  in the same direction that the volute portion  24  project. An end surface  36   a  of the first boss  36  and the end surface  24   a  of the volute portion  24  are substantially on the same plane. The second boss  37  projects from the center of the base plate  23  in the opposite direction from the first boss  36 . 
     An eccentric shaft  14  extends from the second boss  37  to the first boss  36 . In this case, an end surface  14   a  of the eccentric shaft  14  is substantially on the same plane as the end surface  24   a  of the volute portion  24 . Accordingly, a distal section of the eccentric shaft  14  is located in a working region R, which includes the volute portion  24  of the movable scroll  16 . That is, part of the eccentric shaft  14  is radially aligned with the compression chamber  25 . 
     A first bearing  35  is located between the inner surface of the first boss  36  and the outer surface of a disal section of the eccentric shaft  14 . The eccentric shaft  14  supports the movable scroll  16  through the first bearing  35  in the working region R including the volute portion  24 . The first bearing  35  is, for example, a sleeve bearing, and the end surface of the bearing  35  is substantially flush with the end surfaces  36   a,    14   a  of the first boss  36  and the eccentric shaft  14 . A second bearing  34 , which is, for example, a roller bearing, is located between the inner surface of the second boss  37  and a proximal section of the eccentric shaft  14 . The eccentric shaft  14  supports the movable scroll  16  outside the working region R through the second bearing  34 . Accordingly, the eccentric shaft  14  supports the movable scroll  16  both in the region R and outside the region R. The bearings  34 ,  35  facilitate the rotation of the movable scroll  16  with respect to the eccentric shaft  14  and the orbital movement of the movable scroll  16  about the axis L of the drive shaft  13 . 
     Centrifugal force is applied to the movable scroll  16  when it orbits. Also, a compression reaction force generated by the compression of gas in the compression chamber  25  is applied to the movable scroll  16 . The resultant radial working force K based on the centrifugal force and the compression reaction force is highest in the working region R. The force K is received by the eccentric shaft  14  through the first and second bearings  35 ,  34 . The first bearing  35  is located in the region R, where the force K is mainly applied. As a result, the force K is radially received by the eccentric shaft  14 . Accordingly, no inclination moment is applied to the movable scroll  16 , and the movable scroll  16  does not incline with respect to the fixed scroll  12 . This facilitates the orbital movement of the movable scroll  16  and limits gas leakage from the accommodation chamber  27  and the compression chamber  25 . 
     FIG. 3 shows a simplified diagram representing the support structure of FIG.  1 . The bearings  34 ,  35  are located at axially spaced-apart locations. A radial supporting force (not shown) is applied to the movable scroll  16  at each spaced-apart location. A resultant N of the supporting forces is shown oppositely directed with respect to the resultant radial working force K. Note that the resultant supporting force N is located in the same radial plane as the radial working force K. The locations of the bearings  34 ,  35  are selected such that these forces N, K are radially aligned, which prevents an inclining moment from being applied to the movable scroll  16 . 
     The end surfaces  36   a,    14   a  of the first boss  36  and the eccentric shaft  14  are substantially flush with the end surface  24   a  of the volute portion  24  of the movable scroll  16 , and the end surface of the first bearing  35  is substantially flush with the boss and the shaft end surfaces  36   a,    14   a.  In other words, the first bearing  35  extends axially to reach the outer-most end of the region R. This completely prevents an inclination moment from acting on the movable scroll  16 . 
     If the boss  36  and the eccentric shaft  14  extend axially beyond the region R, it becomes necessary to form a recess for accommodating the distal ends of the boss  36  and the eccentric shaft  14  in the base plate  21  of the fixed scroll  12 . However, in the embodiment of FIG. 1, there is no need for this, thus facilitating the manufacture of the fixed scroll  12 . 
     The drive shaft  13  is supported by the front housing  11  in one side of the movable scroll  16 . Accordingly, there is no need to align axes of portions  42   a,    42   b  of a drive shaft  42  with high precision as in the prior art embodiment of FIG.  7 . Further, even though the drive shaft  13  is integrally formed with the eccentric shaft  14 , it is possible to insert the eccentric shaft  14  in the bosses  36 ,  37 . This facilitates machining the parts including the drive shaft  13  and reduces the number of parts, thus facilitating the assembly of parts. As explained, FIG. 1 shows a low-cost pump having a simple structure that is easily manufactured. 
     The first bearing  35  and the second bearing  34  are axially spaced apart. The eccentric shaft  14  supports the movable scroll  16  at sections radially aligned with the bearings  35 ,  34 , and the movable scroll  16  is not supported between the bearings  35 ,  34 . This is because it is possible for the eccentric shaft  14  to stably support the movable scroll  16  at the bearings  35 ,  34  only. Accordingly, it is not necessary to support the movable scroll  16  with large first and second bearings that extend over the whole length of the axis H of the eccentric shaft  14 . This simplifies and reduces the weight of the construction for supporting the movable scroll  16 . 
     The sections including the bosses  36 ,  37 , supported by the eccentric shaft  14  have the same lengths. Further, the first and second bearings  35 ,  34  are arranged at the very ends of the sections supported by the eccentric shaft  14  to make the distance in between as wide as possible. This enables the eccentric shaft  14  to support the movable scroll  16  more stably. 
     The second bearing  34  is larger than the first bearing  35 . In other words, the load applied to the first bearing  35 , which is located in the working region R, is more widely distribution by supporting the movable scroll  16  with the relatively large second bearing  34 . Therefore, the first bearing  35  is compact. The compact first bearing  35  makes it possible to miniaturize the first boss  36  for accommodating the bearing  35 . When the first boss  36  is small, the volute portions  22 ,  24  can be extended to the vicinity of the center of the scrolls  12 ,  16 . This improves gas compression without increasing the size of the pump. 
     FIG. 4 shows a second embodiment of the present invention. In this embodiment, the first boss  36  and the eccentric shaft  14  extend axially beyond the end surface  24   a  of the volute portion  24 , that is, beyond the working region R. Accordingly, the first and second bearings  35 ,  34  straddle the region R. A recess  12   a  for accommodating the distal ends of the first boss  36  and the eccentric shaft  14  is formed in the inner surface of the base plate  21  of the fixed scroll  12 . The structure of this embodiment provides more stable support for the movable scroll  16 . 
     FIG. 5 shows a third embodiment of the present invention. In this embodiment, the second boss  37  of FIG. 1 is omitted. As a result, a part of the second bearing  34  is located in the working region R. 
     In the embodiments of FIG. 1 to FIG. 5, the bearings  34 ,  35  may be omitted, and the movable scroll  16  may be directly supported by the eccentric shaft  14 . In this case, a coating, mainly made of polytetrafluoroethylene, is preferably applied to at least one of the outer surfaces of the eccentric shaft  14  and the inner surface of the movable scroll  16 , or lubricant may be applied in between. In this way, the sliding resistance between the eccentric shaft  14  and the movable scroll  16  becomes small, and frictional wear is prevented, achieving smooth motion of the movable scroll  16 . 
     The present invention is not limited to a vacuum pump and may be applied to a scroll-type compressors applied to air conditioning systems. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.