Patent Publication Number: US-6213741-B1

Title: Scroll type compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a scroll type compressor used in an automotive air-conditioner or the like, and more particularly to the shape of scroll body for the purpose of enhancing the performance of the compressor and durability of the scroll body. 
     As shown in FIG. 6, in general, a conventional scroll body for a scroll type compressor is composed of a stationary scroll body  1  and a movable scroll body  2 . Both of the stationary scroll body  1  and the movable scroll body  2  are each composed of a substantially disc-shaped plate member (not shown) and a spiral member  10 ,  20  formed on one surface of the plate member. The stationary scroll body  1  and the movable scroll body  2  are combined with each other so that their spiral members  10  and  20  are engaged with each other. Then, when the movable scroll body  2  is moved in a circular orbital motion while coming into contact with the stationary scroll body  1  a pair of compression chambers  31  and  32  are formed between the two scroll bodies  1  and  2 . Also, the compression chambers  31  and  32  move toward the center of the spiral members  10  and  20 . In accordance with this movement, the volume of the compression chambers  31  and  32  is decreased so that any coolant gas therein is compressed. 
     It is possible to apply a variety of involutes as a curved line for defining the spiral members  10  and  20 . However, an involute of a circle that is easy to handle is generally used. However, since a large amount of stress is applied to an initial winding part (i.e., the central end part of the spiral member), in order to increase the mechanical strength of this part, the wall thickness of the spiral members is increased and at the same time, this part is formed into a round shape to avoid sharp edges. For this reason, the point where the involute changes is determined at a suitable involute angular position. The outer end part side of the involute change point is formed into an involute curved line, and the central end part side of the involute change point is formed into another curved line. 
     Also, the scroll bodies  1  and  2  are generally made of a cast material such as aluminum alloy, and thereafter, finished by machining such as cutting. The inner wall and the outer wall of the spiral members  10  and  20  are conventionally end-milled. In order to further enhance the mechanical strength of the central end part of the conventional scroll bodies  1  and  2  that is subjected to particularly large stress, a cutting tool of an end mill which is different from the tool for the other portions is used for the central end part. As shown in FIG. 8, a radius of curvature R larger than other portions is formed at a root corner end part  5  where the wall surface meets the plate member so as to be more reinforced than other root corner end parts. 
     For this reason, the machining precision of the wall surface of the central end part is not as good as at the other parts of the scroll bodies. Accordingly, with respect to this central end part, the two spiral members interfere with each other due to machining tolerances, and there is a fear that excessive wear or contact force may occur. Therefore, a relief is formed in order to avoid this interference. For this relief, a cutaway portion  4  is also formed in the inner wall of the central end part as shown in FIG.  7 . 
     FIG. 9 shows a state where the spiral member  20  of the second scroll body (for example, the movable scroll body)  2  is arranged at an interval corresponding to a radius of the revolution relative to the spiral member  10  of the first scroll body (for example, the stationary scroll body)  1 . 
     In FIG. 9, an angular region A 1  between a point a 1  and a point b 1  on the wall surface of the spiral member  10  and an angular region A 2  between a point a 2  and a point b 2  on the wall surface of the spiral member  20  indicate the portions of the spiral members  10  and  20  in which stress is increased. A radius of curvature R larger than that of the other parts is applied to each root corner portion  5  (see FIG. 8) as described above. 
     In FIG. 9, points a 21  and b 21  at which normal lines L 11  and L 12  from the points a 1  and b 1  of the spiral member  10  intersect with the spiral member  20  are theoretically the points of the associated member with which the points a 1  and b 1 , respectively, come into contact when the scroll bodies  1  and  2  are operated. In the same manner, points a 11  and b 11  at which normal lines L 21  and L 22  from the points a 2  and b 2  of the spiral member  20  intersect with the spiral member  10  are theoretically the points of the associated member with which the points a 2  and b 2 , respectively, come into contact when the scroll bodies  1  and  2  are operated. Thus, in FIG. 9, when a normal line is drawn from any desired point of the inner wall of one of the spiral members, the point on the inner wall of the associated member at which the normal line intersects represents a point at which the two members contact with each other. 
     However, in the above-described angular regions A 1  and A 2 , since the radius of curvature R larger than that for the other portion is applied to the root corner portion as described above, machining precision is reduced. Accordingly, in region D including the two regions A 1  and A 2 , as indicated by the dotted line in FIG. 9 (or as shown in the perspective view of FIG.  7 ), the cutaway portion  4  to be used as the relief is provided on the inner wall of the spiral member  20  of the second scroll body  2 . Here, in order to facilitate the understanding of the cutaway portion  4  in the drawings of FIG.  7  and FIG. 9, the size thereof is exaggerated. 
     FIG. 8 is a cross-sectional view of the spiral member  10  of the first scroll body  1  which has been cut away up to the dotted line in FIG.  9 . The wall thickness of this part of the spiral member  20  is cut away up to the dotted line so that the wall is thinner than the theoretical shape. The machining tolerance based on reduced machining precision is dealt with by this cutaway portion  4 . 
     In the above-described conventional compressor, the state of contact between the two spiral members  10  and  20  is categorized into three types, i.e., a region in which the portions having the radius of curvature R larger than that of the other portions, as the portion reinforced more than the other root corner portions, namely, the above-described portions in which machining precision are not good, appear in both the spiral members, a region in which the portions appear in one of the spiral members, and a region in which the portions do not appear in any of the spiral members. In FIG. 9, the region B is the region in which the portions that are machined with less precision having the radius of curvature R appear in both the spiral members. In this case, the machining tolerances of both spiral members  10  and  20  are combined to cause such portions with less precision. Also, the regions C 1  and C 2  are regions in which the portions that are machined with less precision having the radius of curvature R appear in either one of the spiral members  10  and  20 . In this case, errors caused by the machining tolerances of one of the spiral members appear. However, the cutaway portion  4  serving as the relief is formed with a constant relief dimension in the region D including these regions B, C 1  and C 2 . For this reason, in the regions C 1  and C 2  where only one of the machining tolerances appear, the relief action would be excessive, so that the gap between the two spiral members is large. As a result, the performance of the compressor would be degraded. Also, there is a tendency for the durability of the spiral members to become worse due to the extra cutaway portions. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing defects inherent in conventional techniques, the present invention has been made, and therefore, an object of the present invention is to enhance the performance of a compressor and the durability of scroll bodies by optimizing the relief to machining tolerances at a central end part of spiral members for forming the scroll bodies. 
     In order to attain this and other objects, according to a first aspect of the present invention, the two spiral members engaged with each other are characterized in that a root corner portion reinforced more than any other root corner portions is formed at a central end part of both of the spiral members where large stress is generated, and in that in regions where both of said spiral members contact with each other, a first relief is provided where said reinforced portion is present in only one of said spiral members and a second relief larger than said first relief is provided where said reinforced portion is present in both of said spiral members. 
     In this case, “relief” means a relief portion provided on one of the spiral members or both of the spiral members in order to avoid any interference of the two spiral members at the contact point due to machining tolerances caused by providing the root corner portion that is more reinforced than the other root corner portions, at the central end part where the stress is increased. 
     With such an arrangement, it is possible to avoid the excessive relief of the conventional systems. As minimum and reasonable relief as possible is formed between the two spiral members so that the performance of the compressor may be enhanced. Also, since excessive cutaway is avoided in the spiral members, it is possible to enhance their durability. 
     The above-described first and second reliefs may be formed in any desired manner in both the spiral members or in just one of the spiral members. As in the second aspect of the present invention, however, if respective reliefs are formed of the cutaways formed on both the spiral members, the cutaway amount is reduced in each spiral member. As a result, the durability of the spiral members is further enhanced. However, if each relief is thus formed of a cutaway portion provided on each spiral member, the involutes of the spiral members will be changed in three steps, resulting in a complicated shape and complicated machining. Accordingly, as in a third aspect of the invention, if the first relief is formed in one of the spiral members and the second relief is formed in the other spiral member, the cutaways are dispersed between both spiral members so that their durability is enhanced, and at the same time, the involute of each spiral member changes by only two steps so that machining is facilitate. 
     Also, as in a fourth aspect of the present invention, if the first and second reliefs are formed of cutaways formed in only one of the spiral members, since the involutes of the spiral members do not change in a stepped manner, which is the most easy to machine. 
     Also, as in a fifth aspect of the present invention, if the ends of the cutaways for defining the first and second reliefs are connected to each other with smooth lines, it is possible to eliminate the stress concentration at the end part edges of the cutaways to thereby enhance the durability of the spiral members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a structural schematic view showing a central end part of spiral members according to a first embodiment of the present invention; 
     FIG. 2 is a structural schematic view showing a central end part of spiral members according to a second embodiment of the present invention; 
     FIG. 3 is a structural schematic view showing a central end part of spiral members according to a third embodiment of the present invention; 
     FIG. 4 is a structural schematic view showing a central end part of spiral members according to a fourth embodiment of the present invention; 
     FIG. 5 is a structural schematic view showing a central end part of spiral members according to a fifth embodiment of the present invention; 
     FIG. 6 is a structural schematic view showing scroll bodies in a conventional general scroll type compressor; 
     FIG. 7 is a perspective view of a central end part of the scroll bodies shown in FIG. 6; 
     FIG. 8 is a cross-sectional view taken along the line VIII—VIII of FIG. 7; and 
     FIG. 9 is a structural schematic view showing a central end part of spiral members of a conventional scroll type compressor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to FIGS. 1 to  5 . Here, since a scroll type compressor in accordance with the present invention is the same as a general scroll type compressor except for the shape of the two scroll bodies, the main explanation will be made as to the shape of the spiral members according to the present invention. Also, in the following explanation in conjunction with the drawings, the same reference numerals as those of the above-described conventional scroll bodies are used to indicate the like portions or components and their explanation will be omitted. 
     A basic concept of the present invention that is common with the respective embodiments will be described before explanation of the respective embodiments. 
     First of all, in the same manner as in the conventional general compressor, in a central end part of each of the spiral members  10  and  20  of the scroll bodies, a radius of curvature R larger than that of other root corner portions is formed in a root corner portion  5  in which the stress to be applied to each spiral member is increased in comparison with the other portions in order to form a portion more reinforced than the other portions. 
     Next, when the wall surface of the portion  5  is end-milled, a cutting tool that is different from the tool for the other portions is used for the portion  5 , so it is currently inevitable that the portion is machined with less precision. In order to avoid any interference of the two spiral members  10  and  20  with each other due to machining error, a relief is formed in the conventional manner, for the purpose of absorbing the machining tolerances. Accordingly, the provision of the relief per se is the same as that of the conventional system. 
     However the present invention is characterized in how the relief is provided. 
     In the conventional system, as described above, a relief having a constant dimension is formed for regions C 1  and C 2  in which the portion where the radius of curvature R is formed reducing the machining precision is provided in only one of the spiral members that come into contact with each other and for the region B in which the portion of the radius of curvature R is formed in both the spiral members. However, in all of the following embodiments, the two regions C 1  and C 2  and the region B are separated and suitable dimensions are set for the relief. 
     Namely, in each of the following embodiments, a first relief having a small enough dimension absorb machining tolerances of one of the spiral members  10  and  20  is formed in the regions C 1  and C 2  in which the portion where the radius of curvature R is applied to thereby reduce the machining precision appears in only one of the spiral members  10  and  20  that come into contact with each other, and a large second relief (twice as large than the first relief) having such a dimension that the machining tolerances of both the spiral members  10  and  20  may be absorbed is formed in the region B in which the portion where the radius of curvature R is applied to thereby reduce the machining precision appears in both the spiral members  10  and  20  that come into contact with each other. Thus, an excessive large relief may be avoided in the first relief. 
     Also, such first and second reliefs are formed by cutaways provided in one of, or both of the spiral members  10  and  20 . There is a difference in how to make the cutaway portions between each of the embodiments. However, in any of the embodiments, a larger radius of curvature R is formed in a root corner portion  5  of each of the spiral members  10  and  20 , thereby enhancing their durability. At the same time, the first and second reliefs are formed into ones having suitable dimensions, thereby enhancing the performance of the compressor. 
     The following explanation will be made mainly as to the characterizing features of each embodiment in conjunction with the accompanying drawings. Further, in each of the drawings, the cutaway portions  41  to  44 ,  51 ,  52 ,  61 ,  62 ,  71 ,  72 ,  81  and  82  for composing the first reliefs and cutaway portions  45 ,  46 ,  53 ,  63 ,  73 ,  74  and  83  for composing the second reliefs are exaggerated in respect to their actual sizes for the purpose of facilitating understanding of those constructions in the drawings. 
     FIG. 1 shows a first embodiment of the present invention in which the above-described first and second reliefs are formed in the spiral members  10  and  20 , respectively. 
     In FIG. 1, stress is increased in the regions of points a 1  to b 1  and points a 2  to b 2  in a central end part of each of the spiral members  10  and  20  in the same manner as in the conventional system. In a root corner portion of this part, a radius of curvature R larger than that of the other parts is formed in the same manner as in the conventional system. This is also the case in the following embodiments. 
     Also, according to this and the following embodiment of the present invention, the first relief is formed in the regions C 1  and C 2 , and the second relief is formed in the region B. 
     Further, in this embodiment, cutaway portions  41 ,  42 ,  43  and  44  in which the cutaway amount is small are formed between points a 1  and b 11  of the inner wall and between points b 1  and a 11  of the inner wall of the spiral member  10 , and between points a 21  and b 2  and between points b 21  and a 2  of the inner wall of the spiral member  20 . These cutaway portions  41 ,  42 ,  43  and  44  define the first reliefs. 
     Also, cutaway portions  45  and  46  in which the cutaway amount is large are formed between the points b 11  and b 1  of the inner wall of the spiral member  10  and between the points b 2  and b 21  of the inner wall of the spiral member  20 . These cutaway portions  45  and  46  define the second reliefs. 
     The scroll bodies having the spiral members  10  and  20  in accordance with the above-described embodiment are made of cast aluminum alloy and are manufactured by cutting or the like. The inner walls of the spiral members  10  and  20 , the root corner portions of the inner walls, and the cutaway portions  41  to  46  of the inner walls and the outer walls are simultaneously cut by end-mill machining. A different cutting tool is used for cutting portions other than these portions. 
     In the cutaway portions  41  to  46 , when machining tolerances are disregarded, the involutes may be represented by the dotted lines in FIG.  1 . Accordingly, the difference between the dotted lines and the solid lines amount to be cutaway. 
     The amount of the portions to be cut away may be set so that the sum of the cutaway amounts of the corresponding cutaway portions is substantially the same as the value of the machining tolerance. In this embodiment, the cutaway amounts of the cutaway portions  41  and  42  provided on the side of the spiral member  10  are the same as that of the cutaway portions  43  and  44  provided on the side of the spiral member  20 , and the cutaway amount of cutaway  45  provided on the side of the spiral member  10  is the same as that of the cutaway  46  provided on the side of the spiral member  20 . However, the cutaway amount for both the spiral members  10  and  20  may be distributed in any desired manner. It is to be understood that the distribution is not particularly limited to that shown in this embodiment. Also, since the machining tolerance for the region B is about twice as large than that for the regions C 1  and C 2 , the cutaway amounts for the cutaway portions  41  to  44  in the first relief is about half the cutaway amount for the cutaway portions  45  and  46  in the second relief. 
     In this embodiment, in the regions C 1  and C 2 , the two spiral members  10  and  20  perform a circular orbital operation in close proximity to or in contact with each other through the first relief, whereas in the region B, the two spiral members perform a circular orbital operation in close proximity to or in contact with each other through the second relief. Accordingly, there is no wasteful relief in the regions C 1  and C 2 , and only the required minimum relief is formed corresponding to the machining tolerances. Therefore, the performance of the compressor is enhanced. Also, since the cutaways are dispersed in the two spiral members, the respective cutaway amounts are reduced in both the spiral members. Accordingly, reductions of the wall thickness of the spiral members are minimized and the durability of the spiral members  10  and  20  is enhanced. 
     Further, with respect to the two spiral members  10  and  20 , since the involutes must be changed in a stepped manner for the cutaways  41  to  44  defining the first relief, and for the cutaways  45  and  46  defining the second relief, the manufacture therefor would be troublesome in comparison with the second embodiment to be described next. 
     FIG. 2 shows the second embodiment that differs in how to make the cutaways for the first and second reliefs. In FIG. 2, the first relief is composed of a cutaway portion  51  formed between the points a 1  and b 11  on the wall of the spiral member  10  and a cutaway portion  52  formed between the points b 1  and a 11  on the wall of the spiral member  10  but no machining work is effected on the spiral member  20 . Further, the cutaway amount for each of the cutaway portions  51  and  52  is the dimension obtained by adding up the cutaway amounts of each of the cutaway portions  41  and  43  (or the dimension obtained by adding the amounts of each of the above-described cutaway portions  42  and  44 ). 
     On the other hand, the second relief is composed of a cutaway portion  53  formed between the points b 2  and b 21  on the wall of the spiral member  20  but no machining work is effected on the spiral member  10 . Further, the cutaway amount of this cutaway portion  53  is a dimension obtained by adding the amounts for the above-described cutaway portions  45  and  46 . 
     In the case of the second embodiment, as cutaways having the same cutaway amount for each spiral member may be provided, in comparison with the first embodiment, changes in the involutes for defining each of the spiral members may be reduced, making easy to manufacture the spiral members. 
     Further, it is also possible to reverse the portions to which the cutaways are applied by providing them symmetrically opposite in the other spiral member, respectively. Namely, it is possible to form the cutaway portions  51  and  52  for defining the first reliefs between the points a 21  and b 2  on the inner wall and the points b 21  and a 2  on the inner wall on the side of the spiral member  20  and the cutaway portion  53  for defining the second relief between the points b 11  and b 1  on the inner wall on the side of the spiral member  10  to obtain the same effect as described above. 
     FIG. 3 shows a third embodiment in which the cutaway portions for defining the reliefs are formed only on the side of the spiral member  20 . Namely, the cutaway portions  61  and  62  for defining the first relief are formed between the points a 21  and b 2  on the inner wall and between the points b 21  and a 2  on the inner wall of the spiral member  20 . Also, the cutaway amount of the cutaway portions  61  and  62  is the same as that of the cutaway portions  51  and  52  of the above-described second embodiment. 
     The cutaway portion  63  for defining the second relief is formed between the points b 2  and b 21  on the inner wall of the spiral member  20 . The cutaway amount of the cutaway portion  63  is the same as that of the cutaway portion  53  of the above-described second embodiment. 
     In this embodiment, the cutaway portions  61 ,  62  and  63  are formed only in the spiral member  20 . It is unnecessary to provide any cutaway in the other spiral member  10  at all. The formation of the involute on the spiral member  10  is simplified to facilitate the manufacture of the spiral members. 
     Further, even if the cutaways are not formed in the spiral member  20  but made symmetrically opposite in the spiral member  10 , it is possible to ensure the same effect as described above. 
     FIG. 4 shows a fourth embodiment in which the cutaway is formed only in the spiral member  20  for defining the first relief, and the cutaways for defining the second reliefs are distributed in the spiral member  10  and in the spiral member  20 . 
     In FIG. 4, reference numerals  71  and  72  denote cutaway portions for defining the first relief, formed between the points a 21  and b 2  on the inner wall and between the points b 21  and a 2  on the inner wall of the spiral member  20 . Also, the cutaway amount is the same as that of the cutaway portions  61  and  62  of the above-described third embodiment. 
     Numerals  73  and  74  denote cutaway portions for defining the second relief, which are formed between the points b 2  and b 21  on the inner wall of the spiral member  20  and between the points b 11  and b 1  on the inner wall of the spiral member  10 . The cutaway amount therefor is the same as that of the above-described cutaway portions  71  and  72 . Accordingly, the cutaway portions  71  and  72  for defining the first relief and the cutaway portion  73  for defining the second relief are formed in series with each other. 
     Accordingly, in case of this embodiment, the shape of the involute for the spiral member  20  is simplified, and the manufacture thereof is facilitated. Also, since there is no stepped portion between the cutaway portions  71  and  72  for defining the first relief and the cutaway portion  73  for defining the second relief, the mechanical strength of the spiral member  20  is enhanced. Additionally, since the cutaway amounts of the cutaway portions  73  and  74  for defining the second relief are dispersed between the two spiral members, reductions in mechanical strength of the spiral members is avoided. 
     Further, even if the provision of these cutaway portions is symmetrically reversed between the spiral members  10  and  20 , it is possible to ensure the same effect. 
     FIG. 5 shows a fifth embodiment in which ends of the respective cutaways in accordance with the third embodiment are connected with each other and in the inner wall via smooth curved lines. Namely, the cutaway portions  81  and  82  for defining the first relief correspond to the cutaway portions  61  and  62  of FIG. 3, and the cutaway portion  83  defining the second relief corresponds to the cutaway portion  63  of FIG.  3 . Then, the ends of the respective cutaway portions  81  to  83  are connected to each other and in the inner wall via small curved lines  811 ,  812 ,  821  and  822  in a smooth manner. Accordingly, the concentration of stress affecting each end of the respective cutaway portions  81  to  83  is reduced and the mechanical strength of the spiral member  20  is enhanced. 
     Further, it is also possible to adopt a symmetrically reverse arrangement between the spiral members  10  and  20  to ensure the same effect. 
     According to the first through fifth aspects of the present invention, the excessive relief that the conventional system encounters may be avoided, and a reasonable relief is obtained between the two spiral members. Accordingly, it is possible to enhance the performance of the compressor. Also, the durability of the spiral members is enhanced. 
     According to the second aspect of the present invention, in addition to the effect described above, since the cutaways formed in the two spiral members define the above first and second reliefs, it is possible to reduce the cutaway amount for each spiral member and to enhance the durability of the spiral members. 
     According to the third aspect of the present invention, since the first relief is machined in one of the spiral members and the second relief is machined in the other spiral member, the cutaways are dispersed between both the spiral members to thereby enhance the durability of the spiral members, and at the same time, the involutes for each of the spiral members are changed in a two-step manner. This makes it possible to readily machine the spiral members. 
     According to the fourth aspect of the present invention, since the first and second reliefs are formed only in one of the spiral members, it is unnecessary to change the involutes of the other spiral member in a stepped manner, it is easier to machine the spiral members. 
     According to the fifth aspect of the present invention, since the ends of the cutaways for defining the first and second reliefs are connected to each other via smooth lines, it is possible to avoid stress concentration on the end part edges of the cutaways and to further enhance the durability of the spiral member. 
     Various details of the invention may be changed without departing from its spirit or its scope. Furthermore, the foregoing description of the embodiments according to the present invention is provided for the purpose of illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.