Patent Publication Number: US-6708406-B2

Title: Method of manufacturing shoe for compressor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing a shoe for a compressor. 
     2. Description of the Related Art 
     A compressor, that compresses a refrigerant gas, is built into a refrigerating circuit that is used as a vehicle air conditioner or the like. For example, a known variable-displacement-type swash-plate compressor has a plurality of cylinder bores  91   a  formed in a cylinder block  91 , as shown in FIG. 9. A piston  92  is accommodated in each cylinder bore  91   a  so as to be able to carry out a reciprocating motion. Further, a swash plate  93  is supported by a drive shaft, not shown, such that the swash plate  93  is rotatable synchronously with the drive shaft and is tiltable with respect to the drive shaft. A pair of shoes  94  are provided, on each side of the swash plate  93 , between the swash plate  93  and each piston  92 . As shown in FIG. 10, the upper surface of each shoe  94  forms a part of a spherical surface as a spherical surface portion  94   a , and the lower surface of the shoe  94  forms approximately a plane surface as a plane surface portion  94   b . A cylindrical portion  94   c  is formed in the middle between the upper portion and the lower portion via a round portion R. 
     In the compressor having the above structure, the swash plate  93  rotates synchronously with the drive shaft and makes an inclined movement with respect to the drive shaft, and a rotary motion of the swash plate  93  is converted into a linear reciprocating motion of the piston  92  in the cylinder bore  91   a , via the shoes  94 , based on the rotation of the drive shaft, as shown in FIG.  9 . Suction, compression, and discharging of a refrigerant gas are carried out at the head end of the piston  92 , based on these motions. During this period, the spherical surface portion  94   a  of each shoe  94  slides on the surface of a spherical surface seat  92   a  of the piston  92 , and the plane surface portion  94   b  of the shoe slides on the surface of the swash plate  93 . Therefore, the shoe  94  is required to have high size precision and small surface roughness in order to allow a smooth sliding action. 
     Conventionally, the shoe  94  has been manufactured according to the following process which includes a cutting step and a shoe forming step. 
     Cutting Step 
     As shown in FIG. 11, a wire  70  comprising SUJ2 (JIS Japanese Industry Standard G4805), a high carbon chrome bearing steel, is provided. This wire  70  is cut into pieces to obtain cut pieces  71  in a cutting step S 90 . 
     Shoe Forming Step 
     The shoe forming step S 91  is then carried out. In a forging step S 91   a , each cut piece  71  is forged with a forging die  95 , that has a spherical cavity  95   c  comprising a lower die  95   a  and an upper die  95   b , to form a sphere as shown in FIG.  12 . As a result, an approximately spherical steel sphere  72  having a slight flash  72   a  is obtained, as shown in FIG.  13 . 
     Then, in a flash removing (deburring) step S 91   b  in FIG. 11, a flash (a burr) is removed by sandwiching the steel sphere  72  between two rotary casting boards, not shown, and by rotating the casting boards, thereby to obtain a flashless ball  73 . 
     Next, in a heat treating step S 91   c , hardening and tempering are carried out to obtain a heat-treated ball  74 . 
     In a grinding step S 91   d , the heat-treated ball  74  is ground with casting boards similar to those explained above and is ground with a grindstone, thereby to obtain a ground ball  75 . The hard ground ball  75  obtained in this way can also be used as a ball of a rolling bearing. 
     Further, the ground ball  75  is annealed in an annealing step S 91   e , thereby to obtain an annealed ball  76  that has a slightly lower hardness than that of the ground ball  75  and that has no internal distortion. 
     Then, in a rotary grinding step S 91   f , the annealed balls  76  and a slurry are put into a rotary grinder, not shown, and are rotated together. As a result, the annealed balls  76  are brought into contact with each other, and are mutually ground. Gloss is added to these balls, and stains adhered to the surfaces of these balls are removed. 
     Further, in a washing step S 91   g , an ultrasonic cleaning is carried out to remove slight stains adhered to the surfaces. A visual inspection step S 91   h  is carried out, and an anticorrosive is then coated onto the balls in an anticorrosive processing step S 91   i . As a result, a raw ball  77  having a true spherical shape is obtained. 
     In a pressing step S 91   j , the raw ball  77  is pressed to obtain a material  78  formed in a shoe shape. 
     Further, in a heat treating step S 91   k , hardening and tempering are carried out. Then, the shoe-shaped material is ground, to obtain a shoe shape and a surface coarseness within a standard, in a finish grinding step S 91   l . The shoe-shaped material is further cleaned in a washing step S 91   m , and is dried in a drying step S 91   n  to finally obtain a shoe  94  for a compressor. 
     The conventional manufacturing method employs the flash removing step S 91   b  and, therefore, the grinding step S 91   d  and the rotary grinding step S 91   f  are necessary. That is, as the steel sphere  72  is obtained in the forging step S 91   a  by using the forging die  95  comprising the lower die  95   a  and the upper die  95   b , it is difficult to obtain a desired shape, and therefore, the cut piece  71  having a slightly larger volume than that of a desired shoe is obtained so that the flash (burr)  72   a  occurs. As a slight gap is formed between the upper die  95   b  and the lower die  95   a  of the forging die  95 , the flash  72   a  occurs in this gap. 
     According to the above conventional manufacturing method, however, the shoe  94  is manufactured from the raw ball  77 , after the raw ball  77  has been manufactured. Therefore, many steps such as the forging step S 91   a , the flash removing process S 91   b , the heat treating step S 91   c , the grinding step S 91   d , the annealing step S 91   e , and the rotary grinding step S 91   f  are necessary. In addition, as the raw ball  77  is completed through the above steps, and thereafter, the raw ball  77  is again subjected to the pressing step S 91   j  that deforms the raw ball  77  to obtain the material  78  which is in turn subjected to the heat treating step S 91   l  and the finish grinding step S 91   i . Therefore, an extremely large number of steps are carried out on the wire  70 . Consequently, the process takes a long time, and is expensive. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in the light of the above problems. It is, therefore, an object of the present invention to provide a method of manufacturing a shoe for a compressor that can shorten the manufacturing time and can reduce the manufacturing cost. 
     In order to achieve the above object, according to the present invention, there is provided a method of manufacturing a shoe for a compressor comprising the steps of cutting a steel wire to obtain a cut piece, and forming a shoe for a compressor from the cut piece, wherein, in the cutting step, the wire is cut so that the cut piece has a volume approximately equivalent to that of a desired shoe, wherein the forming step comprises the steps of sequentially forging the cut piece with forging dies having three or more cavities to obtain a shoe-shaped material, and finishing said material by at least a heat treatment to obtain the shoe. 
     In this method, after the cut piece is obtained by cutting the wire into the cut piece having a volume approximately equivalent to that of a desired shoe in the cutting step, the shoe is manufactured in the forming step comprising the forging step and the finishing step. Therefore, a heat treating step, a grinding step and an annealing step which are carried out in a conventional manufacturing method to obtain a raw ball can be omitted. 
     Further, according to this method, the cut piece is cut in the cutting step so that it has a volume approximately equivalent to that of a desired shoe, and the cut piece is sequentially forged with forging dies having three or more cavities in the forging step to obtain the shoe. Therefore, there occurs small distortion in the cut piece in each forging step, and the obtained material has a highly precise dimension and there is smaller occurrence of a flash. Therefore, the conventional flash removing process becomes unnecessary. The material is then heat-treated to obtain the shoe in the finishing step. 
     Therefore, according to this manufacturing method, it is possible to omit many steps, compared with the conventional manufacturing method, and it is possible to shorten the manufacturing time, with a reduction in a cost for equipment and goods. It is thus possible to reduce the manufacturing cost. As the number of processes is decreased, it is also possible to prevent wastage of energy since the number of manufacturing steps is reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be more fully understood from the description of the preferred embodiments of the invention, as set forth below, together with the accompanying drawings, in which 
     FIG. 1 is a process diagram according to the embodiment of the present invention; 
     FIG. 2 is a perspective view of a cut piece; 
     FIG. 3 is a partial cross sectional view of a first forging die in a state that a cut piece is inserted into this die; 
     FIG. 4 is a side view of the first material; 
     FIG. 5 is a partial cross sectional view of a second forging die; 
     FIG. 6 is a side view of a second material; 
     FIG. 7 is a partial cross sectional view of a third forging die; 
     FIG. 8 is a side view of a material; 
     FIG. 9 is a cross sectional view of a main part of a compressor having shoes according to the embodiment and a comparative example; 
     FIG. 10 is a side view of the shoe according to the embodiment and the comparative example; 
     FIG. 11 is a process diagram according to a conventional example; 
     FIG. 12 is a partial cross sectional view of a forging die of the conventional example; and 
     FIG. 13 is a side view of the steel sphere of the conventional example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention and a comparative example will be explained below with reference to the drawings. 
     Cutting Step 
     In the method of manufacturing a shoe for a compressor in the embodiment of the present invention, a wire  1  comprising an SUJ2 (JIS G4805), a high carbon chrome bearing steel, is provided, as shown in FIG. 1. A cutting step S 1  is carried out to cut the wire  1  into cut pieces each having a volume approximately equivalent to that of a desired shoe  8  (FIG.  10 ). In this way, a cylindrical cut piece  2  having one end surface  2   a  and the other end surface  2   b , is obtained, as shown in FIG.  2 . 
     Shoe Forming Step 
     A shoe forming step S 2 , which includes the following steps, is then carried out as shown in FIG.  1 . 
     (1) Forging Step 
     The forging step S 21  is carried out. Three forging dies  13 ,  23 , and  33 , as shown in FIG. 3, FIG. 5, and FIG. 7 respectively are prepared, for this purpose. These forging dies  13 ,  23 , and  33  have lower dies  13   a ,  23   a , and  33   a , and upper dies  13   b ,  23   b , and  33   b  that can move relative to the lower dies  13   a ,  23   a , and  33   a , respectively. The lower dies  13   a ,  23   a , and  33   a , and the upper dies  13   b ,  23   b , and  33   b  have cavities  13   c ,  23   d , and  33   e , respectively. 
     First, the forging die  13  shown in FIG. 3, that is used in a first forging step S 21   a , shown in FIG. 1, forms the cavity  13   c , with the lower die  13   a  defining a flat end surface and a peripheral surface, and the upper die  13   b  defining a flat end surface and peripheral surface with a rounded portion therebetween. The flat surface, the rounded portion and the peripheral surface of the upper die  13   b  are smoothly connected to the peripheral surface of the lower die  13 , by a curved line in cross section. When the cut piece  2  is forged within this cavity  13   c,  one end surface  2   a  and the peripheral surface of the cut piece  2  continue in a curved surface, and one end surface  2   a  of this cut piece  2  is rounded as a round portion R. In this case, the role of the upper die  13   b  is to form a curve on one end surface  2   a  of the cut surface  2 . Therefore, it is not necessary that the upper die  13   b  comes extremely close to the lower die  13   a  to be connected. 
     Next, the cut piece  2  of which one end surface  2   a  has been rounded as a round portion R is reversed, and the other end surface  2   b  is forged in the same cavity  13   c  of the same forging die  13 . In this case, it is also possible to form a curved surface without bringing the upper die  13   b  extremely close to the lower die  13   a . In this way, the periphery of the other end surface  2   b  is rounded. The first step  21   a  has been completed, and a first material  4 , having the first end surface  2   a  and the other end surface  2   b  rounded as round portions R, respectively, is obtained as shown in FIG.  1  and FIG.  4 . 
     In a second step S 21   b  shown in FIG. 1, the first material  4  is forged in the forging die  23  having the cavity  23   d  in a shape, like a rugby ball, which is an intermediate shape between the first material  4  and the shoe  8 , as shown in FIG.  5 . The cavity  23   d  is wholly rounded, compared with the cavity  13   c  of the first die  13 . The lower cavity portion is more curved than the upper cavity portion. As a result, a rugby ball shaped second material  6  is obtained as shown in FIG.  6 . In this case, it is preferable that the cavity  23   d  has a volume strictly equivalent to or slightly larger than the capacity of the desired shoe  8 . The upper die  23   b  and the lower die  23   a  that constitute the forging die  23  cannot be precisely and strictly connected with each other and a slight gap is formed between them. Therefore, it is preferable to avoid factors which may generate a flash (burr) in this gap due to the swelling. No flash occurs on the peripheral surface of the rugby ball shaped second material  6  that has a shape slightly approaching a spherical shape. 
     In a third step S 21   c  shown in FIG. 1, the rugby ball shaped second material  6  is forged in the forging die  33  having the cavity  33   e  conforming to the shape of the shoe  8 , as shown in FIG.  7 . As a result, a material  7  having a shoe shape is obtained, as shown in FIG.  8 . The forging step S 2  is completed in this way. In this case, it is also preferable that the cavity  33   e  has a volume strictly equivalent to or slightly larger than the capacity of the desired shoe  8 . As the second material  6  having the rugby ball shape, which is near the shape of the shoe  8 , is changed into the material  7 , the quantity of deformation is small. Consequently, factors which may generate flash become smaller. Flash does not occur on the material  7  in the shoe shape, except that an extremely small belt-shaped recess may possibly occur at the central region. However, if the belt-shaped recess occurs, the recess would be located in the cylindrical portion  8   c  of the shoe  8  between the spherical portion  8   a  and the flat portion  8   b , and when the shoes  8  are arranged in the compressor, the recess is not located in a sliding portion relative to the spherical seat  92   a  of the piston  92  and the swash plate  93 , so the recess has no influence. 
     Finishing Step 
     A finishing step S 22  is then carried out, which includes the following steps. 
     The shoe-shaped material  7  is hardened and tempered in a heat treating step S 22   a . Then, a finish grinding step S 22   b , a washing step S 22   c , and a drying step S 22   d  are carried out. As a result, the shoe  8  for a compressor is obtained. 
     COMPARATIVE EXAMPLE 
     In a manufacturing method of the comparative example, a shoe  94  for a compressor is obtained by employing the conventional method of manufacturing a shoe for a compressor shown in FIG.  11 . 
     The manufacturing method of the embodiment can be compared with that of the comparative example, and the shoes  8  and  94  obtained from these manufacturing methods can be compared with each other as follows. 
     In the manufacturing method of the embodiment, the material  7  in the shoe shape is obtained directly from the cut piece  2 , by forging the cut piece  2  in the forging step S 21 . As a result, the heat treating step S 91   c , the grinding step S 91   d , the annealing step S 91   e , the rotary grinding step S 91   f , the washing step S 91   g  and the inspecting steps  91   h  of the comparative manufacturing method to obtain the raw ball  77  can be omitted. 
     In the inventive manufacturing method, the wire  1  is cut into cut pieces each having a volume approximately equivalent to that of the desired shoe  8 , in the cutting step S 1 . Also, in the inventive manufacturing method, there are used the forging dies  13 ,  23 , and  33  having three cavities  13   c ,  23   d , and  33   e , respectively, to form the material  7  in the shoe shape in the forging step S 21  at the three stages, and the deformation in each forging stage is small. As result, the material  7  formed in the forging step has more precise dimensions and a flash seldom occurs. Therefore, the flash removing (deburring) step S 91   b , which is conventionally carried out, can be also omitted. 
     Therefore, according to the manufacturing method of the embodiment, it is possible to reduce the manufacturing time, to reduce the cost for equipment and goods, and to thereby reduce the manufacturing cost. Also, as the number of steps is decreased, it is also possible to prevent wastage of energy. 
     In the embodiment, the forging step S 21  is carried out by the three stages, i.e., using the forging dies  13 ,  23 , and  33  having the three cavities  13   c ,  23   d , and  33   e , respectively. However, it is also possible to add a further forging die having a separate cavity, between the second step S 21   b  of obtaining the rugby ball shaped second material  6  and the third step S 21   c  of obtaining the material  7  in the shoe shape. Based on this, it is possible to form the rugby ball shaped material  6  into a material in a shape closer to the shoe shape, so that it becomes possible to further minimize the quantity of deformation when the rugby ball shaped material is forged. 
     While the invention has been described by reference to a specific embodiment chosen for the purpose of illustration, it will be apparent that numerous other modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.