Abstract:
A connecting rod for a hermetic compressor is provided. The connecting rod includes a piston connecting portion, a body having an end connected to the piston connecting portion, a crankshaft connecting portion connected to a different end of the body and extending a predetermined length so that a curved surface is formed, an inner peripheral surface of the crankshaft connecting portion making surface contact with an outer peripheral surface of a sleeve fitted to an off-center pin of a crankshaft, and a clamp fastened to both ends of the crankshaft connecting portion and exerting elastic force to retain the sleeve on the inner peripheral surface of the crankshaft connecting portion. The sleeve does not deform, even when retained on the crankshaft connecting portion, and makes uniform surface contact with the off-center pin, which is inserted into the sleeve. This substantially reduces the abrasion of the sleeve and the off-center pin and improves the compressor&#39;s efficiency.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hermetic compressor, and more particularly to a connecting rod for a hermetic compressor capable of converting the rotation of a crankshaft into the reciprocating linear motion of a piston. 
     2. Description of the Prior Art 
       FIG. 1  is a sectional view showing the internal construction of a hermetic compressor according to the prior art. Referring to the drawing, a frame  2  is positioned inside a hermetic container  1 , which includes upper and lower containers  1   t  and  1   b . A stator  3  is fixed to the frame  2 , which is supported inside the hermetic container  1  by a spring  2   s . A crankshaft  5  is positioned so as to extend through the center of the frame  2 . A rotator  4  is integrally formed on the crankshaft  5  and is rotated together with it by electromagnetic interaction with the stator  3 . 
     The crankshaft  5  has an off-center pin  5   b  positioned on the upper end thereof while being offset from the rotational center of the crankshaft  5  and a balance shaft  5   c  positioned opposite the off-center pin  5   b . The crankshaft  5  is rotatably supported on the frame  2 . A crankshaft connecting portion  9   c  of the connecting rod  9  is fitted to the outer peripheral edge of the off-center pin  5   b  so as to rotate relative to the edge while a sleeve  8  is press-fitted and interposed. 
     The crankshaft  5  has an oil passage  5   a  formed therein, through which oil L is guided from the bottom of the hermetic container  1  to the top of the frame  2  to be scattered, and a pumping mechanism  5   d  positioned on the lower end of the crankshaft  5 , in order to pump the oil L into the oil passage  5   a.    
     The frame  2  is provided with a cylinder  6 , which has a compression chamber formed therein. The compression chamber contains a piston  7 , to which the piston connecting portion  9   a  of the connecting rod  9  connects. The cylinder  6  has a valve assembly  10  positioned on the upper end thereof, in order to control the flow of a refrigerant into/out of the compression chamber. A head cover  11  is mounted on the valve assembly  10 , and an intake muffler  12  is positioned on the head cover  11  while connecting to the valve assembly  10 , in order to transmit the refrigerant to the compression chamber. 
     In the drawing, reference numeral  7   a  refers to a pin fitted to the inner peripheral edge of the piston connecting portion  9   a  so as to fasten it to the piston  7 , and  9   b  refers to the body of the connecting rod  9 . 
     The construction of the connecting rod  9  is shown in  FIG. 2  in more detail. The sleeve  8  is press-fitted to the inner peripheral surface of the crankshaft connecting portion  9   c . The inner diameter of the sleeve  8  is determined in such a manner that it can rotate relative to the off-center pin  5   b.    
     However, the conventional hermetic compressor has the following problems. 
     As shown in  FIG. 2 , the sleeve  8 , which is press-fitted to the crankshaft connecting portion  9   c , deforms due to the limited space of the inner peripheral edge of the crankshaft connecting portion  9   c . Particularly, the inner peripheral surface of the sleeve  8  deforms, i.e. protrudes irregularly, and varies the inner diameter. 
     More specifically, part A of the sleeve  8  is enlarged and shown in a separate graph in  FIG. 2  with a scale of 1 micron. In the graph, the straight solid line indicates enlarged part A of the sleeve  8 , before being press-fitted, and the wavy solid line indicates enlarged part A of the sleeve  8 , after being press-fitted. It is clear from the graph that the wavy solid line has a maximum distance of about 6 micron from the straight solid line. This implies that the entire inner diameter of the sleeve  8 , including part A, has similar deformation. 
     If the inner diameter of the sleeve  8  deforms as shown in  FIG. 2 , the sleeve  8  inevitably makes linear contact with the off-center pin  5   b , which is inserted therein. As a result, a vanishing phenomenon occurs on a surface treatment layer of the inner peripheral edge of the off-center pin  5   b , and the frictional force between the sleeve  8  and the off-center pin  5   b  increases. This degrades the efficiency of power transmission from the crankshaft to the connecting rod  9 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a connecting rod for a hermetic compressor capable of minimizing the change of inner diameter of a sleeve which is press-fitted to a crankshaft connecting portion. 
     In order to accomplish this object, there is provided a connecting rod for a hermetic compressor including a piston connecting portion; a body having an end connected to the piston connecting portion; a crankshaft connecting portion connected to a different end of the body and extending a predetermined length so that a curved surface is formed, an inner peripheral surface of the crankshaft connecting portion making surface contact with an outer peripheral surface of a sleeve fitted to an off-center pin of a crankshaft; and a clamp fastened to both ends of the crankshaft connecting portion and exerting elastic force for retaining the sleeve on the inner peripheral surface of the crankshaft connecting portion. 
     In accordance with another aspect of the present invention, there is provided a connecting rod for a hermetic compressor including a piston connecting portion; a body having an end connected to the piston connecting portion; and a crankshaft connecting portion connected to a different end of the body, a sleeve being press-fitted to an inner peripheral edge of the crankshaft connecting portion so that the crankshaft connecting portion makes surface contact with an off-center pin of a crankshaft and rotates together with the sleeve while the sleeve is interposed, a groove being formed on the crankshaft connecting portion so that deformation of the sleeve is concentrated in a predetermined position and change of inner diameter of the sleeve resulting from press-fitting is prevented. 
     The connecting rod for a hermetic compressor according to the present invention is advantageous in that the sleeve makes uniform surface contact with the off-center pin, which is inserted therein. This prevents the inner peripheral edge of the off-center pin from wearing down. In addition, reduced fraction increases the efficiency of power transmission from the crankshaft to the connecting rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a sectional view showing the internal construction of a hermetic compressor equipped with a connecting rod according to the prior art; 
         FIG. 2  is a top view showing a sleeve press-fitted to a crankshaft connecting portion in a connecting rod according to the prior art; 
         FIG. 3  is an exploded perspective view showing a connecting rod and a sleeve according to a preferred embodiment of the present invention; 
         FIG. 4  is a perspective view showing a connecting rod according to an embodiment of the present invention; 
         FIG. 5  is a perspective view showing a sleeve fixed to a connecting rod according to an embodiment of the present invention; 
         FIG. 6  is a top view showing a connecting rod according to another embodiment of the present invention; 
         FIG. 7  is a top view showing a sleeve coupled to the connecting rod shown in  FIG. 6 ; 
         FIG. 8  is an enlarged view of part B of  FIG. 7 ; and 
         FIG. 9  is a top view showing a connecting rod according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, and so repetition of the description on the same or similar components will be omitted. 
       FIG. 3  is an exploded perspective view showing a connecting rod and a sleeve according to a preferred embodiment of the present invention, and  FIG. 4  is a perspective view of the connecting rod. 
     As shown in these drawings, the connecting rod according to the present embodiment has a piston connecting portion  20  positioned on an end thereof. The piston connecting portion  20  connects to a chamber, which is formed inside a piston  7 , via a piston pin  7   a . The piston connecting portion  20  is adapted to rotate inside the chamber of the piston  7  in a predetermined angular range relative to the piston  7   a  so that the piston  7  can reciprocate linearly inside a compression chamber of a cylinder  6 . 
     It can be easily understood by those skilled in the art that, although the piston connecting portion  20  according to the present embodiment has a ring shape as shown in the drawings, it may have a spherical shape, for example, and connect to the piston  7  in a ball-joint mode. 
     An end of a body  22  connects to the piston connecting portion  20 . The body  22  connects the piston connecting portion  20  to a crankshaft connecting portion  24  (described later). Although the body  22  has a bar shape with a square section, it may have a rod shape, for example. 
     The crankshaft connecting portion  24  is positioned on the other end of body  22 . The crankshaft connecting portion  24  extends a predetermined distance from a point of connection to the body  22  in opposite directions, respectively, and forms a curved surface. The curved surface formed on the inner peripheral edge of the crankshaft connecting portion  24  corresponds to a curved surface formed on the outer peripheral edge of a sleeve  28 , which is fitted to an off-center pin  5   b  of a crankshaft  5 . In other words, the crankshaft connecting portion  24  has a curved surface formed on its inner peripheral surface so as to make surface contact with the outer peripheral edge of the sleeve  28 . 
     It is to be noted that the crankshaft connecting portion  24  does not enclose the entire outer peripheral edge of the sleeve  28  in a ring shape, but it spans approximately half the outer peripheral surface of the sleeve  28 . This means that, when viewed from above, the crankshaft  24  has a semi-circular shape corresponding to at most half the outer peripheral edge of the sleeve  28 . This for the purpose of minimizing deformation of the sleeve  28  occurring when it is press-fitted to the crankshaft connecting portion  24 . 
     A clamp  26  connects to the crankshaft connecting portion  24  and retains the sleeve  28 . Particularly, the clamp  26  is made of an elastically deformable metallic material and applies elastic force to the sleeve  28  so that it is continuously retained on the inner peripheral edge of the crankshaft connecting portion  24 . As such, the clamp  26  has a similar role as that of a conventional leaf spring. 
     In order to fasten the clamp  26  to the crankshaft connecting portion  24 , the crankshaft connecting portion  24  has grooves  24   a  formed on both ends thereof, respectively, in such a manner that they extend in the height direction while being indented with a predetermined depth. When both ends of the clamp  26  are inserted into the grooves  24   a,  respectively, the clamp  26  elastically deforms and supports the sleeve  28  while compressing it, as indicated by arrows in  FIG. 5 . 
     The shape of the clamp  26  will now be described in detail. The clamp  26  has an attachment portion  27  formed in a semi-circular shape, when viewed from above, with a predetermined curvature so that it attaches to the inner peripheral surface of the sleeve  28 . The attachment portion  27  exerts elastic force in such a direction that it adheres to the inner peripheral surface of the sleeve  28 . 
     The attachment portion  27  has latches  27 ′ formed on both ends thereof, respectively. The latches  27 ′ are bent in an approximately U-shaped configuration, when viewed from above, so that their front ends engage with the corresponding grooves  24   a . Particularly, the front ends of the latches  27 ′ extend from both ends of the attachment portion  27  towards each other, so that the latches  27 ′ are latched on both ends of the crankshaft connecting portion  24 . 
     Preferably, the connecting rod, which consists of the piston connecting portion  20 , the body  22 , and the crankshaft connecting portion  24 , is integrally fabricated by sintering, and the sleeve  28  is made of aluminum. This is advantageous in that, compared with the case wherein the sleeve  28  is sintered, friction with the off-center pin  5   b  is reduced. 
     The assembly process of the connecting rod according to the present embodiment, which is constructed as mentioned above, will now be described. The sleeve  28  is brought into contact with the crankshaft connecting portion  24  of the connecting rod. Since the crankshaft connecting portion  24  spans from the point of connection to the body  22  to at most half the outer peripheral edge of the sleeve  28 , when viewed from above, an outer surface of one side of the sleeve  28  can easily make contact with the inner peripheral surface of the crankshaft connecting portion  24  without additional force. 
     One of the latches  27 ′ of the clamp  26  is fitted into one of the grooves  24   a  formed on one end of the crankshaft connecting portion  24 . In order to fit the other latch  27 ′ of the clamp  26  into the groove  24   a  formed on the other end of the crankshaft connecting portion  24 , the clamp  26  is deformed elastically. In this state, the other latch  27 ′ of the clamp  26  is latched on the other end of the crankshaft connecting portion  24 . Then, the attachment portion  27  of the clamp  26  elastically attaches to the outer surface of the sleeve  28 . The clamp  26  applies restoration force to one side of the outer peripheral surface of the sleeve  28  so that a part of the sleeve  28 , which is opposite the attachment portion  27 , is forced against the inner peripheral edge of the crankshaft connecting portion  24 . As such, the sleeve  28  is supported and retained by the crankshaft connecting portion  24  and the clamp  26 . 
     The assembly process is preferably performed after connecting the piston  7  to the piston connecting portion  20 , positioning the crankshaft connecting portion  24  adjacent to the off-center pin  5   b  of the crankshaft  5 , and inserting the off-center pin  5   b  into the sleeve  28 . 
     When the compressor is actually driven after the assembly process, rotation of the crankshaft  5  causes the off-center pin  5   b  to rotate along a circular trajectory and the piston  7  to reciprocate linearly. The sleeve  28 , which is fixed to the crankshaft connecting portion  24  of the connecting rod, rotates relative to the outer peripheral surface of the off-center pin  5   b.    
     The clamp  26  is made of metal which can elastically deform to some degree. Particularly, the elastic modulus of the clamp  26  must be determined in such a manner that the resulting restoration force is equal to or larger than force exerted by the connecting rod, which causes the piston  7  to reciprocate linearly. This prevents the sleeve  28  from detaching from the crankshaft connecting portion  24 , when the connecting rod causes the piston  7  to reciprocate linearly. As a result, the sleeve  28  hardly vibrates. 
     The construction of a connecting rod according to another embodiment of the present invention will now be described with reference to  FIGS. 6 to 8 . Referring to the drawings, the connecting rod has a piston connecting portion  120  positioned on an end thereof. The piston connecting portion  120  connects to a piston  7  via a piston pin  7   a  in a chamber, which is formed inside the piston  7 . Alternatively, the piston connecting portion  120  may connect to the piston  7  in a ball joint mode. 
     An end of a body  122  connects to the piston connecting portion  120 . The body  122  has a bar shape with a predetermined section. The body  122  connects the piston connecting portion  120  to a crankshaft connecting portion  124 . 
     The crankshaft connecting portion  124  is positioned on the other end of the body  122 . The inner diameter of the crankshaft connecting portion  124  is determined in such a manner that a sleeve  128  can be press-fitted thereto. This is for the purpose of interlocking the sleeve  128  and the crankshaft connecting portion  124  as a single unit by pressing-fitting the sleeve  128  to the crankshaft connecting portion  124 . When the sleeve  128  is fitted to an off-center pin  5   b  of a crankshaft  5  and the off-center pin  5   b  travels along a circular trajectory in accordance with rotation of the crankshaft  5 , the sleeve  128  moves together with the crankshaft connecting portion  124  while rotating relative to the outer peripheral edge of the off-center pin  5   b.    
     The crankshaft connecting portion  124  according to the present embodiment has a groove  124   a  formed on its inner peripheral edge. Due to the groove  124   a , any deformation occurring when the sleeve  128  is press-fitted to the crankshaft connecting portion  124  is concentrated in the groove  124   a , as shown in  FIG. 7 . This substantially prevents the sleeve  128  from varying its inner diameter. 
     The position of the groove  124   a  on the inner peripheral surface of the crankshaft connecting portion  124  corresponds to a point of coupling between the crankshaft connecting portion  124  and the body  122 . This is for the purpose of directing any movement of inertia, which results from deformation of the sleeve  128 , in the direction of force transmitted from the connecting rod, i.e. the longitudinal direction of the body  122 . It can be easily understood by those skilled in the art that, when the inertia of the sleeve  128  is intentionally offset, the groove  124   a  may deflect from the direction of force transmitted from the connecting rod. 
     The depth of indentation and length of extension of the groove  124   a  are determined based on the degree of deformation of the sleeve  128 . However, the depth and length of the groove  124   a  vary depending on specific conditions, including the material and thickness of the crankshaft connecting portion  124  and the sleeve  128 . Considering this, the groove  124   a  preferably has a depth large enough to accommodate deformation of the sleeve  128 , as long as the strength of the crankshaft connecting portion  124  is guaranteed. 
     When the sleeve  128  is press-fitted into the groove  124   a  of the crankshaft connecting portion  124 , the inner diameter of the sleeve  124  hardly varies, as shown in  FIG. 8 . More particularly, in  FIG. 8 , which has a scale of 1 micron, the straight solid line indicates enlarged part B of the sleeve  128 , before being press-fitted, and the wavy solid line indicates enlarged part B of the sleeve  128 , after being press-fitted. 
     It is clear from  FIG. 8  that the straight solid line substantially overlaps the wavy solid line. This means that there is little deformation of the sleeve  128  before and after it is press-fitted. Therefore, by forming such a groove  124   a  on the crankshaft connecting portion  124  as in the present embodiment, the sleeve  128  retains its shape even when press-fitted. As a result, when an off-center pin  5   b  is inserted into the inner peripheral edge of the sleeve  128  and makes circumferential motion, the sleeve  128  makes uniform surface contact with the off-center pin  5   b  and transmits force to the connecting rod. 
       FIG. 9  is a top view showing a connecting rod according to another embodiment of the present invention. The crankshaft connecting portion  224  of the connecting rod according to the present embodiment has a similar construction to that of the embodiment shown in  FIG. 6 , except for the position of the groove  224   a . Particularly, the position of the groove  224   a  on the inner peripheral edge of the crankshaft  224  has an angular difference of 180° from the point of connection between the crankshaft connecting portion  224  and the body  222 . 
     Such positioning of the groove  224   a  is for the purpose of directing any movement of inertia, which results from deformation of the sleeve, in the direction of force transmitted from the connecting rod, i.e. the longitudinal direction of the body  222 , as in the above-mentioned embodiment. In the drawing, reference numeral  220  refers to the piston connecting portion. 
     As mentioned above, the connecting rod for a hermetic compressor according to the present invention is advantageous in that, since any deformation occurring when the sleeve is press-fitted to the crankshaft connecting portion of the connecting rod is concentrated in a predetermined position or absorbed by elastic deformation of the crankshaft connecting portion or the clamp, change in inner diameter of the sleeve is minimized. 
     The sleeve makes uniform surface contact with the off-center pin, which is inserted therein. This prevents the inner peripheral edge of the off-center pin from wearing down and improves the durability of the compressor. 
     In addition, minimized friction between the sleeve and the off-center pin increases the efficiency of force transmission from the crankshaft to the connecting rod and improves the compressor&#39;s performance. 
     Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.