Patent Publication Number: US-8118577-B2

Title: Scroll compressor having optimized cylinder oil circulation rate of lubricant

Description:
TECHNICAL FIELD 
     The present invention relates to scroll compressors used for air conditioners, refrigerators, and the like. 
     BACKGROUND ART 
     In scroll compressors, a fixed scroll and an orbiting scroll are arranged with their spiral walls being assembled, and the orbiting scroll is made to orbitally revolve around the fixed scroll to gradually reduce the volume of compression spaces formed between the walls, thereby compressing fluid in the compression spaces. Among such scroll compressors, those that employ scroll members having stepped shapes have been put to practical use because the compression ratio can be increased without increasing the size of the compressors themselves, so as to improve the compression performance. In one such scroll compressor that has been proposed a tip seal is provided along a connection edge that connects, at a step portion, the upper edges having different heights, in order to improve the airtightness between the scrolls to improve the compression performance, and which has a mechanism that prevents the tip seal from being removed from the connection edge. (For example, see Patent Document 1.) 
     Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2002-303281 
     DISCLOSURE OF INVENTION 
     At the step portion of each of the scroll members described above, a minute gap is formed between the fixed scroll and the orbiting scroll to allow the orbiting operation of the orbiting scroll. Therefore, when the volume of the compression spaces is gradually reduced as the compression process proceeds, compressed gas leaks from the high-pressure side to the low-pressure side through the minute gap. Accordingly, the minute gap formed at the step portion causes a reduction in the compression efficiency of the scroll compressor. In particular, when recent high-pressure refrigerant (for example, R410A, CO 2 , or the like) is used, the difference in pressure between the high-pressure side and the low-pressure side is increased, so that the leakage of compressed gas causes a more significant reduction in efficiency. 
     From such circumstances, it is demanded that the minute gap at the step portion be sealed with an oil film of lubricant which is taken into and circulated in the scroll compressor when the scroll compressor is operated, to reduce the leakage of compressed gas and improve the compression efficiency. 
     The present invention has been made in view of the circumstances described above, and an object thereof is to provide a scroll compressor in which the cylinder oil circulation rate of lubricant during the operation is optimized to improve the compression efficiency. 
     In order to solve the problems described above, the present invention employs the following solutions. 
     According to the present invention, there is provided a scroll compressor including: a fixed scroll which has a spiral wall formed upright on one side face of an end plate; and an orbiting scroll which has a spiral wall formed upright on one side face of an end plate and which is supported, when the walls are engaged, so as to allow orbital revolving motion thereof while preventing rotation thereof, the one side face of the end plate of at least one of the fixed scroll and the orbiting scroll being provided with a step part formed to be higher at a center portion and lower at an outer end along a spiral of the wall, an upper edge of the wall of the other one of the fixed scroll and the orbiting scroll being divided into a plurality of portions whose height is low at a center portion of a spiral and is high at an outer end of the spiral, to form a stepped shape corresponding to the step part provided on the end plate, in which a cylinder oil circulation rate of lubricant taken into the scroll compressor and circulated together with refrigerant is set to fall within the range from 1% or more to 10% or less. 
     According to this scroll compressor, the cylinder oil circulation rate of lubricant taken into the compressor and circulated together with refrigerant is set to fall within the range from 1% or more to 10% or less. Therefore, a sufficient amount of lubricant to form an oil film to seal a minute gap at the step part can be provided. 
     In the above-described scroll compressor, it is preferable that the lubricant be supplied to the vicinity of the step part. With this structure, it is possible to provide a sufficient amount of lubricant for the vicinity of the step part and to form an oil film effective to seal the minute gap. 
     In the above-described scroll compressor, it is preferable that the lubricant be supplied to the vicinity of the step part located higher in the direction of gravitational force when the fixed scroll and the orbiting scroll are of a horizontal type. With this structure, the lubricant can fall under the influence of the gravitational force to be supplied. 
     According to the aspect described above, since the cylinder oil circulation rate of lubricant is set to fall within the range from 1% or more to 10% or less, it is possible to provide a sufficient amount of lubricant to form an oil film to seal the minute gap at the step part and to improve the sealing properties of the minute gap at the step part. As a result, a significant advantageous effect can be obtained in that the amount of compressed gas leaking from the minute gap at the step part is reduced, thereby improving the compression efficiency of the scroll compressor having the stepped shape. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a graph of experimental results, showing how the efficiency of a scroll compressor according to an embodiment of the present invention changes when a cylinder oil circulation rate (%) is changed. 
         FIG. 2A  is a circuit diagram of a refrigeration cycle including the scroll compressor of the present invention, showing an example configuration that includes an external oil separator. 
         FIG. 2B  is a circuit diagram of a refrigeration cycle including the scroll compressor of the present invention, showing an example configuration that includes a built-in oil separator. 
         FIG. 3  is a partial cross-sectional view showing an example configuration of the scroll compressor of the present invention. 
         FIG. 4A  is a perspective view showing an example configuration of a fixed scroll, placed upside down, of the scroll compressor of the present invention. 
         FIG. 4B  is a perspective view showing an example configuration of an orbiting scroll of the scroll compressor of the present invention. 
         FIG. 5  is a cross-sectional view showing a state where the fixed scroll and the orbiting scroll are assembled to form compression spaces and are about to start compression. 
         FIG. 6  is a main-portion perspective view showing an example configuration where lubricant is supplied to the vicinity of a step part of the present invention. 
     
    
    
     EXPLANATION OF REFERENCE SIGNS 
     
         
           1 : housing 
           11 : outlet port 
           12 : fixed scroll 
           12   a ,  13   a : end plate 
           12   b ,  13   b : wall 
           12   c ,  12   d ,  13   c ,  13   d : upper edge (tip) 
           12   e ,  13   e : connecting edge (tip) 
           12   f ,  12   g ,  13   f ,  13   g : bottom face (bottom) 
           12   h ,  13   h : connecting wall face (bottom) 
           13 : orbiting scroll 
           42 ,  43 : step part 
           51 ,  51 A: oil separator 
         CP: scroll compressor 
         C: compression space 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A scroll compressor according to an embodiment of the present invention will be described below with reference to the drawings. 
       FIG. 3  is a cross-sectional view showing an example configuration of a scroll compressor CP. In  FIG. 3 , reference numeral  1  is a hermetically-sealed housing,  2  is a discharge cover which divides the housing  1  into a high-pressure chamber HR and a low-pressure chamber LR,  5  is a frame,  6  is an inlet pipe,  7  is an outlet pipe,  8  is a motor,  9  is a rotary shaft, and  10  is a rotation preventing mechanism. Reference numeral  12  is a fixed scroll, and  13  is an orbiting scroll engaged with the fixed scroll  12 . 
     The fixed scroll  12  is provided with a spiral wall  12   b  formed upright on one side face of an end plate  12   a , as shown in  FIG. 4A . Similarly to the fixed scroll  12 , the orbiting scroll  13  is provided with a spiral wall  13   b  formed upright on one side face of an end plate  13   a , as shown in  FIG. 4B . In particular, the wall  13   b  has substantially the same shape as the wall  12   b  of the fixed scroll  12 . The walls  12   b  and  13   b  are engaged and assembled such that the orbiting scroll  13  is eccentric relative to the fixed scroll  12  by the radius of orbital revolution and their phases are shifted from each other by 180 degrees. 
     In this case, the orbiting scroll  13  performs orbital revolving motion with respect to the fixed scroll  12 , due to the actions of the rotation preventing mechanism  10  and an eccentric pin  9   a  that is provided on the top of the rotary shaft  9  driven by the motor  8  and that performs orbiting motion. On the other hand, the fixed scroll  12  is fixed to the housing  1 , and an outlet port  11  for compressed fluid is provided at the center of the rear face of the end plate  12   a.    
     On the one side face of the end plate  12   a  of the fixed scroll  12 , where the wall  12   b  is formed upright, a step part  42  is formed to be higher at a center portion and lower at an outer end along the spiral wall  12   b . Similarly to the end plate  12   a  of the fixed scroll  12 , on the one side face of the end plate  13   a  of the orbiting scroll  13 , where the wall  13   b  is formed upright, a step part  43  is formed to be higher at a center portion and lower at an outer end along the spiral wall  13   b . The step parts  42  and  43  are provided starting at locations that are π (rad) away from the outer ends (inlet sides) of the walls  12   b  and  13   b  toward the inner ends (outlet sides) thereof, respectively, with the centers of the spiral walls  12   b  and  13   b  serving as reference points. 
     With the step part  42  being formed, a bottom face of the end plate  12   a  is divided into two portions, that is, a shallow bottom face  12   f  provided nearer the center portion and a deep bottom face  12   g  provided nearer the outer end. Between the adjacent bottom faces  12   f  and  12   g , there is a connecting wall face  12   h  which constitutes the step part  42  and vertically rises to connect the bottom faces  12   f  and  12   g.    
     Similarly to the end plate  12   a  described above, with the step part  43  being formed, a bottom face of the end plate  13   a  is divided into two portions, that is, a shallow bottom face  13   f  provided nearer the center portion and a deep bottom face  13   g  provided nearer the outer end. Between the adjacent bottom faces  13   f  and  13   g , there is a connecting wall face  13   h  which constitutes the step part  43  and vertically rises to connect the bottom faces  13   f  and  13   g.    
     The spiral upper edge of the wall  12   b  of the fixed scroll  12  is divided into two portions which are low at the center portion of the spiral and high at the outer end of the spiral, thereby forming a stepped shape corresponding to the step part  43  of the orbiting scroll  13 . Similarly to the wall  12   b , the spiral upper edge of the wall  13   b  of the orbiting scroll  13  is divided into two portions which are low at the center portion of the spiral and high at the outer end of the spiral, thereby forming a stepped shape corresponding to the step part  42  of the fixed scroll  12 . 
     Specifically, the upper edge of the wall  12   b  is divided into two portions, that is, a low-level upper edge  12   c  provided nearer the center portion and a high-level upper edge  12   d  provided nearer the outer end. Between the adjacent upper edges  12   c  and  12   d , there is a connecting edge  12   e  which connects them and is perpendicular to the orbit plane. Similarly to the wall  12   b  described above, the upper edge of the wall  13   b  is divided into two portions, that is, a low-level upper edge  13   c  provided nearer the center portion and a high-level upper edge  13   d  provided nearer the outer end. Between the adjacent upper edges  13   c  and  13   d , there is a connecting edge  13   e  which connects them and is perpendicular to the orbit plane. 
     When the wall  12   b  is viewed from the orbiting scroll  13 , the connecting edge  12   e  has a semicircular shape which is smoothly connected to both inner and outer side faces of the wall  12   b  and whose diameter is the same as the thickness of the wall  12   b . Similarly to the connecting edge  12   e , the connecting edge  13   e  has a semicircular shape which is smoothly connected to both inner and outer side faces of the wall  13   b  and whose diameter is the same as the thickness of the wall  13   b.    
     When the end plate  12   a  is viewed from the direction of an orbit axis, the connecting wall face  12   h  has an are that matches an envelope curve traced by the connecting edge  13   e  during the orbit of the orbiting scroll. Similarly to the connecting wall face  12   h , the connecting wall face  13   h  has an arc that matches an envelope curve traced by the connecting edge  12   e.    
     Tip seals  14   a  and  14   b  which are separated from each other in the vicinity of the connecting edge  12   e  are respectively provided on the upper edges  12   c  and  12   d  of the wall  12   b  of the fixed scroll  12 . Similarly, tip seals  15   b  and  15   a  which are separated from each other in the vicinity of the connecting edge  13   e  are respectively provided on the upper edges  13   c  and  13   d  of the wall  13   b  of the orbiting scroll  13 . Those tip seals are used to seal tip seal gaps formed between the upper edges (tips) and the bottom faces (bottoms), between the orbiting scroll  13  and the fixed scroll  12 , thereby minimizing the leakage of compressed gas fluid. 
     In other words, when the fixed scroll  12  and the orbiting scroll  13  are assembled, the tip seal  15   b  provided on the low-level upper edge  13   c  is brought into contact with the shallow bottom face  12   f , and the tip seal  15   a  provided on the high-level upper edge  13   d  is brought into contact with the deep bottom face  12   g . At the same time, the tip seal  14   a  provided on the low-level upper edge  12   c  is brought into contact with the shallow bottom face  13   f  and the tip seal  14   b  provided on the high-level upper edge  12   d  is brought into contact with the deep bottom face  13   g . As a result, between the scrolls  12  and  13 , the compression spaces C are defined and formed by the end plates  12   a  and  13   a , which face each other, and by the walls  12   b  and  13   b .  FIG. 4A  shows the fixed scroll  12  placed upside down in order to show the stepped shape of the fixed scroll  12 . 
       FIG. 5  shows a state where the fixed scroll  12  and the orbiting scroll  13  are assembled to form the compression spaces C and are about to start compression. In this compression start state, the outer end of the wall  12   b  is brought into contact with the outer side face of the wall  13   b , the outer end of the wall  13   b  is brought into contact with the outer side face of the wall  12   b , fluid to be compressed is sealed between the end plates  12   a  and  13   a  and between the walls  12   b  and  13   b , and the two compression spaces C, each having the maximum volume, are formed at locations that face each other across the center of the scroll compression mechanism. Although the connecting edge  12   e  and the connecting wall face  13   h , and the connecting edge  13   e  and the connecting wall face  12   h  are brought into contact with each other in a slidable manner at this time, they are immediately separated from each other by the orbiting operation of the orbiting scroll  13 . 
     In the scroll compressor CP having the above-described stepped shape, the cylinder oil circulation rate (hereinafter also referred to as “OC %”) of lubricant taken into the scroll compressor CP and circulated together with refrigerant is set to fall within the range from 1% or more to 10% or less. The lubricant is supplied to each sliding part in the scroll compressor CP for lubrication, and at least part of the lubricant is converted into mist lubricant and compressed together with gas refrigerant. Therefore, the mist lubricant flows out from the scroll compression mechanism together with the gas refrigerant. In order to collect the lubricant, an oil separator  51  is provided in a refrigerant circuit  50  shown in  FIG. 2 , for example. 
     When the lubricant is supplied at the above-mentioned cylinder oil circulation rate, an oil rich state is produced where a larger amount of lubricant than that in a conventional technology is contained, thereby forming good oil films that are excellent in sealing minute gaps at the step parts  42  and  43 . Therefore, the minute gaps can be sealed with the oil films, preventing a reduction in the efficiency of the scroll compressor CP caused by the leakage of compressed high-pressure gas from the step parts  42  and  43 . 
       FIG. 1  is a graph of experimental results, showing how the efficiency of the scroll compressor CP changes when the cylinder oil circulation rate (%) is changed. In the graph, the horizontal axis indicates the cylinder oil circulation rate and the vertical axis indicates the efficiency ratio. The efficiency is improved when the efficiency ratio is increased to 1 or more. The efficiency ratio used in this case is calculated by using, as a reference (denominator), the efficiency of a conventional scroll compressor that has an identical volume but does not employ the stepped shape, and using the efficiency obtained as a result of each experiment as a numerator. 
     From the experimental results, it is found that the efficiency ratio is 1 or more when the cylinder oil circulation rate falls within the range from 1% to 10%. Specifically, when the cylinder oil circulation rate falls within the range from 1% to about 3.5%, the efficiency ratio is increased as the cylinder oil circulation rate is increased. When the cylinder oil circulation rate is increased to as high as about 3.5% or more, the efficiency ratio tends to be reduced. When the cylinder oil circulation rate is 10%, the efficiency ratio returns to 1. Therefore, it is preferable that the cylinder oil circulation rate fall within an optimum usage range of 1% or more to 10% or less. It is more preferable that the cylinder oil circulation rate fall within a range of 1% or more to 3.5% or less, where the efficiency can be improved with the minimum circulation amount. 
     In a refrigerant circuit diagram of a refrigeration cycle shown in  FIG. 2A , reference numeral  51  in the figure is the oil separator,  52  is a condenser,  53  is a throttling mechanism, and  54  is an evaporator. High-temperature and high-pressure gas refrigerant discharged from the scroll compressor CP circulates through a refrigerant pipe  55  to be condensed and evaporated, thereby undergoing repeated changes in state. In  FIG. 2A , reference numeral  60  is a flow-rate adjustment device provided on a lubricant supply pipe  56  to adjust the amount of lubricant to be returned from the oil separator  51  to the scroll compressor CP. 
     In the refrigerant circuit  50 , gas refrigerant supplied to the condenser  52  exchanges heat with surrounding air or the like to radiate heat, and liquid refrigerant supplied to the evaporator  54  exchanges heat with surrounding air or the like to absorb heat. 
     In the refrigerant circuit  50 , the oil separator  51  is externally attached at a location near the outlet side of the scroll compressor CP and upstream of the condenser  52 . Instead of the oil separator  51 , which is externally attached, it is possible to use a built-in oil separator  51 A that is built into the scroll compressor CP in the flow path at the outlet side of the scroll compressor CP, as in a refrigerant circuit  50 A shown in  FIG. 2B , for example. 
     Each of the above-described oil separators  51  and  51 A separates mist lubricant from gas refrigerant discharged from the scroll compressor CP, stores the lubricant, and supplies the lubricant in a necessary amount controlled, for example, by the flow-rate adjustment device  60  to an appropriate portion of the scroll compressor CP by using a lubricant pump mechanism or the like (not shown). 
     In the case of using the external oil separator  51  shown in  FIG. 2A , it is preferable to supply the lubricant to the inside of the housing  1  of the scroll compressor CP or to an intake pipe of the refrigerant pipe  55  (low-pressure pipe upstream of the compressor). In this case, the oil separator  51  and the housing  1  of the scroll compressor CP are coupled by the lubricant supply pipe  56 , and the oil separator  51  and the intake pipe are coupled by a lubricant supply pipe  56 ′. In contrast, in the case of using the built-in oil separator  51 A shown in  FIG. 2B , it is preferable to directly supply the lubricant not only to an appropriate portion inside the housing  1  but also to the scroll compression mechanism, when closed, via lubricant supply passages  57  or the like. When the lubricant is supplied particularly to the vicinity of the step parts  42  and  43 , an abundant amount of lubricant can be provided near the minute gaps, thereby reliably forming good oil films having excellent sealing properties. 
     A specific example where lubricant is supplied to the vicinities of the step parts  42  and  43  will be briefly described with reference to  FIG. 6 . In the example shown in  FIG. 6 , the lubricant supply passages  57  are formed inside the wall  12   b  of the fixed scroll  12  to supply lubricant to the vicinity of the step part. In this case, the lubricant supply passages  57  are communicated with outlet holes  58  which are opened to the connecting edge  12   e  and to the low-level upper edge  12   c  connected to the connecting edge  12   e , to let lubricant flow out from both of the outlet holes  58 . In  FIG. 6 , reference numeral  59  is a minute groove which holds the lubricant. 
     With this structure, it is possible to form the step part and to supply lubricant to a portion where the tip seals  14   a  and  14   b  are not provided, to form an oil film on the minute gap. Therefore, the leakage of compressed gas can be prevented to improve the efficiency. 
     When the scroll compressor CP is of a horizontal type, if lubricant is supplied to the vicinity of one step part, located higher in the direction of gravitational force, of the step parts  42  and  43 , a sufficient amount of lubricant can be provided for the other step part, located lower in the direction of gravitational force, because the lubricant falls due to the gravitational force. Therefore, oil films that are effective in sealing the minute gaps can be efficiently formed in both step parts, located higher and lower in the direction of gravitational force, and the oil films can prevent leakage, thus improving the efficiency of the scroll compressor CP. 
     The above-described cylinder oil circulation rate may be set through lubricant flow-rate control performed by using, for example, the flow-rate adjustment device  60 , to be described below. 
     As shown in  FIG. 2A , the flow-rate adjustment device  60  is located between the scroll compressor CP, which compresses and discharges refrigerant, and the oil separator  51 , which separates mist lubricant included in the refrigerant discharged from the scroll compressor CP. The flow-rate adjustment device  60  has a function of increasing a flow rate of lubricant to be returned from the oil separator  51  to the scroll compressor CP as a refrigerant-circulation-amount parameter is increased. The refrigerant-circulation-amount parameter is a control value expressed by the product of the rotational speed of the scroll compressor CP and the pressure of refrigerant measured at the inlet of the scroll compressor CP. 
     The flow rate of lubricant means the amount of lubricant to be returned to the scroll compressor CP per unit time or the amount of lubricant to be returned to the scroll compressor CP within a predetermined period of time. When lubricant flows in a continuous manner, either the amount of lubricant to be returned to the scroll compressor CP per unit time or the amount of lubricant to be returned to the scroll compressor CP within a predetermined period of time may be used for comparison of the amount of lubricant to be returned to the scroll compressor CP. 
     On the other hand, when an on-off valve (not shown) provided in a lubricant flow path is used, for example, and the average amount of lubricant to be returned to the scroll compressor CP within a predetermined period of time is changed by changing a valve open time within the predetermined period of time, lubricant flows intermittently. In this case, for comparison of the amount of lubricant to be returned to the scroll compressor CP, it is more appropriate to use the amount of lubricant to be returned to the scroll compressor CP within a predetermined period of time, than the amount of lubricant to be returned to the scroll compressor CP per unit time. 
     According to the above-described scroll compressor CP of the present invention, since the cylinder oil circulation rate (OC %) of lubricant is set to fall within the range from 1% or more to 10% or less, it is possible to provide a sufficient amount of lubricant to form oil films to seal the minute gaps at the step parts  42  and  43 , and to improve the sealing properties of the minute gaps at the step parts  42  and  43 . As a result, the amount of compressed gas leaking from the minute gaps at the step parts  42  and  43  can be reduced, thereby improving the compression efficiency of the scroll compressor CP having the stepped shape. 
     The present invention is not limited to the embodiment described above. The present invention can be applied to any types of compressors, such as horizontal compressors, vertical compressors, hermetic type compressors, and open type compressors, as long as the compressors have a scroll compression mechanism having a stepped shape. Modifications can be appropriately made without departing from the scope of the present invention.