Patent Publication Number: US-2004055458-A1

Title: Reciprocating compressor with a linear motor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims the benefit of U.S. Provisional Application No. 60/394,739 filed Jul. 10, 2002, which Provisional Application is incorporated herein by reference. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] The present invention is related generally to a mechanical linkage for connecting a linear motor to a piston or pistons of a reciprocating compressor. Specifically, the present invention is directed to a mechanical linkage for a linear motor that defines a travel path for the piston(s).  
       [0003] A standard refrigeration or heating, ventilation and air conditioning (HVAC) system includes a refrigerant fluid, an evaporator, a compressor, a condenser, and an expansion valve. In a typical refrigeration cycle, the compressor compresses a refrigerant vapor and delivers the vapor to the condenser through a discharge line. The refrigerant vapor delivered to the condenser enters into a heat exchange relationship with another fluid in the condenser and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the other condenser fluid. The condensed liquid refrigerant from the condenser flows through an expansion valve to the evaporator. The liquid refrigerant in the evaporator enters into a heat exchange relationship with another fluid in the evaporator and undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the other evaporator fluid. The vapor refrigerant in the evaporator exits the evaporator and returns to the compressor by a suction line to complete the cycle. By means of example only, the refrigerant fluid used in the system can be ammonia, ethyl chloride, CFCs, HFCs, Freon®, or other known refrigerants.  
       [0004] One type of compressor that can be used in a HVAC or refrigeration system is a reciprocating compressor. A linear motor can be used to drive the reciprocating compressor to improve the efficiency and/or reliability of the compressor. In some applications, linear motors are used with small compressors without positive travel stops for the piston and drive mechanism. However, when the linear motor is connected or attached directly to a piston to compress refrigerant gas, the piston has a tendency to overtravel in light load conditions and undertravel in high load conditions.  
       [0005] Therefore, what is needed is a mechanism to connect between a linear motor and a piston of reciprocating compressor that can operate as a motion stop for a linear motor, define a positive predetermined piston path at all load conditions and prevent undertravel and overtravel of the piston driver assembly.  
       SUMMARY OF THE INVENTION  
       [0006] One embodiment of the present invention is directed to a reciprocating compressor having a linear motor, at least one piston and cylinder arrangement and a mechanism operatively connecting the linear motor to the piston and cylinder arrangement. The piston and cylinder arrangement operates to compress a fluid, preferably a refrigerant gas, and has a cylinder, a piston configured and disposed to travel in the cylinder, and a piston rod connected to the piston. The mechanism connects the linear motor to the piston rod to move the piston in the cylinder upon operation of the linear motor. The mechanism is configured and disposed to limit overtravel of the piston in the cylinder in response to a light load of the reciprocating compressor and to limit undertravel of the piston in the cylinder in response to a heavy load in the reciprocating compressor. The mechanism connecting the linear motor to the piston and cylinder arrangement can include a connecting rod and eccentric, a cam mechanism, a wobble plate mechanism, or a track mechanism, among other things.  
       [0007] Another embodiment of the present invention is directed to a mechanism for connecting a linear motor to a piston-cylinder arrangement such as in a reciprocating compressor. In this embodiment, the mechanism operates to move the piston in the cylinder upon operation of the linear motor, and includes a mechanical configuration to limit overtravel and undertravel of the piston in the cylinder.  
       [0008] One advantage of the present invention is that it prevents undertravel and overtravel of the piston driver assembly when a linear motor is used with a reciprocating compressor.  
       [0009] Another advantage of the present invention is that the piston travels a positive and predetermined path when a linear motor is used with a reciprocating compressor.  
       [0010] Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]FIG. 1 illustrates schematically a first embodiment of a mechanical linkage configuration of the present invention.  
       [0012]FIG. 2 illustrates schematically a second embodiment of a mechanical linkage configuration of the present invention.  
       [0013]FIG. 3 illustrates schematically a third embodiment of a mechanical linkage configuration of the present invention. 
     
    
    
     [0014] Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
     DETAILED DESCRIPTION OF THE INVENTION  
     [0015] FIGS.  1 - 3  illustrate several embodiments of the present invention. A linear motor  10  is used to drive or move a mechanism that defines the path of the piston or pistons  30  in a reciprocating compressor  40 . It is to be understood that the reciprocating compressor  40  includes many other components that are well known in the art which are not shown herein for purposes of simplicity and clarity. The mechanism can be a connecting rod eccentric type mechanism  20  as shown in FIG. 1, or the mechanism can be any other type of piston path defining mechanism, including but not limited to a cam type, gear type, sliding track type, “wobble plate” type or any other suitable piston path defining mechanism. In the embodiments of the present invention, the mechanism controls the path and travel of one or more pistons  30 , thereby preventing each piston  30  from overextension during light loads and underextension during heavy loads. Preferably, the mechanism  20  provides a constant predetermined top dead center piston position and bottom dead center piston position to limit or eliminate overtravel and undertravel of the piston  30  in the cylinder  50 .  
     [0016] The reciprocating compressor  40  of the present invention includes one or more cylinders  50 . Positioned in each of the cylinder(s)  50  is a piston  30  that can move back and forth in the cylinder  50  in an axial direction. The piston  30  is used to compress a refrigerant gas in the cylinder  50  by traveling toward a closed end of the cylinder  50  to compress the refrigerant gas between the piston face and the closed end of the cylinder. A piston rod  32  is connected to the piston  30  to move the piston  30  in the cylinder  50 . The piston rod  32  is connected to a connecting mechanism  20  (see FIG. 1), which in turn is connected to the linear motor  10 . Preferably, the connecting mechanism  20  also operates to limit movement of the piston rod  32  in the axial direction while moving the piston  30  toward the closed end of the cylinder  50  and while withdrawing the piston  30  from the closed end of the cylinder  50 . The operation of the linear motor  10  and connecting mechanism  20  displace the piston rod  32  to move the piston  30  back and forth in the cylinder  50 .  
     [0017] During operation of the linear motor  10 , one or more stators  8  drive or move a rotor  12  back and forth in the same axial direction as the piston  30  as shown in FIG. 1. Connected to the rotor  12  are one or more connecting linkages  14  that connect the rotor  12  to the connecting mechanism  20 . The connecting mechanism  20  shown in FIG. 1 is a connecting rod eccentric type mechanism  20  mounted on bearings  21  or other suitable rotating structures using known methods in the art. The movement of the rotor  12  of the linear motor  10  moves the connecting linkages  14 , which turn or displace the connecting mechanism  20  thereby moving the piston rod  32  to propel the piston  30  back and forth in the cylinder  50 . The movement of the piston  30  and piston rod  32  in the cylinder  50  is dependent on the direction of movement of the rotor  12  and linkages  14  and the particular configuration of the connecting mechanism  20 . The use of the connecting mechanism  20  defines a positive, controlled and predetermined travel path for the piston rod  32  and piston  30 , thereby preventing the overextension or underextension of the piston  30  during certain loading conditions of the compressor.  
     [0018] As shown in FIG. 2, a gear-type mechanism  120  is used to connect the linear motor  10  and the piston rod(s)  32 . The mechanism  120  includes a linear gear  22  that is connected to and driven by the linkage  14  that is driven by the rotor  12 . The liner gear  22  preferably includes opposed first and second gear surfaces  24 ,  26 . Preferably, each gear surface  24 ,  26  is substantially parallel with the longitudinal axis of the linear gear  22 . The gear surface  24 ,  26  may be any suitable gear surface type, such as square-toothed, grooved, or serrated. As shown in FIG. 2, each gear surface  24 ,  26  contacts a connecting gear  28  that is connected to a corresponding piston rod  32 . Each connecting gear  28  is shaped so as to smoothly engage the gear surface  24 ,  26  to drive the connecting rod  32  with a minimum of energy loss, and to provide a pre-determined and controlled travel path for the piston rod  32  and piston  30 . Preferably, the travel path includes predetermined top-dead center piston position and bottom-dead center piston position which remain constant despite load increases and decreases. In an alternative embodiment not illustrated, a single gear surface is provided on the linear gear, with a plurality of connecting gears aligned such that each connecting gear is in contact with the gear surface, each connecting gear driving a corresponding piston rod to propel a corresponding piston.  
     [0019] As shown in FIG. 3, a track-type mechanism  220  is used to connect the linear motor  10  and piston rod(s)  32 . The mechanism  220  includes a drive block  60  having an embedded track  62  for receiving a drive pin  64 . The drive pin  64  is connected to the linkage  14  that is in turn driven by the rotor  12 . The drive pin  64  is also connected to one or more piston rods  32 . As the rotor  12  drives the linkage  14 , the drive pin  64  is moved in the track  62 . As the drive pin  64  moves, it pushes the piston rod  32  to force the piston  30  to move in the cylinder  50 . The track  62  is shaped and sloped so as to smoothly engage the piston connecting rod  32  to drive the piston  30  up and down in the cylinder  50  with a minimum of energy loss, and to provide a pre-determined and controlled travel path for the piston rod  32  and piston  30 . Preferably, the travel path includes predetermined top-dead center piston position and bottom-dead center piston position which remain constant despite load increases and decreases. In the embodiment of FIG. 3, these positions are accomplished by the inclusion of substantially horizontal, non-sloped track sections  66  at each end of the track  62 . When the drive pin  64  enters a horizontal section  66 , the position of the connecting rod  32  remains substantially vertically constant, so that the piston  30  is neither driven up nor pulled down until the pin is pulled or pushed back into the sloped portion of the track by the linkage  14 . Preferably, as shown in FIG. 3, more than one piston rod  32  is connected to the drive pin  64  so that reciprocating opposed pistons  30  can be driven as the pin  64  moves throughout the track  62 .  
     [0020] While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.