Abstract:
A scroll compressor includes an Oldham coupling which prevents the orbiting scroll member from rotating when driven by a rotating shaft. The Oldham coupling is formed of titanium or titanium alloy, thus increasing the strength of the Oldham coupling while minimizing its weight. Reduced coupling weight minimizes unnecessary scroll compressor vibration.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a scroll compressor wherein the Oldham coupling is manufactured of titanium or titanium alloy. 
         [0002]    Scroll compressors are becoming widely utilized in refrigerant compression applications. In typical scroll compressors, a first scroll member has a base and a generally spiral wrap extending from its base. A second scroll member has a base and a generally spiral wrap extending from its base. The second scroll member is driven to orbit by a rotating shaft. An eccentric pin on the shaft extends into a slider block which is received within a boss on a rear face of the second scroll member. An anti-rotation coupling, known as an Oldham coupling, ensures that the second scroll member orbits relative to the first scroll member as driven by the rotating shaft. As the second scroll member orbits relative to the first, compression chambers defined between the wraps of the first and second scroll member decrease in size to compress the refrigerant. 
         [0003]    In the prior art, the Oldham couplings have typically been formed of aluminum, and have often broke. This problem was especially pronounced in larger scroll compressors, and in particular during flooded start operation. Under such flooded starts, the force transmitted to the coupling by the orbiting scroll can be substantially higher than during normal operation, causing the Oldham coupling to break. 
         [0004]    To overcome this problem, it has been proposed in the past, for example, to use cast iron to form the Oldham coupling. However, a cast iron Oldham coupling would be unduly heavy and cause excessive vibration, as the Oldham coupling is an element of a scroll compressor that cannot be fully balanced (such as for example using counterweights). A cast iron coupling would weigh roughly two and a half times as much as an aluminum coupling of the same size. 
         [0005]    Titanium and titanium alloys have been utilized extensively in aerospace applications, and are beginning to find their way in some specialized automotive applications, where weight of the part is of concern. Examples, of some of the automotive applications include: turbocharger wheels, suspension springs, etc. However, titanium or its alloys have not been proposed for Oldham couplings for scroll compressors. 
       SUMMARY OF THE INVENTION 
       [0006]    In a disclosed embodiment of this invention, an Oldham coupling is formed of titanium or titanium alloy. By utilizing titanium or titanium alloy, sufficient strength is provided for the Oldham coupling without the additional weight, as would be found utilizing cast iron. 
         [0007]    Titanium is about 60% as dense as cast iron. As an example, titanium has a density of approximately 4500 kg/m 2  versus 7800 kg/m 3  for cast iron. In addition, the strength of titanium is superior to both aluminum and cast iron. 
         [0008]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1A  is a schematic view of a scroll compressor incorporating the present invention. 
           [0010]      FIG. 1B  is a schematic of an alternative system. 
           [0011]      FIG. 2A  is a view of an Oldham coupling according to the present invention. 
           [0012]      FIG. 2B  is another view along line  2 B- 2 B of  FIG. 2A . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    A compressor  20  is illustrated in  FIG. 1A  having an orbiting scroll  22  orbiting relative to a non-orbiting scroll  24 . As shown in the example a motor  26  drives a rotating shaft  28 . However, as shown in  FIG. 1B , the compressor assembly  104 , as known, can be driven directly by an engine  100  shaft through appropriate coupling mechanisms that would couple the engine shaft rotation to the compressor shaft. The engine shaft can be coupled to the compressor rotating shaft, for example, by means of a coupling, gearbox, or belt drive  102 . The electric motor is normally an induction motor type. The motor speed can additionally be varied by means of variable speed drive. 
         [0014]    An eccentric pin  29  at the top of the shaft extends into a slider block  31 . The slider block  31  is received within a boss  33  on a rear face of an orbiting scroll  22 . As is known, when the rotating shaft  28  rotates, the eccentric pin  29  moves within the slider block  31 . The orbiting scroll  22  is supported on a crankcase  30 . An Oldham coupling  32  ensures that when the rotating shaft  29  drives the orbiting scroll  22  it will be constrained to orbiting movement, and will not rotate. The structure and operation of the Oldham coupling  32  is as known in the art. 
         [0015]    As shown in  FIGS. 2A and 2B , the Oldham coupling  32  includes a generally ring shaped portion  34 , and keys  36 . The keys fit into slots to constrain the orbiting scroll to orbit rather than rotate. 
         [0016]    In the present invention, the Oldham coupling  32  is formed of titanium or titanium alloy. As mentioned above the titanium or titanium alloy material provides additional strength and resistance to breakage as compared to other more conventional materials such as for example aluminum or cast iron. Pure titanium has good mechanical properties, however titanium is often alloyed. Most commonly, small amounts of aluminum and vanadium are added, however, other stabilizing materials, as provided below, can also be used. Such alloys have very high tensile strength and toughness. Titanium alloys that can be used as potential candidates for the Oldham Coupling, normally would fall into three main classes: alpha, beta, and alpha-beta phase that includes most of the titanium alloys now in use. Typical stabilizing materials include: aluminum, gallium, germanium, carbon, oxygen and nitrogen for alpha stabilizers; and chromium, cobalt, copper, iron, manganese molybdenum, nickel niobium silicon, tantalum, vanadium for beta stabilizers. Alpha-phase titanium is more ductile and beta-phase titanium is stronger but more brittle. Alpha-beta-phase titanium falls somewhere between both. One of the most common alloys currently in use is Ti-6Al-4V. A table, in addition to pure titanium, showing typical alfa, alfa-beta, and beta alloys that can be used for an Oldham coupling is shown below. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Alpha alloys 
                 Alpha + Beta alloys 
                 Beta alloys 
               
               
                   
               
             
             
               
                 Ti—2.5Cu 
                 Ti—6Al—4V 
                 Ti—13V—11Cr—3Al 
               
               
                 Ti—5Al—2.5Sn 
                 Ti—6Al—6V—2Sn 
                 Ti—8Mo—8V—2Fe—3Al 
               
               
                 Ti—8Al—1V—1Mo 
                 Ti—6Al—2Sn—2Zr—2Cr—2Mo 
                 Ti—10V—2Fe—3Al 
               
               
                 Ti—6242 
                 Ti—3Al—2.5V 
                 Ti—15—3 
               
               
                 Ti—6Al—2Nb—1Ta—0.8Mo 
                 Ti—8Al—1Mo—1V 
               
               
                 Ti—5Al—5Sn—2Zr—2Mo 
               
               
                   
               
             
          
         
       
     
         [0017]    It should be noted that the titanium coupling can be delivered first as cast titanium parts, before performing final machining operation. It is clear from this statement and from the drawings that the entirety of the Oldham coupling is formed of the titanium. However, the invention would extend to the use of titanium to form the majority of the Oldham coupling body. 
         [0018]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.