You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
     The present invention relates to display cases and, more particularly, to a door closer mechanism for a refrigeration display case. 
     Refrigeration cases circulate air through a refrigeration coil to keep the contents cool and include a door to allow a user to access the contents. The door is at least partially transparent to display the contents. The door is biased toward a closed position to provide insulation of the refrigerated interior compartment when a user is not accessing the interior compartment. 
     SUMMARY 
     In one embodiment, the invention provides a display case including a housing partially surrounding a display space, a door pivotably coupled to the housing and cooperating with the housing to further enclose the display space, and a hinge assembly for pivotably coupling the door to the housing. The hinge assembly includes a biasing member applying a biasing force on the door and a gear drive for adjusting a pre-tension force on the biasing member. 
     In another embodiment, the invention provides a display case including a main housing, a support member, a second housing having a first gear, a second gear, a door pin defining a door axis, a biasing member, and a door coupled to the door pin for co-rotation therewith. The main housing partially encloses a display space and defines an opening. The support member is fixedly coupled to the main housing. The second housing is coupled to the support member. The second gear is supported for rotation by the support member and is in meshing relationship with the first gear. Rotation of the second gear produces a corresponding rotation of the first gear and the second housing. The door pin is supported for rotation about the door axis by the second housing. The biasing member is connected to the door pin and the second housing and operable to provide a biasing force to the door pin. The biasing force is adjusted in response to the rotation of the second housing. The biasing force biases the door toward a closed position. 
     In yet another embodiment, the invention provides a hinge assembly for a door of a display case. The hinge assembly includes a pin for supporting the door, a shell, a spring coupled between the pin and the shell, a first gear secured to the shell, and a second gear engaging the first gear. The pin defines a pivot axis. The shell includes a bore receiving at least a portion of the pin, and the shell is movable relative to the pin. The spring exerts a biasing force on the pin about the pivot axis. Rotation of the second gear causes the shell to pivot relative to the pin, thereby changing the biasing force exerted by the spring member. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a refrigeration case. 
         FIG. 2  is an enlarged perspective view of a portion of the case of  FIG. 1 . 
         FIG. 3  is a perspective view of a hinge assembly. 
         FIG. 4  is a side view of the hinge assembly of  FIG. 3 . 
         FIG. 5  is a front view of the hinge assembly of  FIG. 3 . 
         FIG. 6  is an exploded view of the hinge assembly of  FIG. 3 . 
         FIG. 7  is a side view of a shell. 
         FIG. 8  is a top view of the shell of  FIG. 7 . 
         FIG. 9  is a section view of the hinge assembly of  FIG. 4 , taken along section  9 - 9 . 
         FIG. 10  is a side view of a hinge pin. 
         FIG. 11  is a bottom view of the hinge pin of  FIG. 10 . 
         FIG. 12  is a section view of the hinge assembly of  FIG. 4 , taken along section  12 - 12 . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” and “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a display case  10  including a housing  14  defined by a rear wall  18 , a pair of side walls  22 , a top  26 , and a bottom  30 . The case  10  also includes a pair of doors  34  that swing open to provide access to the contents of the housing  10 . Each door  34  pivots about an upper hinge  38  and a lower hinge  42 . In other embodiments, the case  10  may include fewer or more doors  34 .  FIG. 2  illustrates that the lower hinge  42  includes a bracket  46  supporting a door closer mechanism  50 . The two doors  34  of the display case  10  are hinged on the same side so that both doors  34  open toward the left. Other constructions may reverse this so that the doors both open to the right. Because the doors  34  open in the same direction, the hinges  42  cannot be positioned on the outside of the housing  14  as would be possible with two doors that open in opposite directions (i.e., doors that open outwardly from the center toward the side walls  22 ). 
     As shown in  FIGS. 3-6 , the door closer mechanism  50  includes a support member or cartridge  54 , an inner housing or elongated shell  58  ( FIGS. 4-6 ), a hinge pin  62 , a biasing or spring member  66  ( FIG. 5 ), and a gear shaft  70 . The cartridge  54  includes an outer housing or elongated sleeve  74  and a flange  78  positioned on one end of the sleeve  74 . The sleeve  74  defines a longitudinal axis  82 , and a bore  86  ( FIG. 6 ) extends along the axis  82  through the sleeve  74 . The flange  78  extends perpendicularly with respect to the axis  82  and includes lugs  90  for mounting the door closer mechanism  50  to the bracket  46  ( FIG. 2 ). The flange  78  also includes a groove  94  ( FIGS. 5 and 6 ) for supporting the gear shaft  70 . In other embodiments, the cartridge may be formed simply as a flange (i.e., without the elongated sleeve  74 ), wherein the flange is coupled to the bracket  46  and includes a portion supporting the shell  58  and a portion supporting the gear shaft  70 . 
     Referring to  FIG. 6 , the shell  58  is received within the bore  86  of the sleeve  74  and is aligned with the axis  82  of the sleeve  74 . The shell  58  includes a first end  102  and a second end  106 . A ring gear  110  is coupled to the first end  102  of the shell  58 . In the illustrated embodiment, an internal faceted surface  112  of the ring gear  110  engages an external faceted surface  114  of the shell  58  proximate the first end  102  to rotatably secure the ring gear  110  with respect to the shell  58 . In addition, a lip  118  is positioned on the shell  58  proximate the first end  102  to support the shell  58  for rotation with respect to the sleeve  74 . 
     As best shown in  FIGS. 7 and 8 , the second end  106  of the shell  58  defines an end wall  122 , and a shell bore  126  extends from the first end  102  of the shell  58  to the end wall  122 . The end wall  122  includes an opening  130  in communication with the shell bore  126 . The end wall  122  also includes a first spring coupling  134 . In the illustrated embodiment, the first spring coupling  134  is a hole formed in the end wall. 
     Referring again to  FIG. 6 , the spring member  66  is positioned within the shell  58  and aligned with the longitudinal axis  82  such that the spring member  66  exerts a biasing force about the axis  82 . In the illustrated embodiment, the spring member  66  is a torsional coil spring  142  having a first end  146  secured to the shell  58  at the first spring coupling  134  and a second end  150  secured to the hinge pin  62  as described below. The spring member  66  exerts a force on the hinge pin  62  in order to bias the door  34  toward the closed position. 
       FIG. 9  shows the hinge pin  62  supported for rotation relative to the shell  58  such that a portion of the pin  62  is positioned within the shell bore  126 . In the illustrated embodiment, the hinge pin  62  passes through the center of the coil spring  142  and is supported by a washer made from, for example, plastic. In some embodiments, a retainer may be coupled to the second end  158  of the pin  62  to limit movement of the hinge pin  62  parallel to the axis  82  from the second end  106  of the shell  58  toward the first end  102 . The hinge pin  62  includes a first end  154  extending above the shell  58  and a second end  158  extending through the opening  130  in the end wall  122 . 
     As best shown in  FIGS. 10 and 11 , the hinge pin  62  defines a pivot axis  162  extending between the first end  154  and the second end  158 , and the pivot axis  162  is generally aligned with the axis  82  of the sleeve  74  ( FIG. 6 ). In other embodiments, the pivot axis  162  may be offset from the sleeve axis  82 . The first end  154  of the hinge pin  62  includes a head or shank  170  that is coupled to the door  34  ( FIG. 1 ) such that the pin  62  is secured against rotation relative to the door  34 . The head  170  also includes a second spring coupling  174  for engaging the second end  150  of the spring member  66 . In the illustrated embodiment, the second spring coupling  174  is a hole formed in the head  170  of the pin  62 . 
     Referring again to  FIG. 6 , the gear shaft  70  includes a gear portion  182  and is supported for rotation within the groove  94  of the flange  78 . A retaining plate  194  is coupled to the top of the flange  78  to retain the gear shaft  70  within the groove  94 . The retaining plate  194  also retains the ring gear  110  and shell  58  within the sleeve  74 , and retains the pin  62  within the bore  86 . In one embodiment, the retaining plate  194  is formed from machined steel and is coupled to the flange  78  by fasteners (e.g., screws). 
     As shown in  FIG. 12 , the gear portion  182  engages the ring gear  110  such that rotation of the gear shaft  70  drives the ring gear  110  and the shell  58  to pivot relative to the sleeve  74 . Pivoting the shell  58  about the pivot axis  162  adjusts the pre-tension exerted on the hinge pin  62  by the spring member  66  ( FIG. 11 ), thereby changing the biasing force exerted on the door  34 . In the illustrated embodiment, the gear shaft  70  is positioned transverse to the longitudinal axis  82 , and one end of the gear shaft  70  includes a slot  186  for receiving a tool (e.g., a screwdriver—not shown) for rotating the gear shaft  70  with respect to the groove  94 . In this arrangement, the gear portion  182  includes a worm gear that engages the ring gear  110 . The use of a worm gear allows for fine adjustment as the effective gear ratio between the worm gear and the ring gear  110  is very large. In addition, the worm gear eliminates the need for any locking mechanism to maintain the preload as the worm gear will not turn in response to a torque applied to the ring gear  110 . In the illustrated embodiment, only one end of the gear shaft  70  includes the slot  186 . Because the slot  186  should be accessible to a user, the slot  186  provides an indicator during installation to insure that the door closer mechanism  50  is positioned properly and to prevent a user from installing the door closer mechanism  70  backward. 
     As the door  34  is opened, the hinge pin  62  pivots with respect to the shell  58  about the pivot axis  162  ( FIG. 9 ). Because one end  150  of the spring member  66  is coupled to the hinge pin  62 , the pivoting of the hinge pin  62  causes elastic deformation of the spring member  66 . The spring member  66  exerts a biasing force on the hinge pin  62  and the door  64  to urge the door  64  toward the closed position, with the rotation produced during door opening increasing the biasing force. Referring to  FIG. 5 , the pre-tension force in the spring  66  can be adjusted by rotating the gear shaft  70  (e.g., with a screwdriver). For example, rotating the gear shaft  70  in a first direction causes the ring gear  110  and the shell  58  to pivot in a first direction about the pivot axis  162 , compressing or tightening the spring member  66  and increasing the spring tension when the door  34  is in the closed position. The spring member  66  applies a larger biasing force on the hinge pin  62 , requiring a larger force to open the door  34 . Alternatively, rotating the gear shaft  70  in a second direction opposite the first direction causes the shell  58  to pivot in a second direction about the pivot axis  162 , loosening the spring member  66  and decreasing spring tension so that the door  34  requires less force to open. 
     The door closer mechanism  50  provides a compact system, containing the tension-adjustment device within the sleeve  74 . Some conventional door closer systems incorporate a long torque rod that must be inserted into the glass door to provide closing tension. This requires a thicker door frame to receive and house the torque rod and reduces the transparent viewable portion of the door. By contrast, the door closer mechanism  50  does not require the door  34  to accommodate a long torque rod, resulting in a thinner construction for an opaque frame of the door  34 . Furthermore, some conventional door systems require more extensive dis-assembly and re-assembly to adjust the tension on a biasing member (e.g., by changing the relationship between the upper and lower spring attachment points). The door closer mechanism  50  provides a simple screw adjustment to change the pre-tension of the spring  66  without any significant disassembly of the door  34  or the door closer mechanism  50 . 
     Thus, the invention provides, among other things, a door closer mechanism for a display case. Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described. Various features and advantages of the invention are set forth in the following claims.

Summary:
A display case includes a housing partially surrounding a display space, a door pivotably coupled to the housing and cooperating with the housing to further enclose the display space, and a hinge assembly for pivotably coupling the door to the housing. The hinge assembly includes a biasing member applying a biasing force on the door and a gear drive for adjusting a pre-tension force on the biasing member.