Patent Publication Number: US-8535027-B2

Title: Thermal expansion chambers for airtight containers

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 11/229,615 filed in the United States Patent and Trademark Office on Sep. 20, 2005, now U.S. Pat. No. 8,062,010, the full disclosure of which is incorporated herein by reference and priority to which is claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to thermal expansion chambers for airtight containers such as housings for hydraulic systems and to methods for accommodating changes in volume of hydraulic fluid within such systems. 
     Hydraulic pumps include a hollow housing. The housing is airtight, but has input and output ports for hydraulic fluid. The fluid may become heated during operation of the pump as well as during operation of hydraulic devices connected to the pump. The fluid expands when heated and, where the pump housing is an airtight container, the fluid will generate pressure that can increase stresses on the pump housing which may lead to leakage of the hydraulic fluid or damage to components. 
     Accordingly, it would be desirable to provide a hydraulic pump which could accommodate varying volumes of hydraulic fluid within its housing. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a hydraulic pump comprising a rotor and hollow housing. The housing has a main interior chamber, the rotor being rotatably mounted in the main interior chamber. There is a smaller interior chamber separated from the main interior chamber such that the smaller interior chamber retains gas therein when the main interior chamber is filled with a liquid, thereby accommodating changes of volume of the liquid within the hollow housing. 
     According to another aspect of the invention, there is provided a method for accommodating changes in volume of hydraulic fluid within a main chamber of a hydraulic pump housing for a hydraulic pump. The method comprises providing a smaller interior chamber separated from the main chamber and retaining gas within the smaller chamber when the main interior chamber is filled with liquid. Expansion or contraction of the gas accommodates changes of volume of the liquid within the housing. 
    
    
     
       BRIEF DESCRIPTIONS OF DRAWINGS 
       In the drawings which illustrate embodiments of the invention: 
         FIG. 1  is a fragmentary bottom, isometric view of one section of a housing of a hydraulic pump, showing the interior of the housing and an expansion chamber thereof, according to an embodiment of the invention; 
         FIG. 2  is a front isometric view of an expansion chamber, according to another embodiment of the invention; 
         FIG. 3  is a bottom isometric view of the expansion chamber of  FIG. 2 ; and 
         FIG. 4  is a sectional view of the expansion chamber of  FIG. 1  taken along line  4 - 4  of  FIG. 1 . 
     
    
    
     DESCRIPTIONS OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , this shows a housing  10  of a hydraulic pump which is generally conventional in configuration. The housing  10  has a bearing at each end including bearing  14  disposed adjacent aperture  16  for rotatably supporting the shaft of a rotor (not shown).  FIG. 1  shows only one half  17  of the housing  10 . A plurality of cylindrical recesses  18  are located in enlarged semicylindrical protrusions  20  which are spaced-apart about the inner cylindrical wall  22  of the housing. These recesses receive bolts or other fasteners for securing housing half  17  to another similar half of the housing (not shown) having another bearing similar to bearing  14  for supporting the opposite end of the rotor shaft. A suitable seal (not shown) extends about the housing between the two halves thereof. The housing  10  has a main interior chamber  19  with a top  29 . 
     The overall structure of housing half  17  is conventional and therefore is not disclosed in more detail. However, housing  10  is unconventional because it incorporates a smaller interior chamber or expansion chamber  26  which is separated from the main interior chamber  19 . The expansion chamber  26  in this example has a hollow housing  27  made of thin wall, blowmolded plastic and is located adjacent to the top  29  of the main chamber  19  in this embodiment. Polypropylene is used in this example, although other plastics such as polyethylene or other plastics or metals could be substituted. Polypropylene was found to withstand the oil and temperature better than polyethylene although the latter is more commonly used for such parts. 
     Although the invention, as described above, is used in a rotor piston-type hydraulic pump it will be known to a person skilled in the art that the invention may be used in other types of hydraulic pumps such as gear pumps or gerotor pumps. 
     Referring to  FIG. 2 , another embodiment of the expansion chamber  26 . 1  is shown where like parts have like reference numerals with the additional designation “. 1 ”. The housing  27 . 1  of the expansion chamber  26 . 1  has a convexly curved surface  30  shaped to fit against concavely shaped surface  32  of the housing  10  shown in  FIG. 1 . There is a semicylindrical recess  34  shaped to fit over one of the semicylindrical protrusions  20  of the housing  10 . The expansion chamber housing  27 . 1  in this example has a C-shaped portion  36  adjacent to convexly curved surface  30 . C-shaped portion  36  is connected to two adjacent portions  40  and  42  which extend away from convexly curved surface  30 . There is an opening  44  between adjacent portions  40  and  42  which allows communication between the interior of the housing  10 , shown in  FIG. 1 , and one of the ports of the pump. 
     There is a pair of small passageways  51  and  52  adjacent to the bottom  31  of the housing  27 . 1 . The passageways  51  and  52  permit communication between the expansion chamber  26 . 1  and the main interior chamber  19  of the housing  10 , shown in  FIG. 1 . The passageways  51  and  52  are sufficiently large to permit fluid to enter or exit the expansion chamber  26 . 1 . The passageways  51  and  52  face downwardly to inhibit air or other gas within the expansion chamber  26 . 1  from exiting the expansion chamber. 
     The housing  27 . 1  could be shaped differently than shown in the drawings. Also the blowmolded housing could be replaced with a more rigid structure, optionally integral with the housing  10  or with a flexible bladder containing air or in other gas. Alternatively, the housing  27 . 1  could be replaced by a resilient foam member, preferably a closed cell foam. 
     It will be understood by someone skilled in the art that many of the details provided about are by way of example only and may be varied or deleted without departing from the scope of the invention as set forth in the following claims.