Abstract:
An automotive compressor is provided having a casing defining an intake section for fluid for compression, and a delivery section for delivering the compressed fluid. An impeller is movable angularly inside the casing to increase the pressure of the fluid. A distributor is carried by the intake section of the casing to conduct the fluid for compression to the impeller. The casing and the distributor are defined by separate members connected releasably to each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority of European Patent Application No. 04425351.6, filed on May 18, 2004, the subject matter of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to an automotive compressor, in particular for supplying pressurized fluid to fuel cell systems. 
   Automotive centrifugal compressors are known which substantially comprise a fixed portion, and one or more bladed impellers driven by an external motor. The fixed portion is normally defined by a hollow casing, in which the impeller rotates to produce the desired compression of the fluid flowing through it. 
   More specifically, the casing defines, integrally, an intake section through which the fluid to be compressed is fed to the impeller to increase its kinetic energy; and a delivery section defined by a diffuser, in which the kinetic energy is converted to pressure energy. 
   The intake section may have a number of fixed blades acting as a distributor, i.e. defining respective channels of given shape to conduct and accelerate the fluid intake onto the impeller in the desired direction of impact on the impeller blades. 
   In other words, the fixed blades substantially provide for imparting to the fluid for compression an optimum direction of impact on the movable blades of the impeller, so as to reduce fluid-dynamic losses and improve the overall efficiency of the compressor. 
   Fuel cell drive systems require compressor impellers of variable geometry, both for test purposes and to permit a certain amount of flexibility in the equipping of different types of vehicles. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an automotive compressor designed to permit such flexibility in a straightforward, low-cost manner. 
   According to the present invention, there is provided an automotive compressor comprising: a casing defining an intake section for a fluid for compression, and a delivery section for delivering the compressed fluid; an impeller movable angularly inside said casing to increase the pressure of said fluid; and a distributor carried by said intake section of said casing to conduct the fluid for compression to said impeller; wherein said casing and said distributor are defined by separate members connected releasably to each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
       FIG. 1  shows a partly sectioned view in perspective of a compressor in accordance with the present invention; 
       FIG. 2  shows a view in perspective, with parts removed for clarity, of a detail of the  FIG. 1  compressor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIGS. 1 and 2 , number  1  indicates as a whole a compressor, of axis A, substantially comprising a fixed portion  2 , and an impeller  3  housed inside fixed portion  2  and rotated about axis A by a known drive system  4  (shown only partly in  FIG. 1 ) to increase the pressure of the fluid flowing through compressor  1 . 
   In the following disclosure, drive system  4  is described only as required for a clear understanding of the present invention. More specifically, of drive system  4 ,  FIG. 1  shows only a housing  5 , and an output shaft  6  having an end portion  7  outside housing  5  and connected to impeller  3  as decribed in detail below. 
   Fixed portion  2  substantially comprises a casing  8  defining a through axial cavity housing impeller  3 . 
   Casing  8  comprises a minimum-diameter axial end portion  10  defining an intake section  11  for the fluid for compression; a maximum-diameter opposite axial end portion  12  fixed in conventional manner, e.g. by screws not shown, to a flange  13  integral with housing  5  of drive system  4 ; and an intermediate portion  14  connecting axial end portions  10  and  12 , and defining a screw diffuser  15  extending circumferentially with respect to axis A to deliver the compressed fluid. 
   Impeller  3  is housed substantially in intermediate portion  14  of casing  8 , is fitted to portion  7  of shaft  6  of drive system  4  projecting from housing  5 , and comprises a number of substantially radial blades  16  equally spaced about axis A. According to the exemplary embodiment shown in  FIG. 1 , casing  8  can comprise a one-piece fixed casing. Also shown in the exemplary embodiment of  FIG. 1 , casing  8  can be substantially coaxial with the output shaft  6 . 
   More specifically, impeller  3  has a through axial hole  17  engaged by portion  7  of shaft  6  of drive system  4 , and is gripped axially between a shoulder  20  of portion  7 , adjacent to drive system  4 , and a nut  21  screwed to a threaded free end of portion  7 . 
   When tightened, nut  21  makes impeller  3  integral both axially and angularly with portion  7  of shaft  6  of drive system  4 ; and impeller  3  is removed by simply unscrewing nut  21  completely and withdrawing impeller  3  axially off portion  7  of shaft  6 . 
   An important aspect of the present invention is that fixed portion  2  of compressor  1  also comprises a distributor  22  formed separately from and fitted releasably to casing  8 . 
   Distributor  22  provides for conducting and accelerating the fluid for compression towards impeller  3 , and substantially comprises a shaped central portion  23 ; an outer tubular portion  24  surrounding and spaced radially apart from central portion  23 ; and a number of blades  25  radiating generally between central portion  23  and tubular portion  24 . 
   Distributor  22  is housed inside a cylindrical seat  26  formed in axial end portion  10  of casing  8 . More specifically, seat  26  is bounded towards impeller  3  by an annular shoulder  27  defining an axial stop for tubular portion  24  of distributor  22 . In the example shown, distributor  22  is housed interferentially inside seat  26  of casing  8 , though other releasable retaining systems may obviously be used. 
   As shown in  FIG. 1 , the cylindrical seat  26  can define a first length L 1  along its axis, and the tubular portion  24  of the distributor  22  can define a second length L 2  that is substantially equal to the first length L 1 . As also shown, the annular shoulder  27  of the seat  26  can define a first inner diameter D 1 , and the tubular portion  24  can define a second inner diameter D 2  that is substantially equal to the first inner diameter D 1 . As a result, there can be a flush interface between the tubular portion  24  and the intermediate portion  14  in the region of the annular shoulder  27 . 
   Blades  25  define a number of conducting channels for imparting to the flow entering compressor  1  an appropriate direction with respect to blades  16  of impeller  3 . 
   Central portion  23  is advantageously ogival, increasing in diameter towards impeller  3 , so as to gradually reduce the section of the various channels defined by blades  25  in the flow direction. 
   Central portion  23  also comprises, on the side facing impeller  3 , an axial cavity  28  loosely housing the free end of portion  7  of shaft  6  and relative nut  21 . 
   The advantages of compressor  1  according to the present invention will be clear from the foregoing description. 
   In particular, impellers  3  of different designs can be used on the same compressor  1 , and operation of the compressor within a given flow range can be optimized with no need to replace the whole of fixed portion  2 , but simply by using different distributors  22  suited to different impellers  3 , i.e. having a geometry of fixed blades  25  suited to that of movable blades  16  to minimize fluid-dynamic losses. 
   Distributor  22  may be produced using methods and materials best suited to the operating conditions and function involved. 
   Fixed blades  25  of distributor  22  also support ogival central portion  23  to improve fluid-dynamic performance as a whole. 
   A highly flexible compressor  1  for different types of applications and vehicles is thus obtained relatively simply, with no reduction in efficiency. On the contrary, operation of compressor  1  is optimized using different impellers  3 . 
   Clearly, changes may be made to compressor  1  as described and illustrated herein without, however, departing from the scope of the accompanying claims. 
   The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention.