Abstract:
A vane pump, having an inlet for receiving fuel and an outlet from which fuel is supplied, comprising a generally cylindrical member, a driven rotor arranged within the cylindrical member and a closure member. The cylindrical member and the closure member co-operate to define a recirculation passage interconnecting the outlet and the inlet, the output pressure of fuel discharged from the pump being regulated by a resiliently biased valve means controlling the flow of fuel through said recirculation passage.

Description:
TECHNICAL FIELD 
     The invention relates to a vane pump for supplying fuel, the pump having associated means for regulating the pressure of fuel supplied by the vane pump. In particular, the invention relates to a vane pump for supplying fuel under pressure to a fuel injection pump. 
     BACKGROUND OF THE INVENTION 
     In diesel engines, it is usual to use a transfer pump to supply fuel under pressure to a diesel fuel injection pump. The fuel pressure supplied to the fuel injection pump must be regulated and, in mechanically driven fuel injection pumps, this can be done by using a rotary vane pump as the transfer pump. An associated pressure regulator serves to control the fuel pressure supplied to the fuel injection pump from the outlet of the vane pump. 
     One type of conventional vane pump comprises a driven rotor arranged within a cylindrical member, commonly referred to as a liner, the liner having a non circular bore arranged eccentrically to the centre line of the driven rotor. The rotor rotates within the liner between two closure plates, an upper closure plate, commonly referred to as the distribution plate, and a lower plate. Apertures within the upper and lower closure plates define an inlet port and an outlet port within the vane pump housing. 
     Fuel is introduced into the vane pump through the inlet port and is carried around the pump by means of blades extending from the rotor and biased towards the inner surface of the liner. Fuel from the outlet port is supplied to a regulator arranged remotely from the vane pump which serves to regulate the fuel pressure supplied to a downstream fuel injection pump by recirculating some of the fuel from the vane pump outlet back into the vane pump inlet. 
     The regulator usually consists of a cylindrical body housing a spring biased piston. It is necessary to form several drillings within the regulator body to accommodate the piston and to provide the channels required to effect the regulatory function of the device. Where the regulator body is within a housing common to the vane pump and/or the fuel injector pump itself, it is also necessary to form additional drillings in the housing. The construction of a conventional vane pump is therefore complex and manufacture is difficult and expensive. In addition, the device can be bulky as the regulator is arranged remotely from the rotary part of the vane pump. 
     It is an object of the present invention to provide a vane pump of reduced complexity which alleviates the manufacturability problems of the prior art. It is a further object of the present invention to provide a vane pump which has a reduced size. 
     According to the present invention, there is provided a vane pump, having an inlet for receiving fuel and an outlet from which fuel is supplied, comprising; 
     a generally cylindrical member; 
     a driven rotor arranged within the cylindrical member; and 
     a closure member, the cylindrical member and the closure member co-operating to define a recirculation passage interconnecting said outlet and said inlet, the output pressure of fuel discharged from the pump being regulated by resiliently biased valve means controlling the flow of fuel through said recirculation passage. 
     In one embodiment of the invention, the closure member may form part of the pump housing. 
     The cylindrical member may have a first channel defined therein co-operating with a second channel defined in the closure member, the first and second channels defining the recirculation passage. 
     Alternatively, the recirculation passage may be defined by a channel formed in the cylindrical member, the closure member cooperating with the cylindrical member to define an inner surface of the recirculation passage. 
     As the only machinings required for the regulatory function are the first and second channels within the closure member and the cylindrical member, the vane pump of the invention is considerably less complex than a conventional vane pump, therefore providing advantages in terms of manufacturing difficulty and cost. Additionally, as the means for regulating the fuel pressure are arranged within the cylindrical member and closure member assembly, the vane pump is of reduced size. 
     The valve means may be in the form of a compression spring housed within the recirculation passage, the spring biasing an abutment member into communication with an opening of the recirculation passage to control the flow of fuel supplied to the recirculation passage. Conveniently, the abutment member may be a ball. 
     In an alternative embodiment, the biasing means may be a leaf spring biased into communication with an opening of the recirculation passage to control the flow of fuel supplied to the recirculation passage. In a further alternative embodiment, the vane pump may comprise a third passage defined within the cylindrical member and communicating with the recirculation passage, the supply of fuel to the third passage being regulated by means of a piston member operating under a spring biasing force. This embodiment is particularly useful for supplying fuel to a mechanically driven fuel injection pump, requiring a speed dependent fuel pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the following drawings in which; 
     FIG. 1 is a diagram of a conventional vane pump, including a regulator for regulating the fuel pressure supplied by the vane pump; 
     FIG. 2 is a diagram of a vane pump in accordance with one embodiment of the present invention; 
     FIG. 3 is a cross-sectional view on a line X—X of the vane pump shown in FIG. 2; and 
     FIGS. 4 and 5 are similar cross-sectional views to FIG. 3 of first and second alternatives. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, a conventional vane pump, referred to generally as  10 , comprises a cylindrical liner  12  and an inlet port  14  for receiving fuel from an associated fuel tank (i.e. in the direction of arrow  16 ). The pump also comprises a rotor  18  which is usually driven by the driveshaft driving an associated fuel injection pump (not shown) to which the vane pump supplies fuel. The rotor  18  carries blades  20  maintained in contact with the inner surface of the liner  12  by means of a spring  22 ; fuel pressure at their radially inner ends, centripetal forces, or a combination of all three. Fuel is introduced at the inlet  14  and, as the blades  20  are rotated past the inlet  14 , fuel becomes trapped in a gap  24  between the liner  12  and the rotor  18  and fuel is carried by the blades  20  as the rotor  18  rotates. 
     Eventually, the blades uncover an outlet port  26  such that fuel is expelled from the vane pump in the direction of arrow  28 . Fuel is then either supplied to the downstream fuel injection pump or is returned to the vane pump inlet  14  through a regulator  30 . The regulator  30  serves to regulate the fuel pressure supplied to the fuel injection pump by returning some of the fuel expelled from the outlet  26  to the inlet  14 . 
     The regulator  30  comprises a body  38 , housing a piston  34  biased by a spring  36 , and a retention cap  32 . In order to construct the regulator  30  it is necessary to form several drillings in the regulator body  38  and also in the fuel injection pump downstream. Thus, the construction of the vane pump is complex and manufacture is difficult. The vane pump arrangement, including the regulator, is also rather bulky. 
     FIG. 2 illustrates a vane pump of the present invention, into which fuel is introduced at the inlet  14 , as indicated by arrow  46 . The vane pump comprises a rotary member  18  carrying blades  20  biased into contact with the inner surface of a cylindrical member  50 , commonly referred to as the vane pump liner. The liner  50  has a non circular bore arranged eccentrically to the centre line of the rotor  18 . The inlet  14  and the outlet  26  may be defined in an upper closure plate or closure member (not shown in FIG.  2 ), commonly referred to as a distribution plate, facing the closure member or closure plate  56  (as shown in FIG. 3) and located on the opposite side of the rotor  18  to the closure plate  56 . Alternatively, the inlet  14  and the outlet  26  may be defined by apertures in the upper and lower closure plates. In addition, a partial inlet and outlet may be defined within the liner  50 . 
     The blades  20  carried by the rotor  18  are biased into contact with the liner  50  by means of a spring  22 , fuel pressure at their radially inner ends, centripetal forces, or a combination of all three. As the blades  20  move with the rotor  18  past the inlet  14 , fuel becomes trapped in the gap  24  defined by the liner  50  and the rotor  18  between adjacent blades  20 . Due to the shape of the liner  50 , fuel is expelled through the outlet  26  when blade rotation causes the outlet  26  to be uncovered. Fuel expelled from the outlet  26  either exits the vane pump, in the direction of arrow  48 , to a fuel injection pump located downstream (not shown) or is recirculated back to the inlet  14  by means of a recirculation passage  49  defined partly within the liner  50 . 
     The construction of the recirculation passage  49  can be seen more clearly in FIG. 3 which shows a cross-sectional view on the line X—X of the vane pump shown in FIG.  2 . The liner  50  is cooperably engaged with a lower closure plate  56 . The liner  50  has a channel or groove  52  defined therein, the channel  52  being formed in the axial end-face of the liner  50 . The closure plate  56  has a channel or groove  54  defined in its uppermost face which, together with the channel  52 , defines the recirculation passage  49  for fuel at the vane pump outlet  26 . A spring  58  is housed within the recirculation passage  49  and biases a ball  60  into a seating  62  such that the ball  60  closes an opening  64  to the channel  52 , thus preventing the flow of fuel into the channel  52 , and hence the recirculation passage  49 , from the outlet  26 . 
     At a predetermined pressure of fuel at the outlet  26 , acting on the ball  60  through the face of the opening  64 , the force of the spring  58  is overcome and the ball  60  is moved out of the seating  62  allowing fuel to flow through the passage  49  from the pump outlet  26 , thus serving to regulate the amount of fuel recirculated to the pump inlet  14 . As the fuel pressure at the outlet  26  decreases, the force applied to the ball  60  is reduced and, when the biasing force of the spring  58  overcomes the force of the fuel pressure, the spring  58  biases the ball  60  into communication with the seating  62  so that the opening  64  is closed to fuel. The spring-biased ball  60  therefore provides regulatory control of fuel entering the recirculation passage  49  and recirculating back to the inlet  14 . Fuel which does not enter the recirculation passage  49  is expelled from the outlet  26  (in the direction of arrow  48  in FIG. 2) for supply to the fuel injection pump downstream. 
     The arrangement of the recirculation passage  49  within the cylindrical liner  50  and the closure plate  56 , and the spring-biased ball  60  provides a simplified means of regulating the fuel pressure supplied by the vane pump. In particular, channels  52 , 54  in the cylindrical liner  50  and the closure plate  56  are simpler to form than the complex arrangement of passages required in a conventional regulator. 
     A second embodiment of the invention is shown in FIG.  4  and comprises a leaf spring  70  housed within the channel  52  of the liner  50 . The leaf spring is biased into contact with a seating  72  within the channel  52  and serves to regulate the amount of fuel recirculating back through the recirculation passage  49  in a similar way as described in relation to FIG.  3 . Thus, when the pressure of fuel at the vane pump outlet  26 , and thus opening  64 , overcomes the biasing force of the leaf spring  70 , the spring  70  is moved away from the seating  72  to allow fuel to enter the recirculation passage  49 . In this way, the pressure of fuel expelled from the vane pump to the fuel injection pump downstream can be regulated. 
     A third embodiment of the invention is shown in FIG. 5, in which regulation of fuel pressure is provided by means of a piston member  82 , or plunger, biased into contact with a seating  84  defined in the channel  52  by means of a spring  86 . As the fuel pressure at the outlet  26  of the vane pump increases, the force applied to the end-face of the piston  82  increases until, when the spring force is overcome and the piston  82  is moved away from the seating  84 , fuel is able to enter a secondary passage  80 , defined in the body of the cylindrical liner  50 , the passage  80  being in fluid communication with the recirculation passage  49 . 
     The degree of movement of the piston  82  away from the seating  84  provides graduated regulatory control of fuel entering the secondary passage  80 . The spring-biased piston  82  thereby serves to control the amount of fuel recirculating through the recirculation passage  49  to the inlet  14  of the vane pump, thus regulating the fuel pressure supplied by the vane pump to the fuel injection pump downstream. 
     The embodiment shown in FIG. 5 is particularly suitable for supplying fuel to a mechanically controlled fuel injection pump requiring a speed dependent pressure signal, such as may be used for advance control and inlet metering purposes. 
     It is envisaged that other forms of biasing means may be provided within the recirculation passage  49  to control the amount of fuel recirculated to the inlet  14  and the invention need not be limited to the embodiments hereinbefore described. 
     It will be appreciated that the recirculation passage  49  need not be defined by channels or grooves formed in both the cylindrical liner  50  and the closure plate  56 , but may be defined by a single channel in the cylindrical liner  50 , the closure plate  56  defining an inner surface of the recirculation passage  49  by means of its engagement with the axial end-face of the liner  50 . Thus, the surface of the closure plate  56  closes the channel in the cylindrical member to define the recirculation passage  49  with the channel formed in the liner  50 . A recirculation passage formed in this way is suitable for use with lower fuel flow rates, or if a wider recirculation passage is employed, for example if the outer diameter of the liner is relatively large.