“This application is a divisional of application Ser. No. 09/607,849, filed Jun. 30, 2000, now U.S. Pat. No. 6,553,971 which application(s) are incorporated herein by reference.” 
    
    
     The present invention relates to a high-pressure pumps with an on-off valve for feeding fuel to an internal combustion engine, particularly a vehicle engine. 
     BACKGROUND OF THE INVENTION 
     Various types of high-pressure fuel feed pumps are known, and which are generally supplied with fuel from a normal tank by a low-pressure pump powered by an electric motor. The high-pressure pump normally comprises an on-off valve, which is opened automatically by the fuel fed to it by the low-pressure pump. 
     The body of known high-pressure pumps encloses at least a fuel compression chamber, and an actuating chamber housing pump actuating members; and the on-off valve comprises a shutter designed to ensure fuel flow to the actuating chamber, even when the valve is closed, to lubricate and cool the actuating members. 
     In one known radial-piston pump in particular, the pumps body houses three cylinders, in which slide respective pistons activated by a common cam carried by a shaft activated by the drive shaft; the cam is housed inside the actuating chamber or case of the pump; and the shutter is in the form of a hollow cylinder and slides along the wall of a radial hole in the pump body. 
     The pump body also has a fuel feed conduit for feeding fuel from the radial hole to the cylinders; the feed conduit is closed by the lateral wall of the shutter; and, to lubricate and cool the pump shaft, the cam, and the various pump body and piston friction surfaces, the shutter also has a calibrated axial hole permitting continuous fuel flow to the case. 
     To prevent fuel accumulating in an engine cylinder, in the event the respective injector breaks down, or to prevent fuel from being drawn from the actuating chamber in the event of poor or no supply by the low-pressure punts e.g. due to a fault, the shutter is closed automatically by a compression spring when the pressure of the incoming fuel falls below a given value. 
     The compression spring is housed inside the shutter and rests on a perforated plate, which has a surface for receiving the end of the spring and is normally fixed, e.g. welded, to the opposite end of the guide hole of the shutter. 
     In this known type of pump, machining the radial hole in the pump body, fixing the plate, and assembling the spring are difficult, high-cost operations involving considerable time and highly skilled personnel. Moreover, the perforated plate at the end of the hole facing the case limits to a certain extent the outside diameter of the cam and, hence, the capacity of the pump under given conditions. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an extremely straightforward, reliable high-pressure pump having an on-off valve which is cheap to produce and easy to assemble, so as to eliminate the aforementioned drawbacks of known pumps with on-off valves. 
     According to the present invention, there is provided a high-pressure pump with an on-off valve for feeding fuel to an internal combustion engine, wherein the pump comprises a body including at least a fuel compression chamber and an actuating chamber enclosing actuating members of said pump, and wherein said valve comprises a shutter sliding inside a hole in said body to close a fuel feed conduit; said feed conduit being formed in said body, between said hole and said compression chamber; and said shutter being held in the closed position by a compression spring; characterized in that said spring rests directly or indirectly on a shoulder inside said hole; said shoulder being formed in one piece with said body. 
     In a first embodiment of the invention, the spring rests on the shoulder by virtue of means fixed removably inside the hole and comprising a perforated disk inserted removably inside the hole, and an elastic C-shaped metal element located, between the disk and the shoulder, inside an annular groove adjacent to the shoulder. 
     In a further embodiment of the invention, the spring rests directly on the shoulder, and the wall of the hole has an annular groove permitting precision machining of the wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Two preferred, non-limiting embodiments of the invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a partly sectioned side view of a high-pressure pup with an on-off valve for feeding fuel to en internal combustion engine, in accordance with the invention; 
     FIG. 2 shows a larger-scale section of the valve and a portion of the pump, according to a first embodiment of the invention; 
     FIG. 3 shows a larger-scale plan view of a detail in FIG. 2; 
     FIG. 4 shows a section of a further detail of a variation of FIG. 2; 
     FIG. 5 shows a larger-scale section of the valve and a portion of the pump, according to a further embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  5  in FIG. 1 indicates as a whole a high-pressure pump for feeding fuel to an internal combustion engine, e.g. of a vehicle. Pump  5  is supplied with fuel from, a normal tank by a low-pressure pump (not shown) powered by an electric motor energized when the engine is turned on. 
     High-pressure pump  5  is of the type comprising three radial pistons  6 , which slide inside three cylinders  7  arranged radially inside a body  8  of pump  5 ; each cylinder  7  is closed by a plate  9  supporting an intake valve  11  and a delivery valve  12 ; and each cylinder  7  and respective plate  9  are locked to body  8  by a corresponding lock head  13 . 
     Pistons  6  are activated in sequence by a single cam  14  integral with a shaft  16  powered by the internal combustion engine drive shaft. Cam  14  acts on pistons  6  via a ring  17  having, for each piston  6 , a faced portion  18  cooperating with a shoe  19  fixed to piston  6 ; and each shoe  19  is pushed towards the cam by a corresponding spring  21 . 
     The gap between the end of each piston  6  and respective plate  9  defines a compression chamber  22 , so that the three compression chambers  22  are obviously housed inside body  8 . The space inside body  8  housing cylinders  7  and in which shaft  16  and cam  14  rotate forms an actuating chamber  23  of pump  5 , which chamber is closed by a flange  24  fixed in known manner to body  8 ; shaft  16  is fitted in rotary and fluidtight manner to flange  24 ; and chamber  23  communicates in known manner with a drain conduit  25  draining into the tank. 
     Body  8  is made of cast iron, and heads  13  of steel; body  8  and heads  13  have three intake conduits  26  communicating with a conduit defined by an annular groove  27  on flange  24 ; each conduit  26  also communicates with the corresponding compression chamber  22  via corresponding intake valve  11 ; and each head  13  also has a compression conduit  28 , which, via corresponding delivery valve  12 , connects compression chamber  22  to a delivery conduit  29  of pump  5 . 
     Body  8  also has a feed conduit  30  formed by two holes  31  arranged crosswise to each other and closed outwards by two plugs  32 . At one end, conduit  30  communicates with annular groove  27  of flange  24  and, therefore, with compression chambers  22 ; and, at the other end, conduit  30  comes out at a cylindrical wall  33  of a cylindrical radial hole  34  formed in body  8 . Hole  34  communicates with actuating chamber  23  and projects partly towards flange  24 ; and an inlet conduit  36  connected to the low-pressure pump is inserted inside hole  34 . 
     Hole  34  houses an on-off valve indicated as a whole by  37  and comprising a hollow, cylindrical shutter  38 . More specifically, shutter  38  is piston- or cup-shaped, and comprises a lateral wall  39 , which slides accurately along wall  33  of hole  34 , so that both wall  33  of hole  34  and wall  39  of shutter  38  must be precision machined. 
     Shutter  38  also comprises a flat wall  40 , which has a calibrated hole  41  permitting the passage of a certain amount of fuel, even when conduit  30  is closed by shutter  38 . A helical compression spring  42  is inserted inside shutter  38  and rests on a supporting element fixed to the end of hole  34  facing actuating chamber  23 ; and the supporting element must be perforated to permit fuel passage from hole  34  to actuating chamber  23 , as described in Italian Patent Application N. TO95A 000010. 
     According to the invention, the supporting element of spring  42  is defined by a shoulder  43  of hole  34 , formed in one piece with body  8  and located at the end of hole  34  adjacent to actuating chamber  23 . Shoulder  43  defines a circular opening  45  (FIG. 2) smaller in diameter than hole  34 ; and spring  42  rests directly or indirectly on shoulder  43 , thus simplifying assembly of on-off valve  37 . 
     In the FIG. 2 embodiment, spring  42  rests on shoulder  43  by virtue of means fixed removably inside hole  34  and comprising a disk  44  having a central opening  46  permitting fuel passage from hole  34  to actuating chamber  23 . Advantageously, the difference in diameter between hole  34  and opening  45  ranges between 1 and 3 mm, and shoulder  43  is of a thickness ranging between 2 and 4 mm. 
     Opening  46  in disk  44  has a protruding edge  47  for guiding one of the ends of spring  42 ; and disk  44 , together with opening  46  and protruding edge  47 , may be formed cheaply from sheet metal by means of a punching and cold forming or embossing press. 
     The means fixed removably inside hole  34  also comprise a radially flexible C-shaped metal element  48 , e.g. a standard retaining ring (FIG.  3 ), housed inside hole  34  (FIG.  2 ), between disk  44  and shoulder  43 . More specifically, wall  33  of hole  34  has an annular groove  49  adjacent to shoulder  43 , and into which ring  48  clicks removably and the diameter of opening  45  is such as to enable groove  49  to be machined through opening  45 . 
     Ring  48  is fitted inside groove  49  or removed from the groove by bringing the two ends of ring  48  together, so that the parts of valve  37  are obviously also easy to assemble, the only precaution being to assemble disk  44  with edge  47  facing spring  42 . 
     To eliminate even the above precaution and/or simplify automatic assembly of valve  37 , in the FIG. 4 variation, opening  46  of disk  44  may be provided with a ring  51  forming two edges symmetrical with respect to disk  44  and projecting axially in two opposite directions. Ring  51  may be welded to or formed in one piece with disk  44  by compacting and sintering metal powder. 
     In the FIG. 5 embodiment, spring  42  rests directly on shoulder  43 . Advantageously, the diameter of opening  45  ranges between 3 and 5 mm, and shoulder  43  is of a thickness ranging between 5 and 8 mm. To permit fine machining of wall  33  of hole  34  from outside body  8 , an annular groove  52  is machined in wall  33 , and which may be shallower than groove  49  in FIG. 2, so that valve  37  in FIG. 5 is even cheaper to produce than that in FIG.  2 . 
     As compared with known pumps, the advantages of the high-pressure pump according to the invention will be clear from the foregoing description. In particular, removable assembly of disk  44  and ring  48  reduces production cost of the pump; shoulder  43  eliminates the need to fix the supporting element of spring  42  inside hole  34 ; and there is no interference between cam ring  17  and the supporting element of spring  42 , so that the diameter of cam  14  can be increased to increase pump capacity. 
     Clearly, changes may be made to the high-pressure pump as described herein without, however, departing from the scope of the accompanying claims. For example the pistons of pump  5  may be arranged otherwise than as described; and the pump may be applied to other than a vehicle engine.
The pump has a body including at least a fuel compression chamber and an actuating chamber enclosing the actuating members of the pump. The on-off valve has a shutter sliding inside a hole in the body to close a fuel feed conduit. The shutter is held in the closed position by a compression spring, which rests directly or indirectly on a shoulder in the hole. In one embodiment, the spring rests on the shoulder via a perforated disk held by a retaining ring, which clicks removably inside an annular groove in the hole. In a further embodiment, the spring rests directly on the shoulder.