Abstract:
In a fuel pump for an internal combustion engine, a pumping device is adapted to vary the volume of a first chamber containing the fuel and is formed by a second chamber adapted to contain oil, a deformable diaphragm for the leak-tight separation of the chambers from one another, and by a piston mounted to slide within the second chamber and comprising an active end surface bounding this second chamber; the diaphragm being adapted to be deformed to vary the volume of the first chamber under the action of the thrust exerted by the oil contained in the second chamber following an alternating movement of the piston within this second chamber.

Description:
[0001]     The present invention relates to a fuel pump for an internal combustion engine.  
         [0002]     The present invention relates more particularly to a fuel pump for a unit for the direct injection of fuel, in this case petrol, to which the following description will refer without entering into superfluous detail.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the sector of direct petrol injection units, it is known to use a petrol pump of the type comprising a cylinder having a predetermined longitudinal axis, a piston mounted to slide within the cylinder and actuator means adapted to provide the piston with an alternating rectilinear movement along this cylinder.  
         [0004]     The piston comprises an active end surface which is disposed transversely with respect to the above-mentioned axis and defines, together with the cylinder, a first variable-volume chamber adapted to contain the petrol, is configured so as to define, together with the cylinder, a second chamber of substantially constant volume adapted to contain oil, and is lastly provided with an annular gasket keyed on the piston in order to separate the first chamber from the second chamber in a leak-tight manner.  
         [0005]     Since the piston has to have a diameter substantially equal to a diameter of the cylinder in order to reduce leakage of the petrol and oil along the piston, known petrol pumps of the type described above have some drawbacks due chiefly to the fact that the contaminant particles which are inevitably present within the cylinder may cause the piston to jam within this cylinder.  
         [0006]     Known pumps of the type described above also have a further drawback as the presence of the above-mentioned contaminant particles entails relatively high wear of the annular gasket.  
         [0007]     U.S. Pat. No. 5,520,523-A1 discloses a diaphragm-type pump including a disk-like diaphragm made of an elastic material which is held between an upper housing and a lower housing. In this diaphragm-type pump, the diaphragm, which has a flat shape before it is mounted in the pump, is bent along a diaphragm stopper and mounted in the pump; consequently, an urging force is constantly applied to the diaphragm in such a direction as to press it on the diaphragm stopper. The diaphragm is deformed in response to reciprocation of a plunger, and when the plunger reaches the bottom dead center and a cylinder chamber is decreased in pressure, the diaphragm is pressed on the diaphragm stopper by the urging force toward the diaphragm stopper and a feed pressure of a feed pump  
         [0008]     U.S. Pat. No. 6,071,089-A1 discloses a high pressure hydraulic diaphragm pump having a pressure chamber on one side of a diaphragm and a fluid delivery chamber on the other side of the diaphragm with a reciprocating piston assembly including a piston member being provided for pressurizing the hydraulic fluid in the pressure chamber and having the pressure chamber connected with a pressure regulator which maintains the desired discharge pressure of the fluid and in which the piston assembly is combined with a diaphragm positioning mechanism for maintaining the diaphragm at a desired position relative to the piston member so as to assure full stroke of the diaphragm during normal operation of the pump  
         [0009]     GB-849557-A discloses a hydraulically actuated diaphragm pump; a hydraulic pressure chamber is placed in communication with a hydraulic reservoir by means of a valve secured to a diaphragm and having a part open to the chamber and connecting with either of parts which communicate through valves with the reservoir so that excess liquid is discharged or deficiency made up. In the event of excess pressure on the pumping side of the diaphragm a face carried by the diaphragm seats on a face on the housing. The pumping chamber communicates through a pair of inlet valves with inlet conduits and through a pair of outlet valves with outlet conduits. The pump may comprise a plurality of diaphragm chambers.  
         [0010]     U.S. Pat. No. 6,554,578-B1 relates to a diaphragm pump with a device for controlling the position of a diaphragm separating the conveying chamber from the displacement chamber. As a replacement of the mechanical control of the refilling process, a pressure sensor is arranged in the displacement chamber, which is connected with an evaluation unit designed for generating a refill signal, which is switched so it actuates a refill valve through an operative connection; advantageously, a second sensor for detecting the piston travel is provided, whose signal is linked with the signal from the pressure sensor.  
       SUMMARY OF THE INVENTION  
       [0011]     The object of the present invention is to provide a fuel pump for an internal combustion engine which is free from the drawbacks described above and is simple and economic to embody.  
         [0012]     The present invention therefore relates to a fuel pump for an internal combustion engine as claimed in the attached claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention is described below with reference to the accompanying drawings, which show non-limiting embodiments thereof, and in which:  
         [0014]      FIG. 1  is a diagrammatic longitudinal section through a preferred embodiment of the fuel pump of the present invention;  
         [0015]      FIG. 2  is a diagrammatic longitudinal section through a variant of the fuel pump of  FIG. 1 ;  
         [0016]      FIG. 3  is a plan view of a detail of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     In  FIG. 1 , a petrol pump for an internal combustion engine (not shown) of the direct petrol injection type is shown overall by  1 .  
         [0018]     The pump  1  comprises a cylindrical body  2  having a predetermined longitudinal axis  3  and comprising, in turn, a first plate  4  which is coaxial with respect to the axis  3 , is limited axially by two plane surfaces  5 ,  6  at right angles to the axis  3  and has a cylindrical cavity  7  which opens externally at the location of the plate  6  and is closed by a second plate  8  disposed in contact with the surface  6  and secured to the plate  4 .  
         [0019]     The plate  8  is bounded axially by two plane surfaces  9 ,  10  at right angles to the axis  3 , the surface  9  being disposed in contact with the surface  6  and having a cylindrical cavity  11  which is obtained through the plate  8  coaxially with respect to the axis  3 , and opens externally at the location of the both the surface  9  and the surface  10 .  
         [0020]     The cavities  7  and  11  are separated from one another by means of a deformable diaphragm  12  which is made from stainless steel, is welded between the plates  4  and  8  at the location of its peripheral edge, and defines, together with the cavity  7 , a variable-volume chamber  13  adapted to contain the petrol provided with an intake ball valve  14  and a delivery ball valve  15  of known type.  
         [0021]     The cavity  11  comprises a widened portion  16  disposed in a position facing the diaphragm  12  and a contracted portion  17  engaged in a sliding manner by a piston  18  having an active end surface  19  which extends at right angles to the axis  3  in order axially to limit this piston  18  and defines, together with the cavity  11  and the diaphragm  12 , a chamber  20  of substantially constant volume adapted to contain the oil of the engine (not shown).  
         [0022]     The chamber  20  is provided with an intake valve  21  of known type adapted to supply the chamber  20  with a quantity of oil substantially equal to the quantity of oil emerging from this chamber  20  by drawing between the portion  17  and the piston  18  and therefore adapted to maintain the quantity of oil in the chamber  20  constant, and a maximum pressure valve  22  adapted to be disposed in an open position when the value of the oil pressure within the chamber  20  is substantially equal to a predetermined value.  
         [0023]     The piston  18  may move along the portion  17  in order to perform, under the thrust of an actuation device  23 , an alternating rectilinear movement comprising an outward stroke, during which the diaphragm  12  is displaced from an operational pumping position (shown by a continuous line in the accompanying Figure) to a rest position (shown in dashed lines in the accompanying Figure) and the volume of the chamber  13  increases in order to cause the opening of the intake valve  14 , and a return stroke, during which the diaphragm  12  is displaced from its rest position to its operational pumping position and the volume of the chamber  13  decreases in order to cause the opening of the delivery valve  15 .  
         [0024]     The device  23  comprises a spring  24 , which is keyed on the piston  18  coaxially with respect to the axis  3 , and is interposed between the plate  8  and the piston  18  in order to provide this piston  18  with its outward stroke, and a cam  25  which is mounted in a rotary manner to rotate about its longitudinal axis  26  perpendicular to the axis  3 , and cooperates with a tappet roller  27  coupled in a rotary and axially fixed manner to the piston  18  in order to provide this piston  18  with its return stroke.  
         [0025]     The diaphragm  12 , the chamber  20 , the piston  18  and the actuation device  23  form a pumping device  28  adapted to use the oil in the chamber  20  to deform the diaphragm  12  and thus to vary the volume of the chamber  13 . The deformation of the diaphragm  12  is controlled selectively by providing the diaphragm  12  and the piston  18  such that the value of the ratio between the surface of the diaphragm  12  and the surface of the face  19  is at least equal to five.  
         [0026]     The opening of the valve  15  during the return stroke of the piston  18  and, therefore, the quantity of petrol supplied via the valve  15  at each operating cycle of the pump  1  are controlled selectively by a flow regulation device  29  comprising an electromagnetic actuator  30  mounted at the location of the valve  14 . The actuator  30  comprises an output rod  31  which extends within the valve  14  parallel to the axis  3 , and is mounted in a sliding manner in order to move between an operating position (shown in dashed lines in the accompanying Figure), in which the rod  31  is disposed so as to cause the opening of the valve  14 , and a rest position (shown in continuous lines in the accompanying Figure), in which the rod  31  is disposed so as to enable the closure of the valve  14 .  
         [0027]     Since the valve  15  is calibrated so as to open, during the return stroke of the piston  18 , only when the valve  14  is closed, the actuation of the actuator  30  makes it possible selectively to control the opening of this valve  15 .  
         [0028]     The operation of the pump  1  can be readily deduced from the above description and no further explanation is required.  
         [0029]     The variant shown in  FIG. 2  relates to a pump  32  which differs from the pump  1  in that the intake ball valve  14  is replaced by an intake valve  33  comprising a plate  34  which is mounted at right angles to a longitudinal axis  35  of a duct  36  supplying petrol to the chamber  13  and is provided with a plurality of supply holes  37  obtained through the plate  34  parallel to the axis  35 , and a deformable sheet  38  which is secured to the plate  34  at its peripheral edge, is normally disposed in a position closing ( FIG. 2 ) the holes  37 , and moves, during the outward stroke of the piston  18 , from the closed position to an open position (not shown) of these holes  37  in order to enable the petrol to enter the chamber  13 .  
         [0030]     The pump  32  also differs from the pump  1  in that the diaphragm  12  comprises a central portion  39  clamped between two substantially cup-shaped stiffening members  40 , one of which (designated hereafter by  40   a ) is disposed in the chamber  13  and the other of which (designated hereafter by  40   b ) is disposed in the chamber  20 .  
         [0031]     As shown in  FIG. 2 , the member  40   b  is shaped so as to be disposed in contact, during the outward stroke of the piston  18 , with a wall  41  bounding the chamber  20  and thus to control the deformation of the diaphragm  12  and is further provided with a plurality of radial channels  42  adapted to enable the oil to pass through the member  40   b  when this member  40   b  is disposed in contact with the wall  41 .  
         [0032]     According to a variant which is not shown, the channels  42  are replaced by a plurality of supply channels obtained on the wall  41 .  
         [0033]     The pump  32  lastly differs from the pump  1  in that the intake valve  21 , the maximum pressure valve  22  and the electromagnetic actuator  30  are replaced by a single electromagnetic valve  43  mounted within a cavity  44  which is provided in the plate  8 , has a longitudinal axis  45  transverse to the axis  3  and communicates with the chamber  20  via a hole  46  obtained through this plate  8 .  
         [0034]     The valve  43  comprises an outer tubular jacket  47  which is substantially cup-shaped, is housed within the cavity  44  coaxially with respect to the axis  45 , and is provided with a plurality of radial holes  48  uniformly distributed about the axis  45  in order to enable oil to be supplied into this jacket  47  and with an axial hole  49 .  
         [0035]     The jacket  47  is closed axially by an electromagnet  50  and houses a ball shutter  51  which is coupled in a sliding manner to the jacket  47  and has a ball  52  closing the hole  49 . The shutter  51  and therefore the ball  52  are normally disposed, under the thrust of a spring  53  interposed between the electromagnet  50  and the shutter  51 , in a position ( FIG. 2 ) closing the hole  49 , and are displaced by the electromagnet  50 , against the action of the spring  53 , into a position (not shown) opening the hole  49  in which the oil is supplied to the hole  49  by means of a plurality of supply channels  54  obtained on the outer surface of the ball  52  parallel to the axis  45 .  
         [0036]     In an initial phase of filling of the chamber  20 , the electromagnet  50  is excited in order to displace the shutter  51  and therefore the ball  52  into their position opening the hole  49  so as to supply a predetermined initial quantity of oil to the hole  46  and therefore to the chamber  20 . The initial quantity of oil supplied to the chamber  20  may be maintained constant, in use, by selectively opening the valve  43  in order to supply the chamber  20  with a quantity of oil substantially equal to the quantity of oil emerging from time to time from the chamber  20  as a result of leakage between the portion  17  and the piston  18 .  
         [0037]     It will be appreciated from the above that the pressure exerted on the diaphragm  12  during the return stroke of the piston  18  and therefore the displacement of the diaphragm  12  from its rest position to its operational pumping position, i.e. the opening of the delivery valve  15 , depend on the quantity of oil contained in the chamber  20  and are selectively controlled by means of the valve  43 .  
         [0038]     The positioning of the valve  43  within the oil supply circuit to the chamber  20  makes it possible to supply the petrol suctioned into the chamber  13  directly to the delivery valve  15  and to prevent, in contrast to what happens when using the electromagnetic actuator  30 , the losses of energy deriving from the reflux of the petrol suctioned into the chamber  13  through the intake valve  14 .  
         [0039]     The spring  53  is also calibrated so as to thrust the shutter  51  into its position closing the hole  49  with a force which is in all cases lower than the force of opposite direction exerted on the shutter  51  by the oil contained in the chamber  20  and in the hole  46  when the value of the pressure of the oil in the chamber  20  is substantially equal to a predetermined value. In this way, the oil is discharged through the holes  48  thus avoiding breakages of the diaphragm  12 .