Fuel pump for an internal combustion engine

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.

1 . A fuel pump for an internal combustion engine; which pump comprises: 
 a first variable-volume chamber ( 13 ) adapted to contain fuel, this first chamber ( 13 ) being provided with an intake valve ( 14 ) and a delivery valve ( 15 );    pumping means ( 28 ) to vary the volume of the first chamber ( 13 ) and comprising a second chamber ( 20 ) adapted to contain oil, a piston ( 18 ) mounted to slide within the second chamber ( 20 ), actuator means ( 23 ) adapted to provide the piston ( 18 ) with an alternating movement within this second chamber ( 20 ), and separator means ( 12 ) to separate the first and second chambers ( 13 ,  20 ) from one another in a leak-tight manner; wherein the piston ( 18 ) has an active end surface ( 19 ) bounding the second chamber ( 20 ), and the separator means ( 12 ) comprise a deformable diaphragm ( 12 ) adapted, in use, to be deformed to vary the volume of the first chamber ( 13 ) under the action of the thrust exerted by the oil contained in the second chamber ( 20 ) following the alternating movement of the piston ( 18 ) within this second chamber ( 20 ); and    at least one stiffening member ( 40   a ,  40   b ) secured to a central portion ( 39 ) of the diaphragm ( 12 ), mounted within the second chamber ( 20 ) and adapted to be disposed, in use, in contact with a wall ( 41 ) bounding this second chamber ( 20 );    the fuel pump is characterised in that the second chamber ( 20 ) is provided with a plurality of channels ( 42 ) for the passage of the oil provided through the stiffening member ( 40   a ,  40   b ).    
   
   
       2 . A fuel pump as claimed in  claim 1 , in which the diaphragm ( 12 ) and the active surface ( 19 ) of the piston ( 18 ) comprise a first and second surface respectively, the ratio between the first and the second surface being at least equal to five.  
   
   
       3 . A fuel pump as claimed in  claim 1 , in which the second chamber ( 20 ) is provided with a maximum pressure valve ( 22 ) adapted to be disposed in an open position when the value of the pressure of the oil within the second chamber ( 20 ) is substantially equal to a predetermined value.  
   
   
       4 . A fuel pump as claimed in  claim 1 , in which the diaphragm ( 12 ) is a steel diaphragm.  
   
   
       5 . A fuel pump as claimed in  claim 1 , in which the alternating movement of the piston ( 18 ) comprises an outwards stroke and a return stroke, the actuator means ( 23 ) comprising first thrust means to provide the piston ( 18 ) with its outward stroke and second thrust means to provide the piston ( 18 ) with its return stroke.  
   
   
       6 . A fuel pump as claimed in  claim 5 , in which the first thrust means comprise resilient thrust means.  
   
   
       7 . A fuel pump as claimed in  claim 5 , in which the second thrust means comprises a cam and a tappet roller ( 27 ) mounted on the piston ( 18 ) and cooperating with this cam ( 25 ).  
   
   
       8 . A fuel pump as claimed in  claim 1 , in which the second chamber ( 20 ) is provided with a further intake valve ( 21 ) adapted to maintain a quantity of oil contained in this second chamber ( 20 ) substantially constant.  
   
   
       9 . A fuel pump as claimed in  claim 1 , in which the alternating movement of the piston ( 18 ) comprises an outward stroke to increase the volume of the first chamber ( 13 ) and control the opening of the intake valve ( 14 ) and a return stroke to decrease the volume of the first chamber ( 13 ) and enable the opening of the delivery valve ( 15 ), flow regulation means ( 29 ;  43 ) being provided in order selectively to control the opening of the delivery valve ( 15 ) during the return stroke.  
   
   
       10 . A fuel pump as claimed in  claim 9 , in which the flow regulation means ( 29 ) comprises further actuator means ( 30 ) adapted to open the intake valve ( 14 ) during the return stroke, the delivery valve ( 15 ) being configured to open, during the return stroke, only when the intake valve ( 14 ) is closed.  
   
   
       11 . A fuel pump as claimed in  claim 10 , in which the further actuator means ( 30 ) comprise an electromagnetic actuator.  
   
   
       12 . A fuel pump as claimed in  claim 9 , in which the flow regulation means ( 43 ) comprise a supply valve ( 43 ) adapted selectively to control the supply of oil to the second chamber ( 20 ).  
   
   
       13 . A fuel pump as claimed in  claim 12 , in which the supply valve ( 43 ) comprises a shutter ( 51 ), third thrust means ( 53 ) adapted normally to maintain the shutter ( 51 ) in a position closing the supply valve ( 43 ) and fourth thrust means ( 50 ) adapted to displace the shutter ( 51 ) from the closed position to an open position of the supply valve ( 43 ).  
   
   
       14 . A fuel pump as claimed in  claim 13 , in which the fourth thrust means ( 50 ) comprise a further electromagnetic actuator.  
   
   
       15 . A fuel pump as claimed in  claim 13 , in which the third thrust means ( 53 ) are calibrated in order to maintain the shutter ( 51 ) in the closed position 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 second chamber ( 20 ) when the value of the pressure of the oil within this second chamber ( 20 ) is substantially equal to a predetermined value.  
   
   
       16 . A fuel pump as claimed in  claim 1 , in which the second chamber ( 20 ) is provided with a plurality of channels ( 42 ) for the passage of the oil provided on the wall ( 41 ).