Fuel pump

Abstract

A fuel pump for an engine may include a cylinder, a piston displaceably disposed in the cylinder, and a cam driven by the engine. The cam engages the piston to form a cam-follower mechanism so that the rotation of the cam generates a reciprocal movement of the piston inside the cylinder. The cam preferably includes a variable cam lobe having a maximum radius that is a function of engine speed so that the displacement of the piston generated by the variable cam lobe is a function of the engine speed. The cam may also include a weight that is subject to a centrifugal force when the ram is rotating. Alternatively, the maximum radius of the variable cam lobe may be a function of pump outlet pressure so that the displacement of the piston generated by the variable cam lobe is a function of the pump outlet pressure.

1 . A fuel pump for an engine, the fuel pump comprising: 
 a cylinder;    a piston displaceably disposed in the cylinder; and    a cam driven by the engine, the cam engaging the piston to form a cam-follower mechanism so that the rotation of the cam generates a reciprocal movement of the piston inside the cylinder, the cam including a variable cam lobe having a maximum radius that is a function of engine speed so that the displacement of the piston generated by the variable cam lobe is a function of the engine speed.    
     
     
         2 . The fuel pump of  claim 1 , further comprising: 
 a weight that is subject to a centrifugal force when the ram is rotating;    a pivotable arm that pivotably connects the weight to the cam and is connected to the variable cam lobe, so that the weight extends radially outwards under the centrifugal force to vary the maximum radius of the variable cam lobe.    
     
     
         3 . The fuel pump of  claim 2 , further comprising: 
 a spring biasing the weight radially inwards to counter the centrifugal force.    
     
     
         4 . The fuel pump of  claim 2 , further comprising: 
 a stop for engaging at least one of the arm, the weight and the variable cam lobe when the variable cam lobe is at the extended position, wherein the stop maintains the variable cam lobe at the extended position.    
     
     
         5 . The fuel pump of  claim 2 , wherein the variable cam lobe has only an extended position and a retracted position, wherein when the engine speed is below a given engine speed value the variable cam lobe is at the extended position, and wherein when the engine speed is above a given engine speed value the variable cam lobe is at the retracted position.  
     
     
         6 . The fuel pump of  claim 1 , wherein the variable cam lobe has only an extended position and a retracted position, wherein when the engine speed is below a given engine speed value the variable cam lobe is at the extended position, and wherein when the engine speed is above the given engine speed value the variable cam lobe is at the retracted position.  
     
     
         7 . The fuel pump of  claim 2 , wherein the variable cam lobe is a first cam lobe, and the pump further comprising a second cam lope, wherein the second cam lope has a fixed maximum radius.  
     
     
         8 . The fuel pump of  claim 1 , wherein the variable cam lobe is a first cam lobe, and the pump further comprising a second cam lope, wherein the second cam lope has a fixed maximum radius.  
     
     
         9 . A fuel pump for an engine, the fuel pump comprising: 
 a cylinder having an inlet and an outlet;    a piston displaceably disposed in the cylinder; and    a cam driven by the engine, the cam engaging the piston to form a cam-follower mechanism so that the rotation of the cam generates a reciprocal movement of the piston inside the cylinder, the cam including a variable cam lobe having a maximum radius that is a function of pump outlet pressure so that the displacement of the piston generated by the variable cam lobe is a function of the pump outlet pressure.    
     
     
         10 . The fuel pump of  claim 9 , wherein the maximum radius of the variable cam lobe decreases as the pump outlet pressure increases.  
     
     
         11 . The fuel pump of  claim 10 , further comprising: 
 a spring biasing the variable cam lobe against the pump outlet pressure.    
     
     
         12 . The fuel pump of  claim 9 , wherein the variable cam lobe has only an extended position and a retracted position, wherein when the pump outlet pressure is below a given value the variable cam lobe is at the extended position, and wherein when the pump outlet pressure is above the given value the variable cam lobe is at the retracted position.  
     
     
         13 . The fuel pump of  claim 9 , wherein the variable cam lobe is a first cam lobe, and the pump further comprising a second cam lope, wherein the second cam lope has a fixed maximum radius.