Pump with centralized spring forces

Abstract

A pump including a tappet biased into contact with a camshaft by a return spring is provided. The pump includes a torque transfer reduction interface mechanically interposed between the return spring and the tappet. The torque transfer reduction interface is configured to prevent spring wind-up generated by compressing and expanding the return spring from being transferred to the tappet to prevent the torque from causing the tappet to rotate relative to the camshaft about an axis extending perpendicular to the rotational axis of the camshaft.

What is claimed is: 
     
         1 . A pump comprising:
 a tappet;   a roller rotatably carried by the tappet;   a pumping barrel defining a pumping chamber;   a plunger slidably carried in the pumping chamber for motion along a pumping axis, the plunger operably coupled to the tappet for substantially coordinated movement with the tappet along the pumping axis;   a return spring operably positioned between the pumping barrel and the tappet to axially bias the tappet away from the pumping barrel, the axial biasing forces of the return spring not passing mechanically through the plunger to the tappet, the return spring being generally tubular with a radially inner periphery defining a minimum radial dimension relative to the pumping axis; and   a torque transfer reduction interface provided, at least in part, by first and second surfaces axially abutting and defining a contact area therebetween when the return spring is in a state of compression, the torque transfer reduction interface being mechanically interposed between the return spring and the tappet, the contact area between the first and second surfaces having a maximum radial dimension relative to the pumping axis being less than the minimum radial dimension of the return spring.   
     
     
         2 . The pump of  claim 1 , wherein the torque transfer reduction interface is mechanically interposed between the return spring and the tappet such that an axial compressive force biasing the tappet away from the pumping barrel along the pumping axis is operably transmitted from the return spring to the tappet through the torque transfer reduction interface. 
     
     
         3 . The pump of  claim 1 , wherein at least one of the first and second surfaces is convex. 
     
     
         4 . The pump of  claim 3 , wherein the convex one of the first and second surfaces is generally spherically curved. 
     
     
         5 . The pump of  claim 1 , wherein the contact area of the torque transfer reduction interface is configured to permit angular slip between the first and second surfaces about a rotational axis generally parallel to the pumping axis when a maximum torque is generated on the return spring side of the torque transfer reduction interface, the maximum torque being a torque large enough to cause angular rotation of the tappet relative to the pumping barrel if the torque transfer reduction interface was not present. 
     
     
         6 . The pump of  claim 1 , further comprising:
 a spring plate axially engaged by a distal end of the return spring that is free to rotate relative to the tappet about the pumping axis;   a load button providing one of the first and second surfaces of the torque transfer reduction interface, the load button being mechanically interposed between the spring plate and the tappet such that axial compressive forces of the return spring applied to the spring plate when the return spring is in a state of compression are operably transferred substantially entirely to the tappet through the load button.   
     
     
         7 . The pump of  claim 6 , wherein the load button is free to angularly rotate about the pumping axis relative to the tappet. 
     
     
         8 . The pump of  claim 6 , wherein the return spring and the spring plate are not directly axially pressed against the tappet. 
     
     
         9 . The pump of  claim 6 , wherein the plunger has a plunger head and the spring plate includes a plunger head abutment flange surrounding a plunger receiving aperture, the plunger extending axially through the plunger receiving aperture with the plunger head axially interposed and trapped between the plunger head abutment flange and the load button. 
     
     
         10 . The pump of  claim 9 , wherein the spring plate includes:
 a radially outward extending spring abutment flange having a top surface facing the pumping barrel against which the distal end of the return spring is biased;   a first bottom surface provided by the plunger head abutment flange facing axially away from the pumping barrel against which the plunger head abuts; and   a second bottom surface facing axially away from the pumping barrel axially spaced from and between the first bottom surface and the top surface, the second bottom surface axially engaging the load button.   
     
     
         11 . The pump of  claim 10 , wherein the spring plate is axially secured to the tappet and the return spring is a coil spring. 
     
     
         12 . The pump of  claim 10 , further comprising a plunger head cavity formed axially between the load button and the plunger head abutment flange in which the plunger head is received, the plunger head cavity having an axial dimension configured to provide limited axial movement of the plunger head axially between the plunger head abutment flange and the load button. 
     
     
         13 . The pump of  claim 12 , wherein the plunger head has an axial end surface facing axially away from the pumping barrel, the axial end surface of the plunger head axially biased against a top surface of the load button as the tappet travels towards the pumping barrel as the return spring is compressed, at least one of the axial end surface of the plunger head and top surface of the load button being convex. 
     
     
         14 . The pump of  claim 1 , wherein the maximum radial dimension of the contact area is less than twenty-five percent the minimum radial dimension of the return spring. 
     
     
         15 . The pump of  claim 6 , wherein the load button directly abuts an abutment surface of the tappet axially facing the pumping barrel, the torque transfer reduction interface being positioned axially closer to the pumping barrel than the distal end of the return spring, the abutment surface of the tappet being formed as a distal end of an axially extending land, at least a portion of the spring plate surrounding at least a portion of the axially extending land. 
     
     
         16 . A pump comprising:
 a tappet;   a roller rotatably carried by the tappet;   a pumping barrel defining a pumping chamber;   a plunger slidably carried in the pumping chamber for motion along a pumping axis, the plunger operably coupled to the tappet for substantially coordinated movement with the tappet along the pumping axis, the plunger having a plunger head;   a return spring operably positioned between the pumping barrel and the tappet to axially bias the tappet away from the pumping barrel, the axial biasing forces of the return spring not passing mechanically through the plunger to the tappet, the return spring being generally tubular with a radially inner periphery defining a minimum radial dimension relative to the pumping axis; and   a spring plate axially engaged by a distal end of the return spring, the plunger extending through a plunger aperture in the spring plate with the plunger head axially interposed between the tappet and the spring plate, the plunger head being larger than the plunger aperture, the spring plate being mechanically fixed to the tappet for substantially coordinated axial movement with the tappet in opposite directions along the pumping axis;   a load button axially interposed between the tappet and the plunger head, the load button being mechanically interposed between the spring plate and the tappet such that axial compressive forces of the return spring applied to the spring plate when the return spring is in a state of compression are operably transferred substantially entirely to the tappet through the load button; and   a torque transfer reduction interface provided, at least in part, by first and second surfaces axially abutting and defining a contact area therebetween when the return spring is in a state of compression, the torque transfer reduction interface mechanically interposed between the return spring and the tappet, the contact area between the first and second surfaces having a maximum radial dimension relative to the pumping axis being less than the minimum radial dimension of the return spring, the load button providing one of the first and second surfaces of the torque transfer reduction interface.   
     
     
         17 . The pump of  claim 16 , wherein the spring plate includes a plunger head abutment flange surrounding the plunger aperture, plunger head axially interposed and trapped between the plunger head abutment flange and the load button; and
 a plunger head cavity is formed axially between the load button and the plunger head abutment flange in which the plunger head is received, the plunger head cavity having an axial dimension configured to provide limited axial movement of the plunger head axially between the plunger head abutment flange and the load button; and   wherein the plunger head has an axial end surface facing axially away from the pumping barrel, the axial end surface of the plunger head axially biased against a top surface of the load button as the tappet travels towards the pumping barrel as the return spring is compressed, at least one of the axial end surface of the plunger head and top surface of the load button being convex; and   wherein the plunger head is axially biased against the plunger head abutment flange when the tappet travels away from the pumping barrel along the pumping axis.   
     
     
         18 . A pump comprising:
 a rotating camshaft configured for rotation about a camshaft rotational axis including at least one cam lobe;   a tappet;   a roller carried for rotation by the tappet and following the cam lobe, the tappet and roller converting rotational motion of the camshaft about the camshaft rotational axis into linear displacement of the tappet along a pumping axis;   a pumping barrel defining a pumping chamber;   a plunger slidably carried in the pumping chamber for motion along the pumping axis due to rotation of the camshaft, the plunger operably coupled to the tappet for substantially coordinated movement with the tappet along the pumping axis;   a return spring operably positioned between the pumping barrel and the tappet to axially bias the tappet away from the pumping barrel, the axial biasing forces of the return spring not passing mechanically through the plunger to the tappet, and   a torque transfer reduction interface provided, at least in part, by first and second surfaces axially abutting and defining a contact area therebetween when the return spring is in a state of compression, the torque transfer reduction interface mechanically interposed between the return spring and the tappet, the contact area of the torque transfer reduction interface being configured to permit angular slip between the first and second surfaces about a rotational axis generally parallel to the pumping axis when a minimum torque is present on the return spring side of the torque transfer reduction interface rather than to transfer the minimum torque to the tappet to cause the tappet to rotate about an axis generally parallel to the pumping axis.   
     
     
         19 . The pump of  claim 18 , wherein the return spring is generally tubular with a radially inner periphery defining a minimum radial dimension relative to the pumping axis and the contact area between the first and second surfaces has a maximum radial dimension relative to the pumping axis being less than the minimum radial dimension of the return spring. 
     
     
         20 . The pump of  claim 18 , wherein the minimum torque is a torque at least large enough to cause angular rotation of the tappet relative to the camshaft about an axis generally perpendicular to the rotational axis of the camshaft. 
     
     
         21 . The pump of  claim 20 , wherein the torque transfer reduction interface is mechanically interposed between the return spring and the tappet such that an axial compressive force biasing the tappet away from the pumping barrel and towards the camshaft along the pumping axis is operably transmitted from the return spring to the tappet through the torque transfer reduction interface. 
     
     
         22 . The pump of  claim 21 , wherein at least one of the first and second surfaces is convex. 
     
     
         23 . The pump of  claim 22 , wherein the convex one of the first and second surfaces is generally spherically curved. 
     
     
         24 . The pump of  claim 18 , further comprising:
 a spring plate axially engaged by a distal end of the return spring;   a load button providing one of the first and second surfaces of the torque transfer reduction interface, the load button being mechanically interposed between the spring plate and the tappet such that axial compressive forces of the return spring applied to the spring plate when the return spring is in a state of compression that are operably transferred to the tappet are operably transferred substantially entirely to the tappet through the load button.