Axial piston pump with piston having passive cooling thermal relief feature

Abstract

A piston pump includes a rotor member with a bore therein. The bore is defined by an inner surface. The piston pump also includes a piston supported for reciprocating movement in an axial direction within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member. The piston has an outer surface that faces the inner surface with a leakage interface defined therebetween. The leakage interface is configured to receive a passive leakage flow of a fluid from the pump chamber through the leakage interface to provide cooling. Moreover, the outer surface includes a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface. The cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston.

What is claimed is: 
     
         1 . A piston pump configured to displace a fluid comprising:
 a rotor member with a bore therein, the bore defined by an inner surface;   a piston supported for reciprocating movement in an axial direction within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member, the piston having an outer surface that faces the inner surface with a leakage interface defined therebetween, the leakage interface configured to receive a passive leakage flow of the fluid from the pump chamber through the leakage interface to provide cooling; and   the outer surface including a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface, the cooling pocket moving in the axial direction relative to the inner surface with the reciprocating movement of the piston.   
     
     
         2 . The piston pump of  claim 1 , wherein the bore includes a proximal end and a distal end;
 wherein the piston includes a first end proximate the proximal end and a second end proximate the distal end;   wherein the distal end of the bore and the second end of the piston cooperatively define at least part of the pump chamber;   wherein the second end of the piston terminates at a second terminal end of the piston; and   wherein the relief feature is spaced apart from the second terminal end at a distance measured in the axial direction.   
     
     
         3 . The piston pump of  claim 2 , wherein the outer surface of the piston includes a second end shoulder that defines a terminal end of the relief feature that is proximate the second end. 
     
     
         4 . The piston pump of  claim 3 , wherein the piston includes a first end shoulder that defines a first terminal end of the relief feature, the first end shoulder being spaced apart at a relief width dimension from the second end shoulder along the axial direction. 
     
     
         5 . The piston pump of  claim 4 , wherein the relief feature has a substantially rectangular cross-sectional profile. 
     
     
         6 . The piston pump of  claim 2 , wherein the second end is configured to move between a first axial point and a second axial point of the inner surface as the piston reciprocates within the bore; and
 wherein a stroke of the piston is defined between the first axial point and the second axial point in the axial direction;   wherein the inner surface is smooth and continuous throughout the stroke of the piston.   
     
     
         7 . The piston pump of  claim 6 , wherein the relief feature remains inside the bore throughout the stroke of the piston. 
     
     
         8 . The piston pump of  claim 1 , wherein the fluid is an engine fuel. 
     
     
         9 . The piston pump of  claim 1 , wherein the rotor member and the piston are configured as an axial piston pump. 
     
     
         10 . The piston pump of  claim 1 , wherein the relief feature extends annularly and continuously about the outer surface of the piston. 
     
     
         11 . The piston pump of  claim 10 , wherein the relief feature is the sole relief feature of the piston. 
     
     
         12 . The piston pump of  claim 1 , wherein the rotor member includes a rotor body and an insert sleeve that is attached to the rotor body; and
 wherein the insert sleeve includes the inner surface.   
     
     
         13 . The piston pump of  claim 1 , wherein the relief feature is a groove recessed into the outer surface from a first adjacent area and a second adjacent area of the outer surface, the groove separating the first and second adjacent areas. 
     
     
         14 . The piston pump of  claim 1 , wherein the piston extends between a first end and a second end, wherein the piston includes a hollow and cylindrical wall that extends from the first end and defines the second end; and
 wherein the wall includes the outer surface that includes the relief feature.   
     
     
         15 . A method of operating an axial piston pump comprising:
 providing a rotor member with a bore therein, the bore defined by an inner surface;   selectively moving a piston reciprocally in an axial direction within the bore to move a fluid through a pump chamber that is cooperatively defined by the piston and the rotor member, the piston having an outer surface that faces the inner surface with a leakage interface defined between the outer surface of the piston and the inner surface of the rotor member, the outer surface including a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface; and   passively leaking the fluid from the pump chamber and through the leakage interface as the cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston.   
     
     
         16 . The method of  claim 15 , further comprising:
 receiving, by a control system, sensor input from a sensor, the sensor input based on a condition detected by the sensor; and   controlling, by the control system, an actuator based on the sensor input to change the reciprocating movement of the piston.   
     
     
         17 . The method of  claim 15 , wherein the bore includes a proximal end and a distal end;
 wherein the piston includes a first end proximate the proximal end and a second end proximate the distal end;   wherein the distal end of the bore and the second end of the piston cooperatively define at least part of the pump chamber;   wherein the second end of the piston terminates at a second terminal end of the piston; and   wherein the relief feature is spaced apart from the second terminal end at a distance measured in the axial direction.   
     
     
         18 . The method of  claim 17 , wherein moving the piston includes moving the piston between a first axial point and a second axial point of the inner surface reciprocally within the bore to define a stroke between the first axial point and the second axial point, wherein the inner surface is smooth and continuous throughout the stroke of the piston. 
     
     
         19 . The method of  claim 18 , wherein moving the piston includes maintaining the relief feature inside the bore throughout the stroke of the piston. 
     
     
         20 . An axial piston pump configured to displace an engine fuel comprising:
 a housing with an internal space therein;   a rotor member with a bore therein, the bore defined by an inner surface, the rotor member supported for rotation about a longitudinal axis within the internal space;   a piston supported for reciprocating movement along a bore axis within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member, the bore axis being parallel to the longitudinal axis, the piston having an outer surface that faces the inner surface with a leakage interface defined therebetween, the leakage interface configured to receive a passive leakage flow of the engine fuel from the pump chamber through the leakage interface to provide cooling; and   the outer surface including a relief groove that is recessed into the outer surface, the relief groove separating a first adjacent area of the outer surface and a second adjacent area of the outer surface, the relief groove having a first shoulder that is perpendicular to the bore axis and a second shoulder that is perpendicular to the bore axis, the relief groove defining with the inner surface, a cooling pocket of the leakage interface, the cooling pocket moving in the axial direction relative to the inner surface with the reciprocating movement of the piston, the cooling pocket remaining within the bore throughout a stroke of the piston as the piston reciprocates.