Pump assembly and method

A pilot-controlled inlet throttle valve assembly for controlling the flow of working fluid to a high-pressure pump pressurizing the working fluid of a fuel injection system of a motor vehicle engine, the assembly comprising:

• a body, an inlet throttle valve in the body, an inlet passage to flow working fluid to the inlet throttle valve, an outlet passage to discharge working fluid from the inlet throttle valve to the pump, and a fluid circuit to communicate a pilot fluid to the inlet throttle valve and selectively operate the valve in response to the pilot fluid pressure;
• the inlet throttle valve comprising a bore in the body, the bore having axially spaced first and second ends, a wall extending between the ends, a hollow piston in the bore, the piston slideable in the bore to control the flow of fluid through the valve, a chamber in the bore between the piston and the first end of the bore, and a spring biasing the piston towards the chamber;
• the fluid circuit opening into the chamber, the fluid circuit configured to flow pilot fluid into and out of the chamber for controlling the position of the piston along the bore;
• the inlet passage comprising a first opening in the bore wall and the outlet passage comprising a second opening in the bore wall;
• the piston comprising axially opposed closed ends, an outer surface surrounding the interior of the piston, and a flow passage extending through the interior of the piston between the ends of the piston, the flow passage in fluid communication with the first and second openings to flow working fluid through the inlet throttle valve, and a valving edge opening and closing the flow passage with movement of the piston;
• wherein the position of the piston along the bore is established by a pressure balance between the spring and the pilot pressure in the chamber and is substantially unaffected by pressure fluctuations in the working fluid flowing through the valve.

A method of regulating the flow of working fluid to a high-pressure pump in a fuel injection system of an internal combustion engine, the method comprising the steps of:

• (a) providing an inlet throttle valve and a fluid passage from the inlet throttle valve to the pump, the inlet throttle valve comprising a flow passage to flow fluid through the inlet throttle valve to the fluid passage and a hollow piston in the flow passage, the piston comprising two closed ends, a piston wall extending between the ends and obstructing the flow passage, and an opening extending through the piston wall to flow fluid past the obstruction;
• (b) flowing working fluid through the flow passage to flow fluid through the inlet throttle valve and to the high-pressure pump, this step comprising flowing working fluid in the flow passage through the opening and into the piston and flowing working fluid in the piston through the opening and out of the piston to flow the working fluid past the obstruction;
• (c) generating a signal representing the desired instantaneous rate of flow of working fluid discharged from the pump;
• and
• (d) moving the piston to open or close the opening in response to the signal to control the output of working fluid discharged from the inlet throttle valve and flowed to the pump.