TECHNICAL FIELD OF INVENTION

The present invention relates a fuel pump which supplies fuel to an internal combustion engine, and more particularly to such a fuel pump which includes an inlet valve assembly.

BACKGROUND OF INVENTION

Fuel systems in modern internal combustion engines fueled by gasoline, particularly for use in the automotive market, employ gasoline direct injection (GDi) where fuel injectors are provided which inject fuel directly into combustion chambers of the internal combustion engine. In such systems employing GDi, fuel from a fuel tank is supplied under relatively low pressure by a low-pressure fuel pump which is typically an electric fuel pump located within the fuel tank. The low-pressure fuel pump supplies the fuel to a high-pressure fuel pump which typically includes a pumping plunger which is reciprocated by a camshaft of the internal combustion engine. Reciprocation of the pumping plunger further pressurizes the fuel in order to be supplied to fuel injectors which inject the fuel directly into the combustion chambers of the internal combustion engine. During operation, the internal combustion is subject to varying demands for output torque. In order to accommodate the varying output torque demands, the mass of fuel delivered by each stroke of the pumping plunger must also be varied. One strategy to vary the delivery of fuel by the high-pressure fuel pump is to use a digital inlet valve which allows a full charge of fuel to enter the pumping chamber during each intake stroke, however, the digital inlet valve may be allowed to remain open during a portion of a compression stroke of the pumping plunger to allow some fuel to spill back toward the source. When the digital inlet valve is closed during the remainder of the compression stroke, the fuel is pressurized and the pressurized fuel is supplied to the fuel injectors. Examples of such an arrangement are disclosed in U.S. Pat. No. 7,401,594 to Usui et al. and in U.S. Pat. No. 7,707,996 to Yamada et al. Prior art inlet valves such as those disclosed by Usui et al. and Yamada et al. suffer from the shortfall of the inlet valve being retained within a housing of the high-pressure fuel pump by a secondary means such as one or more of interference fit, threaded connection, welding, and threaded fasteners. Not only do these secondary means increase cost and complexity, but robustness of the connection may be reduced.

What is needed is a fuel pump and inlet valve which minimizes or eliminates one or more of the shortcomings as set forth above.

SUMMARY OF THE INVENTION

Briefly described, a fuel pump includes a fuel pump housing with a pumping chamber defined therein, the fuel pump housing having an inlet valve bore which is connectable to a source of fuel via a pump housing inlet passage, the inlet valve bore extending along an inlet valve bore axis and being stepped such that the inlet valve bore includes a shoulder which is transverse to the inlet valve bore axis; a pumping plunger which reciprocates within a plunger bore along a plunger bore axis such that an intake stroke of the pumping plunger increases volume of the pumping chamber and a compression stroke of the pumping plunger decreases volume of the pumping chamber; and an inlet valve assembly. The inlet valve assembly includes a valve seat with a valve seat flow passage extending therethrough, the valve seat being located within the inlet valve bore such that the valve seat abuts the shoulder and is urged toward the shoulder by pressure within the pumping chamber during the compression stroke; and a valve member which is moveable between 1) an unseated position which provides fluid communication through the valve seat flow passage and 2) a seated position which prevents fluid communication through the valve seat flow passage. By having the valve seat supported by the shoulder of the fuel pump housing, the high cyclic load resulting from the pressurization of fuel in the pumping chamber is carried directly by the fuel pump housing rather than by secondary means such as interference fit, threaded connections, welding, and threaded fasteners as is currently used in the prior art. In this way, the number of components and processes is reduced, thereby reducing cost and providing a more robust connection.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

