| 摘要 |
A valve assembly for a pilot fuel injection system, which system also includes a transfer pump, a high pressure fuel pump, and a fuel injection nozzle. The valve assembly includes a blocking valve and a metering valve in an unitary housing having a high pressure fuel inlet, a metered fuel outlet, and a fuel return outlet. The blocking valve includes a cam ring operating a spool type valving member which opens and closes the high pressure inlet to the metering valve in a timed phase relation with an engine. The metering valve includes a cam ring, a spool type valving member, a spring, and a dump means. The cam ring has a single lobe which smoothly increases on one side and abruptly decreases in two steps on the other side; the smooth side slides the spool in one direction at velocities proportional to engine speed while the inlet is closed by the blocking valve; and the spring moves the spool along a two stepped path at velocities independent of engine speed while the inlet is open. The spool meters a pilot charge to the metered fuel outlet during the second step. The dump means connects the metered fuel outlet to return at some point during the second step, thereby terminating the flow of the main charge to the engine. Spool rotating means responsive to throttle position vary the dump means connecting point, thereby varying the main fuel charge amount flowing to the engine. An alternative embodiment of the stepped cam ring comprises two concentric and relatively moveable rings for varying the timing of the charges with respect to each other and the engine.
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