| 摘要 |
A novel and improved closed nozzle injector is provided which effectively and accurately controls the timing and rate of fuel injection while minimizing parasitic losses and needle valve element wear. The closed nozzle injector includes a needle valve element movable between open and closed positions, an outer control volume, an injection control valve for controlling the flow of pressurized fuel from the outer control volume to affect opening and closing of the needle valve element and a needle valve biasing feature for optimizing the speed of needle valve opening and closing. The needle valve biasing feature includes an inner guide portion formed on the needle valve element with a larger diameter than an outer guide portion, an inner control volume, and an inner restriction orifice for restricting the flow of pressurized supply fuel to the inner control volume to create a fuel pressure bias closing force which advantageously slows down the opening of the needle valve element. The fuel pressure bias closing force increases as the needle valve element opens thereby causing the needle valve element to hover in an open position without contacting a hard stop. The inner control volume and inner restriction orifice also result in a hydraulic damper effect which slows the closing motion of the needle valve element toward the end of the closing event thereby permitting higher needle closing velocity earlier in the closing event.
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