US Patent 9291134 Anti-cavitation throttle for injector control valve

A needle type fuel injector has a needle control chamber at a pressure subject to a control valve in a control valve chamber which in an opening phase is lifted from its seat to expose the control valve chamber, connecting passage, and needle control chamber to a low pressure drain and in a closing phase is urged against the seat to isolate the control valve chamber, connecting passage, and needle control chamber from the drain. The potential for cavitation at high fuel injection pressure is reduced by throttling the flow of fuel past the control valve seat when the control valve opens, thereby maintaining sufficient back pressure in the control valve chamber and upstream connecting passages.