Direct acting fuel injector

A fuel injector for the intermittent direct injection of fuel into an engine combustion chamber, said injector comprising:

• a housing having a spray tip connected in a fuel injection circuit, the spray tip including a valve seat and at least one discharge orifice;
• an injection valve biased against the valve seat but axially movable away from the seat to allow fuel flow through the orifice;
• a control chamber in the housing and connected in a fuel control circuit, the fuel injection and fuel control circuits being connectable with a source of high pressure fuel for providing opposing pressures acting against the injection valve from the spray tip in a valve opening direction and from the control chamber in a valve closing direction, the pressures acting to hold the injection valve closed when the opposing pressures are equal;
• the control chamber being formed between a cylinder portion fixed in the housing and a piston portion movable with the injection valve between a first position spaced from the cylinder portion wherein the control chamber volume is maximized and a second position engaging the cylinder portion wherein the control chamber volume is minimized, one of said portions including a divider separating the minimized control chamber volume into first and second subvolumes when the portions are engaged;
• first and second pressurizing passages in the control circuit and connecting said first and second subvolumes respectively with said pressure fuel source;
• a depressurizing passage in said cylinder portion and forming part of the control circuit connected with the second subvolume and controlled by an electrically actuated control valve to block return fuel flow or open the control circuit to fuel return means;
• the first pressurizing passage being larger than the second pressurizing passage and smaller than the depressurizing passage such that when the control valve is opened, fuel pressure in the control chamber is quickly relieved, allowing opposing fuel pressure to open the injection valve and force the piston portion into engagement with the cylinder portion, thereby requiring return fuel to pass through the smaller second pressurizing passage and second subvolume, limiting return fuel flow;
• and
• when the control valve is again closed, blocking return fuel flow, fuel pressure increases in the second subvolume, thereby separating the cylinder and piston portions and allowing flow through the larger first pressurizing passage to quickly fill the control chamber and force the injection valve to the closed position.