Development of a Battery-Voltage-Driven Fuel Injector for Direct-Injection Gasoline Engines. 2nd Report. Study on Enlargement of Magnetic Force for Higher Pressurised Fuel Injection.

Abstract

The battery-voltage-driven fuel injector for Direct-Injection Gasoline Engines has an opening coil and a holding coil which enable the injector to operate at the battery voltage, thus eliminating the need for either voltage-step-up circuitry or current-control circuitry. The aim of current work was to increase the magnetic force so as to increase the pressure of fuel injection. It is known that a large magneto-motive force, that is, the product of coil current and coil turn numbers, gives a large magnetic force. However, increased coil current produces more heat as a result. To overcome this problem, we have developed a new dual-coil driving method called the "double-hold driving method". This method enables the current to be fed to the opening coil during the valve holding period. The current is limited to a predetermined value by using a holding coil, which is connected in series to the opening coil, as a current-limitation register. We also inserted a diode into the drive circuit in order to block the reverse current flow caused by the mutual magnetic induction force of the two coils. Adding this diode increased the valve-opening force. It is thus concluded that the "double-hold driving method with a diode for preventing reverse current-flow" enables the injector to inject more highly pressurized fuel without any loss of injection controllability.