Electromagnetic fuel injector for a direct injection internal combustion engine

A fuel injector, comprising:

• an injection valve provided with a needle mobile between a closing position and an opening position for regulating the fuel flow through an injection nozzle;
• a supporting body having a tubular shape and displaying a feeding channel which ends with the injection valve;
• and
• an electromagnetic actuator comprising a spring which tends to maintain the needle in the closing position and an electromagnet, which comprises a coil arranged outside the supporting body and formed by a wire of conducing material wound to form a plurality of turns, a fixed magnetic armature arranged within the supporting body, and a keeper arranged within supporting body which is magnetically attracted by magnetic armature against the bias of the spring, and is mechanically connected to the needle;
• the fuel injector is characterised in that the electromagnet comprises an external toroidal core formed by a ferromagnetic material having a high electrical resistivity;
• the magnetic core is arranged outside the supporting body and surrounds the coil which is inserted in an annular cavity obtained within the magnetic core itself.

A fuel injector, comprising:

• an injection valve provided with a needle mobile between a closing position and an opening position for regulating the fuel flow through an injection nozzle;
• a supporting body having a tubular shape and displaying a feeding channel which ends with the injection valve;
• and
• an electromagnetic actuator comprising a spring which tends to maintain the needle in the closing position and an electromagnet, which comprises a coil arranged externally to supporting body and formed by a wire of conducing material wound to form a plurality of turns, a fixed magnetic armature arranged within the supporting body, and a keeper arranged within supporting body which is attracted magnetically by magnetic armature against the bias of the spring, and is mechanically connected to the needle;
• the fuel injector is characterised in that the supporting body is formed by ferromagnetic material and displays an substantially non-magnetic portion which is arranged at the gap between the magnetic armature and the keeper and is formed by a local contribution of non-magnetic material.

A method for making a magnetic core of an electromagnet for a fuel injector;

• the magnetic core displays a toroidal shape, surrounds a coil of the electromagnet which is inserted in an annular cavity obtained within the magnetic core itself, and comprises two toroidal magnetic semi-cores, which are reciprocally overlapped so as to define therebetween the annular cavity in which the coil is arranged;
• the method comprising the steps of:
• arranging a first magnetic semi-core within a mould;
• arranging the coil within the mould and over the first magnetic semi-core;
• arranging a second magnetic semi-core within the mould and over the first magnetic semi-core so as to form the magnetic core and to enclose the coil along with the first magnetic semi-core;
• and
• injecting plastic material within the mould to form a toroidal coating liner around the magnetic core.

A method for making a tubular supporting body for a fuel injector;

• the supporting body is formed by ferromagnetic material and displays a substantially non-magnetic intermediate portion, which is arranged at the gap between a magnetic armature and a keeper of an electromagnetic actuator of the fuel injector;
• the method comprising the steps of:
• making the supporting body entirely of magnetic material, which is homogenous and uniform along the whole supporting body;
• arranging the ring of non-magnetic material about the supporting body) and at the portion of the gap between the magnetic armature and the keeper;
• and
• fusing the ring of non-magnetic material to obtain a local contribution of non-magnetic material in the supporting body.