Fuel injector with balanced metering servovalve for an internal-combustion engine

#This application is related to the following: U.S. patent application Ser. No. 12/491,345 filed Jun. 25, 2009.

#This application claims priority to European Patent Application No. 08425458.0 filed on 27 Jun. 2008, the disclosure of which is incorporated herein, in its entirety, by this reference.

#1. Technical Field

#For a better understanding, some of the embodiments of the present invention are described herein, purely by way of non-limiting example, with the aid of the annexed drawings, wherein:

#FIG. 1 is a partial vertical cross section of a fuel injector with a balanced servovalve for an internal-combustion engine, according to a first embodiment of the invention;

#FIG. 2 is a detail of FIG. 1 at an enlarged scale;

#With reference to FIG. 1, designated as a whole by 1 is a fuel injector for an internal-combustion engine, in particular a diesel engine. The injector 1 comprises a hollow body or casing 2, which extends along a longitudinal axis 3, and has a side inlet 4, designed to be connected to a duct for delivery of the fuel at a high pressure, for example, at a pressure in the region of 1800 bar. The casing 2 terminates with a nozzle, or injection nebulizer (not visible in the figures), which is in communication with the inlet 4, through a duct 4a.

#The casing 2 has an axial cavity 6 in which a metering servovalve 5 comprising a valve body 7 having an axial hole 9 is disposed. A control rod 10 for controlling injection of the fuel under pressure is able to slide axially in the hole 9 in a fluid-tight way. The casing 2 is provided with another cavity 14, which is coaxial with the cavity 6 and houses an electro-actuator 15. The electro-actuator 15 comprises an electromagnet 16 designed to control an armature plate 17 in the form of a notched disk. In particular, the electromagnet 16 comprises a magnetic core 19, which has a polar surface 20 perpendicular to the axis 3, and is kept in position by a support 21.

#The electro-actuator 15 has an axial cavity 22 in communication with the exhaust of the servovalve 5 towards the usual fuel tank. Housed in the cavity 22 are elastic means defined by a helical compression spring 23. The spring 23 is pre-loaded so as to exert an action of thrust on the armature plate 17, in a direction opposite to the attraction exerted by the electromagnet 16 when it is excited. The spring 23 acts upon the armature plate 17 through an intermediate body, designated as a whole by 12a, which comprises engagement means formed by a flange 24 made of a single piece with a guide pin 12 of one end of the spring 23. Set between a plane top surface 17a of the armature plate 17 and the polar surface 20 of the core 19 is a thin lamina 13 made of non-magnetic material in order to guarantee a certain gap between the armature plate 17 and the core 19.