Patent ID: 8230840

Claim:
A fluid injection device having a main injection axis and comprising: a nozzle comprising, on said axis, an injection orifice and a seat and being, at an opposite end, connected to a casing; a needle having, on said axis, a first end defining a valve element, in a zone of contact with the seat and being, at an opposite end, connected to an actuator mounted so as to be able to move axially in the casing to vibrate the needle, providing between the first end of the needle and the seat of the nozzle a relative movement capable of alternately opening and closing the valve element, the actuator comprising, on the axis, a first portion, a second portion and a third portion suitable for being traversed by acoustic waves initiated by vibrations of the second portion, the first portion and third portion being placed axially on either side of the second portion, which comprises an electroactive material, the three portions being squeezed together in order to form a block having axially two opposite limits, including a first limit and a second limit of the block, the first portion being connected to the needle at a location of the first limit of the block; and excitation means for vibrating the second portion of the actuator with a setpoint period τ, wherein a length between the two limits of the block is such that a time for propagating the acoustic waves initiated by the vibrations of the second portion of the actuator and traveling along the length satisfies following equation: T=n*[τ/2], plus or minus a tolerance and where n is a multiplying coefficient, a non-zero positive integer.