Control for a piezo-electric injector when a foot is raised from the accelerator

A method for discharging the pressure in a fuel supply rail of a injection system of an engine of a vehicle, said fuel injection rail being connected to a fuel tank by means of a plurality of piezo-electric injectors, each piezo-electric injector comprising a needle and a piezo-electric actuator able to press on a servo valve of the injector, the injection system further comprising a fuel pressure sensor for the supply rail and an electrical generator able to transmit electric current pulses to the piezo-electric actuator of each injector,

• said process being implemented during a phase of release of the accelerator for which no request for fuel injection has been made, the method comprising:
• comparing, by a computer, on each engine cycle, a defined reference fuel pressure for the fuel supply rail with a measured fuel pressure in the fuel supply rail measured by the pressure sensor, and
• when the measured pressure is greater than the reference pressure:
• sending, by the electrical generator, of a first electrical command to the piezo-electric actuator of at least one injector of the plurality, the first electrical command comprising an electric charge pulse of defined duration and an electric discharge pulse of the piezo-electric actuator,
• the duration being determined so as to cause a complete charge of the piezo-electric actuator of the at least one injector,
• the first electrical command also comprising a defined duration corresponding to the time elapsing between the start of the electric charge pulse and the start of the electric discharge pulse of the piezo-electric actuator of the at least one injector,
• the duration being determined such that the needle of the at least one injector remains immobile,
• determining, from a value of a force exerted by the piezo-electric actuator on the servo valve during the first electrical current command, a charge time duration allowing opening of the servo valve of the at least one injector,
• sending, by the electrical generator, of a second electrical command to the piezo-electric actuator of said at least one injector,
• the second electrical command comprising an electric charge pulse of a defined duration and an electric discharge pulse of the piezo-electric actuator, and also comprising a defined duration corresponding to the time elapsing between the start of the electric charge pulse and the start of the electric discharge pulse of the piezo-electric actuator,
• the duration being determined from the charge time duration of the at least one injector so as to allow an opening of the servo valve of said at least one injector while keeping its needle immobile, so that the voltage at the terminals of the piezo-electric actuator is higher than a first voltage threshold triggering the opening of the servo valve and lower than a second voltage threshold triggering the opening of the needle, the duration being determined as a function of the engine speed, the pressure in the fuel supply rail and the desired pressure discharge.