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 an injection system of an engine of a vehicle, said fuel supply rail being connected to a fuel tank by a plurality of piezo-electric injectors, each of the piezo-electric injectors including a needle and a piezo-electric actuator configured to press on a servo valve of the injector, the injection system including a fuel pressure sensor for the supply rail and an electrical generator configured to transmit electric current pulses to the piezo-electric actuator of each of the piezo-electric injectors, said method being implemented during a phase of release of an 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 fuel pressure is greater than the defined reference fuel pressure:
• sending, by the electrical generator, a first electrical command to the piezo-electric actuator of at least one piezo-electric injector of the plurality of piezo-electric injectors, the first electrical command comprising
• an electric charge pulse of a defined first duration determined to cause a complete charge of the piezo-electric actuator of the at least one injector,
• an electric discharge pulse of the piezo-electric actuator,
• a defined second 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 defined second duration corresponding to the elapsing time 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 currcnt command, a charge time duration allowing an opening of the servo valve of the at least one injector, and
• sending, by the electrical generator, 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 third duration,
• an electric discharge pulse of the piezo- electric actuator, and
• a defined fourth 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 defined fourth duration being determined from the charge time duration of the at least one injector to allow the opening of the servo valve of said at least one injector while keeping the 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 defined second duration being determined as a function of an engine speed, the pressure in the fuel supply rail, and a desired pressure discharge.