Method to control the execution of a shift to a lower gear with a released accelerator pedal in a drivetrain provided with a dual-clutch, servo-assisted transmission

A method to control the execution of a shift to a lower gear with a released accelerator pedal in a drivetrain provided with a dual-clutch, servo-assisted transmission, so as to shift from a current gear to a following gear, which is shorter than the current gear;

• the drivetrain comprises a dual-clutch, servo-assisted transmission having two primary shafts;
• at least one secondary shaft connected to drive wheels;
• and two clutches, each interposed between a drive shaft of an internal combustion engine and a corresponding primary shaft;
• the control method comprises the steps of:
• opening, in a first instant, an outgoing clutch associated with the current gear;
• closing, in the first instant, an incoming clutch associated with the following gear;
• completing the opening of the outgoing clutch by means of a first linear ramp in a second instant;
• closing the incoming clutch by means of a second linear ramp starting from a third instant, which is prior to or coincides with the second instant;
• synchronizing, between the second instant and a fourth instant, a rotation speed of the internal combustion engine with a rotation speed of the incoming clutch, namely with the rotation speed imposed by the gear ratio of the following gear;
• completing the closing of the incoming clutch in a fifth instant, which coincides with or is subsequent to the second instant;
• and
• activating the internal combustion engine so as to generate a torque between the third instant and the fourth instant in order to increase the rotation speed of the internal combustion engine.