Cable-pull actuation system for a parking brake, parking brake and method for unlocking a parking brake thereof

A cable-pull actuation system for a parking brake, comprising:

• a body which houses an electric motor device,
• a rod, suitable to operate along an actuation direction, at a first end, an actuation member of a drum brake and/or a parking brake,
• a transmission device which operatively connects the electric motor device to a second end of the rod integral in translation with a screw, having a thread,
• wherein said screw is engaged, via a thread, to a nut screw actuated in rotation by said transmission device,
• where a pre-loading device is provided, acting in contrast on the screw, said pre-loading device being pre-loaded in compression by a pusher so as to exert a pre-load traction on the rod to offset variations of load on the rod,
• wherein the pre-loading device is configured to exert a thrust action on the rod following the annulment of axial clearances, in the actuation direction, between the nut screw and said body, so as to allow a compression of the incremental pre-loading device with respect to the pre-load value.

A method for releasing a parking brake comprising the steps of:

• providing a cable-pull actuation system, comprising:
• a body which houses an electric motor device,
• a rod, suitable to operate along an actuation direction, at a first end, an actuation member of a drum brake and/or a parking brake,
• a transmission device which operatively connects the electric motor device to a second end of the rod integral in translation with a screw, having a thread,
• wherein said screw is engaged, via a thread, to a nut screw actuated in rotation by said transmission device,
• where a pre-loading device is provided, acting in contrast on the screw, said pre-loading device being pre-loaded in compression by a pusher so as to exert a pre-load traction on the rod to offset variations of load on the rod,
• wherein the pre-loading device is configured to exert a thrust action on the rod following the annulment of axial clearances, in the actuation direction, between the nut screw and said body, so as to allow a compression of the incremental pre-loading device with respect to the pre-load value;
• actuating the electric motor device so as to gradually release the rod,
• monitoring the electrical current absorption of the electric motor device during said release phase,
• interrupting the release phase at the moment in which an increase in current absorption is detected when, following the annulment of the axial clearances, in the actuation direction, between the nut screw and the bushing, the pre-loading device opposes the release of the rod.