Disc brake caliper with piston roll-back device

A disc brake caliper comprising a caliper body arranged astride a brake disc having a rotational axis defining an axial direction (X-X) and opposite friction surfaces, said caliper comprising pads received in said caliper body so as to be slidable substantially in direction (X-X) axial to the brake disc to respectively operate on said opposite friction surfaces, said caliper body comprising at least one piston seat adapted to receive a piston provided with a lateral surface adapted to slide in said piston seat so as to be forced by pressurized brake fluid exiting from said seat to impact at least one of said pads against one of said friction surfaces of the brake disc, wherein:

• said piston has a substantially cylindrical-shaped piston body having a thrust axis (T-T) substantially parallel to the rotational axis (X-X) of the disc and having a radial direction (R-R) perpendicular to said thrust axis (T-T);
• said piston body having a bottom and a cylindrical wall;
• said piston body having a first annular seat provided in said cylindrical wall;
• said first annular seat being adapted to receive a first gasket;
• said piston body having a second annular seat arranged in said cylindrical wall;
• said second seat being different from said first seat;
• said second annular seat having a shape adapted for a controlled elastic deformation of a second gasket received in said second annular seat;
• said second annular seat being in proximity to an edge nearest the bottom of the piston body comprising a portion that is rounded to define a boundary which defines a volume adapted to receive a gasket portion during elastic deformation thereof determined by the movement of the piston exiting from the piston seat;
• said second gasket operating between said piston and said piston seat and being adapted to be deformed elastically in the direction of the thrust axis (T-T) during relative movement of the piston with respect to the piston seat so as to be preloaded elastically to return the piston into the piston seat by a predetermined degree or roll-back upon termination of the braking action,
• and wherein:
• said first annular seat is at least partly radially superimposed on said bottom;
• said first annular seat having a substantially square-shaped cross-section with lateral walls transverse to the thrust direction (T-T) and a bottom substantially parallel to said thrust direction (T-T) to receive said first gasket in order not to deform in the thrust direction (T-T) during the relative movement of the piston with respect to the piston seat;
• said second seat receiving said second gasket being arranged on the side opposite from the bottom with respect to said first seat receiving said first gasket, and nearer the pads than said first seat;
• said first gasket operating between said piston and said piston seat so as to provide a fluid sealing capable of allowing pressurization of the fluid, the first sealing gasket keeping the brake fluid away from the second gasket;
• said first gasket comprising:
• a retention ring having a surface, opposite to an annular seat, providing a fluid sealing by acting as a scraper with an inner sliding surface of the piston seat, said retention ring having a radially inner surface facing radially inside the piston and having an annular groove;
• and
• an underlying gasket partly received in said annular groove of said radially inner surface of the retention ring and prevented by said radially inner surface of the retention ring from deforming in the thrust direction (T-T).