Protective sheathings for disc brake piston-cylinder units

A caliper for a disc brake comprising a piston accommodated with a cylinder of a caliper body of the disc brake to press on a braking pad, said piston having a piston outer surface co-operating with a cylinder inner surface of the caliper body which accommodates the piston, said outer surface having a predefined piston diameter and said cylinder inner surface having a predefined cylinder diameter, wherein said piston comprises a piston body and a head thereof which can press against the pad, the caliper comprising:

• a sheathing housing arranged on the head of the piston having housing walls and a first opening which directly faces the cylinder and a second opening which directly faces the braking pad,
• a flexible sheathing for protecting a piston-cylinder unit for a disc brake which is movable between a retracted condition and an extended condition,
• wherein the flexible sheathing comprises:
• a sheathing body extending radially from an inner diameter to an outer diameter and defining an axial direction, a radial direction orthogonal to the axial direction and a circumferential direction;
• said sheathing body comprising:
• a first hooking ring arranged along the outer diameter of the sheathing which projects in the axial direction and is fixed to a caliper body;
• a second hooking ring arranged along the inner diameter of the sheathing which projects in the axial direction and is fixed to the piston;
• a sheathing portion extending from said inner diameter;
• a plurality of folds connected to and extending radially outward from said second hooking ring and consisting of side by side folds defined by portions of said sheathing body that are folded with adjacent surfaces of the plurality of folds directly facing each other and to facilitate extension of the sheathing and flattening of the plurality of folds during the outward movement of the piston from the cylinder of the caliper body, said plurality of folds being totally arranged on said sheathing portion which extends from the inner diameter;
• said body comprising a joining band connecting the first hooking ring to the plurality of folds, said joining band extending in a substantially planar manner in the radial direction in the shape of a disc;
• wherein:
• the plurality of folds extends in the radial direction by a predetermined first extension or radial extension of folds;
• the joining band extends in the radial direction by a predetermined second extension or radial extension of joining band;
• wherein the size of said predetermined second extension is equal to or greater than said predefined first extension,
• wherein the sheathing housing comprises a fold seat formed in the head of the piston, that entirely contains the plurality of folds, said fold seat having a lower surface and being opened on two sides of which one of the sides is configured to face both the pad and the cylinder when the piston is completely accommodated within the cylinder,
• wherein the sheathing housing further comprises a protuberance extending radially outward to define a first annular groove formed in the fold seat proximate the lower surface and extending away from the cylinder, the first annular groove opening radially outward, wherein the second hooking ring of the flexible sheathing mounts in the first annular groove, the second hooking ring being radially inward and proximate the plurality of folds;
• and wherein the piston comprises a different material comprising the caliper body which forms the cylinder of the piston-cylinder unit
• wherein the caliper body defining the cylinder comprises a second annular groove, the second annular groove having an opening transverse to a radial direction and an annular outer wall and a parallel annular inner wall, the second annular groove receiving the first hooking ring, the first hooking ring engaging the annular outer wall and the annular inner wall of the second annular groove and forming a radially extending edge at the opening of the second annular groove, the joining band extending radially inward from the first hooking ring from the radial edge of the first hooking ring at the opening of the second annular groove.