Patent ID: 6971487

Claim:
A double-wrap band brake apparatus having a double wrap brake band for serving to brake a rotating member fitted therein, which comprises: an annular middle band with a frictional surface formed on the inner peripheral side thereof; a pair of annular outer bands coupled to this middle band in a state that the free ends thereof are respectively opposed to the free end of the middle band and respectively having frictional surfaces formed on the inner peripheral sides thereof; an anchor bracket fixed on an operational end side of one of said middle band and said outer bands and latched on a main body casing side; and an apply bracket fixed on an operational end side of the other of said middle band and said outer bands to receive a force in the direction of contraction of said middle band and said outer bands from an actuator, wherein: said middle band is provided, on an inner peripheral surface, with a first circumferentially elongated frictional member and a second circumferentially elongated frictional member which has, at the first frictional member side, a straight end extended in the axial direction, disposed on an end portion side of said apply bracket, and thinner than said first frictional member, and an oil groove extending in the axial direction and formed between a circumferential end of said first frictional member and said straight end of said second frictional member; and said middle band is further provided, on the inner peripheral surface, with a dynamic pressure groove which is opened to said oil groove and formed radially through said first frictional member to extend in the circumferential direction from said circumferential end of said first frictional member, whereby dynamic pressure is generated, when said rotating member is rotated, so that said middle band is swollen radially.