Patent ID: 6186294
Filing Date: 2001-02-13
Classification: F16D

Abstract:
A drum brake comprising:a first brake shoe having a first end;a second brake shoe having a first end and disposed opposite the first brake shoe within a brake drum;a backing plate supporting the first and second brake shoes;a pressure chamber;a control piston for supplying a hydraulic pressure to the pressure chamber in response to a braking reaction force from the second brake shoe and movable to and from the second brake shoe;a wheel cylinder disposed between the first end of the first brake shoe and the first end of the second brake shoe, the wheel cylinder including a drive piston for pressing the first and the second brake shoes against an inner surface of the brake drum when actuated by the hydraulic pressure from the pressure chamber, the drive piston having a base end in the pressure chamber and a leading end facing the first end of the first brake shoe, the drive piston being movable to and from the first brake shoe by the hydraulic pressure supplied to the pressure chamber;an anchor portion disposed between the first ends of the first and second brake shoes for receiving an anchor reaction force from the second brake shoe; anda control lever for distributing the anchor reaction force to the anchor portion and to the control piston when the anchor reaction force reaches a predetermined braking force magnification,wherein the wheel cylinder further includes:a control chamber behind the pressure chamber and defined by a cylinder wall of the wheel cylinder, the control chamber being pressurized by a hydraulic pressure from a master cylinder,wherein the control piston is aligned with the drive piston and has a base end of the control piston in the control chamber, while a leading end of the control piston faces the first end of the second brake shoe, andwherein the control piston cuts off a supply of the hydraulic pressure to the pressure chamber when the control piston is displaced into the control chamber by the anchor reaction force.