Brake actuator

A single-acting hydraulic actuator for a vehicle brake, comprising:

• a cylinder body;
• said cylinder body having a clutch face;
• an actuator piston slidable within said cylinder body;
• an automatic adjuster which includes a strut of variable length, said strut including strut members threadedly interengaged by a non-reversible screw thread connection;
• one of said strut members being a rotatably supported adjuster shaft;
• a control means adapted to contact said clutch face for controlling rotation of said adjuster shaft;
• said adjuster shaft including a reversible screw thread for engagement with a similar thread on said control means to form a reversible screw thread connection;
• said actuator piston supporting a nut;
• said actuator piston having an area upon which hydraulic pressure acts;
• said nut being one of said strut members and having a threaded portion, said adjuster shaft including a threaded portion in engagement with said nut;
• said engaged, threaded portions forming said non-reversible screw thread connection;
• said nut being separate from but non-rotatably coupled to said actuator piston;
• said actuator piston having a first surface forming a pressure area;
• said adjuster shaft extending within a bore in said actuator piston and being sealed against said bore to form a pressure area smaller than said piston area;
• a means for applying actuating pressure to said actuator piston and said adjuster shaft areas so as to create a first force on said piston area and a second force on said adjuster shaft area;
• said forces acting in the same direction, upon brake actuation, to produce a resultant force loading said non-reversible screw thread connection;
• whereby said resultant force generates a force in said non-reversible screw thread connection such as to resist relative rotation of said strut members.