Actuator for an internal shoe drum brake
AssigneeLucas Industries public limited company
InventorsBrian Ingram, Michael J. England
Life of this patent
Estimating the term…
Abstract
An actuator for a shoe drum brake has a body containing a tappet engaging one of a pair of brake shoes, and a split tappet of which the outermost piston engages the other brake shoe. A mechanical wedge actuator acts between the tappets for emergency and parking operation. The piston cooperates with an automatic adjuster of which a component normally engages an abutment member which bears against a shoulder within the body to isolate the adjuster from the piston of the split tappet and thereby from the other tappet.
Claims12
In an actuator for a shoe drum brake, having an actuator body, an actuating wedge disposed between a pair of force-transmitting tappets slidable in opposed bores of the actuator body and intended, in use, to transmit actuating force to a pair of brake shoes to expand the brake shoes, one of the tappets being split to form outer and inner pistons with a hydraulic chamber between them to permit the pistons to be urged in opposed directions by the application of hydraulic pressure to the chamber, the improvement comprising:
- a respective automatic adjustment means operatively associated with each tappet to maintain a substantially constant shoe-to-drum clearance;
- the adjustment means associated with the split tappet comprising,
- a rotatable screw-threaded member between the inner and outer pistons,
- a screw thread on said outer piston cooperatively engaging with said screw-threaded member,
- abutment means disposed between the inner and outer pistons,
- abutment engaging means on the actuator body, means to resiliently urge said abutment means away from said outer piston into engagement with said abutment engaging means, and
- clutch means operatively engaging said screw-threaded member and said abutment means to control rotation of said screw-threaded member in response to outward movement of said outer piston,
- so that said outer piston is adjusted independently of the tappet on the other side of the wedge.
In an actuator for a shoe drum brake, having an actuator body, an actuating wedge disposed between a pair of force-transmitting tappets slidable in opposed bores of the actuator body and intended, in use, to transmit actuating force to a pair of brake shoes to expand the brake shoes, one of the tappets being split to form outer and inner pistons with a hydraulic chamber between them to permit the pistons to be urged in opposed directions by the application of hydraulic pressure to the chamber, the improvement comprising:
- a respective automatic adjustment means operatively associated with each tappet to maintain a substantially constant shoe-to-drum clearance;
- the adjustment means associated with the split tappet comprising,
- a rotatable screw-threaded member between the inner and outer pistons,
- a screw thread on said outer piston cooperatively engaging with said screw-threaded member,
- said inner piston and the corresponding bore in the actuator body have a smaller cross-sectional area than said outer piston and the corresponding bore in the actuator body, respectively;
- a recess in said inner piston;
- a generally cup-shaped abutment member disposed between the inner and outer pistons and partially contained in said recess;
- an abutment engaging shoulder formed by and between said different cross-sectional areas of said corresponding bores for the inner and outer pistons in the actuator body,
- means to resiliently urge said abutment member away from said outer piston into engagement with said abutment engaging shoulder,
- a clutch face on said abutment member;
- a further screw thread on said screw-threaded member;
- a clutch member having a clutch face thereon operatively engaging said clutch face on said abutment member;
- and
- a screw thread on said clutch member cooperatively engaging said further screw thread, to control rotation of said screw-threaded member in response to outward movement of said outer piston so that said outer piston is adjusted independently of the tappet on the other side of the wedge.
Dependencies are inferred from the claim text.