Valve utilising shape memory alloys and an anti-lock brake system incorporating the valve

摘要

A valve (500) has a pressure port (316) and an exhaust port (320) controlled by a reciprocable valve spool (520). A bias spring (530) maintains the valve spool (520) in its first position in which pressure port (316) is open and exhaust port (322) is closed. Where the valve (500) is used in an anti-lock braking system, in this first position brake fluid is flowed via an inlet (318) and bore (312) out of the pressure port (316) to pressurise a brake. An actuating unit (560) for moving the valve spool (520) comprises a series of pivoted links (542, 544, 546, 548) and an actuating shape memory alloy wire (562) connected to the first link (542) and to an actuating block (563) suspended from the third link (546). Application of electrical current to the wire (562) contracts it causing pivoting of the links and movement of the valve spool (520) to a second position in which the pressure port (316) is closed and the exhaust port (322) is open. The supply of pressuring fluid to the brake is thereby ceased, and fluid can be flowed from the brake via an inlet (320) and a bore (314) to the exhaust port (322) to release pressure from the brake. Removal of the electrical current from the wire (562) relaxes it and the bias spring (530) is able to restore the valve spool (520) to its first position. <MATH>