Automatic braking mechanism

Claim 1

In a traction apparatus having a frame, opposed traction units mounted on said frame, a driving connection for each said unit comprising pairs of spaced sprocket wheels on said frame and an endless chain extending about each said wheel pair, pneumatically operated means for driving each of said wheel pairs, a pneumatic pressure source and valving for regulating the pneumatic pressure, a braking mechanism on said frame for each said unit including movable means for braking one of said sprocket wheels, each said mechanism being pneumatically interconnected with each said valved pneumatic pressure source, each said mechanism also including an air cylinder piston unit connected with said movable means and operable through said source to retract said piston to thereby actuate said movable means into braking engagement with said one sprocket wheel when the pneumatic pressure is discontinued, and to extend said piston to thereby actuate said movable means out of braking engagement with said one sprocket wheel when the pneumatic pressure is valved on, whereby said one sprocket wheel is braked only during inoperation of the driving means, said piston unit being connected with said movable means by a toggle linkage comprising two link member sets each pivotally connected at one end to the piston rod of said unit thereby defining a toggle knee, and pivotally connected at their other ends, respectively, to said movable means and to said frame, the toggle knee during full retraction of said piston rod lying slightly out of alignment with said link member other ends thereby defining an off-deadcenter arrangement of said link members whereby any tendency for accidental release of the brake is substantially avoided.