Patent GB-274084-A (GB)
Title: Improvements in and relating to servo-brakes
IPC: B60T13/24
Filed: 1927-07-06
Abstract: 274,084. Hallot, P. July 7, 1926, [Convention date]. Fluid - pressure; forcetransmitting mechanism; covers or protectors for brakes. - Fluid - pressure brake apparatus for road or rail vehicles or machines actuated either by vacuum or pressure fluid is provided with pulley tackle adapted to give a mechanical advantage for transmitting the effort of the piston to the braking elements and also comprises valve mechanism controlled by a spring and by a piston subject to the pressure of the brake cylinder, so that a graduated braking pressure dependent upon the extent of movement of the control member can be effected, the control member being arranged also to apply the direct effort of the driver to the brakes. As applied to a vacuum system in which the suction of the motor of the vehicle &c. may be used, the apparatus comprises a piston 3 con. nected to a chain or cable 7 passing around a pulley 8 and connected to a fixed point 10. The pulley 8 is mounted upon a forked lever 9 pivoted on a spindle 11 having bearings on a casing 1. A rod 12 is connected to the brakes, and to the lever 9 by a pivot 13 and a device for taking up excessive slack is described below. The operating pedal is connected to an arm 22 secured to the spindle 11 to which is secured a collar 23 provided with a tongue 24 projecting into a slot in the sleeve 23<1> of the lever 9. The sleeve 23 has an arm 25 connected by rod 27 to a tubular part 29 which encloses a spring 30 abutting also on a rod connected to the valve 31. The rod of the valve 31 has a pin and slot connection with a second valve 32 which controls the pipe 39 which may be connected to the inlet pipe of the motor. The valve 31 is adapted to seat on a piston 36 through which, when the valve is open as shown, and an orifice in the valve casing 40 air can be admitted to the brake cylinder 2 by an opening 43 to release the brake. To apply the brakes the pedal is depressed and acting through the rod 27 and a spring 30 first seats the valve 31 on the piston 36 to close the cylinder 2 to atmosphere and then through the pin-and-slot connection 33 opens the exhaust valve 32. The piston 36 has thus been moved to its right hand position and when the difference between the reduced pressure in the cylinder 2 and that of the atmosphere acting upon the opposing faces of the piston is sufficient to overcome the pressure of the spring 30, the piston returns and permits valve 33 to close. The pressure reduction in the cylinder 2 is thus proportional to the movement of the pedal and the compression of the spring 30. The abutting faces of the piston 36 on the casing 37 are ground to prevent leakage of air into the brake cylinder. When the pressure in the cylinder is reduced the piston applies the brakes through the chain &c. 7, lever 9 and rod 12. If upon depressing the pedal the piston 3 fails to function, the play between the tongue 24 on the valve operating mechanism and the sleeve 23<1> on the lever 9 is taken up and the brakes are applied by the direct effort of the operator. Compensating for wear.-An automatic device for taking up excessive slack in the transmission system of the brakes comprises a nut 15 screwed on the end of the rod 12 and abutting on the pivot 13 which extends across the fork of the lever 9 and through which the rod 12 passes. The nut has secured to it a toothed collar 19 engaged bv a second toothed collar 17 rotatably mounted on the nut and held in engagement with the collar 19 by a spring 18. The collar 17 has a pair of fingers 20 which embrace a ball 21 secured to the lever 9. During the application of the brakes the lever turns the collar 17 and if this movement is sufficient to cause the collar to slip a tooth with respect to the collar 19 the collar 19 and the nut 15 will be turned during the return movement of the lever to reduce the effective length of the rod 12.