Patent GB-811486-A (GB)
Title: Improvements in or relating to vacuum servo brake devices
Inventor: BEET FREDERICK LESLIE
IPC: B60T13/24
Filed: 1957-05-21
Abstract: 811,486. Vacuum servo brakes. CLAYTON DEWANDRE CO. Ltd. May 21, 1957, No. 16127/57. Class 103 (1). In a vacuum servo brake device, movements imparted to a hand lever or foot pedal are transmitted. to a distributer valve and servo cylinder through a lever assembly including a reaction lever through which the operation of a piston in the servo cylinder is caused to react on the pedal rod or the like and is utilized to augment the effort transmitted to an output shaft or rod connected to the brake applying means, the distributer valve being formed within and integral with a housing for the lever assembly in a position to be actuated directly by the reaction lever, and the vacuum cylinder being detachably connected to the lever housing. The divided end 9 of a pedal-actuated rod 1, passing through cover 2 of lever housing 5, surrounds a bush 10, Fig. 2, carried by reaction lever 11, a pin 12 through bush 10 carrying brake levers 13, 13a and the fork end 14 of an output rod 15 connected to the brake applying apparatus, the upper ends of levers 13, 13a being movably mounted on a bush 18 surrounding a fixed pivot 16, with the lower ends connected to a reaction lever 11 by pin 17. Two rollers 19 connected to the top of lever 11, by a bush 20 spaced from the pivot 16, bear on a hollow valve plunger 21 which is normally held out of contact with the valve disc 24 by a spring 22 abutting a flange 23 on the plunger and a shoulder 23a on the valve body to provide a connection between the vacuum cylinder 8 and atmosphere via hose 25, port 26, hollow plunger 21 and breather pipe 27 in housing 2. The valve disc 24 is held seated against shoulder 28 by spring 29 between the disc and a plug 30 closing the end of the valve body and being provided with an aperture 31 to receive the vacuum valve stem 38. The lower end of lever 11 is connected by an arm 34 to an eye 39 on bolt 42 connecting dished steel pressings 43, 44, forming the vacuum piston, held on the bolt by nut 53 and washer 45, dish 43 having a short peripheral flange 46 and dish 44 having a frusto-conical outer portion with a skirt 47 forming a space 48 between it and the cylinder wall housing the free end of a cup washer 50 which is held in contact with the wall by leaf spring, the cylinder 8 being detachably secured to a flange of housing 5 by bolts 6 and clamp 7. A dished washer 54 on the bolt 42 retains one end of a spring 55 in contact with the piston. In operation, pressure on the pedal moves rod 1 and bushing 10 to the right causing lever 11 to rock about the pin 17 to cause rollers 19 to move the valve plunger 21 to the right to the closed position and to open valve 24 to connect cylinder 8 to a source of vacuum via hose 32, port 33, port 26 and hose 25. The piston 43, 44 thereby moves to the right and its pull on reaction lever 11 tends to balance the input load upon pin 12 to restore the bush 20 to a concentric position with respect to the rod 16 and so close valve 24. As the load on rod 1 increases valve 24 is re-opened and piston is moved further to the right moving lever 11 around pivot 16 transmitting movement to the output rod 15 via levers 13, 13a. On release of pressure on rod 1, spring 55 moves piston 43, 44 to the left overcoming the reduced load on pin 12 to move lever 11 to the left about pin 17 to open valve plunger 21 until balance exists about the pin 17. In the fully released position valve spring 22 moves the top of lever 11 to the left to the full clearance position around pivot 16 allowing valve 24 to seat and valve 21 to open, the piston 43, 44 returning to the full off position. The brake may be operated manually without moving piston 43, 44 by forming arm 34 with a slot 56 along which lever 11. may travel after adjustment to its connection therewith. The output rod 15 may be connected to an hydraulic master cylinder mounted above cylinder 8 on the studs 37 or coupled by a linkage to the wheel brakes.