Patent GB-516031-A (GB)
Title: Improvements in or relating to servo brake mechanism for vehicles
IPC: B60T13/06
Filed: 1938-07-07
Abstract: 516,031. Brakes. AUTOMOTIVE PRODUCTS CO., Ltd., and GATES, G. R. G. July 7, 1938, No. 20205. [Class 103 (i)] In servo 'brake mechanism for vehicles in which the brakes are applied by a friction clutch of which one part rotates continuously with the power transmission system, the engaging pressure on the clutch is applied by a plunger through a spring so as. to limit this pressure. In Fig. 1, the torque applying unit comprises friction discs 11, 14 respectively, splined to a shaft 12 driven from the gear box and threaded on rods 15 carried by a cover 27 and an end plate 25. Rotation of the parts 14, 27, 25 when the discs are engaged rotates a sleeve 34 by means of a chain 32 attached to the plate 25 at 31 and to a pulley 33 on the sleeve. The sleeve has engagement by a quick-pitch thread 36 with the piston rod 37 of a master-cylinder 21 connected to the vehicle brakes. Rotation of the rod 37 is prevented by its splined engagement at 39 with a fixed sleeve 40. Rotation of the sleeve 34 thus effects longitudinal movement of the rod 37 to apply the brakes. Pressure is applied to the discs 11, 14 by a plunger 44 operated by pressure produced in a chamber 42 by a pedal-operated master cylinder. The plunger 44 contains a precompressed spring 61 in contact through a. plug 62 with a cap 64, the plug 62 normally abutting on retaining ring 63 in the plunger. To limit the pressure-applying movement of the plunger 44, it has an extension 46 slidable in a ring 47 and carrying a sleeve 59 for engagement with the ring 47 which abuts on a part 54 screwed into the plunger cylinder 18. A spring 55 normally holds the plunger in the left-hand position with a shoulder 48 on the extension, 46 engaging the ring. Thus when pressure is transmitted to the chamber 42, the plunger and plug 62 initially move as a rigid unit to engage the discs 11; 14 after which the spring 61 yields and as the movement of the plunger is limited, the maximum pressure applied to the discs is also limited. An auxiliary chamber,. the volume of which increases as the brakes are applied, is connected to the pipe-line between the master cylinder and the chamber 42 as described in Specification 477,173 so that the degree of braking is rendered entirely dependent upon the pedal movement. Adjustment for wear of the discs 11, 14 is effected by turning the member 54 to advance the plunger, the member being locked by a spring detent 67. In a modification in which the friction discs 11, 14 are mounted on the vehicle transmission shaft, the plunger cylinder which cannot then be arranged co-axially with the discs extends obliquely through . the disc casing and the plunger engages the discs through a rocker plate. According to the Provisional Specification the plunger may be operated mechanically by a lever pivoted intermediate its ends to the plunger and at its ends to the driver's control and to the brake rod. Operation of the driver's control pivots the lever about its attachment to the brake rod as to engage the torqueapplying unit and the consequent application of the brakes moves this point of attachment and thus tends to reduce the engaging pressure on the unit. The lever is mounted on a boss screw-threaded on the plunger which may be turned to take up wear of the friction discs.