Patent GB-477173-A (GB)
Title: Improvements in and relating to servo brake mechanism
IPC: B60T13/06
Filed: 1936-07-15
Abstract: 477,173. Brakes applied by running axle; fluid-pressure control; fluidpressure brakes. AUTOMOTIVE PRODUCTS CO., Ltd., and GATES, G. R. G. July 15, 1936, Nos. 19666/36 and 1855/37. [Class 103 (i)] [Also in Group XXIX] Relates to servo brake mechanism suitable for vehicles of the kind in which the brakes are applied by a servo or booster such as 21, Fig. 1, brought into action by a hydraulic slave cylinder 20 controlled from a master cylinder 16 and a pedal &c. 18. Specification 439,882 describes an arrangement in which the hydraulic pressure for operating the booster is reduced by the functioning of the booster in applying the brakes. According to this invention, the hydraulic pressure in the slave unit 20 for engaging the booster 21 is reduced by a cylinder and piston or other variable volume 13, other than the cylinder 16, which volume 13 expands as the brakes are applied and actually reduces the hydraulic pressure in the slave unit 20. The effect is to prevent the power units from taking charge and applying the brakes hard, so that a further depression of the pedal 18 is necessary for each additional application of the brakes. In the arrangement described in Fig. 1, oil is sent from a cylinder 11 along brake lines 12 when a piston 14 is thrust left by the booster 21 which is brought in by the slave unit 20 engaging a friction clutch (not shown), upon an axle or other engine - driven shaft. This leftward displacement of the piston 14 enlarges the chamber 13 which communicates with the slave unit 20 through pipes 15, 19, so that the oil pressure produced in the slave unit 20 by depression of the pedal 18 falls right away, and a further pedal depression is needed to energize the booster 21 farther. In the arrangement shown in Fig. 2, the hydraulic brake lines of Fig. 1 are replaced by a mechanical lever linkage 27, 28, 29, 30 actuated from the boosteractuated piston 14 having the expanding volume 13 behind it. In Fig. 5 is shown an embodiment with a friction-clutch booster 21 like that described in Specification 439,923. This has a single driving plate 101 splined on an axle-driven shaft 102, and the booster is engaged when oil pressure from a pedal (not shown) is admitted to slave cylinders 20. Booster action turns a crank 105 to depress a guided rod 119 and a piston 14 and so expel oil from a cylinder 11 by the brake lines 12. This action enlarges the volume 13 above the piston 14 which expanding volume communicates with the slave cylinders 20 through a union 126 and causes the reduction of pressure there which arrests the booster action. There are described with reference to Figs. 6-8 (not shown), arrangements with multiple-disc clutch boosters like those described in Specification 476,559. In Fig. 3 is shown an embodiment with a suction booster 21. When suction is admitted from a pipe 56, a piston 37 is displaced left carrying with it a piston 14 which actuates a brake line 12 and increases the volume of a chamber 13 which, by expanding by booster action, reduces the hydraulic pressure in the slave unit 20 which actuates the booster. The slave unit 20 actuates a valve chest 47 with a follow-up action in the sense that more depression of the pedal 18 is always needed to get more booster action. In the position shown, the cylinder 21 is open to the atmosphere through a pipe 46, through slots 55 in a barrel valve 53 inside a sleeve valve 57, and through vents 49. The slave unit 20 acts first to close the sleeve 57 against a disc head 52 on the barrel 53, so closing the slots 55 and cutting the cylinder 21 off from the atmosphere. Further slave-unit action lifts the head 52 so that suction in the pipe 56 reaches the cylinder 21 and the booster stroke begins. This stroke lasts only until pressure at 20 reduced by expansion at 13 allows a spring 51 to close the valve head 52. A stop 64 is provided for the piston 61 of the slave unit 20 so that, if the booster fails, the brakes can be applied manually by the pedal 18 driving oil into the chamber 13 behind the piston 14 to actuate the brake line 12 directly. Known means 71, 72, 73 are provided to replenish the pressure oil.