Patent GB-795769-A (GB)
Title: A vehicle vacuum brake system
Inventor: BROWALL BERT HENRY
IPC: B60T8/18
Filed: 1956-08-20
Abstract: 795,769. Vacuum brake systems. SVENSKA AKTIEBOLAGET BROMSREGULATOR. Aug. 20, 1956, No. 25397/56. Class 103 (1). In a vehicle vacuum brake system lower or higher braking effort is set by a vacuum servo motor controlled by a valve operating in response to the vehicle load and constructed to prevent undesirable settling movements during running. In the embodiment illustrated, a valve 11 for control of operation of a vacuum servomotor for setting a vacuum brake system on a vehicle for lower or higher braking effort is mounted on the under frame 1 of the vehicle and is connected through linkage 8, 7, 5, 4a and 4 to one of the vehicle springs 3 so as to be operated in response to vehicle load. One end of the lever 8 is fulcrumed to a fixed bracket 9 and the other end of the lever 8 is resiliently supported by a spring housed in an oil-filled dashpot 10 fixed to bracket 9. The lever 8 operates valve 11 which is provided with two passages; passage 13 leading to the source of vacuum and passage 14 leading to the vacuum servomotor. Lower and upper chambers 15 and 16 respectively are provided within the valve housing 12 which lead to passages 13 and 14 respectively; the chambers being controlled by a valve body 20 normally spring- urged into contact with valve seat 23 and the upper chamber 16 is hermetically closed at its upper end by means of a diaphragm 24 clamped to a valve spindle 28 which is normally spring- urged out of contact with the valve body 20 and into an upper end position where the shoulder of valve spindle 28 abuts internal flange 29 of sleeve 25 to define a clearance between knob 30 and the upper end of extension 27 of sleeve 25 which is greater than the clearance between the end of the lower extension 31 of the valve spindle 28 and the valve body 20. A passage 33 is provided in the valve spindle 28 and is in communication with atmosphere in the position illustrated. When the vehicle is empty or only slightly loaded, the force transmitted from the vehicle spring to the valve operated lever 8 is insufficient to overcome the force of spring housed in dashpot 10 and the spindle 28 of the valve is held in its upper end position by spring 34; the vacuum servomotor connected to passage 14 being shut off from the chamber 15 leading to the source of vacuum and the braking system is set for lower braking effort. When vehicle is loaded sufficiently to overcome the action of the spring and dashpot 10, adjustable screw 35 fixed to lever 8 contacts knob 30 to depress valve spindle 28 against the action of springs 34 and 22 to shut off passage 33 leading to atmosphere and to open the valve body 20 and prevent communication between chambers 15 and 16 so that the brake may be set for higher braking effort. The effected pressure area of the diaphragm 24, which is subjected to atmospheric pressure on its upper side and to vacuum on its lower side when the valve body is opened being greater than the effective pressure area of the valve body 20 when in sealing contact with valve seating 23 ensures that the brake system is still set for higher braking effort until on unloading the vehicle, the load has fallen to a value lower than that at which the brake system on the loading of the vehicle is set for the higher braking effort so that undesirable repeated settling movements caused by vibration and during running are avoided. Specification 554,657 is referred to.