APPLYING SOFT PEDAL

NZ Truth, Issue 1194, 18 October 1928, Page 21

APPLYING SOFT PEDAL

Stopping Gars Made Easier By Mechanical Device

THOUCrH braking mechanisms of the present day are distinctly ; better than they were even four or five years ago, a very bigdrawback still exists m many types m that heavy pressure is needed, to apply the brakes at all strongly. ;

•"THIS is particularly the case as the 1 brake linings become giazad , through constant use. • Some of the mechanical four-wheel brakes are very hard indeed on the foot, and after driving for any length of time m hilly country, the effort of applying becomes almost painful, and certainly laborious. ' Fortunately the end of this trouble is m sight, and already many cars are fitted with the recently developed servo mechanism^ In this system of braking the pressure applied by the foot is multiplied by mechanical means, so that very light pressure is needed to operate the brakes to the fullest extent. One of the most interesting designs of servo mechanism has been introduced by the Hydraulic Cable Brakes Company, of London. This system is very different from any others previously intro- . duced, and its cost of manufacture is far. below that of many other systems already. on the market. ■ The brake pedal rod passes to. a connecting yoke, which is m turn connected rigidly to the main brake operating mechanism, so" that all four brakes can be actuated directly' by the : pedal. Into the yoke, however, fits a block connected by another rod, to an ordin^ary disc valve,. at the front enfl of the servo motor ca:aing. . As the .pedal travels forward when the brake" is applied, the disc valve Is turned, and a port m the valve registers on one side with the mouth of a' pipe entering the. inlet pipe of the engine, and with the mouth of a pas-^ sage- communicating, with a chamber m the. servo motor casing. .: With the valve m this position, the' vacuum.' existing. In the inlet pipe of the engine extract's all tiW air from the. servo motor, casing through the valve, with the . result that external air pressure . causes a" leather dia-

phragm to move -and-, • in- moving 1 , to increase the pressure on the brake mechanism through levers attached a.t one end to the brake mechanism and at the other to the centre of the diaphragm. . '■ When the brake, pedal is /released, the' yoke allows the -ordinary return springs of the brake shoes to bring these shoes to the normal position tirst... , •.'■ As the brake pedal travels back further, the disc valve closes the mouth of the suction pipe from the engine and places the port m the servo motor casing m communication with the atmosphere, thus, destroying the vacuum and allowing: the leather diaphragm to return to its original position. The disc valve is so constructed that the control of the servo mechanism is very sensitive and positive. The servo motor casing itself is simple, and no part calls for exceptionally accurate machining. Nor is the servo motor, as a whole, very large, so that it is easy to find a convenient place for. it on any normal chassis. . A test showed that the brake does not appear to have a servo motor mechanism at all, but merely seems to be very powerful considering the amount of effort expended by the driver, which is exactly .what a servo motor should be. •■■".. The graduation of brake shoe pressure is very nicely controlled, and increases or decreases m exact proportion to the movement of the pedal.i Moreover, .the brake shoes are freed simultaneously with the release of the pedal. The claims made for the mechanism are that the number oC working parts is reduced' to the minimum, and that the proportion of brake action supplied by the servo can be controlled absolutely by the pedal pressure. No lubrication is needed.