Brakes have to be strong

Press, 12 October 1979, Page 9

Brakes have to be strong

Al! energy is created by heat. In a'motor vehicle we burn petrol to create heat and by a series of mechanical manipulations this energy propels the vehicle along the road. This energy is called kinetic energy. To stop the vehicle we must convert the kinetic energy back into heat and the amount of heat so produced depends on the weight and speed of the vehicle. For example, a 100 h.p. engine may accelerate a

1300 kg vehicle up to 100 km/h in a distance of 250 m. The question is, how fast can this vehicle be stopped? The brakes could probably stop it in 50m, which means that they would have to be five times more powerful than the engine. It is not generally recognised that the brakes of a typical modern truck may have to absorb up to eight times the rated brake h.p. of the engine when braking at maximum deceleration from maximum

speed. In other words, the stopping power has to be up to eight times greater than the pulling power. The weight to power ratio for passenger cars is less than that for trucks, but maximum speeds are greater and the energy square factor means that even car brakes have to absorb up to four times the rated maximum h.p. To dissipate the heat that develops in a brake system whilst stopping a car at 100 km/h, it would require an 18-tonne refrigerating plant to keep the brakes cool. Another way to explain this would be that the amount of heat generated by the brakes of every car driven around our city each day would heat an average house for 24 hours on a cold winter’s day, or, the amount of heat produced to bring a Mini to a stop from 100 km/h would boil a 1500 cc kettle in five seconds. Any mechanism which has the capability of pro-

during such dramatic, results as indicated above surely deserves regular and expert servicing. The servicing of engines requires continuous servicing and immaculate records are maintained to ensure that this takes place. The manufacturers of braking mechanisms strongly re-

commend that brake hoses, rubber seals, hydraulic brake fluid, and other working parts be replaced at regular intervals, and that the complicated mechanisms be continuously checked by experts to ensure that the vehicle is capable of being stopped in any emergency.