Brake Usage in a Heavy Vehicle

Abstract

This paper summarizes measurements made of the duties imposed on the brakes of a heavy vehicle when driven over a continental route which included the Susten and other passes in Switzerland and in Austria. On the Susten Pass an investigation was made of the effect of driving in various gears.

The following data were determined for each brake application: vehicle deceleration, rate of energy dissipation and total energy dissipated at the brakes, the energy lost by drag losses, the energy absorbed by engine braking, and the temperatures attained in all drums and linings. Measurements were also made of the amount of energy imparted to the vehicle when it was accelerated by the engine between brake applications.

Analysis of the results shows that a heavy vehicle travels at a fairly uniform speed down the mountain passes and consequently only a small percentage of the total energy dissipated is given to the vehicle by the engine in between braking. The work done at the brakes varied between 15 and 62 per cent of the total energy dissipated, the proportion depending on the steepness of the gradient and the driver's choice of gear for the descent. The maximum amount of work done at the brakes (5·66 times 10⁷ ft.lb) was on the Susten Pass when the vehicle was driven in third gear. During such a journey the drums attained an average temperature varying between 350–400°C while the linings reached an average temperature in the range 275–350°C.

A theoretical analysis is outlined which permits calculation of the temperatures attained at any stage of the descent. This analysis requires a knowledge of the work done in each brake application, together with cooling rates, and gives results in good agreement with the observed temperatures on the Susten Pass.

Little difference was observed between the driving behaviour of the two drivers on the various passes; one driver made more brake applications per mile than the other but the duration of each application was less. Consequently, both applied their brakes for approximately the same total time and dissipated similar amounts of energy at the brakes when both used the same gear over the same descents.