Car Brake Usage and Test Schedules

Abstract

An investigation of car brake usage has been made on different routes and also on hills of various slopes. From the results obtained on a number of cars it has been found possible to define two parameters V₀ and M, which describe the type of route and the manner of driving over the route respectively. V₀ is the speed at which it would be theoretically possible to drive over a route without applying the brakes. The range of values of V₀ was measured over short sections of four routes each approximately 100 miles in length. M was found to relate the average journey speed to V₀ and the maximum speed of the vehicle. The range of M was obtained by observing the behaviour of a large number of private cars over part of two routes.

The brake application and release speeds, the brake line pressure and the deceleration were measured at every brake application. The drag losses at given speeds were also obtained and the amount of energy dissipated at the brakes calculated. On any journey on a flat road the energy dissipated at the brakes per unit weight of vehicle is shown to be related to V₀, M and the journey speed. The work done by the brakes per unit weight of vehicle has also been measured when motoring down hills and shown to be dependent on the slope of the hill.

The results of the brake usage study have been used to formulate test schedules to simulate normal, fast overload driving, and conditions encountered when motoring down hills and Alpine passes. These tests are given in tabular form for cars of maximum speed in the range 70 to 120 mile/h.