Abstract
Reasons are advanced why the processes of adhesion in braking may differ from those in traction, and limitations of adhesion-measuring machines are discussed.
It is shown how the nature of the variation of braking torque with velocity may affect the driver's manner of applying the brakes.
Incidence of pick-up from 2000 brake applications on three different types of brake (cast-iron tread, non-metallic tread, and disc) are studied to investigate the effect of load, the effect of moisture, and the effect of speed on adhesion. The incidence of pick-up is found to be less for a loaded than for an empty train and greater for wet than for dry rails, so confirming known facts and justifying the particular method of approach.
A complex adhesion/speed characteristic with a minimum value in the range 40–50 miles/h for dry tare conditions is shown to exist, which demonstrates that relations generally accepted to be applicable to braking are invalid. On wet rails incidence of pick-up is higher on the leading bogie and the suggestion is made that brake forces to this bogie could be reduced. Off-tread braking increases vulnerability to wheel sliding but with wheel-slide protection the exacting demands of dense suburban traffic are adequately met.
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