1927-01-01

Internal Wheel-Brakes for High-Speed Heavy Vehicles 270052

The paper deals primarily with internal wheel-brakes for trucks and motorcoaches, but passenger-car brakes with similar characteristics are considered possible. A simple two-shoe internal-expanding type developed mainly by empirical methods is found to be the most practical solution in spite of relatively low circumferential contact. Self-energization is necessary to reduce driver effort with normal pedal-travel. The factors controlling self-energization are explained in detail, and the effect of difference in the coefficient of friction of brake-linings is noted.
Distortion of brake-drum and brake-shoes must be limited by a drum of heavy section and by extremely rigid shoes. Rotation of cam with respect to self-energizing shoe should tend to deflect the toe of shoe away from brake-drum surface. A floating cam is necessary to balance unequal wear on the brake-shoes and assure adequate braking with normal pedal-pressure.
High-grade cast-iron brake-drums have been found to be generally more effective than steel drums with fabric-lined brakes.
Air-brakes of the same general design, with metal-to-metal surfaces, are used in all four wheels of the six-cylinder motorcoach, but the floating-cam construction is unnecessary in this case. The metal-to-metal combination of high-carbon drums with low-carbon shoes is found to be effective under all weather conditions, and is regarded as the solution of the problem of brakes with adequate life and effective heat-dissipation for heavy, high-speed motorcoaches.
Various problems of metal-brake design were brought to attention in the discussion, but most interest was shown in the questions of the relative cost of brakes of different types and of heat-dissipating qualities.

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