Disk Brakes for Motor Vehicles

Abstract

The development of disk brakes is reviewed from the early part of the twentieth century to the present time. A number of designs are discussed and the characteristics of disk brakes are compared with those of drum brakes. In particular it is shown that the outstanding feature of the disk brake is its anti-fade characteristic which gives it superiority over the drum brake in installations where space is restricted. The main part of the paper is devoted to a consideration of those factors which control design, and it is shown that rigidity is of paramount importance if a disk brake is to be used without an external servo. Methods of obtaining the required degree of stiffness are discussed and curves are drawn to show the influence of caliper stiffness and other lost motions on displacement ratio and brake pedal travel. The application of disk brakes to commercial vehicles is discussed and details are given of an installation on a passenger service vehicle. Consideration is also given to the hand operated disk brake on the transmission of commercial vehicles, and the paper outlines why this arrangement may become more general when disk brakes are used on the road wheels. Friction pad characteristics are discussed in relation to rate of wear and recommended horsepower absorptions. There are many problems associated with the installation and protection of disk brakes and these are outlined with emphasis on the need for attention to caliper position and wheel-bearing design. It is also suggested that although the exposed disk brake has given satisfactory results it may become necessary to shield the disk which would result in either poorer cooling or complex ducting.