History of the Development of Brakes

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History of the Development of Brakes The first brakes were drum brakes. They were metal upon metal, and made a terrible noise, although they did work. Since then, brakes have been made with asbestos, which is heat resistant, hard wearing, and relatively silent. Drum Brake (1890s~1980s) The working parts of a drum brake are contained in a hard metal drum that is attached to the hub of a wheel and revolves with it. Inside, but unattached to the drum, are a pair of stationary curved brake shoes that are normally held away from the drum by springs. When the brake pedal is depressed, fluid is forced through the brake lines and into the wheel cylinder. Pushrods in the cylinder then apply pressure to both shoes, overcoming the spring tension and pressing the shoes against the drum. Hydraulic drum brakes can also be mechanically activated as parking brakes by a cable attached to the lever. When pressure is removed from the brake pedal, springs on the brake shoes force the shoes back to their normal released position. This movement of the shoes forces the pistons inward, returning the fluid to the master cylinder reservoir. Power Brakes (1940s~present) Power brake units used on passenger cars are of four general types: vacuum suspended; air suspended; hydraulic booster, and electro-hydraulic booster. Most power brakes use vacuum suspended units, which contains a large vacuum-powered booster device to provide the added thrust to the typical power-brake. Pressure on the brake pedal pushes forward a rod connected to the pistons of the two master cylinders. The pistons begin forcing fluid into the front and rear brake lines. At the same time, the brake-pedal pushrod positions the vacuum-control valve so that it closes the vacuum port and seals off the forward half of the booster unit. The engine vacuum line then draws off the air, creating a low-pressure vacuum chamber. Atmospheric pressure in the control chamber then pushes against the diaphragm, dividing the two chambers. The pressure on the diaphragm, which is locked to the pushrod, forces it forward, supplying even more pressure on the pistons. The safe driver is always ready to apply the total force needed to stop their vehicle, even if the engine quits (removing the power assist). Disc Brake Disc (1970s~present) Brakes use a clamping action to produce friction between the wheel and the suspension members which hold the wheel. Firmly mounted to the spindle, the caliper works like a c-clamp to pinch the rotor which is attached to the spinning wheel. "Floating" calipers allow themselves to move slightly when the brakes are applied, because only one pad moves (in relation to the caliper).

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