Despite the protestations of the likes of Monsuier Buggati and Enzo Ferrari unless your car is a Landspeed record contender, brakes are just as important as engines.
The earliest evidence we have of the existence of the wheel dates back almost six thousand years. Presumably, it wouldn't have been too long thereafter when the necessity of impeding the downhill progress of primitive transport became somewhat painfully apparent. The first brake might have been some sort of chock or anchor, or perhaps a sprag attached to the chassis that could be stuck into the ground more in hope and desperation than any great technical achievement.
When the bicycle appeared a couple of centuries ago, the only way to slow it down was to wedge a foot between the front fork and the wheel. But that made deceleration an exercise in twisted legs and precarious balance,
In 1838 Kirkpatrick Macmillan, a Scottish blacksmith, invented the spoon brake -- a lever that pressed a block of wood against the "tyre" (actually an iron band). You've probably seen Western cowboy wagons with the same sort of arrangement.
It was natural that early motor vehicles would resort to the spoon brake, although some used a variation in which the block contacted one of the transmission pulleys. Either way the whole idea was and still is woefully inadequate. Not only was friction limited to what could be produced with a relatively small surface, but the action involved resulted in heavy side-loading of wheel or pulley bearings, and there was no real possibility of stopping evenly.
Next came the external contracting brake, essentially a steel strap or cable encircling the hub, with or without friction blocks between them. This increased drag area, and even had a rudimentary servo action as the turning of the hub helped tighten the strap. This idea was also applied to driveshafts. The idea still made an appearance late in the 20th century. Check out the Transmission brakes fitted to the likes of Land Rovers and such.
Shortly after the turn of the century, a huge improvement in stopping power appeared: the internal expanding drum brake. Attributed to Louis Renault (the French produced a great many of the early advances in automotive engineering), the principle is still in wide use. Many of today's cars have rear drums, and Louis Renault's flat cam arrangement for spreading the shoes can be found on modern motorcycles.
Originally, drums were steel stampings. They flexed, amplifing squeals, and were generally not too great in the stopping department. Cast iron drums showed up shortly after, and in 1919 Hispano-Suiza introduced finned aluminum with iron liners and arrangement used on most Racing Vehicles until the 1950's.
It should mentioned that early cars had rear brakes only. Due to the writings and ramblings of many great Engineers and theorists, It was believed that applying drag to the front wheels would cause swerving and instability, just the opposite of what we know now, Many even believed the car might somersault over its front wheels. Stopping power was greatly limited because of weight transfer. But the idea of braking the wheels that also steered daunted designers for many years, so hard stops resulted in lots of spins and tire skidding until four-wheel brakes finally caught on in the '20s.
All drum brakes have some self-energizing action as rotation tends to wedge the leading shoe against the drum. But, especially with the elephantine conveyances of the Edwardian Era, more help was needed. In 1920, a servo design showed up. This had a leading shoe linked to a trailing shoe with no anchor between so that the rotational action of the first made the second apply forcefully. In 1922 the idea of a star wheel adjuster in the link was adopted.
Other means of increasing the power of mechanical brakes were also tried. After all, it was quite a bit to ask of a human leg to haul down two or three tons of iron from the considerable speeds of which cars were already capable.
Bugatti used a novel approach: The actuation cable was routed in such a way that the twisting of the axle on decel helped pull the cam lever (It was novel but Bugattis were never renowned for their stopping prowess). Two other premium makes, Rolls-Royce and Hispano-Suiza, employed rotational power from the transmission. As the brake pedal was depressed, a clutch was engaged that tried to pull the brake actuating rods with it.
The idea of using engine vacuum to supplement muscle power was developed from about 1920 onwards to what most cars have now. Hydraulic boost, with pressure taken either from the power steering or an electric pump which is a relatively recent addition. The electric pump has the advantages of being more compact and giving numerous fully augmented stops from psi stored in an accumulator should the pump fail.
Drums did a pretty good job, but there was room for improvement. Heat dissipation was the biggest problem -- if you wanted to keep something warm, you could hardly do better than to place it in a cast iron pot. And, as styling trends dictated sheet metal and lower bodies enclosing the wheels, air flow over drums was reduced,as potential top speeds increased. Water was another problem. You could lose stopping ability altogether after driving through a flooded street.
Enter the disc brake, an idea that's been around since the 1890's, believe it or not. One of the earliest versions was used on the front wheels of an electric car designed by Elmer Ambrose Sperry in '98, where an electromagnet forced a pad against the rotor.
The first design we know of that remotely resembles what we have today appeared on the '49 Crosley. After the style of aircraft brakes, the disc was clamped between two round pads. In the mid-'50s, after girlings experiments with racing disc brakes both the British and the French started installing disc brakes as standard equipment on several makes.
At first versions were of the four-piston, rigid-caliper type, but by the late '60s the single piston variety started to show up. While the pads may not have lasted as long, there was only one quarter the potential for fluid leaks, and the calipers were lighter, simpler, and less expensive.
Of course, the evolution of friction materials has been a crucial part of brake history. Spoon brakes usually had wooden blocks, but they were sometimes supplemented with a leather lining. Band-type brakes were either metal-to-metal, or used wood or leather, too. The earliest drum stoppers had iron shoes against steel, then some strange things were used, such as the walrus hide linings of the English Wolseley.
The credit for first taking the scientific approach to friction materials goes to the Englishman, Herbert Frood, and Ferodo, the company he started early in 20th Century. Using a water wheel-powered friction test machine set up in a shed, Frood experimented with numerous materials (even cotton!) and bonding agents. In 1908, he hit upon resin-impregnated woven asbestos reinforced with brass wire, and the era of safe stopping finally began.
But asbestos isn't ideal. Fade is a major problem, and in recent years we've learned to worry about the health effects of breathing the stuff. Sintered iron linings were used in heavy-duty applications to handle the heat, then we got semi-metallics, which had some teething problems such as excessive rotor wear and squealing. New formulas are vastly improved, and now we're seeing non-asbestos, non-metallic materials such as kevlar that seem to do everything right.
The hand lever gave way to the pedal early on, probably due to the force you could excert as much as ergononics. but mechanically applied set-ups -- cams, cables, and levers -- remained for quite a while. But no matter how clever the design, they were almost impossible to balance perfectly, and required constant adjustment, Hydraulics intrigued designers from about 1897 onward. but It took many years to develop reasonably dependable systems, however, and the first American car with fluid ressure-actuated brakes was the '21 Dusenberg.
Mechanical brakes had serious drawbacks, but they'd always stop the car eventually, something that couldn't necessarily be said for early hydraulic systems. Henry Ford was so adamant on this point that the vehicles that bore his name didn't get fluid brakes until 1939, long after almost everybody else had decided the pros far outweighed the cons.
In 1967, it was federally mandated that all cars sold in the U.S. have two separate hydraulic circuits. But that wasn't when they first appeared. Cadillac, Volvo had developed this backup safety system long before
The typical front disc/rear drum arrangement brought with it the need for additional control of the apply pressure. Besides proportioning (which had been used before on four wheel drum cars to mitigate the rear wheels' tendency to lock up on hard stops, but was even more important for the disc/drum combo because discs have no self-energizing or servo action), a metering function was necessary to keep the fronts from doing all the work. Since there's virtually no clearance between the pads and the rotor, disc brakes start dragging the instant there's any pressure in the system, whereas there's space to be taken up before drums begin to apply.
Proportioning was brought to a higher degree of development with the load-sensing proportioning valve, which limits pressure to the rear brakes according to the distance between the chassis and axle. The first one saw life on an early '70s Fiat.
Anti-lock braking systems are becoming de-riguer today. The idea is far from new -- patent applications were made for mechanical versions in the mid-20's, and electronic systems were offered for a while in the early 70's, but neither was dependable or affordable enough to be accepted. With the advances in technology that have occurred in the last decade, however, ABS has become a reality.
How does it work? Basically, the system monitors the speed of each wheel, and if one slows down more than its brethren during brake application, hydraulic pressure to that wheel or circuit is released, then reapplied up to 15 times per second, which prevents lockup. Not only does this greatly increase control during hard deceleration (a locked wheel can't be steered) and reduce stopping distances ( a locked wheel exhibits less friction than a rotating one), it can also save an expensive set of tires from destruction in a panic stop.
Ford gets the prize for being the first company to embrace RABS (Rear Anti-lock Braking System -- at less than $100 per vehicle for about 80% of the benefit of a four-wheel system, it was a safety bargain). In '87, it appeared on its F-series pickups, Broncos, and Bronco II's as standard equipment. Us Europeans though prefer not to be shortchanged by the bean counters, and most Euro cars use 4 wheel anti-lock
The future? It's safe to say we'll be seeing drum brakes at the rear for a long time. After all, they have much less work to do than the fronts, less still with FWD, and they make parking brake design easy.
As far as the friction-producing components, most of the hydraulic system, and boost are concerned, you can expect the same gradual evolution you've become accustomed to. Which is not to say there'll be nothing to keep up with. The number of different brake designs out there is amazing, and it'll continue to grow.
Mercedes have brought out the strange brake assist, this is a system which realises when you are in panic stop mode and excerts maximum force to the brakes. The theorise that many people do not use maximum braking power for fear of skidding, and losing control and hence the computer can assist in shortening stopping distances. Quite why people are afraid of the brake pedal in these days of ABS beats us as we all know that all you have to do in an ABS equipped car is jam on the brake as hard as you can and the electronics will bring you to a quick straight stop.