The brakes of the automobile

The automobile is designed as a vehicle to move you forward. However, an equally important function is that you can also make the car stop (quickly).

As cars have been developed to go ever faster, different braking systems have been developed as well. Before we get into the details of brakes, first the simple question: 'Why do cars have brakes?' The first thought is 'to reduce speed or to stop'. For example, in a situation where someone is crossing the road in front of your car and you want to avoid a collision, or when you have to stop for a traffic light that turns red. But if you look more deeply into the question, it becomes clear that brakes not only let you stop quickly, they also let you drive faster! If you did not have brakes, you would drive very carefully and slowly in the city, with its heavy traffic, intersections and traffic lights, so as not to cause a collision or fly out of a corner. Brakes give us the ability to stop or slow down when needed and therefore make it possible to drive faster! If there is no other traffic for the first 300 meters in front of you, you can even accelerate for a moment because you know you can brake afterwards. So you actually go faster thanks to brakes! In this statement lies the logic that the faster the car goes, the more powerful the braking performance has to be.

The first brake

The first brake was nothing more than a block of wood designed to rub against the iron band around the wooden wagon wheel by means of a lever (see drawing). In this way, the ancient Romans were already slowing down and stopping their carts more than 2000 years ago.

Around 1885, in order to improve ride comfort, people began replacing the iron band around the wooden wagon wheel with a solid rubber tire. This was the moment when the wooden block could no longer be used as a brake, since it would destroy the solid rubber. With the solid rubber tire, the wooden block was replaced by a metal plate, as can be seen, among other places, in the Louwman Museum on the 1895 Benz 5HP Phaeton.

It was Gottlieb Daimler who in 1889 was the first to use a steel band or cable wound around a rotating drum or rim mounted on the rear axle or rear wheel. By pulling a lever or pressing a pedal, the loose end of the band or cable is pulled, and the rotating drum or rim on the rear axle or rear wheel is braked. The band was fitted with friction material, often leather, but that did not have a long service life. Maintenance was required every 350 km.

The drum brake

In 1901 Wilhelm Maybach developed the first concept of the drum brake. An internal ring of friction material was pressed against the inside of the drum by means of rollers. This system was used on the 1903 Mercedes Simplex 40 hp, but it was not a success.

Meanwhile, in 1902, Renault developed the definitive drum brake as we know it today. Renaults mechanical drum brake had two curved shoes, hinged on one side and resting on a cam on the other side. When operating a lever or pressing the brake pedal, the cam rotates and presses both shoes against the inside of the drum (see image). When hydraulic brakes were later introduced, the cam in the drum brake was replaced by a wheel cylinder.

In the beginning the drum brake was only used on the rear wheels because braking on the front wheels can result in skidding and make the car uncontrollable.

The Dutch manufacturer Spyker was the first in 1903 to apply brakes on all four wheels on the Spyker 60 HP (see image). Shortly afterwards, other brands also followed with four wheel brakes. To be able to adjust the braking itself and to prevent skidding, the mechanical brakes on the rear wheels were often operated with a lever next to the driver and the brakes on the front wheels with a brake pedal. The interplay between braking on the rear wheels and on the front wheels required considerable skill and experience, an action that we can now hardly imagine.

The most impressive brake drums were undoubtedly those used on racing cars, such as the Auto Union and Mercedes-Benz Silver Arrows in the 1930s (see the attached photo of the 1937 Mercedes-Benz W125).

The gigantic drums, with a diameter of 40 cm, were fitted with fins and vanes for optimal cooling and to prevent brake fading. This phenomenon occurs when the friction material on the brake shoes becomes too hot and the material starts to glaze. In extreme cases the brake drums can even warp, causing the braking effect to be greatly reduced or even completely lost.

The hydraulically operated brake

The mechanically operated brakes, with their control rods running to the front and rear wheels, had the disadvantage of being heavy and requiring frequent adjustment. In 1918 this changed with the development of the hydraulically operated brake, an invention by the Scot Malcolm Lougheed. To make the pronunciation of his surname easier, he changed his name to Lockheed in 1920, at the same time as founding the Lockheed Hydraulic Brake Company. Compared with the mechanically operated brake, the hydraulically operated brake was light, required far less pedal effort, and distributed the braking force over the four wheels much more evenly. Lockheeds hydraulic system was a major improvement and was first used in 1921 on the Duesenberg Model A. In the 1930s hydraulic brakes finally became standard on virtually all cars.

The disc brake

Because drum brakes can easily overheat at high speeds and with frequent use, people were already looking into the possibility of the disc brake in the early 1900s. However, due to insufficient knowledge of, among other things, the right material for the brake disc and the brake pad lining, this was not a success.

It was only in the early 1950s that Dunlop developed a reliable disc brake for the Jaguar C-Type racing car. Thanks to these disc brakes, Jaguar achieved great success in the 24-hour Le Mans race during that period. In 1955, disc brakes were used for the first time in France on the Citroen DS 19, and in 1956 the Triumph TR3 became the first British production car with modern disc brakes. The first German production car with disc brakes was the 1961 Mercedes-Benz 220 SE. Today, disc brakes are in general use. For fast or heavier passenger cars, both the front and rear wheels are fitted with disc brakes, with the front wheels often using ventilated versions.

The ABS system

To further improve the braking of the car, especially on wet roads, black ice and snow, ABS (Anti-lock Braking System) was introduced. It is an automatically controlled system based on the principle of pumping the brakes, a technique that used to be applied by experienced drivers. The automatic control of the ABS operates at a speed that a human cannot achieve. The system ensures that during braking the car’s wheels maintain traction with the road surface, preventing locking (no rotation) and uncontrolled skidding of the wheels. As a result, the car remains steerable and can avoid obstacles.

ABS was invented in 1929 and first used in the aviation industry by the French car and aircraft pioneer Gabriel Voisin. For airplanes, ABS was a breakthrough and improved braking performance by 30%. It also prevented the common problem of tires overheating due to locking. From 1970 onward, the first ABS-equipped cars from Ford and GM came onto the market.

Regenerative braking

Another braking principle is regenerative braking in electric or hybrid electric cars. With traditional braking, friction converts the kinetic or motion energy mainly into heat, which is lost unused as waste. With regenerative braking, the electric motor acts as a generator (dynamo) and generates electricity. Supplying this electricity places a load on the generator, which produces a braking effect. The electrical energy generated during braking is stored in the batteries and then used to drive the car electrically. Regenerative braking therefore increases the driving range of an electric or hybrid electric car.

Regenerative braking was also introduced in F1 motorsport from 2009, with the so called Kinetic Energy Recovery System (KERS). This KERS system ensures that the braking energy that would normally be converted into heat is stored to be used later. The energy is stored using a flywheel (mechanical) or by means of a generator and a battery (electric). The stored energy in the flywheel or the battery is then used at the desired moment to provide extra power (acceleration) for the F1 car. The system is not ideal. Disadvantages are that the KERS design is complex, the components add extra weight (35 kg), and the conventional friction brakes are still needed.

An example of an F1 car with KERS is the Toyota TF109.

As early as 1903, regenerative braking was already being used on electric trams and later also on trains. In this system, the electric drive motors were also switched to operate as generators to stop the tram or slow it down on descents. This provided the tram company with economic and operational benefits.

The necessity and significance of good brakes for automobiles were not recognized as such by every car manufacturer. In response to a customer who complained about the mediocre brakes on his Bugatti, Ettore Bugatti made the remarkable statement: 'I build my cars to drive, not to stop!'.

The Spyker 60HP, Benz 5HP Phaeton and Toyota TF109 mentioned in this article can be viewed at the Louwman Museum.

Alfred Koeten