PH Origins: Anti-lock brakes

The aviation industry is often cited as the birthplace of anti-lock braking systems. The reality, however, is a little different...

Ask automotive enthusiasts about the history of anti-lock braking systems and you'll likely notice a theme to their answers. Most will say how the technology originated from the aviation industry in the 1950s, then arrived in the automotive market in 1966 with the launch of the Jensen FF - some 12 years before Mercedes-Benz rolled ABS out in earnest.

These answers would not surprise those with an interest in automotive technology. But, while not entirely incorrect, the concept of ABS predates all of the above by decades - and, in fact, didn't originally involve the aviation industry at all.

In 1908, Surrey-based engineer James Edward Francis submitted a patent detailing a system that focused on how to stop the driving wheels of a train slipping while accelerating. Braking, however, was also a problem in that era. The primitive systems available often caused the wheels to lock or decelerate quicker than the train, resulting in an uncontrolled slide. This would damage both the rails and the wheels, or cause more significant damage to whatever the train subsequently ploughed into.

Francis was aware of this issue, too. Consequently, having devised a system that could monitor wheel speeds and reduce the vehicle's power output to maintain traction, he detailed how it could also be employed to avoid skidding. If the brakes locked when 'an emergency braking pressure is employed', it would automatically release then re-engage them, preventing skidding and cutting stopping distances.

His patent, published in 1909, marks the established introduction of the concept of anti-lock braking. Whether Francis's idea ever saw action is unknown but it laid the groundwork for all future anti-lock and traction control systems.

Similar patents followed but, predominantly, many sources alternatively cite engineer and aviation pioneer Gabriel Voisin as the inventor of ABS. It is often stated that he conceived a system, at some point between 1920 and 1929, for use in aircraft. Voisin had abandoned aircraft manufacture by that point, however; the use of his aeroplanes in World War One horrified him to the extent that he shuttered any related activities in 1918.

He did promptly redeploy his engineering talents in another fast-moving field, though - that of the automobile - and built a reputation for developing innovative, fast cars. This shift attracted new talent, including a French Lieutenant called Pierre Cayla. He was well versed in speed and risk, having been a pilot since 1911 - one that was responsible for flying the Voisin 'Canard' seaplane during French naval trials in 1912.

Cayla was also an experienced and talented engineer and, if you trawl the archives, it is his name that is attributed to a patent - filed on 1 February 1923 and approved on 4 August 1925 - describing a braking system with an anti-lock feature.

The system, designed primarily for 'vehicle wheels, and particularly for steering wheels of motor vehicles', was a hub-driven, hydraulically operated, drum brake set-up. When driving along, a wheel-driven pump would draw fluid from an internal reservoir and pump it through a bypass valve - straight back into a reservoir. When the driver triggered the brakes, a linkage would close the bypass valve. This would direct the pressurised fluid into the brake cylinders, which would push the shoes into contact with the wheel-mounted drum and slow the car.

Because the pressure to operate the brake was produced by the wheel-driven pump, it was impossible for it to lock. 'The braking ceases at the same time as the rotation of the wheel,' stated Cayla, 'and therefore cannot occasion the blocking of the latter'. This is later described, quite rightly, as 'a considerable advantage in road operation' - particularly with regards to maintaining steering control, a key feature of modern ABS.

This system would presumably work in conjunction with a conventional set-up fitted on the driveshaft, or one axle, for parking and hill holds. It appears that it was at least tested, with references being made to it in myriad titles - including LJK Setright's 'The Designers: Great automobiles and the men who made them'.

ABS development escalated in the '40s, as jet power and aerodynamic developments increased landing speeds - upping crew workloads, stopping distances and the risk of tyre damage. Boeing promptly equipped its swept-wing B-47 Stratojet with Hydro-Aire Hytrol ABS. Dunlop followed with its Maxaret system in 1952, which could reduce stopping distances by 30 per cent. It featured in a wide range of aircraft, including the Avro Vulcan. In some cases, developers of these systems referenced Francis's original patent from 1909.

It was around this time that the technology began trickling back into cars, as the benefits became clear and technology advanced. Ford tested a system on the rear axle of the Mark II Continental, in 1954, but it was too heavy and expensive. Several other efforts were made but it was the Jensen FF that grabbed the headlines, in 1966, by being the first production car to offer Dunlop Maxaret ABS. The single-channel, single-sensor system would reduce unwanted sliding by releasing the brakes if all four wheels stopped turning.

It took until late 1970 for a multi-channel ABS to be offered to the car-buying public. Chrysler was first past the post with its effective Bendix 'Sure-Brake' set-up for the Imperial, which could monitor individual wheel speeds and modulate braking at each front wheel and across the rear axle.

Then, in 1978, Mercedes rolled out its optional Bosch-developed ABS in the W116 - and the acronym of 'Anti-Blockier System', later known as 'Anti-lock Braking System', was born. Ten years later, around a million Mercedes alone were equipped with ABS. As advancements reduced the cost and complexity of the hardware, its implementation spread at a vast rate of knots - but, ultimately, the principle remained the same as that established by Francis in 1909.

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