With its new E-Class sedan in the coming summer, Mercedes-Benz is launching a new, digitalized generation of steering wheels: the capacitive steering wheel. Its rim contains a two-zone sensor mat that detects whether the driver’s hands are gripping the steering wheel. The touch control buttons placed in the spokes also work with digital signals. The first step towards the modern Mercedes-Benz steering wheel was taken by the then Daimler-Motoren-Gesellschaft more than 120 years ago: with the change from the simple steering crank or steering rod to the significantly more functional steering wheel. This led to the development of today’s high-tech command center, which enables the driver to steer precisely and at the same time operate numerous comfort and assistance systems comfortably and safely.
Developers and designers work hand in hand – and strive for every detail. For example, every millimeter of an electronic circuit board determines how elegantly the surface can be designed. The focus of development is on the appearance and, above all, the feel of the steering wheel. “Steering wheel design is a world of its own and a very special challenge that is often underestimated,” says Hans-Peter Wunderlich, Creative Director Interior Design at Mercedes-Benz.
The world’s first automobile, the patent motor car by Carl Benz from 1886, did not yet have what we consider indispensable in cars today: The steering wheel. The vehicle was equipped with only a simple steering lever. At that time, carriages were also more used to pulling the right or left rein to direct the horses in the desired direction.
The French engineer Alfred Vacheron is considered the inventor of the steering wheel. For the world’s first automobile race, the race from Paris to Rouen in July 1894, he had installed a steering wheel instead of the usual steering lever in his Panhard & Levassor, which was powered by a Daimler engine. He achieved his goal – better control – because the steering movement of the front wheels could be distributed over several turns of the steering column from a neutral central position until it stopped. This enabled more precise steering and thus higher driving speeds. Although the Frenchman was only in 11th place – his “volant” prevailed.
In 1900, Daimler-Motoren-Gesellschaft also equipped its Phoenix racing car with a steering wheel. The steering column was also tilted, which made it easier to operate. Nevertheless, every steering movement required a great deal of effort. In the Mercedes Simplex models introduced in 1902, there were additional levers on the steering wheel which had to be used to regulate essential engine functions such as ignition timing and mixture.
While the levers for manually adjusting the fuel mixture and ignition gradually became superfluous thanks to further development of the engines, an additional function from the early days of the car has remained unchanged to this day: the horn. The simplest form of car-to-x communication began with the balloon horn on the steering wheel rim, followed by the horn button on the steering wheel hub. The horn ring on the steering wheel spokes made its debut in the 1920s. It was standard until the 1970s and became increasingly filigree.
In 1949, the horn ring also took over the function of actuating the turn signals or the direction indicators that were common until the mid-1950s. To turn, it was simply turned to the left or right. Then an approximately 20-centimeter-long indicator arm swung sideways out of the body and indicated the direction of travel. These direction indicators, which seem bizarre from today’s perspective, were replaced by the orange-yellow flashing lights, which were activated by turning the ring via a central control unit.
In the 1950s, the steering wheel gradually became the central interface between car and driver – the control centre for new comfort functions and greater safety. Until the 1970s, the gearshift lever on the steering column remained a widespread way of operating the transmission. In 1955, the lever for the headlamp flasher was added as a further steering wheel function. Steering itself, however, was often exhausting, despite the large steering ratio and protruding steering wheel diameter. Mercedes-Benz therefore introduced power steering in 1958. In 1959, the company introduced a combined lever for indicators and headlamp flasher. In 1963 this lever was extended to include the functions windshield wipers and windshield washer system. Previously, the windshield wiper was activated with a pull switch on the top of the instrument panel.
The further striving for the best possible safety led to the steering wheel design changing significantly once again from 1981 onwards. The reason for this was the introduction of the driver airbag. Behind the protruding baffle plate was the new restraint system, which offered a safety standard never before achieved in the event of a collision. The developers were delighted, the designers pulled their hair out. After all, early airbags were voluminous, so the baffle plate had to be made considerably larger. In the course of further development, however, it was possible to fold the vacuum-packed airbag smaller and smaller, and the designers’ scope for design became greater again. In 1992 the driver airbag became standard equipment in all Mercedes-Benz passenger car models. On impact, the airbag inflates to a diameter of 720 millimetres and a volume of 64 litres within 30 milliseconds. Today, Daimler claims to be the most compact airbag on the market.
Another technical innovation was the multifunction steering wheel, which was introduced in 1998 together with the COMAND (Cockpit Management and Data) system. Not only the multitude of vehicle functions, but also the advance of new devices for information, navigation and entertainment required a rethink of vehicle operation and display concept. An important goal in the development of the S-Class 220 model series was to relieve the driver of so much work that he could concentrate on the essentials: the traffic situation and driving. With the new multifunction steering wheel, he controlled many systems and called up important information at the touch of a thumb. For the first time, the steering wheel was coupled with a car radio, car phone and a display in the middle of the instrument cluster, on which up to eight main menus appeared.
In 2005, the then new M-Class and S-Class models made their debut with a redesigned cockpit: the automatic selector lever moved from the centre console to the steering column. Additional steering wheel gearshift buttons enabled manual preselection of the seven gears. From 2008, the SL Roadster was available with the 7G-TRONIC sports transmission with steering wheel gearshift paddles.
With new functions, more and more cables, circuit boards and sensors found their way into the steering wheel. To hide them and the airbag, the steering wheels were rather bulky in the 2000s. In the course of time the design became more and more refined. From the initially polygonal shapes, geometric forms with a circle in the middle and flowing spoke shapes developed.
Image: Touch control buttons in the E-Class for the first time
The 2016 E-Class was the first car in the world to feature touch control buttons on the steering wheel. They allow the entire infotainment system to be controlled by finger wipes without having to take your hands off the steering wheel. Like the surface of a smartphone, the buttons are touch-sensitive and therefore react to horizontal and vertical wiping movements of a finger. This allows the driver to control all functions of the infotainment system easily and intuitively. Pressing the touch control buttons triggers the function selected with wiping gestures. A further four buttons per switch panel are assigned the familiar functions such as volume control and telephone control.
The new generation of steering wheels with capacitive hands-off detection is now also being launched in the E-Class. A two-zone sensor mat is located in the steering wheel rim. The sensors on the front and rear of the rim register whether the steering wheel is covered. No more steering movement is required to signal to the assistance systems that the vehicle is under control. Even the touch control buttons integrated in the steering wheel spokes now function capacitively. This mechanically reduces the control surfaces at the maximum possible extend.
The seamless control panels, which are divided into several functional areas, are integrated flush into the spokes. As with a smartphone, the touches are recorded and evaluated via capacitive sensor technology, enabling intuitive operation via wiping gestures and pressing the familiar symbols. The materials have been selected to enable operation even in an interior heated by sunlight. The system automatically detects where the finger is currently located. And the buttons are designed for temperatures of over 100 degrees Celsius.
The steering wheel is available in three versions: “Sport”, “Luxury” and “Supersport”. In the “Supersport” version, it is held by two double-decker spokes in black panel design, which are intended to be reminiscent of the wheel wing nuts of sports cars.
The size of the steering wheel has remained the same compared to the previous generation. Mercedes-Benz has developed fixed sizes for steering wheels. The steering wheel average is 370 millimetres (“supersport”) to 380 millimetres (“luxury”), depending on the version. The steering wheel rim is 29 millimetres wide and 42 to 44 millimetres deep. “The steering wheel rim is the secret kingmaker of a steering wheel,” comments Hans-Peter Wunderlich. “Its geometric design is a science that cannot be found in any textbook. The wreath must fit snugly in the hand. If it is a millimetre too much, it feels unpleasantly bulging. If it’s a millimetre too little, it feels like it’s starved. And that impression then clouds the overall feel of the car.”