The F 400 Carving follows in the tracks of other vehicle studies such as the F 200 Imagination and F 300 Life-Jet, which showcased new steering and chassis concepts in 1996 and 1997 respectively: "drive-by-wire" and "active roll control" were just two of the concepts central to these automotive research projects. The research engineers and scientists at DaimlerChrysler have perfected these ideas in the F 400 Carving and are proud to unveil an entirely new system which further enhances active safety and dynamic handling and gives an even more exhilarating driving experience.
20-degree wheel camber for safe and reliable cornering
The "Carving" epithet already hints at the capabilities of the chassis technology in this research vehicle. Each time the car enters a corner or bend, two of its wheels tilt inwards, riding on a tire tread that has been specially optimized for cornering and has a high friction coefficient for optimum directional stability and road adhesion. The dynamics are reminiscent of the movements performed by alpine skiers using carving skis.
The computer-controlled system in the F 400 Carving varies the camber angle on the outer wheels by between 0 and 20 degrees when the car is cornering. The inner wheels and the vehicle body remain in their normal positions.
"Active camber control" is the culmination of a research project spanning several years. It all began with computer simulations and bench tests. But now the time has come for research out on the road.
The F 400 Carving is something of a mobile research laboratory for the Stuttgart-based automotive engineers. They aim to use the open-top two-seater to further research the potential of novel chassis systems and to open up new avenues in chassis technology for the passenger cars of the future. Initial test drives and measurements have delivered extremely encouraging results.
Compared to a modern car chassis, the active camber control in the F 400 Carving enables up to 30 percent more lateral stability and 15 percent more longitudinal forces. The numbers back up these claims: whilst the maximum lateral force on the wheel is usually about 6200 Newtons when the camber is zero degrees, this figure rises to 6900 Newtons when there is a negative camber of 10 degrees and as high as 7800 Newtons when the negative camber is 20 degrees.
Thanks to the high level of lateral stability on the outer wheels during cornering, lateral acceleration in the F 400 Carving is up to 28 percent higher than in sports cars that rely on conventional chassis technology. When the outer wheels of the F 400 Carving are tilted inwards by 20 degrees during cornering, the two-seater achieves a maximum lateral acceleration of 1.28 g.
This impressive figure is not just an indication of high cornering dynamics and sporting agility, it also signals a substantial improvement in active safety, particularly in emergency situations such as cornering at (excessive) speed or sudden obstacle-avoidance maneuvers. The research car remains more directionally stable than a car equipped with conventional chassis technology. What’s more, it does so for longer and at a higher speed.
Tires: the concept of asymmetry
The tires are a major contributing factor to these results: active camber control enables a totally new concept that, for the first time and without compromise, combines the benefits of a passenger car tire with those of a motorcycle tire. Asymmetry is the principle behind this new tire technology, jointly developed by engineers from DaimlerChrysler and Pirelli: the tread pattern, tread blend and contour are all asymmetrical.
The most remarkable feature on the inside of the tire is the rounded-off tread which ensures superlative handling when cornering. The outer shoulder of the tire has a tried-and-tested car tread pattern, offering excellent straight-line stability and low road noise. For the first time, the experts have succeeded in harnessing the benefits of an established physical theory, according to which, at large camber angles, a tire with a curved tread can transmit greater lateral forces than conventional tires. The asymmetrical tread is made possible by the fact that the insides of the tires only come into contact with the road when the active camber control tilts the outer wheels inwards during cornering. This leaves the engineers one clear objective to focus on when harmonizing and optimizing the inner shoulders of the tires: superlative cornering safety.
Rubber blend: tire tread with different friction zones
The rubber blend used for the F 400 tires plays an equally important role, since the softer inner-tread zones enable even greater transmission of the forces – i.e. even better road adhesion – when cornering. These "high-friction compounds" are not usually suitable for car tires as the soft rubber blend is more susceptible to wear than the conventional rubber compounds used. Therefore the new tire would not normally achieve the mileage of which today’s tires are capable.
The active camber control in the F 400 Carving makes up for this short-coming: thanks to this innovative technology, the softer insides of the tires only come into contact with the tarmac when the car is cornering and so do not wear as quickly. In contrast, the rubber compound the experts developed for the outside of the tire is much harder, having been optimized with regard to longevity, straight-line stability and road roar.
In other words, thanks to its asymmetrical contour and special rubber blend, the newly developed tire provides the answer to a previously unresolved conflict of aims: maximum cornering safety and superlative driving dynamics on the one hand; high mileage and superb straight-line stability on the other. For the first time, therefore, two different concepts come to fruition in a single tire, thanks to active camber control.
Active computer-controlled camber adjustment and asymmetrical tires have brought the DaimlerChrysler engineers a major step closer to achieving one of their primary objectives: enhancing already exemplary levels of active safety and driving dynamics for the benefit of future models. But this is just the beginning of what promises to be an extremely fruitful research project: alongside greater lateral acceleration and exemplary cornering stability, this innovative technology provides a whole host of other on-road benefits:
- If there is a risk of skidding, due to understeer or oversteer, the system briefly tilts one or more of the wheels by a precisely calculated amount, thus boosting the lateral forces and stabilizing the car. This means active camber control has the potential to enhance the effect of ESP®. Coupled with electronically controlled steering, which allows automatic steering correction, this can greatly reduce the risk of skidding.
- In the event of emergency braking, all four wheels on the research car tilt at lightning speed, leaving only the insides of the tires – with friction-optimized rubber-compound tread – in contact with the road. This reduces the stopping distance from 100 km/h by a good five meters.
- If there is a risk of aquaplaning, the system is capable of optimizing the tire contact patch by an appropriate amount. A wheel camber of just five degrees is enough to achieve the desired effect: a substantial reduction in the risk of aquaplaning. A new breed of sensor system, currently under development at DaimlerChrysler, detects the water layer on the road surface and sends the measured values to the ECU at the heart of the active camber control, enabling the system to automatically adjust the tilt of the wheels to suit the road conditions.
- Asymmetrical tires would also prove beneficial in winter as the special rubber blend and tread pattern combine to provide extremely high traction as well as short stopping distances and superlative directional stability. To ensure safe driving on snow or ice, the driver can tilt the wheels at the push of a button, thus enabling the car to run solely on the insides of the tires, for better road adhesion.
Tilting hub carriers with hydraulic cylinders
Active computer-controlled camber adjustment is possible thanks to two-piece hub carriers and a powerful hydraulic system. Each hub carrier consists of one tilting section and one rigid section: the wheel locating compo-nents of a double-wishbone suspension system are attached to the rigid inside sections whilst the wheel bearings and the brake caliper linkages are located on the tilting outside sections. During cornering, piston rods in dual hydraulic cylinders press against the tilting hub-carrier sections on the outer wheels, causing them to tilt outwards at the bottom. In this way, the wheel camber can be varied between 0 and 20 degrees, depending on the road situation.
The driven rear axle on the F 400 Carving is designed in much the same way as the front axle, the variable-length axle shafts being the only major difference.
At the heart of the hydraulic system is an axial piston pump with a working pressure of up to 200 bar. Servo valves on the wheels’ dual cylinders regulate the oil flow to control the degree of cylinder retraction and extension. If the driver adopts a dynamic driving style, rapid cylinder movement is required and in this case the pump receives assistance from a hydraulic pressure reservoir. A limp-home function is also provided: special shut-off valves interrupt the oil flow to the hydraulic cylinders and use the pressure available in the system to set the wheel camber angle to zero degrees.
Steer-by-wire and brake-by-wire
Active camber control, as featured in the F 400 Carving, represents a major step forward in chassis development for future car models. Even in its own right. But the Stuttgart-based engineers are taking things a step further, marrying this technology to a whole host of other, equally pioneering systems. The key to it all is drive-by-wire. The F 400 dispenses with mechanical connecting components such as the steering column, with all the shafts and joints that go with it, and the linkage between brake pedal and brake booster. In their place are wires which transmit the driver’s steering or braking inputs by purely electronic means.
- Steering: The electronic steering wheel is equipped with two inductive angle sensors that pick up each movement of the steering wheel, convert the measured angle into an electrical pulse and transmit the signal to the research car’s microcomputers via data line. The computers evaluate these and other current sensor signals, using the data to specify setpoints for the front axle steering angle. In critical situations, the drive-by-wire system can also override the driver’s steering inputs, to keep the car safely on an even keel. Two electric motors, which are directly connected to the rack-and-pinion steering, move the wheels of the F 400 Carving. This is why the automotive researchers refer to an "electric rack" – a new feature which they developed together with the steering experts from Mercedes -Benz Lenkungen GmbH. Each electric motor generates half of the steering torque. In the event of a malfunction, one of the motors alone can assume total responsibility for the steering functions. This is therefore a redundant system, designed to provide maximum functional reliability. Even the research car’s power supply is based on a dual-system concept: besides a standard (12-volt) on-board power supply, the F 400 Carving also has two 42-volt systems which are primarily used for the electronic steering.
- Brakes: Brake-by-wire is already very much a reality at Mercedes-Benz. The Sensotronic Brake Control (SBC) high-pressure brake works on the following principle. When the brake pedal is depressed, an electrical signal is produced which is forwarded to a microcomputer. A sophisticated sensor system ensures that the microcomputer receives a continuous feed of data about the car’s driving dynamics. The electronic system can therefore calculate and modulate the brake pressure for each wheel, according to the situation in hand. The end result is significantly enhanced braking safety when cornering.
Alongside Sensotronic Brake Control, the braking system in the F 400 Carving contains a further technical highlight that really sets it apart: the brake discs (330 millimeters in diameter) are made of carbon-fiber-reinforced ceramic, a high-tech material that is capable of withstanding extreme temperatures of between 1400 and 1600 degrees Celsius. It is also around a third lighter than cast iron.
Suspension and damping: next-generation ABC
The new active hydropneumatic (AHP) suspension system also sees the research engineers entering uncharted territory: the F 400 Carving is being used to test this possible alternative to future generations of the active suspension system which is currently fitted as standard in the Mercedes S-Class, CL-Class and SL-Class models.
In contrast to the today’s Active Body Control (ABC) system, in which active control of the forces between the vehicle body and the wheel is performed by adjusting the spring action, the active hydropneumatic system influences both the suspension and the damping, adapting them at lightning speed to the situation in hand. The benefits of this system include an even higher level of active safety and enhanced ride comfort.
Engine and transmission: Mercedes technology with new detail solutions
Beneath the engine hood of the F 400 Carving is a state-of-the-art 3.2-liter V6 powerplant, a tried-and-tested unit installed in several other Mercedes model series. This six-cylinder engine differs from the standard production version in just one respect: the research engineers have equipped it with a dry sump lubrication system which ensures a constant supply of oil to the powerplant, even when lateral acceleration is extremely high.
The sequential gearbox in the research car is also a standard Mercedes-Benz production model. Only the SEQUENTRONIC controls are different: in the F 400 Carving, the driver changes gear in racing-car style – with selector buttons on the steering wheel.
Xenon light from fiber optics
Equally new is the headlamp system of the F 400 Carving. For the first time, DaimlerChrysler is using state-of-the-art fiber-optic technology to transmit the light produced by the xenon lamps. These optical-fiber bundles, made up of thousands of individual glass-fiber strands, enable physical separation of the light source and the headlamps - an advantage that primarily benefits the sports car’s front-end design, since the headlamps only take up a very small amount of space. This therefore allows an extremely flat and low-slung front.
The light for main and dipped beam is generated in two cylindrical casings beneath the engine hood. Each contains a xenon lamp, and the light given off by these lamps is concentrated by elliptic reflectors. The reflector focal points reflect the light into the fiber-optic lines which, in turn, ensure loss-free transmission of the light to the headlamps. Special lens systems in the headlamps diffuse the light to illuminate the road. In addition, the F 400 Carving has two side-mounted lights for cornering. These fixed-position halogen lamps come on when a certain steering angle is reached. They can also be activated by a button, for use as fog lamps.
A space-saving design is also the hallmark of the indicators: powerful LEDs generate the light which is then dispersed by means of prism lenses.
Vehicle body: lightweight carbon fiber
The open-top two-seater’s body is made from carbon-fiber-reinforced plastic (CFRP). Already tried and tested in the world of Formula One motor racing, its chief properties are minimum weight and maximum strength. It weighs in at about 60 percent less than steel, making the body of the research car 100 kilograms lighter. The DaimlerChrysler engineers use an intelligent three-material mix for the F 400 Carving chassis: steel, aluminum and carbon fiber (CFRP).
Exterior: the language of dynamics
Whichever way one looks at it, from whatever angle, the speedster’s body is like that of a perfectly proportioned and superbly conditioned athlete. The profile is structured by wing-like sections that powerfully span the wheels, harmoniously drawing them into the overall body concept, yet without restricting their freedom of movement. Smaller wing sections fore and aft of the wheels reinforce this effect, making the wheels the dominant focus of attention when the car is viewed from the side.
The design team also adeptly used the distinctive wing sections to give the F 400 Carving a characteristic face, making the headlamps an integral part of the wings and using the light covers to form two "eyes", decisively enhancing the sports car’s enticing allure. This stylistic detail is possible thanks to lighting systems incorporating state-of-the-art fiber-optic technology, since conventional headlamps are simply too large to be incorporated in the limited space available in the wing sections.
And, of course, the two-seater’s face would not be complete without the three-pointed star, centrally positioned in time-honored Mercedes sports car tradition. It forms the focal point of a further important design feature that stretches centrally across the engine hood, evoking images of the unmistakable arrow-shaped nose of the McLaren-Mercedes team’s Silver Arrows. This particular detail is well on the way to becoming a classic Mercedes-Benz sports feature, having already graced the Vision SLR and Vision SLA sports car studies.
Arguably the most striking feature of all, because they are so steeped in tradition, the gullwing doors have come to symbolize the Mercedes-Benz brand. It is now exactly 50 years since the first Mercedes-Benz Gullwing created a sensation, marking the beginning of the SL legend. The F 400 designers took this feature and reinterpreted it in the spirit of contemporary design and technology, proving that the idea is just as stylish and exhilarating now as it was all those years ago. The research car’s gullwing doors are not attached to the roof as they were on the original 300 SL. Instead, they swing upward 60 degrees thanks to special joints, supported by gas springs.
The muscular contour of the door leads into a sweeping, powerfully shaped profile which forms a prominent line stretching back as far as the speedster’s tail end, where it acts as a fender for the rear wheels. The tail part of this section houses the rear lights, in the same way as its counterpart at the front incorporates the headlamps. The slender prism lenses enable the indicators, tail lights and brake lamps to effortlessly blend in with the overall design concept and, furthermore, cast an extremely impressive light on things.
Interior: high-tech in stylish packaging
A look inside the cockpit reveals another major design theme of the F 400 Carving: technology in its purest form. Technology that focuses on the essentials, on what motoring was originally all about and, therefore, on everything absolutely central to this idea. Nothing more, nothing less.
Admittedly, this initially smacks of purism, a totally stripped-down driving machine. But a closer look quickly reveals all: the perfect finish, the very best materials and a passion for detail. The designers at the Mercedes studios – in Como, northern Italy and Sindelfingen, southern Germany – devoted themselves to the task in hand, giving the interior a characteristic appearance that draws on classic aspects of bodystyling and design. Nowhere is this more apparent than in the "wing" theme, the instrument panel being a perfect case in point: there is no firm visual link between the panel and the center tunnel. It seems to be "floating" in space like some majestic wing and thus appears extremely light and almost delicate.
The idea of technology in its purest form is most clearly exemplified by the transmission tunnel, which has the shape, color and texture of a cast-aluminum transmission bell. As such it echoes the racing car cockpits of the twenties and thirties, an era when drivers had to make do with bare metal and little else. The simple sliding controls for the blower and the heater, the metallic lever for the SEQUENTRONIC transmission and the oval ventilation outlet above the transmission tunnel all reinforce these images of bygone days, yet behind each of these classic styling features lies state-of-the-art technology.
Passengers in the F 400 Carving are awaited by carbon seats in which they immediately feel at one with this evocative car and its technology: man and machine in absolutely perfect harmony. The seats provide superlative lateral support and can be individually adjusted, despite their one-piece design. The multi-layered fiber texture means it is possible to vary the backrest inclination without the need for joints or hinges - a small lever mechanism is all that is required. Together with spring and damper systems beneath the seat, the multi-piece upholstery ensures effective vibrational damping for good seating comfort.