Overview: Mercedes-Benz F800 Style research vehicle
Although it’s as much about style as technology, the F800 certainly has technology aplenty. When half of the show cars at Geneva seem to feature an alternative powertrain of some kind, this Mercedes actually gives you a choice of two: hydrogen fuel cell, or plug-in petrol-electric hybrid.
Mercedes-Benz F800 Style research vehicle.
Within the F800’s 4.74m length, all of the powertrain components are installed in a way intended to leave as much space as possible for the passengers: specifically, equipment has been stuffed into the the engine compartment and the gaps in the chassis. Both drive systems are quite compact, and Daimler is particularly pleased with space efficiency of the fuel cell powertrain. With either drive system, the F800’s passenger accommodation is what you would expect of a 4.74m car.
F800 Style plug-in hybrid
In hybrid form, the F800’s drivetrain consists of a V6 petrol engine plus an electric motor. The V6 features ‘next-generation’ direct injection with piezo injectors, delivers 300PS, and is capable of running with stratified lean-burn. The electric motor has an output of 109PS, to give a total system output of 409PS.
The lithium-ion battery pack, which lives under the back seat of the F800, has a capacity of around 10kWh. It can be recharged either at a charging station or from a household power socket. In operation, the battery pack is cooled by way of a water loop connected to the car’s climate control system.
Daimler quotes a range on battery power of 30km. The Company has said that its intention in developing the plug-in hybrid variant was to place emphasis on urban electric running, so this range isn’t overly impressive.
Apart from its lacklustre electric range, the F800 turns in good figures. Fuel consumption of 2.9l/100km (97mpg) and 68g/km CO2 look downright improbable, but remember that a plug-in hybrid can’t be compared directly with a ‘normal’ car, because some of its energy is coming from the electricity grid. On-road performance figures reflect the combination of a combustion engine and an electric motor: 4.8s to reach 100km/h and a maximum of 250km/h should be enough to please anyone. Daimler quotes a maximum speed of 75mph in electric mode, though it would be a brief dash.
Mercedes-Benz F800 Style research vehicle.
The F800 Hybrid’s electric motor is integrated into the 7G-Tronic seven-speed gearbox. To allow fully electric running, a clutch is fitted between the petrol engine and the electric motor allowing the V6 to be de-coupled from the driveline.
As you would expect, the F800 features regenerative braking. The system's effectiveness is boosted by the disengagement of the clutch, which allows more of the car’s kinetic energy is absorbed by the generating system rather than by the engine.
Daimler describes its hybrid powertrain as ‘scalable’ and ‘modular’, meaning that the basic system design can be applied to vehicles of different shapes and sizes and that individual components can be mixed and matched.
The F800 probably marks the last time Daimler will be showing a plug-in hybrid powertrain as a concept. The next generation S-class range will include a plug-in hybrid model.
F800 Style Fuel Cell
The components of the fuel cell drive are taken from the range of e-drive modules which Daimler has developed for a variety of different electric vehicles. These components are already being installed in the limited edition B-Class F-Cell, and they have been designed to be ‘scalable’ in use. The F800 Style, for example, is rear-wheel drive, while the B-Class F-Cell is front-driven. The same components are also installed in commercial vehicles, with developments here being spearheaded by the Citaro fuel cell bus, which is equipped with two of the F-Cell systems used in the B-class.
The F800’s fuel cell stack is fitted in the engine compartment, with the drive motor mounted between the driven wheels. Outputs are 136PS and 290Nm. The air supply for the fuel cells is provided by a small electric turbocharger. The lithium-ion battery is located behind the rear seats. Two of the four 70MPa hydrogen tanks are mounted in the transmission tunnel between the passengers, while the other two are under the rear seat. Total H2 storage capacity is 5.2kg — enough for an operating range approaching 400 miles.
The vehicle’s management system decides whether to use the electric energy from the lithium-ion battery pack, the fuel cell, or both systems together. The aim is to get the best efficiency from the system. In low-speed manoeuvring, the battery pack is the first choice, with the fuel cell cutting in when it’s needed.
The F800 Fuel Cell’s regenerative braking also features ‘regenerative overrun’ — like BMW’s Concept Active E described elsewhere. The drive motor starts to act as a generator — and slow the car — as soon as the accelerator is released, meaning that the mechanical braking ststem is not often needed in gentle driving.
F800 Plug-in Hybrid
F800 Fuel Cell
3.0l V6 petrol
Mercedes-Benz F800 Style research vehicle with fuel cell powertrain.
Mercedes-Benz F800 Style research vehicle with petrol-electric plug-in hybrid powertrain.