Mercedes-Benz is launching its first series-produced electric car with a fuel cell on the road: the new B Class F CELL. The small-scale production of the environmentally friendly electric car is already underway.
The first of around 200 vehicles will be delivered to customers in Europe and the USA in spring next year. At the heart of the B Class F CELL is the new-generation electric drive system powered by a fuel cell, which is compact, powerful, safe and fully suited for everyday use. The fuel cell generates the electrical power on board, while producing little more than pure water and zero emissions.
The key drive components are located in the sandwich floor, where they are protected and do not take up much space, leaving the vehicle’s interior and boot fully usable. Thanks to its long range of around 400 kilometres and short refuelling times, the B Class F CELL combines local zero-emission mobility with long-distance comfort and compelling performance. Driving pleasure and performance on a par with a 2.0-litre petrol car come courtesy of the 100-kW/136-hp electric motor, which develops effortlessly superior torque of 290 Nm.
The B Class F CELL consumes the equivalent of 3.3 litres of diesel per 100 kilometres in the New European Driving Cycle (NEDC).
The technology for the B Class F CELL drive system is based on the optimised latest-generation fuel cell system. It is some 40 percent smaller than the system in the A-Class F CELL from 2004, but develops 30 percent more power while consuming 30 percent less fuel. The main drive system components include:
• A compact fuel cell stack
• A powerful lithium-ion battery
• Three 700-bar tanks for the hydrogen and
• A compact, lightweight drive motor at the front axle.
Cold-start capability down to minus 25 degrees Celsius
The fuel cell module in the B Class F CELL, the stack, boasts outstanding cold-start capability down to minus 25 degrees Celsius. The system features a new humidification system consisting of hollow fibres that ensures, unlike with the first-generation fuel cell, that water no longer freezes in the stack, a characteristic that used to impair cold-start capability. Even at minus 15 degrees Celsius the B Class F CELL starts just as quickly as the very latest diesel engine. A dedicated operating strategy helps ensure the fuel cell stack reaches its optimum operating temperature of around 80 degrees Celsius as quickly as possible each time the vehicle is started. Thanks to the powerful cooling system and intelligent temperature management, this ‚pleasant temperature‘ is maintained constant under all operating conditions.
Range of around 400 kilometres with the tanks full
The hydrogen used to run the fuel cell is stored in three tanks at a pressure of 700 bar. Each tank holds just under 4 kilograms of the gaseous fuel. The tanks are hermetically sealed from the outside world, preventing the loss of hydrogen into the atmosphere even if the vehicle is left to stand for long periods. Thanks to the high compression ratio, the B Class F CELL can cover long ranges of up to 400 kilometres with the tanks full, over twice as far as the A-Class F CELL. If the tanks are empty, they can be filled simply and quickly in less than three minutes, thanks to a standardised refuelling system.
Equivalent of just 3.3 litres of diesel per 100 kilometres
The electric motor – a permanently excited synchronous motor – develops a peak output of 100 kW/136 hp and a maximum torque of 290 Nm – typical of the high torque generated by an electric motor –, which is available from the instant the engine starts to turn. It ensures that the B Class F CELL, whose impressive dynamic handling properties are in some cases far better than those of a two-litre petrol car, gets off to an excellent start. Nonetheless, the local zero-emission electric drive with fuel cells consumes the equivalent of just 3.3 litres of diesel per 100 kilometres (NEDC).
Compact lithium-ion battery with large storage capacity
A powerful high-voltage lithium-ion battery is used to store the power. It boasts an energy capacity of 1.4 kWh and is cooled via the air-conditioning system circuit. When it came to the battery for the B Class F CELL, Mercedes Benz drew on the experience garnered during the development of the lithium-ion technology for the S 400 HYBRID. Advantages of the lithium-ion battery include its compact dimensions and much superior performance compared with nickel metal hydride batteries (NiMH). The energy density is 30 percent higher than with NiMH technology; the power density 50 percent higher by comparison. Furthermore, high recharge efficiency and a long service life make the technology even more compelling.
Intelligent drive system management for superb efficiency
Mercedes-Benz has further enhanced the operating strategy of the electric drive with fuel cells for the B Class F CELL. As the outside temperature plummets, the electric motor receives its electrical energy during a cold start both from the lithium-ion battery and from the fuel cell system as it „powers up“. Battery power is sufficient as the outside temperature warms up; the fuel cell then comes on line later – depending on the power requirements. In drive mode, the energy management system constantly maintains the F CELL system in the optimum operating range. The lithium-ion battery dynamically smoothes out variations with regard to the electrical power required in the current driving situation.
Whenever the driver brakes or as soon as they take their foot off the accelerator, the electric motor converts kinetic energy into electrical energy, which is then stored in the battery, using a process known as recuperation. While manoeuvring or on short journeys, the electric drive motor uses battery power. If the battery capacity is not sufficient, the fuel cell automatically kicks in. In a bid to ensure optimum efficiency and customer benefits, the intelligent drive management system decides whether the electrical energy is used from the lithium-ion battery, the fuel cell, or a combination of the two systems.
Full everyday practicality thanks to sandwich floor
Four fully fledged seats and a boot capacity of 416 litres make the B Class F CELL fully suitable for day-to-day and family use.
The F CELL concept has been realised on the basis of the unique sandwich floor architecture, which Mercedes-Benz introduced 10 years ago in order to integrate alternative drive systems with the first-generation A-Class, and which has been honed consistently since then. The key components for the electric drive with fuel cells are optimally protected in the vehicle underbody, thanks to a space-saving design that also promotes a low centre of gravity. Advantages of the design include:
• The generous interior space in the B Class is fully retained. As the entire fuel cell system is integrated into the spacious sandwich floor, no compromises are necessary with respect to passenger space, luggage capacity, or variability
• The drive technology built into the sandwich floor ensures a low centre of gravity and, consequently, extremely reliable, agile handling
• Crash safety meets the extremely high standards associated with Mercedes thanks to the sandwich concept and housing key drive components and the hydrogen tanks between the axles
The B Class F CELL offers consummate driving pleasure and full day-to-day suitability – without local emissions. The innovative electric car also has a great deal to offer when it comes to equipment and appointments, including the bonamite silver special paint finish and exclusive 10-spoke light-alloy wheels. In the interior, leather upholstery, heated seats, automatic climate control and the COMAND system, as well as other features, ensure a high level of comfort. The dynamic energy flow display in the COMAND system display keeps the driver constantly abreast of the battery charge status, operating mode of the fuel cell system, as well as providing information on nearby hydrogen filling stations.
Safety first: uncompromising safety standards
Mercedes-Benz applies the same high safety standards to the B Class F CELL as to any of its other series-production models. The starting point is the outstanding crash safety of the Mercedes-Benz B Class, which received the highest five-star rating in the European NCAP (New Car Assessment Programme). The integrated safety concept of the B Class F CELL takes the specific characteristics of the innovative drive system into account. The experience garnered over many years by Mercedes-Benz with the electric drive powered by fuel cells from the A-Class F CELL and the high-voltage technology involving the lithium-ion battery from the S 400 HYBRID went into honing the concept.
Mercedes engineers have tested the safety of the drive-specific components including the hydrogen tank in the B Class F CELL in more than 30 crash tests. The hydrogen tanks are installed in the sandwich floor and therefore well protected in the event of an impact. They hold the hydrogen which is pressurised to 700 bar and have been designed to withstand all conceivable loads.
In the event of a crash, safety valves close the hydrogen supply lines to the fuel cell and decouple the tanks from the other system components. Even after a serious accident, the hydrogen poses no risk whatsoever. If a fire leads to excessive heat, a temperature-controlled value vents the tank contents in a controlled manner.
The lithium-ion battery and high-voltage system in the B Class F CELL feature – based on the experience garnered with hybrid technology in the S 400 HYBRID –an extensive, seven-stage safety concept.
• All the wiring is colour-coded to avoid confusion, and marked with safety instructions. This prevents assembly errors in production, and makes the quality checks easier to carry out
• Comprehensive contact protection for the entire system by means of generous insulation and dedicated connectors
• The lithium-ion battery is accommodated in a high-strength steel housing. Further safety features: blow-off vent with a rupture disc and a separate cooling circuit. An internal electronic controller continuously monitors the safety requirements and immediately signals any malfunctions
• All high-voltage components are connected by an electric loop. In the event of a malfunction the high-voltage system is automatically switched off
• As soon as the ignition is switched to „Off“, or in the event of a possible malfunction, the high-voltage system is actively discharged
• During an accident, the high-voltage system is completely switched off within fractions of a second
• The system is continuously monitored for short circuits
The high level of safety means Mercedes-Benz fuel cell vehicles can use underground car parks, multi-storey car parks or tunnels with no restrictions whatsoever.
F CELL – paving the way for the mass-produced fuel cell
With the B-Class F-CELL, Mercedes-Benz has for the first time applied all development and production standards associated with series production to an electric vehicle with fuel cells. All F CELL components meet the familiar Mercedes-Benz high standards in terms of quality, reliability and service life, thus putting in place the ideal conditions for mass production of the fuel cell powered electric drive including battery to improve efficiency and reduce costs. From 2012, the company intends to fit its vehicles with lithium-ion batteries produced by its joint venture Deutsche Accumotive GmbH.
Modular system for tomorrow’s electric cars
Along the same strategy adopted for developing the hybrid, the Mercedes engineers have also developed a modular system for electric vehicles with batteries and fuel cells. This enables amongst others the same parts to be shared efficiently across all electric vehicles. All key components of electric vehicles are ideally suited to modularisation: from the electric motor and the transmission, the battery and high-voltage safety concept to the high-voltage wiring, and software modules. Specific components, such as stacks and hydrogen tanks, can be used as standard components for entirely different vehicles in the F CELL line-up. For instance, simply by varying the quantity as necessary: for example, the Mercedes-Benz fuel cell bus is powered by two passenger car systems of the same type that is also used in a B Class F CELL.
The close to series Concept BlueZERO is testimony to just how the company has implemented the modular concept with future electric vehicles featuring a battery and fuel cells. As with the B Class F CELL, the Concept BlueZERO also houses the key drive components in the sandwich floor in a crash-resistant configuration. Based on a single vehicle architecture, the variable concept paves the way for three variants with different drive system configurations, which can meet all customer requirements for sustainable mobility – also, and in particular as regards the key aspects of safety and range:
• The BlueZERO E-CELL with its pure battery-electric drive boasts a range of up to 200 kilometres
• The BlueZERO F CELL with fuel cell is also suitable for long-distance journeys thanks to its electric range of well over 400 kilometres
• The BlueZERO E-CELL PLUS with electric drive and additional combustion engine as a power generator (range extender) boasts a total range of up to 600 kilometres and can cover a distance of up to 100 kilometres using electric drive alone
Source: Daimler AG