High Performance Fuel Cell Sedan 2004-01-1003

New vehicle technologies open up a vast number of new options for the designer, removing traditional constraints. Some recent conceptual designs, such as GM's Hy-wire, have recognized this and offered innovative new architectures. Unfortunately, many other new technology concept cars do not exploit the freedoms of the new technologies, hampering themselves with traditional design cues developed for conventional powertrains. This paper will present the conceptual design of a high-power, high-speed fuel cell luxury sedan. One of the main motivations of this case study was to explore what could happen when a vehicle was designed from the ground up as a fuel cell vehicle, optimized at the overall system level as well as at the individual component level. The paper will discuss innovations in vehicle architecture and novel concepts for the electrical transmission, fuel cell system and electromagnetic suspension.

Vehicle architecture introduces new topology based upon new criteria which are needed for a fuel cell electric vehicle. The main elements of the vehicle-such as the hydrogen fuel tanks, super-capacitors, electric machines, fuel cell stacks, fuel cell auxiliaries, radiators, brake resistor and power electronics-are located in positions allowing maximum active and passive safety with the same or enhanced functioning performances. These goals can be met, without punishing passenger comfort or trunk volume by using the added freedom in component placement that the electric powertrain provides. General styling introduces a very intimate amphitheater concept together with a low drag body. An adjustable trunk maximizes storage space when necessary and improves drag when the storage is not needed.

The fuel cell design contains new high efficiency concepts for the stack itself as well as the auxiliary systems. Stack design eliminates the need for graphite plates and de-ionized cooling water, improving both the cold startability and the pressure drop across the stack. Integration of a fast auxiliary warm-up system further improves cold startability. This system allows for a 2-4 minute transition time when operating at - 20 °C, and permits the fuel cell to start at temperatures as low as - 40 °C. A continuously controlled pressure wave compressor (Comprex®) offers substantial efficiency gains over a classical electrically driven compressor, with energy savings in excess of 50%.

The electric transmission introduces some aspects of power electronics and energy management for low cost implementation. The fuel cell and the multi-level inverter have been designed together to eliminate any intermediary DC to DC converters. Virtual electromagnetic differentials distribute torque between the front and rear axles. Two such twin rotor electric machines allow for active traction control on all four wheels, while minimizing costs and increasing machine efficiency. A zero-power active levitation system provides the basis for the electro-magnetic suspension, which allows real-time camber control and recovery of some of the energy absorbed by suspension damping.