280 kilometers range without refill, a high-speed of 120 km/h, and zero emissions: In the BREEZE! project, FEV developed a fuel cell range extender and integrated it into an existing battery-electric vehicle (BEV) in the subcompact category. To show the capabilities in terms of very small packaging, the engineers decided for a Fiat 500 based BEV which represents a particular challenge with respect to existing space. The FIAT 500 was selected from FEV’s E-vehicle fleet.
Range extender concepts (REX) are designs that feature serial hybrid powertrains in which the drive power is provided primarily through an external, rechargeable battery, as opposed to plug-in hybrids, where the primary functions of the battery are to provide boosting, brake energy regeneration, load point shifting, or local, emission-free driving in urban traffic.
Dimensioning of the range extender
In the design layout, the REX-performance was compared with the drive power of the BEV and FEV experts chose a scenario-based design instead of a cycle-based approach, so the battery can provide the full vehicle power even when the battery is at a low State-of-Charge (SoC). As a result, the vehicle has a top speed of 120 km/h regardless of the SoC and also has a small performance reserve, so that uphill slopes and highway travel do not have to be entirely compensated by using the battery.
Due to installation space restrictions, the range of the battery is 80 km while the additional range of approximately 200 km, provided by the REX fuel cells, is limited by the size of the hydrogen tank. However, a tank refill of hydrogen can be completed within a few short minutes, and travel can be continued at the same maximum speed.
The volume of the cell stacks is approximately 15.5 l, leading to a volumetric gross power density of 2.2 kW/l. With a volume of 67 l, the entire REX module achieves a volumetric gross power density of 0.45 kW/l and a gravimetric gross power density of 0.25 kW/l, including operating materials. The fuel cell range extender thus lies in the same range as combustion engine range extenders.
Package-optimised system design
The space available in the Fiat 500 is very limited. For this reason, FEV fitted the entire REX module into the spare wheel area while the tank is located under the rear seat. This made extensive measures and precise planning necessary to integrate the module, various components, auxiliary equipment, and sensors which are necessary to supply the fuel cell with air, hydrogen, and coolant.
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