Fortis Saxonia is
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Powertrain
The basis for a low energy consumption vehicle must be an extremely efficient powertrain. Furthermore, the powertrain should be as compact as possible and capable of flexible arrangement. This is necessary in order for the drive system and monocoque chassis to be less limited in design to achieve good aerodynamic efficiency. In general the powertrain should be trendsetting and environmentally friendly.
This goal will be realized by utilizing a PEM-hydrogen-air fuel cell as the primary component. The hydrogen fuel cell supplies electric energy to the motor which then drives the back wheel via a hub-gear and a chain.
 Powertrain, schematical |
 Powertrain |
The vehicle's power demand is derived from a combination of the overall efficiency of all components, that is to say the track characteristics, the aerodynamics and the rolling resistance. Since the 2005 vehicle was our first attempt the team Fortis Saxonia had no practical experience and only few measured results to base its design on. The track profile was used to approximately calculate the vehicle's power requirements and the physical dimensions of the powertrain.
 Stack, schematical |
 Power output |
These calculations resulted in an approximate peak power requirement of 250 watt. An electronic controller is required to vary the voltage from 0 to 24 volts for purposes of acceleration. This electronic controller uses a PWM-signal generator incorporating an analog potentiometer.
Initial track test-runs showed that vehicle performed below expectations and the required average velocity was not achieved. Experiments confirmed that environmental influences, such as humidity and temperature affected the power output of the hydrogen fuel cell dramatically. After changes were made to control the hydrogen fuel cell environment Sax 1 completed the track successfully. Through permanent hydrogen purging of the fuel cell, in order to remove water condensate, its peak power output was raised by 40 percent.
Fuel cell units for mobile applications are at present not readily available since prices for fuel cells are comparatively high in relation to their durability. Hydrogen fuel cell technology has not yet entered large scale production in vehicles. We hope to contribute to hydrogen fuel cell technology for the large scale production of vehicles through the experience we gain by competing in the Shell Eco-marathon. Since the difficulties involved with hydrogen storage are often underestimated this aspect plays an important role. SAX I uses a metalhydride cartridge. This cartridge can carry 23 grams of hydrogen in a small volume at low filling pressure. The hydrogen is dissolved into the metalhydride by a chemically reversible reaction. This hydrogen storage technique is considered to be very safe in case of impact or leakage because the hydrogen can not be rapidly released due to self-freezing of the cartridge at the leakage spot.
| Specifications of the powertrain of Sax 1: | |
| Type of fuel cell: | PEMFC |
| Number of cells: | 25 |
| Electric power of the fuel cell: | 250 watts |
| Efficiency of the fuel cell: | 37 percent |
| Controller efficiency: | 95 percent |
| Mechanical power of the motor: | 300 watts |
| Motor efficiency: | 80 percent |
| Transmission efficiency: | 80 percent |
| Total mass of powertrain: | 21 kilogramms |
