GM debuts fourth-generation Hydrogen fuel cell car

4.2 kg of pressurized hydrogen provides an operating range of up to 320 km

During the HydroGen4’s development, scientists and engineers from GM fuel cell centers in Honeoye Falls (New York), Torrance (California) and Mainz-Kastel (Germany) were able to make use of a wealth of knowledge and experiences that were gathered during the extensive and rigorous practical testing of its predecessor introduced in 2002 (see corresponding chapter).

There were two versions of HydroGen3, for example. While one variant operated on liquid hydrogen at -253°C and another on compressed hydrogen, the decision has now been taken to focus on gaseous hydrogen. "The main reason for this is the unavoidable ‘boil off’ that occurs with liquid hydrogen," explains Dr. Udo Winter, Director, GME Fuel Cell Activities. "Even with optimum insulation, the tank’s contents warm up slowly, so that the liquid hydrogen vaporizes and the pressure in the tank increases. After a few days, gaseous hydrogen has to be released from the parked vehicle, leading to a loss in fuel. There are no such vapor losses ("boil off") with compressed gas, however."

The HydroGen4 has a tank system with three, 700-bar high-pressure tanks made from carbon-fiber composite material, which can hold 4.2 kg of hydrogen. This provides an operating range of up to 320 kilometers.

Buffer battery enables regenerative braking

The new fuel cell propulsion system also has a nickel-metal-hydride buffer battery and a capacity of 1.8 kWh. The battery ensures improved driving performance and covers the system’s performance peaks. The efficiency of the entire propulsion system has also been improved, as the buffer battery enables regenerative braking in the HydroGen4. When braking or overrunning, the electric motor switches to generator operation and uses the electrical energy produced when braking to charge the battery.

If the driver has to brake harder, the car will also be decelerated hydraulically, as is the case in a conventional car. This combination of regenerative and hydraulic brake performance is called "brake blending". It is applied by driving stability programs such as ABS or ESP, or when the required deceleration exceeds the maximum regenerative braking performance. This is determined by the size of the generator and battery input capacity.

Battery and braking technology are also important links to the innovative GM E-Flex electric vehicle architecture that the company is also working on.

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