Toyota Motor Corp held a lecture titled "Development of Fuel Cell Hybrid Vehicle-Cruising Range" at EVS23. The lecture was focused on Toyota's efforts to improve the cruising range of its FCHV fuel cell vehicle.
The fuel efficiency of the 2005 model FCHV based on the 10-15 Japanese test cycle is 103km/kg. Compared with the result of the test cycle, the fuel efficiency during the actual driving is reportedly degraded by about 30% to about 70km/kg due to the influence of the variation in driving pattern and electric components such as air conditioner.
As a result, the 2005 FCHV only drives about 220km on one hydrogen charge.
To improve the cruising range of FCHV per charge to 500km, which is on par with that of the gasoline vehicles, the company focused on the enhancement of fuel tank pressure and the improvement of fuel efficiency. The pressure in the fuel tank was increased from 35 to 70MPa so that the tank can store about 6kg of fuel, which is 1.9 times that in the existing tank.
The consumption of hydrogen fuel is equivalent to what is obtained by subtracting the energy generated by the regeneration brake from the energy consumed by driving. To improve the fuel efficiency, the energy consumption during driving should be reduced while increasing the energy produced at the regeneration braking.
According to the test cycle (LA4) specified by the US Environmental Protection Agency (EPA), the energy required to drive FCHV is slightly more than 40% of the total energy consumption during driving. The rest of the hydrogen is consumed by the heat loss in the fuel cell stack, crossover from the fuel electrode, purging of the fuel electrode, etc.
In addition, loss at the compressor, which supplies the fuel cell stack with air and losses in the boost converter and motor inverter were consuming fuel, the company said.
Toyota focused on the reduction of energy loss in the fuel cell system and the converter of the hybrid system, both of which consume a large amount of energy. In the fuel cell system, the air supply pressure to the air electrode side was reduced for all engine loads. As a result, the efficiency of the fuel cell system as a whole improved although the output voltage from the fuel cell was reduced by about 1%, the company said.
The heat loss in the fuel cell stack and the loss in the compressor to supply the stack with air were both reduced by 12%, thereby improving the fuel efficiency of FCHV by 5%, the company added.
In the existing converter, three bridges are used for all engine loads. The company improved the efficiency of the converter in the low load region by using only one bridge. This resulted in a 3% increase in the fuel efficiency of the fuel cell vehicle, the company said.
Toyota also optimized the ratio of regeneration and mechanical brakes at the time of braking to enhance the energy recovery rate at regeneration braking.
With these improvements, the energy consumption of the remodeled FCHV during driving was reduced by 15% compared to the 2005 model, while the regeneration energy was increased by 25%, the company said. The company also said that the fuel efficiency based on the US LA-4 test cycle was improved by 25%, and the fuel efficiency during the actual driving exceeded 85km/kg, resulting in a cruising range of 500km or longer.
The company conducted a long-distance field test between Osaka and Tokyo on Sept 28, 2007. According to the company, the vehicle drove a distance of about 560km with the air conditioner turned on.
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