Abstract
The commercial vehicle is required recently to change the power sources and materials for every part of the vehicle more ecological and for any environmental problem such as CO2 emission and air pollution.
The compressed air vehicle (CAV) has been studied for several years, but it seems difficult at this moment to complete with a commercial vehicle which uses fossil fuel to get a dynamic performance such as acceleration and running range. Hence the hybrid CAV with a few electric power source and CVT is considered. The analysis of how the CAV runs and its efficiency are shown in this paper.
The plug-in hybrid CAV concept is used to design a compressed air, electrical energy storage, and kinetic energy recovery system to provide the torque to each CVT. In order to make this system possible for a compressed air based vehicle (not an electrically based vehicle), the battery is filled with a half of the total energy of the main air tank. In our simulation, the main air tank of 70.0 MPa and its volume of 100 L to 800 L are applied in the present case. The volume of the sub air tank is 100 L. Two Lithium ion battery cells are connected in series and the 160 of them are connected parallelly.
The specification of typical Japanese light track made by Mitsubishi Motor Company is included in the simulation program since a simple CAV prototype was made a few years ago. Then the 10/15 mode of simulation is performed to analyze the commercial vehicle in Japan on the test bench. The CVT is defined for its each power source while running and the different strategy for the typical conditions such as velocity, acceleration, and braking G is used to improve the whole performance. There are three phases in the strategy; Phase 1 to use the main air tank and the sub air tank for the acceleration, Phase 2 to use the sub air system and electric motor without the main air system when the velocity reaches to Vc, and Phase 3 to use the sub air system as a kinetic energy regenerator while gracing. The acceleration is controlled by the CVT during the operation. When the reduction ratio of the CVT reaches out of its range (say, 0.3 to 1.4), it will be locked and while braking, the general friction brake system is operated.
The simulation results will be sown in this paper. The Vc is defined as 20.0km/h. Although the 800L main tank is large, it can run 470km. This vehicle can be used as a city commuter. But at lower volume, the running range rapidly becomes shorter, which is not practical. However, the 800L CAV shows 15.9% Well-to-Wheel Efficiency. Although this efficiency is higher than Gasoline vehicle, it is about a half of the efficiency of Fuel Cell Hybrid car. Thinking about the Well-to-Wheel Efficiency, which is good analysis way for using natural energy resource, it seems not enough and must improve the efficiency.
In conclusion, although the acceleration and running range are not satisfied, our CAV concept shows a possibility for a practical use such as about 470 km of running range with the 800 L tank, which can run the public road the same as the fossil fuel vehicle. The real prototype CAV is now developed to see how it can run.
Keywords: Compressed air, Air Car, Ecology, Environmental problem, Hybrid