Ultracapacitors in micro-and mild hybrids with lead-acid batteries: Simulations and laboratory and in-vehicle testing

This paper describes work directed toward the demonstration of ultracapacitors in a 2001 Honda Insight. The general approach used in this project is to replace the NMH battery with ultracapacitor modules maintaining the 12V lead-acid battery to power the accessories. Both the ultracapacitors and the 12V battery will be recharged from the electric motor/generator driven by the engine. The Insight is being modified so that it can operate as a stop-start hybrid with and without power assist and as a mild hybrid using the full power capability of its 10 kW electric motor. In the case of the start-stop hybrid, the modified Insight will use 16V ultracapacitor modules; in the case of the mild hybrid, the vehicle will use 48V modules as part of a 176V electric driveline. The energy storage units have been tested in the laboratory using cycles appropriate for the vehicle tests. The energy storage and maximum power capability of each of the storage units was found to be sufficient to meet the project requirements at high efficiency for the vehicle test cycles. Careful laboratory testing of the vehicle systems is being performed in the laboratory using a Bitrode battery tester, which controls the discharge of the ultracapacitors and the lead-acid battery and provides for their appropriate charge as specified in the control strategy for the system. The Honda Insight has been equipped with a modified on-board diagnostics (OBD) readout unit which plugs into the standard OBD port in the vehicle. The readout displays conventional engine and electric driveline component data. A MIMA (Manual Integrated Motor Assist) kit, which has been installed in the Insight, permits the driver to modify and control manually the operation of the hybrid powertrain via a manual joy stick. A circuit board, which will replace the joystick with a programmed digital signal, is being developed. The operation of the Honda Insight has been simulated using the Advisor program, which has been modified at UC Davis to treat various hybrid drivelines including the micro-HEV and the mild hybrid cases. The simulation results indicate that the fuel economy of the micro-hybrid can be significantly higher than the conventional ICE vehicle, but significantly lower than that of a mild-hybrid using a higher power electric motor and a more extensive energy storage unit (battery or ultracapacitor). The simulations indicate that the fuel economies of the mild-hybrid using the NMH battery or the ultracapacitors are not expected to be much different.