Panasonic Corporation has developed a NiMH-based 12V Energy Recovery System for start-stop systems in vehicles. This system allows the energy generated during braking to be stored in the batteries and use the stored energy to power the vehicle’s electrical components, thus ensuring power availability even when the engine is not being used. The system is also designed to supply power to the drive assist motor, improving fuel economy.
With this 12V Energy Recovery System, Panasonic aims to approximately double the fuel economy improvement rate of existing start-stop systems over conventional gasoline-engine vehicles.
The 12V Energy Recovery System, which is designed to be connected in parallel with the main lead-acid battery, is based on new D-size nickel metal hydride (NiMH) battery cells. The main lead-acid battery is often placed in the engine compartment. As the new energy recovery system can be installed in the same compartment, it is possible to reduce cable connection resistance and simplify wiring.
To enable such a setup, Panasonic has developed battery cells that can endure the high-temperatures of the engine compartment. Using technology acquired in developing HEV batteries, Panasonic has improved the battery design, such as the polar plates, electrolyte and other battery parts to increase charging efficiency and improve durability in high temperature environments.
As a result, the cell’s maximum charging/discharging temperature is significantly improved from 60 °C to 75 °C compared to existing cells. This ensures that the system can be installed in the engine compartment, and provides a high degree of design flexibility for the system's installation.
Panasonic’s 12V system, comprising 10 1.2V Ni-MH battery cells, eliminates the need for voltage transformation. This helps lower the system’s costs and uses energy more efficiently.
Because conventional start-stop systems depend on a single lead-acid battery to take care of all electrical needs of the vehicle, from restarting the engine to running the air-conditioner and other electrical components with the engine off, the battery is put under too much load, Panasonic says. The new 12V Energy Recovery System addresses this problem and thus extends the service life of the main lead-acid battery.
Tests conducted by Panasonic using a 12V Energy Recovery System together with a lead-acid battery showed that the service-life of the main battery was extended by approximately six times compared to when a lead battery was used alone. (Results of charge/discharge life tests for idle-stop (SBA S0101) conducted at 60°C aging conditions by Panasonic. A Panasonic lead-acid battery (Q-55) and 12V Energy Recovery System were used.)
Panasonic started developing Ni-MH batteries for HEVs in 1997, and has been mass producing them since 2004. Its Ni-MH batteries are durable and able to maintain a high charging/discharging capacity over an extended period of time. This is supported by the company’s proprietary battery manufacturing technologies, including polar plate sintering technology, which involves the firing of metal nickel powder at high temperatures for manufacturing rigid, porous nickel substrate.
