Dual voltage battery for a motor vehicle

A method for managing battery energy for a main battery of a motor vehicle, said vehicle including an engine having a drive shaft, a motor connected to said drive shaft, a first controller operatively associated with said motor to operate said motor in one of a drive, regenerating, or power generating mode, said main battery being operable to supply electrical energy to said motor to power said motor and permit said motor to drive said drive shaft, said main battery having a first power supply supplying a first voltage and a second power supply supplying a second voltage, said second voltage being of a lower value than said first voltage, said method comprising the steps of:

• determining that the motor vehicle is in an idle stop condition;
• charging said main battery upon determining said vehicle is in said idle stop condition;
• determining that the motor vehicle is in a starting condition;
• operating said motor to assist in driving said motor vehicle upon determining that the motor vehicle is in a high load driving condition;
• monitoring said voltage of said battery;
• operating said motor in a power generating mode upon determining that the voltage of said battery is below a predetermine value;
• determining that the motor vehicle is in a low load driving condition;
• and
• operating said motor in a regenerating mode upon determining that the motor vehicle is in a low load driving condition.

A vehicle drive system comprising:

• an engine having a drive shaft;
• a motor connected to said drive shaft;
• a first controlling means operatively associated with said motor to operate said motor in one of a drive, regenerating, or power generating mode;
• a main battery supplying voltage to said motor to drive said drive shaft, said main battery having a first power supply supplying a first voltage and a second power supply supplying a second voltage for an electrical load, said second voltage being of a lower value than said first voltage;
• a constant voltage converting means connected between said second power supply and said first controller for controlling the voltage supplied to said second power supply such that said second power supply supplies said second voltage for said electrical load constantly;
• and
• a second controlling means connected to said constant voltage converting means for switching on or off said constant voltage converting means and causing said first controller to operate said motor in said drive, regeneration, or power generation mode.