Patent ID: 7911078

Claim:
A dual type vehicle power-supply apparatus comprising: a high voltage power supply including a generator and a high voltage rechargeable battery charged by said generator; a high voltage system including an engine starter supplied with electric power from said high voltage power supply; a low voltage power supply including a low voltage rechargeable battery whose output voltage is lower than an output voltage of said high voltage rechargeable battery; a low voltage system including a low-voltage electrical load supplied with electric power from said low voltage power supply; a bidirectional power transmission unit connecting said high voltage power supply and said low voltage power supply to each other such that electric power can be transmitted between said high voltage power supply and said low voltage power supply; and a power transmission controller which controls transmission of electric power between said high voltage power supply and said low voltage power supply through said bidirectional power transmission unit; wherein said power transmission controller is configured to: calculate an engine starting electric power amount necessary to start an engine with an idle stop function; calculate a difference between a charge amount of said high voltage power supply and said engine starting electric power as an electric power shortage amount; detect, as a surplus electric power amount, an electric power amount which said low voltage power supply can afford to supply other than an electric power to be supplied to said low-voltage electrical load; determine whether said surplus electric power amount is greater or less than said shortage electric power amount; command said bidirectional power transmission unit to transmit electric power from said low voltage power supply to said high voltage power supply when said surplus electric power amount is determined to be greater than said shortage electric power amount; and disable said idle-stop function when said surplus electric power amount is determined to be less than said shortage electric power amount.