1. Field of the Invention
The invention relates to a charging apparatus for an electric storage device, a vehicle equipped with the charging apparatus, and a method of controlling the charging apparatus.
2. Description of Related Art
In recent years, vehicles that run with driving force using electric power stored in an electric storage device installed on the vehicle have been attracting attention, as environment-conscious vehicles. Examples of the electric storage device include a second battery and a capacitor. The vehicles of the above type include, for example, electric vehicles, hybrid vehicles, fuel-cell vehicles, etc. It has been proposed to charge the electric storage device installed on the above type of vehicle, using a commercial power supply. Generally, the commercial power supply has high power generation efficiency.
As one type of the hybrid vehicles, a vehicle that permits an on-board electric storage device to be charged using electric power from a power supply located outside the vehicle (which may also be simply called “external power supply”), like an electric vehicle, is known. The charging of the on-board electric storage device with electric power from the external power supply may also be simply called “external charging”. Typically, the vehicle as described above is known as so-called “plug-in hybrid vehicle”. For example, a charge port or socket provided on the plug-in hybrid vehicle is connected to an outlet of a power supply provided in a house, or the like, via a charging cable. With this arrangement, the on-board electric storage device can be charged with electric power from a standard home power supply. By using the external power supply, it is expected to enhance the fuel consumption efficiency of the hybrid vehicle.
Japanese Patent Application Publication No. 2007-178215 (JP 2007-178215 A) discloses a power supply system capable of charging a secondary battery. The power supply system restricts charging current in view of the temperature dependence of the internal resistance of the secondary battery. With the charging current thus restricted, the charging status (which may also be called “state of charge” or “SOC”) of the secondary battery is estimated with improved accuracy, as described in JP 2007-178215 A.
A vehicle capable of external charging assures a long running distance if the electric storage device is in a sufficiently charged state when driving of the vehicle is started next time. In the meantime, if the electric storage device is kept in a high SOC condition for a long period of time, degradation of the electric storage device may be accelerated. Therefore, a vehicle having a timer charging function has been proposed. The user of the vehicle sets a scheduled time at which charging is to be completed (or a scheduled time at which driving of the vehicle is to be started). The charging of the electric storage device is controlled so as to maximize the SOC immediately before the scheduled time set by the user.
In the vehicle having the timer charging function as described above, if the estimated charging time of the electric storage device is not accurate, a shortage of charge may occur at the scheduled charging completion time, or charging may be completed earlier than scheduled. In the latter ease, the electric storage device may be kept in a high SOC condition for a long period of time, which may result in degradation of the electric storage device.
In the meantime, charging power that can be received by the electric storage device may be restricted by the temperature and SOC of the electric storage device. Therefore, it is important to take account of charging characteristics of the electric storage device, for accurate estimation of the charging time.