Method for maintaining the charge capacity of traction battery modules

Abstract

A hybrid electric vehicle includes a lead-acid traction battery made up of a plurality of series-connected modules. During operation of the vehicle, the traction battery is discharged for acceleration, and charged by an ancillary power source. The traction battery is desirably not fully charged at the beginning of a day's operation, so that overcharging cannot occur, so the battery spends long periods of time in a partially charged condition. When not fully charged for long periods of time, sulfation may reduce the charge storage capacity of the battery. A maintenance procedure takes place when the vehicle is not operating, in which one or more modules of the traction battery, but less than all the modules, are fully charged, then partially discharged. The full charging tends to reduce sulfation in the particular module being maintained, and the partial discharge restores its charge condition to that prior to the full charge. Each of the modules is eventually maintained by a programmed controller. The charging energy comes from an auxiliary battery, and the discharge energy is returned to the auxiliary battery, so there is little net loss of energy. If maintenance procedure is interrupted before full charge of a module, that module is scheduled for the next maintenance. If the maintenance is interrupted before partial discharge, the partial discharge is accomplished by equalizing the voltage of the battery modules.