Patent ID: 6876098

Claim:
The method of operating a series hybrid vehicle having a primary power source and a secondary power source, the method comprising: monitoring an amount of available stored energy within an energy storage device; based on the amount of available stored energy, selectively powering the secondary power source with either 1) a portion of the amount of available stored energy, 2) a portion of an amount of direct input energy, or 3) a combination of the portion of the amount of available stored energy and the portion of the amount of direct input energy; powering the secondary power source with the portion of the amount of available stored energy when the amount of available stored energy is above a first selected level; powering the secondary power source with the portion of the amount of direct input energy when the available stored energy is either 1) below the first selected level and the amount of direct input energy is sufficient enough to meet a power demand, or 2) below a second selected level; powering the secondary power source with the combination of a portion of the amount of available stored energy and a portion of the amount of direct input energy if the available stored energy is either 1) below a first selected level and the amount of direct input energy is not sufficient enough to meet a power demand, or 2) above the second selected level; using an engine to generate the amount of direct input energy and to generate a first amount of storable energy; based on the amount of available stored energy, operating the engine at or near one of 1) a first predefined power level when the amount of available stored energy is within a predetermined upper range of stored energy, 2) a second predefined power level when the amount of available stored energy is within a predetermined lower range of stored energy, and 3) a third predefined power level within a range of power levels that is inversely proportional to the amount of available energy within a predetermined middle range of stored energy.