Power assist hybrids use the ICE for primary power, with a torque-boosting electric motor also connected to a largely conventional powertrain. The electric motor, mounted between the engine and transmission, is essentially a vast starter motor, which operates when the engine needs to be turned over and when the driver “steps on the gas” and requires extra power.
The electric motor may also be used to restart the combustion engine, deriving the same benefits as shutting down the main engine at idle. In contrast, the enhanced battery system is used to power accessories.