Part of the problem with internal combustion engines is that they are most efficient at or near their rated load. At low loads they are very inefficient. The other part of the problem is that the force needed to accelerate your car is an exponential function. It takes a lot of power to accelerate and we like to accelerate quickly, so the tendency is to put big engines in our cars for better acceleration but operate them very inefficiently by only using a small fraction of the power most of the time. A hybrid improves efficiency in this scenario by putting a heavier load on the engine in low-power situations by charging the battery and mechanically powering the car simultaneously. When the battery can no longer accept charge, we shut the engine off and use the excess stored power. We also conserve some kinetic energy with regenerative braking.
It's more efficient to power the car mechanically with the ICE than it is to use the ICE to run a generator, charge a battery, then use the battery to power the car via an electric motor. Otherwise all our cars would be simple series hybrids instead of the much more complex parallel hybrids we now have. Nevertheless, we gain efficiency with an HEV by putting extra load on the ICE in low-load conditions, storing the extra and then using the stored energy under high-load conditions to aid the ICE or shutting the ICE off entirely in low-load conditions.
It's more efficient to power the car mechanically with the ICE than it is to use the ICE to run a generator, charge a battery, then use the battery to power the car via an electric motor. Otherwise all our cars would be simple series hybrids instead of the much more complex parallel hybrids we now have. Nevertheless, we gain efficiency with an HEV by putting extra load on the ICE in low-load conditions, storing the extra and then using the stored energy under high-load conditions to aid the ICE or shutting the ICE off entirely in low-load conditions.
