This paper focuses on comparing the performance of the embedded control of a hybrid powertrain with the original and downsized engine. Optimal robust control approach is used to develop a real time energy management strategy. The main idea is to store the normally wasted mechanical regenerative energy in energy storage devices for later usage. The regenerative energy recovery opportunity exists in any condition where the speed of motion is in the opposite direction to the applied force or torque. This is the case when the vehicle is braking, decelerating, the motion is driven by gravitational force, or load driven. The real time control challenge is to balance the system power demands from the engine and the hybrid storage device, without depleting the energy storage device or stalling the engine in any work cycle. In the worst case scenario, only engine is used and hybrid system is completely disabled. A rule based control algorithm is developed and is tuned for different work cycles and might be linked to a gain scheduling algorithm. A comparison of the fuel savings using the hybrid system with the original and downsized engines is performed.