Overall Fuel Economy Improved with Combination of Exhaust Energy Recovery and Brake Energy Recovery: Honda engineers chose the Rankine cycle for their study to develop a small exhaust gas energy recovery system. Engineers focused their study on the elements of the Rankine cycle exhaust gas energy recovery system and steam control technologies for efficiently recovering exhaust gas energy under various vehicle-operating conditions. According to vehicle test results, thermal efficiency could be improved under the operating conditions where the brake energy recovery system could not effectively recover the energy. As a result, the engine's brake thermal efficiency improved by 3.8 points (the improvement rate of 13.2 percent) when the vehicle was driven at 100 km/hour. Thus, the Rankine-cycle exhaust gas energy recovery system combined with the brake energy recovery system can significantly improve the overall fuel economy of a hybrid electric vehicle.