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Braking energy recovery can significantly contribute to fuel economy and emission reduction, particularly for commercial vehicles driving in urban environment. By using the compressed air storage, rather than expensive and vulnerable batteries, this paper proposes a pneumatic hybrid system with an integrated compressor/expander unit (CEU) for commercial vehicles, in order to achieve stop/start function and braking energy recovery. During braking, the compressed air is recovered by CEU working in compressor mode and is charged to the air tanks. When the vehicle starts from stop, the CEU works as an expander to crank the engine with compressed air. The compressed air can also be used to supply the air tank of brake boost system, thus reducing its energy consumption. The mathematical models of energy conversion units, including the two modes of CEU and the air brake system, are established and analyzed.

To optimally allocate control authorities to co-existing active actuators, an integrated chassis controller with main/servo-loop structure is designed to coordinate direct yaw moment control and active steering. Firstly, a sliding mode controller in the main-loop calculates the desired stabilizing forces. Then in the servo-loop, by directly considering limits of road friction and actuators, a quadratic programming based control allocation approach is adopted to reasonably and optimally distribute these deisired forces to tire actuator actions. Co-simulation of Matlab/Simulink and Carsim clarifies that the proposed controller could significantly improve vehicle handling performances.