Fuel efficiency improvement in HEVs using electromechanical brake system

Today, two of the main concerns in transportation industry are reducing fuel consumption and emissions, and tough regulations are put on the vehicle manufacturers in these regards. One of the main approaches towards reducing CO₂ emissions is hybridization of the powertrain system. Substantial R&D in this area over the last couple of years has resulted in rather optimal components and control strategies, and hence that further substantial improvements are difficult. This motivates research on other energy consuming vehicle subsystems, e.g. pneumatic and hydraulic systems. In this paper, the brake system of a hybrid city bus is studied. A complete electrification of the primary brake system would eliminate the use of low efficiency pneumatics for braking. It is therefore interesting to investigate how much energy can be saved by using electrically actuated and controlled primary brakes. The study is based on simulations in Autonomie which is a MATLAB/SIMULINK based vehicle simulation software package. Different representative driving cycles are studied. It is shown that fuel consumption can be reduced in the range of 0.5 to 1.5% by substituting the pneumatic brake system with a mechatronic one. This may seem limited, but can, combined with substitution of also other less efficient subsystems with their mechatronic counterparts, result in a substantial environmental and economic improvement.