Estimating the energy consumption of steering assist systems in commercial hybrid electric vehicles : A basis for utilization strategies

Abstract: The commercial vehicle manufacturer Scania CV AB has introduced a new steering functionality called Redundant Brake Steering (RBS) in vehicles with batteries as energy storage, i.e. hybrid-electric and electric vehicles. Although, the primary steering system in Scania’s electrified vehicles consists of an electrohydraulic steering system (EHS) and an electrical active steering system (EAS). The purpose of introducing RBS is to facilitate the implementation of the EAS as a secondary steering system according to current laws. Consequently, a major benefit is that the conventional back-up hydraulic steering system can be removed. By replacing the back-up system with the active steering system and RBS an entire auxiliary system in the vehicle is eliminated. One of the main ambitions of this study has been to investigate whether the new steering functionality could lead to reduced energy consumption related to steering systems. The approach in this thesis included a literature study of steering systems, brake-steering concepts and available vehicle data to establish methods to quantify the energy consumption of the involved systems. The methods were used to develop a numerical model in the software Matlab which could use collected vehicle data to estimate the energy consumption of the steering systems. To facilitate the data collection a case study was performed using a plug-in hybrid electric vehicle (PHEV) at Scania’s test track in Södertälje, Sweden. The results suggested that the combination of EAS and RBS has potential to assist as primary steering as the energy consumption related to steering could be decreased by up to 90.6%. Also, the results indicated that the load on the vehicle’s electrical circuit could be reduced significantly, while the main drawback is increased steering effort by the driver.