F2008-12-166
Hardware-in-the-Loop Simulation: Customer-Oriented Comparison of the Influence of Power Steering Systems on the Vehicle Fuel Consumption and Energy Management
From a viewpoint of recent global ecological problems, CO2 emission regulations and an improvement of vehicle fuel consumption have been coming to be world wide important issues. In addition, vehicle manufactures are finding themselves under increasing pressure to keep up with ever-increasing customer requirements (i.e. comfort functions). Vehicle energy management that has been proven successful in the past may no longer be sufficient in order to meet these new complex challenges. The development of power-on-demand power steering systems has proceeded with the aim of saving energy and adding additional functions of safety and comfort in accordance with the progress in electronics technology. In the past little work has been done to investigate and compare their energy saving possibilities besides the European longitudinal driving cycle MVEG (Motor Vehicle Emissions Group). However, since power steering systems consume energy during not steering operation (standby mode) and increase it when any steering operation requires power assistance (power mode), it is required to take account of vehicle lateral dynamics in addition to longitudinal dynamics. This paper describes a method of applying hardware-in-the-loop simulation (HILS) to power steering systems, along with the procedure for determining the fuel consumption in customer-oriented driving cycles. HILS integrates actual power steering systems with the vehicle model, forming a closed loop to be simulated in real time. It makes possible the identical test procedures that are difficult or even impossible to hit in actual driving tests. Provided that the test procedures (i.e. driver input, vehicle parameters and road conditions) are identical, an objective comparison of the influence of power steering systems on the vehicle fuel consumption and energy management can be made. The results of the HILS have better credibility than that from pure numerical simulation. The HIL test system has been built up at the Lehrstuhl für Fahrzeugtechnik (Institute for Automotive Technology) of the Technical University of Munich. The modular design of the HIL test system allows integrating various power steering systems such as for conventional hydraulic power steering, electro-hydraulic power steering and electric power steering. The efficiency analysis and comparison is based on driving cycles which synthesise various day-to-day driving patterns with steering actions (urban, road, motorway). Data is provided which demonstrates the total sum of fuel savings in liter/100 kilometres through power-on-demand systems. A method for accounting the multi-disciplinary influences on the vehicle fuel consumption and energy management is provided, along with correlation results for a conventional and an optimised hydraulic power steering system. This method allows an objective quantification by detailing what constitutes the influences of various power steering systems on the fuel consumption under customer-oriented driving conditions.
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