In order to reduce parasitic loss, improvements may be implemented on pump and or gear. Replacing conventional fixed displacement pump by variable displacement pump (VDP) saves energy. Closed loop controlled variable displacement pump, a way of adjusting pump's displacement continuously according to steering load and pressure sensing, has been used in off-road application, where the pump is usually designed in the form of axial piston. This paper is concerned with the energy saving analysis for the closed center gear steering system and its design and performance. After reviewing the recent efforts in developing steering system with high energetic efficiency, the new system using closed center steering gear is proposed to reduce power consumption while keeping the conventional steering feel. The mathematical model of the closed-center for steering gear is derived and its stability and performance are analyzed. If the steering feel introduced by the closed center valve is not satisfying, an impedance controlled haptic device (TRW developed, named Column Drive) may be used. The advantage of this system's energy saving will be evaluated for different duty cycles. In order to simplify the analysis, the power consumption for steering is ignored. This approximation is good enough for highway vehicles. The separating of idling engine and cruising engine may apply to highway vehicles pretty well because the intermediate status occupies little time, but not necessarily to city suburban transit vehicle. The mathematical analysis result indicates that we may improve its dynamic response through some modifications, such as increasing the fillet area, making small orifices for center's narrow opening and large orifices for wide opening instead of using same orifices for both, and reducing cylinder port area faster. Of course, all these modifications are limited by not destabilizing the system. The current design, being conservative to ensure stability, has a considerable dead zone, which generates the so-called 'bump' steering feel. In order to improve steering feel, Column Drive is used. Though it is not able to eliminate the nonlinearity of the system, the 'bump' feel is indeed reduced.
Energetic efficiency analysis and performance evaluation for a closed center steering system
2007
6 Seiten, 7 Bilder, 7 Quellen
Conference paper
English
Energetic Efficiency Analysis and Performance Evaluation for a Closed Center Steering System
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