Abstract
In the attached article, possibilities regarding the reduction of energy consumption in power steering systems will be presented and discussed. Conventionally driven steering systems consume approximately 0.4 - 0.7 l / 100 km of fuel [1]. The electrically powered hydraulic "open-center" steering system EPHS decreases this consumption by up to 70 %, whilst guaranteeing the same steering wheel comfort with a limited steering boost at very fast steering manoeuvres. Energy consumption at low steering loads when driving can be reduced with the help of a steering sensor and control system which regulates the electric motor speed. The average power consumption of the open-center system is strongly dependant on the frequency distribution of pressure during mixed driving conditions. The closed-center EPHS system allows power assisted steering even at high dynamics and at the same time low load on the vehicle electrical system. In this case the accumulator size defines the efficiency limit. Below the response level - at low steering wheel torques - the system does not consume energy. Energy consumption during a drive is strongly dependant on the average steering wheel velocity under hydraulic assistance. This is why the choice of one of the above mentioned concepts for general use cannot be generalized. Only a precise study of the frequency distribution of steering angle and steering wheel effort of the vehicle can show advantages and disadvantages of these concepts. The ideal low energy steering system for any given vehicle may be either an open center or closed center system, depending on the average driving conditions which the manufacturer considers normal for that vehicle. However, packaging and cost restraints may also play a significant part in the selection of a suitable system.