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In the automobile industries, weight reduction has been investigated to improve fuel efficiency together with reduction of CO2 emission. In such circumstance, it becomes necessity to make an electric power steering (EPS) more compact and lightweight. In this study, we aimed to have a smaller and lighter EPS gear size by focusing on an impact load caused at steering end. In order to increase the shock absorption energy without increase of stopper bush size, we propose new theory of impact energy absorption by not only spring function but also friction, and a new stopper bush was designed on the basis of the theory. The profile of the new stopper bush is cylinder form with wedge-shaped grooves, and when the new stopper bush is compressed by the end of rack and the gear housing at steering end, it enables to expand the external diameter and produce friction. In this study, we considered the durability in the proposed profile.

This paper will discuss the stress reduction of the worm wheel for an electric power steering (EPS) system. The research discussed in this paper focused on the worm wheel, the EPS component that determines the maximum diameter of the system. If the stress of the worm wheel could be reduced without increasing in size, it would be possible to reduce the size of the worm wheel and EPS system. In order to reduce the stress of the worm wheel, the conventional design method has extended the line-of-action toward outside of the worm wheel to increase the contact ratio of the gears and these method lead to an increase in the outer diameter. In order to address this issue, past research proposes the basic concept to extend line-of-action toward the inside of the worm wheel. And this new meshing theory was named MUB (Meshing Under Base-circle) theory. In this paper, characteristics of meshing of the gear formed by MUB theory are determined in more detail.

A new electric power steering (EPS) was developed which uses an electric motor to provide assistance. It is a system combinning the latest in power electronics and high power motor technologies. The development was aimed at enhancing the existing hydraulic power steering's energy efficiency, driver comfort as well as increasing active stability. This paper describies the overall concept of EPS and outlines the components and control strategies using electronics. The EPS was tested on a front wheel drive vehicle weighing 1000kg in front axle load. The results showed a 5.5% improvement in fuel economy. The EPS has also achieved returnability that gives the driver more moderate feelings matching the vehicle in action as well as the active stability control strategy for high speed driving.

In this research, we investigate the methods for controlling moment of rotational inertia in the electric power steering (EPS) system. We first look at the effects of moment of rotational inertia on conventional EPS systems. Methods for evaluating those effects and countermeasures for controlling the moment of inertia are proposed. After explaining the evaluation method, we describe a design procedure for filters for controlling the moment of rotational inertia by H∞ control method. We also describe the formation of low-order systems of filters obtained, in addition to control block diagrams using filters in the system and their stabilization. Finally, we have equipped a vehicle with this controlled EPS system. The evaluation results have confirmed that the moment of rotational inertia can be satisfactorily controlled.

A change of vehicle handling characteristics due to increase of lateral acceleration as well as effects of the steering gain adaptation of VGS to that was analyzed by quasi-steady-state analysis to find out a basic strategy for the adaptive gain scheduling in the VGS. A study using a simple fixed base type of simulator showed the upper and lower limit of the appropriate gain of the steering system. A computer simulation study on lane-change response of the driver-vehicle-system gave us a view that there exists a suitable gain setting for the VGS from a view point of driver-vehicle-system stability.

Steering gear ratios in existing automobiles are made almost constant. Therefore, at low speed, the larger steering wheel angle needed increases drivers' physical workload especially in the case of a maneuver with large directional angle change such as parking, and may impair quickness in response necessary for a sudden lane change maneuver such as obstacle avoidance at low speed. On the contrary, at high speed, a relatively small steering angle input can generate comparatively large vehicle lateral acceleration, and this larger overall steering gain may necessitate drivers' more meticulous steering operation which can produce increased mental workload. In addition, for understeer vehicle, steering gain tends to decrease as lateral acceleration increases because of saturation in lateral force of the tire, and this may also reduce maneuverability in directional change, especially during cornering.