Abstract
Keywords - EPS, Rack assist type EPS, Ball Screw, Noise, Delivery Path
Abstract - Recently the automobile makers tend to adopt an EPS (Electric Power Steering) system which uses an Electric motor for automobile steering assist force in order to reduce the fuel consumption and the emission.
Among the electric power steering, Rack assist type EPS (R-EPS) which assists a rack bar has been a noise problem from the ball screw mechanism. And it is founded that this noise is generated from the ball screw gear itself, in other words, there is an obvious limit to reduce the rate of noise. In this reason, it is true that many steering system manufacturers are trying to develop the modified R-EPS system that can reduce the noise by decreasing RPM of the ball nut and that does not use the ball screw mechanism.
This paper describes the process of understanding a change of noise property (frequency) while noise being transmitted from the ball screw to the driver and an approximate noise delivery path by testing and analyzing a noise in several states (a ball screw assembly, a steering gear assembly and a vehicle state). This process is summarized as finding the main point of countermeasure of noise problems by analyzing a change (increase or decrease) of the sound pressure at any frequency in the above several states. Hereby this paper provides the approximate measures of reducing the noise for composing steering system components and other components (e.g. dash panel, etc) when the R-EPS is equipped with the vehicle. These results are useful to steering system engineers.