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Design of Experiments on Steering Shimmy in Hydraulic versus Electric Power Steering Systems

Article of Honda R&D Technical Review Vol.24 No.1


Research was conducted on automotive power steering systems at a component level to examine system sensitivity to an oscillatory loading condition. This series of experiments was aimed at quantifying system response of hydraulic power steering (HPS) and electric power steering (EPS) to objectively compare vibration attenuation capability of the two systems.
Steering shimmy is caused by an imbalance in a wheel/tire rotational assembly. The energy of this phenomenon is usually too great for a HPS system to completely attenuate while an EPS system is commonly capable of absorbing most of the vibration. With a HPS system, vibration can be partially attenuated through steering system parameter variation such as increasing friction or inertia. In an EPS system, the motor inertia, programming control, and gear reduction make it comparatively simple to attenuate the vibration before it reaches the steering wheel. This ability of an EPS system to partially or completely attenuate vibration caused by other chassis components has yet to be quantified. Furthermore, it has yet to be objectively compared with HPS and is thus the primary focus of this research.
The test results confirm that increased inertia and friction have a dramatic effect on steering vibration regardless of application. There is a friction threshold that can be used in partially mitigating some small vibrations such as tire imbalance. Furthermore, it shows that in an EPS system, the motor inertia and electric motor gear reduction are beneficial in stopping vibration from reaching the steering wheel. Through this research, we have shown that future developments are better equipped to attenuate steering shimmy per the application of an EPS system.


(1) Yu, J., Nutwell, B., Brickner, B., Johnson, M.: Analysis of Vehicle Chassis Transmissibility of Steering Shimmy and Brake Judder: Mechanism Study and Design of Experiments, SAE Technical Paper, 2007-01-2342 (2007)
(2) Yu, J.: An Analysis of Fluid-Mechanically-Coupled, Non-Linear Rotational Vibration Sensitivity of Automotive Hydraulic Power Steering Systems, International Mechanical Engineering Congress and Exposition, Anaheim, California, U.S.A. (2004)
(3) Yu, J., Slattengren, J., Motoyama, K.: Modeling and Factor Analysis of Hydraulic Power Steering Systems for Rotational Steering Vibration by Using MSC. ADAMS, MSC Software Virtual Product Development Conference, Huntington Beach, California, U.S.A. (2004)

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