A Methodology for Accounting for Uneven Ride Height in Soft Suspensions with Large Lateral Separation

This study pertains to motion control algorithms using statistical calculations based on relative displacement measurements, in particular where the rattle space is strictly limited by fixed end-stops and a load leveling system that allows for roll to go undetected by the sensors. One such application is the cab suspension of semi trucks that use widely-spaced springs and dampers and a load leveling system that is placed between the suspensions, near the center line of the cab. In such systems it is possible for the suspension on the two sides of the vehicle to settle at different ride heights due to uneven loading or the crown of the road. This paper will compare the use of two moving average signals (one positive and one negative) to the use of one root mean square (RMS) signal, all calculated based on the relative displacement measurement. It will illustrate the advantage of using two moving average relative displacement signals for motion control application with concrete examples. If the nominal ride height is assumed to be the zero point of the relative displacement measurements, the two moving average signals are computed for both the positive and the negative portion independently. The highest value of the two is used for motion control. The results show that a clear distinction can be noticed between a high amplitude displacement signal and a low amplitude displacement with a high DC offset, two scenarios that may not be distinguishable using RMS calculations. The results suggest that the method that involves two moving averages is a better alternative to using one RMS calculation.

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See papers presented at SAE 2009 Commercial Vehicle Engineering Congress & Exhibition, October 2009, Rosemont, IL, USA, Session: Vehicle Dynamics Simulation (Part 2 of 2)

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