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This paper describes a hydraulic suspension which is shown by simulation to give lower body accelerations and lower dynamic tyre forces than a conventional suspension. Eigenvalue analysis is used to help explain how the advanced system simulates an active suspension, operating with a “sky-hook” damper control strategy. A 3-dimensional mathematical model is used to explore the performance of the advanced system. Comparisons with a conventional suspension showed that the advanced system offers 30% lower ISO weighted, root mean square body vertical acceleration and 10% lower root mean square dynamic tyre forces.

The ride dynamics of articulated heavy trucks were studied to assess the benefits of applying electronically controlled suspension elements. Computer simulations were used to compare passive, two-state and continuous semi-active, and fully active suspensions. These results prompted further work to develop a prototype active suspension, operating according to a limited bandwidth strategy, which was tested on a full size, single-wheel-station vibration rig. With the active prototype, root mean square body vertical acceleration was 30% lower than with a production air suspension, during a test simulating travel over a very good road profile. RMS dynamic tyre forces, generated by the active prototype were similarly 20% lower. Mean power consumption during this test was 1.2kW. Further consideration of the limited bandwidth active suspension led to the invention of a substantially passive equivalent.