Summary

Vehicle drivers in various work sectors in Quebec are exposed to significant levels of whole-body vibration (WBV) and intermittent shocks, which have been associated with an increased risk of lower back pain and degeneration of the spine. Suspension seats are widely used to limit WBV exposure of operators. The vibration reduction performance of a suspension seat is strongly affected by the nature of vibration (magnitude, direction and frequency components) of the vehicle. An optimal performance of a suspension seat can thus be realized only when the suspension is tuned for the specific target vehicle.

Suspension seat manufacturers generally recommend a particular suspension seat design for a wide range of vehicles, which may not provide optimal suspension performance considering significant differences in vibration characteristics of vehicles. Although widely different designs of suspension seats have been commercially available for the past decades, only limited knowledge exists in the tuning and in the adaptation of suspension seats to specific vehicles.

The researchers have frequently encountered inquiries from vehicle operators regarding specific recommendations for an appropriate suspension seat for their vehicle. This study was motivated considering the need for a suspension seat advisor for vehicle operators. The overall objective of this activity was formulated to conduct a review of the state-of-the-art developments in suspension seats so as to gain knowledge towards an eventual development of a suspension seat advisor. The specific goal of the activity is twofold. The reported advances in suspension seats are firstly explored through a comprehensive review of scientific publications and patents, to identify desirable technical features and to gain knowledge of methods for designing vehicle-specific suspension seats. The technical features of commercially available suspension seats are subsequently reviewed to build knowledge of the performance characteristics of suspension seats for different vehicles in view of the attenuation of multi-axis vibration and of adequate ergonomic design factors.

This research activity involved comprehensive reviews of various technical features of commercially available suspension seats, and critical reviews of reported technical advances in passive, semi-active and active suspension seats, including the performance characteristics and the assessment methods. The technical features of commercially available suspension seats were mostly compiled from the data provided by the manufacturers’ websites. This was supplemented by personal discussions with leading suspension seat manufacturers in the USA and in Europe, as well as with a leading manufacturer of agricultural machines in the USA. The review was particularly focused on vibration isolation performance of suspension seats and their adaptation to vehicles employed in different work sectors such as construction, forestry, mining, agriculture, material handling and public transportation. In addition, ergonomic design features of suspension seats, namely, lumbar support, cushion design, height/weight adjustment and other adjustments were gathered and examined. The scientific studies reporting advances in suspension seat design were reviewed with particular focus on: (i) performance assessment methods; (ii) concepts in passive, semi-active and active suspension seats and their practical implementations; (iii) developments in fore-aft and lateral vibration isolators; (iv) laboratory/field assessments of suspension seats; and (v) numerical modelling and assessments.

From the reviews of the available suspension seats, it was evident that the vast majority of them employed a cross-linkage platform, with either mechanical or air spring, one or two hydraulic dampers and elastic suspension travel limiters. All designs provided an adjustable seat height, which was generally coupled with an adjustment for the occupant weight. Some designs provided automatic ride height adjustment to ensure mid-ride suspension position and thereby a reduced risk of shocks induced by interactions with the suspension travel limiters. The seats also provided a fore-aft adjustment apart from adjustable cushion and backrest inclinations in order to provide more comfortable and controlled sitting posture. Some of the seats were equipped with an either fixed or adjustable lumbar support, although a quantitative assessment of such support could not be found. In addition, the same suspension designs were recommended for widely different vehicles with notably different WBV patterns, while very little to negligible information was available on shock/vibration isolation performance of the different seats. Moreover, data on the effectiveness of fore-aft and lateral seat isolators were not available.

In recent years, developments in semi-active and active suspension systems have been emphasized and a large number of controller designs have been proposed to achieve enhanced attenuation of WBV. These are mostly focused on vertical vibration isolation. The practical implementations of active suspension seats have been limited to only a few, while a number of manufacturers have developed semi-active suspension seats using controllable magnetorheological dampers. These devices have shown a superior performance in eliminating impacts with the suspension travel limiters, but with only minimal gain in the vibration isolation effectiveness of the suspension. Moreover, the assessments of active and semi-active suspension seats have been limited to only a few classes of vehicle excitation.