Paul-Émile Boileau

Vibration attenuation performance of suspension seats for off-road forestry vehicles

Abstract Four different types of vertical suspension seats were evaluated in the laboratory and in the field in order to measure their adaptability for attenuating whole-body vibration in log skidders used in the forest industry. Laboratory testing first consisted of determining the static and dynamic characteristics of the seats such as the static stiffness of the cushions and suspension systems and the hysteresis parameters and damping properties of the cushions. The vibration attenuation characteristics of the seats were then measured using a laboratory test rig simulating a driver work station. The influence of amplitude of excitation and the variations in seat height on the vibration attenuation performance of the suspension seats was evaluated for sinusoidal excitations in the frequency range of 0.2–8.0 Hz. The seats were then field tested during normal skidding operations to determine their vertical transmissibility characteristics and to compare the vibration exposure that results from operating a skidder while being equipped with a suspended seat, as opposed to having an unsuspended one. There was generally good agreement between the transmissibility characteristics measured in the laboratory and in the field. The results of vibration transmissibility and exposure are helpful in identifying one of the suspension seats as being the most appropriate for attenuating vertical whole-body vibration on skidders, while conforming at the same time to the basic dimensional characteristics and stability required for safe operation of such vehicles.

Effect of Back Support Condition on Seat to Head Transmissibilities of Seated Occupants under Vertical Vibration

The seat-to-head transmissibility (STHT) of seated human subjects has been investigated through measurements of vertical seat vibration transmitted to the head in both vertical and fore-and-aft directions. The experiment was performed using 12 adult male subjects exposed to whole-body vertical random vibration in the 0.5–15 Hz frequency range. The effects of back support conditions on the transmitted vibration were investigated by considering three back support conditions (No back support, vertical back support, and inclined back support), and two different hands positions (hands in lap and hands on the steering wheel) while exposed to three magnitudes of excitation (0.25, 0.5 and 1.0 m/s2 rms acceleration). A helmet-strap-mounted accelerometer mounting system was designed to measure the head acceleration motions along the three translational axes. The results attained from ANOVA suggested a strong influence of the back support condition on the magnitude of both the vertical and fore-and-aft STHT. The results also revealed the nonlinear response of the seated body with respect to the excitation magnitude, while the effect of hands position was judged to be insignificant.

Ride dynamic evaluations and design optimisation of a torsio-elastic off-road vehicle suspension

The ride dynamic characteristics of a novel torsio-elastic suspension for off-road vehicle applications are investigated through field measurements and simulations. A prototype suspension was realised and integrated within the rear axle of a forestry skidder for field evaluations. Field measurements were performed on forestry terrains at a constant forward speed of 5 km/h under the loaded and unloaded conditions, and the ride responses were acquired in terms of accelerations along the vertical, lateral, roll, longitudinal and pitch axes. The measurements were also performed on a conventional skidder to investigate the relative ride performance potentials of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in magnitudes of transmitted vibration to the operator seat. Compared with the unsuspended vehicle, the prototype suspended vehicle resulted in nearly 35%, 43% and 57% reductions in the frequency-weighted rms accelerations along the x-, y- and z-axis, respectively. A 13-degree-of-freedom ride dynamic model of the vehicle with rear-axle torsio-elastic suspension was subsequently derived and validated in order to study the sensitivity of the ride responses to suspension parameters. Optimal suspension parameters were identified using the Pareto technique based on the genetic algorithm to obtain minimal un-weighted and frequency-weighted rms acceleration responses. The optimal solutions resulted in further reduction in the pitch acceleration in the order of 20%, while the reductions in roll and vertical accelerations ranged from 3.5 to 6%.

Multi-Axis Sinusoidal Whole-Body Vibrations: Part II — Relationship between Vibration Total Value and Discomfort Varies between Vibration Axes

The influence of vibration duration and the amount of rest between successive vibrations was addressed in Part I of this study. The relationship between discomfort and Vibration Total Value for different axes of vibration is assessed in Part II. Ten subjects were exposed to repeated single axis, planar, and 6 degree of freedom multi-axial vibrations. We observed statistically significant differences in discomfort between the different axes of vibration for similar ranges of Vibration Total Values. In particular. we observed that discomfort reports for vibrations in the Z axis and XY plane were less than discomfort reports associated with XZ plane and 6 df vibrations when the same range of Vibration Total Values were compared. Furthermore, single axis vertical vibrations were typically associated with less discomfort than multi-axis vibrations when similar ranges of Vibration Total Values were compared. This finding infers that the frequency weighting scheme presented in ISO 2631–1 does not achieve inter-axis equivalence and indicates that a more comprehensive study of multi-axis vibration is required to suggest changes to the ISO 2631–1 weighting factors.

Multi-axis sinusoidal whole-body vibrations: Part I - How long should the vibration and rest exposures be for reliable discomfort measures?

Laboratory-based whole-body vibration studies often involve complex experimental designs, dozens of vibration exposures and multiple sessions. Shortening the test vibration duration would increase experimental efficiency by permitting more trials in the same time period. This study evaluated reported discomfort based on different sinusoidal vibration durations and amounts of rest between successive vibrations. Ten subjects were exposed to four blocks of vibration trials (15/20 second vibration and 5/10 second rest durations). Each block of 37 trials included repeated single axis, planar, and 6 degree of freedom multi-axial vibrations. These repeated trials were analysed to evaluate whether discomfort varied between the different blocks. We did not observe any statistically significant differences in discomfort between the different vibration and rest durations. This finding is useful for designing future vibration experiments. Part II of this study evaluates the relationship between discomfort and vibration exposure.

Influence of Vehicle Size, Haulage Capacity and Ride Control on Vibration Exposure and Predicted Health Risks for LHD Vehicle Operators

Documented whole-body vibration (WBV) exposure levels at the operator/seat interface are limited for underground mining load-haul-dump (LHD) vehicles. Therefore, WBV exposure during the operation of eight small and nine large LHD vehicles, under loaded and empty haulage, was measured in accordance with ISO 2631–1 guidelines. Vibration exposure was also measured for a subsample of LHD vehicles equipped with a feature designed to reduce vibration exposure (ride-control). Operator health risks were predicted according to ISO 2631–1 health guidance caution zone (HGCZ) limits for daily vibration exposure. Vibration exposure was not significantly different for vehicle size or ride control but was significantly lower when driving with a loaded haulage bucket. All operators of small LHDs and one large LHD operator were exposed to vibration levels above the HGCZ.

Evaluation of whole-body vibration exposure using a fourth power method and comparison with ISO 2631

Abstract Vertical whole-body vibrations recorded at the driver-seat interface on skidders were analyzed by using a “fourth power” procedure for predicting the discomfort and the degradation in health caused by the motions. The root-mean-square acceleration and the crest factor of the vibrations were also evaluated for eight skidder vehicles by fixing the integration period at 1 minute. For motions with large crest factor values, a relationship was found for predicting the “fourth power” vibration parameters, such as the root-mean-quad acceleration and the Vibration Dose Value from the root-mean-square acceleration and the crest factor. That relationship was found to be in good general agreemnt with the experimental results, indicating that, for the same rms level, greater discomfort would be felt with increasing peak levels. With respect to the “fourth power” procedure, it was established that for vibration exposure on skidders, the ISO 2631 evaluation procedure would underestimate the vibration dose by up to three times for comfort and as much as seven times for health, depending on the creast factor value.

Energy Absorption of Seated Body Exposed to Single and Three-axis Whole Body Vibration

The absorbed power characteristics of seated body exposed to whole-body vibration along the individual and combined fore-aft (x), lateral (y) and vertical (z) axes are investigated through measurements of body-seat interactions at the two driving-points formed by the body and the seat-pan, and upper body and the seat backrest. The experiments involved two levels of back support (no back support and vertical backrest) and two levels of broad-band vibration with nearly constant acceleration power spectral density in the 0.5–20 Hz frequency range applied along the individual x-, y- and z- axis (0.25 and 0.4 m/s2 rms acceleration), and along the three-axis (0.23 and 0.4 m/s2 rms acceleration along each axis). The biodynamic responses, measured at the seat-pan and the backrest are applied to characterize the total seated bodys energy transfer along each axis. Furthermore, an alternative frequency response function method Hv is employed to capture the coupling in the seated body responses to uncorrelated multi-axis vibration. The total vibration absorbed power responses to simultaneous x, y and z –axis vibration are subsequently derived as the summation of vibration absorbed power along the individual axis within each one-third frequency band. The mean responses measured at the seat-pan suggest strong effects of the back support, and the direction and magnitude of vibration. The total vibration power absorbed by the seated body is further estimated under a multi-axis vibration environment of four different work vehicles. The results suggest that total average power absorbed under reported vehicular vibration varies with the effective acceleration in a nearly quadratic manner.

A modified resonance method for determining elastic moduli

Abstract This preliminary investigation deals with the correlation of the measured resonance frequencies of cylinders and their elastic properties. By using signals which are generated directly by the materials upon collision in rotating beds of samples, constraints inherent to the usual dynamic resonance methods are eliminated; in particular, concern for the practical limitations to specimen size is eliminated. The availability of modern signal processing equipment provides the means for deriving the elastic moduli of rigid materials with ease, speed, accuracy and precision. Further investigations of this direct method of frequency analysis, on specimens with varying configuration ratios and over an extended frequency range, would seem to provide a significant improvement to existing resonance methods.

Multi-performance analyses and design optimisation of hydro-pneumatic suspension system for an articulated frame-steered vehicle

ABSTRACT This study investigates the coupled ride and directional performance characteristics of an articulated frame-steered vehicle (AFSV). A three-dimensional multi-body dynamic model of the vehicle is formulated integrating the hydro-mechanical frame steering and hydro-pneumatic suspension (HPS) systems. The model parameters are obtained from field-measured data acquired for an unsuspended AFSV prototype and a validated scaled HPS model. The HPS is implemented only at the front axle, which supports the driver cabin. The main parameters of the HPS, including the piston area, and flow areas of bleed orifices and check valves, are selected through design sensitivity analyses and optimisation, considering ride vibration, and roll- and yaw-plane stability performance measures. These include the frequency-weighted vertical vibration of the front unit, root-mean-square lateral acceleration during the sustained lateral load transfer ratio period prior to absolute rollover of the rear unit, and yaw-mode oscillation frequency following a lateral perturbation of the vehicle. The results suggested that the implementation of the HPS to the front unit alone could help preserve the directional stability limits compared to the unsuspended prototype vehicle and reduce the ride vibration exposure by nearly 30%. The results of sensitivity analyses revealed that the directional stability performance limits are only slightly affected by the HPS parameters. Further reduction in the ride vibration exposure was attained with the optimal design, irrespective of the payload variations. The vehicle operation at relatively higher speeds, however, would yield greater vibration exposure.