In-vehicle vibration study of child safety seats

This paper reports experimental measurements of the in-vehicle vibrational behaviour of stage 0&1 child safety seats. Road tests were performed for eight combinations of child, child seat and automobile. Four accelerometers were installed in the vehicles and orientated to measure as closely as possible in the vertical direction; two were attached to the floor and two located at the human interfaces. An SAE pad was placed under the ischial tuberosities of the driver at the seat cushion and a child pad, designed for the purpose of this study, was placed under the child. 4 test runs were made over a pave’ (cobblestone) surface for the driver’s seat and 4 for the child seat at both 20 km/h and 40 km/h. Power spectral densities were determined for all measurement points and acceleration transmissibility functions (ATFs) were estimated from the floor of the vehicle to the human interfaces. The system composed of automobile seat, child seat and child was found to transmit greater vibration than the system composed of automobile seat and driver. The ensemble mean transmissibility in the frequency range from 1 to 60 Hz was found to be 77% for the child seat systems as opposed to 61% for the driver’s seats. The acceleration transmissibility for the child seat system was found to be higher than that of the driver’s seat at most frequencies above 10 Hz for all eight systems tested. The measured ATFs suggest that the principal whole-body vibration resonance of the children occurred at a mean frequency of 8.5, rather than the 3.5 to 5.0 Hz typically found in the case of seated adults. It can be concluded that current belt-fastened child seats are less effective than the vehicle primary seating systems in attenuating vibrational disturbances. The results also suggest the potential inability of evaluating child comfort by means of existing whole-body vibration standards

Absorbed power of small children

Objective. To experimentally measure the seated vertical direction whole-body absorbed power characteristics of small children less than 18 kg in mass. Background. Several studies have reported whole-body absorbed power for adult humans, but no data has been published previously for small children. Methods. Eight children were tested in a laboratory test rig which incorporated safety features which satisfy existing international standards for human testing. Force and acceleration were measured at the point of input to a rigid seat at a sampling rate of 200 Hz, and analysis was performed over the interval from 1.0 to 45.0 Hz. A double normalised (both input acceleration and test subject mass) measure of absorbed power was used. Results. The vertical whole-body power absorption characteristics of the small children were found to present differences with respect to those of adults. The mean frequency of peak absorption was found to be 7.4 Hz as opposed to approximately 4.0–5.0 for adults. The interval of absorption was found to be from approximately 3 to 16 Hz and the total double normalised absorbed power was found to be 86% that of adults. Conclusions. The differences in dynamic response between small children and adults raise questions regarding the applicability of whole-body vibration guidelines such as ISO-2631 in the case of small children since these guidelines were developed from mechanical and subjective response data of adults

Facilitating the driver detection of road surface type by selective manipulation of the steering-wheel acceleration signal

Copyright @ 2012 by Institution of Mechanical Engineers.Previous research has investigated the possibility of facilitating the driver detection of road surface type by means of selective manipulation of the steering-wheel acceleration signal. In previous studies a selective increase in acceleration amplitude has been found to facilitate road-surface-type detection, as has selective manipulation of the individual transient events which are present in the signal. The previous research results have been collected into a first guideline for the optimization of the steering-wheel acceleration signal, and the guideline has been tested in the current study. The test stimuli used in the current study were ten steering-wheel acceleration-time histories which were selected from an extensive database of road test measurements performed by the research group. The time histories, which were all from midsized European automobiles and European roads, were selected such that the widest possible operating envelope could be achieved in terms of the r.m.s. value of the steering acceleration, the kurtosis, the power spectral density function, and the number of transient events present in the signal. The time histories were manipulated by means of the mildly non-stationary mission synthesis algorithm in order to increase, by a factor of 2, both the number and the size of the transient events contained within the frequency interval from 20 Hz to 60Hz. The ensemble, composed of both the unmanipulated and the manipulated time histories, was used to perform a laboratory-based detection task with 15 participants, who were presented the individual stimuli in random order. The participants were asked to state, by answering 'yes' or 'no', whether each stimulus was considered to be from the road surface that was displayed in front of them by means of a large photograph on a board. The results suggest that the selectively manipulated steering-wheel acceleration stimuli produced improved detection for eight of the ten road surface types which were tested, with a maximum improvement of 14 per cent in the case of the broken road surface. The selective manipulation did lead, however, to some degradation in detection for the motorway road stimulus and for the noise road stimulus, thus suggesting that the current guideline is not universally optimal for all road surfaces

Apparent mass of small children: Modelling

Mass-spring-damper models are widely available for quantifying the whole-body vibration characteristics of primates, human adolescents and human adults, but no models have previously been developed for small children. In this study a single degree of freedom, linear, mass-spring-damper with base support model was determined from the seated vertical apparent mass modulus function of each of eight small children of less than 18 kg in mass. A Differential Evolution optimisation algorithm was used in conjunction with a mean squared error measure and penalty functions to identify the optimal child model parameter values. The eight child models were characterised by a mean moving mass m1 of 8.5 kg, a mean body stiffness k1 of 21131 N/m and a mean damping coefficient c1 of 329 Ns/m. Comparison to the parameter values of similar models reported in the literature for Rhesus monkeys, Baboons, large children and adults suggests that the values obtained in the current study for small children are intermediate between the smaller primates and the larger humans. A regression analysis of the model parameters was performed as a function of subject mass for a data set consisting of the eight child models, twelve similar models for primates, and 60 similar models for large children and adults. The moving mass m1 of the group of models grew with a power exponent of approximately unity, the body stiffness k1 grew with a power exponent of approximately +1/2, the damping coefficient c1 grew with a power exponent of approximately +3/4 and the dimensionless damping ratio was independent of subject mass. The natural frequency of the models grew with a power exponent of approximately –1/4

Perception enhancement for steer-by-wire systems

Modern automobiles are safer and more comfortable than ever before. If there is one criticism that can be made, however, it is that the achievement of higher levels of comfort has sometimes come at the expense of a lack of driver involvement. The issue of driver involvement can become critical in the case of by-wire systems since these systems do not necessarily have a predetermined path or transfer mechanism for carrying stimuli to the driver. This article discusses the technical requirements of perception enhancing systems for the vehicle steering

Self-Reported Upper Body Discomfort due to Driving: Effect of Driving Experience, Gender and Automobile Age

This study investigated the human upper body discomfort caused by automobile driving. Both global and local discomfort estimates were achieved by means of a self-administered questionnaire. The questionnaire used a Borg CR10 scale to evaluate human discomfort, and contained sections to gather information regarding the driving experience, gender and most frequently used automobile of the respondent. The geographic area surveyed was the city of Turin, Italy, and data from a total of 269 drivers was analysed. For all subgroups analysed, the back region was reported to suffer the greatest discomfort, followed in order of decreasing discomfort by the neck, shoulder, arm, hand-wrist, forearm, head, chest and mandible. Generally, female drivers provided higher discomfort responses than male drivers. Subdividing the data according to driving experience lead to large and statistically significant (a<0.05) differences inboth global and local discomfort. Subdividing by gender suggested some significant differences, while subdividing by automobile age produced few differences. The results suggest the usefulness of controlling for test subject driving experience and gender when performing subjective evaluations of automobiles. Further, comparison of the global and the local discomfort responses suggested that individuals were able to form a stable estimate of global discomfort based on the sensations perceived in each of the individual body regions involved. This suggests the interesting possibility that global evaluations may not always provide an accurate understanding of human discomfort since situations can be imagined in which different distributions of upper body discomfort might produce the same, global, response

Analysis of variations in diesel engine idle vibration

The variations in diesel engine idle vibration caused by fuels of different composition and their contributions to the variations in steering wheel vibrations were assessed. The time-varying covariance method (TV-AutoCov) and time-frequency continuous wavelet transform (CWT) techniques were used to obtain the cyclic and instantaneous characteristics of the vibration data acquired from two turbocharged four-cylinder, four-stroke diesel engine vehicles at idle under 12 different fuel conditions. The analysis revealed that TV-AutoCov analysis was the most effective for detecting changes in cycle-to-cycle combustion energy (22.61 per cent), whereas changes in the instantaneous Values of the combustion peaks were best measured using the CWT method (2.47 per cent). On the other hand, both methods showed that diesel idle vibration was more affected by amplitude modulation ( 12.54 per cent) than frequency modulation (4.46 per cent). The results of this work suggest the use of amplitude modulated signals for studying the human subjective response to diesel idle vibration at the steering wheel in passenger cars

The role of the scale and the frequency bandwidth of steering wheel vibration on road surface recognition

Automobile drivers are regularly exposed to vibrational stimuli in their vehicle. Of the automobile subsystems, the steering wheel is one of the most important due to its role in controlling the vehicle. In particular, the steering wheel plays an important role in transmitting information about the road and about the vehicle to the driver. This paper investigates the effect of steering system feedback gain and steering system feedback bandwidth on the human interpretation of the driving information transmitted by the steering wheel. Human recognition of road surface type was found to be highly dependent on the feedback gain and the feedback bandwidth of the steering wheel vibration. The results provide some basic guidelines for designing the control logic of steer by wire systems

Human Perception of Diesel Engine Idle Vibration

While the human perception of diesel engine noise has been the subject of numerous studies, the perception of the vibrational disturbance reaching the driver has not previously been investigated. This contribution presents the results of a recent research study performed at Sheffield University which analysed the nature of diesel engine idle, and modelled the associated human growth function. The results have shown that the largest component of diesel idle irregularity arriving at the steering wheel is amplitude modulation of the firing frequency and that the human subjective response grows with a power exponent greater than 1.0 for modulation values greater than 0.2