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Health & Safety
Mathematical modelling of the stability of passengercarrying tandem seat all terrain vehicle (ATV)
Prepared by MIRA Ltd for the
Health and Safety Executive 2004
RESEARCH REPORT 223
Health & Safety
Mathematical modelling of the stability of passengercarrying tandem seat all terrain vehicle (ATV)
Jonathan Webb, MEng CEng MIMechE
For the first time, passenger carrying tandem all terrain vehicles (ATVs) are being introduced to the UK market. The Health and Safety Executive’s (HSE) policy to date has been that passengers must not be carried on sit-astride ATVs. This policy was formulated when only single seat sit-astride ATVs were available and needs reviewing now the new vehicles are being marketed. To develop the policy it was necessary to gain a greater understanding of the stability of these ATVs with passenger carrying capability. MIRA has been requested by the HSE to conduct a roll-over study on a tandem seat ATV.
The stability assessment conducted involved examining the behaviour of the vehicle in a number of roll-over scenarios with only a rider on board, and then with both a rider and passenger on board. The position of the rider and passenger was also adjusted in order to understand their contribution to vehicle stability during the manoeuvres.
This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.
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2 Experimental procedures
2.1 Model build
2.2 Rider and passenger configurations
2.3 Scenario setting
3.1 Static test results
3.2 Roll-over test results
4.1 Static tests
4.2 Dynamic roll-over tests
Appendix 1 Figure Presentation
iii EXECUTIVE SUMMARY
Due to developments in the All Terrain Vehicle (ATV) market, tandem seat ATVs with the capability to carry passengers are being introduced. Current Health and Safety Executive (HSE) policy advises that passengers should not be carried on sit-astride ATVs, but this policy was based on single seat ATVs only and needs reviewing in light of the new vehicles becoming available. With little information available on the roll-over stability of ATVs with passenger carrying capabilities, MIRA has been requested by the HSE to conduct a roll-over study on a Tandem Seat ATV.
MIRA previously conducted a roll-over analysis for the HSE on an ATV for the purpose of assessing the effectiveness of a Roll-Over Protection System and the roll-over scenarios developed during this exercise have been adopted for this
study. The programme of work was set with these objectives:
• To create a vehicle model of the new ATV including rider and passenger • To simulate the performance of the ATV in five roll-over initiating scenarios • To assess the effect of rider and passenger position on the stability of the vehicle during the manoeuvres
As a result of the study, the following recommendations are made:
• Riders of the ATV should exercise caution when operating the vehicle with a passenger on board, as the presence of the passenger reduces the ATV‘s stability. However, with a maximum recorded reduction in stability of 11 %, the increased hazard is not considered to be overtly high • It should be made clear to both riders and passengers that although their position on the vehicle has only a small effect on its stability, at all times they should try and resist the motion of the vehicle as this will act to increase the ATV‘s stability • The stability of the ATV is most sensitive to rider and passenger positioning when it is involved in scenarios that induce sidewards roll-over. Riders and passengers should therefore be made aware that their position on the vehicle is more important when encountering situations involving traversing slopes, driving sidewards over an edge and negotiating bumps • This study only considers low speed roll-over stability and the results cannot be interpreted to cover high speed handling stability or low friction surfaces. It is advised that additional tests and analyses are conducted if these situations are to be considered
MIRA has been requested by The Health and Safety Executive (HSE) to conduct a roll-over analysis on a new All Terrain Vehicle (ATV). MIRA previously performed a roll-over analysis on an ATV for the purpose of assessing the effectiveness of a Roll-Over Protection System. The results of this study were issued in MIRA report 98-464736.1 This project has been designed to assess the stability of the ATV with both rider and passenger on board. It uses the same test scenarios as in the previous analysis, but with the intention of assessing the effects of rider and passenger position on the point of initiation of vehicle roll-over.
The objectives for this study were:
• To create a vehicle model of the new ATV including rider and passenger
• To simulate the performance of the ATV in five roll-over initiating scenarios
• To assess the effect of rider and passenger position on the stability of the vehicle during the manoeuvres
2.1.1 Vehicle Measurements The vehicle under investigation was a Bombardier Traxter Max, a two seater quad bike. An example of this vehicle was supplied for testing at MIRA by Jets Marivent UK Ltd. Vehicle tests and component measurements were conducted in order to characterise the suspension and steering systems, and the overall vehicle mass and inertia in the kerb condition was measured.
The data collected from these tests were used to construct a detailed mathematical model of the vehicle. This was done using ADAMS/Car v12.0 APN-120-180; a dedicated vehicle dynamics simulation tool produced by MSC.Software. The vehicle model generated can be seen in Figure 1.
Due to the nature of the project, it was not necessary to obtain accurate tyre characteristic data. Therefore, a generic data set from MIRA‘s library was taken and adjusted to suit the size and type of tyre fitted to the ATV.
2.1.2 Rider measurements The rider and passenger were each represented by a 50th percentile human figure. In order to ascertain the geometric positions the rider and passenger would assume when seated on the ATV, a 50th percentile Hybrid II crash dummy was fitted to the supplied ATV. The geometric position data of the dummy was measured in the normal seated attitude for both the rider and passenger positions.
Using the human body modelling package, ADAMS/Figure, a 50th percentile body model was generated. This has equivalent mass and inertial properties of a 50th percentile human and was designed such that its position on the vehicle could be adjusted. An example of the body model in a seated position can be seen in Figure 2.
The body models were adjusted to match the measured rider and passenger seated positions on the ATV and these are shown in Figure 3.
Mathematical Modelling of an ATV and rider in an overturn RSU REF: 3787/R36.072 1998
2.2 Rider and passenger configurations The aim of the simulation exercise was to determine the sensitivity of the ATV to roll-over. This included comparing the vehicle performance with both a rider and passenger on board to that of the vehicle with just a rider, and the effect of rider and passenger positioning on the roll-over sensitivity. To understand these effects, the six following rider and passenger configurations were simulated.
• Rider only, seated upright on vehicle throughout manoeuvre
• Rider only, seated, leaning to resist roll-over
• Rider and passenger, seated upright on vehicle
• Rider and passenger, seated, both leaning to resist roll-over
• Rider and passenger, seated, both leaning to assist roll-over
• Rider and passenger, seated, rider alone leaning to resist roll-over With these configurations defined, it was necessary to determine the envelope of rider and passenger movement astride the vehicle, and to what extent they could adjust their positions to either assist or resist roll-over.
This was accomplished using the 50th percentile dummy. Starting with the dummy in the natural seating position, its posture was adjusted to lean as far forward, rearward and sideward as possible. The position of the dummy was then recorded. The maximum lean angles were 30 deg sidewards, 30 deg forwards and 21 deg rearwards for both rider and passenger seating positions. Figures 4 to 14 show the positions of the rider and passenger for each configuration.
2.3 Scenario setting The previous study identified five scenarios for roll-over and these same scenarios were adopted for this study. For each scenario it was necessary to determine the road conditions required to initiate roll-over in each of the rider and passenger configurations. The soil friction coefficient was fixed at 1.0 throughout all studies. By having a high value of friction coefficient, the point at which sliding occurs rises and therefore roll-over is more likely to occur. The study neither considers the effects of soil mechanics nor the effect of available grip.
In studying the factors influencing roll-over it was necessary to define the condition of roll-over and to understand the roll-over mechanism for each scenario. Tables 1 to 5 below provide definitions for each roll-over test scenario, the mechanisms by which roll-over was initiated and the measures used to define the point at which roll-over occurs.
Description Vehicle driven at 10 mph at an approach angle of 10 deg over an edge Mechanism The vehicle tends to roll laterally Test Procedure The gradient of the slope is increased in 1 deg increments until roll-over occurs
Description Vehicle traverses a slope of increasing gradient at 4 mph Mechanism The vehicle tends to roll laterally Test Procedure The gradient of the slope is increased in 1 deg increments until roll-over occurs Measure The uphill rear tyre load is monitored. Roll-over is determined to have occurred when the normal tyre force is completely removed
Test Procedure Angle of the slope is increased in 1 deg increments until roll-over occurs Measure Pitch rate, pitch angle and front tyre forces are monitored. Roll-over is determined to have occurred when the pitch rate does not exhibit a reversal through 0 deg/s and normal tyre force is removed completely
3.1 Static test results Table 6 shows the measured mass, centre of gravity position and inertia of the ATV at kerb weight with a full tank of petrol. These measurements were conducted at Cranfield Impact Centre Limited.2
The coordinate system is defined as follows:
XY plane at ground level, positive x to rear, positive y to right YZ plane through centre line of vehicle, positive z up X = 0 at front axle centre line
Table 7 shows the equivalent simulation data for the ATV model in three load conditions: kerb, kerb + rider and kerb + rider and passenger. At kerb, the model data is comparable with the measured data.
Table 8 shows the corner weights of the vehicle in each of the three load conditions defined above and gives the percentage increase from the kerb condition.
Table 9 shows the effect on the corner weights of the rider on board and leaning. Results are given for 30 deg sideways lean, 30 deg forward lean and 21 deg rearward lean. Percentage changes are also given.
Table 10 shows the effect on the corner weights of the rider and passenger on board and both leaning. Results are given for both rider and passenger with a 30 deg sideward lean, 30 deg forward lean and 21 deg rearward lean. Again, percentage changes are also provided.
Table 10 Model results for vehicle corner weights with rider and passenger leaning
3.2 Roll-over test results Simulation results for Scenario 1 are given in Table 12. Corresponding animations for these results are provided on the accompanying CD.
Results for Scenario 4 are given in Table 15. It was evident when conducting the simulations that the vehicle‘s behaviour was dependant on how much load there was on the rear tyres as the vehicle descended the slope and dropped down the dip. If the gradient of the slope was steep, the load was on the rear tyres was light and the vehicle was difficult to control down the slope and dip. If the gradient of the slope was shallow, the vehicle was more stable and hence required a high drop to initiate roll-over. A good compromise was found with a gradient of 40 deg. This was sufficient to keep the vehicle stable and under control, but in combination with the dip, could initiate roll-over.
Therefore, the gradient of the slope was fixed at 40 deg for all configurations and just the height of the dip adjusted until roll-over occurred. Corresponding animations for these results are provided on the CD.