Motion resistance measurements on large lug tyres

doi:10.1016/j.jterra.2019.12.005

Journal of Terramechanics

Volume 88, April 2020, Pages 17-27

https://doi.org/10.1016/j.jterra.2019.12.005 Get rights and content

Highlights

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Measuring the motion resistance of large lug tyres.
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Very low longitudinal force measurements compared to large vertical loads on tyres.
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Motion resistance measured with drawbar pull, coast down, drum and trailer tests.
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Compare the measured motion resistance results on the same tyre with four different methods.
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Investigating the effect that tyre inflation pressure and operating speed has on motion resistance measurements.

Abstract

Motion resistance of tyres directly contribute to the operational costs of all vehicles. Advances in the design and simulation of large off-road vehicles (construction, mining, agriculture etc.) have increased the need for accurate models of large off-road tyres. Vehicle OEMs use coast down and drawbar pull tests to determine the motion resistance of tyres used. Drum test rigs and motion resistance test trailers can also be used to determine motion resistance. Most research on motion resistance to date have been conducted on passenger car tyres with on-road truck tyres coming into focus. Motion resistance studies on agricultural tyres traversing over deformable terrain have been conducted in the past. However as more off-road vehicle are being used on-road OEMs of off-road vehicle are infesting in motion resistance measurements on non-deformable terrain. This paper compares different methods used to measure the motion resistance of a large lug tyre, as used in agricultural applications, on non-deformable terrain. Some basic considerations that need to be taken into account are the very low longitudinal forces that need to be measured compared to the large vertical load carried by the tyre and tyre operating conditions.

Introduction

Over the last decade considerable advances have been made in the levels of detail design and simulation of large off-road vehicles. This includes vehicles for the construction, mining and agricultural industries amongst others. These advances in simulation have been driven as many of these large vehicles, which still fits within the legal road limits, are being used on public roads thus they need to comply with strict national road traffic and Carbon Dioxide (CO₂₎ emissions regulations all over the world. Even with the larger vehicles the Original Equipment Manufacturers (OEMs) have to compete with increased production requirements on the one hand, which means operating at higher velocities and on the other hand stricter industrial regulations, CO₂ emissions regulations as well as Occupational Health and Safety (OHS) regulations. This has forced OEMs to invest in more detailed simulation orientated design processes to increase efficiency of the vehicles. The increase in production operating conditions typically drives improved handling characteristics and lower operating costs as the vehicles need to travel safely at higher velocities over longer distances. OHS regulations together with CO₂ emission regulations and end-user requirements drives operator comfort, lower CO₂ emissions, lower operating costs and payload isolation.

On large off-road vehicles, as with passenger cars, the tyres play a very important role in the dynamic behavior of the vehicle as all of the tractive forces (lateral and longitudinal directions) acting on the vehicle goes through the tyre to the terrain. The motion resistance of the tyres contributes continuously to the operating costs of the vehicle together with the efficiency of the vehicle drivetrain. These vehicles also operate at different vertical loads (between un-laden and laden conditions) and large variants of tyre pressures for different terrains and loads. All of this adds to the complexity of the vehicles behavior and changes the contribution of the motion resistance in the operating cost and efficiency of the vehicle. The vehicle OEMs can drive the design for improved drivetrain efficiency and the tyre manufacturer drives improved tyre design for lower motion resistance and improve traction in tyres. Vehicle OEMs frequently use drawbar pull and coast down tests to determine the motion resistance of tyres which enables them to decide on which tyre to use on their vehicles to run at the highest efficiency on deformable and non-deformable terrain. Tyre manufacturers mostly use drum test rigs to determine the motion resistance of their tyres in indoor laboratories. This paper describes and compares different methods used to measure the motion resistance of a large lug/ high lug profile tyre, as used on agricultural vehicles, on non-deformable terrain. Research and test procedures are well established for passenger car tyres, but very limited for large tyres, especially with off-road construction and large lugs/high lug profile or large tread blocks. With the limitation of test equipment capable to test large tyres, OEM’s of agricultural, construction and mining vehicles have internal test procedures/specifications to measure motion resistance, which does not always result in the same results obtained during independent third party vehicle evaluation testing. As a result OEM’s are asking the question of which method should be used to measure motion resistance?

Section snippets

Motion resistance measurements

Several methods exist to determine the motion resistance of tyres on passenger cars, commercial, heavy duty, agricultural and construction vehicles. These methods include coast down tests, drawbar pull tests, motion resistance test trailers and drum test rigs. However no comparison could be found in literature where all these methods are compared on the same tyre as each method has its own complicating factors and limitations. Motion resistance is a very difficult measurement as the

Motion resistance test setups and theory

The intent of this paper is to compare motion resistance values calculated from different test methods, in the form of drum, coast down, drawbar pull and trailer tests, on the same tyre. The tyre of interest for this study is a Trelleborg TM700 280/70R16 agricultural large lug tyre with a load index of 109 and velocity rating of 40 km/h. This specific tyre was chosen as it has large lug/ high lug profile tyre which causes vibration which can be seen in the measurements, it is a typical

Results

The results for the tests conducted on the drum test rig, revealed the relationship between motion resistance coefficient, inflation temperature and tyre carcass temperature as they are all directly related. Tests were conducted at a constant velocity of 18 km/h, from an ambient temperature of 25 °C and initial inflation pressure of 200 kPa, for 10 h on day 1 and for 5 h on day 2. Data sets were recorded at 1000 Hz, on a 16 bit resolution data acquisition system, for one minute out of every

Conclusions

The four methods used to measure the C_r in this paper has produced very interesting results. Very consistent C_r were obtained with the use of the drum test rig, motion resistance test trailer method as well as with the drawbar pull test method. The coast down C_r measurement illustrates the effect the inertial effect, drive train inertia and aerodynamic drag has on the measurements. The fact that a lower C_r is calculated below 5 m/s, with the coast down method compared to the other three

Funding

This research was fully funded and supported by the Vehicle Dynamics Group at the Department of Mechanical and Aeronautical Engineering of the University of Pretoria, South Africa.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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View full text

Motion resistance measurements on large lug tyres

Highlights

Abstract

Introduction

Section snippets

Motion resistance measurements

Motion resistance test setups and theory

Results

Conclusions

Funding

Declaration of Competing Interest

J. Terrramech.

Development of a single wheel tester for measurement on driven angled wheel

The NIAE Mk II single wheel tester

J. Agric. Eng. Res.

Road vehicles – Vehicle Dynamics and Road-holding Ability – Vocabulary