ROlling resistance, Skid resistance, ANd Noise Emission measurement standards for road surfaces

Collaborative Project FP7-SST-2013-RTD-1 Seventh Framework Programme Theme SST.2013.5-3: Innovative, cost-effective construction and maintenance for safer, greener and climate resilient roads

Start date: 1 November 2013 Duration: 36 months

Deliverable D3.1

State of the art on rolling resistance measurement devices

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n°605368 Main Editor(s) Marek Zöller

Due Date 28.02.2014

Delivery Date 28.02.2014

Work Package WP3

Dissemination level PU

Project Coordinator Manfred Haider, AIT Austrian Institute of Technology GmbH, Giefinggasse 2, 1210 Vienna, Austria. Tel: +43(0) 50550-6256 , Fax: +43(0) 50550-6599. E-mail: [email protected]. Website: http:/rosanne.fehrl.org

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Deliverable D3.1: State of the art on rolling resistance measurement devices

Contributor(s)

Main Contributor(s) Marek Zöller, BASt, +49-2204-43-0, [email protected]

Contributor(s) (alphabetical order)

Review

Reviewer(s) 1. Manfred Haider , AIT

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Deliverable D3.1: State of the art on rolling resistance measurement devices

Control Sheet

Version History

Version Date Editor Summary of Modifications v1.0 27.02.2014 Marek Zöller Initial version

Final Version released by Circulated to

Name Date Recipient Date

Manfred Haider 28.02.2014 Coordinator 28.02.2014

Consortium 28.02.2014

European Commission 28.02.2014

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Table of Contents

List of Figures ...... 7

Executive Summary ...... 8

1 Introduction ...... 9

2 Definition of rolling resistance ...... 10

3 Test methods for road-based measurements ...... 12

4 Existing trailer equipment ...... 14

4.1 General ...... 14

4.2 BRRC ...... 14

4.2.1 Rolling resistance trailer for passenger car tyres ...... 14

4.2.2 Measurement method ...... 15 4.2.3 Calibration procedure ...... 17 4.3 TUG ...... 19

4.3.1 Rolling resistance trailer for passenger car tyres ...... 19 4.3.2 Measurement method ...... 20 4.3.3 Calibration procedure ...... 21 4.4 BASt ...... 22

4.4.1 Rolling resistance trailer for passenger car tyres ...... 22 4.4.2 Measurement method ...... 23 4.4.3 Calibration procedure ...... 25

4.5 FKFS ...... 26

4.5.1 Rolling resistance trailer for passenger car tyres ...... 26 4.5.2 Measurement method ...... 27 4.6 IPW automotive ...... 28

4.6.1 Rolling resistance trailer for passenger car tyres ...... 28 4.6.2 Measurement method ...... 29 4.6.3 Rolling resistance trailer for heavy vehicle tyres...... 29 4.6.4 Measurement method ...... 30

4.6.5 Rolling resistance semitrailer for heavy vehicle tyres (mobile tyre lab) [8] ...... 31 4.6.6 Measurement method ...... 32

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4.7 ika/ RWTH Aachen [1], [9] ...... 32

4.7.1 Rolling resistance semitrailer for heavy vehicle and passenger car tyres (“FaReP”) .... 32

4.7.2 Measurement method ...... 33

4.7.3 Calibration procedure ...... 34

4.8 Dufourniers Technologies/ Colas...... 34

4.8.1 Skid/ rolling resistance trailer for passenger car tyres ...... 34

4.8.2 Measurement method ...... 36

5 Existing special vehicle equipment ...... 37

5.1 General ...... 37

5.2 Daimler AG/ FKFS [12] ...... 37 5.2.1 Truck Tyre Measuring Vehicle ...... 37 5.2.2 Measurement method ...... 39

5.2.3 Calibration procedure ...... 40 6 Conclusion ...... 42 References ...... 43

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Abbreviations

Abbreviation Meaning

BASt Bundesanstalt für Straßenwesen (Federal Highway Research Institute)

BRRC Belgian Road Research Centre

Cr Rolling resistance coefficient

Fr Rolling resistance force

FX Horizontal force (including Fr)

FZ Vertical force (tyre load)

FaReP Fahrender Reifenprüfstand

FKFS Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart ika Institut für Kraftfahrzeuge der RWTH Aachen university

IPW IPW automotive GmbH

ISO International Organization for Standardization

Models for rolling resistance In Road Infrastructure Asset Management MIRIAM systems

TUG Technical University of Gdansk

TYDEX Tyre Data Exchange Format

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List of Figures

Figure 1 – Illustration of the suggested terminology structure (see further explanation in [1]) ...... 10 Figure 2 – Forces at a rolling tyre [A. Zomotor, Fahrwerktechnik, 1991] ...... 10 Figure 3 – Overview of the most important influences on rolling resistance [4] ...... 11 Figure 4 – Setups and methods to measure rolling resistance [4] ...... 12 Figure 5 – The new BRRC trailer and its towing car ...... 14 Figure 6 – The new (left) and the old (right) BRRC test tyre ...... 15 Figure 7 – The measuring principle of the BRRC trailer (simplified) [5] ...... 15 Figure 8 – The BRRC rolling resistance test trailer and illustration of the three inclination angles measured ...... 16 Figure 9 – The Angles μ and α in the BRRC rolling resistance trailer influencing the measured Cr (which is the angle θ expressed in radians) ...... 17 Figure 10 – The Moveable and non-moveable parts of the BRRC rolling resistance trailer ...... 18 Figure 11 – The TUG rolling resistance trailer in the shape and condition of 2010 and its towing car 19 Figure 12 – The measurement principle of the TUG trailer ...... 20 Figure 13 – The mechanical setup for calibration of the TUG trailer (see the text for explanations) .. 21 Figure 14 – The BASt rolling resistance trailer and its towing van ...... 22 Figure 15 – Principle of the additional suspension for the test tyre-wheel assembly ...... 23 Figure 16 – Additional suspension of the BASt trailer ...... 23 Figure 17 – The two-point procedure (0.8RL is 80% of max. tyre load; R is rolling resistance) ...... 24 Figure 18 – The FKFS rolling resistance trailer and its towing car [photo FKFS] ...... 27 Figure 19 – The suspension for the test tyre of the FKFS trailer [photo FKFS] ...... 27 Figure 20 – Detailed view of supporting (left) and test tyre (right) [photo FKFS]...... 28 Figure 21 – The IPW rolling resistance trailer and its towing car [photo IPW] ...... 29 Figure 22 – The IPW rolling resistance trailer and its towing truck [7] ...... 30 Figure 23 – The in-house developed drawbar force transducer [7] ...... 30 Figure 24 – The direct measurement principle of the IPW trailer [7] ...... 30 Figure 25 – The IPW mobile lab semitrailer and its towing tractor (photomontage with measuring rig) [photo IPW] ...... 31 Figure 26 – The ika semitrailer FaReP and its towing tractor [9] ...... 32 Figure 27 – Slip measurements on flat road with test tyre mounted on measuring wheel [1] ...... 33 Figure 28 – Rolling resistance measurements on flat road with measuring hub (left) [10] and on ika drum (right) [9] ...... 33 Figure 28 – The Dufourniers/ Colas skid and rolling resistance trailer [9] ...... 35 Figure 29 – The Dufourniers/ Colas skid and rolling resistance trailer with opened enclosure (left) and detailed view to the test tyre (right) [9] ...... 35 Figure 30 – Design drawing of the Dufourniers/ Colas skid and rolling resistance trailer [9]...... 35 Figure 32 – The Daimler/ FKFS truck tyre measuring vehicle [12] ...... 37 Figure 33 – The Daimler/ FKFS truck tyre measuring vehicle with raised rear axle [12] ...... 38 Figure 34 – The measuring axle with a six-component-measuring hub [12] ...... 38 Figure 35 – The basic approach for rolling resistance measurement with the Daimler/ FKFS truck [12] ...... 39

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Executive Summary

ROSANNE has established a work-package (WP), designated WP3, to to prepare for International and European standardization of measurement methods for representative and accurate characterization of road surface rolling resistance properties. Based on previous work in the project MIRIAM, the trailer method shall be further improved in order to qualify this method as a standard method. The work will explore various effects on rolling resistance which need to be controlled. The objective is also to analyse and compare the properties of available test equipment for rolling resistance. The ultimate aim is to provide a draft for standardization of a procedure for harmonized rolling resistance classification of road surfaces across Europe, based on the available measurement methods. The work shall be performed in close cooperation with the CEN standardization body and the MIRIAM project. Within task 3.1 of WP3 the preparation of a draft standard for harmonized, consistent and practical measurement of rolling resistance properties of road surfaces based on trailer (or vehicle) measurements, applicable to both light and heavy vehicle traffic. At the end, all influencing factors must be considered and controlled; based on the results of Task 3.2 of WP3. The use of texture indicators to harmonize and/or supplement the methods shall be studied. This will include enveloping of texture profiles to simulate the tyre/road contact and considerations of whether a texture parameter can serve as a proxy for rolling resistance. This work will be performed in close cooperation with CEN/TC 227/WG 5 This report is intended to provide basic knowledge about the road-based method of measuring rolling resistance of passenger car and truck tyres, the different types of measuring methods and to provide some detailed state-of-the-art knowledge about measurement equipment and basic knowledge about the direct/ indirect measurement methods. Although many types of measurement equipment known to the author is presented no claim to be complete is beeing made.

This report is based on literature studies, compiling information from different owners of measurement equipment and Deliverables from the MIRIAM Phase One sub project SP1.

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1 Introduction

Environmental questions have become an important part of the decision-making processes for highway projects in many countries. There are many factors that impact the energy/fuel consumption for a vehicle. Amongst others rolling resistance plays a major role. The type of road pavement and its surface influence the rolling resistance of the tyre-road unit.

Advantages of different road pavements from environmental viewpoint and their effects to the energy consumption for different types of vehicles using these roads are therefore an important part of the road construction planning progress.

It is therefore important to be able to measure the influence of rolling resistance properties of pavements by a standardized method. Within the constraints of the road-based method this deliverable of the project ROSANNE provides basic knowledge about measurement methods which relate to the road surface influence on rolling resistance, as well as some information about equipment that are useful for collecting rolling resistance data. In combination with a draft standard for harmonized, consistent and practical measurement of rolling resistance properties of road surfaces an objective rating of the road characteristics can be offered to satisfy a need currently expressed by road planners, road administrators, contractors and other parties concerned with the

CO2 reduction problems. The objective of this report is to focus on the measurement equipment suitable to determine the road surface influence on rolling resistance. It illustrates the major measurement problems inherent to each system and presents how the operators of these equipments managed to solve or get around them and finally presents a first draft for a standard for a road- method, applicable to both light and heavy vehicle traffic. This report is based on literature studies, compiling information from different owners of measurement equipment and Deliverables from the MIRIAM Phase One sub project SP1. Since the projects MIRIAM and ROSANNE are closely linked much of the text in clause 4 is taken from [1] and [2].

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2 Definition of rolling resistance

While driving a vehicle on a plain energy is necessary to overcome losses and resistances inherent to its movement. These are summarized to the driving resistance. The resistance of the pneumatic tyres of a vehicle are therefore a part of the driving resistance and consists of tyre and road surface components. An overview of the various contributions to driving and rolling resistance of a driving vehicle and a logical terminology was made in [1]. A graph from that report is shown in Figure 1.

Inertial resistance (Vehicle) Gravitational resistance Propulsion resistance Engine resistance

Auxiliary equipment resistance

(Vehicle) (Vehicle) Body air resistance Driving Aerodynamic resistance resistance Tyre air resistance

Tyre/road rolling resistance

Vehicle rolling Bearing resistance resistance Transmission resist. (churning & mech.) Suspension resistance

Level 1 Level 2 Level 3 Figure 1 – Illustration of the suggested terminology structure (see further explanation in [1]) The tyre based rolling resistance on paved roads is mainly caused by the deflection and deformation of the tyre during the rolling and the hysteresis of the rubber and the tyre structure. Other minor effects are friction and adhesion losses between the tyre rubber and the road surface at the contact patch area. By definition rolling resistance is applied as a physical phenomenon that results in energy loss per distance travelled (Nm/m) or more commonly used as a rolling resistance force Fr in (N). Therefore the loss of energy can be measured as a force opposite to the driving direction (Figure 2).

FZ tyre load

FN normal force resulting from asymmetric contact pressure

FR rolling resistance

rdyn dynamic tyre diameter e distance to centre line

Figure 2 – Forces at a rolling tyre [A. Zomotor, Fahrwerktechnik, 1991]

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The rolling resistance is dependent on the deflection (amplitude of tyre deformation) of the tyre and for this reason on the tyre load and inflation. The ratio of the rolling resistance to the load on the tyre provides the dimensionless rolling resistance coefficient Cr which is nearly constant over a wide range of tyre load (without correction of tyre inflation) is gained. Additional influence on rolling resistance has the driving speed (frequency of tyre deformation).

More influencing parameters on rolling resistance can be found in Figure 3.

ROAD SURFACE TEST CONDITIONS TYRES

Texture properties Speed Temperature Tyre load Geometry  Microtexture Tyre inflation Size  Macrotexture  Megatextur Slip angle Speed index  Roughness Camber angle Aspect ratio  Longitudinal irregularity Wheel diameter and width  Grip Ambient temperature

Airflow Material properties Surface temperature  Rubber compound  Carcass  Belt  Core

ROLLING RESISTANCE

Figure 3 – Overview of the most important influences on rolling resistance [4]

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3 Test methods for road-based measurements

It is not easy to measure the rolling resistance of a tyre. The eqivalent forces are extremely low, in the range of 30 – 40 N for a passenger car tyre load of approx. 3.5 kN (gross vehicle weight of 1400 kg distributed evenly onto four tyres), i.e. rolling resistance is approximately 1% of the tyre load.

At least at present and in the foreseeable future, the direct measurement of rolling resistance is very difficult and requires the use of rather advanced equipment and methodology, operated by very skilled and experienced staff. Consequently, direct measurement of rolling resistance is practical only on a very small part of the road network and for research purposes.

Figure 4 gives an overview on different methods for measuring rolling resistance.

Figure 4 – Setups and methods to measure rolling resistance [4]

For conducting rolling resistance measurements on real roads either a vehicle or a trailer can be towed (drag force method), when using the coast down method a vehicle is accelerated to a certain speed and then seperated from the drivetrain. By measuring its deceleration the rolling resistance can be calculated. The major disadvantage of both methods is the sensitivity to various influences like gradients and cross winds. Also specially designed trailers and vehicles for measuring reaction forces respectivly displacement angle or torque at the spindle of a tyre-wheel assembly can be used. Here the test tyre(s) are commonly covered by a kind of enclosure to avoid wind influence and and the test tyre-wheel assembly is mounted on a seperate suspension.

Generally two measuring principles - direct and indirect - for measurements of rolling resistance can be applied. The direct principles measure the rolling resistance force of a tyre related to a fixed reference point. The indirect principles make use of the measurement of the effect towards other physical quantities - like torque or displacement angle. The force methods can be subdivided and described as follows:

− The reaction force measured at the wheel spindle of a test tyre-wheel assembly mounted on a separate suspension fitted either into a vehicle (passenger car, truck or bus) or to a trailer

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− The reaction force measured by an assembly of a wheel force transducer unit and a test tyre or a measuring hub mounted on one of the axles fitted to a vehicle (passenger car, truck or bus) or to a trailer axle

− The reaction force of a whole axle equipped with (at least) two identical wheel and test tyre assemblies fitted either as a rear axle in a vehicle or as a trailer axle The angle method can be described as follows:

The reaction force at the tyre spindle of a wheel and test tyre assembly mounted at the end of a pivoted vertical arm is commensurate to its deflection rate. This means that the angle between a vertical arm and the horizontal line can also be measured.

The torque method can be described as follows: The absolute value of the reaction force at the tyre spindle of a wheel and test tyre assembly is equal to the reaction force at the contact patch of the tyre. Multiplied with the dynamic radius of the rolling tyre the result is the driving torque of the tyre at a steady speed.

More detailed information than in this chapter can be found in a State-of-the-Art report about rolling resistance measurements [1] and in [2] (both are deliverables from the project MIRIAM phase I).

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4 Existing trailer equipment

4.1 General The trailer method is a method where rolling resistance measurements are made with test tyre(s) in a special towed trailer, while rolling at constant speed. The trailer may be designed either for passenger car tyres or for heavy truck tyres. The measurement may be made either of the torque on the test tyre, the towing force between towing vehicle and trailer, the force in one of the longitudinal links of the suspension for the test tyre or the angle by which the tyre vertical support is displaced when a rolling resistance force is acting in the tyre/road interface (which is actually a measurement of the rolling resistance force on the tyre).

4.2 BRRC 4.2.1 Rolling resistance trailer for passenger car tyres The BRRC trailer uses the indirect mesuring principle. Here the reaction force at the tyre spindle of a test tyre-wheel assembly mounted at the end of a pivoted vertical arm is commensurate to its deflection rate (i.e. the angle between a vertical arm and the horizontal). In 2009 BRRC decided to continue research started in the early 1980’s and refurbished the original trailer. New sensors were added and calibration procedures were tweaked. Figure 5 shows the new trailer and its towing car.

Figure 5 – The new BRRC trailer and its towing car The BRRC trailer is designed as a “quarter-car” with an ordinary car suspension. The suspension dates from the 1980’s and was originally designed for a small car. Technological developments over the last years lead to larger tyres and heavier vehicles. As the trailer of BRRC was originally designed for tyres and cars commonly used in the 1980’s, it now encounters some limitations. Only tyres with a maximum size of 14” and a maximum width of 195 mm can be mounted. A maximum tyre load of 2000 N is imposed in order not to force the suspension system.

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In 2011 a new tyre was mounted on the trailer: Michelin Energy Saver 195/70 R14 91T (see Figure 6). Until then a slick tyre had been used: Michelin SB-15/63-14X (see Figure 6.5). A tyre inflation pressure of 200 kPa was used for the old tyre, while for the new test tyre a pressure of 220 kPa is used.

Figure 6 – The new (left) and the old (right) BRRC test tyre

4.2.2 Measurement method

Figure 7 – The measuring principle of the BRRC trailer (simplified) [5] The measuring principle is shown in Figure 7. The rolling resistance force causes the tyre-wheel assembly to incline backwards with an angle θ with respect to the frame of the trailer. The rolling resistance coefficient is defined as the ratio of the rolling resistance force and the tyre load and equals the tangent of θ. For small angles, θ is equal to the rolling resistance coefficient provided it is expressed in radians. A symmetric, friction-free pneumatic damper of bellows damps fluctuations of θ.

Different parameters are recorded continuously during measurement:

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• Inclination θ of the tyre-wheel carrier with respect to the frame of the trailer (Figure 8) • Inclination μ of the frame of the trailer with respect to the horizontal plane (Figure 8) • Inclination α between the trailer and the towing vehicle (Figure 8) • An external infrared sensor is directed at the sidewall near the shoulder of the tyre to record tyre temperature • Speed • Acceleration

Figure 8 – The BRRC rolling resistance test trailer and illustration of the three inclination angles measured A software tool for data acquisition has been developed by means of a graphical programming platform. During monitoring, the graphs of the different parameters are shown on the laptop screen. In this way the operator may be notified of possible errors during measurement. All data are registered in a file. Corrections are applied afterwards according to this formula:

Cr = θ + ε1 * μ + ε2 * α (1) where ε1 and ε2 are experimentally determined coefficients. So far, only a correction of the inclination α0 at standstill has been applied and measurements have been performed only at constant speed.

In general, the following measurement procedure is applied:

- Cold tyre inflation is adjusted to 220 kPa.

- The height of the trailer with respect to the towing vehicle is measured to determine α0 at standstill.

- A calibration round is made to adjust μ0 and to eliminate the influence of differences in the car load (e.g. by a different number of passengers). - A test tyre warm-up procedure is carried out, consisting of driving about 15 minutes at approxi- mately 80 km/h.

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- The test section is measured three times each. - Ambient air and road surface temperature are measured. - Corrections of the data are applied in the laboratory. - Data are corrected for tyre temperature according the following formula: ( (T - T) / T ) Cr (T) = Cr (T0) * e 0 1 (2) where T = 30 °C, T1 = 50 °C

- Average Cr and corresponding standard deviation are calculated.

4.2.3 Calibration procedure

Two angles in the trailer system influence the measured Cr (where Cr is measured as the angle θ expressed in radians); see Figure 9. These are:

• The longitudinal inclination μ (longitudinal gradient)

• The angle α between the shaft of the towing vehicle and the shaft of the trailer Small deviations in these two angles have a significant influence on θ and, therefore, the trailer setup regarding these are checked before every measurement. A deviation of only 0,1° leads to a deviation of 10 % of the Cr and a deviation of 0,1° on μ to an error of 3 %.

Figure 9 – The Angles μ and α in the BRRC rolling resistance trailer influencing the measured Cr (which is the angle θ expressed in radians) The angle μ is checked every time the trailer is attached to the towing vehicle. This is done by measuring the angle μ while the trailer is run "full circle" around a paved area. The average value of the angle, which is denoted μ0 at calibration, must then be adjusted to be zero. Normally this procedure is carried out at the BRRC premises in Sterrebeek, before driving to the test sites. The

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vehicle starts at a given point and the measurement of μ0 is started. The vehicle drives over a distance of about 320 m until it arrives again at the starting point where the measurement is stopped. The sensor is readjusted to show zero if the average of μ0 was found to be outside the interval [-0.1°, +0.1°]. If a recalibration is necessary, it is checked by driving a second round.

When there is a non-zero slope μ during a road measurement, it is used as a correction to the Cr value according to the equation (1) given in 4.2.2.

As the second part of the calibration, the angle α is measured, which can be deduced from height measurements of the frame of the non-moveable part of the trailer with respect to the pavement; see Figure 9 and Figure 10. The calibration value of α is denoted α0.

Moveable Non-moveable part of part of frame frame with load

Figure 10 – The Moveable and non-moveable parts of the BRRC rolling resistance trailer

The towing car and trailer are, therefore, first parked “perfectly” aligned and on a “perfectly” horizontal surface, which can be checked with a manual inclinometer. The heights of the non- moveable part of the trailer frame are measured at the four corners. From the two heights at the left hand side the “left hand α0” is calculated and the “right hand α0” is calculated and determined in an analogue way. The average of the left hand and right hand angle α0 is then further denoted as the angle α0. Calculations are done by means of a simple spread sheet. Important is that α0 is determined with the vehicle loaded in the same way as during the Cr measurement. If the operator is not in the vehicle during the measurements of the heights of the frame, it has to be indicated in the spread sheet, which will take this into account for the calculation of α0.

If larger distances are driven between measurement locations, α0 is measured before Cr measurements take place and recalculated to compensate for the loss of load of the consumed fuel.

If α during an Cr measurement is found to be different from zero it is used as a correction α to the Cr value according to the equation given in 4.2.2. After a series of road measurements, this calibration round is repeated to verify that the angle is still inside the accepted interval around zero. If this is not the case, the road measurement is considered as incorrect and the calibration and measurement have to be redone.

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4.3 TUG 4.3.1 Rolling resistance trailer for passenger car tyres The Technical University of Gdańsk (TUG) designed and built a test trailer for rolling resistance measurements of passenger car tyres in the late 1990's, but the first "production" measurements were made around 2005. The idea with this construction was taken from the original BRRC trailer from the 1980's shown in Fig. 10.1 in [1], but TUG developed it further and improved the concept in several ways. Some of the constructions are patented, and it has been improved continuously during the past 10 years. The TUG trailer, called the R2 trailer, in its condition of 2010 is shown in Figure 11.

Figure 11 – The TUG rolling resistance trailer in the shape and condition of 2010 and its towing car The trailer is designed to be towed by a reasonably powerful passenger car. The construction of the trailer is self-supporting (three-wheeler) which means that the trailer may be easily connected/dis- connected from the towing car. The front tyre-wheel assemblies that stabilize the trailer have self- aligning properties. The hydraulic brake system of the trailer is operating on front wheels only and provides efficient braking of the trailer during transportation and tests. Trailer construction assures good stability of the trailer. Independent front suspension, based on double transverse arms was constructed as an adaptation of passenger car suspension. During tests the suspension is blocked by removable bars. Blocking of the suspension ascertains proper leveling of the trailer. The test tyre- wheel assembly is supported by a vertical arm (4) that is an important element of the force measuring system (see Figure 12). The front and rear suspension are connected to the horizontal arm (1). Rotation axis (3) is placed directly in the geometrical centre of the rotation axis of the front wheels. The load is provided by arm (2) that has a common rotation axis with arm (1). The load block (6) is resting on arm (2).

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Suspension element (7) carries the load from arm (2) to arm (1). The rear end of the horizontal arm (1) is connected to the vertical arm (4) which is equipped with the test wheel hub. Undesirable vibrations of the vertical arm (4) that may be induced during tests are suppressed by Foucault currents electromagnetic brake (not shown in Figure 12). Inflation pressure in the test tyre is maintained by remote controlled release valve and pressure sensor.

Figure 12 – The measurement principle of the TUG trailer During tests the rolling resistance force acting on the test tyre pulls at the end of the pivoted vertical arm (4). The deflection rate is measured by the laser sensor installed on arm (1) and sending the laser beam towards arm (4). Rolling resistance coefficient is defined as a ratio of rolling resistance force Fr

= Pf and vertical load FZ. The trailer is equipped with a patented compensation device that eliminates influence of factors such as road inclination and longitudinal acceleration that otherwise very substantially would disturb the measurements. The position of arm (1) in relation to the road surface is monitored by two laser sensors. A data logger which is installed in the car receives signals form three laser sensors and two wheel speed sensors. All measurements are controlled via a notebook computer. The test tyre-wheel assembly and the vertical arm, as well as the inclination compensation system are covered by a protecting enclosure (see Figure 11). Both theoretical considerations and practical experience show that such an enclosure is necessary to reduce the influence of the air drag on the test results. During measurements the front suspension system is blocked by special bars to ascertain stable position of the trailer frame in relation to the plane of the road. Steel loads that load the test tyre are mounted on the arm (see (2) in Figure 12) that has its own suspension based on a motorcycle spring and damper unit. This suspension unit is in operation both during transportation and testing.

4.3.2 Measurement method Before each measuring session the trailer is calibrated in the laboratory on a flat, horizontal surface (see clause 4.3.3). When the test tyres have reached their warmed-up condition (warmed-up at least

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for 15 minutes, but always long enough to stabilize the inflation pressure) during the measurements, the tyre inflation pressure is regulated.

At least two tests runs at each speed are performed. When possible the number of runs is higher and the runs are made in both road directions. Generally, a measurement distance per run of 400 m or more is required, but measurements over distances as short as 100 m are sometimes performed. Short distances require more runs in order to maintain an acceptable uncertainty. The data are analyzed in laboratory.

4.3.3 Calibration procedure The measuring system of the R2 trailer is calibrated in the TUG or another laboratory before each measuring campaign. The calibration procedure is illustrated in Figure 13. The trailer is placed on a level, flat, horizontal surface (4). The measuring wheel is replaced by a steel arch (1) that has known radius and very smooth outer surface that rests on a polished steel plate (2). The measuring arm is pulled by the test loads (8, 9) via a textile band (6). The band is supported by a steel bar construction (5, 7). During calibration the relation between the output signal from the laser sensor, representing the measuring position of the test arm, and the load is established. The calibration is repeated for 3 different steel arches (1) that simulate tyres of different radius. This makes it possible to establish the relation between laser sensor output signal and tyre radius. The front supporting wheels of the trailer are also placed on two different spacers to establish the potential influence of road surface rutting. No calibrations are made in the field.

Figure 13 – The mechanical setup for calibration of the TUG trailer (see the text for explanations)

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4.4 BASt 4.4.1 Rolling resistance trailer for passenger car tyres The BASt rolling resistance trailer for passenger car tyres was developed in 1992 and has been in used sporadically for measurements since 1994. It uses the direct measuring principle where the reaction force at the wheel spindle of a test tyre-wheel assembly mounted on a seperate suspension is measured (see Figure 15). This wheel suspension is mounted in the same geometric axis as the supporting tyres of the two-wheeled trailer. For applying the desired tyre load a pneumatic cylinder in combination with a nitrogen reservoir is used.

The test tyre-wheel assembly is joined at point "B" and "C" (see Figure 15) with five links (three transversal and two longitudinal links in a parallelogram alignment) to the trailer chassis with a camber angle of 0°. The lower longitudinal suspension link is equipped with a force transducer K1 for the longitudinal force. The pressure accumulator - based vertical force FZ is passed via a force transducer K2 and a bearing towards point "C".

Figure 14 – The BASt rolling resistance trailer and its towing van

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Figure 15 – Principle of the additional suspension for the test tyre-wheel assembly

Figure 16 – Additional suspension of the BASt trailer

4.4.2 Measurement method

Besides the rolling resistance force Fr measured by a force transducer (e.g. K1 in the lower suspension link B-E of Figure 15) there are other influences (bearing friction, air drag caused by wind turbulences of the tyre-wheel assembly, influence on the gross longitudinal force caused by a suboptimal vertical position of the wheel suspension, electrical and mechanical offset or zero drift of

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the force transducer used) on the measurement value of FX. The general relation for the gross longitudinal force is:

FX = Fr + FW + FB + FXZ + FO (3) where

Fr Rolling resistance FW Loss by Air drag and wind turbulences

FB Loss by bearing friction FXZ Influence of vertical load FZ on

longitudinal force FX (to be determined by a “static” calibration)

FO Zero drift of force transducer

Figure 17 – The two-point procedure (0.8RL is 80% of max. tyre load; R is rolling resistance)

Provided that there is a linear relation between tyre load (FZ) and gross longitudinal force (FX) for a certain tyre/ road assembly a so called "two point procedure" (Figure 17) can be used to eliminate the additive parts of FX which are not causally associated to the rolling resistance force Fr. The two points are called "high" and "low".

FX high =R + FW + FB + FXZhigh + FO FXhigh - FXlow = Fr + FXZ (4)

F =F + F + F + F X low W B XZ low O

At the BASt trailer the different tyre loads FZ high and FZ low are obtained by a dual pressure control unit with adjustable pressure values. Two electro-pneumatic valves supply the pressure for the tyre load cylinder. The signal from the force transducers for the forces FX and FZ is sampled at a rate of 500 Hz and the speed and temperature signals are sampled at 5 Hz. The rolling resistance value Fr is calculated from the mean values of FX and FZ at high and low load, so there is only one single value for the whole test track length. It is assumed that the rolling resistance value does not change significantly along the test track.

Besides the two force transducers for vertical tyre load FZ and longitudinal force FX (= FLU) the trailer is equipped with a platinum temperature sensor (Pt100) to measure the ambient air temperature either in an enclosure around the test tyre or outside of it, as well as an infrared temperature sensor

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to measure the tyre temperature at its shoulder. Since there is an unavoidable influence from FZ towards FX if the trailer chassis is not parallel to the road, it is necessary to measure the position of the trailer platform with two laser displacement sensors mounted in the front and rear.

The error of the longitudinal force FXZ must be determined by a separate measurement (static calibration, see clause 4.4.3).

4.4.3 Calibration procedure The operating point of the trailer measurement mechanism (suspension linkage with force transducers); i.e. the position of the trailer in relation to the ground, plus the appropriate error of the longitudinal force FXZ, and the functional correlation between longitudinal force and difference of height, are determined by two separate measurements in a so-called "static calibration".

The position of the trailer chassis platform is determined by two laser displacement sensors (mounted at the front and at the rear of the trailer chassis) during a rolling resistance measurement and during the static calibration. This so called "static calibration" (when the vehicle or trailer is at standstill) is also carried out by using the “two point measurement” method. For that reason the tested tyre-wheel assembly is mounted on the vehicle or trailer placed on flat and even ground of a hall. The tyre is loaded with the same nominal vertical load (FZ high) and a reduced load (FZ low) as when operated on the road. This must be redone for each tyre-wheel assembly that has a different diameter compared to the previous one, for each change in vertical tyre load, and for each adaption of the suspension links to the current tyre size used.

FX high S = FXZ high S + FO S FX high S - FX low S = FXZ S (5)

FX low S = FXZ low S + FO S where

FXZ high S Influence on longitudinal force FXZ low S Influence on longitudinal force during “static” condition at vertical during “static” conditions at

load FZ high S vertical load FZ low S

FO S Zero drift of force transducer during “static” conditions

For a very low tyre load FZ low S (~100...150 N) the value of FXZ low S can be neglected. If the conditions during a road measurement are largely the same as during a static calibration then FXZ S can be equated with FXZ.

In order to determine the influence FX high = f(∂h) of the clearance of the coupling point (between towing vehicle and trailer at a certain operating point of the trailer) to the ground the boot of the towing vehicle is loaded stepwise with weights. For each step of weight the tyre load FZ high is applied.

FX high = f([hfront - hrear]S - [hfront - hrear]C) = f(ΔhS - ΔhC) = f(∂h) (6)

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with

hfront clearance between front of trailer hrear clearance between rear of trailer

chassis and ground chassis and ground

ΔhS difference of height during static ΔhC difference of height during calibration determining f(∂h)

FX high longitudinal force at high vertical ∂h difference between difference of

tyre load FZ high height at the static calibration and difference of height when determining the function f(∂h)

With the functional correlation between longitudinal force and difference of height, together with the calibrated operating point, it is possible to correct FX at all subsequent measurements. Calibrations are made only in the laboratory before each measurement campaign, or when there is a change in the setup, such as change to a test tyre with different diameter. Calibrations are not made in the field as it would be too complicated and probably not needed.

4.5 FKFS 4.5.1 Rolling resistance trailer for passenger car tyres The FKFS rolling resistance trailer [6] for passenger cars was developed in the mid-nineties and is equipped with a dual axle. The rear (seen in the direction of driving) pair of tyre-wheel assemblies serves as a supporting pair whereas the front tyre-wheel assemblies are used for measurement purpose. For that reason the test tyres can be lifted during transportation. Also an independent variation of the tyre load is possible. Based on the symmetric arrangement of two test tyres in each track, variations as regards camber and toe-in are also possible without influencing the directional stability of the trailer. Both the camber and the toe can be set in a defined manner for the test tyre- wheel assemblies, whereby realistic rolling conditions of passenger car tires can be simulated. The whole trailer is covered by an enclosure. The FKFS trailer is based on the same principle as the BASt trailer: three longitudinal (two of them parallel linked to a force transducer) and three transverse suspension links for the test tyre suspension. Due to non-suspended masses any road unevenness can cause tyre-load fluctuation and changes in rolling resistance. Therefore the tyre loads are not applied by any kind of weight but variably applied by two pneumatic cylinders (one for each test tyre). The cylinder force needs to pass in the suspension exactly rectangular to the road surface - otherwise a reduction or enlargement of the gross longitudinal force will result.

In addition to the camber, toe-in and wheel load, other influencing parameters, such as the tyre inflation pressure and the road surface conditions, can be examined using the rolling resistance trailer. All parameters which influence these measurements, such as the tyre temperature, surface temperature, acceleration and setting angle are also measured to compensate for and document their influence. Date:27-02-2014/ Version: 1.0 26 (43)

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Figure 18 – The FKFS rolling resistance trailer and its towing car [photo FKFS]

4.5.2 Measurement method The suspension for the test tyre-wheel alignment is shown Figure 19. The wheel carrier (1) is transversely guided via two tie rods (2, 3) and a cardan shaft (4). The cardan shaft prevents the carrier from being distorted. In measurement position the cardan shaft falls in line with the wheel rotation axis. The guidance of the carrier in longitudinal direction is carried out by a force transducer (5) for measuring the gross longitudinal force. In order to avoid bending forces to the transducer it is flexibly joined to a plate (6). This plate is guided by two long tie rods (7, 8). The huge length of the rods ensures a minimum of horizontal movement of the carrier in relation to the trailer chassis. The load resp. the compressive force of the pneumatic cylinder is guided via a push bar and a force transducer (11) towards the cardan shaft (4). The push bar itself is guided via two tie Figure 19 – The suspension for the test tyre of the FKFS trailer [photo FKFS]

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rods (12, 13) to keep the horizontal alignment independent from any vertical movement. Tyre and ambient air temperature are captured by two sensors (10, 14).

By using a sensitive level control system the trailer chassis is nearly kept parallel to the road surface. Additionally two laser sensors measure the position of the trailer chassis relatively towards the road surface. If chassis and road surface are not exactly parallel this deviation in combination with the tyre load is used to correct the gross longitudinal force.

Figure 20 – Detailed view of supporting (left) and test tyre (right) [photo FKFS] When conducted on roads with gradients rolling resistance measurements are influenced by a road surface parallel component of gravity. Therefore also the longitudinal acceleration is measured and a correction value is calculated to determine the influence on the gross longitudinal force. Unwanted changes in vehicle speed during a rolling resistance measurement lead to longitudinal and circular accelerations. The influence of circular accelerations of the test tyre-wheel assembly is determined by differentiating the tyre-wheel speed signal of both test tyres.

4.6 IPW automotive 4.6.1 Rolling resistance trailer for passenger car tyres The IPW rolling resistance trailer (see Figure 21 and the enclosed numbers referred to in the following text) for passenger car tyres ROWIMAN (Rollwiderstandsmessanhänger) uses the direct measuring principle. It is constructed by using a specially designed axle (3) which is mounted to the chassis of a commercially available trailer with a long drawbar (5). An self-developed high resolution force transducer unit (1) is mounted in the front part of the drawbar. The driving resistance of the whole trailer including the rolling resistance of two identical tyres (2) is measured. The tyre load is applied by different steel ballast plates in a range of 200...750 kg (4). These plates are positioned in

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such a way that the vertical load at the vehicle-trailer linkage point is at a minimum. Due to the split axle toe-in can be adjusted in a certain range while camber is fixed. Because of the long drawbar an the low position of the centre of gravity the trailer shows a robust driving behaviour up to 150 km/h.

The tyre-wheel assemblies can be easily changed by an installed hydraulic lifting device.

Figure 21 – The IPW rolling resistance trailer and its towing car [photo IPW]

4.6.2 Measurement method Based on the direct measurement principle of the gross longitudinal force caused by the driving resistance of the trailer and its high inertia changes in driving speed of the towing vehicle (even when equipped with a cruise control) have a direct influence to the longitudinal force measured at the force transducer. Therefore also the longitudinal acceleration is measured and a correction value is calculated to compensate this influence. When conducted on roads with gradients rolling resistance measurements are influenced by a road surface parallel component of gravity. Therefore the longitudinal gradient of the road section where the measurement takes place is continuously determined by the use of two laser displacement sensors and an inertial measurement unit to calculate a correction factor.

Due to the construction principle and the lack of any enclosures the trailer is highly sensitive to all kinds of changing environmental influencess (like wind and ambient temperature). Hence it can not measure an absolute value of the rolling resistance as a part of the driving resistance.

4.6.3 Rolling resistance trailer for heavy vehicle tyres The IPW rolling resistance trailer for heavy vehicle tyres (Figure 22) is constructed according the same principle like the IPW rolling resistance trailer for passenger car tyres. The trailer is a full-size commercial trailer for swap systems. Nevertheless it is not equipped with a container box but loaded with several weights to the appropriate value (~18 t), so that the front and rear axle loads are balanced to ~9 t each. The sum of the gross longitudinal force (inluding the rolling resistance of the

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four tyres) is measured by a drawbar force transducer between truck and trailer. To separate the rolling resistance from the Other loads are possible. The trailer is towed by a truck, which drives with a constant speed of 15 km/h to avoid wind effects (aerodynamic resistances) on the measuring results. Tyre tread and shoulder temperatures as well as ambient and road surface temperatures are measured.

Figure 22 – The IPW rolling resistance trailer and its towing truck [7]

4.6.4 Measurement method The four trailer tyres are not covered by special housings, but at speeds of 15 km/h this seems not to be necessary. The trailer has air springs and at a test speed of 15 km/h and operation on even surfaces a damping component has not to be considered. Figure 23 shows the drawbar force transducer (covered with insulation material) for truck tyre rolling resistance measurements.

Figure 23 – The in-house developed drawbar force transducer [7]

Figure 24 – The direct measurement principle of the IPW trailer [7]

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The rolling resistance coefficient in [%] is calculated by relating the draw bar force FD = Fx res to a gross tyre loading force Fz of ~180000 N for the whole trailer (see Figure 24). With the test set-up shown in Figure 24 it is important to have an (almost) even test ground which allows travelling with low speed (15 km/h) in both directions to eliminate the influence of longitudinal gradients and cross winds. The values of the rolling resistance measurements from both driving directions have to be averaged. Since the trailer is a commercially available one it is equipped with brakes. Special care has to be taken that brake pads and brake drums do not get in contact during the measurement. With this demands the test trailer method can only be used on local roads which have equal pavements in both directions (and no disturbance of traffic) or on special testing grounds. Highway measurements cannot be undertaken.

To warm up the tyre, a running time before the measurement of rolling resistance can begin, is specified by ISO 28580 to 3 hrs. This can easily be done by towing the trailer over this time period before measurement. By the warming up process the tyre pressure is increased and stabilized.

4.6.5 Rolling resistance semitrailer for heavy vehicle tyres (mobile tyre lab) [8] The IPW rolling resistance semitrailer is derived from a special semitrailer with an integrated quarter- vehicle built for investigations and measurements of dynamic forces and vertical motions of suspension elements as well as for studying tyre-road interaction (truck/ bus) and sprung mass when driving on real road surfaces. Finished in Janaury 2014 the new measuring rig combines a double wishbone suspension (for loads up to 50 kN) and a laboratory measuring hub. The IPW mobile tyre lab will be used for investigations of steady state and transient rolling resistance behaviour.

Figure 25 – The IPW mobile lab semitrailer and its towing tractor (photomontage with measuring rig) [photo IPW] The mobile lab will be able to perform measurements of test tyres mounted on standard wheels with diameters of 17.5”, 19.5” and 22.5” and tyre loads between 14 kN and 45 kN at a driving speed up to 90 km/h. Toe and camber will be variable. Tyre pressure control and tyre core temperature measurement are in preparation.

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4.6.6 Measurement method The horizontal and vertical forces are determined by the direct force method using a three- component-measuring hub with non-rotating force transducers having a high resolution of ± 1 N at a measuring range of ± 1.2 kN (for FX) and ± 30 N at a measuring range of ± 60 kN (for FZ). As pointed out in most of the previous descriptions of measuring equipment also here special care needs to be taken as regards the elimination of influences resulting from acceleration/ deceleration caused by the towing vehicle, any longitudinal gradient of the road and air drag.

4.7 ika/ RWTH Aachen [1], [9] 4.7.1 Rolling resistance semitrailer for heavy vehicle and passenger car tyres (“FaReP”) Due to the intention to conduct tyre measurements under real operation conditions on real roads and to investigate other influences on tyre characteristics (like road surfaces and environmental conditions) a mobile test semitrailer (Figure 26) has been developed and manufactured in 2010/ 2011 at the Institut für Kraftfahrzeuge (ika), RWTH Aachen University.

Figure 26 – The ika semitrailer FaReP and its towing tractor [9] The test rig is able to measure all types of tyres between 600 mm and 1300 mm diameter. The tyres are mounted to a strain gauges based measuring wheel which is mounted in the centre of the wheel carrier. In a so-called handling mode static and dynamic tyre characteristics can be measured. All important parameters like camber angle, side slip angle, tyre load and tyre speed can be measured and dynamically adjusted. Thus, up to 100 % longitudinal slip can be applied to the test tyre by a disc brake, inflation pressure etc. can be adjusted dynamically. The five-component measuring wheel

(Figure 27) used in the handling mode is capable of measuring tyre loads up to 60 kN (Fx and Fy up to 50 kN). Depending on the tractor, the test rig can be operated at driving speeds from 5 km/h up to 100 km/h. Both rear axles of the trailer can be steered in order to compensate any side slip angles of the trailer which might occur from the lateral forces of the test tyre.

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In order to compare these real road measurements from any public road or proving ground with laboratory measurements, the trailer can also be positioned on a 2.54 m (diameter) outer drum, coated with a P80-corundum sand paper surface (see right picture in Figure 28) without changing the technical equipment. On a laboratory drum it is much easier to reproduce and repeat measurements free from many of the other influences. A final target of the investigations of ika on the tyres is a kind of conversion map to transform laboratory measurements to user-defined test tracks by certain additional real road measurements.

Figure 27 – Slip measurements on flat road with test tyre mounted on measuring wheel [1]

4.7.2 Measurement method As an additional feature FaReP can also be operated in a rolling resistance mode. Then it is equipped with a three-component-measuring hub (Figure 28) with non-rotating force transducers having a high resolution of ± 1 N ( or ± 0.5%) at a measuring range of ± 1.2 kN (for FX) and ± 30 N (or ± 0.5%) at a measuring range of ± 60 kN (for FZ).

Figure 28 – Rolling resistance measurements on flat road with measuring hub (left) [10] and on ika drum (right) [9]

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The tyres are mounted on standard wheels and can be attached to the measuring hub via an adapter flange to consider different pitch circle diameters, wheel sizes and offsets. With this rolling resistance configuration FaReP is capable of measuring the rolling resistance of the most common passenger car and truck tyres.

As pointed out in most of the previous descriptions of measuring equipment also here special care needs to be taken as regards the elimination of influences resulting from acceleration/ deceleration caused by the towing vehicle, any longitudinal gradient of the road and air drag. Therefore, rolling resistance measurements have been conducted on proving grounds only at low driving speeds (< 25...30 km/h) so far, using an appropiate gear ratio to get a maximum engine rotation speed. An additional housing of the tyre can be adapted to the wheel carrier to avoid disturbing wind and air drag influences on the RR measurements. Possible transversal movements of the trailer and angular changes of the wheel carrier are detected and adjusted for to ensure that tyre test tyre is hardly exposed to side forces.

4.7.3 Calibration procedure Regarding rolling resistance measurements the test rig can be calibrated on the drum mentioned above by an external torque sensor in the drum drive shaft ("torque method"). Then the complete truck can repeat measurements on a test track. Here both FX and FZ are measured in the hub as well as the position (inclination angles) of the wheel carrier. Most of clause 4.7 is adapted from a text supplied by Mr Oliver Sipply at ika/ RWTH in Aachen, who has also kindly supplied many of the photos [9]

4.8 Dufourniers Technologies/ Colas 4.8.1 Skid/ rolling resistance trailer for passenger car tyres The Dufourniers Technologies trailer is offered to the market as a specific skid trailer for rolling resistance characterization. The skid trailer is claimed to have the ability to perform rolling resistance measurement according to the protocol of ISO 28580 and SAE J1269. The four tyre-wheel assemblies mounted on the tandem axle are used for support and carriage of chassis only whereas the test tyre-wheel assembly is mounted to a separate suspension (double wishbone kinematic) movably linked to the chassis. The upper wishbone is formed as a kind of rocker (see part (1) in Figure 31) where the load (2) is drawn towards the test tyre position (3) by power assistance to a position depending on the requested tyre load. Aeronautic ball joints are used for all suspension linkages of the test rig to be free from play. Toe and camber are variable in a certain range. The trailer is capable of performing measurements of test tyres with a minimum diameter of 500 mm mounted on standard wheels with diameters from 12” up to 22”. The maximum tyre load FZ depends on the trailer model used (mass ranging from 800 kg up to 1500 kg). Sensors for ambient, road surface and tyre tread temperature are used.

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Figure 29 – The Dufourniers/ Colas skid and rolling resistance trailer [11]

Figure 30 – The Dufourniers/ Colas skid and rolling resistance trailer with opened enclosure (left) and detailed view to the test tyre (right) [11]

Figure 31 – Design drawing of the Dufourniers/ Colas skid and rolling resistance trailer [11]

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4.8.2 Measurement method The horizontal and vertical forces are determined by the direct force method using a non-rotating two-component-measuring hub with force transducers having a measuring range of ± 0.4 kN (for FX) and ± 10 kN (for FZ). As the centre of the test tyre-wheel assembly is located out of the middle of the tandem axle side forces will occur and influence the measurement when not driving straight ahead. The measuring hub used is claimed to compensate for transversal forces on rolling resistance.

As pointed out in most of the previous descriptions of measuring equipment also here special care needs to be taken as regards the elimination of influences resulting from acceleration/ deceleration caused by the towing vehicle and any longitudinal gradient of the road.

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5 Existing special vehicle equipment

5.1 General The self-powered vehicle method is a method where rolling resistance measurements are made with test tyre(s) in a (specially designed) vehicle, while rolling at constant speed. The measurements may be made of either the torque on the test tyre (by using a wheel force transducer unit or a measuring hub), the towing force between vehicle chassis and seperate suspension/axle, the force in one of the longitudinal links of the suspension for the test tyre-wheel assembly or the angle by which the tyre vertical support is displaced when a rolling resistance force is acting in the tyre/road interface. Most commonly a truck or bus with an specially designed suspension for an additional axle for either passenger car tyres or heavy truck tyres is used.

5.2 Daimler AG/ FKFS [12] 5.2.1 Truck Tyre Measuring Vehicle For the various measuring tasks like tyre performance when braking under wet conditions as well as cornering stiffness and rolling resistance the Daimler AG owns a special truck tyre characteristics test and measurement vehicle based on an ACTROS MB 4151 AK 8x8/4. This truck was designed to measure rolling resistance and any force and moment characteristics of typical commercial vehicle tyres of different dimensions on real road surfaces under dry and wet conditions. The measurement equipment was designed and built by FKFS (see Figure 32). Besides the measurement of tyre forces and moments in response to brake slip, slip and camber angle for direct comparison or parameterization of tyre models for driving dynamics simulations, special focus was set to an accurate determination of the tyre rolling resistance under realistic conditions.

Figure 32 – The Daimler/ FKFS truck tyre measuring vehicle [12]

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The base truck was elongated to install a special measuring axle construction. Additional weight and frame stiffening was added to the base truck to realize an appropriate axle load distribution and safe driving dynamics in any operation condition during the measurements. A powerful and chip tuned motorization and a chassis with four driven axles was chosen to provide adequate driving force and traction when performing braking tests. Figure 33 shows the Daimler Truck Tyre Measuring Vehicle with raised measuring axle.

Figure 33 – The Daimler/ FKFS truck tyre measuring vehicle with raised rear axle [12]

Figure 34 – The measuring axle with a six-component-measuring hub [12] Figure 34 shows a close-up of the measuring axle with a measuring hub (4). The measuring axle consists of a central axle suspension unit, which can be adjusted in height to test different tyre dimensions. The layout considers wheel diameters from 17,5 ” up to 22,5 ” and tyre (single, super

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single and twin) radius from 332 mm up to 565 mm. Vertical loads up to 13 t per axle can be applied by a special air suspension system. To consider different ground clearances depending on the tyre diameter two sets of air springs (1) are mounted on top of each other. A variable damper is integrated into the lifting device (3) of the measuring axle. The central axle suspension unit is guided via two parallel control arms (2) in longitudinal direction on each side. The fixing points of the control arms on the chassis side can be adjusted continuously in height (5) to maintain a horizontal position of the control arms. Together with a special air suspension system for the base truck rear axles, this height adjustment ensures a correct control arm alignment, parallel to the road and parallel to the truck chassis. The longitudinal control arms transmit the longitudinal forces and the parallel alignment prevents any crosstalk from braking forces to the tyre load. The central element of the measuring axle is a six component measuring hub: it is a modular concept design with strain gauge based rotating measuring cells for measurement of forces and torques in all six degrees of freedom in the wheel center. The tyres are mounted on standard wheels and can be attached to the measuring hub via an adapter flange to consider different pitch circle diameters, wheel sizes and offsets.

Various additional sensors measure the pitch and roll angle of the measuring axle relative to the road surface, longitudinal and lateral tyre slip, ambient and road surface temperature and so on.

5.2.2 Measurement method The basic approach for rolling resistance measurement with the Daimler Truck Tire Measuring Vehicle is displayed in Figure 35. The coordinate systems of the measuring hub, the measuring axle and the road surface are displayed. All three coordinate systems can – at least to some extent – be rotated against each other and against the inertial system. For accurate rolling resistance measurements it is necessary to compensate the resulting influences.

Figure 35 – The basic approach for rolling resistance measurement with the Daimler/ FKFS truck [12]

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The longitudinal force resulting from the rolling resistance of test tyre has to be measured in a coordinate system whose longitudinal axis is parallel to the road surface. Therefore, the tyre-wheel forces determined by the measuring hub are primarily transformed to the measuring axle system and then to a tyre-coordinate system parallel to the road surface (TYDEX H-Axis System).

Furthermore, an existing inclination angle φFB,I of the measuring track against the inertial system results in a downhill-slope force acting on the test tyre. This effect needs to be compensated in order to obtain the actual longitudinal tyre force, which is done by performing measurements in both directions of the same test section. With this demands this self-powered vehicle method can only be used on local roads which have equal pavements in both directions (and no disturbance of traffic) or on special testing grounds. Highway measurements cannot be undertaken.

Inertial forces due to acceleration or deceleration of the measuring vehicle are avoided by performing the measurements with activated cruise control and by selecting data with zero mean acceleration. In general, data averaging is used to remove the influence of short-term fluctuations and stochastic errors from the measured signals. The transformation of the forces determined by the measuring hub to the road parallel coordinate system requires an exceptionally high measuring accuracy. If, for example, the rolling resistance force of a tyre with a rolling resistance coefficient of Cr = 0.006 shall be evaluated, the longitudinal force FX due to rolling resistance at Fz = 30 kN tyre load the would be 180 N. If furthermore, a measurement error of 0.01 ° in either the angle φN,A (between measuring hub and measuring axle) or in the angle

φA,FB (between measuring axle and road surface) would cause an absolute error (resulting from a crosstalk from FZ to FX) of

ΔFX = 30 kN · sin(0.01°) = 5.24 N then a relative error of 2.9 % in the measured rolling resistance is obtained. As a consequence, the angles φN,A and φA,FB need to be determined with very high accuracy. The angle φN,A is determined by the measuring hub with a repeatability of 0.01° or better. The angle φA,FB between measuring axle and road surface is measured by means of two laser displacement sensors (see Figure 35). They are mounted at the measuring axle with a longitudinal distance of 1.55 m, allowing an angle measurement with a very good repeatability. Stochastic influences on the laser transducer signals like road unevenness and surface texture are eliminated by averaging the measurement data. In order to obtain reliable absolute values for the rolling resistance it must be ensured that the aforementioned angle measurements do not have an absolute offset. Referring to Figure 35 this means that the horizontal axis of the tyre coordinate system, where the measured forces are finally transformed into (TYDEX H-Axis System), has to be adjusted parallelly towards the road surface with an error in angle < 0.01 °.

5.2.3 Calibration procedure Since no measurement equipment that handles such a precise zero point setting for in-field testing is currently available the zero points of the angle measurements are determined by zero point

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measurements of the longitudinal force instead. This is done by measuring the longitudinal force FX with the test tyre/wheel assembly lifted off the road. Again the influences of road gradient and inertial forces must be taken into account for as described before. With lifted tyre-wheel assembly mounted on the measuring hub the rolling resistance force should be zero. Any measured value which differs from zero is consequently due to uncompensated influences, e.g. road inclination angle, or due to an offset of the angle measurement described in 5.2.2. If an absolute value of FX is measured (e.g. due to a longitudinal gradient) a compensation of this effect has to be achieved by performing measurements in both directions of the same test section. Nevertheless, since the lifted tyre-wheel assembly only provides a vertical load of about 1440 N, a precision of approximately

0.25 N can be observed. This actually corresponds to an error of 0.01° in the angles φN,A or φA,FB. Therefore, it is necessary to repeat the determination zero-point several times in order to compensate for stochastic error.

The approach to the zero-point determination of the of rolling resistance measurement described above denotes that possible offsets in φN,A, φA,FB and in the longitudinal force determined by the measuring hub are treated as a single error. This is possible as on the one hand the measuring hub does not generate any longitudinal force offsets because of the measurement principle (any force offsets are canceled out due to the rotation of the hub) and on the other hand, the effect of small remaining errors in either φN,A or φA,FB on the overall coordinate transformation is negligible. If necessary the procedure can be applied at any time to recheck the accuracy of the measurement system. The whole clause 5.2 section is adapted from a text supplied by Mr Jens Neubeck at FKFS [12].

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Deliverable D3.1: State of the art on rolling resistance measurement devices

6 Conclusion

As an overall conclusion it may be stated that all kinds of rolling resistance measurements on real roads are complicated and subject to many potential problems and sources of error. This mainly applies to measuring of the absolute value of tyre rolling resistance on real roads, where field testing appears to be extremely difficult. Many measurement devices have their advantages and disadvantages depending on the measuring principle they use.

Standard test methods are available only for testing tyre rolling resistance in laboratories whereas standard methods for testing rolling resistance related to road surfaces must be developed.

Further investigantions on how to eliminate the unwanted environmental influences have to be carried out. At the end of the ROSANNE project The Draft Standard of WP3 should give a stricter approach on how to provide modified test equipment for a road-based method for rolling resistance measurements.

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Deliverable D3.1: State of the art on rolling resistance measurement devices

References

[1] Sandberg, U. (ed): “Rolling Resistance - Basic Information and State-of-the-Art on Measurement methods”, Report MIRIAM SP1 Deliv. #1, 2011 [2] Sandberg, U.; Bergiers, A.; Ejsmont, J.; Goubert, L.; Zöller, M.: “Rolling Resistance - Measurement Methods for Studies of Road Surface Effects”, Report MIRIAM SP1 Deliv. #2, Feb. 2012 [3] Bergiers, A.; Goubert, L.; Anfosso-Lédée, F.; Dujardin, N.; Ejsmont, J.; Sandberg, U., Zöller, M.: „Comparison of Rolling Resistance Measuring Equipment - Pilot Study“, Report MIRIAM SP1 Deliv. #3, Dec. 2011 [4] Zöller, M.; Glaeser, K.-P.: “Der Rollwiderstand von Reifen auf Fahrbahnen”, 3. Symposium Reifen und Fahrwerk IVK, Wien, Sept. 2005 [5] Centre de recherches routières (CRR, now Belgian Road Research Centre BRRC): Résistance au roulement; Fiche d’information F52, 1990 [6] Haken, K.-L.: “Messung des Rollwiderstandes unter realen Bedingungen”; Kraftfahrwesen und Verbrennungsmotoren, 3. Stuttgarter Symposium, 23.-25. Feb. 1999 [7] Bode, M.; Bode, O.; Glaeser, K.-P.; Neubauer, J.; Pflug, H.-C.: „Der Rollwiderstand von Nutzfahrzeugen - Wie korrelieren die Werte bei unterschiedlichen Messverfahren?“; Vortrag, 13. Int. VDI Tagung Hannover, 2011 [8] Personal communication with Dr. Otto Bode, CEO, IPW automotive GmbH, Isernhagen [9] Sipply, O.; Bachmann, C.; Eckstein, L.: “Tyre measurements on real roads with the mobile tyre test rig “FaReP” Institute for automotive engineering (ika), RWTH Aachen university/ Forschungsgesellschaft Kraftfahrwesen mbH (fka), Aachen 2014 [10] Prüfstandskatalog fka-ika: downloadable from http://www.ika.rwth aachen.de/ueber_uns/ ausstattung-filme/pruefstandskatalog-fka-ika.pdf (accessed 2014-02-25) [11] Colas/ Dufourniers-Technologies: “Skid Trailer For Rolling Resistance Characterization”; presentation from www.dufourniers-technologies.com [12] Neubeck, J.; Krantz, W.; Wiedemann, J.; Mierisch, U.; Franke, G.; Wehner, K.: „Evaluation of the Tire-Road Interaction to Optimize Efficiency and Driving Dynamics of Heavy-Duty Commercial Vehicles”; 2. Internationales Münchner Fahrwerk-Symposium, 2011

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

ROSANNE Draft standard outline: Methods of measuring rolling resistance — The road-based method (WP3) Working document

Version History

Version Date What Who no. v1.0 2014-01-10 Initial version M. Zöller (BASt) v1.1 2014-02-03 remarks from BRRC A. Bergiers (BRRC) J. Maeck (BRRC) changes from BASt M. Zöller (BASt) v1.2 2014-02-11 changes from BRRC A. Bergiers (BRRC) v1.3 2014-02-16 changes and comments from TUG J. Ejsmont (TUG) B. Świeczko-Żurek (TUG) v1.4 2014-02-20 changes from BASt M. Zöller (BASt)

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

Table of Contents

Action List / Timetable ...... 3 Foreword ...... 4 Introduction ...... 5 1 Scope ...... 5 2 Normative references ...... 5 3 Terms and definitions ...... 6 3.1 Rolling resistance, Fr ...... 6

3.2 Rolling resistance coefficient, C r ...... 6 3.3 Parasitic loss ...... 6 4 Test methods ...... 6 5 Test equipment ...... 7 5.1 Self-powered vehicle ...... 7 5.1.1 Force methods ...... 7 5.1.2 Angle method ...... 8 5.2 Towed trailer ...... 9 5.2.1 Force methods ...... 9 5.2.2 Angle method ...... 10 5.3 Reference tyres and wheels ...... 11 5.4 Load, alignment, control and instrumentation accuracies ...... 12 5.5 Thermal environment ...... 12 5.5.1 Reference conditions ...... 12 5.5.2 Alternative conditions ...... 12 5.5.3 Temperature measurements ...... 12 6 Test conditions ...... 13 6.1 Test equipment ...... 13 6.2 Reference speeds ...... 13 6.3 Tyre load ...... 13 6.4 Tyre inflation ...... 13 6.5 Test tyre-wheel assembly ...... 14 6.5.1 Alignment ...... 14 6.5.2 Mounting ...... 14 6.6 Test site ...... 14 7 Test procedure ...... 14 7.1 Thermal conditioning ...... 15 7.2 Pressure adjustment ...... 15 7.3 Warm up ...... 15 7.4 Measurement and recording ...... 15 7.5 Measurement of parasitic losses ...... 15 7.5.1 The “two-point” procedure (related to force method) ...... 15 7.5.2 The device inherent procedure (related to all methods) ...... 17 7.5.3 The calculation procedure (related to angle method) ...... 17 8 Data interpretations ...... 18 8.1 Determination of parasitic losses ...... 18 8.2 Rolling resistance calculation ...... 18 9 Data analysis ...... 19 9.1 Rolling resistance coefficient ...... 19 9.2 Temperature correction ...... 19

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9.3 Gradient correction ...... 19 9.4 Longitudinal acceleration/ deceleration correction ...... 20 Annex A (normative) Test equipment tolerances ...... 21 A.1 Introduction ...... 21 A.2 Test wheel dimensions ...... 21 A.2.1 Width ...... 21 A.2.2 Run-out ...... 21 A.3 Instrumentation accuracy ...... 21 Annex B (normative) Certification of the test equipment ...... 22 B.1 Introduction ...... 22 B.2 Compensation for load/spindle force interaction and load misalignment (force methods only) ...... 22 B.3 Compensation for the influence of longitudinal gradient ...... 22 B.4 Compensation for the influence of acceleration/ deceleration ...... 22 Annex C (informative) Parasitic losses ...... 23 C.1 Introduction ...... 23

Action List / Timetable

What? Until when? Who? adding text to clause 7.5.3 week 8 A. Bergiers (BRRC) adding text to clause 7.5.2 and Annex C week 8 J. Ejsmont (TUG)

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

Foreword This draft has been prepared by members of WP3 from the EU project ROSANNE (“Rolling resistance, Skid resistance, And Noise Emission measurement standards for road surfaces”). This document is a working document.

Note

This Draft Standard Outline is distributed in the ROSANNE project for review and comment. It is therefore subject to change within the project due to further research.

Many parameters and equations used in this document have to be examined further in the ROSANNE project and should be considered as a first indication only (marked in light-grey). They will be adapted later. Important remarks from reviewers are described in a footnote. The aim of this document is to point out which parameters are still unsure and which research has to be done in the near future to be able to produce a Draft Standard.

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Introduction Environmental questions have become an important part of the decision-making processes for highway projects in many countries. Advantages of different road pavements from environmental viewpoint and their effects to the energy consumption for different types of vehicles using these roads are therefore an important part of the planning progress. Numerous requirements are made for modern vehicle tyres. Besides properties such as comfort, low noise level, lateral traction, stopping power, useful life span, etc., the property of "rolling resistance" has been gaining in significance recently, both from the point of view of (fuel) consumption reasons and ecological reasons (CO 2 debate). There are many factors that impact the energy/fuel consumption of a vehicle. Amongst others rolling resistance plays a major role. The type of road pavement and its surface influence the rolling resistance of the tyre-road unit. It is therefore important to be able to measure the influence of rolling resistance properties of pavements by a standardized method. Within the constraints of the road-based method this deliverable from the project ROSANNE offers an objective rating of the road characteristics to satisfy a need currently expressed by road planners, road administrators, contractors and other parties concerned with the CO 2 reduction problems.

1 Scope This recommendation specifies methods for measuring rolling resistance, under realistic conditions on real road surfaces, for pneumatic reference tyres. Measurement of road surface properties using this method enables comparison to be made between the rolling resistance of road surfaces by using reference tyres when they are free-rolling straight ahead, in a position perpendicular to the road surface, and in steady state conditions. For that a self- propelled vehicle or a towed trailer driving at a constant speed can be used. In measuring tyre-road rolling resistance, it is necessary to measure small forces or angles. It is, therefore, essential that equipment and instrumentation of appropriate accuracy are used.

2 Normative references The following normative documents are indispensable for the application of this document: ASTM E1136-10, Standard Specification for P195/75R14 Radial Standard Reference Test Tire ASTM F2493-08, Standard Specification for P225/60R16 97S Radial Standard Reference Test Tire ASTM F2870-11, Standard Specification for 315/70R22.5 154/150L Radial Truck Standard Reference Test Tire ASTM F2871-11, Standard Specification for 245/70R19.5 136/134M Radial Truck Standard Reference Test Tire ASTM F2872-11, Standard Specification for 225/75R16C 116/114S M+S Radial Light Truck Standard Reference Test Tire ISO 28580, Passenger car, truck and bus tyres - Methods of measuring - Single point test and correlation of measurement results"

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ISO 3911:2004, Wheels and rims for pneumatic tyres ISO 4000-1, Passenger car tyres and rims - Part 1: Tyres ISO 4209-1, Commercial Vehicle Tyres and rims - Part 1: Tyres ISO 11819-3, Acoustics — Measurement of the influence of road surfaces on traffic noise — Part 3: Reference tyres

3 Terms and definitions For the purposes of this document, the following definitions apply. NOTE Several general terms used in this technical specification are defined in ISO 28580.

3.1 Rolling resistance, Fr Loss of energy (or energy consumed) per unit of distance travelled NOTE 1 The SI unit conventionally used for the rolling resistance is the Newton metre per metre (Nm/m). This is equivalent to a drag force in Newtons (N). NOTE 2 Fr is the final result of a measurement and therefore free of any influence of parasitic losses.

3.2 Rolling resistance coefficient, C r Ratio of the rolling resistance (in N) to the load on the tyre (in kN). The quantity is dimensionless although sometimes the ratio is multiplied with 100 and therefore expressed in %.

3.3 Parasitic loss Loss of energy (or energy consumed) per unit of distance excluding internal tyre losses, attributable to aerodynamic loss of the different rotating elements of the test equipment, bearing friction, parasitic force influence from the tyre load to the drag force (caused by suboptimal alignment of the suspension used) and other sources of systematic loss which may be inherent in the measurement.

4 Test methods The following alternative measurement methods are given in this recommendation. The choice of an individual method is left to the tester. For each method, the test measurements shall be converted to a force acting at the tyre/road interface. The measured parameters are: a) Force methods: a1) The reaction force measured at the wheel spindle of a wheel and test tyre assembly mounted on a separate suspension fitted either into a vehicle (passenger car, truck or bus) or to a trailer a2) The reaction force measured by a wheel force transducer unit and tyre assembly mounted on one of the axles fitted to a vehicle (passenger car, truck or bus) or to a trailer axle a3) The reaction force of a whole axle equipped with at least two identical wheel and test tyre assemblies fitted either as a rear axle in a vehicle or as a trailer axle b) Angle method

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The reaction force at the tyre spindle of a test tyre-wheel assembly mounted at the end of a pivoted vertical arm is commensurate to its deflection rate (i.e. the angle between a vertical arm and the horizontal)

5 Test equipment

5.1 Self-powered vehicle The rolling resistance measurements are made with test tyre(s) in a passenger car, truck or bus, while rolling at constant speed. The wheel and test tyre assembly can either be mounted on an additional suspension independent from the trailer axle(s) or be mounted on an axle belonging to the chassis suspension of the trailer.

5.1.1 Force methods

5.1.1.1 Measurement principle

Figure 1: Measurement principle of force method a3 (left) and a2 (right)

Figure 2: Measurement principle of force method a1 NOTE The schematic diagrams shown in Figure 1 and Figure 2 only illustrate one possible principle on how to measure the reaction force. Owed to a simplified illustration not all technical necessary linkage elements and pivots are shown. All force sensing elements (transducers) are highlighted in red, all linkage and suspension parts are drawn in with a narrow line.

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5.1.1.2 Implementation

Figure 3: Example for the implementation of the force method a3

Figure 4: Example for the implementation of the force method a2

5.1.2 Angle method

Figure 5: Measurement principle of the angle method

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5.2 Towed trailer The rolling resistance measurements are made with test tyre(s) in a special towed trailer, while rolling at constant speed. The trailer may be designed either for passenger car tyres or for heavy truck tyres. The wheel and test tyre assembly can either be mounted on an additional suspension independent from the trailer axle(s) or be mounted on an axle belonging to the chassis suspension of the trailer.

5.2.1 Force methods

5.2.1.1 Measurement principles

Figure 6: Measurement principle of force method a1

Figure 7 – The measurement principle of the force method a2

Figure 8 – The measurement principle of the force method a3

NOTE The schematic diagrams shown in Figure 6, Figure 7 and Figure 8 only illustrate one possible principle on how to measure the reaction force. Owed to a simplified illustration not all technical necessary linkage elements and pivots are shown. All force sensing elements (transducers) are highlighted in red, all linkage and suspension parts are drawn in with a narrow line.

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5.2.1.2 Implementation

Figure 9 – Example for the implementation of the force method a1

Figure 10 – Example for the implementation of the force method a1

5.2.2 Angle method

5.2.2.1 Measurement principle

Figure 11 – The measurement principle of the angle method

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5.2.2.2 Implementation

Figure 12 – Example for the implementation of the angle method (three wheeled trailer)

5.3 Reference tyres and wheels The test tyres shall be the reference tyres shown in Table 1. Depending on the purpose of measurement, tyre P0, P1, H1, H2, H3 or H4 are used to represent the properties and behaviour of either passenger car or truck tyres. Tyres other then the reference tyres may be used for research or special survey purposes. However, it should be noted that in this case it is not possible to report any results according to this method.

Table 1: Reference tyres

Tyre Shore Tread depth b Normative reference Name Dimension type hardness a P0 Radial Standard Reference Test Uniroyal P195/75 R14 65 +4/-1 Tyre according ASTM Tiger Paw 92 specification E1136-10 Plus P1 Radial Standard Reference Test Uniroyal P225/60 R16 64 ± 2 8 mm Tyre according ASTM Tiger Paw 97S specification F2493-08 H1 Radial Standard Reference Test Avon AV4 195R14C 63 ± 2 10 mm Tyre according ISO/TS 11819-3 Supervan 106/104 Radial Light Truck Standard 225/75 R16C H2 Reference Test Tyre according Michelin 65 ± 2 116/114S ASTM specification F2872-11 Radial Truck Standard 245/70 H3 Reference Test Tyre according Michelin R19.5 65 ± 2 ASTM specification F2871-11 136/134M Radial Truck Standard 315/70 H4 Reference Test Tyre according Michelin R22.5 65 ± 2 ASTM specification F2870-11 154/150L a Type A for new condition; when in use max. deviation of these values is 2 Shore A above upper limit b for new condition ; when in use max. deviation is 2 mm less

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All reference tyres shall be run-in for a minimum of 200 km before first use. If the run-in is made with tyres mounted on a passenger car or truck, reduce the distance to a minimum of 100 km.

Table 2: Wheels for reference tyres

Tyre type

P1 P0/ H1 H2 H3 H4 Wheel 6.5J x 16 5.5J x 14 6J x 16 19.5 x 6.75 a 22.5 x 9.00 a dimension The offset of all wheels shall be oriented by the space available towards brakes, axles, suspension, vehicle or trailer chass is a Disc wheels with 15° drop center

5.4 Load, alignment, control and instrumentation accuracies Measurement of these parameters shall be sufficiently accurate and precise to provide the requested test data. The specific and respective values are shown in Annex A.

5.5 Thermal environment

5.5.1 Reference conditions The reference ambient air temperature, measured at a distance not less than 0.15 m 1 and not more than 1 m from the tyre sidewall, shall be 25 °C.

5.5.2 Alternative conditions If the rolling resistance measurement is conducted at an ambient air temperature differing from the reference ambient air temperature the results shall be corrected to the reference ambient air temperature in accordance with clause 9.2.

5.5.3 Temperature measurements Measurements of air and tyre temperature are mandatory, whereas measurements of road surface temperature are recommended as a supplement. The measurements shall be conducted simultaneously with the rolling resistance measurement. All temperature measurements should be made continuously. It is preferred that the sensor(s) be placed on the vehicle or on the trailer (on the towing vehicle allowed only for road surface temperature measurements). The ambient air temperature sensor shall be located within the windshield for the test tyre in such a way that it is exposed to the turbulent airflow inside of the windshield and protected from direct solar radiation. The tyre temperature (at tread area) sensor shall be placed either inside or outside of the windshield (in line of sight with the tread area if a non-contact sensor is used) or inside the tyre (at the inner surface of the tread area). Any possible influence from direct solar radiation shall be avoided. 2

1 Clause 5.5.1 might be discarded if the position is impractical for use. Then the requirements in clause 5.5.3 should be sufficient. 2 TUG will make thermography tests in summer 2014 to study the temperature variation between tread and sidewall to propose a location for the tire temperature sensor(s). Date: 20-02-2014, Version: 1.4 12 (23)

ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

The road surface temperature sensor shall be placed where the temperature is representative of the temperature in the test tyre tracks.

6 Test conditions

6.1 Test equipment The test vehicle or trailer and measurement system performance shall have been certified according to the procedures described in Annex B.

6.2 Reference speeds The value shall be obtained at the appropriate vehicle or vehicle/trailer speed specified in Table 3.

Table 3: Reference speeds

Tyre type

P0/ P1 H1 -H4 H2 H3 H4 Reference test speed (highways and rural roads) 80 80 80 80 80 km/h Reference test speed (urban roads) 50 50 50 50 50 km/h Reference test speed (inner urban roads) 30 30 30 30 30 km/h

During a test run the reference speed shall not deviate more than ± 2 km/h from the reference test speed.

6.3 Tyre load The reference test load shall be taken or computed from the values shown in Table 4 and shall be kept within a tolerance of ± 20 N or ± 0.5 % (for LI ≤ 121) and ± 50 N or ± 0.5 % (for LI > 121), whichever is greater. Load variations caused by excitations of the road surface through unevenness are not taken into account. NOTE Wherever this is not possible (e.g. caused by the adjustability of a pneumatic or hydraulic cylinder for load appliance) the rolling resistance value at the load chosen shall be extrapolated to the reference load by a calculation considering characteristics inherent to the measurement system.

6.4 Tyre inflation The inflation pressure after the thermal conditioning (see clause 7.1) shall be in accordance with that shown in Table 4 and shall be kept within the tolerance of 10 kPa.

Table 4: Tyre loads and inflation pressure

Tyre type

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

P0 P1/ H1 H2 H3 H4 Load [% of max. load 80 80 80 a 85 85 capacity] Inflation pressure [kPa] 200 200 350 650 750 Load b [kN] 2 4 7 12 20 a As a percentage of single load b Wherever it is not possible to apply a load in % of maximum load capacity due to the characteristics of the measurement system these values can be used 3

6.5 Test tyre-wheel assembly

6.5.1 Alignment The camber angle of the test tyre/wheel assembly shall be no more than 1.0° and (static) toe-in no more than ±0.1°.

6.5.2 Mounting Due to the stringent requirements in clause 6.5.1 a test tyre/wheel assembly shall not be mounted on the steering axle of a vehicle. If mounted on the front axle of a draw-bar trailer no steering activities during the measurement are allowed. The test tyre/wheel assembly shall not be mounted on a drive axle of a vehicle.

6.6 Test site In performing a rolling resistance measurement, there are a number of practical constraints which define the minimum requirements for the road section to be suitable for assessment. These can be summarized as follows. − There shall be a run-in of at least 20 m of the same surface type before the road section begins. − The road section (excluding the run-in) shall be at least 100 m long, and preferably longer than 500 m. If a measurement device is capable of detecting the rolling resistance reliably for a shorter section length then a number of runs sufficient to give a total length of 200 m shall be carried out to get the final result. − The road section shall not include bends with a radius of curvature less than 250 m at 50 km/h and 500 m at 80 km/h − The surface of the road section in the tracks of the reference test tyre(s) shall be in very good condition (no bumps, potholes, free from deterioration and pull out of chippings) − The longitudinal gradient of the road section shall be as small as possible (≤ 1%) 4.

7 Test procedure The test procedure steps described below are to be followed in the sequence given.

3 TUG: With the proposals from Table 4 inflation pressure values for P0 and P1 are very unrealistic. Tyres will have too much deflection. Existing ISO standards for laboratory measurements of rolling resistance are totally unrealistic and on the drum tyres look seriously underinflated. A better way of connecting load and inflation pressure must be found. It is also important to decide if cold or regulated inflation pressure shall be used! It is unknow if Cr is independant on load or not. To propose (b) it must be sure that C r is not related to load. 4 TUG: can also be related to the measurement system Date: 20-02-2014, Version: 1.4 14 (23)

ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

7.1 Thermal conditioning The inflated tyre shall be placed in the thermal environment of the test location for a minimum of 5: − 1 h for passenger car tyres; − 2 h for truck and bus tyres

7.2 Pressure adjustment After thermal conditioning, the inflation pressure shall be adjusted to the test pressure specified in Table 4 and verified 10 min 6 after the adjustment is made.

7.3 Warm up Mount the wheel/tyre assembly on the vehicle or trailer and drive it in the thermal environment of the road test location according the warm-up durations specified in Table 5.

Table 5: Warm up durations

Tyre type

P0/ P1/ H1 H2 H3 H4

Warm up duration [min] 20 40 150 180

The warm-up shall be conducted at the reference speed chosen from Table 3.

7.4 Measurement and recording The following shall be measured and recorded: a) the test speed v b) the load on the test tyre Fz c) the ambient air temperature Ta d) the tyre temperature Tt e) the method chosen f) the reference tyre and wheel chosen g) ...

7.5 Measurement of parasitic losses The origin of parasitic losses is described in Annex C. The parasitic losses shall be determined by one of the procedures described below.

7.5.1 The “two-point” procedure (related to force method)7

Besides the rolling resistance force F r measured by a force transducer (e.g. K1 in the lower suspension link B-E of Figure 9) there are other influences (bearing friction, air drag caused by wind

5 BASt: in some cases (when a test tyre is taken from a storage in a climate chamber) it is necessary to pre-adapt the tyre temperature. Otherwise the warm-up durations given in Table 5 are too short. 6 TUG: depending on the fact if cold or regulated inflation pressure is used 7 BASt/TUG : some more text will be added later after discussion in view of the influence of static to dynamic tyre radius Date: 20-02-2014, Version: 1.4 15 (23)

ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

turbulences of the tyre-wheel assembly, influence on the gross longitudinal force caused by a suboptimal vertical position of the wheel suspension, electrical and mechanical offset or zero drift of the force transducer used) on the measurement value of F X. The general relation for the gross longitudinal force is:

FX = F r + F W + F B + F XZ + F O (1) where

Fr Rolling resistance FW Los s by a ir drag and wind turbulences

FB Loss by bearing friction FXZ Influence of vertical load F Z on

longitudinal force F X (to be determined by a “static” calibration)

FO Zero drift of force transducer

Figure 13 – The two-point procedure (0.8RL is 80% of max. tyre load; R is rolling resistance)

Provided that there is a linear relation between tyre load (F Z) and gross longitudinal force (F X) for a certain tyre/ road assembly a so called "two point procedure" (Figure 13) can be used to eliminate the additive parts of F X which are not causally associated to the rolling resistance force F r. The two points are called "high" and "low".

= + + + + FX high R FW FB FXZhigh FO FXhigh - FXlow = F r + F XZ (2) F =F +F +F +F lowX W B XZ low O

The error of the longitudinal force FXZ can be determined by a separate measurement. This so called "static calibration" (when the vehicle or trailer is at standstill) is also carried out by using the “two point measurement” method. For that reason the tested tyre-wheel assembly is mounted on the vehicle or trailer placed on flat and even ground of a hall. The tyre is loaded with the same nominal vertical load (F Z high ) and a reduced load (F Z low ) as when operated on the road. This must be redone for each tyre-wheel assembly that has a different diameter compared to the previous one, for each change in vertical tyre load, and for each adaption of the suspension links to the current tyre size used. = + F highX S FXZ high S F SO FXhighS - FXlowS = F XZ S (3)

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

F = F + F SlowX SlowXZ SO where

FXZ high S Inf luence on longitudinal force FXZ low S Influence on longitudinal force during “static” condition at vertical during “static” conditions at

load F Z high S vertical load F Z low S

FO S Zero drift of force transducer during “static” conditions

For a very low tyre load F Z low S (~100...150 N) the value of F XZ low S can be neglected. If the conditions during a road measurement are largely the same as during a static calibration then F XZ S can be equated with F XZ .

7.5.2 The device inherent procedure (related to all methods)

7.5.3 The calculation procedure (related to angle method) The rolling resistance force causes the wheel to incline backwards with an angle θ with respect to the frame of the trailer. The rolling resistance coefficient is defined as the ratio of the rolling resistance force and the load on the wheel and equals the tangent of θ. For small angles, θ is equal to the rolling resistance coefficient provided it is expressed in radians.

Small angle deviations have a significant influence on θ and, therefore, different parameters are recorded continuously during measurement:

• Inclination θ of the wheel carrier with respect to the frame of the trailer • Inclination α between the trailer and the towing vehicle (influenced by load of fuel and passengers) • The longitudinal inclination γ (slope of the road)

All data are registered in a file during the measurement. Corrections are applied afterwards according to this formula:

Cr = θ r = θ m - ε1* α - ε2 * γ (4) where

− ε1 and ε 2 are experimentally determined coefficients which are related to the method used, − θm is the “measured” C r including parasitic effects and

− θr is the calculated “real” C r.

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

Figure 14 – Angles γ and α influencing the measured C r (which is the angle θ expressed in radians). μ is the angle of the frame of the trailer with respect to the horizontal plane.

8 Data interpretations

8.1 Determination of parasitic losses

The parasitic losses, FPL , related to the environment of the tyre/road interface shall be determined from the measurements described in Clause 7.5.

8.2 Rolling resistance calculation To get the final result of rolling resistance parasitic losses must be subtracted from the measurement result. 8 Fr = F X - FPL = F X - [F XZ * + F W* + F B* + F O* + F Grad ± F Acc ] (5) where

FX Gross longitudinal force FXZ Influence on gross longitudinal force during “static” conditions at

vertical load F Z (crosstalk)

FGrad Influence of longitudinal gradient FO Zero shift of sensor(s) of a road section

FPL Parasitic losses FW Loss by air drag and wind turbulences

FB Loss by bearin g friction FAcc Loss by longitudinal acceleration/ deceleration

Parasitic losses marked with an asterisk do not need to be considered when using the “Two-point” procedure.

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

9 Data analysis

9.1 Rolling resistance coefficient The rolling resistance coefficient, Cr, is calculated as shown in Equation 5 by dividing the rolling resistance by the load on the tyre:

Cr = F r/F z (6) where

Fz is the test load, expressed in kilonewtons.

The quantity is dimensionless although when multiplied with 100 the ratio can therefore be expressed in %. The rolling resistance coefficient of a surface shall be reported as one value for the whole length of the test section (mandatory). Wherever it is possible consecutive values at a certain resolution can be reported too (optional).

9.2 Temperature correction Only temperatures ≥ 15 °C and ≤ 35 °C are acceptable. If measurements at temperatures other than 25 °C are to be conducted, then a correction for temperature shall be made by means of Equation 2, where F r25 is the rolling resistance at 25 °C, expressed in newtons:

Fr25 = Fr [1+ Kt (tamb -25)] (7) where

Fr is the rolling resistance, expressed in newtons;

tamb is the ambient air temperature, expressed in degrees Celsius;

Kt is the constant, with the following values: 0.008 for passenger car tyres 0.010 for truck and bus tyres with LI ≤ 121 0.006 for truck and bus tyres with LI > 121

9.3 Gradient correction Any gradient of a road section can influence the results of a rolling resistance measurement significantly. This influence shall be avoided by applying the following corrective measures: − correction by a mechanical or electrical device (actuator) compensating those parts of the force of gravity induced by driving slightly up- or downhill and being additive or subtractive to the spindle force − correction by driving in both directions (i.e. uphill and downhill) on the desired road section and calculating the average of each pair of measurements − correction by calculating the influence mathematically for a given longitudinal gradient If none of these corrections is made the results shall only be reported with these constraints.

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

9.4 Longitudinal acceleration/ deceleration correction Any acceleration/ deceleration of a self-powered (towing) vehicle can influence the results of a rolling resistance measurement significantly. This influence shall be avoided by applying the following corrective measure:

− measurement of the longitudinal acceleration/ deceleration by an appropriate sensor mounted to the trailer or the vehicle − calculation of the product of longitudinal acceleration/ deceleration and mass of the towed trailer or the measuring unit built into a trailer or into a vehicle − correction of the gross longitudinal force

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

Annex A (normative)

Test equipment tolerances

A.1 Introduction

The limits specified in this annex are necessary in order to achieve levels of repeatable test results, which can also be correlated among various measurement systems. These tolerances are not intended to represent a complete set of engineering specifications for test equipment; rather, they should serve as guidelines for reliable test results.

A.2 Test wheel dimensions A.2.1 Width

See Table 2 in clause 5.3. A.2.2 Run-out

Run out shall meet the following criteria: − maximum radial run-out: 1.0 mm − maximum lateral run-out: 1.0 mm

A.3 Instrumentation accuracy

The instrumentation used for readout and recording of data shall be accurate within the tolerances stated in

Table A.1 - Instrumentation accuracy

Parameter Accuracy

Tyre load Inflation

pressure Spindle force Angle Temperature Speed Acceleration/

Deceleration

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

Annex B (normative)

Certification of the test equipment

B.1 Introduction

The test vehicle or trailer and measurement system performance shall be certified prior to the initial use of the system. Subsequent certification of the influence of parasitic losses and tyre and wheel alignment shall be repeated at least biannually. This may require replacement of aged or damaged components prior to re-certification. The description and the results of the tests performed shall be reported in a publicly available report. Annex B specifies all tests that must be performed to certify that the measuring system (vehicle or trailer) is capable to perform measurements with the required precision.

B.2 Compensation for load/spindle force interaction and load misalignment (force methods only)

Compensation of both load/spindle force interaction (“cross talk”) and load misalignment shall be achieved during the calibration process.

B.3 Compensation for the influence of longitudinal gradient

B.4 Compensation for the influence of acceleration/ deceleration

...

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ROSANNE Working Document Draft standard outline: Methods of measuring rolling resistance — The road-based method

Annex C (informative)

Parasitic losses

C.1 Introduction

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