Rolling resistance dictates a large part of the energy consumption of trucks. Therefore, it is necessary to have a sound understanding of the parameters affecting rolling resistance. This article proposes a semi-physical thermodynamic tyre rolling resistance model, which captures the essential properties of rolling resistance, such as transient changes due to temperature effects and the strain-amplitude dependency of the viscous properties. In addition, the model includes cooling effects from the surroundings. Both tyre temperature and rolling resistance are obtained simultaneously in the simulation model for each time step. The nonlinear viscoelasticity in rubber is modelled using the Bergström–Boyce model, where the viscous creep function is scaled with temperature changes. The cooling of the tyre is considered with both convective and radiative cooling. Moreover, the article explains different material parameters and their physical meaning. Additionally, examples of how the model could be used in parameter studies are presented.

Background: Rolling resistance and aerodynamic losses cause a significant part of a truck’s energy consumption. Therefore there is an interest from both vehicle manufacturers and regulators to measure these losses to understand, quantify and reduce the energy consumption of vehicles. On-road measurements are particularly interesting because it enables testing in various ambient conditions and road surfaces with vehicles in service. Objective: Common driving loss measurement devices require unique instrumented measurement wheels, which hinders effective measurements of multiple tyre sets or measurements of vehicles in service. For this purpose, the objective is to develop a novel load-sensing device for measuring braking or driving torque. Methods: The strength of the measurement device is calculated using finite element methods, and the output signal is simulated using virtual strain gauge simulations. In addition to the signal simulation, the device is calibrated using a torsional test rig. Results: The simulation results confirm that the device fulfils the strength requirements and is able to resolve low torque levels. The output signal is simulated for the novel cascaded multi-Wheatstone bridge using the strains extracted from the finite element analysis. The simulations and measurements show that the measurement signal is linear and not sensitive to other load directions. The device is tested on a truck, and the effort of mounting the device is comparable to a regular tyre change. Conclusions: A novel driving loss measurement device design is presented with an innovative positioning of strain gauges decoupling the parasitic loads from the driving loss measurements. The design allows on-road testing using conventional wheels without requiring special measurement wheels or instrumentation of drive shafts, enabling more affordable and accurate measurements.

Knowing the tire pressure during driving is essential since it affects multiple tire properties such as rolling resistance, uneven wear, and how prone the tire is to tire bursts. Tire temperature and cavity pressure are closely tied to each other; a change in tire temperature will cause an alteration in tire cavity pressure. This article gives insights into which tire temperature measurement position is representative enough to estimate pressure changes inside the tire, and whether the pressure changes can be assumed to be nearly isochoric. Climate wind tunnel and road measurements were conducted where tire pressure and temperature at the tire inner liner, the tire shoulder, and the tread surface were monitored. The measurements show that tires do not have a uniform temperature distribution. The ideal gas law is used to estimate the tire pressure from the measured temperatures. The results indicate that of the compared temperature points, the inner liner temperature is the most accurate for estimating tire pressure changes (average error 0.63%), and the pressure changes during driving are nearly isochoric. This conclusion can be drawn because the ratio between inner liner temperature and tire pressure is nearly constant, and the pressure can be simulated well using the isochoric gas law.

Due to legislations introduced to prevent global warming, vehicle manufacturers must find new ways to reduce CO2 emissions. This paper explores a way to reduce rolling resistance by heat-insulating and covering a truck’s wheelhouse. Truck tyre rolling resistance was measured at +5 °C ambient temperature for consecutive speed steps in a climate wind chamber with and without heat insulation. The study showed that by encapsulating and insulating the wheelhouse, already generated strain-induced heat could be kept in the tyre, consequently leading to reduced rolling resistance. The tyre shoulder temperature was monitored during the experiments along with the tyre pressure. When the wheelhouses were encapsulated, a significant reduction in rolling resistance and an increase in tyre pressure and temperature were measured at all evaluated speed levels.

The range of an electrically assisted bicycle, which is constrained by the rider's cycling ability and the battery capacity, is heavily influenced by rolling resistance. Furthermore, the magnitude of rolling resistance affects commuters' motivation to decide whether to cycle or to choose another way to commute. This paper presents a way to simulate the transient rolling resistance of bicycle tyres as a function of ambient temperature. The significance of the change in driving resistance at different ambient temperatures is demonstrated through the range simulation of an electrically assisted bicycle at varying ambient temperatures. A representative driving cycle for bicycle commuters was created, enabling comparison of dynamic behaviour in a standardised set, to evaluate the effect of ambient temperature on the battery capacity and the increase in driving resistances. To the authors' knowledge, this kind of model has not previously been created for bicycles. The model calculates tyre temperature based on the heat transfer, considering the heating-i. e., rolling resistance-and cooling effects-i. e., convective and radiative cooling. The decrease in tyre temperature results in an increase in rolling resistance and a decrease in the battery capacity, which was considered in the simulations. The results show significantly increased energy demand at a very low ambient temperature (down to -30 degrees C) compared to + 20 degrees C. The novelty of this article is simulating energy expenditure of bicycle dynamically as a function of ambient temperature. This model includes a temperature-dependent transient bicycle rolling resistance model as well as a battery capacity model. The findings provide researchers with a better comprehension of parameters affecting energy expenditure of bicycles at different ambient or tyre temperatures. The models can be used as a tool during the design process of bicycles to quantify the required battery capacities at different climates. In addition, traffic planners can use the model to assess the effect of changes in infrastructure on motivation to utilise bicycles.

Tyres are a vital vehicle component forming an interface between a vehicle and the road, enabling the generation of braking, steering and traction forces. However, they also generate rolling resistance which researchers have tried to minimise through the years for environmental and economic reasons. Despite numerous attempts to model rolling resistance of tyres there still does not seem to exist a simple, flexible and accepted way of modelling rolling resistance in the time domain as well as parametrising models in an easy and accessible way. This study explores a simple and intuitive way of parametrising a hyperviscoplastic parallel rheological framework. In the experimental part of this study, rubber samples with various amounts of carbon black filler are extracted from a truck tyre section and tested using dynamic mechanical analysis. The test data was used to parametrise the material model. The model consists of Mooney-Rivlin hyperelasticity, 40 Prony elements and 8 perfectly plastic elements with Ogden hyperelasticity. The paper introduces a method to obtain a large number of parameters using only six tuneable parameters, which simplifies the tuning of the model drastically. The parametrised model is suitable for tyre rolling resistance simulations with frequency and strain amplitude dependency of the storage and loss modulus. A wide range of strain amplitudes and frequencies can be covered with the proposed method and it is possible to achieve a good fit for the storage and loss modulus values with the benefit of only a few tuneable parameters. Additional Prony or plastic networks do not increase the amount of tuneable parameters. Moreover, the method can be used to parametrise the material using manual iterations which is generally not possible for a parallel rheological framework with such a large amount of parameters. 

Truck transport offers a versatile way to ship goods in regional, long haulage and urban applications. However, the heavy truck sector accounts for 6 % of total greenhouse gas emissions in the European Union. Therefore, there is a need for a substantial reduction of these emissions to secure the sustainability of Earth for future generations. A key parameter to be considered is rolling resistance, which is the source of approximately half of truck energy consumption.

This thesis aims to provide knowledge and insights about rolling resistance simulations and testing, as well as contribute to a better understanding of parameters affecting rolling resistance. Tests in a climate wind tunnel and on the road were conducted at various speeds and a wide range of ambient temperatures (-30 to +25 °C), providing measurement results that are generally unavailable. The measurements show a considerable increase in the stabilised and non-stationary rolling resistance with lower tyre and ambient temperatures. Furthermore, a way to reduce tyre cooling is suggested in order to increase tyre temperature and thereby reduce rolling resistance. Another key result of this thesis is the design of an on-road driving loss device, which enables quick and convenient validation of energy consumption simulations by retaining the standard interface between the rim and axle while measuring required driving torque during on-road testing. 

Three different simulation models of varying complexity are proposed to simulate rolling resistance: (I) a phenomenological real-time capable rolling resistance estimation model that utilises time-temperature-superposition and a variable thermal inertia temperature model; (II) a semi-physical thermodynamic tyre rolling resistance model with a temperature-dependent nonlinear viscoelastic model that can be used in different parameter studies, such as to analyse the effect of tyre cooling on tyre temperature and rolling resistance; and (III) a finite element simulation model with a hyperviscoplastic PRF rubber model for detailed structural analyses. Furthermore, a convenient method for parametrising a complicated PRF rubber model utilising reduced material parameters was developed and parametrised against measurement data. The reduced material constants simplify the parametrisation, allowing the model to be parametrised with only manual iterations, which is generally not possible. 

Electric vehicles, such as trucks, passenger cars and electrically assisted bicycles, suffer from a reduced driving range at cold temperatures. Increasing the understanding of the influence of rolling resistance on range aspects can help accelerate the adoption of battery-electric trucks and other vehicles that use sustainable energy sources. Therefore, a driving range simulation of a battery-electric truck was conducted where the truck tyre rolling and aerodynamic resistance were varied with ambient temperature, showing a considerable decrease in driving range at cold temperatures. 

The experiments, simulations and the developed measurement device contribute to an increased understanding of rolling resistance and the factors affecting it. These insights are an essential part of developing future resource-efficient vehicles and transport systems where, e.g., transport flow can be optimised by taking into account rolling resistance, aerodynamic resistance and other essential factors.

Lastbilstransporter erbjuder ett flexibelt sätt att frakta varor, samtidigt som sektorn för tunga vägtransporter står för 6 % av de totala växthusgaserna i EU. Därför finns det ett behov av en avsevärd minskning av dessa utsläpp för att säkerställa ett hållbart samhälle. En av nyckelparametrarna är rullmotståndet, som orsakar ungefär hälften av en lastbils energiförbrukning.

Denna avhandling syftar till att ge ökad kunskap om rullmotståndssimuleringar och mätningar samt bidra till en fördjupad förståelse hur olika parametrar påverkar rullmotståndet, vilket kan leda till lägre energiförbrukning för tunga transporter. Tester i en klimatvindtunnel och på väg har utförts i olika hastigheter och ett brett område av omgivningstemperaturer (-30 till +25 °C). Mätningarna visar på en avsevärd ökning av det stabiliserade och icke-stationära rullmotståndet med lägre däck- och omgivningstemperaturer. Dessutom har ett sätt att minska däckkylningen föreslagits för att öka däcktemperaturen och därmed minska rullmotståndet. Därutöver har en mätutrustning för att mäta vridmomentet och drivförluster under körning konstruerats, som möjliggör snabb, kostnadseffektiv och lätthanterlig validering av energiförbrukningssimuleringar genom att behålla standardgränssnittet mellan fälgen och axeln.

Tre olika simuleringsmodeller med varierande komplexitet har föreslagits för att simulera rullmotstånd; (I) en fenomenologisk realtidskapabel rullmotståndsmodell som kan användas för att uppskatta rullmotstånd vid körning, (II) en semi-fysikalisk termodynamisk däcksrullmotståndsmodell med ickelinjär viskoelasticitet som kan användas i olika parameterstudier, såsom att analysera effekten av däckkylning på däckets temperatur och rullmotstånd, och (III) en finita element däckmodell med en hyperviskoplastisk PRF-gummimodell för detaljerade strukturella analyser. Dessutom har en metod utvecklats som underlättar parametriseringen av en komplicerad PRF-gummimodell genom reducerade materialparametrar. De reducerade materialparametrarna förenklar parametriseringen mot mätdata, vilket gör att modellen kan parametriseras genom manuella iterationer, som vanligtvis inte är möjligt.

Elektriska fordon, som lastbilar, personbilar och elektriskt assisterade cyklar, lider av en minskad räckvidd vid kalla temperaturer. Ökad förståelse av räckviddsaspekter underlättar introduktionen av batterielektriska lastbilar och andra fordon som använder hållbara energikällor. Därför genomfördes en räckviddssimulering av en batterielektrisk lastbil där rullmotstånd och aerodynamisk motstånd varierades med omgivningstemperaturen, där simuleringarna visade en betydande minskning av körräckvidden vid kalla temperaturer. 

Experimenten, simuleringarna och den utvecklade mätutrustningen bidrar till en ökad förståelse för rullmotståndet och de faktorer som påverkar det. Dessa insikter är en viktig del i att utveckla framtidens resurseffektiva fordon och transportsystem, där till exempel transportflödet kan optimeras med hänsyn till rullmotstånd, aerodynamiskt motstånd och andra viktiga aspekter.

Rolling resistance is causing a significant part of the energy consumption in truck applications, especially at lowspeed levels. To be able to better estimate the energy consumption or remaining driving range, the truck tyre rolling resistance must be understood well. Temperature is a vital parameter for rolling resistance estimations. This article shows truck tyre rolling resistance and temperature measurements in a climate wind tunnel and simulations of tyre temperature and rolling resistance. During the climate wind tunnel tests, tyre temperature at the shoulder and tread was measured. In addition, on-road driving was conducted with inner-liner infrared temperature measurements. Tyre temperature simulations were conducted using a thermal tyre model with speed-variable thermal inertia. The comparison of tyre temperature simulations with measured inner-liner and shoulder temperatures showed good agreement with the test data. The rolling resistance was simulated using the principle of time-temperature superposition, and a master curve for rolling resistance and a curve for tyre temperature shift were constructed. These curves were used to simulate rolling resistance at a wide range of speed levels with good agreement to the experimental results. The investigation showed that the tyre shoulder temperature is a better indicator of rolling resistance than infrared measurements from the tyre tread.

Rolling resistance is consuming a large portion of the generated powertrain torque and thus have a substantial effect on truck energy consumption and greenhouse gas emissions. EU labelling of tyres mandates the manufacturers to measure rolling resistance at +25 degrees C ambient temperature after stabilised rolling resistance has been established. This is a convenient way of comparing rolling resistance but disregards aspects such as transient rolling resistance and influence of the ambient temperature. For many purposes, such as dimensioning batteries for electric vehicles, this value is not representative enough to give a good understanding of the rolling resistance. In this article, the rolling resistance of a truck tyre was measured at different ambient temperatures (-30 to +25 degrees C) in a climate wind tunnel and a considerable tyre and ambient temperature dependency on rolling resistance was found. The investigation shows that the temperature inside the tyre shoulder has a good correlation with rolling resistance. Measurements with spraying water on tyres were conducted showing a considerable increase in rolling resistance due to higher cooling effect. Driving range simulations of a long haulage battery-electric truck have been conducted with temperature-dependent rolling and aerodynamic resistance, showing a significant decrease in driving range at decreasing temperature.

Rolling resistance is consuming a large portion of the generated powertrain torque and thus have a substantial effect on truck energy consumption and greenhouse gas emissions. EU labelling of tyres mandates the manufacturers to measure rolling resistance at +25 °C ambient temperature after stabilised rolling resistance has been established. This is a convenient way of comparing rolling resistance but disregards aspects such as transient rolling resistance and influence of the ambient temperature. For many purposes, such as dimensioning batteries for electric vehicles, this value is not representative enough to give a good understanding of the rolling resistance. In this article, the rolling resistance of a truck tyre was measured at different ambient temperatures (-30 to +25 °C) in a climate wind tunnel and a considerable tyre and ambient temperature dependency on rolling resistance was found. The investigation shows that the temperature inside the tyre shoulder has a good correlation with rolling resistance. Measurements with spraying water on tyres were conducted showing a considerable increase in rolling resistance due to higher cooling effect. Driving range simulations of a long haulage battery-electric truck have been conducted with temperature-dependent rolling and aerodynamic resistance, showing a significant decrease in driving range at decreasing temperature.