Research and/or Engineering Question/Objective:
The fine dust contribution (<10µm) of motor vehicles represents a considerable health risk for people in urban areas. Due to an increasing percentage of electric vehicles, exhaust emissions are steadily reduced. Consequently, particles from non-exhaust sources (brake, tire and road ware) are considered to be the future main vehicle related pollutant. While regenerative braking, tungsten carbide coatings and filter devices can effectively reduce brake wear emissions, there is currently no methodology available in order to reduce tire wear particles, road abrasion and resuspension. In addition, the tire is one of the main sources of environmental microplastic pollution. Although there are initial approaches to determine the emission characteristics of tire and road ware particles, there is a lack of basic understanding of the underlying physical processes.

Methodology:
The particle flow around the vehicle wheelhouse is dominated by highly dynamic vortex structures. The numerical flow simulation (CFD) is a well suited tool for the investigation of these processes and allows a detailed analysis of the particle-flow interaction. Within this paper, a CFD flow model of a vehicle wheelhouse is presented, which analytically describes the underlying physical effects of particle dispersion by the vehicle tire. The CFD model was applied in order to define a suitable measurement strategy for the measurement of TRW particles based on a measurement vehicle.

Results:
In order to develop a CFD Modell for tire-induced particle emissions, comprehensive analysis of mesh generation, geometric influencing factors and turbulence models was conducted. An essential element of the presented model is the modelling of the wheel rotation, tire-road contact and tire-profile related effects. In addition, particle models were adapted according to the physical properties of tire and road wear particles. In a second step, the CFD methodology was applied in order to design a constant volume sampling system (CVS) which ensures a maximum sampling and transport efficiency for TRW particles.

Limitations of this study:
In general, numerical simulation requires strong simplification of the physical problem and can cover aspects of the flow and particle behavior only partially. Thus, more experiments are necessary to fully validate the CFD model.

What does the paper offer that is new in the field in comparison to other works of the author:
The paper offers a new CFD-based tire and road wear model including flow processes in proximity to the tire-road interface, in order to describe tire induced particle emissions.

Conclusion:
Within this paper a novel CFD-based methodology is presented whereby special emphasis was placed towards the modelling of tire-induced particle emissions. This model was applied in order to design a constant volume sampling system that ensures a maximum sampling as well as transport efficiency for TRW particle measurement.

KEYWORDS - Tire and Road Wear Particles (TRW), Particle Resuspension, Non-Exhaust-Emissions, Computational Fluid Dynamics (CFD), Constant Volume Sampling System (CVS)

Research and/or Engineering Question/Objective:

The measurement of non-exhaust particle emissions is a complex challenge due to the open system configuration of the vehicle brakes as well as tires. Consequently, particles are diluted immediately by the ambient air, which makes reproducible measurement a complex task. Furthermore, measurement conditions on the road are strongly influenced by continuously changing parameters (e.g., flow conditions, changing traffic conditions, particulate matter from other sources). The motivation of the present paper is to describe a methodology for the measurement of all vehicle related non-exhaust particle sources based on a mobile measurement vehicle. The objective is to compare different sources of particle emissions (brake, tire and road wear) under real driving conditions in real time.

Methodology:

A mobile measurement vehicle, which includes sampling systems for all relevant particle sources, is presented. A computational fluid dynamics model (CFD) is applied to enhance the layout of sampling systems for brake as well as for tire and road wear emissions (TRW). Based on a real drive emissions compliant (RDE) Ilmenau cycle, emission factors of brake dust emission are determined. Additionally emissions caused by the tire-road interface are investigated. Furthermore, the influence of the driving behavior is characterized.

Results:

An existing CFD simulation methodology was adjusted in order to account for tire and road wear specific effects of disperse phase flows. In addition to an existing sampling system for brake dust particles, a sampling device for TRW particles was developed. The CFD simulation was applied to increase the sampling and transport efficiency of the system as well as to reduce the influence of other particle sources. The sampling devices were adapted to a mobile measurement vehicle in order to measure particle emissions in dependency of the driving behavior of various test drivers. Based on this study a clear correlation between friction power and increased emissions was determined.

Limitations of this study:

Reproducibility of measurement results is significantly influenced by various factors such as driving behavior and ambient conditions. Numerical simulation in general can only provide an insight into the particle-flow interaction. Extensive experiments are necessary to validate the CFD model in terms of particle resuspension and dispersion caused by the vehicle tire. The influence of ambient particle sources (such as older diesel cars) on the measurement of TRW particles cannot be accurately estimated up to this point.

What does the paper offer that is new in the field in comparison to other works of the author:

The paper introduces a sampling setup suitable for the measurement of all non-exhaust particle sources emitted by passenger cars. A novel CFD-model was introduced accounting for the flow conditions around the vehicle wheelhouse and its effects on particle dilution. For test drives under RDE-conditions the influence of vehicle dynamic properties on different particle sources was analyzed.

Conclusion:

Within this paper, a methodology was described including the development of suitable sampling devices for brake and TRW emissions using CFD simulation software. Applied to a mobile measurement vehicle, emission factors for brake dust emissions were determined. For TRW particles correlations between vehicle dynamic parameters and particle formation were shown.

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Since ZF-TRW first launched the Electric Parking Brake System (EPB) in 2001 the market demand for this technology was continuously growing. Meanwhile the EPB is available in all vehicle platforms and produced globally. The production of the 60 millionth EPB caliper in 2015 was a remarkable milestone.

Technically the EPB interacts with several other driver assistance systems and therefore is not only required as a conventional park brake but more and more to further improve the overall safety, performance and comfort of passenger cars on the path to autonomous driving. In recent years new EPB suppliers entered the globally growing market and OEMs started to individually develop specifications for EPB systems. So there is a growing need to establish globally harmonized standards to efficiently release a safe EPB system on both, OEM and OES side to avoid distortion of competition.

Within the VDA, working groups were formed who deal with system development, fatigue and durability testing. This paper gives an overview of the status and results achieved so far. It has been agreed on mechatronic system endurance tests with actuator, calliper, ECU and Software. Load collectives, temperature- and pressure profiles have been aligned. Experience in actual projects shows that so far achievements of the working groups are very much appreciated by the global braking industry. Environmental component tests should be aligned in a similar way. Standards from ISO16750 could be tailored to the EPB needs. Another fundamental area is the alignment of core tests and regression test strategies.