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Particle emissions from car brakes: The influence of contact conditions on the pad-to-rotor interface
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.ORCID iD: 0000-0003-3345-5469
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to their adverse health effects emissions have been regulated for over three decades. Brake wear particulate matter is the most important non-exhaust source, however current knowledge is mainly limited to observational studies. This thesis aims to investigate relations between the brake system contact conditions and the related emissions on a model scale; validate the results on a component level; and understand to what extent they are significant on a full-scale.

Paper A investigates the influence of nominal contact pressure on a model scale. Results show that higher pressure corresponds to higher emissions

Paper B investigates the influence of the nominal contact pressure, for different friction materials, on a model scale. A temperature threshold, responsible for a relevant emission increase, is identified.

Paper C investigates particle characteristics and wear mechanisms for different nominal contact pressures, on a model scale. Results show an enhanced tribo-layer at higher pressure levels.

Paper D investigates the influence of brake system conditions on emissions, on a model scale. Results show that frictional power is the most important parameter. A transition temperature independent of the contact condition is identified.

Paper E investigates similarities occurring on a component scale and a model scale in terms of emissions. Results show a promising correlation, and the possibility of using a pin-on-disc tribometer for R&D activities.

Paper F investigates analogies occurring on a component scale and a model scale, in terms of friction performance, fictional surface and chemical composition. Results show similar phenomena occurring for the two test stands.

Paper G analyses real brake system working conditions in a urban environment defining, by means of an inertia dyno bench, the related emissions. Results reveal emission factors compliant to EURO6 and EURO2 regulations, in terms of number and mass, respectively.

Abstract [sv]

På grund av deras negativa hälsoeffekter har partikel emissioner reglerats i över tre årtionden. Bromsslitagepartiklar är den viktigaste icke-avgaskällan, men nuvarande kunskaper är huvudsakligen begränsade till observationsstudier. Avhandlingen syftar till att undersöka förhållandena mellan bromssystemets kontaktförhållanden och de relaterade utsläppen på modellskala. Validera resultaten på komponentnivå och förstå i vilken utsträckning de är betydande i full skala.

Papper A undersöker påverkan av nominellt kontakttryck i en modellskala. Resultat visar att högre tryck motsvarar högre utsläpp.

Papper B undersöker påverkan av det nominella kontakttrycket, för olika friktionsmaterial, i modellskala. En temperaturtröskel,  för en emissionsökning identifieras.

Papper C undersöker partikelegenskaper och slitagemekanismer för olika nominella kontakttryck, i en modellskala. Resultat visar ett förbättrat triboskikt vid högre trycknivåer.

Papper D undersöker påverkan av bromssystemets förhållanden på utsläpp i en modellskala. Resultat visar att friktionskraften är den viktigaste parametern. En övergångstemperatur oberoende av kontaktförhållandet identifieras.

Papper E undersöker likheter som uppträder på komponentskala och  modellskala när det gäller emissioner. Resultatet visar en lovande korrelation, och möjligheten att använda en pinne-på-skiva-tribometer för FoU-aktiviteter.

Papper F undersöker analogier som förekommer på en komponentskala och en modellskala, vad gäller friktionsprestanda, friktionsyta och kemisk sammansättning. Resultat visar liknande fenomen som förekommer för de två testskalorna.

Papper G analyserar verkliga bromssystem arbetsförhållanden i en stadsmiljö som definierar, med hjälp av en tröghetsdyno bänk, de relaterade utsläppen. Resultatet visar utsläppsfaktorer som är förenliga med EURO6 och EURO2-reglerna, i fråga om antal respektive massa.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , 52 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2017:03
Keyword [en]
Car brakes emissions, transition temperature, working conditions, environmental design, pin-on-disc
Keyword [sv]
Bilbromsutsläpp, övergångstemperatur, arbetsförhållanden, miljödesign, pinne-på-skiva
National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:kth:diva-208701ISBN: 978-91-7729-462-7 (print)OAI: oai:DiVA.org:kth-208701DiVA: diva2:1108806
Public defence
2017-09-29, Gladan, Brinellvägen, 83, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
REBRAKE Project
Note

QC 20170808

Available from: 2017-08-08 Created: 2017-06-13 Last updated: 2017-09-08Bibliographically approved
List of papers
1. A study on the load level influence on particulate matter emissions from the sliding contact between a low steel friction material and cast iron
Open this publication in new window or tab >>A study on the load level influence on particulate matter emissions from the sliding contact between a low steel friction material and cast iron
Show others...
2015 (English)Conference paper, Published paper (Refereed)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-166668 (URN)
Conference
Eurobrake 2015, Dredsen, Germany 4-6 May
Note

QC 20150513

Available from: 2015-05-13 Created: 2015-05-13 Last updated: 2017-06-13Bibliographically approved
2. A study on emission of airborne wear particles from car brake friction pairs
Open this publication in new window or tab >>A study on emission of airborne wear particles from car brake friction pairs
2015 (English)In: SAE International Journal of Materials & Manufacturing, ISSN 1946-3979, E-ISSN 1946-3987, Vol. 9, no 1, 147-157 p., 2015-01-2665Article in journal (Refereed) Published
Abstract [en]

The emission of airborne wear particles from friction material / cast iron pairs used in car brakes was investigated, paying special attention to the influence of temperature. Five low-metallic materials and one non-asbestos organic material were tested using a pin-on-disc machine. The machine was placed in a sealed chamber to allow airborne particle collection. The concentration and size distribution of 0.0056 to 10 μm particles were obtained by a fast mobility particle sizer and an optical particle sizer. The temperature was measured by a thermocouple installed in the disc. The experiments show that as the temperature increases from 100 to 300 °C the emission of ultrafine particles intensifies while that of coarse particles decreases. There is a critical temperature at which the ultrafine particle emission rate rises stepwise by 4 to 6 orders of magnitude. For the friction pairs investigated, the critical temperature was found to be between 165 and 190 °C. Below the critical temperature, fine particles outnumber coarse and ultrafine particles, although coarse particles make up the bulk of the particulate matter mass. The friction pairs differ in the ultrafine particle emission rate by 1 to 2 orders of magnitude. Above the critical temperature, ultrafine particles constitute almost 100% of the total particle number and their relative mass contribution can exceed 50%. Analysis of the particle size distributions revealed peaks at 0.19-0.29, 0.9 and 1.7 μm. Above the critical temperature, one more peak appears in the ultrafine particle range at 0.011-0.034 μm.

National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-169695 (URN)10.4271/2015-01-2665 (DOI)000386445700018 ()2-s2.0-84975807242 (Scopus ID)
Projects
Rebrake
Funder
EU, FP7, Seventh Framework Programme, 324385
Note

QC 20160211

Available from: 2015-06-22 Created: 2015-06-22 Last updated: 2017-12-04Bibliographically approved
3. Dry sliding of a low steel friction material against cast iron at different loads: characterization of the friction layer and wear debris
Open this publication in new window or tab >>Dry sliding of a low steel friction material against cast iron at different loads: characterization of the friction layer and wear debris
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1 kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7 kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

Keyword
Wear testing, debris collection, electron microscopy, single particle analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-208690 (URN)
Projects
REBRAKE - G.A. 324385
Note

QCR 20170613

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-13Bibliographically approved
4. ON THE INFLUENCE OF CAR BRAKE SYSTEM PARAMETERS ON PARTICULATE MATTER EMISSIONS
Open this publication in new window or tab >>ON THE INFLUENCE OF CAR BRAKE SYSTEM PARAMETERS ON PARTICULATE MATTER EMISSIONS
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The influence of car brake system parameters on particulate matter emissions was investigated using a pin-on-disc tribometer. Samples from a low-steel friction material and a cast iron disc were tested for different sliding velocities, nominal contact pressures and frictional powers. Disc temperatures were also measured. Their impact on total concentration, size distribution, particle coefficient and transition temperature was analysed. Results show that frictional power is the most significant brake system parameter. However, temperature, as a response parameter, is the most influential, inducing a shift towards the ultrafine particulate fraction and raising emissions. A transition temperature, independent of the system parameters, was identified.

Keyword
Brake environmental design, Frictional heating, Particulate Matter, Particle Coefficient
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-208691 (URN)
Note

QCR 20170613

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-13Bibliographically approved
5. On the scaling effects of measuring disc brake airborne particulate matter emissions – a comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions
Open this publication in new window or tab >>On the scaling effects of measuring disc brake airborne particulate matter emissions – a comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions
(English)Manuscript (preprint) (Other academic)
Abstract [en]

An important contributor to non-exhaust emissions in urban areas is airborne particulate matter originating from brake systems. A well-established way to test such systems in industry is to use Inertia dynamometer benches; although they are quite expensive to run. Pin-on-disc tribometers, on the other hand, are relatively cheap to run, but simplify the real system. The literature indicates promising correlations between these two test stands with regard to measured airborne number distribution. Recent studies also show a strong dependency between the airborne number concentration and the disc temperature. However, a direct comparison that also takes into account temperature effects is missing. The aim of this paper is, therefore, to investigate how the transition temperature is affected by the different test scales, under dragging conditions, and the effects on total concentration and size distribution. New and used low-steel pins/pads were tested against cast iron discs/rotors on both the aforementioned test stands, appositely designed for particulate emission studies. A constant normal load and constant rotational velocity were imposed in both test stands. Results show that a transition temperature can always be identified. However, it is influenced by the test scale and the frictional pair status. Nevertheless, emissions are assessed similarly when an equivalent frictional pair status is analysed (e.g. run-in). Further investigations for fully run-in samples on the pin-on-disc should be performed in order to finally assess the possibility of using the tribometers for the initial assessment of different friction materials.

Keyword
airborne particulate matter, pin-on-disc, inertia dynamometer bench, number
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-208692 (URN)
Projects
REBRAKE - G.A. 324385
Note

QCR 20170613

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-13Bibliographically approved
6. COULD PIN-ON-DISC TRIBOMETERS BE USED TO STUDY THE FRICTION/WEAR PERFORMANCE OF DISC BRAKE MATERIALS?
Open this publication in new window or tab >>COULD PIN-ON-DISC TRIBOMETERS BE USED TO STUDY THE FRICTION/WEAR PERFORMANCE OF DISC BRAKE MATERIALS?
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2016 (English)In: EUROBRAKE 2016 / [ed] FISITA, Milan, 2016Conference paper, Published paper (Other academic)
Abstract [en]

Pin-on-disc tribometers are used by the academia to study friction and wear of disc brake materials. It has been debated if a simplified set-up could reproduce the friction and wear behaviour of the disc brake assembly. The aim of this paper is to investigate and discuss this topic by comparing the friction surfaces with diverse microscopy techniques. Also, coefficients of friction, wear, and collected airborne wear particles are compared. Although the tests are based on different testing procedures (tribometers - drag test and dyno-bench test – single station), the results show that tribometers provide information related to the friction-wear performance, character of friction surfaces, and character of wear particles, which mirror the behaviour of the samples during dyno-bench tests.

Place, publisher, year, edition, pages
Milan: , 2016
Keyword
Friction Materials, Friction Couple Characterisation, Scale Testing for Research, pin-on-disc, dynamometer
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-208693 (URN)
Conference
Eurobrake 2016
Projects
REBRAKE - G.A. 324385
Note

QC 20170613

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-13Bibliographically approved
7. A test stand investigation on a real driving cycle emission factor for car brakes
Open this publication in new window or tab >>A test stand investigation on a real driving cycle emission factor for car brakes
(English)Manuscript (preprint) (Other academic)
Keyword
car brake emission factors; non-exhaust emissions; real driving cycle; airborne particles; inertia brake dynamometer
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-208694 (URN)
Projects
REBRAKE - G.A. 324385
Note

QCR 20170613

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-13Bibliographically approved

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