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Predicting friction in synchronizer systems
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Scania CV AB, Sweden.ORCID iD: 0000-0002-6644-7441
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).ORCID iD: 0000-0002-2578-9453
2016 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 97, p. 89-96Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

The coefficient of friction in synchronizers is important from both a performance and a functional point of view. The synchronization process is highly transient, and the parameters affecting the coefficient of friction have strong mutual dependences, making analysis highly complex. A new friction model for a lubricated molybdenum-steel contact has been developed based on integrating results from physical rig tests and FEM simulations. A simplified thermal model has also been developed, with the purpose to quickly assess the coefficient of friction based on transient force and synchronizer dimensions. The results show good correlation with measured data except at very low sliding speed.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 97, p. 89-96
Keywords [en]
Friction, Sliding contact, Boundary lubrication
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
URN: urn:nbn:se:kth:diva-182346DOI: 10.1016/j.triboint.2015.12.038ISI: 000374194900011Scopus ID: 2-s2.0-84956892595OAI: oai:DiVA.org:kth-182346DiVA, id: diva2:904215
Note

QC 20160218

Available from: 2016-02-18 Created: 2016-02-18 Last updated: 2018-10-24Bibliographically approved
In thesis
1. On synchronization of heavy truck transmissions
Open this publication in new window or tab >>On synchronization of heavy truck transmissions
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Gear shifts are becoming more and more important as engines are adapted to low speed high torque working conditions. Synchronizers are key components for successful gear shifts. To adapt the synchronizers to new working conditions due to adaptations to new engines, improved development tools are needed. The presented thesis describes the development of two types of numerical models for the synchronization process, namely fluid-structure interaction to simulate the pre-synchronization phase and thermomechanical FE models to simulate the main synchronization phase. A methodology for developing friction models based on a combination of physical testing and numerical simulations is presented. Additionally, a comprehensive gear shift and synchronizer frame of reference section is presented.

In paper A, two numerical fluid-structure interaction simulation models for assessing the pre-synchronization phase are presented. Simulations show that the synchronizer functionality is highly dependent on the gear shift maneuvering system, and that grooves in the synchronizer surface have a positive effect on the oil evacuation during the pre-synchronization phase.

Paper B describes the development of a numerical thermomechanical model for simulating the main synchronization phase. Two parameter studies were performed, one based on external loads and one based on synchronizer geometry. The effect on the temperature increase from differences in thermal properties between molybdenum and carbon friction linings are presented.

In paper C, a verification and validation methodology for highly transient thermomechanical processes was presented. Numerical verification, bulk temperature measurement, surface temperature measurement and qualitative visual inspection were combined to verify and validate the simulation model presented in paper B.

In paper D, a methodology combining physical testing with an thermomechanical simulation model to develop a friction model was exemplified by a molybdenum coated synchronizer. A simplified thermal model was developed to remove the dependence of full finite element thermal models. The friction models shows good agreement with measured data.

Abstract [sv]

Betydelsen av växlingar i en växellåda har ökat, och synkroniseringsenheter är viktiga komponenter för snabba och robusta växlingar. För att anpassa synkroniseringsenheterna till nya arbetsförhållanden och laster krävs nya utvecklingsverktyg. Denna avhandling innehåller två typer av numeriska modeller för att simulera synkroniseringsförloppet. Multifysikmodeller som kopplar samman oljeflöde och solida kroppar används för att simulera försynkroniseringsfasen. En termomekanisk modell används för att simulera synkroniseringsfasen. En metod för att utveckla friktionsmodeller under synkroniseringsfasen genom att kombinera fysisk provning med numerisk simulering presenteras. Dessutom finns ett utförligt kapitel om synkroniserings- och växlingsteori.

I artikel A presenteras två olika "Fluid-Structure interaction" ("Interaktion mellan vätskeflöde och solida kroppar") för att simulera försynkroniseringsfasen. Simuleringarna visar att synkroniseringsenheter är väldigt beroende av de aktuatorer de är kopplade till, samt att oljedräneringsspår i kontaktytan har en positiv effekt för försynkroniseringsförloppet.

Artikel B beskriver utvecklingen av en termomekanisk modell för att simulera synkroniseringsförloppet. Två parameterstudier utfördes, en där de externa lasterna utvärderas, och en där geometrin på synkroniseringsenheten utvärderas. Effekten av skillnaden i termiska egenskaper hos molybden och kolfiber utvärderas också.

Artikel C beskriver metodik för verifiering och validering av termomekaniska simuleringar av starkt transienta förlopp. En kombination av numerisk verifiering, temperaturmätning i materialet, yttemperaturmätning samt kvalitativ visuell bedömning används för att verifiera och validera simuleringsmodellen som utvecklades i artikel B.

I artikel D beskrivs en metodik för att kombinera fysiska prover med en uppdaterad termomekanisk simuleringsmodell för att beskriva friktionsbeteendet under synkronisering. Metoden exemplifieras med en molybdenbelagd synkroniseringsenhet. En förenklad termisk modell utvecklas för att kunna beskriva friktionsbeteendet utan att använda tidskrävande finita elementmodeller. Den nya friktionsmodellen överensstämmer väl med uppmätt data.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. p. ix, 38
Series
TRITA-MMK, ISSN 1400-1179 ; 2016:02
Keywords
synchronization, synchronizers, gear shift, gearbox, synkronisering, växling, växellåda
National Category
Other Mechanical Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-181108 (URN)978-91-7595-851-4 (ISBN)
Presentation
2016-03-08, Sal Gladan, Brinellvägen 85, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160218

Available from: 2016-02-18 Created: 2016-01-29 Last updated: 2016-02-18Bibliographically approved
2. Towards model-based development of heavy truck synchronizers
Open this publication in new window or tab >>Towards model-based development of heavy truck synchronizers
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gear shifts are becoming more and more important as engines are adapted to low speed and high torque working conditions. Synchronizers are key components for successful gear shifts. To adapt the synchronizers to future engines and thus new working conditions, improved development tools are needed. This thesis includes a comprehensive gear shift and synchronizer frame of reference section with detailed explanations of how a synchronizer works. The thesis also presents two types of numerical models that enable design analyses of the synchronization process.

Fluid-structure interaction models were used to simulate oil evacuation between the synchronizer cones to assess the synchronizer performance during the pre-synchronization phase. For the main synchronization phase, thermomechanical finite element models were used to simulate the transient temperature in the synchronizer contact surfaces. To verify and validate the thermomechanical simulations, both bulk and surface temperature measurements were used, as well as a qualitative comparison of the position of initial wear marks relative to the position of high surface temperature areas in the simulation. The validated thermomechanical model was used to predict failure in molybdenum coated synchronizers. It was shown that the simulated temperature is a better predictor of synchronizer failure than the commonly used parameters “synchronization energy” and “synchronization power”.

A methodology to develop friction models based on sliding speed, contact pressure and surface temperature was developed, and applied for a molybdenum coated synchronizer.

To allow for improved accuracy of carbon fiber reinforced polymer (CFRP) lined synchronizer simulations, material data for a CFRP friction lining was estimated with different test methods. A contact surface temperature threshold where a reduction in coefficient of friction, accelerated wear and formation of hot spots starts was identified.

To reduce the maximum surface temperature, a relative angle between the cone contact surfaces can be introduced. The optimum relative cone angle was determined based on measured geometric deviations for a population of manufactured synchronizers. It was shown that there is an optimum relative cone angle that significantly can reduce the maximum surface temperature during synchronization.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 94
Series
TRITA-ITM-AVL ; 2018:51
Keywords
synchronization, synchronizers, gear shift, gearbox
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-237235 (URN)978-91-7873-002-5 (ISBN)
Public defence
2018-11-22, Gladan (B319), Brinellvägen 85, holm, 10:00 (English)
Opponent
Supervisors
Funder
VINNOVA, 2112-04619
Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2018-10-24Bibliographically approved

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