Diss. (sammanfattning) Luleå : Luleå tekniska univ., 2009. / Härtill 6 uppsatser.

Diss.(sammanfattning) Luleå : Luleå tekniska universitet, 2009.

Diss. Linköping : Univ., 2003.

Diss. (sammanfattning) Uppsala : Univ., 2005. / Härtill 6 uppsatser.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 5 uppsatser.

Diss. Luleå : Luleå tekniska univ., 2008.

Lead (Pb) containing alloys such as white metals and Cu-Pb-Sn (lining) with Pb-based overlay plating have been extensively used as materials for internal combustion engine bearings during the last several decades. However, owing to environmental and health concerns, the use of Pb containing materials in automotive engine components is being restricted. In view of this, attempts are under way to develop and replace Pb-containing materials with Pb–free bearing materials. The tribological characteristics of these recently developed Pb-free bearing materials have, however, not been fully investigated and only a limited results about their tribological performance are available in open literature. This thesis therefore focuses on investigating the tribological performance of some recently developed Pb-free engine bearing materials. Although engine bearings are designed to operate in full film lubrication conditions yet they also operate in mixed and boundary lubrication regimes where the material properties do affect their tribological performance. There is thus a need to study the tribological behaviour of these new Pb-free bearing materials in mixed and boundary lubrication conditions vis a vis that of conventional Pb-containing bearing linings and overlays. This work has therefore aimed at investigating the tribological characteristics such as friction and wear, seizure behaviour, interaction with different oil formulations and embeddability behaviour of some selected Pb-free engine bearing materials. Friction and wear properties of Pb-free bearing materials Al-Sn based lining without overlay, bronze lining coated with Polyamide-Imide (PAI) based overlay containing MoS2 and graphite, bronze lining coated with Al-Sn based and PAI based overlay containing MoS2 and graphite, bronze lining coated with Sn-based overlay, and bismuth (Bi) containing bronze lining coated with Sn-based overlay have been studied using a block-on-ring test configuration under unidirectional sliding conditions in mixed and boundary lubrication regimes. The conventional Pb-containing bearing material was also studied as a reference material. Al-Sn based material showed considerably higher friction compared to the other bearing materials. The bearing material with PAI based overlay containing MoS2 and graphite showed superior friction and wear properties compared to all other materials. Sn-based overlay coated materials resulted in comparable friction and wear properties to that of Pbbased overlay. Wear mechanism in Al-Sn based material is mainly adhesive and abrasive in case of Sn based overlay. Seizure behaviour of the bearing materials were also studied using the block-on-ring test configuration in dry as well as lubricated conditions using pure base oil and a fully formulated engine oil. The PAI based overlay containing MoS2 and graphite showed no sign of seizure even at the highest test load in dry as well as lubricated conditions. Al-Sn based lining without overlay seizes at relatively lower load in dry condition compared to the other bearing materials. Adhesion or wear debris smearing onto the counter surface is the main causes of seizure in dry condition. In lubricated condition, seizure occurred at relatively higher load and the conventional Pb-containing material was found to have better seizure performance compared to the Al-Sn based and Sn-based overlay plated materials. Tribological compatibility of Pb-free bearing materials with different oil formulations was studied using a ball-on-bearing specimen test configuration in boundary lubrication under reciprocating sliding conditions. Four different bearing materials were investigated using different lubricants with and without oil additives. In general, the bearing materials lubricated with pure PAO base oil showed higher friction compared to those lubricated with oils containing additives. Lubricants containing additives improved wear properties of the bearing materials except in the case of Al-Sn based lining without overlay. It was also observed that the anti-wear additive level did not significantly influence the wear performance of bearing overlays. The embeddability behaviour of Pb-free bearing materials was studied using a fully formulated engine oil contaminated with SiC particles. Pb-free bearing materials with Snbased overlay, Bi-based overlay, PAI-based overlay containing MoS2 and composite overlay containing PAI, Al, PTFE were investigated. Tests at different rotational speeds (i.e. different oil film thickness) and a constant load were carried out using a journal bearing test rig. It was found that material removal from bearing and shaft surfaces due to abrasive wear is influenced by the lubricant film thickness. The steel counter surface showed lower wear in tests using Sn based overlay and a PAI, Al and PTFE containing composite overlay compared to Bi-based overlay and PAI-based overlay containing MoS2.

With today’s striving towards reduction of fuel consumption it is moreimportant than ever to understand the function of different componentsin the internal combustion engine. There is a need to develop and usetools to investigate and predict the result of specific design changesmade on the components. In this work, the mechanics and the tribologyof the power cylinder unit and more specifically the operation of thepiston rings was investigated both numerically and experimentally. Theobjectives of the numerical part of this thesis were to develop simulationtools that can be used to quantify design changes to the TLOCR andthe cylinder liner. Such as the dimensions of the ring itself but also ringtension, running land profile, out of roundness of the cylinder liner andsurface texture of dimple type applied on the cylinder liner. Numericalsimulation models were developed and used to investigate operation of atwin land oil control ring (TLOCR). TLOCR are typically used in heavyduty diesel engines (HDDE). The TLOCR plays a very important role inthe engine since it is supposed to distribute the correct amount of oil onthe liner to lubricate the other rings. It is important that the TLOCRdoes not leave too much oil on the liner for the two top rings since itcould lead too high oil consumption. In a HDDE the piston assemblyis the largest contributor to frictional losses where the piston ring packaccounts for the major part of this. The oil control ring is the largestcontributor to frictional losses in the piston ring pack therefore makingit very interesting to study from a fuel consumption perspective. One ofthe models developed in this work accounts for the tribological interfaceof the TLOCR against the cylinder liner and piston ring groove as wellas the elastic deformation of the ring and the ring dynamics within thepiston ring groove. The actual ring cross section was modelled in orderto account for the full three dimensional elastic deformation of the ring.By solving all of these problems as a coupled system, the entire operation of the oil control ring can be understood in a better way than earlierand this opens up new optimisation possibilities for the TLOCR. Sincethe cylinder liner in an engine will always have some deviation fromperfectly round this is important. The full ring is modelled in order toaccount for out of round cylinder liners. The model can therefore beused to investigate the effect on oil distribution by reduced ring tensionwhich will affect the frictional losses of the system. It was found that thereduction in tangential force on the TLOCR with kept sealing capability,enabled by reduced out-of-roundness, could result in friction reductionof 40 % at mid-stroke.Because of the complexity, a multi-physics model of this type introducesdifficulties with convergence. Especially when implementinga mass conserving cavitation model and solving for the reversal of thepiston ring. Implementation and numerical verification of a mass conservingcavitation model was therefore performed. A method for dealingwith the convergence problem close to reversal was implemented and discussed.A model considering texture, of dimple type, on the cylinder linerwas also developed to find dimple dimensions optimal for reduced fuelconsumption. Since the dimples are modelled in a deterministic manner,only a periodic section of one land of the TLOCR was considered. Themodel takes mixed lubrication and inertia of the ring into considerationand a mass conserving cavitation algorithm were implemented. Theresults from the model predict friction reduction of approximately 40 %at mid-stroke speeds.The objective of the experimental part of this thesis is to developa novel test method for evaluation of piston ring friction at realisticspeeds. The test-rig was designed and constructed during the first halfof the project. The rig was designed so that standard HDDE productionpiston rings and cylinder liners could be easily mounted, and so thatpiston ring friction could be measured without influence from pistonfriction. Both cylinder liner and oil tank were equipped with heaters,where the oil supply resembles that in an actual engine. Repeatabilityof the results was found to be good. Influence on friction by differentcylinder liner surface roughness and coatings were investigated. Variouspiston ring designs, ring tension and coatings were also investigated. Itwas found that friction of the TLOCR could be reduced with close to50 % with kept sealing capability by reduced ring tension and differentgeometry on the lands in contact with the cylinder liner. The numerical simulation model governing the full cross section of the TLOCR wasvalidated against measured piston ring friction data at a number ofdifferent speeds and excellent correlation was found.

Diss. (sammanfattning) Uppsala : Univ., 2005. / Härtill 7 uppsatser.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 7 uppsatser.