Transient concentrated finite line roller-to-race contact under combined entraining, tilting and squeeze film motions

Kushwaha, Manvir S.; Rahnejat, Homer

doi:10.1088/0022-3727/37/14/019

Cited by 41 publications

(40 citation statements)

References 41 publications

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“…The spatial transition of the secondary pressure peak induces a localized wave front, which creates a moving dimple in the contact surface purely as a kinematic effect, inducing squeeze. This is in line with the observations of Kushwaha and Rahnejat [28], who described this as a squeeze caving phenomenon. The presence of a dimple enhances the lubricant film thickness and reduces the chance of direct boundary interactions.…”

Section: Resultssupporting

confidence: 92%

Mixed thermo-elastohydrodynamic cam-tappet power loss in low-speed emission cycles

Chong

Teodorescu

Rahnejat

2012

International Journal of Engine Research

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The key driving forces in engine development are fuel efficiency and emission levels. These aspects are particularly poignant under vehicle idling or low crawling motions in typical city driving. Under these conditions the parasitic frictional losses are exacerbated and the emission levels are especially high. A key engine sub-system is the valve train system. Although it accounts for only 2-3% of the overall engine losses, it is the highest loaded conjunction in the engine, thus limiting the opportunity for lowering the lubricant bulk viscosity. The paper presents detailed tribology of cam-tappet contact, subjected to a mixed thermo-elastohydrodynamic regime of lubrication. In particular, the frictional behaviour of the conjunction is investigated under the stringent North American emission testing city cycle. Such a comprehensive approach has not hitherto been reported in literature. The predictions show good conformance with vehicle frictional assessments in industry. It further demonstrates that under the aforementioned cycle, highest power losses occur which are mainly as the result of lubricant film viscous shear at low sliding speeds and below the lubricant limiting Eyring shear stress.

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Section: Resultssupporting

confidence: 92%

Mixed thermo-elastohydrodynamic cam-tappet power loss in low-speed emission cycles

Chong

Teodorescu

Rahnejat

2012

International Journal of Engine Research

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“…It is an unintentional fortunate event that happens to be also engrained in nature, such as in natural mammalian joints [24]. The results here also corroborate the conclusions of Kushwaha and Rahnejat [25] that squeeze caving phenomenon is really a by-product of kinematics of the contact. Figure 8(b) shows the corresponding shear stress distribution for those cases shown in Fig.…”

Section: Down-cascading From System Level To Microscale Contact Intersupporting

confidence: 88%

“…8(a), the inset at the bottom left-hand corner). The predictions here show that squeeze caving is essentially governed by contact kinematics, as correctly observed by Kushwaha and Rahnejat [25] and need not be explained in terms of a thermal wedge as has been invariably suggested as a cause, which is in fact clearly an effect.…”

Section: Down-cascading From System Level To Microscale Contact Intersupporting

confidence: 83%

Multi-physics analysis of valve train systems: From system level to microscale interactions

Teodorescu

Kushwaha

Rahnejat

et al. 2007

Proceedings of the Institution of Mechanical Engineers, Part K:

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The paper highlights a holistic, integrated, and multi-disciplinary approach to design analysis of valve train systems, referred to as multi-physics. The analysis comprises various forms of physical phenomena and their interactions, including large displacement inertial dynamics, small amplitude oscillations due to system compliances, tribology, contact mechanics, and durability at the cam-tappet contact. Therefore, it also represents a multi-scale investigation, where the phenomena can be investigated at system level and referred back to underlying causes at subsystem or component level, in other words, implications of an event at microcosm can be ascertained on the overall system performance. This approach is often referred to in industry as down-cascading and up-cascading. The particular case reported here to outline the merits of this approach concerns a four-stroke single-cylinder engine. This promotes a system approach to engineering analysis for integrated noise, vibration, and harshness, durability and frictional assessment (efficiency). Experimental validation is provided with a motored test rig, using laser doppler vibrometry.

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“…Furthermore, under transient conditions the squeeze film effect should also be taken into account. Inclusion of squeeze effect ensures the continuity of transient effect of changes upon plates' separations and can in fact enhance the load carrying capacity of the contact as has been shown in many load bearing applications, such as in bearings, gears, rings and seals [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Efficiency of disengaged wet brake packs

Leighton

Morris

Trimmer

et al. 2018

Proceedings of the Institution of Mechanical Engineers, Part D:

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Key objectives in off-highway vehicular powertrain development are fuel efficiency and environmental protection. As a result palliative measures are made to reduce parasitic frictional losses, whilst sustaining machine operational performance and reliability. A potential key contributor to the overall power loss is the rotation of disengaged wet multi-plate pack brake friction. Despite the numerous advantages of wet brake pack design, during high speed manoeuvre in highway travel or at start-up conditions significant frictional power losses occur.The addition of recessed grooves on the brake friction lining is used to dissipate heat during engagement. These complicate the prediction of performance of the system, particularly when disengaged. To characterise the losses produced by these components, a combined numerical and experimental approach is required. This paper presents a Reynolds-based numerical model including the effect of fluid inertia and squeeze film transience for prediction of performance of wet brake systems. Model predictions are compared with very detailed combined Navier-Stokes and Raleigh-Plesset fluid dynamics analysis to ascertain its degree of conformity to representative physical operating conditions, as well the use of a developed experimental rig. The combined numerical and experimental approach is used to predict significant losses produced during various operating conditions. It is shown that cavitation becomes significant at low temperatures due to micro-hydrodynamic action, enhanced by high fluid viscosity. The magnitude of the losses for these components under various operating conditions is presented.The combined numerical-experimental study of wet multi-plate brakes of off-highway vehicles with cavitation flow dynamics has not hitherto been reported in literature.2

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Transient concentrated finite line roller-to-race contact under combined entraining, tilting and squeeze film motions

Cited by 41 publications

References 41 publications

Mixed thermo-elastohydrodynamic cam-tappet power loss in low-speed emission cycles

Mixed thermo-elastohydrodynamic cam-tappet power loss in low-speed emission cycles

Multi-physics analysis of valve train systems: From system level to microscale interactions

Efficiency of disengaged wet brake packs

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