Elastohydrodynamic Lubrication
Also known as: EHL, Elastohydrodynamic film, Hydrodynamic lubrication
Elastohydrodynamic lubrication (EHL) is the regime of fluid film lubrication in which elastic deformation of the surfaces plays a crucial role in maintaining a fluid layer between sliding or rolling surfaces. In applications like roller bearings and gears, the contact pressure is extremely high, causing the lubricant viscosity to increase dramatically and the surfaces to deform elastically. EHL theory, developed rigorously by Dowson and Higginson, predicts the film thickness, pressure distribution, and friction in these heavily loaded contacts.
Key highlights
- Explains how fluid films sustain under extreme pressures where hydrodynamic lubrication would fail
- Predicts film thickness as a function of load, speed, and lubricant properties, enabling optimal design
- Enables selection of appropriate lubricants (viscosity, pressure-viscosity coefficient) for given operating conditions
- Provides criteria for assessing film thickness relative to surface roughness (full-film vs. mixed lubrication)
- Scales to complex geometries using numerical solution techniques
Intuition
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How it works
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When to use it
Use EHL analysis for rolling or sliding contacts operating under high pressure: roller bearings, gear teeth, cam-follower pairs, and rail-wheel contacts. Essential for predicting film thickness, selecting lubricants, and assessing wear risk. Assume isothermal operation (temperature effects ignored) and smooth surfaces; account for roughness separately.
Strengths & limitations
- Explains how fluid films sustain under extreme pressures where hydrodynamic lubrication would fail
- Predicts film thickness as a function of load, speed, and lubricant properties, enabling optimal design
- Enables selection of appropriate lubricants (viscosity, pressure-viscosity coefficient) for given operating conditions
- Provides criteria for assessing film thickness relative to surface roughness (full-film vs. mixed lubrication)
- Scales to complex geometries using numerical solution techniques
- Computational solution is complex; requires iterative coupling of fluid mechanics and elasticity
- Temperature effects (thermal EHL) require additional thermal analysis; most theory assumes isothermal
- Surface roughness effects require micro-contact models layered on top of EHL solution
- Chemical reactions and additive effects in the lubricant are not included in classical EHL
Common pitfalls
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Applications
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Frequently asked
Why is the pressure-viscosity effect of the lubricant so important in EHL?
In EHL contacts, pressure rises to 1-3 GPa, causing lubricant viscosity to increase exponentially. This viscosity rise dramatically increases resistance to squeeze-out, enabling maintenance of the fluid film. Neglecting this effect would incorrectly predict film collapse.
What is the difference between full-film and mixed lubrication?
Full-film (EHL) occurs when the fluid film thickness exceeds the combined roughness of the surfaces, preventing asperity contact. Mixed lubrication occurs when the film is comparable to roughness; some asperities contact while fluid film supports part of the load. Mixed lubrication causes higher friction and accelerated wear.
How does speed affect EHL film thickness?
Higher sliding or rolling speeds increase lubricant supply and film thickness. The relationship is approximately V^0.4 to V^0.6 depending on the lubricant. Lower speeds reduce film thickness, worsening lubrication and increasing wear risk.
Can EHL theory be applied to heavily loaded sliding contacts?
Yes, EHL applies to both rolling and sliding contacts. The main difference is that sliding contacts generate more heat and experience higher friction due to shear heating and viscosity reduction, complicating analysis. Thermal EHL is often necessary for sliding applications.
Sources
- 1.Dowson, D., & Higginson, G. R. (1977). Elastohydrodynamic Lubrication: The Fundamentals of Roller and Gear Lubrication. Pergamon Press.ISBN 0-08-021710-4
- 2.Hamrock, B. J., Schmid, S. R., & Jacobson, B. O. (1994). Fundamentals of Fluid Film Lubrication (2nd ed.). Marcel Dekker.ISBN 0-8247-9163-0
- 3.Masjedi, M., & Khonsari, M. M. (2014). Film thickness and asperity load formulas for elastohydrodynamic lubrication of rollers. Tribology International, 81, 1-14.
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Cite this page
ScholarGate. (2026, June 3). Elastohydrodynamic Lubrication. ScholarGate. https://scholargate.app/manufacturing/elastohydrodynamic-lubrication