Elastohydrodynamic lubrication

Definition

Elastohydrodynamic lubrication (EHL) is a lubrication regime that occurs when the pressure in a lubricant film is sufficiently high to cause elastic deformation of the surfaces in contact. This process allows for improved load-carrying capacity and reduced wear, which is crucial in applications involving rolling or sliding contact between surfaces, such as bearings and gears. EHL plays a vital role in optimizing performance and longevity in mechanical systems by balancing friction, wear, and lubrication.

5 Must Know Facts For Your Next Test

1. EHL occurs under high load and low speed conditions where significant elastic deformation of the surfaces happens.
2. The lubricant used in EHL conditions must have specific properties, including high viscosity and shear stability, to maintain an effective lubricating film.
3. Temperature rise during EHL can affect lubricant viscosity, impacting its performance and potentially leading to thermal breakdown.
4. EHL is critical for the performance of rolling element bearings, where it significantly reduces wear rates and enhances lifespan.
5. The design and materials used in gears can be optimized with EHL principles to minimize energy loss and improve efficiency during operation.

Review Questions

• How does elastohydrodynamic lubrication contribute to reducing wear in mechanical systems?
  • Elastohydrodynamic lubrication reduces wear by creating a thick lubricant film that separates the surfaces under high pressure. The elastic deformation allows the surfaces to conform to each other while maintaining a protective layer of lubricant, which minimizes direct metal-to-metal contact. This mechanism is essential in applications like bearings and gears, where excessive wear can lead to failure.
• In what ways does the selection of lubricant influence the performance of elastohydrodynamic lubrication?
  • The selection of lubricant is crucial for elastohydrodynamic lubrication because it affects viscosity, shear strength, and thermal stability. A suitable lubricant maintains a consistent film thickness under varying loads and temperatures, ensuring effective separation of surfaces. If the lubricant fails to meet these requirements, it could lead to inadequate lubrication, increased friction, and higher wear rates.
• Evaluate the impact of elastohydrodynamic lubrication on the design of modern bearings and gears in engineering applications.
  • Elastohydrodynamic lubrication has significantly influenced the design of modern bearings and gears by emphasizing materials that can withstand high contact pressures and temperatures. Engineers now focus on optimizing geometries and surface finishes to enhance EHL performance. As a result, bearings and gears exhibit lower friction losses, reduced wear rates, and improved energy efficiency, contributing to the overall reliability and longevity of mechanical systems in diverse engineering applications.

Related terms

Hydrodynamic lubrication: A lubrication regime where a continuous film of lubricant separates two surfaces in relative motion, primarily relying on the viscosity of the fluid to support the load.

Contact pressure: The pressure exerted at the interface of two contacting surfaces, influencing the behavior of lubricants and the extent of surface deformation.

Boundary lubrication: A lubrication regime that occurs when the lubricant film is insufficient to separate the surfaces, leading to direct contact and increased wear.