ISO 7902-1:2020

Overview

ISO 7902-1:2020 defines a standardized calculation procedure for oil-lubricated, hydrodynamic plain journal bearings operating in steady-state conditions. The standard covers circular cylindrical bearings with angular spans of 360°, 180°, 150°, 120° and 90° (centrally loaded arc segments) and assumes complete separation of shaft and bearing sliding surfaces by a lubricant film. It is the authoritative guide for sizing and optimizing plain bearings where clearance geometry is effectively constant (except for negligible deformations from film pressure and temperature). The third edition (2020) updates the calculation method and annexed examples for practical design use.

Key Topics

• Calculation basis: Numerical solution of the Reynolds equation for finite bearing length with physically correct pressure boundary conditions.
• Assumptions & scope: Oil-lubricated, full-film hydrodynamic operation under steady-state (constant load magnitude/direction and constant rotational speeds). Dynamic or time-varying loads (e.g., rotor vibration, transient events) are excluded.
• Geometry covered: Circular cylindrical bearings with specified angular spans and centrally loaded arc segments.
• Performance criteria & limits:
  • Freedom from wear and minimum lubricant film thickness requirements
  • Mechanical and thermal loading limits and permissible operational parameters
  • Frictional power loss and heat balance (including convection and lubricant heat flow)
• Hydrodynamic and hydraulic factors:
  • Reynolds number, Sommerfeld number, lubricant flow rates (hydrodynamic, feed, pocket/groove effects)
  • Calculation factors for resistance to rotation and lubricant supply
• Symbols, units and definitions: Complete lists for load-carrying capacity, frictional losses, lubricant flow, temperatures, clearances, and more
• Practical tools: Iterative heat-balance approach and worked examples (Annex A) to converge bearing temperature and lubricant conditions

Applications

ISO 7902-1 is intended for engineers and designers who need reliable plain bearing designs in rotating equipment, including:

• Turbines and generators
• Electric motors and gear units
• Pumps and compressors
• Rolling mills and heavy machinery
• OEMs, tribologists, rotating equipment engineers, maintenance and reliability teams

Use cases: bearing dimensioning, optimization for minimal wear and acceptable temperature rise, estimation of frictional losses and lubricant flow needs, and pre-checking operating conditions against permissible parameters.

Related Standards

• ISO 7902-2 - Functions used in the calculation procedure (normative reference)
• ISO 7902-3 - Permissible operational parameters (normative reference)

Note: Equivalent calculation procedures that yield comparable operating-condition estimates are also admissible under the scope of this standard.