ISO 31657-2:2025

Overview

ISO 31657-2:2025 - Plain bearings - Hydrodynamic plain journal bearings under steady‑state conditions - Part 2 specifies characteristic values required for the safe design and calculation of multilobed (two-, three- and four‑lobe) hydrodynamic journal bearings. Intended to be used together with ISO 31657-1:2025 (calculation methods), this first edition replaces ISO/TS 31657-2:2020 and provides tabulated and graphical characteristic data for selected bearing geometries under steady‑state operation.

Key topics

• Scope and data coverage
  • Characteristic values for selected two-, three- and four‑lobe bearings with relative lubrication pocket width b* = 0.8.
  • Geometrical parameters addressed include angular span (Ω), lubricant pocket centreline angles (φ), gap ratios (h) and bearing width ratios (B*).
  • Operating range indicated (gap ratio h in the specified domain).
• Dimensionless parameters and charts
  • Provides values and curves for important dimensionless parameters used in bearing calculation and design: Sommerfeld number, relative eccentricity, attitude angle, minimum relative film thickness, friction parameters, hydrodynamic flow parameters, film pressure indicators, and non‑dimensional stiffness and damping coefficients.
  • Results are presented in detailed tables (Tables 1–43) and characteristic curves (Annex A for selected four‑lobe bearings).
• Use with ISO 31657-1
  • The characteristic values are intended to be applied with the calculation procedures and symbol definitions given in ISO 31657-1:2025. Equivalent calculation methods are acknowledged as admissible when justified.

Applications

ISO 31657-2:2025 is practical for engineers and organizations involved in:

• Bearing design and sizing of multilobed hydrodynamic journal bearings for rotating machinery (turbines, compressors, generators, large electric motors and industrial shafts).
• Performance prediction and validation-estimating eccentricity, load capacity, film thickness, friction and lubricant flow under steady‑state conditions.
• Tribology analysis and optimization of lubrication pocket geometry to improve stability and minimize wear.
• Maintenance, troubleshooting and retrofitting of existing journal bearing systems where multilobe geometries are used to improve stability and load distribution.
• OEMs, consulting engineers, Tribologists and standards/compliance teams who need authoritative characteristic data for calculation and verification.

Related standards

• ISO 31657-1:2025 - Plain bearings - Hydrodynamic plain journal bearings under steady‑state conditions - Part 1: Calculation of multi‑lobed and tilting pad journal bearings
• Other parts of the ISO 31657 series (refer to ISO catalogue for the full list).

Keywords: ISO 31657-2:2025, multilobed journal bearings, hydrodynamic plain journal bearings, characteristic values, Sommerfeld number, bearing calculation, two‑lobe bearings, three‑lobe bearings, four‑lobe bearings, bearing stiffness and damping.