ISO 9981:2020

Overview

ISO 9981:2020 - "Belt drives - Pulleys and V‑ribbed belts for the automotive industry - PK profile: Dimensions" specifies the principal dimensional characteristics and measurement methods for PK‑profile V‑ribbed pulleys and endless V‑ribbed belts used predominantly in automotive accessory drives. The standard defines groove geometries, dimensional tolerances, inspection conditions and a method to determine effective belt length. It excludes the broader set of industrial profiles covered by ISO 9982 and notes that clauses on length measurement do not apply to elastic belts.

Key topics and technical requirements

• Groove and rib geometry
  • Groove/rib pitch: 3.56 mm (tolerance ±0.05 mm)
  • Groove angle: nominal 40°
  • Belt rib pitch (p): 3.56 mm; belt height: approximately 4–6 mm
  • Maximum transitional/tip groove radius and other profile limits are specified for correct mating.
• Dimensional tolerances and run-out
  • Groove‑to‑groove diameter variation: ≤ 0.15 mm per pulley
  • Radial and axial circular run‑out: ≤ 0.25 mm full indicator movement (FIM)
  • Diameter over balls (K) tolerance: ±0.6 mm
  • Cumulative deviations of groove pitch in a pulley limited (sum of deviations ≤ ±0.3 mm).
• Surface finish
  • Pulley groove roughness: Ra ≤ 3.2 µm (see ISO 254 / ISO 4287 for measurement methods).
  • For belt effective‑length measurement, measuring pulleys require Ra ≤ 1.6 µm.
• Measurement of effective belt length
  • Uses a two‑pulley measuring fixture (one fixed, one movable) with specified measuring pulley circumference (300 mm) and measuring force per rib of 100 N.
  • Procedure: seat the belt by rotating at least two revolutions, apply measuring force, measure centre distance and calculate effective length per the standard formula.
• Designation formats
  • Pulley: P [number of grooves] PK [effective diameter in mm] (e.g., P 6 PK 100)
  • Belt: [number of ribs] PK [effective length in mm] (e.g., 6 PK 1500)

Applications and users

ISO 9981:2020 is essential for:

• Automotive OEMs and tier‑1 suppliers designing accessory drives (alternator, A/C, power‑steering)
• Pulley and V‑ribbed belt manufacturers ensuring interchangeability and quality
• Testing and inspection laboratories performing dimensional and functional checks
• Maintenance and service engineers specifying replacement belts/pulleys

Using ISO 9981 helps ensure reliable frictional engagement between belt ribs and pulley grooves, consistent belt drive performance, and compatibility across suppliers.

Related standards

• ISO 9982 (industrial V‑ribbed profiles PH–PM)
• ISO 254 (pulley quality, finish and balance)
• ISO 4287 (surface texture)
  Keywords: ISO 9981:2020, V‑ribbed belts, PK profile, pulleys, belt drives, automotive accessory drive, groove dimensions, effective belt length, measurement, tolerances.