Overview
ISO 21995:2008 - "Road vehicles - Test of vehicle air braking systems with a permissible mass of over 3,5 t - Acquisition and use of reference values using a roller brake tester" - defines a method for acquiring and applying reference braking values supplied by vehicle manufacturers for use in periodical technical inspection (PTI) of heavy vehicle air brake systems. The standard links type‑approval data (UNECE Regulation No.13, para. 5.1.4.6) with practical roller brake tester checks so single‑axle roller tests can validate whole‑vehicle brake efficiency in service.
Key topics and technical requirements
- Scope: Applies to road vehicles with air braking systems and permissible mass over 3.5 t.
- Reference braking forces: Manufacturers must provide axle‑level brake force vs. brake actuator/cylinder pressure data (reference tables or graphs) obtained at type approval.
- PTI target: Roller bench tests use manufacturer reference values to verify a vehicle meets required deceleration or brake efficiency (e.g., calculation using F = z_min × G, where z_min is the minimum demanded deceleration or efficiency and G is total normal force).
- Single‑axle testing: Roller brake testers measure axle braking forces; PTI pass/fail is determined by comparing measured force at a specified cylinder pressure to the corresponding reference value.
- Pressure range and measurement guidance: Reference values normally cover 100 kPa (1 bar) up to the Type 0 test pressure (examples up to ~450 kPa). PTI measurements should be taken at as high a pressure as possible and not below 200 kPa (2 bar) to avoid instability.
- Brake force distribution: The standard distinguishes static (geometric/actuator sizing) and dynamic (pressure distribution during braking) brake force distribution and prescribes methods to derive axle reference forces so that summed axle forces meet PTI requirements.
- Data handling: Manufacturer data acquisition, documentation and distribution requirements for reference values are covered to ensure usable PTI inputs.
Practical applications and users
Who uses ISO 21995:2008:
- Vehicle manufacturers (to produce and publish compliant reference braking values for type approval and PTI).
- PTI centres and inspection agencies (to perform roller brake tests and assess in‑service brake efficiency).
- Test equipment manufacturers and calibration labs (to implement roller brake tester procedures and ensure correct pressure/force mapping).
- Type approval authorities and regulators (to harmonize in‑service testing with UNECE and national requirements).
Practical benefits:
- Enables repeatable, single‑axle roller testing for heavy vehicles without full road testing.
- Provides a standardized link between type approval reference data and in‑service brake checks, improving safety and inspection consistency.
Related standards
- UNECE Regulation No.13 (Uniform provisions concerning approval of vehicles - braking) - referenced for Type 0 reference values and approval data.