Overview - ISO 18868:2013 (Coupling equipment strength requirements)
ISO 18868:2013 specifies strength and performance calculation methods for coupling equipment used in multiple‑vehicle combinations (combinations with more than one coupling point). The standard defines five ISO vehicle combinations (e.g., truck + dolly + semi‑trailer, B‑train) and provides formulae to calculate the minimum required D‑value (longitudinal force capability) and V‑value (vertical force capability) for each coupling point. Vehicle categories covered include N2, N3, O3, and O4. The document also contains worked numerical examples to illustrate calculations.
Key topics and technical requirements
- Vehicle combinations defined: ISO combinations 1–5 (e.g., tractor + A‑semi + centre‑axle trailer; tractor + link‑trailer + A‑semi).
- Coupling types addressed: drawbar couplings and drawbar eyes, fifth wheels and king pins - used on tractors, trucks, converter dollies, semi‑trailers, link‑trailers and full trailers.
- Performance metrics:
- D‑value - comparative measure for longitudinal forces (expressed in kN).
- V‑value - comparative measure for vertical forces (support/vertical loading).
- Calculation rules:
- Minimum D and V requirements are calculated per coupling point using the formulae in Clause 5.2.2.
- The highest required value for a given type of coupling in the combination applies throughout the combination.
- Some parameters and sample constants appear in the standard (e.g., typical CAT support load S often shown as 1 000 kg in examples; equivalent vertical acceleration a depends on suspension type - ~1.8 m/s² for air suspension, ~2.4 m/s² for other suspension).
- Prerequisites: vehicle combination design must ensure acceptable handling and ride stability before applying coupling strength calculations.
- Testing note: although ISO 18868 provides design/calculation rules for multiple‑coupling situations, the actual capability of coupling equipment is still determined by test procedures referenced in other coupling standards.
Practical applications
- Ensures correct sizing and specification of couplings for road trains, modular systems and multi‑unit freight combinations.
- Used by:
- Vehicle and trailer manufacturers designing converter dollies, fifth wheels, drawbars and link‑trailers.
- Component suppliers specifying D/V ratings for coupling equipment.
- Regulatory bodies and type‑approval labs assessing compliance for multi‑vehicle combinations.
- Fleet operators and specifiers deploying B‑trains or multi‑trailer combinations seeking safe, certified coupling choices.
- Helpful for route planning and interoperability where multi‑vehicle combinations are becoming more common (e.g., European modular systems).
Related standards
- ISO 18868 interacts with single‑coupling formulae and test methods referenced elsewhere (the standard notes it overrides formulae in several single‑coupling references for multi‑coupling cases). Symbols align with UNECE R55 conventions. For laboratory testing and type approval, consult the test standards referenced in ISO 18868.
Open preview (PDF)Commercial road vehicles — Coupling equipment between vehicles in multiple vehicle combinations — Strength requirements
