Overview
ISO 18375:2016 - Heavy commercial vehicles and buses - Test method for yaw stability - Sine with dwell test - specifies an open‑loop test method to evaluate yaw stability on a low-friction road surface. It targets heavy vehicles (commercial vehicles, combinations, buses, articulated buses) as defined in ISO 3833 and vehicle classes M3, N2, N3, O3, O4. The method is intended primarily for vehicles equipped with electronic yaw-stability control systems and is designed to produce repeatable, discriminatory results when surface friction is kept uniform.
Key technical topics and requirements
- Test principle: a steering-wheel input of a sine waveform with a dwell period (“sine with dwell”) is applied by a steering machine; steering amplitude is increased until yaw instability is observed.
- Target surface friction: recommended coefficient 0.2; acceptable range 0.10–0.30. Friction must be estimated before each series (e.g., full ABS braking) and maintained uniformly for reproducibility.
- Vehicle scope and conditions:
- Applies to heavy trucks, trailers and buses per ISO 3833 (weights >3.5 t for trucks/trailers, >5 t for buses).
- Initial longitudinal velocity typically 40–80 km/h (standard 50 km/h).
- Steer input parameters:
- Recommended frequency range 0.2–0.5 Hz; standard f = 0.3 Hz.
- Recommended dwell time 0.5–1.0 s; standard Td = 0.75 s.
- Equipment & measurement:
- Steering machine with emergency driver override; programmable for sine-with-dwell inputs.
- Measurement according to ISO 15037-2: steering-wheel angle, longitudinal velocity, lateral acceleration, yaw velocity/angle, articulation angles, ESC intervention indications, and other optional channels (roll, wheel speeds, brake pressures).
- Steering machine performance examples: torque range −40 to 40 Nm; steering-wheel amplitude ±360°; angle accuracy ~0.25°.
- Safety: anti-jack-knife devices for combinations, outriggers when rollover risk exists; follow ISO 15037-2 loading and safety rules.
Practical applications and users
Who uses ISO 18375:2016:
- Vehicle OEMs and chassis engineers for validation and tuning of yaw-stability control systems.
- Automotive R&D and test laboratories conducting handling and stability assessments.
- Tier‑1 suppliers of ESC/ yaw-control components for system verification.
- Safety and homologation engineers exploring correlations between dynamic behavior and accident avoidance (note: regulatory use requires proven correlation with accident data).
Practical uses:
- Quantifying ESC performance and responsiveness on low-friction surfaces.
- Comparing vehicle stability across configurations, loading conditions and control strategies.
- Supporting product development, system calibration and supplier testing.
Related standards
- ISO 15037-2: Road vehicles - Vehicle dynamics test methods - Part 2: General conditions for heavy vehicles and buses (normative reference).
- ISO 3833: Vehicle classification definitions.
- ISO 8855: Road vehicle dynamics terminology.
Keywords: ISO 18375:2016, yaw stability, sine with dwell test, heavy commercial vehicles, buses, yaw-stability control, low friction surface, vehicle dynamics testing.
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