ISO 21233:2021

Overview

ISO 21233:2021 specifies a repeatable method to validate vehicle dynamics simulations of heavy commercial vehicles and buses using the closing-curve test (as defined in ISO 11026). The standard’s aim is to demonstrate that a vehicle model, together with an integrated electronic stability control (ESC) system, can predict roll and yaw stability behavior - including ESC interventions - observed on a physical vehicle. Validation can be performed using hardware-in-the-loop (HiL) with the original ECU or software-in-the-loop (SiL) using ECU-equivalent code.

Key topics and technical requirements

• Scope: Applies to heavy vehicles (trucks, trailers, buses, articulated buses) per ISO 3833 and ECE/EC categories M3, N2, N3, O3, O4.
• Validation goal: Show simulation predicts wheel lift-off, yaw and roll stability, and timing/type of ESC interventions within defined tolerances by comparing simulation outputs to measured test data.
• Prior validation: A steady-state cornering validation per ISO 19585 is required before closing-curve validation.
• Simulation methods: HiL (original ECU on test stand) or SiL (software code from the same source as ECU).
• Model parameter requirements:
  • Basic vehicle parameters per ISO 19585.
  • Principal moments of inertia derived from measurement/design and not altered by more than ±20% during validation.
  • Tyre model must represent transient tyre force behaviour, longitudinal force and combined lateral/longitudinal slip to simulate ESC brake interventions.
• Measured and simulated variables (examples):
  • Longitudinal velocity, steering-wheel angle, lateral acceleration, yaw velocity
  • ESC outputs: intervention flags, desired engine torque limits, desired brake torques/pressures
  • Wheel speed sensors (to indicate inner-wheel lift-off)
  • Optional: roll angles, side-slip, articulation angles
• Data and reporting: Define reference curves and characteristic values from physical tests and compare simulation results; measurement from ESC sensors on the vehicle bus is acceptable for certain signals.

Applications

• Validate vehicle dynamics models used in design, safety assessment, and ESC tuning.
• Support virtual testing to reduce physical prototypes and accelerate development of heavy commercial vehicles and buses.
• Aid compliance testing and safety assurance for ESC systems related to rollover and stability.

Who should use this standard

• Vehicle manufacturers and OEM simulation teams
• ESC and ECU developers (HiL/SiL test engineers)
• Test laboratories and validation engineers
• Regulatory bodies and conformity assessors involved in heavy-vehicle safety

Related standards

• ISO 11026 - Closing-curve test (roll stability)
• ISO 19585:2019 - Steady-state circular driving behaviour (validation prerequisite)
• ISO 3833, ISO 8855, ISO 15037-2 - Definitions, vocabulary and general test conditions

Keywords: ISO 21233:2021, closing-curve test, vehicle dynamics simulation, ESC validation, HiL, SiL, heavy commercial vehicles, bus rollover stability.