Overview
ISO 17288-2:2011 - Passenger cars - Free-steer behaviour - Part 2: Steering-pulse open-loop test method specifies a repeatable laboratory/test-track procedure to quantify a passenger car’s free-control stability. The method measures transient vehicle response after a single steering-pulse input applied from steady, straight-ahead running. Results characterize how the vehicle returns to a straight path (oscillation, damping and settling) and provide objective metrics for vehicle dynamics and handling assessment.
Key technical topics and requirements
- Test principle: Apply a single steering-wheel pulse, immediately release the wheel and record the vehicle’s free response (open-loop). The steering wheel is then free and the vehicle dynamics determine the response.
- Measured variables: longitudinal velocity (v), lateral acceleration (aY), yaw velocity (ψ), and steering‑wheel angle (δ).
- Measuring equipment & accuracy: Multi-channel recording with suitable transducers. Typical recommended maximum errors include:
- longitudinal velocity ±0.3 m/s
- lateral acceleration ±0.1 m/s²
- yaw velocity ±0.3°/s
- steering-wheel angle ±2° for |δ| ≤ 180° (±4° otherwise)
- Test conditions & execution: Tests at a minimum of three longitudinal velocities (including the standard 100 km/h and ±20 km/h steps). Initial steering amplitude targets an initial lateral acceleration of 1 m/s², increased in ≤0.5 m/s² steps up to at least 5 m/s². Pulse rise time is specified (0.20 s ± 0.05 s); data recording windows and warm-up requirements follow ISO 15037-1.
- Data analysis: Compute damping (logarithmic-decrement style) and damping time of yaw velocity from successive peak amplitudes, evaluate peak‑2/peak‑1 ratios when oscillation is weak, perform linear regressions over specified lateral-acceleration ranges, and derive summary metrics (q and m) as a function of velocity and initial lateral acceleration.
Practical applications and users
Who benefits:
- Automotive test engineers and vehicle dynamics teams (OEMs and suppliers)
- Independent test laboratories and validation facilities
- R&D groups developing steering systems, chassis tuning, and stability control algorithms
- Researchers comparing vehicle models and validating simulation tools
Typical uses:
- Objective comparison of handling and free-steer stability between vehicle variants
- Development and validation of steering hardware (inertia, friction) and software (ESC calibration)
- Regression testing during prototype iterations and production-change assessments
- Correlating physical tests with simulation models for vehicle dynamics
Note: ISO 17288-2 defines a deliberately non‑typical, open-loop manoeuvre for controlled measurement; its results are one part of a broader handling evaluation. Application for regulation requires demonstrated correlation with real-world safety outcomes.
Related standards
- ISO 3833 - Road vehicles - Types - Terms and definitions
- ISO 8855 - Road vehicles - Vehicle dynamics and road‑holding ability - Vocabulary
- ISO 15037-1:2006 - Road vehicles - Vehicle dynamics test methods - General conditions for passenger cars
Keywords: ISO 17288-2:2011, free‑steer behaviour, steering‑pulse open‑loop test method, passenger cars, vehicle dynamics, yaw velocity, lateral acceleration, steering‑wheel angle, damping, handling test.