Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Linear Impact Procedure for Occupant Ejection Protection: SAE J2937-2021 Overview
The SAE J2937-2021 standard defines a linear impact test procedure for evaluating inflatable curtains (ICs) and other side window ejection mitigation systems. This procedure, referenced in NHTSA’s FMVSS 226 Final Rule, provides a consistent method for assessing occupant retention performance during side impacts. The following sections outline the key technical requirements, target location methodology, and reporting guidelines of this important automotive safety standard.
🛠️ Scope of the Standard — SAE J2937 covers the use of an 18 kg guided linear impactor with a featureless headform designed specifically for ejection mitigation testing. The procedure applies to inflatable curtains, laminated glass, and other countermeasures.
Testing Device and Setup
The linear impactor assembly must meet precise specifications to ensure repeatable and comparable results. Key parameters include:
| Parameter | Specification |
|---|---|
| Impactor mass | 18 kg |
| Impact speeds | 4.4 m/s (16 km/h) and 5.6 m/s (20 km/h) |
| Headform type | Featureless, designed for ejection mitigation testing |
| Instrumentation | Accelerometers with specified polarity and sign convention |
| Test fixture | Representative of body-in-white or test buck |
| Friction condition | Defined coefficient for headform–window interface |
Time zero is defined as the moment current is initiated to deploy the inflatable curtain. This timing is critical for correlating headform impact with curtain deployment phase.
Determining Head Target Locations
Headform target locations are derived from the vehicle’s daylight opening and the rearmost offset line per FMVSS 226 §5.2. The procedure includes:
- Identifying primary and secondary target points for each row and window configuration.
- Eliminating targets that fall outside the inflatable curtain coverage zone.
- Reconstructing and reorienting targets after curtain deployment to account for changes in geometry.
⚠️ Engineering Design Insight — Test outcomes are highly sensitive to trim fit and IC mounting integrity. Inaccurate reconstruction of the rearmost offset line or failure to verify curtain coverage can lead to invalid results. Always confirm that the test fixture reproduces the vehicle’s interior trim and IC attachment points faithfully.
Data Acquisition and Test Reporting
Data processing must follow specified filter classes (e.g., CFC 60 for headform acceleration) and polarity conventions. The test report should include headform acceleration traces, impact velocity, framing images from multiple cameras, and confirmation of headform friction. Proper documentation ensures traceability and supports regulatory submission.
Frequently Asked Questions
1. What is the purpose of the linear impact test in SAE J2937?
The test evaluates the ability of inflatable curtains and other countermeasures to retain an occupant’s head and torso during a side impact, reducing the risk of ejection.
2. How are headform target locations determined?
Targets are based on the rearmost offset line of each window row, using vehicle-specific geometry defined in FMVSS 226. The procedure involves multiple steps for different window configurations and coverage scenarios.
3. What impact speeds are required?
Two speeds are prescribed: 4.4 m/s (16 km/h) and 5.6 m/s (20 km/h). The higher speed typically tests the curtain’s ability to deploy and engage before head contact.
4. What are common mistakes in this test?
Common errors include incorrect identification of the rearmost offset line, failure to account for data polarity, using non-specified headform friction, and inadequate reconstruction of target locations after IC deployment.
For full details, refer to the SAE J2937-2021 document.
