Evaluation of Harness Tightening Procedures for Child Restraint System (CRS) Sled Testing 2019-01-0617

Sled testing procedures should reflect a rigorous level of repeatability across trials and reproducibility across testing facilities. Currently, different testing facilities use various methods to set the harness tension for child restraint system (CRS) sled tests. The objective of this study is to identify which harness tightening procedure(s) produce tensions within a reasonable target range while showing adequate reproducibility, repeatability, and ease-of-use. Five harness tightening procedures were selected: A) FMVSS 213 procedure, B) a 3-prong tension gauge, C) ECE R44/R129 procedure, D) two finger method, and E) pinch test. Two CRS models were instrumented with a tension load cell in the harness system. Seven sled room operators were recruited to perform each of the five harness tightening procedures for ten repetitions apiece on both instrumented CRS using a Hybrid III 3-year-old. The static harness tension measured by the load cell was recorded after each procedure was completed. Data were analyzed for mean, variance, reproducibility, and repeatability. Operator feedback surveys were used to quantify ease-of-use.

The ECE R44/R129 procedure produced harness tensions which were quite low. The two finger procedure produced the highest tensions while the 3-prong tension gauge, pinch test, and FMVSS 213 procedures produced mid-level tensions. Poor repeatability was apparent for all five harness tightening procedures. The FMVSS 213 method ranked lowest for ease-of-use. Operators preferred using the 3-prong gauge, two finger method, and pinch test.

The load cell readings were sensitive to the order and direction in which the operators adjusted the harness components. High amounts of friction within the harness might prevent it from acting as a homogeneous, continuous system. Sequential tightening of the various sections of harness and/or monitoring the tension at multiple locations might be valuable.