Interpretation ID: nht92-4.19

DATE: September 4, 1992

FROM: Dale E. Dawkins -- Director, Vehicle Compliance and Safety Affairs, Chrysler

TO: Paul Jackson Rice -- Chief Counsel, NHTSA

COPYEE: S. R. Kratzke -- NHTSA; S. Backaitis -- NHTSA; D. Cohen -- NHTSA

TITLE: None

ATTACHMT: Attached to letter dated 10/2/92 from Paul Jackson Rice to Dale E. Dawkins (A40; Std. 208)

TEXT:

Chrysler Corporation herein announces its intention of making a modification to the Hybrid III (49 CFR Part 572 Subpart E) test dummy for the purpose of enhancing the reliability of the chest deflection measurement system.

Several years ago Chrysler elected to use the Hybrid III test dummy for motor vehicle occupant protection development and compliance testing. Recently, we have discovered what we consider to be a technical shortcoming of the Hybrid III test dummy chest deflection measurement system that makes it unacceptable, without modification, for testing two-point motorized seat belt systems. Chest deflection measurements have been an ongoing issue between the industry and NHTSA for some time. In angular and frontal impacts, the torso belt deflects the chest in a combination of fore-aft and lateral directions. The lateral deflection component in conjunction with fore-aft deflection causes the rubber bump stops (PN 78051-356) on the inside surface of the sternum to interfere with the slider rod (PN 78051-353) of the chest deflection transducer. When this interference occurs during a vehicle barrier impact test, frequently the ball on the end of the chest deflection rod will pop out of the Delrin guide track it rides in causing the chest deflection measurement to be erroneous. This malfunction of the Hybrid III test dummy has caused us to question several tests of future vehicles necessitating retest.

We have made high speed fiber optic video recordings that confirm the sternum bump stops can interfere with the chest deflection rod, act as a fulcrum and pry the ball on the deflection rod out of its slider track. The rod and rotary potentiometer then indicate erroneous, erratic, nonsensical chest defections. Chrysler and others, through the SAE Dummy Testing Equipment Subcommittee, have learned that relocating one or both of the bump stops from the sternum to the spine of the Hybrid III dummy can alleviate this measurement problem and permit Hybrid III chest deflection measurements. We believe the relocation of the bump stops from the sternum to the spine box is useful and necessary and with due care will not affect the calibration or measurement accuracy of the chest deflection transducer or biofidelity of the Hybrid III thorax.

It is our understanding that the changes proposed are consistent with NHTSA policy. Chrysler hereby notifies the agency of its intentions to relocate the sternum bump stops to the spine (as shown) so that certification testing of a 1994 model year motor vehicle to MVSS 208 may proceed using the Hybrid III.

We understand that using the Hybrid II (49 CFR Part 572 Subpart B) test dummy is an option we have available to us. However, we are reluctant to use the Hybrid II because we prefer the Hybrid III for its superior biofidelity.

Your expeditious acknowledgement of this notice will be very appreciated.