At last month’s SAE 2017 Government/Industry Meeting, two NASCAR safety experts were presented the Ralph H. Isbrandt Automotive Safety Engineering Award for their SAE International technical paper, “Development and Implementation of a Quasi-Static Test for Seat Integrated Seat Belt Restraint System Anchorages” (2015-01-0739).
The paper was written by John Patalak, Senior Director of Safety Engineering, NASCAR Research and Development; and Tom Gideon, recently retired Senior Director of Safety Engineering, NASCAR Research Development and Safety.
Patalak’s work at NASCAR includes researching, developing, and approving driver and vehicle safety systems and investigating vehicle crashworthiness and occupant protection issues. Gideon retired as Senior Director of Safety from NASCAR in 2016. He joined NASCAR in 2009 as Director–Safety R&D; before that, he served as Safety Manager for GM Racing.
Their paper describes the development of the quasi-static test for the seat integrated seatbelt restraint system portion of the NASCAR Seat Submission and Test Protocol Criteria. It reviews the methodology used to develop the testing, including the developmental dynamic sled tests. In conjunction with the start of the 2017 Monster Energy NASCAR Cup Series, following is an excerpt of their award-winning paper.
Over the past decade, large safety improvements have been made in crash protection for motorsports drivers. It has been well established that in side and rear impacts the driver seat provides the primary source for occupant retention and restraint. Beginning in the 2015 season, NASCAR required the use of driver seats with all seatbelt restraint system anchorage locations integrated internally to the seat with a minimum of seven anchorage locations. These seats are referred to as All Belts To Seat (ABTS) seats.
Incorporating seatbelt anchorages into the driver’s seat provides several distinct restraint system advantages over chassis-mounted seatbelts. Specifically, ABTS seats allow for shorter seatbelt lengths, improved seatbelt mounting geometry, the elimination of seatbelt pass-through holes, and other seatbelt interference issues. Shorter seatbelt lengths (the length from where the belt leaves the occupant body to the belt anchorage location) reduce the permissible amplitude of occupant motion. Seatbelt mounting geometry can be optimized when using ABTS seats due to eliminating obstructions in the seatbelt routing paths. Eliminating pass-through holes in seats for the seatbelts greatly reduces the possibility of interference issues between the seat and the seatbelt during the crash. This interference may include seatbelt adjusters or hardware becoming stuck or misaligned in seat openings or seatbelt webbing edges being deformed around seat opening edges. These issues can initiate webbing failure, adjuster slippage, hardware deformation, or a combination of these malfunctions.
Additionally, using ABTS seats allows for the future use of deformable seat mounting brackets. The purpose of the deformable seat mounting brackets would not be to lower occupant accelerations, but rather could be used to permit the driver’s seat to be moved away from intrusion during severe impacts, thus limiting the driver’s exposure to intruding structure. If seatbelts are mounted to the vehicle chassis, moving the driver’s seat is not possible.
To realize the advantages of an ABTS seat, a quasi-static test to prove the structural reliability of the seat belt anchorages was designed, developed, and implemented. As a basis for the load magnitudes of the quasi-static test, sled testing was conducted.
For the shoulder belts, the minimum quasi-static load was 9000 lb (4080 k g) with the lap and anti-submarine belts each at a minimum quasi-static load of 6000 lb (2700 kg).
The shoulder belts’ minimum quasi-static load of 9000 lb resulted in a significantly larger safety factor than the lap and anti-submarine belts. This high safety factor for the shoulder belts was selected due to a lack of seatbelt system redundancy for shoulder belts (assuming the minimum single shoulder belt configuration [2 belts] and not the over/under or double shoulder belt system [four belts]) as well as readily available vehicle structure at the shoulder level.
When comparing this quasi-static ABTS test to the FMVSS 210 anchorage test, this ABTS test has a 1.2 times (6000 vs. 5000 lb) greater load for the lap belt alone and a 3.5 times (21,000 vs. 6000 lb) greater load on the total restraint harness combination.
While not all of the minimum quasi-static test loads exhibited a 1.5 safety factor, such as the negative G belt load, this test methodology is being implemented as part of an ongoing process to continue with incremental improvements to occupant safety and is intended to be used as a minimum guideline for integrated seat belt anchorage strength. As such it sets a minimum performance requirement for seat manufacturers to meet and exceed with future designs.
This article is based on SAE International tech paper 2015-01-0739 by John Patalak and Thomas Gideon of NASCAR.