Search Interpretations

07-002015--31 Oct 07--rls

Mr. Dick Sabath

Senior Manager, Compliance

Country Coach, LLC

135 East First Avenue

P.O. Box 400

Junction City, OR 97448

Dear Mr. Sabath:

This responds to your letter concerning testing of driver and front row passenger bucket seats and seat belt systems to the requirements of Federal Motor Vehicle Safety Standards (FMVSSs) No. 207 and 210. Specifically, you asked whether a longitudinal movement of - to -inch of these seats during testing constitute[s] an out-of-compliance or safety concern under FMVSS No. 207. Based on the information you provided and the analysis below, we would not consider this amount of movement to constitute a test failure under FMVSS No. 207.

By way of background information, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment. NHTSA does not, however, approve or certify any vehicles or items of equipment. Instead, the Safety Act establishes a self-certification process under which each manufacturer is responsible for certifying that its products meet all applicable safety standards.

In your letter, you stated that all three anchorage points of both seats (type 2 seat belts) are on the seat. You further describe the forward and rearward movements of these seats as being motorized with a single electric motor. It appears that the electric adjustment motor affects the performance of your seats in the compliance tests for FMVSSs No. 207 and 210. You explain that During the (repetitive) forward pull tests . . . we have observed a consistent and repetitive forward travel of to -inch in the longitudinal adjusted position due to the backlash of the electric adjustment motor. You further state that:

Once the backlash has occurred, the entire seat and seat belt assembly holds the prescribed test loads for the time specified in the FMVSS 207/210. No other movement or breakage was observed during the four different tests we conducted on the same seat models to verify the cause of the to inch forward displacement. The to -inch of travel remains consistent throughout all tests.

S4.2.1 of FMVSS No. 207 states that Except for vertical movement of nonlocking suspension type occupant seats in trucks or buses, each seat shall remain in its adjusted position when tested in accordance with the test procedures specified in S5. (Emphasis added.) We have long interpreted S4.2.1 to allow some deformation of the seats during the force test, provided that structural integrity of the seats is maintained.[1] For example, we have stated that bending and twisting of the seat or seat components during the force test would not result in non-compliance with FMVSS No. 207, unless the bending or twisting resulted in the seat moving from one adjustment position to another, which would violate S4.2.1s requirement that the seat remain in its adjusted position when tested.

You indicate that the movement of the seat is due to backlash in the electrical adjustment motor. The term backlash in this context typically refers to the gap between mechanical elements such as mating gears used to drive or move a device.[2] As such, backlash may also be present in a manual seat adjustment, such as the detents in a typical seat fore-aft adjustment mechanism. As such, forward movement of a seat during the application of the required loading strictly due to backlash, whether or not the mechanism of adjustment is an electrical motor, would not be considered in violation of the requirement in S4.2.1 that the seat remain in its adjusted position when tested. Thus, in terms of the specific factual situation described in your letter, we would not consider such movement a test failure under FMVSS No. 207. However, if any of the seat movement were due to a factor such as movement of the driving mechanism, such as rotation of the gear providing the seat adjustment, S4.2.1 would be violated. In addition, as we have previously stated, if a change in the adjusted position of the seat back is caused by the gear mechanism being destroyed, the seat would also not comply with S4.2.1.[3] Thus, in terms of the specific factual situation described in your letter, we would not consider such movement a test failure under FMVSS No. 207.

If you have any further questions, please feel free to contact Rebecca Schade of my staff at (202) 366-2992.

Sincerely yours,

Anthony M. Cooke

Chief Counsel




[1] See, e.g., Letter to Glenn L. Duncan, Aug. 26, 1988, and Letter to Paul N. Wagner, Dec. 23, 1994 (enclosed).

[2] The Standard Handbook of Machine Design by Joseph Shigley and Charles Mischke (McGraw-Hill, 1996) defines backlash as the amount by which the width of a tooth space exceeds the thickness of the engaging tooth measured on the pitch circle.

[3] See Letter to Paul N. Wagner, Dec. 23, 1994.