Vice President of Engineering
1515 Industrial Street
Reedsburg, WI 53959
Dear Mr. Hofrichter:
This responds to your January 11, 2011 letter concerning whether a new seating application for trucks meets the requirements of Federal Motor Vehicle Safety Standard (FMVSS)
No. 207, which governs vehicle seating systems. Specifically, you ask several questions about vertical movement of a seating system during testing and whether such movement would mean that the seat was not compliant with the requirements of S4.2.1 of FMVSS
No. 207. As explained below, we believe that the movement you describe may constitute a test failure under FMVSS No. 207.
By way of background, NHTSA is authorized by the National Traffic and Motor Vehicle Safety Act (49 U.S.C. Chapter 301, Safety Act) to issue FMVSSs that set performance requirements for new motor vehicles and new items of motor vehicle equipment. NHTSA does not provide approvals of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture.
The following is our interpretation of the Safety Act and the FMVSSs based on the description contained in your letter.
S4.2.1, Seat Adjustment, states, 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.
You describe your application as an upper seat on a motor-powered seat adjuster with both horizontal and vertical adjustment. You indicate that when you perform the pull test specified by FMVSS No. 207 and FMVSS No. 210 and apply the specified forces to the seat through the lap belt, shoulder belt, and seat center of gravity, with the seat riser initially set in the lowest position, the rear linkage of the riser rotates up about 1.5 inches to the highest position. You ask several questions regarding the requirements of S4.2.1 of FMVSS No. 207 and whether this movement violates the requirements of that paragraph.
You first ask whether paragraph S4.2.1 of FMVSS No. 207 applies to vertical movement of a motor-powered seat adjuster.
S4.2.1 contains only one exception to its requirement that a seat shall remain in its adjusted position when tested. The exception is for the vertical movement of nonlocking suspension type occupant seats in trucks or buses. Our understanding is that your seat is not a nonlocking suspension type occupant seat. It appears to adjust and lock in a manner similar to the seat described in a letter we sent to Paul Wagner (See enclosed March 21, 1995 letter). The standard does not provide an exception encompassing vertical movement in other types of seats.
You next ask, If the seat power riser vertical movement was due to rotation of the motorized parts beyond that due to backlash, would it be compliant if the seat is able to withstand the required FMVSS [No.] 207 forces?
We have interpreted FMVSS No. 207 to allow some deformation of the seats (e.g., bending or twisting) during the force test, provided that the structural integrity of the seats is maintained. We do not consider such deformation, by itself, to constitute a change in adjustment position. However, if deformation allows the seat to move from one adjustment position to another, that movement would violate S4.2.1s requirement that the seat remain in its adjusted position when tested.
In a previous interpretation letter, we discussed movement due to backlash, which typically refers to the gap between mechanical elements such as mating gears used to drive or move a device (See enclosed November 13, 2007 letter to Dick Sabath). We do not consider movement of a seat strictly due to backlash, regardless of whether the mechanism of adjustment is an electric motor, to be a change in adjustment position. Thus, such movement would not violate the requirement in S4.2.1 that the seat remain in its adjusted position when tested.
However, movement beyond backlash may violate S4.2.1. For example, if any of the seat movement is due to movement of the driving mechanism, such as rotation of the gear providing the seat adjustment, we would consider such movement to be a change in adjustment position and thus to be in violation of S4.2.1. In addition, if a change in the adjusted position is caused by the gear mechanism being destroyed, the seat would not comply with S4.2.1 (See enclosed December 23, 1994 letter to Paul N. Wagner).
You next ask, If the seat power riser vertical movement was due to adjustment teeth shearing, misaligning or slipping and moving from one position to another, would it be compliant if it is able to withstand the required FMVSS [No.] 207 forces?
As stated above, movement of the seat from one adjustment position to another during testing violates the requirements of S4.2.1. Accordingly, we would consider the seat movement described in your second question to be a test failure under FMVSS No. 207.
I hope this information is helpful. If you have further questions, please contact William Shakely of my staff at (202) 366-2992.
O. Kevin Vincent
Ref: Standard No. 207