Interpretation ID: NCC-211019-002 Zorn VW EPB FMVSS 135 2024.05.31_Interp
May 31, 2024
Mr. Thomas Zorn
Vice President
Vehicle Safety Office
Volkswagen Group of America
2200 Woodland Pointe Ave.
Herndon, VA 20171
Dear Mr. Zorn:
This interpretation responds to your letter asking whether Volkswagen’s new Electronic Parking Brake (EPB) system complies with Federal Motor Vehicle Safety Standard (FMVSS) No. 135, Light vehicle brake systems. Specifically, you asked (1) whether paragraph S5.2 of FMVSS No. 135 would permit an EPB system that uses a traditional friction brake combined with a mechanical drivetrain lock; and (2) whether Volkswagen may rely on the entire EPB system for compliance with the test set out in paragraph S7.12. Based on the information you have provided, our answer to both of your questions is yes.
By way of background information, the National Highway Traffic Safety Administration (NHTSA) does not provide advance approvals of motor vehicles or motor vehicle equipment. Under 49 U.S.C. Chapter 301, manufacturers are required to ensure that their vehicles and equipment meet applicable requirements. The following represents our opinion based on the facts provided in your letter.
In addition, in responding to this request, NHTSA notes that the contents of this letter do not have the force and effect of law and are not meant to bind the public in any way. This letter is only intended to provide clarity regarding existing requirements under the law at the time of signature.
Paragraph S5.2 of FMVSS No. 135 provides: “Each vehicle shall be equipped with a parking brake system of a friction type with solely mechanical means to retain engagement.” The term “parking brake” is defined in 49 C.F.R. Part 571.3(c) as “a mechanism designed to prevent the movement of a stationary motor vehicle.” Thus, a compliant parking brake must prevent movement of a stationary motor vehicle by means of friction. Additionally, the parking brake system must also have “solely mechanical means to retain engagement,” meaning it cannot be held in place by non-mechanical means such as fluid, air, or electricity.
Paragraph S7.12.2 of FMVSS No. 135 describes NHTSA’s conditions and procedures for testing whether a parking brake system complies with our standard. The test procedures require a test conductor to, among other things, drive the vehicle onto a 20 percent grade, apply the
Mr. Thomas Zorn
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service brake with enough force to hold the vehicle stationary, shift the transmission into neutral, engage the parking brake system, and remove all force from the service brake. After the test conductor has taken the above steps, the vehicle must then remain stationary for five minutes. If the vehicle remains stationary for the required five minutes, the test conductor then repeats the test with the vehicle facing in the opposite direction on the grade. If the vehicle once again meets the stationary time requirement, and meets all other requirements in the paragraph, the parking brake system passes the compliance test.
The EPB system described in your letter appears to be a parking brake of a friction type with solely mechanical means to retain engagement. You describe Volkswagen’s new EPB as a system that will “utilize a traditional friction brake combined with a mechanical lock that is automatically engaged in the vehicle drivetrain when the EPB is activated.” Based on this description, the system has a friction element combined with a mechanical drivetrain lock designed to hold the vehicle stationary. Additionally, based on the information provided in your letter, engagement of the friction element of the EPB is not retained by pneumatic or hydraulic means. To the best of our knowledge, the only ways to retain engagement of a friction type brake are by pneumatic, hydraulic, or mechanical means. Because your friction brake is not retained by pneumatic or hydraulic means, for the sake of this letter, we are assuming that engagement of the friction element of the EPB is retained by mechanical means.1 Applying that assumption, the Volkswagen EPB system described in your letter appears to meet the requirements of S5.2 of FMVSS No. 135. 2
You also state that Volkswagen intends to rely on the entire EPB system to demonstrate compliance with paragraph S7.12 and ask whether NHTSA would conduct its compliance tests similarly. In conducting compliance testing for parking brakes, NHTSA follows the testing procedures set out in S7.12, as described above. You state that the friction element and mechanical lock are “designed to operate together only, and cannot be engaged individually by the vehicle operator.” Additionally, you indicate that it would be impossible for Volkswagen’s EPB system to engage the friction brake exclusively without the mechanical lock engaging. The testing procedure specified in S7.12 does not mandate a parking brake system hold a vehicle stationary by exclusively friction means. Accordingly, if NHTSA conducted compliance testing on the EPB described in your letter, it would follow the procedures as written in S7.12.
I hope this answers your questions. If you have any further questions regarding this matter, please feel free to contact Mr. Matthew Filpi of my staff at (202) 366-2992.
Sincerely,
ADAM RAVIV
Adam Raviv Chief Counsel
Dated: 5/31/24
Ref: Standard No. 135