Interpretation ID: nht87-2.71

TYPE: INTERPRETATION-NHTSA

DATE: 08/13/87

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Mr. Jack Quinn

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Jack Quinn Ms. Terri Southwick Arnold & Porter 1200 New Hampshire Avenue, NW Washington, DC 20036

Dear Mr. Quinn and Ms. Southwick:

This responds to your letter requesting an interpretation of Safety Standard No. 102, Transmission Shift Lever Sequence, Starter Interlock, and Transmission Braking Effect. We regret the delay in our response. You described an automatic transmission and asked whether the transmission complies with Standard No. 102. Also, you asked several specific questions about the standard. Your questions are addressed below.

By way of background information, the National Highway Traffic Safety Administration (NHTSA) does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, it is the responsibility of the manufacturer to ensure that its motor vehicles or equipment comply with applicable safety standards. The following represents our opinion based on the facts provided in your letter.

You provided the following description of the automatic transmission at issue:

. . . downshift occurs automatically from "drive" to "second" at 29 mph and from "second" to "first" gear at 13 mph. Forced manual downshift is possible at and below 25 mph (from "second" to " first"). Thus, at speeds between 13 and 29 mph, there is at l east one forward drive position ("first") manually available which provides a greater degree of engine braking than does the gear then automatically in use ("second"). At 13 mph and below, the transmission is automatically in a gear ("first") that provid es greater engine braking than would the highest speed transmission ratio if that position ("drive") were available at such low speeds. Of course, in the lowest gear, there is no lower gear available which would provide greater engine braking effect.

In your first question, you asked whether the described transmission complies with Standard No. 102. Your letter indicates that your concern is limited to section S3.1.2 of the standard.

Section S3.1.2 provide:

S3.1.2 Transmission braking effect. In vehicles having more than one forward transmission gear ratio, one forward drive position shall provide a greater degree of engine braking than the highest speed transmission ratio at vehicle speeds below 25 miles p er hour.

It should be noted that Standard No. 102 applies to motor vehicles and not to transmissions per se. Thus, compliance with the standard is determined with respect to the vehicle.

I would also note that, as we have stated in past interpretations, the phrase "at vehicle speeds below 25 miles per hour" is inclusive. Thus, it means at all speeds below 25 mph, and not at a speed.

One issue raised by your design is whether there must be at least two gears available at some or all speeds below 25 mph. for vehicles with two or more forward transmission gear ratios. The answer to this question is no. It is our interpretation that the standard requires that one forward drive position must provide a greater degree of engine braking than the highest gear ratio and that it must provide that degree of engine braking at all speeds below 25 mph. The standard does not require that the highe st (or other higher) ratio be available at some or all speeds below 25 mph.

A second issue is whether the requirement for greater braking effect at vehicle speeds below 25 mph must be met by one (and only one) forward drive shift lever position or whether more than one position providing greater braking effect may be utilized. I t is our opinion that where a manufacturer chooses to provide more than one forward transmission gear position, each of which provides a greater degree of engine braking than the highest gear ratio, all such positions may be counted toward meeting this r equirement.

A third issue is whether the requirements of section S3.1.2 can be met by automatic downshifting (to a gear ratio that provides a greater degree of engine braking) or whether manual downshifting must be available. In considering this issue, one question is whether more than one forward drive shift lever position is required. First, it is our opinion that Standard No. 102 does not require more than one forward drive shift lever position. Section S3.1.2's requirement that "one forward drive position" must provide a greater degree of engine braking than the highest speed transmission ratio at vehicle speeds below 25 mph can be met by a vehicle with only one forward drive position if that position always provides such engine braking at the specified speeds . This would, of course, presuppose automatic downshifting . The requirements of section S3.1.2 can be met by automatic downshifting so long as such downshifting always takes place at a speed no lower than 25 mph. If automatic downshifting took place at a speed below 25 mph and manual downshifting has not possible, the requirement would not be met for some speeds below 25 mph.

With this background in mind, I will address the transmission described above with respect to section S3.1.2. The "highest speed transmission ratio" of the vehicle is "drive." We note that your letter does not indicate whether "second" gear provides a gr eater degree of engine braking than "drive." However, your letter does state that "first" gear provides a greater degree of engine braking than "drive" and that the vehicle will either automatically be in first gear, or can manually be downshifted to fir st gear, for all speeds at and below 25 mph. Thus, one forward drive position (either "first" by virtue of manual downshifting or the standard position by virtue of automatic downshifting) would provide a greater degree of engine braking than the highest speed transmission ratio ("drive") at all vehicle speeds below 25 mph.

Your second question is whether the availability of forced, manual downshifting above 25 mph is relevant to compliance with Standard No. 102. Such availability could be relevant, depending on the design. As indicated above, for example. if automatic down shifting took place at a speed below 25 mph, it would be necessary to provide manual downshifting at or above 25 mph in order to ensure that the requirements of section 53.1.2 be met for all speeds below 25 mph.

The answer to your third question, whether the standard can be satisfied by virtue of automatic shifting of gears, is provided above. Similarly, the answer to your fourth question, whether more than one drive position can be counted toward meeting the re quirement for greater engine braking, is also provided above.

Your fifth question is how compliance is measured, since engine braking is not the same as net vehicle braking. We understand your use of the term "net vehicle braking" to refer to all vehicle braking forces other than those attributable to application o f the service and emergency brakes. These vehicle braking forces include engine braking and various parasitic drags, such as tire rolling resistance and aerodynamic drag. You also asked what guidance the agency has available for ensuring compliance. The National Traffic and Motor Vehicle Safety Act establishes a "self-certification" process under which each manufacturer is responsible for certifying that its products meet all applicable safety standards. This process requires each manufacturer to exerci se due care in conducting the mathematical calculations, computer simulations or testing that form the basis for that certification. With respect to your specific question, manufacturers can use any or all of these techniques to analyze the engine brakin g capability of their vehicles. Such analysis can, among other things, separate out various other effects on braking, such as aerodynamic drag and tire rolling resistance.

Sincerely,

Erika Z. Jones Chief Counsel

Erika Jones, Esquire Chief Counsel National Highway Traffic Safety Administration U.S. Department of Transportation 400 Seventh Street. S.W.

Washington, D.C. 20590

Re: Interpretation of Federal Motor Vehicle Safety Standard No. 102 (49 C.F.R. S 571.102)

Dear Ms. Jones:

On behalf of a manufacturer of transmissions for use in buses, we hereby request an interpretation of Federal Motor Vehicle Standard No. 102, paragraph S3. 1.2 of which states that:

In vehicles having more than one forward transmission gear ratio, one forward drive position shall provide a greater degree of engine braking than the highest speed transmission ratio at vehicle speeds below 25 miles per hour.

In the transmission at issue, downshift occurs automatically from "drive" to "second" at 29 m.p.h. and from "second" to "first" gear at 13 m.p.h. Forced manual downshift is possible at and below 25 m.p.h. (from "second" to "first"). Thus, at speeds betwe en 13 and 29 m.p.h. , there is at least one forward drive position ("first") manually available which provides a greater degree of engine braking than does the gear then automatically in use ("second" ). At 13 m.p.h. and below, the transmission is automa tically in a gear ("first") that provides greater engine braking than would the highest speed transmission ratio if that position ("drive" ) were available at such low speeds. Of course, in the lowest gear, there is no lower gear available which would pr ovide greater engine braking effect.

Erika Jones, Esquire September 29, 1986 Page 2

Our questions are:

1. Does the system described comply with Standard 102?

2. Is the availability of forced, manual down- shifting above 25 m.p.h. relevant to compliance with Standard 102?

3. Is the standard satisfied by virtue of the automatic shifting of gears as described or does it require the availability under any circumstances of forced, manual downshifting of gears at or below 25 m.p.h.?

Would a transmission that shifts automatically from "drive" to "second" at 29 m.p.h. (and from "second" to "first" at 13 m.p.h.) comply?

If not, and manual down-shifting to a gear with greater engine braking effect must be available, at what speed must such manual (or automatic) downshifting be available -- at 25 m.p.h., or at any speed "below" 25 m.p.h., e.g.,24m.p.h.?

4. Must the requirement of greater engine braking effect be fulfilled by one (and only one ) forward drive position, or may two drive positions (providing greater engine braking effect than the "drive" position) be utilized?

5. Since engine braking is not the same as net vehicle braking, how is compliance to be measured? What guidance does the agency have available for ensuring compliance?

Thank you for considering these questions and providing an opinion.

Sincerely,

Jack Quinn Terri Southwick