ID: nht74-1.5

DATE: 09/19/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: U. S. Technical Research Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

NOA-30 (ZTV) Sep 19 1974

Mr. Bernard Belier U.S. Resident Engineer for Citroen, S.A. U.S. Technical Research Corporation 801 Second Avenue New York, New York 10017

Dear Mr. Belier:

This is in further reply to the petition of November 16, 1973, by Citroen, S. A. for rulemaking to amend Motor Vehicle Safety Standard No. 105-75, Hydraulic Brake Systems.

The petition has been thoroughly reviewed by engineering and legal staff personnel of this agency. Before a recommendation is made to the Administrator on the merits of your petition, we request that you furnish further information to us.

First of all, NHTSA is interested in obtaining any available data which will support the contention that the Citroen central power braking system provides a level of safety equivalent to a fully split system with indefinite residual failure mode performance such as is currently required by FMVSS 105-75. Do the highway accident statistics provide such support? Is the incidence of accidents occurring to Citroen vehicles attributable in whole or part to brake failures significantly different from the norm for other European passenger cars? Can it be demonstrated that when failures of the service brakes do occur in emergency situations, drivers are able to adjust their behavior patterns sufficiently quicly to bring the vehicles to a safe stop using the hand operated emergency brakes?

We wuld also like Citroen to provide data to substantiate that the "emergency" system can meet the deceleration requirement of 10 fpsps. What are Citroen's views on an appropriate burnish procedure for testing the emergency braking system? In addition to this, can the 10 fpsps deceleration requirement be achieved using the service brakes with a subsystem accumulator depleted?

Finally, we request data on the costs and leadtime required for Citroen to convert the single central power system to a dual, or full split system.

Yours truly,

Richard B. Dyson Acting Chief Counsel

cc: Maurice Clavel Assistant to the President S.A. Automobiles Citroen

ID: nht74-1.50

DATE: 07/11/74

FROM: AUTHOR UNAVAILABLE; Armstrong for R. L. Carter; NHTSA

TO: Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your May 10, 1974, request for interpetation of the volume requirements for service brake chambers in S5.2.1.2 and S5.1.2.1 of Standard No. 121, Air Brake System:

S5.1.2.1 The combined volume of all service reservoirs and supply reservoirs shall be at least twelve times the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms.

You also requested that reservoir volume be based on manufacturer "rated volume" based on the designed volume of the reservoir.

In testing for compliance with S5.1.2.1 and S5.2.1.2, the NHTSA will accept a manufacturer's published "rated volume" of the brake chamber with the piston or diaphragm at maximum travel. This means that the manufacturer may specify the full stroke of the piston or diaphragm and compute the "rated volume" based on the designed volume of the chamber and the full stroke he has established. This volume may be somewhat larger than "nominal brake chamber displacement" which does not necessarily account for the void ahead of the relaxed diaphragm or piston, the so-called "prefill volume." This volume must be included because it must be pressurized along with the displaced volume.

In the absence of manufacturer's published ratings, the NHTSA will measure the brake chamber volume with the push rod at maximum stroke.

With regard to air reservoir volumes, the NHTSA will determine the volume of reservoirs by actual measurement. As a practical matter air reservoirs are simple structures whose volumes are relatively easy to measure.

Sincerely yours,

ATTACH.

Bendix

Heavy Vehicle Systems Group

Chief Counsel -- National Highway Traffic Safety Administration

May 10, 1974

Subject: Title 49 CFR, Part 571, Motor Vehicle Safety Standard No. 121, Air Brake Systems

Dear Sir:

Concern has arisen in the motor vehicle industry relative to the matter of brake chamber and reservoir volumes as set forth in Section 5.1.2.1, of the subject standard which provides:

"The combined volume of all service reservoirs and supply reservoirs shall be at least twelve times the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms."

The question posed is: How will the sizing be verified for compliance purposes? Hence, an interpretation of Section 5.1.2.1 is requested.

Historically, the Industry has used the "nominal" or rated full stroke of brake actuators, in determining available stroke. In practice, it was understood that the nominal or rated full stroke is all that can be counted on to provide braking. (The recommended readjustment stroke followed by the Industry has been from 3/8 to 3/4 inch less than the "rated full stroke" depending upon actuator size.) Further, SAE recommended Practice J813, "Automotive Air Brake Reservoir Volume" does not go into any detail relating to strokes, tolerances, etc. of the various components involved in the actuation of a foundation brake.

The design of a braking system requires that a component, such as an actuator, which is called upon to give a specified stroke must have its own dimensions and tolerances so designated that its "minimum" travel provisions are those required for the system. To use the actuator's maximum stroke, taking into account tolerance stack up, as the basis for sizing a reservoir, appears to be unreasonable and would not increase the safety of the vehicle. (The maximum possible stroke is, of course, not available in every actuator and thus cannot be counted on for braking.)

It is therefore recommended that NHTSA give favorable consideration to an interpretation of Section 5.1.2.1 to provide that the brake chamber volume be specified at the advertised nominal or rated full stroke of the brake chamber. This volume can be determined by a manufacturer and precludes the necessity of adding additional reservoir volume to compensate for theoretical tolerances that in all likelihood will never become cumulative in the system.

An analogous situation exists with reservoirs. Because of the profusion of sizes and special configurations (different sizes and quantities of ferrules, and a variety of lengths and diameters) the minimum volume determined by physically filling several reservoirs of each configuration to measure the exact volume does not appear to add any reasonable degree of accuracy or safety.

Therefore, it is also recommended that the reservoir volumes be certified based on a "rated volume" produced by calculation using the actual nominal Engineering drawing dimensions. Ferrules would be ignored in the calculations as being insignificant and at any rate generally a "plus" for volume.

We solicit your comments on these matters and would be happy to discuss our recommendations with you if you feel that additional information is necessary.

Very truly yours,

R. W. Hildebrandt -- Group Director of Engineering

ID: nht74-1.6

DATE: 09/11/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: International Harvester

TITLE: FMVSS INTERPRETATION

TEXT:

SEP 11 1974

Mr. K. W. Berner Manager Component Design & Development International Harvester Truck Division Engineering 2911 Meyer Road Fort Wayne, Indiana 46803

Dear Mr. Berner:

This is in reply to your letter of August 13, 1974, to Dr. Gregory asking for confirmation of your interpretation of S5.3.1(b) of Motor Vehicle Safety Standard No. 105.

Paragraph S5.3.1(b) states that an indicator lamp shall be ?????? whenever there is "A drop in the level of brake fluid in a master cylinder reservoir to less than . . . one-fourth of the fluid reservoir capacity in any reservoir compartment ...." This will confirm that the lamp must activate whenever the fluid in any compartment is less than one-fourth the capacity of that compartment, rather than one-fourth the total capacity of the reservoir regardless of the number of compartments.

Yours truly,

Richard B. Dyson Acting Chief Counsel

ID: nht74-1.7

DATE: 12/18/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

Dec 18 1974 N40-30 (TWH)

Mr. J. R. Farron Group Director of Engineering The Bendix Corporation 401 Bendix Drive P. 0. Box 4001 South Bend, Indiana 46634

Dear Mr. Farron:

This responds to your undated letter which requests a determination that the Bendix "Hydro-boost" qualifies as a brake power assist unit" as that term is defined in Standard No. 105-75. You describe the unit as designed with a "push through" cabability in both the "normal" and "failed power" operating conditions, and with an accumulator that permits low pedal effort for a limited number of brake applications after a power failure has occurred.

The following definitions distinguish a "Brake power assist unit" from a "Brake power unit":

"Brake power assist unit" means a device installed in a hydraulic brake system that reduces the operator effort required to actuate the system, and that if inoperative does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control.

"Brake power unit" means a device installed in a brake system that provides the energy required to actuate the brakes, either directly or indirectly through an auxiliary device, with the operator action consisting only of modulating the energy application level.

In the preaamble to Notice 8 of Docket No. 70-27, we made the further clarification that the capabilities of the unit in the "failed power" condition determine whether it is a brake power assist unit. A copy of this discussion is enclosed. Because the Bendix "Hydro--boost" in the "failed power" condition does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control (i.e.. with "push through" capability), it qualifies as a brake power assist unit under the definitions of Standard No. 105-75.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

Enclosure SECURITY=000

ID: nht74-1.8

DATE: 10/16/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Volkswagen of America, Inc.

TITLE: FMVSS INTERPRETATION

TEXT:

OCT 16 1974 NOA-30 (ZTV)

Mr. Joseph W. Kennebeck, Manager Emissions, Safety & Development Volkswagen of America, Inc. Englewood Cliffs, N. J. 07632

Dear Mr. Kennebeck:

This is in reply to your letter of September 24, 1974. You informed us that Volkswagen intends to introduce a new model, the Rabbit, in January 1975 that meets all requirements of Standard No.105-75 except S5.3.1.(b), requiring a brake fluid reservoir capacity indicator, which it will meet as of September 1, 1975. You also informed us that "one version of the Rabbit which meets FMVSS 105-75 exceeds the currently required preburnish check permissible pedal force." You therefore asked for an "interpretation of whether the Volkswagen Rabbit could comply with FMVSS 105-75 except for S5.3.1.(b) prior to September 1975, in lieu of complying with FMVSS 105 in effect up to that time."

In our view, the fact that the Rabbit exceeds the maximum specified preburnish check pedal force does not by itself indicate a failure to comply with existing Standard No. 105. Paragraph S4.1 of Standard No. 105 requires the performance ability of a passenger car service brake system to be "not less than that described in Section D of Society of Automotive Engineers Recommended Practice J937, 'Service Brake System Performance Requirements - Passenger Cars', June 1966." and tested in accordance with SAE Recommended Practice J843c, 'Brake System Road Test Code - Passenger Cars', June 1966." Section D of J937, Preburnish check, subreferences "SAE J843, Section C item 1".

The subreferenced item says that the purpose of the preburnish check is "to allow for a general check of instrumentation, brakes, and vehicle function," rather than a test of the effectiveness of the service brake system. Thus the preburnish check is not actually a test requirement. Although the distinction between test requirements, conditions and procedures is not made in the SAE materials incorporated into Standard No. 105, the successor Standard No. 105-75 distinguishes the three. It makes brake burnish part of the test procedure and sequence. Burnishing appears in the test procedure section, S7.4, and Table I, showing test requirements and corresponding procedures, does not relate it to any of the requirements of S5.

A manufacturer's certification covers only the performance requirements of the standard, and is his representation that if testing is conducted in the manner the standard specifies, the vehicle will meet those requirements. Therefore, no "waiver" of Standard No. 105-75 or amendment to Standard No. 105 appears necessary for Volkswagen to certify that the Rabbit complies with Standard No. 105, assuming, of course, that it meets all actual performance requirements of that standard.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

ID: nht74-1.9

DATE: 03/15/74

FROM: AUTHOR UNAVAILABLE; J. B. Gregory; NHTSA

TO: General Motors Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in further reply to your letter of November 19, 1974, petitioning the NHTSA to amend Part 567, Certification (@ 567.4(f)), to allow the use of certification labels on which the lettering is embossed or engraved without regard to whether it contrasts with its background.

The NHTSA has decided that your petition should be denied. Our experience has been that certain types of engraving, those that are stencil-typed or stamped, are difficult to read without color contrast. The NHTSA considers it essential that certification labels be readable under all lighting conditions, and has not found embossing or engraving to produce by themselves sufficiently readable lettering for these labels. Of course, there is no prohibition against embossing or engraving if the finished lettering contrasts with its background.

We appreciate your point that Standard No. 105a accepts embossed or engraved lettering on the master cylinder reservoir label without requiring a color contrast. We are presently considering amending Standard No. 105a to eliminate this discrepancy.

ID: nht74-2.1

DATE: 01/17/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Aeroquip Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your request of January 8, 1974, made to Mr. Herlihy of this office, for an interpretation of S5.1.2.3 of Standard No. 121, Air brake systems, as it applies to a check valve which is designed to bleed back no more than 5 psi pressure from the service reservoir toward the source of air pressure.

The check valve described in the specification you enclosed would satisfy the requirements of S5.1.2.3 as long as there is no air loss in excess of the designed bleed off, and that total air loss never lowers the pressure at any time below the air compressor "cut in" pressure.

Yours truly,

ATTACH.

AEROQUIP CORPORATION/INDUSTRIAL DIVISION

January 4, 1974

John Womack and Richard Dyson -- Chief Council, National Highway Traffic Safety Administration

Gentlemen:

This letter is a request for approval of our XFF9260-50 check valve for use in truck and bus air brake systems as detailed in the Motor Vehicle Safety Standards #121, Paragraph S5.1.2.3.

The function of the subject check valve is to allow air bleed back of no more than 5 psi pressure from the maximum pressure setting on the primary reservoir. The purpose of the air bleed back is to increase the service life of our Aerofiner Air Purifier (P/N FF9260-01). The air volume used off the #1 air reservoir (pre-dried air) is used to back flush the desiccant bed in the Aerofiner at approximately 3 cfm until the pressure in the reservoir drops to the relief valve setting, (5 psi below maximum reservoir operating pressure) at which time the valve is completely closed. In all other respects, it functions as a typical safety check valve.

Attached is a layout sketch of the subject check valve showing the seal surfaces and flow paths under various conditions.

Also attached, is a copy of Bulletin #5212, describing our Aerofiner brake system air purifier.

Please supply me in writing, the council's approval of our XFF9260-50 check valve in truck and bus air brake systems.

If there are any questions, feel free to contact me.

Sincerely yours

Donald T. Fischer -- Project Engineer, Coupling Section

ID: nht74-2.10

DATE: 11/07/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Columbia Body & Equipment Co.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to CBE's October 24, 1974, question whether a trailer equipped with a telescoping drawbar that varies the distance between axles to conform to various State regulations would qualify as a "Heavy hauler trailer" as that term is defined in Standard No. 121, Air brake systems:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) Its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @ 393.106 of this title.

The answer to your question is no. The extension of the drawbar is not an "extension of the vehicle frame." This characteristic is intended only to describe trailers whose function necessitates a highly specialized configuration that significantly interferes with brake design. In contrast, the telescoping drawbar is not related to the trailer's function, but simply permits the vehicle to conform to State highway regulations.

Yours truly,

ATTACH.

October 24, 1974

Acting Chief Consel -- U.S. Dept. of Transportation

Attn: Richard Dyson

Dear Mr. Dyson;

Does the Pony Trailor on our drawing number T65-497 (enclosed) qualify as a heavy hauler trailer and exempt from the S121 or any other antiskid requirement until Sept. 1, 1976 as Mr. Tadd Herllhy defined in our phone conversation Oct. 23, 1974. Please reply as soon as possible.

Sincerely yours,

COLUMBIA BODY & EQUIPMENT COMPANY

John C. Hansen -- Sales Manager

ID: nht74-2.11

DATE: 08/19/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Dura Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Dura Corporation's July 24, 1974, questions whether S5.6 of Standard No. 121, Air brake systems, requires parking brakes on air suspension liftable axles, and whether the "no lockup" requirements of the standard apply to a liftable axle on a "tandem axle rig".

The parking brake performance options of S5.6 do not require parking brakes on an air suspension liftable axle such as you describe. S5.6.2 requires only that the parking brakes installed on a vehicle meet minimum performance levels. S5.6.1 requires parking brake retardation force on "an axle other than a steerable front axle". We do not consider this requirement to apply to an axle which is not on the ground when the parking brake system is activated.

The standard's "no lockup" requirement (S5.3.1) applies to

"any wheel at speeds above 10 mph except for . . .

(b) Lockup of wheels on nonsteerable axles other than the two rearmost nonliftable, nonsteerable axles on a vehicle with more than two nonsteerable axles.

Under this provision, if a vehicle has two nonliftable, nonsteerable axles at the rear which do not lock up (such as an antilock-equipped tandem axle rig) it may be equipped with a liftable nonsteerable axle which does not meet the "no lockup" requirements.

Yours truly,

July 24, 1974

Sidney F. Williams -- Office of Operating Systems, National Highway Traffic Safety Administration, Department of Transportation

Dear Sir:

Dura Corporation is presently involved in manufacturing add-on liftable axle/suspension assemblies which are marketed with OEM and body builders. Due to the impending effectivity dates of FMVSS 121 we are presently preparing to equip our products to comply. Our liftable airide axle/suspension assemblies are applicable to both pusher and tag situations.

The intent of this letter is to request an official interpretation of FMVSS 121. Our present understanding of the standard is as follows:

An anti-lock system will be required with the add-on axle/suspension if added to a single axle rig but not required if added to a tandem axle rig.

II. An emergency/parking spring brake will not be required with the add-on axle/suspension. This supposition is based on a loss of air pressure will automatically lift the axle rendering the spring brake inoperable.

Please indicate if the above statements are correct. Your consideration and cooperation in this matter is truly appreciated.

Sincerely,

Raymond E. Jones, Project Engineer -- DURA CORPORATION

cc: W. Locke

ID: nht74-2.12

DATE: 11/14/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Truck Trailer Manufacturers Association

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your October 23, 1974, question in behalf of Steadman Containers, Ltd., asking if Standard No. 121, Air brake systems, applies to the Steadman "liftainer", which is described as a semi-trailer frame capable of carrying 20- and 40-foot cargo containers that are loaded by means of cranes mounted at each end of the semi-trailer. The vehicle is used to move containers in terminal areas and is used on the highway only in relocation to another terminal.

The "liftainer" is a motor vehicle as that term is defined in the National Traffic and Motor Vehicle Safety Act of 1966, because it uses the highway on a necessary and recurring basis to move between work sites. A discussion of the motor vehicle definition is enclosed for your information. As a motor vehicle, it is subject to the requirements of Standard No. 121 for trailers, effective January 1, 1975.

I have also enclosed a discussion of Standard No. 121's applicability to vehicles purchased by Canadians for use between Canadian and United States points. The standard would apply to Steadman trailers if they are purchased for use on U.S. highways.

Yours truly,

ATTACH.

October 23, 1974

James B. Gregory -- National Highway Traffic Safety Administration, Department of Transportation

Dear Dr. Gregory:

Could you please furnish us with an interpretation in connection with the enclosed described equipment and its relationship with the anti-skid devices to be placed on equipment by January 1, 1975?

You will note that Steadman containers indicates that "The Liftainer Container handling unit is not intended, nor used, as a highway unit, but is used in terminals where it is moved by means of a conventional highway tractor. Its highway use is limited only to possible occasional re-positioning from one yard to another. As its width in the closed, unfolded condition, is in excess of 8', road movement always involves use of special permits."

We will appreciate your consideration and response to the above.

Sincerely yours, Charles J. Calvin -- President