Interpretation ID: nht92-8.5

DATE: April 3, 1992

FROM: Frank J. Sonzala -- Senior Vice President, International Transquip Industries, Inc.

TO: Paul Jackson Rice -- Chief Counsel, NHTSA

TITLE: Re: Single Service Diaphragm Failure Test per FMVSS 121

ATTACHMT: Attached to letter dated 6/1/92 from Paul J. Rice to Frank J. Sonzala (A39; Std. 121); Also attached to letter dated 5/20/92 from Frederick H. Grubbe to Phil Gramm (A39; Std. 121); Also attached to letter dated 4/3/92 from Frank J. Sonzala to Phil Gramm (OCC 7206)

TEXT:

Under the current FMVSS 121 regulation, a diaphragm has been ruled as not being part of a brake chamber housing. The current regulation amendment, which is effective December 9, 1991, states:

In S5.6.6.2 and S5.6.6.3, the test sequence for S5.6.6.1 is as follows: The engine is turned off. Any single leakage type failure in any other brake system of a part designed to contain compressed air or brake fluid (excluding failure of a component of a brake chamber housing, but including failure of any brake chamber diaphragm that is part of any other brake system, including a diaphragm which is common to the parking brake system and any other brake system) is then introduced in the brake system.

An application actuation of the parking brake control is then made.

Thirty seconds after such actuation, a release actuation of the parking brake control is made. Thirty seconds after the release actuation, a final application actuation of the parking brake control is made.

During this particular test, it is assumed that the diaphragm has been failed. However, there is no determination as to what constitutes a failed diaphragm. ITI's testing and years of experience have shown that a hole in a diaphragm starts as a small tear, a wear point between the push rod plate and the diaphragm. By design, the diaphragm has a scrim of layered material interwoven and sandwiched between two pieces of neoprene or rubber.

As the rubber or neoprene wears, a part of the surface wears away, and the scrim material, made of a nylon glass woven material will start to be exposed. This woven material is a rip-stop design which does not allow the diaphragm to rip quickly or cultivate further tearing. Once the rip-stop has been worn by the push rod plate to an 1/8" hole, then any subsequent parking brake application in the ITI system, after such an 1/8" hole, will cause the brake chambers to apply, hold the proper grade as per FMVSS 121, and not be able to release. Original equipment manufacturers generally do not recognize that an 1/8" hole is sufficient to call a diaphragm failed. ITI has tested diaphragms extensively for their tear proclivities, and those test results are found in Exhibit C, attached.

In the ITI system, a hole as small as 1/8" in the diaphragm is detected and the brakes are automatically held in a mechanically locked position by the first parking application after the hole is created. In a spring brake system, a hole in a service diaphragm on the service side of a spring type parking brake goes physically undetected, so that a hole in a spring brake diaphragm can be ripped at 1/8" to 1/2" to 1" and beyond. This design fault in spring brake

systems allows vehicles to be on the highway without proper service brake applications. A soft or weak brake may not even be noticeable to a driver at low air pressure applications. But in the need for a hard application such as in a panic stop, this service diaphragm can be ripped too far, causing the vehicle to go beyond a safe stopping mode.

In the case of the ITI Air Brake System, the system incorporates a constant air check of every component that is designed to hold compressed air. If a component that is designed to hold compressed air has failed, and specifically if a diaphragm has failed, it is detected at the moment of its failure. In the case of the diaphragm, a hole of approximately 1/8" would still allow the brake to be applied, therefore meeting the sequence testing. But an 1/8" hole will not allow the mechanical locking piston to release, therefore holding the retardation force through the second phase of this test sequence. Because the retardation force is being held, the brake remains applied through all phases of the test procedure. By design, the ITI Air Brake chamber cannot develop over 1/8" hole in its parking or service diaphragm. This particular chamber uses one diaphragm to accomplish both tasks.

In a demonstration done at the National Highway Traffic Safety Administration's offices on October 31, 1991, a failed diaphragm with an 1/8" hole was shown to the following parties: Blaine Laubis, Richard Carter, George Entwistle, Scott Schadle, and Larry Minor.

The demonstration showed clearly that the brakes can be applied with adequate air pressure and mechanically locked. Because the system senses the failure, the chamber cannot be released from that park position, and it will remain applied in a safe failure mode. The demonstration was done because many of the original equipment manufacturers with whom we wish to do business have a problem with the testing sequence of the failed diaphragm, and we hoped that NHTSA would be able to clarify the test procedure and the failed diaphragm parameters. The problems with S5.6.6.1 are as follows:

#1 The size of the failure hole in a diaphragm has not been defined.

#2 The common position of the failure hole in the diaphragm has not been defined.

International Transquip Industries has designed a fail safe mode into their non-spring brake type brake actuator that prevents any vehicle from being put on the road with a hole in the diaphragm greater than 1/8". This design is far superior to the spring brake systems that are now in use on our highways. A hole in a parking diaphragm in a spring brake system may begin or start while the vehicle is in motion. Once that hole starts, air pressure will allow the spring to creep on, possibly causing fires, possibly causing jackknifes, possibly causing a moving vehicle accident. This cannot happen with the ITI Air Brake System. ITI's system prevents spring brake accidents such as the one reported in Docket Part 571 (amended) Docket 87-04 Notice 6 (copy of which is enclosed - Exhibit A).

ITI requires a ruling that will state that an 1/8" hole in a service system diaphragm constitutes a failed diaphragm for the purposes of the test sequence in S5.6.6.3, and that the hole must be placed on the service diaphragm within 1 inch of where the push rod plate meets the diaphragm. A drawing accompanies this letter showing the common area where these failures tend to occur.

(Exhibit B). A hole much larger than 1/8" or placed anywhere else in the diaphragm would not constitute a realistic and valid test. Additionally, in the ITI Air Brake System, the hole in the diaphragm can only be put into the system after the system is fully aired up to 100 psi with all brakes released. The diaphragm must be taken out of the chamber and reinserted with a 1/8" hole for the test procedure as outlined in S5.6.6.3.

It should be borne in mind that the OEM test for all components is performed on new vehicles and all items are to pass a performance test to meet the regulations as outlined in FMVSS 121. It takes up to two million applications for a hole to wear into a diaphragm and therefore the failed diaphragm test under FMVSS 121 does not seem realistically justified. (We recommend that the diaphragm in a brake chamber should be considered a brake chamber component that does not require a separate test under FMVSS 121. If a torn diaphragm is to be tested, then the suggested test and size and placement of the diaphragm tear should be as stated in the previous paragraphs.

Our questions, therefore, for interpretation are:

1. Should a torn diaphragm be considered during a FMVSS 121 test, and if so, should the parameters as requested by ITI of 1/8" tear at one inch from the push rod plate area be used by OEMs for compliance testing?

2. Should other broken components such as heavy parking springs, brake shoes, lining and drums be part of the OEMs FMVSS 121 test requirements, based on the premise that a torn diaphragm should be tested?

Your prompt and positive response to these questions will prevent further loss of revenue to our company. Because of the ambiguity of the test procedure, and comments made by NHTSA personnel to OEM inquiries that refer to larger diaphragm failures as "being possible", International Transquip Industries, Inc. has lost hundreds of thousands of dollars in sales to major customers.

Attachments

Exhibit A. Letter dated 3/26/90 from Bob Brinton, owner, Friction Advisory Service, to NHTSA regarding Docket Revision Part 571 (Amended) - Docket #87-04 Notice 6.

Exhibit B. Drawing.

Exhibit C. Summary of Diaphragm Test Results.

(Text of attachments omitted.)