Interpretation ID: nht74-2.21

DATE: 08/12/74

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

TO: B. F. Goodrich Aerospace and Defense Products

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your June 4 and June 20, 1974, letters asking if a parking brake system which locks mechanically after the brake is applied by any emergency air supply acting through the service air brake chamber would comply with Standard No. 121, Air brake systems. The parking brake provisions require in part:

S5.6.3 Application and holding. The parking brake shall be applied by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system. Once applied, the parking brakes shall be held in the applied position solely by mechanical means.

The arrangement described would not meet this requirement because the energy source to apply the brakes (the emergency air supply) would be affected by loss of air pressure in the service brake system. For example, any failure in the service brake piston diaphragm would cause a loss of air pressure that would in turn "affect" the energy source that applies the parking brakes. The brake chamber housing assembly is an element which is not considered to be part of the service brake system for this requirement.

I would like to point out that the provisions of Standard No. 121 do not apply to trailers manufactured before January 1, 1975.

Your truly,

ATTACH.

June 4, 1974

CHIEF COUNCIL -- U. S. Department of Transportation National Highway Traffic Safety Administration

Dear Sirs:

The following inquiry is submitted to you with regards to telephone conversations with Mr. S. F. Williams on Friday afternoon, May 31, 1974, and Monday morning June 3, 1974.

Will MVSS 121 permit actuation of a mechanically locking parking and/or emergency brake, using air that is applied to the service brake diaphragm?

The air is supplied, of course, from an isolated emergency source.

Yours truly, B. F. GOODRICH ENGINEERED SYSTEMS COMPANY A Division of The B. F. Goodrich Company;

A. J. Burt -- Sales Engineer

CC: S. F. Williams, D.O.T.; R. D. Buehler, B. F. Goodrich, Washington D. C.; C. R. Collins, B. F. Goodrich, Springfield, Virginia

B. F. Goodrich Aerospace and Defense Products

June 20, 1974

S. F. WILLIAMS -- U. S. Department of Transportation, National Highway Traffic Safety Administration

Dear Sid:

Relative to our phone conversation this afternoon, attached is a copy of all the technical information we have concerning the Park-Lock brake.

The Park-Lock people that we talked to in February of this year were Mr. Joe D'Angelo and Mr. Paul Mantle.

I should note that my inquiry to the Chief Council dated June 4, 1974 and copied to you, is meant to be interpreted as a generalized question concerning the use of a service brake diaphragm. The "mechanically locking parking and/or emergency brake" was not meant to refer specifically to the "Park Lock" device, but any general device which would require actuation by emergency air applied to a service brake diaphragm, and then mechanically locking once the actuation stroke is completed.

Yours truly,

A. J. Burt -- Sales Engineer, Highway Products

CC: R. D. Buehler -- B. F. Goodrich, Washington, D.C.; C. R. Collins -- B. F. Goodrich, Springfield, Virginia

Park-Lock

(Illegible Word) PARK LOCK?

Park Lock is an Automatic Brake Holding Device that holds your brakes, once applied . . . A New Friend to the Trucks.

WHAT DOES PARK LOCK DO?

Park Lock prevents trailer roll offs; climinates wheel chocking; prevents release of brakes when service system air pressure is below safe operating level.

HOW IS PARK LOCK APPLIED?

In emergency conditions, such as loss of air, the Relay Emergency Valve applies your brakes. . . As the air leaks off, Park Lock gently applies, automatically, and holds your brakes by mechanical means.

HOW IS PARK LOCK RELEASED?

There are two ways to release Park Lock.

1. With the application of air, Park Lock releases automatically.

2. By mechanical means. No special wrench is required. Pliers, screw-driver or coin can be used.

IS PARK LOCK SAFE?

Park Lock is a true safety device. Any child can dismantle it without danger (no explosion hazard).

DOES PARK LOCK WORK ON EQUIPMENT PRESENTLY IN USE?

(Units in service prior to S-121 and September 1, 1974)

Park Lock can be installed on all trailers, new and used. The Relay Emergency Value and air tank, currently on all trailers, applies your brakes. Park Lock holds your brakes mechanically, thus preventing trailer roll-offs.

IS PARK LOCK DURABLE?

The Park Lock casting is made of especially treated aluminum, for long, tough wear. Park Lock has four movable parts that include a special brake rod. Park Lock is mounted on your present brake chamber and plumbed into the Relay Emergency Value. Installation is easy and simple. The Park Lock weighs about two pounds.

PARK LOCK AND S-121 (After September 1, 1974)

Park Lock passes all requirements under S-121, pertaining to both parking brakes and emergency brakes for your trailers. It is used in conjunction with a Relay Emergency Value and air tank (same tank used under S-121 to release the spring brake).

Park Lock works in conjunction with your New Anti-Skid Braking System and allows you to come to a complete anti-skid stop. This is accomplished by plumbing the air (emergency mode) back through the anti-skid computer valve.

Park Lock can be released from the tractor cab by the same method used to release the spring brake. As required by S-121, Park Lock has a manual release that can be released from the unit.

HOW DOES PARK LOCK SAVE YOU MONEY?

Park Lock eliminates trailer roll-off accidents. This will reduce insurance claims. . . thus reduce insurance premiums.

Park Lock virtually eliminates replacement costs. There are few moving parts.

The sole function of Park Lock is to hold your brakes, once applied; therefore there is virtually no wear on the units.

Park Lock requires very little maintenance, which eliminates down time.

Park Lock eliminates wheel-chocking and need for expensive chocks, chains, and locks.

Park Lock protects your landing gears. No more damage to the landing gear caused by hooking the tractor to the trailer, running fork lifts into the trailer while loading, etc.

(Illegible Words) FIND OUT MORE ABOUT PARK LOCK?

For more information about Park Lock write or call

PARK LOCK, INC. 8240 C Moberly Dallas, Texas 75272 (214) 381-2237

(Illegible Text)

(Graphics omitted)

INVENTORS

Woller Case William F. Benefield to and communicating with said first bore, the said brake actuating red having a series of rack teeth transversely thereof and operatively extending through said first bore and connected at one end to said power element and connected at its opposite end through a linkage to said brake crank and a spring biased pawl rod in said second bore and a salenoid coil connected into the electrical system of said vehicle and embracing said pawl rod whereby, which said salenoid coil is energized, the pawl rod is operated to (Illegible Word) the rack teeth on said brake actuating rod and restrain the same in position to set the brakes.

2. In a brake getting mechanism, as described in claim 1, the said spring actually biasing the pawl rod in retracted position to (Illegible Words) said pawl rod being extended to engage said brake actuating rod by said solenoid against the tension of said spring.

3. In a device as described in claim 1, and a collar on said pawl rod for adjusting the tension of said compression spring.

(Illegible Line)

UNITED STATES PATENTS

(Illegible Table)

GEORGE E. A. HALVOSA, Primary Examiner

UR Ct. XR 74-503; 192-3; 188-163