Interpretation ID: nht72-6.61

DATE: DECEMBER 28, 1972

FROM: TATSUO KATO -- ENGINEERING REP, NISSAN MOTOR CO., LTD.

TO: LAWRENCE SCHNEIDER -- NHTSA

COPYEE: J. W. CARSON

TITLE: NONE

ATTACHMT: ATTACHED TO LETTER DATED FEBRUARY 16, 1973 FROM E.T. DRIVER, NHTSA, TO TATSUO KATO, NISSAN MOTOR CO.

TEXT: This is to request the answer to the following questions regarding MVSS 124 which we explained at a meeting held in the Office of NHTSA, on Friday, December 8, 1972.

1. We are using a two-barrel, down draft type carburetor with a linkage as shown in the attached schematic drawing (see Figure 1). We have designed the accelerator control system that has at least two sources of energy capable of returning the throttle to the idle position, that is, whenever the driver removes the opposing actuating force, the primary valve of the carburetor is closed by sources of energy of spring A and B and the secondary valve is done by spring A, B and C. Although in the event of failure of the spring C, the secondary valve is usually returned to the initial closed position by the lever L which is actuated by the torsion spring A and B as explained at the meeting, there is a possibility of slightly opening the secondary valve because of endplay by the tolerance of the production so that engine speed might slightly increase more than engine idle speed specified in our manuals.

Under the aforementioned situation, may be understand that the increase of engine idle speed resulting from the endplay caused by failure of the spring C will not be included in the scope of "Overspeed" which is stated in S2 of MVSS 124, that is, in the case of malfunctions, tolerance to the idle speed will be accepted by NHTSA.

If the tolerance is accepted, we would like to know the acceptable range (if possible, by rpm = revolution per minute of engine) of the increase of engine idle speed.

2. It is difficult to decide the components of accelerator control system which we have to consider a severence or disconnection which is specified in MVSS 124, S5.2, "The throttle shall return to the idle position from any accelerator position or any speed of which the engine is capable whenever any one component of the accelerator control system becomes disconnected or severed!'

Under the abovementioned situation, in case of our model PL610, we do not consider breakage of parts such as mounting brackets or mounting bolts as a portion of severence or disconnection, but we do only the portion with the mark X in the attached drawing. (see Figure 2). May we understand the definition of the portion of severence or disconnection as mentioned above?

Your prompt reply would be greatly appreciated.

Attachments

CONDITION OF FULL THROTTLE

In case of breakage of Spring "C" secondary valve is returned - by Linkage L.

Condition of Secondary Valve with possibility of opening.

(Graphics omitted)

FIGURE 2 SIDE VIEW

Graphics omitted)

FIGURE 2 FRONT VIEW

Graphics omitted)