Interpretation ID: nht87-1.72
TYPE: INTERPRETATION-NHTSA
DATE: APRIL 27, 1987
FROM: KOJI TOKUNAGA -- MANAGER, ISUZU MOTORS
TO: ERIKA Z. JONES -- CHIEF COUNSEL, NHTSA
TITLE: FMVSS 124 - ACCELERATOR CONTROL SYSTEMS
ATTACHMT: ATTACHED TO MEMO DATED 8-8-88, TO KOJI TOKUNAGA, FROM ERIKA Z. JONES, STD. 124
TEXT: The purpose of this letter is to seek your agency's interpretation of some requirements of FMVSS 124 - Accelerator Control Systems in the specific context of a new system to be used for our vehicles.
This system features electric control. The system's outline is explained below and illustrated on the attached sheet.
As the accelerator pedal is depressed by the driver, the amount of pedal displacement is converted into proportional electric signals by the accelerator pedal sensor which is in fact a potentiometer equipped with two accelerator pedal position switches. These signals are fed into the control unit where position switch, and then fed into the stepping motor. The stepping motor works to move the throttle lever through the motor's arm and linkage. Thus, the engine speed is controlled in proportion to the amount of accelerator pedal displacement.
The moving components in this system are the accelerator pedal, stepping motor arm, linkage and throttle lever. I would like to receive your answer to the following questions regarding the interpretation of the requirements:
1. Energy sources (S5. 1)
In this vehicle, Isuzu considers the battery that drives the stepping motor to be one of the energy sources under S5. 1, and the return springs (accelerator pedal and throttle lever return springs) the other sources. Is this interpretation correct?
2. Disconnection or severance (S5. 2)
a. Is a severance in electric wires in this system a severance or disconnection within the meaning of S5.2? Isuzu considers negative because electric wires are not a moving part.
b. If a severance in electric wires were a severance or disconnection under S5.2, what about a short-circuiting that may result from such a severance? Does the Standard require that the throttle returns to the idle position even in such a condition?
c. Our understanding is that a failure (other than severance or disconnection) of a system component itself (i.e. a failure in the accelerator pedal sensor with pedal position switches, control unit, throttle valve position switch, or stepping motor) is not subject to the throttle return requirement under the Standard. Is this correct?
3. Definition of "driver-operated accelerator control system"
It is our interpretation that the battery and the electric wires from the battery to the control unit are not a part of the accelerator control system under this definition. Is this interpretation correct?
Vehicles equipped with this control system are already distributed in Japan, and we would like to introduce such vehicles to our U.S. customers as soon as possible. Therefore, your prompt review of, and answer to, these questions would be greatly apprec iated.
I am looking forward to hearing from you on this subject.
Attached sheet
Battery
Throttle valve position switch
Accelerator pedal sensor with accelerator pedal position switches
Arm
Throttle lever
Linkage
Return springs
Stepping motor
Accelerator pedal
Return spring
Control unit
Electric wire
Accelerator Control System