Interpretation ID: nht91-4.26

DATE: June 20, 1991

FROM: Brett Reed -- Design Engineer, Morse Controls, Inc.

TO: Office of the Chief Counsel, NHTSA

COPYEE: R. Breitenstein; A. Paynter; F. Witt

TITLE: None

ATTACHMT: Attached to letter dated 9-16-91 from Paul Jackson Rice to Brett Reed (A38; Std. 102)

TEXT:

Morse Controls requests that your office issue an interpretation of Motor Motor Vehicle Safety Standard No. 102 and its application to electronic transmission shift controls. Specifically, as it relates to controls that operate automatic transmissions used in heavy duty trucks and RV's and on solenoid operated powershift transmissions used in various on and off highway vehicles.

Section S3.1.3 of this standard reads as follows:

S3.1.3 Starter Interlock - The engine starter shall be inoperative when the transmission shift lever is in a forward or reverse drive position.

Is the intent of this standard to render the engine starter inoperative when the transmission is in a forward or reverse drive gear or when the shift lever, the driver's interface to the transmission, is in such a gear? It would seem that the real thrust of this standard would be to inhibit the operation of the engine starter when the transmission is in a drive gear, thus avoiding the obvious safety hazards. The position of the shift lever, the driver's interface to the transmission, may well be dismissed in certain operational scenarios, provided this prime safety consideration has been met.

At the time this specification was written, transmissions were generally controlled by mechanical linkages or cables that were directly connected to the shift lever. Thus, the shift lever (the human interface) always matched the gear that the transmission was in. With the introduction of electronic shift systems and fully electronic transmissions, the connection between the shift lever and the transmission is rarely performed by direct mechanical means. This raises the possibility that the shift lever position may not match the gear currently engaged by the transmission in situations where the transmission control circuitry overrides the shift lever selection in the interest of safety, transmission protection or other criteria related to specific applications.

Such systems do require that the transmission be in neutral before enabling the operation of the engine starter, in accordance with the perceived intent of MVSS No. 102.

Any attempt to artificially match the electronic shift lever's position to the gear currently engaged by the transmission in such override situations not only burdens the shift lever with considerable cost and complexity, but also raises safety and reliability concerns. Similarly, requiring the

shift lever to be moved to neutral when the transmission itself is already in neutral due to some override condition imposes unnecessary safety hazards in some applications. The interests of public safety will be best served by requiring that the engine starter be inoperative when the transmission itself, not the transmission shift lever, is in a forward or reverse drive gear.

We, therefore, respectfully request that you review this matter and render an interpretation of the intent of this standard. Feel free to contact us for clarification of any points we have raised. Thank you in advance for your consideration of this matter.