Interpretation ID: nht94-6.47

DATE: April 7, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Ulrich Metz -- Automotive Division, Robert Bosch GmbH (Germany)

TITLE: None

ATTACHMT: Attached to letter dated 6/9/93 from Ulrich Metz to NHTSA (OCC 9194)

TEXT:

This responds to your letter to this agency regarding a new windshield wiper system you intend to develop for front windshield. I apologize for the delay in responding.

The drawing you enclosed with your letter shows a wiper system consisting of one wiper arm and blade, as distinguished from the conventional systems consisting of two wiper arms and blades. Your wiper system takes different paths on the forward and the return strokes of the wiper cycle. Thus, as you stated in your letter, "the vision areas are fulfilled only in the sum of forward and return movement." You asked whether that is permissible under Federal Motor Vehicle Safety Standard (FMVSS) No. 104, Windshield Wiping and Washing systems (copy enclosed), and if so, whether the minimum frequencies specified by FMVSS 104 apply to this wiper system. As explained below, the answer to both questions is yes.

The essential feature of a windshield wiper system, from a safety standpoint, is its ability to clear a specific portion of the windshield. The number of wipers necessary to provide the driver with a sufficient field of view is not specified in FMVSS 104. Therefore, the number of wipers is immaterial so long as the minimum percentages of critical areas are cleared.

The areas to be wiped are specified in paragraphs S4.1.2 and S4.1.2.1 of the standard. S4.1.2 establishes three windshield areas for passenger car windshields, designated as areas "A," "B," and "C." Each area is required to have a certain percentage of the glazing area wiped as shown in Figures 1 and 2 of SAE Recommended Practice J903a, May 1966 (copy enclosed), using the angles specified in Tables I, II, III, and IV of FMVSS 104, as applicable. Those tables apply to passenger cars of varying overall widths, namely, from less than 60 inches to more than 68 inches. The angles set forth in the tables vary according to the overall width of the vehicle. Finally, paragraph S4.1.2 provides that the percentage of each area required to be cleared must also be within the area bounded by a perimeter line on the glazing surface one inch from the edge of the daylight opening.

With that background in mind, I will address your first question. FMVSS 104 does not specify whether the wiper needs to clear a windshield on either or both strokes. SAE Recommended Practice J903a, at paragraph 2.5, however, defines an effective wipe pattern as "that portion of the windshield glazing surface which is cleaned when the wiper blade travels THROUGH A CYCLE) (emphasis added). A "cycle" is defined in paragraph 2.14 of SAE Recommended Practice J903a as consisting of "wiper blade movement during system operation from one extreme of the windshield wipe pattern to the other extreme AND RETURN" (emphasis added). It is NHTSA's opinion, therefore, that so long as the required windshield area is cleared by your wiper in a complete cycle, the

requirements of paragraphs S4.1.2 and S4.1.2.1, FMVSS 104, have been met.

As indicated above, your wiper system must comply with the minimum frequencies specified in section S4.1.1, Frequency, of FMVSS 104. That section requires that each windshield wiping system must have at least two frequencies or speeds. One must be at least 45 cycles per minute (cpm), regardless of engine load and speed. The other must be at least 20 cpm, also regardless of engine load and speed. In addition, the difference between the higher and lower speeds must be at least 15 cpm, regardless of engine load and speed. There are no exceptions to these frequency requirements, regardless of the number or design of the wiper arms comprising the system.

Your letter did not indicate whether your wiper system is designed to be used on passenger cars or motor vehicles other than passenger cars, or both. Please note that section S2 of FMVSS 104, Application, provides that the standard applies to multipurpose passenger vehicles, trucks, and buses in addition to passenger cars. All those vehicles are required to have power-driven windshield wiping systems that meet the frequency requirements of section S4.1.1. The wiped area requirements of S4.1.2, however, apply only to passenger cars.

I hope this information will be helpful to you. Should you have any further questions or need any additional information, please feel free to contact Walter Myers of my staff at this address or at (202) 366-2992.