SAE J2255_199605

This SAE Recommended Practice provides instructions and test procedures for measuring air consumption of air braked vehicles equipped with Antilock Brake Systems (ABS) used on highways. Antilock Brake Systems (ABS) on commercial vehicles with air brakes is back and here to stay. This proposed SAE Recommended Practice provides a standard procedure for dynamically testing Antilock Braking Systems equipped vehicle braking systems (truck tractors, buses, trailers, and dollies) for air consumption. This recommended practice defines the method, instrumentation, equipment, and applicable documents required to perform the procedure. This document provides a method of determining the air consumption of highway type vehicles when the brake system must maintain its performance when the service brake control line is applied for long periods of time. There is a need in the industry for a standardized procedure to compare the air consumption of antilock brake systems when installed with various vehicle braking systems for a variety of vehicle types. The vehicle braking system can be comprised of various brake components. Antilock systems are available in various configurations (2Sensor/1Modulator, 2S/2M, 4S/2M, 4S/3M, 4S/4M, 6S/4M, and 6S/6M). The brake components and the antilock system configuration used in the vehicle braking system can effect upon the rate of air consumption. This recommended practice is a standardized procedure for vehicle manufacturers to measure the amount of air being consumed by an ABS equipped vehicle braking system during a major ABS braking event. This document contains no requirements regarding the amount of air pressure in the reservoir either after performing the procedure or after a major ABS braking event. This minimum amount of air pressure in the reservoir is determined by the vehicle manufacturer, although the amount of pressure remaining in the reservoir should be enough to keep the spring brakes retracted. Testing performed has shown that minimal air is actually transferred from tractor to trailer when performing the test procedure. The test surface for performing this procedure should be 3.7 m (12 ft) wide, 152.4 m (500 ft) straight and level with a PFC = 0.5 or less (wet Jennite in good condition). The surface friction is determined by the peak friction coefficient (PFC) as identified in SAE J1626. Vehicle manufacturers may elect to perform this procedure on a surface with a PFC less than 0.5 for a greater safety factor in determining the minimum reservoir size.