Performance-based Brake Testers

Download or read book Performance-based Brake Testers written by United States. Federal Highway Administration. Office of Motor Carriers and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This report documents the results of a series of tests in which several different types of performance-based brake testers (PBBTs) were compared side-by-side (i.e. a round robin test) in their ability to accurately measure brake forces (BFs) and wheel loads (WLs) of commercial vehicles (CVs), and to then predict the vehicle deceleration capability for a 32.2 km/hr on-road stopping test. The PBBTs consisted of five roller dynamometers (RD), two flat plate (FP) testers, and one breakaway torque tester (BTT). A PBBT that can also meet a set of functional specifications could be used for law enforcement by safety inspectors once performance-based criteria are codified. In the test program, specific ratios of BF to WL were imposed on both a 5-axle combination tractor semi-trailer and a two-axle straight truck, in both the fully laden and unladen conditions. In each loading condition, the overall vehicle braking capability was set to achieve a proposed minimum requirement of 0.4g, where g is the acceleration due to gravity. In addition, the brakes on specific individual wheels were set to provide a BF/WL of 0.25 and 0.35, for a steer and a non-steer wheel, respectively. The vehicles were also instrumented to record stopping distances and decelerations from on-road stopping tests performed from 32.2 km/hr. In general, nearly all of the PBBTs were able to accurately measure the CVs' brake forces. Only one of the FP-type testers experienced erratic performance during the round robin. In contrast several of the PBBTs had difficulty in reporting the accurate gross vehicle weight. In some cases, particularly with the portable PBBTs the reported wheel loads for axles 2 and 4 (the lead axle on the tandem set) of the 5-axle vehicle were very high, leading to an under-prediction of the vehicle deceleration capability. Calibration checks of the PBBT weighing mechanisms indicated that all could meet the functional specifications. As such, it was concluded that accounting for the redistribution of axle loads due to the vehicle suspension and the geometry of the PBBT ramp would require special test procedures or remote entry of vehicle or axle weights for use in law enforcement. The repeatability of all the PBBTs was good, meeting the acceptability criteria in more than 93 percent of the test cases.