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Efforts to develope a harmonized brake standard have led to the developement and evaluation of procedures for measuring the brake balance and braking efficiency of passenger cars. The European braking regulations include a procedure for direct measurment of the braking efficiency of a vehicle equiped with an antilock system (ECE Regulation No. 13. Annex 13/EEC Directive 71/320 Annex X). The procedure is a two step process including the measurement of the peak coefficient of friction (mu) for the vehicle tire on the test surface, and then finding the maximum deceleration of the vehicle on the test surface for calculation of the braking efficiency. Tests were conducted to evaluate the feasibility of using this procedure for vehicles not equiped with ABS. Comparisons were made between the peak coefficient of friction as measured by the Annex 13 procedure and as measured by a traction trailer with the vehicle tires installed.

In this study, experimental methods were used to compare the consequences of employing snubbing versus dragging strategies to control the speeds of trucks on downgrades. Vehicle tests were performed on a long steep grade. A mobile dynamometer was used to study cooling rates and hot spotting. The basic findings of the study are: (1) the average temperature per pound (kilogram) of brake drum is practically equivalent whether light dragging or snubbing is used; (2) the hottest brakes will be cooler if snubbing is used; and(3) on short downhill descents, the dragging strategy will cause hot spots to develop to a greater extent. For many years there has been controversy between those that recommend dragging brakes versus those that recommend snubbing (pulsing) to control vehicle speed during downhill descents. Recently, interest in commercial driver licensing (CDL) has stimulated discussions of the merits of these two braking strategies.

Enhancements have been developed for low speed roller brake testers that make them more useful devices for testing and diagnosing braking systems. The enhancements are primarily designed for the evaluation of air brake systems but have application to hydraulic brake systems as well.

This paper focuses on two types of electronics-based object detection systems for heavy truck applications: those sensing the presence of objects to the rear of the vehicle, and those sensing the presence of objects on the right side of the vehicle. The rearward sensing systems are intended to aid drivers when backing their vehicles, typically at very low “crawl” speeds. Six rear object detection systems that were commercially available at the time that this study was initiated were evaluated. The right side looking systems are intended primarily as supplements to side view mirror systems and as an aid for detecting the presence of adjacent vehicles when making lane changes or merging maneuvers. Four side systems, two commercially available systems and two prototypes, were evaluated.

A number of methods and types of equipment have been developed to measure a heavy vehicle's braking forces both for use as an inspection tool and for diagnosis of brake system problems. The systems and procedures evaluated included a vehicle deceleration test, a road transducer plate, roller dynamometers, a flat plate tester, a breakaway torque tester, and an infrared brake temperature measurement system. Evaluations of these devices have been conducted to ensure that the results produced are meaningful. In general, the devices compare very well and, in most cases, were found to be useful in determining the status of a brake system.

A vehicle test procedure for determining the adhesion utilization properties of braking systems has been developed. The procedure requires minima instrumentation and equipment. It was applied to 19 passenger cars over a range of conditions and the effects of factors such as load, center of gravity height, speed, parasitic drag, engine braking, drive configuration (front or rear), brake conditioning, and tire properties on adhesion utilization were determined. The vehicles were also subjected to a series of stopping tests on six different surfaces to evaluate the degree of correlation between predictions from the adhesion utilization curves and actual performance. Frictional properties of the tires from 11 of the vehicles were measured on the surfaces to aid in this correlation study.

A Supplemental Notice of Proposed Rulemaking (SNPRM, Notice 4) for FMVSS 135 has recently been issued proposing a new braking regulation for passenger cars. Due to interest in light truck braking performance as it relates to that of passenger cars, a sample of 13 light trucks was tested to the FMVSS 135 Notice 4 procedure for purposes of comparison with the performance of a sample of 19 passenger cars tested to the same procedure. The brake force balance and braking efficiency of the light trucks were also measured and compared to the same parameters of the set of 19 cars.

This paper serves as the seventh report in a series of reports on NHTSA's Heavy Vehicle Brake Research Program and deals with the subject of tractor and trailer brake system compatibility. It provides a detailed definition of compatibility, discusses the factors that influence it and presents data and analyses which indicate the degree of compatibility in the heavy duty combination vehicle fleet at large. The paper suggests ways in which compatibility can be improved so that combination vehicle brake systems will be more durable and provide an enhanced level of safety.

Currently there are no adequate standards or regulations that address the performance of aftermarket replacement brake linings to insure that the use of these materials does not degrade vehicle braking performance from the original equipment (OE) design intent level. This paper discusses the results of an evaluation of a large sampling of aftermarket linings available for the rear brake of a specific model passenger car and shows that many of these linings have significantly different performance than the OE material. The paper also shows how this deviation can adversely affect vehicle braking efficiency or the ability of the brake system to utilize available tire/roadway friction without locking wheels and losing control.

This paper addresses the issue of front wheel braking on heavy trucks and reviews testing that has been performed over the years dating back to 1948 to evaluate the effect of front brakes on braking performance. It also describes in detail a test and demonstration program on front wheel brakes that was conducted in September 1986. The paper indicates that front wheel brakes have a strong effect on braking performance and that vehicles without front wheel brakes take longer distances to stop and are more likely to lose control in emergency situations. The paper also indicates that the use of front brake pressure limiting valves with typical, current design front brakes degrades vehicle braking performance.