Pumping systems using frequency inverters to achieve variable speed control have often been reported to become unstable under certain operating conditions. An experimental study has shown that harmonics present in the output current of a frequency inverter give rise to corresponding pressure harmonics at the discharge of the pump. Moreover, certain harmonics can occur at frequencies low enough actively to excite the piping system and give rise to resonance.
This study compares dry stopping performance of various foundation brake systems on Class VIII truck tractors. Four configurations of foundation brakes were fitted to two modern 6x4 conventional truck tractors without modification to the control, application or antilock brake systems. The foundation brake configurations included: standard S-cam drum brakes on all six positions, high output S-cam drum and then air disc brakes on the steer axles, and air disc brakes on all six brake positions. The stopping distances from 60 mph were analyzed for all test conditions. The truck tractors were tested in two weight configurations: LLVW (i.e., bobtail) and GVWR (50,000 lb total axle weight) using an unbraked control semitrailer. Analysis of variance tests indicate statistically different stopping distance means between all foundation brake configurations, whether the results for both weight configurations were combined or analyzed separately. Combining the results for both tractors, an all disc brake configuration could yield a 20% improvement in stopping distance at GVWR over the standard all S-cam brake configuration on dry pavement, and a 16% improvement at LLVW. With hybrid disc brakes, the improvements were 12% for GVWR and 19% for LLVW. For hybrid drum brakes, the improvements were 10% for both GVWR and LLVW. Margins of compliance for the minimum stopping distances (versus a 30% reduction in current standards) are shown for each brake configuration.
<div class="section abstract"><div class="htmlview paragraph">There have been many studies regarding the stability of vehicles following a sudden air loss event in a tire. Previous works have included literature reviews, full-scale vehicle testing, and computer modeling analyses. Some works have validated physics-based computer vehicle simulation models for passenger vehicles and other works have validated models for heavy commercial vehicles. This work describes a study wherein a validated vehicle dynamics computer model has been applied to extrapolate results to higher event speeds that are consistent with travel speeds on contemporary North American highways. This work applies previously validated vehicle dynamics models to study the stability of a five-axle commercial tractor-semitrailer vehicle following a sudden air loss event for a steer axle tire. Further, the work endeavors to understand the analytical tire model for tires that experience a sudden air loss. The studies discussed include executing physics-based vehicle dynamics models at speeds ranging from 88.5 kilometers per hour (55 miles per hour) up to 125.5 kilometers per hour (78 miles per hour), at various vehicle loading conditions and differing levels of velocity-dependent rolling resistance. The effects of speed and payload on vehicle response are analyzed and discussed.</div><div class="htmlview paragraph">For all the simulations in this study, a left steer axle tire sudden deflation was modeled. The results of the work revealed that after a modeled sudden air loss event, a manageable steering wheel angle would have to be input into the tractor steering system to arrest the initial yaw to the left caused by unbalanced longitudinal forces on the steer axle. The resultant initial corrective steer angle was found to be consistent with testing results and was in the range of 36 to 59 degrees steering wheel angle (SWA). As control of the tractor-semitrailer is maintained, the steering wheel angle required to hold the vehicle in a lane, steady-state, was found to be in the range of 24 to 38 degrees SWA.</div></div>
This study compares wet stopping performance of various foundation brake systems on Class VIII truck tractors. Four configurations of foundation brakes were fitted to two modern 6x4 conventional truck tractors without modification to the control, application or antilock brake systems. The foundation brakes configurations included: standard S-cam drum brakes on all six positions, high output S-cam drum and then air disc brakes on the steer axles, and air disc brakes on all six brake positions. The stopping distances from 60 mph were analyzed for all test conditions. The truck tractors were tested in two weight configurations: LLVW (i.e., bobtail) and GVWR (50,000 lb total axle weight) using an unbraked control semitrailer. Analytical analyses of wet brake-in-curve testing indicate that the hybrid brake systems (employing higher-torque brakes on the steer axle only) might degrade brake-in-curve performance. This disadvantage appeared to exist for both load conditions. Techniques are offered to normalize maximum brake-in-curve speeds evaluated over a long period of time. Analyses of variance indicate significant effects from each brake configuration change on stopping distance on a wet surface. Both truck tractors experienced a 3-8% improvement in stopping performance with the all-disc brake configuration, regardless of load. These results lead to the conclusion that mechanical properties of the air disc brake assemblies might have inherent advantages over the traditional S-cam brake in terms of cycling efficiency during ABS-assisted stops.
This paper will discuss how markings or observable anomalies on vehicle seat belt restraint systems can be classified into two categories: Those caused by collision forces, or marks and (2) those created by non-collision situations, or normal usage marks. A survey was conducted of both crash-tested and non-crash-tested vehicles in order to collect data on both categories of markings. This paper examines and analyzes the markings caused by both collision and non-collision load scenarios in order to illustrate and evaluate their unique differences as well as provide a general pattern of severity relative to different loading conditions.
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