Scott B. Zagorski

Control Strategies for a Roll Simulator for Recreational Off-Highway Vehicles

Control strategies for a two degree-of-freedom roll simulator are presented. The simulator consists of a sled-platform assembly that translates along rails. A Recreational Off-Highway Vehicle (ROV) is mounted on the platform, which has the freedom to rotate about a roll axis. The roll axis is nominally perpendicular to the rails and parallel to the ground plane. This can be altered by using the third degree-of-freedom (static) that yaws the platform and changes the angle of the roll axis with respect to the rails. This angle is incorporated to achieve the appropriate acceleration vector. The assembly accelerates to a desired speed via a hydraulic motor and is decelerated with a magnetic particle brake at a specified deceleration level (nominally 0.7 g). Coordination of two mechanical systems proved to be difficult due to inherent lags in both systems. The cable-drum system created many problems as tension needs to be maintained in the cable at all times. Using only knowledge of the physical system, results showed reasonable agreement with desired levels. The roll motions showed excellent correlation with the desired levels.Copyright

Braking of commercial vehicles equipped with air-disc brakes from high speed - effects on stopping distance

Due to increased speed limits at the state level, NHTSA has pursued additional testing of heavy trucks at higher test maneuver entry speeds. Test results from three vehicles, a Class 7 school bus, a Class 8 truck tractor and a Class 8 straight-truck are presented here. Results are discussed for full treadle straight-ahead stops from 60, 70 and 75 mph. Each vehicle was tested with two different brake configurations. As expected, higher entry speeds resulted in increased stopping distances. Causes for increased stopping distances are briefly discussed. Comparisons show that vehicles in the hybrid configuration (air-disc brakes on steer axle and S-cam brakes on drive axle(s)) had superior stopping performance to the vehicles equipped with traditional S-cam brakes. The vehicles in the hybrid configuration were less susceptible to increased stopping distances from higher entry speeds. A linear regression of stopping distance versus speed reinforced the benefit of placing air-disc brakes on the vehicles. In terms of reduced deceleration levels, only the S-cam configured vehicles at LLVW were adversely affected due to increased entry speeds, whereas at GVWR both S-cam and hybrid configurations were. The truck tractor, when equipped with all S-cam brakes, consistently performed the worst of the three vehicles. Finally, it was demonstrated that the vehicles exhibited an increase, not a decrease, in braking performance throughout the stop.

Modeling and Validation of a Roll Simulator for Recreational Off-Highway Vehicles

A model of a roll simulator for recreational off-highway vehicles (ROV) is presented. Models of each sub-system are described including the equations of motion, the braking, hydraulic and roll motor systems. Derivation of the equations of motion, obtained using Lagrange’s energy equation, demonstrates that they have three degrees-of-freedom (two dynamic, one static) and are coupled and highly non-linear. Results from the hydraulic sub-system illustrated that the amount of entrapped air in the system can significantly influence the response. Comparisons of the model with experimental data from the actual roll simulator showed close agreement. The greatest difference was with motor pressure. The acceleration levels and roll motions for both the model and experimental data showed excellent correlation.Copyright

The Development of a Heavy Truck ABS Model

This paper discusses the improvement of a heavy truck anti-lock brake system (ABS) model currently used by the National Highway Traffic Safety Administration (NHTSA) in conjunction with multibody vehicle dynamics software. Accurate modeling of this complex system is paramount in predicting real-world dynamics, and significant improvements in model accuracy are now possible due to recent access to ABS system data during on-track experimental testing. This paper focuses on improving an existing ABS model to accurately simulate braking under limit braking maneuvers on high and low-coefficient surfaces. To accomplish this, an ABS controller model with slip ratio and wheel acceleration thresholds was developed to handle these scenarios. The model was verified through testing of a Class VIII 6x4 straight truck. The Simulink brake system and ABS model both run simultaneously with TruckSim, with the initialization and results being acquired through Matlab. This paper provides a description of the ABS controller and TruckSim vehicle models, an analysis of the field test data, and a comparison of the simulation and field test results.

A Study of Jackknife Stability of Class VIII Vehicles with Multiple Trailers with ABS Disc/Drum Brakes

This paper presents the development of a antilock brake system (ABS) model for a double tractor-trailer combination vehicle in order to investigate the jackknife stability of these vehicles with mixed braking configurations between the tractor (disc brakes) and trailers and dolly (pneumatic drum brakes). Simulation software was used to model the ABS behavior of the vehicle and vehicle dynamics. Brake-in-turn maneuvers were performed with varying vehicle loads and surface conditions. Conditions with ABS ON for the entire vehicle (and select-high control algorithm on the trailers and dolly) found that instabilities (i.e., lane excursions and/or jackknifes) were exhibited under conditions when the surface friction coefficient was 0.3. It was demonstrated that these instabilities could be avoided while using a select-low control algorithm on the trailers and dolly. Simulation results with the ABS OFF for the tractor showed that a tractor equipped with disc brakes had greater jackknife stability. However, the vehicle left the intended path at an earlier moment in the maneuver than a vehicle equipped with drum brakes under the same simulated conditions. A comparison showed that the tractor was the least stable unit with the ABS OFF conditions, while the dolly was the least stable unit with the ABS ON conditions.

The Effects of Foundation Brake Configuration on Class-8 Tractor Dry Stopping Performance

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.

Development of a higher-order model for a roll simulator

A four degree-of-freedom model of a roll simulator is developed. The roll simulator consists of a sled-platform assembly, where a recreational off-highway vehicle (ROV) is mounted to the platform which has the freedom to rotate up to 90 degrees. The purpose of the roll simulator is to re-create rollover manoeuvres ascertained from in-field vehicle dynamic experiments. Previous studies developed a two degree-of-freedom model; one for translational and one for rotational motion. This study expands on that model and increases the number of degrees-of-freedom to more closely emulate the roll simulator. The model incorporates non-linear stiffness models of the wire ropes and enables the model to have three translational degrees-of-freedom and one rotational degree- of-freedom. The equations of motion (EOM) are numerically simulated using Matlab’s Simulink. Comparisons are made with experimental data derived from the roll simulator to validate the model.

The Effects of Foundation Brake Configuration on Class-8 Tractor Wet Stopping Performance and Stability

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.