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Technical Paper

Test Results: Ford PCM Downloads Compared to Instrumented Vehicle Response in High Slip Angle Turning and other Dynamic Maneuvers

An instrumented 2005 Ford Explorer was used to evaluate speed data provided from its Powertrain Control Module (PCM) at high slip angles. PCM speed was compared to speed and slip angle collected from a calibrated Datron S-400 velocity sensor. In addition to speed, slip angle and other standard handling test measurements the vehicle brake switch and throttle were recorded so PCM data could be synchronized. After each test run the vehicle ignition was turned off and the PCM was downloaded using commercially available Bosch hardware and software. The principal maneuver was the National Highway Traffic Safety Administration (NHTSA) sine-with-dwell test consisting of a 0.7 HZ sinusoidal steer with a 0.5 second dwell at the steer reversal peak. Runs were conducted with the vehicle’s Electronic Stability Control (ESC) disengaged so that the test vehicle would achieve large slip angles.
Technical Paper

Motor Vehicle Mass Property Envelopes

A vehicle may be loaded in varying configurations that affect its mass properties during normal use. These properties include total mass, center-of-gravity (Cg) location, and moments of inertia. The ranges of these parameters, which are determined by the varied load configurations, define the vehicle's mass property envelopes. These envelopes are useful for evaluating the effect of any load configuration relative to vehicle performance/design specifications. Mass property envelopes provide a clear visual representation of a range of key parameters that significantly affect motor vehicle control. Examples are provided in this paper that illustrate the usefulness of the vehicle mass property envelopes.
Technical Paper

Influence of Passenger and Cargo Load on the At Limit Handling of a Mini Van

Using analysis of a mini-van test vehicle’s static load conditions as a guide, four different vehicle loading situation were constructed. The loading situations represent the corners of the vehicle’s center of gravity position envelope. For the testing described in this paper a single vehicle under conditions of varied load was subjected to a series of test maneuvers designed to elicit objective measure and comparison of vehicle steady-state and transient response. The purpose of this paper is to describe the test method and present the results of handling testing and limit stability testing of a 1991 Ford Aerostar mini-van/extended van under four different loading conditions. Differences observed in the plotted results of vehicle steady state response for different load condition are detectable, but small. The test results demonstrate differences in vehicle transient response for different loading configuration.
Technical Paper

Evaluation of Vehicle Velocity Predictions Using the Critical Speed Formula

Tire marks left by the vehicle prior to impact, rollover, or other event, are important forensic evidence reconstruction of motor vehicle accidents. Often these tire marks have some curvature that is measured and used to calculate the speed of vehicles prior to the event. This calculation is based on the coefficient of friction of the tire/road interface and the radius of curvature of the vehicle center of gravity (c.g.) path. There is controversy about the validity of this approach. To explore this theory, a test vehicle was driven through a series of maneuvers that produced yaw marks for direct comparison of actual vehicle velocity to the velocity calculated by the critical speed formula. Test results show the critical speed formula is inaccurate for most circumstances and does not correctly describe vehicle limit performance behavior.
Technical Paper

Error Analysis of Center-of-Gravity Measurement Techniques

The height of a vehicle's center-of-gravity (CG) is one factor that influences its handling characteristics. A number of height methods are used to measure CG within the automotive industry. This research determined which method has the greatest potential to produce accurate CG height measurements, given anticipated measurement tolerances. Several techniques for measuring vehicle CG height were analyzed mathematically. The contributions of various parameters to total error were determined and the total error inherent in each method was then compared.
Technical Paper

Effects of Outrigger Design on Vehicle Dynamics

Outriggers are devices that arrest vehicle rollover during handling test maneuvers to protect the test vehicle and/or test driver. Validity of data in these tests has been questioned because the effect outriggers have on vehicle dynamics is not well understood. This research quantifies changes in handling characteristics with outriggers attached to a test vehicle. Three outrigger systems of different masses were developed and tested through various limit and sub-limit handling maneuvers. Analysis of the data generated during testing indicates improvements necessary for future outrigger designs leading to better understanding of vehicle dynamics and potentially reduced injuries from rollovers.
Journal Article

Effectiveness of Electronic Stability Control on Maintaining Yaw Stability When an SUV Has a Rear Tire Tread Separation

Electronic Stability Control (ESC) has the potential of improving yaw stability and reducing the occurrence of a crash when a vehicle experiences a rear tire tread separation. Two instrumented 4-door, RWD SUV’s equipped with ESC were tested to evaluate the effectiveness of their ESC systems on maintaining yaw stability under these circumstances. The test vehicles were evaluated with the tread and outer steel belt removed from the right rear tire. Tests were run with the ESC engaged and then repeated with the ESC disengaged. All runs were completed with the tires inflated to the manufacturer’s recommended pressure. An analysis of the data collected shows that there are significant differences in the steering input required to generate a loss of control response with and without ESC enabled. Results of Sine with Dwell testing demonstrate a significant reduction in vehicle spinout response with the ESC engaged.
Technical Paper

Comparison of Linear Variable Deceleration Rate Rollover Reconstruction to Steer-Induced Rollover Tests

A variable deceleration rate approach to rollover crash reconstruction was proposed in 2009 by Rose and Beauchamp. A detailed description of Rose and Beauchamp's method was outlined in 2010. The method used a Linearly Variable Deceleration Rate (LVDR) as a function of roll distance. Improvements in responses as a function of time was demonstrated by Rose and Beauchamp using test data from two 208 dolly rollover tests; however, they noted that additional validation work using steering-induced rollover tests would be desirable. This paper provides additional validation of the LVDR model using the steer-induced rollover test data reported in 2011 by Stevens et al. The Over-The-Ground Speed (OGS) and recorded roll rate results from the five steer-induced rollover tests reported by Stevens' in 2011 were compared to reconstructed speed and roll rates as a function of time using the 2010 Rose and Beauchamp LVDR method.