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Technical Paper

Reconstructing Vehicle Dynamics from On-Board Event Data

These data can be used to reconstruct the behavior of a vehicle, although the accuracy of these reconstructions has not yet been quantified. Here, we evaluated various methods of reconstructing the vehicle kinematics of a 2017 and a 2018 Toyota Corolla based on Vehicle Control History (VCH) data from overlapping events generated by the pre-collision system (PCS), sudden braking (SB) and anti-lock brake (ABS) activation. ...The results of these analyses provide insights into the best methods for reconstructing vehicle kinematics from VCH data and estimates of the errors associated with different reconstruction techniques.
Technical Paper

Finite Element Analysis to Analyze the Properties of Pole Impacts

The objectives of this study were to use Finite Element (FE) simulations to predict the crush profile resulting from frontal pole impacts and to compare the results of the FE simulations to existing reconstruction methods. A 2001 Ford Taurus FE model created by the National Crash Analysis Center (NCAC) was used to simulate four pole impact tests performed by the Insurance Institute of Highway Safety (IIHS) involving the same generation of Ford Taurus.
Journal Article

Sensitivity of Collision Simulation Results to Initial Assumptions

PC-Crash simulations of staged collisions require dozens of parameters describing vehicle and impact parameters. The Collision Optimizer will vary initial speeds and impact parameters to obtain a best fit to a desired end state, but vehicle parameters are left unchanged. The present paper allows these other parameters to vary in thousands of combinations, re-optimizing the solution in each to find the relationships between the previously fixed parameters and the resulting impact speeds. The results show that tire friction and vehicle inertial properties have the most influence on impact speeds. Other parameters have little influence on the results.
Technical Paper

Estimating the Speed Change and Relative Approach Speed of Aligned Offset Impacts using CRASH3 Techniques

CRASH3 techniques are often used to reconstruct aligned offset vehicle impacts. The goal of this study was to evaluate the accuracy of the CRASH3 technique using a series of aligned staged collision with varying degrees of overlap. Five front-to-rear vehicle impacts using the same vehicle model were staged using 25, 33, 50, 75 and 100% overlap. Impact kinematics were measured using overhead high speed video. The CRASH3 coefficients and methods developed previously (SAE 2010-01-0069) were used to reconstruct the impact speed and speed changes of both vehicles based on the residual crush. Overall, the CRASH3 analysis yielded good results for the 33 to 100% overlap collisions: predicted speed changes were within 29% of the measured speed change and predicted impact speeds were within 16% of the measured impact speed.
Technical Paper

Measuring and Modeling Suspensions of Passenger Vehicles

Numerical parameters describing suspension stiffness and damping are required for 3D simulation of vehicle trajectories, but may not be available. This paper outlines a simple, portable method of measuring these properties with a coefficient of variation of 5% on stiffness. 24 of 26 vehicles tested were significantly stiffer in roll than pitch, complicating analyses with models that don't include anti-roll. Suspension parameters did not correlate with static wheel load distribution, and damping coefficient did not correlate with natural frequency. Computer simulations of the speed required to initiate rollover in an S-curve were highly sensitive to the suspension parameters used. When pre-impact tire marks and rollover distance were considered, the simulations became almost insensitive to suspension parameters.
Technical Paper

Front and Rear Car Crush Coefficients for Energy Calculations

Quantifying the energy associated with vehicle damage is the basis of common methods used to reconstruct car crashes. This study sought to characterize the relationship between crush and energy for the front and rear surfaces of a passenger car. Nine stationary barrier crash tests and one aligned car-to-car test were conducted using several cars of the same model with impact speeds ranging from 4.3 to 15.2 m/s generating as much as 0.47 m of crush. The results revealed a linear speed-crush relationship for front and rear car surfaces and a restitution coefficient that decreased from a maximum of 0.33 at low speed to a relatively constant value of 0.15 for crush levels above 0.2 m. Crush coefficients derived from the crash tests were compared to the coefficients from three other sources: i) default values from the CRASH3 computer program, ii) values from a published database and iii) values derived from an assumed damage threshold value and an NHTSA high-speed crash test.
Technical Paper

The Accuracy of Toyota Vehicle Control History Data during Autonomous Emergency Braking

Newer Toyota vehicles store information about more than 50 parameters for 5 s before and after non-collision events in the Vehicle Control History (VCH) records. The goals of this study were to assess the accuracy of VCH data acquired during Autonomous Emergency Braking (AEB) events and to investigate the effects of speed, acceleration, and system settings on AEB performance. A 2017 Toyota Corolla with Safety Sense P Pre-Collision System (PCS) was driven in a straight line towards a car-like target at different combinations of four speeds (20, 25, 30, and 40 km/h; or 12, 15, 19, and 25 mph) and three accelerator pedal positions (constant 30%, 40%, and 50% accelerator opening ratios) until the AEB system activated. The vehicle speed, vehicle acceleration, radar target closing speed, and radar target distance recorded in the VCH were compared to a reference 5th wheel. We found that errors in the VCH distance, speed, and acceleration data varied with the test conditions.
Technical Paper

Behavior of Toyota Airbag Control Modules Exposed to Low and Mid-Severity Collision Pulses

The repeatability and accuracy of front and rear speed changes reported by Toyota’s Airbag Control Modules (ACMs) have been previously characterized for low-severity collisions simulated on a linear sled. The goals of the present study are (i) to determine the accuracy and repeatability of Toyota ACMs in mid-severity crashes, and (ii) to validate the assumption that ACMs function similarly for idealized sled pulses and full-scale vehicle-to-barrier and vehicle-to-vehicle crashes. We exposed three Toyota Corollas to a series of full-scale aligned frontal and rear-end crash tests with speed changes (ΔV) of 4 to 12 km/h. We then characterized the response of another 16 isolated Toyota ACMs from three vehicle models (Corolla, Prius and Camry) and 3 generations (Gen 1, 2 and 3) using idealized sled pulses and replicated vehicle-to-vehicle and vehicle-to-barrier pulses in both frontal and rear-end crashes (ΔV = 9 to 17 km/h).
Technical Paper

On the Directionality of Rollover Damage and Abrasions

Vehicle rollovers generate complicated damage patterns as a result of multiple vehicle-to-ground contacts. The goal of this work was to isolate and characterize specific directional features in coarse- and fine-scale scratch damage generated during a rollover crash. Four rollover tests were completed using stock 2001 Chevrolet Trackers. Vehicles were decelerated and launched from a rollover test device to initiate driver's side leading rolls onto concrete and dirt surfaces. Gross vehicle damage and both macroscopic and microscopic features of the scratch damage were documented using standard and macro lenses, a stereomicroscope, and a scanning electron microscope (SEM). The most evident indicators of scratch direction, and thus roll direction, were accumulations of abraded material found at the termination points of scratch-damaged areas. Abrasive wear mechanisms caused local plastic deformation patterns that were evident on painted sheet metal surfaces as well as plastic trim pieces.
Technical Paper

Using Adjusted Force-Displacement Data to Predict the EBS of Car into Barrier Impacts

Our goal was to evaluate whether modifications to the force-displacement curves derived from a high-speed NHTSA frontal barrier test could be used to improve predictions of the equivalent barrier speed of a low-speed crash involving the same vehicle. Using an earlier iteration of the technique described here, Hunter et al. [2] showed that the F-D curves from higher-speed tests over-predicted the EBS of lower-speed tests by 21±17%. After modifying the earlier technique to account for powertrain stack-up and barrier force attenuation prior to reaching peak dynamic crush, the technique evaluated here reduced this error to 1% with a standard deviation that varied between ±9% and ±13% depending on which engine accelerometers were chosen for the adjustment. These findings suggest that the method and modifications proposed here can be used to reconstruct car crashes provided that there is a relationship between dynamic crush and residual crush.
Technical Paper

Mechanisms of Wheel Separations

Wheel separations from passenger cars, light trucks and RV’s are reviewed, and the causes are analyzed through component and full vehicle testing. Wheel separations have led to injuries from the vehicle losing control, from the separated wheel colliding with another vehicle or pedestrian, or from another vehicle maneuvering to avoid the projectile. Separations are often soon after a wheel installation. This paper describes the physical evidence often seen after a wheel separation. Interpretation of the evidence through analysis and experiment indicates a low clamping force by the wheel studs and nuts leads to nut detachment or stud fatigue fracture. A low clamping force can result from improperly tightened nuts or from a loss in clamping force due to a very small amount of wear in the mating components clamped by properly tightened studs and nuts.