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Technical Paper

Measuring and Modeling Suspensions of Passenger Vehicles

2013-04-08
2013-01-0774
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

Post-Impact Dynamics for Vehicles with a High Yaw Velocity

2016-04-05
2016-01-1470
Calculating the speed of a yawing and braked vehicle often requires an estimate of the vehicle deceleration. During a steering induced yaw, the rotational velocity of the vehicle will typically be small enough that it will not make up a significant portion of the vehicle’s energy. However, when a yaw is impact induced and the resulting yaw velocity is high, the rotational component of the vehicle’s kinetic energy can be significant relative to the translational component. In such cases, the rotational velocity can have a meaningful effect on the deceleration, since there is additional energy that needs dissipated and since the vehicle tires can travel a substantially different distance than the vehicle center of gravity. In addition to the effects of rotational energy on the deceleration, high yaw velocities can also cause steering angles to develop at the front tires. This too can affect the deceleration since it will influence the slip angles at the front tires.
Technical Paper

Tire Models for Vehicle Dynamic Simulation and Accident Reconstruction

2009-04-20
2009-01-0102
Various vehicle dynamic simulation software programs have been developed for use in reconstructing accidents. Typically these are used to analyze and reconstruct preimpact and postimpact vehicle motion. These simulation programs range from proprietary programs to commercially available packages. While the basic theory behind these simulations is Newton's laws of motion, some component modeling techniques differ from one program to another. This is particularly true of the modeling of tire force mechanics. Since tire forces control the vehicle motion predicted by a simulation, the tire mechanics model is a critical feature in simulation use, performance and accuracy. This is particularly true for accident reconstruction applications where vehicle motions can occur over wide ranging kinematic wheel conditions. Therefore a thorough understanding of the nature of tire forces is a necessary aspect of the proper formulation and use of a vehicle dynamics program.
Technical Paper

Comparisons of Devices for Measuring Acceleration vs. Time in Braking Tests

2008-04-14
2008-01-0180
The coefficient of friction between a vehicle's tires and the roadway is a key parameter in any accident reconstruction. With the proliferation of vehicle dynamics software, it is often important to have more details regarding the tires interaction with the road than simply the average deceleration rate. Devices which can provide the peak friction as the braking develops, along with the average deceleration during the fully developed sliding phase, are necessary. There are now products widely available to the accident reconstruction market which provides these parameters as well as detailed acceleration vs. time curves. The following products capable of providing these results were tested: Accelerex, Vericom VC3000, and two general purpose accelerometers made by Silicon Designs and Dimension Engineering. Tests were conducted on wet and dry asphalt surfaces using a variety of passenger vehicles and transit buses which confirmed the agreement between these devices.
Technical Paper

Empirical Testing of Vehicular Rotational Motion

2012-04-16
2012-01-0602
Vehicles often rotate during traffic collisions due to impact forces or excessive steering maneuvers. In analyzing these situations, accident reconstructionists need to apply accurate deceleration rates for vehicles that are both rotating and translating to a final resting position. Determining a proper rate of deceleration is a challenging but critical step in calculating energy or momentum-based solutions for analytical purposes. In this research, multiple empirical tests were performed using an instrumented vehicle that was subjected to induced rotational maneuvers. A Ford Crown Victoria passenger car was equipped with a modified brake system where selected wheels could be isolated. The tests were performed on a dry asphalt surface at speeds of approximately 50 mph. In each of the tests, the vehicle rotated approximately 180 degrees with the wheels on one side being completely locked.
Technical Paper

SMASH – Program for Car Accident Simulation

2000-03-06
2000-01-0848
In the paper SMASH - a computer program for road accident simulation is presented. Besides the logic of the program the models of vehicle, tire and crash itself are analyzed briefly. Data and diagrams showing the comparison between SMASH results and actual tests data are presented.
Technical Paper

Uncertainty in Calculations Using Lambourn's Critical Speed Procedure

2013-04-08
2013-01-0779
Critical Speed Formula (CSF) belongs to the canon of tools used in reconstruction of vehicle accidents. It is used to calculate vehicle speed at the beginning of tire yaw marks and, together with the entire methodology of processing the information contained in the marks into the data, is often referred to as the Critical Speed Method (CSM). Its great practical importance as well as recurring doubts as to the reliability make it one of the best experimentally and theoretically studied methods. Although the CSF applies in fact to a point mass, it is used with reference to a vehicle, i.e., an increasingly complicated multi-body system. Accident reconstruction experts point out the particular usefulness of Lambourn's research concerning the CSM in respect to a passenger car.
Technical Paper

Computer Simulation of Steer-Induced Rollover Events Via SIMON

2011-04-12
2011-01-1122
This study examines through computer simulation the reconstruction of on-road vehicle rollover accidents induced by a driver steering maneuver. The three-dimensional vehicle dynamics software package SIMON is used to model a set of four test vehicles as six degree-of-freedom sprung masses with up to five degrees-of-freedom for each unsprung mass. The performance of the simulator's physics model, in the context of accident reconstruction, is evaluated through correlation with full-scale vehicle rollover tests. Of specific interest to this study was simulation of the trip phase of the vehicle's motion. The correlation parameters include vehicle trajectory, speed, heading angle, yaw rate, roll angle, roll rate and lateral acceleration. SIMON's capacity to accurately model the physics of a test vehicle's suspension and tire kinetics in the pre-trip and trip phases of motion is evaluated by modeling a set of four instrumented full-scale tests of steering-induced rollovers.
Technical Paper

Determination of Critical Speed, Slip Angle and Longitudinal Wheel Slip based on Yaw Marks Left by a Wheel with Zero Tire Pressure

2016-04-05
2016-01-1480
This article presents the results of an analysis of the yaw marks left by a car with normal pressure in all tires and then normal pressure in three tires and zero in one rear tire. The analysis is a continuation of research on influence of reduced tire pressure on car lateral dynamics in a passing maneuver, discussed in the SAE paper No. 2014-01-0466. Preliminary analysis of yaw marks has shown, that a wheel with zero pressure deposits a yaw mark whose geometry differs from the yaw mark made by a wheel with normal pressure based on which we could calculate: critical speed, slip angle and longitudinal wheel slip. The aim of the presented research was to analyze the yaw marks left by car with zero pressure in one rear wheel in order to check the possibility of determining the vehicle critical speed, slip angle and longitudinal wheel slip. It was reached by performing bench and road tests during which the vehicle motion parameters were recorded using GPS Data Logging System.
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