Nicholas J. Durisek

The Design of a Vehicle Inertia Measurement Facility

This paper describes the design of a vehicle inertia measurement facility (VIMF) used to measure: (1) vehicle center of gravity position; (2) vehicle roll, pitch, and yaw mass moments of inertia; and (3) vehicle roll/yaw mass product of inertia. The rationale for general design decisions and the methods used to arrive at the decisions are discussed. The design is inspired by the desire to have minimal measurement error and short test time. The design was guided by analytical error analyses of the contributions of individual system errors to the overall measurement error. A National Highway Traffic Safety Administration (NHTSA) database of center of gravity position and mass moment of inertia data for over 300 vehicles was used. This database was used in conjunction with the error analyses to design various VIMF components such as the roll and yaw spring sizes. This provides for a design that yields good experimental repeatability for the full range of lightvehicles that can be tested on the VIMF. The paper also discusses aspects of the VIMF software, for example: (a) the analytical curve fitting; and (b) the error checking of results. Results from the VIMF for two calibration fixtures are presented and compared to the computed center of gravity position and inertia values. For the covering abstract of the conference see IRRD 875861.

An Analysis of Yaw Inducing Drag Forces Imparted During Tire Tread Belt Detachments

In this study, tests were performed to understand the effects of asymmetric longitudinal forces on vehicle response which may be created in certain staged partial tire tread belt detachment tests. In a very small number of tests performed by others, tires cut to simulate partial tire tread belt detachments created longitudinal drag forces at the separating tire that induced substantial vehicle yaw. This drag force and yaw response are independent of vehicle type and suspension type; they are created by the separating tire tread interacting with the road surface and/or vehicle. Similar yaw inducing drag forces are further demonstrated by applying braking to only the right rear wheel location of an instrumented test vehicle. It is shown that vehicle yaw response results from this longitudinal force as opposed to vertical axle motion.

DEVELOPMENTS IN VEHICLE CENTER OF GRAVITY AND INERTIAL PARAMETER ESTIMATION AND MEASUREMENT

For some vehicle dynamics applications, an estimate of a vehicless center of gravity (cg) height and mass moments of inertia can suffice. For other applications, such as vehicle models and vehicle simulations used for vehicle development, these values should be as accurate as possible. This paper presents several topics related to inertial parameter estimation and measurement. The first is a simple but reliable method of estimating vehicle mass moment of inertia values from data such as the cg height, roof height, track width, and other easily measurable values of any light road vehicle. The second is an error analysis showing the effect, during a simple static cg height test, of vehicle motion on the vehicles calculated cg height. The third topic is a method of measuring the ratio of the sprung mass to the unsprung mass of any light vehicle without disassembly. Knowledge of this ratio is also important for vehicle development. For the covering abstract of the conference see IRRD 882390.

Delta-V, Barrier Equivalent Velocity and Acceleration Pulse of a Vehicle During an Impact

Delta-V and barrier equivalent velocity (BEV) are both terms used to describe some physical change in the vehicle state before an impact as compared to after an impact. Delta-V describes the change in the vehicle velocity vector from just before the impact until just after the impact, while BEV attempts to quantify the energy required to cause the damage associated with an impact. In order to understand what happens to a vehicle and its occupants during an impact, the acceleration pulse undergone by the vehicle during the impact must be examined. The acceleration pulse describes how the Delta-V occurs as a function of time, and is related with the deformation of the vehicle as well as the object contacted by the vehicle during an impact. While Delta-V and BEV are often used to describe the thresholds at which a passive restraint system will function, it is the acceleration pulse that the sensors of a restraint system measure, and that ultimately determines if, when and how passive vehicle restraints will be deployed in an impact. This paper examines this issue and presents vehicle acceleration pulses for several types of impacts. Findings show that the shape and duration of the acceleration pulse experienced by a vehicle in an impact can be affected by many variables, including the structure of the vehicle, the stiffness of the object impacted, and the location of the impact.

Vehicle Characterization Through Pole Impact Testing, Part I: Vehicle Response in Terms of Acceleration Pulses

The shape of an acceleration pulse in an impact is not only affected by the change in velocity, but also by the geometry and stiffness of the both the striking vehicle and the struck object. In this paper, the frontal crash performance of a full-size pickup is studied through a series of impact tests with a rigid pole and with a flat barrier. Each rigid pole test is conducted at one of four locations across the front of the vehicle and at impact speeds of 10 mph, 20 mph, or 30 mph. The flat barrier tests are conducted at 10 mph, 15 mph, 20 mph, and 30 mph. The vehicle crush and acceleration pulses resulting from the pole tests are compared to those resulting from the barrier tests. The severity of pole impacts and the severity of flat barrier impacts are compared based on peak accelerations and pulse durations of the occupant compartment.

Vehicle Characterization Through Pole Impact Testing, Part II: Analysis of Center and Offset Center Impacts

This paper addresses the vehicle acceleration and crush characteristics for frontal pole impacts with body-on-frame vehicles. The frontal impact response of a full-sized pickup to 10 mph and 20 mph pole impacts at the centerline and at a location nearer the frame rails is compared using the acceleration pulse shape, the average acceleration in the occupant compartment, and the residual crush. A bilinear curve relating impact speed to residual crush is developed. The vehicle center pole impact response at 30 mph is compared for the same make pickup truck with different engine configurations (V6 and V8). An equivalent energy analysis also is presented that uses the results from the 30 mph center pole tests to estimate the speed of lower speed impacts. Results showed that vehicle response between center and offset center pole impacts was similar. The crush profiles and relationship of maximum crush and impact speed also were similar between the center pole and offset center pole impacts. Bilinear curves derived from center pole impact tests were shown to be useful in estimating impact speeds for offset center pole impacts. Although the 30 mph center pole impact response of the vehicle was similar for both engine configurations, differences did exist in the vehicle response as a result of the difference in distance between the front of the engine and the front bumper. The equivalent energy analysis estimated impact speeds higher than the test impact speeds for the 10 mph tests. For the 20 mph test estimates, it was shown that if the engine is engaged, the equivalent energy analysis should be applied to vehicles with the same engine configuration. A reasonable range for the impact speed was estimated in the 30 mph center pole tests with the V8 engine.

A STUDY OF VEHICLE CLASS SEGREGATION USING LINEAR HANDLING MODELS

This paper examines the possibility of characterizing vehicle classes through the use of a three degree-of-freedom linear model. Segregation is studied by evaluating the eigenvalue location in the complex domain for vehicle sideslip velocity, yaw rate, and roll angle. The influence of numerator dynamics on vehicle behaviour is studied. Vehicle class segregation is attempted through evaluation of the amplitude ratio of the frequency responses for sideslip velocity, yaw rate, and roll angle. Limited ability to definitively segregate vehicles into classes is found to exist. For the covering abstract of the conference see IRRD 875861.