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The (Vehicle Inertia Parameter Evaluation Rig) VIPER II is a full vehicle mass and inertia parameter measurement machine. The VIPER II expands upon the capabilities of its predecessor and is capable of measuring vehicles with a mass of up to 45,360 kg (100,000 lb), an increase in capacity of 18,100 kg (40,000 lb). The VIPER II also exceeds its predecessor in both the length and width of vehicles it can measure. The VIPER II's maximum vehicle width is 381 cm (150 in) an increase of 76 cm (30 in) and maximum distance from the vehicle CG to the outer most axle is 648 cm (255 in) an additional 152 cm (60 in) The VIPER II is capable of performing measurements including vehicle CG height, pitch, roll, and yaw moments of inertia and the roll/yaw cross product of inertia. While being able to measure both heavier and larger vehicles, the VIPER II is designed to maintain a maximum error of 3% for all inertia measurements and 1% for CG height.

This paper presents a feedback linearization control technique as applied to a Roll Simulator. The purpose of the Roll Simulator is to reproduce in-field rollovers of ROVs and study occupant kinematics in a laboratory setting. For a system with known parameters, non-linear dynamics and trajectories, the feedback linearization algorithm cancels out the non-linearities such that the closed-loop dynamics behave in a linear fashion. The control inputs are computed values that are needed to attain certain desired motions. The computed values are a form of inverse dynamics or feed-forward calculation. With increasing system eigenvalue, the controller exhibits greater response time. This, however, puts a greater demand on the translational actuator. The controller also demonstrates that it is able to compensate for and reject a disturbance in force level.

This paper describes the mechanical design of a Suspension Parameter Identification Device and Evaluation Rig (SPIDER) for wheeled military vehicles. This is a facility used to measure quasi-static suspension and steering system properties as well as tire vertical static stiffness. The machine operates by holding the vehicle body nominally fixed while hydraulic cylinders move an “axle frame” in bounce or roll under each axle being tested. The axle frame holds wheel pads (representing the ground plane) for each wheel. Specific design considerations are presented on the wheel pads and the measurement system used to measure wheel center motion. The constraints on the axle frames are in the form of a simple mechanism that allows roll and bounce motion while constraining all other motions. An overview of the design is presented along with typical results.

Vehicle dynamics models employed in heavy truck simulation often treat the semitrailer as a torsionally rigid member, assuming zero deflection along its longitudinal axis as a moment is applied to its frame. Experimental testing, however, reveals that semitrailers do twist, sometimes enough to precipitate rollover when a rigid trailer may have remained upright. Improving the model by incorporating realistic trailer roll stiffness values can improve assessment of heavy truck dynamics, as well as an increased understanding of the effectiveness of stability control systems in limit handling maneuvers. Torsional stiffness measurements were conducted by the National Highway Traffic Safety Administration (NHTSA) for eight semitrailers of different types, including different length box vans, traditional and spread axle flat beds, and a tanker.

This paper describes an experimental program of tire research used to quantify the concept of the “relaxation length” of the fully rolling, steered tire. Two methods of developing lateral force are compared for the general car with the result that a first-order differential equation is obtained from which the change is lateral force with time, or distance, as the steer angle variation is computed.

This paper describes the development of a more accurate shock absorber model in order to obtain better vehicle simulation results. Previous shock models used a single spline to represent shock force versus shock velocity curves. These models produced errors in vehicle simulations because the damper characteristics are better represented by the application of a hysteresis loop in the model. Thus, a new damper model that includes a hysteresis loop is developed using Matlab Simulink. The damper characteristics for the new model were extracted from measurements made on a shock dynamometer. The new model better represents experimental shock data. The new shock model is incorporated into two different lumped-parameter vehicle models: one is a three degree-of-freedom vehicle handling model and the other is a seven degree-of-freedom vehicle ride model. The new damper model is compared with the previous model for different shock mileages (different degrees of wear).

The paper discusses the development of a vehicle dynamics model and model validation of the 2003 Ford Expedition in CarSim. The accuracy of results obtained from simulations depends on the realism of the model which in turn depends on the measured data used to define the model parameters. The paper describes the tests used to measure the vehicle data and also gives a detailed account of the methodology used to determine parameters for the CarSim Ford Expedition model. The vehicle model was validated by comparing simulation results with experimental testing. Bounce and Roll tests in CarSim were used to validate the suspension and steering kinematics and compliances. Field test data of the Sine with Dwell maneuver was used for the vehicle model validation. The paper also discusses the development of a functional electronic stability control system and its effect on vehicle handling response in the Sine with Dwell maneuver.

In 2007, a software model of a Roll Stability Control (RSC) system was developed based on test data for a Volvo tractor at NHTSA's Vehicle Research and Test Center (VRTC). This model was designed to simulate the RSC performance of a commercially available Electronic Stability Control (ESC) system. The RSC model was developed in Simulink and integrated with the available braking model (TruckSim) for the truck. The Simulink models were run in parallel with the vehicle dynamics model of a truck in TruckSim. The complete vehicle model including the RSC system model is used to simulate the behavior of the actual truck and determine the capability of the RSC system in preventing rollovers under different conditions. Several simulations were performed to study the behavior of the model developed and to compare its performance with that of an actual test vehicle equipped with RSC.

Validation was performed on an existing heavy truck vehicle dynamics computer model with roll stability control (RSC). The first stage in this validation was to compare the response of the simulated tractor to that of the experimental tractor. By looking at the steady-state gains of the tractor, adjustments were made to the model to more closely match the experimental results. These adjustments included suspension and steering compliances, as well as auxiliary roll moment modifications. Once the validation of the truck tractor was completed for the current configuration, the existing 53-foot box trailer model was added to the vehicle model. The next stage in experimental validation for the current tractor-trailer model was to incorporate suspension compliances and modify the auxiliary roll stiffness to more closely model the experimental response of the vehicle. The final validation stage was to implement some minor modifications to the existing RSC model.

This paper presents the results of an in-depth study of the measurement of occupant kinematic response on the S-E-A Roll Simulator. This roll simulator was built to provide an accurate and repeatable test procedure for the evaluation of occupant protection and restraint systems during roll events within a variety of occupant compartments. In the present work this roll simulator was utilized for minimum-energy, or threshold type, rollover events of recreational off-highway vehicles (ROVs). Input profiles for these tests were obtained through a separate study involving autonomous full vehicle tests [1]. During simulated roll events anthropomorphic test device (ATD) responses were measured using on-board high speed video, an optical three-dimensional motion capture system (OCMS) and an array of string potentiometers.

This paper will illustrate the development of the modeling of rollover sequences. During the past few years, a lot of research has been focused on the rollover propensity of vehicles. As to what happens after the vehicle rolls over, attention is only paid to occupant kinematics and occupant injury. Some simple questions such as how many rolls in the rollover are not answered unless a rollover test is run. The rollover sequences including roll number, roll speed and roll distance are very important to the accident reconstructionists as well as design engineers. Since the cost for running a rollover test is so high today, it is very economic and time-efficient to obtain the preliminary results from a mathematical model. Roll number and roll distance versus time are to be obtained through the mathematical model which is based on several rollover tests, vehicle inertia parameters, and the Coulomb friction, a non-linear term in the equation.

The handling, stability, and rollover resistance of vehicles is presently being studied by both the automotive industry and the National Highway and Traffic Safety Administration (NHTSA). However, to study the handling and rollover behavior of each vehicle on the road is not feasible. The ability to categorize and compare the rollover and handling behavior of various vehicles is a subject of considerable research interest. This paper examines the possibility of characterizing vehicle classes through the use of a three degree-of-freedom linear model. Initially, segregation is studied by evaluating the eigenvalue location in the complex domain for vehicle sideslip velocity, yaw rate, and roll angle. Then the influence of numerator dynamics on vehicle behavior is studied and vehicle class segregation is attempted through evaluation of the amplitude ratio of the frequency responses for sideslip velocity, yaw rate, and roll angle.

This paper describes the design of a vehicle inertia measurement facility (VIMF): a facility used to measure vehicle center of gravity position; vehicle roll, pitch, and yaw mass moments of inertia; and 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 in conjunction with the error analyses to design various VIMF components, such as the roll and yaw spring sizes.

This paper presents a method of measuring a vehicle's sprung mass without vehicle disassembly. The method involves measuring whole vehicle properties at different trim heights. The accuracy of the method is tested using results for several vehicles. As an extension of the sprung mass determination, this paper also demonstrates the feasibility of determining the inertial properties of a vehicle's sprung mass without vehicle disassembly. Lastly, measured vehicle roll/yaw product of inertia values are presented for a selection of vehicles.

The intent of this research is to understand the effects worn dampers have on vehicle stability and safety through dynamic model simulation. Dampers, an integral component of a vehicle's suspension system, play an important role in isolating road disturbances from the driver by controlling the motions of the sprung and unsprung masses. This paper will show that a decrease in damping leads to excessive body motions and a potentially unstable vehicle. The concept of poor damping affecting vehicle stability is well established through linear models. The next step is to extend this concept for non-linear models. This is accomplished through creating a vehicle simulation model and executing several driving maneuvers with various damper characteristics. The damper models used in this study are based on splines representing peak force versus velocity relationships.

Kinetic Pty Ltd and Tenneco Automotive have developed a passive suspension system called a Kinetic system. The motivation for the design of the system is discussed, and the function of the system is explained. The system improves handling, stability, and ride by passively decoupling roll stiffness from articulation stiffness and roll damping from bounce damping. Improved stability is evaluated by conducting NHTSA's Roll Rate Feedback Fishhook tests on a small SUV equipped with the Kinetic system. Results of the testing are presented, and benefits to rollover are discussed.

Seat belt usage in the United States is increasing dramatically, due in part to legislative action. In addition, education programs have improved public awareness of the need for automotive restraints in achieving crash survival and injury reduction. The safety consciousness level of automobile passengers is particularly strong among pregnant women. It is reasonable to expect wider use of seat belts by expectant mothers due to this acute attention to safety. The literature demonstrates that incorrect usage of seat belts is a cause of injury. This can be especially applicable during pregnancy when changes in anatomy dictate a change in belt positioning, Review of the literature shows that the technical issues associated with the use of current production belt restraint systems by pregnant women has not been addressed.

Representative vehicle inertial characteristics are important parameters for the development of motor vehicles and the proper operation of on-board systems. The Vehicle Inertia Measurement Facility (VIMF) measures vehicle center of gravity location, principal moments of inertia, and the roll/yaw product of inertia. It is important to understand the VIMF’s accuracy and repeatability, as well as the underlying methodology and assumptions, when performing tests or using the results of the test. This study reports on a repeatability analysis performed at the lower and upper limits of the VIMF. Each test performed is a complete drive-on/drive-off test. The test sequence involves the repeatability evaluation of several different machine configurations. Ten complete tests are performed for each vehicle. To better address the possibility of measurement bias, the design and verification of a calibration fixture for inertial characteristics is presented.

This paper describes a new laboratory test facility for measuring suspension parameters that affect rollover. The Side-Pull mechanism rolls the test vehicle through a cable attached rigidly at its center of gravity (CG). Changes in wheel camber and wheel steer angles are measured as a function of body roll angle. The roll test simulates a steady-state cornering. Thus, both compliance and kinematic forces are fed simultaneously to the vehicle as they would be applied in a real cornering situation. The lateral load transfer, and roll angle as a function of simulated lateral acceleration is determined. The Side-Pull Roll Measurement has advantages over the conventional roll tests where the rolling force couple is applied vertically. The Side-Pull mechanism rolls the vehicle in a unrestricted way with horizontal forces applied at the tire / pad contact and the CG location. Thus, the measurements take into account coupling of compliance with roll.

The paper discusses the development of a model of the 2003 Ford Expedition using ADAMS View and its validation with experimental data. The front and rear suspensions are independent double A-arm type suspensions modeled using rigid links and ideal joints. The suspension springs and shock absorbers are modeled as force elements. The plots comparing the experimental tests and the simulation results are shown in this paper. Quasi-static roll and bounce tests are used to validate the suspension characteristics of the model while the Sine with Dwell and Slowly Increasing Steer maneuvers are used to validate the vehicle handling and tire-road interaction characteristics of the model. This paper also details the incorporation of an ESC model, originally developed by Kinjawadekar et al. [2] for CarSim, with the ADAMS model. The ESC is modeled in Simulink and co-simulated with the ADAMS vehicle model. Plots validating the ESC model with experimental data are also included.