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Technical Paper

Passenger Car Handling Characteristics Associated with Space-Saver Spare Tires

Space-saver spare tires have become near-standard equipment in passenger cars, replacing full-size spares. The properties of space-saver spare tires (cornering stiffness, self-aligning torque, etc.) exhibit some differences when compared to standard size tires. We examine potential handling changes when a space-saver tire is installed on the vehicle by examining steady-state behavior, initial step steering response, and vehicle understeer gradient as functions of the mounting location of the space-saver tire (front or rear axle). Results show that space-saver spare tires perform well and are quite capable in low-ay, linear handling maneuvers.
Technical Paper

Modeling Cruise Control Initiated Wheelspin in Rear Wheel Drive Vehicles

There are driving situations in which a rear-wheel-drive vehicle, operating with an active closed-loop cruise control, can experience wheelspin and a subsequent oversteer/loss of control. The situations involve low-μ surfaces (ice), weather-related phenomenon (rear-wheel hydroplaning), slope-climbing or a combination of these external effects. Although traction control and stability control, depending on the sophistication of the system, can negate many of these situations, the active fleet contains many vehicles not equipped with these features. In the present work, we calculate the conditions under which cruise-control-initiated rear wheel spin can occur.
Technical Paper

Mathematical Analysis of Tire Delamination & Rupture Failures

We examine the characteristics, properties and potential idealized delamination failure modes of tires in this work. Calculations regarding tire failure stresses during tire failure scenarios, as well as during normal operation, are made. The calculations, though idealized, indicate that large chassis loads can result from the idealized failures.
Technical Paper

Vehicle Dynamics Simulation Associated with Pothole Encounters Using the HVE SIMON Program and Radial Spring Tire Model

Deteriorated roadway surfaces (potholes) encountered under everyday driving conditions may produce external vehicle disturbance inputs that are both destabilizing and highly transient. We examine vehicle behavior in response to such inputs through simulation. Idealized pothole geometry configurations are used to represent deteriorated roadway surfaces, and as environments in the HVE simulation suite of programs. Differences in vehicle response and behavior are cataloged, and the potential for destabilized vehicle behavior is examined, particularly under conditions in which only one side of the vehicle contracts the pothole. Vehicle types used in the simulation ensemble represent three classes of vehicles: a sedan, a sports car and an SUV. Results show that many combinations of vehicle speed, vehicle type and pothole configuration have essentially no destabilizing effects on the vehicle trajectory.
Technical Paper

Simulation of Transient Maneuver Hydroplaning Events Using HVE

Recent research into the phenomenon of tire hydroplaning has concentrated on the effects of possible path clearing of the rear tires by the front tires. When this occurs, the rear tire behavior and hydroplaning properties will be different from what would occur had the tire been running in an undisturbed flow field. In the present work, we modify rear tire properties to simulate the path clearing effect and utilize the SIMON/HVE suite of simulation programs with a standardized double lane change maneuver to examine path clearing potential during transient vehicle behavior.
Technical Paper

Potential for Hydroplaning Behavior during Transient Maneuvers

Recent research on the effects of tire hydroplaning has examined the hydroplaning phenomenon and its potential effects on vehicle maneuvering from (1) geometric, (2) straight line braking/acceleration and (3) steady-state cornering maneuver points of view. In this work, we focus on the potential for hydroplaning during a transient maneuver: a standardized double lane change maneuver (ISO3888-1). Using both closed-form calculations and the HVE software suite, it is shown that partial hydroplaning has only a small-to- moderate potential to occur during portions of such maneuvers, but is not likely throughout the entire duration of the maneuver.
Technical Paper

Calculating Tire Overlap during Steady-State Cornering Maneuvers

Vehicles running in wet conditions may experience hydroplaning of one or more tires. Hydroplaning can, and often does, change vehicle braking, acceleration and handling characteristics dramatically. Proper analysis of this behavior requires accommodating the clearing of paths for the rear tires that may result from the front tires engaging the water-coated surface first. In this work, tire overlap is calculated for vehicles in steady-state cornering maneuvers for generalized vehicle dimensions and tire characteristics.
Technical Paper

Experimental Measurements of the Effect of Path Clearing on Hydroplaning Behavior

Vehicles operating in wet conditions may experience hydroplaning of one or more tires. Proper analysis of this behavior requires accommodating the clearing of paths for the rear tires that may result from the front tires engaging the water coated surface first. An experimental program was developed to study tire/road behavior during straight line braking maneuvers on a wet surface. Wheel rpm values were measured with operating ABS via CAN bus data. The experiments allowed qualitative estimation and visualization of the effects of path clearing on rear tires.
Journal Article

Hydroplaning Behavior during Steady- State Cornering Maneuvers

Vehicles running in wet conditions may experience hydroplaning of one or more tires. Hydroplaning can, and often does, change vehicle braking, acceleration and handling characteristics dramatically. Proper analysis of this behavior requires accommodating the clearing of paths for the rear tires that may result from the front tires engaging the water-coated surface first. In this work, a hydroplaning analysis is presented that examines steady-state cornering under potential hydroplaning situations and includes lateral weight transfer, tire load sensitivity and path clearing potential. The sensitivity of vehicle understeer/oversteer characteristics to path clearing and vehicle dimensional characteristics is also examined.
Technical Paper

Controlled Braking Experiments with and without ABS

An experimental program to measure braking characteristics developed under emergency braking conditions by ABS-equipped vehicles was designed and performed. Variables examined included initial braking speed, vehicle type, tire pressure and data recording equipment utilized. All experiments were conducted on a closed airport taxiway constructed of sharp, brushed and heavily striated concrete. Tests were conducted with and without activated ABS systems on the test vehicles. Results showed that (1) with the ABS activated, faint roadway markings were visible only under a very few special circumstances, (2) tire/road μ-values and corresponding deceleration values varied only slightly for differing speeds and ABS conditions, (3) tire pressure made little difference in limited test results, and (4) there were differences in recorded results depending on the equipment used for data acquisition.
Technical Paper

Soft Walls for Racetrack Barriers through the Use of Slatted Wall Design: A Conceptual First Analysis

For a number of years, racetrack designers have been considering various designs for energy-absorbing or “soft” walls. Moving walls, water-filled barrels, tire walls and walls coated with various materials have all been suggested or employed to varying degrees of success. In this paper, a new concept involving a series of slats placed outward from the walls is outlined. First, fundamental requirements for a soft wall design are laid down. Then the development of the slatted wall is presented, along with a series of design variables able to be adjusted for particular applications. The slats have multiple modes of energy dissipation and absorption, and calculations show that the concept has good promise. Evaluation of various design alternatives can be largely done computationally, rather than experimentally, a great advantage given the expense of full-scale barrier testing.
Technical Paper

Potential for a Ground-Effects Top Fuel Dragster

The current performance of a top fuel (T/F) dragster racing car is very high. The cars can accelerate from a standing start to well over 330 mph (528 km/h) in < 4.6 seconds! The engine of a T/F dragster can make considerably more power than can be put down to the track surface. Intentional clutch slippage prevents wheelspin for most of the ¼-mile (0.4 km) standard length racing run. Even though the drive tires used are highly specialized and specifically designed for this type of racing environment, more traction is needed. To create more traction, especially during the second ½ of the run, external wings have been employed by the designers of such cars. The size and configuration of the wings is limited according to sanctioning rules. Recent wing failures and accidents have made other options for the creation of downforce appear attractive. In the present work, we consider the potential for using the shape of the car itself to create the required down-force.
Technical Paper

Oversteer/Understeer Characteristics of a Locked Differential

The type of differential used in a vehicle has an important and often-neglected effect on handling performance. This is particularly important in racing applications, such as in IndyCar racing, in which the type of differential chosen depends on the course being raced (superspeedway ovals, short ovals, temporary street courses and permanent road courses). In the present work, we examine the effect of a locked rear differential on oversteer/understeer behavior. Using a linear tire model, it is shown that employing a locked differential adds a constant understeer offset to the steering wheel angle (SWA) -v- lateral acceleration vehicle signature. A computer simulation of steady-state cornering behavior showed that the actual effect is much more complicated, and is strongly influenced by static weight distribution, front/rear roll couple distribution, available traction and the radius of the turn being negotiated.
Technical Paper

Evasive Maneuver Capability Without and In the Presence of a Flat Tire

The relatively fragile nature of racing tires, coupled with the inevitable track debris which results from racing accidents, ensures that racing drivers will routinely experience conditions involving flat tire vehicle dynamics. We define flat tire vehicle dynamics as a situation which requires the driver to provide steering and/or braking and acceleration control while the vehicle is running on one or more tires which have dramatically reduced tire pressure. In the present work, we simulate the handling and braking vehicle dynamics which occur in the presence of a single flat tire on the vehicle. The flat tire was simulated via drastically reduced cornering stiffness, partially reduced limiting frictional capability and increased rolling resistance, and was alternatively simulated on both the front and rear axle. No simulations were conducted with more than a single flat tire because multiple tire failures which do not involve an actual accident contact and/or damage are rare.
Technical Paper

Dynamics of Four-Wheel-Steer Off-Highway Vehicles

Off road vehicle dynamics present fundamental differences to the engineer than those of highway vehicles. In this work, we examine off-road dynamics for a class of industrial vehicles: front-end loaders. After a review of terramechanics and off-road tire behavior, equations of motion for a front-end loader are developed. Kinematic steering relationships, steady-state performance and understeer and oversteer characteristics are also derived. Off-road front-end loader characteristics and performance in terms of vehicle handling, overturn behavior and obstacle avoidance are presented, and some design characteristics and parameter values for a typical vehicle are given to aid the designer in analysis and synthesis.
Technical Paper

Post-Impact Spin, 1968-1993

In the reconstruction of initial speeds from the evidence available in the aftermath of an impact, if there was appreciable post-impact spin, the effect of that spin on the deceleration of the vehicle should be taken into account. This task was first studied in Germany in 1968, when Marquard published values of two useful correction factors from forward calculations of 3 spins to rest. This landmark German study was extended in the United States in 1975, when McHenry fitted polynomials to the values of five correction factors computed for 18 spins simulated with the just-completed SMAC program. These polynomials were used within the computerized reconstruction program CRASH. However, the individual data points were never published; and since 1975, no further quantitative treatment of post-spin reconstruction has been published. Further studies now have been performed using a verified proprietary version of SMAC, for the same family of 18 spins.
Technical Paper

Moments of Inertia of Mounted and Unmounted Passenger Car and Motorcycle Tires

The mass moments of inertia of 44 mounted and unmounted passenger, racing and motorcycle tires were measured about the spin axis. In addition, for some of the unmounted tires, mass moment of inertia about an axis perpendicular to the spin axis was also measured. Simplistic models for calculation of tire mass moment of inertia were developed, and may be adequate if only approximate results are required. Following measurement of inertias using a torsional pendulum technique, linear correlation of inertia values with tire weight and diameter was performed. A simple pair of linear correlation equations (one for mounted tires, one for unmounted tires) gives highly accurate values for mass moment of inertia about the tire spin axis. Finally, a rule of thumb expression for estimating moment of inertia about a vertical axis was also developed.
Technical Paper

Controllability and Stability Aspects of Actively Controlled 4WS Vehicles

Four wheel steering (4WS) of passenger cars has become a topic of interest in recent vehicle dynamics literature. In the present work, a linear two-degree of freedom model (L2DF) has been used to examine controllability and stability aspects of various 4WS algorithms. Yaw rate r and lateral velocity v were used as model degrees of freedom, and as state feedback variables for the implementation of 4WS controllers of various types. With controllers developed using the L2DF model, investigations were performed into the performance of such controllers when implemented using a nonlinear three-degree of freedom model (N3DF) which included roll and the possibility of tire saturation. Desirable steady-state properties for v and r can be obtained using the robust controllers developed through the use of the L2DF model. Finally, the stability of the system is shown to depend upon tire cornering stiffness, and is examined both qualitatively and quantitatively.