Search Results

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.

Coast down testing with full-scale vehicles on level and inclined roads offers an inexpensive approach to road load determination and, in particular, aerodynamic force evaluation, provided that drag component extractions can be accurately achieved under random instrumental disturbances and biased environmental conditions. Wind tunnel testing of large vehicles, especially truck/trailers, to establish their aerodynamic drag is costly and also may produce questionable results when the effects of the moving road, blockage, wake/diffuser interaction, and rotating tires are not properly simulated. On the road, testing is now conveniently and speedily carried out using GPS-based data acquisition and file storage on laptops, allowing instantaneous on-board data processing.

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.

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.

The various forms of professional and amateur motor sports all require barriers, fences and deceleration/run-off areas for driver and spectator safety. We examine the translational and rotational kinetic energies involved for various types of race vehicles, and present some comparisons to typical energies encountered in everyday situations. Stopping distance vs. deceleration rates are also calculated, and some simplified trajectory analyses are performed for parts potentially launched during racing accidents.

The ability to categorize, compare and segregate the roll dynamical behavior of various vehicles from one another is a subject of considerable research interest. A number of comparison paradigms have been developed (static stability index, roll couple methods, etc.), but all suffer from lack of robustness: results developed on the basis of a particular comparison metric are often not able to be generalized across vehicle lines and types, etc., or they simply do not segregate vehicles at all. In addition, most models do not describe vehicle dynamics in sufficient detail, and some contain no dynamics at all (e.g., static stability index = t/2h). In the present work, static stability index, a two-degree-of-freedom roll model and a three-degree-of-freedom roll and handling model were used to locate eigenvalues for a sample of 43 vehicles consisting of (1) passenger cars, (2) light trucks, (3) sport/utility vehicles and (4) minivans.

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.

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.

This research compares the responses of a vehicle modeled in the 3D vehicle simulation program SIMON in the HVE simulation operating system against instrumented responses of a 3-axle tractor, 2-axle semi-trailer combination. The instrumented tests were previously described in SAE 2001-01-0139 and SAE 2003-01-1324 as part of a continuous research effort in the area of vehicle dynamics undertaken at the Vehicle Research and Test Center (VRTC). The vehicle inertial and mechanical parameters were measured at the University of Michigan Transportation Research Institute (UMTRI). The tire data was provided by Smithers Scientific Services, Inc. and UMTRI. The series of tests discussed herein compares the modeled and instrumented vehicle responses during quasi-steady state, steady state and transient handling maneuvers, producing lateral accelerations ranging nominally from 0.05 to 0.5 G's.

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.

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.

During the month of May, 1994, there were a total of 15 accidents at the Indianapolis Motor Speedway (IMS). Of this total, six accidents occurred during practice and/or Qualifications Attempts and nine occurred during the 78th running of the Indianapolis 500-Mile Race. All six practice accidents were analyzed through the use of videography, skidmark measurements, photographs, angle of wall impact (if a wall impact occurred), vehicle damage and yaw angle measurements. The accidents were categorized according to type and severity, mechanical failure or driver error, speed at the initiation of the accident sequence, driver injury (if injuries occurred), weather, track and traffic conditions. Race accidents were also analyzed. The study represents the continuation of a long-term program to catalog, analyze and reconstruct accidents at IMS.

Open-wheel dirt-track racing represents one of the most dangerous forms of motor racing. The potential for touching and/or interlocking of rotating wheels, combined with the frangible and rutted nature of the track surface itself, makes the occurrence of x-axis [8] rollovers routine. In addition, the rollovers themselves are usually at a high enough speed so that very violent dynamics and occupant accelerations occur. The accelerative vectors present an unusual set of challenges to the restraint systems employed. In this work, we examine a single dirt-track rollover event.

Various mechanical and electromechanical configurations have been proposed for the recapture of vehicle kinetic energy during deceleration. For example, in Formula One racing, a KERS (Kinetic Energy Recovery System) was mandated by the FIA for each racing car during the 2011 World Championship season and beyond, and many passenger car manufacturers are examining the potential for implementation of such systems or have already done so. In this work, we examine the potential energy savings benefits available with a KERS, as well as a few design considerations. Some sample calculations are provided to illustrate the concepts.

When undertaking investigations into the aerodynamic behavior of automobiles using scale models in a wind tunnel, Reynolds number dynamic equivalence is often difficult or impossible to obtain. The boundary layer transition from laminar to turbulent flow thus does not occur at a point on the model which corresponds to the transitional location on the real vehicle. To improve results obtained in such tests, roughness elements can be applied to the scale model to be tested and the transitional position of the boundary layer manipulated to correspond to the position of transition on the actual vehicle of interest. This paper describes such techniques and illustrates their use.

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.

A. brief survey of vehicle dynamics and aerodynamics papers pertinent to open wheeled racing cars is presented. In this work, the aerodynamics of Indy cars have been studied from both a lift and drag point of view. A standardized definition of lifting area for ground effects vehicles and performance observations made through the use of radar and track simulations were used. Values for negative lift magnitude were determined, lifting area was photogrammetrically measured, and a lift coefficient appropriate for Indy cars was developed. Drag area, also obtained photogrammetrically, and drag coefficients were developed. Mechanical measurements of vehicles and wind tunnel experiments were used to estimate total drag and subsequent values for drag coefficients. These values correspond with energy balance calculations based on available engine power. A sensitivity study of the performance parameters of Indy cars was performed, with emphasis on enhancing top speed.

An experimental study was performed in order to determine whether or not ABS equipped automobiles leave skidmark signatures during emergency braking. The purpose of the study was to determine the feasibility of using conventional accident reconstruction methods on ABS equipped cars. Vehicles were braked from 65 mph (105 kph) on both asphalt and brushed concrete surfaces. A 1988 BMW 325 ES, a 1989 Mazda 626, a 1989 Nissan Maxima, a 1989 Oldsmobile Touring Sedan and a 1989 Toyota Supra Turbo were used as test vehicles. A 1987 Dodge Lancer, without ABS, was tested as a control vehicle. Data taken included stopping distance, skid mark lengths and deceleration rate. Vehicle handling and skid mark visibility were also noted. The experimental program showed that ABS equipped automobiles produce no discernable skidmarks under emergency, dry pavement braking conditions.

Enthusiasts, accident reconstructionists and racing personnel have always been interested in wheel torque and HP values for vehicles. Modifications to the engine and/or driveline cause factory data to be in error, and special racing engines have no such data available in any case. Engine dynamometers provide useful information, but require the engine to be removed from the car before any testing can occur. Of more interest, particularly in competition situations, is the effect of changes at the driving wheels. We focus here on a simple method of deriving rim torque and HP values from accelerometer data. The data can be acquired using nearly any sufficiently accurate accelerometer package, and the calculations involved can be done by hand or with a spreadsheet program. Unknown vehicle characteristics can be extracted from coastdown tests. Use of a chassis dynamometer is not required.

In the scientific design of racing facilities and cars, a strong interplay exists between the aerodynamic characteristics permitted by the vehicle formula and the banking present at each track. We explore this relationship and in particular the sensitivity of various car and track combinations to changes in nominal values for banking and aerodynamic performance. Specific example calculations for NASCAR and IRL/CART vehicles and tracks are given.