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This paper gives a history of simulation of commercial vehicles, starting with the early models and progressing to today's multibody models. This is followed by a discussion of the key questions faced by simulators. Finally, the paper presents a new method to postprocess results through videoanimation.

The continuing increase of routinely available computing power now allows optimization with objective functions based on time domain simulations of vehicle dynamics. This paper uses this technique to determine the steering controls which lead to very large transient lateral load transfer. The vehicle simulation uses a yaw plane vehicle model with a very capable tire model. The steering controls to be optimized are a function of their Fourier coefficients. Examples using a SUV model illustrate that very inexpensive computing platforms are able to implement millions of time domain runs in a reasonably short time in support of the optimization. Comparisons with simulations of the NHSTA fishhook maneuver provide context for the results, which lead to simulated load transfer slightly in excess of the simulated NHTSA test. The optimized runs exhibit maximum load transfer well within the confines of a two lane highway.

This paper applies basic statistics to the simulation of vehicle dynamics in the time domain and the frequency domain. The methods presented here yield an expectation for the variation of the computed results as a function of variation in input parameters. Applications include important steady state measures of vehicle performance such as understeer gradient and yaw rate gain. Follow up analysis includes measures of transient response in the time domain and of amplitude and phase relationships in the frequency domain. There are several potential applications for this methodology, perhaps most important, an understanding of the consequences of parameter uncertainty on the credibility of simulated results.

Linear analysis and corresponding vehicle tests have been used since the late 1950's to help understand the directional response of automobiles and commercial vehicles. This work is now well accepted, and linear terms such as understeer gradient and response time are descriptors routinely used to characterize vehicle performance in the linear range. This paper assesses the use of various levels of complexity in linear models. It verifies that, for steady state measures such as understeer gradient, all important effects can be handled quasistatically and a two degree of freedom model is adequate. The paper then illustrates situations in which the roll degree of freedom can be important for transient calculations, and assesses the changes in calculated transient results deriving from the addition to the model of time lags in lateral tire force buildup.

It has long been recognized by vehicle dynamicists that tire properties are of utmost importance in the determination of vehicle handling. Trucks and tractor-trailers are no exception; thus, to provide a reasonable simulation of commercial vehicle handling, careful attention must be paid to the representation of the mechanics of the tire-road interface. In this paper, a newly developed simulation of commercial vehicles is discussed, with special consideration given to the modeling of the tire-road interface. Comparisons are also presented which show a high degree of correlation between commercial vehicle test data and simulation results for steady turn and braking-in-a-turn maneuvers.

Certain sections of Motor Vehicle Safety Standard 121 require that air braked commercial vehicles have the capacity to produce an average deceleration of more than 17 feet/sec2 from 60 mph to stop without prolonged wheel lockup on a surface characterized by an ASTM skid number of 75. Since commercial vehicles commonly include a wide variety of geometric and load configurations, careful steps must be taken by the manufacturer to assure conformance of each vehicle produced. Ford Motor Co. has found it useful to approach this problem with a program combining vehicle testing and computer simulation. A simple computer model is employed to select critical vehicles for subsequent testing. These vehicles serve a twofold purpose; to demonstrate empirically conformance to the stopping distance requirements of MVSS 121, and to permit correlation of a more sophisticated simulation. This more comprehensive model is then utilized to calculate the longitudinal braking performance of other vehicles.

The subject of offtracking has been considered as a low speed phenomenon, amenable to analysis via small mechanical models or straightforward calculations. This paper views offtracking from a high speed as well as a low speed vantage point. A mathematical model with one degree of freedom is used to show that there is a speed, well within the routine driving range and independent of radius, at which there will be no offtracking in a steady turn. At higher speeds the trailer will track outside the steady turn circle, and at lower speeds the trailer will track inside the steady turn circle. The analysis indicates similar behavior in a lane change maneuver - small offtracking was found to occur at the steady turn zero-off tracking speed, and larger off tracking was found to occur at both higher and lower speeds.

A new over-the-road brake dynamometer has recently been developed to measure commercial vehicle brake torque at nearly constant speed. In this paper, results are presented from the initial test program of this vehicle. The program included tests to assess the influence of initial drum temperature and rubbing velocity on brake torque, as well as the occurrence and nature of brake fade and hysteresis effects. Results of these tests indicated that the rate of energy flow into the brake system had a more significant effect on brake torque than initial temperature. Greater hysteresis was found in the S-Cam brakes than in the dual-wedge brakes.