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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.

This paper examines the validation process for computer simulations of ground vehicle dynamics. Validation in this context may be defined as the process of gaining confidence that the calculations yield useful insights into the behavior of the simulated vehicle. It is our view that this process requires three separate questions to be addressed: Is the model appropriate for the vehicle and maneuver of interest? Is the simulation based on equations that faithfully replicate the model? Are the input parameters reasonable? This paper addresses each of these questions, mainly from an analytical point of view. The paper then addresses strengths and weaknesses of vehicle testing as part of the validation process.

The success of agricultural and construction machinery owes a great deal to the effective use of fluid power. Most fluid power systems are configured with a positive displacement fluid pump that is large enough to meet the flow requirements of many work circuits. Different work functions require a variety of fluid flow and pressure values to provide the desired operation. System branches, therefore, must include specialized flow and pressure regulating valves. The development of a mathematical model of a fluid flow control valve follows.

An exploratory concept for a chassis suspension system for improving the operator ride comfort of an agricultural tractor is presented in this paper. The first section of the paper describes the criteria and concepts that have been incorporated into the design of a hybrid leading and trailing arm chassis suspension system. The second section of the paper discusses the evaluation of this suspension system and its parameters by simulating nine (9) different tractor and nine (9) different tractor-plow models, derived from the various combination of suspension configurations and operator cab locations. A generalized mechanical system simulation program is utilized to predict the dynamic linear transfer function behavior of each vehicle model. With frequency domain analysis techniques and the Fast Fourier Transform (FFT) algorithm, the dynamic vehicle response to the ISO 5007 Smooth Track excitation is computed.

European and American suspension systems are described for improving the operator ride comfort on off-road vehicles. Analytical methods are then described to predict the dynamic behavior of a vehicle and human ride response criteria. The approach includes the selection of a terrain input to excite the vehicle model formulated by the generalized mechanical system simulation programs. An example involving an agricultural tractor-plow system is presented to illustrate the techniques.

Linear anaylsis is a frequently used tool to aid in the understanding of directional response. Understeer gradient, characteristic or critical speed, and yaw rate and lateral acceleration response times have been particularly helpful. This paper studies the use of these measures in the context of vehicles with four-wheel steering. The paper shows that, with only a slight change in SAE definitions, the understeer gradient retains its traditional meaning, but the characteristic speed will depend on the steering system if the steady state part of the steering control algorithm is speed sensitive. The paper also discusses testing for the understeer gradient, and the anticipated changes in response time due to four-wheel steering.

This paper presents linear first-order differential equations for a four-wheel steer vehicle which can be solved for yaw rate and sideslip angle as a function of lateral acceleration. These so-called inverse equations are useful for studying the steer angle needed to follow a given path. A root locus analysis of the inverse equations shows that the required frequencies of steer will decrease with increasing ratio of rear steer to front steer. Integration of the equations illustrates the phenomenon in the time domain. The analysis supports speculation that a driver will find it easier to track, closely to a desired path at high speeds with an appropriate ratio of rear to front steer.

The purpose of this paper is to demonstrate a computer program developed for interactive optimization of dynamic systems represented by ordinary differential equations. The program is capable of minimizing a cost function with respect to from one to five design variables. The program is command driven with on line help and has interactive graphics capability for displaying output. Three vehicle dynamics examples are used to demonstrate the capabilities of the program, and in doing so reveal some interesting vehicle handling results.

Pressure waves in hydraulic systems can cause control valves to become un-stable during operation and also contribute to vibration and noise. These undesirable pulses must be filter-filtered out or at least reduced in magnitude, in order to optimize the performance of fluid power systems and their controls. Reduction in pressure wave amplitude also reduces wear and damage to system parts [13].* The fluid pump is usually the primary source of pressure pulsations. These waves travel throughout the fluid system. Therefore, it becomes advantageous to reduce the amplitude of the pressure waves as close to the source as possible [16]. A method of reducing the pressure waves by use of a carefully selected volume in the flow line is described. A successful mathematical means of sizing the desired attenuator volume is outlined. The mathematical model can be used with any computer simulation program. Some of these are mentioned by Bowns and others [1,2,3,4,5,6,7,18,19].

A strong air/water interaction theory is used to develop a fast simplified model for the trapping of water in a film that flows over sub-grid surface roughness. The sub-grid model is used to compute correction factors that can alter mass transport within the film. The sub-grid model is integrated into a covariant film mass transport model of film flow past three-dimensional surfaces in a form that is suitable for use in aircraft icing codes. Sample calculations are presented to illustrate the application of the model.

This study attempts to establish a quantitative linkage between deployment of dynamic wireless power transfer (DWPT) and the market adoption of plug-in electric vehicles (PEV). This linkage can be useful for analyzing the societal benefits of DWPT and justifying investments in its research, development, demonstration and deployment. Spatial relationships between charging opportunity and DWPT availability are estimated for four metropolitan areas. The consumer value of DWPT is formulated as a function of key DWPT deployment parameters and then integrated into an existing validated consumer choice model, where sales of PEVs are endogenous. Results indicate significant impacts on PEV sales of DWPT deployment, even only at 0.5% of road length by 2050. Significant impact heterogeneity is observed.

Both tilt table testing and the calculation of so-called Critical Sliding Velocity (CSV) have the goal of determining conditions wherein a vehicle can be tripped by sideways impact with an obstacle and roll exactly one-quarter turn. This paper first reviews the mechanics associated with each of these metrics, verifying that (i) the tangent of the measured tilt table angle can be expected to yield a metric less than but closely related to T/2h, and (ii) CSV calculations are by and large dependent only on the vehicle's calculated cg height h and the ratio T/2h. The paper then addresses what we view to be an important related issue: How well do the mechanics of these measures and/or calculations carry over to calculations related to incidents which include more than one-quarter turn? We approach this question by extending the derivation of the CSV calculation to compute initial sideways velocities V2 needed to initiate a tripped roll of more than one-quarter turn.

Vehicle dynamics simulations typically use semi-empirical tire models. The input to these models are normal load, sideslip angle and longitudinal slip, and the output are shear forces, aligning moment, and overturning moment. Since the longitudinal speed is in the denominator of both sideslip angle and longitudinal slip, the calculation of sideslip angle and longitudinal slip at very low longitudinal velocities leads to numerical problems. This has not been a particular stumbling point in the past because vehicle dynamics calculations were largely concerned with high speed analysis. In situations wherein the vehicle was braked to a stop, patchwork techniques sufficed for calculations at low speeds. Now, however, with the advent of serious attention to driving simulators, low speed tire modelling has become more important.