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The US Army uses a light tactical High-Mobility Multi-Purpose Wheeled Vehicle (HMMWV) which, due to the amount of armor added, requires air conditioning to keep its occupants comfortable. The current system uses R134a in a dual evaporator, remote-mounted condenser, engine-driven compressor system. This vehicle has been adapted to use an environmentally friendly refrigerant (carbon dioxide) to provide performance, efficiency, comfort and logistical benefits to the Army. The unusual thermal heat management issues and the fact that the vehicle is required to operate under extreme ambient conditions have made the project extremely challenging. This paper is a continuation of work presented at the SAE Alternate Refrigerants Symposium held in Phoenix last June [1].

Using a three-degree-of-freedom vehicle model (side-slip, yaw and roll degrees of freedom) and a nonlinear, saturating rire model, the behavior of a typical exemplar vehicle (1986 Dodge Lancer Turbo) was simulated. Steady state performance was examined through simulating a skidpad lateral accelerarion maneuver. A lane change maneuver was used to reprcsenr transient performance characteristics. A few simple experiments were conducted wirh rhe exemplar vehicle to establish parameters and verify some performance properties. Results of both steady srare and rransienr simulations showed that four -wheel steer offers lirrle or no demonstrated performance advanrages over two-wheel steer.

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.

Neural networks are massively parallel computational models for knowledge representation and information processing. The capabilities of neural networks, namely learning, noise tolerance, adaptivity, and parallel structure make them good candidates for application to a wide range of engineering problems including diagnostics problems. The general approach in developing neural network based diagnostic methods is described through a case study. The development of an acoustic wayside train inspection system using neural networks is described. The study is aimed at developing a neural network based method for detection defective wheels from acoustic measurements. The actual signals recorded when a train passes a wayside station are used to develop a neural network based wheel defect detector and to study its performance. Signal averaging and scoring techniques are developed to improve the performance of the constructed neural inspection system.

Understanding lubrication failures at the shoe/swashplate contact of automotive swashplate compressors will greatly enhance the reliability of the air conditioning system. Maintaining proper lubrication is not always possible during transient conditions. Therefore, a method for detection of lubricant loss is of great interest to the automotive industry. Three methods for detecting lubrication loss were examined: contact resistance, acoustic emission, and dynamic pressure oscillations. A mobile air conditioning test stand capable of recording many system parameters was used. Oil return to the compressor was monitored using an oil separator and a refrigerant/oil concentration sensor. Data were taken during steady oil return rates and after oil shut off. The electrical contact resistance between the shoe and swashplate was used to indicate changes in the lubrication conditions at this critical interface. Measurements were taken at two oil return rates during steady oil return tests.

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.

Roll bars are currently a primary source of operator protection for recreational vehicles, for certain lawn and garden tractors and for small agricultural tractors. In this paper we describe a family of nonlinear models to predict the large deflection response of a roll bar due to yielding of the material. This yielding permits the structure to absorb energy. The stress-strain relationship employs a power law model. Subsequent calculation of the complementary energy stored in the structure and application of Castigliano's second theorem yield the deflection at the point of loading. To demonstrate the feasibility of this energy method in the simulation of testing of roll bars, we present numerical results for the side, vertical, and fore-aft loading cases. Results include the load-deflection response for each load case as well as the strain energy stored in the roll bar as it deforms.

An empirical method which is based principally on estimates of the fatigue crack initiation life (NI) has been developed which predicts the fatigue resistance of tensile-shear spot welds in the long life regime. The method uses Basquin’s law and Peterson’s equation to estimate NI and thus is founded on the fatigue behavior of smooth specimens and modelling of the fatigue notch size effect. The fatigue notch factor (Kf) required in this analysis was obtained from Pook’s relationships for the stress intensity factors of tensile-shear spot welds. Estimates of NI are added to estimates of the fatigue crack propagation life NP to obtain the total fatigue life (NT) but in the long life regime NP can usually be neglected. The improvement of tensile-shear spot weld fatigue resistance through manipulation of geometry and material property variables are discussed with the aid of the model.

An empirical Three Stage Initiation-Propagation (TSIP) model has been developed which predicts the fatigue resistance of tensile-shear spot welds under constant amplitude loading. The improvements of tensile-shear spot weld fatigue resistance caused by changes in weld geometry, residual stresses and material properties variables are discussed with the aid of the model. The TSIP model suggests that, in addition to the influence of geometry, residual stresses at the site of crack initiation greatly influence the fatigue resistance of tensile-shear spot welds. The TSIP model predicts that material properties play a subtle role in determining the fatigue resistance of tensile-shear spot welds.