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As mass reduction becomes an increasingly important enabler for fuel economy improvement, having a robust structural development process that can comprehend Vehicle Dynamics-specific requirements is correspondingly important. There is a correlation between the stiffness of the body structure and the performance of the vehicle when evaluated for ride and handling. However, an unconstrained approach to body stiffening will result in an overly-massive body structure. In this paper, the authors employ loads generated from simulation of quasi-static and dynamic vehicle events in ADAMS, and exercise structural finite element models to recover displacements and deflected shapes. In doing so, a quantitative basis for considering structural vehicle dynamics requirements can be established early in the design/development process.

One of the issues in stamping of advanced high strength steels (AHSS) is the stretch bending fracture on a sharp radius (commonly referred to as shear fracture). Shear fracture typically occurs at a strain level below the conventional forming limit curve (FLC). Therefore it is difficult to predict in computer simulations using the FLC as the failure criterion. A modified Mohr-Coulomb (M-C) fracture criterion has been developed to predict shear fracture. The model parameters for several AHSS have been calibrated using various tests including the butter-fly shaped shear test. In this paper, validation simulations are conducted using the modified (M-C) fracture criterion for a dual phase (DP) 780 steel to predict fracture in the stretch forming simulator (SFS) test and the bending under tension (BUT) test. Various deformation fracture modes are analyzed, and the range of usability of the criterion is identified.

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. A model of the oil seals is developed to calculate internal oil consumption (oil leakage from the crankcase through the oil seals) as a function of engine geometry and operating conditions. The deformation of the oil seals trying to conform to housing distortion is calculated to balance spring force, O-ring and groove friction, and asperity contact and hydrodynamic pressure at the interface. A control volume approach is used to track the oil over a cycle on the seals, the rotor and the housing as the seals are moving following the eccentric rotation of the rotor. The dominant cause of internal oil consumption is the non-conformability of the oil seals to the housing distortion generating net outward scraping, particularly next to the intake and exhaust port where the housing distortion valleys are deep and narrow.

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. In order to better understand oil transport, a laser induced fluorescence technique is used to visualize oil motion on the side of the rotor during engine operation. Oil transport from both metered oil and internal oil is observed. Starting from inside, oil accumulates in the rotor land during inward motion of the rotor created by its eccentric motion. Oil seals are then scraping the oil outward due to seal-housing clearance asymmetry between inward and outward motion. Cut-off seal does not provide an additional barrier to internal oil consumption. Internal oil then mixes with metered oil brought to the side of the rotor by gas leakage. Oil is finally pushed outward by centrifugal force, passes the side seals, and is thrown off in the combustion chamber.

Piston rings are large contributors to friction losses in internal combustion engines. To achieve higher engine efficiency, low friction ring packs that can maintain good sealing performance must be designed. To support this effort, simulation tools have been developed to model the performance of piston rings during engine operation. However, the challenge of predicting oil consumption, blow by, and ring pack friction with sufficient accuracy remains. This is mostly due to the complexity of this system. Ring dynamics, deformation, interaction with liner and piston, gas and lubricant flow must all be studied together to make relevant predictions. In this paper, a new curved beam finite element model of piston rings is proposed. Ring structural deformation and contact with the liner are treated on two separate grids. A comparison with ring models in the literature and analytical solutions shows that it can provide accurate results efficiently.

As the piston pin works under significant mechanical load, it is susceptible to wear, seizure, and structural failure, especially in heavy duty internal combustion engines. It has been found that the friction loss associated with the pin is comparable to that of the piston, and can be reduced when the interface geometry is properly modified. However, the mechanism that leads to such friction reduction, as well as the approaches towards further improvement, remain unknown. This work develops a piston pin lubrication model capable of simulating the interaction between the pin, the piston, and the connecting rod. The model integrates dynamics, solid contact, oil transport, and lubrication theory, and applies an efficient numerical scheme with second order accuracy to solve the highly stiff equations. As a first approach, the current model assumes every component to be rigid.

General Motors has developed an all-new Ecotec 1.5 L range extender engine for use in the 2016 next generation Voltec propulsion system. This engine is part of a new Ecotec family of small displacement gasoline engines introduced in the 2015 model year. Major enhancements over the range extender engine in the current generation Voltec propulsion system include the adoption of direct injection (DI), cooled external exhaust gas recirculation (EGR), and a high 12.5:1 geometric compression ratio (CR). Additional enhancements include the adoption of high-authority phasers on both the intake and exhaust camshafts, and an integrated exhaust manifold (IEM). The combination of DI with cooled EGR has enabled significant thermal efficiency gains over the 1.4 L range extender engine in the current generation Voltec propulsion system at high engine loads.

This article is concerned with identification of true stress-strain curve under biaxial tension of thermoplastic polymers. A new type of biaxial tension attachment was embedded first in a universal material test machine, which is able to transform unidirectional loading of the test machine to biaxial loading on the specimen with constant velocity. Cruciform specimen geometry was optimized via FE modeling. Three methods of calculating true stress in biaxial tension tests were compared, based on incompressibility assumption, linear elastic theory and inverse engineering method, respectively. The inverse engineering method is more appropriate for thermoplastic polymers since it considers the practical volume change of the material during biaxial tension deformation. The strategy of data processing was established to obtain biaxial tension true stress-strain curves of different thermoplastic polymers.

Engine acoustics measured by microphones near the engine have been used in controlled laboratory settings for combustion feedback and even combustion phasing control, but the use of these techniques in a vehicle where many other noise sources exist is problematic. In this study, surface-mounted acoustic emissions sensors are embedded in the block of a 2.0L turbocharged GDI engine, and the signal is analyzed to identify useful feedback features. The use of acoustic emissions sensors, which have a very high frequency response and are commonly used for detecting material failures for health monitoring, including detecting gear pitting and ring scuffing on test stands, enables detection of acoustics both within the range of human hearing and in the ultrasonic spectrum. The high-speed acoustic time-domain data are synchronized with the crank-angle-domain combustion data to investigate the acoustic emissions response caused by various engine events.

The first 3 cycles in the cold crank-start process at 20°C are studied in a GDI engine. The focus is on the dependence of the HC and PM/PN emissions of each cycle on the injection strategy and combustion phasing of the current and previous cycles. The PM/PN emissions per cycle decrease by more than an order of magnitude as the crank-start progresses from the 1st to the 3rd cycle, while the HC emissions stay relatively constant. The wall heat transfer, as controlled by the combustion phasing, during the previous cycles has a more significant influence on the mixture formation process for the current cycle than the amount of residual fuel. The results show that the rise in HC emissions caused by the injection spray interacting with the intake valves and piston crown is reduced as the cranking process progresses. Combustion phasing retard significantly reduces the PM emission. The HC emissions, however, are relatively not sensitive to combustion phasing in the range of interest.

A new ring pack model has been developed based on the curved beam finite element method. This paper describes the first part of this model: simulating gas pressure in different regions above piston skirt and ring dynamic behavior of two compression rings and a twin-land oil control ring. The model allows separate grid divisions to resolve ring structure dynamics, local force/pressure generation, and gas pressure distribution. Doing so enables the model to capture both global and local processes at their proper length scales. The effects of bore distortion, piston secondary motion, and groove distortion are considered. Gas flows, gas pressure distribution in the ring pack, and ring structural dynamics are coupled with ring-groove and ring-liner interactions, and an implicit scheme is employed to ensure numerical stability. The model is applied to a passenger car engine to demonstrate its ability to predict global and local effects on ring dynamics and oil transport.

This paper describes rationale for determining the apportionment of variable or ‘shuttered’ airflow and non-variable or static airflow through openings in the front of a vehicle as needed for vehicle cooling. Variable airflow can be achieved by means of a shutter system, which throttles airflow through the front end and into the Condenser, Radiator, and Fan Module, (CRFM). Shutters originated early in the history of the auto industry and acted as a thermostat [1]. They controlled airflow as opposed to coolant flow through the radiator. Two benefits that are realized today are aerodynamic and thermal gains, achieved by restricting unneeded cooling airflow. Other benefits exist and justify the use of shutters; however, there are also difficulties in both execution and practical use. This paper will focus on optimizing system performance and execution in terms of the two benefits of reduced aerodynamic drag and reduced mechanical drag through thermal control.

Presented in the paper is a comprehensive analysis for floating piston pin. It is more challenging because it is a special type of journal bearing where the rotation of the journal is coupled with the friction between the journal and the bearing. In this analysis, the multi-degree freedom mass-conserving mixed-EHD equations are solved to determine the coupled pin rotation and friction. Other bearing characteristics, such as minimum film thickness, pin secondary motions in both connecting-rod small-end bearing and piston pin-boss bearing, power loss etc are also determined. The mechanism for floating pin to have better scuffing resistance is discovered. The theoretical and numerical model is implemented in the GM internal software FLARE (Friction and Lubrication Analysis for Reciprocating Engines).

Compressed natural gas (CNG) currently is used as an alternative fuel for internal combustion engines in motor vehicles. This paper presents results of an analysis of leaks from a model isolated section of CNG fuel system. Discharge of CNG was modeled as vent flow of a real gas hydrocarbon mixture through an orifice from a reservoir with finite volume. Pressures typically used in CNG fuel systems result in choked flow for gas venting directly to atmosphere, producing an under-expanded, momentum-dominated, turbulent free jet with well defined velocity and concentration fields. This paper presents results of analyses of reservoir pressure decay, and vent flow and concentrations fields for CNG venting from a pressurized reservoir into the atmosphere. A combination of empirically-derived analytical relationships and detailed two-dimensional high resolution computational fluid dynamic modeling was used to determine the velocity and concentrations fields of the resulting CNG jet.

A comprehensive experimental and theoretical approach was undertaken to understand the phenomenon of pre-ignition and to assess parameters to improve or even eliminate it completely. Oil mixing with fuel was identified as the leading theory of self ignition of the fuel. End of compression temperature has to meet a minimum level for pre-ignition to take place. In this work a comprehensive list of parameters were identified that have a direct and crucial role in the onset of pre-ignition including liner wetting, injection targeting, stratification, mixture motion and oil formulation. Many secondary effects were identified including ring dynamics, ring tension, spark plug electrode temperature and coolant temperature. CFD has been extensively used to understand test results including wall film, A/F ratio distribution and temperature at the end of compression when looked at in the context of fuel evaporation and mixing.

As the new features for driver assistance and active safety systems are growing rapidly in vehicles, the simulation within a virtual environment has become a necessity. The current active safety system consists of Electronic Control Units (ECUs) which are coupled to camera and radar sensors. Two methods of implementation exists, integrated sensors with control modules or separation of sensors form control modules. The subsystem integration testing poses new challenges for virtual environment for simulation of active safety features. The comprehensive simulation environment for integration testing consists of chassis controls, powertrain, driver assistance, body and displays controllers. Additional complexity in the system is the serial communication strategy. Multiple communication protocols such as GMLAN, LIN, standard CAN, and Flexray could be present within the same vehicle topology.

Three different acoustic finite element models of an automobile passenger compartment are developed and experimentally assessed. The three different models are a traditional model, an improved model, and an optimized model. The traditional model represents the passenger and trunk compartment cavities and the coupling between them through the rear seat cavity. The improved model includes traditional acoustic models of the passenger and trunk compartments, as well as equivalent-acoustic finite element models of the front and rear seats, parcel shelf, door volumes, instrument panel, and trunk wheel well volume. An optimized version of the improved acoustic model is developed by modifying the equivalent-acoustic properties. Modal analysis tests of a vehicle were conducted using loudspeaker excitation to identify the compartment cavity modes and sound pressure response to 500 Hz to assess the accuracy of the acoustic models.

At elevated temperatures, such as those encountered under race track or fade test conditions, the closed-form solution to the lumped capacitance model for characterizing brake cooling (fitted to a standard cooling test temperature range) tends to break down and provide an inaccurate representation of brake rotor cooling behavior. Accurate prediction of cooling is fundamental to brake system component sizing and selection of materials at the early stages of a vehicle program; this is especially true of a high performance vehicle with track performance requirements. To this end, alternative approaches to characterizing brake cooling have been examined to determine their suitability for use in measurement and simulation of brake performance.

Cast aluminum alloys are normally quenched after solution treatment or solidification process to improve aging responses. Rapid quenching can lead to high residual stress and severe distortion which significantly affects dimension stability, functionality and particularly performance of the product. To simulate residual stress and distortion induced during quenching, a finite element based approach was developed by coupling an iterative zone-based transient heat transfer algorithm with material thermo-viscoplastic constitutive model. With the integrated models, the numeric predictions of residual stresses and distortion in the quenched aluminum castings are in a good agreement with experimental measurements.

This paper presents some of the challenges and successful outcomes in developing the aerodynamic characteristics of the Chevrolet Volt, an electric vehicle with an extended-range capability. While the Volt's propulsion system doesn't directly affect its shape efficiency, it does make aerodynamics much more important than in traditional vehicles. Aerodynamic performance is the second largest contributor to electric range, behind vehicle mass. Therefore, it was critical to reduce aerodynamic drag as much as possible while maintaining the key styling cues from the original concept car. This presented a number of challenges during the development, such as evaluating drag due to underbody features, balancing aerodynamics with wind noise and cooling flow, and interfacing with other engineering requirements. These issues were resolved by spending hundreds of hours in the wind tunnel and running numerous Computational Fluid Dynamics (CFD) analyses.