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A 1D Real-Time Engine Manifold Gas Dynamics Model Using Orthogonal Collocation Coupled with the Method of Characteristics

University of Waterloo-Amer Keblawi, John McPhee
Published 2019-04-02 by SAE International in United States
In this paper, a new solution method is presented to study the effect of wave propagation in engine manifolds, which includes solving one-dimensional models for compressible flow of air. Velocity, pressure, and density profiles are found by solving a system of non-linear Partial Differential Equations (PDEs) in space and time derived from Euler’s equations. The 1D model includes frictional losses, area change, and heat transfer. The solution is traditionally found by utilizing the Method of Characteristics and applying finite difference solutions to the resulting system of ordinary differential equations (ODEs) over a discretized grid. In this work, orthogonal collocation is used to solve the system of ODEs that is defined along the characteristic curves. Orthogonal polynomials are utilized to approximate velocity, pressure, sound speed, and the characteristic curves along which the system of PDEs reduce to a system of ODEs. The approximation polynomials are defined over the whole manifold domain, transforming Euler’s equations into a system of ODEs that can be solved using a generic ODE solver. This reduction is done symbolically using a computer…
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Notch Plasticity and Fatigue Modelling of AZ31B-H24 Magnesium Alloy Sheet

University of Waterloo-Lin Feng Victor Qian, Ali A. Roostaei, Grzegorz Glinka, Hamid Jahed
FCA US LLC-Umesh Dighrasker
Published 2019-04-02 by SAE International in United States
Vehicle weight reduction through the use of components made of magnesium alloys is an effective way to reduce carbon dioxide emission and improve fuel economy. In the design of these components, which are mostly under cyclic loading, notches are inevitably present. In this study, surface strain distribution and crack initiation sites in the notch region of AZ31B-H24 magnesium alloy notched specimens under uniaxial load are measured via digital image correlation. Predicted strains from finite element analysis using Abaqus and LS-DYNA material types 124 and 233 are then compared against the experimental measurements during quasi-static and cyclic loading. It is concluded that MAT_233, when calibrated using cyclic tensile and compressive stress-strain curves, is capable of predicting strain at the notch root. Finally, employing Smith-Watson-Topper model together with MAT_233 results, fatigue lives of the notched specimens are estimated and compared with experimental results.
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Crack Initiation and Propagation Fatigue Life Prediction for an A36 Steel Welded Plate Specimen

University of Waterloo-F.A. Conle
Published 2019-04-02 by SAE International in United States
Fatigue crack initiation and propagation models predict the fatigue life of welded "T" specimens tested by the Fatigue Design and Evaluation (FDE) Committee of SAE under constant and variable amplitude load histories. The crack propagation equations stipulated by British Standard BS-7910 have been incorporated in a material memory model for cyclic deformation. The simulations begin with the crack initiation model and show how it is used to account for cyclic mean stress relaxation and the effects of periodic overloads. After the cracks initiate the BS-7910 model is applied to predict the crack advance due to either constant or variable amplitude histories. Simulation results correspond to the experimental results with good accuracy.
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Efficient Electro-Thermal Model for Lithium Iron Phosphate Batteries

University of Waterloo-Manoj Mathew, Mehrdad Mastali, John Catton, Ehsan Samadani, Michael Fowler
Published 2018-04-03 by SAE International in United States
The development of a comprehensive battery simulator is essential for future improvements in the durability, performance and service life of lithium-ion batteries. Although simulations can never replace actual experimental data, they can still be used to provide valuable insights into the performance of the battery, especially under different operating conditions. In addition, a single-cell model can be easily extended to the pack level and can be used in the optimization of a battery pack. The first step in building a simulator is to create a model that can effectively capture both the voltage response and thermal behavior of the battery. Since these effects are coupled together, creating a robust simulator requires modeling both components. This paper will develop a battery simulator, where the entire battery model will be composed of four smaller submodels: a heat generation model, a thermal model, a battery parameter model and a voltage response model. The paper will provide a brief description on each of these four sub-models and how they are correlated with each other. In addition, this work will…
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Parameter Identification and Validation for Combined Slip Tire Models Using a Vehicle Measurement System

SAE International Journal of Vehicle Dynamics, Stability, and NVH

University of Waterloo-Matthew D. Van Gennip, John McPhee
  • Journal Article
  • 2018-01-1339
Published 2018-04-03 by SAE International in United States
It is imperative to have accurate tire models when trying to control the trajectory of a vehicle. With the emergence of autonomous vehicles, it is more important than ever before to have models that predict how the vehicle will operate in any situation. Many different types of tire models have been developed and validated, including physics-based models such as brush models, black box models, finite element-based models, and empirical models driven by data such as the Magic Formula model. The latter is widely acknowledged to be one of the most accurate tire models available; however, collecting data for this model is not an easy task. Collecting data is often accomplished through rigorous testing in a dedicated facility. This is a long and expensive procedure which generally destroys many tires before a comprehensive data set is acquired. Using a Vehicle Measurement System (VMS), tires can be modeled through on-road data alone. This reduces the time and cost significantly and does not require destroying multiple tires. Previous works regarding this parameter identification method have used only the…
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Powertrain Modeling and Model Predictive Longitudinal Dynamics Control for Hybrid Electric Vehicles

University of Waterloo-Bryce Antony Hosking, John McPhee
Published 2018-04-03 by SAE International in United States
This paper discusses modeling of a power-split hybrid electric vehicle and the design of a longitudinal dynamics controller for the University of Waterloo’s self-driving vehicle project. The powertrain of Waterloo’s vehicle platform, a Lincoln MKZ Hybrid, is controlled only by accelerator pedal actuation. The vehicle’s power management strategy cannot be altered, so a novel approach to grey-box modeling of the OEM powertrain control architecture and dynamics was developed. The model uses a system of multiple neural networks to mimic the response of the vehicle’s torque control module and estimate the distribution of torque between the powertrain’s internal combustion engine and electric motors. The vehicle’s power-split drivetrain and longitudinal dynamics were modeled in MapleSim, a modeling and simulation software, using a physics-based analytical approach. All model parameters were identified using Controller Area Network (CAN) data and measurements of wheel torque data that were gathered during vehicle road testing. Using the grey-box powertrain model as a framework, a look-ahead linear time-varying (LTV) model predictive controller (MPC) for reference velocity tracking is proposed. Using some simplifying assumptions about the…
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Design Optimization of the Transmission System for Electric Vehicles Considering the Dynamic Efficiency of the Regenerative Brake

University of Waterloo-Dongpu Cao
Cranfield University-Chen Lv
Published 2018-04-03 by SAE International in United States
In this paper, gear ratios of a two-speed transmission system are optimized for an electric passenger car. Quasi static system models, including the vehicle model, the motor, the battery, the transmission system, and drive cycles are established in MATLAB/Simulink at first. Specifically, since the regenerative braking capability of the motor is affected by the SoC of battery and motors torque limitation in real time, the dynamical variation of the regenerative brake efficiency is considered in this study. To obtain the optimal gear ratios, iterations are carried out through Nelder-Mead algorithm under constraints in MATLAB/Simulink. During the optimization process, the motor efficiency is observed along with the drive cycle, and the gear shift strategy is determined based on the vehicle velocity and acceleration demand. Simulation results show that the electric motor works in a relative high efficiency range during the whole drive cycle. The energy economy of the case-study vehicle with the optimized a two-speed transmission is also compared to that of the baseline vehicle with fixed-ratio reduction gear.
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An Analysis of ISO 26262: Machine Learning and Safety in Automotive Software

University of Waterloo-Rick Salay, Rodrigo Queiroz, Krzysztof Czarnecki
Published 2018-04-03 by SAE International in United States
Machine learning (ML) plays an ever-increasing role in advanced automotive functionality for driver assistance and autonomous operation; however, its adequacy from the perspective of safety certification remains controversial. In this paper, we analyze the impacts that the use of ML within software has on the ISO 26262 safety lifecycle and ask what could be done to address them. We then provide a set of recommendations on how to adapt the standard to better accommodate ML.
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Road Classification Based on System Response with Consideration of Tire Enveloping

University of Waterloo-Yanjun Huang
Beijing Institute of Technology-Yechen Qin, Zhenfeng Wang, Mingming Dong
Published 2018-04-03 by SAE International in United States
This paper presents a road classifier based on the system response with consideration of the tire enveloping. The aim is to provide an easily applicable yet accurate road classification approach for automotive engineers. For this purpose, tire enveloping effect is firstly modeled based on the flexible roller contact (FRC) theory, then transfer functions between road input and commonly used suspension responses i.e. the sprung mass acceleration, unsprung mass acceleration, and rattle space, are calculated for a quarter vehicle model. The influence of parameter variations, vehicle velocity, and measurement noise on transfer functions are comprehensively analyzed to derive the most suitable system response thereafter. In addition, this paper proposes a vehicle speed correction mechanism to further improve the classification accuracy under complex driving conditions. A random forest based classifier is finally trained by treating center spatial frequencies of the octave bands as the classifier input as per ISO-8608. Simulation results validate the proposed approach for various road levels with various velocities, and the overall classification accuracy improved from F-score of 0.7547 (without velocity correction) to F-score…
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The Influence of the Through-Thickness Strain Gradients on the Fracture Characterization of Advanced High-Strength Steels

SAE International Journal of Materials and Manufacturing

University of Waterloo-Kenneth Cheong, Clifford Butcher
Honda-James Dykeman
  • Journal Article
  • 2018-01-0627
Published 2018-04-03 by SAE International in United States
The development and calibration of stress state-dependent failure criteria for advanced high-strength steel (AHSS) and aluminum alloys requires characterization under proportional loading conditions. Traditional tests to construct a forming limit diagram (FLD), such as Marciniak or Nakazima tests, are based upon identifying the onset of strain localization or a tensile instability (neck). However, the onset of localization is strongly dependent on the through-thickness strain gradient that can delay or suppress the formation of a tensile instability so that cracking may occur before localization. As a result, the material fracture limit becomes the effective forming limit in deformation modes with severe through-thickness strain gradients, and this is not considered in the traditional FLD. In this study, a novel bending test apparatus was developed based upon the VDA 238-100 specification to characterize fracture in plane strain bending using digital image correlation (DIC). Three punches with tip radii of 0.2, 0.4, and 1.0 mm were used to demonstrate the influence of the bend severity on the fracture limit in plane strain tension. Moreover, the influence of the through-thickness…
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