Aerodynamic Optimization Using Add-On Devices: Comparison between CFD and Wind Tunnel Experimental Test

JUNO is an urban concept vehicle (developed at the Politecnico of Torino), equipped by an ethanol combustion engine, designed to obtain low consumptions and reduced environmental impact. For these goals the main requirements that were considered during the designing process were mass reduction and aerodynamic optimization, at first on the shape of the car body and then, thanks to add-on devices. JUNO's aerodynamic development follows a defined workflow: geometry definition and modelling, CFD simulations and analysis, and finally geometry changes and CFD new verification. In this paper the results of the CFD simulations (using STARCCM#x0002B; and RANS k-?) with a corresponding 1/1 scale wind tunnel tests made using the real vehicle. Particularly, the results in term of: total drag coefficient (Cx), total lift coefficient (Cz), the total pressure in the side and rear analyzing twenty different aerodynamics configurations made up of different combination of some aerodynamics add-on devices. From the analysis of the results is emerged that CFD simulations using RANS k-? methods are able to predict the trend of total drag coefficient and its absolute value. Regarding the trend and the absolute value for lift coefficient, much larger deviation than Cx has been identified. For total pressure scene, there is a high similarity between the two ways of testing, especially on the side and on the central rear zone. The CFD results simulations, RANS k-? model is correct to develop and test symmetrical wide body. The obtained results are in good agreement with experimental wind tunnel results but, with particular attention to geometry, that suddenly change the way of air-flow

Design and Validation of a High-Level Controller for Automotive Active Systems

Active systems, from active safety to energy management, play a crucial role in the development of new road vehicles. However, the increasing number of controllers creates an important issue regarding complexity and system integration. This article proposes a high-level controller managing the individual active systems - namely, Torque Vectoring (TV), Active Aerodynamics, Active Suspension, and Active Safety (Anti-lock Braking System [ABS], Traction Control, and Electronic Stability Program [ESP]) - through a dynamic state variation. The high-level controller is implemented and validated in a simulation environment, with a series of tests, and evaluate the performance of the original design and the proposed high-level control. Then, a comparison of the Virtual Driver (VD) response and the Driver-in-the-Loop (DiL) behavior is performed to assess the limits between virtual simulation and real-driver response in a lap time condition. The main advantages of the proposed design methodology are its simplicity and overall cooperation of different active systems, where the proposed model was able to improve the vehicle behavior both in terms of safety and performance, giving more confidence to the driver when cornering and under braking. Some differences were discovered between the behavior of the VD and the DiL, especially regarding the sensitivity to external disturbances

Influence of Freeze-Thaw Aging on the Impact Performance of Damped Carbon Fiber Reinforced Plastics for Automotive Applications

The increasing use of composite materials in the automotive field requires more attention with regards to the appearance of noise, vibration and harshness (NVH) study in cars construction. However, in car door panels production, impact characteristics need to be evaluated in sandwich laminates. Furthermore, it is important to consider the effect of prolonged environmental aging on crashworthiness properties. The innovative content of the work is the hygrothermal effects evaluation on impact performance for two damped CFRP sandwich laminates. In this paper, two damping materials, Kraibon HHZ9578/99 and SUT9609/24, were used as core between two skins of CFRP for sandwich composite production. Freeze-Thaw aging treatment according to IEC 60068, specific for Automotive, was performed to investigate environmental effects on components. Up to 750 h, it was demonstrated that water absorption is regulated by Fick’s Law. The low-velocity impact behavior of the damped sandwiches has been studied according to ASTM D7136 throughout drop dart test equipment. Both main peak forces and energy absorption characteristics are negatively affected by aging condition. The introduction of damping core inside the composite structure of vehicle components can satisfy NVH constrictions. By contrast, at least same operating conditions must be assured in relation to not-damped components

Flow rate test bench: automated and compliant to ISO standards

he issue of measuring the flow rate through a pneumatic component is a critical one. Several methods exist, each with its own pros and cons regarding the type of gas, measurement range, and accuracy. ISO Standards, however, consider only a few of them: orifice plates, nozzles, Venturi nozzles, Venturi tubes. Although amenable to possible criticism, the International Organization for Standardization is an important reference. Designing a test bench according to its Standards is often more than reasonable: advantages include certification, assessment of test methods and accuracy, worldwide recognition. On the other hand, however detailed the Standards may be, they often lack the designer's (and perhaps the user's) point of view. This aspect leads to complicated realizations, low usability or long test execution times. This article proposes a flow rate test bench compliant to ISO Standards allowing a partially automated testing, rational installation, high configurability, user-friendliness, and accuracy. © 2012, Society for Experimental Mechanics

Preliminary design of eddy current brake to improve sustainable mobility

In recent years, the need to reduce CO2 emissions has developed a change in the transport sector. E-mobility is emerging as a zero-emissions way of travel, but not only the combustion engine produces emission. In fact, a significant part of the vehicle's total pollution is produced by tires and conventional brakes. The eddy current brake is a possible alternative to the well-known mechanical brake to obtain zero-emissions braking with low maintenance. This type of brake converts the vehicle's kinetic energy into thermal energy through the magnetic generation of the eddy currents, which generate Lorentz braking forces. This paper proposes a preliminary design of a zero-emission eddy current brake with a first geometry variation to increase the brake performance, that has been evaluated with an analytical approach and EMS by EMWorks, a 3D finite element method magnetic software able to calculate brake torque and electromagnetic effects

Multibody parameter estimation: A comprehensive case-study for an innovative rear suspension

Numerical and virtual simulation of mechanical systems is a standard part of product development in the automotive sector, and multibody techniques are a consolidated tool to describe vehicle dynamics, elasto- kinematic behavior, handling, and comfort. To achieve high precision results as output of simulations, it is essential to provide the system with reliable data as input, and to accurately describe the vehicle and its subsystems. The task of gathering objective parameters to fully describe a vehicle can seem trivial to the stakeholders directly connected to a project, that can access detailed design data and a plethora of schemes and datasheets covering all subsystems of a vehicle. However, whenever this task regards benchmarking, prototyping, research projects or niche/low-volume products, data availability decreases drastically, and alternative forms of data acquisition become essential. This paper proposes a comprehensive overview of data gathering and experimental procedures used to reliably extract parameters of an existing vehicle using quick and accessible strategies. The analysis is based on a case-study project of an A-segment vehicle mounted with an innovative rear suspension scheme, whose behavior should be described by a dedicated elasto- kinematic multibody model as well as a full vehicle model for dynamic validation. The multibody model is based on Adams/Car with the inclusion of flexible elements, which is briefly described, while a closer focus is given to the experimental extraction of key features, such as: total mass, longitudinal and lateral position of the center of gravity, CoG height, wheel travel and wheel rate, shock-absorber damping coefficient, steering ratio, components inertia and flexible elements strain. The results obtained in the static and dynamic experimental validation suggest a good outcome from the methodology, that can be replicated on many kinds of vehicle modelling activities as an approachable and affordable experimental methodology for small projects

Design and Modelling of the Powertrain of a Hybrid Fuel Cell Electric Vehicle

This paper presents a Fuel Cell Electric Vehicle (FCEV) powertrain development and optimization, aiming to minimize hydrogen consumption. The vehicle is a prototype that run at the Shell Eco-marathon race and its powertrain is composed by a PEM fuel cell, supercapacitors and a DC electric motor. The supercapacitors serve as an energy buffer to satisfy the load peaks requested by the electric motor, allowing a smoother (and closer to a stationary application) working condition for the fuel cell. Thus, the fuel cell can achieve higher efficiency rates and the fuel consumption is minimized. Several models of the powertrain were developed using MATLAB-Simulink and then experimentally validated in laboratory and on the track. The proposed models allow to evaluate two main arrangements between fuel cell and supercapacitors: 1) through a DC/DC converter that sets the FC current to a desired value; 2) using a direct parallel connection between fuel cell and supercapacitors. The results obtained with the direct parallel connection (with the appropriate sizing of the overall capacity) have highlighted a significant efficiency advantage, while the DC/DC converter insertion enables an improved control of the fuel cell current and requires a smaller capacitance. Furthermore, a sizing methodology for the supercapacitors capacitance is proposed for both layouts: with the DC/DC converter it mainly depends on the energy range provided by supercapacitors to the electric motor, while in the direct parallel connection the supercapacitors sizing is outlined by concurrently evaluating the circuit's predicted hydrogen consumption and granting the most suitable conditions to increase the fuel cell performance. Finally, the results obtained from the model were validated by comparing them with experimental data obtained in the laboratory and on the track

Temperature-Dependent Thévenin Model of a Li-Ion Battery for Automotive Management and Control

This paper focuses on the analysis of Li-ion battery behavior at different temperatures through the Thévenin electrical circuit model. First, evaluations for both steady-state and dynamic battery applications are provided, then an overview of the different battery models to describe their dynamic behavior is analyzed. The focus is dedicated to the double polarization Thévenin-based equivalent circuit model since it represents an optimal trade-off between accuracy and computation effort, which justifies its implementation in a Battery Management System (BMS) for automotive real-time monitoring and control. The model is composed of a voltage source, one series resistor and two series RC blocks. The Hybrid Pulse Power Characterization test (HPPC) is performed inside a climatic chamber to extract the electrical parameters of the model and their dependency from both temperature and State Of Charge (SOC). The load-current effects on the battery performance are not considered for the simplicity and lightness of the presented model. The presented procedure has broader validity and is mostly independent of cell format and Li-ion chemistry, despite a specific cylindrical battery cell is chosen for the study. The results of the test are suitable for the future implementation of a proper algorithm for SOC and State Of Health SOH estimations. Moreover, they provide an effective electrical and thermal characterization of the cell to evaluate the heat generation rate inside the cell

Dynamic Electro-Thermal Li-ion Battery Model for Control Algorithms

This paper presents a fast and effective approach to evaluate the heat generation of a Li-ion battery system. The thermal characterization of Li-ion batteries is a relevant topic for the correct monitoring of the battery pack. In particular, a reduced-order model, that estimates the thermal dynamics of a Li-ion battery cell, is reported. The proposed approach relies on the definition of a boundary-value problem for heat conduction, in the form of a linear partial differential equation with the integration of Equivalent Circuit Model. The model is based on the double polarization Thévenin equivalent circuit model since it represents an optimal trade-off between accuracy and computation effort, which justifies its implementation in a Battery Management System (BMS) for automotive real-time monitoring and control. The resulting model predicts the temperature dynamics at the external surface in relation with the rate of the internal heat generation. In this paper, the model is applied to estimate the temperature of a cylindrical cell during a discharging transient and it uses electrical data acquired from experimental tests and is validated Computational fluid dynamics simulation. The results of the test are suitable for the future implementation of a proper algorithm for State of Charge SOC and State of Health SOH estimations

Electrothermal battery pack model for automotive application: Design and validation

Thermal modeling of the battery is an important way to understand how the design and operating variables affect the thermal response during its operation. This paper presents a method for modeling the electrical and thermal behavior of a battery pack, starting from the characterization of the single Lithium-ion battery cell up to extend its validity to module and pack level. The model takes into account both the reversible entropic heat generation and the irreversible resistive heat to predict the temperature of the battery. A coupled CFD and thermal analysis on an elementary module is proposed and experimentally tested to validate the results obtained from the proposed model. Furthermore, the experimental test will verify the effectiveness of air cooling