Contactless magnetic brake for automotive applications

Road and rail vehicles and aircraft rely mainly or solely on friction brakes. These brakes pose several problems, especially in hybrid vehicles: significant wear, fading, complex and slow actuation, lack of fail-safe features, increased fuel consumption due to power assistance, and requirement for anti-lock controls. To solve these problems, a contactless magnetic brake has been developed. This concept includes a novel flux-shunting structure to control the excitation flux generated by permanent magnets. This brake is wear-free, less-sensitive to temperature than friction brakes, has fast and simple actuation, and has a reduced sensitivity to wheel-lock. The present dissertation includes an introduction to friction braking, a theory of eddy-current braking, analytical and numerical models of the eddy-current brake, its excitation and power generation, record of experimental validation, investigation and simulation of the integration of the brake in conventional and hybrid vehicles

Mild Hybrid Electric Vehicles: Powertrain Optimization for Energy Consumption, Driveability and Vehicle Dynamics Enhancements

This thesis deals with the modeling, the design and the control of mild hybrid electric vehicles. The main goal is to develop accurate design tools and methodologies for preliminary system and component level analysis. Particular attention is devoted to the configuration in which an electric machine is mounted on the rear axle of a passenger car. The use of such a machine in parallel with the internal combustion engine allows one to exploit different functionalities that are able to reduce the overall fuel consumption of the vehicle. In addition, the indirect coupling between the thermal and the electric machine, realized through the road and not by means of mechanical couplers, together with the position of the latter in the overall vehicle chassis system, enables such an architecture to be efficient both from the energy recovery and the full electric driving point of view. Chapter 1 introduces the problem of fuel consumption and emissions reduction in the overall world context and presents the main hybrid architectures available. Chapter 2 is devoted to the study of the influence of the electric machine position in the powertrain regarding the regenerative braking potentialities concerned. The model considered for the analysis will be described on each of its subcomponents. The braking performance of the vehicle in electric mode is presented considering no losses in the electric powertrain (electric motor, battery, inverter). Chapter 3 is dedicated to the design of an electric machine for a rear axle powertrain. The specifications of such machine are optimized considering both the vehicle and the application under analysis. The design takes into account analytical techniques for the computation of electrical parameters (such as phase and DC currents) and the torque - speed map, as well as numerical ones for its thermal behavior. In Chapter 4 the electrical and thermal characteristics of the designed electric motor are implemented in the model presented in Chapter 2. The overall vehicle model is therefore used both to assess a simple torque split strategy between thermal and electric machine and to perform an optimal sizing of the battery considering all the limitations imposed by the electric powertrain (e. g. maximum currents, maximum temperatures). Chapter 5 makes a step forward and analyzes the different implications that the use of the rear axle electric motor to brake the vehicle has on the vehicle dynamics. Open loop analysis will present a degradation of the vehicle handling comfort caused by the introduction of an oversteering moment to the vehicle. Through the use of a simplified vehicle model, the introduced oversteering yaw moment is evaluated, while a control strategy based on a new stability detector will show how to find a trade off between handling comfort and regenerable energy. At last, Chapter 6 deals with the problem of longitudinal driving comfort. Drivelines and chassis are lightly damped systems and the application of an impulsive torque imposed by the driver can cause the vehicle longitudinal acceleration (directly perceived by the driver) to be oscillating and non smooth. A sensitivity analysis on a conventional powertrain is presented demonstrating which of the different components are more influential in the different modes of vibration, and possible solutions to improve the driveability are proposed. One of these relates to the use of the rear axle electric machine in order to give more responsiveness to the vehicle. Finally, concluding remarks are given in Chapter 7

VEHICLE DYNAMICS ANALYSIS IN A FORMULA STUDENT RACING CAR

One of the most important concepts in motorsport is vehicle dynamics. Being able to predict the manoeuvre behaviour of a racing vehicle, not only reduces test time but also optimizes the development process. Once it is possible to isolate external factors, one can study a particular group of variables and anticipate their consequence on the overall vehicle performance. This work is focused on two different approaches to the problem of predicting vehicle behaviour. The first procedure consisted in the development of a simulation tool, more precisely, a Lap Time Simulator using Simulink. Given the specific requirements of the team, the simulator was built without the use of any predefined vehicle dynamics block sets, this means, the algorithm is fully customizable. The developed simulator uses a single point mass approach, so the vehicle body was converted to a single point neglecting the effects of body roll and load transfer. Nevertheless, the algorithm can predict the effects of different vehicle systems on lap time. The calculations include, for example, a powertrain model defined by engine torque, gear ratios, rotational inertia and fuel consumption. The aerodynamic module controls the negative lift and drag force present at each step. The tyre behaviour was defined by a basic tyre model, which predicts longitudinal, lateral and rolling resistance forces. The second method utilizes a commercially available solution using a quasi-steadystate approach with optional transient properties. Instead of a single point mass, the vehicle body model uses a four-track model with the motion of each wheel/suspension to formulate the vehicle manoeuvre. The tyre model was extended to include slip angle, slip ratio and combined slip. For that purpose, the software utilizes the Pacejka magic formula with formula student tyre data. One of the most important factors of simulation tools is the validation of the results. For that reason, the thesis also includes an experimental procedure regarding the behaviour of a formula student on a controlled environment track. The obtained data were used to compare the simulation results with the real logged data provided by a vehicle instrumentation apparatus

The Development of Motor Tandem Axle Module in Series Hybrid Commercial Vehicles

The growing issues of energy shortage and the environmental crisis have resulted in new challenges for the automotive industry. Conventional commercial vehicles such as refuse trucks and delivery vehicles consume significantly more energy than other on-road vehicles and emit more emissions. It is important to make these vehicles more fuel efficient and environmentally friendly. Hybrid power-trains provide a good solution for commercial vehicles because they not only provide optimum dynamic properties but also substantially reduce emissions. For most commercial vehicle power-trains, the internal combustion engine (ICE) is the only power source that provides power to the drive-line. The emission reduction faces a limit since a high-powered engine is required to meet the dynamic properties of those heavy-duty vehicles. Also, the high-powered engine cannot avoid operating in low efficient areas due to the fact that these vehicles continually drive at low speeds on designated city routes. However, hybrid power-trains allow commercial vehicles to select lower powered engines because they are equipped with multi-power sources to supply torque together to the drive-line. Therefore, hybrid power-trains are a natural fit for commercial vehicles. For this reason, an alternative series hybrid drive-train system, which contains an electric tandem axle module, has been designed for those heavy-duty commercial vehicles like city transits and refuse trucks. In order to prove the theoretical efficiency and practicability of this application, the modeling methodology for specification of system architectures and hybrid drive-train control strategies will be provided in this paper with the demonstration of simulation methods and results

Experimental and numerical approach to investigate tire and ABS combined influence on wet braking performance of passenger cars.

This PhD activity is mainly focused on the study of the emergency braking test, where the tire behaviour can be influenced by the ABS system during such manoeuvre on wet roads. The main goal is to investigate and optimize the optimal shape of the longitudinal force characteristics of the tire in order to reduce the braking distance. The only evaluation of the μ-peak could not be sufficient for reliable assessments but the whole shape of the longitudinal curve should be considered. Nowadays, the Wet Grip Index (WGI) is the parameter with which it is possible to classify the quality of a tire in wet conditions in the EU tire label and it is mainly based on maximum grip that a tire can perform interacting with the wet road. Understanding the optimal shape of the curve could also mean to understand if the WGI approach can give a complete evaluation of tire performance during the braking, or there could be something more to take into account. A numerical approach was considered and a ABS logic has been modelled with the aim to replicate the fundamental strategies of a passenger car. A half vehicle model has been considered for this research work. A more physical approach on ABS modelling is proposed in this thesis, with the aim to estimate the optimal working range of the logic without any pre-set information. Regarding the implemented tire model, the focuses were on trying to find a method to characterize the tire in wet conditions and understand how the longitudinal relaxation length can influence the ABS work in simulation environment. A method is proposed to get a possible estimation of the longitudinal relaxation length of the tire from vehicle measurements. Moreover, a study about the relaxation length evaluation with respect to the excitation frequency coming from the longitudinal slippage will be described in this thesis. The emergency braking model was used to optimize the reference curve in order to reduce the braking distance. The analysis is focused on three parameters that can identify the longitudinal characteristics of the tire: the braking stiffness, μ-peak and drop down of the grip after the peak condition. The main outcome of the simulation results shows that the μ-peak could not be considered as the only critical parameter to evaluate the braking performance of the tire and that the drop-down of the grip seems to play a very important role to reduce braking distances

Aerodynamic cooling of automotive disc brakes

Sufficient heat dissipation is crucial to the effective operation of friction based braking systems. Such cooling is generally provided by ensuring a sufficient supply of cooling air to the heated components, hence the aerodynamics in the region of the brake components is extremely important. The objective of the research was to develop an understanding of how aerodynamics could be used to improve the cooling of automotive disc brakes. Two separate sets of wind tunnel experiments were developed. Tests were performed on a vented disc (rotor) to measure the internal flow through the vents on a rotating vented disc under various conditions, including an isolated disc in still air, the disc in still air with the wheel on, the disc in moving air with the wheel on, and an on-road simulation using a ¼ car. On vehicle tests were also performed in a wind tunnel using a purpose built brake test rig. These tests measured the thermal performance of different brake discs under various operating parameters; including constant load braking, and cooling from high temperature under various speeds, wheels and disc types. It was found that airflow through vented rotors was significantly reduced during simulated on-road driving, compared to when measured in isolation, but not particularly affected by the vehicles speed. In the situations tested, vented discs offered a 40+% improvement in cooling over an equivalent sized solid rotors. However the research indicates that the greatest benefit of vented rotors over solid will be in vehicles where air entering the wheel cavity is limited, such as low drag vehicles. It was also found that the most significant improvements in brake thermal performance could be achieved by maximising the airflow into the region of the brake components; including increasing the open area of the wheel, and increasing the vehicle velocity. Other improvements can be achieved by using a wheel material with good conductive capability, and increasing the mass of the disc. Evidence of vortex shedding was also discovered in the airflow at the exit of an internal vented rotor, any reduction in this flow disturbance should lead to increased airflow with associated improvements in thermal performance

Test stand design and automated sequences implementation

Chemnitz University of Technology has been involved since 2018 in an academic automotive championship gathering 1:10 fuel cell/battery-powered vehicles. The goal of the race being to travel the longest distance with a limited amount of hydrogen and electricity, it would be meaningful to predict the vehicle fuel consumption prior to the race for a given driving style. For this purpose, the present work proposes a new approach which consisted in designing a chassis dynamometer allowing to implement race driving cycles and to emulate the related road load thanks to a real time industrial automation PLC software. In particular, the chassis dynamometer was designed with PTC CREO and is composed of four trunnionmounted hub dynamometers whose power absorption is performed by hysteresis brakes. The four modules can be controlled independently to adapt the type of 1:10 vehicle powertrain and are controlled from sequences that are implemented by using TwinCAT 3. The data acquisition system from Beckho Automation based on the real time eld bus EtherCAT has enabled the system to be tested under high transient driving cycles. The work has resulted of a chassis dynamometer capable of assessing the vehicle speed from 0 to 30 km=h with an accuracy lower than 3%. The vehicle battery voltage can be measuredin the range 0 to 10 V with an uncertainty lower than 0.1 %. Moreover, the test bench allow to compute the wheel's torque with a proper stability but considering a long delay between the reference torque value and dynamometer response. Finally, a driving cycle has been implemented and the vehicle associated to the PID controller has showed a response time lower than 80 ms.Chemnitz University of Technology has been involved since 2018 in an academic automotive championship gathering 1:10 fuel cell/battery-powered vehicles. The goal of the race being to travel the longest distance with a limited amount of hydrogen and electricity, it would be meaningful to predict the vehicle fuel consumption prior to the race for a given driving style. For this purpose, the present work proposes a new approach which consisted in designing a chassis dynamometer allowing to implement race driving cycles and to emulate the related road load thanks to a real time industrial automation PLC software. In particular, the chassis dynamometer was designed with PTC CREO and is composed of four trunnionmounted hub dynamometers whose power absorption is performed by hysteresis brakes. The four modules can be controlled independently to adapt the type of 1:10 vehicle powertrain and are controlled from sequences that are implemented by using TwinCAT 3. The data acquisition system from Beckho Automation based on the real time eld bus EtherCAT has enabled the system to be tested under high transient driving cycles. The work has resulted of a chassis dynamometer capable of assessing the vehicle speed from 0 to 30 km=h with an accuracy lower than 3%. The vehicle battery voltage can be measuredin the range 0 to 10 V with an uncertainty lower than 0.1 %. Moreover, the test bench allow to compute the wheel's torque with a proper stability but considering a long delay between the reference torque value and dynamometer response. Finally, a driving cycle has been implemented and the vehicle associated to the PID controller has showed a response time lower than 80 ms

Development of a fuel-saving algorithm for a vehicle's driver assistant system

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2018.A fim de reduzir o consumo de combustível em sistemas de propulsão automotivos, a implementação de conjuntos motrizes híbridos, o downsizing de motores à combustão interna e a automatização do câmbio têm crescido no mercado de veículos de passeio. No entanto, as melhorias individuais em sistemas de um veículo não necessariamente aproximam a sua operação do ponto de ótima eficiência, e a adição de diferentes fontes de energia deve ser feita de forma metódica e estruturada, a fim de proporcionar ganhos consideráveis em consumo de combustível. Ademais, o comportamento do condutor e as trajetórias percorridas pelo veículo são características extremamente dependentes da região em análise, dificultando ainda mais o desenvolvimento de uma estratégia única de redução de consumo de combustível. Assim, a partir de um modelo de dinâmica longitudinal com três graus de liberdade para um veículo genérico, desenvolvido utilizando as equações de Euler-Lagrange do segundo tipo, essa dissertação tem como objetivo principal a proposta de um algoritmo para um assistente de direção automotivo, o qual promove a redução do consumo de combustível a partir do ajuste da relação de transmissão e abertura da válvula borboleta, em função da demanda de torque imposta pelo condutor, dinâmica do powertrain e características da fonte de potência. As características de desempenho do motor foram modeladas utilizando Redes Neurais Artificiais do tipo Feedforward Multi-Layer Perceptron, viabilizando a simulação de ciclos urbanos em tempo hábil e a inserção de propriedades relacionadas ao gradiente dos mapas estáticos no algoritmo do assistente de direção. O sistema foi implementado e simulado em Matlab , e seu desempenho avaliado através de um estudo de caso, utilizando modelos da literatura como referência.Abstract : The adoption of hybrid powertrain systems in passenger vehicles, as well as downsized engines and automatic transmissions, has been increasing in the last years as solutions to reduce the fuel consumption. However, the individual optimization of components or layout does not necessarily approximates the operation to conditions of maximum efficiency, and the addition of power sources should be done methodically, such that improvements of fuel efficiency can actually be achieved. Furthermore, the behavior of the driver and traffic conditions, factors which have major influence on the fuel consumption, vary with the geographic region, increasing the difficulty to develop a single solution to minimize the fuel consumption. Given such complex scenario, this dissertation proposes an algorithm for a Fuel-saving Driver Assistant System, which actuates on the throttle valve and gearbox, based on the demand of torque imposed by the driver, powertrain dynamics and characteristics of the power sources. In order to do so, a mathematical model of powertrain and longitudinal dynamics with 3 Degrees of Freedom was developed, which allows the simulation of urban traffic conditions. The performance of the engine was modeled using Artificial Neural Networks (ANN), which allies a flexible representation of the nonlinear characteristics of the power source, low computational costs and possibility to derive gradient information from the static maps, which is used by the Driver Assistant Algorithm. The system was implemented on Matlab and its performance compared to different models available in the literature

Robust control of brake systems with decoupled architecture

Modern brake systems have the tendency to decoupled brake system design involving electric and/or electrohydraulic brake actuators. In this thesis, a corresponding brake control architecture applicable for electric and automated vehicles is proposed and includes (i) base braking, (ii) brake blending and (iii) wheel slip control functions. Main focus has been given to the robustness of continuous wheel slip control during emergency braking in high and low road friction conditions. As the solution, several control laws were designed and experimentally validated during road tests. Results obtained for three vehicle prototypes with individual on-board and in-wheel electric motors and electrohydraulic brake-by-wire system present significant improvement in braking performance and ride quality compared to the conventional wheel slip control strategies.Moderne Bremssysteme tendieren zur entkoppelten Konstruktion mit involvierten elektrischen und/oder elektrohydraulischen Aktuatoren. In der vorliegenden Arbeit ist die entsprechende Bremsregelungsarchitektur für die elektrischen und automatisierten Fahrzeuge vorgeschlagen, die beinhaltet Funktionen zur (i) primären Bremsung, (ii) gemischten Bremsung und (iii) Radschlupfregelung. Der Schwerpunkt dieser Arbeit ist auf die Robustheit der kontinuierlichen Radschlupfregelung während einer Notbremsung bei hoher und niedriger Fahrbahnreibung gelegt. Als die Lösung sind mehrere Regelungsstrategien entwickelt und experimentell validiert. Die Ergebnisse für drei Fahrzeugprototypen mit individuellen Board- und Radnabemotoren und einem elektrohydraulischen Brake-by-Wire System demonstrieren wesentliche Verbesserung der Bremsleistung und Fahrqualität im Vergleich zu den konventionellen Strategien der Radschlupfregelung