This thesis proposes a new methodology of predicting squeal using the finite element method in which three validation stages are established. A detailed 3-dimensional finite element model of a real disc brake is not only validated through modal analysis at the components and assembly levels but also through contact analysis where static contact pressure distribution and its contact area match with the experimental results. The main key issue in this research is the refinement of contact interface model of the friction material. Having assumed a smooth and flat surface (or perfect contact interface) in the past, current research considers a real surface topography of which measurementsa re carried out in order to obtain a realistic contact interface model. It is found that with the refined disc brake model, a good correlation is achieved between the predicted results and experimental ones on the contact pressure distribution and contact area at the piston and finger pads. Complex eigenvalue analysis that is available in ABAQUS software package is used as the main tool to predict squeal generation. Prediction of squeal occurrence is limited to a frequency range of I kHz to 8 kHz. Simulations of disc brake squeal are performed at different friction characteristics with the inclusion of friction damping for the perfect contact interface and real contact interface models. It is shown that the real contact interface model predicts squeal occurrences much better than the perfect contact interface model by considering the effect of negative u-v slope and friction damping. Comparison between complex eigenvalue analysis and dynamic transient analysis using a reduced FE model is also made for different contact schemes. It is found that using small sliding with Lagrange multiplier contact scheme predicted results in both analyses in a good agreement. Wear effects on instability of the disc brake assembly are also simulated. The results show that with the inclusion of wear, unstable frequencies are predicted to appear and disappear as wear progresses even though similar boundary conditions and operating conditions are imposed to apparently the same disc brake model. This phenomenon may explain the fugitive nature of squeal behaviour.

No description available.

Research in brake squeal has been conducted for over fifty years in many different areas and still it is not completely understood. Experimental testing is very time consuming, therefore, there is a need for the development of an analytical model to simulate the test results prior to the prototype stage has arisen in order to gain a deeper understanding of the physics of the system. In this thesis analytical beam and annular plate models in order to investigate the vibrational behaviour of an automotive brake discs are presented and compared to experimental measurements.

Σκοπός της παρούσας διπλωματικής εργασίας είναι ο σχεδιασμός ενός ελεγκτή πέδησης για την ρυμουλκόμενη μονάδα μιας νταλίκας, ώστε αυτή να μην αποκλίνει της πορείας της κατά το φρενάρισμα. Αναλυτικότερα, στο κεφάλαιο 1 παρουσιάζεται η μορφή των τυπικών και πιο συνηθισμένων ρυμουλκόμενων οχημάτων (οδικά τρένα) και ορίζονται τα βασικά κομμάτια που το αποτελούν. Στο κεφάλαιο 2 παρουσιάζονται με χρήση κατάλληλων μαθηματικών και φυσικών προτύπων οι ταχύτητες και οι επιταχύνσεις καθώς και τα διάφορα συστήματα συντεταγμένων που απαιτούνται για την περιγραφή της κίνησης του οχήματος. Στο κεφάλαιο 3 αναλύεται το σύνθετο αλλά και το απλουστευμένο μοντέλο των οδικών τρένων, ενώ στο κεφάλαιο 4 αναλύουμε το δυναμικό μοντέλο του οχήματος tractorsemitrailer που αποτελεί και το αντικείμενο έρευνας της εργασίας. Υπολογίζουμε πλήρως τις εξισώσεις που περιγράφουν το σύστημα, με βάση κάποιες προϋποθέσεις όπως ότι κινείται στην ευθεία, με σταθερή διαμήκη ταχύτητα ενώ επίσης δεχόμαστε και το γραμμικό μοντέλο για τα ελαστικά. Τέλος, στο κεφάλαιο 5 σχεδιάζουμε ένα PD ελεγκτή και βρίσκουμε τις βέλτιστες τιμές των παραμέτρων του ώστε το σύστημα μας να παρουσιάζει όσο το δυνατόν μικρότερα σφάλματα. / Aim of present diplomatic work is the planning of controller of braking for the followinf unit of lorry, in order that this does not deviate her course at the break. More analytically, in capital 1 is presented the form the formal and more usual road trains and is fixed the basic pieces where constituting. In capital 2 are presented with use suitable mathematic and natural models the speeds and the accelerations as well as the various systems of coordinates that are required for the description of movement of vehicle. In capital 3 is analyzed the complex but also simplified model of road trains, while in capital 4 we analyze the dynamic model of vehicle tractorsemitrailer that is the subject of this work. We calculate the equations that describe the system, with base certain conditions as that it is moved in the straight line, with constant speed while also we accepted the linear model for the tyres. Finally, in capital 5 we draw a PD controller and we find the most optimal prices of parameters in order that our system presents as much as possible smaller faults.

The thesis presents research into the understanding and improvement of heat dissipation from friction brakes. The investigations involved two brake types, considered to be the most thermally loaded and therefore most challenging; axle mounted high speed railway and commercial vehicle disc brakes. All three modes of heat transfer (conduction, convection and radiation) and airflow characteristics have been analysed experimentally and theoretically in order to increase the understanding of heat dissipation. Despite the very practical aspects of this research, a 'generic heat transfer approach' was applied, enabling wider engineering applications of the results. Experimental analyses conducted on a specially developed Spin Rig allowed measurements of cooling and airflow characteristics for different designs. Methodologies have been developed to determine thermal contact resistance, heat transfer coefficients, emissivity and aerodynamic (pumping) losses. Established values and relationships compared very favourably with theoretical work. Analytical, FE and CFD analyses were employed to further investigate design variations and perform sensitivity studies. Inertia dynamometer route simulations provided disc temperatures for validation of the overall work. Recommendations have been made for optimising heat dissipation, by proposing practically acceptable and economically viable design solutions. A proposed ventilated disc design efficiency ratio allows large, high speed ventilated disc designs, to be efficiently and accurately evaluated and compared, providing a valuable disc design optimisation tool. The determination of the methodologies, parameters and functions defining cooling characteristics, enable heat dissipation to be predicted confidently and accurately for brakes and other engineering assemblies at early design stages.

Στόχος της εργασίας είναι η μοντελοποίηση και ο έλεγχος με τη χρήση υπολογιστή του συστήματος της πέδησης του αυτοκινήτου καθώς και της επιτάχυνσης (γκάζι - throttle) του κινητήρα. Για την πέδηση μελετήθηκε και υλοποιήθηκε στο Simulink το μοντέλο που περιγράφεται στην εργασία των Humair Raza, Zhigang Xu, Bingen Yang και Petros A. Ioannou με τον τίτλο “Modeling and Control Design for a Computer-Controlled Brake System”. Για την πέδηση και την επιτάχυνση, ενοποιημένα σε ένα ενιαίο μοντέλο που περιγράφει το όχημα, μελετήθηκε η εργασία των P. Ioannou και Z. Xu με τίτλο “Throttle and Brake Control Systems for Automatic Vehicle Following”, και στη συνέχεια υλοποιήθηκαν στο Simulink τα μοντέλα για την πέδηση και το throttle. Στην συνέχεια δοκιμάσαμε τους ελεγκτές εφαρμόζοντας διάφορες εισόδους (σενάρια φρεναρίσματος) και λάβαμε τις αναμενόμενες από τη θεωρία εξόδους, επαληθεύοντας έτσι την ορθότητά τους. / The aim of this study is to model and control with the computer the car brake system and the engine throttle. For the brake system we studied and implemented in the Simulink the model described in the work of Humair Raza, Zhigang Xu, Bingen Yang and Petros A. Ioannou titled "Modeling and Control Design for a Computer-Controlled Brake System ". For the braking and the acceleration, consolidated into a single model describing the vehicle, we studied the work of P. Ioannou, Z. Xu entitled "Throttle and Brake Control Systems for Automatic Vehicle Following ", and then we implemented the models in Simulink. Then we tried applying different controllers inputs (braking and acceleration scenarios) and we verified the models' correctness.

The thesis presents an intermediate modelling approach to study transient behaviour of vehicle systems, with emphasis put on simplified yet accurate representation of important system elements. A representative non-linear vehicle model is developed in MA TLAB/Simulink environment, where non-linear characteristics of tyre, suspension and braking system are included to capture the dynamic behaviour of a vehicle under transient conditions. The novel aspect of this work is the application of a representative full vehicle-tyre-ABS integrated set-up to study the complicated interaction between tyre and anti-lock braking, under a range of demanding operating conditions, including combined cornering and braking. The modelling methodology involves development of low end vehicle models, based on the Newton-Euler formulation. Subsequently, an intermediate vehicle model is devised, where more details are incorporated such as additional DOF to capture the sprung mass motion in space, along with its non-linear interactions with the un-sprung masses, large angle effects, kinematics of steering/wheels and an appropriate tyre model suitable for transient manoeuvres. Particular attention is paid to the suspension system modelling, through inclusion of non-linear effects in springs, dampers, bump-stops, and anti-roll bars, along with the jacking and anti-dive effects using the virtual work method. The model also incorporates a hydraulic brake model, based on the reduced order brake system dynamics for realistic simulation of the braking manoeuvres. A complex multi-body ADAMS/Chassis model, with much greater level of detail, has also been established to extensively compare and enhance the realistic behaviour of the intermediate vehicle model. During the simulation exercise, the intermediate vehicle model has shown good agreement with the complex ADAMS model, thus justifying the accurate representation of vehicle.non-linear characteristics, particularly the suspension system. The realistic behaviour of the vehicle model is further ascertained with a reliable GPS enabled test vehicle, by performing number of manoeuvres on test tracks, including combined cornering and braking. A representative 4-channel conventional ABS system is modelled and integrated in the intermediate vehicle model. The ABS adopts generic peak seeking approach, employing wheel deceleration and brake slip as control variables. External braking inputs, in form of stepped pressure pulses, are also separately used to represent the transient braking system dynamics. In the current work, different transient tyre models based on the single point contact approach and using Magic Formula steady-state characteristics are applied, while studying the influence of their dynamic behaviour on the ABS system. By employing a representative ABS system in a multi-body vehicle model and considering the particularly demanding situation of combined braking I cornering, it is shown that the models which are adequate for pure braking might struggle when the complicated full vehicle dynamics are excited. It is shown that the first order relaxation length approach may not be sufficient to fully satisfy the requirements of an ABS braking, especially if the relaxation length is not modelled as a variable dependent on tyre slip. In comparison, the modelling approach, where the carcass compliances and contact patch properties are explicitly represented, can handle the oscillatory tyre behaviour associated with ABS braking, in a far more accurate manner. In comparison to the earlier studies, which were mostly conducted for straight-line braking, this thesis stresses the fact that the tyre behaviour can be influenced by the complex interaction of handling and braking, and hence the effect should be captured while investigating or evaluating the performance of a tyre model in relation with ABS simulation.