| Abstract | One of the main topics in automotive industry is improvement of vehicles driving characteristics and development of safety systems. Market demand and new rigorous legislation are forcing car manufacturers on further developing of already existing systems with the goal of improving safety and overall driving experience. One of the pioneering systems is ABS (Anti-lock braking system), which has a main goal of preventing tendency of wheel lock during emergency braking, which in the end shortens the braking distance. Also, stability and manoeuvrability during braking must be left, so possible obstacles can be avoided. ABS systems have improved, owing to the development of new technologies, but also owing to acquired experience and deeper understanding of braking systems. Of course, conventional ABS systems have disadvantages which are resulting from its design. Main disadvantages like slower actuation time when the braking fluid is cold, brake pressure hysteresis, furious brake pedal oscillations during ABS engage-release valve switching and lastly the inability of keeping the tire slip in optimal working point are still present in current vehicles. These problems are trying to be solved with brake-by-wire systems. Brake-by-wire implicates that there is no mechanical or hydraulic connection between the brake pedal and the actuator, but instead the braking demand is sent over the micro-controller to the electromechanical actuator. The main goal of this thesis is to proof feasibility of this kind of systems paired with ABS control on electric vehicles to achieve faster actuation times, which results in shortening of braking distance and better vehicle manoeuvrability. First, model of the electromechanical brakes is presented in MATLAB/Simulink® environment. Then, equations have been derived with the help of quarter car model and wheel dynamics, on which two control architectures and observers are based. Browsing through literature it can be noticed that for ABS control of brake-by-wire systems, Gain Scheduling PI and Sliding mode control architectures have been used and have proven to be robust, so the mentioned controllers are presented in this work. Later, co-simulation model of AVL VSMTM and MATLAB/Simulink® has been presented and how these software packages are connected. Finally, two different electromechanical and electric motor brake configuration layouts are examined and how the ABS controllers are performing paired up with said brakes on typical braking test manoeuvres. |
| Abstract (croatian) | Poboljšanje voznih karakteristika i sigurnosnih sustava jedna je od glavnih tema u automobilskoj industriji. Potražnja tržišta i novi rigorozni zakoni tjeraju proizvođače automobila na razvoj novih i unapređenje već postojećih sustava u svrhu podizanja sigurnosti i kvalitete iskustva vožnje automobila. Jedan od pionirskih sustava je i ABS (eng. Anti-lock braking system), kojemu je glavni cilj da se prilikom jakog i agresivnog kočenja spriječi tendencija blokiranja kotača te time ostvari kratki zaustavni put te zadrži visoki stupanj upravljivosti i stabilnosti za zaobilaženje mogućih prepreka. ABS sustavi su se s vremenom sve više unapređivali, zahvaljujući razvoju novih tehnologija, a i zahvaljujući iskustvu i dubljem razumijevanju problematike kočionih sustava. Unatoč tome konvencionalni ABS sustavi imaju određene nedostatke koji proizlaze iz samog dizajna. Glavni nedostatci poput sporijeg uključivanja ABS-a prilikom hladne kočione tekućine, histereza kočionog pritiska, jako vibriranje kočione pedale uslijed otvaranja i zatvaranja ABS ventila te nemogućnost održavanja klizanja kotača u optimalnoj radnoj točci i dalje su prisutni u današnjim vozilima. Ovom problemu pokušava se doskočiti primjenom električnih kočionih sustava (engl. brake-by-wire systems). Kod njih ne postoji mehanička ili hidraulička veza između kočione pedale i samih kočnica, već se zahtjev za kočenjem šalje od upravljačke jedinice do elektromehaničkog aktuatora. Upravo je tema ovog rada ispitati izvedivost takvih sustava uparenih s ABS upravljanjem na električnim vozilima, kako bi se postiglo još brže, tj. optimalno kočenje u smislu skraćenja zaustavnog puta i poboljšanja upravljivosti prilikom kočenja. Prvo se predstavlja način modeliranja elektromehaničke kočnice unutar MATLAB/Simulink® okruženja. Zatim se, uz pomoć četvrtinskog modela automobila i dinamike kotača izvode jednadžbe na kojima se temelje dvije arhitekture regulatora i pomoćni algoritmi koji su razmatrani u ovom radu. Pregledom literature uočeno je da se za ABS upravljanje e-kočnicama najčešće koriste PI regulatori s planiranom adaptacijom pojačanja te regulatori zasnovani na kliznim režimima te su isti razmatrani u ovom radu. Nadalje je prikazan kooperativni simulacijski model AVL VSMTM-a i MATLAB/Simulink®-a te način na koji su ovi programski paketi povezani. Naposlijetku prikazan je model vozila za dva različita rasporeda elektromehaničkih kočnica i elektromotora, uz pomoć kojeg se ispituje robusnost samih regulatora na testnim manevrima uobičajenim za ispitivanje kočionih sustava. |
