Identifikacija termičkih naprezanja disk kočnice za različite radne parametre kočenja
Identification of disc brake thermal strains for different braking operating parameters
Author
Stojanović, NadicaMentor
Glišović, JasnaCommittee members
Lukić, JovankaMiloradović, Danijela
Taranović, Dragan
Dorić, Jovan
Metadata
Show full item recordAbstract
Termička naprezanja disk kočnica i njihov uticaj na efikasnost kočenja predstavljaju
jedan od najvećih problema tokom eksploatacije vozila. U doktorskoj disertaciji
objašnjen je najpre uzrok nastanka problema zagrevanja kočnica, kao i njegove posledice
na funkcionisanje kočnog sistema, pa čak i na bezbednost saobraćaja. Rezultati ove
doktorske disertacije ogledaju se u razvoju i realizaciji specifičnog probnog stola za
ispitivanja termičkih naprezanja disk kočnica, koji je primenjen za dobijanje
eksperimentalnih rezultata korišćenih u analizi uticaja radnih parametara kočenja
na disk kočnice. Eksperimentalna ispitivanja disk kočnice su vršena po testovima
koji su definisani u okviru doktorske disertacije. Prema razvijenim testovima
izvršena su i ispitivanja, kao i utvrđivanje koja od nezavisno promenljivih (ulaznih)
veličina, kao što su početna brzina simuliranog vozila, kočni pritisak i masa
četvrtine vozila, ima najveći uticaj na izlazne parametre – temperaturu kočnog disk...a
i kočnih pločica, kočni moment, koeficijent trenja i vreme zaustavljanja.
U skladu sa napretkom tehnologije i numeričkih alata za rešavanja različitih
inženjerskih problema, u doktorskoj disertaciji je primenjen softverski paket ANSYS,
modul Transient Structural, u cilju razvoja modela za prikazivanje termičkog ponašanja
disk kočnica. Izvršena je analiza termičkih naprezanja na virtuelnom modelu koji
dimenziono i prema karakteristikama primenjenih materijala u potpunosti odgovara
realnom modelu, pri čemu su granični uslovi bili isti kao u slučaju laboratorijskog
eksperimenta. Analiza se koristi za određivanje odstupanja između rezultata
eksperimentalnih i numeričkih ispitivanja, kao i za utvrđivanje da li se razvijeni
numerički model može uspešno primenjivati za dalja istraživanja. Razvijeni model je
imao odstupanja u dozvoljenim granicama, pa je korišćen za analizu još dve disk
kočnice, koje su se razlikovale po konstrukciji rebara diska. Primenjeni oblici
rebara kod kočnog diska su: radijalni, zakrivljeni i stubičasti.
Danas se od kočnih diskova očekuje da odvedu što veću količinu toplote u okolinu,
odnosno, da imaju sposobnost da omoguće dobro hlađenje u širokom opsegu brzina. Kroz
analizu koja je izvršena u softverskom paketu ANSYS, ali pomoću modula Fluid Flow
(Fluent), pokazano je da oblik rebara utiče u velikoj meri na rasipanje toplote, kao i da
se kočni disk sa zakrivljenim rebrima najmanje zagreva. Rezultati analize pokazuju da
kočni disk sa zakrivljenim rebrima omogućava da vazduh velikom brzinom prođe između
rebara i da se na taj način velika količina toplote odvede u okolinu. U cilju
predviđanja vrednosti temperature na najopterećenijem delu kočne pločice, razvijen je
model za predikciju temperature kočnih pločica visoke tačnosti, u kome su varirani:
masa vozila, brzina kretanja, kočni pritisak i vreme zaustavljanja.
Rezultati ove doktorske disertacije, kao što su realizovani probni sto i numerički
model, mogu poslužiti firmama koje se bave proizvodnjom kočnih diskova i kočnih
pločica za predviđanje njihovog ponašanja u eksploataciji. Takođe, dobijeni
eksperimentalni rezultati mogu se koristiti za kreiranje virtuelnih modela za
ispitivanje disk kočnice. Virtuelni model razvijen za potrebe ove doktorske
disertacije može se koristiti za razvoj/poboljšanje kočnog diska i kočnih pločica u
cilju smanjenja troškova razvoja.
Thermal strains of disc brakes and their influences on the braking efficiency are representing
one of the greatest problems during the vehicle exploitation. The cause of the brake heating
problem is explained in PhD thesis, as well as its consequence on the braking system
functionality, and even on the traffic safety. Results of this PhD thesis are reflected in the
development and realization of the specific test rig for investigation of disc brake’s thermal
stresses, which was applied to obtain experimental results used in the analysis of the influence
of operating braking parameters on disc brakes. Experimental tests of the disc brake were
performed according to the tests defined in the doctoral dissertation. According to the developed
tests, various laboratory tests were performed, as well as determining which of the
independently (input) variables, such as the initial speed of the simulated vehicle, braking
pressure and vehicle mass quarter, has the greatest influence on ...the output parameters –
temperature of the braking disc and braking pads, braking torque, friction coefficient and
stopping time.
In line with advances in technology and the numerical tools for solving various engineering
problems, the ANSYS software package, Transient Structural module, was applied in PhD
thesis in order to develop the model for the representation of disc brake’s thermal behaviour.
The analysis on the thermal stresses was performed on a virtual model that dimensionally and
according to the characteristics of the applied materials fully corresponds to the real model, and
the boundary conditions were the same as in the case of the laboratory experiment. Such
analysis is used to determine the discrepancies between the results obtained experimentally and
numerically, as well as to determine whether the developed numerical model can be
successfully applied for further research. The developed model had deviations within the
allowed limits, so it was used for the analysis of two more disc brakes, which differed in the
construction of the disc ribs. The rib shapes used in the brake disc are: radial, curved and pillar.
Today, brake discs are expected to dissipate as much heat as possible into the environment, that
is, to have the capability to provide better cooling for a wide range of speeds. Through the
analysis performed in the ANSYS software package, using the Fluid Flow (Fluent) module, it
has shown that the shape of the ribs greatly affects the heat dissipation, as well as that the brake
disc with curved ribs heats up the least. Results of the analysis show that the brake disc with
curved ribs provides to the air to pass with high speed between ribs, and in that way, the great
amount of heat is dissipated into the environment. In order to predict the temperature values at
the most loaded part of the brake pad, a model with high-accuracy prediction was developed,
in which the following factors were varied: vehicle mass, moving speed, braking pressure, and
stopping time.
Results of this PhD thesis, such as the realized test rig and numerical model, can be used by
companies engaged in the production of brake discs and brake pads, with the aim to predict
their behaviour in the exploitation. Also, the obtained experimental results can be used to create
of virtual models for disc brake’s testing. The virtual model developed for the purposes of this
PhD thesis, can be used to develop/improve the brake disc and brake pads in order to reduce
development costs.