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Investigação do desgaste de freios e embreagens em prensas mecânicas. / Clutch and brakes wear in mechanical presses.Philip von Pritzelwitz 17 June 2010 (has links)
Embreagens de prensas mecânicas, principalmente as de forja a quente se caracterizam por um intenso regime de trabalho com espaços muito curtos entre acionamentos. Muitas das embreagens apresentam desgaste acentuado obrigando a paradas frequentes para manutenção. Neste trabalho são discutidos os princípios de funcionamento de prensas excêntricas e os parâmetros de projeto de embreagens e freios. Pontos importantes são: o balanço entre torque de operação, número de inserções por minuto e a dissipação de calor. É feita uma breve revisão da literatura sobre compósitos, lonas e seu comportamento. Discute-se a diferença das premissas de projeto de uma lona automotiva e a lona para uso industrial com alto número de aplicações por minuto. Apresenta-se um pressuposto quanto ao processo de transmissão de calor na embreagem e o que influência no desgaste da mesma, relacionando-o com a pressão de contato. Nas manutenções se verificam resíduos (debris) diferentes sugerindo regimes diferentes de desgaste. Há um resíduo preto que caracteriza um regime severo de desgaste. Pode-se associar esse resíduo ao fenômeno da degradação da base polimérica que compõe a lona. A degradação da base polimérica é causada pela alta temperatura de operação dessas embreagens. Em ensaios simples de pino e disco consegue-se reproduzir desgaste das lonas, que comprova o observado na prática e as condições que isso ocorre. Finalmente são apresentadas sugestões para o dimensionamento das embreagens e cuidados necessários no projeto de freios e embreagens. / Mechanical press clutches, especially clutches for hot forging presses have a hard working cycle with a little time between engagements. Many of those clutches present a severe lining wear, needing frequent maintenance stops. This work is discusse, the basics of eccentric presses and the clutch design parameters. Important points are: the balance between operation torque, engagements per minute and heat dissipation. This also presents a short literature review regarding composites and linings. It is discussed the design baselines differences between automotive linings and this specific case. It is presented a hypothesis about the heat transfer process in the clutch and how its related with wear, associating it with the contact pressure. In maintenance it is found different kinds of wear debris, suggesting more than one wear regime. The black debris indicates a severe wear regime. This debris can be associated to the lining polymeric matrix degradation. The polymeric matrix degradation is caused by the high op eration temperatures in these clutches. Based on simple pin-on-disc tests can be obtained results that show what is practical observed and the conditions this occurs, proving the hypothesis. Finally are presented suggestions for clutch dimensioning and necessary project cares.
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Design and construction of a linear magnetic particle brakeThompson, Matthew Valentine January 1981 (has links)
Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Matthew Valentine Thompson. / B.S.
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Avaliação das variações na força de atrito de materiais de fricção utilizando um tribômetroMoraes, Tiago Roberto Borges de January 2016 (has links)
A demanda crescente por veículos mais confortáveis e mais seguros apresenta desafios à indústria. Os freios são um dos mais importantes sistemas de segurança dos veículos e também são frequentemente objeto de reclamações de consumidores por motivo de ruído. Os materiais de atrito empregados nos sistemas de freio devem apresentar desempenho satisfatório sob diferentes condições de temperatura e umidade, possuindo resistência à corrosão, longa vida útil, baixo custo e produzindo baixos níveis de ruído. Com o objetivo de caracterizar diferentes materiais quanto ao coeficiente de atrito e à produção de ruído, foram realizados ensaios de frenagem em diferentes condições utilizando um tribômetro. Esse equipamento possui sistemas de medição e controle capazes de registrar os coeficientes de atrito a cada frenagem simulada. O tribômetro também foi instrumentado com uma célula de carga capaz de medir variações da força de atrito. Os ensaios foram realizados em diferentes condições de temperatura e de intervalos de tempo entre as frenagens, alternando etapas quentes e frias. Durante o assentamento dos materiais, foram verificados diferentes comportamentos do coeficiente de atrito. Os materiais ensaiados apresentaram sensibilidade às variações de temperatura e de intervalos de tempo entre frenagens. Foi observada correlação entre as variações da força de atrito e o coeficiente de atrito. Também foram evidenciados os efeitos da velocidade de deslizamento sobre o espectro de frequências de variação da força de atrito. / The growing demand for more comfortable and safer vehicles comes up with new challenges to the industry. The brakes are one of the most important vehicle safety systems and are also often the subject of customer complaints about noise. The brake friction materials need to perform properly under different conditions of temperature and humidity, presenting resistance to corrosion, long life, low cost and producing low noise levels. In order to characterize the friction coefficient and noise generation of different friction materials, different conditions were tested using a tribometer. This equipment has measurement and control systems capable of record each brake stop friction coefficient. The tribometer was also instrumented with a load cell capable of measuring friction force variations. The tests were performed at different temperatures and time intervals between brake applications, alternating hot and cold stages. During the materials running-in, different behaviors of the friction coefficients were found. The friction materials tested showed sensitivity to temperature variations and time intervals between brake applications. There was a correlation between friction force variations and coefficient of friction. There were also effects of the slip speed on the frequency spectrum of the frictional force variations.
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Development of Diagnostic Algorithms for Air Brakes in TrucksDhar, Sandeep 2010 August 1900 (has links)
In this dissertation, we focus on development of algorithms for estimating the severity
of air leakage and for predicting the out-of-adjustment of pushrod in an air brake
system of heavy commercial vehicles. The leakage of air from the brake system
causes a reduction in the steady-state pressure in the brake chamber and an increase
in the lag of the braking pressure response thereby increasing the stopping distance
of the vehicle. Currently a presence of leak in the system is detected for the severities
of leak that cause the reservoir pressure to drop below a threshold, such as, the
leakage of compressed air due to rupture of the reservoir or of the hoses carrying the
compressed air. The leakage of air is also possible due to several other reasons such
as, cracks in the hoses, loose couplings between the hoses etc. The severities of leak,
corresponding to such situations, do not lead to the reservoir pressure drop below
the threshold; therefore, their presence remains undetected. For the detection and
estimation of such severities of leak, a diagnostic scheme has been given and is based
on a model developed for the mass
ow rate of the leakage of air from the air brake
system.
Out-of-adjustment of the pushrod is the extension of pushrod beyond a prede-
ned value and for safety concerns, an extension beyond this value is not desired.
Currently no warning system is available for monitoring the out-of-adjustment of
pushrod, except, during the safety inspection. Inspection of the pushrod for outof-
adjustment is the most labor-intensive and time consuming task during a typical
safety inspection procedure. For efficient and continuous monitoring of the pushrod
for out-of-adjustment, a diagnostic algorithm for estimating the steady-state pushrod
stroke has been developed. The scheme is expected to expedite the inspection process
for the out-of-adjustment of pushrod. Experimental data from the air brake test
setup at Texas A and M University has been used for corroborating both the models.
Also, the problem of parameter estimation of sequential hybrid systems such as
the air brake system, has been addressed. The \hybrid" nature of the air brake system
stems from the system being in di erent modes corresponding to di erent values
of the displacement of the pushrod and is a result of di erent spring compliances
associated with the pushrod in di erent ranges of its displacement. The air brake
system is \sequential" in the sense that as the pressure increases, the displacement
of the pushrod increases and there is a distinct sequence of modes that the system
will transition through and upon a reduction in pressure, the sequence of modes is
revisited in the reverse order. The mode to mode transition of the air brake system
is governed by the parameters, such as, the clearance between the brake pad and
the brake drum. The problem of estimation, that has been addressed, is as follows:
Suppose the pressure in the air brake system were to be measured and that the motion
of the pushrod is not measured. Is it possible to estimate the nal displacement of
the pushrod without knowing the parameters, such as the clearance, that govern the
system to transition from one mode to another?
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A diagnostic system for air brakes in commercial vehiclesCoimbatore Subramanian, Shankar Ram 17 September 2007 (has links)
This dissertation deals with the development of a model-based diagnostic system
for air brake systems that are widely used in commercial vehicles, such as trucks,
tractor-trailers, buses, etc. The performance of these brake systems is sensitive to
maintenance and hence they require frequent inspections. Current inspection techniques
require an inspector to go underneath a vehicle to check the brake system
for possible faults, such as leaks, worn brake pads, out-of-adjustment of push rods,
etc. Such inspections are time consuming, labor intensive and difficult to perform
on vehicles with a low ground clearance. In this context, the development of an onboard/
handheld diagnostic tool for air brakes would be of significant value. Such a
tool would automate the brake inspection process, thereby reducing the inspection
time and improving the safety of operation of commercial vehicles. In this dissertation,
diagnostic schemes are developed to automatically detect two important and
prevalent faults that can occur in air brake systems â leaks and out-of-adjustment of
push rods.
These diagnostic schemes are developed based on a nonlinear model for the pneumatic
subsystem of the air brake system that correlates the pressure transients in the
brake chamber with the supply pressure to the treadle valve and the displacement of the treadle valve plunger. These diagnostic schemes have been corroborated with
data obtained from the experimental facility at Texas A&M University and the results
are presented.
The response of the pneumatic subsystem of the air brake system is such that it
can be classified as what is known as a âÂÂSequential Hybrid SystemâÂÂ. In this dissertation,
the term âÂÂhybrid systemsâ is used to denote those systems whose mathematical
representation involves a finite set of governing ordinary differential equations corresponding
to a finite set of modes of operation. The problem of estimating the push
rod stroke is posed as a parameter estimation problem and a transition detection
problem involving the hybrid model of the pneumatic subsystem of the air brake system.
Also, parameter estimation schemes for a class of sequential hybrid systems are
developed. The efficacy of these schemes is illustrated with some examples.
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A mathematical model for air brake systems in the presence of leaksRamaratham, Srivatsan 10 October 2008 (has links)
This thesis deals with the development of a mathematical model for an air brake
system in the presence of leaks. Brake systems in trucks are crucial for ensuring
the safety of vehicles and passengers on the roadways. Most trucks in the US are
equipped with S-cam drum brake systems and they are sensitive to maintenance.
Brake defects such as leaks are a major cause of accidents involving trucks. Leaks in
the air brake systems affect braking performance drastically by decreasing the peak
braking pressures attained and also increasing the time required to attain the same,
thereby resulting in longer stopping distances. Hence there is a need for detecting
leaks in an air brake system.
In this thesis, a mathematical model for an air brake system in the presence of
leaks is developed with a view towards developing an automatic leak detection system
in the near future. The model developed here builds on an earlier research at Texas
A&M University in which a "fault free" model of an air brake system is developed,
i.e., a mathematical model of an air brake system that predicts how the pressure in
the brake chamber evolves as a function of the brake pedal input when there are no
leaks in the air brake system.In order to develop a model for an air brake system in
the presence of leaks, one must characterize a "leak". A leak may be characterized by
the location and its size. Since the pipes are short, the location of the leak does not significantly affect the evolution in the brake pressure as much as its size. For this
reason, "effective area" of the leak was chosen as a characteristic of the leak. It was
estimated by fitting an empirical relation for leak with leak flow measurement data.
The supply pressure and effective area of leak comprised the inputs to the model
along with the displacement of the foot pedal (treadle valve plunger). The model was
corroborated with the experimental data collected using the setup at Texas A&M
University.
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Modelling and control of an automotive electromechanical brake /Line, Christopher Leonard James. January 2007 (has links)
Thesis (Ph.D.)--University of Melbourne, Dept. of Mechanical and Manufacturing Engineering, 2007. / Typescript. Includes bibliographical references (leaves 251-258).
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Modeling, design, testing and control of a two-stage actuation mechanism using piezoelectric actuators for automotive applicationsNeelakantan, Vijay Anand, January 2005 (has links)
Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvii, 213 p.; also includes graphics (some col.). Includes bibliographical references (p. 206-213). Available online via OhioLINK's ETD Center
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Avaliação das variações na força de atrito de materiais de fricção utilizando um tribômetroMoraes, Tiago Roberto Borges de January 2016 (has links)
A demanda crescente por veículos mais confortáveis e mais seguros apresenta desafios à indústria. Os freios são um dos mais importantes sistemas de segurança dos veículos e também são frequentemente objeto de reclamações de consumidores por motivo de ruído. Os materiais de atrito empregados nos sistemas de freio devem apresentar desempenho satisfatório sob diferentes condições de temperatura e umidade, possuindo resistência à corrosão, longa vida útil, baixo custo e produzindo baixos níveis de ruído. Com o objetivo de caracterizar diferentes materiais quanto ao coeficiente de atrito e à produção de ruído, foram realizados ensaios de frenagem em diferentes condições utilizando um tribômetro. Esse equipamento possui sistemas de medição e controle capazes de registrar os coeficientes de atrito a cada frenagem simulada. O tribômetro também foi instrumentado com uma célula de carga capaz de medir variações da força de atrito. Os ensaios foram realizados em diferentes condições de temperatura e de intervalos de tempo entre as frenagens, alternando etapas quentes e frias. Durante o assentamento dos materiais, foram verificados diferentes comportamentos do coeficiente de atrito. Os materiais ensaiados apresentaram sensibilidade às variações de temperatura e de intervalos de tempo entre frenagens. Foi observada correlação entre as variações da força de atrito e o coeficiente de atrito. Também foram evidenciados os efeitos da velocidade de deslizamento sobre o espectro de frequências de variação da força de atrito. / The growing demand for more comfortable and safer vehicles comes up with new challenges to the industry. The brakes are one of the most important vehicle safety systems and are also often the subject of customer complaints about noise. The brake friction materials need to perform properly under different conditions of temperature and humidity, presenting resistance to corrosion, long life, low cost and producing low noise levels. In order to characterize the friction coefficient and noise generation of different friction materials, different conditions were tested using a tribometer. This equipment has measurement and control systems capable of record each brake stop friction coefficient. The tribometer was also instrumented with a load cell capable of measuring friction force variations. The tests were performed at different temperatures and time intervals between brake applications, alternating hot and cold stages. During the materials running-in, different behaviors of the friction coefficients were found. The friction materials tested showed sensitivity to temperature variations and time intervals between brake applications. There was a correlation between friction force variations and coefficient of friction. There were also effects of the slip speed on the frequency spectrum of the frictional force variations.
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Avaliação das variações na força de atrito de materiais de fricção utilizando um tribômetroMoraes, Tiago Roberto Borges de January 2016 (has links)
A demanda crescente por veículos mais confortáveis e mais seguros apresenta desafios à indústria. Os freios são um dos mais importantes sistemas de segurança dos veículos e também são frequentemente objeto de reclamações de consumidores por motivo de ruído. Os materiais de atrito empregados nos sistemas de freio devem apresentar desempenho satisfatório sob diferentes condições de temperatura e umidade, possuindo resistência à corrosão, longa vida útil, baixo custo e produzindo baixos níveis de ruído. Com o objetivo de caracterizar diferentes materiais quanto ao coeficiente de atrito e à produção de ruído, foram realizados ensaios de frenagem em diferentes condições utilizando um tribômetro. Esse equipamento possui sistemas de medição e controle capazes de registrar os coeficientes de atrito a cada frenagem simulada. O tribômetro também foi instrumentado com uma célula de carga capaz de medir variações da força de atrito. Os ensaios foram realizados em diferentes condições de temperatura e de intervalos de tempo entre as frenagens, alternando etapas quentes e frias. Durante o assentamento dos materiais, foram verificados diferentes comportamentos do coeficiente de atrito. Os materiais ensaiados apresentaram sensibilidade às variações de temperatura e de intervalos de tempo entre frenagens. Foi observada correlação entre as variações da força de atrito e o coeficiente de atrito. Também foram evidenciados os efeitos da velocidade de deslizamento sobre o espectro de frequências de variação da força de atrito. / The growing demand for more comfortable and safer vehicles comes up with new challenges to the industry. The brakes are one of the most important vehicle safety systems and are also often the subject of customer complaints about noise. The brake friction materials need to perform properly under different conditions of temperature and humidity, presenting resistance to corrosion, long life, low cost and producing low noise levels. In order to characterize the friction coefficient and noise generation of different friction materials, different conditions were tested using a tribometer. This equipment has measurement and control systems capable of record each brake stop friction coefficient. The tribometer was also instrumented with a load cell capable of measuring friction force variations. The tests were performed at different temperatures and time intervals between brake applications, alternating hot and cold stages. During the materials running-in, different behaviors of the friction coefficients were found. The friction materials tested showed sensitivity to temperature variations and time intervals between brake applications. There was a correlation between friction force variations and coefficient of friction. There were also effects of the slip speed on the frequency spectrum of the frictional force variations.
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