88,880 research outputs found
Design oriented simulation of contact-friction instabilities in application to realistic brake assemblies
No full textThis paper presents advances in non-linear simulations for systems with contact-friction, with an application to brake squeal. A method is proposed to orient component structural modifications from brake assembly simulations in the frequency and time domains. A reduction method implementing explicitly component-wise degrees of freedom at the system level allows quick parametric analyses giving modification clues. The effect of the modification is then validated in the time domain where non-linearities can be fully considered. A reduction method adapted for models showing local non-linearities is purposely presented along with an optimization of a modified non linear Newmark scheme to make such computation possible for industrial models. The paper then illustrates the importance of structural effects in brake squeal, and suggests solutions
The phenomenon of vehicle park brake rollaway
No full textWhen a vehicle is parked on a slope with hot brakes, what appears to be a sufficient parking brake action can sometimes become insufficient. When the brakes cool
down, the braking force reduces due to relaxation of the entire parking brake system, and the vehicle may start to move, leading to obvious catastrophic consequences. This phenomenon is known as vehicle rollaway. This thesis describes the problem in detail and postulates a mechanism that accounts for the occurrence of the rollaway event on vehicles using integrated rear callipers.
Different testing methods are presented that are used to investigate the propensity of a vehicle's parking brake system to rollaway. These include on-vehicle evaluations
and laboratory based measurements. A description is given of a novel dynamometer facility that was developed for this research that is capable of testing vehicle parking
brake systems for rollaway.
Two mathematical modelling techniques are presented that demonstrate how the parking brake system parameters influence the likelihood of rollaway occurring. A
finite element model was used to simulate the change in contact pressure at the frictional interface during a rollaway event. A numerical model was also used to
predict the change in torque developed by a parking brake system cooling from an initial elevated temperature. The change in clamp load at the frictional interface was
modelled using an essentially I-D quasi-static system that showed how the stiffness and the thermal properties of the system qualitatively affect the phenomenon.
The research found that rollaway does not always start with a uniform motion, but with a stick/slip motion. The likelihood of rollaway occurring was found to be directly linked to the temperature of the brake when the vehicle is parked. Rollaway can be reduced by lowering the initial temperature of the brake prior to parking. Rollaway can also be reduced by increasing the input load to the system when applying the parking brake. The research identifies the key design parameters of the brake system components whose values require close control within the real system
if rollaway is to be avoided
Aerodynamic investigations of ventilated brake discs.
No full textThe heat dissipation and performance of a ventilated brake disc strongly depends
on the aerodynamic characteristics of the flow through the rotor passages. The
aim of this investigation was to provide an improved understanding of ventilated
brake rotor flow phenomena, with a view to improving heat dissipation, as well
as providing a measurement data set for validation of computational fluid
dynamics methods. The flow fields at the exit of four different brake rotor
geometries, rotated in free air, were measured using a five-hole pressure probe
and a hot-wire anemometry system. The principal measurements were taken using
two-component hot-wire techniques and were used to determine mean and unsteady
flow characteristics at the exit of the brake rotors. Using phase-locked data
processing, it was possible to reveal the spatial and temporal flow variation
within individual rotor passages. The effects of disc geometry and rotational
speed on the mean flow, passage turbulence intensity, and mass flow were
determined. The rotor exit jet and wake flow were clearly observed as
characterized by the passage geometry as well as definite regions of high and
low turbulence. The aerodynamic flow characteristics were found to be reasonably
independent of rotational speed but highly dependent upon rotor geometry
An Investigation into the Influence of the Contact Pressure Distribution at the Friction Pair Interface on Disc Brake Squeal
No full textThe main purpose of this thesis is to investigate the dynamic centre of pressure during a noisy brake application. A novel technique is employed to measure the centre of pressure and contact pressure distribution between the disc/pad interfaces during braking events.
The test rig was developed to study the contact pressure distribution between disc/pad interfaces. The caliper and set of pads were modified to measure both static and dynamic centre of pressure during braking events. The brake uses a 12 piston opposed caliper arranged to allow a number of the pistons to be controlled independently using 4 master cylinders. This allows the interface centre of pressure to be adjusted both along the length of the pad and radially. The tests included static pressure measurements with the sensor film between the pad friction face and the disc, the centre of pressure being adjusted using the master cylinders to provide a “system benchmark”. Once the static characteristic behaviour of the modified pad is established, the centre of pressure variation is measured under dynamic conditions. This allows the movement of the centre of pressure to be plotted against brake pressure and rotor speed.
Furthermore, a detailed finite element model of a disc brake assembly is developed. Contact analysis was performed to determine the pressure distribution, interfacial contact area and normal contact forces under both frictionless (μ=0) and frictional braking conditions. The effect of varying friction coefficients and the brake hydraulic pressure is also examined. Preliminary finite element results of contact pressure distribution between the disc/pad interfaces were compared with the experimental results, followed by a detailed modal analysis of disc brake to predict the natural frequencies and the mode shapes of disc brake. In addition, a stability analysis of brake assembly is carried out to distinguish the unstable frequencies. Structure modification of disc brake assembly was also investigated to understand the characteristics behaviour of brake system in terms of squeal noise performance.
It is established from the results that there is a strong relationship between the interface pressure distribution, the effective centre of pressure and the propensity of the brake to generate noise. It is noticed that the centre of pressure may vary both along the pad and radially during braking which adds to the complex analysis of instability.
The finite element results compared well with the experimental results. It is observed that the contact pressure distribution and the magnitude of normal contact forces are much higher towards the leading edge of the pads comparing to the trailing edge. It is also established yet again that with a leading centre of pressure the brake is more prone to noise whereas with a trailing centre of pressure the system is more likely to be stable
Brake-lights detection result.
No full text(a) Brake on condition in a day environment. (b) Brake off condition in a day environment. (c) Brake on condition in a night environment. (d) Brake off condition in a night environment. (e) Brake on condition in a cloudy environment. (f) Brake off condition in a cloudy environment. (g) Brake on situation in a rainy environment. (h) Brake off condition in a rainy environment.</p
The measurement of the absolute displacement of a noisy disc brake
No full textThe investigation of in-plane vibration of a noisy disc brake is problematic because it is difficult both to measure and to verify. Because of the disc structure and the inability to visualize disc in-plane vibration, there has been reluctance by researchers to accept the contribution of a displacement parallel to the surface of the object, or in-plane displacement, to noise generation. In addition to measuring absolute displacement, it has been difficult to isolate the in-plane and out-of-plane components of displacement using either non-contact or conventional displacement measurement techniques. This paper investigates absolute displacement of a brake disc during noise generation. Double-pulsed holographic interferometry is used to record a series of time-related images of the brake head from three different angles of observation. Because each image views the brake head from a different perspective, each of them records a different degree of in-plane and out-of-plane displacement. By careful analysis of the three images, it is possible to isolate the in-plane displacement from the out-of-plane displacement. The time-related series allows the displacement to be investigated over a full cycle of excitation and so create an animation of the mode of vibration. It is seen that the in-plane displacement is complex and that its amplitude may be about twice that of the out-of-plane displacement
Evaluation of a sudden brake warning system: Effect on the response time of the following driver
No full textThis study used a video-based braking simulation dual task to carry out a preliminary evaluation of the effect of a sudden brake warning system (SBWS) in a leading passenger vehicle on the response time of the following driver. The primary task required the participants (N = 25, 16 females, full NZ license holders) to respond to sudden braking manoeuvres of a lead vehicle during day and night driving, wet and dry conditions and in rural and urban traffic, while concurrently performing a secondary tracking task using a computer mouse. The SBWS in the lead vehicle consisted of g-force controlled activation of the rear hazard lights (the rear indicators flashed), in addition to the standard brake lights. Overall, the results revealed that responses to the braking manoeuvres of the leading vehicles when the hazard lights were activated by the warning system were 0.34 s (19%) faster compared to the standard brake lights. The SBWS was particularly effective when the simulated braking scenario of the leading vehicle did not require an immediate and abrupt braking response. Given this, the SBWS may also be beneficial for allowing smoother deceleration, thus reducing fuel consumption. These preliminary findings justify a larger, more ecologically valid laboratory evaluation which may lead to a naturalistic study in order to test this new technology in ‘real world’ braking situations
Optimisation of convective heat dissipation from ventilated brake discs
No full textFast heat dissipation from brake discs is sought in current vehicles, where high power braking
duties demand harmonic combination of strength, (undamped) disc mass and cooling abilities
for a wide speed range. This work analyses the convective heat dissipation from ventilated
brake discs and proposes means for its optimisation.
The focus of research is the ventilation geometry of a standard brake disc with an outer
diameter of 434mm and radial channels of 101mm in length. After analysing in detail
data calculated with CFD simulations and from experimental work for various ventilation
patterns, a parameter relating the local channel-averaged convective heat transfer coefficient
to channel circumferential width, and radial location was derived. This new numerical
parameter termed Flow Index, depicts graphically the link between channel geometry (width
and position) to the heat transfer coefficient level attained. The FI was not only used as a
tool to analyse the convective performance of conventional and new ventilation geometries,
but it also allowed clear identification of changes necessary in the channel width in order to
improve its convective heat transfer coefficients. New, optimised for convective heat transfer,
ventilation geometries designed with the FI were achieved in this Thesis.
Industrial (patenting) and academic applications are foreseen from the results of this Thesis
and its future activities. Also, the work developed in this Thesis gives path and supporting
frame for future research in the field of brake disc convective heat dissipation
Analysis of heat dissipation from railway and automotive friction brakes
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.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
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