04-06-2013, 02:58 PM
Analyzing an Equivalent Single Layer Shim Model to be used for Brake
Squeal Reduction
Analyzing an Equivalent.pdf (Size: 1.21 MB / Downloads: 53)
ABSTRACT
The goal in this thesis was to reduce a multilayer shim
model, which was modeled from steel and polymer (isotropic
materials), into an equivalent single layer shim model. The
procedure was to use mathematical formulations to convert a
multilayer shim into an ESL (equivalent single layer) shim.
Here, a transverse isotropic model is used to prepare for
future orthotropic layers. The results show that the ESL
model behaves isotropically. In the 2 layer model there was
no squeal noise whereas in the ESL models there is.
Introduction
In automobile industry, the brake system is one of the most
important parts and a lot of improvements have been achieved
in brake systems technology. In the last decades, to increase
performance and efficiency, brake systems are changed from
drum brake systems to disc brake systems. Brake squeal, which
usually occurs in the frequency range between 1 and 16 kHz,
has been one of the most difficult concerns associated with
vehicle brake systems [1]. The challenge is to reduce the
squeal noise in the disc brake system; this is often made by
using shims. A typical brake shim or insulator consists of a
multilayer of steel and polymer (visco-elastic) and this
sandwich shape layout is designed for decreasing the squeal.
Background
As a historical background after mid-1890s, disc brake systems
have begun developing. In 1902 the British Engineer F. William
Lanchester (1868–1946) patented a disc brake which consists of
a disc of sheet metal which is connected rigidly to one of the
rear wheels of the vehicle, and it is used for slowing down
the vehicle, the disc is pinched at its edge with a pair of
jaws [2]. Also an American inventor E.A.Sperry (1860-1930)
worked on a disc in which a disc magnet is placed in contact
with another disc making a couple. This couple produce a
torque due to friction between the discs. As a result it
reduces the speed of the vehicle.
Drum Brake System
For a drum brake, shoes work against the rotating surface,
which is called a Drum. Drum brakes are made of special type
of cast iron, and they are usually used on the rear wheels. A
drum brake has more parts than a disc brake and it is harder
to service, but it has low cost in manufacturing.
Disc Brake System
Disk brakes are more common in modern vehicles because of its
advantages like;
It dissipates heat better than a drum brake,
It is more efficient,
It has lower squeal noise,
It is better in wet weather conditions, and
It takes longer time to loss its effectiveness.
The mechanism of a disc brake system works by applying
hydraulic pressure to a caliper piston; by increasing the
pressure, the caliper moves and causes the outside pads to
contact the disc. The generated braking force is created by
the friction between the pads and the disc rotor. More
pressure causes more friction due to compression against a
rotating surface, and more heat is generated due to friction.
Reliability, Validity and Objectivity
Preventing brake squeal noise is a difficult process; some
authors assume that the system is linear. Difficulty is to
cover the non linear behavior in the linear.
In this paper, instead of assuming the system as a whole
linear system we will take the problem into two steps.
The first is a nonlinear step in which the load is applied and
the second step is a linear perturbation extracting the
complex eigenmodes. To make the calculations easier an ESL
will be used.
Conclusions
This thesis work has come up with a conclusion that the ESL
shim model can be used in automobiles in the future instead
of multilayer shim model if the other calculations of ESL
shim model; shear deformation, tension analysis and the
other details are same or close to two layers shim model.