Note: Descriptions are shown in the official language in which they were submitted.
CA 02300401 2000-02-08
WO 99/64762 . PCT/CA99/00011
DISC BRAKE BACKING PLATE AND METHOD OF MANUFACTURING SAME
TECHNICAL FIELD
This invention relates to disc brakes for motor vehicles, and in particular to
an
improved disc brake backing plate, as well as a method of manufacturing the
backing plate.
BACKGROUND ART
Although disc brakes have been used on motor vehicles for many years, their
use has increased substantially in recent years. In particular, there has been
a significantly
~o increased use of disc brakes on lower priced cars and trucks. with a
consequent interest in
methods of reducing the cost of manufacturing disc brakes and replacement
parts therefor
on the part of both motor vehicle manufacturers and suppliers of parts for
disc brakes. This
increased use has also led to a significant increase in the after-market for
disc brake
replacement and repair.
~s Disc brakes, as currently manufactured, combine two main parts. namely a
backing plate and a friction pad. The backing plate is mounted in a brake
assembly, and
may be formed by stamping a suitable metal blank to produce a backing plate
with a variety
of bosses, holes, or other features for receiving and retaining the friction
pad. The need to
use high speed low cost manufacturing methods often results in irregularities
in the backing
2o plate which may lead to difficulties in attaching and/or retaining the
friction pad on the
backing plate during braking, when the friction pad is in contact with the
rapidly turning
brake rotor, or even during the pre-installation handling of the brake pad
assembly.
There are a variety of known ways of attaching a friction pad to a backing
plate. One such way is to attach the friction pad to the backing plates using
rivets. One
2s disadvantage of the riveting process is that it creates a rigid bond
between the backing plate
and the friction pad, which can, as a result of a sudden impact, lead to
breaking of the
friction pad. Furthermore, this process often requires one or more additional
manufacturing
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steps with a consequent increase in cost. In addition, when the friction pad
is worn down
over time, the rivets become exposed and rub against the brake rotor, causing
scoring on
the rotor which is.costly to repair.
Another, more recently developed method of mounting the friction pad on the
backing plate is to use a pressurised molding process to mold the friction
material directly
onto the backing plate. In this process, the friction pad may be prepared by
blending the
components of the friction pad into a pre-form material or cake. A
conventional pressurized
molding system is used to mold the friction pad pre-form onto the backing
plate. A layer of
adhesive, such as cement or glue is often applied to the contact surface of
the backing plate
to improve the adhesion between the backing plate and the friction pad.
As pressure is applied to the mold assembly, the pre-form becomes heated
and begins to flow, filling the mold and covering the appropriate surface of
the backing plate.
In this process, the pre-form material is intended to flow into and around the
various
features to improve the bond between the backing plate and the friction pad.
~5 There is a need for a backing plate which provides improved shear and
tensile strength in the bond between the friction pad and backing plate,
compared to the
strength which is provided by features, such as holes and bosses, stamped into
the backing
plate. Furthermore, when additional features are stamped into prior art
backing plates to
increase bond strength, additional manufacturing steps are required, adding to
the cost.
2o The most common prior art features stamped into backing plates are circular
holes. These holes often provide unsatisfactory results because, during the
molding
process, the pre-form cake does not completely fill all of the holes, which in
turn, leads to
deficient bonding between the backing plate and the pre-form. The incomplete
hole fills can
are clearly visible, and often raise quality concerns when inspected by
buyers. The
25 incomplete hole fills also have an aesthetically displeasing appearance,
which can also
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make them less attractive to customers. Accordingly, it has become common
practice in
prior art backing plates to fill the incomplete hole fills with putty and to
paint over them, to
both hide the unsatisfactory molding results and to improve appearance. These
additional
manufacturing steps have the added disadvantage of increasing the cost of
manufacturing
the disc brake.
Another example of a prior art backing plate is disclosed in United States .
Patent No. 5,141,083. This patent discloses retaining structures which include
a ridge
surrounding a depression. However, the patent does not disclose a nib
surrounded by a
ridge which together act to trap the friction material to provide an improved
bond between
the backing plate and the friction material.
The backing plate is subjected to a number of forces, such as the jarring of
the moving vehicle, as well as vibration caused by the rotor and noise.
Accordingly, there is
a need for a backing plate which provides improved structural strength, and is
able to
reduce the likelihood of premature failure.
Consequently, there is a need for a disc brake backing plate and a method of
manufacturing same which can provide improved bonding with the friction pad
without
increasing the cost of producing the backing plate.
DISCLOSURE OF INVENTION
2o It is an object of the invention to provide a backing plate which provides
an
improved bond between it and the friction pad, thereby eliminating the need
for adhesive
application. In addition, it is an object of the invention to increase the
structural strength of
the backing plate, without increasing the cost of producing the backing plate.
According to a first aspect of the invention, a disc brake backing plate
comprises a plate having at least one retaining structure defined on a first
surface thereof
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for securing a friction material to the first surface. Each retaining
structure has at least one
nib surrounded by a ridge. Preferably, each retaining structure includes two
diverging nibs
projecting out of a circular depression formed in the first surface. The ridge
preferably
surrounds the depression.
According to a second aspect of the invention, a method of manufacturing the
backing plate is disclosed which reduces time and cost by requiring fewer
manufacturing
steps, while at the same time improving the structural strength of the backing
plate.
A method of manufacturing a disc brake backing plate for securing a friction
material to a first surface thereof is disclosed. The method comprises the
step of punching
~o a plate to form a depression within the first surface thereof, the
depression having a
projection protruding outwardly therefrom. Preferably, the frrst surface of
the plate is
punched with a first punching tool to form a cylindrical projection surrounded
by an annular
depression. The first punching tool preferably comprises an elongate
cylindrical member
having a cylindrical longitudinal channel defined therein.
~5 Preferably, before the first step, a second surface of the plate is placed
against a flat surface having a cylindrical recess defined therein. The recess
preferably
defines a central opening therein. The opening is preferably adapted to secure
a first
bushing therein. The first bushing preferably projects from the recess.
Preferably, the method comprises a second step of punching the plate to
2o form a ridge surrounding the depression. Preferably, the first surface
punched with a
second punching tool to divide the projection into two nibs and to form an
annular ridge
surrounding the depression. The second punching tool preferably has a chisel
projecting
from a central recessed portion thereof. Preferably, the second punching tool
has a larger
diameter than the first punching tool.
25 Prior the second step, the second surface of the plate is preferably placed
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against a flat surface having a second surface opening defined therein. The
second surface
opening is preferably adapted to secure a second bushing therein.
Further features of the invention will be described or will become apparent in
the course of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more clearly understood, the preferred
embodiment thereof will now be described in detail by way of example, with
reference to the
accompanying drawings, in which:
~o Fig. 1 is a perspective view of a preferred embodiment of the invention
showing the first surface;
Fig. 2 is a perspective view of the preferred embodiment showing the second
surface;
Fig. 3 is a plan view of the second surtace of the preferred embodiment;
~5 Fig. 4 is an elevation view of the preferred embodiment;
Fig. 5 is a plan view of the first surface of the preferred embodiment;
Fig. 6 is a cross-sectional view along line A-A of Fig. 3;
Fig. 7 is a cross-sectional view along line A-A of Fig. 3 showing the friction
pad;
2o Fig. 8 is a partial cross-sectional view of the first step of the process
according to a preferred embodiment of the present invention; and
Fig. 9 is a partial cross-sectional view of the second step of the process.
BEST MODE FOR CARRYING OUT THE INVENTION
25 Figs. 1 and 2 show the preferred embodiment of the present invention, where
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a backing plate 1 of a conventional shape and thickness ('18 - '/z of an
inch), made
preferably from metal or a metal composite, is adapted to withstand the rigors
of a
conventional disc braking system. The backing plate has a first surtace 2 and
a second
surface 7. A friction pad 10 (shown in Fig. 7) is to be molded to the first
surface by a
conventional molding process. Any suitable number of retaining structures 3
are connected
to the first surface of the backing plate. Preferably, the retaining
structures are integrally
formed by punching or stamping the backing plate, as described in more detail
below. The
number of the retaining structures can vary with the size of the backing plate
and the
strength of the bond required, which. in turn, varies depending on the type of
vehicle. The
~o preferred arrangement of the retaining structures is for each group of
three structures to
form the vertices of an equilateral triangle. The perimeter of the triangle
again depends on
the type of vehicle where the backing plate will be installed.
Referring to Figs.1, 5, 6, and 7, each retaining structure preferably
comprises
a circular depression 4 surrounded by an annular ridge 5 projecting from the
first surface 2.
At least one nib projects out of the depression. It will be understood by
those skilled in the
art that the nib can be one or more of any kind of projecting members or boss.
Preferably,
two nibs 6 divergingly project from the surface of the depression 4 above the
first surface 2.
Preferably, the outside diameter of the annular ridge is between '/" (1.28cm)
and 1"
(2.56cm), and the height of the nibs and the ridge is between 0.07" (1.8mm)
and 0.1"
(2.6mm), such that they protrude below wear sensor specification dimensions.
The backing plate 1 according to the present invention does not need to be
coated with an any adhesive to achieve the required bond strength with the
friction pad. In
addition, the surfaces of the backing plate can be plated to improve its
resistance to rust and
its aesthetic appearance. The plating eliminates the need to paint the backing
plate.
Fig. 8 shows the first.step in the method of manufacturing the backing plate
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1, according to the preferred embodiment of the present invention. Preferably,
the second
surface 7 of the backing plate rests on a flat surface 20 having a cylindrical
recess 21
defined .therein. Preferably the recess has a central opening 22 within which
a bushing 23 is
secured in a conventional manner. The bushing is positioned such that it
projects from the
recess 21 and preferably projects out the first surface. The first face 2 of
the backing plate
is then punched by a first punching tool 25. The first punching tool is
preferably a cylindrical
member with a longitudinal central channel 22 preferably having a circular
cross-section.
The force of the first punching tool forms the depression 4 from which a
projection, such as
the generally cylindrical projection 30, projects into the longitudinal
central channel of the
~o first punching tool. The force of the first punching tool drives the
backing plate material into
the recess 21, which surrounds the bushing 23, to form an annular protrusion
31 in the
second surface 7. The height of the projection 30 can be adjusted by
increasing or
decreasing the force of the impact.
Fig 9 shows the final step in the method. The second surface 7 of the
~s backing plate is placed on a flat surface 40, such that each retaining
structure 3 is
positioned over a second bushing 43 which is conventionally secured within a
second
surface opening of the flat surface 40. The second bushing preferably projects
from the flat
surface by 0.005" (0.13mm). Alternatively, the second bushing may be flush
with the flat
surtace 40; or may project from the flat surface by less than 0.005" (0.13mm).
2o The first surface 2 is then punched by a second punching tool 41. The
second punching tool is preferably a cylindrical member of a larger diameter
than the first
punching tool. Preferably, a chisel 42 is conventionally secured within a
central portion of
the second punching tool. The impact of the second punching tool causes the
material of
the annular protrusion 31 to compress and flow to form the annular ridge 5.
The protruding
25 second bushing 43 insures that all backing plate material is flush with or
below the second
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surface 7 of the backing plate 1. as required by design specifications for
disc brake backing
plates. At the same time, the chisel splits the cylindrical projection 30 into
preferably two
diverging nibs 6 to complete the retaining structure 3. 1t will be understood
by those skilled
in the art that the second punching tool may be altered to create any suitable
number of nibs
or other projecting members, and such variations are within the scope of this
invention.
The process is then repeated to form additional retaining structures on the .
backing plate, as needed to develop the required tensile and shear strength in
the bond
between the backing plate and friction pad.
During the process of molding and securing the friction pad to the backing
plate, the pre-form material is set into a mold and pressed against the
backing plate. The
material flows into and surrounds each retaining structure 3 to bond with the
backing plate 1.
The inner surface of the ridge 5 and the diverging nibs 6 trap all compressed
friction
material to provide improved tensile strength, and thereby reduce the
likelihood of
separation of the friction pad from the backing plate. The outer surface of
the ridge provides
~5 resistance to shear forces generated between the friction pad and the
backing plate. The
tensile and shear strengths can be varied by changing either the height of the
ridge and
nibs, or the number of nibs, depending on the bond strength required for a
particular
application. These results are accomplished using a two step process, and
without the need
for additional features, such as holes, leading to a decreased manufacturing
time and
2o significant cost savings.
It will be appreciated that the above description relates to the preferred
embodiment by way of example only. Many variations on the invention wiH be
obvious to
those knowledgeable in the field, and such obvious variations are within the
scope of the
invention as described and claimed, whether or not expressly described.
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INDUSTRIAL APPLICABILITY
The disc brake backing plate and the process of manufacturing same
according to the present invention are useful in the field of manufacturing of
automotive
parts.
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