Note: Descriptions are shown in the official language in which they were submitted.
CA 02299110 2000-02-18
BRAKE PLATE AND METHOD AND APPARATUS FOR MANUFACTURING SAME
TECHNICAL FIELD
This invention relates to brakes, and in particular to an improved brake
plate, as
well as a method and apparatus for manufacturing the plate.
BACKGROUND ART
The number of motor vehicles has increased greatly in recent years. There is
an
interest in methods of reducing the cost of manufacturing brakes and
replacement parts on the
part of both motor vehicle manufacturers and suppliers of parts for brakes.
This increased use
has also led to a significant increase in the after-market for brake
replacement and repair.
Brakes are also in increasing demand for motor vehicles such as airplanes,
trains, bicycles, all
terrain vehicles and motorcycles.
Brakes, as currently manufactured, combine two main parts, namely a plate
(often called a backing plate) and a friction pad. The plate is mounted in a
brake assembly, and
may be formed by making a 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 plate which may lead to difficulties in
attaching and/or
retaining the friction pad on the 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 plate. One
such way is to attach the friction pad to the backing plates using rivets. One
disadvantage of
the riveting process is that it creates a rigid bond between the plate and the
friction pad, which
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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 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
plate is to use a pressurised molding process to mold the friction pad
directly onto the plate. In
this process, the friction pad may be prepared by blending the components of
the friction pad
into a pre-form or cake. A conventional pressurized molding system is used to
mold the friction
pad pre-form onto the plate. A layer of cement or glue if often applied to the
contact surface of
the plate to improve the adhesion between the 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
plate. In this
process, the pre-form material is intended to flow into and around the various
features to
improve the bond between the plate and the friction pad.
The 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. The problem with
the prior art
processes and plates is that features, such as holes and bosses, stamped into
the plate often
provided insufficient shear and/or tensile strength in the bond between the
friction pad and
plate. When additional features are stamped into the plate to increase bond
strength, additional
manufacturing steps are required, adding to the cost.
The most common prior art features stamped into 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
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between the plate and the pre-form. The incomplete hole fills can are clearly
visible, and often
raise quality concerns when inspected by buyers. The incomplete hole fills
also have an
aesthetically displeasing appearance, which can also make them less attractive
to customers.
Accordingly, it has become common practice in prior art plates to fill the
incomplete hole ~Ils
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.
Furthermore, the holes stamped by prior art processes reduce structural
strength
of the plate, and make it more vulnerable to the various forces acting on it.
These forces may
distort the shape of the plate, leading to uneven wear on the friction pad, or
can lead to
structural failure of the plate.
Another problem with brake plates is caused by the heat generated by friction.
The expansion and contraction values of the plate are different from those of
the friction
material. Braking generates heat so the plate and material are exposed to
frequent heating and
cooling. Since the expansion and contraction values differ, there may be a
separation between
the plate and the material, particularly where the plate is flat or has large
flat areas. Rust can
then form between the plate, which leads to noise and brake failure.
Accordingly, there is a need for a brake plate and a method of manufacturing
same which can provide improved bonding with the friction pad without
increasing the cost of
producing the plate
SUMMARY OF THE INVENTION
It is an object of the invention to provide a plate which provides an improved
bond between it and the friction pad, as well as increasing the structural
strength of the plate,
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without increasing the cost of producing the plate. In addition, it is an
object of the invention to
provide a method and apparatus for manufacturing the plate which reduces time
and cost by
requiring fewer manufacturing steps, while at the same time retaining the
structural strength of
the backing plate.
Further features of the invention will be described or will become apparent in
the
course of the following detailed description.
The invention includes a plate for holding a friction material in a brake
assembly,
the plate comprising:
a contact surface for attaching the friction material to the plate,
a second surface opposing the contact surface;
a plurality of retaining structures formed on the contact surface, each
retaining structure
comprising a projecting member extending from a point between the contact
surface and the
second surface, so that the member extends outwardly from the contact surface
for
engagement with the friction material. The retaining structure may further
comprise a
depression surface abutting the projecting member, the depression surface
extending into the
contact surface. The contact surface may be curved or substantially flat. The
brake may
comprise a disk brake or a drum brake. The plate may comprise integral
retaining structures.
The retaining structures can be formed from the plate, and preferably cut or
scored. In a
variation, the projecting member may be a burr. The burr optionally comprises
a hook shape,
wherein a distal end of the hook points away from the depression adjacent to
the hook. The
retaining structures are optionally disposed in a plurality of rows. The rows
are optionally
substantially parallel. The rows may be usefully disposed longitudinally.
The invention also includes a method of manufacturing a brake plate for
securing
a friction material to a contact surface thereof, the method comprising
providing:
a contact surface for attaching the friction pad to the plate,
a second surface opposing the contact surface;
a plurality of retaining structures formed on the contact surface, each
retaining structure
comprising a projecting member extending from a point between the contact
surface and the
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second surface, so that the member extends outwardly from the contact surface
for
engagement with the friction pad.
The invention includes a brake plate, preferably a drum brake plate or a disc
brake plate made according to a method of the invention or with the apparatus
of the invention.
In one method, the retaining structures are formed by cutting the contact
surface. The retaining structures are alternatively formed by scoring the
contact surface. In
another variation, the retaining structures are formed by cutting a plurality
of rows of retaining
structures on the contact surface. The rows are optionally substantially
parallel and/or disposed
longitudinally.
In one embodiment, the cutting is done by a plurality of knives, each knife
having
a cutting edge, the edge having a plurality of teeth connected thereto. Each
retaining structure
is preferably made by one tooth. Each tooth preferably cuts a projecting
member from the
contact surface to form an adjacent depression. The knives are preferably
disposed
longitudinally in relation to the plate. The knives may be substantially
parallel. Adjacent knives
preferably move in opposing directions. The plurality of knives are preferably
moving parallel to
the contact surface prior to impacting the plate. The plurality of knives
preferably commence to
move parallel to the contact surface upon impact with the plate. The plate may
be stationary
while it is punched by the knives. The knives are optionally fixed in the
direction perpendicular
to the contact surface and the plate is impacted onto the knives.
Another variation of the invention relates to an apparatus for manufacturing a
brake plate having a plurality of retaining structures formed on a contact
surface thereof for
retaining a friction material, comprising:
a means for cutting a plurality of retaining structures on the contact
surface, each
retaining structure comprising a projecting member extending from a point
between the contact
surface and the second surface, so that the member extends outwardly from the
contact
surface for engagement with the friction pad, the cutting means being adapted
to move
generally parallel to the contact surface to cut the retaining structures;
a driving means for impacting the cutting means and the contact surface of the
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plate to form the retaining structures.
The cutting means preferably comprises a plurality of knives, each knife
having a
cutting edge, the edge having a plurality of teeth connected thereto, each
tooth adapted to form
one of the plurality of retaining structures upon impact with the contact
surface.
The apparatus optionally further comprises:
at least one drive member slidably connected to at least one side of each of
the
plurality of knives;
at least one slide member slidably connected to the drive member;
Duuring impact between the knives and the contact surface, the slide member is
preferably
adapted to move away from the contact surface, the slide member being adapted
to move the
drive member generally parallel to the contact surface, the drive member being
adapted to
move the knives generally parallel to the contact surface.
The slide member may have an inclined sliding surface, the sliding surface
being
adapted to move the drive member generally parallel to the contact surface
upon movement of
the slide member. The at least one slide member can be two slide members, the
at least one
drive member can comprise first and second drive members, and the at least one
side of the
each of the knives can comprise a first side and a second side, wherein first
drive member is
proximate to the first side of at least one knife, and the second drive member
is proximate the
second side of the remaining knives. The first and second sides of alternate
knives are
preferably proximate to the first and second drive members, respectively. The
adjacent knives
preferably move in opposing directions upon impact with the contact surface.
The apparatus
may further comprise a return means for returning the knives to a starting
position. The return
means is optionally at least one spring attached to a first and second slide
rod, the slide rods
being located within a first and second guide slots defined proximate to the
first and second
side of each knife. The plurality of knives are preferably disposed
longitudinally in relation to
the plate. The apparatus knives are preferably substantially parallel to each
other.
The slide member and the plurality of knives are preferably adapted to move
generally parallel to the contact surface prior to impact with the plate. The
plurality of knives
are preferably adapted to move parallel to the contact surface upon impact
with the plate. The
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plate is optionally stationary while punched by the knives. The knives are
optionally fixed in the
direction perpendicular to the contact surface, and the plate is driven onto
the knives. The
impacting means optionally comprises a press having a top movable portion and
a bottom
stationary portion.
The apparatus of optionally further comprises:
a base plate secured to the top portion of the press;
two side plates secured to the base plate, the side plates projecting
downwardly
therefrom;
a positioning means for maintaining the knives in proximate to each other; the
positioning means being connected to the side plates;
a force adjustment means for adjusting the force of impact of the knives
against
the contact surface, the force adjustment means having a pressure plate
generally parallel to
the base plate and at least one spring disposed between the base plate and the
pressure plate,
the pressure plate being connected to the knives;
wherein the first and second slide rods are suspended from the base plate.
The first and second sliding members preferably impact the bottom portion of
the press prior to
the knives impacting the contact surface, thereby causing the knives to move
generally parallel
to the contact surface prior to impact of the knives against the contact
surface. The first and
second sliding members preferably impact the bottom portion of the press
substantially
simultaneously with the knives impacting the contact surface, thereby causing
the knives to
move generally parallel to the contact surface substantially simultaneously
with impact of the
knives against the contact surface.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more clearly understood, preferred
embodiments thereof will now be described in detail by way of example, with
reference to the
accompanying drawings, in which:
Fig. 1 is a perspective view of a preferred embodiment of a plate according to
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the present invention;
Fig. 2 is a perspective view of a preferred embodiment of an apparatus for
manufacturing the plate according to the present invention;
Fig. 3A is a plan view of the apparatus;
Fig. 3B is a magnified view showing the knives and teeth of the apparatus
shown
in Fig. 3A;
Fig. 4 is an elevation view of the apparatus with the side plates removed;
Fig. 5A is a cross-sectional view showing the apparatus impacting the bottom
of
a conventional press;
Fig. 5B is a cross-sectional view showing the knives beginning to cut into a
blank;
Fig. 5C is a cross-sectional view showing the knives completing the cut into a
blank;
Fig. 5D is a cross sectional view showing the apparatus impacting a press. The
spring is beneath the press. A spring or a nitro spring may be used.
Fig. 6 is a perspective view of an alternate preferred embodiment of a plate
according to the present invention;
Fig. 7 is a perspective view of a preferred embodiment of a knife with rows of
offset teeth for manufacturing the backing plate according to the present
invention. The figure
shows an insert allowing one or more teeth to be releasably inserted into the
knife.
Fig. 8A is a top plan view of a knife;
Fig. 8B is a side plan view of a knife;
Fig. 8C is a top plan view of a knife;
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Fig. 8D is a side plan view of a knife;
Figs. 9A and B are perspective views of a releasable knife insert having
offset
teeth;
Figs. 9C is a perspective view of a releasable knife insert.
DETAILED DESCRIPTION OF THE INVENTION
The invention is a plate for holding a friction material in a brake assembly.
The plate
preferably comprises:
(a) a contact surface for attaching the friction material to the plate,
(b) a second surface opposing the contact surface;
(c) a plurality of retaining structures formed on the contact surface, each
retaining
structure comprising a projecting member extending from a point between the
contact surface and the second surface, so that the member extends outwardly
from the contact surface for engagement with the friction material.
The retaining structure may further comprise a depression surface abutting the
projecting member, the depression surface extending into the contact surface.
The brake plate, as well as the process and apparatus for manufacturing same
according to the present invention are useful in the field of manufacturing of
vehicle brake parts.
The plate is useful in brakes for any motor vehicle, such as cars, trucks,
airplanes, trains,
bicycles, all terrain vehicles or motorcycles.
Fig. 1 shows a brake plate 1 according to a preferred embodiment of the
present
invention. The plate 1 has a conventional shape and any suitable thickness
('/8 -'/Z of an inch),
and is preferably manufactured from metal or a metal composite adapted to
withstand the rigors
of a conventional braking system. The circular holes shown on the plate are
not necessary and
are included for illustrative purposes only. The backing plate has a contact
surface 2 for
molding a friction material (not shown) thereto by a conventional molding
process.
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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 the
backing plate, as described in more detail below. Each retaining structure
includes a burr 4
projecting out of the first surface, which is located adjacent to a
corresponding depression 5
defined in the contact surface 2. Preferably, each burr is integrally formed
by cutting the burr
out of the first surface of the backing plate, which creates the corresponding
depression 5. The
projecting member extends from a point between the contact surface and the
second surface
36 (in figure 6, the second surface is opposite the contact surface and
appears as the flat
bottom surface of the plate), so that the member extends outwardly from the
contact surface for
engagement with the friction material. Each burr preferably has a curved
shape, which curves
away from its corresponding depression.
The retaining structures 3 are preferably arranged in longitudinally disposed
substantially parallel rows 6. Preferably, the position of the burr 4 and
depression 5 is identical
for each row, but alternates with adjacent rows, as shown in Fig. 1.
Preferably, the number of
rows is sufficient to cover substantially the entire surface area of the
backing plate 1 in order to
provide maximum bond strength. The depth of the depressions and the height of
the burrs
depends on the bond strength required for a particular application. Figure 6
shows a variation
of the plate in which there is increased space between the structures of each
row. The
retaining structures in each row are spaced apart farther than those in figure
1.
The 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
material. Since the plate
has a large number of projecting members, there will be no separation between
the plate and
the material as the plate and material are subjected to frequent heating and
cooling. The plate
CA 02299110 2000-02-18
lasts longer and is safer.
For a disc brake as shown in Figure 1, the height of the members may
preferably
be about 0.030 inches to 0.075 inches above the contact surface. There are
preferably at least
about 20 projecting members per square inch. The horizontal pitch (distance
between each
member) between members in the direction of chip formation may preferably
range between
0.120 and 0.250 inches. The pitch between rows is preferably about 0.100 to
0.200 inches.
The coverage of members on the contact surface is preferably at least about
65% for a disc
brake.
For a disc brake as shown in Figure 6, the height of the members may
preferably
be about 0.030 inches to 0.075 inches and more preferably about 0.045 to 0.060
inches above
the contact surface. There are preferably at least about 30 projecting members
per square
inch. The horizontal pitch (distance between each ) between members in the
direction of chip
formation may preferably range between 0.120 and 0.250 inches and is more
preferably 0.060
inches. The coverage of members on the contact surface is preferably at least
about 65% for a
disc brake.
The method of manufacturing the backing plate 1 according to the present
invention comprises placing the backing plate on a flat surface under a
conventional press and
punching the contact surface 2 of the backing plate with a series of
substantially parallel knives
10. Referring to Fig. 2, the knives are preferably disposed substantially
parallel to the
longitudinal axis of the backing plate. Each knife has a plurality of
preferably identical teeth 11
defined along a cutting edge thereof. Each tooth forms the depression 5 and
burr 4 of one
retaining structure 3. The configuration of the teeth may alternate from row
to row, such that
every other row has an identical configuration. In Fig. 6, a knife with offset
teeth is preferably
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used to create a checkerboard pattern (alternating retaining structure
pattern) between rows cut
by the same knife.
Fig. 2 shows the apparatus 12 for manufacturing the backing plate according to
the present invention. The apparatus is mounted to a conventional press in any
suitable
manner for punching the backing plate 1, as described above.
Referring to Figs. 2-4, the apparatus 12 includes a base plate 13 from which
two
side plates 14 are suspended by preferably four conventional screws 15.
Preferably, two
transverse slide rods 16 are suspended from four support springs (not shown)
which are each
attached to one of the screws at one end and to an end of the slide rod at the
other end. The
slide rods are slidably secured to the knives 10 by preferably locating in
guide slots 17 defined
in the knives. A biasing means, such as, for example, two return springs 18
are connected to
each slide rod to bias the slide rods toward each other. A pressure plate 19
is disposed above
the non-cutting edges of the knives. Preferably, a plurality of adjustment
springs 20 are
disposed between the base plate and the pressure plate to urge the two apart.
Two block
housings 21 are mounted transversely onto the base plate adjacent to the edges
of the knives.
A drive block 22 is mounted on each block housing by a slide bolt 23 which is
disposed
substantially parallel to the longitudinal axis of the knives. A slide block
24 is slidably mounted
in each housing adjacent to the drive block.
Fig. 5A shows the initial step of operation of the apparatus 12. A
conventional
press (not shown) drives the apparatus 12 onto a plate blank 25, such that the
slide block 24
preferably impacts the bottom surface of the press 26 before the knives 10
impact the blank.
The impact against the bottom surface of the plate drives the slide block up
relative to the drive
block 22, causing the slide block sliding surface 27 to exert a force on the
drive block
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substantially parallel to the longitudinal axis of the knives. This force
causes each drive block to
move alternate knives along their longitudinal axis. Because only alternate
knives contact each
drive block before impact, adjacent knives are pushed in opposite directions
by each drive
block. Preferably, the knives are moving before the blank contacts the knives.
The teeth of the knives may be arranged along the longitudinal axis of the
knife,
so that they form a single row. There may be portions where no teeth are
present, as in Fig.
8D. Each tooth has a leading surface which is transverse to the axis of the
knife. The leading
surface may be angled to determine the burr shape, in the same manner as a
plow is angled.
All the teeth may have a similar leading angle or they may be varied.
In a knife variation, the teeth are offset, preferably so that the teeth are
arranged
in two or more rows, as shown in Fig. 9. Each knife thus cuts rows of teeth
along two
longitudinal axes (forming two rows that are preferably substantially
parallel) to provide a brake
pad as shown in Fig. 6.
Referring to Figs. 5B and 5C, the impact of the knives 10 against the blank 25
may be regulated by the biasing means, preferably adjustment springs 20 (shown
in Fig. 2).
The adjustment springs allow the apparatus 12 to be mounted on presses having
different force
specifications. The adjustment springs effectively ensure that a constant
force is exerted
against the knives, regardless of the force applied by the press. In a
variation, the springs are
located beneath the plate as shown in Fig. 5D. As the knives are pushed down
into the blank,
they also slide along the slide rods 16 parallel to their longitudinal axis,
such that adjacent
knives are moving in opposite directions as they cut. These simultaneous
downward and
sliding movements cause each tooth 11 of a knife to form one retaining
structure 3.
The apparatus is able to complete an entire plate in one punch. After the
press
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lifts the apparatus 12, the slide block 24 is returned into its starting
position by gravity, and the
knives 10 and drive block 22 are returned to their starting positions by the
slide springs 19.
One skilled in the art could readily use the knives to prepare drum brake
plates.
During the process of molding and securing the friction material to the plate,
the
pre-form material is set into a mold and pressed against the plate. The
material flows into and
surrounds each retaining structure 3 to bond with the plate 1. The retaining
structures provide
improved tensile strength, as well as providing improved shear resistance. The
tensile and
shear strengths can be varied by changing either the depth of the cut (i.e.
the depression 5),
which also increases the height of the burr 4. 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 significant cost savings.
Figure 5D shows a variation of the apparatus in which a spring is mounted on a
fixed press bed so that the spring is beneath the press. The spring may be a
conventional coil
spring or a nitrogen spring. Any other suitable biasing means may be used. A
knife of the
invention is shown in Figs. 7 and 8. In these figures, the teeth of each knife
are aligned along
an axis defined by the knife. However, the teeth may be offset to provide a
brake pad of the
type shown in Fig. 6. Figure 7 shows a knife with offset teeth.
Figure 7 also shows that the knife may be made with releasable inserts. Broken
or dull teeth may be readily changed without discarding the knife. A blank
insert with no teeth
may also be used. Inserts may optionally be permanently fixed in the knife.
Figures 8A and 8B
show the knife with continuous teeth. Figs. 8C and 8D show the knife having a
blank surface
where no teeth are present. The plate will have no retaining surfaces formed
where the knife is
blank. Figs. 9A and 9B show offset teeth. Fig. 9C shows that the offset teeth
are preferably
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about the same height above the knife.
It will be appreciated that the above description relates to the preferred
embodiment by way of example only. Many variations on the invention will 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.