Note: Descriptions are shown in the official language in which they were submitted.
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CONCENTRIC COMPENSATOR CFIAMBER AND MASTER
CYLINDER FOR DISC BRAKE SYSTEM
This application claims priority on U.S. Provisional
Application No. 60/083,276, filed April 28, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention. The invention
disclosed herein relates to design of disc brake systems
for use in connection with vehicles. The present invention
is particularly suited for use in connection with bicycle
disc brake systems.
2. Description of the Prior Art. The use of
vehicle disc brakes has become increasingly popular over
the years, and recently has experienced a dramatic increase
in connection with "mountain bikes," i.e., bicycles
designed to be ridden over rough, off-road terrain. To
ease the effort of traversing off-road terrain, there has
been a continuous effort to design disc brake systems that
are as light as possible, particularly with respect to
pedal driven vehicles such as bicycles, the weight of which
must be propelled by a rider in addition to the rider's own
weight.
Another important design criterion for off-road
vehicle components in particular, and for vehicle
components generally, is durability. In the past, for
example, reservoirs used in fluid-based disc brake systems
have been made of plastic and have been formed and mounted
separately from and/or external to the master cylinder
assembly of such disc brake systems. The reservoirs
therefore have typically been undesirably exposed and
susceptible to being damaged.
Typical disc brake systems are also undesirably
bulky and therefore less aerodynamic and more unsightly
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than desirable, due not only to the use of external
reservoirs but also to the use in such systems of an
unnecessary number of parts. The excess number of parts
also results in conventional systems being unnecessarily
costly. Accordingly, there is a need for a vehicle disc
brake system that is more compact than typical conventional
systems, and which may potentially be manufactured at a
lower cost due to a reduction and consolidation of parts.
In addition, typical hydraulic disc brake systems
are designed to have an air pocket disposed above the fluid
in the reservoir. Thus, if such a disc brake system is
turned upside-down - which occurs frequently in
applications such as bicycles - air is able to enter the
fluid circuit and cause a deterioration of brake
performance, or a loss of braking altogether. As a result,
the brakes must be bled when turned upright again.
Accordingly, there is a need for a disc brake system having
the compact, cost-efficient and durable qualities
previously described, and which eliminates the need to
bleed the brake system if the system is turned upside-down.
It is an object of the subject invention to
provide a disc brake assembly which includes concentrically
disposed master cylinder and compensator chamber.
It is also an object of the subject invention to
provide a compensator piston in a disc brake assembly which
is responsive to volume changes in the brake fluid.
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SUI~ARY OF THE INVENTION
The above-stated objects are met by a disc brake
assembly which is formed with a concentric cylinder that
defines concentrically disposed master cylinder chamber and
internal thermal compensation chamber. The two chambers
are provided with brake fluid for actuating disc brakes,
which may be remotely or directly mounted to the subject
invention. Additionally, the invention may be actuated
through an actuator, such as a brake lever, mounted
directly onto the assembly, or remotely through a brake
wire.
The combination of the concentrically disposed
internal thermal compensation chamber and the master
cylinder chamber advantageously provide for a compact
design which eliminates the need for an external reservoir.
Additionally, a spring-biased compensator piston is
disposed within the internal thermal compensation chamber
to be pressed into fluid engagement with brake fluid to
prevent the creation of an air pocket therein. By
eliminating air pockets, the disc brake assembly may be
oriented in any manner, without an air pocket being formed
which requires removal through bleeding.
These and other features of the invention will be
better understood through a study of the following detailed
description and accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a first embodiment
of the disc brake assembly of the present invention.
FIG. 1A is an enlarged partial sectional view of
the first embodiment showing the additional feature of
using a screw to control depth of the compensator piston
during bleeding.
FIG. 2 is a sectional view of the first
embodiment of the disc brake assembly of FIG. 1,
illustrating the actuation of the assembly's master
cylinder.
FTG. 3 is a partial sectional view of a second
embodiment of the disc brake assembly of the present
invention, in which the disc brake assembly is connected to
a handlebar mounting boss for actuation by a pushrod
attached to a brake lever.
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DETAINED DESCRIPTION OF T~iE INVENTION
The disc brake assembly of the present invention
will now be described with reference to the figures. As
illustrated in FIGS. 1 and 2, the disc brake assembly 10 of
5 the present invention comprises a main unit 12 and an
actuator which extends from a remote location, such as a
brake lever. In a first embodiment, the main unit 12
comprises a caliper body 16 and a concentric cylinder 18,
which are preferably attached or integrally formed.
The caliper body 16 of the disc brake assembly 10
includes two caliper piston bores 20 that house two caliper
pistons (not shown) for operation as described, for
example, in U.S. Patent No. 5,632,362 to Leitner, issued
May 27, 1997 (the "Leitner patent"), the disclosure of
which is incorporated herein by reference in its entirety.
A cylindrical wall 22 is mounted onto, or as shown in
FIGS. 1 and 2 is formed integrally with, the caliper body
16 to define a cylindrical chamber 24 adjacent to the
caliper body 16. Alternatively, the cylindrical wall 22,
the caliper body 16 and the concentric cylinder 18 can be
integrally formed together, thus eliminating the concentric
cylinder seals described below.
The concentric cylinder 18 has an interior
surface 26 and an exterior surface 28. The interior
surface 26 defines a master cylinder chamber 30 for
receiving a master cylinder piston 32 and a master cylinder
spring 34. A master cylinder port 36 extends from the
interior surface 26 to define a fluid passage between the
master cylinder chamber 30 and one or more caliper piston
ports 38 which enable the master cylinder piston 32 to
actuate the disc brake. An annular interior surface seal
2T is seated into the interior surface 26 adjacent to the
master cylinder port 36.
The master cylinder piston 32 is generally
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tubular shaped with an annular pressure seal 33 and an
annular secondary seal 35 being seated on outer portions
thereof. The master cylinder spring 34 is disposed
between, and preferably connected to, a shoulder 37 formed
inside of the master cylinder piston 32 and a flange 39
formed to extend inwardly from the interior surface 2&.
Accordingly, the master cylinder spring 34 is arranged to
urge the master cylinder piston 32 leftward with reference
to the figures. A lip 43 may be formed on the interior
surface 26 to act as a stop against the master cylinder
spring's 34 biasing force.
The exterior surface 28 of the concentric
cylinder 18 has two portions: a first exterior surface
portion 28A and a second exterior surface portion 28B. The
first exterior surface portion 28A is preferably formed to
define a first diameter Dl, whereas, the second exterior
surface portion 28B is preferably formed to define a second
diameter D2, which is greater than the first diameter Dl.
As a result in the change of the diameters Dl and DZ, a
generally annular step 41, preferably being planar, is
defined.
The first exterior surface portion 28A defines an
inner surface of an annular-shaped internal thermal
compensation chamber 42 that is disposed concentrically
about the master cylinder chamber 30. A compensator port 44
and a relief port 46 extend through the first exterior
surface portion 28A to communicate the master cylinder
chamber 30 with the internal thermal compensation chamber
42. In addition, the first exterior surface portion 28A
provides an axial guide for an annular compensator piston
described below.
The second exterior surface portion 28B is
disposed to be at least partially disposed in engagement
with the cylindrical wall 22 of the caliper body 16 and is
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preferably provided with a pair of annular concentric
cylinder seals 48 seated thereon. The concentric cylinder
seals 48 are used to seal the junction of the master
cylinder port 36 and the caliper body 16 around the caliper
piston port 38.
As clearly shown in the figures, two annular
subchambers are formed in the master cylinder chamber 30
that extend about the master cylinder piston 32. Namely,
a pressure chamber 45 is located between the interior
surface seal 27 and the pressure seal 33, and a relief
chamber 47 is located between the pressure seal 33 and the
secondary seal 35. As depicted in FIG. 1, the compensator
port 44 is in communication with the pressure chamber 45,
and the relief port 46 is in communication with the relief
chamber 47 in an unactuated state of the disc brake
assembly 10 with the master cylinder piston 32 being fully
seated leftwardly.
In the first embodiment, the concentric cylinder
18 is formed with a cable housing boss 40 at one axial end
for connecting to a brake cable housing BCH (shown in FIG.
2) using any technique known by those skilled in the art.
A cap or cover 49 may be mounted onto the other axial end
of the concentric cylinder 18 to prevent the ingress of
dirt and debris into the disc brake assembly.
As is readily appreciated by those skilled in the
art, a volume of brake fluid (shown schematically by dashed
lines in the figures) is disposed within the disc brake
assembly 10 to cause actuation thereof. To actuate the
caliper pistons, sufficient brake fluid must be provided to
flood the caliper piston bores 20, the caliper piston port
38, the master cylinder port 36, and the pressure chamber
45. Due to thermal effects, brake fluid expands and
contracts. To ensure a working volume of brake fluid is
maintained within the required areas, the internal thermal
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compensation chamber 42 is also flooded with brake fluid
which acts as a reservoir. A compensator piston 50
is disposed in the internal thermal compensation chamber
42. The compensator piston 50 is an annular or thru-hole
design with annular inner and outer seals 52 and 54,
respectively. The inner seal 52 prevents fluid leakage
between the inside diameter of the compensator piston 50
and the first exterior surface portion 28A of the
concentric cylinder 18. The outer seal 54 prevents fluid
leakage between the outside diameter of the compensator
piston 50 and the cylindrical wall 22.
As illustrated in FIGS. 1-2, the compensator
piston 50 is biased by a compensator spring 56 on one side
and acts upon the internal thermal compensation chamber 42
on the other. The compensator spring 56 is disposed between
the compensator piston 50 and a surface such as a disc
and/or retaining ring, such as the disc described below, to
bias the compensator piston 50 in a direction pushing fluid
into the master cylinder chamber 30 through the compensator
port 44. Preferably, the compensator spring 56 is a coil
spring disposed to encircle the concentric cylinder 18.
The compensator spring 56 is used both to overcome the
friction of the inner and outer compensator piston seals
52, 54 and to ensure positive filling of the master
cylinder chamber 30 as the brake fluid volume changes.
As shown in FIG. 2, the compensator piston 50
moves axially with respect to the major axis of the
concentric cylinder 18 as the brake fluid expands and
contracts due to increases and decreases in the temperature
of the brake fluid. In addition, the compensator piston 50
moves to the right when the brake fluid contracts due to a
decrease in ambient air temperatures, and/or when the
caliper pistons move out of the caliper body 16 due to
brake pad wear. The compensator piston 50 moves to the
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left due to the thermal expansion of the fluid as a result
of an increase in ambient air temperatures, and/or as a
result of braking. A stop 58 may be provided to limit the
leftward travel of the compensator piston 50.
A disc 60 and a retaining ring 62, as shown in
FIGS. 1-2, may be used to fix the concentric cylinder 18
axially to the cylindrical wall 22. In addition, the disc
60 and the retaining ring 62 preferably are configured to
allow for the removal and installation of the compensator
piston 50 and the compensator spring 56.
Unlike disc brake assemblies comprising typical
external fluid reservoir systems, the disc brake assembly
10 of the present invention does not require bleeding of
the brake system when, for example, the internal thermal
compensation chamber 42 is turned upside-down. However, the
disc brake assembly 10 still will require bleeding when,
for example, the system's brake fluid is changed. TnThen
such bleeding is necessary, the compensator piston 50 must
be maintained at a specific depth during the bleeding
operation. For this purpose, as shown representatively in
FIG. 1A, small screws S could be passed through thru-holes
59 in the disc 60, preferably located at evenly-spaced
locations in the disc 60, and threaded into threaded holes
61 of the compensator piston 50. The user could then push
on the heads of the screws S until the shoulders of the
screws S touch the disc 60. The disc brake assembly 10
would then be bled and the screws removed. Although not
shown, alternatively, an internal or external machined
feature on the.compensator piston 50, such as an undercut,
could be used to permit special tools with a hook or flange
to control the depth of the compensator piston 50 during
the bleeding process.
As will be appreciated by those having skill in
the art, bleed screws 64 shown in FIGS. 1 and 2 (and the
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filler plug 65 shown in FIG. 3) are used to conduct the
bleeding operation. For example, the two bleed screws 64
of the first embodiment may be removed, and fluid may be
pumped into one bleed port 63 using a plastic bottle,
5 flexible hose, or other such implement. The other bleed
port 63 may be simultaneously observed to detect the
presence of air bubbles until the bubbles have dissipated.
Alternatively, one of the two bleed screws 64 may be
removed and the disc brake assembly may be bled in a vacuum
10 fluid tank. Other methods of and arrangements for bleeding
known to those skilled in the art may be utilized, such as
that described below with respect to the second embodiment.
In operation, the disc brake assembly 10 is
initially in an unactuated state as shown in FIG. 1. In
the first embodiment, the disc brake assembly 10 is located
in proximity to the disc brake which is controlled.
Various modes of actuation may be located remotely
therefrom and controlled through various methods known in
the prior art. Thus, for example, the disc brake assembly
10 is mounted onto the frame of a bicycle adjacent to the
tire to be braked, and actuated through a brake cable B
which passes through the brake cable housing BCH that is
fastened to the cable housing boss 40. Although not shown,
the brake cable B is threaded through the flange 29 and
connected to the master cylinder piston 32 using any method
known to those skilled in the art, such as through mounting
to a bar or flange that extends across the inner portion of
the master cylinder piston 32.
Upon actuation, the brake cable B is caused to be
withdrawn from the master cylinder chamber 30, thus
applying a pulling force to the master cylinder piston 32
against the biasing force of the master cylinder spring 34.
The pulling force of the brake cable B is generated to be
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greater than the biasing force of the master cylinder
spring 34, resulting in movement of the master cylinder
piston 32 in a rightward direction relative to the figures.
Further, the pressure seal 33 slides with the movement of
the master cylinder piston 32 to cause a reduction in
volume in the pressure chamber 45. Eventually, the
pressure seal 33 passes the compensator port 44 with
further reduction in volume in the pressure chamber 45.
This action causes pressure build-up in the brake fluid
which is communicated through the master cylinder port 36,
the caliper piston port 38, and into the caliper piston
bores 20. The build-up of pressure of the brake fluid
enables actuation of the disc brakes. Any excess brake
fluid found in the pressure chamber 45 is expelled through
the compensator port 44 during the compression stroke
described above.
Upon release of the brake cable, the master
cylinder spring 34 urges the master cylinder piston 32
leftwardly and back into its unactuated position. As the
pressure chamber 45 increases in volume, brake fluid is
drawn out of the caliper piston bores 20, thus reducing the
pressure therein and allowing for release of the disc
brakes.
The internal compensation chamber 42 acts as a
reservoir for the pressure chamber 45. Under ideal
conditions, a fixed volume of brake fluid would be required
to actuate the disc brake assembly 10 in a manner as
described above. However, losses due to leakage, and
thermal effects of expansion and contraction, cause changes
in volume of the brake fluid which may result in severe
degradation in or altogether a lack of performance. To
ensure a sufficient working volume of brake fluid is
maintained, the internal thermal compensation chamber 42
feeds additional brake fluid through the compensator port
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44 into the pressure chamber 45. Similarly, excess brake
fluid is forced out of the pressure chamber 45 during
operation and into the internal thermal compensation
chamber 42. The relief chamber 47 accepts excess brake
fluid which is passed through the relief port 46.
The first embodiment of the present invention as
illustrated in FIGS. 1 and 2, in which the concentric
cylinder 18 of the present invention is integrally mounted
to the caliper body 16 of the disc brake assembly 10, is
compact and convenient, and therefore ideal for use on
pedal driven vehicles such as bicycles.
In a second embodiment, the principles of the
present invention may be used in connection with a
concentric cylinder 18 housing a lever-actuated master
cylinder. Such a disc brake system is shown in FIG. 3 and
is generally designated with the reference numeral 100.
Like components from the first embodiment are designated
with the same reference numerals in FIG. 3 and in
discussing the second embodiment. The disc brake assembly
100 operates in conjunction with a remote caliper unit (not
shown) connected to the assembly 100 by a brake hose H
which conducts the brake fluid to the caliper unit. This
type of system is particularly useful, for example, in
connection with bicycles, motorcycles, snowmobiles and
quad-runners.
The disc brake assembly 100 is similar to that of
FIGS. 1 and 2. Here, however, the concentric cylinder 18
is housed within a cylindrical wall 68, that is defined by
a handlebar mounting boss 70. The handlebar mounting boss
70 is formed with a filler port 72, configured to receive
the filler plug 66, and be in communication with the
internal thermal compensation chamber 42. Also, the
handlebar mounting boss 70 is formed with a delivery port
74 provided to communicate the brake hose H with the
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pressure chamber 45. Further,~a mounting groove or recess
is defined in the handlebar mounting boss 76 which is
shaped for mounting onto a bicycle handlebar or other
location.
A modified flange 39A is provided to seal off
entirely one axial end of the concentric cylinder 18. A
cap 78 is mounted at the other axial end of the concentric
cylinder 18 through which passes a pushrod 80. The pushrod
80 is mounted to a brake lever 82 through an articulating
connection 84. The brake lever 82 is also pivotally
mounted to the handlebar mounting boss 70 through a pivot
connection 86.
Other than where noted, the first and second
embodiments are structurally the same. In operation, the
second embodiment relies on the pushrod 80, through
manipulation of the brake lever 82, to depress the master
cylinder piston 32 and cause actuation of the disc brake
assembly 100 in the same manner as described with respect
to the first embodiment. Release of the brake lever 82
causes withdrawal of the pushrod 80 and a return of the
disc brake assembly 100 to an unactuated state.
With respect to bleeding the second embodiment,
the filler plug 66 may be removed and fluid may be pumped
through the filler port 72 with a plastic bottle, flexible
hose, or other such implement. The delivery port 74 on the
remote caliper unit connected to the lever-actuated
assembly may be opened and observed while pumping fluid
through the filler port 72 to detect the presence of
bubbles, until the bubbles have dissipated. This design is
the most appropriate use of the present invention in
connection with motorcycles, snowmobiles and quad-runners
due to the ease of bleeding the disc brake system.
As shown, the present invention represents an
improvement over conventional disc brake assemblies due to
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use of an internal thermal compensation chamber 42 which
replaces and eliminates the external fluid reservoir of
such conventional systems. The internal thermal
compensation chamber 42 is more compact than typical
external fluid reservoir designs due to it being concentric
to and integrated with the master cylinder chamber 30. The
internal thermal compensation chamber 42 is also less
susceptible to damage on open cockpit vehicles such as
bicycles, motorcycles, snowmobiles and quad-runners due to
the elimination of the external fluid reservoir, which
typically is made of plastic.
Also unlike external fluid reservoir designs,
which typically have an air chamber disposed above the
fluid in the reservoir, the internal thermal compensation
chamber 42 of the present invention is a sealed system.
The internal thermal compensation chamber 42 of the present
invention therefore does not suffer the drawback of
external fluid reservoir systems which, if turned upside-
down, risk having air enter the fluid circuit and cause a
deterioration or less of brakes. Thus, unlike such systems
which must be bled when turned upright again, the sealed
system of the present invention eliminates the need to
bleed the brake system. This feature is particularly
useful when the present invention is applied to bicycles,
which are frequently turned upside-down.
The integrated internal thermal compensation
chamber 42 and the master cylinder chamber 30 of the
present invention allow for the elimination of the
conventional external reservoir tank on a disc brake
system. The disc brake assembly 10, 100 of the present
invention performs all of the same functions as described,
for example, in connection with the disc brake assembly of
the Leitner patent, such as providing disc brake fluid to
the master cylinder chamber through the compensator port,
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providing a chamber to accommodate increases in brake fluid
volume due to thermal expansion or decreases in brake fluid
volume due to thermal contraction, and providing additional
disc brake fluid to the master cylinder chamber when
5 necessary due to brake pad wear. In addition, however, the
assembly of the present invention can be manufactured at a
lower cost due to a reduction and consolidation of parts
used in such disc brake assemblies. The use of the
concentric cylinder of the present invention also enhances
10 the manufacturing cost savings due to the increase in
lathe-turned parts, and the reduction in the complexity and
number of machining operations required in connection with
a caliper body in comparison to those that would be
required in connection with designs such as that described
15 in the Leitner patent.
Tnlhile there are shown and described herein
certain specific structures comprising aspects of the
invention, it will be clear to those skilled in the art
that various modifications and rearrangements of the parts
may be made without departing from the spirit and scope of
the underlying inventive concept, and that the same is not
limited to the particular forms herein shown and described.
