Note: Descriptions are shown in the official language in which they were submitted.
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A WEDG~; BRAKE ARRANGEME~T FOR EIEAVY ROAD V~EII CL~S
Technical E~ield
This invention relates to a wedge brake arrangement
namely a wedge shaped actuator for drum brakes, especially
for heavy road vehicles, including a brake cylinder
push rod axially movable in a housing, plungers axially
movable in the housing substantially perpendicularly
to the push rod, and force transmitting rollers between
parallel wedge surfaces at the end of the push rod and
on the respective plungers, so that the plungers are
pushed apart upon axial movement of the push rod.
Background of the Invention
Arrangements of the kind referred to are well
known in the art. The plungers forming part of the
brake actuation system are intended for cooperation
with the ends of a pair of opposed pivoted brake shoes
brakingly engaging a rotating brake drum of the vehicle
by urging the brake shoes apart against the interior
surface of the brake drum. Numerous examples from the
patent literature could be given; just one and a rather
typical example is DE-B-23 56 075.
A well known drawback with presently known wedge
brakes of the above mentioned type is the uneven distri-
bution of braking forces between the brake shoes and
the resulting uneven brake lining wear. Depending on
the direction of rotation for the wheel to be braked,
one of the brake shoes is "leading" and the other one
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"trailing". The prior art wedge brake arrangements
described as "floating", are unable t~ contr~l the proper
distribution of the braking forces to the respective
brake shoes.
Summary of the Invention
This basic drawback with presently known wedge
brake arangements as described above, is eliminated
by the present invention. A compact, cheap and reliable
design is provided wherein the push rod is guided within
the housing for complete control over the reaction forces
from the plungers. Guide rollers are arranged between
plane surfaces at the end of the push rod and in the
housing, respectively to guide the movement of the push
rod, the surfaces being parallel with each other and
with the axis of the push rod. A guide roller is
preferably positioned on each side of the force trans-
mitting roller.
It is common to provide a roller cage for the
proper guiding of the force transmitting rollers in
conventional designs. According to one aspect of the
invention, both the guide rollers and the force trans-
mitting rollers are arranged in suitably shaped openings
in the roller cage.
The reaction forces in the arrangement are
substantial, and a long life with safe operation is
essential, which means that all the mentioned surfaces
and rollers have to be strong and highly wear-resistant.
In order not to require a costly material in the whole
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housing, a separate, high~quality reaction plate is posltloned
within the hou~ing to serve as the housing portlon of the plane
surface for the guide rollers.
Accordingly, the invention provides a hrake shoe
operation apparatus for actuating plvotable brake shoes carried
within a rotatab].e brake drum, said apparatus comprising,
a)- housiny means;
b)- a pair of opposed, spaced plungers slidably
positioned within the housing, each plunger engageable
with a respective brake shoe and movable relative to
each other along respective plunger movement
directions to move the associated brake shoe into
braking contac~ with the brake drum, the plungers each
having inner plunger faces inclined to the respective
plunger movement directions;
c)- wedge means positioned between the plungers and
movable transversely relative to the plunger movement
directions along a wedge movement direction, the wedge
means including wedge surfaces substantially parallel
with and opposed to respective plunger inner faces;
d)- wedge actuating means for moving the wed~e in a
wedge movement direction;
e)- force transmitting roller means positioned between
and in contact with the respective plunger inner facqs
and the opposed wedge surfaces for rolling contact
therewith and for transmitting movement of the wedge
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means ~o the plungers to move the plungers relaklve
to the brake drum and cause movement of the brake
shoes relative to the brake drum;
f)~ stationary guide surface means positioned opposite
at least one wedge surface and including a stationary
guide surface; and
g) guide roller means positioned on at least one side
of the wedge means and between and in rolling contact
with the wedge means and w.ith the stationary guide
surface means for guiding movement of the wedge means
relative to the guide surface means.
Brief Description of the Drawings
The invention will be described in fu.rther detail
below reference beiny made to the accompanying drawings:
Fig. 1 is a schematic side view, partly in sectionr
of a known wedge brake arrangement according to the sta~e of
the art
Fig. 2 is a corresponding, but enlarged side view
showing a wedge brake actuator and associated struc~ure in
accordance with one aspect of the invention;
Fig. 3 is an enlarged side view, partly in sectionr
of one embodiment of a wedge brake arrangemen~. according to ~he
present invention; and
Fig. 4 is a fragmentary sectional view taken
perpendicularly through Fig. 3 to show the interaction of the
different details.
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Detailed Description of Preferred Embodiments
A typical conventional wedge brake arrangement as
presently used for heavy roacl vehicles is shown in Flg. 1.
~rake shoes 1 provided with brake lining 2 are movable into
braking engagement with a brake clrum 3, rotating with a wheel
~not shown) of ~,he vehicle, by means of a so calle~ wedcJe brake
unit 4, whereas the return movement
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of the shoes is performed by a draw spring 5.
The wedge brake unit 4 includes a brake ~luid
operated brake cylinder 6, whose outgoing push rod is
in the form of a wedge 7. There is a return spring ~
of the helical compression type for the push rod~ Rollers
9 are arranged between the wedge 7 and plungers 10 ancl
the plungers are axially movable suhstantially perpen~
dicularly to the direction of movement of the wed~e 7
so as to push the brake shoes 1 into braking engagement
with the brake drum 3. The inclination of the plunger
ends cooperating with the rollers 9 is the same as that
of the respective opposed surfaces o~ the wedge 7, so
that the rollers 9 roll between parallel surfaces. In
practical embodiments the rollers 9 are provided with
roller cages or similar guiding means, which for the
sake of simplicity are not shown in Fig. 1.
Depending on the direction of rotation of the
brake drum 3, one of the brake shoes 1 will be "leading",
whereas the other one will be "trailing", when the two
plungers 10 are pressed apart by the wedge 7 via the
rollers 9 for performing a brake operation. ~his means
that the arrangement can be characterized as "floating"
and that no control over the force transmission to the
respective brake shoe is attained, resulting for example
in uneven distribution of the brake force and in uneven
brake lining wear.
A solution according to the invention is
illustrated in Fig. 2, where only those parts of the
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general arrangement according to Fig. 1 which are of
interest for a proper understanding of the invention
are shown.
As in the conventional arrangement two plungers
15 are axially movable in a housing 16. A bra~e cylinder
push rod 17 is axially movable perpendicularly to the
axis of plungers 15. The push rod 17 is provided wi-th a
wedge 18, and force transmitting rollers 19 are positioned
between the respective wedge surfaces and a parallel end
surface of the opposed plunger 15, giving the function
described above with reference to Fig. 1.
However, the wedge 13 is also provided with
surfaces 20 parallel with each other and with the axis
of the push rod 17, and corresponding parallel guide
surfaces 21 are fixedly positioned within the housing 16
in any suitable way. Guide rollers 22 are arranged
between these surfaces 20, 21. Rollers 19 and 22 need
to be properly guided, and a roller cage or the like is
shown in Figs 3 and 4 and will be described hereinafter.
The control over the wedge that is lacking in
the conventional arrangement according to Fig. 1 is
completely obtained with the modification disclosed in
Fig. 2, where the guide rollers 22 will provide the
necessary control over the reaction forces in the
arrangement .
A practical embodiment of an arrangement of the
modified kind disclosed in Fig. 2 is shown in Figs.
3 and 4. In Fig. 3 only the left half of the arrangement
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is sectioned, but the contents of the right half is
the same as that shown.
In a housing 25 a plunger 26 is axially movable.
At its end extending out of the housing 25, the plunger
26 is provided with a member 27 for engaging the
respective brake shoe (see Fig. 1). A bellows 28 (shown
on the right in Fig. 3) between the housing 25 and the
member 27 prevents moisture, dirt and the like from
entering the housing 25. Only a smaller part of the
plunger 26 is sectioned; conventionally a slack adjuster
is provided therein but forms no part of the invention
and is not disclosed or described. In order to take
full advantage of the arrangement according to the
invention the two slack adjusters in the plungers 26
need to be synchronized in a way not shown.
A brake cylinder push rod 29 is axially movable
in the housing 25 perpendicularly to the plunger 26.
A return spring 30 of the helical compression type is
provided for the push rod 29. At the end of the push
rod 29 there is a central wedge surface 31 cooperating
with a plunger end surface 26' parallel with the wedge
surface 31.
On either siae of the wed~e surface 31 at the
end of the push rod 29 is a guide surface 33 parallel
with the axis of the push rod 29. A hardened reaction
plate 34 is positioned within the housin~ 25 and in
parallel with the guide surfaces 33. A guide roller
35 is positioned between the guide surface 33 and the
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reaction plate 34. ~ositive guiding for the guide rollers
35 in the direction of the axis of push rod 29 is provided
by a small flange 34' on the reaction plate 34 or on
the housing 25.
A roller cage 36 pro~ides the necessary carrier
for the three rollers 32 and 35 (see Fig. 4) at either
side of the push rod 29. A cover 37 is attached to the
bottom of the housing 25.
The arrangement for the proper guiding of the
push rod along the push rod axis as shown and described
is preferred as the most suitable under the circumstances,
but many other practical solutions are conceivable.
hroughout the specification the expression "push
rod" has been used to identify the means for introducing
a brake force from a brake cylinder to plungers that act
upon the brake shoes. ~owever, it is apparent to those
skilled in the art that it is an easy task to modify any
arrangement of this kind to include a "pull rod" as a
modification, which is intended to be included in the
scope of the claims. Also other means than the rollers
32 and 35 for transmitting the forces are conceivable,
for exa~ple pinions bet~een rack-shaped surfaces.
A perpendicular force transmission between the
push rod and the plungers has been presumed, but
deviations from the exact perpendicularity are possible.
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SUPPL~MENTARY DISC~OSURE
In an altexnative embodiment of the present inventlon,
it has been found that in the wedge-brake actuation of ~he
present apparatusr gu~de rollers may be provided on only one
side of the push rod.
The present invention provides one embodiment wherein
a stationary guide surface is positioned opposite one wedge
surface of the wedge. A quide roller is posltioned on the side
of the wedge and between the wedge and a plunger innerface, and
is in rolling contact with the wedge and with a stationary
guide surface for grinding the movemen~ of the wedge relative
to the guide surface.
Accordingly, in a broad aspect~ the invention provides
a guide apparatus for wedge operated drum brakes including
brake shoes movable toward a brake d.rum braking surface throu~h
plungers operated by the wedge and contacting the brake shoe,
said apparatus comprising:
a. force ~ransmitting roller means positioned between
and in contact with the plungers and the wedge for
transmitting bra~e actuation forces from the wedge to
each of the plungers by movement of the wedge relative
to the plungers; and
b. wedge guide means including ~upport means spaced
from the wedge, and guide roller means positioned
between and in contact with the wedge and the support
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m~ns for guiding mo~ement of the wedge relati~e ~o
the support means.
The invention also provides a brake actuation
apparatus for actuating drum brakes, wherein brake shoes are
urged against an inner surface of a rotatable hrake drum to
provide a braking orce, said apparatus compri.sing:
a. a housing;
b. push rod means movable within the houslng to and
from a brake actuation position, the push rod means
carrying wedge means;
c. operating means for moving the push rod means
relative to the housing;
d. brake shoe actuation means carried within the
housiny for engagement with the brake shoes and with
the wedge means;
e. rotatable force transmitting maans positioned
between the wedge means and the brake shoe actuation
means for transmitting movemènt of the push rod means
to the brake shoe operating means for moving the brake
shoes into contact with the brake drum; and
f. yuide means carried within the housing ~or guiding
and supporting the wedge means for movement parallel
to the axis of the push rod means in response to
reaction forces from the brake shoe actuation means,
the guide means positioned between the wedge means and
the brake shoe actuation means.
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In drawings whi~h illustrate a ~urth~r emh~diment o~
the inven~ion;
Fi~. 5 is a cross-sectional view of ano-ther embodiment
of the present invention, in which a guide roller is provided
on only one side of the push rod;
Fig. 6 is a cross-se~tional view taken alon~ the llne
6-6 of Figure S; and
Fig. 7 is a fragmentary view, partially in section,
taken along the line 7-7 of Figure 5.
Another embodiment of the present invention is
illustrated in Figures 5 through 7, in which a wedge-brake
actuation apparatus is disclosed wherein guide rollers are
provided on only one side of the push rod. This embodiment
provides a distinct advantage over the
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embodiment illustrated in Figures 2 through 4 in that
the parts can be provided in a smaller housing, and
consequently the structure can be incorporated within
a smaller brake drum, thereby rendering it suitable
for use with smaller vehicles than txucks or other heavy
road vehicles.
Referring now to Figure 5, the embodiment
illustrated includes a housing 50, which defines two
opposed and spaced coaxial cylinders 52, 54 each of
which slidably carries a plunger 56, 5B, respectively.
Each of plungers 56, 58 includes an outer, brake shoe-
contacting member 60, 62, respectively, on its outwardly
facing surface, and each plunger includes an inclined
inner face 64, 66, respectively on its innermost surface.
Stop rings 68, 70 are provided adjacent the outermost
surface of the respective plungers to limit inward
movement thereof.
Housing 50 also includes an opening 72 ~hat has
an axis that extends substantially perpendicular to
and intersects the common axis of cylinders 52 and 5~.
Opening 72 permits the passage therethrough of a push
rod 74, which extends from a brake cylinder (not shown).
Push rod 74 is enclosed by a cylindrical, accordian-type
protective sleeve 76, only part of which is illustrated,
to prevent the entry o~ dirt and foreign material into
the housing through opening 72. A return spring 78,
only part of which is illustrated, is provided to act
on the outer end (not shown) of push rod 74 to bias
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it into an outer, non-brake-actuating position. The
inner end of spring 78 is recei.ved in an annular spring
retainer 80, that seats agains-t an annular flange 82
that is concentric with opening 72.
The innermost end of push rod 7~, relative to
housing 50, carries a wedge 84 that is of generall~
rectangular cross-section, as best seen in Figure 7.
Wedge 84 includes a flat, inclined first wedge surface
86 that is in substantially parallel relationship with
and opposed to inclined inner face 64 of plunger 56,
and is inclined relative to the axis of push rod 74.
The opposite side of wedge 84 includes a second wedge
surface 88, that is narrower than the first wedge surface
86, and is also a flat surface that is inclined relative
to the push rod axis and is substantially parallel to
inclined inner surface 66 of plunger 58. Preferably,
the angles of inclination of the respective opposed
wedge surfaces are the same, although, if desired, the
angle of one pair of surfaces can be different than
that of the other pair. Outwardly of second wedge surface
88 and on each side thereof are generally rectangular
planar surfaces 90, 92 that extend along the length
of wedge 84 and are substantially parallel with the
push rod axis. The two outer surfaces 90, 92 define
guide roll surfaces, as will hereinafter be further
explained.
Between each of the wedge surfaces ~6, 88 and
the respective inner faces 64, 66 of plungers 56, 58,
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a respective force transmitting roller 94, 96 is
positioned and is in contact with the respective opposed
surfaces, so that it can roll along the respective opposed
surfaces as wedge 84 is moved along the wedge movement
direction, which is along the push rod axis. As shown,
the respectlve ~orce transmitting rollers 94, 96 are
of unequal diameters, which, again, contributes to a
smaller total volume of the parts within housing 50,
thereby permitting the housing to be made smaller in
size, so that it can fit within a smaller diameter brake
drum. However, if desired, the diameters of the force
transmitting rollers can be equal.
Force transmitting roller 94 extends across
substantially the entire width of wedge surface 86 and
includes stub end shafts 98, 100 that are rotatably
and slidably received in respective transverse slots
102, 103 that are provided in opposite sides of roller
cage 104. The slots are so configured and arranged
that the axis of force transmitting roller 94 can move
toward and away from the axis of push rod 74, when wedge
84 moves along the push rod axis, although the roller
is constrained to move along the push rod axis together
with roller cage 104.
Force transmitting roller 96, which is positioned
on the opposite side of wedge 84 from force transmitting
roller 94, is of a narrower width, as best s~en in Figure
7 7 and bears against narrower second wedge surface 88
and the corresponding inner surface 66 of plunger 58.
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The opposed lateral ends of force transmitting roller
96 each carry a guide roller 106, 108, respectively,
which are in rolling contact with respective guide roll
surfaces 90, 92 on wedge 84. As best seen in Figures
5 and 7, the respective guide rollers 106, 108, although
co-axial with each other, are offset from the axis of
second force-transmitting roller 96. Additionally, a
reaction plate 110 is positioned within housing 50 to
define a second guide roller guide surface 112 that
extends in a direction parallel with the axis of push
road 84. The respective guide roller guide surfaces
90, 92, and 112 guide each of guide rollers 106, 108,
respectively, for movement in a direction parallel with
the axis of push rod 74, and thereby guide and provide
support for push rod 74 and wedge 84. Preferably, reaction
plate 110 is made from a high quality, hardened steel,
or the like, for long wear. Alternatively, if desired,
second guide surface 112 can be defined by a surface
formed integrally within the interior of housing 50,
although to do so would require that the entire housing
be made of a wear-resistant material, which would render
the housing more expensive. As is apparent from ~igures
5 and 7, reaction plate 110 includes a suitable opening
to permit force transmitting roller 96 to extend
therethroug~ and to contact inner face 66 of plunger 58.
Roller cage 104 supports second force transmitting
roller 96, as well as the adjacent guide rollers 106
and 108, in a floating relationship by defining a cage
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end wall 114 (see E'igure S) that includes an opening
defined by a pair of outwardly extending flanges 116,
118 to receive and carry the second force transmitting
roller and associated guide rollers for movement along
with the movement of the cage, as the cage moves in an
up and down direction as viewed in Figure 5~ ~'urther,
and as clearly shown in Figures 5 and 6, roller cage
104 includes a collar 120 that fits around a major portion
of the periphery of push rod 74, and includes a pair of
spaced, parallel sidewalls 122, 124 that include slots
102, 103, respectively, that rotatably and slidably
receive stub shafts 98, 100 of force transmitting roller
94.
The embodiment illustrated in Figures 5 through 7
operates in a manner similar to that of the embodiment
illustrated in Figures 2 through 4, in that downward
movement of push rod 74, as viewed in Figure 5, by
actuation of the brake cylinder (not shown) causes wedge
84 to move downwardly, thereby urging the respective
force transmitting rollers 94 and 96 downwardly along
the push rod axis, and outwardly in opposite directions,
relative to the push rod axisl to thereby cause the
respective plungers 56 and 58 to each move outwardly
relative to housing 50, and thus to push the associated
brake shoes (not shown) against the brake drum inner
surface (not shown) to provide the desired braking effect~
As the force transmitting rollers move in the direction
just described, guide rollers 106 and 108 are carried
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between the guide surfaces 90 and 92 of wedge 84 and
opposed guide surface 112 on reaction plate 110, and
serve to provide a stabilization of the movement of
push rod 74. In the orientation of the parts as
illustrated in Figure 5, first force transmitting roller
94 and its associated plunger 56 are intended to actuate
the trailing brake shoe, which would correspond with
the brake shoe 1 illustrated in the left-hand portion
of Figure 1 when the brake drum there shown is rotating
in the clockwise direction. Thus, the brake shoe 1 on
the right-hand side of that drawing (Figure 1) would be
designated the leading brake shoe. Because the rotation
of the brake drum in the direction described requires
that a larger braking force be applied to the trailing
shoe, as compared with the leading shoe, there is a
greater reaction caused by the greater force acting
on the trailing brake shoe, and that reaction operates
to urge wedge 84 sideways, relative to the axis of push
rod 74, in a direction toward the leading brake shoe.
However, because of the guide surface 112 defined by
reaction plate 110, and the guide rollers 106, 108 between
tha~ guide surface and guide surfaces 90 and 92 on wedge
~4, excessive reaction force, which would otherwise
be transmitted to the leading brake shoe is avoided,
thereby providing more uniform braking action between
the leading and trailing brake shoes, with consequently
more even brake shoe wear than if the guide rollers
and guide roller surfaces were not provided. Furthermore,
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because most vehicles perform most of their movement
in what is designated as a forward direction, the
provision of the guide rollers only on the leading shoe
side of the brake drum permits a smaller volume of parts
to be provided within the brake drum, and permits the
invention to be incorporated into smaller diameter brake
drums thereby rendering it applicable to smaller vehicles,
such as automobiles.
Although particular embodiments of the present
invention have been illustrated and described, it will
be apparent to those skilled in the art that various
changes and modifications can be made without departing
from the spirit of the invention. Accordingly, it is
intended to encompass within the appended claims all
such changes and modifications that fall within the
scope of the present invention.
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