Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a drum brake
assembly, and more particularly, to a brake assembly
including an extendible assembly and a parking assembly
cooperating therewith.
In a drum brake assembly, such as illustrated in
Canadian Patent No. 1,072,459, issued February 26, 1980, a
parking strut and a lever generally cooperate to manually
urge a pair of brake shoes to a braking position. The
strut extends between the pair of brake shoes near a
hydraulic actuator and the lever is pivotally mounted on
one of the brake shoes such that the lever is pivoted to
push the strut and other brake shoe away from the one brake
shoe which pivotally supports the lever.
When large diameter axle shafts are required, the
amount of space available within a drum brake assembly is -~
reduced so that a parking brake strut, which extends between
a pair of brake shoes near the hydraulic actuator, inter-
feres with the axle shaft between the pair of brake shoes.
~- Consequently, it is desirable to eliminate the parking brake
strut, but retain the parking brake feature.
The present invention resides in a drum brake
assembly having a brake drum rotatable about an axis and
a pair of brake shoes which are movable radially by a
hydraulic actuator from a non-braking position to a braking
position in engagement with the drum during a service
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brake application. An extendibIe assembly is provided
which has a longitudinal axis and is engageable with the
- pair of brake shoes to substantially define the non-
braking position. A pair of levers is secured to the
; 30 extendible assembly, and the pair of levers is pivotal in
opposite directions relative to the extendible assembly
to move the pair of brake shoes from the non-braking position
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to the braking position during a parking brake application.
The extendible assembly includes a pair of projections
extending radially therefrom in opposite directions from
the extendible assembly to define mountings which are
radially offset from each other relative to the drum axis
and axially offset from each other in a direction parallel
to the drum axis. The mountings pivotally secure the
pair of levers to the extendible assembly such that the
pair of levers are pivotally secured on opposite sides of
the extendible assembly at axially spaced locations.
In a specific embodiment of the invention, the
extendible assembly is movable with one of the pair of
brake shoes as the one brake shoe is moved relative to the
other brake shoe in response to pivoting of the pair of
levers, and the extendible assembly movingly carries a -
spacer engageable with the pair of levers and the other
brake shoe.
It is a primary object of the present invention
to incorporate a parking mechanism with an adjustment
means for a drum brake assembly so that a conventional
parking brake strut extending between a pair of brake
shoes can be eliminated.
BRIEF DESCRIPTION OF T~E DRAWINGS
Figure 1 is a side view of a drum brake assembly --
constructed in accordance with the present invention;
: Figure 2 is a cross-sectional view taken along
- line 2-2 of Figure l; and
' Figure 3 is a cross-sectional view taken along
line 3-3 of Figure 2.
DETAILED DESCRIPTION
The drum brake assembly 10 illustrated in Figure
1 is similar to the drum brake assembly of Canadian Patent
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No. 1,075,176, issued April 8, 1980 of which I am a
co-inventor. A backing plate 12 is secured by any suitable
means to an-axle housing (not shown) and an opening 14 is
~`; dimensioned to permit a large diameter axle shaft to
extend axially therethrough.
A plurality of lugs at 16 extend radially from
the backing plate 12 to slidably support a pair of brake
shoes 18 and 20 and a hydraulic actuator 22 is engageable
with one end of the brake shoes 18 and 20. The hydraulic
` 10 actuator 22 operates to move the pair of brake shoes 18
and 20 to a braking position engaging the drum 24. In
order to maintain the pair of brake shoes adjacent the
drum 24, regardless the friction lining dimension of each
brake shoe, an adjustment means 26 is engageable with the
other end of each brake shoe to take up the wear of the
friction lining of each brake shoe. The adjustment means
26 comprises an extendible member 28 which includes a nut
- 30, a sleeve 32 and a threaded stem 34. A star wheel 36
is engageable with a pawl 38 so that the pawl imparts
rotation to the star wheel and threaded stem when the
clearance between the pair of brake shoes and the drum is
greater than a predetermined value.
Turning to Figure 2, it is seen that the brake
shoes 18 and 20 include bifurcated webs for fixedly securing
- a plate 40 which is attached to the brake shoe 20 and a
; plate 42 which is attached to the brake shoe 18. The nut
30 and the sleeve 32 i~clude slots 44 and 46 which receive
the plate 40 and 42, respectively. Consequently, the
,~ extendible member 28 is carried between the pair of brake
shoes opposite the hydraulic actuator 22.
In accordance with the invention the nut 30 forms
projections 48 and 50, see Figure 3, which extend radially
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therefrom to define pins 52 and 54, respectively. The
projections and pins extend from opposite sides of the nut
and are offset from each other, so that the lever 58 is
pivotally mounted on the top side of the extrudible member
28 and the lever 56 is pivotally moun,ed on the bottom
side of the extrudible member 28, as shown in Figure 1.
In Figure 3 it is seen that the projection 50 extends
upward from the nut 30 and the projection 48 extends down-
ward from the nut 30. Moreover, the projection 50 and pin
54 are offset to the right of the center of the nut 30,
while the projection 48 and pin 52 are offset to the left
of the center of nut 30. The pair of levers 56 and 58 are
pivotally anchored on the respective pins 52 and 54 and
the pair of levers 56 and 58 extend from their pivotal
connection with the nut 30 to engage a conduit 60 and a cable
62 extending from the conduit 60, respectively. Because
the cable 62 is substantially concentric with the conduit
60, the lever 56 and the lever 58 are bent to provide for
the engagement between the pair of levers and the conduit
and cable to coincide with the axis of the conduit. The
:~ pair of levers cooperate with the extendible member and
the pair of brake shoes to substantially define a parking
mechanism.
; A spacer 70 is slidably carried by the nut 30
between the projections 48 and 50 and the engagement with
~ - the plate 40 of the brake shoe 20. Adjoining the spacer is
- a washer 72 which is free to slide with the spacer on the
- nut 30 and rotate relative to the nut 30. The spacer is
1 engageable with the brake shoe plate 40 and the washer 72
;¦ 30 is engageable with an abutment surface 74 on the lever 56
, and an abutment surface 76 on the lever 58. The abutment
,.
~ surface 74 on lover 56 is disposed above the pivotal
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connection at pin 52 while the abutment surface 76 on lever
58 i~ disposed below the pivotal connection at pin 54.
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MODE OF OPERATION
When a vehicle operator steps on a brake pedal, pressurized fluid
is comnunicated to the hydraulic actuator 22 to radially expand the pair of
brake shoes 18 and 20 into engagement with the rotating drum 24, thereby ~ -
retarding the rotation of the latter. The operation of the drum brake assem-
bly 10 during service braking is the same as the operation of a conventional
drum brake.
When the vehicle is parked, the vehicle operator steps on the
parking brake pedal (not shown) which retracts the cable 62 within the con-
10 duit 60 as the cable 62 is connected by any suitable means to the parking
brake pedal. In addition, the conduit 60 moves relative to the cable 62 to
telescope the cable into the conduit 60. Therefore, the lever 56 is pivoted
counterclockwise, viewing Figure 2, about pin 52 and the lever 58 is pivoted
clockwise about pin 54. The pivoting of the pair of levers causes the abut-
ment surfaces 74 and 76 to rotate relative to the pins, thereby imparting
movement to the washer 72 and spacer 70 towards the brake shoe plate 40.
With the spacer 70 in engagement with the plate 40, the piwting of the
abutment surfaces toward the washer 72 imparts a force to the nut 30 urging
the nut 30 to move away from the plate 40. Consequently, further pivoting
20 of the levers and abutment surfaces causes the nut 30, stem 34 and sleeve 32,' to move away from the plate 40, thereby radially expanding the brake shoe 18
into engagement with the drum 24. When the brake shoe 18 is in engagement
with the drum 24, the pivoting levers and abutment surfaces continue to
slide the spacer and washer on the nut 30 away from the brake shoe 18,
thereby urging the brake shoe 20 to radially expand into engagement with the
; drum 24. When both brake shoes are in engagement with the drum 24 the drum
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is prevented fro~ rotating so that the vehicle is rendered stationary.
Viewing Figure 1, it is seen that the pair of levers 56 and ~8
extend axially inwardly relative to the backing plate 12 between two con-
30 secutive lugs 16 so that the levers take up a small radial width and are
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spaced from the central space defined by the inner periphery of the pair of
brake shoes. Therefore, the opening 14 can be dimensioned large enough to
accept large diameter axle shafts.
With the pair of levers 56 and 58 rotating in opposite directions,
the w3sher 72 is urged to rotate in a counterclockwise direction, viewing
Figure 3, by both levers. As a result, the abutment surfaces 74 and 76 slide
over the rotating washer, thereby preventing scoring of the washer at one
location.
Although the parking mechanism described hereinabove is illustrated
with a pair of brake shoes which include bifurcated webs, it is intended
that such a parking mechanism is readily adaptable for use with any type
of drum brake assembly. In addition, many variations of the present
invention are possible by one skilled in the art and these variations are
included within the scope of the appended claims.
