Note: Descriptions are shown in the official language in which they were submitted.
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This inven-tion relates to a drum brake assembly.
A non-servo drum brake provides a support assembly on a
backing ~late to pivotall~ ancl~or a pair of brake shoes. A
hydraulic actuator is engageable with the pair of brake shoes
to pivot the brake shoes about the support assembly from a rest
position to a braking position. An adjustable strut extends
bet~een the pair of brake shoes to compensate for lining wear
and a parking arm cooperates with the strut to move the pair
of brake shoes to the braking position during a parking brake
application,
The non-servo drum brake is ~requently used as a
rear brake on vehicles wit~ front wheel disc brakes. The non-
servo rear drum brake is sufficient to assist the ~ront wheel
disc brakes in stopping the vehicle. It is designed to develop
less torque than the disc brake to reduce the chance of wheel
skidding. A problem exists during a parking brake mode because
the rear non-servo drum brake is required to hold the vehicle
stationary without any assistance from the front wheel disc brake.
One solution to this problem is to free the support
assembly during a parking brake mode as taught in United States
Patent 4,249,646. Such an arrangement converts the non-servo
drum brake to a DUO-SERVO (Trademark) drum brake only during
a parking brake application.
The present invention covers an improvement in a non-
serva drum brake wherein a support asser~ly or anchor bracket is
altqred to expand a pair oE brake shoes during a parking brake
application.
The present invention resicles in a drum brake assembl~
having a hydraulic actuator which cooperates with a pair o~ brake
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shoes to radially expand -the latter from a res-t position
to a braking position dwring a service brake application.
A backing plate is provided for carrying the hydraulic
actuator and the pair of brake shoes, and a parking assembly
cooperates with the pair of brake shoes to radially expand
the latter ~rom a rest position to a braking position
during a parking brake application. The parking brake
assembly includes a strut extending between the pair of
brake shoes substantially adjacent to the hydraulic
actuator, and the parking assembly also includes an arm
pivotal relative to one of the pair of brake shoes and
engaged with the strut. A support assembly is engageable
with the pair of brake shoes to absorb braking torque
developed by the pair of brake shoes, the support assembly
i including a pair of blocks engageable, respectively, with
the pair of brake shoes and also abutting the backing plate
to transfer torque thereto during a service brake application.
The support assem~ly further includes a Iever responsive to
actuation of the parking assembly and cooperating with the
pair of blocks to furkher expand the latter when the parking
assembly is actuated. The pair of blocks move away from
the abutment with the backing pIate to form a clearance
therebetween which permits the pair of blocks and the pair
of brake shoes to move slightly with the drum relative to
the backing plate when the parking assembly is actuated.
More specifically, the support assembly may
include a pair o~ pins ~ixedly secured to the 4acking plat.e
and loosely carxying the pair oE blocks wikhin a cage attached
to khe backing plate by the pins. Each block is engageable
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with a respective brake shoe and a retraction spring
extending between the shoes biases the shoes and blocks
to a rest position in abutment with the pins. The lever
is pivotally carried within the cage between the blocks.
The lever extends outwardly of the cage and connects with
a connector and a link attached to the parking arm. The
link is coupled to a parking brake cable with is movable
by a vehicle operator to actuate a parking brake application.
When a parking brake application is initiated, the
cable is pulled to pivot the link relative to the lever
which causes the parking arm to pivot relative to the brake
shoes and cooperates with the strut to move the brake shoes
to the braking position. Thereafter, further movement of
the cable pivots the link about the parking arm to actuate
the lever within the cage. Cam surfaces may be provided
on the lever facing the blocks so as to move the latter
away from each other in response to pivotal movement of
the lever. As the blocks separate from each other, the
pair of brake shoes are expanded to further engage the
rotatable member.
When the parking brake application is terminated,
a pair of retraction springs adjacent the hydraulic
actuator and -the support assembly withdraw the pair of
brake shoes to the rest position.
BRI~F DESCRIPT~ON OE1 ~IE DRAWINGS
Figure l is a ~ront view oE a dr~ brake assembly
with a partial cutaway of a support assembly according to
the present invention;
~` - 2a -
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- 3 -
Figure 2 is a cross-sectional view taken along line 2-2 of
F;gure l;
Figure 3 is a cross~sectional view taken along line 3-3 of
Figure l; and
Figure 4 is a cross-secttonal view taken along l~ne 4-4 of
Figure 2.
DETAILED DESCRIPTION
In Figure 1, a drurn brake assembly 10 includes a backing
plate 12 wlth an opening 14 for receiving an axle shaft (not shownJ.
The backing plate 12 supports a hydraulic actuator or wheel cylinder 16
at the top of the backing plate and a support assembly or anchor
device 18 is carried at the bottom of the backing plate opposite the
hydraulic actuator. A pair of b~ake shoes 20 and 22 are movably
mounted on the backing plate via holddown springs 24 and 26. The
brake shoes engage the hydraliuc actuator and the support assembly
so that actuation of the hydraulic actuator during a servlce brake
applicat,ion causes the brake shoes to move outwardly into engagement
with a drum 28 by pivoting on the support assembly 18.
An adjuster device 30 includes an extendible strut 32
and a pawl 34. The pawl cooperates with the strut to extend the
latter when the clearance be,tween the brake shoes and rotor is
greater than desired~ A parklng arm 36 is pivotally supported
on the brake shoes 20 via pin 38 and is engageable wl~h the strut 32.
During a parking brake applicatlon the arm 36 15 pivoted clockwise
in Figure I to push the strut 32 and shoe 22 to the left while the
shoe 20 and pln 38 are moved to the right until the shoes engage
the drum 28,
In accordance with the invention the support assembly 18
Includes a pair of pins 40 and 42 extanding outwardly from the backing
ptate 12 to carry a cage 44 wIth a pair of blocks 46 and 48 and a
lever 50 dtsposed ~hereIn. Each block de~ines an elIptlcal opening 52
and 54 for recelvlng the respecttve pins 40 and 42, The cage 44
Includes a top plate 56 and a U-shaped bottom cup 58. Spacers 60
and 62 flt over the pins and oppose the top plate and bottom cup so
that when the plate is secured to the bottom cup vla nuts 64 on the
~5~5
pins. the btocks are free to move a llmi~ed amount withln the cage.
Consequently, viewing Figure 1, the blocks can move horizontally within
the cage through a distance defined by the clearance between the
elipttcal openings and the spacers.
The lever 50 extends radially inwardly and is bent at 66 to
tilt toward the parking arm 36. The parking arm 36 terminates in
a link 68 opposite pin 38 and a connector 70 connects the end of
lever 50 with one end of the link 68, The other end of the link 68
is coupled to a parking brake cable 7~ which is movabTe by a vehicTe
operator during a parking brake app~ication. A pin 74 pivotally
connects the link 68 to the end of the parking arm 36 intermediate
the connector 70 and cable 72.
A fTrst re~raction spring 76 adjacent the hydraulic actuator
biases the brake shoes into engagement with the hydraulic ac~uator.
A second retraction spring 78 extends between the pair of brake shoes
adjacent the support assembly 18. The spring 78 biases the shoes
into engagement with the blocks 46 and 48 and also biases the blocks
to a rest position abutting plns 4a and 42, such that the left wall
of opening 54 is engaging pin spacer 62 and the right wall of opening 52
is engaging pin spacer 60.
MODE OF OPERATION
___
Durlng a service brake application, the hydraulic actuator
moves the palr of brake shoes to pivot relative to the pins 46 and 48
until the shoes engage the drum 28. Torque developed during braking
is transmttted ta either pin 40 or 42, depending on the dlrectlon of
rotation for the drum.
During a parking brake application, the cabls 72 is pulled
to the left in Figure I so that link is biased to rotate clockwise
about pin 74. The spring 78 acting through the shoes and blocks
opposes pivoting of the lever 50 so that durtng inittal parktng
brake application, the cable moves the ltnk and parking arm to
spread the shoes apart at the hydraullc actuator. The movement
of the parktng arm about ptn 38 pushes the strut 32 and shoe 22 to
the left whtle the ptn 38 and shoe 20 ar~ moved to the rlght In
Flgure 1~ Further pulllng on the cable 72 after the shoes engage
.
the drum near the hydraulic actuator causes the link 68 to rotate
clockwise about pin 74 as the parking arm 36 is substant7ally
stationar/. The rotating link 68 acts through the connector 70
to pivot the lever 50 clockwise relative to the cage 44. A sub
stantially rectangular base 80 on the lever is rotated so that cam
surfaces 82 and 84 push against the respective blocks 46 and 48
to move the blocks and adjoining ends of the brake shoes outwardly.
Consequently, the shoes are expanded further in response to move-
ment of the parking arm 36 and lever 50 ~o increase the frictional
engagement between the shoes and drum. Moreover, the blocks and
base act as a rigid member connecting the shoes together, and the
blocks are moved sltghtly away from the pins so that the pair of
shoes respond in a duo-servo mode to movement of the drum.
It is evident from the foregoing description that
many modifications and/or changes are feasible by one skilled
in the art. For example, the lever 50 could be directly connected
to the link 68 or to the parking arm 36 and means other than a pair
of blocks 46 and 48 could be used to separate the shoes in response
to actuatton of the parking arm. As such, these and other modifi-
cations and/or changes are intended to be covered by the appendedclaims.
