Note: Descriptions are shown in the official language in which they were submitted.
~0S9044
This invention relates to an automatic slack adjuster
for a vehicle brake linkage, the adjuster being of the kind
comprising a housing which constitutes a lever in the linkage
and is mounted for rocking movement about the axis of a shaft
which is adapted to be partially rotated about an axis for
applying or releasing a brake, and force is adapted to be
transmitted between the housing and the shaft by means of a
worm mounted in the housing and meshing with a worm wheel mounted
on and secured against rotation relative to the shaft, the
arrangement being such that adjustment of slack in the linkage is
effected by rotation of the worm to alter the angular position
of the worm wheel with respect to the housing, automatic worm
driving means being incorporated for rotating the worm for
adjustment of the slack in the linkage in response to relative
. movement between the lever and a relatively stationary part.
In some known automatic slack adjusters of the kind
set forth the worm drive means includes a one-way clutch and
the worm is displaced axially against an energy-storing return
spring to disengage the clutch when relative movement between
the lever and the stationary part has exceeded a predetermined
value and, on release of the brake, the clutch is re-engaged
by the release of energy in the spring which is operative to
rotate the worm.as the worm is returned axially to its initial
po si tlon .
According to the present invention there is provided
an automatic slack adjuster for a vehicle brake applying linkage
of the type comprising a shaft mounted for rotation about its
longitudinal axis for applying or releasing the brake, and a
housing which constitutes a lever in the linkage and is mounted
for rocking movement about the axis of the shaft and with respect
to a relatively stationary part, wherein the adjuster comprises
a worm wheel mounted on and secured against rotation relative
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to the shaft, a worm mounted in the housin~ and meshing with
the worm wheel to transmit angular movement of the lever to
the shaft, and automatic worm driving means for rotating the
worm with respect to the housing to compensate for slack in
the linkage.in response to relative movement between the lever
and the relatively stationary part, the automatic worm driving
means incorporating a connection having a degree of lost-motion
.equivalent to a desired braking clearance, the connection
including a clutch comprising first clutch means coupled to the
worm, second clutch means, and resilient means for urglng the
second clutch means normally into driving engagement with the
first clutch means, and a linearly slidable pawl acting between
the second clutch means and the stationary part to effect
rotation of the second clutch means whenever relative movement
between the lever and the stationary part has exceeded a value
equivalent to the degree of lost-motion.
~otation of the second clutch means is transmitted
~: through the first clutch means to cause corresponding rotation
of the worm and the worm wheel until the frictional force of.an
engagement between the braking surfaces exceeds the force of
engagement between the clutch means whereafter the clutch slips
to prevent further rotation of the worm with respect to the
housing.
Rotation of the worm to compensate for wear of the
braking surfaces occurs during brake applying movements, while
the braking clearance is being taken up. Thus,such adjustment
is independent of thermal or other deflections which may occur
in any part of the brake or brake applying mechanism incorporating
the slack adjuster.
The connection having lost-motion may be located
between the pawl and the second clutch means so ~hat rotation
of the second clutch means occurs only upon direct engagement
l
ywl/Jc~ ~ ~ 3 -
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of the pawl with the second clutch means, and a one-way drive
is disposed between the first clutch means and a spindle with
which the worm is fast, a return spring provided for urging
the pawl into an inoperative position deflecting to store
energy therein as the pawl is moved linearly on each angular
movement of the lever, release of the stored energy in a brake
application after the lost-motion has been taken up and which
is operative to return the pawl to the inoperative position also
being operative to effect rotation of both clutch means with
respect to the spindle and through the one-way drive, thereby
re-establishing the desired degree of lost-motion.
The second clutch means may be provided wi~h at least
one tooth which is received in a notch in the pawl and the
notch is of greater length than the circumferential length
. of the tooth to define the lost-motion.
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i" ,
lOS9044
The clutch may be of the cone type comprising single
first and second interengaging clutch members.
Preferably, however, the clutch comprises a clutch of
the multi-plate type with the first clutch means comprising a
plurality of primary clutch plates interposed alternatively
between a plurality of secondary clutch plates which define
the second clutch means, each secondary clutch plate being
provided with a tooth and all the teeth being received in the
notch in the pawl.
This has the advantage of providing a clutch capable of
transmitting a relatively high torque of which the efficiency
is less likely to be reduced due to wear of the lining of
the clutch plates than is a clutch of the cone type where
the clutch means each comprises a single member.
Conveniently a sleeve surrounds and is coupled to a
spindle fast with the worm and the clutch plates surround a
portion of the sleeve which is of reduced diameter, being
clamped into engagement and against a step at the change in
diameter by the resilient means which act between the plates
and an abutment at the outer end of the spindle remote from
the worm, the primary clutch plates are keyed to the sleeve
and the secondary clutch plates are freely rotatable in
and located by a bore in the housing and by the pawl.
Incorporating the clutch in the sleeve provides
a self-contained assembly which can simply be withdrawn
for replacement and/or maintenance without affecting the
spindle.
Conveniently the pawl is positively urged linearly
by means of an engagement with an adjusting shaft which is
eccentrically mounted with respect to the axis of rotation
of the lever and is angularly movable through an arc of a
circle centred on the stationary part with respect to
which the lever lS angularly movable.
The adjusting shaft itself rotates within the lever in
response to movement of the lever and an arm of the adjusting
shaft which locates in a stationary bracket.
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` ~059044
Two embodiments of our invention are illustrated inthe accompanying drawings in which:-
Figure 1 is a side elevation of anautomatic slack ad~uster for a vehicle brake
linkage with a side coverplate xemoved;
Figure 2 is a section on the line 2-2 of
Figure l;
Fi~ure _ is a section on the line 3-3 of
Figure l;
Figure 4 is a section on the line 4-4 of
Figure l;
Figure 5 is a section on the line 5-5 of
Figure l;
Figure 6 is a section on the line 6-6 of Figure l;
Figure 7 is a modified spring loading for the
clutch;
Figure 8 is a side elevation of an automatic
slack adjuster for a vehicle brake linkage
with a side cover plate removed and including
a section substantially on the line 8-8 of
Figure 9;
Figure 9 i5 a section on the line 9-9 of
Figure 8;
Figure 10 is a section on the line 10-10 of
Figure 8;
Figure 11 is a view of one end of the
adjuster;and
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lOS9044
Figure 12 is a side elevation of the
opposite end of the adjuster.
The automatic slack adjuster illustrated in Figures
1 to 7 of the accompanying drawings comprises a housing 1
constituted by a lever of a brake linkage which is adapted
to be mounted for rocking movement with respect to the
axis of a splined brake-applying shaft (not shown) and
which has a free upper end for connection to a brake actuatox
through any one of three spaced eyes. The lever 1 acts on
the shaft through a worm wheel 2 which is splined at 3
to the shaft and which is journalled for rotation in the
housing 1 between spaced end closure plates 4 and 5
clamped against opposite sides of the housing.
The shat is conveniently provided with at least
one cam expander for applying friction members, for example
shoes, to a rotatable braking member, for example a drum.
A worm 6 engaging with the worm wheel 2 is fast with
a spindle 7 which is journalled for rotation in a
hore 8 in the housing 1. The bore 8 is tangential to
the axis of the brake-applying shaft and is enlarged
at an intermediate point in its length to define spaced
walls 9 and 10 between which opposite ends of the worm
6 are located in close pro~imity therewith.
One end of the bore 8 is counterbored at 12 into
which an end portion 14 of the spindle 7 projects. The
free end of that end portion 14 which projects from a
closure cap 15 for the counterbore is of square or
other non-circular outline to receive a key by means
of which the spindle and worm can be rotated.
The housing incorporates automatic worm driving
means 16 to rotate the worm 6 and the worm wheel 2 in
order to compensate for wear of the linings of the
friction members and thereby maintain a predetermined
desired braking clearance between the friction members
and the braking member. As illustrated the worm driving
means comprises an adjuster shaft 17 journalled in the
1~)59044
housing 1 or rotation in a bore 18 parallel to the axis
of the worm wheel 2 but spaced radially therefrom in a
direction away from the spindle 7. The adjuster shaft 17
is coupled to a member or bracket 19 which is
stationary relative to the axis of the brake applying
shaft by means of diametrical pin 20 and the pin 20 has
an end portion 21 cranked to lie parallel to the axis of the
spindle 7 and received in a notch in the bracket 19. As
the lever 1 is moved angularly about the axis of the
brake-applying shaft, the adjuster shaft 17 also rotates as
it is moved with the lever 1. The adjuster shaft 17 is
connected to the spindle 7 through a pawl 23 and a clutch
assembly 24 located in the counterbore 12 and in a
second counterbore 25 at that end of the housing 1.
The pawl 23 comprises a parallel sided elongate
strip 26 which is guided for movement in a straight line
between the sides of a parallel sided slot 27 which is
tangential to the brake-applying shaft and normal to the
spindle 7. The pawl 23 is cut back along one edge to
define an abutment for one end of a compression return
spring 28 which urges the pawl at all times into engagement
with a cam formation 29 on the adjuster shaft 17.
The clutch assembly 24 is of the multi-plate type
comprising alternately arranged inner and outer relatively rot-
àtableprimary and secondary clutch plates 30 and 31 which surr-
ound areduced diameter portion 32 of a sleeve 33, in turn
surrounding the spindle 14. The sleeve 33 is coupled to
the spindle 14 through a one-way drive 34 and the plates
30 and 31 are clamped together and against a shoulder
35 at a step in the change in diameter by means of
a compression spring 36. The spring 36 abuts against
an abutment washer 37 of U shaped outline of
which the limbs are received in diametrically opposed
slots 38 in the sleeve 14.
The inner primary plates 30 are keyed to the sleeve 33, and
the outer secondary plates 31 are freely rotatable within, and
located by, the second counterbore 39 of which the outer end is
lOS9044
closed by the closure cap 15, Each outer plate 31
is provided with a pair of angularly spaced axial
slots 40 and 41 between which a tooth 42 is defined, and
all the teeth 42 are received in a notch 43 at the
inner end of the pawl 26. In a normal inoperative pos-
ition the teeth 42 are in engagement with a face 44 at
the outer end of the notch 43 and the teeth 42 are spaced
from a face 45 at the inner end of the notch 43 by a
distance corresponding to a predetermined clearance
between the friction members and the braking member.
The clutch assembly 24 serves two purposes. The first
is to protect the one-way drive 34 by limiting the torque
that the drive is required to transmit. This limiting
torque is determined by the force exerted by the spring
36. The second purpose is to stop adjustment taking place
after-the braking clearances have been taken up. The torque
that can be transmitted by the clutch assembly 24 is
limited as described above, hence the one-way drive 34
can only rotate the spindle 7 against a limiting reaction
torque. Beyond such torque the clutch assembly will slip,
with the outer plates 31 rotating relative to inner plates
30 which remain rotationally stationary Lelative to the
housing 1. The aforementioned limited reaction torque is
derived from the reaction torque in the brake applying
shaft and the worm wheel 2 and through the engagement forces
between the worm wheel 2 and the worm 6.
In operation, angular movement of the housing 1
in a clockwise brake-applying direction with reference
to Figure 1, rotates the brake-applying shaft through the
worm 6 and the worm wheel 2, characteristically a one-way
drive, until the braking clearances have been taken
up. During this movement the adjuster shaft 17 is also
rotated to cause the pawl 26 to slide linearly in the
slot 27 against the force in the spring 28 with the face
44 moving away from the teeth 42 and the face 45 moving
towards them to reduce the lost-motion clearance therebetween.
Normally the face 45 will not contact the teeth 42
unless ad~ustment is required to compensate for wear of
the frictio~ members.
105~044
When the angular movement of the lever 1 is trans~
mitted through the worm 6 and worm-wheel 2 to the brake
applying shaft to apply the brake and further rotate
the adjuster shaft 17, the face 45 of the pawl 23 rotates
the outer clutch plates 31 through the teeth 42. Once the
aforementioned braking clearances have been taken up the
engagement forces between the worm 6 and the worm wheel 2
are of such a magnitude that the aforementioned limiting
clutch torque is insufficient to rotate the worm 6. The
clutch assembly 24 then slips as described above and no
adjustment takes place.
When wear of the friction members has occurred,
during the initial angular movement to take up the ~raking
clearances once the lost-motion has been taken up,
the outer clutch plates 31 are rotated by the pawl 26
and the inner clutch plates 30 rotate with them due to
the engagement of adjacent faces of the plates. The
inner clutch plates 30 rotate the spindle 7 and hence the
worm 6 through the one-way drive 34. The worm rotates the
worm wheel 2 relative to the housing 1 and adjustment is
achieved. When all the braking clearances have been taken
up the clutch assembly 24 slips as described above without
impeding movement of the pawl 23 or the adjuster shaft
17.
When the brake is released the stored energy in the
spring 28 maintains the pawl 26 in engagement with the
adjuster shaft 17 so that the outer clutch plates 31 are
returned to their initial positions by the face 44 engag-
ing with the tooth 42, Due to the provision of the one-way
drive 34 the inner clutch plates 30 also rotate with the
outer clutch plates 31, but with respect to the spindle
7.
Annular sealing rings 46 are located between the
cover plates 4 and 5 and the wo~m wheel 2, an gaskets 47
are located between the housing 1 and the plates 4 and 5.
Thus the unit is sealed completely against the ingress of
dirt and other foreign matter.
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In the modi~lcation of Figure 7 the compression spring
36 is replaced by a series of Belleville or like spring
washers 48.
In the automatic slack adjuster illustrated in Figures
8 to 12, the clutch assembly 24 is of the cone type compris-
ing inner and outer rotatable clutch members 50 and 51 of
which the inner member 50 is rotatable in a friction ring
52 in the ~unterbore 12 and is coupled to the sprindle 7
through the one-way drive 34. The friction ring 52 serves
to prevent inadvertant rotation of the clutch assembly. The
inner member 50 is of cup-shaped outline and is also
rotatably mounted on a reduced diameter portion 52 at
that end of the spindle 7. The member 50 has an inclined
external clutch face 55 which is urged by means of a
spring washer 56 into engagement with a complementary
internal clutch face 57 on the outer clutch member 51
which, in turn, is rotatable in the counterbore 25. The
outer clutch member 51 is provided in its outer end with
a pair of angularly spaced axial slots 58 and 59 between
which is defined a tooth 60, and the tooth 60 is received
in the notch 43 at the inner end of the pawl 26.
The clutch assembly operates in the same manner as
the clutch assembly of the preceding embodiment with the
tooth 60 functioning in the same way as the teeth 42.
The closure cap 15 is omitted and the counterbore 25 is
closed by a removable resilient sealing disc 61.
The opposite end of the spindle 7 projects into a
counterbore 62 at that end of the bore and is provided with
an end portion 63 of square or other non-circular outline
to receive a key by means of which the spindle 7 and the
worm 6 can be rotated, after removal of a closure cap
64 normal]y closing the counterbore 62.
The construction and operation of the adjuster of
Figures 8 to 12 is otherwise the same as that of Figures
1 to 7 and corresponding reference numerals have been
applied to corresponding parts.
.10.
