Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This is a division of our co-pending Canadian Patent Application
No. 288,338 filed October 7thJ 1977.
~ his invention relates to friction brake apparatus and slack adjus-
ter means therefor.
Friction brake apparatus is well known in the field of railway
braking to comprise a brake force actuator which operates via a linkage on a
brake force applying member provided with a brake block or pad of frictional
material to urge the block or pad against a wheel or a disc attached to the `~
wheel or its axle for rotation therewith. As the block or pad of frictional
materiai wears away, slack builds up in the linkage and it is therefore desir-
able to provide friction brake apparatus with slack adjusting means sensitive
to the clearance between the brake block or pad and the wheel or disc.
~ccording to the present invention there is provided friction brake
apparatus comprising a pair of brake Eorce applying members forming a caliper
brake configuration, a brake force actuator to effect an application of the
brakes upon an outward actuator stroke and to effect release of the brakes
upon a return actuator stroke, slack adjusting means coupled to the brake
force actuator to permit ull stroke return oE the brake force actuator, and
a linkage intercoupling the slack adjusting means and the brake force applying
members, said linkage including a caliper having two arms respectively coup-
led to the brake force applying members, a one-way clutch between said arms
to-resist, when effective, moYement apart of the brake force applying members
under the brake force actuator's return motion, and means to permit such move-
ment apart by a predetermined distance before the one-way clutch becomes
effective to resist further such movement apart.
The inYention also proYides friction brake apparatus comprising a
brake force applying member, a brake force actuator to effect an application
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of the brakes upon an outward actuator stroke and to effect release of the
brakes upon a return actuator stroke, slack adjusting means between the brake
force actuator and the force applying member to permit full stroke return of
the actuator, and a reaction responsive linkage between the slack adjusting
means and the brake force applying member, said linkage being coupled to a one-
way clutch to resist, when engaged, return movement of the brake force apply-
ing member, and means to permit such return movement for a predetermined
distance corresponding to required brake clearance before the one-way clutch
b~ecomes effective to resist further such return movement.
In one arrangement, the one-way clutch may be included in position
sensing means incorporating means which resiliently opposes the force exerted
by the actuator and takes up a position corresponding to the position of the
force ~pplying member in a brake application, said predetermined distance being
provided by lost motion as between the one-way clutch and the force applying
member.
Said predetermined distance may be taken up by compression of re-
silient spacing means between the one-way clu1;ch and the brake force applying
member,
In the caliper `brake configuration the one-way clutch may be provided
~etween the arms of a caliper with caliper ends coupled between respective
orce applying members.
~n the case of such a caliper, predetermined distances may be pro-
yided for by compression of resilient means between at least one said caliper
end and the respective force applying members.
By way of non-limiting example, embodiments of this invention will
now be described with reference to the accompanying drawings of which
~igures la and lb illustrate two states of a brake force supplying
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arrangement providing, in combination, force actuator means and slack adjust-
ing means.
Figure 2 is a diagrammatic perspective view of friction brake
apparatus embodying this invention, and
Figure 3 illustrates schematically another form of friction brake
apparatus embodying this invention.
Referring to Figures la and lb the brake force supplying arrangement
comprises a tubular actuator member or rod 28 projecting from a housing 8. The
housing 8 comprises a brake actuator portion including a cylinder 21 within
which a piston 22 is sealingly slidable. The cylinder 21 is pressurable via a
fluid pressure input port 24 Cfor the purposes of making a brake application)
to urge the piston 22 to the left ~when viewed as illustrated~ against the force
of a return spring 23. The piston 22 has a trunk 25 which includes an internal
helical thread which is engaged non-lockingly by an externally threaded clutch
member or element 27 of which the left-hand radial end face is clutchingly
engageable with the right-hand radial end ace of the tubular actuator rod 28.
Adjacent piston 22~ the tuhular actuator rod 28 has a reduced diameter inner
end portion and its external surface htlS a groove 29 milled therein. A key 30
i`n the groove 2~ engages the trunk 25 to prevent relative rotational movement
hut permit longitudinal relatiYe movement as between the actuator rod 28 and the
piston trunk 25. rhe threaded clutch member 27 is connected via rod 31, extend-
ing internally of the rod 28, to a caged ball-bearing 32 that is disposed in an
internal cYlindrical cavity region 33 of the rod 28. The cage is urged by a
spring 34, housed in the cayity region 33, in a direction tending to maintain
the threaded clutch member 27 in engagement with the inner end of the actuator
rod 28, i.e. in the clutched condition. The cage, ~Yhich is denoted by the
reference numeral 35, is provided with a resetting tappet rod 36 operable by a
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resetting mechanism comprising a combined retaining clip and resettlng handle
39 for use in rotating a rotatahle plug 37 extending transversely into the
actuator rod 28, the plug 37 being formed with an intermedlate resetting cam
portion 38 to engage the adjacent end of tappet rod 36. The houslng 8 ls pro-
vided wlth a plvot bush lug 40, and the end of the actuator rod member 28 that
projects from houslng 8 ls provlded wlth a plvot bush lug 41. The arrangement
of ~igures la and lb is mounted ln a frlctlon brake apparatus by means of the
plvot bush lugs 40 and 41 to two points of the apparatus that are to be mutually
separated to effect a brake appllcatlon.
On appllcatlon of a brake fluid pressure applled to port 24, the
plston 22 moves leftwardly ~when viewed as in Figures la and lb) overcoming
the force of the return spring 23 and transmitting the resultant brake apply-
lng force to the inner end of the actuator rod 28 vla the threaded clutch
member 27, the latter belng locked by lts threads to the trunk 25 and by lts
radlal clutch face to the rod member 28. Due inter alia to the rlgging and/or
the llnkage of the apparatus, an outward reactlon ls created between the pivot
bush lugs 40 and 41 acting oppositely to the braking force transmitted to the
brake pad or block via said llnkage and supplied by the arrangeloent of Flgures
la and lb. On release of the braklng pressure at 24, the return spring 23
returns the piston 22 and trunk 25 in a rightward direction ~when viewed as in
Figures la, lb) and the force of spring 34 is sufficiently high to maintain,
initially, the threaded clutch member 27 in clutching engagement of the right
hand ~inner) radial end of the actuator rod 28. The actuator rod 28 is
accordingly withdrawn into the housing 8 up to a point where the resistance (to
such inward motion of the rod~ exerted by the clearance sensing means incorporat-
ed in the linkage becomes effective to resist further return movement of the
actuator rod 28. ~t this point, the force of spr~ng 34 is overcome and the
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reaction forces ~till then acting in the inter-engaged threads of element 27
and trunk 25) relieved so that, as represented in Figure 1_, the trunk 25 urges
the clutch member 27 sufficiently out of engagement of the inner radial end of
the actuator rod 28 so as to tend to reduce or remove the clutching forces be-
tween them,i.e. effect a de-clutching operation. I~ith the clutching forces
reduced or removed, the threaded clutch member 27 can rotate relative to and
within the inner threaded portion of trunk 25 and thus can move longitudinally
relative to the trunk 25 by a distance corresponding to any excess excursion
(i.e. greater than that nominally desired) of the rod member 28 in its initial
movement relatively outwardly of housing 8, which excess excursion may, for
example, have arisen due to wear of the brake pad or block. The ability of the
trunk 25 to move longitudinally relative to the threaded clutch member 27 (and
the actuator rod 28~ enables the piston 22 and trunk 25 to return to their
initial position and leave the clutch member 27 adjacent the inner radial end
of actuator rod 28 in readiness for immediate clutching engagement upon the next
brake application and with the separation between the pivot bush lugs 40 and
~1 newly set to providt-~ the requirt-~d nominal t:learance between the brake block
or pad and the wheel or disc it is frictionally to engage~ Thus the total amount
of any slack in the system has been automatically taken up and compensated for
in a single operation, i.e. application and release, of the brakes.
rn order to reset the slack adjuster of Figures la? l_ for re-blocking
the brakes with new friction blocks or pads, the lever 39 is lifted pivotally
clockwise (when viewed as in F~gures la. l_) to enable it to be used as a
convenient handle for rotating the cam 38 formed in member 37 as described
above (see Figure lb?, Such rotation causes leftward movement of actuator rod
28 relative to the tappet rod 36, bearing cage 35, bearing 32 and rod 31 against
the force of spring 34 to disengage or de-clutch the clutching face of member 27.
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~fter re-blockillg, the member 39 is returned to its normal position shown in
Figure la and the arrangement is ready for re-operation.
Referring now to Figure 2 which illustrates friction brake apparatus
this apparatus has a caliper configuration supporting two brake force applying
members 1 and 2 carrying friction pads 3 and 4 tYhich engage one each side of
a vehicle wheel to be braked. The member 1 is pivotally carried on one end
5a of a lever 5 by means of a pivot pin 12, and the member 2 is pivotally
carried on one end 6a of a lever 6 by means of a pivot pin 13. The two levers
5, 6 are pivotally supported intermediate their ends 5a, 5b and 6a~ 6b on a
yoke 7 which is supported beneath the chassis of the vehicle ~not shown).
The inner end 5b of the lever 5 is bifurcated and pivotally coupled to a brake
force supplying arrangement ~Yhich preferably is that described above with
reference to Figure 2, comprising a housing 8 including a combination of a
brake force actuator means and a slack adjusting means including an actuator
member having one end projecting from the housing 8. The said projecting end
of the actuator member is pivotally coupled to the inner end 6b of the lever
6 and it will be seen that by expanding the spacing between the inner ends 5_
and 6b of the levers 5 and 6, the outer ends 5a and 6a thereof supporting
the brake Eorce applying means 1-4 move towards one another such that the
friction pads 3 and 4 can engage the rotating wheel or disc to achieve braking.
Resilient bushes 10 and 11 are respectively provided on depending
extensions of the pivot pins 12 and 13, and via these resilient bushes 10 and
11 the respective ends of calipers ~C" of a restraining means are coupled to
the ~rake force applying me~bers 1 and 2 so that the calipers are flexibly
hung horizontally beneath the yoke 7. The arms 14, 15 of the calipers "C" are
pivotally connected and include spring-urging means ~not shown~ tending to
urge the arms 14, 15 outwardly such as to tend to oppose the force of the
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actuator tending (w}len operated) to close the calipers. Also included within
the central pivoting region or hub 16 of the calipers "C" is a one-war clutch
arranged such that after movement of the arms 14 and 15 relatively towards one
another, the clutch operates to retain the calipers in such a condition of
mutual approach of the caliper arms 14, 15 (the only outward return movement
of the brake force applying means 1 and 2 which is normally possible being
the limited movement which is permitted by the return or deflection of the
resilient bushes 10 and 111,
The one-way clutch between the arms of tlle calipers is additionally
provided with suitable means operable from the outside thereof ~o disengage
the one-way clutch so as to permit resetting of the whole assem~ly to enabLe
re-blocking of the brake force applying members ~hen tha friction pads 3, 4
are worn out.
Typically, the one-way clutch may be stepless and com~rise a single
heavy rate helical spring which Erictionally engages co-operating hub portions
at the common pivot of the caliper arms 14 and 15, and the means for disengag-
ing the clutch may be arranged to provide relative movement of the ends of the
helical spring to temporarily disengage it Erom one or other hub portion and
free the arms so that their ends can be mutua:Lly further re-separated.
l~ere the apparatus of Figure 2 is used in conjunction with the
brake force supplying arrangement of Figures la and lb, the pivot bush lug 40
of the housing 8 is coupled to the inner end 5b of lever 5, and the pivot
hush lug 41 at the outl~ardly projecting end oE the actuator rod member 28 is
coupled to the inner end 6b of lever 6.
The operation of the apparatus of Figure 2 associ,ated with the
arrangement of Figures la and 1~, is as follo~s. On application of a brake
fluid pressure applied to the port 24, the piston 22 moves leftwardly (~when
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viewed as in Figures la and lb) overcoming the force of the return spring 23 and
transmits the resultant brake applying force via the threaded clutch member 27
(which is locked by its threads to the trunk 25) to the inner end of the actuator
rod 28. An outward reaction is thereby created between the ends 5b, 6b of the
levers 5 and 6 to exert a braking force to the vehicle wheel via the brake force
applying members 1 and 2. In doing this, the brake force applying members 1,
2 overcome the force of the spring (not shown~ acting between the caliper arms
14 and 15, and the arms 14 and 15 are carried inwardly the total amount of move-
ment of the members 1 and 2 less the amount of movement which is permitted by
lQ the resilience and/or lost motion provided by the bushes 10 and 11. On release
of the braking pressure at 24, the return spring 23 exerts sufficient force to
return the piston 22 and trunk 25 in a rightward direction and the force of the
spring 34 is suff:iciently high, initially, to maintain the threaded clutch
member 27 in engagement with the right-hand (innerl radial end of the actuator
rod 28. ~he actuator rod 28 is there:Eore withdrawn into the housing 8 up to a
point where the resistance (to such inward m(~tion of the rod 281 exerted by the
one-way clutch in the caliper hub 16 becomes efEective to resist further return
movement of the brake Eorce applying members 1 and 2. ~t this point, which is
the point at which the brake force applying n~embers 1 and 2 have lifted away
from the wheel by a total amount determined by the resilience and/or lost motion
at 10 and 11, the force of the spring 34 is oYercome and, as shown in the state
of afairs in Figure 2b, the trunk 25 urges the clutch member 27 sufficiently
out of engagement of the inner radial end of the actuator rod 28 to tend to
reduce or remoYe the clutching forces between them. ~ith these clutching forces
reduced or removed, the threaded clutch member 27 rotates relative to and within
the inner threaded portion of the trunk 25 to permit the piston 22 and trunk 25
to return to their initial position and leaye the clutch member 27 adjacent the
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inner radial end of actuator rod 28. Accordingly the linkage connected to the
actuator housing 8 and the rod 28 is left in a new position providing substan-
tially only the clearance of the members 1 and 2 as referred to above, and all
the slack in the system has been automatically taken up in a single application
and release of the brakes.
In order to reset the slack adjuster to permit re-opening of the
force-applying members 1 and 2 to enable re-blocking by new friction blocks, the
lever 39 is operated as described above to disengage the clutching face of member
27. On now operating also the one-way clutch releasing means of the calipers
"C", the whole assembly is permitted to return to its fully retracted condition
by virtue of the outward force ~hich continues ~o be applied on the resilient
bushes and pivot pins by the spring ~not shown) between the caliper arms 14 and
15. On subsequent return of the caliper clutch release and return of the member
39 to its normal shown position in Figure la, the mechanism is ready for re-
operation after re-blocking of the brake force applying members with new blocks
3 and 4.
Figure 3 illustrates schematically a friction brake apparatus of the
so-called "clasp brake" type for a rail~ay wlleel 250. This apparatus comprises
two brake force applying members 251, 252 pivotally mounted on the lower ends of
support links 253, 254 that are pivotally mo-mted by their upper ends to the
chassis of the railway ~ehicle. The arrangement is such that friction pads or
blocks carried by the members 251, 252 can engage the rim of the ~heel at sub-
stantially diametrically opposite locations. The two members 251, 252 are
pivotally connected by intermediate links 255, 256 to the lower ends of two arms
257, 258 that are interconnected intermediate their ends by a link 259. The
upper end of arm 257 is pivo~ally mounted on the chassis of the railway vehicle,
and the upper end of arm 258 is connected to a brake force supplying arrangement
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for supplying a brake force in the direction A. Two mutually pivoted limbs
261, 262, forming a caliper 260 are connected by their free ends to the lower
ends of arms 257, 258 via resilient bushes. The mutual pivotal connection
of the limbs 261, 262 is by means including a one-way clutch, for example ~ormed
as described above for the caliper hub 16 of Figure 2, so as to permit the
mutual approach of limbs 261, 262 when a braking force is applied in direction
A but prevent mutual separation of limbs 261, 262 when the braking force is
released. When the braking force is released, the arms 257, 258 can neverthe-
less pivot to separate fLIrther their lower ends since the latter are connected
to the arms 261, 262 by the resilient bushes which permit this separating
movement to a limited extent which is predetermined (by appropriate design of
the resilient bushes~ to correspond to the clearance normally desired between
the friction pads or blocks and the wheel rim.
ConYeniently the brake force supplying arrangement employed for the
embodiment of Figure 3 may comprise an arrangement similar to that of Figure
la? or may comprise a brake force actuator, e.g. a simple piston-cylinder de-
yice, coupled to a separate slack adjuster.
In general mode o~ operation, the aboYe-described caliper devices of
Figures 2 and 3 freely follow movement of the frictIonal brake element (i.e.
the block or pad~ in a "closing" direction after a small lost motion correspond-
,~ ing to the correct brake_released-clearance that is taken up durin9 brake force
application~ On brake release, the only "opening" mo~ement permitted is that
arising from the lost motion, thus maintaining the desired clearance between
the block or pad and the wheel or disc~ Thus, in practice, after the first
operation Cwllen any large e~ces~s of clearance will be "gulped"~, successive
operating cycles will cause the caliper units to creep progressively towards
the ultimate permissible closed pOsitioll in detecting and following up normal
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wear throughout the life of the brake friction elements. It will be appreciated
that because the illustrated caliper devices are mounted at po;nts in the rigging
system where excess movement arising from elastic strain is minimal, the effect
of total strain in the rigging under load is not significant in the achievement
of desired practical release clearances and hence significantl~ constant
actuator strokes.
