CA1201984A

CA1201984A - Automatic slack adjuster

Info

Publication number: CA1201984A
Application number: CA000429178A
Authority: CA
Inventors: Sven E. Camph
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-06-14
Filing date: 1983-05-30
Publication date: 1986-03-18
Also published as: SE453420B; DE3321319A1; DE3321319C2; GB8316049D0; IT8321598A0; GB2121896A; JPS596440A; BR8303084A; IT1163513B; SE8303331D0; FR2528513B1; SE8303331L; GB2121896B; FR2528513A1; JPH0427411B2

Abstract

ABSTRACT

An automatic slack adjuster having compression force trans-mitting elements of adjustable length mounted between a key and a pair of brake shoes is provided with a wheel journalled on the key shaft and at one side in tooth engagement with parts of the force transmitting elements. On the other side of the wheel a spring latch rigidly mounted to the key shaft is arranged to contact ridges and grooves on the wheel to establish a one-way clutch.

Description

BACKGROUND OF THE IN~ENTION

F~eld of the invention This invention relates to an ~utomatic slack adjuster for ( a vehicle drum brake of the type actuated by a key rigidly mounted on ~ key shaf connected to a cylinder-piston acti-` vator. The said key ~s acting upon a pair of brake shoes ~ through force transmitting devices ea~h of ~ h comprising two telescopically displaceable elements, one being an ex-ternally threaded rod, while the other is an internally threaded sleeve receivi~g said rod. Each of the two sleeves of the two elements is provided with a circuMferential tooth rack engaging grooves e~tending radially on an axial shoulder surface of a wheel journalled on the key shat, the grooves having such shape that any straight rad~al movements of the tooth r~ck relatlve the wheel would cause a torque on both sleeves in the directi~n causing increase of the total length - of the two telescop~cally displaceable elements.
Descript~on o~ the prior art, The U S Patent Specific~tions No~ 3,891,068-and 4,161,999 l~ s~ow slack ad~usters o this and similar types.
æy~ Jr?~el~
Sla~k ad~ust~r~ o~ l:he aol:ual type should be o~ slow acting i.e. the ad~ustment per~ormed per braking cycle should ~e very small. Otherwise there will be a substantial risk of ,.
fal~e adju~kment~ performed part~y because of increased slack during shor~ time intervals caused by heating the brake drum.
I the automatlc ad~ustment is sufficiently slow a1~ost no adjustment is carried out during several subseq~nt brakinig operatlons performed with hot braking drums.

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~owever, if the automatic adjustment is set to be extremely slow it will be almost impossible to check that a correct slack will be obtained because of the very large n~mber of braking cycle8 r~quired ~or thi~ purpo8e~ Th~rfore, i~ will be necessary to rely on the accuracy of the installation and the elements of the slack adjuster.
As a rule the slack adjustment may be initiated either be-cause of excessive movements of certain brake force trans~
mitting elements relative a stationary par~ of the brake or it may be initiated due to excess~ve relative movements of two force transmitting elements.
In the flrst o these two cases it i5 ~vident that false mounting of the stationary part or a subsequent dlsplace-ment of said part will cause error~ in the slack.
In the latter of the two cases - the group to which ths present invention belongs - the ach~evement of the correct slack is dependent on a correc~ installation as any deviation from movements tn the correct planes and angles will cause deviations from the de.sired slack, It is almost impossible to check this when mounting the slack adjuster.

Object of the invention The object of the present inven~ion is to provlde a slack adjuster of the type referred to above in whlch the parts determlnating the slack adjustment practically cannot he ~t displaced ~ dur~ny mounting nor afterwards. This will ,l make it pos~lble to rely on obtainlng correct slack without verlfying on the ~pot.

SUMMARY OF THE INVENTIt)N
According ~o ~he present invention the slack adjuster of th type refexrad to i5 characterised in that the said wheel 1s provided with a second axially extending shoulder surface area having radially directed ~rooves and ridges adapted to receive a resilient spring latch rigidly connected to the key shaft, 12~1g~4 The invention will be described in more detail reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows the brake force transmitting parts of a brake to be provided with a slack adjuster according to the invention;
Fig. 2 the brake of Fig. 1 with the brake force transmit-ting parts in a different position;
Fig. 3 a section along the line III-III of Fig. 1 showing additional parts of the automatic slack adjuster accord-ing to the invention;
Fig. 4 at a greater scale one side of a wheel forming an element of the adjuster;
Fig. 5 the other side of the wheel shown in Fig. 4;
Fig. 6 shows a view along ~ine VI-VI of Fig. 3 which includes the wheel of Fig. 5 together with the collabor-ating latch shown in Fig. 7;
Fig. 7 at a greater scale a section along the line VII-VII of Fig. 6;
Fig. 8 a force transmitting element of the type in Figs.
1, 2 and 3 but at a larger scale and partly in section;
and Fig. 9 and 10 show diagrams illustrating how an amend ment of the element shown in Fig. 8 can make it suitable for different types of ~rakes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Th~ brake shown in Fig~ 1 comprises a cylinder-piston acti-vator 1 havlng a pi~ton rod 2 which at ~ts outer end is p~votally connected to a lever 3 rigidly connected to a key shaft 4 protrudiny into a bxake drum 5 rigidly connected to a wheel (not shown)~ The key shaft 4 carries a key 6 having concave depres~lon~ adapted to receive convex end surfaces of force transmlttlng elements 7, 8 each of which comprising two telescopically displaceable elements 9, 10 and 11; 12 respectively. Sa~d devices 7, 8 act upon brake shoes 13, 14 prov1ded with linings 15 and 16 respectively. Figl 1 shows the parts of the brake when in their released brake posltl~
ons leaving gaps between the linlngs 15, 16 and ~e inner surface of the drum 5.
A braking cycle i~ initiated by supplying compre~sed air to the activator 1. ThiR will cause the rod 2 to he expelled ,;, .
and turn the key shaft 4 and the key 6 ln such direction as to cau~e such movement of the devtces 7, 8 that the brake shoes will reach contact with theix linings 15, 16 against the drum 5. Thi~ pos~tion is shown in Fig. 2.
It will be understood that wear on the linings 15, 16 and the drum 5 i~herently may have a detrlmental influence on the brake a~ it may cause a substantlal change in the force tran~mitted and in the time necessary for obtaining appli-cat~on of the brake.
However, if it.is possible to lncrease the length of the devices 7, 8 correspondlng to the wear of the braking sur-f`aces tha brake Will maintain it~ brakin~ properties. Thi~
possibility is reaiised by an automatic angular displace-ment of the elements 9, 10 and 11, 12 respectively. ~he ele-ments 10 and ll are interiorly threaded sleeves adap~ed to receive the corre~pondingly threaded ~lements 9 and 12 which are pre~ented rom rotation by means not shown.
Each o~ the two slee~es 10, 11 are provided with a circum-ferential tooth rack 17 carrying a number of teeth 18.

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Flg. 3 showY a ~e!ctlon along the line III-III of Fig. l, but in Fig~ 3 the key 6 has been omitted. HoFwever, Fig. 3 shows two further items not belng shown in ~ . l and 2.
One o ~ald it~m~ i~ a wheel 19 ~reely ~ournalled on an extention of the shat 4. The other item is a resilient spring latch 20 rigidly ~onnected to the outer end surface of the shat 4. The spring latch 20 urges the wheel l9 ln the direction away from the end o~ the shaft 4O The wheel l9 is at its lower side (wh~ch is shown in Fig. 4) provided with incl~ned groove~ 21 extending between radii A and B
and adapted to receive at least one too~h 18. On its oppo-site surface - shown in Fig. 5 - the wheel 19 ls provided with radially directed grooves 22 and ridges 23. The grooves 22 are adapted to recei~e a part 24 of the spri.ng la~ch 20.
Fig. 6 shows a wiew along the line VI~VI of Fig. 3 but to the same scale as the one used in ~ 4 and 5, . , .
An end 25 of the spring oppos~te the part.24 slides against . . the tops o the ridges 23 and thus balance the spring ~oad on the wheel l9 caused by.the part 24.
,!','i'r. ~ The xelative ln1uence o the spring latch 20 and the wheel ?', ` '' 19 ls illustrated in Fiy~ 7. It will ~e understood that rela-tive anguIar mo~ements greater than the angular distance be-~; tween two ridges 23 will cause the part 24 of the spring .~f latch 20 ~o enter into a neighboring groove 22, Only rela-tive movement3 in one direct~on.are posslble.
~b Forces of the.spring latch part 24 in the direction towards the left in Fig. 7 will cause contact between the surface of a ridge side and a surface 26 of the part 24~ This.surface ~6 .` will not be ~ub0tantlally worn, be¢au~e of i~ ra~her gre~t - .` . area. An edge 27 of the part 24 i~ determining the ~ltuation when the part 24 shall enter into a neiyhboring groove 22.
~hi~ edge 27 i~ protected again~t wear during ~he movement .:~ of the wheel.19 caused by the latch 20, .

t The function of tne device described is as follows:
During applicat~on of the brake the ~orce transmitting de-vlce~ 7, 8 are moved outwardly relative the axis of the key shaft 4 thus causlng the braklng surfaces to engage each other. During said outward movement at least one tooth 18 of each device 7, 8 is slidirlg radially in a groove 21 of the wheel 19~
It will be und~rstood that due to th~ inclined shape of the grooves 21 radial oppositely movements of the two teeth 18 of the devices 7, 8 will cause a rotar~ movement of the wheel 19. However, the turning o the key 6 will also cau~e a rotary movement of the devices 7~ 8 in the same plane and in the same direc~ion. Therefore, the actual rotation of the wheel 19 relative a statlonary part - e.g. a not-shown back-ing plate in which the shaft 4 is journalled - will be smal-ler.Also the rotation of the key sha~t 4 and thus the rota-tion of the spring latch 20 rigidly secured thereto will be performed in the same direction. However, due to the s~hape o the grooves 21 a slight relative rotatlon will be perform-y ed betweén the wheel 19 and the spring latch 20 and said re-A lative rotation is a ~ of the angular travel o-f the key shaft 4.
At excessive angular movements of the key shaft 4 the sal~d relative movement is suficient to cause the spring latch part 24 to enter into a nelghboring groove 22 of th~e wheel 19, Upon release of the brake the key shaft 4 is moved in the opposite d~rection and the latch part 24 will cause a torque on the wheel 19 and thus on the tooth carrying elements 10, 11 relatlve the elemen~s 9, 12 ~o ~ o incre~a~ ~he t~al lengths of the devices 7, 8.
Due to symmetric design of the elements conveying slack ad-justments and due to th~ lack of tationary reference ele-ments deciding the adjustment the described device may be made extremely accurate and the proper function will b~ en-sured even in ~ase of gr~ater variations o the geome~ry of the brake causing leverage variations due to tolerances in the manufacture of the force transmitting parts.

The same parts such as the devices 7, 8, the wheel l9 and the spring latch 20 ma~ even be used for brakes of varying types having keys 6 of.different size and shape. This is ~ossible by maklng the tooth rack 17laxially adjustable re-lative the element~ lO and ll. As shown in Fig. 8 this is done by loosening a set screw 28 axially displacing the rack 17 to its desired position and mounting the set screw 28 in the appropriate one of a number of holes 29.
9 ana 10 shows two differerlt keys ~. The key 6 of Fig. 9 having a rather great active len~th and a larger angle c~ between the active radius R and an imaginary line 30 connecting the axis 31 of the key shaft 4 w.ith the a~is 32 of rotation of the device 7 relat~ve the brake shoe 13.
The key 6 of Fig, lO is shorter and has a smaller angle between the active radius r and the imaginary line 30.
In Fig. 9 the displaceable rack 17 is in its ~extreme end position and duxing a braking operation a tooth 18 will move to a final position 18a while the axis 32 will move , .
to the positlon 32a. The radial distances of the tooth po-~itions 18 and 18a from the axis 31 determine the radial path of the teeth.in the grooves 21 of the wheel 19 (not i~hown in Fig. 9~.
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Fig. 10 shows how the displaceable rack 17 makes it possib-~ . le to use the same wheel 19 having the same grooves 21 al-.i.-" so ~or a brake having the smaller angle ~ and the shorter . . activ~ xadius r~ It will be understood that the.displaceab-'s.-j.-- ;le rack 17 in Fig-. 10 has been displaced so that a tooth end position 18a is' loca~ed n~ar the outer end of the groov~s 21, whereas tha ~tar po~ltion 18 i~ betw~n t:he ends o the . grooves 21. It w~ll also be unde~ood tha~ ~he po~ition o~
the rack 17 shown in Fig. 9 would not be suitable for a brake.
having the key o~ F1~. lO. In such case the wheel l9 would ;. have insufficient diameter.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An automatic slack adjuster for a vehicle drum brake that need not be referenced to a stationary con-nection on the vehicle of the type actuated by a key rigidly mounted on a key shaft connected to a cylinder-piston activator, said key acting upon a pair of brake shoes through force transmitting devices each comprising two telescopically displaceable elements, one being an externally threaded rod, while the other is an internally threaded sleeve receiving said rod, each of the two sleeves of the two elements being provided with a circum-ferential tooth rack axially adjustable along both said telescopically displaceable elements for adjusting brakes in systems having keys of different size comprising, a spring latch having a dog secured to the key shaft, a freely journalled wheel mounted on one end of said key shaft and having teeth and grooves on a first shoulder surface area of one side thereof engageable with the dog of said spring latch and engageable on the other side with a second shoulder surface area with said circumfer-ential tooth racks on said telescopically displaceable elements so that any straight radial movement of the tooth racks relative to said wheel would cause a torque on both sleeves in the direction causing increase of the total length of the said telescopically displaceable elements, said telescopically displaceable elements having symmetric design permitting telescopic rotation in opposite direc-tions and slack adjusting means preventing rotation of said wheel relative to the key in one direction of rotation to thereby effect a torque to cause both the telescopically displaceable elements to increase in length together as the key and wheel rotate together in a direction opposite to said one direction of rotation, and wherein the means for preventing rotation of said wheel includes said resilient spring latch, said grooves being of such shape as to permit the dog to ride over one groove and enter neighboring grooves only in one direction of rotation of the shaft when the brakes are applied and to cause a torque tending to turn the wheel in the opposite direc-tion of rotation of the shaft when the brakes are released.