FR2504222A1 - OPERATING DEVICE FOR A DRUM BRAKE - Google Patents

Abstract

DEVICE INCLUDING A CYLINDER BODY 20 ARRANGED BETWEEN THE TWO ENDS 14, 16 OF THE SEGMENTS 14, 16, A PISTON ACTING ON AN END 14 OF THE SEGMENT 14 AND A LEVER 66 THROUGH THE BRAKE BRACKET 10 AND CONNECTED TO A DRIVING CABLE 70 LEVER 66 IS ARTICULATED TO A SPACER 78 BY WHICH IT LIES ON END 14 OF THE SEGMENT. THE LEVER 66 ALSO SWIVELS ON THE CYLINDER BODY 20 BY AN AXIS C FURTHER FROM THE PLANE E IN WHICH THE CYLINDER BODY 20 IS GUIDED ON THE BRAKE BRACKET 10 THAN THE AXIS D OF THE ARTICULATION OF THE LEVER 66 A THE SPACER 78. THE ACTUATOR CABLE 70 BELONGS TO A BOWDEN TRANSMISSION WHOSE SHEATH 72 LIES AGAINST THE CYLINDER BODY 20. THE MOMENTS OF FORCES EXERCISED ON THE CYLINDER BODY BY THE SHEATH 72, THE LEVER 66 AND THE FIRST END OF SEGMENT 16 ARE IN EQUILIBRIUM.

Description

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i

  The invention relates to an action device.

  for drum brake with internal segments, in particular

  culier for motor vehicles, comprising:

  a cylinder body arranged between two opposite ends

  segment lines, guided in a floating direction

  tion of its axis on a brake support in the form of a plate

  that and pressing against one of the segment ends, a piston guided in the cylinder body and acting on the second segment end when the brake is actuated hydraulically, and a lever passing through the brake support, the part of which is situated inside the brake is mounted on the cylinder body and which acts on the second segment end when the brake is actuated mechanically and

  is connected by its external part to an action cable

  is lying. In a known actuation device of this type (DE-OS 15 25 352), the axis around which the lever is pivotally mounted on the cylinder body is in an intermediate position between the brake support

  in the form of a plate and the common median plane of the two seg-

  In the region of one of its ends, the le-

  vier abuts directly against a rib of that of the seg-

  which acts on the piston when the brake is applied-

  born hydraulically The part of the lever which projects outside through the brake support is angular and

  designed to fix an approximate actuation cable

  perpendicular to the axis of the cylinder, i.e. ap-

  approximately parallel to the axis of rotation of the wheel

to brake.

  One of the brake shoes is directly supported

  by its end opposite the mentioned end,

  be a stop which is fixed to the brake support and diametre

  trally opposite to the cylinder body The other brake segment bears, by its end opposite to the second segment end mentioned, against a threaded rod which is prevented from turning and screwed into a mounted nut

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  so that the nut can be turned into the stopper

  feels an external ratchet toothing and cooperates with

  one end of a pawl mounted pivotally

  te on the second segment The end of the pawl which is opposite the toothing and which is close to the cylinder body is urged by a preloaded spring to cooperate normally with a spacer fixed to the first

brake shoe.

  With this known actuation device, a

  traction exerted on the lever by the operating cable

  ment generates a twist as a result of which the lever moves the floating cylinder body in one direction, at the same time as the segment end which bears against it, along the cylinder axis and moves in the direction

  opposite the other segment end which rests directly-

  against the lever So the two segments are even

  born to pivot respectively around the fixed stop and the end of the threaded rod and are therefore requested to apply to the associated brake drum The force exerted by the lever on the cylinder body when the brake

  is mechanically actuated with a considerable lever arm

  ble relative to the common median plane of the two segments, perpendicular to the axis of rotation of the wheel to be braked and in which is located the line of application of the reaction force acting on the cylinder body As a result, the two forces mentioned form a torque whose moment acts on the guide formed on the brake support

  for floating movements of the cylinder body,

  Dranting transverse forces and a re-

  corresponding friction resistance which opposes de-

  positioning of the cylinder body The movement of the cylinder body is considerably hampered and it is even possible that sufficient mechanical actuation of the brake is

  impossible unless, by maintenance and lubrication

  appropriate cation of the guides, it is ensured that their coef-

  friction friction remains low The device for

  known operation of the type described at the beginning, including its

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  adjuster, is further complicated to assemble because the different elements provided for applying and adjusting the brake shoes are very far apart

others.

  An object of the invention is therefore to improve an actuation device of the type defined at the start of

  so as to reduce the complication of assembly and

  maintenance without having to fear, however, a

  high resistance to floating movements required

cylinder body res.

  The object is achieved, according to the invention, thanks to the fact: that at the lever is articulated a spacer by which it bears against the second segment end, that the axis around which the lever can pivot on the cylinder body is further from the plane in which the cylinder body is guided on the brake support than the axis of articulation of the lever at the spacer,

  and that the actuation cable belongs to a trans-

  Bowden mission whose sheath leans against the body of

  cylinder so that when you actuate mechanically-

  the brake, the moments exerted on the cylinder body

  dre by the sheath, by the lever and by the first end

  segment mites are at least approximately equal

free.

  We can very easily achieve balance

  moments if, according to a preferred mode of execution of the

  vention, the axis of articulation of the lever to the spacer is located at least approximately in the median plane ccmmun of the two brake segments It is especially advantageous that this articulation is oriented such

  so that the axis passes through the common plane of the two seg-

  brake elements when the brake is applied mechanically-

is lying.

  Another special feature of the pre-

  fairy of the invention is that the Bowden transmission, in its terminal part where the sheath bears against the body of

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  cylinder, is at least approximately parallel to

  the cylinder axis So when a given force is ap-

  plicated through the Bowden transmission and

  when the operating lever has a gear ratio

  given mission, the maximum contact pressure can be established at the brake shoes because all the thrust

  exerted by the sheath of the Bowden transmission is used

  on the one hand for the necessary displacement of the cylinder body and on the other hand to compensate for the moment of the force exerted on the cylinder body by the actuating lever.

  It is advantageous that, just as in the dis-

  positive actuation known, the cylinder body pre-

  feels a projection which passes through a slot in the support

  brake port and which is guided at the edge of this slot.

  In this case, it is advantageous that, according to another par-

  particularity of the invention, the edge of the slot is

  dark in a rim of anti-friction material.

  The guide flange preferably has the configuration

  tion of a closed ring It is especially advantageous

  that the part of the projection of the cylinder body which coo-

  father with the guide rim has a section deviating from the circular shape It is also advantageous that, according to the invention, this section has a smaller area

  in the direction parallel to the cylinder axis that per-

  pendulum to it, which allows you to do-

  ser the projection through the slot and, by rotating the cylinder body, bring it to its assembled position o the guide flange is housed between lateral groove faces formed on the projection This design, which

  makes it considerably easier to assemble the

  actuation according to the invention, is made possible

  ble by the characteristics of the invention which were exposed first and gr 9 what the body of

  cylinder is largely if not completely free of mo-

  when the brake is mechanically actuated The parts

  guide courses can therefore be relatively short

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  without the cylinder body being likely to deviate under the ef-

  of the brake actuation forces.

  However, it is also possible that the body of cy-

  lindre is exposed to a tendency to deflection by forces caused, regardless of the actuation of the brake,

  by the inertia of the cylinder body and the elements

  tees above, as can be the case during an acceleration

  ration due for example to uneven pavement.

  To improve the guidance of the cylinder body at this

  regard also, despite short guide courses, an-

  The development of the invention envisages that the piston is provided with a split extension intended to receive, like a fork, the second segment end and a transverse pin fixed to this segment If the relatively short guide of the body of the cylinder on or in the brake support can be designed as

  two-point guidance, additional guidance -

  that is to say in three points is ensured by the pin

  the transverse fixed to the second segment end

  and the forked configuration of the piston extension.

  This three-point guidance constantly ensures mobility

  required float of the cylinder body.

  In addition to the generic features indicated at the beginning, another starting point for the invention is a

  additional feature of the action device

  known known above (DE-OS 15 25 352), according to the-

  which it includes an automatic adjustment device comprising a threaded rod prevented from turning and a

  nut mounted so that it can rotate, fitted with a

  ratchet and cooperating with a ratchet When the

  two brake shoes move relatively, one

  training spell applying to the pawl exerts on

  the latter a torque limited by the characteristic of the res-

  sort An actuating device thus completed is further improved, according to the invention, by the fact that a lever is articulated with a spacer by which it bears against the second segment end,

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  that the threaded rod rests against the first end

  segment mite and the nut and pawl are mounted on the cylinder body

  and that the drive spring is fixed between the

  quet and the spacer so that on the one hand it normally maintains an abutment part of the pawl in cooperation with the second segment end and that on the other hand it exerts a moment of recovery on the

  lever through the spacer.

  According to an advantageous embodiment of the in-

  vention, a bimetallic spring is fixed to the cy-

  luster and requests the pawl to move away from the teeth

  ratchet if the brake overheats.

  As a whole, the invention provides a dis-

  positive actuation for drum brake with segments

  interiors in which the actuating elements

  brake and hydraulic system are combined in a simple and space-saving manner with capable elements,

  in both actuation modes, make a setting

automatic age of segments.

  An embodiment of the invention is described below with respect to the schematic drawings in which: FIG. 1 is a front view of a brake drum, showing only a fragment of the brake support and not showing the drum ; Figure 2 is a plan view in the direction of arrow II in Figure 1; Figure 3 a horizontal section along line III-III of Figure 1;

  Figure 4 a partial vertical section following

vant line IV-IV of Figure 1;

  Figure 5 a partial vertical section following

  vant line V-V of Figure 1; Figure 6 a partial horizontal section along the line VI-VI of Figure 3;

  Figure 7 a partial vertical section following

  before line VII-VII of figure 1 and

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  Figure 8 shows elements partially

concealed in Figure 2.

  The drum brake shown has a sup-

  brake port 10 in the form of a plate or cup, intended to be fixed to the rear axle of a motor vehicle. On the inside of the brake support 10, which is enclosed in the assembled state by a drum brake 12,

  is fixed a stop 12 (bottom in Figure 1) against the-

  which two brake shoes 14 and 16 support each other

  swivel by their respective lower ends

  ves 14 * and 16 'A combined actuation and adjustment device 18 is arranged between the upper ends

  14 "and 16" segments and diametrically opposite the bu-

tee 12.

  The actuating and adjusting device 18 comprises a cylinder body 20 in which are formed

  a cylinder bore 24 opening in the direction of the ex-

  segment end 14 "and a guide bore 26 opens

  veering towards the segment end 16 "The two bores 24 and 26 are separated from each other by a bell-shaped cylinder bottom 22 and have a common axis spaced radially from the axis of rotation A of the brake drum and perpendicular to this axis The first axis will hereinafter be called cylinder axis B. The guide bore 26 receives part of a threaded rod 28 bolted to a nut 30 The threaded rod has a free end split surrounding the segment end 16 "so that the latter rests against the cylinder body 20 via the threaded rod 28 and the nut 30 and simultaneously prevents

  the threaded rod to turn The nut 30 is assembled

  nière able to rotate in a cylindrical depression 32 of the guide bore 26 and bears against the cylinder body 20 in the axial direction by means of a sealing ring 34 The ring 54 is formed of a

  elastomer having a relative coefficient of friction-

  high and prevents the nut 30 from turning

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desired.

  A piston 36 is guided in the cylinder bore.

  dre 24 and has an extension 38 split in a cross.

  One of the slots of extension 38, deeper, re-

  part of the 14 "segment end while

  the other slot receives a transverse pin 40 shore

  tee at the end of segment 14 "This allows movement

  relative ment between the piston 36 and the end of segment

  lies 14 "in the direction of the B axis and a movement of

  pivot around pin 40 but prevents slackening

  relative bearing in all directions perpendicular to the cylinder axis B. The two segments 14 and 16 are interconnected near the stop 12 by a return spring 42 and near the combined actuation and adjustment device

  18, by a return spring 44 The two return springs

  pel are in the form of tension springs When the brake is in the non-actuated state, the return spring 44 holds the piston 36 against the bottom 22 of the cylinder,

as shown in figure 1.

  The cylinder body 20 has a projection 46

  passing, perpendicular to the axis B of the cylinder, through

  towards an oval slot 48 of the brake support in the form of

  -plate 10 According to Figure 6, the projection 46 has a sec-

  tion which clearly deviates from the circular shape and is

  defined in the region of the longitudinal sides of the window

  te 48 by a groove 50 on each side, these grooves

  having the shape of a circular sector The ma-

  ximal of the section, measured in the longitudinal direction

  slot 48 and in the assembled position se-

  lon figure 6, is such that it is clearly inferred

  smaller than the width of the slot 48 The two grooves 50 are each defined by two lateral faces 52 between which is housed, in the assembled position according to FIGS. 4 to 6, a guide flange 54 of U-section The guide flange 54 extends all along the edge of the

  slot 48 and therefore forms an oval ring The lar-

250 + 222

  inner section of the U-shaped section of the guide rim 54 is such that a wing of a sealing rim 56

  can be lodged between its wings, very close to the edge of the

  brake port 10 which limits the slot 48 The guide flange 54 is formed of a hard plastic resistant

  both in heat, having a low coefficient of friction-

  like "Bakelite" The sealing edge 56 is

  made of softer synthetic material such as a

  lyamide A bellows 58 made of elastic oil-resistant plastic material is fixed by one end to the sealing rim 56 and tightly fixed by its other

  end to free end of projection 46.

  A brake fluid supply perforation

  and a vent 62 placed above are practically per-

  pendulars to axis B of the cylinder and pass through

  the projection 46, from the outside to the cylinder bore 24.

  Inside the brake drum, between the segment ends 14 "and 16", a lever 66 is mounted on the cylinder body 20 by means of a rivet 64 The axis C of the rivet 64, around which can pivot lever 66, cuts at a right angle the axis of rotation A of the brake drum and the axis B of the cylinder, the points of intersection

  being spaced from each other The lever 66 is approxi-

  matively parallel to the axis of rotation A of the brake drum, moves outward through the slot 48 and has an outer end 68 to which is

  attached an actuation cable 70 The actuation cable

  ment 70 belongs to a Bowden transmission 70, 72 the sheath 72 of which rests against an ear 74 formed on the

  projection 46 of the cylinder body 20 The actuating cable

  ment 70 goes from the ear 74 to the outer end 68 of the lever 66, the orientation of this cable relatively

  to the axis B of the cylinder being more or less approximate-

  parallel, depending on the position of the lever.

  Inside the drum brake, one of the ex-

  hoppers of a spacer 78 is coupled to the lever 66

  by means of another rivet 76 The spacer 78 is made

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  only parallel to the axis B of the cylinder and has a

  second split end 80 engaging in an enco-

  che 82 of segment end 14 "This commitment

  puts segment 14 to move in the longitu-

  distance from spacer 78 away from rivet 76 tan-

  say that the relative movements of the spacer 78 rela-

  segment 14 are pocketed in other directions

tions.

  The lever 66 serves, at the same time as the trans-

  mission Bowden 70, 72 and spacer 78, to operate

  mechanical brake It is especially important,

  in this context, that the axis D of the articulation between the

  tretoise 78 and lever 66, as defined by

  rivet 76, or located between the axis C around which the

  vier 66 can pivot relative to the cylinder body and the point where the actuation cable 70 applies

  at the free end 68 of the lever 66 In the mode of exe

  cution shown, axis D is located approximately

  halfway between axis C and plane E The plane E is pa-

  parallel to the two above-mentioned axes, perpendicular to the axis of rotation A of the brake drum and this is the plane where the cylinder body 20 is guided by: sliding way on the brake support 10 As shown in FIG. 3, the D axis is located as exactly as possible in the

  median plane F of segments 14 and 16, which is perpendicular

  cular to the axis of rotation A of the drum and in which

  is also located the axis B of the cylinder.

  A pawl 86 is mounted on the body c O of the cy-

  line by means of another rivet 84 whose axis G is pa-

  aligns with the rotation axis A of the drum The pawl 86

* is mounted with a certain clearance so that in addition to

  pivoting around the G axis, it is

  re to perform limited tilting movements

  axis revolution intersecting the axis G At one of its ends,

  the pawl 86 has a spout 88 cooperating with a den-

  ratchet frame 90 formed on the outer circumference

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  of nut 30 The pawl 86 presents at its other end

  mite a stop part 92 normally maintained in co-

  peration with a shoulder 96 of the segment end

  14 "by a drive spring 94 The spring 94 pre-

  feels like a tension spring and is fixed

  part at the stop part 92 and on the other hand at the end

  Mity 80 of the spacer 78 Consequently, the drive spring 94 tends on the one hand to impart to the abutment part 92 the movement of the shoulder 96 each time the brake is actuated and therefore to pivot the

  pawl 86 clockwise rela-

  tively in Figure 1 On the other hand, the spring 94 tends to urge the spacer 78 to move away from the segment end 14 "and therefore, when the brake is in the non-actuated state, to rotate the lever 66 clockwise against the pulling direction of the actuating cable 70 to bring it to the position of

  rest shown in Figure 3, where the lever 66 is

  puie against the end of segment 16 ".

  Above the rivet 84 + the ratchet presents a

  button 98 which normally leans against the body of cy-

  line 20 as shown in figure 7 On the cylinder body

  dre 20 is fixed, by means of another rivet 100, a res-

  bimetallic spell 102 of which the free terminal part is

  normally bends to the cylinder body when the brake is cold enough A stopper, in the form of a

  clamping sleeve 104, is placed parallel to the

  free terminal tie of bimetallic spring 102 and fixed

in a hole in the rivet 64.

  The normal direction of rotation of the brake drum

  (not shown), towards the front, is indicated by an arrow

  che H in Figure 1 When the hydraulic brake is actuated

  only, the piston 56 pushes the segment 14 outwards.

  laughing and as a result of the reaction force which thus occurs, the brake fluid pressure which prevails in the cylinder bore 24 displaces the cylinder body 20 to the right, along the axis B, according to FIGS. 1 and 2,

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  so that the segment 16 is also pushed against the drum. The segment end 14 "normally drives the stop portion 92 of the pawl 86 via

  of the drive spring 94 so that the pawl pi-

  vote clockwise and that

  the nut 30 turns If due to wear of the packing

  ture, the actuation paths of the segments 14 and 16 and therefore also the pivoting movement of the pawl 86 exceed a certain magnitude when the actuator is actuated

  brake, beak 88 jumps from one or more teeth of the dent-

  ratchet 90 when the brake is released and the pawl 86 returns to its initial position, because the friction exerted by the sealing ring 34 on the nut prevents it from turning backwards In this way, the effective length of the threaded rod 28 which protrudes from the guide bore 26 of the cylinder body 20 increases gradually as a function of the wear of the brake lining. When the brake is applied mechanically, the

  traction exerted by the actuating cable 70 pivots

  counter lever 66 anticlockwise

  be relative to FIGS. 2 and 3 The lever 66 thus exerts via the rivet 76, on the spacer

  78, a force directed to the left (of FIG. 3) tan-

  say that the lever 66 exerts via the rivet 64, on the cylinder body 20, a force directed to the right The cylinder body 20 is further exposed to the force with which the sheath 72 pushes on the ear 74 ,

  this force being directed against the tensile force exerted by

  created on the lever 66 by the actuating cable 70, but

  being of the same magnitude Therefore, during the action-

  mechanical action of the brake, the cylinder body 20 moves in the same way as during hydraulic actuation, that is to say to the right of FIGS. 1 to 3, so that the segment 16 is pushed against the drum while the segment 14 is simultaneously pushed against the drum by the spacer 78 The reaction force exerted on the body

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  cylinder 20 by the segment end 16 ", by the

  end of the threaded rod 28, is in equilibrium with

  the actuating forces acting on the cylinder body

  dre via the rivet 64 and the ear 74 The moment of these forces relative to any axis is

  at least approximately zero So the cylinder body

  dre 20 is not subject, or only to a limited extent

  gligeable, to a tendency to deflection Consequently, the cylinder body 20 remains easy to move along

  of slot 48, in the activated state and in the non-activated state

brake applied.

  You can also adjust the nut 50 in the

  crite with mechanical actuation of the brake In the event that an excessive actuation force must be exerted when the wear of the lining has not yet reached

  the stage which justifies an adjustment, the driving spring

  ment 94 is designed so that when the force acting on it exceeds a certain magnitude, it yields and allows the stop part 92 and therefore the pawl 86

  as a whole to remain still while the shoulder-

  ment 96 moves in the direction of actuation.

  To prevent adjustment when the brake is on

  heated and that consequently the diameter of the drum is increased, the bimetallic spring 102 is designed so that in the event of heating, it stresses the part of the

  pawl 86 located between the rivet 84 and the spout 88 to be fitted

  bend against the clamping sleeve 104, according to the figure, so that the spout 88 is released from the teeth to

  ratchet When the brake has cooled, the dual spring

  metal 102 returns to its original position, as well as

  the pawl 86, under the action of the drive spring 94.

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Claims (11)

  1 actuation device for drum brake   inner segment bour (14, 16), in particular for motor vehicles, comprising: a cylinder body (20) disposed between two opposite segment ends (14 ", 16"), guided in a floating manner in the direction of its axis (B) on a brake support   in the form of a plate (10) and pressing against one of the ex-   segment hoppers (16 "), a piston (36) guided in the cylinder body (20) and   acting on the second segment end (14 ") when   that the brake is actuated hydraulically, and a lever (66) passing through the brake support (10), the part of which located inside the brake is mounted on the cylinder body (20) and which acts on the second end of segment (14 ") when the brake is actuated mechanically and is connected by its external part to an actuating cable (70) 1 device characterized in that: at the lever (66) is articulated a spacer (78) by   which it leans against the second end of seg-   ment (14 "), that the axis (C) around which the lever (66) can pivot on the cylinder body (20) is further from the plane (E) in which the cylinder body (20) is guided on the brake support (10) that the axis (D) of the articulation of the lever (66) to the spacer (78) and that the actuation cable (70) belongs to a Bowden transmission (70, 72) whose sheath (72) is supported   against the cylinder body (20) so that when   that the brake is mechanically actuated, the moments exer-   cés on the cylinder body (20) by the sheath (72), by the lever (66) and by the first segment end   (16 ") are at least approximately in equilibrium.   2 Device according to claim 1, character-   laughed at by the fact that the axis (D) of the articulation of the   sink (66) at the spacer (78) is located at least approxi- 250 ft 222   matively in the common median plane (F) of the two seg-   brake elements (12, 14), plane which is perpendicular to the axis of rotation (A) of the drum.   3 Device according to claim 2, charac-   terified by the fact that the joint is oriented in such a way that its axis (D) passes through the common median plane   (F) of the two segments (14, 16) when the brake is applied mechanically actuated.   4 Device according to claim 1, charac-   terified by the fact that the Bowden transmission (70, 72), in its terminal part o its sheath (72) bears against the   cylinder body (20), is at least approximately pa-   parallel to the axis (B) of the cylinder 'Device according to claim 1, charac-   terrified by the fact that a projection (46) of the cylinder body   dre (20) passes through a slot (48) of the brake support (10) and is guided to the edge of this slot (48) and that the edge of the slot (48) is pressed into a flange   guide (54) in anti-friction material.   6 Device according to claim 5, charac-   terrified by the fact that the guide flange (54) has the figuration of a closed ring.   7 Device according to claim 5 or 6, ca-   characterized by the fact that the part of the projection (46) of the   cylinder body (20) which cooperates with the guide flange   dage (54) has a section deviating from the circular form   cular, that this section has a smaller area in the   direction parallel to the axis (B) of the cylinder that perpendi-   culially to this, which allows to pass the   projection (46) through the slot (48) and, turning   ner the cylinder body (20), to bring it to its assembled position where the guide flange (54) coalesces between lateral groove faces (52) formed on the projection (46).   8 Device according to claim 1, charac-   terrified by the fact that the piston (36) has a prolongation   split slot (38) intended to receive in the manner of a 2504 222   fork the second segment end (14 ") and a   transverse pillar (40) fixed to this segment.   9 Actuation device for drum brake   inner segment bour (14, 16), in particular for motor vehicles, comprising: a cylinder body (20) disposed between two opposite segment ends (14 ", 16"), guided in a floating manner in the direction of sound axis (B) on a brake support   in the form of a plate (10) and pressing against one of the ex-   segment hoppers (16 "), a piston (36) guided in the cylinder body (20) and   acting on the second segment end (14 ") when   that the brake is actuated hydraulically, and a lever (66) passing through the brake support (10), the part of which located inside the brake is mounted on the cylinder body (20) and which acts on the second end of segment (14 ") when the brake is actuated mechanically and is connected by its external part to an actuating cable (70), as well as an automatic adjustment device comprising a threaded rod (28) pocketed to turn and a nut ( 30) mounted so that it can rotate, provided with a ratchet toothing (90) and cooperating with a ratchet (86) so that when the two segments (14, 16) move relatively, a entrainment spring (94 ) applying to the ratchet (86)   exerts on the latter a couple limited by the characteristic   spring tick, device characterized in that: at the lever (66) is articulated a spacer (78) by   which it leans against the second end of seg- ment (14 "),   that the threaded rod (28) bears against the first ex-   segment end (16 ") and the nut (30) and the pawl (86) are mounted on the cylinder body (20), and that the drive spring (94) is fixed between the pawl (86) and the spacer (78) so that on the one hand it normally maintains an abutment part (92) of the pawl (86) in cooperation with the second end of 2504 222   segment (14 ") and that on the other hand it exerts a moment of recovery on the lever (66) via the spacer (78).   Device according to claim 9, charac-   terrified by the fact that a bimetallic spring (100) is fixed to the cylinder body (20) and urges the pawl (86) to move away from the ratchet teeth (90) in the event of brake overheating.