FR2886699A1 - DRUM BRAKE WITH LOCKING DEVICE - Google Patents

Abstract

Drum brake with parking brake function for locking a vehicle, comprising a brake drum (4), at least a first and a second brake shoe (2, 3), a mechanical locking device (8) for locking the brake parking brake position and motor drive means (11) for operating the mechanical locking device (8). This installation (8) comprises a driven member in direct or indirect contact with the first and second brake shoes (2, 3) to mechanically lock the position of the first and second brake shoes (2, 3).

Description

Field of the invention

  The present invention relates to a drum brake provided with a locking device for mechanically locking the parking brake position.

  STATE OF THE ART According to the state of the art, drum brakes actuated by a cable are known. These are, for example, duo-servo parking brakes with two brake jaws which support each other by a common support. The brake linings of the jaws are mechanically applied against the brake drum that surrounds the jaws. Such drum brakes are heretofore mechanically actuated for example by means of a cable. Such traction cable installations are however relatively bulky in the vehicle and are perceived as troublesome in the passenger compartment. It is further known to replace in such brakes, the handbrake lever by a motor. This motorized unit or motor then actuates the traction cable. Thus, the driver can for example actuate a button or a switch to drive the engine and block the vehicle.

  Such parking brakes are known as traction rope brakes.

  DESCRIPTION AND ADVANTAGES OF THE INVENTION The present invention relates to a parking brake function drum brake for locking a vehicle, comprising a brake drum, at least a first and a second brake jaw, a mechanical locking device. for locking the parking brake position and motor drive means for actuating the mechanical interlocking arrangement, the apparatus comprising a driven member in direct or indirect contact with the first and second brake jaws for mechanically locking the position of the first and second brake shoes.

  The drum brake according to the invention can be made in a particularly compact manner by virtue of the mechanical locking arrangement of the parking brake position with a motor drive means and a driven member. The drive means drives this member and the driven member comes directly or indirectly into contact with the drum brake shoes. This allows the mechanical locking of the jaws in the parking position.

  Preferably, between the drive means and the driven member there is a transmission. In a very preferential manner, the transmission is housed in the brake drum. In addition, the drive means is installed perpendicularly to the plate forming the back of the drum brake. This allows a particularly compact construction.

  To avoid additional security elements, the transmission is preferably self-locking. According to the invention, it suffices that only two transmission elements in engagement are made in a self-locking manner.

  According to a preferred development, the brake shoes are actuated by the pressure of a fluid, in particular the pressure of a liquid against the brake drum. This makes it possible to develop a drum brake that can be used as a normal service brake and as a parking brake while being very compact.

  Preferably, the driven member includes a cam member with a first and a second cam. During rotation of the cam member, the first cam comes directly or indirectly into contact with the first brake shoe and the second cam, in contact with the second brake shoe to mechanically lock the parking position.

  Preferably, a planetary transmission is provided between the cam member and the drive means. In a very preferential manner, the cam element is the hollow wheel of a planetary transmission.

  In order to guarantee a final position or defined rest position of the cam element, at least one stop is preferably provided for limiting the rotation of the cam element. This ensures in particular the return of the cam member in a position of rest identical, defined.

  According to another preferred embodiment of the invention, the locking installation comprises a spindle installation with a double spindle. The double spindle has first and second threads and these two threads have opposite directions. The first thread is engaged with a first freewheel member and the second thread engaged with a second freewheel member. When rotating the double spindle, the two freewheel elements move in opposite directions. This makes it possible to guarantee the taking or release of the locking device.

  To have a particularly compact and economical construction, the first and the second freewheel element are each made as the brake shoe of a drum brake. This reduces the number of pieces.

  According to another preferred embodiment of the invention, the locking device comprises a spindle installation with a spindle and a freewheel element. When the driving means is actuated, the pin applies the locking force to one brake shoe and the free wheel member applies the locking force to the other brake shoe. This realization with a single pin allows a particularly simple construction.

  The locking device with a single spindle preferably has a first gear and a second gear each with straight teeth. The second gear forms the freewheel element of the spindle or is connected to the freewheel element and the width of the two toothed wheels is different. Thus, the second gear wheel can move axially relative to the first gear when one arrives in the locking position or that this position is released.

  According to another preferred embodiment of the invention, the locking installation comprises a nutation disk transmission. The nutation disk transmission is installed between a first and a second actuating element which apply the brake shoes against the brake drum and the drive means. The use of a nutation disk transmission allows a very compact construction for a very large reduction.

  According to another preferred embodiment of the invention, the locking device comprises a device with a lever. A first end of the lever is connected to the drive means and its second end is mounted on the rotational point. The lever is connected directly or indirectly to the first and second brake shoes. Upon actuation of the drive means, the lever pivots about the point of rotation so that it can exert a locking force on the first and second brake shoes.

  Preferably, the lever device has a pin engaged with the first end of the lever. The pin is connected to the drive means; upon actuation of the drive means the spindle rotates so that the first end of the lever moves in the axial direction of the spindle. The lever then switches around the point of rotation which is not fixed but whose position may vary.

  According to another advantageous characteristic, the lever device comprises a mechanical compensation element for the wear-related variations of stroke of the locking device, for example the wear of the brake linings. The mechanical compensation element is mounted at a first end at the point of rotation of the lever and at a second end directly or indirectly in contact with one of the brake beads.

  Preferably, the locking device is floating between the brake shoes. This ensures the regularity of the grip of the brake shoes.

  With respect to the embodiments described above with pin solutions, all of which may have an adjustment stroke reserve, compensation for stroke variations resulting from wear is taken into account. This eliminates a compensating device to compensate for wear.

  The drive of the locking device according to the invention is preferably provided by an electric motor. To avoid damaging the electric motor, it is furthermore advantageous to equip it with an intensity limiting device and / or a torque limiting installation. The values entered by these installations can be used to diagnose the locking device as to the state of lock.

  The present invention is particularly applicable to vehicles of higher types and light commercial vehicles or so-called SUV vehicles.

  Drawings The present invention will now be described in more detail with the aid of exemplary embodiments shown in the accompanying drawings, in which: FIG. 1 is a schematic view of a drum brake according to the invention with a stop brake function, FIG. 2 is a schematic view of a locking installation corresponding to a first exemplary embodiment of the invention; FIG. 3 is a diagrammatic top view of the locking installation of FIG. 2, FIG. 4 is a schematic top view of a second embodiment of a locking installation according to the invention, FIG. 5 is a diagrammatic view of a third embodiment of an installation of FIG. FIG. 6 is a schematic view of a fourth embodiment of a locking device according to the invention, FIG. 7 is a schematic view of a fifth embodiment of a device according to the invention. e lock installation according to the invention, and Figure 8 is a schematic view of a sixth embodiment of a locking installation according to the invention.

  Description of Embodiments of the Invention

  Figure 1 shows schematically a drum brake 1 with a stop brake function without traction cable according to the invention. The drum brake 1 comprises a first brake shoe 2 and a second brake shoe 3. The brake shoes 2, 3 comprise brake linings 5. The radial movement of the brake shoes 2, 3 makes it possible to apply the linings brake 5 against the inner periphery of a brake drum 4. The brake shoes 2, 3 are symmetrical with respect to the brake drum 4 and are connected at one end to a compensation device 9. This compensation device 9 is not essential and can be deleted. Between each other end of the two brake jaws 2, 3 is a locking device 8 according to the invention.

  According to FIG. 1, the locking device 8 is pre-viewed between a first brake lug 6 and a second brake lug 7. The locking device 8 is driven preferably by an electric motor perpendicular to the plane of the drawing of Figure 1; this electric motor is installed on the cover plate of the drum brake 1. Note that to have a particularly compact construction, the drive can also be housed in the two brake shoes 2, 3. In Figure 1, the reference 10 designates a return spring of the brake shoes which provides the return of the drum brake in its rest position shown in Figure 1.

  With reference to FIGS. 2 and 3, a first exemplary embodiment of a drum brake locking device 8 according to the invention will be described below. The locking device 8 comprises, as drive means 11, an electric motor. The electric motor drives an output shaft 20 connected to a first screw wheel 21. The first screw wheel 21 meshes with a toothed pinion 22 with an inclined gear which in turn drives a connecting shaft 23. The sun gear 24 of a planetary transmission is carried by the connecting shaft 23. The sun gear 24 meshes with three planetary wheels 25 meshing themselves with a hollow wheel 26. As shown in Figure 3, the hollow wheel 26 is made in the form of an element. cam member having a first cam 27 and a second cam 28. The outer periphery of the hollow wheel 26 is thus in contact with a first brake lug 6 and a second brake lug 7 oppositely disposed with respect to the hollow wheel 26 .

  When the driving means 11 is activated, the rotation of the output shaft 20 is transmitted by the screw transmission to the sun gear 24 and the planetary transmission to the hollow wheel 26. Thus, the hollow wheel 26 rotates around its axis to spread the first and the second heel 6, 7 in the direction of the arrows B, C. As the brake heels 6, 7 are in contact each time with the brake shoes 2, 3, the movement of the heels of brake 6, 7 applies the brake lining to the brake drum. For the movement of the brake beads 6, 7 to be as simple as possible, these beads are mounted in respective bearings 29.

  Note that either the elements of the planetary transmission or those of the transmission screw are made in the form of a self-locking transmission to prevent the parking brake is released automatically. When the brake linings are applied against the brake drum, the electric motor cuts off. The self-locking transmission thus mechanically locks the position of the parking brake. The stopping of the electric motor can be done for example by means of signals detected by a current receiving sensor or by a torque limiting sensor.

  According to Figure 3, the cam member can be rotated at a maximum of 90. Note that for safety reasons, in operation, the maximum rotation angle of the cam element must be less than 90. This avoids with certainty that the cam element can rotate beyond 90 and that the braking force of the parking brake may again decrease. For this purpose it is possible to provide, for example, another sensor for monitoring or a stop defining a limit position. The monitoring of the force-stroke diagram of the motor current during the rotation of the hollow wheel 26 can also be done to check the plausibility of the state of wear of the lining. If, for example, the angle of rotation of the hollow wheel 26 should exceed a predefined value, this also indicates excessive wear of the lining which can be indicated to the driver, for example by a warning device.

  In order to release the parking brake, the drive means 11 are simply operated in the opposite direction. The rotational movement of the drive shaft 20 is again transmitted by the screw transmission and the planetary transmission to the hollow wheel 26 which then rotates in the opposite direction.

  A second embodiment of a drum brake according to the invention will be described hereinafter with reference to FIG. 4. In this figure and the corresponding description, the same references will be used to designate the same elements or functional elements. identical to those of the previous embodiment.

  The second embodiment corresponds essentially to the first embodiment. The driving torque is transmitted to the hollow wheel 30 via the sun gear 24 and the planetary wheels 25. The hollow wheel 30 itself comprises a first cam 31 and a second cam 31. According to FIG. the cams 31, 32 only have a leading surface on one side. On the other side, there is a recess or shoulder 33, 34 through which the hollow wheel 30 abuts in its rest position shown in Figure 4 against the stop 35 or 36. This embodiment has the advantage that the cams 31, 32 are turned back, in their rest position, accurate, because then they come against the stops 35, 36. Thus, when the release of the parking brake, the locking device always takes a defined zero point.

  In other words, the cam element comprises at least one stop to limit its rotation.

  A third embodiment of a drum brake according to the invention will be described hereinafter with reference to FIG. 5 in which the same references as in the embodiments described above have been used for identical functional elements or like.

  According to FIG. 5, the locking device 8 according to this third embodiment comprises an electric motor drive 11 and a screw transmission 21, 22. The toothed gear 22 with inclined toothing is connected in this case to a first gear wheel 40 through the shaft 23. The first gear 40 has a straight toothing and the latter has a width (a). The first toothed gear 40 with the right teeth meshes with a second toothed wheel 41 with a right tooth of width (b). The width (a) of the first spur gear is less than the width (b) of the second spur gear 41. The second spur gear is integrally connected to a sleeve 42 axially mounted in the spur gear. direction of movement of the first or second brake pad 6, 7 in a bearing 43.

  The sleeve 42 has an internal thread and is part of a spindle arrangement composed of the sleeve 42 and a pin 44. The pin 44 is locked in rotation. The head 44a of the pin 44 carries the second brake heel 7; the first brake shoe 6 is in contact with the second right-hand wheel 41. The entire structure formed of the brake shoes 7, 6, the pin 46, the sleeve 42 and the second right gear 41, is mounted floating.

  To switch to the parking brake position, the electric motor driving means 11 is driven to transmit the rotational torque by the screw transmission 21, 22 and the first toothed gear 40 to the second toothed wheel 41 to straight teeth. As the sleeve 42 is integrally connected to the toothed wheel 41, it rotates. The pin 44 being rotatable, the sleeve 42 moves along the pin 44. Thus, the first and the second brake heel 6, 7 are spaced in the direction of the arrows B, C; the floating assembly ensures that the brake shoes 2, 3 are regularly biased. To avoid an automatic recall of the spindle installation, it is self-locking.

  When the brake linings are applied against the brake drum by the rotation of the sleeve 42 around the pin 44, the locking position is blocked. In order to release, only the electric motor drive 11 is moved in the opposite direction so that the sleeve 42 is also displaced in the opposite direction on the pin 44 and the brake shoes 6, 7 return to their rest position. .

  Optionally, the pin 44 or the sleeve 42 may include a limit stop to ensure that the locking mechanism 8 can return after release of the parking brake back to a defined state.

  Referring to Figure 6 will be described below a drum brake corresponding to a fourth embodiment of the invention; for this description and the drawings will be used the same references as in the embodiments above to designate the same parts or the same function.

  The fourth embodiment is analogous to the third embodiment of FIG. 5. An electric motor drive 11 is connected by a screw transmission 21, 22 to a first spur gear 50. The first gear wheel the right 50 meshes with a second right gear 51. The width (c) of the first gear 50 is greater than the width (d) of the second gear 51. The second gear with right gear 51 is connected in solidarity to a double pin 52 of a spindle installation. As shown in Fig. 6, the double spindle 52 is a shaft member which passes both sides of the gear 51. The double spindle 52 has a first thread 53 and a second thread 54. The first thread 53 is opposite direction to the second thread 54.

  The first thread 53 is engaged with an internal thread 57 made in a cavity of the first brake pad 6. The second thread 54 is engaged with a thread 58 made in the cavity of the second bead 7. Thus, the brake beads 6 , 7 are part of the double broach or double thread. The brake beads 6, 7 are mounted in bearings 55, 56 and can be displaced axially in the direction of the arrows B, C. This embodiment allows a reduced number of parts and a particularly compact construction of the locking device 8. The brake beads 6, 7 are for example locked in rotation by a groove and keyway embodiment. The threads of the double spindle 52 and the brake heels 6, 7 are also self-locking. The entire spindle installation, including the second spur gear 51, is mounted floating, which also compensates for a difference in wear of the brake linings. The second right-sided wheel 51 then moves relative to the first right-tooth gear 50 in the axial direction.

  To lock the parking brake the drive means 11 is actuated to transmit the torque via the screw transmission and the right-toothed gears 50, 51 to the double-pin 52. The brake shoes 6, 7 are thus move in the direction of the arrows and mechanically lock the parking brake. To release the brake, the drive means 11 is operated in the opposite direction to recall the brake shoes 6, 7. Note that the base surface of the inner cavity of the brake beads 6, 7 can serve as a stop . But it is also possible to have a separate stop. Thanks to the stop, one arrives again in a defined rest position in which one can always recall without difficulty the locking installation 8.

  Referring to Figure 7 will be described hereinafter a fifth embodiment of a drum brake according to the invention; for this description and the drawings will be used the same references as in the previous embodiments for identical parts or the same function.

  According to the above exemplary embodiments, the motor drive means 11 transmits a torque by a first screw wheel 21 and a toothed gear 22 with bias teeth. The toothed gear 22 with bias teeth also has on one of its lateral surfaces a toothing 61 at its outer periphery; this toothing is engaged with the second screw wheel 22 of a nutation disk 60.

  As shown in FIG. 7, the swash plate 60 is installed at a predefined angle with respect to the second screw wheel 22. The side surface of the swash plate 60, opposite the second screw wheel 22, comprises a second toothing 62; thus, the swash plate 60 meshes with the toothing of a disk 63. The disk 63 is integrally connected to the axis 64 and the other end of the shaft carries a threaded spindle 65. As shown in FIG. Shaft 64 passes through nut ring 60 and second screw wheel 22.

  The swash plate 60 is mounted on a part 67. The part 67 comprises a support installation 67a for mounting the swash plate 60 by its outer periphery. The support installation 67 may be pot-shaped or have a plurality of support arms. The support installation 67a is connected to a plate 67b and to an axis 67c. It is particularly advantageous to make the piece 67 in one piece, the axis 67c further comprises a thread 68 in the form of pin.

  As shown in Figure 7, a bearing 66 is provided between the plate 67b of the part 67 and the disc 63. The thread 68 is thus engaged with the internal thread of a second brake heel 7; the thread 69 of the shaft 67 is in connection with the internal thread of the first brake lug 6. The bottom zones of the brake bead cavities 6, 7 can thus also serve as stops.

  The operation of the fifth embodiment of the locking device 8 is as follows: to mechanically lock the position of the parking brake the drive means 11 is controlled to transmit its torque by the first screw wheel 21 to the The second screw wheel 22 drives the swash plate 60 through the toothing 61. The disk 60 itself drives the disk 63 through the toothing 62 so that the spindle 64 rotates with the disk 63. Since the first brake shoe 6 is rotatably mounted, it moves on the thread 65 in the direction of the arrow C and actuates the first brake shoe 2. The rotational nut 60 also drives the brake shoe 6 to rotate. axis 67d via the support installation 67a and the plate 67b. The brake heel 7 is thus moved in the direction B of the arrow which actuates the second jaw 3. The threading between the brake shoes 6, 7 and the axes 67c and 64 are self-locking threads to prevent any automatic return of the brake. parking brake system. For the return it is sufficient to operate the drive means 11 in the opposite direction to move the brake beads 6, 7 in the opposite directions and return them to their rest position.

  The advantage of the lock installation 8 and of a nutation dis-60 is that the nutation disk provides a great reduction. In this exemplary embodiment, the driving means 11 may be fixed perpendicularly to the drum brake cover plate and the assembly of the lock installation is housed in the drum brake.

  A sixth exemplary embodiment of a drum brake according to the invention will be described hereinafter with reference to FIG. 8; in this case we have also used the same references as in the embodiments above to designate the same elements or elements of the same function.

  According to FIG. 8, the locking device 8 of this sixth embodiment is formed by a lever mechanism. The lever mechanism is installed between a first brake shoe 6 and a second brake heel 7. The brake shoes 6, 7 thus move apart on the axis XX to lock in the direction of the arrows B, C The lever mechanism comprises a first lever 73 pivoting about a point of rotation D. The lever 73 has a freewheel member 72 engaged with the thread 71 of a pin 70. The pin 70 is driven by means The lever 73 and more precisely the pivot point D carries another intermediate piece 74. The intermediate piece 74 comprises a compensating installation 75. A spring 76 is provided between the lever 73 and the workpiece. intermediate 74 to assist the recall in the output position.

  As shown in FIG. 8, the first brake pad 6 is mounted at the end of the intermediate piece 74 opposite the lever 73. The second brake heel 7 is installed directly on the lever 73 near the point of rotation. D and substantially above it.

  To mechanically lock the position of the parking brake, the electric motor driving means 11 which turns the spindle 70 is controlled. The lever 73 thus moves on the thread 71 of the spindle 70 in the direction of the arrow A. This results in the pivoting movement of the lever 73 around the rotation point D of the lever. In other words, the lever 73 is itself moved towards the second brake heel 7 and in addition there is a rotation around the point of rotation D; the intermediate piece 74 thus moves towards the first brake pad 6. The brake shoes 6, 7 are moved in opposite directions which ensures the mechanical locking of the position of the parking brake. It should be noted that the point of rotation D is not fixed but moves on the spindle 70 according to the position of the freewheel element 72. The threading between the spindle 70 and the freewheel element 72 is self-locking. to avoid any automatic return. Thanks to the production of the lever mechanism according to the invention, the circular movement of the lever mechanism does not fall back with too great a transverse force on the spindle 70. This avoids damaging the spindle and guarantees the operation of the spindle. - is lying. The lever mechanism according to the invention has a particularly compact construction and comprises only a minimum number of parts. In addition, either by increasing the stroke of the freewheel element 72 on the spindle 70 or the compensation at the compensating installation 75, the wear of the brake linings is compensated. Note also that it is also possible to provide a limit stop so that when the locking device 8 is returned to a defined end position position.

  Release of the locked blocking position is according to the sixth embodiment by controlling the drive means 11 in the opposite direction so that the freewheel member 72 moves in the opposite direction on the spindle 70. intermediate piece 74 is then recalled by the spring 76. Note further that it can also provide a transmission between the drive means 11 and the spindle 70.

  According to another characteristic, the electric motor comprises a current limiting installation and / or a torque limiting installation which, when a predetermined threshold is reached, cuts off the electric motor.

  For all the embodiments described above, it is noted that a current and / or torque detection of the drive means 11 is used to make a plausibility check of the locked position or of the position taken. end of race. This is done using a diagnostic installation.

  It should further be noted that all the previous embodiments only start or lock in the parking brake position in a purely mechanical manner. Other possibilities for all the exemplary embodiments presented consist in controlling the drum brake by a fluidic means, in particular a hydraulic or pneumatic means, to switch to the parking brake position, and then the locking device only provides mechanical locking. In particular, the parking brake function can be combined with existing brake control systems for the vehicle such as ESP or ABS systems.

Claims (22)

  1) Drum brake with parking brake function for locking a vehicle, comprising a brake drum (4), at least a first and a second brake shoe (2, 3), a mechanical locking device (8) ) for locking the parking brake position and motor drive means (11) for operating the mechanical locking device (8), characterized by a driven member in direct or indirect contact with the first and second jaws of brake (2, 3) for mechanically locking the position of the first and second brake shoes (2, 3).   2) Drum brake according to claim 1, characterized by a transmission (21, 22; 24, 25, 26) between the drive means (11) and the driven member.   3) Drum brake according to claim 2, characterized in that the transmission is self-locking.   4) Drum brake according to claim 1, characterized in that the first and the second brake shoes (2, 3) are applied against the brake drum (4) by a fluidic actuating installation, in particular an installation of hydraulic actuation.   A drum brake according to claim 1, characterized in that the driven member is a cam member (26) having a first cam (27) and a second cam (28), the rotation of the cam member ( 26) locking by the first cam (27) the first brake shoe (2) and by the second cam (28), the second brake shoe (3).   6) drum brake according to claim 5, characterized by a planetary transmission (24, 25) installed between the cam member (26) and the drive means (11).   7) drum brake according to claim 6, characterized in that the cam member (26) is a hollow wheel of a planetary transmission-taire.   8) Drum brake according to one of claims 5 to 7, characterized in that the cam member (30) has at least one stop (35, 36) to limit its rotation.   9) Drum brake according to claim 1, characterized in that the locking device (8) comprises a spindle system with a double spindle (52), this double spindle having a first thread (53) and a second thread. (54) and these two threads are of opposite direction.   A drum brake according to claim 9, characterized in that the first thread (53) is engaged with a thread of a first brake shoe (6) and the second thread (54) is engaged with a second thread (53). brake heel (7).   11) Drum brake according to claim 9, characterized in that the double spindle (52) is connected to a spur gear (51) movable with respect to a first spur gear (50) in the axial direction. double spindle (52).   12) Drum brake according to claim 1, characterized in that the locking device (8) comprises a spindle system having a spindle (44) and a freewheel element (42), the freewheel element (42) applying a locking force to the first brake shoe (2) and the pin (44) applying a locking force to the second brake shoe (3).   13) Drum brake according to claim 12, characterized in that the locking device (8) further comprises a first toothed gear (40) with a straight cut and a second gear (41) with a straight cut, the second gear serrated gear (41) being a freewheel element of the spindle system or integrally connected to a sleeve-like freewheel element (42).   14) drum brake according to claim 1, characterized in that the locking device (8) comprises a nutation disk transmission between a first brake heel (6) and a second brake heel (7).   15) Drum brake according to claim 1, characterized in that the locking device (8) comprises a lever device with a lever (73), a first end of the lever (73) being connected to the drive means ( 11) and its second end is mounted on a point of rotation (D), the lever (73) pivoting about the point of rotation (D) when it is actuated by the driving means, while during the movement pivoting the lever (73), the rotation point (D) changes position.   16) Drum brake according to claim 15, characterized in that the lever device comprises a pin (70) engaged with a free wheel element (72) on the lever (73).   17) Drum brake according to claim 15, characterized in that the lever device comprises an intermediate piece (74) installed between the brake heel (6) and the point of rotation (D) and the lever (73) is in position. Contact with the second brake heel (7).   18) drum brake according to claim 17, characterized in that the intermediate piece (74) comprises a mechanical compensation installation 1 o (75).   19) Drum brake according to claim 1, characterized in that the locking device (8) is mounted floating between the first and the second brake shoes (2, 3).   20) drum brake according to claim 1, characterized in that the drive means (11) is an electric motor.   21) Drum brake according to claim 20, characterized in that the electric motor comprises a current limiting device and / or a torque limiting device which, when a predetermined threshold is reached, cuts off the electric motor.   22) drum brake according to claim 20, characterized in that it comprises a diagnostic installation which, based on va-30 their characteristics of the electric motor, defines a state of the locking installation.