FR2869661A1 - Drum brake control device for motor vehicle, has brake cylinder with case, two pistons movable in translation in case, and seat belt pretensioner mounted partially in one of two pistons - Google Patents

Abstract

The device has a brake cylinder with a case (3), and pistons (15, 16) movable in translation in the case. A sector gear (14) is movable in rotation around an axle (38) coaxial to an axis of the piston. A seat belt pretensioner is mounted partially in the piston (15). The pretensioner has a screw maintained in a position by a toothed swivel that is disposed in an extension of the piston (15). An independent claim is also included for a drum brake equipped with a brake control device.

Description

Drum brake control device for a motor vehicle.

  The invention relates to a drum brake control device for a motor vehicle. More specifically, the invention relates to an electrically controlled brake cylinder for actuating a drum brake.

  An object of the invention is to provide a brake cylinder for rapid reaction of a drum brake. Another object of the invention is to allow braking of a vehicle with drum brakes that do not require significant muscular effort. A further object of the invention is to allow automatic play catch-up, thanks to a device having a small footprint.

  In a drum brake, a brake control actuates a brake cylinder. One end of a first segment is supported on one end of a brake cylinder housing. One end of a second segment bears on an opposite end of the housing. The segments, in an arc, are arranged inside a drum of a wheel of the vehicle. The drum, moving with the wheel, is circular. The two segments follow the contour of the drum. Each segment is provided on one outer face with a brake lining. By outer face of a segment is meant face facing the drum.

  During braking, a brake control, for example a brake pedal, actuates the brake cylinder. The brake cylinder pushes the segments against an inner wall of the drum. By inner wall of the drum is meant wall directed towards the linings. The fittings, respectively worn by each of the segments, are then in contact with the inner wall of the drum. Friction of the linings against the drum opposes rotation of the drum. A braking of the vehicle then takes place.

  Recalling the segments in the rest position is, for example, by a return spring. By rest position is meant position in which the segments are not removed. The segments move away from the inner wall of the drum. The pads do not rub against the drum anymore. The braking is finished.

  As a brake cylinder, a brake cylinder actuated hydraulically is known. This brake cylinder, of generally cylindrical shape, has two pistons oriented in opposite directions. Each piston is directed towards one end of a segment bearing on the brake cylinder. The opposite ends of the segments are for example interconnected by means of a pivot. An intermediate spring is disposed between the two pistons of the brake cylinder. The intermediate spring is housed in a hydraulic chamber, communicating with a hydraulic reservoir. During braking, a brake fluid is sent from the hydraulic reservoir to the brake cylinder. Hydraulic pressure is installed in the hydraulic chamber, pushing the two pistons. The two pistons in turn push the two segments against the drum of the wheel. Friction between the segment linings and the drum of the wheel brakes the vehicle. At the end of the braking, the segments are recalled, for example by a spring. The pistons return to their initial position in the brake cylinder, pushing the brake fluid out of the hydraulic chamber. The drum is free again.

  Such a drum brake has many disadvantages, arising in particular from the use of a brake fluid. Indeed, during braking, a temperature at a wheel can reach 500 C. It is therefore necessary to use a brake fluid having a very high boiling point. In addition, it should be regularly checked that the amount of brake fluid in the braking system is sufficient. Indeed, if the amount of brake fluid is insufficient, braking will not be optimum. Finally, it is necessary to regularly check the purity of the brake fluid. In fact, impurities in the brake fluid can cause, among other things, a drop in the boiling point. If the brake fluid boils during braking, braking can not be done properly, and the brake can be badly damaged.

  Another disadvantage of drum brakes is that the quality of braking depends essentially on the condition of the linings. However, the pads being subjected to friction with the drum, they wear out. When the thickness of a liner is decreased, the distance between this lining and the drum is higher. Also, the segment will have to travel a larger race before being in contact with the drum and allow the braking. This race during which no braking takes place, called dead race, is detrimental, especially when it is necessary to have a fast braking.

  To avoid this dead race, we know different systems of 5 retrofits of automatic games.

  For example, there is known a device comprising a link provided with a spring. The rod is respectively supported by two opposite ends on the two segments. When braking, the brake cylinder allows the two segments to move away from each other. A device then allows an elongation of the link. When the braking is finished, the return spring brings the two segments back to the rest position. However, the rod remains stuck in its new, longer position. The game is thus caught up, and the dead race does not exist. Such a play catch device is provided with an additional piece to be mounted in the drum brake.

  Game retrofit devices of the state of the art have many disadvantages. In particular, it is necessary to provide the starting length of the connecting rod before attaching each of the ends of the link to a segment respectively. The presence of this play catching device also increases the internal dimensions of the drum brake. It is therefore necessary to position the rod sufficiently high so as not to hinder the fixing of the flange.

  In the invention, it seeks to solve the problems described above, by proposing an electrically actuated drum brake, without the use of hydraulic fluid. There is also provided a play retrofit device resulting in no additional space requirement in a drum brake. The present invention applies equally well to so-called Duo Servo drum brakes, as drum brakes said fixed point.

  The principle of the invention is based on a drum brake having the same shape as a hydraulically actuated drum brake. However, the brake cylinder is electrically actuated. A particular shape of the pistons contained in the brake cylinder makes it possible, during braking, to discard the segments. No liquid is used. The pistons are mounted in translation in a housing of the brake cylinder. The displacement of the pistons is allowed by a mechanical part or plate disposed between the two pistons. This intermediate plate is itself electrically actuated by an auxiliary engine. A spring makes it possible to bring back instantly, when the braking is finished, the intermediate plate in the rest position. The pistons are simultaneously brought back to the rest position, bringing with them the segments.

  The brake cylinder of the invention may comprise a play retraction device. This device is housed inside the brake cylinder, and is in contact with a segment. This catch-up device is for example integrated in one of the pistons.

  The play catch device is, for example, a device provided with a screw nut system. The screw is in relation with a piston and a segment. The segment rests on the piston and more particularly on a head of the screw housed in the piston.

  The invention therefore relates to a drum brake control device for a motor vehicle, said drum brake comprising at least one segment capable of being applied against a drum integral in rotation with a wheel hub, characterized in that said device comprises - a brake cylinder provided with a housing, - at least one piston movable in translation in said housing and stationary in rotation, said piston being supported by a first end against the segment and having at a second end at least one ball ramp, - a member movable in rotation about an axis coaxial with the axis of said piston, said rotatable element being provided with at least one ball ramp on a side facing the second end of said piston, at least one ball housed in the piston ball ramp and in the ball ramp of the movable element.

  In a particular embodiment of the invention, the element movable in rotation is a toothed sector driven by a gear. The brake cylinder is for example electrically actuated. The device of the invention may be provided with an automatic game-catching device housed in the casing of the brake cylinder. The catch-up device is preferably mounted on one of the pistons.

  The invention will be better understood on reading the following description and examining the figures which accompany it. These are presented 2869661 5 only indicative and not limiting of the invention. The figures show: FIG. 1: A general view of a drum brake provided with a brake cylinder which may be a brake cylinder of the invention; Figure 2: An overview of a Duo Servo type drum brake with a brake cylinder can be a brake cylinder of the invention; Figure 3a: A portion of the brake cylinder of the invention, as well as an electric motor operating the brake cylinder; - Figure 3b: A front view of a toothed sector, according to a particular embodiment of the invention; - Figure 4: A representation of a drum brake control device of the invention; - Figure 5: A longitudinal section of a brake cylinder according to a particular embodiment of the invention; - Figure 6: A longitudinal section of another particular embodiment of the invention.

  In Figure 1 is shown a drum brake 1. A flange 2 carries a cylindrical housing 3. The flange 2 has a circular shape. The housing 3 is fixed on the flange 2 at a location remote from a center of the circle forming the flange 2. The flange is provided at its center with an orifice 25. It is through this orifice 25 that a fixing means (not shown) fixes the flange 2 to a fork of a vehicle.

  Two segments 4 and 5 bear respectively on two opposite ends of the housing 3. More specifically, one end 6 of the segment 4 bears on one face forming an end of the housing 3, while one end 7 of the segment 5 is on an opposite side of the housing 3. The segment 4 carries, on an outer face, a brake lining 8. The segment 5 carries, on an outer face, a brake lining 9. Segments 4 and 5 are in an arc. A circle formed by the segments 4 and 5 follows a contour of the circle forming the flange 2. An end 10 of the segment 4, opposite the end 6, is pivotally mounted, via a pivot 12, relative to the flange 2. Likewise, one end 11 of the segment 5 is pivotally mounted, via the pivot 12, with respect to the flange 2. The pivot 12 makes it possible to articulate the segments 4 and 5 by means of the ends 10 and 11. In Figure 1, the pivot 12 is a double pivot. It is also possible to have a single pivot for 2869661 6 articulate the two segments.

  A return spring 13, brings the segments 4 and 5 to the rest position, when braking is completed. By rest position, is meant position in which the segments 4 and 5 are as close as possible to the center of the flange 2. In contrast, during braking, a centrifugal force distributed via the brake cylinder 3 move the segments 4 and 5 away from the center of the flange 2.

  In Figure 2, we can see another example of drum 49 drum said Duo Servo which the invention can be applied. A first end 53 of a segment 50 bears on one end of a housing 52. A first end 54 of a second segment 51 bears on an opposite end of the housing 52. A second end 55 of the segment 50 and a second end 56 of the segment 51 are integral, for example, with a device 57 of clearance clearance. Each segment 50 and 51 carries on an outer face a gasket, respectively 58 and 59. A return spring (not shown) can return the segments 50 and 51 to the rest position when braking is completed.

  The brake cylinder of the invention may have the same external shape as a brake cylinder of the state of the art.

  The description of FIGS. 3 to 6, below, is made with reference to FIG. 1, but can be transposed in all respects to FIG. 2.

  The housing 3 contains a device for separating the segments 4 and 5 during braking.

  In FIG. 4, one can see the device of the invention forming the brake cylinder, outside the case 3. A rotational element 14, such as a toothed sector, is arranged between two pistons 15 and 16. For example, an end 17 of the piston 15 abuts against the end 7 of the segment 5 (Figure 1), while an end 18 of the piston 16 abuts against an end 6 of the segment 4 (Figure 1). The toothed sector 14 can be rotated by a gear 19. The gear 19, such as a gear train, is driven by an electric motor. The gear train 19 may be provided with several gears. One of the wheels 29 rotates the toothed sector 14.

  The pistons 15 and 16 and the toothed sector 14 are housed in the housing 3. The gear train 19 can itself be located outside the housing 3.

  In Figure 3a, one can see more precisely the shape of the toothed sector 14. The toothed sector 14 is circular. A side 21 of the toothed sector 14 is provided with three ramps 22 balls.

  In Figure 3b, one can see more precisely the structure of these ball ramps 22. A ball 22 ramp has, for example, a crescent shape. The ball ramp may also have an oval shape, diamond ... A cavity, or cavity, is hollowed in a thickness of the toothed sector 14, and forms a ramp 22 ball. The cavity has a variable depth, a function in particular of the diameter of a ball (not shown) housed in the ramp 22 ball. The depth of the cavity may also be a function of the distance that is desired between the toothed sector 14 and the pistons 15 and 16. A declivity of the cavity forming the ramp 22 makes it possible to guide the ball housed in this ramp 22. The depth of the cavity varies angularly. In a particular embodiment of the invention, as shown in FIG. 3b, the cavity of the ball ramp 22 has an angularly symmetrical profile with respect to a median line 23. Also, the path of a ball, since a center 24 of the ramp 22, to an end 26 of the same ramp 22 is exactly the same as the path of the ball from the center 24 to an opposite end 27. The cavity of the ramp 22 may have a slope discontinuity. The largest depth is then preferably located at the center 24 of the ball ramp 22. Thus, when the ball moves from the center 24 to an end 26 or 27 of the ball ramp 22, it comes out slightly of the ball. cavity.

  An orifice 28 may be provided in the center of the toothed sector 14. The orifice 28 may, for example, allow to introduce an axis (not shown in Figure 3). This axis 38 can make it possible to center the toothed sector 14 on the two pistons 16 and 17 (FIGS. 5 and 6).

  It is possible to provide that the wheel 29 of the gear train 19, in direct contact with the toothed sector 14, is provided with a clutch spring 30 (FIG. 3a). The spring 30 makes it possible to return the toothed sector 14 to the rest position, without the use of external energy, at the end of braking.

  Sector 14 does not have to be dented throughout its perimeter. Indeed, it suffices that it is toothed on a part of the perimeter in contact with the teeth of the wheel 29 (Figures 3a, 3b and 4).

  In FIG. 4, the pistons 15 and 16 are mounted on either side of the toothed sector 14. A first end of the pistons 15 and 16 bears respectively on the ends 6 and 7 of the segments 8 and 9. One of the two pistons, 15 or 16, is provided on a second end, or flank, of three ramps 22 identical to the ramps of the toothed sector 14. The side of the piston provided with these ball ramps is in contact with the side 21 of the toothed sector 14. It is also possible that the two pistons 15 and 16 are provided with a flank provided with ramps 22 balls. In this case, the toothed sector 14 is provided on its two sides with ramps 22 ball.

  In FIG. 4, it is also possible to see a recess 31 in an outer perimeter of the piston 15 and a similar recess 32 in an outer perimeter of the piston 16. These recesses 31 and 32 accommodate, for example, means (not shown) for locking in Pistons 15 and 16 rotate. Thus, when the toothed sector 14 is rotated through the gear train 19 driven by the motor 20, the pistons 15 and 16 can not rotate. By against the pistons 15 and 16 are mounted in translation in the housing 3.

  In Figure 5, is shown a longitudinal section of a housing 3, a brake cylinder, according to a particular embodiment of the invention. The toothed sector 14 is disposed between the piston 15 and the piston 16. A ball 33 is interposed between a flank 21 of the toothed sector 14 and a flank 34 of the piston 16. The ball 33 is housed in two recesses forming ball ramps 22, as described above, and formed respectively on the sidewall 21 and the sidewall 34. A single ball 33 is visible on the section of Figure 5. It is possible, however, that several balls 33 are interposed between the sidewall 21 and the sidewall 34.

  In the example shown in Figure 5, the piston 15 is not provided on a flank 35 of ball ramp. The piston 15 is provided, for example, at the location of the sidewall 35, with an abutment 36. The abutment 36 is supported on the one hand on the sidewall 35 of the piston 15 and on the other side on a sidewall 37 of the toothed sector 14.

  The axis 38, passing through the orifice 28 of the toothed sector 14, has an end 39 housed inside the piston 15 and an opposite end 40 housed inside the piston 16. The axis 38 makes it possible to center the toothed sector 14 on the pistons 15 and 16.

  During braking, a brake control (not shown) actuates the electric motor. The motor 20 rotates the gearing 19. The gear 19, and more precisely the wheel 29, in turn rotates the toothed sector 14. By rotating about the axis 38, the toothed sector 14 forces the ball 33 to change position in the ramp 22 ball. Thus, for example, the ball 33 moves from the center 24 (FIG. 3b) of the ball ramp 22 towards the end 26 of the same ramp 22. The end 26 being shallower than the center 24, the ball 33 goes back up. Piston side 16, the ball 33 remains in its initial position. Indeed, the piston 16 is locked in rotation. However, a rise of the ball 33 allows the displacement in translation of the piston 16, in a direction FI opposite to the toothed sector 14. By reaction, the piston 15, via the abutment 36 in contact with the toothed sector 14, is pushed in translation towards a direction F2, opposite to the toothed sector 14. Thus, the pistons 15 and 16 move away from each other, imposing on the segments (not shown in FIG. 5), in support respectively on the piston 15 and on the piston 16, a centrifugal movement. The lining, carried by the two segments, then come into contact with a drum mounted in the wheel. Friction of the linings on the drum causes the braking of the vehicle. When the braking is finished, the toothed sector 14 is returned to the rest position, for example by means of the clutch spring 29. The pistons 15 and 16 are for example brought back to the rest position by return springs 41. Although in the example described above, only one of the pistons has a side provided with at least one ball 22, it is possible to provide at least one ramp 22 on each of the pistons 15 and 16.

  In Figure 6, is shown a longitudinal section of a housing 3 of a brake cylinder according to another particular embodiment of the invention. The piston 15 and the piston 16 are provided, respectively on a sidewall 35 and on a sidewall 34, of at least one ball ramp accommodating a ball 33. Each ball 33 is thus housed, on the one hand, in a hollow space. a ball ramp formed on a flank 35 or 34, and secondly in a cavity of a ball ramp formed on a flank 37 or 21 of the toothed sector 14. When the toothed sector 14 is rotated, a ramp Ball placed on the toothed sector 14 moves accordingly. This displacement imposes a rise to the ball 33 in the cavity. The displacement of the ball causes the translational movement of the piston 15 or 16, with which it is in contact. Thus, the two pistons 15 and 16 are driven in translation in two opposite directions F2 and FI, directly by the displacement of a ball 33 in its ramp.

  In this embodiment, there is also shown a device 42 of play catching. This device 42 is at least partially integrated in a piston. In the example shown in Figure 5, a body 43 of screw 44 is housed in a piston body 15. A head 45 of the screw 44 spring outside the piston 15. The head 45 is in contact with one end a segment (not shown). The segment blocks the screw 44 in rotation. For example, one end 60 of the head 45 is provided with a notch. The end 7 of the segment 5 is housed in this notch, preventing rotation of the screw. The screw 44 is also maintained in a position by a toothed nut 46. The nut 46 is, for example, disposed in an extension of the piston 15.

  When the linings carried by the segments are worn out, a dead stroke settles between the linings and the drum. In this case, during braking, it is necessary that the toothed sector rotates further to bring the linings against the drum. It is therefore necessary that the displacement of the ball 33 in its housings (two ball ramps 22 facing each other) is greater, so that the pistons 15 and 16 have a translational movement respectively F2 and FI of greater amplitude. In this case, the translation movement F2 is such that a finger 47 of a click 48 passes at least one tooth of the toothed nut 46, driving the toothed nut in rotation. The screw 44 being locked in rotation by the segment 5, it moves in translation towards the outside of the piston 15. The finger 47 is for example a rigid rod, fixedly mounted on an outer wall of the housing 3. A length of the finger 47 is such that one end of the finger is in contact with the nut 46, housed in a tooth of said nut 46. The body 43 then exits slightly outside the piston 15. The length of the portion of the screw 44 located at the outside of the piston 15 increases. The finger 47 blocks the rotation in the opposite direction of the nut 46. Thus, the screw 44 is locked in this new position. The screw head 45 pushes and holds the segment 5 towards the drum 1 (FIG. 1). The game is caught up.

  It is possible to provide at least one ball ramp on only one of the two pistons, the second piston then being supported on the toothed sector by means of a stop. This piston can be indifferently the piston in which is housed the play catch device or the other piston.

  Since such a game-catching device is at least partially integrated in a piston contained in a casing of a brake cylinder, the space requirement resulting from the addition of this device is minimal. Indeed, it is not necessary to provide a particular and additional positioning for the play catch device.

  The drum brake control device of the invention can be associated with any force or torque measurement system in order to manage the braking level.

Claims (1)

12 CLAIMS   1-drum brake control device for a motor vehicle, said drum brake comprising at least one segment (4, 5, 50, 51), adapted to be applied against a drum integral in rotation with a wheel hub, characterized in that said device comprises - a brake cylinder provided with a housing (3), - at least one piston (15, 16) movable in translation in said housing and stationary in rotation, said piston being supported by a first end against the segment and comprising at a second end at least one ball ramp (22), - a displaceable element (14) rotating about an axis coaxial with the axis of said piston, said rotatable element being provided with at least one ball ramp (22) on a flank (21, 37) opposite the second end of said piston, at least one ball (33) housed in the piston ball ramp and in the ball ramp. the moving element.   2- Device according to claim 1, characterized in that the element 20 movable in rotation is a toothed sector (14) driven by a gear (19).   3- Device according to one of claims 1 to 2, characterized in that the element movable in rotation is provided on its two sides (21 and 37) of at least one ball ramp, the device being provided with two pistons (15 and 16), said pistons each being provided on their second end (34, 35) with at least one ball ramp, a side of the rotational element facing the second end provided with a ramp having ball of a first piston, another side of the element movable in rotation facing the second end provided with a ball ramp of a second piston.   4- Device according to one of claims 1 to 2, characterized in that the rotatable element is provided on one side of at least one ball ramp, the second end of a piston being provided with at least a ball ramp facing the flank of the rotatable member provided with at least one ball ramp, the second end of another piston being provided with a stop (36) facing a flank of the movable element in rotation 2869661 13 rotation without ball ramp.   5. Device according to one of claims 1 to 4, characterized in that a flank of the element movable in rotation and the second end of a piston are each provided with three ball ramps, three balls being interposed between the flank of the displaceable element and the second end of the piston 6- Device according to one of claims 2 to 5, characterized in that the gear is electrically actuated.   7- Device according to one of claims 1 to 6, characterized in that an axis (38) centers the element movable in rotation on the two pistons.   8- Device according to one of claims 1 to 7, characterized in that a spring (30) clutch returns the toothed sector in the rest position.   9- Device according to one of claims 1 to 8, characterized in that a return spring (41) brings a piston in the rest position.   10- Device according to one of claims 1 to 9, characterized in that the drum brake actuated by the brake cylinder is of the type segments (4, 5) floating.   11- Device according to claim 10, characterized in that it is provided with a device (42) for automatic play adjustment, mounted at least partially in a piston.   12- Device according to claim 11, characterized in that the clearance device clearance is provided with a screw system (44) nut (46), a body (43) of the screw being housed at least partially in the piston, a head (45) of screws in contact with a segment and the nut being outside the piston, said screw being locked in rotation but free in translation.   13- Device according to claim 12, characterized in that the nut is a toothed nut.   14- A drum brake with a brake control device according to one of claims 1 to 13.