FR2895777A1 - Brake cable driving device for electric parking brake controlling device of motor vehicle, has guiding path with grooves for guiding finger of screw between stop sections under effect of displacement of nut along screw - Google Patents

Abstract

The device (1) has a screw (2) driven in two rotation directions by an output shaft, and a nut (4) driving in translation a brake cable and cooperating with the screw. A fixed cylindrical case (6) surrounds the screw and comprises a guiding path (10), which guides a radial finger (7) of the screw. The path has two stop sections (12, 14) and grooves (16, 18) for guiding the finger between the sections under the effect of displacement of the nut along the screw.

Description

1

  The invention generally relates to motion transmission devices, in particular for controlling an electric parking brake of a motor vehicle. More specifically, the invention relates, according to a first aspect, to a drive device capable of converting a rotational movement of a driving member into a translational movement of a driven member, this device being of the type comprising: a screw capable of to be driven in two opposite directions of rotation by the driving member, - a nut capable of driving in translation the member driven longitudinally along the screw, the nut cooperating with the screw and having at least one pointing finger opposite the screw, - a fixed housing at least partially surrounding the screw and comprising at least one guideway of the finger, the track having first and second beaches, and a first passage adapted to guide the finger between the first and second ranges under the effect of the displacement of the nut along the screw. The document EP-BO 802 098 describes a drive device of this type, the passage of which is a slot which comprises, from the first range, a longitudinal portion and then a portion curving from a first side of the portion. longitudinal. The operation of this training device is as follows. In the initial state, the nut occupies a position along the screw such that the finger occupies the first range. Then, the screw is rotated towards the first side. The threads of the screw and the nut are chosen so that the nut moves along the screw in a direction such that the finger is driven along the passage to the second range. Along the longitudinal portion of the pas-sage, the finger is locked in rotation around the screw by the edges of the passage. The nut then undergoes a pure translational movement, and moves rapidly along the screw, exerting a slight force on the driven member. On the contrary, along the curved portion of the passage, the finger is guided in rotation of the first side by the passage. The nut then undergoes both a movement 2

  rotation of the first side and translation along the screw. The relative speed of rotation between the nut and the screw is lower along the curved portion than along the longitudinal portion, because the nut and the screw both turn on the first side. As a result, the nut only moves slowly along the screw and exerts a high force on the driven member. The device thus makes it possible to obtain a variable gear ratio between the driving member and the follower member, since the screw, rotating at a constant speed, drives the follower member in translation more or less quickly depending on the shape of the step. -sage traveled by the finger.

  In this context, the invention aims to increase the field of application of the drive devices of the type described above, making them more flexible. To this end, the invention relates to a drive device of the aforementioned type, characterized in that the guideway comprises at least one sewn passage adapted to guide the finger between the first and second ranges under the effect of the moving the nut along the screw. The device may also include one or more of the following characteristics, considered individually or in any technically possible combination: each of the passages comprises at least one left portion wrapping around the screw; each of the passages comprises at least one portion of longitudinal orientation extending along the axis of the screw; the portion of longitudinal orientation and the left portion succeed each other along the first passage in the opposite order of the second passage; the longitudinal orientation portions of the first and second passages are of different longitudinal lengths; at least one of the passages comprises at least one circular portion extending substantially in an arc around the screw; - At least one of the passages comprises at least a heli-coidal portion winding substantially helically around the screw; the two passages form a closed loop; 3

  - The device comprises at intersections between the two passages of the orientation means disposed on one of the passages, these means allowing the movement of the finger in one direction along said passage and prohibiting the movement of the finger in the opposite direction; - The guideway comprises at least a third passage adapted to guide the finger between the first and second beaches under the effect of displacement-ment of the nut along the screw; and the housing comprises several tracks distributed around the screw, the nut comprising several fingers guided in the tracks.

  According to a second aspect, the invention relates to a device for controlling an electric parking brake for a motor vehicle, this device comprising an electric motor, a brake cable and a device for driving the brake cable by the electric motor. as described above.

  Other features and advantages of the invention will emerge from the description given below, by way of non-limiting example, with reference to the appended figures, among which: - Figure 1 is a schematic elevational view of a first embodiment of a drive device according to the invention, the housing surrounding the screw being shown in plan, in a developed manner; FIG. 2A is a graphical representation of the law characterizing the behavior of an electric parking brake control device for a motor vehicle equipped with the driving device of FIG. 1, the curve representing the force F exerted on the cable. brake depending on the displacement d of the drive nut of this cable; FIG. 2B is a graphical representation of the force F exerted on the brake cable by the device of FIG. 1 as a function of time t, during a brake engagement phase during which the finger starts from the first track and follows the first pass (period A), and during a disengagement phase of the brake during which the finger returns to the first range by the first pass (period R); 4

  FIG. 2C is a representation similar to that of FIG. 2B, the finger following the first passage during the engagement phase (period A) and returning to the first range by the second passage (period R) during the disengagement phase ; and FIG. 3 is a view similar to that of FIG. 1, for a second embodiment of the drive device of the invention. The drive device 1 shown in Figure 1 is intended to be integrated in an electric parking brake control device for a motor vehicle.

  This control device typically comprises an electric motor (not shown), and a brake cable (not shown), the driving device 1 ensuring the conversion of the rotational movement of the output shaft of the electric motor into a translation movement of the brake cable. The drive device 1 comprises: - a longitudinal screw 2 which can be rotated by the electric motor; - a nut 4 capable of driving the brake cable longitudinally along the screw 2, the nut 4 being mounted freely around the screw 2, the threads of the screw and the nut being in engagement, - a cylindrical fixed housing 6 surrounding the screw 2. The housing 6 is shown in an expanded manner in FIG. The screw 2 can be driven in the two opposite directions of rotation by the electric motor, depending on whether one seeks to engage or disengage the parking brake.

  An end (not shown) of the brake cable is connected to the nut 4 by a device (not shown) so that the axial displacement of the nut is transmitted to said cable. Furthermore, the nut 4 comprises a radial finger pointing 7 opposite the screw 2, comprising at its free end a rotary roller 8. The screw 2 extends along the central axis of the cylindrical housing 6. This housing 6 comprises a channel 10 for guiding the finger 7 in which the roller 8 is engaged.

  The channel 10 is a slot in the housing 6 and comprises first and second stop areas 12 and 14 of the finger, and first and second separate passages 16 and 18, each adapted to guide the finger 7 between the first and second tracks 12 and 14 under the effect of the displacement of the nut 4 along the screw 2. The finger 7 occupies the first range 12 when the parking brake-ment is at rest. It occupies the second range 14 when the parking brake is engaged. The first passage 16 comprises a rectilinear longitudinal portion -10 blade extending from the range 12 to a range 20. The rectilinear portion 19 extends along the axis of the screw 2. It also comprises a left portion 21 wrapping around the screw 2 and extending the longitudinal portion 19. The left portion 21 extends from the beach 20 to a beach 22. The left portion 21 has the shape of a portion of a propeller 15 the central axis is constituted by the screw 2, and whose pitch varies continuously. In the expanded view of Figure 1, the left portion 21 has a circular arc shape. The first groove 16 also comprises a circular portion 23 extending substantially in an arc around the screw 2, from the range 22 to the second stop zone 14. This circular portion 23 is represented as a rectilinear segment perpendicular to the screw 2 in the developed view of FIG. 1. The second passage 18 comprises, from the second stopping area 14, a left portion 25 extending to a range 26. This portion 25 left 25, in the expanded representation of Figure 1, has a concavity turned on the same side as the left portion 21 of the first step-wise. The passage 18 then comprises a rectilinear longitudinal portion 27 extending from the beach 26 to a beach 28. This rectilinear portion 27 is substantially of the same longitudinal length as the rectilinear portion 19 of the first passage. The second passage 18 then comprises another left portion 29 extending from the position 28 to the range 30. In the developed view of FIG. 1, this other left portion 29 has a concavity turned away from the left portion 21 of the first pass.

  Finally, the passage 18 has an arcuate portion 31 extending around the screw 2 from the range 30 to the first stopping area 12. The left portions 25 and 29 have similar shapes in space to that of the left portion 21.

  The stop zones 12 and 14 constitute points of intersection between the two passages 16 and 18. In order to direct the movement of the finger from these stop zones 12 and 14, the driving device comprises ratchets anti-return swivels 32 and 34. Each of the pawls 32 and 34 comprises a hook-shaped guide piece 36 pivotally mounted on the housing 6 about a pivot 38 substantially perpendicular to this housing, and a compression spring 40 biasing the guide member 36 against a stop 37. The stop defines a rest position of the guide piece 36. In its rest position, the pawl guide piece 32 is located at a range 24 of the passage 16 intermediate between the range 22 and the second stop range 14. The guide piece 36 has a cam surface 41 facing the beach 22 and allowing the erasure of this piece under the action of the finger 7 flowing in the passage 16 from beach 22 to l A second stop range 14. The movement of the finger 7 in the opposite direction, from the second range 14 to the range 22, is prohibited by the guide piece 36 coming against the abutment 37. The piece 36 has a face 42 concave facing the stop range 14, adapted to guide the finger 7, from the beach 14, along the left portion 25 of the second passage to the straight portion 27 of this passage.

  The pawl 34 has the same structure as the pawl 32. It is disposed in the second passage 18. It allows the movement of the finger 7 since 7

  the range 30 to the first stop range 12, but prohibits the movement of the finger 7 in the opposite direction from the range 12 to the range 30. We will now describe in detail the operation of the drive device 1 described herein. -above. In the initial state, it is considered that the parking brake is disengaged, the finger 7 thus occupying the first stopping area 12. To engage the parking brake, the electric motor drags the screw 2 in rotation in the direction of the arrow F of Figure 1. The respective threads of the screw 2 and the nut 4 are such that the nut 4 is driven in translation to the left of Figure 1. The ratchet 34 does not allow the finger 7 to engage in the second passage 18, so that it necessarily engages in the first passage 16, and follows the rectilinear portion 19 thereof, to the beach 20. Beyond the beach 20, the finger 7 engages in the left portion 21 of the passage 16, which wraps around the screw 2 from the track 20 in a direction corresponding to the direction of rotation of the screw 2 (symbolized by the arrow F in Figure 1). In the left portion, the nut 4 will undergo both a translational movement along the screw 2 to the left of Figure 1 and a rotational movement in the direction of the arrow F relative to the housing 6. From As a result of this rotational movement of the nut 4 relative to the housing 6, the speed of rotation of the nut relative to the screw 2 is lower than in the straight portion 19 of the passage 16. For the same speed of rotation of the screw 2, the longitudinal displacement speed of the nut 4 will be lower along the left portion 21 that along the longitudinal portion 19 of the passage 16. In contrast, the force exerted by the nut 4 on the pulling cable will be larger along the left portion 21 than along the longitudinal portion 19 of the passage 16. Once the finger 7 reaches the range 22, the nut 4 undergoes a pure rotational movement around of the screw 2, and no longer moves longitudinally along the screw 2. It passes thus from the range 22 to the stopping area 14. By the way, it moves the guide piece 36 from its stop 37 against 8

  the restoring force of the spring 40. Once the finger 7 has passed, the spring 40 places the piece 36 against this stop 37. Once the finger 7 has reached the stop zone 14, it can no longer be used. move in longitudinal translation to the left nor in rotation around the screw 2 in the direction of the arrow F. The electric motor driving the screw 2 is then stopped. In this state of the driving device, the parking brake is engaged. To disengage the parking brake, the electric motor drives the screw 2 in rotation in the opposite direction to the arrow F in FIG. 1. The finger 7 then leaves the stop zone 14 and follows the left portion 25 of the passage 18 to the position 26. The pawl 32 does not allow it to engage in the pas-sage 16, so that it necessarily follows the left portion 25. Along this left portion, the nut 4 undergoes both a rotation in the downward direction of the arrow F, and a translation to the right of Figure 1. Then, the finger 7 follows the straight portion 27 of the passage 18, from the beach 26 to the beach 28. The nut 4 then undergoes a displacement in pure translation along the screw 2, to the right of Figure 1. The finger 7 then approaches the other left portion 29 of the passage 18, from the beach 28 to 30. The nut 4 then undergoes both a rotation in the opposite direction of the arrow F and a translation to the right of the 1 along the screw 2. Finally, the finger 7 moves in the arcuate portion 31 of the passage 18, from the range 30 to the stop range 12. The nut 4 then undergoes a movement of pure rotation in the opposite direction of the arrow F. The finger 7, passing from the range 30 to the stopping area 12, moves the guide piece 36 of the pawl 34 of its abutment against the restoring force 40. Once the finger 7 in the stop position 12, the spring 40 repositions the piece 36 against its stop. For the reasons indicated above, the nut 4 moves longitudinally slowly in the left portions 25 and 29 of the passage 18, and more rapidly in the longitudinal rectilinear portion 27 of this pas-sage 18. Conversely, the nut 4 exerts a significant force on the brake cable in the left portions 25 and 29 of the passage 18 and a lower force in the straight portion 27. Figures 2A to 2C highlight one of the advantages of the invention.

  FIG. 2A is a graphical representation of the law giving the force exerted on the cable as a function of the displacement of the cable, that is to say of the displacement of the nut 4 along the screw 2. This graph clearly shows during the tightening phase, the force initially increases slowly as a function of the displacement of the nut. Then, in a second phase, the effort increases rapidly depending on the displacement of the nut. The shape of the passage 16 is therefore well adapted to obtain such a law for the reasons explained above. The evolution over time of the force exerted on the brake cable is illustrated in FIG. 2B, in the case where the finger moves, during the period of engagement of the brake, from the range 12 to the range 22 by the first step-wise 16 and then, during the period R disengagement of the brake, from the range 22 to the range 12 in the opposite direction in the first passage 16. The brake receivers (that is, say disc or drum brakes) can be likened to springs, capable of storing energy. This is why the disengagement (period R) is a little faster than the commitment (period A). In the engagement phase, it is necessary to provide energy to compress these springs. In the disengagement phase, these springs restore this energy. As an indication, we can consider that the disengagement is 10% faster than the commitment. For example, if t1 is the engagement time needed to go from 10% to 100% of the maximum clamping force, and t2 the disengagement time required to go from 100% to 10% of the maximum clamping force then t2 is about 90% of t1. FIG. 2C illustrates the evolution over time of the force exerted on the brake cable, when the finger moves, during the period of engagement of the brake, from the range 12 to the range 14 by the first passage 16 , then during the period R disengagement of the brake, from the range 14 to the range 12 by the second passage 18. The time t3 required to go from 100% of the maximum clamping force to 10% is considerably shorter only in the case of FIG. 2B. It can be considered that t3 is about 50% of t1. A second embodiment of the invention is illustrated in FIG. 3. Only the elements which differ from the embodiment of FIG. 1 will be described below. The elements common to the embodiments or playing the same role, have the same references. The portion 49 of the first passage 16 extending between the track 22 and the stop zone 14 does not extend in an arc around the screw 2 but has the shape of a constant pitch helix. Wrapping around the screw 2. In the developed view of the housing shown in FIG. 3, this helicoidal portion 49 extends in a direction slightly inclined with respect to the perpendicular to the screw 2. In addition, the track guide 10 comprises a third passage 50 adapted to guide the finger 7 between the first and second stop zones 12 and 14. This third passage 50 comprises a left portion 51 extending between the tracks 52 and 54, a rectilinear longitudinal portion 55 between the beach 54 and a beach 56, and another left portion 57 extending from the beach 56 to a beach 58. The left portion 51 has, in the developed view of Figure 3, a concavity turned on the same side as the left portion 21 of the passage 16. The left portion 51 joins the helical portion 49 of the passage 16 to the range 52, substantially in the center of the helical portion 49. The portion of the passage 16 extending between the range 52 and the stop position 14 is therefore common at the first passage 16 and the third passage 50. The left portion 57 has a concavity turned on an op-posed side to the left portion 51, and joins the arcuate portion 31 of step 18 to the beach 58, substantially at the center of the arcuate portion 31. The portion of the arcuate portion 31 extending from the beach 58 11

  up to the stop position 12 is therefore common to both the second passage 18 and the third passage 50. The device further comprises three additional pawls 60, 62 and 64. These pawls are of the type described above. The pawl 60 is disposed in the helicoidal portion 49 of the groove 16, between the track 52 and the track 22. It allows the finger 7 to move from the beach 22 to the beach 52 along the helical portion 49, but forbids the movement of the finger in the opposite direction. Its concave face 42 directs the finger from the beach 52 towards the beach 51 when it moves along the third passage 50 towards the beach 12. The pawl 62 is disposed in the second passageway 18, between the beach 30 and the beach 58. It allows the movement of the finger 7 from the beach 30 to the beach 58 and banned in the opposite direction. Its concave face 42 guides the finger flowing in the third passage 50 of the track 56 to the track 58.

  The third pawl 64 is disposed in the third passage 50, at the level of the beach 56. It allows the movement of the finger from the beach 30 to the beach 58 but prohibits this circulation in the opposite direction. It has a plane face 66 opposite to the axis 38, which closes the third passage 50 at the level of the range 56 in the rest position of the orientation piece 36.

  The operation of the driving device shown in Figure 3 is as follows. To engage the parking brake, the screw 2 is rotated by the electric motor according to the arrow F of Figure 3, as in the first embodiment of the invention. The finger travels the first passage 16, while the nut 4 moves longitudinally to the left of Figure 3. It should be noted that in the helical portion 49 of the first passage, the nut 4 moves at a time. rotating in the direction of the arrow F around the screw 2 and longitudinally to the left along the screw 2. The longitudinal speed of displacement of the nut 4 is very slow, and the force exerted by the nut 4 on the brake cable is very high.

  If the direction of rotation of the screw 2 is reversed before the finger 7 has passed the pawl 60, the nut 4 moves longitudinally to the right of the 12

  3 along the screw 2, while the finger 7 traverses the first passage 16 in the opposite direction until it returns to the stop range 12. If the direction of rotation of the screw 2 is reversed while the finger has already crossed the pawl 60 but has not yet crossed the pawl 32, the nut again is driven in translation along the screw 2 to the right of Figure 3, and the finger 7 returns to the stopping range 12 at the third passage 50. At the beach 58, the pawl 62 prevents him from taking the second passage 18. If the direction of rotation of the screw 2 is reversed only after the finger 7 has reached the stopping range 14, this finger returns from the range 14 to the beach 12 by passing the second passage 18, as explained in relation to the first embodiment of the invention. This second embodiment therefore makes it possible to have three possible passages to bring the finger from the stop range 14 to the stop range 12. These three passages correspond to three characteristic curves force exerted on the cable vs displacement of the nut, different from each other. The training device described above has many advantages. It allows to choose the temporal evolution of the force on the cable for the disengagement of the parking brake, independently of the law for the engagement of the parking brake. The law for disengagement can be chosen freely, depending on the form conferred on passages 18 and 50. The law for disengagement may be similar to the law for commitment, or be different. This free choice of the law for the disengagement makes it easier to adapt the training device to the specifications of the motor vehicle manufacturers concerning the engagement and the disengagement of the parking brakes, and thus makes it possible to extend the field of application of the driving device. Moreover, it is also possible to vary the temporal evolution of the force exerted on the cable along the engagement or disengagement path by choosing the drawing of the first passage 16 connecting the first and second ranges of stop.

  The guiding track may comprise two, three or even more than three passages making it possible to return the finger of the nut 4 of the stop zone 14 towards the stopping area 12. Moreover, the frame 6 may comprise several identical tracks arranged around the screw 2, the nut 4 having the same number of fingers 7, each associated with a roller 8 engaged in one of the channels 10. The housing 6 can carry for example two lanes 10 arranged at 180 l ' one of the other around the screw 2, or three lanes 10 arranged at 120, or even more than three lanes. The finger 7 may not carry a roller 8 and be directly guided in the lane 10.

Claims (12)

  1. Drive device (1) adapted to convert a rotational movement of a driving member into a translational movement of a me-born body, this device comprising - a screw (2) capable of being driven in two opposite direction of rotation by the driving member, - a nut (4) capable of driving in translation the member driven longitudinally along the screw (2), the nut (4) cooperating with the screw (2) and comprising at least one finger (7) pointing away from the screw (2), a fixed housing (6) at least partially surrounding the screw (2) and comprising at least one guide channel (10) finger (7), the track (10) having first and second lands (12, 14), and a first passage (16) adapted to guide the finger between the first and second lands (12, 14) under the influence of moving the nut (4) along the screw (2), characterized in that the guideway (10) comprises at least a second passage (18) capable of guiding the finger between the first and second e and second ranges (12, 14) under the effect of the displacement of the nut (4) along the screw (2).   2. Drive device according to claim 1, characterized in that each of the passages (16, 18) comprises at least a left portion 20 (21, 25, 29) wrapping around the screw (2).   3. Drive device according to claim 2, characterized in that each of the passages (16, 18) comprises at least a longitudinally oriented portion (19, 27) extending along the axis of the screw (2). .   4. Drive device according to claim 3, characterized in that the longitudinal orientation portion and the left portion succeed each other along the first passage (16) in reverse order of the second passage (18).   5. Drive device according to claim 3 or 4, characterized in that the longitudinal orientation portions (19, 27) of the first and second passages (16, 18) are of different longitudinal lengths. 30   6. Drive device according to any one of claims 1 to 5, characterized in that at least one of the passages (16, 18) comprises at least one circular portion (23, 31) extending substantially in arc around the screw (2).   7. Drive device according to any one of claims 1 to 6, characterized in that at least one of the passages (16, 18) comprises at least one helical portion (49) winding substantially helically turn around of the screw (2).   8. Drive device according to any one of claims 1 to 7, characterized in that the two passages (16, 18) form a closed loop.   9. Drive device according to any one of claims 1 to 8, characterized in that it comprises at intersections between the two passages (16, 18) orientation means (32, 34) arranged on one of the not-wise (16, 18), these means (32, 34) allowing the movement of the finger (7) in one direction along said passage (16, 18) and prohibiting the movement of the finger (7) in the opposite direction.   10. Drive device according to any one of the preceding claims, characterized in that the guide path (10) comprises at least a third passage (50) adapted to guide the finger (7) between the first and second ranges ( 12, 14) due to the displacement of the nut (4) along the screw (2).   11. Drive device according to any one of the preceding claims, characterized in that the housing (6) comprises a plurality of channels (10) distributed around the screw (2), the nut (4) comprising several fingers guided in the lanes (10).   12. Device for controlling an electric parking brake for a motor vehicle, this device comprising an electric motor, a brake cable and a drive device (1) for the brake cable by the electric motor according to any one of the preceding claims.