Patent Application
20230373433
The invention relates to a belt retractor comprising a frame, a belt reel which is rotatably arranged in the frame and is adapted to receive a seat belt, at least one load limiter which enables the belt reel, when it overcomes a braking torque provided by the load limiter, to rotate relative to the frame so as to release seat belt, and a switchable clutch which has a switching cage and coupling elements, wherein the switching cage can be shifted, by means of an actor, from an open position in which the coupling elements are maintained disengaged from the belt reel into a closed position in which the coupling elements engage the belt reel.
A belt retractor of this type is known from DE 10 2017 111 398 A1. The switching cage is rotatably supported and has a radially projecting actuating pin. For being able to turn the switching cage from the open position to the closed position, there is provided a micro gas generator having a piston associated therewith which in turn engages the actuating pin.
When the switching cage is in the closed position and, accordingly, the load limiter is coupled to the belt reel, the switching cage is caught, when the belt reel rotates during a load limiting operation. Accordingly, also the actuating pin must be capable of rotating. For this purpose, the actuating pin and the micro gas generator are disposed so that the travel distance of the piston of the micro gas generator is a tangent to the trajectory of the actuating pin, and the actuating pin, while carrying out a complete revolution, immerses into a laterally disposed window of the micro gas generator.
It is the drawback of this design that a comparatively large axial space is required for the micro gas generator, the actuating pin and the switching cage.
Therefore, it is the object of the invention to improve the belt retractor so that an axially compact design is resulting.
In order to achieve this object, according to the invention, there are provided an actuator that is arranged to be operable with the actor and a freewheel that couples the switching cage to the actuator so that the actuator can shift the switching cage from the open position into the closed position. The invention is based on the fundamental idea to achieve the free rotatability of the switching cage required to operate the load limiter by a simple and axially flat freewheel.
The freewheel allows the torque required to close the clutch to be transmitted in a direction of rotation. At the same time, the switching cage can rotate in one direction freely relative to the actuator. Conversely, the actuator can remain stationary after activation of the clutch so that no space must be provided for allowing the actuator to rotate about 360°, when the belt reel rotates while the clutch is closed.
Since no space needs to be provided in the circumferential direction, the actuator provided according to the invention may be designed to be longer in the radial direction than the known actuating pin. When the actuator is longer as compared to the known actuating pin, i.e., it is located remote from the belt reel, the actor may overlap the clutch further axially, as compared to the known prior art, so that an axially more compact design is resulting. The construction according to the invention thus is suited to save axial space in two ways, namely, on the one hand, by the axially flat freewheel and, on the other hand, by the actor axially overlapping the freewheel. Moreover, a less powerful actor can be used or, if an actor of continuously equal power is used, quicker operation can be obtained, as a higher torque can be achieved by a longer actuator.
When the actuator is a flat plate, an axially particularly flat design is obtained.
For a mechanically simple and reliable belt retractor, the switching cage may include at least one freewheel pawl which interacts with a freewheel toothing provided on the actuator. The combination of the switchable clutch and the freewheel allows the freewheel to run freely only after triggering of the actor. For this reason, a simple freewheel design can be chosen. When the at least one freewheel pawl and the freewheel toothing are formed to be complementary, a surface tension in the contact area decreases to a uniform level so that, ultimately, a flat design of the freewheel is achieved.
When the actuator is configured to symmetrically introduce a torque to the freewheel, the switching cage is prevented from eccentrically deforming or displacing. For example, the actuator may have two, three or more transfer points which are arranged regularly or at equal angular intervals, respectively, in the circumferential direction.
When the switching cage includes a plurality of freewheel pawls arranged uniformly in the circumferential direction, an unbalance of the switching cage is suppressed. Thus, the switching cage can rotate smoothly even at high speeds and angular accelerations.
A switching cage which is easy to manufacture contains plastic material or is even made of plastic material, and the freewheel pawls are preferably formed integrally with the switching cage.
In order to be reliable even at extremely high angular accelerations, the freewheel toothing may be configured to be undercut. The undercutting may involve, for example, the fact that the tooth head angularly projects from or leads the corresponding tooth root in the transfer direction of the freewheel. The undercutting may include a cavity in the tooth flank, for example. Said examples of undercutting may be combined. An undercutting further offers the advantage of causing the retaining force to be self-reinforcing, i.e., the retaining force is the higher, the higher the torque transmitted. In other words, the pawl is caught.
When the actuator is an adjusting collar, the latter can guide and transfer, due to its closed shape, the torque to be transmitted in a particular stable manner. When the adjusting collar encompasses the switching cage, a radially inner support of the adjusting collar is dispensed with so that space is saved, resulting in an even flatter design. Moreover, the freewheel toothing may be an internal toothing which extends along an inner opening of the adjusting collar so that many tooth-and-pawl contacts cause a high torque to be transmittable.
When the number of the freewheel pawls is identical to the number of teeth of the freewheel toothing, the transmittable torque is maximally high, as all freewheel pawls are simultaneously supporting. As a result, the axial width of the freewheel can be reduced so that a flat design is resulting.
For the benefit of an axially preferably flat belt tensioner, the actuator may be supported between a housing of the actor and the switching cage. The actuator thus is radially supported so that it is positioned concentrically to the switching cage and, secondarily, to the belt reel. The housing of the actor may be configured and arranged to transfer a reaction force of the actor. For this purpose, the housing of the actor can be tightly connected to the frame, such as by a screwed connection. When the housing of the actor both absorbs the reaction force of the actor and supports the actuator, it ensures the action force of the actor to be transmitted to the actuator with high efficiency. By the actuator being supported by the housing of the actor, undesired radially migrating movement of the actuator during triggering of the actor can be prevented: Hence, the actuator introduces the torque uniformly to the freewheel. The housing of the actor may also act as housing of the load limiter to protect the latter from penetrating dirt, for example.
When the housing of the actor includes a flat indentation in which the actuator is disposed, no separate housing is required for the actuator so that, on the one hand, fewer parts are used and assembled and, on the other hand, the belt retractor has an axially flatter design. The flat indentation can axially support and, resp., guide the actuator during a feed motion.
Further advantages and features will be evident from the following description in combination with the attached drawings, wherein:
Based on
The belt retractor includes a frame 10. A belt reel 12 is rotatably supported in the frame 10. In the Figures, a seat belt 14 is partly wound onto the belt reel 12. By means of the seat belt 14, a vehicle occupant of the vehicle in which the belt retractor is installed can be belted so that he/she participates in strong decelerations of the vehicle.
As far as hereinafter directional indications such as axial, radial or circumferential direction will be used, in case of doubt they relate to the axis of rotation of the belt reel.
The belt retractor includes plural load limiters by which a braking torque can be generated against which the belt reel 12 can be rotated so that the seat belt 14 can be extended from the belt retractor. This operation helps limit the loads acting on the seat belt 14 and, thus, on the vehicle occupant, if particularly high decelerations act on the vehicle.
In this case, only one of the load limiters is relevant so that the others shall not be explained in detail. The load limiter relevant here includes a shaft washer 16 which can be coupled to the belt reel 12 for a load limiting operation and, when being caught by the belt reel, provides the braking torque by a mixture of friction and deformation work.
The shaft washer 16 is guided within a peripheral passage. The passage is guided in wave shape, on the one hand, by an axial end face of the frame 10 with projections attached thereto and, on the other hand, by a housing 18 flanged to the end face of the frame 10 with projections and/or recesses provided thereto. The shaft washer 16 is approximately annular, and it encompasses a clutch cage 20. The shaft washer 16 is tightly coupled to the clutch cage 20 in the circumferential direction. The clutch cage 20 is generally annular and radially inside has recesses 58 which are narrowed in one direction and in each of which a driver 60 and a retaining finger 62 of a switching cage 22 engage. Between the driver 60 and the retaining finger 62 a coupling element 24 is received in each recess 58. The coupling elements 24 are rollers in this case.
The clutch cage 20 is received on a clamping surface 13 or a clamping shoulder, respectively, which is connected to co-rotate with or is formed integrally with the belt reel 12.
The clutch cage 20, the switching cage 22 and the coupling elements 24 form a switchable clutch 26 by means of which the shaft washer 16 can be tightly coupled to the clamping shoulder 13 of the belt reel 12 in one direction of rotation. The switching cage 22 is shiftable between an open position and a closed position by a rotation Rk.
In the open position of the switching cage 22, the coupling elements 24 do not act on the clamping shoulder 13 of the belt reel 12 in a load transmitting manner, as they are retained by the drivers 60 and the retaining fingers 62 of the switching cage 22 in the wide portion of the recesses 58. Therefore, the belt reel 12 is freely rotatable inside the clutch cage 20 in the open position of the clutch 26.
In the closed position of the switching cage 22, the coupling elements 24 are shifted to the narrow portion of the recesses 58 so that they get jammed between an inclined outer wall of the corresponding recess 58 and the outer surface of the clamping shoulder 13. For this reason, in the closed position of the coupling 26 a high torque can be transmitted from the belt reel 12 to the clutch cage 20, viz. in the direction of rotation in which the belt reel 12 rotates clockwise in the
For activating the clutch 26, an actor 28 containing a micro gas generator 30 and a piston 32 in the shown embodiment is received in the housing 18. The housing 18 forms a cylinder 34 in which the piston 32 is movable. The switching cage 22 is shifted to the closed position by shifting the piston 32, under the effect of compression gas provided upon activation by the micro gas generator 30, from an initial position (see
The movement of the piston 32 is transmitted to the switching cage 22 by means of an actuator 38 and a freewheel 40 or a freewheel clutch, respectively, by which the switching cage 22 is carried in the direction toward the closed position of the clutch 26, but enables relative rotation in the opposite direction.
The actuator 38 is operatively connected to a main portion 36 of the switching cage 22 via the freewheel 40 so that an extension movement A of the piston 32 is translated to the shifting rotation Rk of the switching cage 22. When the piston 32 is in the standby position, the switching cage 22 is in the open position. When the piston 32 is in the extended position, the switching cage 22 is in the closed position.
In the embodiment shown in all Figures, the actuator 38 includes an annularly closed inner portion 42. Consequently, the actuator 38 is in the form of an adjusting collar or switching collar. The actuator 38 moreover has a cam 44 projecting purely radially from the inner portion 42. The actuator 38 in the present case is a flat plate. The actuator 38 preferably has the same thickness as the main portion 36 of the switching cage 22. Thus, the belt tensioner has an axially compact design. The cam 44 is axially guided in an indentation 46 of the housing 18. The indentation 46 is formed to have slitted portions and open portions.
The actuator 38 is maintained in an initial position shown in
A housing part 48 is flanged to the housing 18.
The cam 44 is provided with a convex bearing face 50 the curvature of which interacts with an end face 52 of the piston 32 during the extension movement A of the piston 32 and, resp., the corresponding rotation Rs of the actuator 38. Since the end face 52 of the piston 32 abuts on the contact surface 50, the actuator 38 is forcedly caught when the piston is shifted in the direction A. Thus, the end face 52 and the contact surface 50 form a contact coupling. The actor 28 is put in the axial plane of the flat actuator 38 which results in an axially compact design of the belt tensioner.
The freewheel 40 is formed by at least one freewheel pawl 54 and one freewheel toothing 56 which are operatively engaged in each other.
The at least one freewheel pawl 54 is formed on an outer circumferential surface of the main portion 36 of the switching cage 22. The main portion 36 is in the form of a flat plate here which annularly surrounds the clamping shoulder 13 of the belt reel 12. The driver 60 and the retaining fingers 62 protrude from the main portion 36. The main portion 36 is disposed axially next to the clutch cage 20 so that the drivers 60 of the switching cage 22 protrude into the recesses 58 of the clutch cage 20.
The freewheel pawls 54 are formed integrally with the switching cage 22 in this case. The switching cage 22 may be configured together with the freewheel pawls 54 as an injection-molded part. The material is selected to be a suitable plastic material which results, on the one hand, in the desired strength and, on the other hand, in the required elasticity of the freewheel pawls 54.
The freewheel toothing 56 extends along an inner opening of the inner portion 42 of the actuator 38. An as high transmittable torque as possible is achieved by a plurality of freewheel pawls 54 being provided on the switching cage 22 and an identical number of teeth of the freewheel toothing 56 being provided on the inner portion 42. Accordingly, the freewheel pawls 54 and the teeth of the freewheel toothing 56 are respectively arranged uniformly in the circumferential direction. As a precaution, it is noted that the outer circumferential surface of the main portion 36 may be a purely constructive variable.
The freewheel toothing 56 is undercut in the direction of transmission so that a one-sided grating is resulting, causing the freewheel pawls 54 to be caught. This increases the transmittable torque in a self-reinforcing manner. An angle at which the freewheel pawls 54 project from the circumferential surface of the main portion 36 of the switching cage, a length of the freewheel pawls 54 and—put simply—the diameters of the outer circumferential surface of the main portion 36 and the freewheel toothing 56 are adapted to each other such that the individual freewheel pawls 54 project in the direction of transmission, when unloaded, about tangentially from the outer circumferential surface of the main portion 36. This increases the thrust force transferable for each freewheel pawl 54 and, thus, the transmittable torque.
The sectional views of the
The
In the
In the
For the purpose of operational safety, the angle required to move the switching cage 22 during the rotation Rk to the position in which the clutch 26 is closed is preferably smaller than or equal to the angle about which the actuator 38 rotates during the rotation Rs, while the piston 32 extends from the standby position to the activated position.
It is evident from
In the state shown in the
In the state shown in the
In total, the
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 126 197.7 | Oct 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/077284 | 10/4/2021 | WO |
