Coupling for a belt tensioner

A controllable clutch (18) for a belt tensioner (16) comprises a drive member (32), a driven element (24) and a clutch pawl (40) that is movably supported on the input side (30) between a home position and an engaged position and in the engaged position couples the drive member (32) to the driven element (24), wherein the clutch pawl (40) is tension-loaded in the engaged position.

RELATED APPLICATIONS

This application corresponds to PCT/EP2012/004802, filed Nov. 20, 2012, which claims the benefit of German Application No. 10 2011 119 343.3, filed Nov. 25, 2011, the subject matter, of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The invention relates to a controllable clutch for a belt tensioner, especially a reversible belt tensioner.

Reversible belt tensioners include a drive adapted to be coupled to the retractor axle of a belt reel by means of a clutch. During regular operation of the belt retractor the belt reel is uncoupled from said drive so that retracting or unwinding of the webbing from the belt reel is possible. In the case of tensioning the clutch is coupled to the belt reel by activation of the drive so that the webbing is wound onto the belt reel and thus is retracted.

Usually the clutch comprises a driven member having a toothing and being adapted to be coupled to a drive member via plural pawls. The pawls usually are arranged so that they are forced into the toothing by the force acting from the drive member, after the connection between the drive member and the driven element has been established. The pawls are uniformly distributed over the periphery of the driven element so that uniform force transmission takes place between the drive and the retractor axle. This is necessary to prevent additional forces due to an off-center force application. It is a drawback of those clutches that a control ensuring simultaneous engagement of all pawls is required. When the pawls are not synchronized, it is possible that individual pawls cannot be engaged and thus non-uniform force transmission to the driven element takes place.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a controllable clutch for a belt tensioner that permits simple structure and more uniform force transmission between the drive and the retractor axle.

In accordance with the invention, a controllable clutch for a belt tensioner is provided comprising a drive member, a driven element and a clutch pawl which is movably supported in the drive member between a home position and an engaged position and in the engaged position couples the drive member to the driven element, wherein the clutch pawl is tension-loaded in the engaged position. The invention is based on the fundamental idea that the clutch pawl is not compression-loaded, as known in the state of the art, but is tension-loaded. The previously known clutch pawls can bear only punctually on the driven element due to the design based on compression load. The clutch pawl designed for tension load can encompass the driven element partly in the circumferential direction and thus offers a larger contact face for force transmission. Depending on the configuration of the clutch pawl, also an embodiment having merely one clutch pawl is possible, for example.

Of preference, on the drive member a bearing stud is provided on which the clutch pawl is pivoted. The bearing stud is arranged ahead of the engaging position between the driven element and the clutch pawl viewed in the direction of rotation of the drive member. For activation the clutch pawl is merely guided to the outer periphery of the driven element and is caught with the same upon rotation of the drive member. Thus simple swiveling and activation of the clutch without any additional control elements as well as simple transmission of the tensile force is possible.

Diametrically opposed to the bearing stud, a support element in the form of a stud or rivet, for example, is provided to which the free end of the clutch pawl is adjacent when the clutch pawl is provided in the engaged position. In this embodiment the clutch pawl in the engaged position encompasses the driven element in the circumferential direction over a maximum of half the periphery. In this way a connection between the clutch pawl and the driven element is possible at two approximately opposing locations so that the force application can be evenly distributed over the periphery of the driven element. In this case the support element serves for determining the position of the clutch pawl in the engaged position.

The bearing stud and/or the support element can be formed by a rivet of the housing, for example.

In order to enclose the driven element in the circumferential direction the clutch pawl extends arc-shaped starting from a bearing portion, a first clutch tooth being arranged on the side of the clutch pawl facing the driven element. Preferably the force is transmitted via at least one clutch tooth adapted to engage in a toothing on the driven element.

In order to facilitate uniform force transmission and to prevent additional moment loads due to non-uniform load transfer, at least a second clutch tooth can be provided at the clutch pawl. Ideally a third clutch tooth is provided further to the second clutch tooth.

In this embodiment, the angular distance between the second and the third clutch tooth, resp., and the bearing portion amounts to at least 120°, preferably more than 140°, especially approx. 180° related to a central axis of the clutch and an engaged condition of the clutch pawl. This minimizes an off-center loading of the driven element and thus reliably prevents additionally occurring moments.

Between the first and second clutch teeth a support surface may be provided to which the driven element is adjacent when the clutch pawl is in the engaged position. Through this support surface the clutch pawl is also adjacent to the driven element between the clutch teeth. In this way, on the one hand the position of the clutch pawl is determined independently of a support element in the engaged position. On the other hand, deformation of the bent clutch pawl is minimized with increasing tensile forces, as the clutch pawl is supported by the driven element.

Preferably, exactly one clutch pawl is provided which is capable of partly encompassing the driven element in the circumferential direction, wherein force application is possible via approximately opposing locations so that off-center force application is almost excluded. It is not required to arrange plural pawls for achieving uniform force application. Nor is any synchronization is required so that complicated control is not necessary, either.

The clutch may have a fixed housing within which the drive member is arranged so that the clutch forms an outwardly closed protected unit. In the housing a control element adapted to transfer the clutch pawl from the home position to the engaged position is preferably arranged. The drive member including the clutch pawl supported thereon is usually moved by the drive. The control element is coupled to the drive so that by the rotating drive member it causes the clutch pawl to swivel against the driven element. The clutch pawl can be rotated, for example, with the driven element and thus can be displaced against the control element so that the clutch pawl is forced against the driven element, for example, by a ramp provided at the control element. In this way the clutch pawl can be engaged without any additional moving parts or a control unit.

After a tensioning operation the belt tensioner usually is intended to be returned to the home position in which the clutch pawl is not coupled to the driven element so that regular operation of the belt retractor is possible. For this, a disengaging geometry which is adapted to reset the clutch pawl from the engaged position to the home position and thus uncouples the drive from the belt reel is preferably provided at the control element. The disengaging geometry is configured, for example, so that upon rotation of the control element in an opposite direction of rotation the clutch pawl is disengaged.

The control element can be, for instance, a ring that is friction-borne in the housing.

Such ring is not intended to co-rotate with the belt reel during regular operation of the belt retractor but is to be restrictedly rotatable with the latter upon activation of the belt tensioner. For this, the ring is preferably slotted and is biased by a compression spring in the housing. The compression spring urges the slot apart so that the ring is forced radially outwardly against the housing due to the larger diameter.

Preferably, a reset spring for biasing and de-rattling the control element in the direction of the home position is provided between the drive member and the control element. In this way disturbing noise is prevented and additionally inadvertent engagement of the control element by acceleration of the belt retractor is excluded.

DESCRIPTION OF EXEMPLARY EMBODIMENT

InFIG. 1a belt retractor10for a seat belt is illustrated. The belt retractor10comprises a housing12in which a belt reel14for a seat belt is arranged and on which a belt tensioner16is disposed. The belt reel14is pivoted in the housing12and can be coupled to the drive20of the belt tensioner16by a clutch18shown in detail inFIGS. 4 to 6and can be rotated in a winding direction A so as to wind up the seat belt on the belt reel14. For this purpose, a stub shaft22of the belt reel projects through the housing12. A toothing24is fixedly mounted on said stub shaft. In the embodiment illustrated here the toothing24at the same time forms the driven element of the clutch.

The drive20of the belt tensioner16includes a drive motor26having a motor gearwheel28coupled to a spur gear system30. Said spur gear system30is coupled to the belt reel14via the clutch18.

The input side of the clutch18is formed by a clutch support32connected to an input gearwheel34of the clutch in a rotationally fixed manner. The clutch support32is arranged inside a retaining ring36supported on a retaining element38which is arranged to be stationary on the belt tensioner so that the retaining ring is prevented from twisting. The center of said retaining ring36is located on an axis with the belt reel14and the stub shaft22, respectively. Within said retaining ring36the clutch support32is pivoted which in turn is permanently coupled to the spur gear system through the input gearwheel34. Hence the clutch support32is driven by the drive motor26.

As is especially evident fromFIGS. 4 to 6, on the clutch support32a clutch pawl40is provided through which a friction-type connection can be made between the clutch support32and the belt reel, as will be explained hereinafter. The drive motor26can rotate the belt reel14via the motor gearwheel28, the spur gear system30, the input gearwheel34, the clutch support32, the clutch pawl40and the drive toothing24(the driven element of the clutch) and thus retract webbing.

The clutch pawl40is pivoted to the clutch support30by a bearing stud42. As is visible especially inFIGS. 4 to 6, the clutch pawl40is arc-shaped starting from a bearing portion44bearing the clutch pawl40on the bearing stud42and extends in the circumferential direction around the drive toothing24of the belt reel. The clutch pawl40has a substantially semi-circular shape, wherein the center of the semi-circle in the engaged position of the clutch pawl—in which the clutch pawl40is coupled to the drive toothing24—is located on the central axis of the belt reel14. Diametrically opposed to the bearing stud42a stud-shaped support element46is provided to which the end of the arc-shaped clutch pawl40opposing the bearing portion44is adjacent or on which it is supported, resp., in the engaged position.

On the inside of the arc-shaped clutch pawl40a first clutch tooth48as well as second and third clutch teeth50,52are provided. When the clutch pawl40is moved around the bearing stud42from the home position shown inFIGS. 4 and 5into the engaged position shown inFIG. 6, the clutch pawl40engages in the drive toothing24with the clutch teeth48,50,52. When the clutch support32is moved in the retracting direction A, a friction-type connection to the drive toothing24is established in this way and the belt reel14is rotated in the retracting direction A by the drive20. The clutch pawl40is tension-loaded with force being transmitted by all of the clutch teeth48,50,52.

In addition to the support on the support element46, the clutch pawl40includes a support surface72by which the clutch pawl40is adjacent to the drive toothing in the engaged position between the first clutch tooth48and the second clutch tooth50at the inner arc side. Thus the position of the clutch pawl40in the engaged condition is fixed. Moreover, deformation due to the occurring tensile forces is reliably prevented as the clutch pawl40is supported by the drive toothing24.

For control of the clutch pawl between the engaged position and the home position a control element54is provided inside the retaining ring36.

The control element54includes a ring56arranged inside the retaining ring36. The ring56has a gap58in which a compression spring60urging the ring56apart is provided. The ring56is thus friction-forced radially outwardly against the inside of the retaining ring36. For controlling the clutch pawl40an engaging geometry62and a disengaging geometry64are provided at the ring56. The engaging geometry62includes a ramp66. The disengaging geometry64forms a guide in which a link68provided at the clutch pawl is guided.

A tensile spring70for biasing the control element in the direction of the home position is disposed between the ring56of the control element54and the clutch support32.

For activating the belt tensioner the drive20is activated so that the input side of the clutch, i.e. the clutch support32, is rotated with the input gearwheel34in a retracting direction A. The clutch pawl40supported on the clutch support32is equally moved in the retracting direction A and is thus displaced against the control element54and the engaging geometry62. The clutch pawl40is swiveled against the drive toothing24by the ramp66of the engaging geometry62. Thus the clutch teeth48,50,52engage in the drive toothing24, thereby the drive element of the clutch formed by the drive toothing24being coupled to the clutch support32and the input side of the clutch, respectively. As is especially evident fromFIG. 6, by further rotation of the clutch support32the drive toothing24is equally rotated in the retracting direction A, whereby a seat belt is wound onto the belt reel14. The clutch pawl40is tension-loaded with the force being applied to the drive toothing24evenly distributed over all teeth48,50,52.

Since the clutch pawl40is tension-loaded in this case, it can be designed to be substantially longer than the usually employed compression-loaded clutch pawls so that the clutch pawl40can act on the drive toothing24by plural clutch teeth48,50,52. The clutch teeth48,50,52are distributed so that the force is applied evenly over the periphery of the drive toothing so that despite only one clutch pawl additional loads can be prevented from acting on the drive toothing24by off-center load transfer. Preferably, the angle between the first clutch tooth48and the second clutch tooth50in a double-toothed configuration or between the first and the third clutch tooth52in a triple-toothed configuration amounts to at least 120°. Said angle may also amount to approx. 180° so that the first clutch tooth48and the second clutch tooth50or the third clutch tooth52, resp., act approximately diametrically opposed on the drive toothing24.

The connection between the drive20or the clutch support32and the drive toothing24can be released by rotating the drive member30against the retracting direction A. Then the disengaging geometry64acts on the link68of the clutch pawl40, wherein the clutch pawl40is swiveled radially outwardly and is disconnected from the drive toothing24.