Abstract:
A shiftable clamping-type locking mechanism, includes two track-defining elements and a plurality of clamping members, e.g. rollers or balls, arranged between the tracks of the elements and so spring-biased as to seek a clamped position. The clamping members are shiftable by a control unit from the clamped position into a release position in which the clamping members are liberated from the tracks so that the two elements can be freely moved relative to one another. A coupling unit positively connects the two elements to one another in order to prevent an undesired slip between the elements.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application Serial No. 198 03 448.2, filed Jan. 30, 1998, the subject matter of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a shiftable clamping-type locking mechanism, and in particular to a locking mechanism used in gearboxes for adjusting a seat position of a car seat. 
     In general, clamping-type locking mechanism of this type are used to secure the position between two elements. When releasing a locking mechanism, both elements can be moved in directions that have been previously locked. The locking mechanism is provided with tracks between which clamping members are positioned and so spring-loaded against these tracks as to seek a clamped position. The tracks may, for example, be formed on opposing outer cylindrical surface areas of both elements. It is also conceivable to design the tracks along confronting sides of longitudinally displaceable elements. Locking mechanisms of this type may be installed, for example, in gearboxes in which a shaft should be securely fixed in both directions of rotation. Such gearboxes are used, for example in seat adjustments of motor vehicles or in mechanisms for raising and lowering windows in motor vehicles. 
     International patent publication WO 96/20352 discloses a clamping-type locking mechanism for adjusting the seat position of a seat. The locking mechanism includes two elements nested within its other, with the outer element forming a cylindrical track about its inner surface area, and with the inner element being provided with several circumferentially spaced ramps extending about the outer surface area in opposition to the cylindrical track and inclined in opposite directions. Each ramp forms with the cylindrical track a wedge-shaped clamping gap in which a clamping roller is positioned under spring tension. As the imaginary peaks of the wedge-shaped clamping gap either face one another or, as in this case, face away from one another, the clamping rollers positioned under spring tension in the clamping gap prevent a rotation of the inner element relative to the outer element in both directions of rotation. When the clamping rollers are released and thus in cleared position, only those clamping rollers are actually freed which are functionally relevant for this direction of rotation. The clamping rollers are arranged in pockets of a cage at clearance in circumferential directions, whereby the cage can be slightly pivoted relative to the inner element. This pivot path is utilized for releasing the clamping rollers from their pertaining clamping gaps. A torque acts on the inner element and is effected by a force impacting on the seat. In the clamping situation, these types of locking mechanisms retain the seat at a set level. 
     These types of locking mechanisms are however subject not only to static torque in their clamped position but also to oscillating, dynamic loads with changing torque. In such a changing load, the clamping force, which is transmitted from the inner element via the clamped rollers into the outer element, is initially reduced in the conventional locking mechanism, until the changing load reaches a value at least approximating zero. Although in this stage, the clamping rollers are still resiliently received in their clamping gap by means of the provided springs; However, relative movements between the inner element and the outer element are possible because of the reduced clamping action as a result of the changing load. Thus, an undesired slip may be caused. In case of a seat adjustment, such relative movements result in an unintended change of the seat level. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the present invention to provide an improved clamping-type locking mechanism, obviating the afore-stated drawbacks. 
     In particular, it is an object of the present invention to provide an improved clamping-type locking mechanism, in which a slip between clamped elements is positively eliminated. 
     These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a plurality of clamping members, e.g. rollers or balls, arranged between confronting tracks of two elements and so spring-biased as to seek a clamped position, a control unit which acts on the two elements for moving the clamping members from the clamped position into a release position in which the clamping members are liberated from the tracks so that the elements are freely movable relative to one another; and a coupling unit for detachably connecting both elements in a form-fitting manner. 
     Through the provision of an additional coupling unit, the locking mechanism according to the present invention can be operated without experiencing an undesired slip between both elements. The coupling unit can be dimensioned for small loads as the loads are predominantly transmitted via the locking mechanism. Only in circumstances when dynamic or changing loads reach or pass the value zero is the coupling unit subject to these small dynamic loads, preferably at zero crossing. The form-fitting engagement of both elements to one another is then able to positively eliminate undesired slip between the two elements. 
     The coupling unit is preferably disengaged when the clamping members occupy their release position and thus are liberated from the tracks. An adjustment of both elements relative to one another is then possible in a manner known per se. The coupling unit is engaged when the clamping members occupy their clamped position and thus are in engagement with the tracks. 
     According to another feature of the present invention, an actuating device is provided for operating the control unit and the coupling unit. In a neutral position of the actuating device, the clamping members are arranged in their clamped position, with the coupling unit being engaged. An actuating device of this type can be designed in many ways to initially engage the coupling unit and to subsequently liberate the clamping members to occupy their release position, when operating the actuating device in an actuating direction. 
     Advantageously, the coupling unit can be realized in a particularly simple manner by providing the one element with a first tooth profile and the other element with a second tooth profile, with both tooth profiles being displaceable relative to one another for effecting a tooth engagement. Suitably, the first element includes a shaft and a gear which represents the tooth profile of the first element and is so secured on the shaft that the gear is prevented from executing a rotation relative to the shaft but is able to move in axial direction relative to the shaft. The other element is then provided with the second tooth profile, with the shaft being rotatably mounted with respect to the other element. The coupling unit is engaged when the gear is so axially displaced as to mesh with the second tooth profile. When the gear is axially shifted along the shaft and dissociated from the second tooth profile, the coupling unit is disengaged. 
     Preferably, the coupling unit is operated by an actuating mechanism which includes a rotatably mounted actuator, whereby an indexing mechanism is positioned between the actuator and the gear for converting a rotational movement of the actuator into an axial movement of the gear for engaging and disengaging the coupling unit. The conversion of the rotational movement into an axial movement may be realized by providing the actuator with a cam surface for support of the gear, with the cam surface including at least one ramp and a support area following the ramp, whereby the ramp is inclined in rotational direction of the actuator with respect to a plane in which rotations of the actuator take place, and the support area extends parallel to the plane. When turning the actuator relative to the gear, the gear glides initially with its contact surface along the cam surface, i.e. along the sloped ramp and subsequently along the support area. When situated in the region of the support area of the cam surface, the gear of the one element has been shifted in axial direction to such an extent as to detach from the second tooth profile of the other element. 
     According to yet another feature of the present invention, the indexing mechanism may include at least one intermediate member, e.g. a ball, which is interposed between the gear and the cam surface, so that the gear is urged against the cam surface via the ball. Preferably, the other element is formed with a bore for receiving the ball, with the ball lying against the cam surface and the gear. When being operated, the actuator pivots relative to the other element and thus relative to the ball, with the cam surface moving along the ball. In the phase during which the ramp passes by the ball, the ball is shifted in axial direction. As the ball bears against the gear, a conjoint axial displacement of the gear is realized, resulting in a disconnection of the gear from the tooth profile of the other element. 
     Suitably, a helical compression spring extends between the shaft and the gear for loading the gear against the actuator. This ensures a permanent contact of the gear with the cam surface. 
     The locking mechanism according to the present invention is especially suitable for a configuration in which the one element is so mounted as to rotate relative to the other element about a pivot axis, whereby the track of the other element is of cylindrical configuration and positioned concentrically to the pivot axis, and the track of the one element is formed by circumferentially spaced clamping ramps positioned in opposition to the track of the other element. The clamping members are retained in a rotatable cage and positioned under spring tension in wedge-shaped clamping gaps bounded by the ramps of the one element and the track of the other element. Thus, a rotation of the cage moves the clamping members from the clamped position into the release position. Preferably, the actuator is linked to the cage for realizing a conjoint rotational movement. In such locking mechanisms, the clamping rollers are arranged in the pockets of the cage at clearance in circumferential direction. When operating the actuating device, the coupling unit is disengaged in a manner as described above, whereby the rotation of the actuator needed for this action is smaller than the clearance of the clamping rollers in circumferential direction. Overlapping between the travel of the turned actuator for disengaging the coupling unit and the switching path for releasing the clamping rollers is possible. The coupling unit is already disengaged when further turning the actuator, and the cage pushes the clamping rollers out of their wedge-shaped clamping gaps. In this phase, a relative rotation of both elements is possible, for example, for adjusting the seat level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features and advantages of the present invention will now be described in more detail with reference to the accompanying drawing, in which: 
     FIG. 1 is a longitudinal section of a shiftable clamping-type locking mechanism according to the invention; 
     FIG. 2 is a partial sectional view of the shiftable locking mechanism taken along the line II—II of FIG. 1; and 
     FIG. 3 is a partial sectional view of the shiftable locking mechanism taken along the line III-III of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. 
     Turning now to the drawing, and in particular to FIG. 1, there is shown a shiftable longitudinal section of a clamping-type locking mechanism according to the invention, suitable e.g. for vertically adjusting a seat. A shaft  1  is rotatably supported in a housing  2 . Outside the housing  2 , the shaft  1  is provided with an output pinion  3  which meshes with a not shown tooth profile, whereby a rotation of the shaft  1  results in a vertical adjustment of the seat. A clamping ring  4  is securely fixed on the shaft  1  and prevented from rotating relative thereto. Formed at the inner surface area of the housing  2  is a cylindrical clamping track  5  which is opposed by clamping ramps  6  formed about the circumference of the output pinion  3 . Clamping rollers  7  are arranged between the clamping ring  4  and the housing  2  and retained in pockets  8  of a cage  9  which is part of a control unit to move the clamping rollers  7  between a clamped position and a release position, as will be described furtherbelow. 
     As best seen in FIG. 3, the ramps  6  are spaced from one another by valleys  26 , with each ramp  6  being comprised of two neighboring ramp sections  6   a ,  6   b  which are inclined in opposite directions so as to define an obtuse angle therebetween. Two clamping rollers  7  are so arranged on each ramp  6  that one roller  7  travels on ramp section  6   a  and the other roller  7  travels on ramp section  6   b . Positioned between the clamping rollers  7  for each ramp  6  is a spring element  27  which tends to push apart the clamping rollers  7  to thereby keep them in a clamped position with the inner track  5  of the housing  2  and the ramp sections  6   a ,  6   b . The cage  9  is formed with claws  28  which project axially into the area of the valleys  26  at clearance in the circumferential directions, thereby bounding wedge-shaped clamping gaps in conjunction with the track  5  and the ramp  6  for receiving the clamping rollers  7  under tension by the springs  27 . The cage  9  has wall surfaces  25  which bound the pockets  8  and are formed in one piece with a lugs  30  for engaging behind the clamping rollers  7  in circumferential direction, whereby the clearance in circumferential direction between the pocket walls  25  and their neighboring clamping rollers  7  is smaller than the clearance between the claws  28  and peripheral walls  31  of the valleys  26 . As neighboring ramp sections  6   a ,  6   b  of the ramps  6  are inclined in opposite directions and thus the wedge peaks of the wedge-shaped clamping gap point in opposite directions, a rotation of the shaft  1  relative to the housing  2  is prevented in both directions of rotation in the shown illustration. 
     As further shown in FIG. 1, the locking mechanism is provided with a coupling unit, generally designated by reference numeral  10 , for realizing a detachable connection between the shaft  1  and the housing  2  in a form-fitting manner. The coupling unit  10  includes a gear ring  11  which is mounted to the housing  2  and has inner teeth  12  for meshing with outer teeth  14  of a gear  13 , as shown in particular in FIG.  2 . The gear  13  is so securely mounted on the shaft  1  so as to be shiftable in axial direction but not rotatable relative to the shaft  1 . A helical compression spring  15  extends between the shaft  1  and the gear  13  to load the gear  13  in the direction of the gear rim  11 . 
     In the illustration of FIG. 1, the upper half shows the coupling unit  10  in engaged position and the lower half shows the coupling unit  10  in disengaged position. A comparison shows that the teeth  12  mesh with teeth  14 , when the coupling unit  10  is engaged, and are out of mesh, when the coupling unit  10  is disengaged. 
     The coupling unit  10  is operated by an actuating device, generally designated by reference numeral  16 , which includes an actuator in the form of a lever  17  which is arranged concentric to and pivotable relative to the shaft  1 . The housing  2  has a housing wall  19  which is formed with throughbores  18  for receiving balls  20  almost without circumferential clearance. The balls  20  are under tension of the helical compression spring  15  and clamped between an end face of the gear  13  and a cam surface  21  of the lever  17 . The cam surface  21  for cooperation with each of the balls  20  is comprised of a ramp  22  and a support area  23  which follows the ramp  22 . The ramp  22  extends in circumferential direction and slopes with respect to a plane in which the lever is pivoted, with the support area  23  extending parallel to this plane. When the coupling unit  10  is engaged, the balls  20  are pressed against the ramp  22 . Conversely, when the coupling unit  10  is disengaged, the balls  20  are urged against the support area  23 . Pivoting the lever  17  in circumferential direction causes the balls  22  to travel along the ramps  22  until reaching the support areas  23 . When traveling from the ramps  22  to the support areas  23 , the balls  20  are shifted axially in the direction of the gear  13 , whereby the gear  13  is displaced in opposition to the force of the helical compression spring  15  for detachment from the inner teeth  12  of the gear rim  11 . 
     The lever  17  is connected to the clamping ring  4  by a crossbar  24  for realizing conjoint pivoting movements. In the phase of disengagement of the coupling unit  10 , the lever  17  together with the crossbar  24  and the cage  9  commonly pivot, whereby initially the clamping rollers  7  remain in resilient contact with the track  5  and the ramps  6  as a consequence of the clearance by which the clamping rollers  7  are retained in the cage pockets  8 . Once the coupling unit  10  is disengaged and the lever  17  and the cage  9  are further turned, the clamping rollers  7  impact on the wall surfaces  25  of the cage pockets  8 . A continued common rotation of the lever  17  and the cage  9  results in a disengagement of the clamping rollers  7  from the wedge-shaped clamping gaps. In this position, a rotation of the shaft  1  relative to the housing  2  is possible to realize an adjustment of the seat level. 
     When the coupling unit  10  is engaged, the cage  9  occupies the position shown in FIG. 3, in which the clamping rollers  7  are resiliently urged against the ramps  6  and the track  5  under the action of the springs  27 . In this situation of the locking mechanism, an undesired slip of the shaft  1  relative to the housing  2  is positively eliminated. Torque acting on the shaft  1  is introduced into the housing  2  via the clamping rollers  7 . As a consequence, the clamping rollers  7  are subject to smaller loads when the torque decreases, so that the clamped formation loosens. This may result in conventional locking mechanisms to a rotation of the shaft relative to the housing when the torque loads change because the clamping force between the shaft and the housing is significantly reduced during zero passage upon such an oscillation, ultimately leading to a slip. By incorporating a coupling unit  10  in the locking mechanism in accordance with the present invention, a slip of the shaft relative to the housing is reliably eliminated as the shaft  1  is positively connected with the housing  2 . The coupling unit  10  is subject to loads in slip situations. Greater torque loads are transmitted via the clamping rollers  7 . 
     While the invention has been illustrated and described as embodied in a shiftable clamping-type locking mechanism, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.