Clutch device

A clutch device including at least one torque transmission device engageable and/or disengageable in an axial direction by a lever element and forming a friction-locking connection when engaged, at least one wear readjustment device that includes at least one rotatable ramp ring at least temporarily clampable by the lever element and at least one spindle drive rotatably supported to act on the ramp ring and including a spindle shaft, where the wear readjustment device includes at least one infinitely variable freewheel unit to rotate the spindle shaft in the case of a sensed wear condition of the torque transmission device, the infinitely variable freewheel unit including at least one wrap spring or at least one freewheel sleeve.

FIELD OF THE INVENTION

The present invention relates generally to clutch devices and, more particularly, to a clutch device that permits correction of a changing operating point in a simple way and with maximum accuracy.

BACKGROUND OF THE INVENTION

German Patent Specification DE 10 2008 051 100 A1 discloses a clutch device. In this friction clutch, an operating point that changes due to wear on the friction linings is automatically readjusted. A spindle drive is provided on the pressure plate to rotate the ramp ring in one direction in the case of wear. For this purpose, a pawl is fixedly arranged on the housing. When a predetermined amount of wear is exceeded, the pawl rotates a pinion of the spindle drive before the friction clutch is disengaged by creating a form-locking connection between the pinion and the pawl. As the friction clutch is being disengaged, the operating point is corrected by a rotation of the pinion caused by the pawl. This method only provides discontinuous step-by-step compensation of the friction lining wear.

Non-published German Patent Application No. 10 2010 052 021.7 furthermore discloses a friction clutch with a readjustment device where the sensing and actuating device consisting of a pawl and a pinion is replaced by a wrap rope connected to the housing and wrapped around the spindle of the spindle drive. The wrap rope rotates the spindle of the spindle drive as a function of the wear on the lining to correct the operating point, which has changed due to lining wear, in a continuous and infinitely variable way. An operating point that changes in both directions, for example in one direction due to lining wear and in the other direction due to swelling friction linings and/or potting of the pressure plate and/or counter pressure plate, cannot be completely corrected.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a clutch device that permits to correct a changing operating point in a simple way and with maximum accuracy.

In accordance with the invention, this object is attained by a clutch device which comprises at least one torque transmission device engageable and/or disengageable in an axial direction by a lever element and having a frictional engagement when engaged, and at least one wear readjustment device that includes at least one rotatable ramp ring at least temporarily clampable by the lever element and at least one spindle drive supported for rotation to act on the ramp ring and including a spindle shaft. The clutch device is characterized by the fact that the wear readjustment device includes at least one infinitely variable freewheel unit to rotate the spindle shaft in the case of a sensed wear condition of the torque transmission device, the infinitely variable freewheel unit including at least one wrap spring or at least one freewheel sleeve.

The clutch device, for example, includes a housing in which the torque transmission device is arranged. The torque transmission device preferably includes at least one counter pressure plate fixed to the housing, at least one pressure plate arranged to be fixed against rotation relative to the housing and displaceable to a limited extent relative to the counter pressure plate in an axial direction of the clutch device, and at least one clutch disc having at least one friction lining clampable in frictional engagement between the pressure plate and the counter pressure plate to transmit a torque. The infinitely variable freewheel unit is preferably designed to transmit a direction-of-rotation-dependent torque in a force-locking, preferably frictionally engaged way to the spindle shaft.

Preferably a sensing device is provided to sense a condition of wear of the torque transmission device during an engagement of the torque transmission device as a function of a distance to a clutch device component fixed to the housing, preferably a counter pressure plate of the torque transmission device. The infinitely variable freewheel unit is drivable for wear readjustment purposes by the sensing device by rotating the spindle shaft upon a disengagement of the torque transmission device.

In particular, the aforementioned object is advantageously attained by a clutch device that includes a counter pressure plate fixed against rotation relative to a housing and a pressure plate received to be fixed against rotation and axially displaceable relative to the counter pressure plate by means of leaf springs and pre-tensioned to a pre-set operating point by a lever element while clamping friction linings, as well as a wear readjustment device for readjusting a changing operating point by means of a ramp ring received by means of ramps distributed in the circumferential direction and along the circumference on complementary counter-ramps of the pressure plate between pressure plate and lever element, the ramp ring being driven to rotate as a function of a change of the operating point by a spindle drive received on the pressure plate and formed by a spindle shaft and a spindle nut received thereon and axially displaceable upon a rotation of the spindle shaft, as well as a sensing device detecting a change of the operating point and controlling the spindle drive as a function of a distance to a component fixed to the housing, where at least one infinitely variable freewheel unit for readjusting the operating point is provided on the spindle shaft, the freewheel unit establishing a friction-locking connection with the spindle shaft as a function of the position of the operating point. The lever element is preferably a diaphragm spring; however, it may also be a lever spring.

In accordance with an advantageous further feature, the wrap spring of the infinitely variable freewheel unit wraps around the spindle shaft under inherent pre-tension and is designed to establish a force-locking, preferably frictionally engaged connection with the spindle shaft for the purpose of wear readjustment by a rotation of the ramp ring relative to complementary counter-ramps as a function of a wear-induced change of the position of an operating point of the torque transmission device. In particular, the wrap spring is preferably designed as one piece.

The infinitely variable freewheel unit preferably includes a wrap spring that is actable upon on the spindle shaft at its spring ends, enters into a frictional engagement with the spindle shaft as a function of the position of the operating point, and is readjusted in terms of its pre-tensioning relative to the spindle shaft in accordance with the rotation of the ramp ring. The spring ends of the wrap spring are preferably actable upon on the pressure plate side and on the side of the sensing device if the spindle drive is supported on the pressure plate side. If the spindle drive is supported on the clutch cover side, the spring ends of the wrap spring are preferably actable upon on the clutch cover side and on the sensing device side.

In both cases the wrap spring is used as a controllable freewheel that transmits torque in a direction of rotation of the spindle shaft after actuation by the sensing device. For this purpose, the wrap spring is connected to the spindle shaft in a switchable and frictionally engaged way as a result of belt friction in accordance with the capstan equation/Eytelwein's formula by acting upon the spring ends of the wrap springs in a corresponding way. One spring end is axially supported on the pressure plate side, i.e. on a component that is axially displaced during an actuating process, for example on the pressure plate, ramp ring, lever element and/or diaphragm spring, or on a component connected thereto. The other spring end of the wrap spring is supported on the sensing device, i.e. directly on the sensing device or on a component connected thereto. The same applies to the actuating lever of a freewheel sleeve.

In accordance with a further advantageous feature, the freewheel sleeve of the infinitely variable freewheel unit is arranged on the spindle shaft and is designed to enter into a force-locking, preferably frictionally engaged connection with the spindle shaft for the purpose of wear readjustment by a rotation of the ramp ring relative to complementary counter-ramps as a function of the position of a wear-induced change of an operating point of the torque transmission device.

The sensing device preferably includes a finger that is preferably arranged on a pressure plate of the torque transmission device and acts on a spring end of the wrap spring or on an actuating lever of the freewheel sleeve against the action of an energy storage element preferably embodied as a helical spring or leaf spring.

The sensing device comprises a finger or pin for detecting deviations of the operating point by registering the position of the pressure plate relative to the counter pressure plate or to components in fixed axially association with the counter pressure plate, for example the housing, when the torque transmission device is engaged. The finger or pin may be arranged on the pressure plate side and may sense the deviation of the operating point relative to the counter pressure plate or it may be arranged on the counter pressure plate or housing and may sense the deviation of the operating point relative to the pressure plate. As a rotation of the ramp ring located between the pressure plate and the diaphragm spring is impossible due to the contacting pressure applied to the pressure plate by the diaphragm spring when the torque transmission device is engaged, the angle of rotation required to correct a shifted operating point is buffered in the form of a pre-tensioned condition of the sensing device and is at least partly converted into an angle of rotation of the ramp ring under reduction of the pre-tension during the subsequent disengagement process in which the ramp ring is released. An operating point that has previously not been corrected in a final way may be continuously corrected in subsequent engagement and disengagement operations of the clutch device.

In accordance with an advantageous exemplary embodiment the sensing device may be formed by a finger that is arranged on the pressure plate to be displaceable against the action of an energy storage element and acts upon a spring end of the wrap spring. In this case, the wrap spring remains under pre-tension on the spindle shaft during an actuation of the clutch device in the case of a correct operating point due to the fact that one end is supported on the pressure plate side while the other end is pre-tensioned by the energy storage element. Thus no rotation occurs, not even accidental rotation of the ramp ring due to a blocking of the spindle shaft by the wrap spring, even if the torque transmission device is disengaged and the ramp ring is released. When, during an engagement process of the torque transmission device, the finger impinges on a stop fixed to the housing, for example on the counter pressure plate, as a result of a shifting operating point, the wrap spring is released relative to the spindle shaft and rotates relative to the spindle shaft through a pre-determined amount. In the subsequent disengagement process of the torque transmission device, the friction-locking connection is reestablished due to the action on the wrap spring and entrains the drive shaft, rotating the spindle shaft and thus the ramp ring. The energy storage element that pre-tensions the finger in the direction of the counter pressure plate may be a helical spring, for example.

In accordance with an alternative exemplary embodiment, the sensing device may be formed by a leaf spring elastically received on the housing and acting on a spring end of the wrap spring. The wrap spring is pre-tensioned against a stop on the pressure plate side, forming a frictional engagement with the spindle shaft. When the pressure plate is displaced in the direction of the counter pressure plate as the operating point shifts, the pre-tensioning of the wrap spring by the leaf spring, which is preferably arranged on the housing, is removed and the wrap spring is rotated relative to the spindle shaft. In the subsequent disengagement process, the spindle shaft and the wrap spring rotate together under the action of the leaf spring to readjust the ramp ring.

The wear readjustment device preferably includes a readjustment unit for readjusting the pre-tension and/or the angular position of the infinitely variable freewheel unit arranged on the spindle shaft.

In accordance with a particularly advantageous feature, the readjustment unit may be wedge-shaped and displaceable in the transverse direction of the clutch device or in the circumferential direction of the clutch device.

In particular, the readjustment unit may advantageously be fixed to the ramp ring or to a spindle nut of the spindle drive or be integral with the ramp ring or of the spindle nut.

Advantageously, a spring end of the wrap spring or an actuating lever of the freewheel sleeve may be slideably engaged with a support surface of the readjustment unit.

In accordance with a further exemplary embodiment, the wrap spring end or the freewheel sleeve actuating lever that is slideably engaged with the support surface of the readjustment unit preferably and the wrap spring end or actuating lever that is actable upon by the finger are preferably the same. With wrap springs in particular, it is not necessary for the second spring end remote from the finger to be supported on a component. However, for the purpose of readjusting the pre-tensioning of the wrap spring and/or the angular position of the wrap spring, this second spring end remote from the finger may be supported on a readjustment unit, preferably on the ramp ring or a component fixed against rotation relative thereto.

To compensate for a continuous rotation of the wrap spring during the succession of readjusting processes occurring during the useful life of the clutch device, corresponding stops of at least one spring end of the wrap spring are readjusted. For example, the readjustment of the pre-tensioning of the wrap spring arranged on the spindle shaft may be achieved by means of a component, for example made of sheet metal, that forms a support surface for a spring end of the wrap spring and rises progressively in the direction of rotation of the ramp ring. Thus the path of the spring end that is acted upon on the sensing device side is limited by the support surface. Alternatively, the spring end of the wrap spring on the pressure plate side may rest against the support surface.

These and other objects and advantages of the present invention will be readily appreciable from the following description of preferred embodiments of the invention and from the accompanying drawings and claims.

DETAILED DESCRIPTION OF THE INVENTION

Identical elements are provided with the same reference numerals in the figures and are described only once.

FIGS. 1 to 4are different representations of a first exemplary embodiment of a clutch device. Clutch device1includes counter pressure plate3(only partly shown) connected to housing2. Clutch device1further includes pressure plate4fixed against rotation relative to housing2and movable in axial direction A by means of non-illustrated leaf springs and lever element6supported on housing2and urging pressure plate4in axial direction A against counter pressure plate3, clamping friction linings5in the process. Lever element6is preferably embodied as a diaphragm spring.

Counter pressure plate3that is fixed to the housing, pressure plate4that is fixed against rotation relative to the housing and movable to a limited extend relative to counter pressure plate3in axial direction A of clutch device1, and the clutch disc, which includes at least one friction lining5clampable in a friction-locking way between pressure plate4and counter pressure plate3to transmit a torque, preferably from torque transmission device26of clutch device1.

To disengage clutch1or torque transmission device26, on the inside in radial direction R, a release system acts on lever element6, i.e., the diaphragm spring, in an axial direction towards counter pressure plate3. Assisted by the pre-tensioned leaf springs, pressure plate4is caused to disengage from friction linings5of the otherwise non-illustrated clutch disc.

If the thickness of friction linings5is reduced as a result of friction lining wear, with the clutch engaged, a virtual clutch operating point on the friction surface of pressure plate4relative to friction linings5shifts towards counter pressure plate3. As a result, lever element6lifts up radially on the inside and the pressure behavior and the disengagement paths change. To regain the original condition in the case of friction lining wear, clutch device1includes an infinitely self-adjusting wear readjustment device7formed by ramp ring8, spindle drive9driving ramp ring8in the case of a readjustment, and sensing device10. Ramp ring8is arranged between lever element6and pressure plate4and has ramps that are distributed across the circumference, rise in circumferential direction U, and rest against complementary counter-ramps on pressure plate4.

Mount11, on which spindle shaft12is received for rotation, fixedly connects spindle drive9to pressure plate4. Spindle nut25(only shown inFIG. 9) that shifts when spindle shaft12is rotated is arranged on spindle shaft12to engage with ramp ring8in a form-locking way and to rotate ramp ring8through a defined angle of rotation in accordance with the selected, preferably self-locking translation of the spindle drive when spindle shaft12is rotated.

Infinitely variable freewheel unit27is provided on spindle shaft12to drive spindle shaft12. Infinitely variable freewheel unit27preferably includes wrap spring13or is embodied as wrap spring13. In a non-illustrated exemplary embodiment, infinitely variable freewheel unit27includes a freewheel sleeve or is embodied as a freewheel sleeve.

Wrap spring13, whose inner diameter is smaller than the outer diameter of spindle shaft12, is received under tension on the outer diameter of spindle shaft12. Depending on the actuation of spring ends14,15thereof, in the form of a freewheel, wrap spring13releases spindle shaft12in one direction of rotation and blocks it in the other direction.

In the first exemplary embodiment, sensing device10includes mount16fixedly received on pressure plate4and finger17received on mount16so as to be movable in axial direction A to a limited extent towards counter pressure plate3through the action of energy storage element18, in the present example helical spring19a.

Wrap spring end14on the side of the lever element may contact lever element6on the pressure plate side. However, wrap spring end14may likewise terminate freely on spindle shaft12, i.e., without direct support on the pressure plate side. The other wrap spring end15on the side of the finger is acted upon by sensing device10as a function of the friction lining wear of friction linings5and thus as a function of the operating point. The same applies in the case of a freewheel sleeve to a finger-side actuating lever of the freewheel sleeve and, if applicable, to a (further) actuating lever on the lever element side.

Wear readjustment device7preferably includes readjustment unit21to readjust the pre-tensioning and/or the angular position of infinitely variable freewheel unit27, in particular of wrap spring13arranged on the spindle shaft. Readjustment unit21is wedge-shaped and displaceable in the transverse direction of clutch device1. Advantageously, readjustment unit21may be fixed to spindle nut25of spindle drive9or may be integral with spindle nut25.

In the illustrated exemplary embodiment, to prevent excess wear readjustment, i.e., to ensure correct readjustment, finger-side spring end15of wrap spring13is slideably engaged with support surface20of readjustment unit21. The same applies to a finger-side actuating lever of a non-illustrated freewheel sleeve.

The arrangement of wear readjustment device7in clutch device1results in the following functionality. With clutch device1and torque transmission device26engaged and the operating point unchanged, finger17at most touches counter pressure plate3but is not displaced or only displaced to such an extent that its engagement portion, for example a hole in finger17, engaging in spring end15is not displaced by support surface20of readjustment unit21. Due to the axial height of the hole in the finger in which spring end15is received, i.e., due to the clearance between stops22,23, the formation of the frictional engagement between wrap spring13and spindle shaft12may be controlled and adjusted.

When torque transmission device26is disengaged, pressure plate4is moved axially away from counter pressure plate3and finger17lifts off counter pressure plate3. The frictional engagement between wrap spring13and spindle shaft12remains, preventing an undesired readjustment of the ramp ring8which may occur due to vibrations of pressure plate4. Wrap spring13does not move and spring end15facing towards counter pressure plate3rests on support surface20of readjustment unit21.

If the friction lining thickness of friction linings5is reduced due to wear, pressure plate4and thus the operating point of clutch device1shifts towards counter pressure plate3so that with torque transmission device26in the process of being engaged or in an engaged condition, finger17comes to rest on counter pressure plate3and is axially displaced against the action of helical spring19a. As a consequence, spring end15of wrap spring13is lifted and the frictional engagement between wrap spring13and spindle shaft12is released as the coils of wrap spring13are widened and spring13opens. On the one hand, the opening of wrap spring13may occur as a result of ramp ring8being clamped by lever element6, which results in a support via blocked spindle drive9connected to ramp ring8by spindle nut25. On the other hand, spring end14may be directly supported on lever element6, which may at least assist in the opening of wrap spring13.

When the operating point has shifted to a sufficient extent, wrap spring13is at least partially rotated relative to spindle shaft12. Ramp ring8is protected against undesired rotation by the contacting pressure exerted by lever element6when clutch device1is engaged.

When clutch device1is subsequently disengaged, the engagement between finger17and counter pressure plate3is released and finger17is shifted back by helical spring19aso that the pre-tensioning effect on spring end15of wrap spring13is removed, allowing wrap spring13to reestablish the frictional engagement with spindle shaft12. Furthermore once the frictional engagement is established, wrap spring13rotates spindle shaft12and thus ramp ring8, which is released when clutch device1is in the disengaged condition, until the path of spring end15is limited by support surface20.

Support surface20is provided by readjustment device21, which is fixedly connected to spindle nut25in the illustrated exemplary embodiment or is integral therewith. The increasing height of support surface20in the direction of rotation of ramp ring8allows wrap spring13to rotate to an increasing extent as the number of readjustments increases, and allows finger17to shift to an increasing extent due to the fact that counter pressure plate3moves closer to pressure plate4as the wear increases over the useful life of the device. Thus, finger17senses the same shifting distance of the operating point over the entire useful life.

In contrast to the exemplary embodiment shown inFIGS. 1 to 4, the second exemplary embodiment of clutch device1, which is shown inFIGS. 5 and 6, includes modified wear readjustment device7with modified spring ends14,15of wrap spring13and modified readjustment unit21for readjusting the position of rotation of wrap spring13. In particular, readjustment unit21is fixed to ramp ring8or is integral with ramp ring8. Thus, readjustment unit21is displaceable in circumferential direction U of clutch device1, preferably rotationally fixed relative to ramp ring8.

For this purpose, ends14,15of wrap spring13are preferably offset relative to each other in terms of the axis of rotation of wrap spring13and of spindle shaft12. Thus, pressure-plate-side spring end14, which is located further inward in radial direction R in the illustrated example, may be supported by ramp-ring-side support surface20of readjustment unit21in a slideably movable way to readjust the pre-tensioning and/or the angular position of wrap spring13.

The functionality of sensing device10in interaction with spring end15essentially corresponds to the functionality of wear readjustment device7ofFIGS. 1 to 4.

FIGS. 7 to 9illustrate a third exemplary embodiment of clutch device1including modified wear readjustment device7. In contrast to the wear readjustment devices of the previous figures, sensing device10of the third exemplary embodiment is formed as leaf spring19barranged on housing2to be elastically deformable relative thereto. Leaf spring19bhas finger17, which is preferably integral with leaf spring19band acts on spring end15of wrap spring13, thus controlling the wrap effect of wrap spring13. In the process, finger-side spring end15is supported by stop24formed by mount11.

As a result, a path of wear of pressure plate4relative to housing2that is fixedly connected to the non-illustrated counter pressure plate is sensed as follows. During a movement to disengage torque transmission device26, which is illustrated in the engaged condition in the drawing, pressure plate4shifts in the axial direction towards housing2between stops22,23of finger17. Due to the frictional engagement between wrap spring13and spindle shaft12, an undesired rotation thereof in the disengaged condition is prevented.

With pressure plate4and its operating point shifting away from housing2in the process of engaging or in the engaged condition of torque transmission device26due to friction lining wear spring end15is displaced by stop23. The result is that the wrap effect of wrap spring13on spindle shaft12is released and wrap spring13is rotated relative to the spindle shaft.

In the subsequent disengagement process of torque transmission device26, pressure plate4shifts in the direction of housing2. In the process, spring end15of wrap spring13is released by stop23and the frictional engagement with spindle shaft12is reestablished. Subsequently, stop22acts on spring end15and rotates wrap spring13and spindle shaft12, causing spindle nut25engaged with ramp ring8to move on spindle shaft12and to rotate ramp ring8.

It is to be understood that readjustment device7ofFIGS. 1 to 9may be designed initially to readjust by an amount that is smaller than the wear distance between the shifted operating point and the correct operating point and successively to readjust to the correct operating point in subsequent readjustment cycles. It is also to be understood that like in the first exemplary embodiment, in the second and third exemplary embodiments, wrap spring13may likewise be replaced by a freewheel sleeve as infinitely variable freewheel unit27.

In summary, the aforementioned exemplary embodiments relate to clutch device1having at least one torque transmission device26that is engageable and/or disengageable in axial direction A by lever element6and forms a friction-locking connection when engaged, and at least one wear readjustment device7that includes at least one rotatable ramp ring8at least temporarily clampable by lever element6, and at least one spindle drive9rotatably supported to act on ramp ring8and including spindle shaft12. Wear readjustment device7includes at least one infinitely variable freewheel unit27to rotate spindle shaft12in the case of a sensed wear condition of torque transmission device26. Infinitely variable freewheel unit27preferably includes at least one wrap spring13or at least one freewheel sleeve.

LIST OF REFERENCE SYMBOLS