FRICTION CLUTCH WITH ADJUSTING DEVICE

Abstract

A friction clutch with a back-pressure plate, which is connected to a housing so as to rotate with it, and a pressure plate, which is received by leaf springs such that it can be displaced axially and is fixed with respect to the back-pressure plate so as to rotate with it and which is prestressed by a disc spring to a preset operating point with friction linings clamped in between, and an adjusting device, for adjusting a changing operating point by a ramp ring which is distributed in the circumferential direction and over the circumference, is received on the pressure plate on complementary mating ramps of the pressure plate and is rotated by a spindle device depending on a change in the operating point, and a sensing device which detects a change in the operating point and controls the spindle drive.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under 35 U.S.C. §120 and §365(c) as a continuation of International Patent Application No. PCT/DE2011/001939 filed Nov. 7, 2011 and claims priority of German Patent Application No. 10 2010 052 021.7 filed Nov. 19, 2010, German Patent Application No. 10 2011 081 476.0 filed Aug. 24, 2011, and German Patent Application No. 10 2011 081 475.2 filed Aug. 24, 2011, which applications are incorporated herein by reference to their entireties.

FIELD OF THE INVENTION

The invention relates to a friction clutch that includes a counter-pressure plate connected to a housing in a rotationally fixed way and a pressure plate received to be rotationally fixed 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 diaphragm spring while clamping friction linings, as well as a readjustment device for readjusting a changing operating point by means of a ramp ring received on complementary counter-ramps of the pressure plate by ramps that are distributed in the circumferential direction along the circumference, the ramp ring being rotated by a spindle drive as a function of a change of the operating point, as well as a sensing device detecting a change of the operating point and controlling the spindle drive.

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.

German Patent Application No. 10 2010 052 021.7 furthermore discloses a friction clutch with a readjustment device wherein 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

A friction clutch with a back-pressure plate, which is connected fixedly to a housing so as to rotate with it, and a pressure plate, which is received by leaf springs such that it can be displaced axially and is fixed with respect to the back-pressure plate so as to rotate with it and which is prestressed by a disc spring to a preset operating point with friction linings clamped in between, and an adjusting device, for adjusting a changing operating point by a ramp ring which is distributed in the circumferential direction and over the circumference, is received on the pressure plate on complementary mating ramps of the pressure plate and is rotated by a spindle device depending on a change in the operating point, and a sensing device which detects a change in the operating point and controls the spindle drive. To compensate for displacements of the operating point in both directions in an infinitely variable manner, the spindle drive is received fixedly on the housing and contains three shaft sections which are arranged concentrically with respect to one another and can be rotated to a limited extent with respect to the housing and with respect to one another, wherein the inner shaft section has a spindle mechanism, which drives the ramp ring, and can be rotated firmly in one rotational direction with respect to the middle shaft section and can be rotated to a limited extent in the other rotational direction counter to the action of first energy stores, and the middle shaft section and the outer shaft section which contains the sensing device with respect to the ramp ring are arranged such that they are secured against rotation with respect to the housing in each case by two switchable wraparound belts which are connected counter to one another.

An object of the invention is to refine a friction clutch with readjustment device wherein an operating point that changes in both directions can be continuously corrected in an infinitely variable way.

In accordance with the invention, this object is attained by a friction clutch that includes a counter-pressure plate connected to a housing so as to be fixed against rotation relative thereto 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 pretensioned to a pre-set operating point by a diaphragm spring while clamping friction linings, as well as a readjustment device for readjusting a changing operating point by means of a ramp ring received on the pressure plate by ramps that are distributed in the circumferential direction along the circumference and rest on complementary counter-ramps on the pressure plate, the ramp ring being rotated by a spindle drive as a function of a change of the operating point, as well as a sensing device detecting a change of the operating point and controlling the spindle drive, wherein the spindle drive is fixedly received on the housing and includes three shaft portions arranged to be concentric with each other and rotatable relative to the housing and relative to each other to a limited extent, the inner shaft portion containing a spindle drive that drives the ramp ring and arranged so as to be fixed in one direction of rotation relative to the central shaft portion and rotatable to a limited extent against the action of first energy storage elements in the other direction of rotation, and each of the central and outer shaft portion, which latter contains the sensing device towards the ramp ring, being respectively arranged to be secured against rotation relative to the housing by means of two respective switchable wrap belts arranged to act in opposite directions.

Due to the fact that the spindle drive is received on the housing, insulation thereof relative to vibrations of the pressure plate is achieved, thus at least minimizing vibration-induced erroneous readjustments.

Due to the fact that the switchable wrap belts or wrap ropes are arranged to act in opposite directions, the shaft portions are held in a way to be secured against rotation, thus stabilizing a predetermined operating point or a corrected operating point after a readjustment. The spindle itself may be arranged to be secured against rotation in that it is arranged to be secured against rotation relative to the second shaft portion in one direction and rotatable against the action of energy storage elements such as leaf springs in the other direction. With the second shaft portion correspondingly secured against rotation, the spindle of the spindle drive may automatically rotate in one direction of rotation, a rotation in this direction of rotation being precluded due to the interlocking of ramp ring and pressure plate due to the diaphragm spring when the friction clutch is engaged. The rotation of the spindle thus depends on the rotatability of the second shaft portion. A first pair of wrap belts that are arranged to act in opposite directions and wrapped around the central shaft portion may be arranged to be fixed relative to the housing by one end and to be elastic by the other end due to an energy storage element that is connected in-between. Due to this arrangement, a rotation of the second portion is possible only when one of the two wrap belts is switched off. The control thereof occurs by the third shaft portion against the action of the energy storage elements of these wrap belts. For this purpose, a second pair of wrap belts that are arranged to act in opposite directions may be fixedly connected to the third shaft portion by one end and elastically connected to the housing by the other end with an energy storage element such as a leaf spring connected in-between and may be wrapped around the central shaft portion.

The central shaft portion is controlled by the third shaft portion by means of the sensing device arranged between the ramp ring and the third shaft portion to detect the need for readjustment when the pressure plate leaves a predetermined stroke range. A need for readjustment in the case of an operating point shifting towards the counter-pressure plate, for example, due to lining wear of the friction linings is detected when the friction clutch is engaged and stored in an energy storage element. When the friction clutch is disengaged, the operating point is corrected by a corresponding rotation of the first shaft portion and thus of the spindle that rotates the ramp ring in a corresponding way. An operating point that has shifted in the direction of the diaphragm spring, for example, due to swelling friction linings and/or potting of clutch components is detected by the sensing device when the friction clutch is being disengaged or in the disengaged state so that the operating point may be corrected without buffering as a result of a lack of blocking of the ramp ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and mode of the proposed friction clutch with readjustment device will be explained in more detail in the following detailed description of the invention taken with the accompanying drawing figures, in which:

FIG. 1 is a partial sectional view of a friction clutch with readjustment device;

FIG. 2 is a diagrammatic three-dimensional view of a functional example;

FIG. 3 is a diagrammatic side view of a functional example;

FIG. 4a is a view of the first and second shaft portions in a functional condition;

FIG. 4b is a view of the first and second shaft portions in another functional condition; and,

FIG. 4c is a view of the first and second shaft portions in yet another functional condition.

DETAILED DESCRIPTION OF THE INVENTION

At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention.

While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspects.

Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and, as such, may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described.

FIG. 1 is a partial sectional view of a friction clutch 1 arranged about an axis of rotation 2 and including a counter-pressure plate 3 fixedly connected to a housing 4. In the housing 4, the pressure plate 5 is received as to be fixed rotationally and axially displaceable relative to the counter-pressure plate 3 by means of non-illustrated leaf springs and is urged against the counter-pressure plate 3 of the pressure plate 5 by the diaphragm spring 6 supported on the housing 4. Between friction surfaces 9, 10 of the counter-pressure plate 3 and the pressure plate 5, friction linings 7 of the clutch disc 8 are clamped and in a frictional engagement therewith, thus forming the operating point, which may be defined as an axial position of the friction surface relative to the axis of rotation 2. If the pre-tensioning of the diaphragm spring 6 is reduced by a non-illustrated disengagement system, the frictional engagement is released due to a shifting of the pressure plate 5 as a result of the effect of the leaf springs that are axially pre-tensioned in the engaged condition of the friction clutch.

The friction clutch 1 includes the readjustment device 11 that is self-adjusting in the case of a changing operating point. The readjustment device 11 includes the spindle drive 12 received on the housing 4 and the ramp ring 13 arranged between the diaphragm spring 6 and the pressure plate 5. The ramp ring 13 has rising ramps 14 distributed about the circumference and facing the pressure plate 5. Rising ramps 14 rest on counter-ramps 15 of the pressure plate 5 so that when the ramp ring 13 rotates, the distance between the friction surface 10 and the diaphragm spring 6 increases or decreases, depending on the direction of rotation. Thus, the operating point may be changed relative to the diaphragm spring, and when the operating point shifts due to wear or swelling of the friction linings or as a result of other variables such as potting of the pressure plate 5, the operating point may be changed in such a way that the diaphragm spring may maintain its predefined angle of engagement relative to the ramp ring 13, thus maintaining the transmission of power predefined by the release stroke.

To detect a changing operating point, the sensing device 16 is provided between the ramp ring 13 and the spindle drive 12. In FIG. 1, the sensing device 16 is formed by a sensing element 17 provided on the spindle drive 12 and by the two stops 18, 19 provided on the ramp ring 13 with clearance relative thereto. With the operating point unchanged, during the operating processes of the friction clutch, the sensing element 17 is located between the stops 18, 19 shifted back and forth. When the operating point changes, in the disengaged and in the engaged state, respectively, one of the stops 18, 19 impinges on the sensing element 17 and displaces the latter to correct the changed operating point.

For example, if the operating point shifts in the direction of the counter-pressure plate 3 due to lining wear, in the engaged state the sensing element17 impinges on stop 19 and a need for readjustment is registered. In the case of a swelling of the friction linings 7 and/or potting of the pressure plates 5, the operating point shifts in the direction of the diaphragm spring 6 and when the friction clutch is disengaged the sensing element 17 impinges on stop 18 and a need for readjustment is registered. It is to be understood that the release system of the friction clutch is designed for a constant stroke and is correspondingly calibrated and continuously readjusted.

FIG. 2 is a three-dimensional view of a functional model of the readjustment device 11 to illustrate the structure and functioning of the spindle drive 12 when a need for readjustment has been registered. The spindle drive 12 contains three shaft portions 20, 21, 22 arranged to be concentric with each other. The inner shaft portion 20 contains the spindle in a non-illustrated way and a spindle nut arranged thereon to be rotationally fixed and to be axially displaceable in the case of a rotation of the spindle. The spindle nut engages the ramp ring 13 in a form-locking way and rotates the latter in a clockwise or counter-clockwise direction, depending on the direction of rotation of the spindle, thus being capable of correcting the operating point in both axial directions. The inner shaft portion 20 is received for rotation in the housing 4 of the friction clutch 1 (FIG. 1). In the form of a hollow shaft the central shaft portion 21 is received on shaft portion 20 to rotate to a limited extent.

As becomes apparent from FIG. 2 and in more detail from FIGS. 4a to 4c, shaft portions 20, 21 are rotationally coupled to each other. In one direction of rotation, the connection is inelastic by means of the stops 23 and in the other direction of rotation, the connection is elastic by means of the energy storage elements 24 such as leaf springs. Thus, if, in the illustrated example, shaft portion 20 is entrained by shaft portion 21 in a counter-clockwise direction, (FIG. 4c), the rotation is torsionally stiff and occurs without buffering of the rotational travel to correct the operating point; with the friction clutch disengaged, the spindle, which is formed on the shaft portion as an axial extension, for example, immediately rotates the then released ramp ring via the spindle nut. When shaft portion 21 is rotated with the friction clutch closed, for example, if the friction lining thickness has decreased, shaft portion 20 is blocked by the spindle and the axially loaded ramp ring 13 (FIG. 2), causing shaft portions 20, 21 to be rotated against the action of the energy storage elements 24. Thus, the rotational travel is buffered until the ramp ring 13 is released upon a subsequent disengagement of the friction clutch and the energy storage elements 24 drive shaft portion 20 and subsequently, the spindle, spindle nut, and ramp ring 13, thus effecting a correction of the operating point.

As further becomes apparent from FIG. 2, shaft portion 21 is secured against rotation by means of a wrap belts 25, 26 that form a pair and are arranged to act in opposite directions. One end 27, 29 of each wrap belt 25, 26 is fixedly connected to the housing 4 and the other end 28, 30 is elastically connected by means of the energy storage elements 31, 32, which in the illustrated example are leaf springs 33, 34 connected to the housing 4 on one side. The wrap belts 25, 26 arranged about shaft portion 21 pull tight in opposite directions and block the rotary movement of shaft portion 21 and are loosened in the other direction of rotation as soon as the pre-tensioning of the leaf springs 33, 34 is released.

In the case of a readjustment, this torque is transmitted in a direction-of-rotation-specific way from shaft portion 22 to shaft portion 21 by means of the wrap belts 35, 36 that are arranged to act in opposite directions. For this purpose, one end 37, 39 of each of the wrap belts 35, 36 wrapped around shaft portion 21 is fixedly connected to shaft portion 22 whereas the other end 38, 40 is elastically connected by means of the energy storage elements 41, 42, which in the illustrated example leaf are springs 43, 44 connected to the housing 4 on one side. Shaft portion 22 includes the sensing element 17, which extends into the opening 45 with stops 18, 19.

The pre-tensioning of the wrap belts 25, 26, 35, 36 is released in a targeted way by means of the ramp ring 13 as a function of the latter's movement perpendicular to the axis of rotation of the shaft portions 20, 21, 22. For this purpose, stops 46, 47 are provided on the ramp ring 13. In respective pairs, stops 46, 47 release the pre-tensioning of the leaf springs 33, 34, 43, 44 as a function of the direction of movement of the ramp ring 13, thus eliminating the wrapping effect of the wrap belts 25, 26, 35, 36.

During normal operation of the friction clutch 1 (FIG. 1) without readjustment the sensing element 17 moves between the stops 18, 19 of the ramp ring and no readjustment is made. Due to the fact that shaft portion 21 is locked in both directions of rotation, shaft portion 20 remains positioned relative thereto by means of the stops 23 and energy storage elements 24 (FIG. 4a); the spindle does not rotate and no readjustment of the ramp ring 13 occurs.

When the ramp ring 13 with the sensing element 17 moves as a result of friction lining 7 wear (FIG. 1) and thus of a shifting of the pressure plate 5 (FIG. 1)in the direction of stop 19 in the engaged state of the friction clutch 1, the sensing element 17 is entrained by stop 19. In the process, the wrap belt 35 pulls and, releasing wrap belts 25, 36 by means of stop 47, entrains shaft portion 21 in a counter-clockwise direction. As a result of the fact that the ramp ring 13 is clamped between the diaphragm spring 6 and the pressure plate 5 (FIG. 1) when the friction clutch 1 is engaged and the fact that the spindle is prevented from rotating on shaft portion 20, shaft portion 21 rotates relative thereto against the action of the energy storage elements 24 (FIG. 4b). Once the friction clutch 1 has been disengaged, the pre-tensioning of the ramp ring 13 by the diaphragm spring 6 is released and, shaft portion 20 rotates relative to shaft portion 21 in a counter-clockwise direction thereby reducing the pre-tensioning of the energy storage elements 24 (FIG. 4c) and the spindle rotates the ramp ring 13 in the circumferential direction to correct the changed operating point.

In the reverse case, for example, due to potting of the pressure plate 5 and/or swelling friction linings 7, the sensing element 17 moves in the direction of stop 18 and is entrained by stop 18 when the friction clutch 1 is being disengaged. In the process, wrap belts 26, 35 are loosened by stop 46 and shaft portion 21 is entrained in a clockwise direction by wrap belts 25, 36. As the ramp ring 13 is released when the friction clutch 1 is being disengaged, a buffering of the rotary movement may be dispensed with and the rotation of shaft portion 20 by shaft portion 21 may occur directly by stops 23 without an elasticity connected in-between, causing the ramp ring 13 to be driven by the spindle.

FIG. 3 is a diagrammatic representation of the friction clutch 1 with the readjustment device 11. On the one hand as it is rotated, the ramp ring 13, which is received between the pressure plate 5 and the diaphragm spring 6 received on the housing 4, corrects a changing operating point by changing the distance between the pressure plate 5 and the diaphragm spring 6 by means of the ramps 14. On the other hand, the ramp ring 13 forms the sensing device 16 for sensing the need for readjustment when the operating point has changed. For this purpose, the ramp ring 13 includes stops 18, 19, which move relative to the sensing element 17 of the spindle drive 12.

In the illustrated exemplary embodiment, stop 19 impinges on the sensing element 17, which means that the operating point starts to shift towards counter-pressure plate 3 (FIG. 1) and away from the diaphragm spring 6 due to a reduced friction lining thickness. As a result, wrap belts 25, 36 begin to loosen due to stop 47 of the ramp ring 13, whereas the active wrap belts 26, 36 transmit the rotary movement of shaft portion 22 enforced by the ramp ring 13 via the sensing element 17 to shaft portion 21. As a result of the fact that the friction clutch 1 is engaged, shaft portion 20, which is kinematically coupled to the ramp ring 13 via the spindle and the spindle nut, is blocked and prevented from rotating. With increasing lining wear, a relative rotation between shaft portions 20, 21 is build up via the energy storage elements 24. When the friction clutch 1 is being disengaged and the ramp ring 13 is released, relative rotation is reduced as the ramp ring 13 is rotated and the operating point is corrected until stops 23 limit the relative rotation of shaft portions 20, 21.

Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention.

REFERENCE NUMERALS

• 1 friction clutch
• 2 axis of rotation
• 3 counter-pressure plate
• 4 housing
• 5 pressure plate
• 6 diaphragm spring
• 7 friction lining
• 8 clutch disc
• 9 friction surface
• 10 friction surface
• 11 readjustment device
• 12 spindle drive
• 13 ramp ring
• 14 ramp
• 15 counter-ramp
• 16 sensing device
• 17 sensing element
• 18 stop
• 19 stop
• 20 shaft portion
• 21 shaft portion
• 22 shaft portion
• 23 stop
• 24 energy storage element
• 25 wrap belt
• 26 wrap belt
• 27 end
• 28 end
• 29 end
• 30 end
• 31 energy storage element
• 32 energy storage element
• 33 leaf spring
• 34 leaf spring
• 35 wrap belt
• 36 wrap belt
• 37 end
• 38 end
• 39 end
• 40 end
• 41 energy storage element
• 42 energy storage element
• 43 leaf spring
• 44 leaf spring
• 45 opening
• 46 stop
• 47 stop

Claims

1. A friction clutch (1), comprising:

a counter-pressure plate (3) connected to a housing (4) in a rotationally fixed way;

a pressure plate (5) received to be rotationally fixed and axially displaceable relative to said counter-pressure plate (3) by means of leaf springs and pre-tensioned to a pre-set operating point by a diaphragm spring (6);

clamping friction linings (7) received between said pressure plate (5) and said diaphragm spring (6);

a readjustment device (11) for readjusting a changing operating point by means of a ramp ring (13) received between said pressure plate (5) and said diaphragm spring (6) by means of ramps (14) distributed in the circumferential direction and along the circumference resting on complementary counter-ramps (15) of said pressure plate (5), said ramp ring (13) being rotated by a spindle drive (12) as a function of a change of said operating point; and,

a sensing device (16) detecting a change of said operating point and controlling said spindle drive (12), wherein said spindle drive (12) is fixedly received on said housing (4) and includes three shaft portions (20, 21, 22) arranged to be concentric with each other and rotatable relative to said housing (4) and relative to each other to a limited extent, an inner shaft portion (20) containing a spindle drive that drives said ramp ring (13) and arranged relative to a central shaft portion (21) in a way to be fixed in one direction of rotation and rotatable to a limited extent against the action of first energy storage elements (24) in the other direction of rotation, and said central and an outer shaft portion (21, 22), which contains said sensing device (16) towards said ramp ring (13), being respectively arranged to be secured against rotation relative to said housing (4) by means of two respective switchable wrap belts (25, 26, 35, 36) arranged to act in opposite directions.

2. The friction clutch (1) recited in claim 1, wherein a first pair of wrap belts (25, 26) arranged to act in opposite directions is fixedly connected to said housing (4) by an end (27, 29) and elastically connected to said housing (4) by another end, with an energy storage element (31, 32) connected in-between, and is wrapped around said central shaft portion (21).

3. The friction clutch (1) recited in claim 2, wherein a second pair of wrap belts (35, 36) arranged to act in opposite directions is fixedly connected to the third shaft portion (22) by an end (37, 39) and elastically connected to said housing (4) by another end (38, 40), with an energy storage element (41, 42) connected in-between, and is wrapped around said central shaft portion (21).

4. The friction clutch (1) recited in claim 2, wherein said energy storage elements (31, 32) are leaf springs (33, 34).

5. The friction clutch (1) recited in claim 3, wherein said energy storage elements (41, 42) are leaf springs (43, 44).

6. The friction clutch (1) recited in claim 1, wherein when detected with said friction clutch (1) in an engaged condition, a shifting of said operating point in a direction of said counter-pressure plate (3) is stored in said first energy storage element (24) and said operating point is corrected in a disengagement process of said friction clutch.

7. The friction clutch (1) recited in claim 1, wherein a shifting of said operating point in a direction of said diaphragm spring (6) in a disengagement process of said friction clutch (1) is corrected without intermediate storage.

8. The friction clutch (1) recited in claim 1, wherein a stop (18, 19) arranged with clearance is provided between said ramp ring (13) and said third shaft portion (22) in both directions of said shifting operating point.

9. The friction clutch (1) recited in claim 8, wherein an amount of said clearance between said stops (18, 19) of said ramp ring (13) and of said third shaft portion (22) corresponds to a stroke of said friction clutch (1) between engaged and disengaged conditions.