FRICTION CLUTCH

Abstract

A friction clutch for a drivetrain includes an input shaft, an output shaft, a compressible friction pack including a normally closed spring system, and an actuating device. The compressible friction pack is for transmitting a torque between the input shaft and the output shaft in a closed state of the friction clutch. The actuating device is for producing an axial actuating force to compress the compressible friction pack. The actuating device includes an opening spring for exerting an opening force, a centrifugal mass unit including a ramp, and a switching element including a counterpart ramp. The centrifugal mass unit is movable through a radial travel at a predetermined rotational speed of the input shaft. The ramp and the counterpart ramp form a ramp pairing with a ramp gradient to convert the radial travel into the axial actuating force acting counter to the opening force to compress the compressible friction pack.

Claims

1.-7. (canceled)

8. A friction clutch for a drivetrain, comprising: an axis of rotation; an input shaft; an output shaft; a compressible friction pack, comprising a normally closed spring system, for transmitting a torque between the input shaft and the output shaft in a closed state of the friction clutch; and an actuating device for producing an axial actuating force to compress the compressible friction pack, the actuating device comprising: an opening spring for exerting an opening force; a centrifugal mass unit, comprising a ramp, movable through a radial travel at a predetermined rotational speed of the input shaft; and a switching element comprising a counterpart ramp that, together with the ramp, forms a ramp pairing comprising a ramp gradient to convert the radial travel into the axial actuating force acting counter to the opening force to compress the compressible friction pack.

9. The friction clutch of claim 8, wherein the compressible friction pack is only compressed by the normally closed spring system in the closed state.

10. The friction clutch of claim 8, wherein: the ramp pairing is of multistage design and is the only ramp pairing of the actuating device; the ramp gradient is variable over the radial travel of the centrifugal mass unit; and the opening force can only be overcome by the actuating device.

11. The friction clutch of claim 10, wherein: the ramp is formed by the centrifugal mass unit; the counterpart ramp is formed by the switching element; and the counterpart ramp comprises: a first partial ramp comprising a first ramp slope; and a second partial ramp, radially outside of the first partial ramp, comprising a second ramp slope less than the first ramp slope.

12. The friction clutch of claim 8, wherein: the opening spring is a diaphragm spring comprising: an outer edge; an inner edge; and an intermediate region between the outer edge and the inner edge; the diaphragm spring is supported on the outer edge; the inner edge operates on the compressible friction pack; and that axial actuating force acts on the intermediate region.

13. A drivetrain comprising: the friction clutch of claim 8; a consuming unit; and a drive assembly comprising a driven shaft, wherein the driven shaft is connectable to the consuming unit by the friction clutch for torque transmission with a variable transmission ratio.

14. A motor vehicle comprising a driven wheel drivable by the drivetrain of claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The disclosure described above is explained in detail below in relation to the relevant technical background, with reference to the associated drawings, which show example embodiments. The disclosure is not in any way restricted by the purely schematic drawings, and it should be noted that the drawings are not to scale and are not suitable for defining size ratios. In the drawings:

[0039] FIG. 1 shows a friction clutch having two centrifugal mass units in section;

[0040] FIG. 2 shows a friction clutch having a single centrifugal mass unit in section;

[0041] FIG. 3 shows a force/spring travel diagram of a friction clutch with a normally-closed friction pack;

[0042] FIG. 4 shows a torque transmission diagram as a function of the rotational speed with a friction clutch having two centrifugal mass units;

[0043] FIG. 5 shows a centrifugal mass unit in section with two partial ramps in the engaged position; and

[0044] FIG. 6 shows a drivetrain in a motor vehicle having a friction clutch.

DETAILED DESCRIPTION

[0045] FIG. 1 shows a friction clutch 38 having two centrifugal mass units and having an axis of rotation 2, in which a friction pack 42 is provided. This friction pack 42 is embodied as a normally-open lamella pack. This friction clutch 38 switchably connects an input shaft 4 to an output shaft 5 along the axis of rotation 2, depending on the input speed of rotation, i.e. semiautomatically. To close the friction pack 42, a first centrifugal mass unit 40 and a second centrifugal mass unit 41 of an actuating device 39 are provided. In this arrangement, the first centrifugal mass unit 40 is connected to the input shaft 4, with the result that the friction pack 42 is compressed when a predetermined rotational speed is applied to the input shaft 4. The second centrifugal mass unit 41 is connected to the output shaft 5, and therefore the closure of the friction pack 42 is assisted by the second centrifugal mass unit 41 only when the input shaft 4 is synchronized with the output shaft 5.

[0046] FIG. 2 illustrates a friction clutch 1 having an actuating device 8, which comprises only a single centrifugal mass unit 10. In this case, the actuating device 8 is furthermore equipped with an opening spring 21 because, in this case, a friction pack 6 has a normally-closed friction clutch configuration. By means of a normally-closed spring system 18, in this case by means of leaf springs 58, the friction pack 6 thus exerts the pressing force 45 in the unactuated state, as a result of which the friction pack 6 is compressed and a predetermined traction torque 52 (ref. FIG. 4) can be transmitted. The opening spring 21, in this case embodied as a diaphragm spring, rests with its inner edge supported on the output shaft 5 and, by means of its outer edge 36, acts on the friction pack 6, in this case by means of a stepped bolt, in a manner antagonistic to the normally-closed spring system 18.

[0047] The opening spring 21 is therefore designed to open the friction pack 6 in the state of rest, i.e. normally. Overall, therefore, the friction clutch 1 has a normally-open friction clutch configuration. If there is a rotational speed below a predetermined rotational speed 16 (ref. FIG. 4), the friction pack 6 is open. When a predetermined rotational speed 16 is applied, the centrifugal mass unit 10 interacts with the switching element 11 to counter the opening force 20 of the opening spring 21, with the result that the friction pack 6 closes automatically without the action of the actuating force 9, i.e. due to the movement of the centrifugal mass unit 10. In the closed state, the input shaft 4 and the output shaft 5 are synchronous or synchronized with one another.

[0048] FIG. 3 illustrates a diagram of the force variation against the spring travel. The vertical axis shows the force 43 and the transverse axis shows the spring travel 47. In the region of the release process 57, i.e. on the right of the operating point 46 in the diagram, the friction pack is held closed by means of the normally-closed spring force 19. This is counteracted by the (larger) opening force 20 of the opening spring 21 (ref. FIG. 2), which holds the friction pack open on the left of the operating point 46. At the operating point 46, synchronization of the friction partners of the friction pack, referred to as clutch slip, takes place. The operating point 46 is therefore the point of transition from open to closed. Here, there is no travel before the necessary pressing force has been built up. Owing to the fixing of the normally-closed spring system 18 (ref. FIG. 2) to one friction partner of the friction pack, e.g. the inner cage, and to the engagement of the opening spring 21 on the opposite corresponding friction partner, e.g. the outer cage, the normally-closed spring force 19 engages only when the opening spring 21 is released to such an extent that the (slipping) plane of the operating point 46 is reached. To engage the friction pack, the opening force 20 must first of all be overcome by means of the centrifugal mass unit alone, without assistance from the normally-closed spring force 19. Only in the closed state does the normally-closed spring force 19 engage, and only a small actuating force 9 is required to keep the friction pack closed.

[0049] FIG. 4 shows a torque transmission diagram of the semiautomatic friction clutch, wherein a transmissible torque 7 is illustrated as a function of the rotational speed 16. The figure furthermore shows, by way of example, a torque characteristic 49 of a drive assembly, which is below a lower safety limit 55 and an upper safety limit 56, and therefore the output torque can be transmitted safely by means of the friction clutch. When driving away, the transmissible traction torque 48 is achieved only at a high rotational speed 16 in accordance with the profile of the closing traction torque rise 50, and therefore driving away takes place only when a high rotational speed is present. As soon as the input shaft and the output shaft are synchronized with one another, the rotational speed required to open the friction clutch shifts to a lower range. Moreover, the friction clutch is opened more quickly, i.e. above a lower rotational speed range, namely along the profile of the opening traction torque rise 51. In the overrun mode, only a lower torque can be transmitted, namely the overrun torque 52, wherein the respective limiting rotational speeds on the profile of the closing overrun torque rise 53 and the opening overrun torque rise 54, respectively, of the overrun mode are at the same rotational speeds 16 in comparison with the traction mode.

[0050] FIG. 5 shows (at least a section of) an actuating device 8, in which a switching element 11 forms a ramp pairing 12 together with a centrifugal mass unit 10. The centrifugal mass unit 10, or the centrifugal mass shown here, moves outward away from the axis of rotation 2 along the radial travel 17. The centrifugal mass unit 10 is situated in an end position at the end of the radial travel 17. The centrifugal mass unit 10 has a ramp 14, and the switching element 11 has a corresponding counterpart ramp 15. The counterpart ramp 15 is subdivided into a first partial ramp 31 and a second partial ramp 32. The ramp gradient 13 of the counterpart ramp 15 is thereby divided into two sections, namely with the first ramp slope 33 on the first partial ramp 31 and with the second ramp slope 34 on the second partial ramp 32.

[0051] On the first partial ramp 31, the first ramp slope 33 is steeper than the second ramp slope 34, and therefore the centrifugal mass unit 10 must produce a higher centrifugal force on a first section of the radial travel 17 to force the switching element 11 axially, i.e. in the direction of the opening travel 44. This results in closure of the friction pack (cf. FIG. 2) only at a higher rotational speed than if the first ramp slope 33 were of shallower configuration, as is the case with the second partial ramp 32 for example.

[0052] As illustrated here, the centrifugal mass unit 10 rests on the second partial ramp 32 with the second ramp slope 34, and the second ramp slope 34 is shallower than the first ramp slope 33. As a result, a lower rotational speed is now required to hold the centrifugal mass unit 10 in the illustrated position at the end of the radial travel 17 and to produce the required pressing force 45 or actuating force 9. This effect thus corresponds to the use of a higher mass at a constant ramp slope. For this reason, the practice hitherto has been to use a second centrifugal mass unit with, furthermore, a higher mass on the transmission side. It may be pointed out here that this actuating device 8 can be used both with a friction pack 42 of the kind shown in FIG. 1 and a friction pack 6 of the kind shown in FIG. 2. It may also be pointed out that the actuating device 8 shown can furthermore comprise a second centrifugal mass unit and/or a diaphragm spring.

[0053] In FIG. 6, a drivetrain 3 comprising a drive assembly 22, here in the form of an internal combustion engine, a driven shaft 23 (input shaft 4), a friction clutch 1 and a consuming unit 24 forming a left-hand driven wheel 26 and a right-hand driven wheel 27 connected in a torque-transmitting manner by means of output shaft 5, is illustrated schematically. Here, the drivetrain 3 is arranged in a motor vehicle 25, wherein the drive assembly 22 is arranged with its motor axis 30 (axis of rotation 2) transversely to the longitudinal axis 29, in front of the driver's cab 28.

[0054] A construction of a semiautomatic actuating system that is simple and simple to check is made possible with the friction clutch proposed here.

LIST OF REFERENCE SIGNS

[0055] 1 friction clutch [0056] 2 axis of rotation [0057] 3 drivetrain [0058] 4 input shaft [0059] 5 output shaft [0060] 6 friction pack [0061] 7 torque [0062] 8 actuating device [0063] 9 actuating force [0064] 10 centrifugal mass unit [0065] 11 switching element [0066] 12 ramp pairing [0067] 13 ramp gradient [0068] 14 ramp [0069] 15 counterpart ramp [0070] 16 rotational speed [0071] 17 radial travel [0072] 18 normally-closed spring system [0073] 19 normally-closed spring force [0074] 20 opening force [0075] 21 opening spring [0076] 22 drive assembly [0077] 23 driven shaft [0078] 24 consuming unit [0079] 25 motor vehicle [0080] 26 left-hand driven wheel [0081] 27 right-hand driven wheel [0082] 28 driver's cab [0083] 29 longitudinal axis [0084] 30 motor axis [0085] 31 first partial ramp [0086] 32 second partial ramp [0087] 33 first ramp slope [0088] 34 second ramp slope [0089] 35 inner edge of the diaphragm spring [0090] 36 outer edge of the diaphragm spring [0091] 37 intermediate region of the diaphragm spring [0092] 38 friction clutch having two centrifugal mass units [0093] 39 actuating device having two centrifugal mass units [0094] 40 first centrifugal mass unit [0095] 41 second centrifugal mass unit [0096] 42 normally-open friction pack [0097] 43 force [0098] 44 opening travel [0099] 45 pressing force [0100] 46 operating point [0101] 47 spring travel [0102] 48 transmissible traction torque [0103] 49 torque characteristic [0104] 50 closing traction torque rise [0105] 51 opening traction torque rise [0106] 52 transmissible overrun torque [0107] 53 closing overrun torque rise [0108] 54 opening overrun torque rise [0109] 55 lower safety limit [0110] 56 upper safety limit [0111] 57 release process [0112] 58 leaf springs