GB2296748A

GB2296748A - Friction clutch

Info

Publication number: GB2296748A
Application number: GB9526553A
Authority: GB
Inventors: Wolfgang Reik; Gunter Bauerle; Ingo Heitel
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 1995-01-05
Filing date: 1995-12-27
Publication date: 1996-07-10
Anticipated expiration: 2015-12-27
Also published as: FR2729196A1; BR9600022A; DE19548459B4; ITMI960009A0; DE19548459A1; GB2296748B; GB9526553D0; KR960029654A; IT1281590B1; ITMI960009A1

Abstract

A friction clutch 1 for use in motor vehicles wherein an input member 3,5 receives torque from the engine of the vehicle and an output member 8 transmits torque to the input shaft 10 of a transmission is engaged by a device which generates a force that is proportional to the magnitude of the transmitted torque. The device has two relatively rotatable parts 13, 15 between which are balls engaging ramp surfaces. The part 13 rotates with the clutch input and the part 15 is connectible to the shaft 10 through an electromagnetic clutch 19. Engagement of the clutch 19 causes relative rotation between the parts 13 and 15 and the ramp surfaces to move the part 13 axially to engage the main clutch through resilient levers 12. <IMAGE>

Description

FRICTION CLUTCH The present invention relates to friction clutches in general, and more particularly to improvements in friction clutches which can be utilized for the transmission of torque in power trains, for example, in power trains between the combustion engines and automatic, semiautomatic or manually operable transmissions in motor vehicles.

A friction clutch of the above outlined character which is utilized in the power train of a motor vehicle normally comprises a rotary input member which can receive torque from the camshaft, crankshaft or another rotary output element of the combustion engine, a rotary output member which can transmit torque to the rotary input element (e.g., a shaft) of a variable-speed transmission, and means for engaging and disengaging the clutch, ie, for establishing or interrupting a torque transmitting connection between the input and output members.

Engaging/disengaging units for friction clutches of the above outlined character are disclosed, for example, in U.S. Pats. Nos. 5,267,635 and 4,865,173. A drawback of the patented units is that they are complex, bulky and expensive. In addition, the energy requirements for the operation of such clutches are relatively high.One of the reasons for high energy requirements of engaging/disengaging units in heretofore known friction clutches is that such units must overcome the maximum bias of the customary clutch spring (such as a diaphragm spring), which urges the pressure plate of the clutch against the adjacent friction linings of the clutch disc when the clutch is engaged, in order to disengage the clutch, ie, to interrupt the frictional engagement between the friction linings of the clutch disc on the one hand, and the friction faces of the pressure plate and the counter pressure plate on the other hand.

An object of the invention is to provide a friction clutch with novel and improved engaging/disengaging means.

Another object of the invention is to provide a clutch engaging/disengaging unit which is simpler and less expensive than heretofore known units.

A further object of the invention is to provide a friction clutch which can be disengaged in response to the application of a relatively small force.

An additional object of the invention is to provide a power train which employs the above outlined friction clutch and the above outlined clutch engaging/disengaging unit.

Still another object of the invention is to provide a novel and improved friction clutch which can be utilized with particular advantage in the power trains of motor vehicles.

A further object of the invention is to provide a novel and improved method of automating the operation of a friction clutch.

Another object of the invention is to provide an automated friction clutch which can be utilized with advantage in conjunction with semiautomatic or even fully automatic transmissions.

An additional object of the invention is to provide a friction clutch which can dispense with a fulcrum between the clutch spring and the clutch cover or housing.

Still another object of the invention is to provide a novel and improved clutch spring which can be utilized in the above outlined friction clutch.

A further object of the invention is to provide a novel and improved combination of clutches for use in the power train between the output element of a combustion engine and the input element of a transmission in a motor vehicle.

A feature of the present invention resides in the provision of an engageable and disengageable friction clutch for use in a power train to transmit torques having different magnitudes. The improved friction clutch comprises an input member which is connectable with a rotary output element of a prime mover (e.g., with the camshaft or the crankshaft of a combustion engine in a motor vehicle), an output member which is connectable with a rotary input element (e.g., a clutch disc or clutch plate which can be non-rotatably assembled with the input shaft of a variable-speed transmission), and an engagingdisengaging unit comprising means for generating a clutch engaging force which varies as a function of changes of the magnitude of transmitted torque.The force generating means includes a first rotary component which is arranged to be driven by the input member, and a second rotary component which can drive, and can be separably connected with, the output member.

The first and second components of the force generating means are or can be rotatable about a common axis, and the force generating means can comprise means for converting rotary movements of one of the components into axial movements of the other component. Otherwise stated, the force generating means can comprise means for converting torque being transmitted by the friction clutch into a force acting in the direction of the common rotational axis of the first and second components.

In accordance with a presently preferred more specific embodiment, the input member of the improved friction clutch comprises a flywheel which can receive torque from the output element of a prime mover, and such friction clutch further comprises a housing which is rotatable with the flywheel about a common axis, a pressure plate which forms part of the input member and is coaxial with and disposed between the flywheel and the housing and is movable in the direction of the common axis, and a clutch disc which is coaxial with and is disposed between confronting friction faces provided on the flywheel and the pressure plate and forms part of or includes or constitutes the output member. The engaging-disengaging unit of such friction clutch can further comprise means for moving the pressure plate relative to the housing.

Such moving means can comprise at least one lever but preferably two or more (ie, a plurality of) levers. The levers can be mounted in such a way that they include first portions nearer to and second portions more distant from the common axis, and the force generating means of such engaging/disengaging unit can include means for pivoting the lever or levers relative to the housing by way of the first portion(s) of the lever(s). The lever(s) can be pivotably carried by the housing and can be operated by the force generating means to urge the pressure plate in the direction of the common axis toward the flywheel to thus engage the friction clutch.

The force generating means can include a servo mechanism, and such servo mechanism can be interposed between the first and second components of the force generating means.

For example, the servo mechanism can comprise a system of ramps, and such system of ramps can include means for engaging the friction clutch in response to transmission of torque from the input member to the output member. If the output member is operable to transmit torque to the input member by way of the force generating means (e.g., when the friction clutch is installed in the power train between the combustion engine and the transmission of a motor vehicle and the vehicle is coasting), the system of ramps can include means for engaging the friction clutch in response to the transmission of torque from the output member to the input member of the force generating means.

The arrangement can be such that the system of ramps can include means for engaging the friction clutch in response to operation of the vehicle to pull a load as well as in response to coasting of the vehicle.

The engaging-disengaging unit of the friction clutch can further comprise an engageable and disengageable second clutch which operates between the second component of the force generating means and the output member. The second clutch can include or constitute a friction clutch, an electrically operated clutch (such as an electromagnetic clutch) or any other suitable clutch. The electrically operated second clutch can comprise at least one winding, a non-rotatable carrier for the at least one winding, and an armature which is movable within limits relative to the carrier in the direction of the common rotational axis of the first and second components of the force generating means.The armature can include one or more discs, and the second clutch can further comprise means for nonrotatably connecting the armature with the second component of the force generating means; for example, such connecting means can comprise at least one resilient membrane and/or at least one leaf spring. The second clutch can comprise a permanent magnet which is provided on the armature; alternatively, the armature can include, constitute or form part of a permanent magnet. Still further, the second clutch can include an intermediate member which is disposed between the carrier for the at least one winding and the armature (as seen in the direction of the common axis of the first and second components). Such intermediate member is non-rotatably connected with the output member and can be caused to fictionally engage the armature (and/or vice versa).In accordance with a presently preferred embodiment, the intermediate member can comprise one or more discs and can be non-rotatably affixed to the aforementioned input element (such as the input shaft of a transmission) at least substantially without freedom of movement in the direction of the common axis of the first and second components of the force generating means.

The second component of the force generating means can be mounted in such a way that it is rotatable relative to the output member of the improved friction clutch.

If the improved friction clutch is installed in the power train between the engine and a driven element (e.g., the input shaft of a variable-speed transmission) of a motor vehicle, and if the aforementioned engaging-disengaging unit further comprises the aforementioned second clutch which operates between the second component of the force generating means and the output member, the vehicle can be further equipped with means for operating the second clutch can include an electronic circuit arrangement which comprises means for processing signals denoting one or more variable parameters of the motor vehicle.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved friction clutch itself, however, both as to its construction and the mode of assembling, installing and utilizing the same, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.

Figure 1 is a fragmentary axial sectional view of a friction clutch which embodies one form of the invention; Figure 2 is a fragmentary developed view of a system of ramps in the clutch engaging-disengaging unit in the friction clutch of Figure 1; and Figure 3 is a diagram showing the torque-exciting current curve of a second clutch forming part of the clutch engaging-disengaging unit.

The friction clutch 1 which is shown in Figure 1 comprises a housing or cover 2 which is coaxial with and is non-rotatably connected with a flywheel 3. The flywheel 3 forms part of the input member of the friction clutch 1 and is non-rotatably coupled to the rotary output element 4 (e.g., a camshaft or a crankshaft) of a prime mover (not shown) such as the combustion engine of a motor vehicle. The input member of the friction clutch 1 further comprises a rotary pressure plate 5 which is installed between the housing 2 and the flywheel 3 and is non-rotatably but axially movably coupled to the housing 2 by customary leaf springs 6.

The output member of the friction clutch 1 comprises a clutch plate or clutch disc 8 having two sets of friction linings 7 disposed between confronting friction faces 3a and 5a of the flywheel 3 and pressure plate 5, respectively. When the clutch is engaged, the friction face 5a is caused to bear against the adjacent set of friction linings 7 to thereby urge the other set of friction linings against the friction face 3a of the flywheel 3. This enables the hub 9 of the clutch disc 8 to transmit torque to a rotary input element 10 when the prime mover is on to drive the flywheel 3 by way of the output element 4.

The clutch disc 8 can further comprise resilient elements (not specifically shown) which are installed between the two sets of friction linings 7 and urge such friction linings axially of the clutch disc and away from each other. The resilient elements render it possible to effect a more gradual engagement as well as a more gradual disengagement of the clutch 1 because they can expand gradually in response to axial movement of the pressure plate 5 away from the flywheel 3 and yield during axial movement of the pressure plate 5 away from the housing 2, ler toward the flywheel 3. Reference may be had, for example, to Figure 11 in commonly owned U.S. Pat. No.

5,123,877 granted January 23, 1992 to Paul Maucher et al.

for "Torsion damping apparatus for use with friction clutches in the power trains of motor vehicles11. This patent further shows an engine which can be utilized to drive the output element 4 shown in Figure 1 of the present application and a transmission having an input shaft corresponding to the input element 10 receiving torque from the hub 9 of the clutch disc 8 shown in Figure 1 of the present case. The disclosure of the patent to Maucher et al (as well as of each other patent mentioned in the present application) is incorporated herein by reference.

In accordance with a feature of the invention, the friction clutch 1 further comprises a novel and improved clutch engaging-disengaging unit 11 having means including a set of resilient levers, prongs or tongues 12 for moving the pressure plate 5 relative to the housing 2 at least in a direction (ie, toward the flywheel 3) to engage the clutch. The radially outer portions 12a of the levers 12 are pivotally anchored in the housing 2 (ie, they need not be mounted between a pair of seats as is customary in heretofore known friction clutches), and the radially inner portions 12b of such levers can be engaged and moved in the direction of the common axis X-X of the input member 3, 5 and output member 8 by a first component 13 of a composite force generating device 14 also forming part of the clutch engaging-disengaging unit 11. The intermediate portions 12c of the levers 12 engage and urge the pressure plate 5 toward the flywheel 3 when the friction clutch 1 is engaged, ie, when the flywheel 3 and the pressure plate 5 are to transmit torque from the output element 4 to the input element 10.

The levers 12 perform a force multiplying action because the forces which the device 14 applies to the inner portions 12b of such levers are much smaller than (normally only very small or minute fractions of) the forces which the levers 12 apply to the pressure plate 5 in the fully engaged condition of the friction clutch 1.

The moving means of the unit 11 can employ a plurality of discrete levers 12 each having a radially outer portion 12a anchored in the housing 2, or a plurality of levers having their radially outer portions 12a joined into an annular body which is anchored in or otherwise suitably affixed to the housing 2. Such modification simplifies the assembly of the friction clutch 1 by contributing to a significant reduction of the number of discrete parts.

Reference may be had, for example, to the German Patent No. 838 094 which shows a one-piece body with a plurality of interconnected levers or arms.

The force generating device 14 comprises the aforementioned first component 13 and a second component 15 which can be separably connected to the clutch disc 8, ie, to the output member of the friction clutch 1. The component 13 is rotatable with the housing 2, ie, with the flywheel 3 and the pressure plate 5 constituting the input member of the friction clutch 1. The components 13, 15 have limited freedom of angular movement relative to each other, and the force generating device 14 further comprises a system 16 which serves to convert rotary movements of one of the components 13, 15 into axial movements of the other component, ie, to convert torque being transmitted by the friction clutch 1 into a force acting in the direction of the common axis X-X of the input member 3, 5, output member 8, input element 10, first component 13 and second component 15.The system 16 of the force generating device 14 is a servo mechanism which is interposed between the components 13 and 15 and, in the illustrated embodiment, includes or constitutes a system of ramps 17.

As can be seen in Figure 2, the ramp system 17 includes a first annulus of ramps 13a on the component 13, a second annulus of ramps 15a on the component 15, and a set of spherical rolling elements 18 between the confronting pairs of ramps 13a, 15a. It is also possible to omit the ramps 13a or 15a, ie, to use the spherical rolling elements 18 (or analogous rolling elements) with the ramps 13a or with the ramps 15a. The force amplifying factor of the servo mechanism 16 (ie, of the ramp system 17) is a function of the angle or slope (inclination) of the ramps 13a, 15a.

The construction of the improved friction clutch 1 is such that the force generating device 14 of the engaging-disengaging unit 11 engages the clutch in response to transmission of torque from the output element 4 of the prime mover toward the input element 10 of a driven unit, such as a variable-speed transmission having a housing or case 23. The transmission of torque in a direction from the output element 4 toward and to the input element 10 takes place when the vehicle embodying the power train including the friction clutch 1 is in the process of pulling a load. However, and due to the mirror symmetrical design of the ramps 13a, 15a shown in Figure 2, the device 14 can engage the clutch 1 also when the vehicle is coasting, ie, when the clutch disc 8 serves to transmit torque from the (normally) input element 10 to the (normally) output element 4.

In accordance with another feature of the invention, the friction clutch 1 comprises a second clutch 19 which can be engaged to transmit torque between the component 15 of the force generating device 14 and the input element 10 (ie, the output element of clutch disc 8 whose hub 9 is non-rotatably coupled to the element 10). The illustrated second clutch is a friction clutch, and more specifically an electrically operated clutch. Still more specifically, the illustrated clutch 19 is an electromagnetic clutch having a carrier 22 for at least one energizable winding, a disc-shaped armature 20, and a disc-shaped intermediate member 21 between the armature 20 and the carrier 22. The intermediate member 21 can be said to perform the function of a braking or coupling disc and is non-rotatably affixed to the input element 10.In addition, the parts 10 and 21 have no freedom of movement relative to each other in the direction of the axis X-X.

The armature 20 is non-rotatably coupled with the component 15 of the force generating device 14. Such nonrotatable connection can be established by resorting to one or more elastic membranes and/or by resorting to one or more leaf springs analogous to the leaf springs 6. The carrier 22 for one or more windings of the second clutch 19 is held against rotation about the axis X-X, e g., by being affixed to the case 23 of the transmission having an input shaft constituted by or connected to the element 10. Figure 1 shows that the intermediate member 21 is not in actual (direct) contact with the carrier 22; this intermediate member is or can be made of a magnetizable material and is electrically separated from the input element 10 by an insulator 24.

The armature 20 can carry or can he made in part or entirely of a material which is a permanent magnet. By utilizing an armature which at least exhibits residual magnetic properties, one can ensure that a certain predetermined frictional engagement exists between armature 20 and the intermediate member 21 even at times when the winding or windings on the carrier 22 are not connected in circuit with a source of electrical energy.

This, in turn, ensures that the friction clutch 1 can be engaged even when the vehicle is brought to a halt, its engine is arrested and the transmission is shifted into a gear other than neutral. This is ensured in that, when the output element 4 and the input element 10 exhibit a tendency to turn relative to each other, the frictional engagement between armature 20 and the intermediate member 21 of the second clutch 19 results in the generation of torque which causes the parts 13 and 15 of the force generating device 14 to turn relative to each other whereby the ramps 13a, 15a of the system 17 cooperate with the respective rolling elements 18 to engage the friction clutch 1 because the component 13 acts upon the radially inner portions 12a of the levers 12 and causes the intermediate portions 12c of such levers to urge the pressure plate 5 toward the flywheel 3, ie, to engage the friction faces 3a, 5a with the respective friction linings 7 of the clutch disc 8.

The winding or windings on the carrier 22 can be connected with a source of d-c current at least when the vehicle having a power train embodying the friction clutch 1 is to be put to use. By properly selecting the direction of current flow, one establishes a magnetic field which pulls the armature 20 axially in a direction toward the intermediate member 21 to thus enhance the intensity of frictional engagement between the parts 20 and 21 of the second clutch 19. The intensity of frictional engagement between the armature 20 and the intermediate member 21 is dependent upon the intensity or magnitude of the exciter current. By reversing the direction of current flow through the winding or windings of the second clutch 19, one can cause the winding(s) to repel the armature 20 from the intermediate member 2L in the direction of the axis X-X, and, due to magnetizing of the armature 20, one can also terminate the initial or basic frictional engagement between the parts 20 and 21. When the frictional engagement between the parts 20, 21 is interrupted or is reduced to a predetermined low value, the clutch 1 is disengaged, for example, to shift the transmission including the case 23 into a different gear. To this end, the unit 11 is operated in a direction to disengage the friction clutch 1 whereby the component 13 of the device 14 tends to assume the starting or neutral position shown in Figure 2.Such neutral position of the component 13 corresponds to that position of the lever 12 actually shown in Figure 1 which is denoted by the character A.

An antifriction bearing 25 (or an equivalent bearing) is interposed between the component 15 and the input element 10, ie, the component 15 can turn relative to the element 10 as well as relative to the carrier 22 and intermediate member 21 of the second clutch 19. The bearing 25 serves as a means for intercepting the actuating force and for transmitting such force to the input element 10 which, in turn, transmits the force to the case 23 by way of one or more additional bearings, not shown. It is also possible to cause the input element 10 to transmit the actuating force (transmitted thereto by the component 15 via bearing 25) to a part other than the case 23 of the variable-speed transmission.

The intensity of exciting current which is to be applied to the winding or windings on the carrier 22 is selected by an electronic circuit arrangement 26 which has one or more inputs for signals denoting one or more variable parameters of the motor vehicle. For example, the circuit arrangement 26 can process signals denoting the various settings of the transmission including the case 23 and/or other parameters of such transmission. Furthermore, the circuit arrangement 26 can process signals denoting the momentary setting of the braking system of the motor vehicle and/or the magnitude of the load which is to be pulled or which is being pulled by the vehicle.

The unit 11 can constitute or include means for disengaging the friction clutch 1. For example, the unit 11 can include one or more resilient membranes which urge the pressure plate 5 axially and away from the adjacent friction linings 7 of the clutch disc 8. The diaphragm springs 6 also tend to move the pressure plate 5 axially and away from the flywheel 3, ie, toward the housing 2.

The diagram of Figure 3 shows the torque-exciting current curve of the second clutch 19. The point 27 on the curve of Figure 3 denotes the basic torque which is being transmitted by the second clutch 19 in the deenergized condition of the winding or windings on the carrier 22.

As already explained hereinbefore, such basic torque develops as a result of frictional engagement between the armature 20 and the intermediate member 21 in the disengaged condition of the clutch 19. The frictional engagement between the parts 20, 21 increases in response to appropriate manipulation of current which is being applied to the winding(s) on the carrier 22, ie, such selection of the current can be used to select the torque being transmitted or transmittable by the second clutch 19.The frictional engagement between the parts 20, 21 can be weakened by reversing the direction of current flow through the winding(s), ie, one can reduce the magnitude of torque being transmitted by the second clutch 19 and such torque can be reduced to zero by reducing the intensity of the current to a value at which the axially movable armature 20 is completely disengaged from the intermediate member 21. For example, such disengagement of the friction clutch will take place prior to starting of the combustion engine, and this can take place while the transmission is shifted into a gear other than neutral and even if the power train is under stress.

An important advantage of the improved friction clutch 1 is that, at least while the clutch is being engaged, the device 14 can generate a force which determines the intensity of frictional engagement between the input member 3, 5 and the output member 8 in dependency upon the magnitude of the torque which is to be transmitted by the friction clutch. This is accomplished by the simple expedient of providing the device 14 with a first component 13 which receives torque from the input member 3, 5 and a second component 15 which can transmit torque to but can also be separated from the output member 8.

The components 13, 15 of the device 14 cooperate in such a way that they can generate an engaging or closing force for the friction clutch 1. In other words, the torque to be transmitted by the friction clutch 1 is being utilized to generate the force (preferably an engaging force) which is required for an optimal operation of the friction clutch. The force being applied by the device 14 is preferably proportional to the torque being transmitted by the friction clutch 1. The device 14 can regulate the torque being transmitted by the friction clutch 1 in such a way that it barely suffices to prevent a slippage of the friction face 3a and/or 5a relative to the adjacent set of friction linings 7 on the clutch disc 8.The device 14 can generate the required clutch engaging force in a very simple and reliable way, namely in response to angular displacement of the input member 3, 5 and the output member 8 relative to each other. This is accomplished by equipping the unit 11 with the aforediscussed servo mechanism 16 including the ramp system 17, ie, a system which can convert the angular movement of the input member 3, 5 and output member 8 relative to each other into a movement taking place in the direction of the axis X-X.This induces the component 15 to change axial positions of the radially inner portions 12b of the levers 12 so that the intermediate portions 12c can move the pressure plate 5 axially toward the flywheel 3 in order to initiate the transmission of torque or to increase the magnitude of the torque to be transmitted or being transmitted from the output element 4 to the input element 10.

It is equally within the purview of the invention to replace the illustrated levers 12 with differently mounted levers. For example, the friction clutch 1 can be modified in such a way that the radially outer portions 12a of the levers 12 are positioned to bias the pressure plate 5 toward the flywheel 3 in the engaged condition of the thus modified friction clutch and that the radially inner portions 12b of such levers are anchored in and can be flexed relative to the housing or cover 2.

Irrespective of whether the radially inner or the radially outer portions of the levers 12 are anchored in the housing 2, these levers can be mounted in such a way (e.g., in prestressed condition) that they invariably tend to disengage the friction clutch 1, ie, that they tend to permit the pressure plate 5 to move axially and away from the flywheel 3 (e.g., under the bias of the leaf springs 6). This can be accomplished in a particularly simple and efficient way by replacing an annulus of discrete levers 12 with an annulus of levers which are of one piece with an annular portion to form therewith a sort of diaphragm spring which tends to move its levers away from the flywheel 3.

An advantage of the servo mechanism 16 including the ramp system 17 is that it renders it possible to ensure that at a relatively small external force suffices to ensure adequate engagement of the friction clutch 1. As shown in Figure 2 and as already described hereinbefore, the ramp system 17 of the servo mechanism 16 can include ramps 13a, 15a which are provided directly on the respective components 13, 15 of the force generating device 14, or ramps which are provided on at least one of the components 13 and 15. The slope of each of the two portions of each of the illustrated ramps 13a and 15a may but need not be the same.For example, if such ramps are to be used to ensure an engagement of the friction clutch 1 not only when the vehicle is to pull or is actually pulling a load but also when the vehicle is coasting, the slope of the ramps is preferably selected in such a way that the slope of those portions of the ramps which are engaged by the respective rolling elements 18 while the vehicle is coasting is greater than the slope of ramp portions which are engaged by the elements 18 when the vehicle is pulling a load. At least in many instances, it suffices if the slopes of both portions of each of the ramps are at least substantially identical.

The illustrated electrically operated second clutch 19 can be replaced with any one of a variety of other types of clutches without departing from the spirit of the invention. For example, the illustrated clutch 19 can be replaced by a hydraulically or pneumatically operated clutch which is capable of establishing and terminating a torque transmitting connection between the component 15 of the force generating device 14 and the output member 8. The illustrated electromagnetic clutch 19 exhibits the advantage that it enables the friction clutch 1 to act as a parking brake when the engine is arrested and the vehicle is at a standstill while the transmission is shifted in a gear ratio other than neutral.Thus, if the input member 3, 5 and the output member 8 tend to turn relative to each other, the friction clutch 1 is automatically engaged due to at least slight frictional engagement between the armature 20 and the intermediate member 21 of the second clutch 19. Accordingly, and by the simple expedient of properly designing the ramp system 17, one can safely park the vehicle on an upwardly or downwardly sloping surface as long as the transmission is engaged because the engine then acts as a brake.

The second component 15 of the force generating device 14 has limited freedom of angular movement relative to the first component 13 (namely to the extent determined by the ramp system 17) and an unlimited freedom of angular movement relative to the intermediate member 21 and the carrier 22 of winding(s) forming part of the second clutch 19. Furthermore, and as also mentioned hereinbefore, the intermediate member 21 is free to rotate relative to the carrier 22.

Another important advantage of the improved friction clutch 1 is that its operation can be in a very simple and inexpensive way so it can be that utilized in combination with semi automated or fully automated transmissions in the power trains of motor vehicles. This can be accomplished by resorting to the aforediscussed electronic circuit arrangement 26 which processes signals denoting one or more parameters of the motor vehicle. The circuit arrangement 26 can be put to use with particular advantage with the illustrated electromagnetic clutch 19 or an analogous electrically operated clutch. Thus, all the circuit arrangement 26 must do is to regulate the intensity and the direction of the flow of current in the winding or windings on the carrier 22 of the second clutch 19.By properly regulating the intensity and the direction of current flow in the winding or windings on the carrier 22, the circuit arrangement 26 can cause an engagement or disengagement of the friction clutch 1 and can select the magnitude of frictional engagement between the armature 20 and the intermediate member 21 of the second clutch 19. The advantages of an armature 20 which supports or includes or constitutes or is part of at least one permanent magnet were pointed out hereinbefore, ie, such selection of the armature ensures that the clutch 19 can transmit some torque even when the winding or windings on the carrier 22 are disconnected from the source of electrical energy.In order to disengage the friction clutch 1, it is merely necessary to use the winding or windings of the second clutch 19 as a means for building up a magnetic field which opposes the magnetic field of the armature 20.

The armature 20 (ie, an armature which carries one or more permanent magnets or forms part of or includes or constitutes a permanent magnet) can be replaced with a disc-shaped or an otherwise configurated member which is preferably or which can be made of a suitable metallic material and is biased against the intermediate member 21 with a predetermined force. Such predetermined force can be furnished by one or more energy storing elements (not shown), e.g., the energy storing element or elements serving to ensure the transmission of torque between the armature 20 and the second component 15 of the force generating device 14.

If the second clutch 19 is replaced with a fluid operated (pneumatic or hydraulic) clutch, the movable part of the cylinder and piston assembly of such fluid-operated clutch can be caused to perform its movements in response to actuation of one or more valves which, in turn, can receive signals from the output or outputs of the electronic circuit arrangement 26 or any other arrangement which can ensure proper operation of the fluid-operated second clutch as a function of changes of one or more parameters of the motor vehicle. It has been found that relatively low (or even extremely low) pressures of the selected (hydraulic or pneumatic) fluid suffice to ensure adequate operation of the friction clutch 1; this is attributable to the aforediscussed design and mode of operation of the clutch engaging-disengaging unit 11.

In place of an electromagnetic clutch 19, a clutch operating on a magnetorheological basis can be used as auxiliary clutch. It can be particularly advantageous if the clutch is constructed so that the magnetorheological fluid interrupts the operation of permanent magnets so that when the clutch is not fed with current, it is in practice closed and can transmit a torque so that this can take over a parking blocking function. The magnetic field of the or each permanent magnet can be reduced or removed entirely by the application of current so that then the torque transmissible by the clutch is reduced or is completely absent. Such a solution has the advantage that no friction vibrations can arise within the auxiliary clutch. Such frictional vibrations can be disadvantageous as a result of the high amplification produced by the servo mechanism, because they influence the ability to modulate torque transmitted by the main clutch.

The improved friction clutch is susceptible of additional modifications without departing from the spirit of the aforedescribed invention. By way of example only, the improved friction clutch can be installed in any one of a variety of different power trains in motor vehicles and/or elsewhere, and its parts can be modified, combined and/or otherwise rearranged in a number of ways.

Furthermore, at least some of the elements of the improved friction clutch are believed to constitute independent inventions, and applicants reserve the right to seek such protection in the present application and/or in one or more divisions, continuations and/or continuations- in-part of the present application. Still further, applicants reserve the right to seek protection for combinations of two or more elements forming part of the improved friction clutch as well as for the method or methods of assembling such elements into the improved friction clutch and/or of installing such friction clutch in a power train.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of the above outlined contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.

Claims

1. An engageable and disengageable friction clutch for use in a power train to transmit torques having different magnitudes, comprising an input member connectable with a rotary output element of a prime mover; an output member connectable with a rotary input element; and an engaging-disengaging unit comprising means for generating a clutch engaging force which varies as a function of changes of the magnitude of transmitted torque, said force generating means including a first rotary component arranged to be driven by said input member and a second rotary component arranged to drive and being separably connectable with said output member.

2. A friction clutch as claimed in Claim 1, wherein said components are rotatable about a common axis and said force generating means comprises means for converting rotary movements of one of said components into axial movements of the other of said components.

3. A friction clutch as claimed in Claim 1, wherein said force generating means comprises means for converting torque being transmitted by the friction clutch into a force acting in the direction of a common rotational axis of said components.

4. A friction clutch as claimed in any preceding claim, wherein said input member comprises a flywheel and the clutch further comprises a housing rotatable with said flywheel about a common axis, a pressure plate forming part of said input member, coaxial with and disposed between said flywheel and said housing and movable in the direction of said axis, and a clutch disc coaxial with and disposed between confronting friction faces provided on said flywheel and said pressure plate and forming part of said output member, said unit further comprising means for moving said pressure plate relative to said housing.

5. A friction clutch as claimed in Claim 4, wherein said means for moving comprises a plurality of levers.

6. A friction clutch as claimed in Claim 5, wherein said levers include first portions nearer to and second portions more distant from said axis, said force generating means including means for pivoting said levers relative to said housing by way of said first portions of said levers.

7. A friction clutch as claimed in Claim 5 or Claim 6, wherein said levers are pivotally carried by said housing and are operable by said force generating means to urge said pressure plate in the direction of said axis toward said flywheel to thus engage the friction clutch.

8. A friction clutch as claimed in any preceding claim, wherein said input element includes an input shaft of a transmission.

9. A friction clutch as claimed in any preceding claim, wherein said force generating means includes a servo mechanism.

10. A friction clutch as claimed in Claim 9, wherein said servo mechanism is interposed between said first and second components of said force generating means.

11. A friction clutch as claimed in Claim 9 or Claim 10, wherein said servo mechanism comprises a system of ramps.

12. A friction clutch as claimed in Claim 11, wherein said system of ramps includes means for engaging the friction clutch in response to transmission of torque from said input member to said output member.

13. A friction clutch as claimed in Claim 11 or Claim 12, wherein said output member is operable to transmit torque to said input member by way of said force generating means and said system of ramps includes means for engaging the friction clutch in response to transmission of torque from said output member to said input member.

14. A friction clutch as claimed in any one of Claims 11 to 13, wherein said power train is installed in a motor vehicle which is operable to pull a load and to coast, said system of ramps including means for engaging the friction clutch in response to operation of the vehicle to pull a load as well as in response to coasting of the vehicle.

15. A friction clutch as claimed in any preceding claim, wherein said unit further comprises an engageable and disengageable second clutch between said second component and said output member.

16. A friction clutch as claimed in Claim 15, wherein said second clutch includes a friction clutch.

17. A friction clutch as claimed in Claim 15, wherein said second clutch includes an electromagnetic clutch.

18. A friction clutch as claimed in Claim 15, wherein said second clutch includes an electrically operated clutch.

19. A friction clutch as claimed in Claim 18, wherein said input and output members are rotatable about a common axis and said second clutch comprises at least one winding, a non-rotatable carrier for said at least one winding, and an armature movable within limits relative to said carrier in the direction of said axis.

20. A friction clutch as claimed in Claim 19, wherein said armature includes at least one disc.

21. A friction clutch as claimed in Claim 19 or Claim 20, further comprising means for non-rotatably connecting said armature with said second component of said force generating means.

22. A friction clutch as claimed in Claim 21, wherein said connecting means comprises a resilient membrane.

23. A friction clutch as claimed in Claim 21, wherein said connecting means comprises at least one leaf spring.

24. A friction clutch as claimed in any one of Claims 19 to 23, wherein said second clutch comprises a permanent magnet provided on said armature.

25. A friction clutch as claimed in any one of Claims 19 to 24, wherein said armature includes a permanent magnet.

26. A friction clutch as claimed in any one of Claims 19 to 25, wherein said second clutch further comprises an intermediate member disposed between said carrier and said armature in the directions of said axis, non-rotatably connected with said output member and fictionally engageable with said armature.

27. A friction clutch as claimed in Claim 26, wherein said intermediate member comprises at least one disc.

28. A friction clutch as claimed in Claim 26 or Claim 27, wherein said intermediate member is non-rotatably affixed to said input element at least substantially without freedom of movement in the direction of said axis.

29. A friction clutch as claimed in any preceding claim, wherein said second component is rotatable relative to said output member.

30. A friction clutch as claimed in any preceding claim, wherein said power train is installed in a motor vehicle and said unit further comprises a second clutch between said second component and said output member and means for operating said second clutch including an electronic circuit arrangement, said circuit arrangement comprising means for processing signals denoting at least one variable parameter of the motor vehicle.

31. A friction clutch substantially as herein described with reference to the accompanying drawings.