Friction clutch

A friction clutch having a clutch ring and having two clutch disks, which are mounted so as to be rotatable about a clutch axis of rotation and on which friction surfaces are formed, is presented. In this case, the clutch ring and the clutch disks can be moved parallel to the clutch axis of rotation and relative to one another in such a way that, for torque transmission, first friction surfaces on each of the clutch disks can be moved into frictional surface contact with a respective second friction surface on the clutch ring. A first and a second friction surface in each case are matched to one another as a friction surface pair, having in each case a friction surface curved convexly in the direction of the clutch axis of rotation and a friction surface curved concavely in the direction of the clutch axis of rotation.

CROSS REFERENCE TO RELATED APPLICATION

FIELD OF THE INVENTION

The invention relates to a friction clutch.

BACKGROUND OF THE INVENTION

Friction clutches are known in a very wide variety of embodiments, especially in the area of vehicle construction. Here, a construction which is as compact and space-saving as possible is the aim, especially for the transmission of rotary motion to an auxiliary unit.

For example, friction clutches are known in which two clutch disks and a clutch ring are mounted so as to be rotatable about a common clutch axis of rotation, wherein the two clutch disks are mounted so as to be movable axially along the clutch axis of rotation relative to one another and with respect to a clutch ring. The clutch disks can each be mounted for conjoint rotation and axial movement on a common rotary shaft, allowing them to be brought into frictional contact with the clutch ring, which is mounted so as to be rotatable separately from the clutch disks, by moving them together or moving them apart, for example. Moreover, the two clutch disks can also be mounted separately from one another and, for example, coaxially in order, for example, to transmit a rotary motion from a first one of the clutch disks to a second one of the clutch disks via the clutch ring.

In such clutches, the friction surfaces are often formed on conical surface regions of the clutch disks and the clutch ring. In this case, the clutch disks can be pushed like wedges into the clutch ring, for example, thereby making it possible to achieve a wedging effect, by means of which a transmissible torque can advantageously be increased. However, large amounts of heat can arise during the closing or release of such clutches, and these can not only subject the interacting friction surfaces to relatively high stress but can also make it more difficult to separate the friction surfaces for decoupling if the actuating forces are too high.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improved friction clutch which has increased stability and reliability for the same overall size.

The invention starts from a friction clutch having a clutch ring and having two clutch disks, wherein the clutch ring and the clutch disks are mounted so as to be rotatable about a clutch axis of rotation, in particular a common clutch axis of rotation. Friction surfaces are formed on the clutch ring and on the clutch disks. The clutch ring and the clutch disks can be moved parallel to the clutch axis of rotation and relative to one another in such a way that, for torque transmission, first friction surfaces on each of the clutch disks can be moved into frictional surface contact with a respective second friction surface on the clutch ring.

The heart of the invention is that a first and a second friction surface in each case are matched to one another as a friction surface pair, having in each case a friction surface curved convexly in the direction of the clutch axis of rotation and a friction surface curved concavely in the direction of the clutch axis of rotation.

The friction surfaces are therefore not arranged exclusively perpendicular to the clutch axis of rotation but have surface regions with a tangential surface, the normal vector of which has a component oriented radially outward. In this context, a friction surface curvature which is concave or convex in the direction of the clutch axis of rotation means that, in addition to the curvature defined by the clutch axis of rotation, each individual friction surface of a friction surface pair also has at least one center of curvature which has at least one radius of curvature perpendicular to the clutch axis of rotation. The radii of curvature can be different. Conceptually, the additional curvature can be represented with the aid of a plane which is parallel to the clutch axis of rotation, passes through the clutch axis of rotation and intersects one of the friction surfaces, wherein a convexly or concavely curved friction surface is formed on this plane as an arcuately curved line segment which has a finite, constant or variable radius of curvature.

A first and a second friction surface of a friction surface pair are preferably matched to one another in such a way that, when in frictional contact, the centers of curvature, for example, and the radii of curvature, for example, of mutually contacting friction surface regions curved along the clutch axis of rotation coincide, in particular in all the touching friction surface regions. As a result, the friction surfaces are advantageously fully in contact in the coupled state and contribute as a whole to torque transmission.

Since, apart from a curvature about the axis of rotation of the clutch, the friction surfaces additionally have another curvature in a direction parallel to the clutch axis of rotation, the clutch according to the invention can provide a larger friction surface over a given length along the clutch axis of rotation than, for example, a clutch with conical friction surfaces. Moreover, the curved friction surfaces advantageously counteract self-locking of the clutch disks on the clutch ring. This is due to the fact that, when the friction surfaces are pressed together, the additional curvature of the friction surfaces along the clutch axis of rotation means that the forces on a radially outer friction surface over a corresponding segment of the clutch axis of rotation are not inclined at a uniform angle with respect to a plane perpendicularly intersecting the clutch axis of rotation but that this inclination of the direction of force varies along the clutch axis of rotation. As a result, a friction surface pair can have both surface segments with a relatively powerful wedging effect and also surface regions which counteract sticking in the coupled state.

In this case, the concavely and the convexly curved friction surfaces can have at least approximately a spherical profile. This offers the advantage that, for example, a convex friction surface has a convex shape not only around the clutch axis but also in the direction along the clutch axis. In this case, the centers of curvature of curves which extend in mutually independent directions of one of the friction surfaces advantageously lie on a common side with respect to the friction surface under consideration. Because the production of spherical surface shapes can be controlled more effectively, it is preferred, in particular, if the friction surfaces have a spherical profile in accordance with a surface segment of a sphere or of a spherical cavity.

In principle, it is also possible to conceive of embodiments of the friction clutch according to the invention in which the friction surfaces are convexly and concavely curved, thereby making it possible for them to resemble the surface segments of a torus, for example.

The friction surfaces of a friction surface pair are preferably shaped in the manner of a segment of a boundary surface, in particular having surface segments a spherical surface. In particular, the friction surfaces have the form of a surface of a spherical segment. In the present invention, the term spherical segment is understood in accordance with the mathematical definition to be a segment of a sphere with plane-parallel side faces. In the text which follows, this kind of surface shape is referred to as a spherical surface strip. In the case of a concave friction surface, the surface segment preferably corresponds to a spherical surface strip of the inner surface of a hollow sphere, at least in part. Such an embodiment offers the advantage that the friction surfaces of a friction surface pair and surface segment of a sphere or of a hollow sphere always remain in frictional surface contact, even in the case of different axial forces parallel to the clutch axis of rotation.

The second friction surfaces on the clutch ring can be convexly curved. For a preferred embodiment of the invention, provision is made for the second friction surfaces on the clutch ring to be concavely curved. In this case, the first friction surfaces of the clutch disk can fit into the concave friction surfaces of the clutch ring, in the case of an axial movement until abutment against the clutch ring, for example, and thereby advantageously achieve a relatively high wedging effect.

In particular, if the second friction surfaces on the clutch ring are not only concavely curved but also slope toward one another, this offers the advantage that the friction clutch can be designed in such a way that the clutch disks, lying within the clutch ring, come into frictional contact with the second friction surfaces when moved apart and, in frictional engagement, form a substantially closed system, into which penetration of contaminants is entirely or virtually impossible.

For a preferred embodiment of the invention, the clutch ring is designed as a component produced in one continuous piece and preferably from a single material. As a result, the clutch ring advantageously has a high stability. If the clutch ring is produced in one continuous piece from a single material, the homogeneous material composition which can thereby be achieved offers better thermal conductivity for the dissipation of frictional heat, for example.

The diameters of the clutch disks can be reduced in such a way over an angle segment around a predetermined axis of rotation that the clutch disks can be introduced jointly into the clutch ring. This makes it possible to assemble a clutch according to the invention even with an integrally formed clutch ring.

In order to avoid an unbalance during rotary motion of the clutch disks, the diameters of the two clutch disks are each reduced symmetrically with respect to a predetermined axis of rotation over an angle segment.

Moreover, assembly of the clutch can also be made easier if at least one recess, with the aid of which the clutch disks can be introduced into the clutch ring, is formed on the clutch ring.

One or more springs, which push the clutch disks away from one another, can be arranged between the clutch disks. It is furthermore possible for one or more spring elements that can move the clutch disks away from one another out of a decoupled position, for example, to act on the clutch disks.

In order to ensure release of both clutch disks from the clutch ring when the friction clutch according to the invention is actuated for decoupling, a stop element, e.g. an annular stop element, is preferably formed in the clutch ring between two concave friction surfaces of the clutch ring, for example. By way of example, the clutch ring can have one or more openings, in particular one or more openings between interior friction surfaces, at which a stop element, e.g. a stop ring, can be introduced into the clutch ring and preferably between the clutch disks. It is thereby advantageously possible to mount a stop element in the clutch ring after installation of the clutch disks. In order to avoid openings in the clutch ring, fixing means can be provided, by means of which a stop element can be mounted temporarily on at least one of the clutch disks for joint assembly with the clutch disks. It is thereby possible to achieve a relatively higher strength for the clutch ring.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a section of a compressor40having a friction clutch1according to the invention. The friction clutch1is provided for the purpose of transmitting a rotary motion from a driving wheel to a rotary shaft11,12or of decoupling the two parts, as the case may be.

InFIG. 1, the friction clutch1is shown in the coupled state. A clutch ring2provides an input side of the clutch and is connected by driver element8to the driving wheel10. The driver element8can be of single- or multi-part design and is secured on the driving wheel10by means of a screw9, for example.

The driving wheel10is mounted coaxially with a front shaft section and coaxially with the driven shaft by means of a rotary bearing. The clutch1, the driving wheel10and the rotary shaft11,12rotate about a common axis A, which simultaneously defines a clutch axis of rotation.

Two clutch disks3and4are arranged between the clutch ring2and the shaft section11and are mounted so as to be axially movable parallel to the clutch axis of rotation A. One or more spring elements5are arranged between the clutch disks3and4and can consist of two stacks of diaphragm springs, for example. The springs5hold the clutch disks3and4in a disengaged position, with a first friction surface pair18abeing in frictional contact between clutch disk3and the clutch ring2, and a second friction surface pair18bbeing in frictional contact between clutch disk4and the clutch ring2. By means of a spherical convex curvature of the friction surface pairs18aand18bon the part of the clutch ring2, the extent to which the clutch disks3and4can move apart in the axial direction A is limited.

In the region of a central plane perpendicular to the axis of rotation A, the clutch ring2has a groove-shaped recess19, into which a stop ring6projects, thereby fixing the position of the stop ring6.

A retaining ring7, which limits axial movements parallel to the axis of rotation in the direction of the driving wheel10, is mounted on the shaft section11. An annular piston14is provided for actuation of the clutch1. The annular piston14is mounted so as to be movable in a cylinder15and is sealed off with respect to the cylinder15by sealing rings14ain such a way that pressures by means of which the piston14can move clutch disk4toward clutch disk3, counter to the force of the spring5, can be set in a pressure space15aof the cylinder15. By means of the stop ring6, it is possible to ensure that the clutch ring2is released from both clutch disks3and4when the clutch disks3and4move together and hence that the driving wheel10is decoupled from the shaft11,12.

Another illustrative embodiment of a friction clutch1according to the invention is shown inFIG. 2. The friction clutch1has a clutch ring2, which is preferably of integral design. Two friction surfaces20aand20b, each fully encompassing the axis of rotation of symmetry of the clutch ring2, are formed on the inside of the clutch ring2. In this case, the friction surfaces20aand20bhave a spherical curvature, i.e. they not only have a curvature around the principal axis of the clutch ring but additionally have a nonlinear curved profile along the principal axis. By virtue of the curvature, the two friction surfaces20aand20bhave the largest inside diameter in the center. At the same time, the two friction surfaces20aand20bslope concavely toward one another in such a way that each of the two friction surfaces20aand20breaches the smallest inside diameter at the respective end face28aand28b. At these end faces28aand28b, the friction surfaces20aand20bare each bounded by an outer edge29aand29b.

The friction surfaces20aand20bare separated from one another by a groove19extending between them on the inside of the clutch ring2. The clutch ring2can have slots27, at which the clutch ring2is penetrated as far as the groove19and through which segments of a stop ring6, for example, can be introduced into the region within the clutch ring2.

The friction clutch1comprises two clutch disks3and4, which are of annular design. On their central inner opening, the clutch disks3and4can have a spline system25, by means of which the clutch disks can be mounted for conjoint rotation and axial movement on a splined shaft (not shown).

Friction surfaces21aand21bare formed on a radially outward-facing edge surface of the clutch disks3. Clutch disk4likewise has frictional surfaces22aand22bon an outer edge surface. The friction surfaces21a,21b,22aand22bof the clutch disks3and4are matched to the respective friction surfaces20aand20bof the clutch ring20. In particular, they can be of convex design with the same sphere radius of a spherical surface as the concave frictional surfaces20aand20bon the inside of the clutch ring2.

The central point of the friction surfaces formed as spherical surface segments is at the center of the clutch ring2, toward which the clutch disks3and4can be moved in order to release the friction surfaces21a,21band22a,22bfrom the respective friction surface20aand20bon the clutch ring.

Another illustrative embodiment of a friction clutch1according to the invention, with the aid of which a procedure for assembling the friction clutch1will be explained below, is shown inFIGS. 3,4,5,6,7aand7b.

InFIGS. 3 and 4, the friction clutch is shown in a first assembly position. Two friction clutches3and4are pressed together counter to a force of spring elements5, wherein a passage disk16and a stop spring6are arranged between the clutch disks3and4. The clutch disks3and4are arranged symmetrically above and below an intermediate plane, horizontal plane H (FIG. 4), in which the clutch axis A is embedded and which intersects a central plane M of the clutch ring2at right angles.

On the inside, the clutch ring2has two concave spherical friction surfaces20aand20b, which are separated from one another by a groove19. Here, the two friction surfaces20aand20bcorrespond to spherical segment boundary surfaces on an inside of a common spherical shell. Accordingly, the friction surfaces20aand20bare curved with an identical constant radius of curvature around a common center of curvature.

At an outer edge29a, a concave spherical friction surface20aand an end face28ameet. In the same way, a friction surface20band an end face28bof the clutch ring2meet at an outer edge29b. The outer edges29aand29bpreferably have an identical inside diameter or inner radius.

A central plane M of the clutch ring2, the plane being shown inFIG. 3, is perpendicular to the clutch axis of rotation and forms a section plane for a view along the clutch axis of rotation A, the view being shown inFIG. 4. The horizontal plane which lies between the clutch disks3,4passes through the center of curvature Z of the friction surfaces20aand20b. The center of curvature Z simultaneously forms the center of the friction clutch and lies at the point of intersection of the central plane M and the clutch axis of rotation A.

Convex friction surfaces21a,21b,22a,22b, the geometrical shape of which corresponds to a boundary surface of spherical segments with plane-parallel end faces and which is matched to the friction surfaces20a,20bof the clutch ring2, are formed on the clutch disks3and4.

The clutch disks3and4have narrowed portions23a,23b,24aand24b, at which edge regions of the clutch disks3and4deviate from the shape of spherical segment surfaces. InFIG. 4, it can be seen that the narrowed portions23a,23b,24aand24bare matched to an inner radius of outer edges29aand29b. On each of the clutch disks3and4, the narrowed portions are formed so as to run parallel to one another, on opposite narrow sides of the clutch disks3,4. As a result, a body axis for a position and direction is defined on each of the clutch disks3and4for an assembly movement. During assembly of the clutch disks3,4, provision is made for the narrowed portions23a,23b,24aand24bto be arranged congruently with one another to enable the clutch disks3,4to be brought simultaneously into a position which allows a subsequent assembly step.

By pressing the clutch disks3,4together parallel to the principal axes of symmetry or axes of rotation thereof, the outline of a cross section formed jointly by both clutch disks3and4can be reduced in such a way that the narrowed portions23a,23b,24aand24bof the clutch disks can be introduced past the outer edges29aand29binto the clutch ring2. By this means, the clutch disks3and4can be positioned in the clutch ring in such a way that the central point of the pressed-together clutch disks3and4coincides with the center of curvature Z of the concave spherical friction surfaces20aand20b.

By virtue of the spherical symmetry of the adjacent surfaces in the clutch ring2—namely of the concave friction surfaces20aand20b—in the position centered with respect to the clutch ring2, the pressed-together clutch disks3and4can be rotated about the center of curvature Z, as shown inFIG. 5. They can therefore be pivoted into a position which is coplanar with the center plane M of the clutch ring2, in which position they can rotate jointly with the clutch ring2about the clutch axis of rotation A in the coupled, frictionally engaged state.

In the clutch disks3,4, it is possible, for example, for two holes30to pass through the clutch disks3,4non-centrally, in particular in the vicinity of the friction surfaces21a,21b,22aand22b, parallel to the axis of rotation. The holes30are provided for the purpose of enabling pins31to be pushed through both clutch disks3,4, at least in the state in which they are pressed together for assembly. This enables the two rotary disks to be fixed relative to one another in such a way that the splines25aof a spline system are arranged in alignment with one another in the aperture25, parallel to the clutch axis of rotation. In this case, the two clutch disks3,4can be secured against twisting relative to one another by means of the pins, thereby ensuring that the clutch disks continue to be held congruent with one another in respect of the narrowed portions23a,23b,24aand24bduring assembly. The holes30and the pins31furthermore offer the possibility of installing not only a passage disk16but, in particular, also a stop spring6in the clutch ring2together with the clutch disks3,4.

In the widened arcuate segments35, the stop spring6has holes32, through which the pins31can be passed. A tapered region33is formed between the widened segments35on one side, by means of which region spring6can be compressed elastically in order to bring the holes32of the stop spring6into overlap with the holes30in clutch disk3and to pass the pins31through the holes32. Through the fixing of the stressed stop spring6on clutch disk3by means of the fixing pins31, it is possible to reduce the external outline of the stop spring6in such a way that the stop spring6is arranged completely within the external outline of clutch disk3and thus cannot protrude beyond the outline of the clutch disks3,4at any point. In this way, the stop spring6is set between the clutch disks3,4in such a way that it can be inserted into the clutch disks2simultaneously with the clutch disks. If appropriate, the fixing pins31can be designed for fixing of the clutch disks with springs5compressed.

Once the clutch disks have been brought into a coplanar central position in the clutch ring, the fixing pins31can be released in order to allow the stop ring6to expand, it being possible for the latter to penetrate into the groove19between the friction surfaces20aand20bof the clutch ring2. This offers the advantage that the clutch ring2can be designed as a self-contained body, thereby necessitating in the clutch ring an opening or aperture which passes radially from the outside to the groove19, impairing the strength of the clutch ring2.

FIGS. 8a-8cshow details of another embodiment of a friction clutch according to the invention.FIGS. 8aand8bshow a clutch ring2on which two friction surfaces20aand20bare provided circumferentially at the inside of the clutch ring2. Between the friction surfaces20aand20b, a groove19is formed circumferentially at the inside of the ring2and in a central position between outer faces28aand28bof the ring2.

The friction surfaces20aand20bare concavely formed with a curvature around an axis of rotational symmetry and with an additional curvature along the axis A. Preferably, each of the friction surfaces20aand20bis formed like a section of a hollow sphere. The concave friction surfaces20aand20bare partially facing each other in the direction of axis A. The friction clutch further comprises two disks3and4which are provided for being placed together within the clutch ring2. Between a maximum outer perimeter43aand an a minimum outer perimeter43bof the clutch ring3a convex friction surface21ais formed which is essentially adapted to at least one of the friction surfaces20aand20bof the clutch ring2. Similarly, a convex friction surface22ais formed between a maximum outer perimeter44aand a minimum outer perimeter44bof the clutch disk4which is at least adapted to the other one of the two friction surfaces20aand20b.

In large part the embodiment shown inFIGS. 8a-8ccan be similar to the ones described above except for the following details. Each of the friction surfaces20aand20bis interrupted by two recesses42which are placed at opposite positions at the inside of the clutch ring2. Each recess42reaches from one outer face28ato a second outer face28bon opposite sides of the clutch ring2which are delimiting the clutch ring2in a direction along the axis A.

Furthermore, circumferential contours of the clutch disks along the perimeters43a,43b,44aand44bcan be perfectly circular in contrast to the clutch disks3and4of the embodiment shown inFIG. 2, for example.

In their combination, the recesses42are adapted to a maximum contour of a cross section of a tight arrangement—as shown inFIG. 8c—of two the two clutch disks3and4having a stop ring6and springs (not shown) placed between the two disks3and4. Hence, the recesses42allow for inserting the arrangement of the disks3and4into the clutch ring2. After arriving at a central position within the clutch ring2the assembly with the clutch disks3and4can be turned by an angle of 90°. Then the assembly can be released as described for the previous embodiments so that friction surfaces21aand22aof the disks3and4are pressed against the friction surfaces20aand20bof the ring2by the springs (not shown here) pushing the disks3and4apart.

LIST OF REFERENCE SIGNS