Friction coupling

A friction coupling for locking a shaft relative to a hub is disclosed. The friction coupling includes a radially deformable inner sleeve, a radially deformable outer sleeve, an annular piston which is axially movable relative to the inner sleeve and the outer sleeve, the annular piston having a conical surface, which cooperates with the inner sleeve and/or the outer sleeve and which is arranged to deform the inner sleeve and/or the outer sleeve when the annular piston is moved relative to the inner sleeve and the outer sleeve so as to provide the locking. In at least one embodiment, the friction coupling further includes at least one actuating device to produce a movement of the annular piston for locking the friction coupling, and at least one deactuating device to produce a movement of the annular piston for unlocking the friction coupling. The at least one actuating and deactuating devices are located, seen in the axial direction, on the same side of the annular piston.

FIELD OF THE INVENTION

The invention relates to a friction coupling for locking a shaft relative to a hub.

BACKGROUND ART

U.S. Pat. No. 4,616,948, the entire disclosure of which is incorporated herein by reference, discloses a friction coupling for locking a shaft relative to a hub. The friction coupling comprises a radially deformable inner sleeve and a radially deformable outer sleeve, and an annular piston which is axially movable relative to the inner sleeve and the outer sleeve. The annular piston has a conical surface, which cooperates with the outer sleeve and which is arranged to deform the inner sleeve and/or the outer sleeve when the annular piston is moved relative to the inner sleeve and the outer sleeve, thus applying a contact force between, on the one hand, the inner sleeve and the shaft and, on the other hand, the outer sleeve and the hub. The contact force produces a frictional force, which causes the shaft and the hub to be locked relative to each other. The friction coupling further comprises an actuating pressure chamber, which when pressurised produces a movement of the annular piston for locking the coupling, and a deactuating pressure chamber, which when pressurised produces a movement of the annular piston for unlocking the coupling. The actuating pressure chamber and the deactuating pressure chamber are located, seen in the axial direction, on opposite sides of the annular piston.

Other examples of friction couplings of similar type are known from U.S. Pat. No. 4,859,106, U.S. Pat. No. 5,149,220 and U.S. Pat. No. 5,156,480, the entire disclosure of which is incorporated herein by reference.

A drawback of the above-mentioned friction coupling is that if connecting means for feeding of compressed fluid to the actuating pressure chamber and the deactuating pressure chamber are to be arranged on the same side of the coupling, seen in the axial direction, a duct has to be provided through the inner sleeve or the outer sleeve, which makes it difficult to reduce the radial extension of the friction coupling, thus making the friction coupling radially unwieldy, and also increasing its weight.

Another drawback is that the presence of the duct causes problems of strength, which have to be compensated for by an increase of the material thickness of the coupling or by load limits on the coupling.

Yet another drawback is that the above-mentioned friction coupling requires relatively heavy forces for actuation or deactuation. Since the piston surface facing the actuating pressure chamber and the deactuating pressure chamber is relatively small, a very high pressure is required, for instance, often a pressure of up to 1000 bar for assembling and of up to 1200 bar for disassembling. This puts great demands on the equipment needed for actuation and deactuation, which results in higher costs of the equipment.

SUMMARY OF THE INVENTION

One object is to provide an improved or alternative friction coupling. A specific object is to provide a friction coupling which is less unwieldy in the radial direction. A further object is to provide a friction coupling having a lower weight. Yet another object is to provide a friction coupling which enables the use of less expensive equipment for actuation and deactuation.

The above objects are wholly or partly achieved by a friction coupling according to the independent claim. Embodiments will be evident from the dependent claims, from the following description and the accompanying drawings.

Thus, a friction coupling is provided for locking a shaft relative to a hub. The friction coupling comprises a radially deformable inner sleeve, which is arranged for frictional engagement with the shaft, a radially deformable outer sleeve, which is arranged for frictional engagement with the hub, and an annular piston, which is axially movable relative to the inner sleeve and the outer sleeve. The annular piston has a conical surface, which cooperates with the inner sleeve and/or the outer sleeve and which is arranged to deform the inner sleeve and/or the outer sleeve when the annular piston is moved relative to the inner sleeve and the outer sleeve, so as to provide said locking. The friction coupling further comprises actuating means arranged to produce a movement of the annular piston for locking the friction coupling, and deactuating means arranged to produce a movement of the annular piston for unlocking the friction coupling. The actuating means and the deactuating means are located, seen in the axial direction, on the same side of the annular piston.

“Shaft” and “hub” are schematic designations. By “hub” is here meant any machine element. By “shaft” is correspondingly meant a machine element of any cross-section, which in its non-locked state can perform an axial and/or rotary movement relative to the hub.

By arranging the actuating and the deactuating means on the same side, or at the same end, of the piston, it is no longer necessary to provide a connection through the inner sleeve or the outer sleeve for controlling an actuating or deactuating means provided at the other side of the piston, whereby a thinner, lighter and/or stronger coupling can be obtained.

By arranging the actuating and the deactuating means on the same side of the piston, their dimensions are not limited by the size of the piston, which makes it possible to adjust the surfaces absorbing the forces which are to be transferred to the piston.

The deactuating means can comprise a deactuating pressure chamber, which when pressurised produces said movement of the annular piston for unlocking the friction coupling.

Furthermore, the actuating means can comprise an actuating pressure chamber, which when pressurised produces said movement of the annular piston for locking the friction coupling.

By “pressure chamber” is meant a space which when pressurised affects the activation of the friction coupling.

By arranging the pressure chambers on the same side, or at the same end, of the piston, it is in particular unnecessary to provide a duct for compressed fluid through the inner sleeve or the outer sleeve, whereby a thinner, lighter and/or stronger coupling can be obtained. The friction coupling can further comprise a flange, which is joined to the annular piston and which separates said actuating pressure chamber from said deactuating pressure chamber. The extension of the flange in the radial direction from the shaft can be selected so that it obtains assembling and disassembling surfaces of suitable dimensions. Tests performed by the applicant have shown that a reduction from about 1000 bar to about 350 bar can be made possible by an appropriate selection of the dimensions of the assembling and disassembling surfaces.

According to one embodiment, the flange can be integrated with the annular piston. The flange can, for instance, be formed integrally with the annular piston.

The flange can have an assembling surface, which defines the actuating pressure chamber, and a disassembling surface, which defines the deactuating pressure chamber. The assembling surface and the disassembling surface both have a radial extension from the shaft, and can coincide with the extension of the flange in the same direction.

According to one embodiment, the disassembling surface is greater than the assembling surface, which results in a greater disassembling force than assembling force at the same pressure and which makes it possible to perform the disassembling operation at a lower pressure.

The assembling surface can have a greater area than a first cross-sectional area of the piston, which first cross-sectional area is located at a first end of a piston portion active against the inner sleeve and the outer sleeve, and is oriented in the same axial direction as the assembling surface.

This makes it possible to perform the assembling operation at a considerably lower pressure than in prior art.

The disassembling surface can have a greater area than a second cross-sectional area of the piston, which second cross-sectional area is located at a second end of a piston portion active against the inner sleeve and the outer sleeve, and is oriented in the same axial direction as the disassembling surface.

This makes it possible to perform the disassembling operation at a considerably lower pressure than in prior art.

Alternatively, the actuating means can comprise an elastically compressible actuating means, which is arranged to produce said movement of the annular piston for locking the friction coupling. Thus a self-locking coupling can be obtained.

According to one embodiment, at least one of the inner sleeve and the outer sleeve can have a slot extending in said axial direction. By such slots, the force needed to produce the compression/expansion of the inner and/or the outer sleeve can be reduced.

A friction modified surface can be provided on at least one of a surface of the annular piston cooperating with the inner sleeve, a surface of the annular piston cooperating with the outer sleeve, a surface of the outer sleeve cooperating with the piston and a surface of the inner sleeve cooperating with the piston.

A lubricating duct can be arranged on at least one of a surface of the annular piston cooperating with the inner sleeve, a surface of the annular piston cooperating with the outer sleeve, a surface of the outer sleeve cooperating with the piston and a surface of the inner sleeve cooperating with the piston.

The conical surface can consist of a contact surface between the inner sleeve and the annular piston.

Alternatively, or as a complement, the conical surface can consist of a contact surface between the outer sleeve and the annular piston.

Examples of embodiments will be described in more detail below with reference to the accompanying drawings.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a schematic sectional view of an embodiment of a friction coupling1, which is arranged to connect a shaft20to a hub21. The friction coupling1comprises an inner sleeve2, which has a shaft contact surface22and a piston contact surface14; and an outer sleeve3, which has a hub contact surface24and a piston contact surface13. An axially movable annular piston12is arranged between the inner sleeve2and the outer sleeve3.

The material thicknesses shown inFIG. 1are only schematic. The thickness of the inner sleeve2, the outer sleeve3and the piston12can be dimensioned according to the application in which the friction coupling is to be used.

According to the embodiment shown inFIG. 1, the contact surface14between the inner sleeve2and the piston12is a conical surface, so that a movement of the piston12in the direction D2(to the left inFIG. 1) causes an expansion of the outer sleeve3and a compression of the inner sleeve2. To elucidate the description, the conical surface shown inFIG. 1has a considerably greater conical angle than in a real application. For details concerning the selection of the conical shape of the conical surface, reference is made to the above-mentioned U.S. Pat. No. 4,616,948.

The piston12has a flange17, which projects radially from one end of the piston12and which has an assembling surface7and a disassembling surface6located on an opposite side of the flange17. The assembling surface7is part of a boundary surface of an actuating pressure chamber5. A radially projecting part16of the outer sleeve3forms yet another delimiting part of the actuating pressure chamber5. Also a portion of the piston forms a boundary surface of the actuating pressure chamber5. The disassembling surface6is part of a boundary surface of a deactuating pressure chamber4. A radially projecting part15of the inner sleeve2forms yet another delimiting part of the deactuating pressure chamber4. Also a portion of the outer sleeve located at the flange forms a boundary surface of the deactuating pressure chamber4.

Connecting means10,11for compressed fluid communicate via ducts8,9with the actuating pressure chamber5and the deactuating pressure chamber4, respectively.

InFIG. 1, the designation P indicates the piston portion active against both the outer sleeve3and the inner sleeve2, i.e. the piston portion engaged in the power transmission between the shaft and the hub. The designations E1and E2indicate the respective ends of the portion P.

The description will now be aimed at the function of the friction coupling1.

The friction coupling1is arranged with normal machine tolerance requirements between the shaft20and the hub21, so as to obtain some play (not shown) between the friction coupling1and, respectively, the shaft20and the hub21.

By pressurising the actuating pressure chamber5, a force is applied to the assembling surface7, which causes the annular piston12to move in the direction D2(to the left inFIG. 1), whereby cooperation at the contact surface14of the piston12and the inner sleeve2causes the compression of the inner sleeve2and thus produces a contact pressure in the contact surface22between the inner sleeve2and the shaft20. The deactuating pressure chamber4can optionally be drained or unloaded in some other way when pressurising the actuating pressure chamber5.

Simultaneously, cooperation at the contact surface13of the piston12and the outer sleeve3causes the expansion of the outer sleeve3, thus producing a contact pressure in the contact surface24between the outer sleeve and the hub21.

The contact pressures in the contact surfaces22,24, together with the friction in the contact surfaces, connect the shaft20to the hub21, so that any relative movement between them is counteracted or prevented. The coupling is thus in an assembled state.

By instead pressurising the deactuating pressure chamber4, a force is applied to the disassembling surface6, which causes the annular piston12to move in the direction D1(to the right inFIG. 1), whereby the pressure in the contact surfaces13,14between the piston12and the outer sleeve3and the inner sleeve2, respectively, is unloaded, and thus also the pressure in the contact surfaces22,24between the inner sleeve2and the shaft20and between the outer sleeve3and the hub21is unloaded, so that a relative movement between the shaft20and the hub21is made possible.

One or both contact surfaces13,14between the piston12and, respectively, the outer sleeve3and the inner sleeve2can have a modified friction coefficient. The aim of such a modification may be to obtain a low and even friction coefficient and/or to obtain a difference which is as small as possible between the static and the dynamic friction coefficients of the contact surfaces13,14.

As a non-limiting example of a friction-reducing coating, mention can be made of a surface coating of so-called chemical nickel.

According to an alternative embodiment of a friction coupling1′, which is shown inFIG. 2, the contact surface14between the outer sleeve3and the piston12is instead a conical surface.

Thus, in the embodiment shown inFIG. 2, the actuating pressure chamber5and the deactuating pressure chamber4, on the one hand, and the assembling surface7and the disassembling surface6, on the other hand, are reversed, the conical surface tapering instead in the direction D1, so that the actuation or assembling is achieved by the left pressure chamber (reference numeral5inFIG. 2) being pressurised, and the deactuation or disassembling is achieved by the right pressure chamber (reference numeral4inFIG. 2) being pressurised. This embodiment results in the assembling surface7being greater than the disassembling surface6.

According to another alternative embodiment (not shown), the contact surface14between the inner sleeve2and the piston12, and the contact surface13between the outer sleeve and the piston12are both conical surfaces.

According to yet another embodiment, one or both of the contact surfaces13,14are provided with lubricating ducts, such as those disclosed in U.S. Pat. No. 4,616,948.

The pressurisation of the actuating and the deactuating pressure chambers5,4, respectively, can be obtained by connecting a hydraulic pump. As an alternative, movable pistons (not shown) arranged in flanges in the inner sleeve2and/or the outer sleeve3may be used to obtain the pressurisation of the respective pressure chambers4,5.

In the embodiment of a friction coupling1″ shown inFIGS. 3 and 4, the actuating pressure chamber (reference numeral5inFIG. 1andFIG. 2) is replaced with an elastically resilient actuating means18, which is arranged to bias the piston in the direction D2, i.e. to provide the locking of the friction coupling1″ without the use of a hydraulic pump.

The actuating means18can be a spring means, such as a cup spring, a helical spring, a gas spring, a compressible material or the like.

The deactuating pressure chamber4described with reference toFIG. 1is still the same and works exactly as described in connection withFIG. 1, i.e. when the deactuating pressure chamber4is pressurised a movement of the piston is produced in the direction D1, which unlocks the coupling1″.

FIG. 3also illustrates how the outer sleeve3and the inner sleeve2are each provided with longitudinal slots25a,25b;26a,26bfacilitating the expansion/contraction of the sleeves which arises when the piston12is moved and the coupling1″ is locked, thus reducing the force needed to lock/unlock the coupling1″. The slots are arranged in the part of the inner sleeve2and/or the outer sleeve3that cooperates with the piston12and extend in the radial direction through the entirety of the inner sleeve2and the outer sleeve3, respectively.

According to an alternative embodiment, only the inner sleeve2is provided with one or more slots25a,25b. According to a further alternative embodiment, the inner sleeve is provided with only one slot25aor25b.

According to another alternative embodiment, only the outer sleeve3is provided with one or more slots26a,26b. According to a further alternative embodiment, the outer sleeve is provided with only one slot26aor26b.

According to yet another alternative embodiment, also the piston, in conformity with the above-described slotted inner and/or outer sleeves, is provided with one or more slots (not shown).

The above-described slots25a,25b,26a,26bare particularly suitable for use together with an elastically resilient actuating means18, which is not capable of exerting a force as great as, for instance, that of the actuating pressure chamber5described with reference toFIG. 1.

According to further alternative embodiments, also the inner and/or outer sleeves2,3in the couplings1,1′ described with reference toFIG. 1andFIG. 2can be provided with one or more such slots.

Furthermore, the gap between the inner sleeve2and the outer sleeve3where the piston12is positioned can be wholly or partly uncovered in the direction D1, which makes it possible to limit the axial extension of the coupling1,1′,1″, thus contributing to making the coupling more compact in the axial direction.

In a corresponding manner, the embodiment shown inFIG. 2can be modified (not shown) in accordance with that shown inFIGS. 3 and 4, the actuating pressure chamber5being replaceable with an elastically resilient actuating means.

The one skilled in the art will realise that, inFIG. 1or2, it would instead be possible to replace the deactuating pressure chamber4with an elastically resilient deactuating means (corresponding to the elastically resilient actuating means18), thus obtaining a self-unlocking coupling (not shown).

The flange17can be integrated with the piston12. According to one embodiment, the flange and the piston are formed in one piece of material, and in another embodiment they are formed of separate pieces of material which are subsequently joined together, for instance, by a threaded coupling or by a weld joint.

The inner sleeve and the outer sleeve can be joined together, for instance, by means of bolts or weld joints. A plurality of gaskets can be arranged in a manner known per se to prevent leakage.