Title

A friction coupling

Field of the invention According to a first aspect, the invention concerns a friction coupling.

According to a second aspect, the invention concerns a method to join two shafts.

According to a third aspect, the invention concerns a method to disjoin two shafts.

According to a fourth aspect, the invention concerns a wind turbine axle having the friction coupling according to the first aspect.

Background of the invention

There are several different ways of connecting two shafts in order to transfer rotation and torque. One such way is to connect two shafts with end flanges including holes to bolt the two shafts together. This type of design leads to that the shaft diameter increases at the connection area. Furthermore, the cost of manufacturing that type of shaft is higher than a standard type of shaft. Therefore, there is a need to have a coupling between two shafts that doesn't need any expensively designed shafts, which is compact in the radial and in the axial direction, and at the same time can transfer a high torque between the two shafts. This is especially a need in wind turbine applications. Furthermore, in wind turbine applications, there is a need to be able to easily mount and dismount two shafts. There is also a need to have a low weight.

Summary of the invention

A first object of the invention is to provide a shaft coupling that has a reduced size in a radial direction of the shaft.

A second object of the invention is to provide a compact coupling in an axial direction of the shaft.

A third object of the invention is to provide a shaft coupling that is low in weight. A fourth object of the invention is to provide a shaft coupling that allows using standard shafts.

A fifth object of the invention is to provide a shaft coupling that allows easy mounting of two shafts.

A sixth object of the invention is to provide a shaft coupling that allows easy dismounting of two shafts.

According to the first aspect, the objects of the invention are achieved by a friction coupling. The friction coupling comprises an inner sleeve and an outer sleeve. The inner sleeve presents a radially inner cylindrical surface constituting a bore, and a radially outer surface constituting an essentially conical form. The outer sleeve presents a radially inner surface constituting an essentially conical form. The radially outer surface of the inner sleeve essentially matches the radially inner surface of the outer sleeve. A cavity, when in use acts as a pressure chamber, is between the inner sleeve and the outer sleeve. Furthermore, at least a part of the cylindrical surface of the bore presents a friction coating.

The invention provides a compact coupling solution. Due to the compact design, the coupling also has a low weight and no specially designed shafts are needed due to that the coupling inner surface being in contact with the shafts is cylindrically shaped. Furthermore, the design allows easy- mounting and dismounting. In an embodiment, the friction coupling has a friction coefficient μ of the coated surface that is μ ≥ 0.2.

In an embodiment, the friction coupling has a friction coefficient μ of the coated surface that is μ ≥ 0.3.

In an embodiment, the friction coupling has a friction coefficient μ of the coated surface that is μ ≥ 0.4.

In an embodiment, the friction coupling has a friction coefficient μ of the coated surface that is μ ≥ 0.5.

In an embodiment, the friction coating of the friction coupling of the invention is a carbide type coating. In an embodiment, the friction coating is applied onto the friction coupling by plasma spraying. Plasma spraying, one of the thermal spraying family, is a materials processing technique for producing coatings and freestanding parts using a plasma jet. Deposits having thickness from micrometers to several millimeters can be produced from a variety of materials, such as metals, ceramics, polymers and composites. The thickness of the coating on the friction coupling may be around 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm or any other preferred thickness recognized by a skilled person.

In an embodiment, the friction coupling further comprises a ring-shaped element between the inner sleeve and the outer sleeve at an axial end of at least one of the inner and the outer sleeve. In addition, an axial inner side of the ring-shaped element is a surface in the cavity. The ring-shaped element may be attached to any of the inner or outer sleeve by a threaded connection, a weld or any other fixing technique recognized by a skilled person.

In an embodiment, the friction coupling further comprises a fluid duct from an outer peripheral surface of the friction coupling into the cavity. The fluid duct is meant to lead a fluid, such as oil, in to the cavity in order to pressurize it during mounting or dismounting.

In an embodiment, the friction coupling further comprises a fluid duct from an outer peripheral surface of the friction coupling to the contact surface between the inner sleeve and the outer sleeve. This duct is meant to be used during mounting and dismounting for lubricating the contact surfaces and during dismounting for pressurizing the contact surfaces.

In an embodiment, the friction coupling further comprises a flange integrated with any of the inner sleeve

and the outer sleeve meant to be connected to a mechanical element .

According to the second aspect, the fifth object of the invention is achieved by a method to join a first and a second shaft, comprising the friction coupling according to the first aspect of the invention, and comprises the following steps:

• inserting the first shaft into the bore of the inner sleeve, and pushing the first shaft to an axial position in the friction coupling,

• inserting the second shaft into the bore of the inner sleeve until a contact between the first and the second shaft occurs,

• driving up the outer sleeve onto the inner sleeve by pressurizing the cavity, and thereby increasing a radial pressure between the inner sleeve and the first shaft, and between the inner sleeve and the second part.

All features and embodiments of the second aspect are applicable to all embodiments and features of the first aspect and vice versa.

According to the third aspect, the sixth object of the invention is achieved by a method to disjoin a first and a second shaft, comprising the friction coupling having a fluid duct leading to the contact surface of the inner and the outer sleeve. In addition, the first shaft and the second shaft are axially and rotatably fixed into the bore of the friction coupling, and comprises the following steps:

• pressurizing the fluid duct and the cavity, and continuously increasing the pressure in the fluid duct, wherein an axial force is obtained leading to driving off the outer sleeve of the inner sleeve, and

• pulling the first shaft and the second shaft out of the bore of the inner sleeve.

All features and embodiments of the third aspect are applicable to all embodiments and features of the first aspect and vice versa.

According to the fourth aspect of the invention, the objects are achieved by a wind turbine axle having the friction coupling according to the first aspect of the invention. The wind turbine axle comprises a first shaft connected to a wind turbine rotor. The first shaft is positioned inside and in connection with the radially inner cylindrical surface of the inner sleeve. Furthermore, the wind turbine axle comprises a second shaft connected to a gearbox. The second shaft is positioned inside and in connection with the radially inner cylindrical surface of the inner sleeve. The outer sleeve is driven up onto the inner sleeve, creating a radial pressure between the inner sleeve and the first shaft and the inner sleeve and the second shaft, wherein the radial pressure allows a high torque to be transmitted between the first and the second shaft .

All features and embodiments of the fourth aspect are applicable to all embodiments and features of the first, second and third aspect and vice versa.

Brief description of drawings

Figure 1. A friction coupling according to the invention.

Figure 2. Another friction coupling according to the invention. Figure 3. A friction coupling joining two shafts according to the invention

Figure 4. A conventional coupling of two shafts.

Detailed description of preferred embodiments It should be understood that some features of the drawings might be exaggerated in order to clarify the inventive idea.

In figure 1, a cross-section of a friction coupling 1 according to the invention is disclosed. The friction coupling 1 has an inner sleeve 2 presenting a radially inner

cylindrical surface constituting a bore 3, and a radially outer surface 4 constituting an essentially conical form. In addition, the friction coupling 1 has an outer sleeve 5. The outer sleeve 5 presents a radially inner surface 6 constituting an essentially conical form. A cavity 7, which in use acts as a pressure chamber, is located between the inner sleeve 2 and the outer sleeve 5. At least a part of the cylindrical surface of the bore 3 presents a friction coating. The friction coating may have a friction coefficient being equal or larger than 0.2 μ, 0.3 μ , 0,4 μ or 0.5 μ. The friction coating may further be a carbide type coating, or any other high friction coating recognized by a skilled person. Furthermore, in this embodiment, the friction coupling 1 presents a ring-shaped element 8 between the inner sleeve 2 and the outer sleeve 5. A surface of the ring-shaped element 8 is a surface in the cavity 7. The ring-shaped element 8 may be attached by a threaded connection, a weld or any other fixing technique to the inner sleeve 2. In figure 2, another friction coupling 1 according to the invention is disclosed. The friction coupling comprises, as described in figure 1, an inner sleeve 2 having a cylindrical inner bore 3 and a radially outer essentially conical surface 4, an outer sleeve 5 having a radially inner surface 6 constituting an essentially conical form, a cavity 7, a ring-shaped element 8, a fluid duct 9 and a fluid duct 10. Furthermore, the friction coupling presents a flange 11 on the inner sleeve 2. The flange 11 may also be on the outer sleeve 5. The flange 11 of the friction coupling 1 may be used to connect a mechanical element to a shaft, wherein the shaft is inserted into the cylindrical bore 3 of the inner sleeve 2. The cylindrical surface of the bore 3 presents a friction coating. The friction coating may have a friction coefficient being equal or larger than 0.2 μ, 0.3 μ, 0.4 μ or 0,5 μ. The friction coating may be a carbide type coating, or any other coating leading to an increased friction between the inner sleeve and the outer sleeve.

In figure 3, a friction coupling 1 is disclosed where two shafts 12 and 13 are joined. The friction coupling

comprises, as described in figure 1 and 2, an inner sleeve 2 having a cylindrical inner bore 3 and a radially outer essentially conical surface 4, an outer sleeve 5 having a radially inner surface 6 constituting an essentially conical form, a cavity 7, a ring-shaped element 8, a fluid duct 9 and a fluid duct 10. The shafts 12 and 13 may be joined by the joining method described above. In addition, the two shafts may be disjoined by the disjoining method described above. The cylindrical surface of the bore 3 presents a friction coating

The shaft 12 or 13 may be connected to a rotor of a wind turbine and the corresponding shaft 12 or 13 may be connected to a wind turbine gearbox.

Figure 4 illustrate an example of a conventional shaft coupling. The coupling comprises a flange 16 connected to the shaft 14 and a second flange 17 connected to the shaft 15. The two shafts 14 and 15 may be connected by bolts inserted in holes on the flanges 16 and 17, as seen in the figure. The coupling leads to a large diameter due to the two flanges 16 and 17 and is thus not compact. Furthermore, handling of the bolts may be complicated and there may also be corrosion problems on the bolts.