Method for connecting a low speed main shaft of a wind turbine to an input shaft of a transmission gearbox of the wind turbine and a connection obtained by said method

1. A method for connecting a low speed main shaft of a wind turbine to an input shaft of a transmission gearbox of the wind turbine, the method comprising:

providing a connection surface on the main shaft and a corresponding connection surface on the input shaft, the connection surfaces being opposing surfaces, respectively, at an axially innermost side of the low speed main shaft, and on the input shaft at an axial side toward a rotor of the wind turbine, the connection surfaces of the main shaft and the input shaft being configured to be pressed together, the connection surfaces being opposing front faces at which the main shaft and the input shaft come together in a connected state;

providing a friction enhancing means on at least one of said connection surfaces, the friction enhancing means comprising a coating comprising a friction enhancing powder containing diamond grains; and

firmly connecting both connection surfaces with one another by a pre-tensioning means by applying a permanent load on the connection surfaces, application of the permanent load causing the diamond grains of the friction enhancing means to penetrate the connection surfaces,

wherein the friction enhancing means is provided in between both of the connection surfaces and is configured to contact both of the connection surfaces in the connected state of the main shaft and the input shaft to provide an increased friction coefficient between the connection surfaces in relation to a friction coefficient between the connection surfaces without the friction enhancing means.

2. The method according to claim 1 , wherein the friction enhancing means comprises a shim that is coated with the friction enhancing powder, the shim being placed in between the connection surfaces.

3. The method according to claim 1 , wherein the coating is directly applied on at least one of the connection surfaces.

4. The method according to claim 1 , wherein the connection surfaces are connected to one another by a bolted pre-tensioned joint comprising one or more of bolts, nuts, studs, and pretension means.

5. The method according to claim 1 , wherein the low speed main shaft is a rotor hub of the wind turbine.

6. The method according to claim 1 , wherein the transmission gearbox of the wind turbine comprises a planetary gear system with a planet carrier which forms the input shaft of the transmission gearbox.

7. A connector of a low speed main shaft of a wind turbine and an input shaft of a transmission gearbox of said wind turbine, the connector comprising:

a connection surface on the low speed main shaft at an axially innermost side of the low speed main shaft;

a corresponding connection surface on the input shaft at an axial side toward a rotor of the wind turbine, the corresponding connection surface being an opposing surface to the connection surface on the main shaft, the connection surfaces of the input shaft and the main shaft being configured to be pressed together, the connection surfaces being opposing front faces at which the main shaft and the input shaft come together in a connected state;

pre-tensioning means configured to press together the connection surfaces by applying a permanent load on the connection surfaces; and

friction enhancing means provided in between both of the connection surfaces, the friction enhancing means comprising a coating comprising a friction enhancing powder containing diamond grains, application of the permanent load by the pre-tensioning means causing the diamond grains of the friction enhancing means to penetrate the connection surfaces,

wherein the friction enhancing means is configured to contact both of the connection surfaces in the connected state of the main shaft and the input shaft to provide an increased friction coefficient between the connection surfaces in relation to a friction coefficient between the connection surfaces without the friction enhancing means.

8. The connector according to claim 7 , wherein the coating containing the friction enhancing powder is applied directly on one of the connection surfaces or on a shim that is installed in between the connection surfaces.

9. The connector according to claim 7 , wherein the low speed main shaft is a rotor hub of the wind turbine, and the input shaft is a planet carrier of a planetary system in the transmission gearbox of the wind turbine.

10. The method according to claim 2 , wherein the coating is directly applied on at least one of the connection surfaces.

11. The method according to claim 2 , wherein the connection surfaces are connected to one another by a bolted pre-tensioned joint comprising one or more of bolts, nuts, studs, and pretension means.

12. The method according to claim 3 , wherein the connection surfaces are connected to one another by a bolted pre-tensioned joint comprising one or more of bolts, nuts, studs, and pretension means.

13. The method according to claim 2 , wherein the low speed main shaft is a rotor hub of the wind turbine.

14. The method according to claim 3 , wherein the low speed main shaft is a rotor hub of the wind turbine.

15. The method according to claim 4 , wherein the low speed main shaft is a rotor hub of the wind turbine.

16. The method according to claim 4 , wherein the transmission gearbox of the wind turbine comprises a planetary gear system with a planet carrier which forms the input shaft of the transmission gearbox.

17. A method for connecting a low speed main shaft of a wind turbine to an input shaft of a transmission gearbox of the wind turbine, the method comprising:

providing a connection surface on the main shaft and a corresponding connection surface on the input shaft, the connection surfaces being opposing surfaces, respectively, at an axially innermost side of the low speed main shaft, and on the input shaft at an axial side toward a rotor of the wind turbine, the connection surfaces of the main shaft and the input shaft being configured to be pressed together, the connection surfaces being opposing front faces at which the main shaft and the input shaft come together in a connected state;

providing a shim on at least one of said connection surfaces, the shim comprising a coating comprising a friction enhancing powder contains diamond grains; and

firmly connecting both connection surfaces with one another by a pre-tensioning system provided between the connection surfaces by applying a permanent load on the connection surfaces, application of the permanent load causing the diamond grains of the friction enhancing powder to penetrate the connection surfaces,

wherein the shim is provided in between both of the connection surfaces and is configured to contact both of the connection surfaces in the connected state of the main shaft and the input shaft to provide an increased friction coefficient between the connection surfaces in relation to a friction coefficient between the connection surfaces without the shim.

18. The method according to claim 1 , wherein the main shaft is of a size sufficient to support rotor blades of the wind turbine.