Drive shafts

Abstract

A drive shaft including an inner shaft having a first end that is adapted to be connectable to a first connecting shaft that is rotated by torque applied by an external electrical machine, and a second end that is adapted to be connectable to a second connecting shaft. A hollow outer shaft, coaxial with the inner shaft, defines at least part of a rotor assembly of an associated electrical machine. The outer shaft is adapted to be releasably connected to the inner shaft so that the drive shaft is selectively configurable in a first arrangement for normal operating conditions where the outer shaft is connected to the inner shaft for rotation therewith, and a second arrangement where the outer shaft is not connected to the inner shaft.

What is claimed is: 
     
         1 . A drive shaft comprising:
 an inner shaft comprising:
 a first end configured to be connectable to a first connecting shaft that is rotated by torque applied by an external electrical machine; and 
 a second end configured to be connectable to a second connecting shaft; and 
   a hollow outer shaft, coaxial with the inner shaft, the outer shaft defining at least part of, or being operatively coupled to, a rotor assembly of an associated electrical machine, and being configured to be releasably connected to the inner shaft so that the drive shaft is selectively configurable in a first arrangement for normal operating conditions where the outer shaft is connected to the inner shaft for rotation therewith, and a second arrangement where the outer shaft is not connected to the inner shaft.   
     
     
         2 . The drive shaft according to  claim 1 , wherein the inner shaft further comprises a first intermediate flange releasably connected to a flange provided at a first end of the outer shaft. 
     
     
         3 . The drive shaft according to  claim 2 , further comprising a spacer between the first intermediate flange and a first end flange of the outer shaft. 
     
     
         4 . The drive shaft according to  claim 2 , wherein the inner shaft further comprises a second intermediate flange releasably connected to a flange provided at a second end of the outer shaft. 
     
     
         5 . The drive shaft according to  claim 4 , further comprising a spacer between the second intermediate flange and a second end flange of the outer shaft. 
     
     
         6 . The drive shaft according to  claim 5 , further comprising a spacer between the first intermediate flange and a first end flange of the outer shaft. 
     
     
         7 . The drive shaft according to  claim 1 , wherein the inner and outer shafts are releasably connected using mechanical fixings that can be removed to configure the drive shaft in the second arrangement. 
     
     
         8 . The drive shaft according to  claim 2 , wherein the inner and outer shafts are releasably connected using mechanical fixings that can be removed to configure the drive shaft in the second arrangement. 
     
     
         9 . The drive shaft according to  claim 4 , wherein the inner and outer shafts are releasably connected using mechanical fixings that can be removed to configure the drive shaft in the second arrangement. 
     
     
         10 . The drive shaft according to  claim 1 , wherein the inner and outer shafts are releasably connected using a clutch assembly. 
     
     
         11 . The drive shaft according to  claim 7 , wherein the inner and outer shafts are releasably connected using a clutch assembly. 
     
     
         12 . The drive shaft according to  claim 1 , wherein the outer shaft further comprises one or more collars to prevent lateral movement of the drive shaft. 
     
     
         13 . The drive shaft according to  claim 11 , wherein the outer shaft further comprises one or more collars to prevent lateral movement of the drive shaft. 
     
     
         14 . A drive assembly, comprising
 a drive shaft comprising:
 an inner shaft comprising:
 a first end configured to be connectable to a first connecting shaft that is rotated by torque applied by an external electrical machine; and 
 a second end configured to be connectable to a second connecting shaft; and 
 
 a hollow outer shaft, coaxial with the inner shaft, the outer shaft defining at least part of, or being operatively coupled to a rotor assembly, and being configured to be releasably connected to the inner shaft so that the drive shaft is selectively configurable in a first arrangement for normal operating conditions where the outer shaft is connected to the inner shaft for rotation therewith, and a second arrangement where the outer shaft is not connected to the inner shaft; and 
   an electrical machine comprising the rotor assembly.   
     
     
         15 . The drive assembly according to  claim 14 , further comprising one or more bearings for supporting the drive shaft. 
     
     
         16 . The drive assembly according to  claim 14 , further comprising a lock configured to selectively prevent rotation of the outer shaft when the drive shaft is in the second arrangement. 
     
     
         17 . A marine propulsion assembly comprising a drive shaft according to  claim 1 , wherein the second connecting shaft is used to drive a propulsion. 
     
     
         18 . A method of operating a drive shaft, wherein the drive shaft includes an inner shaft having a first end configured to be connectable to a first connecting shaft that is rotated by torque applied by an external electrical machine, and a second end configured to be connectable to a second connecting shaft, and a hollow outer shaft, coaxial with the inner shaft, the outer shaft defining at least part of, or being operatively coupled to, a rotor assembly of an associated electrical machine, and being configured to be releasably connected to the inner shaft, the method comprising:
 connecting the outer shaft to the inner shaft during normal operating conditions; and   disconnecting the outer shaft from the inner shaft in response to a fault condition.   
     
     
         19 . The method according to  claim 18 , wherein the inner and outer shafts are releasably connected by mechanical fixings or a clutch assembly, the method further comprising:
 removing the mechanical fixings or operating the clutch assembly to disconnect the outer shaft from the inner shaft in response to a fault condition.   
     
     
         20 . The method according to  claim 18 , further comprising preventing rotation of the outer shaft when disconnected from the inner shaft.