Turbocharger Brake

Abstract

Exhaust gases can bypass a turbocharger to reduce its speed, but energy in the gases is then lost. A brake for a turbocharger can be implemented using at least one rotor driven by the turbocharger rotatable shaft and at least one stator. Either the rotor or stator are magnetic, the other being ferrous, such that rotation of the shaft induces eddy currents in the ferrous part, thereby extracting energy from the shaft. The magnetic field experienced by the ferrous part can be adjusted in response to an input parameter to control the level of braking.

1 . A turbocharger for providing boost to an engine, comprising:
 a rotatable shaft;   one or more permanent magnet braking rotors arranged to be driven by the rotatable shaft;   one or more braking stators positioned relative to the one or more braking rotors, such that rotation of the rotatable shaft induces eddy currents in the one or more braking stators to extract energy from the rotatable shaft thereby; and   a controller, arranged to receive an input parameter, and in response to said input parameter, to adjust a distance between the one or more braking rotors and the one or more braking stators to vary the level of generation of eddy currents and control braking of the rotatable shaft thereby.   
     
     
         2 . A turbocharger for providing boost to an engine, comprising:
 a rotatable shaft;   one or more braking rotors arranged to be driven by the rotatable shaft;   one or more magnetic braking stators positioned relative to the one or more braking rotors, such that rotation of the rotatable shaft induces eddy currents in the one or more braking rotors to extract energy from the rotatable shaft thereby; and   a controller, arranged to receive an input parameter, and in response to said input parameter, to adjust the magnetic field strength at the one or more braking rotors to vary the level of generation of eddy currents and control braking of the rotatable shaft thereby.   
     
     
         3 . The turbocharger of  claim 2 , wherein the one or more magnetic braking stators comprise a permanent magnet. 
     
     
         4 . The turbocharger of  claim 2 , wherein the one or more magnetic braking stators comprise an electromagnet arranged to receive a current. 
     
     
         5 . The turbocharger of  claim 4 , wherein the controller is arranged to adjust the magnetic field strength at the one or more braking rotors by adjusting the current received by the electromagnet. 
     
     
         6 . The turbocharger of  claim 5 , wherein the controller is arranged to adjust the magnetic field strength at the one or more braking rotors by adjusting a distance between the one or more braking rotors and the one or more braking stators. 
     
     
         7 . The turbocharger of  claim 6 , wherein in response to the input parameter indicating a reduction in the required boost level, the controller is arranged to reduce the distance between the one or more braking rotors and the one or more braking stators. 
     
     
         8 . The turbocharger of  claim 7 , wherein the controller further comprises a braking actuator, arranged to move the one or more braking stators relative to the rotatable shaft, to adjust the distance between the one or more braking rotors and the one or more braking stators thereby. 
     
     
         9 . The turbocharger of  claim 8 , wherein the braking actuator comprises a stepper motor. 
     
     
         10 . The turbocharger of  claim 9 , wherein the input parameter is representative of at least one of: a required boost level; an engine temperature; an engine speed; and a turbocharger temperature. 
     
     
         11 . The turbocharger of  claim 1 , further comprising an electrical generator arrangement, comprising:
 one or more permanent magnet generator rotors arranged to be driven by the rotatable shaft; and   a generator stator, positioned relative to the one or more generator rotors such that rotation of the rotatable shaft induces a generation current in the generator stator.   
     
     
         12 . The turbocharger of  claim 11 , wherein at least one of the generator rotors is also a braking rotor. 
     
     
         13 . A turbo-compound engine system comprising the turbocharger of  claim 12 . 
     
     
         14 . A method of operating a turbocharger, the turbocharger comprising a rotatable shaft and a braking arrangement comprising one or more permanent magnet braking rotors and one or more braking stators, the method comprising:
 rotating the rotatable shaft during operation of the turbocharger to generate boost, thereby driving rotation of the one or more braking rotors relative to the braking stator;   receiving an input parameter of the turbocharger; and   adjusting a distance between the one or more braking rotors and the one or more braking stators in response to said input parameter, to control the level of generation of eddy currents in the one or more braking stators and thereby control the rate of energy extraction from the rotatable shaft and braking of the rotatable shaft.   
     
     
         15 . A method of operating a turbocharger, the turbocharger comprising a rotatable shaft and a braking arrangement comprising one or more braking rotors and one or more magnetic braking stators, the method comprising:
 rotating the rotatable shaft during operation of the turbocharger to generate boost, thereby driving rotation of the one or more braking rotors relative to the braking stator;   receiving an input parameter of the turbocharger; and   adjusting the magnetic field strength at the one or more braking rotors in response to said input parameter, to control the level of generation of eddy currents in the one or more braking rotors and thereby control the rate of energy extraction from the rotatable shaft and braking of the rotatable shaft.