Gas turbine engine braking method

Abstract

The present disclosure discloses an engine braking system, especially for vehicles powered by a gas turbine. The engine braking system allows for control of engine braking force; control of over-speed of the power turbine and further includes means of recovering some or all of the braking energy of the engine braking system. Dissipative engine braking devices include an auxiliary compressor, or electrical generator, or an eddy current clutch or an eddy current brake, or fluid pump. Several methods of controlling the engine braking force of a dissipative braking device are disclosed and include (1) a continuously variable transmission (“CVT”); (2) an electrical generator and an optional thermal storage device; (3) an eddy current clutch; and (4) a fluid pump system. The various control devices may be operated automatically by appropriate algorithms. One of these control methods utilizes an eddy current clutch assembly. An innovative configuration of eddy current clutch assembly based on a brushless alternator is disclosed. Additional innovations include vehicle braking systems that utilize some or all the braking features to recoup a portion of braking energy available with either or both of a hybrid transmission and a dissipative braking device such as a compressor, an electrical generator or a fluid pump system.

1 . In a vehicle comprising a gas turbine engine and a transmission, the gas turbine engine comprising at least one turbo-compressor spool assembly, wherein the at least one turbo-compressor spool assembly comprises a compressor in mechanical communication with a turbine, the turbine outputting a gas, and a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, a system comprising:
 a braking device in mechanical communication with the free power turbine and the transmission to at least one of dissipate energy of the free power turbine and provide a braking force to the vehicle, wherein at least one of the following is true:
 (a) the braking device comprises a compressor selectively mechanically engaged and disengaged from the free power turbine and/or the transmission of the vehicle by a clutch assembly: 
 (b) the braking device comprises a continuously variable transmission; 
 (c) the braking device comprises an electrical generator configured to generate a selected amount of electrical energy; 
 (d) the braking device comprises at least one of an eddy current clutch and an eddy current brake; and 
 (e) the braking device comprises a fluid pump circuit. 
   
     
     
         2 . The system of  claim 1 , wherein the transmission comprises:
 a first gear assembly comprising a high speed bull gear in mechanical communication with a first shaft, a high speed pinion gear in mechanical communication with the free power turbine, and a power take off pinion gear in mechanical communication with the braking device, the high speed bull gear being in mechanical communication with the high speed pinion and the power takeoff pinion; and   a second gear assembly comprising a low speed bull gear in mechanical communication with a second shaft and a low speed pinion in mechanical communication with the first shaft, the low speed bull gear being in mechanical communication with the low speed pinion.   
     
     
         3 . The system of  claim 2 , wherein the transmission comprises:
 a clutch assembly to selectively engage and disengage the braking device with the transmission wherein:   in a normal driving mode, the clutch assembly disengages the braking device from the transmission; and   in a braking mode, the clutch assembly engages the braking device with the transmission.   
     
     
         4 . The system of  claim 2 , wherein (a) is true. 
     
     
         5 . The system of  claim 4 , wherein the braking compressor comprises at least one of an inlet and outlet nozzle of a variable area, and wherein:
 in a normal driving mode, the nozzle has a first cross-sectional area normal to gas flow; and   in a braking mode, the nozzle has a second cross-sectional area normal to gas flow, the first cross-sectional area being different from the second cross-sectional area, wherein less power is dissipated by the braking compressor in the normal driving mode than in the braking mode.   
     
     
         6 . The system of  claim 5 , wherein output gas from the braking compressor is at least one of used to charge a pneumatic storage tank and quench a hot gas from a recuperator to assist in engine turndown, the output gas being introduced into an exhaust flow upstream of an input to a hot side of the recuperator. 
     
     
         7 . The system of  claim 1 , wherein (b) is true and wherein the continuously variable transmission is positioned mechanically between a load and the free power turbine. 
     
     
         8 . The system of  claim 7 , further comprising an increasing gearbox positioned mechanically between the continuously variable transmission and a braking compressor. 
     
     
         9 . The system of  claim 7 , further comprising a clutch assembly to selectively engage and disengage the continuously variable transmission from mechanical communication with the free power turbine and the transmission. 
     
     
         10 . The system of  claim 1 , wherein (c) is true, wherein the electrical generator is configured to generate the electrical energy in response to free power turbine rotation. 
     
     
         11 . The system of  claim 10 , wherein a control excitation of the electrical generator is controlled to generate the selected amount of electrical energy and wherein the generated electrical energy is carried via a conductive path to at least one of a dynamic braking grid, an electrical energy storage system, and a thermal energy storage device. 
     
     
         12 . The system of  claim 11 , wherein the generator is positioned mechanically between a clutch assembly and a braking compressor. 
     
     
         13 . The system of  claim 1 , wherein (d) is true. 
     
     
         14 . The system of  claim 13 , wherein the braking device comprises an eddy current clutch positioned mechanically between a load and the free power turbine and wherein the eddy current clutch comprises:
 an exciter armature rigidly connected to an input shaft and at least one diode;   a main field coil mechanically connected to the at least one diode;   a main armature rigidly connected to an output shaft; and   an exciter field coil, the exciter field coil being substantially fixed relative to the free power turbine and activated by one of a direct current and alternating current control system;   wherein the exciter armature is electrically connected to the at least one diode by one of an alternative current and direct current wire and the at least one diode is electrically connected to the main field coil by the other of an alternating current and direct current wire; and   wherein the exciter armature, at least one diode and main field coil rotate when the input shaft rotates.   
     
     
         15 . The system of  claim 1 , wherein (e) is true. 
     
     
         16 . The system of  claim 15 , wherein the fluid pump circuit is engaged mechanically with the free power turbine and comprises:
 a fluid pump; and
 a restrictor valve having a variable orifice size, wherein the orifice size is varied to provide a variable retarding force on at least one of the free power turbine and the transmission. 
   
     
     
         17 . The system of  claim 16 , wherein the pump is in mechanical and fluid communication with a lubrication system of at least one of the engine and the transmission. 
     
     
         18 . The system of  claim 1 , further comprising:
 a spur gear mechanically connected to the braking device;   a plurality of planet gears;   a planet carrier in mechanical communication with the plurality of planet gears;   a sun gear in mechanical communication with plurality of planet gears; and   a ring gear in mechanical communication with the spur gear and the plurality of planet gears, wherein the spur gear is in mechanical communication with a first braking device, wherein the sun gear is in mechanical communication with a second braking device, and wherein a low input shaft is in mechanical communication with the planet carrier and a clutch assembly to selectively engage and disengage the first and second braking devices from mechanical communication with the free power turbine and the transmission.   
     
     
         19 . In a vehicle comprising a gas turbine engine and a transmission comprising at least one turbo-compressor spool assembly, the at least one turbo-compressor spool assembly comprising a compressor in mechanical communication with a turbine, the turbine outputting a gas, a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, and a braking device in mechanical communication with the free power turbine and the transmission, a method comprising:
 performing at least one of the following steps:
 (a) in response to a sensed revolutions-per-minute of the free power turbine, selectively engaging and disengaging a braking device from mechanical communication with the free power turbine, the braking device retarding rotation of the free power turbine; 
 (b) in response to a sensed braking request of the vehicle, selectively engaging and disengaging a braking device from mechanical communication with the free power turbine, the braking device providing a braking force to the vehicle; 
 (c) varying, by an continuously variable transmission, a gear ratio continuously between first and second gear ratios, the gear ratio being for a mechanical linkage between a braking device and the clutch assembly; 
 (d) generating, by an electrical generator, a selected amount of electrical energy to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle; 
 (e) applying torque by at least one of an eddy current brake and eddy current clutch to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle; and 
 (f) intermittently operating a fluid pump in mechanical communication with the free power turbine to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle. 
   
     
     
         20 . The method of  claim 19 , wherein the braking device is selectively mechanically engaged and disengaged from the free power turbine and/or the transmission of the vehicle by a clutch assembly and wherein the transmission comprises:
 a first gear assembly comprising a high speed bull gear in mechanical communication with a first shaft, a high speed pinion gear in mechanical communication with the free power turbine, and a power take off pinion gear in mechanical communication with the braking device, the high speed bull gear being in mechanical communication with the high speed pinion and the power takeoff pinion; and   a second gear assembly comprising a low speed bull gear in mechanical communication with a second shaft and a low speed pinion in mechanical communication with the first shaft, the low speed bull gear being in mechanical communication with the low speed pinion.   
     
     
         21 . The method of  claim 20 , further comprising:
 selectively disengaging the braking device with the transmission in a normal driving mode; and   selectively engaging the braking device with the transmission in a braking mode.   
     
     
         22 . The method of  claim 19 , wherein at least one of step (a) and step (b) is performed. 
     
     
         23 . The method of  claim 22 , wherein the braking device comprises at least one of an inlet and outlet nozzle of a variable area and wherein:
 in a normal driving mode, the nozzle has a first cross-sectional area normal to the at least a portion of the gas flow; and   in a braking mode, the nozzle has a second cross-sectional area normal to gas flow, the first cross-sectional area being different from the second cross-sectional area, wherein less power is dissipated by the braking device in the normal driving mode than in the braking mode.   
     
     
         24 . The method of  claim 23 , wherein output gas from the braking compressor is at least one of used to charge a pneumatic storage tank and quench a hot gas from a recuperator to assist in engine turndown, the output gas being introduced into an exhaust flow upstream of an input to a hot side of the recuperator. 
     
     
         25 . The method of  claim 19 , wherein step (c) is performed. 
     
     
         26 . The method of  claim 25 , further comprising positioning an increasing gearbox positioned between the continuously variable transmission and a braking compressor. 
     
     
         27 . The method of  claim 26 , wherein step (d) is performed. 
     
     
         28 . The method of  claim 19 , wherein a control excitation of the electrical generator is controlled to generate the selected amount of electrical energy and wherein the generated electrical energy is carried via a conductive path to at least one of a dynamic braking grid, an electrical energy storage system, and a thermal energy storage device. 
     
     
         29 . The method of  claim 27 , wherein the generator is positioned mechanically between a clutch assembly and a load. 
     
     
         30 . The method of  claim 19 , wherein step (e) is performed. 
     
     
         31 . The method of  claim 20 , wherein the at least one of eddy current brake and clutch is the eddy current clutch and wherein the eddy current clutch comprises:
 applying one of a direct and alternating electrical current to an exciter field coil to induce the other of a direct and alternating current in an exciter armature;   rectifying the induced current to the one of direct and alternating current and causing the one of the direct and alternating current in a main field coil;   causing a rotational force in a main armature;   wherein the exciter armature and main field coil rotate when an input shaft rotates and the main armature rotates when an output shaft rotates.   
     
     
         32 . The method of  claim 19 , wherein step (f) is performed. 
     
     
         33 . The method of  claim 32 , wherein the fluid pump is in communication with a restrictor valve having a variable orifice size, wherein the orifice size is varied to provide a variable retarding force on at least one of the free power turbine and the transmission. 
     
     
         34 . The method of  claim 33 , wherein the fluid pump is in mechanical communication with a lubrication system of at least one of the engine and the transmission. 
     
     
         35 . The method of  claim 20 , wherein the braking device further comprises:
 a spur gear mechanically connected to the braking device;   a plurality of planet gears;   a planet carrier in mechanical communication with the plurality of planet gears;   a sun gear in mechanical communication with plurality of planet gears; and   a ring gear in mechanical communication with the spur gear and the plurality of planet gears, wherein the spur gear is in mechanical communication with a first braking device, wherein the sun gear is in mechanical communication with a second braking device, and wherein a low input shaft is in mechanical communication with the planet carrier and clutch assembly to selectively engage and disengage the first and second braking devices from mechanical communication with the free power turbine and the transmission.   
     
     
         36 . A vehicle, comprising:
 (a) an engine;   (b) a transmission;   (c) a braking device to maintain or reduce the ground velocity of the vehicle; and at least one of the following braking device control devices:
 (C1) a continuously variable transmission positioned mechanically with respect to the braking device, the transmission and the engine; 
 (C2) an electrical generator configured to generate a selected amount of electrical energy to provide a selected amount of retardation force against rotation of a shaft of the engine; 
 (C3) at least one of an eddy current clutch and eddy current brake positioned mechanically with respect to the braking device, the transmission and the engine; and 
 (C4) a pump and restrictor valve in fluid communication with the braking device. 
   
     
     
         37 . The vehicle of  claim 36 , wherein the engine is a gas turbine engine and comprises at least one turbo-compressor spool assembly, wherein the at least one turbo-compressor spool assembly comprises a compressor in mechanical communication with a turbine, the turbine outputting a gas and a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, wherein the braking compressor is in mechanical communication with the free power turbine to dissipate power of the free power turbine. 
     
     
         38 . The vehicle of  claim 37 , wherein the transmission comprises:
 (B1) a first gear assembly comprising a high speed bull gear in mechanical communication with a first shaft, a high speed pinion gear in mechanical communication with the free power turbine, and a power take off pinion gear in mechanical communication with the braking compressor, the high speed bull gear being in mechanical communication with the high speed pinion and the power takeoff pinion; and   (B2) a second gear assembly comprising a low speed bull gear in mechanical communication with a second shaft and a low speed pinion in mechanical communication with the first shaft, the low speed bull gear being in mechanical communication with the low speed pinion.   
     
     
         39 . The vehicle of  claim 36 , further comprising:
 (C3) a clutch assembly to selectively engage and disengage the braking compressor with the transmission wherein:   in a normal driving mode, the clutch assembly disengages the braking compressor from the transmission; and   in a braking mode, the clutch assembly engages the braking compressor with the transmission.   
     
     
         40 . The vehicle of  claim 37 , wherein the braking compressor comprises at least one of an inlet and outlet nozzle of a variable area, and wherein:
 in a normal driving mode, the nozzle has a first cross-sectional area normal to gas flow; and   in a braking mode, the nozzle has a second cross-sectional area normal to gas flow, the first cross-sectional area being different from the second cross-sectional area, wherein less power is dissipated by the braking compressor in the normal driving mode than in the braking mode.   
     
     
         41 . The vehicle of  claim 40  wherein output gas from the braking compressor is at least one of used to charge a pneumatic storage tank and quench a hot gas from a recuperator to assist in engine turndown, the output gas being introduced into an exhaust flow upstream of an input to a hot side of the recuperator. 
     
     
         42 . The vehicle of  claim 37 , wherein (C1) is true. 
     
     
         43 . The vehicle of  claim 42 , further comprising an increasing gearbox positioned mechanically between the continuously variable transmission and a braking compressor. 
     
     
         44 . The vehicle of  claim 42 , further comprising a clutch assembly to selectively engage and disengage the continuously variable transmission from mechanical communication with the free power turbine and the transmission. 
     
     
         45 . The vehicle of  claim 37 , wherein (C2) is true. 
     
     
         46 . The vehicle of  claim 45 , wherein a control excitation of the electrical generator is controlled to generate the selected amount of electrical energy and wherein the generated electrical energy is carried via a conductive path to at least one of a dynamic braking grid, an electrical energy storage system, and a thermal energy storage device. 
     
     
         47 . The vehicle of  claim 46 , wherein the generator is positioned mechanically between a clutch assembly and a braking compressor. 
     
     
         48 . The vehicle of  claim 37 , wherein (C3) is true. 
     
     
         49 . The vehicle of  claim 48 , wherein the eddy current clutch comprises:
 an exciter armature rigidly connected to an input shaft and at least one diode;   a main field coil mechanically connected to the at least one diode;   a main armature rigidly connected to an output shaft; and   an exciter field coil, the exciter field coil being substantially fixed relative to the free power turbine and activated by one of a direct current and alternating current control system;   wherein the exciter armature is electrically connected to the at least one diode by one of an alternative current and direct current wire and the at least one diode is electrically connected to the main field coil by the other of an alternating current and direct current wire; and   wherein the exciter armature, at least one diode and main field coil rotate when the input shaft rotates.   
     
     
         50 . The vehicle of  claim 37 , wherein (C4) is true. 
     
     
         51 . The vehicle of  claim 50 , wherein the fluid pump circuit comprises:
 a fluid pump; and
 a restrictor valve having a variable orifice size, wherein the orifice size is varied to provide a variable load on the free power turbine. 
   
     
     
         52 . The vehicle of  claim 51 , wherein the pump is in mechanical communication with a lubrication system of at least one of the engine and the transmission. 
     
     
         53 . The braking device of  claim 37 , wherein the transmission comprises:
 (B1) a spur gear mechanically connected to the braking compressor;   (B2) a plurality of planet gears;   (B3) a planet carrier in mechanical communication with the plurality of planet gears;   (B4) a sun gear in mechanical communication with plurality of planet gears; and   (B5) a ring gear in mechanical communication with the spur gear and the plurality of planet gears, wherein the spur gear is in mechanical communication with a first braking device, wherein the sun gear is in mechanical communication with a second braking device, and wherein a low input shaft is in mechanical communication with the planet carrier and a clutch assembly to selectively engage and disengage the first and second braking devices from mechanical communication with the free power turbine and the transmission.   
     
     
         54 . A tangible or non-transient computer readable medium comprising microprocessor-executable instructions operable to perform at least the following steps:
 a) sensing at least one of a revolutions per minute (“rpms”) of a free power turbine, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting;   b) based on the sensed at least one of a revolutions per minute (“rpms”) of a free power turbine, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting, determining that the free power turbine requires over-speed control;   c) in response to step (b), disengaging the transmission clutch and engaging the braking device clutch;   d) reducing the rpms of the free power turbine by controlling an amount of energy dissipation of the braking device;   e) during step (d), sensing rpms of the free power turbine and reducing the rpms of the free power turbine until the rpms of the free power turbine are reduced to less than or equal to a selected value; and   f) when the rpms of the free power turbine are less than the selected value, disengaging the braking device clutch.   
     
     
         55 . A tangible or non-transient computer readable medium comprising microprocessor-executable instructions operable to perform at least the following steps:
 a) sensing at least one of an on and off state of braking device clutch, at least one of an on and off state of a transmission clutch, a vehicle ground velocity, a transmission gear setting, and a braking device control setting;   b) based on the sensed at least one of a vehicle ground velocity, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting, determining that engine braking is required;   c) in response to step (b), engaging the braking device clutch and engaging the transmission clutch for engine braking;   d) increasing a vehicle braking force opposing a direction of motion of the vehicle by controlling an amount of energy dissipation of the braking device;   e) during step (d), sensing a vehicle ground velocity and applying the engine braking force until the vehicle ground velocity is less than or equal to a selected value; and   f) when the vehicle ground velocity is less than or equal to the selected value, disengaging the braking device clutch.