Hybrid-electric propulsion system equipped with a coupler for switching between modes of operation
A propulsion assembly includes a first torque source coupled with a first shaft and a second torque source coupled with a second shaft. A coupler selectively couples the first and second torque sources. When the first and second torque sources are coupled via the coupler, in response to a command to decouple the first torque source, an unloading operation is performed to decrease the torque output provided by the first torque source to a threshold, and when reached, the first shaft is decoupled from the coupler. When the first torque source is coupled with the coupler but the second torque source is not, in response to a command to couple the second torque source, a speed matching operation is performed to increase the speed of the second shaft to match a speed of the first shaft, and when the speeds are matched, the second shaft is coupled to the coupler.
1 . A method, comprising:
operating an electric machine in a generator mode, the electric machine being mechanically coupled with a coupler to which a propulsor and a power turbine of a gas turbine engine are also mechanically coupled;
in response to an electric machine decouple command, decreasing a generator torque output that the electric machine applies on the coupler over an unloading period; and
when the generator torque output that the electric machine applies on the coupler reaches a predetermined threshold, decoupling the electric machine from the coupler, wherein during the unloading period, a torque output provided by the power turbine on the coupler is decreased.
2 . The method of claim 1 , wherein the generator torque output is decreased linearly over the unloading period.
3 . The method of claim 1 , wherein during the unloading period, the torque output provided by the power turbine on the coupler is decreased linearly.
4 . The method of claim 1 , wherein the generator torque output provided by the electric machine on the coupler is decreased linearly over the unloading period and the torque output provided by the power turbine on the coupler is decreased linearly over the unloading period.
5 . The method of claim 1 , wherein the generator torque output provided by the electric machine on the coupler is decreased over the unloading period at a first rate and a torque output provided by the power turbine on the coupler is decreased over the unloading period at a second rate, the first rate being different than the second rate.
6 . The method of claim 1 , wherein decoupling the electric machine from the coupler comprises modulating one or more actuators to move a coupler electric machine shaft of the coupler so that torque transmitting features of the coupler electric machine shaft disengage from torque transmitting features of an electric machine shaft associated with the electric machine.