System and method for detecting a mechanical transmission failure

1 . A method of detecting a mechanical transmission failure in a driveline connected to a hydrostatic transmission, the method comprising:

transmitting torque between a first shaft of the driveline and a second shaft via the hydrostatic transmission operating with a hydraulic fluid at an expected pressure by:

delivering the hydraulic fluid from a pump of the hydrostatic transmission to a motor of the hydrostatic transmission at a first pressure via a first conduit; and

returning the hydraulic fluid from the motor of the hydrostatic transmission to the pump of the hydrostatic transmission at a second pressure via a second conduit;

operating the hydrostatic transmission when the mechanical transmission failure occurs while the torque is being transmitted between the first shaft and the second shaft, the mechanical transmission failure causing a pressure change in the hydraulic fluid from the expected pressure;

measuring a difference between the first pressure and the second pressure with a delta pressure sensor operatively connected to the first conduit and to the second conduit; and

detecting the pressure change in the hydraulic fluid from the expected pressure, wherein:

the expected pressure includes an expected value of the difference between the first pressure and the second pressure; and

the pressure change includes a deviation from the expected value of the difference between the first pressure and the second pressure.

2 . The method as defined in claim 1 , wherein the mechanical transmission failure is a shaft shear in the driveline connected to the hydrostatic transmission.

3 . The method as defined in claim 1 , comprising initiating a mitigating action in response to detecting the pressure change in the hydraulic fluid from the expected pressure.

4 . The method as defined in claim 1 , comprising:

driving the first shaft with a thermal engine;

transmitting the torque from the first shaft to the second shaft via the hydrostatic transmission;

driving a compressor with the second shaft; and

supplying compressed air from the compressor to the thermal engine.

5 . The method as defined in claim 1 , comprising:

driving a turbine using exhaust gas from a thermal engine drivingly connected to the first shaft;

driving the second shaft with the turbine; and

transmitting the torque from the second shaft to the first shaft via the hydrostatic transmission.

6 . The method as defined in claim 5 , wherein:

the turbine is part of a turbo-compressor;

the method includes:

driving a compressor of the turbo-compressor with the turbine; and

supplying compressed air from the compressor to the thermal engine.

7 . The method as defined in claim 6 , wherein:

the hydrostatic transmission is part of a compound drive operatively connecting the thermal engine and the turbo-compressor; and

the compound drive includes a speed-changing epicyclic gear train.

8 . The method as defined in claim 1 , wherein:

the first shaft drivingly connects a thermal engine to the hydrostatic transmission;

the second shaft drivingly connects a turbine to the hydrostatic transmission; and

the method includes driving the turbine with exhaust gas from the thermal engine.

9 . The method as defined in claim 8 , comprising:

driving a compressor with the turbine; and

supplying compressed air to the thermal engine using the compressor.

10 . The method as defined in claim 9 , comprising stopping a fuel flow to the thermal engine in response to detecting the pressure change in the hydraulic fluid from the expected pressure.

11 . The method as defined in claim 1 , wherein the pressure change is detected using a computer that is dedicated only to detecting the mechanical transmission failure.

12 . A mechanical transmission system with failure detection, the system comprising:

a hydrostatic transmission configured to transmit torque between a first shaft and a second shaft using hydraulic fluid; and

a failure detector including a sensor configured to, when a torque transmission failure causes a pressure change in the hydraulic fluid, detect the pressure change in the hydraulic fluid, the failure detector being configured to generate an output indicative of the torque transmission failure in response to the pressure change having crossed a threshold,

wherein:

the hydrostatic transmission includes:

a first conduit conveying the hydraulic fluid from a pump of the hydrostatic transmission to a motor of the hydrostatic transmission during operation of the hydrostatic transmission; and

a second conduit conveying the hydraulic fluid from the motor to the pump during operation of the hydrostatic transmission;

the pressure change includes a change in a difference in pressure of the hydraulic fluid in the first conduit and the hydraulic fluid in the second conduit;

the sensor is a delta pressure sensor operatively connected to the first conduit and to the second conduit.

13 . An aircraft power plant with shaft shear mitigation, the aircraft power plant comprising:

a thermal engine drivingly connectable to an air mover configured to propel an aircraft;

a hydrostatic transmission for transmitting torque between the thermal engine and a shaft using hydraulic fluid;

a sensor for detecting a pressure of the hydraulic fluid; and

a computer operatively connected to the sensor and configured to initiate a mitigating action when a shaft shear event causes a load change on the hydrostatic transmission and the pressure of the hydraulic fluid detected by the sensor is indicative of the shaft shear event,

wherein:

the hydrostatic transmission includes:

a first conduit conveying the hydraulic fluid from a pump of the hydrostatic transmission to a motor of the hydrostatic transmission during operation of the hydrostatic transmission; and

a second conduit conveying the hydraulic fluid from the motor to the pump during operation of the hydrostatic transmission;

the pressure of the hydraulic fluid is indicative of the shaft shear event when a change in a difference in pressure of the hydraulic fluid in the first conduit and the hydraulic fluid in the second conduit has crossed a threshold; and

the sensor is a delta pressure sensor operatively connected to the first conduit and to the second conduit.

14 . The aircraft power plant as defined in claim 13 , wherein:

the shaft is drivingly connected to a turbo-compressor;

a turbine of the turbo-compressor is configured to be driven using exhaust gas from the thermal engine;

a compressor of the turbo-compressor is configured to be driven by the turbine; and

the compressor is configured to supply compressed air for combustion in the thermal engine.

15 . The aircraft power plant as defined in claim 14 , comprising a speed-changing gear train operatively connected between the thermal engine and the turbo-compressor.

16 . The aircraft power plant as defined in claim 15 , wherein the aircraft power plant is a hybrid aircraft power plant including an electric motor drivingly connectable to the air mover.

17 . The aircraft power plant as defined in claim 16 , wherein the mitigating action includes stopping a fuel delivery to the thermal engine.