Method of measuring torque and torque measuring system for said method

1. A method of measuring torque at a drive shaft of a helicopter drive having at least a main gear in a main gearbox and at least a tail gear in a tail gearbox, said drive shaft being arranged for transmitting torque between said main gear and the tail gear, said method comprising the following steps:

providing at least first and second vibration sensors with said vibration sensors being respectively attached to each of said main gearbox and said tail gearbox,

applying torque to said drive shaft,

detecting main gearbox vibrations related to gear mesh vibrations resulting from interaction of said drive shaft with said main gear by the first vibration sensor attached to said main gearbox vibrating in response to the main gearbox vibrating,

detecting tail gearbox vibrations related to gear mesh vibrations resulting from interaction of said drive shaft with said tail gear by the second vibration sensor attached to said tail gearbox vibrating in response to the tail gearbox vibrating,

communicating the main gearbox vibrations detected by the first vibration sensor to an evaluation unit,

communicating the tail gearbox vibrations detected by the second vibration sensor to the evaluation unit,

acquiring data related to the main gearbox vibrations related to the gear mesh vibrations communicated from the first vibration sensor to the evaluation unit,

acquiring data related the tail gearbox vibrations related to the gear mesh vibrations communicated from the second vibration sensor to the evaluation unit,

bandpass filtering said acquired data for each of said first and second vibration sensors separately,

extracting separate phase information from said data filtered separately for each of said first and second vibration sensors,

detecting the phase difference from the separately extracted phase information from each of said first and second vibration sensors,

computing the rotations per minute for the drive shaft from the extracted phase information from said data filtered separately for each of said first and second vibration sensors, and

computing the torque applied to the drive shaft from the phase difference computed from the separately extracted phase information for each of said first and second vibration sensors.

2. The method according to claim 1 , wherein detecting the phase difference from said separately extracted phase information from said data filtered separately for each of said first and second vibration sensors and computing the torque applied to said drive shaft by applying a scaling parameter to said detected phase difference, said scaling parameter depending from the torsional stiffness of said drive shaft.

3. A torque measurement system for measuring torque at a drive shaft of a helicopter drive having a main gear in a main gearbox and a tail gear in a tail gearbox, said drive shaft being arranged for transmitting torque between said main gear and the tail gear, the system comprising:

a first vibration sensor attached to the main gearbox and configured to vibrate in response to the main gearbox vibrating to detect main gearbox vibrations related to gear mesh vibrations resulting from interaction of the drive shaft with the main gear while a torque is applied to the drive shaft;

a second vibration sensor attached to the tail gearbox and configured to vibrate in response to the tail gearbox vibrating to detect tail gearbox vibrations related to gear mesh vibrations resulting from interaction of the drive shaft with said tail gear while the torque is applied to the drive shaft; and

an evaluation unit configured to acquire data related to the detected main gearbox vibrations from the first vibration sensor and data related to the detected tail gearbox vibrations from the second vibration sensor, bandpass filter the acquired data for each of the first and second vibration sensors separately, extract phase information from the filtered data for each of the first and second vibration sensors, and detect a phase difference from the phase information for each of the first and second vibration sensors;

the evaluation unit further configured to compute rotations per minute for the drive shaft from the phase information for each of the first and second vibration sensors and to compute the torque applied to the drive shaft from the phase difference.

4. The torque measurement system according to claim 3 , wherein said evaluation unit is provided with data acquiring means, bandpass filtering means, phase extraction means, phase difference and rotations per minute computation means and torque computation means.

5. The torque measurement system according to claim 4 , wherein said data acquiring means, bandpass filtering means and phase extraction means are respectively provided separately in parallel for each of said first and second vibration sensors.