Gas turbine speed detection

1. A gas turbine engine having at least one rotor shaft operatively connecting a compressor apparatus and a turbine apparatus, the gas turbine engine comprising an auxiliary gear box and a phonic wheel apparatus, the auxiliary gear box being drivingly connected to the rotor shaft, and the phonic wheel apparatus including a toothed gear of an oil pump and a sensor, the oil pump mounted to the auxiliary gear box, the sensor mounted to a housing of the oil pump and adapted to sense a rotational speed of the toothed gear.

2. The gas turbine engine as defined in claim 1 wherein the oil pump is a scavenge gear pump.

3. The gas turbine engine as defined in claim 1 wherein the oil pump further comprises a cavity defined in the housing and a pair of rotatable gears within the cavity, the housing further defining a hole intersecting the cavity for receiving the sensor therein in a position in which the sensor faces tooth tips of one of the gears when the gears rotate.

4. A speed sensing apparatus for a gas turbine engine comprising an oil pump drivingly connected to a turbine rotor shaft of the engine, the oil pump including at least one gear rotating in a fixed ratio relative to the rotor shaft, and sensor means mounted to the oil pump for determining a rotational speed of the rotor shaft from rotation of said gear.

5. The apparatus as defined in claim 4 wherein the oil pump is a gear pump.

6. The apparatus as defined in claim 5 wherein the oil pump comprises a body defining a cavity therein for operatively containing a pair of gears including said at least one gear, the body further defining a hole extending thereinto and intersecting the cavity for receiving the sensor means therein.

7. The apparatus as defined in claim 5 further comprising clearance means to ensure a clearance between said sensor means held in position and tooth tips of the gear when the gear rotates.

8. A method for detecting a rotational speed of a rotor shaft of a gas turbine engine, the rotor shaft operatively connecting a compressor apparatus and a turbine apparatus, and drivingly connecting an auxiliary gear box, the method comprising:

detecting a rotational speed of one toothed gear of an oil pump associated with the auxiliary gear box, the toothed gear rotating in a fixed ratio with respect to the rotational speed of the rotor shaft; and

determining a rotational speed of the rotor shaft based on the detected rotational speed of the toothed gear and the fixed ratio.

9. The method as defined in claim 8 wherein detection of the rotational speed of the toothed gear is conducted using the toothed gear as a phonic wheel.