Gear reducer
Apparatus and methods relate to a gear reducer, which may be used downhole to reduce rotational speed output from a downhole motor, such as a turbine motor, to a slower speed desired for rotation of a drill bit. The gear reducer includes a planetary gear arrangement coupled to receive rotational input from the downhole motor and a cycloidal gear arrangement driven by rotation resulting from the planetary gear arrangement. An output shaft couples to the cycloidal gear arrangement and rotates during operation slower than the rotational input from the downhole motor.
1. A gear reducer for a downhole motor in a well, comprising:
a planetary gear arrangement coupled to receive rotational input from the downhole motor, wherein the planetary gear arrangement comprises:
a ring gear coupled to rotate with a powered rotor of the downhole motor;
a first planetary gear meshed with the ring gear and disposed on the first crankshaft; and
a second planetary gear meshed with the ring gear and disposed on a second crankshaft;
a cycloidal gear arrangement coupled to be driven by rotation resulting from the planetary gear arrangement; and
an output shaft coupled to the cycloidal gear arrangement, wherein during operation the output shaft rotates slower than the rotational input from the downhole motor.
2. The gear reducer of claim 1 , wherein the cycloidal gear arrangement comprises:
a first cycloidal rotor partially meshed with teeth inside a cycloidal stator, wherein a first offset cam of the first crankshaft passes through the first cycloidal rotor and a second offset cam of the second crankshaft passes through the first cycloidal rotor; and
a second cycloidal rotor partially meshed with the teeth inside the cycloidal stator, wherein a third offset cam of the first crankshaft passes through the second cycloidal rotor and a fourth offset cam of the second crankshaft passes through the second cycloidal rotor.
3. The gear reducer of claim 2 , wherein the output shaft has a top end with first and second bores to respectively receive bottom ends of the first and second crankshafts that are rotated together about a center rotational axis of the output shaft by the first and second cycloidal rotors.
4. The gear reducer of claim 1 , wherein during operation the rotational input from the downhole motor is at a first revolutions per minute (RPM) and crankshafts of the planetary gear arrangement individually rotate during operation at a second RPM greater than the first RPM.
5. The gear reducer of claim 1 , wherein the output shaft rotates slower than the rotational input from the downhole motor due to increasing revolutions per minute (RPM) with the planetary gear arrangement and then decreasing RPM with the cycloidal gear arrangement.
6. The gear reducer of claim 1 , wherein during operation the rotational input from the downhole motor is lefthand rotation opposite of righthand rotation of the output shaft.
7. The gear reducer of claim 1 , further comprising a positive pressure lubricant supply to the planetary and cycloidal gear arrangements, wherein the positive pressure lubricant supply includes a piston acted on by drilling fluid taken at least one stage up along a turbine motor that is the downhole motor.
8. A method of reducing rotational speed of a downhole motor in a well, comprising:
providing a gear reducer in the well coupled to receive rotational input from the downhole motor and having an output shaft;
receiving the rotational input from the downhole motor into a planetary gear arrangement of the gear reducer;
driving a cycloidal gear arrangement by rotation resulting from the planetary gear arrangement; and
rotating the output shaft coupled to the cycloidal gear arrangement slower than the rotational input from the downhole motor;
wherein the output shaft rotates slower than the rotational input from the downhole motor due to increasing revolutions per minute (RPM) with the planetary gear arrangement and then decreasing RPM with the cycloidal gear arrangement.
9. The method of claim 8 , wherein the gear reducer receives rotational input from the downhole motor that is a turbine motor.
10. The method of claim 8 , wherein the planetary gear arrangement of the gear reducer is a sun gear driven planetary system.
11. The method of claim 8 , wherein the rotational input from the downhole motor is lefthand rotation opposite of righthand rotation of the output shaft.
12. The method of claim 8 , further comprising supplying lubricant to the planetary and cycloidal gear arrangements, wherein a piston acted on by drilling fluid taken at least one stage up along a turbine motor that is the downhole motor pressurizes the lubricant.
13. A downhole assembly for drilling a well, comprising:
a downhole motor having a powered rotor, wherein the downhole motor is one of a turbine motor and a positive displacement motor;
a gear reducer, comprising:
a ring gear coupled to rotate with the powered rotor of the downhole motor;
a first planetary gear meshed with the ring gear and disposed on a first crankshaft;
a second planetary gear meshed with the ring gear and disposed on a second crankshaft;
a first cycloidal rotor partially meshed with teeth inside a cycloidal stator, wherein a first offset cam of the first crankshaft passes through the first cycloidal rotor and a second offset cam of the second crankshaft passes through the first cycloidal rotor;
a second cycloidal rotor partially meshed with the teeth inside the cycloidal stator, wherein a third offset cam of the first crankshaft passes through the second cycloidal rotor and a fourth offset cam of the second crankshaft passes through the second cycloidal rotor; and
an output shaft having a top end with first and second bores to respectively receive bottom ends of the first and second crankshafts that are rotated together about a center rotational axis of the output shaft by the first and second cycloidal rotors; and
a drill bit coupled to rotate with the output shaft of the gear reducer.
14. The downhole assembly of claim 13 , wherein the downhole motor is the turbine motor.
15. The downhole assembly of claim 14 , wherein the gear reducer further comprises a positive pressure lubricant supply with a piston acted on by drilling fluid taken at least one stage up along the turbine motor.
16. The downhole assembly of claim 13 , wherein the teeth inside the cycloidal stator are at least one more than on outside of each of the first and second cycloidal rotors.
17. The downhole assembly of claim 13 , wherein the first and second cycloidal rotors are offset 180 degrees such that the first cycloidal rotor is partially meshed with the teeth inside the cycloidal stator on an opposite side of the cycloidal stator from where the second cycloidal rotor is partially meshed with the teeth inside the cycloidal stator.
18. The downhole assembly of claim 13 , wherein gear reducer further comprises a third planetary gear meshed with the ring gear and disposed on a third crankshaft.