Torque control device for a downhole drilling assembly
This invention relates to a torque control device for a downhole drilling assembly, the torque control device being adapted for connection to a drill bit. The torque control device includes an outer sleeve and an inner shaft, the outer sleeve being movable longitudinally relative to the inner shaft. The torque control device has a cylinder, a piston located within the cylinder, and a rotary valve to control the volume of the cylinder. The volume of the cylinder can be changed by way of the rotary valve whereby to adjust the weight on bit and thereby control the torque upon the drill bit.
1. A torque control device for a downhole drilling assembly, the torque control device being adapted for connection to a drill bit, the torque control device including an outer sleeve and an inner shaft, the outer sleeve being movable longitudinally relative to the inner shaft, the torque control device having a cylinder, a piston located within the cylinder, and a rotary valve to control the volume of the cylinder, the rotary valve having a valve opening, the rotary valve having a first position and a second position, the area of the valve opening being larger in the second position than in the first position, the rotary valve changing between its first and second positions in use depending upon relative rotation between the outer sleeve and the inner shaft.
2. A torque control device according to claim 1 in which the cylinder is filled with drilling fluid in use.
3. A torque control device according to claim 2 in which the torque control device has a through-bore for carrying drilling fluid to the drill bit.
4. A torque control device according to claim 3 in which the through-bore is located within the inner shaft.
5. A torque control device according to claim 1 in which the cylinder has an exhaust port permitting the flow of drilling fluid out of the cylinder.
6. A torque control device according to claim 5 in which the exhaust port is permanently open.
7. A torque control device according to claim 5 in which the exhaust port is a conduit through the piston.
8. A torque control device for a downhole drilling assembly, the torque control device being adapted for connection to a drill bit, the torque control device including an outer sleeve and an inner shaft, the outer sleeve being movable longitudinally relative to the inner shaft, the torque control device having a cylinder, a piston located within the cylinder, and a rotary valve to control the volume of the cylinder, the inner shaft comprising a first part and a second part, the first part of the inner shaft being rotatable relative to the second part of the inner shaft.
9. A torque control device according to claim 8 in which the piston is connected to the first part of the inner shaft.
10. A torque control device according to claim 9 in which the rotary valve comprises a fluid entry port in the second part of inner shaft and a conduit through the piston, relative rotation of the piston and the second part of the inner shaft varying the overlap between the fluid entry port and the conduit.
11. A torque control device according to claim 10 including a torsion spring which acts to rotate the piston relative to the second part of the inner shaft whereby to reduce the overlap between the fluid entry port and the conduit.
12. A torque control device according to claim 11 in which the torsion spring also acts to reduce the volume of the cylinder.
13. A torque control device according to claim 9 having stops to limit the rotation of the piston relative to the second part of the inner shaft.