Drive means

1. In a downhole progressive cavity pump, a drive means comprising an input shaft and an output shaft, the input shaft being coupled to a means of rotation, the output shaft being coupled to a rotor of the progressive cavity pump, the input shaft and the output shaft being non-collinear so that the output shaft rotates about an axis of the output shaft while describing a circular path with respect to the input shaft, wherein the input shaft and output shaft are coupled by a male inner rotor and a female outer rotor, the rotors being coupled by a group of interengaged projections, the said projections consisting of n first projections and n+1 second projections, the male inner rotor comprising the first projections, the female outer rotor comprising the second projections, the second projections of the female outer rotor extending radially inwardly to engage the first projections of the male inner rotor and transmit torque from the input shaft to the output shaft;

and the male and female rotors being operatively positioned within a housing having at least one eccentric bearing for constraining at least one of the input shaft and the output shaft.

2. The drive means according to claim 1 , wherein the output shaft is supported on the said eccentric bearing in the said housing.

3. The drive means according to claim 2 , wherein the eccentric bearing is crescent shaped.

4. The drive means according to claim 1 , wherein the male inner rotor has only two first projections and the female outer rotor has only three second projections.

5. The drive means according to claim 1 , wherein the interface of the male inner rotor and the female outer rotor comprise a gerotor shape.

6. The drive means according to claim 5 , wherein the female outer rotor is a three-lobed gerotor shape and the male inner rotor is a two-lobed gerotor shape.

7. The drive means according to claim 1 , wherein a single revolution of the input shaft causes the output shaft to turn by approximately 1.5 revolutions.

8. A drive means for driving a rotor of a progressive cavity pump, comprising:

an input shaft operative to transfer torque to an output shaft, the input shaft positioned along an axis of rotation that is offset from an axis of rotation of the output shaft;

the input shaft and the output shaft being coupled by a male rotor and a female rotor, the rotors being coupled by a group of interengaged projections, the said projections consisting of a plurality of first projections and a plurality of second projections, the male rotor comprising the first projections, the female rotor comprising the second projections,

such that the first projections and the second projections have a generally gerotor shape;

wherein the output shaft is adapted to be coupled to the rotor of the pump so as to describe a circular path together with the rotor of the pump relative to the axis of rotation of the input shaft;

wherein the male and female rotors are operatively positioned within a housing having at least one eccentric bearing for constraining at least one of the input shaft and the output shaft.

9. The drive means according to claim 8 , wherein the plurality of second projections extend radially inwardly to engage the plurality of first projections.

10. The drive means according to claim 9 , wherein the interface is operatively positioned within a housing having at least one eccentric bearing for constraining at least one of the input shaft and the output shaft.

11. The drive means according to claim 8 , wherein the said plurality of first projections consists of n first projections and the said plurality of second projections consists of n+1 second projections.

12. The drive means according to claim 8 , wherein the male rotor has only two first projections and the female rotor has only three second projections.