No. 6,279,670, the disclosure of which is incorporated herein by reference.

The motor 16 does not occupy all of the area defined within the tool body 12, and an annular bypass passage 32 is provided between the stator housing 24 and the tool body 12. A bypass passage inlet 34 is formed between a bypass control collar 36, which is spring mounted on the tool body 12, and a tubular stator extension 38 provided on the upper end of the stator housing 24. Fluid passage through the tubular extension 38, and into the motor 16, is also controlled, in part, by a valve 40 provided within the stator extension 38. A light spring 42 normally maintains the valve 40 in the closed position.

As noted above, the collar 36 isthe rotor 318 by a stator extension 374, the coupling between the sleeve 372 and the extension 374 being adapted to accommodate the rotation and transverse movement of the rotor 318.

The lower end of the sleeve 372 defines restricted flow outlets 376, such that pumping drilling fluid through the sleeve 372 creates a downwardly directed differential fluid pressure force on the sleeve 372, which force is resisted by a compression spring 378 provided between the sleeve 372 and the tool body 312.

At lower flow rates, the spring 378 maintains the valve members 326, 328 in a spaced apart configuration, as illustrated in FIG. 8. The motor 316 is actuated by the flow of fluid through the string, however the corresponding rotation of the valve member 326 has no