Hydraulic motor

1 . A hydraulic motor, comprising:

(a) a top sub for connecting to a tubing string, a main barrel and a bottom bit sub;

(b) an impeller housing connected to the top sub and disposed within the main barrel, the impeller housing defining: (i) at least one inlet port for directing fluid, received from an intake plenum, into an impeller chamber, and in a direction substantially transverse to a longitudinal axis of the motor, and (ii) at least one exhaust port for exhausting fluid from the impeller chamber into an annular exhaust plenum, wherein outside of the impeller chamber the at least one inlet port is fluidically isolated from the at least one exhaust port;

(c) an impeller disposed within the impeller chamber and comprising a longitudinal impeller shaft and a hub bearing a plurality of outwardly extending impeller vanes which are positionally and orientationally fixed relative to the hub, wherein fluid directed onto the impeller through the at least one inlet port causes rotation of the impeller; and

(d) a bottom bearing assembly for supporting an adapter shaft disposed within the bit sub;

wherein the motor defines a fluid path through the top sub, through the impeller housing and an annular space within the main barrel, and which exits through the adapter shaft and the bit sub, and

a gap exists between a distal outward end of one or more impeller vanes, and an inner surface of the impeller housing.

2 . The motor of claim 1 , wherein the impeller vanes are non-helical.

3 . The motor of claim 2 , wherein the impeller vanes have an extended end portion forming an impeller bucket.

4 . The motor of claim 1 further comprising a gearbox and/or a speed reducer connected to the impeller shaft.

5 . The motor of claim 1 , wherein the bottom bearing assembly comprises a solid, dry-running bearing.

6 . The motor of claim 5 wherein the solid, dry-running bearing comprises a first thrust bearing ring for supporting an upper portion of the adapter shaft, and a second thrust/rotary bearing for supporting a lower portion of the adapter shaft and the bit sub.

7 . The motor of claim 1 wherein the impeller housing is a unitary monolithic element which defines an inlet plenum within the main barrel.

8 . The motor of claim 1 wherein the at least one inlet port comprises three ports aligned in a longitudinal direction.

9 . The motor of claim 1 wherein the combined opening area of the at least one exhaust port from the impeller housing exceeds the combined opening area of the at least one inlet port.