CA2256069A1

CA2256069A1 - Free-wheeling clutch for a downhole drilling assembly

Info

Publication number: CA2256069A1
Application number: CA 2256069
Authority: CA
Inventors: Ian Gillis
Original assignee: Dresser Industries Inc
Current assignee: Dresser Industries Inc
Priority date: 1998-12-15
Filing date: 1998-12-15
Publication date: 2000-06-15

Abstract

The invention is a free-wheeling clutch for a downhole drilling assembly of the type comprising a rotatable drive train contained within a housing.
The clutch is comprised of an exterior surface on the drive train, an interior surface on the housing, and a torque transmitting member contained within a space defined by the exterior surface on the drive train and the interior surface on the housing.
The torque transmitting member and the space are configured such that when the drive train and the housing are rotated relative to each other in a first direction the torque transmitting member is not capable of transmitting torque between the drive train and the housing and when the drive train and the housing are rotated relative to each other in a second direction the torque transmitting member is capable of transmitting torque between the drive train and the housing.

Description

FREE-WHEELING CLUTCH FOR A DOWNHOLE DRILLING ASSEMBLY
FIELD OF INVENTION
The present invention relates to a free-wheeling clutch for a downhole drilling assembly. More particularly, the free-wheeling clutch is for use with a downhole drilling assembly of the type comprising a rotatable drive train contained within a housing.
BACKGROUND OF INVENTION
Boreholes are drilled into the earth to a subterranean formation utilizing a drill string having an attached drilling bit. First, the entire drill string may be rotated from the surface, which in turn rotates the drilling bit connected to the end of the drill string. Second, the drilling bit may be rotated by a downhole motor or downhole drilling assembly, having a housing or stator and a rotatable rotor therein for connection to the drilling bit, which is powered by the circulation of fluid supplied from the surface. Third, rotation of the drill string may be superimposed upon rotation of the drilling bit by the downhole motor.
Regardless of the manner of drilling, for various reasons, the drilling bit may become stuck within the borehole, thus preventing further rotation of the drilling bit within the borehole and preventing the removal of the drill string and drilling bit from the borehole.
When drilling the borehole by rotation of the entire drill string, a further rotary force may be applied to the drill string, with or without the application of an upward force, in order to release the stuck drilling bit.
However, this technique is not useful when drilling the borehole utilizing a downhole drilling assembly. In this case, rotation of the drill string or housing will not typically result in the rotation of the rotor with the attached drilling bit since there is no positive drive between the stator and the rotor. As a result, various jarring devices have been developed which apply an upward force to the drill string and drilling bit, without rotation of the drilling bit, in order to attempt to dislodge the i CA 02256069 1998-12-15 stuck drilling bit. However, these jarring devices are not always successfully applied. In the event such devices are unsuccessful in removing the stuck drilling bit, the only solution may require that the drill string be broken such that the drilling bit is left downhole, while the remainder of the drill string is removed from the borehole.
Given the cost, inconvenience and other disadvantages of leaving the drilling bit within the borehole, various further devices have been developed for use with a downhole drilling assembly or motor for dislodging a stuck drilling bit.
Specifically, each of these devices is designed to provide a positive drive or coupling between the housing and the rotor connected to the drilling bit. As a result, rotation of the drill string from the surface results in the rotation of the drilling bit in order to assist in its removal. However, none of these devices have provided a fully satisfactory solution.
United States of America Patent No. 4,232,751 issued November 11, 1980 to T'r~eciak relates to an in-hole motor drill apparatus in which the rotor of the motor is connected to the drilling bit by a rotary drive connection, including torque transmitting members. In the event the drilling bit becomes stuck, the torque transmitting members, being lugs of a clutch means, can be interlocked to enable the stator or housing of the motor to positively transmit torque and an upward pulling force to the drilling bit.
However, the lugs are interlocked when weight is applied through the motor housing in excess of that normally applied during the drilling of the borehole. As a result, a greater weight is applied to the drilling bit, which may in some circumstances result in further sticking of the drilling bit or damage to the drilling bit. Further, interlocking of the lugs is prevented during normal drilling operations by the presence of shear pins which hold the lugs out of engagement with each other. When the excess weight is applied through the motor housing, the shear pins are sheared in order to permit the engagement or interlocking of the lugs.
As a result, following the unsticking of the drilling bit, normal drilling operations may not be resumed. Rather, the drill string and in-hole motor drilling apparatus must be removed from the borehole in order to permit the replacement of the shear pin and the disengagement of the lugs.

' CA 02256069 1998-12-15 United States of America Patent No. 4,253,532 issued March 3, 1981 to and United States of America Patent No. 4,386,666 issued June 7, 1983 to ra et. al. relate to a clutch device which can be engaged without increasing the weight applied to the drilling bit. Rather, the clutch is engaged by applying an upward strain or pull to the drill string and the motor housing or by increasing the tension on the drill string. However, the drill string may require some lifting during normal drilling operations. Thus, the clutch device must be specifically designed to engage only upon the application of a predetermined lifting force in order to prevent its engagement during normal drilling operations.
More particularly, the clutch is comprised of opposing torque transmitting clutch members or clutch rings having engageable jaw clutch teeth. A
number of Belleville springs, provided adjacent an upper bearing, are specifically selected to maintain an axially spaced condition of the clutch members during normal drilling operations. Thus, the engagement of the clutch teeth is prevented until such time that a sufficient lifting force is applied to overcome these springs, as well as a number of further Belleville springs disposed between the clutch members.
In Geczy and Crase et. al.. upon a release or slackening of the lifting force, the clutch is no longer engaged. Thus, the necessary lifting force must be maintained throughout the rotation of the drilling bit, and unsticking process, in order to secure its release. Further, Crase et. al. provides a frangible or shearable member for holding an abutment at a location such that sufficient movement of the housing relative to the drive shaft of the motor to engage the clutch members is prevented. Upon application of a sufficient lifting force, the shearable member is sheared and the abutment no longer prevents the engagement of the clutch members. Thus, in order to further use the clutch, the drill string and clutch must be removed from the borehole in order to permit the replacement of the shearable member.
United States of America Patent No. 4,295,535 issued October 20, 1981 to Crase et. al. similarly provides a clutch which is engaged by pulling upwards on the drill string. Specifically, upon sticking of the drilling bit, the necessary longitudinal upward movement of the housing relative to the shaft, to engage the clutch, can ' CA 02256069 1998-12-15 t occur when a shearable spacer is sheared by additional pull on the drill string to permit the additional displacement for engagement of the clutch.
Once the shearable spacer is sheared, the clutch is locked in engagement. As a result, the upward pulling force may be released or slackened off, as desired, before rotating the drill string in order to release the drilling bit. In addition, if desired, some weight may be applied to the drilling bit during rotation to release the drilling bit. However, given the locked engagement of the clutch, following the unsticking of the drilling bit, normal drilling operations may not be resumed. Rather, the drill string and clutch must be removed from the borehole in order to permit the disengagement of the clutch and the replacement of the shearable spacer.
United States of America Patent No. 4,299,296 issued November 10, 1981 to Gecz~ also provides an in-hole motor drill with a bit clutch for locking the drilling bit and motor housing together for rotation of the drilling bit by rotation of the motor housing. The clutch is comprised of normally disengaged torque transmitting members which are engageable without changing the load on the bit.
Rather, the clutch engages in response to changing the differential pressure in the motor drill and in the annulus outside the motor drill. More particularly, the clutch is held disengaged responsive to the circulation of drilling fluid through a bearing assembly for the drilling bit or the nozzles of the drilling bit into the annulus outside of the drilling apparatus. As a result, upon cessation of the circulation of the drilling fluid, the clutch automatically engages, which may not necessarily be desired.
Therefore, there remains a need in the industry for an improved clutch assembly for a downhole drilling assembly. More particularly, there is a need for an improved clutch assembly which locks the rotatable drive train of the downhole drilling assembly with the housing of the downhole drilling assembly such that torque may be transmitted between the housing and the drive train. Further, there is a need for the clutch assembly to be engageable without changing the load on the drilling bit and for the engagement of the clutch assembly to be independent of the circulation of drilling fluids through the downhole .drilling assembly. As well, there is a need for the clutch assembly to be disengageable upon unsticking of the drilling bit so that normal drilling operations may be resumed, without the need to remove the drill string or the downhole drilling assembly from the borehole.
SUMMARY OF THE INVENTION
The present invention relates to a drilling assembly of the type comprising a rotatable drive train contained within a housing. In particular, the present invention relates to a free-wheeling clutch for such a drilling assembly, which free-wheeling clutch will permit relative rotation of the drive train and the housing in a first direction but will restrict relative rotation of the drive train and the housing in a second direction.
Any type of free-wheeling clutch which can perform the function set out above may be used in the invention. In one aspect, however, the invention is a free-wheeling clutch for a downhole drilling assembly, wherein the drilling assembly is of the type comprising a rotatable drive train contained within a housing, the clutch comprising:
(a) an exterior surface on the drive train;
(b) an interior surface on the housing; and (c) a torque transmitting member contained within a space defined by the exterior surface on the drive train and the interior surface on the housing;
wherein the torque transmitting member and the space are configured such that when the drive train and the housing are rotated relative to each other in a first direction the torque transmitting member is not capable of transmitting torque between the drive train and the housing and when the drive train and the housing are rotated relative to each other in a second direction the torque transmitting member is capable of transmitting torque between the drive train and the housing.
The torque transmitting member may be comprised of one member or a plurality of members. The torque transmitting members may be contained within one space or within a plurality of spaces.
In one embodiment, one of the exterior surface on the drive train and the interior surface on the housing define at least one ratchet tooth and the torque . transmitting member is comprised of at least one pawl which is associated with the other of the exterior surface on the drive train and the interior surface on the housing such that the pawl engages the ratchet tooth to transmit torque between the drive train and the housing in response to relative rotation of the drive train and the housing in the second direction. Preferably, the torque transmitting member is comprised of a plurality of ratchet teeth and more than one pawl. Preferably the 'ratchet teeth are located on the exterior surface of the drive train and the pawls are associated with the interior surface of the housing.
In a second embodiment, the torque transmitting member has a radial member dimension, the space has a radial space dimension, and the torque transmitting member and the space are configured such that at least one of the radial member dimension and the radial space dimension are variable so that when the drive. train and the housing are rotated relative to each other in the second direction the torque transmitting member becomes wedged between the exterior surface on the drive train and the interior surface on the housing in order to transmit torque between the drive train and the housing. In this second embodiment, either or both of the radial member dimension and the radial space dimension may vary.
In the second embodiment, the torque transmitting member may be any shape or configuration which is compatible with the shape and configuration of the space so that the torque transmitting member can perform the wedging function in response to relative rotation between the drive train and the housing in the second direction. The torque transmitting member may perform the wedging function in any manner, such as by pivoting, rolling or sliding within the space.
A pivoting torque transmitting member is referred to in this specification as a sprag. The torque transmitting member may therefore be comprised of a sprag which pivots between the exterior surface on the drive train and the interior surface on the housing in response to relative rotation between the drive train and the housing in order to vary the radial member dimension. The sprag may be any shape or configuration which is capable of pivoting in order to vary the radial member dimension and thus become wedged between the exterior surface on the drive train and the interior surface on the housing. The use of a sprag as the torque transmitting member renders optional the need for the space to have a varying radial space dimension, since the pivoting of the sprag varies the radial member dimension so that the torque transmitting member can perform its wedging function.
The clutch may be comprised of one or a plurality of sprags. The sprags may be contained within one or more spaces defined by an exterior surface on the drive train and an interior surface on the housing. Preferably, one sprag is contained in each of a plurality of spaces defined by the exterior surface on the drive train and the interior surface on the housing. The clutch may also be comprised of a sprag retainer or sprag retainers for retaining the sprag or sprags in position between the exterior surface on the drive train and the interior surface on the housing.
In the second embodiment, the torque transmitting member may also be comprised of a member that does not have a varying radial member dimension.
In these circumstances, the space preferably has a circumferential space dimension and the radial space dimension preferably varies along the circumferential space dimension. Most preferably, the radial space dimension varies along the circumferential space dimension by providing a camming surface on at least one of the exterior surface on the drive train and the interior surface on the housing so that the radial space dimension varies along the circumferential space dimension between an enlarged radial space dimension and a reduced radial space dimension.
Most preferably, a camming surface is provided only on the exterior surface on the drive train so that the interior surface on the housing has no discontinuities.
Where one or more camming surfaces are provided, the torque transmitting member may be comprised of a rolling member which tends to roll along at least one of the camming surfaces in response to relative rotation between the drive train and the housing.

The rolling member may be of any geometric shape which facilitates rolling. Preferably the rolling member is a roller or a ball which will tend to roll toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which will tend to roll toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.
Where one or more caroming surfaces are provided, the torque transmitting member may also be comprised of a sliding member which tends to slide along at least one of the caroming surfaces in response to relative rotation between the drive train and the housing.
The sliding member may be of any size and shape which is compatible with the space. Preferably the sliding member has a shape which will conform to the exterior surface on the drive train and the interior surface on the housing as it slides along the caroming surface. Most preferably the sliding member is a truncated wedge which will tend to slide toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which will tend to slide toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.
The clutch may be comprised of a combination of different types of torque transmitting members, such as a combination of ratchet teeth and pawls, sprags, rolling members and sliding members. Preferably the clutch is comprised of a plurality of one type of torque transmitting member.
Where the clutch is comprised of a rolling member or a sliding member, the clutch may be further comprised of a biasing device positioned in the space for urging the member toward the reduced radial space dimension. The biasing device may be of any design, but is preferably a spring.
Where the clutch is comprised of a plurality of rolling members or sliding members, they may be contained within one or more spaces defined by an exterior surface on the drive train and an interior surface on the housing.
_g_ Preferably, one member is contained in each of a plurality of spaces defined by the exterior surface on the drive train and the interior surface on the housing.
Preferably a biasing device is positioned in each of the plurality of spaces to urge the member contained within the space toward the reduced radial space dimension.
The clutch may be located at any longitudinal position along the drilling assembly which contains a portion of the drive train. Preferably, the clutch is located at a position where there is sufficient space to insert the torque transmitting member or members between the drive train and the housing without compromising the structural integrity of the drive train or the housing. Most preferably, the clutch is located toward the lower end of the drilling assembly within the lower bearing sub.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a longitudinal section view of a preferred embodiment of a free-wheeling clutch for a downhole drilling assembly;
Figure 2 is a detailed longitudinal section view of the free-wheeling clutch, as shown by box 2 - 2 of Figure 1;
Figure 3 is a cross section view of the free-wheeling clutch taken along line 3 - 3 of Figure 1, wherein the clutch is in an unlocked or disengaged position and wherein the clutch comprises a plurality of rollers;
Figure 4 is a cross section view of the free-wheeling clutch taken along line 3 - 3 of Figure 1, wherein the clutch is in a locked or engaged position and wherein the clutch comprises a plurality of rollers;
Figure 5 is a cross section view of a first further embodiment of a free wheeling clutch for the downhole drilling assembly, wherein the clutch comprises a ratchet and pawl assembly;

Figure 6 is a cross section view of a second further embodiment of a free-wheeling clutch for the downhole drilling assembly, wherein the clutch comprises a plurality of sprags;
Figure 7 is a cross section view of a third further embodiment of a free-wheeling clutch for the downhole drilling assembly, wherein the clutch comprises a plurality of sprags;
Figure 8 is a cross section view of a fourth further embodiment of a free-wheeling clutch for the downhole drilling assembly, wherein the clutch comprises a plurality of truncated wedges; and Figure 9 is a cross section view of a fifth further embodiment of a free wheeling clutch for the downhole drilling assembly, wherein the clutch comprises a plurality of balls.
DETAILED DESCRIPTION
Referring to Figure 1, the present invention relates to a free-wheeling clutch (20) for a downhole drilling assembly (22). More particularly, the free-wheeling clutch (20) is for use with a downhole drilling assembly (22) of the type comprising a rotatable drive train (24) contained within a housing (26). The free-wheeling clutch (20) is engageable such that torque is capable of being transmitted between the housing (26) and the drive train (24) and is disengageable such that torque is no longer capable of being transmitted therebetween.
Specifically, when the drive train (24) and the housing (26) are rotated relative to each other in a first direction, the clutch (20) is not capable of transmitting torque between the drive train (24) and the housing (26). Thus, free movement is permitted therebetween. However, when the drive train (24) and the housing (26) are rotated relative to each other in a second direction, the clutch (20) is capable of transmitting torque between the drive train (24) and the housing (26). Thus, rotation of the housing (26) drives the drive train (24), resulting in rotation of the drive train (24).

More particularly, the housing (26) comprises an outer race of the clutch (20), while the drive train (24) comprises an inner race of the clutch (20). In the preferred embodiment, the drive train (24) or inner race rotates in a clockwise direction during normal drilling operations. In this instance, the drive train (24) and the housing (26) are rotated relative to each other in the first direction when the drive train (24) is rotated in a clockwise direction relative to the housing (26) or the housing (26) is rotated in a counter-clockwise direction relative to the drive train (24). When the drive train (24) and the housing (26) are rotated relative to each other in the first direction, the clutch (20) is not capable of transmitting torque between the drive train (24) and the housing (26). In other words, the clutch (20) is disengaged.
In the preferred embodiment, to achieve this relative movement in the first direction, either the drive train (24) or the housing (26) may be stationary while the other rotates. Alternatively, both the drive train (24) and the housing (26) may be rotating in opposing directions. Finally, the drive train (24) and the housing (26) may both be rotating in the same direction. If both are rotating in a clockwise direction, at all times, the rotation of the drive train (24) must overtake the rotation of the housing (26). If both are rotating in a counter-clockwise direction, at all times, the rotation of the housing (26) must overtake the rotation of the drive train (24).
Further, in the preferred embodiment, the drive train (24) and the housing (26) are rotated relative to each other in the second direction when the drive train (24) is rotated in a counter-clockwise direction relative to the housing (26) or the housing (26) is rotated in a clockwise direction relative to the drive train (24). When rotated relative to each other in the second direction, the clutch (20) is capable of transmitting torque between the drive train (24) and the housing (26). In other words, the clutch (20) is engaged. Once engaged, further rotation of the housing (26) in the clockwise direction will result in the rotation of the drive train (24) in the clockwise direction.
Similarly, to achieve this relative movement in the second direction, either the drive train (24) or the housing (26) may be stationary while the other rotates. Alternatively, both the drive train (24) and the housing (26) may be rotating in opposing directions. Finally, the drive train (24) and the housing (26) may both be rotating in the same direction. If both are rotating in a clockwise direction, at all times, the rotation of the housing (26) must overtake the rotation of the drive train (24). If both are rotating in a counter-clockwise direction, at all times, the rotation of the drive train (24) must overtake the rotation of the housing (26).
Although the above relative directions are preferred, alternatively, the drive shaft (24) may rotate in a counter-clockwise direction during normal drilling operations. In this instance, each of the above noted directions is reversed.
Thus, the drive train (24) and the housing (26) are rotated relative to each other in the first direction when the drive train (24) is rotated in a counter-clockwise direction relative to the housing (26) or the housing (26) is rotated in a clockwise direction relative to the drive train (24). Further, the drive train (24) and the housing (26) are rotated relative to each other in the second direction when the drive train (24) is rotated in a clockwise direction relative to the housing (26) or the housing (26) is rotated in a counter-clockwise direction relative to the drive train (24).
The free-wheeling clutch (20) is intended for use with any downhole drilling assembly (22) or downhole drilling motor of the type comprising a rotatable drive train (24) contained within a housing (26). The drilling assembly (22) may comprise any number or type of components, units or subs connected together.
For instance, the drilling assembly (22) includes a power unit or motor (not shown) and may further include a crossover sub (not shown), a transmission unit (not shown), a bearing sub (30) and a lower bearing sub (32), all preferably connected end to end with threaded connections. During drilling operations, a drilling bit (not shown) is located at a lower end (28) of the drilling assembly (22) and the upper end of the drilling assembly (22) is connected to the remainder of the drill string (not shown).
The drilling assembly (22) may also be made up of a single component or of a number of components other than as are described for the preferred embodiment of the invention. In addition, the components of the drilling assembly (22) may be connected together other than by using threaded connections. For example, some or all of the components may be connected by welding or with spline connections.

' CA 02256069 1998-12-15 As indicated, the drilling assembly (20) is of a type comprising a rotatable drive train (24) contained within a housing (26). The drive train (24) includes any inner rotatable member or component of the drilling assembly (22).
More particularly, the drive train (24) includes any member or component of the drilling assembly (22) which is rotatable during normal drilling operations.
The housing (26) includes any member or component of the drilling assembly (22) containing any portion or part of the rotatable drive train (24). Thus, as discussed above, the drive train (24) and the housing (26) may be made up of any part or portion of the of the drilling assembly (22), including parts or portions of the lower bearing sub (32), the bearing sub (30), the transmission unit, the power unit and the crossover sub.
In the preferred embodiment, beginning at the lower end (28) of the drilling assembly (22), the rotatable drive train (24) includes a drive shaft (34). The drive shaft (34) includes a distal end (36) which is adapted to be connected to the drilling bit. The drive shaft (34) may include a drive shaft extension (not shown).
During drilling operations, the drive train (24) also includes the drilling bit. A
proximal end (38) of the drive shaft (34) is threadably connected to a distal end (40) of a drive shaft cap (42). A proximal end (44) of the drive shaft cap (42) is threadably connected to the remainder of the drive train (24).
The remainder of the drive train (24) may include a lower universal coupling (not shown). The lower universal coupling may be threadably connected to a distal end of a transmission shaft (not shown). A proximal end of the transmission shaft may be threadably connected to an upper universal coupling (not shown). The upper universal coupling may be threadably connected to a distal end of a rotor (not shown). A proximal end of the rotor may define the uppermost end of the drive train (24). The drive train (24) is rotationally supported within the housing (26).
In the preferred embodiment, beginning at the lower end (28) of the drilling assembly (22), the housing (26) includes a lower bearing housing (46). The lower bearing housing (46) includes a distal end (48) from which the drive shaft (34) protrudes. A proximal end (50) of the lower bearing housing (46) is threadably connected to a distal end (52) of a bearing housing (54). A proximal end (56) of the bearing housing (54) is threadably connected to the remainder of the housing (26).
The remainder of the housing (26) may include a transmission unit housing (not shown). The proximal end (56) of the bearing housing (54) may be connected to a distal end of the transmission unit housing. A proximal end of the transmission unit housing may be threadably connected to a distal end of a power unit housing (not shown). A proximal end of the power unit housing may be threadably connected to a distal end of a crossover sub housing (not shown). A
proximal end of the crossover sub housing may include a threaded connection which facilitates connection of the drilling assembly (22) to the remainder of the drill string.
The free-wheeling clutch (20) for the downhole drilling assembly (22) is intended to be incorporated into the drill string such that it is associated with the drilling assembly (22). In the preferred embodiment, the clutch (20) is incorporated into the downhole drilling assembly (22) itself and thus forms part of the downhole drilling assembly (22). The downhole drilling assembly (22) in turn is incorporated into or connected with the remainder, or other components, of the drill string during drilling operations so that the downhole drilling assembly (22) forms part of the complete drill string. However, the clutch (20) may be incorporated into the drill string as a component that is separate or distinct from the downhole drilling assembly (22) such that it does not form an integral part of the downhole drilling assembly (22).
The clutch (20) may be located at any longitudinal position along the drilling assembly (22) which is comprised of a portion of the rotatable drive train (24) contained within a portion of the housing (26). Thus, the clutch (20) may be associated with any of the components, units or subs comprising the drilling assembly (22), as described above. Preferably, the clutch (20) is located along the drilling assembly (22) at a position where the clutch (20) may be inserted without compromising or significantly affecting with the structural integrity of the drilling assembly (22), including the structural integrity of the drive train (24) and the housing (26). Further, the clutch (20) is preferably located at a position at which an open or free space is provided between the drive train (24) and the housing (26). In other words, it is preferably located at a position where other components or hardware, such as bearings, are not typically located between the drive train (24) and the housing (26).
The free-wheeling clutch (20) may be comprised of any mechanism or structure able to perform the function set out herein. Specifically, the clutch (20) may be comprised of any coupling mechanism or structure capable of connecting the drive train ~(24) and the housing (26) upon relative rotation in one direction, such that torque is capable of being transmitted therebetween, and capable of disconnecting the drive train (24) and the housing (26) upon relative rotation in the other direction, such that torque is not capable of being transmitted therebetween.
In other words, the free-wheeling clutch (20) may be comprised of any coupling structure or mechanism capable of transmitting torque between the drive train (24) and the housing (26) upon relative rotation of the drive train (24) and the housing (26) in one direction only. Further, the coupling mechanism or structure preferably permits the connection and disconnection at the will of the operator, without the need to remove or refit any of the components of the clutch (20) or the downhole drilling assembly (22) or the need to remove the downhole drilling assembly (22) from the borehole.
In the preferred embodiment, the clutch (20) is comprised of an exterior surface (58) on the drive train (24), an interior surface (60) on the housing (26) and at least one torque transmitting member (62) contained within a space (64) defined by the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26). Thus, further to the discussion above, the clutch (20) is preferably located at a position along the drilling assembly (22) which can provide the space (64) for the insertion of the torque transmitting member (62). More preferably, the clutch (20) is located at a position along the drilling assembly (22) where the space (64) is sufficient for the insertion of the torque transmitting member (62) without compromising the structural integrity of the drive train (24) or the housing (26).
Although the space (64), and thus the torque transmitting member (62), may be located at any suitable longitudinal position along the drilling assembly (22), the clutch (20) is preferably located toward the lower end (28) of the drilling assembly (22). In the preferred embodiment, as shown in Figure 1, the clutch (20) is associated with, and preferably is incorporated into, the lower bearing sub (32) comprising the drilling assembly (22). Thus, as described in greater detail below, the torque transmitting member (62) is contained within a space (64) associated with the lower bearing sub (32).
The exterior surface (58) on the drive train (24) may be comprised of an outer portion of the drive train (24) such that the exterior surface (58) is integral or formed therewith. However, preferably, a separate component or member comprising the exterior surface (58) may be connected or attached to the drive train (24) such that the exterior surface (58) rotates with the drive train (24). By providing a separate component or member, the exterior surface (58) may be more readily adapted to provide a sufficient space (64) to accommodate the specific torque transmitting member (62) to be inserted therein.
Similarly, the interior surface (60) on the housing (26) may be comprised of a separate component or member connected or attached to the housing (26) such that the separate component or member, and thus the interior surface (60), rotates with the housing (26). By providing a separate component or member, the interior surface (60) may also be more readily adapted to provide a sufficient space (64) to accommodate the specific torque transmitting member (62) to be inserted therein. However, preferably, the interior surface (60) on the housing (26) is comprised of an inner portion or surface of the housing (26) such that the interior surface (60) is integral or formed therewith.
The space (64), defined by the interior surface (60) and the exterior surface (58), and the torque transmitting member (62) contained within the space (64) are configured such that when the drive train (24) and the housing (26) are rotated relative to each other in the first direction, the torque transmitting member (62) is not capable of transmitting torque between the drive train (24) and the housing (26). Further, the space (64) and the torque transmitting member (62) are configured such that when the drive train (24) and the housing (26) are rotated relative to each other in the second direction, the torque transmitting member (62) is capable of transmitting torque between the drive train (24) and the housing (26).

The torque transmitting member (62) may be comprised of one or more members (62). The torque transmitting member or members (62) may be contained within one or more spaces (64). In the preferred embodiment, the clutch (20) is comprised of a plurality of torque transmitting members (62) which are contained within a plurality of spaces (64). The specific number of members (62) and spaces (64) and the specific configuration of the members (62) and spaces (64) will be dependent upon, amongst other factors, the amount of torque to be transmitted between the drive train (24) and the housing (26). For instance, preferably, the contact between the torque transmitting member (62) and the interior and exterior surfaces (60, 58) is maximized upon relative rotation of the drive train (24) and the housing (26) in the second direction, such that a larger surface area is provided for the transmission of the torque.
In the preferred embodiment, referring to Figures 1 and 2, the lower bearing sub (32) includes the lower bearing housing (46). The lower bearing housing (46) surrounds the drive shaft (34) and provides an annular space (66) between the lower bearing housing (46) and the drive shaft (60). The distal end (36) of the drive shaft (34) extends through the distal end (48) of the lower bearing housing (46) and the proximal end (38) of the drive shaft (34) extends through the proximal end (50) of the lower bearing housing (46).
Further, in the preferred embodiment, the lower bearing sub (32) is connected to the bearing sub (30) in the manner as previously described. The bearing sub (30) includes the bearing housing (54). The bearing housing (54) contains one or more bearings (68), being a combination of radial and thrust bearings, fixed to the bearing housing (54) and which function to rotatably and axially support the drive train (24) in the housing (26). The bearings (68) are contained in an annular space (70) between the bearing housing (54) and the drive shaft (34).
The proximal end (38) of the drive shaft (34) extends into the distal end (52) of the bearing housing (54) for connection to the drive shaft cap (42).
Specifically, the distal end (40) of the drive shaft cap (42) extends into the proximal end (56) of the bearing housing (54) where it connects with the proximal end (38) of the drive shaft (34). The drive shaft (34) and the drive shaft cap (42) are connected in the manner as previously described.
As well, as shown in Figures 1 and 2, in the preferred embodiment, the drilling assembly (22) includes a stabilizer (72) surrounding the drilling assembly (22). The stabilizer (72) preferably surrounds the drilling assembly (22) adjacent or in proximity to the longitudinal position of the clutch (20) in the drilling assembly (22) in order to assist in the stabilization of the clutch (20), particularly upon the engagement of the clutch (20) such that torque is transmittable between the drive train (24) and the housing (26). In the preferred embodiment, the stabilizer (72) surrounds the drilling assembly (22) at the location of the connection of the lower bearing housing (46) with the bearing housing (54).
Further, as discussed above, in the preferred embodiment as shown in Figure 2, the interior surface (60) on the housing (26) is comprised of the housing (26) such that it is integral therewith. More particularly, the interior surface (60) is comprised of an inner portion or surface of the lower bearing housing (46), preferably in proximity to or adjacent the proximal end (50) of the lower bearing housing (46). Thus, the inner surface of the lower bearing housing (46) provides the outer race for the clutch (20).
Referring again to Figure 2, in the preferred embodiment, the exterior surface (58) on the drive train (24) is comprised of an outer portion or surface of a separate component or member connected or attached to the drive train (24) adjacent the interior surface (60) on the housing (26). Specifically, a drive shaft locknut (74) surrounds the drive shaft (34) adjacent the proximal end (50) of the lower bearing housing (46) such that an outer portion or surface of the drive shaft locknut (74), which comprises the exterior surface (58) on the drive train (24), opposes the interior surface (60) on the housing (26). The drive shaft locknut (74) is connected, attached or affixed to the drive shaft (34) by any fastener or mechanism permitting the drive shaft locknut (74) to rotate upon the rotation of the drive train (24). In the preferred embodiment, the drive shaft locknut (74) is affixed to the drive shaft (34) by one or more screws or bolts (76) extending through the drive shaft locknut (74) into the adjacent drive shaft (34).

The , torque transmitting member (62) may be comprised of any member, mechanism or structure able to perform the function set out herein.
Specifically, the torque transmitting member (62) may be comprised of any member, mechanism or structure capable of transmitting torque between the drive train (24) and the housing (26) upon the relative rotation of the drive train (24) and the housing (26) in the second direction.
For instance, referring to Figure 5, in one embodiment, the clutch (20) may be comprised of a ratchet and pawl assembly. More particularly, one of the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26) may define at least one ratchet tooth (78). Further, the torque transmitting member (62) may be comprised of at least one pawl (80), which may be associated with the other of the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26) such that the pawl (80) engages the ratchet tooth (78) to transmit torque between the drive train (24) and the housing (26) in response to relative rotation of the drive train (24) and the housing (26) in the second direction.
In this embodiment, as shown in Figure 5, the exterior surface (58) on the drive train (24) preferably defines a plurality of ratchet teeth (78).
Further, the torque transmitting member (62) is preferably comprised of at least one pawl (80), and preferably greater than one pawl (80), associated with the interior surface (60) of the housing (26). The pawl (80) may be associated with the interior surface (60) in any suitable manner permitting the functioning of the clutch (20) as described herein. Further, the specific number of pawls (80) will be dependent upon, amongst other factors, the magnitude of the torque to be transmitted between the drive train (24) and the housing (26) and the number of ratchet teeth (78).
In operation, referring to Figure 5, upon the relative rotation of the drive train (24) and the housing (26) in the first direction, wherein the drive train (24) preferably rotates in a clockwise direction relative to the housing (26), the pawl (80) remains disengaged from the ratchet teeth (78). However, upon the relative rotation of the drive train (24) and the housing (26) in the second direction, wherein the drive train (24) rotates in a counter-clockwise direction relative to the housing (26), the pawl (80) engages the ratchet teeth (78) such that torque may be transmitted between the drive train (24) and the housing (26).
However, in the preferred embodiment, the torque transmitting member (62) has a radial member dimension (82) and the space (64) defined by the interior and exterior surfaces (60, 58) has a radial space dimension (84).
Each of the radial dimensions (82, 84) is measured perpendicular to a longitudinal axis of the drilling assembly (22) extending between the upper end and the lower end (28) of the drilling assembly (22). Further, the space (64) has a circumferential space.
dimension (86) which is measured about the longitudinal axis of the drilling assembly (22), perpendicular to the radial space dimension (84).
The torque transmitting member (62) and the space (64) are preferably configured such that at least one of the radial member dimension (82) and the radial space dimension (84) are variable so that when the drive train (24) and the housing (26) are rotated relative to each other in the second direction, the torque transmitting member (62) becomes wedged between the exterior surface (58) and the inferior surface (60) in order to transmit torque between the drive train (24) and the housing (26). Either or both of the radial member dimension (82) and the radial space dimension (84) may vary, as desired.
The torque transmitting member (62) may be any shape or configuration which is compatible with the shape and configuration of the space (64) so that the torque transmitting member (62) can perform the wedging function in response to relative rotation between the drive train (24) and the housing (26) in the second direction. The torque transmitting member (62) may perform the wedging function in any manner, such as by pivoting, rolling or sliding within the space (64).
For instance, in a further embodiment of the clutch (20), as shown in Figures 6 and 7, the radial member dimension (78) varies upon performance of the wedging function by a pivoting action of the torque transmitting member (62).
A
pivoting torque transmitting member (62) is referred to herein as a sprag. The torque transmitting member (62) may therefore be comprised of at least one sprag which pivots between the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26) in response to relative rotation between the drive train (24) and the housing (26) in order to vary the radial member dimension (82).
The sprag (62) may have any shape or configuration which is capable of pivoting in order to vary the radial member dimension (82) and thus perform the wedging function. More particularly, the sprag (62) may have any shape or configuration able to become wedged between the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26) upon pivoting of the sprag (62). When using a sprag as the torque transmitting member (62), the space (64) need not have a varying radial space dimension(84). As stated, the pivoting of the sprag (62) varies the radial member dimension (82) so that the torque transmitting member (62) can perform its wedging function. However, if desired, the radial space dimension (84) may also vary to assist in or enhance the wedging action of the sprag (62).
Referring to Figures 6 and 7, in this embodiment, the clutch (20) is comprised of at least one sprag (62). However, the clutch (20) is preferably comprised of a plurality of sprags (62). The specific number of sprags (62) will be dependent upon, amongst other factors, the magnitude of the torque to be transmitted between the drive train (24) and the housing (26) and the specific configuration of the sprags (62).
Further, the sprags (62) may be contained within one or more spaces (64) defined by the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26). For instance, as shown in Figure 6, a plurality of sprags (62) may be contained within one space (64). However, preferably as shown in Figure 7, one sprag (62) is contained in each of a plurality of spaces (64) defined by the exterior surface (58) and the interior surface (60).
Finally, where necessary to maintain the position of the sprags (62) within the space or spaces (64), the clutch (20) may also be comprised of one or more sprag retainers (88), as shown in Figure 6. The sprag retainer (88) may be comprised of any structure or mechanism able to retain the sprag or sprags (62) in a position between the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26) which permits or allows the necessary pivoting action of the sprags (62). For instance, referring to Figure 6, the sprag retainer (88) is comprised of a spring which extends through the entire space (64), about the circumference of the drive train (24), passing through each of the sprags (62) in turn.
In operation, referring to Figures 6 and 7, upon the relative rotation of the drive train (24) and the housing (26) in the first direction, wherein the drive train (24) preferably rotates in a clockwise direction relative to the housing (26), the radial member dimension (82) remains less than the radial space dimension (84) and no wedging action occurs. However, upon the relative rotation of the drive train (24) and the housing (26) in the second direction, wherein the drive train (24) rotates in a counter-clockwise direction relative to the housing (26), the sprags (62) pivot causing the radial member dimension (82) to become greater than the radial space dimension (84). Thus, the sprags (62) become wedged between the drive train (24) and the housing (26) such that torque may be transmitted therebetween.
However, in the preferred embodiment, the torque transmitting member (62) does not have a varying radial member dimension (82). Rather, the radial space dimension (84) preferably varies along the circumferential space dimension (86). The radial space dimension (84) may vary along the circumferential space dimension (86) in any manner. However, preferably, the radial space dimension (84) varies along the circumferential space dimension (86) by providing a camming surface (90) on at least one of the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26). Thus, the camming surface (90) may be provided on either or both of the exterior surface (58) and the interior surface (60). The provision of the camming surface or surfaces (90) results in the variation of the radial space dimension (84) along the circumferential space dimension (86) between an enlarged radial space dimension (92) and a reduced radial space dimension (94), as shown in Figures 3, 4, 8 and 9. Most preferably, a camming surface (90) is provided only on the exterior surface (58) on the drive train (24) so that the interior surface (60) on the housing (26) has no discontinuities.
Where one or more camming surfaces (90) are provided, the torque transmitting member (62) may be comprised of a sliding member or a rolling member. For instance, as shown in Figure 8, the torque transmitting member (62) may be comprised of a sliding member which tends to slide along at least one of the caroming surfaces (90) in response to relative rotation between the drive train (24) and the housing (26). A sliding member may be preferable in some instances to a rolling member as a sliding member tends to provide a larger surface area for contacting the interior and exterior surfaces (60, 58) than a rolling member, which tends to provide point contact only.
The sliding torque transmitting member (62) may have any size, shape or configuration compatible with the space (64), including the caroming surface or surfaces (90), and which will permit the transmission of torque between the drive train (24) and the housing (26) upon wedging of the sliding member (62) therebetween. Preferably, as shown in Figure 8, the caroming surface (90) is provided by the interior surface (60) on the housing (26). Thus, the sliding member (62) preferably has a shape and configuration which will conform to the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26) as the sliding member (62) slides along the caroming surface (90).
Preferably, in this embodiment, the sliding member (62) is comprised of a truncated wedge, as shown in Figure 8, which will tend to slide toward the enlarged radial space dimension (92) in response to relative rotation between the drive train (24) and the housing (26) in the first direction and which will tend to slide toward the reduced radial space dimension (94) in response to relative rotation between the drive train (24) and the housing (26) in the second direction.
One or more sliding members (62) or truncated wedges may be contained within one or more spaces (64) defined by the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26).
Preferably, a plurality of members (62) are each contained in one of a plurality of compatible spaces (64) defined by the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26). However, the specific number of sliding members (62) will be dependent upon, amongst other factors, the magnitude of the torque to be transmitted between the drive train (24) and the housing (26) and the specific configuration of the sliding members (62) and compatible spaces (64).
Further, the truncated wedges (62) are preferably configured such that the wedges (62) are closely conformed to the interior surface (60) on the housing (26) and the exterior surface (58) on the drive train (24) in order to maximize the contact therebetween and thus enhance the transmission of the torque. As well, the wedge (62) is preferably configured such that it does not substantially contact the interior surface (60) on the housing (26) during normal drilling operations in order to minimize any friction therebetween. If necessary, a biasing device (not shown), such as a spring may be used to bias the wedge (62) within the space (64) in a direction toward the exterior surface (58) on the drive train (24) during normal drilling operations.
Further, the sliding member or truncated wedge (62) may be maintained in a desired or proper position within the space (64) by any mechanism or structure permitting the functioning of the sliding member (62) as described herein. Alternatively, the compatible shapes of the sliding member (62) and the space (64) may be sufficient to maintain the sliding member (62) in proper positioning within the space (64) such that the sliding and wedging action may occur.
As well, where desired or required, the clutch (20) may be further comprised of a biasing device (96) positioned in the space (64) for urging the sliding member (62) toward the reduced radial space dimension (94). The biasing device (96) may be of any design, but is preferably a spring. Further, where a biasing device (96) is present, at least one biasing device (96) is preferably positioned in each of the plurality of spaces (64) to urge the sliding member (62) contained within that space (64) toward the reduced radial space dimension (94). The biasing device (96) may act directly or indirectly upon the sliding member (62).
More particularly, referring to Figure 8, in operation, upon the relative rotation of the drive train (24) and the housing (26) in the first direction, wherein the drive train (24) preferably rotates in a clockwise direction relative to the housing (26), the truncated wedge (62) moves towards the enlarged radial space dimension (92) and no wedging action occurs. However, upon the relative rotation of the drive train (24) and the housing (26) in the second direction, wherein the drive train (24) rotates in a counter-clockwise direction relative to the housing (26), the truncated wedge (62) moves towards the reduced radial space dimension (94). Thus, the truncated wedge (62) becomes wedged between the drive train (24) and the housing (26) within the reduced radial space dimension (94) such that torque may be transmitted therebetween.
However, in the preferred embodiment, where one or more caroming surfaces (90) are provided, the torque transmitting member (62) is comprised of a rolling member which tends to roll along at least one of the caroming surfaces (90) in response to relative rotation between the drive train (24) and the housing (26).
The rolling member (62) may have any geometric shape which facilitates rolling. For instance, as shown in Figure 9, the rolling member (62) may be comprised of a ball (98). However, in the preferred embodiment, as shown in Figures 1 - 4, the rolling member (62) is comprised of a roller (100). A
roller (100) is preferable to a ball (98) since a roller (100) provides a greater surface area for contacting the interior and exterior surfaces (60, 58) of the housing (26) and drive train (24) respectively, as compared to a ball (98). Further, the space (64) may have any shape, size and configuration compatible with the rolling member (62).
In each instance, the rolling member (62) and the space (64) are configured such that the rolling member (62) will tend to roll toward the enlarged radial space dimension (92) in response to relative rotation between the drive train (24) and the housing (26) in the first direction and will tend to roll toward the reduced radial space dimension (94) in response to relative rotation between the drive train (24) and the housing (26) in the second direction. More particularly, in the preferred embodiment, the rolling member (62) will roll along the caroming surface (90) provided by the exterior surface (58) on the drive train (24).
One or more rolling members (62) may be contained within one or more spaces (64) defined by the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26). However, preferably, the clutch (20) is comprised of a plurality of rolling members (62), one rolling member (62) contained in each of a plurality of compatible spaces (64) defined by the exterior surface (58) on the drive train (24) and the interior surface (60) on the housing (26).
However, the specific number of rolling members (62) will be dependent upon, amongst other factors, the magnitude of the torque to be transmitted between the drive train (24) and the housing (26) and the specific configuration of the rolling members (62) and compatible spaces (64).
Further, the rolling member (62) may be maintained in a desired or proper position within the space (64) by any mechanism or structure permitting the functioning of the rolling member (62) as described herein. Alternatively, the compatible shapes of the rolling member (62) and the space (64) may be sufficient to maintain the rolling member (62) in proper positioning within the space (64) such that the rolling and wedging action may occur.
For instance, referring to Figures 1 and 2, in the preferred embodiment, the roller or rollers (100) are maintained in a desired position within the compatible space (64) by a retainer (102). More particularly, a retaining pin (104), having an upper end (106) and a lower end (108), passes through each roller (100) such that the ends (106, 108) of the retaining pin (104) extend from the roller (100). The lower end (108) of each retaining pin (104) is preferably maintained within a compatible groove (110) defined by the drive shaft locknut (74), which permits the roller (100) to roll within the space (64) between the enlarged and reduced radial space dimensions (92, 94). The upper end (106) of each retaining pin (104) is similarly maintained within a compatible groove (112) defined by the drive shaft locknut (74) and the retainer (102), which similarly permits the roller (100) to roll within the space (64) between the enlarged and reduced radial space dimensions (92, 94).
More particularly, the retainer (102) surrounds and is connected, attached or affixed to the drive shaft locknut (74). The retainer (102) is connected, attached or affixed to the drive shaft locknut (74) by any fastener or mechanism permitting the retainer (102) to rotate upon the rotation of the drive shaft locknut (74) and the drive train (24). In the preferred embodiment, the retainer (102) is affixed to drive shaft locknut (74) by the screws or bolts (76) affixing the drive shaft locknut (74) to the drive shaft (34), which extend through the retainer (102) and the drive shaft locknut (74) and into the adjacent drive shaft (34). This form of retainer (102) permits the rollers (100) to be removed for servicing and replacement as required. However, as stated, any other removable or permanent retaining mechanism may be used.

In addition, where desired or required, the rolling member (62) may also be associated with a biasing device (96) positioned in the space (64) for urging the rolling member (62) toward the reduced radial space dimension (94). The biasing device (96) for the rolling member 962) may also be of any design, but is preferably a spring. Further, as shown in Figures 3, 4 and 9, where a biasing device (96) is present, at least one biasing device (96) is preferably positioned in each of the plurality of spaces (64) to urge the rolling member (62) contained within that space (64) toward the reduced radial space dimension (94). The biasing device (96) may act directly or indirectly upon the rolling member (62).
More particularly, referring to Figures 3 and 4 for the preferred embodiment comprising a roller (100), and referring to Figure 9 for the embodiment comprising a ball (98), in operation, upon the relative rotation of the drive train (24) and the housing (26) in the first direction, wherein the drive train (24) preferably rotates in a clockwise direction relative to the housing (26), the rolling member (62) moves towards the enlarged radial space dimension (92) and no wedging action occurs, as shown in Figures 3 and 9. However, upon the relative rotation of the drive train (24) and the housing (26) in the second direction, wherein the drive train (24) rotates in a counter-clockwise direction relative to the housing (26), the rolling member (62) moves towards the reduced radial space dimension (94). Thus, the rolling member (62) become wedged between the drive train (24) and the housing (26) within the reduced radial space dimension (94) such that torque may be transmitted therebetween, as shown in Figure 4.
Finally the clutch (20) may be comprised of a combination of different types of torque transmitting members (62), such as a combination of ratchet teeth (78) and pawls (80), sprags, rolling members and sliding members. However, preferably the clutch (20) is comprised of a plurality of one type of torque transmitting member (62).

Claims

1. A free-wheeling clutch for a downhole drilling assembly, wherein the downhole drilling assembly is of the type comprising a rotatable drive train contained within a housing, the clutch comprising:
(a) an exterior surface on the drive train;
(b) an interior surface on the housing; and (c) a torque transmitting member contained within a space defined by the exterior surface on the drive train and the interior surface on the housing;
wherein the torque transmitting member and the space are configured such that when the drive train and the housing are rotated relative to each other in a first direction the torque transmitting member is not capable of transmitting torque between the drive train and the housing and when the drive train and the housing are rotated relative to each other in a second direction the torque transmitting member is capable of transmitting torque between the drive train and the housing.

2. The clutch as claimed in claim 1 wherein the torque transmitting member has a radial member dimension, wherein the space has a radial space dimension, and wherein the torque transmitting member and the space are configured such that at least one of the radial member dimension and the radial space dimension are variable so that when the drive train and the housing are rotated relative to each other in the second direction the torque transmitting member becomes wedged between the exterior surface on the drive train and the interior surface on the housing in order to transmit torque between the drive train and the housing.

3. The clutch as claimed in claim 2 wherein the torque transmitting member is comprised of a sprag which pivots between the exterior surface on the drive train and the interior surface on the housing in response to relative rotation between the drive train and the housing in order to vary the radial member dimension.

4. The clutch as claimed in claim 3 wherein the clutch is comprised of a plurality of sprags which pivot between the exterior surface on the drive train and the interior surface on the housing in response to relative rotation between the drive train and the housing in order to vary the radial member dimension.

5. The clutch as claimed in claim 4 wherein the clutch is further comprised of a sprag retainer for retaining the sprags in position between the exterior surface on the drive train and the interior surface on the housing.

6. The clutch as claimed in claim 4 wherein one of the plurality of sprags is contained within each of a plurality of spaces, wherein each of the plurality of spaces is defined by an exterior surface on the drive train and an interior surface on the housing.

7. The clutch as claimed in claim 6 wherein the housing is comprised of a lower bearing sub housing and wherein the interior surfaces on the housing are located on the lower bearing sub housing.

8. The clutch as claimed in claim 2 wherein the space has a circumferential space dimension and wherein the radial space dimension varies along the circumferential space dimension.

9. The clutch as claimed in claim 8 wherein at least one of the exterior surface on the drive train and the interior surface on the housing provides a camming surface so that the radial space dimension varies along the circumferential space dimension between an enlarged radial space dimension and a reduced radial space dimension.

10. The clutch as claimed in claim 9 wherein the torque transmitting member is comprised of a rolling member which tends to roll along at least one of the camming surfaces in response to relative rotation between the drive train and the housing.

11. The clutch as claimed in claim 10 wherein the torque transmitting member is comprised of a ball which tends to roll toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which tends to roll toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.

12. The clutch as claimed in claim 10 wherein the torque transmitting member is comprised of a roller which tends to roll toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which tends to roll toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.

13. The clutch as claimed in claim 9 wherein the torque transmitting member is comprised of a sliding member which tends to slide along at least one of the camming surfaces in response to relative rotation between the drive train and the housing.

14. The clutch as claimed in claim 13 wherein the sliding member is comprised of a truncated wedge which tends to slide toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which tends to slide toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.

15. The clutch as claimed in claim 1 wherein one of the exterior surface on the drive train and the interior surface on the housing define at least one ratchet tooth and wherein the torque transmitting member is comprised of at least one pawl which is associated with the other of the exterior surface on the drive train and the interior surface on the housing such that the pawl engages the ratchet tooth to transmit torque between the drive train and the housing in response to relative rotation between the drive train and the housing in the second direction.

16. The clutch as claimed in claim 9 wherein the camming surface is located on the exterior surface on the drive train.

17. The clutch as claimed in claim 16 wherein the torque transmitting member is comprised of a roller which tends to roll toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which tends to roll toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.

18. The clutch as claimed in claim 17 wherein the clutch is further comprised of a biasing device positioned in the space for urging the roller toward the reduced radial space dimension.

19. The clutch as claimed in claim 18 wherein the clutch is comprised of:
(a) a plurality of rollers, one roller being contained in each of a plurality of spaces, each of such spaces being defined by an exterior surface on the drive train and an interior surface on the housing; and (b) a plurality of biasing devices, one biasing device being positioned in each of the plurality of spaces.

20. The clutch as claimed in claim 19 wherein the housing is comprised of a lower bearing sub housing and wherein the interior surfaces on the housing are located on the lower bearing sub housing.

21. The clutch as claimed in claim 16 wherein the torque transmitting member is comprised of a ball which tends to roll toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which tends to roll toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.

22. The clutch as claimed in claim 21 wherein the clutch is further comprised of a biasing device positioned in the space for urging the ball toward the reduced radial space dimension.

23. The clutch as claimed in claim 22 wherein the clutch is comprised of:
(a) a plurality of balls, one ball being contained in each of a plurality of spaces, each of such spaces being defined by an exterior surface on the drive train and an interior surface on the housing; and (b) a plurality of biasing devices, one biasing device being positioned in each of the plurality of spaces.

24. The clutch as claimed in claim 23 wherein the housing is comprised of a lower bearing sub housing and wherein the interior surfaces on the housing are located on the lower bearing sub housing.

25. The clutch as claimed in claim 16 wherein the torque transmitting member is comprised of a sliding member which slides along the camming surface in response to relative rotation between the drive train and the housing.

26. The clutch as claimed in claim 25 wherein the sliding member is comprised of a truncated wedge which tends to slide toward the enlarged radial space dimension in response to relative rotation between the drive train and the housing in the first direction and which tends to slide toward the reduced radial space dimension in response to relative rotation between the drive train and the housing in the second direction.

27. The clutch as claimed in claim 26 wherein the clutch is further comprised of a biasing device positioned in the space for urging the truncated wedge toward the reduced radial space dimension.

28. The clutch as claimed in claim 27 wherein the clutch is comprised of:
(a) a plurality of truncated wedges, one truncated wedge being contained in each of a plurality of spaces, each of such spaces being defined by an exterior surface on the drive train and an interior surface on the housing; and (b) a plurality of biasing devices, one biasing device being positioned in each of the plurality of spaces.

29. The clutch as claimed in claim 28 wherein the housing is comprised of a lower bearing sub housing and wherein the interior surfaces on the housing are located on the lower bearing sub housing.