Note: Descriptions are shown in the official language in which they were submitted.
CA 02813912 2013-04-25
Improved Bearing Assembly for Downhole Motor
Cross Reference to related applications
This regular United States patent application is a continuation-in-part
application of
pending United States patent application 13/023693, filed 02/09/2011, and
claims priority to
that application and to United States provisional patent application serial
no. 61/337656, filed
February 11,2010, for all purposes.
Background
Traditionally, earthen boreholes for oil and gas production, fluid injection,
etc.,
frequently referred to as "wells," were drilled by rotating a drillstring from
the drilling rig, by
means of a rotary table and kelly. The drill bit on the lowermost end of the
drillstring was in
turn rotated, and with the addition of weight applied to the drill bit by
drill collars and other
components of the drillstring, drilling took place.
An alternative way of rotating the drill bit is by means of a downhole device,
either a
downhole motor such as a positive displacement motor (frequently called a
Moineau motor), or
a downhole turbine. For purposes of this patent application, the term
"downhole motor" will be
used to broadly encompass any means of generating drill bit rotation, which is
positioned
downhole in the drillstring. Generally, when a downhole motor is being used,
the drillstring is
not rotated, or rotated slowly to reduce drag on the drillstring. Downhole
motors utilize drilling
fluid ("mud," or in some cases gas) circulation, down through the drill string
and through the
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downhole motor, to generate rotation (as described further below).
Do wnhole motors are also used in settings other than conventional drilling,
for example
with coiled tubing, or workstrings used in well cleanout work and the like.
Downhole motors, while taking various forms, generally comprise an outer
housing
which is fixed (generally by a threaded connection) to the drillstring, and a
rotatable mandrel
positioned within the housing and extending from the lowermost end of the
housing. It is the
mandrel that is rotated by means of fluid circulation through the drillstring
and through the
downhole motor. The drill bit is connected to the lowermost end of the
mandrel, which usually
has a "bit box" connection thereon. The mandrel therefore is free to rotate
with respect to the
housing, yet is fixed longitudinally within the housing.
Forces between the housing and the mandrel are both radial (side-to-side) and
axial or
thrust loads (acting along the longitudinal axis of the downhole motor).
Radial bearings are
positioned within the housing, between the housing and the mandrel, to take up
the radial loads.
Thrust loads may be further separated into (1) loads or forces tending to push
the
mandrel out of the housing; and (2) loads or forces tending to push the
mandrel up into the
housing, or said another way, which are transferred from the housing to the
mandrel to force it
downward, such as to impose weight on the bit during drilling. With regard to
the first category
of thrust load, thrust bearings are positioned within the housing to sustain
loads tending to force
the mandrel axially out the lower end of the housing; such loads are generated
by fluid
circulation with the bit off bottom (such fluid pressure tending to push the
mandrel out of the
housing), or by pulling on the drill string with the bit and/or mandrel stuck
in the hole. These
thrust bearings will be referred to as secondary thrust bearings.
With respect to the first category of thrust load, in order to transmit a load
to the drill
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bit, drillstring weight is transferred first to the housing, and from the
housing to the mandrel,
and thence to the drill bit. This downward weight or force transfer between
the housing and
mandrel is done by one or more thrust bearings, which for purposes of this
application will be
called the primary thrust bearings. Known prior art primary thrust bearings in
downhole motors
have taken various forms, including ball bearing assemblies, etc., all share
one common
structural attribute, namely that the primary thrust bearing assembly is
contained within the
bore of the housing, and positioned between the inner diameter of the housing
and the mandrel.
This limits the size of the primary thrust bearings which may be used, which
in turn results in
higher unit force (pressure) loads on the thrust bearings. Higher unit force
loads result in
increased wear and failure of the primary thrust bearings.
Yet other disadvantages exist with prior art designs. In such designs, a space
or gap
exists between the lowermost end of the housing and any upwardly facing
surface (i.e. a
shoulder) of the mandrel. This space creates an area of the mandrel which is
exposed to the
wellbore and fluids therein. Cuttings from drilling operations can damage or
sever the mandrel
at this unprotected location. Also, in through tubing or coiled tubing
operations, this space
creates a ledge or shoulder which can cause a motor to become lodged or stuck
in the wellbore.
Yet another disadvantage is increased length of the tool, due to placement of
the thrust bearings
within the body of the housing.
Summary
The present invention comprises a do wnhole motor which positions the primary
thrust
bearings between the lowermost end of the housing, and the mandrel. This
position permits the
primary thrust bearing area to extend to the full extent of the outer diameter
of the housing,
which results in an increased bearing surface area. This larger bearing
surface area results in
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,
,
w
greatly reduced unit thrust loads, which in turn results in longer bearing and
downhole motor
life. Preferably, a very hard material, such as poly crystalline diamond
compact (commonly
known as "PDC") elements are used as the bearing surfaces, although other
bearing materials
and ball bearing assemblies could be used.
Another embodiment of the present invention comprises a radial bearing
assembly
comprising upper and lower sets of hardened sleeves, and a secondary thrust
bearing assembly
comprising a vertically stacked ball bearing and race assembly, disposed
between the mandrel
and the housing, wherein the balls are dimensioned so as to provide wall
contact with both the
mandrel and the housing and thereby provide additional radial support.
Yet another embodiment of the present invention comprises a radial bearing
assembly
positioned outboard of, i.e. not between, the secondary (upper) and primary
(lower) thrust
bearing assemblies, typically above (i.e. in an uphole direction from) the two
thrust bearing
assemblies. No radial bearing assembly is positioned between the secondary and
primary thrust
bearings. In this embodiment, the secondary thrust bearing assembly may
comprise a pair of
opposed shoulders with carbide, polycrystalline diamond compact, or other
bearing surfaces
therebetween, or may comprise the stacked ball bearing and race assembly
previously described.
Other attributes of the present invention will be set out in the following
description.
Brief Description of the Drawings
Fig. 1 is a simplified cross section view of a downhole motor embodying the
principles
of the present invention.
Figs. lA and 1B are views of alternative arrangements of the primary thrust
bearing.
Fig. 2 is a section view of one embodiment of the downhole motor of the
present
invention, particularly the bearing assemblies thereof.
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Fig. 3 is a section view of another embodiment of the downhole motor of the
present
invention, particularly the bearing assemblies thereof.
Fig. 4 is a sectioned detail view of the area circled as "B" in Fig. 2.
Fig. 5 is a sectioned detail view of the area circled as "D" in Fig. 3.
Fig. 6 is an end view of element 4 (a bearing element) as seen in Fig. 5.
Fig. 7 is a side view of the bearing element shown in Fig. 6.
Fig. 8 is an end view of one embodiment of a radial bearing (seen as element 9
in Fig.
2).
Fig. 9 is a side view of the radial bearing of Fig. 8.
Fig. 10 is a view of one embodiment of a lower mandrel section, illustrating a
threaded
connection for attachment of a bearing sleeve.
Fig. 11 is a view of one embodiment of a lower mandrel section, illustrating
an
engaging surface connection for attachment of a bearing sleeve.
Fig. 12 is a view of the upper mandrel section.
Fig. 13 is an end view of one embodiment of a PDC or carbide inserted thrust
bearing
which can be either a rotor or stator thrust bearing.
Fig. 14 is a side view of the thrust bearing of Fig. 13, with certain of the
inserts not
shown for clarity.
Fig. 15 is a section view of an embodiment of the downhole motor, comprising a
stacked ball bearing/race secondary thrust bearing assembly.
Fig. 16 shows additional detail of the stacked ball bearing/race secondary
thrust bearing
assembly.
Fig. 17 is a section view of another embodiment of the downhole motor, with
the radial
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bearing assembly positioned outboard (not between) the secondary and primary
thrust bearings.
Detailed Description
The present invention comprises a downhole motor for use in drilling,
workover, coiled
tubing, snubbing, hydraulic workover, fishing and like operations, having an
improved bearing
assembly, in particular the primary thrust bearing assembly. In one
embodiment, this downhole
motor bearing assembly utilizes poly crystalline diamond compact or PDC
materials in the
fabrication of bearings, particularly the primary thrust bearings. PDC
materials, typically in the
form of inserts, are used in lieu of or in conjunction with more traditional
types of bearings,
primarily ball bearings and races. PDC materials may also be utilized in the
fabrication of the
radial bearings. These thrust bearings may also utilize carbide materials
alone or in conjunction
with PDC materials. Other suitable bearing materials include ceramics,
diamond, diamond
coatings or other hard materials (generally exceeding Rc 60).
It is to be understood that orientational terms used herein are intended to
reflect the
usual orientation of the downhole motor in a wellbore. As such, "downward"
means generally
in a direction toward the bottom of a borehole; "upward" is the opposite
direction. "Axial"
loads are loads generally along the longitudinal axis of the downhole motor
(which is generally
coincident with that of the drillstring and the borehole).
One of several novel aspects of the present downhole motor is that the primary
thrust
bearings which support weight on bit loads (loads and or forces in a downward,
axial direction
in relation to a vertical wellbore) are disposed between the lower surface of
the housing, and an
upwardly facing surface of the mandrel. Typically, the mandrel terminates (at
its lower end) in
a threaded female receptacle (called a "box") or a male threaded portion
(called a "pin").
Placement of the primary thrust bearing between the lower surface of the
housing and an
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upwardly facing surface of the mandrel provides several advantages over known
prior art
designs. First, these primary thrust bearings fill the gap (in prior art
designs) between the lower
surface of the housing and the upwardly facing surface of the mandrel. A
second advantage is
the reduction in length. This is due to the weight on bit supporting thrust
bearings to be located
in an area of the motor which would normally be open, unoccupied space rather
than inside of a
housing. A third advantage is that the outside diameter of the primary thrust
bearings are
enabled to be the same as the outside diameter (OD) of the housing. This
increases the overall
size of the bearing and thus bearing contact surface, with the result of
dramatically increasing
the longevity of the bearing because the loads are shared over a larger
surface area (lowering the
load per unit area - typically measure in pounds per square inch (psi)). It is
understood that
either or both of the housing and mandrel may be fabricated in a single,
unitary piece, or made
up of multiple elements joined together by threaded connections or other means
known in the
art.
Another point of novelty of the present design is the provision of
interlocking face
grooves or face features to connect abutting components, thereby preventing
relative rotation
therebetween. Certain components within a bearing assembly must be constrained
from
rotation with respect to the structure on which the component is attached. In
the case of PDC,
carbide, or ceramic insert bearings, the stationary bearing or race is known
as the stator and is
generally connected to the housing, so as to be rotationally fixed with
respect to the housing.
The rotating bearing or race is known as the rotor and is rotationally fixed
to, and therefore
rotates with, the mandrel. With radial bearings, the outer radial bearing
component is usually
connected to the housing such that relative rotation takes place between the
outer diameter of a
rotating mandrel (disposed within the bore of the housing) and inner diameter
of the radial
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bearing. In some radial bearing designs, the radial bearing itself comprises
two components, a
rotor and stator. Again, the inner radial bearing is rotationally fixed with
respect to the mandrel
and the outer radial bearing is rotationally fixed with respect to the
housing.
The various bearing assemblies of the present invention may be sealed, thereby
retaining lubricants inside of the bearing assembly and excluding wellbore
fluids from entering
the bearing assembly. Seals may take various forms, including 0-rings,
"PolyPakTM" seals by
Parker or other manufacturers, "KalsiTM" seals from Kalsi or other
manufacturers, machined
seals, molded seals, etc. and may be used in conjunction with an anti-
extrusion rings,
generally made of copper. The sealing system may also include a pressure
balancing
component which balances the pressure within the lubricant with that of the
wellbore.
One preferred embodiment of the downhole motor of the present invention
comprises a
multi-piece, preferably two piece, mandrel. The lower mandrel section
comprises a shaft and a
bit box (for connection to a drillbit or the like), with either female (box)
threads, or male (pin)
threads. The upper end of the bit box contains some means to constrain a rotor
thrust bearing,
such as a thread, face groove, etc. The upper and lower mandrel sections are
preferably
threadably connected. The upper mandrel comprises a shaft and some means for
transmitting
torque, such as a flexshaft, constant velocity shaft, clutch type shaft, or
other shafts commonly
known as "transmissions." The lower face of the upper mandrel may also contain
a face
groove to rotationally lock an inner rotor thrust bearing.
The lower mandrel may also have a downwardly facing shoulder disposed within
the
mandrel. This shoulder comprises a redundant means of insuring that the lower
mandrel is
retained to or within the bearing assembly. This becomes important especially
in the event that
the drillbit becomes stuck and the operator must begin pulling and or jarring
on the motor in an
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attempt to free it. In this case, it is important that the mandrel does not
become dislodged from
the bearing assembly, thereby creating a fishing operation. In the bearing
assembly design
utilizing this shoulder, the lower stator bearing race and or housing must be
split axially in two
halves to accommodate assembly of the bearing assembly. These two halves would
contain a
male threaded portion. To assemble, these two halves would be abutted together
with their
upper and lower faces flush, then threaded into a female threaded receptacle,
whereby the two
male halves would thread simultaneously. Upon shouldering up, the threaded
connection would
be tightened to the proper torque.
Turning to the drawings, some of the presently preferred embodiments of the
present
invention can now be described.
Fig. 1 is a simplified cross section view of a downhole motor embodying the
principles
of the present invention. Downhole motor 10 comprises a housing 20 having a
lower end 22
with a downwardly facing surface 24. As readily understood from the drawing,
housing 20 has
a longitudinal bore 26 therethrough. Mandrel 30 is disposed within housing 20,
and is rotatable
therein, driven by a means for generating rotation (whether positive
displacement means,
turbine, etc.). Mandrel 30 extends beyond the lower end of housing 20, and has
an upwardly
facing surface 32, and a longitudinal bore 34, through which drilling fluids
are pumped.
Typically, mandrel 30 has at its lowermost end a so-called bit box 40, with a
threaded
connection (typically female) for receiving a drill bit or similar tool.
A primary thrust bearing 50 is disposed between lower end of housing 20 and
mandrel
30, for example between the downwardly facing surface 22 at the lower end of
housing 20, and
the upwardly facing surface 32 of mandrel 30. It can be readily understood
that downward axial
forces are transferred from housing 20, through primary thrust bearing 50, to
mandrel 30, and
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then to the drill bit or other tool. Primary thrust bearing 50 preferably is
dimensioned to extend
radially to or nearly to the outer diameter of housing 20, so as to maximize
surface area
available for the bearing surface. It is understood that either or both of
housing 20 and mandrel
30 may comprise multiple parts.
Primary thrust bearing 50 may take various forms. One form is simply hardened
steel
for the opposing surfaces or faces of the housing and the mandrel. Preferably,
however, some
form of hardened material is used for the bearing. One presently preferred
bearing material
comprises poly crystalline diamond compact material, which may take the form
of a plurality of
inserts (of circular or other shape), set into the opposing face surfaces. The
bearing inserts could
also be set into removable rings or sleeves, which engage locking surfaces in
the opposing face
surfaces (more fully described hereafter), which rings or sleeves can be
readily changed out for
replacement or repair. Other hard material such as carbide or ceramics could
be used for the
bearing surfaces. If desired, the bearing can be sealed so as to prevent drill
solids or drilling
fluid from entry into the bearing.
Other types of bearing assemblies may be used, including ball bearings,
preferably
sealed to protect from solids and drilling fluids.
It can be readily seen from Fig. 1 that the present invention permits use of a
relatively
large primary thrust bearing, with a maximum diameter at or near the outer
diameter of the
housing, to yield lower unit loads and longer bearing life.
Figs. lA and 1B show alternative orientations of the downwardly facing surface
on
housing 20 and the upwardly facing surface on mandrel 30. In Fig. 1, the faces
are substantially
at right angles to the longitudinal axis of downhole motor 10; in Figs. lA and
1B, the faces are
oriented at other than a right angle to the longitudinal axis of downhole
motor 10, namely at an
CA 02813912 2013-04-25
obtuse or acute angle with respect to such longitudinal axis (depending upon
the reference
direction). It is understood that with such angular orientation, the force
transfer through
primary thrust bearing 50 has both an axial (parallel to the longitudinal axis
of downhole motor
10) and radial component.
The downhole motor further comprises one or more secondary thrust bearings 60.
While
primary thrust bearing 50 transfers most or all downward forces from housing
20 to mandrel 30,
secondary thrust bearing 60 transfers forces between housing 20 and mandrel 30
in the opposite
direction. Such forces arise when fluids are pumped through downhole motor 10
with little or
no weight on bit, and tend to push mandrel 30 out of the lower end of housing
20. In addition,
in the event that the bit and/or mandrel 30 become stuck in the well, pulling
on the drillstring
will tend to pull mandrel 30 out of housing 20. Secondary thrust bearing 60
may comprise
bearing elements of PDC material, carbide, ceramics, balls and bearings, etc.
Side loading between mandrel 30 and housing 20 is primarily transferred by one
or more
radial bearings 70 between mandrel 30 and housing 20. Radial bearings 70 may
comprise ball
bearings or bearing elements of PDC, carbide, ceramic or other hard materials,
bronze or self
lubricating materials.
Further Embodiments of the Downhole Motor
Figs. 2 and 3 illustrate downhole motors embodying other principles of the
invention,
differing mainly in the structure of the primary thrust bearing arrangements.
Turning to Figs. 2 and 4 (Fig. 4 being a more detailed view of the section
noted as "B"),
a downhole motor is shown which comprises multi-piece mandrel and housing.
Mandrel 30
comprises a lower mandrel section 2 having a threaded connection (as
previously described) on
its lower most end for attachment to a drill bit or the like. Lower mandrel
section 2 terminates
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in a "bit box" 21. Sleeve member 3 is threadably attached to lower mandrel
section 2, and
provides an upwardly facing surface 32 on which bearing surface 15 is present.
Lower housing
section 5 has a lower end piece 4 attached thereto, for example by threads 41.
Lower end piece
4 has a lower end 22 having a downwardly facing surface 24, in opposition to
the upwardly
facing surface of sleeve member 3. Bearing surface 15 is positioned on the
downwardly facing
surface. As is readily understood, axial loads are thereby transmitted between
housing 20 and
mandrel 30. The embodiment of Figs. 2 and 4 preferably comprise threaded
connections
between mandrel 30 and sleeve member 3, and lower housing section 5 and lower
end piece 4;
however, it is understood that other means of connecting same are possible.
Fig. 10 shows a
lower mandrel section 2 with threaded section 23, which engages sleeve member
3.
Yet another embodiment comprises engaging surfaces, namely a face groove or
spline,
to connect sleeve member 3 to mandrel 30, and lower end piece 4 to lower
housing section 5.
With reference to Figs. 3, 5, 6, 7, and 11, this embodiment can be described.
Sleeve member 3
comprises one or more, preferably two or more, engaging surfaces 18, which
mate with like
surfaces or notches in lower mandrel section 2. Such surfaces prevent relative
rotation between
sleeve member 3 and lower mandrel section 2. Figs. 6 and 7 show side and end
views of sleeve
member 3. Bearing surfaces 15 are affixed to sleeve member. Lower end piece 4
and lower
housing section 5 have similar engaging surfaces to rotationally lock lower
end piece and lower
housing section. The lower most housing may have provisions for a guide ring
13. Guide rings
13 may be used to restrict fluid flow through bearing assemblies.
Radial bearings 9 provide radial support for the mandrel sections 2 and 8.
These radial
bearings 9 may also have face grooves or splines to prevent relative rotation
with mating
components. They may also utilize press fits, shrink fits, or heat fits to
keep them stationary.
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Figs. 8 and 9 show additional detail of one embodiment of radial bearings.
Radial bearing 9
may be provided with engaging surfaces 16 to rotationally lock same.
The downhole motor preferably comprises an additional set of thrust bearings
for axial
forces in an upward direction - that is, forces tending to push or pull
mandrel 30 out of the
lower end of housing 20. Such secondary thrust bearings were shown in Fig. 1
as element 60.
In more detail, with reference to Fig. 2, stator thrust bearing 6 and rotor
thrust bearing 7 provide
support for loads created by pulling on the bearing assembly. Preferably,
thrust bearings 6 and
7 comprise face grooves or splines, as shown in Fig. 14, to rotationally lock
the thrust bearings
to their respective components. Bearing elements 27, as seen in Fig. 13, are
mounted on the
thrust bearings to provide bearing surface.
Mandrel 30 can be in multiple parts. As seen in Fig. 2, in one embodiment
lower
mandrel section 2 is threadedly coupled to upper mandrel section 8. Upper
mandrel section 8
may be provided with port holes 12 to divert all or some of the drilling
fluids to the fluid
passage which is centrally disposed within each mandrel. The upper mandrel may
also be
provided with a flex shaft 11 for connection to the rotor of a power section
of a downhole
motor. In some directional drilling applications, the need arises for a motor
to have a bend,
generally between 0 and 4 degrees. For this application, the upper mandrel 8
may consist of
two components, a mandrel and a flexible coupling. Upper end 26 connects to
the rotor of the
power section of a downhole motor. The flexible couplings are known as
"transmissions" in the
industry. The upper end 100 of housing 20 is typically fitted with a male pin
for coupling to the
stator of a power section.
Fig. 4 is a detailed view of the area designated as "B" in Fig. 2, and shows
one
embodiment of the lower set of thrust bearings. This embodiment affixes the
bearing material,
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which may PDC, carbide, or ceramic, to a housing to connect to the bit box and
lower housings.
Fig. 5 is a detail view of the area designated as "D" in Fig. 3, and shows a
second
embodiment of the lower set of thrust bearings. This embodiment affixes the
bearing material,
PDC or carbide, to a ring or sleeve to connect to the bit box and lower
housing. Each ring
contains face grooves or features such that relative rotation between abutting
components does
not take place. Relative rotation only takes place at surface15.
Figs. 6 and 7 illustrate one possible embodiment for the face grooves or
splines 18 or
features which prevent relative rotation on the rotor and stator thrust
bearing races. A similar
interlocking feature may be used on the radial bearings as well. The actual
profile and shape of
these interlocking features can vary widely and thus the embodiment shown is
only one
possibility within the scope of this invention.
Fig. 8 is an end view of one embodiment of a radial bearing 9 containing face
grooves or
interlocking features.
Fig. 9 is a side view of the radial bearing of Fig. 8.
Fig. 10 is a side view of one embodiment of lower mandrel section 2
illustrating a
threaded portion 23 on the upper end of the bit box 22, for attachment of
sleeve member 3.
Fig. 11 is a side view of a second embodiment of the lower mandrel section 2
illustrating face grooves 24 on the upper end of the bit box 22, for
connection of sleeve member
3. These face grooves are one of many various types and or styles of
interlocking face grooves
within the scope of this invention.
FIG. 12 is a side view of upper mandrel section 8 showing the interlocking
face grooves
25.
Fig. 13 is an end view of one embodiment of a PDC or carbide insert bearing,
with the
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inserts designated as element 27. This bearing can be either a rotor 7 or
stator 6 thrust bearing.
These inserts are shown as cylindrical but can be oval, wafers, or can
encompass the entire face
of the bearing, or can be of any shape. The cylindrical inserts shown are
merely as an example
of one of many variations possible. Fig. 14 is a side view of the bearing of
Fig. 13, showing the
face grooves 25 for interlocking abutting components.
Additional, alternate embodiments of the downhole motor
Various additional embodiments of the downhole motor, particularly the bearing
assemblies thereof, will now be addressed.
Ball bearing/race secondary thrust bearing
A first additional embodiment is disclosed in Figs. 15 and 16. This embodiment
comprises a pair of sleeve type radial bearings, preferably hardened carbide
sleeve bearing
assemblies, in combination with a stacked ball bearing and race secondary
thrust bearing
assembly, both of which take up radial loads. Referring to Fig. 15, sleeve
type radial bearing
assemblies 80 and 100 are disposed between mandrel 30 and the inner surface
(bore 26) of
housing 20. Each of the sleeve type radial bearing assemblies comprises one
sleeve fixed to
mandrel 30, by way of illustration sleeve 100B, and one sleeve fixed to
housing 20, by way of
illustration 100A. The large surface area of the sleeve type radial bearings
reduces unit loading
between the structural members, creating a very strong radial structure.
This embodiment of the downhole motor further comprises a secondary (upper)
thrust
bearing assembly 130 (which takes loads tending to move the rotor out of the
outer housing)
comprising a plurality of vertically stacked balls and races. As can be seen
in Fig. 15, and in
more detail in Fig. 16, a plurality (three in the illustrated embodiment) of
balls 90 are stacked
(it being understood that balls 90 are spaced about the circumference of the
bearing assembly;
CA 02813912 2013-04-25
the three balls 90 being visible in cross section), with races 92
therebetween. The respective
dimensions of balls 90, races 92, and the distance A between the outer
diameter of mandrel 30
and the inner diameter of housing 20 are important. Preferably, the diameter B
of balls 90 is
approximately equal to the spacing between the outer diameter of mandrel 30
and the inner
diameter of housing 20, allowing for sufficient clearance to assemble the
downhole motor
assembly. Preferably, with this configuration, balls 90 contact both surfaces
at the same time
(that is, the outer diameter of mandrel 30 and the inner diameter of housing
20), providing a
roller bearing support (radially) therebetween. In this manner, balls 90
provide additional radial
bearing support for a much greater length of the rotor. The radial dimension C
of races 92 is
less than the diameter of balls 90, such that races 92 are centered (by
interaction with balls 90,
seated in the channels of races 92), do not contact either of the two
adjoining surfaces, and are
free to rotate independently of any other structure.
As noted above, the ball bearing assembly transfers axial forces between the
rotor and
the outer housing, such forces tending to push the rotor out of the outer
housing, and this force
transfer can now be described. Starting with a force pushing mandrel 30 in a
direction out of
housing 20 (or toward bit box 40), the lowermost shoulder 31 of mandrel 30
bears against
uppermost race 92. This force, as can be readily understood, is transferred
through the sequence
of balls and races to the lowermost race 92. Lowermost race 92 bears against
radial bearing
member 100A, which is fixed to housing 20, thereby transferring the axial
force to housing 20.
Bit box 40 is attached to mandrel 30 by threading or other means known in the
art; therefore,
any axial force tending to pull bit box 40 out of housing 20 is ultimately
transferred to housing
20 as just described. As is well known in the art, other forces tending to
push mandrel 30 out of
housing 20 include the thrusting force generated by fluid flow around mandrel
30 (which
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generates rotation of mandrel 30), particularly when the bit is off bottom,
and the weight of the
mandrel/bit assembly when the tool is off bottom.
Radial bearing positioned outboard (not between) secondary and primary thrust
bearings
Fig. 17 shows additional detail of another embodiment of the downhole motor of
the
present invention. This embodiment positions the radial bearing outboard (not
between), and
preferably above (in an uphole direction) the secondary (upper) thrust bearing
- - or said another
way, the radial sleeve type bearing is not between the secondary (upper) and
primary (lower)
thrust bearings, but is above both of them.
This embodiment preferably comprises one or more sleeve type radial bearings
(preferably, carbide sleeve type bearings), in combination with the secondary
and primary thrust
bearing assemblies. As disclosed in other embodiments, primary thrust bearing
assembly 50 is
disposed between the lowermost end of housing 20 and an upward-facing surface
of bit box 40;
preferably, primary thrust bearing assembly 50 comprises a plurality of PDC
"buttons," on both
surfaces, as previously described. As shown in Fig. 17 (and in previous
drawings), the facing
surfaces are preferably angled so as to form a self-centering structure. In
addition, the self-
centering structure provides a means for transferring both thrust and radial
loads. Secondary
thrust bearing assembly 110 may comprise sleeves 120 and 130 having facing
shoulders having
PDC button bearing surfaces thereon, as seen in Fig. 17. Alternatively,
secondary thrust bearing
assembly 110 may comprise a ball bearing and race stack, as described in the
previous
embodiment, as shown in Fig. 15.
Positioned outboard of, and not between, primary and secondary thrust bearing
assemblies 50 and 110, and generally positioned above (in an uphole direction)
of said thrust
bearing assemblies, is a radial bearing assembly 150. While this radial
bearing assembly may
17
CA 02813912 2013-04-25
take various forms, one presently preferred embodiment is a pair of hardened
sleeves, one each
fixed to mandrel 30 and housing 20, as shown in Fig. 15 previously. This
embodiment
positions the thrust bearing assemblies relatively close together, with the
radial bearing
assembly positioned above, and has advantages in certain applications.
Conclusion
While the preceding description contains many specificities, it is to be
understood that
same are presented only to describe some of the presently preferred
embodiments of the
invention, and not by way of limitation. Changes can be made to various
aspects of the
invention, without departing from the scope thereof. For example:
= various materials may be used for the bearing materials, such as PDC,
carbide, ceramic,
hardened steels, in some applications brass or bronze, or even non-metallic
materials
= materials for the various components of the downhole motor may be varied
= dimensions may be varied to suit different applications
= different components of the downhole motor may be made in multiple parts,
for
example the mandrel and the housing; references to such components are all-
encompassing, whether of one part or multiple parts.
Therefore, the scope of the invention is to be determined not by the
illustrative
examples set forth above, but by the appended claims and their legal
equivalents.
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