Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BOTTOI`~ ~OL~ ~';OTOR FOR DRIVING ROCK-B~EAKIli~ TOOL
The present inve~tion relates to mining and, more part-
icularly, it relates to bottom hole motors for driving rock-
-breaking tools, desi~ned for drilling and repair of oil,
gas and exploratory wells. This invention can also be used
in other bottom hole mechanisms.
There is known in the art a bottom hole motor for driv-
ing a rock-breaking tool, comprising a motor unit coupled
kinematically with a spindle unit having a housing. Passing
inside said housing is a shaft connected with the rock-
-breaking tool and mounted in the housing with the aid of
radial bearings and a thrust one. The thrust bearing is es-
sentially a set of outer and inner races serving to retain
rollin~ bodies located therebetween.
~ rrespective of the configuration of the working sur-
faces of prior art races of the thrust bearin~, provision
is made for ti~htening the inner races located on the shaft
and the outer races located in the spindle unit housing.
Said prior art bottom hole motor is used advantageously
in drilling wells of large and medium diameter, however, a
multicomponent nature of the spindle unit and relatively lar-
~e crosssectional area taken by the thrust bearing elements
render the prior art structure unsuitable for drilling wells
of small diameter due to impossibility to ensure its reliab-
le and duxable operation. This is due to the fact that the
utilization of a conventional spindle unit structure when
using the prior art bottom hole motor for drilling wells of
small diameter calls for a reduced shaft diameter which, in
-- 2
turn, results in the reduction of permissible power
developed by the bottom hole motor.
The choice of required shaft diameter from con-
siderations of strength leads to a considerable reduction
in the diameter of rolling bodies, this leading to further
reduction of the service life of the bottom hole motor
because of the reduced carrying capacity of the rolling
bodies used.
It is the object of the present invention to
develop a bottom hole motor for driving a rock-breaking
tool, featuring such a structural embodiment of the
spindle unit as would ensure an increased durability and
reliability of the bottom hole motor operation when drill-
ing wells of small diameter, as well as facilitate con-
siderably the repair operations.
In accordance with the present invention, there
is thus provided a bottom hole drill comprising a motor,
a spindle assembly having a housing, a shaft extending
through the housing and coupled at one end to the motor,
a thrust bearing comprising a plurality of races and
rings arranged coaxial about the shaft, and a radial
roller bearing the outer races of which are formed by
the races of the thrust bearing and the inner races of
which comprise peripheralgrooves formed in the surface
of the shaft, and a tool mounted on the other end of the
shaft.
-- 3 --
Such structural arrangement permits of increased
dimensions of the rolling bodies at a fixed diameter of the
shaft which allows for considerably increasing the durabi-
lity of both the thrust bearing and bottom hole motor as a
whole, owing to an increased carrying capacity of the
rolling bodies.
It is expedient that the shaft of the spindle
unit be composed of at least three rigidly interconnected
portions including a middle portion provided with the toroidal
grooves and two end portions interacting with the radial
bearings. This helps improve considerably the quality of
the shaft portion provided with grooves and simplify the
manufacture of the shaft as a whole.
In addition, such a structural arrangement of the
shaft renders the latter more compact, while the improved
quality of toroidal grooves makes for a sharp increase of
the thrust bearing life.
In order to ensure minimum contact stresses while
fully ensuring the possibility of successive assembly of
each specific series of the thrust bearing, as well as to
maintain the shaft strength, it is expedient that the toroidal
grooves for the rolling bodies have a ratio of the radius of
the toroidal grooves cross-section to the inner diameter of
:
425
- 3a -
the torus lying substantially within 0.1-0.25.
The present invention will be more apparent upon
considering the following detailed description of an exemplary
embodiment thereof, with references to the accompanying
drawings in which:
Figure 1 is a general view of a bottom hole motor
for driving xock-breaking tools, according to the invention,
longitudinal section, and
1~14ZS
-- 4 _
Figure 2 is a view taken along arrow A of ~ig. 1.
The herein disclosed bottom hole motor for driving
rock-breaking tools comprises a motor unit 1 and a spindle
unit 2. The motor unit 1 includes a body 3 ~hich accommoda-
tes working members such as a helical stator 4 and a heli-
cal rotor 5 mounted thereinside.
The spindle unit 2 includes a composite shaft 6 con-
sisting of an adapter 7, a portion of the shaft 6 adapted
to carry spherical rolling bodies 8 and made as an insert
9, and an output shaft lOt rubber-coated radial bearings 11
and a thrust bearing 12.
The thrust bearing 12 proper is a special multiple
thrust-radial ball bearing includin~ outer races 13 and
rings 14 interacting with the rolling bodies 8. The latter,
in their turn, are in contact ~ith toroidal grooves 15 pro-
vided on the outer surface of the insert 9. The outer races
13 and rinp`s 14 are tightened into a monolith set with the
aid of thread provided on a housing 16 of the spindle unit
2.
In the absence of technological difficulties when manu-
facturing the shaft 6, in general, and in the case of a high
guality of manufacturing of the toroidal grooves 15, in Dar-
ticular, the sha~t 6 is manufactured in one piece (not shown
in the drawings).
The bottom hole motor for driving roc~-breaking tools
o~ the present invention further comprises a coupling ele-
ment 17 serving to interconnect the helical rotor 5 o~ the
5 --
motor unit 1 and the shaft 6 of the spindle unit 2, and an
adapter 18 over the bit. ~he bottom hole motor is suspended
from a drill or tubin~ string (not shown) with the aid of
an adapter 19.
The bottom hole motor of the present invention for
driving rock-breaking tools operates in the following man-
ner.
Drilling mud is supplied to the bottom hole motor over
the inner space of drill pipes through the adapter 19. When
~assing throu~h the helical stator 4 and helical rotor 5,
drilling mud acts to rotate the latter and is delivered to
the bottom hole via inner holes in the adapter 7, insert 9
and output shaft 10. ~he torque developed in the motor unit
1 is transmitted from the helical rotor 5 to the shaft 6 of
the spindle unit 2 via the coupling element 17.
An axial force arising in the helical rotor 5 from the
hydraulic load and forces acting iD the stator-rotor ~air,
as well as from the load from the bottom hol.e, is taken up
by the thrust bearing 12~ while radial loads caused by unba-
lance of the shaft 6 and by other factors are taken up by
the rubber-coated radial bearin~s 11.
Axial loads from the insert 9 are transmitted via the
rollin~ bodies 8 to the outer race 13 and further to the
housing 16. The angle of contact is selected such as to en-
sure the minimum contact stresses ~hile full~ ensuring the
possibility of successive assembly of each s~ecific series
of the thrust bearing 12~ The dimensions of the rolling bo-
4~S
~, _
dies 8 and diameter of the toroidal grooves 15 are selectedfrom the same considerations, while retaining the strength
of the shaft 6. It has been found that a reduction of dia-
meter of the rolling bodies 8, at the same size or sli~ht
increase of the toroidal grooves 15 provided on the insert
9, affects considerably the carrying capacity of the thrust
bearing 12.
At the same time, as sho~n by relevant studies, a re-
duction of diameter causes, along with deterioration of the
carrying capacity, ~ro~ressing wear of the rolling bodies 8,
especially, in open-type bearin~s such as the thrust bearing
12 of the bottom hole motor for driving a rock-breaking tool.
This ~rocess tends to get more intensive in the presence of
abrasive particles in drilling mud pumped throu~h the bottom
hole motor.
However, an i.ncreased size of the rollin~ bodi.es 8 may
lead to a reduced safety margin of the shaft 6 when transmi.t-
ting high torques whose absolute value increases sharply upon
instantaneous stoppage of the shaft 6 of the bottom hole mo-
tor (braking state). This imposes necessary technological li-
mitations on the bottom hole motor operation (such as redu-
ced flow rate of drilling mud which, in turn, results in a
reduction of permissible power developed by the bottom hole
motor).
Therefore, the ratio of the radius r of the cross-
-section of the toroidal groove 15 to its inner diameter D
should lie substantially within the 0.1-0.25 range.
2S
-- 7 --
The herein disclosed design of a bottom hole motor for
driving a rock-breaking tool, featuring the recommended di-
mensions of the toroidal ~roove 15 for the rollin~ bodies 8,
provides an increased load capacity of the thrust bearing
12 owing to a more efficient utilization of the cross-sec-
tional area designed to accommodate large-size rolling bod-
ies 8 as com~ared with the prior art bottom hole motor thrust
bearing. In addition, the assembl~ of the spindle unit 2 is
facilitated owing to a small number of components in the
latter and to the obviation of the need to tighten the set
of inner races of the thrust bearing 12 on the shaft 6.
