Motor shaft security apparatus

Abstract

An interference structure is provided in a drilling motor to engage the motor drive shaft assembly if the thrust bearings fail and the drive shaft moves axially a preselected amount. The interference structure is protected from wear common to drilling motor use. The structure assures the recovery of all drilling motor parts if all thrust bearings fail.

Description

This invention pertains to down hole motors. More particularly, it pertains to structure that secures the motor as a single assembly, for recovery from a well bore, if some parts fail.

BACKGROUND OF THE INVENTION

Drilling motors are used as part of a drill string, near the drill head, to drive the drill head rotationally relative to the upwardly continuing drill string. The drilling fluid flow is usually used to power the motor.

Drilling motors are often used on coiled tubing which cannot be rotated. In some cases the motor is used to rotationally attach the drill string to hardware down hole that is to be recovered by tension forces. Jars are sometimes used to deliver shock to the hardware. Motors that are designed for drilling are sometimes not designed to accept axial shock forces.

Axial shock loads imposed upon motors can separate their output drive shafts. The usual structure of motors includes capture rings that will usually extract all of the output shaft when the damaged motor is removed from the well. The part of the output shaft that extends outside the motor body is about the size of the body. The shaft diameter decreases before the capture contrivance can engage the shaft. If the shaft breaks below the capture device, debris is left in the well.

The U.S. Pat. No. 7,445,061 issued Nov. 4, 2008 provided a sleeve that engaged the largest part of the output shaft and extended upward to engage at least some of the thrust bearings. That enabled the recovery of all motor parts and the bit even if the shaft broke below the capture device.

During the use of drilling motors, they may be miles below the surface and the evidence of failing bearings may not be realized until they are destroyed and the supported shaft drops out of the motor. The cited patent depends upon bearings and they too can fail totally. The present improvement can function independently of any bearings. Further, the friction of the preferred configuration makes the motor have to produce more torque, or stall, when the bearings have failed. That can be detected in the form of a mud pressure jump at the stand pipe. The machine can be stopped before the capture device is destroyed.

SUMMARY OF THE DISCLOSURE

A sleeve is threadedly secured to the projecting end of the motor output shaft and extends into the motor housing, up to the lower end of the thrust bearing assembly. Optional arrangement includes some thrust bearing races in the sleeve.

At the top end of the sleeve, a peripheral capture groove receives a stator mounted interference structure that will not allow the sleeve to pass through axially.

These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view, in cut-away, of a prior art embodiment of the apparatus to which the improvement pertains. The area to which the improvement applies is captioned IMP. Body 1 has bearing housing 2 which captures the stator components of bearings 5. Sleeve 4 transmits forces from the IMP area to the enlarged end of the output shaft 3.

FIG. 2 is a side view, mostly cut away, of the major components in the vicinity of the improvement, and of one version of the improvement itself.

FIG. 3 is a section taken along line 3-3 of FIG. 2. Balls 6 are allowed to roll in the peripheral groove 4a.

FIG. 4 is a section taken along line 4-4.

FIG. 5 is a side view, mostly in cut-away, of the improved portion of the apparatus.

FIG. 6 is a sectional view taken along line 6-6 of FIG. 7.

FIG. 7 is a side view, mostly in cut-away, of an alternate form of the apparatus.

FIG. 8 is a sectional view taken along line 8-8 of FIG. 9.

FIG. 9 is a side view, mostly in cut-away of an alternate form of the apparatus.

DETAILED DESCRIPTION OF DRAWINGS

In the down hole motor art, a general housing may consist of several parts. In function, however, the assembled general housing attaches to a drill string, supports a confined motor and has a lower bearing housing which forms a housing closure from which an output shaft extends to engage and drive a drill bit.

FIG. 1 shows the lower end of a drilling motor according to prior art, excepting the area, IMP, shown in a heavy dashed rectangle. The present improvement is, preferably, installed in the area of that rectangle. No power producing structure is shown. A power producing assembly is normally situated in the upper end of tube 1, above the limit of FIG. 1, and drives the output shaft through an attachment situated above (left of) nut N. Body housing 1 is threadedly attached to lower bearing housing 2 by threads. The body housing compresses bearing outer race stack SS which defines outer races 5a. The inner race stack RS, carries bearing balls 5. The rotor stack of bearings is usually compressed by nut N, unless they are keyed to the shaft 3. Sleeve 4 is threadedly attached to the shaft 3 at the large diameter end.

Sleeve 4 can stress the shaft in compression if it bears on the shoulder 3a. If the sleeve does not bear on the shoulder 3a the nut N, by compressing the rotor stack RS, can stress the shaft in tension under the sleeve. The choice of the nature of the stress is usually dictated by expected drilling conditions.

FIG. 2 shows one construction option in which balls 6 are free to rotate and move peripherally in inner race 4a. The inner race 4a is elongated to prevent axial loads until the upper thrust bearings fail. After the thrust bearings fail balls 6 axially trap groove 4a and prevent the ejection of the drive shaft from the housing.

FIG. 3 is a section taken along line 3-3.

FIG. 4 is a section taken along line 4-4.

FIG. 5 shows interference ring 11 instead of balls. The ring 11 will capture groove 10a, and the rotor assembly if the thrust bearings fail. Also shown is the optional extension 10b of the sleeve, now captioned 10, to provide at least one race to receive at least part of the thrust bearing stack. This option should be construed to apply to the assemblies according to FIGS. 2, 7, and 9.

FIG. 6 is a section taken along line 6-6 of FIG. 7.

FIG. 7 is similar to FIG. 2 but balls 12, distributed about groove 4a are held firmly in the stator stack by the radial bearing housing, now captioned 2A, and cannot move peripherally. When the thrust bearings fail, the rotor will engage a non-rotating structure, the balls 12, and a change in torque experienced by the motor will yield a drilling fluid pressure change to be detected at the surface to signal for motor shut down.

FIG. 8 is a section taken along line 8-8 of FIG. 9.

FIG. 9 shows a plurality of pins 14 peripherally distributed through bores in the extended, non-threaded, part 2Ba of the radial bearing housing, now captioned 2B. The pins serve the same purpose as the non-rotating balls 12 of FIG. 7 in that they produce drag after thrust bearing failure. The increased torque demanded of the motor will be detectable as stand pipe pressure change detectable at the surface. Eight pins are shown but any practical number of pins may be installed.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the apparatus of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Claims

1. A down hole drilling motor apparatus with an output shaft secured to the general housing by interference structure directly connecting the general housing to an extending portion of the output shaft, the apparatus comprising: a). a down hole motor with said general housing, said output shaft, and a bearing assembly to secure the output shaft within the general housing;b) an intermediate sleeve threadedly attached to an enlarged portion of said extending portion of the output shaft, having a capture groove therein; andc) an interference structure secured to said general housing and situated to engage said capture groove to retain said output shaft if said intermediate sleeve moves a preselected axial distance relative to said general housing.

2. The apparatus of claim 1 wherein spherical elements axially secured to said general housing comprise said interference structure.

3. The apparatus of claim 1 wherein said spherical elements are balls free to roll peripherally in a housing supported race and said capture groove is elongated to prevent said balls from carrying thrust loads until said output shaft moves axially a preselected amount.

4. The apparatus of claim 1 wherein said interference structure is a ring that extends radially into said capture groove.

5. The apparatus of claim 1 wherein said interference structure comprises pins extending radially from said housing into said capture groove.

6. The apparatus of claim 1 wherein said intermediate sleeve is extended to include at least one race to engage at least part of said bearing assembly.

7. A down hole drilling motor apparatus with an output shaft secured to a general housing, by bearings directly connecting the general housing to a portion of the output shaft extending from the general housing, the motor comprising: a) a down hole motor with said general housing, and said output shaft;b) an intermediate sleeve threadedly attached to said portion of the output shaft, and having at least one capture groove;c) an interference structure, secured to said general housing and extending radially into said capture groove to secure said intermediate sleeve, and said output shaft, to said general housing in the event of axial movement of said sleeve a preselected amount.

8. The apparatus of claim 7 wherein said interference structure comprises rolling elements.

9. The apparatus of claim 7 wherein said interference structure is a ring that extends radially into said capture groove.

10. The apparatus of claim 7 wherein said interference structure comprises pins extending radially from said housing into said capture groove.

11. The apparatus of claim 10 wherein said pins are secured to said general housing by extending from a radial bearing housing which is part of said general housing.

12. The apparatus of claim 10 wherein said interference structure comprises balls peripherally distributed, and secured against rotation, within said general housing.