GB2294737A - Reducing axial load on bearings - Google Patents

Abstract

In a torque transmission device (eg in a drill string), an output shaft (16) which in use is subject to an axial force is rotatably mounted in a housing by means of thrust roller bearings (24). The shaft comprises an annular piston (30) located within a pressure chamber (32) such that by pressurising the chamber an oppositely directed axial force is exerted on the shaft. Pressure fluid is admitted to the chamber through a bore (40), or alternatively working fluid is admitted through a bore (50). Means for sensing the axial force acting on the shaft may be provided such that the fluid pressure in the chamber may be varied to accommodate changes in the forces acting on the shaft. <IMAGE>

Description

FORCE OR TOROUE TRANSMISSION DEVICE This invention relates to a force or torque transmission device and in particular to a device or tool for use in drilling applications, such as a wireline side entry tool.

According to the present invention there is provided a force or torque transmission device comprising a body and at least one input or output shaft rotatably mounted on the body and, in use, the shaft being subject to an axial force, the shaft defining a surface of a pressure chamber in the body such that by pressurising the chamber an oppositely directed axial force is exerted on the shaft.

In use, the invention allows balancing of axial fores acting on the device, for example te reduce the forces actir.g on the bearings supporting the shaft, and thus reduces the bearing friction and wear. An immedIate benefit of the inventicn is a reduction in the power input to te shaft necessary to provide a desired power output, through. a reduction of friction losses.

The invention has particular plication in drilling operations, where the device may force part of a drill string. The shaft may thus experience an axial pressure force from drilling fluid or well fluid within the body, and also an axial force from the weight of drill string connected to the shaft. Such forces, af not balanced, can substantially increase the power required to rotate a shaft on its bearings.

Preferably, the device comprises an input shaft and an output shaft, each rotatably mounted in the body.

Preferably also, the shaft defines a piston which is axially moveable, with the shaft, relative to the chamber.

The piston may be integral with the shaft or may be fixed thereto.

Preferably also, the device is provided in combination with a source of pressurised fluid for connection to the chamber. Means for sensing the axial force acting on the shaft may also be provided and linked to means for pressurising the fluid, such that the pressure of the fluid in the chamber may be varied to accommodate changes in the forces acting on the shaft.

The body may define a second chamber and the shaft may define a through bore. In drilling applications, fluids such as drilling mud are pumped, under pressure, through the body and shaft, ar.: porting may be provided to allow fluid pressure communication between the second chamber or bore and the pressure chamber. In certain applications, this will obviate the requirement to provide a separate source of pressurised fluid.

ThIs and other aspects of the present invention, will now e described, by way of example, with reference te the acccmpanying drawings, in which: inure 1 is a sectional side view of a wireline side entry tool in accordance with a preferred embodiment of the present invention; Figure 2 is a plan view of the tool of Figure 1; and Figure 3 is an enlarged view of area 3 of Figure 1.

Figures 1 and 2 of the drawings illustrate a wireline side entry tool 10, as an example of a device incorporating an embodiment of the present invention. The tool 10 would typically be located on the drill string beneath the top drive motor. The tool 10 comprises a generally cylindrical body 12, an input shaft 14 and an output shaft 16. The toothed shaft ends 18, 19 are connected by a planetary shaft and gear arrangement 20 located within the body 12.

The body 12 and the shafts 14, 16 are hollow such that drilling fluid or well fluid may pass therethrough.

In use, the body 12 is secured against rotation, while the planetary gear and shaft arrangement 20 allows the transfer of torque from the input shaft 14 to the output shaft lo. The stationary body 12 permits, for example, a wireilne to be introduced into one of three openings 22 in the upper face of the body 12, and thus into the output shaft 1 and the drill string.

The drilling fluid or mud which is normally pumped through the body and shafts is under pressure and this pressure produces axial forces on the shafts 14, 16.

Further, the weight of the drill string may also exert signIfIcant axial forces on the tool 10. To a certain extent these forces are accommodated by the shaft bearings 24 (~irXre 3) provided between the body 12 and the output shafts 16. Figure 3 illustrates the mounting arrangement for the shaft 16 and a similar arrangement is provided for the input shaft 14. The bearings 24 are located within an endplate 26 of the body 12, the endplate 26 also providing mounting for a cap 28. An annular piston 30 is screwed and pinned to the shaft 16 and is located within a chamber 32 defined by the cap 28. Seals 34, 36, 38 are provided between the piston 30 and the chamber wall, between the piston and the shaft 16, and also between the cap 28 and the shaft 16.The section of shaft 16 above the piston 30 is provided with seals 42 and a bush 44, the area between the piston 30 and the seals 42 being vented to atmosphere via a bore 46.

A tapped bore 40 extending into the chamber 32 connects to a hydraulic line (not shown) which extends from a suitable source of hydraulic pressure. Thus, by pressurising fluid in the chamber 32 an upward axial force is produced on the piston, and thus on the shaft 16, which force tray be selected to balance the pressure forces and drill string weight acting in the downward direction. The load o-. the bearings 24 is thus reduced, and the fluid filled pressurised camber 32 acts as a fluid bearing.

A drilling fluid pressure sensor and a strain sensor may be mounted at suitable location on the body 1; to determine the axial forces on the shaft. The sensors are linked to the pressurised fluid source which may vary the pressure of the fluid in the chamber 32 to balance the bearIng load on the shaft 16.

n use, the reduction of load on the bearings 24 reduces the frictional losses in the tcol 10 to a minimum, thereby ensuring that as a large a proportion as possible of the torque output from the top motor is transmitted to the drill string.

In another embodiment of the invention, the balancing hydraulic pressure may be provided by the drilling fluid being pumped through the body 12 and shafts 14, 16; a port 50 (Figure 3) is provided through the shaft 16 to communicate with chamber 32, the bore 40 being capped.

This avoids the requirement to provide a separate source of pressurised fluid.

It will be obvious to those of skill in the art that the above-described embodiment is merely exemplary of the present invention, and that varicus modifications and imprcvements may be made thereto without departing from the scope of the present invention. Further, it will be noted that te present inventIon may be utilised in a wide range of tools where torques or thrusts are to be transmitted, and Is not limited to use in the wireline side entry tool illustrated and described above, nor to rotary drilling toois.

Claims (7)

1. A force or torque transmission device comprisir.g a body and at least one input or output shaft rotatably mounted on the body and, in use, the shaft being subject to an axial force, the shaft defining a surface of a pressure chamber in the body such that by pressurising the chamber and oppositely directed axial force is inserted on the shaft.

2. The device of claim 1 including an input shaft and output shaft, both rotatably mounted on the body.

3. A device of claim 1 or claim 2 wherein the shaft defines a piston which Is axially movable, with the shaft, relative to the chamber.

4. The device of claIm 1, 2 or 3 in combination with a source of pressurised fluid for connection to the chamber.

5. The device of claim 4 further inzluding a means for sensIng the axial force acting on the s-.aft, the said cans being : nked for means for pressurlsing the fluid, such that the pressure of the fluid in the camber may be varied to accommodate changes in the forces acting upon the shaft.

6. The device of claims 1, 2 or 3, wherein at least one of the shaft and body are hollow for containing a pressurised fluid, and a port is provided to allow fluid pressure communication between the fluid and the pressure chamber.

7. A force or transmission device as substantially as described herein, and as illustrated in the accompanying drawings.