GB2240880A - Electromagnetic actuator for a valve - Google Patents

Abstract

The actuator for a valve 70 in a downhole tool comprises a first yoke (2), a coil (52) and an armature (18) and a second yoke (12), a coil (53) and an armature (32), the second armature (32) being fixed to a shaft (40) and having a planar end face spaced from a planar end face of the second yoke (12) by a pre-set distance. The first armature (18) is slidable upon the shaft (40) and has a stepped end face spaced from a complementary end face of the first yoke (2) by a distance less than the pre-set distance. Energisation of the coils (52, 53) causes the first armature (18) to move towards the first yoke (2) until it engages a shoulder 46 of the shaft (40) and moves the second armature (32) towards the second yoke (12), the second armature (32) subsequently engaging the second yoke under the attractive force between their planar faces. The coil 52 is than de-energised and the valve is held open against the bias of a spring 72 by the attraction between the yoke 12 and the armature 32. On de-energising the coil 53, the valve closes. <IMAGE>

Description

"Solenoid Assembly" This invention relates to a solenoid assembly.

Solenoids are employed in many situations in which remote actuation of valves and other movable items is required. One such situation is in downhole monitoring systems in the oil industry in which conditions of temperature, pressure and the like are detected in an oil well and the results transmitted to the surface; the transmission can be by introducing a pulse or series of pulses of pressure in the drilling fluid delivery system by opening and closing a valve to direct the drilling fluid from its normal route. This valve is actuated by solenoids.

Since the valve must be both opened and closed, some existing systems include double-acting solenoid assemblies in which a first solenoid is directed to moving an armature in one direction and a second solenoid moves it in the opposite direction. This means that the assembly must be of substantial size, and difficult to fit successfully within a downhole unit. The speed of opening of the valve is important and consequently the solenoid must develop a high force.

Further, the positive actuation of the solenoid assembly in opening and closing the valve causes substantial demands on the downhole battery pack power supply.

According to the present invention there is provided a solenoid assembly comprising a first armature having a planar end face engageable with a corresponding planar end face of a first yoke and a second armature having a non-planar end face engageable with a generally complementary, non-planar end face of a second yoke, the first and second armatures being mounted on a common shaft and movable towards and away from the first and second yokes respectively, said first and second yokes each having an electrical coil associated therewith, the shaft being movable between a first position, wherein said first armature is spaced from said first yoke by a first distance and said second armature is spaced from said second yoke by a second distance less than said first distance, and a second position wherein said first armature engages said first yoke.

The non-planar faces of the second armature and the second yoke are preferably closely mating and may be, for example, of stepped or conical configuration.

The assembly may be disposed in an oil-filled chamber, for example when used in a downhole monitoring system, in which case the movement of the armatures into and out of engagement with their respective yokes may be subjected to substantial resistance from the oil thus preventing rapid movement of the armatures. This can be alleviated by providing passageways through the armatures, preferably opening through the end faces, to allow rapid displacement of the oil from between the opposed faces.

The assembly may be connected to a valve member so that actuation of the assembly actuates the valve. This is of especial use in downhole monitoring systems where rapid actuation of the valve is necessary. In such cases the assembly is preferably arranged to actuate the valve in one direction only, for example to open it, and movement in the opposite direction is accomplished by the effect of a spring or other resilient means.

The armatures are preferably of low resistivity material so that deactuation of the yokes causes degradation of the magnetic attraction between the yokes and the armatures instead of a more rapid effect.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 (a), (b) and (c) are respectively an end elevation, a sectional elevation and an elevation of a first yoke of an assembly of the invention; Fig. 2 (a), (b) and (c) are respectively an end elevation, a sectional elevation and an elevation of a second yoke of the assembly; Fig. 3 (a) and (b) are respectively an end elevation and a sectional elevation of a first armature of the assembly; Fig. 4 (a) and (b) are respectively an end elevation and a sectional elevation of a second armature of the assembly; Fig. 5 is an elevation of a shaft for mounting the yokes and armatures of Figs 1 to 4; Fig. 6 is a schematic sectional elevation of a part of the assembly showing the arrangement of the armatures on a central shaft;; Fig. 7 is an exploded view of a downhole assembly which include a solenoid assembly of this embodiment; and Fig. 8 is a graph of current flowing through the second armature against time during the phase in which the valve is being held open.

Referring to the drawings, the assembly of this embodiment of the invention is designed for use downhole in an oil well to actuate a valve for transmitting signals from a monitoring system through a drilling fluid circulation system to the surface.

The assembly includes a first yoke 2 (Fig. 1) of generally cylindrical form with a central axial bore 4 therethrough. The yoke has its outer wall stepped inwardly towards one end, having a shoulder 5 for receiving a first coil (52, Fig. 6) terminating in a small-diameter portion 6. Oil through-passageways 8 are provided in the yoke 2. The end face 10 is planar and normal to the yoke's main axis.

A second yoke 12 (Fig. 2) also is of cylindrical form with a through bore 14 and has a planar end face 16 normal to the main axis of the yoke 12. A shoulder 17 is provided for receiving a second coil (53, Fig. 6).

A first armature 18 (Fig. 3) is generally cylindrical with a through bore 20 which increases in diameter in steps from a central portion 26 to an end portion where it forms a rebate 22 whose end face 24 is planar. Oil through-passageways 28 extend from the face 24 through the armature 18 and oil grooves 30 are formed in the outer cylindrical wall. The stepped end portions of the first yoke 2 and first armature 18 provide complementary, non-planar end faces.

A second armature 32 (Fig. 4) is of cylindrical form and has a partial bore 34 internally screw-threaded at 36. Oil through-passageways 38 extend from an end planar face 38 through the armature 32.

Fig. 5 shows a stepped shaft 40 for receiving the yokes 2, 12 and armatures 18, 32 as shown in Fig. 6, the second armature 32 being engageable through its screw thread 36 with a corresponding external screw thread 42 on the shaft 40, so that the second armature 32 is fixed in position at one end of the shaft 40. The first armature 18 fits over a smaller-diameter length 44 of the shaft 40 and is slidable axially thereon, being limited in its movement in one direction by a shoulder 46. An end portion 48 of the shaft 40 opposite to that having the screw thread 42 also has a screw thread 50 for receiving a connection to a valve member (70, indicated schematically by broken lines in Fig. 6) for opening and closing passage of drilling fluid.

As seen in Fig. 6, the shaft 40, with the second armature 32 attached to one end, extends through the central bore of the first yoke 2. The second yoke 12 engages the open cylindrical end of the first yoke 2, enclosing the second coil 53 mounted on the second yoke 12 and the second armature 32. A bush 54 is located in the central bore of the first yoke 10, and includes a spacer portion 55 which limits the movement of the second armature 38 to the right (as seen in the drawing), so defining the spacing between the opposed end faces of the second yoke 12 and armature 32.

A sleeve member 56, somewhat similar to the first yoke 2, engages the end of the first yoke 2 remote from the second yoke 12 to enclose the first coil 52 and the first armature 18. A further bush 58 is located in a bore 60 formed in the outer end of the sleeve portion 56, the bush 58 also including a spacer portion 59 which limits the movement to the right of the first armature 18.

Further bushes 62, 64 are located in either end of the central bore of the first armature 18, and cylindrical brass sleeves 66, 68 are located on the interior surfaces of the coils 52 and 53.

The operation of the assembly will now be described with reference particularly to Fig. 6.

The coils 52, 53 are electrically connected (not shown) to a 34 volt downhole power pack, and the valve member 70 on the screw thread 50 of the shaft 40 is held normally closed by a substantial spring 72, or other biasing means, acting on the shaft\armature assembly 40, 18, 32. The solenoid assembly is connected to the output of a downhole "measurement while drilling" monitoring system and is actuated in response to signals therefrom.

The yokes 2, 12 and sleeve portion 56 define a housing which surrounds the shaft 40 and armatures 18, 32, the shaft passing freely through the bore 20 of the first yoke 2. The second yoke 12 is located beyond the end of the shaft 40 adjacent the second armature 32, with its planar face 16 opposing the planar face 38 of the armature 32. The first yoke 2 is spaced with its end face 6 slightly less far from the corresponding end face 24 of the first armature 18 than are the corresponding end faces 16, 38 of the second yoke 12 and second armature 32 On actuation, the power pack energises the coils 52, 53 which induces movement in the armatures 18, 32.The non-planar form of the adjacent end faces of the first yoke 2 and first armature 18 result in a greater force being induced between them than between the second yoke 12 and second armature 32, especially when they are spaced from one another as is the case before actuation. The first armature 18 therefore moves in direction A towards the first yoke 2 and, by acting against the shoulder 46, moves the shaft 40 and second armature in the same direction until the end face 24 of the first armature 18 abuts against the end face 6 of the first yoke 2. At this point the second armature 32 is still spaced slightly (about 0.030 inch) from the second yoke 12 and because of this small spacing can maintain the full opening force.Continued current from the power pack causes the second yoke 12 to continue to attract the second armature 32, and the second armature 32 and shaft 40 therefore move further in direction A until their end faces 16, 38 engage.

This movement in direction A is against the action of the spring 72, and the valve is then fully open. The final movement of the second armature 32 and shaft 40 takes the shoulder 46 out of engagement with the first armature 18.

The power requirement to maintain the valve in this fully-open position is greatly reduced from that required during movement of the shaft 40 and armatures 18, 32 due principally to the mating planar end faces 16, 38; the stepped configuration of the first yoke 2 and first armature 18 would be more energy-efficient in moving the assembly to open the valve, but would be less so in maintaining the valve open. Because of the disengagement from the shoulder the stepped armature plays no part in holding the valve open and the current to the first coil 52 is cut off.

The valve remains open in response to a continuing signal from the monitoring system, and the power requirement is only of the order of 80 mA when the second yoke 12 and second armature 32 are mating. The actuation and movement of the assembly is very rapid in order to reflect accurately the signals from the monitoring system (being of the order of 20 milliseconds from the initial application of current) and it will be seen that the provision of the oil passageways 8, 28, 38 of the armatures 18, 32 and first yoke 2, and the through bore 14 of the second yoke 12, are very important in allowing rapid flow of oil from between the mating faces of the respective yokes and armatures.

The material of construction of the yokes and armatures is iron of relatively low resistivity, which has the benefit of allowing eddy currents to built up within it, and the eddy currents maintain magnetic flux with only slow degradation on deactuation of the power pack.

This is useful in conserving power while the valve is being held open, as the power pack can be programmed to provide regular pulses of current to the yokes instead of a steady current; between the pulses the magnetic attraction of the second yokes 12 and second armature 32 is maintained as a result of the eddy currents at a sufficiently high level to hold the valve open against the action of the spring. This is illustrated in Fig.

7.

When the valve is to be closed, the monitoring system sends an appropriate signal to the power pack which is then deactuated, and after a controlled and consistent delay (resulting from the eddy current effect) the attraction between the second yoke 12 and second armature 32 degrades to an extent whereby the spring 72 moves the assembly back to its original position, closing the valve.

The combination of a strong spring of sufficient strength to close the valve without additional force being needed from a solenoid, and a low-resistivity material of construction, especially of the second yoke 12 and second armature 32, allows close consistency in the delay between power shut-off and valve closure, so that this delay can be accurately included in a detection system of drilling fluid pressure at the surface.

This embodiment of the invention therefore provides an energy-efficient means of opening, maintaining open and closing a valve in downhole monitoring apparatus which allows solenoid actuation of the valve in one direction only with non-energy-consuming spring actuation of the valve in the opposite direction.

The solenoid is included in a downhole assembly shown in Fig. 7 in which a pulser sub 50 houses a mud pulser unit 52, and a collar 54 screw-threaded to the pulser sub 50 houses solenoid driver capacitors 56, the power pack 58 and the monitoring system 66 comprising wellbore direction and temperature sensors and their associated electronics. A sub 64 and drill bit 62 are connected to the lower end of the collar 54.

Referring once again to Fig. 6, it will be seen that the assembly may be modified by the addition of further yokes and armatures to the right of the first armature 18. The shaft 40 would be extended, and further yokes similar to the first yoke 2 and further armatures similar to the first armature 18 (together with further coils, bushes and sleeves) inserted between the first yoke 2 and sleeve portion 56, each additional armature having a corresponding shoulder formed on the shaft 40.

The spacings between each yoke and armature may be varied (e.g. by making the distance between each successive yoke and armature slightly smaller than the preceding set), allowing the characteristics of the assembly to be programmed. The configuration of the opposed non-planar faces of each yoke/armature set might also be varied.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims (22)

1. A solenoid assembly comprising a first armature having a planar end face engageable with a corresponding planar end face of a first yoke and a second armature having a non-planar end face engageable with a generally complementary, non-planar end face of a second yoke, the first and second armatures being mounted on a common shaft and movable towards and away from the first and second yokes respectively, said first and second yokes each having an electrical coil associated therewith, the shaft being movable between a first position, wherein said first armature is spaced from said first yoke by a first distance and said second armature is spaced from said second yoke by a second distance less than said first distance, and a second position wherein said first armature engages said first yoke.

2. The assembly of Claim 1, wherein said non-planar faces of the second armature and second yoke are closely mating.

3. The assembly of Claim 2, wherein said non-planar faces have a complementary stepped configuration.

4. The assembly of Claim 3, wherein said non-planar faces have a complementary part-conical configuration.

5. The assembly of any of Claims 1 to 4, wherein said first and second yokes and armatures are formed from material of low resistivity.

6. The assembly of any preceding Claim, wherein said first and second yokes, first and second armatures and said shaft are all disposed along a common axis, said first and second yokes being spaced apart along said axis and said shaft extending through an axial through-bore formed in said second yoke, said first armature being fixed to said shaft intermediate said first and second yokes, and said second armature being located on said shaft adjacent said second yoke on the opposite side thereof from said first armature.

7. The assembly of Claim 6, wherein said first and second yokes are connected to one another by a sleeve defining a chamber surrounding said axis and enclosing said first armature and said first coil, and a further sleeve portion encloses said second armature and said second coil.

8. The assembly of Claim 6 or Claim 7, wherein said shaft includes a shoulder engageable by said second armature such that movement of said second armature in a first axial direction towards said second yoke causes corresponding axial movement of said shaft.

9. The assembly of Claim 8, wherein said shaft is axially movable between a first position wherein said first armature is axially spaced from said first yoke by a first distance and said second armature is axially spaced from said second yoke by a second distance, said second distance being less than said first distance, and a second position wherein said planar face of the first armature engages said planar face of the second armature, said shaft being biased by bias means towards said first position.

10. The assembly of Claim 9, wherein energisation of the coils causes said second armature to move in said first axial direction until said non-planar face thereof engages the complementary non-planar face of said second yoke, thereby urging said shaft in said first axial direction to a position intermediate said first and second positions, the shaft subsequently being moved to said second position by the attractive force between the planar faces of the first yoke and first armature.

11. The assembly of Claim 10, wherein said shaft may be maintained in said second position by periodic current pulses supplied to the first coil.

12. The assembly of any preceding Claim, wherein the assembly is enclosed within a chamber and wherein passageways are provided extending through said armatures to allow rapid displacement of fluid from one side thereof to another in response to movement of the armatures within the chamber.

13. The assembly of Claim 12, wherein the first yoke is also provided with fluid displacement passages.

14. The assembly of Claim 12 or Claim 13, wherein the second yoke is also provided with fluid displacement passageways.

15. The assembly of any preceding Claim, wherein an end of said shaft remote from said yokes and armatures is operably connected to an actuating member of a valve.

16. The assembly of Claim 15, wherein energising the coils causes said actuating member to move from a first position to a second position.

17. The assembly of Claim 16, wherein upon de-energising the assembly said actuating member is returned to its first position by bias means.

18. The assembly of any preceding Claim, wherein at least a third yoke and a third armature having complementary, non-planar, opposed faces are disposed along the shaft on said axis, spaced from said second armature on the side thereof remote from said second yoke.

19. The assembly of Claim 18, wherein the distance between the opposing faces of said third yoke and said third armature and of any further yokes and armatures is less than the distance between the opposed faces of each preceding yoke and armature.

20. A downhole tool including a solenoid assembly as claimed in any preceding Claim.

21. A solenoid assembly substantially as hereinbefore described with reference to the accompanying drawings.

22. A downhole tool substantially as hereinbefore described with reference to the accompanying drawings.