Note: Descriptions are shown in the official language in which they were submitted.
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1 TITLE OF INVENTION
3 "Solenoid Assembly"
This invention relates to a solenoid assembly.
7 BACKGROUND OF THE INVENTION
9 Solenoids are employed in many situations in which
remote actuation of valves and other movable items is
11 required. One such situation is in downhole
12 monitoring systems in the oil industry in which
13 conditions of temperature, pressure and the like are
14 detected in an oil well and the results transmitted to
the surface; the transmission can be by introducing a
16 pulse or series of pulses of pressure in the drilling
17 fluid delivery system by opening and closing a valve to
18 direct the drilling fluid from its normal route. This
19 valve is actuated by solenoids.
21 Since the valve must be both opened and closed, some
22 existing systems include double-acting solenoid
23 assemblies in which a first solenoid is directed to
24 moving an armature in one direction and a second
solenoid moves it in the opposite direction. This
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1 means that the assembly must be of substantial size,2 and difficult to fit successfully within a downhole
3 unit. The speed of opening of the valve is important
4 and consequently the solenoid must develop a high
force.
7 . Further, the positive actuation of the solenoid
8 assembly in opening and closing the valve causes
9 substantial demands on the downhole battery pack power
supply.
11
12 SUMMARY OF THE INVENTION
13
14 According to the present invention there is provided a
solenoid assembly comprising a first armature having a
16 planar end face engageable with a corresponding planar
17 end face of a first yoke and a second armature having a
18 non-planar end face engageable with a generally
19 complementary, non-planar end face of a second yoke,
the first and second armatures being mounted on a
21 common shaft and movable towards and away from the
22 first and second yokes respectively, said first and
23 second yokes each having an electrical coil associated
24 therewith, the shaft being movable between a first
position, wherein said first armature is spaced from
26 said first yoke by a first distance and said second
27 armature is spaced from said second yoke by a second
28 distance less than said first distance, and a second
29 position wherein said first armature engages said first
yoke.
31
32 The ~on-planar faces of the second armature and the
33 second yoke are preferably closely mating and may be,
34 for example, of stepped or conical configuration.
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1 The assembly may be disposed in an oil-filled chamber,
2 for example when used in a downhole monitoring system,
3 in which case the movement of the armatures into and
4 out of engagement with their respective yokes may be
subjected to substantial resistance from the oil thus
6 preventing rapid movement of the armatures. This can
7 be alleviated by providing passageways through the
8 armatures, preferably opening through the end faces, to
9 allow rapid displacement of the oil from between the
opposed faces.
11
12 The assembly may be connected to a valve member so that
13 actuation of the assembly actuates the valve. This is
14 of especial use in downhole monitoring systems where
rapid actuation of the valve is necessary. In such
16 cases the assembly is preferably arranged to actuate
17 the valve in one direction only, for example to open
18 it, and movement in the opposite direction is
19 accomplished by the effect of a spring or other
resilient means.
21
22 The armatures are preferably of low resistivity
23 material so that deactuation of the yokes causes
24 degradation of the magnetic attraction between the
yokes and the armatures instead of a more rapid effect.
26
27 BRIEF DESCRIPTION OF THE DRAWINGS
28
29 Embodiments of the invention will now be described by
way of example with reference to the accompanying
31 drawings, in which:-
32
33 Fig. 1 ~a), (b) and (c) are respectively an end
34 elevation, a sectional elevation and an elevation
of a first yoke of an assembly of the invention;
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1 Fig. 2 (a), (b) and (c) are respectively an end
2 elevation, a sectional elevation and an elevation
3 of a second yoke of the assembly;
4 Fig. 3 (a) and (b) are respectively an end
elevation and a sectional elevation of a first
6 armature of the assembly;
7 Fig. 4 (a) and (b) are respectively an end
8 elevation and a sectional elevation of a second
9 armature of the assembly:
Fig. 5 is an elevation of a shaft for mounting the
11 yokes and armatures of Figs 1 to 4;
12 Fig. 6 is a schematic sectional elevation of a
13 part of the assembly showing the arrangement of
14 the armatures on a central shaft;
Fig. 7 is an exploded view of a downhole assembly
16 which include a solenoid assembly of this
17 embodiment; and
18 Fig. 8 is a graph of current flowing through the
19 second armature against time during the phase in
which the valve is being held open.
21
22 DESCRIPTION OF PREFERRED EMBODIMENTS
23
24 Referring to the drawings, the assembly of this
embodiment of the invention is designed for use
26 downhole in an oil well to actuate a valve for
27 transmitting signals from a monitoring system through a
28 drilling fluid circulation system to the surface.
29
The assembly includes a first yoke 2 (Fig. 1) of
31 generally cylindrical form with a central axial bore 4
32 therethrough. The yoke has its outer wall stepped
33 inwardly towards one end, having a shoulder 5 for
34 receiving a first coil (52, Fig. 6) terminating in a
small-diameter portion 6. Oil through-passageways 8
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1 are provided in the yoke 2. The end face 10 is planar
2 and normal to the yoke's main axis.
4 A second yoke 12 (Fig. 2) also is of cylindrical form
with a through bore 14 and has a planar end face 16
6 normal to the main axis of the yoke 12. A shoulder 17
7 is provided for receiving a second coil t53, Fig. 6).
9 A first armature 18 (Fig. 3) is generally cylindrical
with a through bore 20 which increases in diameter in
11 steps from a central portion 26 to an end portion where
12 it forms a rebate 22 whose end face 24 is planar. oil
13 through-passageways 28 extend from the face 24 through
14 the armature 18 and oil grooves 30 are formed in the
outer cylindrical wall. The stepped end portions of
16 the first yoke 2 and first armature 18 provide
17 complementary, non-planar end faces.
18
19 A second armature 32 (Fig. 4) is of cylindrical form
and has a partial bore 34 internally screw-threaded at
21 36. Oil through-passageways 38 extend from an end
22 planar face 38 through the armature 32.
23
24 Fig. 5 shows a stepped shaft 40 for receiving the yokes
2, 12 and armatures 18, 32 as shown in Fig. 6, the
26 second armature 32 being engageable through its screw
27 thread 36 with a corresponding external screw thread 42
28 on the shaft 40, so that the second armature 32 is
29 fixed in position at one end of the shaft 40. The
first armature 18 fits over a smaller-diameter length
31 44 of the shaft 40 and is slidable axially thereon,
32 being limited in its movement in one direction by a
33 shoulder 46. An end portion 48 of the shaft 40
34 opposite to that having the screw thread 42 also has a
screw thread 50 for receiving a connection to a valve
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1 member (70, indicated schematically by broken lines in
2 Fig. 6) for opening and closing passage of drilling
3 fluid.
As seen in Fig. 6, the shaft 40, with the second
6 armature 32 attached to one end, extends through the
7 central bore of the first yoke 2. The second yoke 12
8 engages the open cylindrical end of the first yoke 2,
g enclosing the second coil 53 mounted on the second yoke
12 and the second armature 32. A bush 54 is located in
11 the central bore of the first yoke 10, and includes a
12 spacer portion 55 which limits the movement of the
13 second armature 38 to the right (as seen in the
14 drawing)~ so defining the spacing between the opposed
end faces of the second yoke 12 and armature 32.
i6
17 A sleeve member 56, somewhat similar to the first yoke
18 2, engages the end of the first yoke 2 remote from the
19 second yoke 12 to enclose the first coil 52 and the
first armature 18. A further bush 58 is located in a
21 bore 60 formed in the outer end of the sleeve portion
22 56, the bush 58 also including a spacer portion 59
23 which limits the movement to the right of the first
24 armature 18.
26 Further bushes 62, 64 are located in either end of the
27 central bore of the first armature 18, and cylindrical
28 brass sleeves 66, 68 are located on the interior
29 surfaces of the coils 52 and 53.
31 The operation of the assembly will now be described
32 with reference particularly to Fig. 6.
33
34 The coils 52, 53 are electrically connected (not shown)
to a 34 volt downhole power pack, and the valve member
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1 70 on the screw thread 50 of the shaft 40 is held
2 normally closed by a substantial spring 72, or other
3 biasing means, acting on the shaft\armature assembly
4 40, 18, 32. The solenoid assembly is connected to the
output of a downhole "measurement while drilling"
6 monitoring system and is actuated in response to
7 signals therefrom.
9 The yokes 2, 12 and sleeve portion 56 define a housing
which surrounds the shaft 40 and armatures 18, 32, the
11 shaft passing freely through the bore 20 of the first
12 yoke 2. The second yoke 12 is located beyond the end
13 of the shaft 40 adjacent the second armature 32, with
14 its planar face 16 opposing the planar face 38 of the
armature 32. The first yoke 2 is spaced with its end
16 face 6 slightly less far from the corresponding end
17 face 24 of the first armature 18 than are the
18 corresponding end faces 16, 38 of the second yoke 12
19 and second armature 32
21 On actuation, the power pack energises the coils 52, 53
22 which induces movement in the armatures 18, 32. The
23 non-planar form of the adjacent end faces of the first
24 yoke 2 and first armature 18 result in a greater force
being induced between them than between the second yoke
26 12 and second armature 32, especially when they are
27 spaced from one another as is the case before
28 actuation. The first armature 18 therefore moves in
29 direction A towards the first yoke 2 and, by acting
against the shoulder 46, moves the shaft 40 and second
31 armature in the same direction until the end face 24 of
32 the first armature 18 abuts against the end face 6 of
33 the first yoke 2. At this point the second armature 32
34 is still spaced slightly (about 0.030 inch) from the
second yoke 12 and because of this small spacing can
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1 maintain the full opening force. Continued current
2 from the power pack causes the second yoke 12 to
3 continue to attract the second armature 32, and the
4 second armature 32 and shaft 40 therefore move further
in direction A until their end faces 16, 38 engage.
6 This movement in direction A is against the action of
7 the spring 72, and the valve is then fully open. The
8 final movement of the second armature 32 and shaft 40
g takes the shoulder 46 out of engagement with the first
lo armature 18.
11
12 The power requirement to maintain the valve in this
13 fully-open position is greatly reduced from that
14 required during movement of the shaft 40 and armatures
18, 32 due principally to the mating planar end faces
16 16, 38; the stepped configuration of the first yoke 2
17 and first armature 18 would be more energy-efficient in
18 moving the assembly to open the valve, but would be
19 less so in maintaining the valve open. Because of the
disengagement from the shoulder the stepped armature
21 plays no part in holding the valve open and the current
22 to the first coil 52 is cut off.
23
24 The valve remains open in response to a continuing
signal from the monitoring system, and the power
26 requirement is only of the order of 80 mA when the
27 second yoke 12 and second armature 32 are mating. The
28 actuation and movement of the assembly is very rapid in
29 order to reflect accurately the signals from the
monitoring system (being of the order of 20
31 milliseconds from the initial application of current)
32 and it will be seen that the provision of the oil
33 passageways 8, 28, 38 of the armatures 18, 32 and first
34 yoke 2, and the through bore 14 of the second yoke 12,
are very important in allowing rapid flow of oil from
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1 between the mating faces of the respective yokes and
2 armatures.
4 The material of construction of the yokes and armatures
is iron of relatively low resistivity, which has the
6 benefit of allowing eddy currents to built up within
7 it, and the eddy currents maintain magnetic flux with
8 only slow degradation on deactuation of the power pack.
9 This is useful in conserving power while the valve is
being held open, as the power pack can be programmed to
11 provide regular pulses of current to the yokes instead
12 of a steady current; between the pulses the magnetic
13 attraction of the second yokes 12 and second armature
14 32 is maintained as a result of the eddy currents at a
sufficiently high level to hold the valve open against
16 the action of the spring. This is illustrated in Fig.
17 7.
18
19 When the valve is to be closed, the monitoring system
sends an appropriate signal to the power pack which is
21 then deactuated, and after a controlled and consistent
22 delay (resulting from the eddy current effect) the
23 attraction between the second yoke 12 and second
24 armature 32 degrades to an extent whereby the spring 72
moves the assembly back to its original position,
26 closing the valve.
27
28 The combination of a strong spring of sufficient
29 strength to close the valve without additional force
being needed from a solenoid, and a low-resistivity
31 material of construction, especially of the second yoke
32 12 and second armature 32, allows close consistency in
33 the delay between power shut-off and valve closure, so
34 that this delay can be accurately included in a
detection system of drilling fluid pressure at the
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1 surface.
3 This embodiment of the invention therefore provides an
4 energy-efficient means of opening, maintaining open and
closing a valve in downhole monitoring apparatus which
6 allows solenoid actuation of the valve in one direction
7 only with non-energy-consuming spring actuation of the
8 valve in the opposite direction.
The solenoid is included in a downhole assembly shown
11 in Fig. 7 in which a pulser sub 50 houses a mud pulser
12 unit 52, and a collar 54 screw-threaded to the pulser
13 sub 50 houses solenoid driver capacitors 56, the power
14 pack 58 and the monitoring system 66 comprising
wellbore direction and temperature sensors and their
16 associated electronics. ~ sub 64 and drill bit 62 are
17 connected to the lower end of the collar 54.
18
19 Referring once again to Fig. 6, it will be seen that
the assembly may be modified by the addition of further
21 yokes and armatures to the right of the first armature
22 18. The shaft 40 would be extended, and further yokes
23 similar to the first yoke 2 and further armatures
24 similar to the first armature 18 (together with further
coils, bushes and sleeves) inserted between the first
26 yoke 2 and sleeve portion 56, each additional armature
27 having a corresponding shoulder formed on the shaft 40.
28 The spacings between each yoke and armature may be
29 varied (e.g. by making the distance between each
successive yoke and armature slightly smaller than the
31 preceding set), allowing the characteristics of the
32 assembly to be programmed. The configuration of the
33 opposed non-planar faces of each yoke/armature set
34 might also be varied.
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l Modifications and improvements may be incorporated
2 without departing from the scope of the invention.
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