Electro fluidic actuator

An electro-hydraulic (EH) actuator for converting electrical inputs into hydraulic output signals is described. The actuator features a pressure balanced design which permits operation at high absolute pressures without performance degradation. Internal portions of the EH actuator are filled with a non-conducting fluid, while a flexible diaphragm provides a movable interface between the fluid and the environment in order to equalize the internal and external pressures on the actuator.

BACKGROUND OF THE INVENTION 
Electro-hydraulic actuators can be used as signal generators in general 
hydraulic applications. Of particular interest is the use of an EH 
actuator in conjunction with a fluidic mud-pulse telemetry transmittor. 
Mud-pulse telemetry is a technique for transmitting information from the 
bottom of a well bore to a position at the top of the well where the 
information may be utilized to control the drilling operation. Sensors 
located near the drill bit provide electrically coded signals 
representative of conditions such as temperature, pressure, etc. existing 
at the bottom of the wellbore. These signals are applied to an EH actuator 
which controls the operation of a fluidic pulsing device. Pulses are 
generated in the drilling fluid which flows through the drill string, and 
may be detected by suitable transducers located at a convenient position 
at the well head. The coded information represented by the pulses may be 
interpreted by the drill string operator for use in controlling the 
drilling operation. The operation of a mud-pulse telemetry system is more 
particularly described in U.S. Pat. No. 4,276,943 issued July 7, 1981 to 
Holmes and in U.S. Pat. No. 4,323,991 issued Apr. 6, 1982 to Holmes et 
al., the disclosures of which are incorporated herein by reference. 
In most drilling operations pressures at the drill bit are extremely high, 
generally on the order of 20,000 psi. Electro-hydraulic actuators 
currently known are incapable of operating efficiently at such high 
pressures. Generally, a great deal of power must be provided to the 
actuator in order to counteract the high pressure and provide a control 
impulse. This is troublesome as power at the drill bit is generally 
limited, normally being provided by batteries or a low powered mud 
turbine. Also, the tremendous pressures encountered by the actuator 
normally slow the actuators response time to a rate which is insufficient 
to transmit adequate amounts of data to the drill bit operator. 
Accordingly, it is an object of this invention to provide an EH actuator 
which is capable of operation at very high bore hole pressures with only 
minimal electrical power. 
It is an object of the invention to provide such an actuator having a rapid 
response rate at high pressures enabling the device to transmit large 
quantities of information as required in a mud-pulse telemetry system. 
It is yet another object of the invention to provide an EH actuator which 
is durable when operating under very high pressure conditions, the 
components of which are insulated from the corrosive and erosive effects 
of working fluids. 
SUMMARY OF THE INVENTION 
The actuator of the present invention comprises a casing or housing which 
contains a solenoid actuated plunger for generating hydraulic pressure 
pulses. A flexible diaphragm or bellows extends between the plunger faces 
and the housing. All internal portions of the actuator are filled with a 
non-conducting fluid, while a flexible diaphragm provides an interface for 
equalizing the internal and external pressures acting on the actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a first embodiment of the actuator, generally designated 
by the reference numeral 12. The actuator comprises a housing 4 containing 
a coil 8 and the plunger or rod 6 which extends axially through opposite 
openings 7, 9 in the housing 4. The housing 4 is generally made of iron to 
provide a magnetic circuit. The rod 6 has working faces 10 and 12 at the 
ends thereof, and an annular stop member 26 secured thereto. Flexible 
diaphragms, shown here as lightweight, low inertia, highly compliant, 
metallic bellows 14 and 16, extend between the working faces 10 and 12, 
respectively, and the housing 4. The bellows 14, 16 include closed outer 
end portions 13, 15 which respectively overlie and connect with the rod 
working faces 10, 12, pleated side portions 17, 19 which extend coaxially 
along the rod 6, and open inner end portions 18, 20 which are secured to 
the housing 4 about the openings 7, 9, respectively by means of a 
permanent metallic bond such as welding or brazing. The diameters of the 
housing openings 7 and 9 are considerably larger than the diameter of the 
rod 6 extending concentrically through these openings 7 and 9, to provide 
passages between the interior of the housing 4 and the interiors of the 
bellows 14 and 16, respectively. 
The actuator comprises an additional lightweight, low inertia, highly 
compliant, bellows 22, similar to the bellows 14 or 16. This bellows is 
also metallic, and includes an open inner end portion 24 which is 
permanently secured to the housing 4 concentrically about another opening 
21 of the housing 4. As shown in FIG. 1, the diameter of the housing 
opening 21 is larger than the minimum diameter of the pleated side portion 
23 extending between the inner end portion 24 and the closed outer end 
portion 25 of the bellows 22, to establish essentially unrestricted 
communication between the interior of the housing 4 and the interior of 
the bellows 22. Switch circuit 34 provides power to the coil 8 by means of 
electrical leads which pass through openings 35 in the housing. These 
openings 35 are sealed by suitable means such as epoxy. Thus, the housing 
4 and the bellows 14, 16 and 22 bonded thereto form a completely sealed 
and fluid tight enclosure for the elements of the actuator. 
The internal portion of the actuator is filled with a non-conducting fluid 
36 which is, for example, Dow Corning silicon oil or other transformer 
oils which are well known. This fluid provides for electrical insulation 
of the internal contacts and for maintaining internal pressure. When the 
actuator is submerged in a fluid, such as the drilling fluid passing 
through a drill string, external pressure acting on bellows 22 will 
pressurize the fluid 36 inside the actuator housing. This will transmit 
the external pressure to all of the internal elements of the actuator 
device. Since the bellows 22 is free to move and react to changes in the 
external pressure, the pressure inside the actuator will always be equal 
to the pressure on the exterior thereof. 
This equalization of pressure results in a zero net force acting on all 
working elements of the actuator. There is no existing pressure 
differential which must be overcome by the device. Therefore, the 
electrical power necessary to move the rod 6 and create a pressure pulse 
is greatly reduced as compared to prior art devices. Also, the reduced 
pressure eliminates much or all of the strain normally imposed on the 
structural elements of the apparatus. 
In operation, when the circuit 34 is in opened condition as shown in FIG. 
1, the rod or plunger 6 is urged to the right by means of spring 30 
compressed between the housing and the working face 10. Travel of the 
plunger to the right is limited by abutment of element 26 with the housing 
4. If a control signal is provided to circuit 34, thereby closing the 
circuit, coil 8 is energized urging plunger 6 to the left against the 
action of the spring 30. Travel of the plunger to the left will be limited 
by the fact that spring 30 is interposed between the housing and the 
working face 10. As the plunger moves to the left, the bellows 16 will be 
extended while the bellows 14 will be compressed. A positive pressure 
pulse will be generated in the fluid contacting the face of the working 
element 12. When the circuit 34 is again opened, the spring 30 will urge 
the plunger 6 back toward the right thus generating a pressure pulse in 
the fluid contacting the face of the working element 10. 
FIG. 2 shows another embodiment of the present invention which is 
substantially similar to that of FIG. 1, similar elements being denoted by 
like reference numerals. In this embodiment the spring 30 is eliminated 
and a second coil 9 is provided. The electrical circuit is modified so 
that either of coils 8 or 9 may be energized by closing either of circuits 
34 or 34', respectively. When coil 8 is energized the plunger 6 is urged 
to the right, while the coil 9 will urge the plunger to the left. 
Alternately energizing the two coils will cause the plunger or rod 6 to 
oscillate back and forth. Travel of the plunger is limited by the abutment 
elements 26 and 28. 
The embodiments of FIG. 2 is capable of more rapid oscillation than that of 
FIG. 1. Therefore, more rapid control of a fluidic pulsing device may be 
achieved. The travel rate of the plunger 6 in either the left or the right 
directions is determined by the magnetic circuit rather than the spring as 
shown in FIG. 1. Also, since the plunger would not have to work against 
the spring in travelling in the left direction, response time will be 
reduced as well as the power required to move the plunger. Due to the 
pressure balanced design of the present invention, this action can be 
accomplished regardless of the magnitude of the external ambient pressure. 
FIG. 3 shows an embodiment of the present invention substantially similar 
to that of FIG. 1. In this embodiment, the plunger 6 comprises only a 
single working face 10. When circuit 34 is closed the plunger 6 will be 
urged to the left, thus creating a negative pressure pulse in the fluid 
contacting the working face 10. When the circuit is again opened, spring 
30 will urge the plunger back toward the right, generating a positive 
pressure pulse in the fluid contacting the working face. 
FIG. 4 illustrates the manner in which the EH actuator of the present 
invention is mounted in a fluidic pulsing device. The actuator 2 is 
positioned at the junction of control channels 40 and 41 of the 
amplification device. An additional opening 42 is provided in the 
amplification device to facilitate exposure of the diaphragm 22 to ambient 
fluid pressure. The actuator shown in FIG. 4 is constructed in the manner 
as shown in FIG. 1 or FIG. 2. As the bellows 14 and 16 extend alternately 
into channels 41 and 40, respectively, positive pressure pulses are 
generated in these channels. 
As shown in FIG. 5A, when a pressure pulse P is generated in channel 40, 
fluid flow F through the fluid amplification device will be deflected 
toward the right-most outlet channel. When the plunger of the actuator 
moves to the right as shown in FIG. 5B, the pressure pulse P generated in 
channel 41 will deflect the flow F to the left-most output channel of the 
amplification device. 
FIGS. 6A and 6B illustrate the manner in which the device as shown in FIG. 
3 will control fluid flow through an amplification device. As shown in 
FIG. 6A, when the bellows 14 is extended by the actuator 2 a positive 
pulse P will deflect the flow F to the right-most outlet channel. When the 
bellows is retracted by the actuator, as shown in FIG. 6B, the negative 
pressure pulse P will deflect the flow F to the left-most channel of the 
fluid amplification device. 
FIG. 7 illustrates a modified form of the invention. In the device of FIG. 
7 an integral bladder element 44 is formed over the entire actuator 
device. This may be formed, for example, by molding an envelope of rubber 
or like material about the device. Portions of the bladder overlie the 
housing 4 in intimate contact therewith, while other portions of the 
bladder form the diaphragms or bellows 14, 16 and 22. Use of the integral 
bladder of FIG. 7 eliminates the need for securing each metallic bellows 
individually to the housing 4 as in the other embodiments described. The 
bladder also provides for fluid tight seals at the openings 35, thus 
eliminating the need to seal these openings with epoxy or the like. In all 
other respects, the embodiment of FIG. 7 operates in the same manner as 
the previously described form of the invention. While FIG. 7 shows a 
single coil and a spring, as shown in FIG. 1, it is to be understood that 
the internal working elements of such an embodiment could comprise the 
dual coils as shown in FIG. 2. Also, the bladder enclosure shown in FIG. 7 
could comprise a single working bellows 14, as shown in FIG. 3, rather 
than dual bellows 14 and 16 as shown. 
The pressure balanced design of the actuator of the present invention 
enables it to operate at very high fluid pressures with only minimal 
electrical power. This is extremely advantageous in applications such as 
bore hole telemetry wherein power is severely limited. The highly 
compliant, lightweight low inertia bellows materials also provide for 
lower power consumption. 
The pressure balanced design also eliminates most substantial stresses on 
the structural elements of the actuator of the present invention. Also, 
complete isolation of the internal components from the working fluids 
eliminates the erosive and corrosive effects of these fluids. The actuator 
is therefore extremely durable as compared to such devices known in the 
prior art. 
Operating temperatures are limited only by magnetic circuit restrictions. 
Depending on coil design, digital or analog output signals may be provided 
by the device of the present invention. The short stroke of the plunger 
which is possible with the present device (0.05 inches) makes it suitable 
for use in extremely confined locations, such as a mud pulse telemetry 
transmitter. 
While the invention has been disclosed with reference to the accompanying 
drawings, I do not wish to be limited to the details shown therein as 
obvious modifications can be made by one of ordinary skill in the art.