Thermochemical Actuation Method and Apparatus

The present invention relates to mechanical power supplies. It finds particular application in conjunction with creating a high pressure fluid for extensible piston actuators and will be described with particular reference thereto. However, it is to be appreciated that the invention will also find application in conjunction with other high pressure fluid systems, as well as, other mechanical power supplies, such as solenoid type actuators, pumps, motors, valve controllers, and the like.

Heretofore, various sources of mechanical power have been provided. Solenoids are a common extensible actuator. Although solenoids are relatively simple to control and relatively inexpensive, they have several drawbacks. First, solenoids produce relatively little force for their physical size. Second, solenoids generate relatively small starting forces, i.e. they do not generate full force from a dead start. Even once extended, solenoids require full power to remain in their actuated state. Further, under low voltages or marginally higher loads, solenoids stall or fail to pull. Third, the inductive coil can generate RF interference that interferes with electronic control circuitry. Also, solenoids tend to be noisy. They "clack" when pressed open and tend to chatter or buzz under heavy loads.

Electric gear motors are less easy to control than solenoids but produce more force for their physical size. However, gear motors, particularly AC operated gear motors, tend to induce RF interference which interferes with control circuitry. Like a solenoid, gear motors do not start at full force. Gear motors can stall under high start up load conditions. Gear motors tend to be relatively slow. Like solenoids, when first actuated, gear motors draw a large initial surge current. Gear motors tend to be noisy, making a growling sound as they operate.

For higher power densities, hydraulic actuators are commonly utilized. However, the control lines, pumps, fluid reservoirs, pressure regulators, and other associated support devices render hydraulic and pneumatic cylinder assemblies complex to use and space inefficient. Moreover, hydraulic systems tend to be dangerous in a failure mode. When the high pressure fluids are unexpectedly released, the pressure is sufficiently great that they can penetrate or break surrounding structures, injure human attendants either directly and though high pressure oil induced blood poisoning, or the like. Moreover, hydraulic systems tend to be associated with an undesirable whine.

The present invention contemplates a new and improved actuator which overcomes the above-referenced problems and others.

In accordance with the present invention, a pressure vessel construction is provided. The vessel defines a plurality of thin paths filled with a compound that controllably changes phases. The paths are defined by a plurality of thin structures arranged to optimize heat transfer with the phase change compound.

In accordance with a more limited aspect of the present invention, every point within the thin paths is within 0.010 inches of a fin structure. Preferably, all molecules of the compound are within 0.005 inches of the heat transfer structure.

In accordance with another more limited aspect of the present invention, the vessel and heat transfer structure are constructed of a material which has a thermal conductivity exceeding 70 BTU/hr. ft. .degree.F. and preferably at least 140 BTU/hr. ft. .degree.F.

In accordance with another more limited aspect of the present invention, a core vessel material has a tensile strength exceeding 50,000 PSI. Preferably, the vessel is a beryllium copper that is heat-treated to a state in which it has at least 95,000 PSI tensile strength.

In accordance with another more limited aspect of the present invention, the outer wall thickness is at least twice the thin path thickness.

In accordance with another more limited aspect of the present invention, the pressure vessel has a strength exceeding 5,000 PSI, preferably at least 30,000 PSI.

In accordance with another aspect of the present invention, the pressure vessel is interconnected with a fluid pressure mechanical work means for converting the fluid pressure into mechanical work.

In accordance with more limited aspects of the present invention, the fluid pressure mechanical work means includes extensible pistons, pressure domes, valve actuators, motors, and the like.

In accordance with another more limited aspect of the present invention, a means introduces heat into the pressure vessel to cause the phase change compound to change from a solid to a fluid state and for withdrawing heat from the pressure vessel to cause the phase change compounds to solidify.

In accordance with another more limited aspect of the present invention, the heat is supplied to and removed from the pressure vessel by a heat pump. More specifically to the preferred embodiment, two pressure vessels each have a vapor coil which are interconnected by a reversible compressor and an expansion valve. The compressor is selectively reversible such that either coil may function as the evaporator as the other functions as the condenser. In this manner, heat is selectively moved back and forth between the two pressure vessels.

In accordance with another aspect of the present invention, the pressure vessels move between hot and cold reservoirs alternately. Peltier chips and other means for adding or removing heat are also contemplated.

In accordance with another more limited aspect of the present invention, the fluid-mechanical means includes an extensible piston assembly and further including an extension monitoring means. A means is provided for adding and removing heat from the pressure vessel in order to maintain the piston assembly substantially at each of a plurality of monitored, preselected set points.

In accordance with another aspect of the present invention, pairs of the pressure vessels are mounted with pistons in opposing relationships. Each piston is interconnected with feedback sensors for measuring relative extension and force.

One advantage of the present invention resides in its high power density.

Another advantage of the present invention is its flexibility and simplicity of operation.

Still further advantages of the present invention reside in its silent operation, its relative freedom from stallout, the elimination of RF interference by the use of DC control currents, reduced power consumption to maintain an extended state, adaptive peak force level that automatically adapts to the application, and reliability of service even over a large number of repetitions.

Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.

The invention may take part in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiment and are not to be construed as limiting the invention.

FIG. 1 is a perspective view in partial section of an actuator including a fluid pressure generating vessel and fluid pressure to mechanical motion converter in accordance with the present invention;

FIG. 2 is a longitudinal sectional view of the system of FIG. 1;

FIG. 3 is an enlarged transverse sectional view of a portion of the pressure vessel portion of FIG. 1;

FIG. 4 is a sectional view of a motor employing a plurality of the actuators of FIG. 1;

FIG. 5 is a side sectional view of the motor of FIG. 4;

FIG. 6 is an enlarged transverse sectional view illustrating actuator mounting;

FIG. 7 illustrates an alternate embodiment of a motor utilizing a vapor phase heat pump;

FIG. 8 is an exploded view of another alternate embodiment of the present invention using thermoelectric heating and cooling means;

FIG. 9 illustrates a valve assembly incorporating an actuator analogous to that of FIG. 1 utilizing Peltier heating and cooling;

FIG. 10 is a sectional view through the pressure vessel of the actuator of FIG. 9;

FIG. 11 illustrates a multi-position spool valve controlled by the actuator of FIG. 1 utilizing Peltier heating and cooling;

FIG. 12 illustrates a pair of actuators of FIG. 1 mounted to provide differential movement utilizing Peltier heating and cooling;

FIG. 13 illustrates a plurality of the actuator pairs of FIG. 12 assembled into a robotic hand;

FIG. 14 illustrates an alternate pressure vessel core construction technique; and,

FIG. 15 illustrates a pressure vessel core assembled with the technique of FIG. 14.

With reference to FIGS. 1, 2, and 3, a pressure vessel means A selectively generates a high pressure fluid which is converted into mechanical movement by a fluid pressure-mechanical motion converting means B. The pressure o vessel means includes a multiplicity of thin paths 10 defined by a multiplicity of heat carrying and structural strength providing members or fins 12. The thin paths merge at a manifold area 14 which is interconnected with the fluid pressure to mechanical movement generating means The pressure vessel is further defined by relatively strong end walls 16 and strong, readily heat conductive faces 18. In the preferred embodiment, the thin paths 10 are cut in a single block 20 leaving three end walls 16, one face 18, and fins 12 all integrally connected. The second of faces 18 is defined by a plate 22 that is brazed by silver braze 24 to the end walls and the fins. The brazing not only provides effective heat transfers, but provides with the fins and opposite face an I-beam like structure for pressure stability.

More specifically, the pressure vessel is designed to optimize heat transfer into and out of a phase change material 26, such as a wax or polymer, that fills the thin paths and manifold area of the pressure vessel. To this end, the pressure vessel is constructed of a high thermal conductivity metal, such as beryllium copper that is alloyed to have a conductivity of at least 140 BTU/hr. ft. .degree.F. In each path, there is a point 30 which is most remote from a thermally conductive fin or metal portion. It is advantageous to make point 30 as close as possible to one of the fins or conductive surfaces. To this end, a minimum dimension 32 of the thin paths is less than 0.010 inches, at preferably less than 0.005 inches. Because most phase change materials tend to have relatively poor thermal conductivity properties relative to the thermal conductivity properties of the fins and housing, it is desirable for the minimum dimension to be only the thickness of a few molecules of the phase change material. Alternately, additional heat conductive structures can be provided for carrying heat into the thin paths more quickly. For example, thin wires or rods could extend transversely through the thin paths to improve heat transfer. As yet another alternative, the chambers may be partially filled with a porous, highly thermally conductive material such as a highly thermally conductive foam, a sintered thermally conductive material, or the like. As yet another alternative, thermally conductive particles may be suspended in the material.

The end walls 16 and faces 18 are at least as thick as the width of the thin paths and preferably at least twice as thick and of heat treated beryllium copper which has a tensile strength of 95,000 PSI. Materials with a higher tensile strength may enable the walls to be thinner, as may a willingness to work at lower pressures. Conversely, when using materials with less tensile strength, thicker walls will achieve the same vessel strength. Preferably, the overall vessel has the capacity to hold an internal pressure of 30,000 PSI. However, for some applications, only lower internal pressures are generated.

The use of fins or other heat conductive structures is provided to define a long, thin path or plurality of interconnected path segments. In an embodiment in which the pressure vessel is about 11/2" square, about 75 11/2" long path segments each having a width of 0.01" are provided. This provides a path width to length ratio of about 11,000:1. Preferably, the path length to minimum width ratio is at least 10,000:1.

The fluid pressure to mechanical movement converting means B includes a bore 40 in which a piston 42 is slidably received. Preferably, the piston and piston bore are of high strength materials, such as metal. To prevent fluid from flowing between the piston and piston bore under the high pressures generated, a low durometer seal member, such as a soft rubber disk 44 is slidably mounted in the bore 40 between the piston 42 and the fluid 26. Under the very high pressures generated, there is a tendency for the low durometer seal to flow partially in between the piston and the bore. Accordingly, a higher durometer seal member, such as a nylon or teflon disk 46, is interposed between the low durometer member and the piston. The higher durometer seal deforms sufficiently under pressure that it is pressed into sufficient conformity with the bore that the low durometer seal cannot move flow therebetween. Yet, the higher durometer seal has sufficient stiffness that the pressure does not cause the higher durometer seal to flow between the piston and the bore. Optionally, additional intermediate durometer members may be interposed, as necessary, to assure that the fluid 26 is restrained by the lowest durometer seal and that the shape integrity of each seal is maintained.

Of course, other pressure to mechanical movement devices are also contemplated. For example, a snap dome may be utilized instead of the piston. A snap dome is advantageous in that a fluid tight seal can be made between the edges of the dome and the vessel. Bellows type expansible chambers can also be utilized. As another alternative, the low durometer seal may interface with the phase change compound 26 on one side and a second fluid to be pressurized or compressed at the other. In this manner, pumping or pressurizing of a fluid is achieved without intervening mechanical members.

Although the fluid pressure to mechanical movement means B is illustrated as being at one end of the pressure vessel A, other arrangements are contemplated. For example, a second pressure reservoir may be connected to an opposite side of the piston bore and fluidly interconnected with the manifold area. Additional pressure vessels can also be interconnected at various angles with the manifold area. As yet another alternative, the manifold area may be defined in the brazed-on end plate 22 in a generally central region thereof. Conversely, a second fluid pressure to mechanical motion converting means can be connected with the pressure vessel. If the fluid pressure to mechanical motion converting means each include a piston, the pistons extend with equal pressure, but not necessarily equal travel. Numerous other placements of the pressure to mechanical motion converting means B relative to the pressure vessel A are also contemplated as may be appropriate to the application.

The phase change compound can be any of a wide variety of compounds which change dimension as they undergo a generally isothermal phase change between liquid and solid phases. The compound preferably increases about 10%-15% in volume am it changes from its solid to its liquid state. It is to be appreciated that the invention functions analogously, but inversely, with a compound that expands as it solidifies. By using a generally isothermal phase change, the compound can be expanded and contracted, i.e. moved back and forth between its solid and liquid states, by using heating and cooling sources that are only a couple of degrees apart. A suitable compound is a wax that melts at 125.degree. F. Other polymers and substances are also contemplated.

With reference to FIGS. 4, 5, and 6, a rotary motor is configured with a plurality of the actuators of FIG. 1. Specifically, a plurality of actuators 50 with rollers or cam surfaces 52 on the ends of the pistons 42 are mounted to a movable member 54, e.g. a ring. The fluid vessels extend radially outward from the ring 54. The ring and actuators are mounted to an output shaft 54 which is mounted by bearings 58 in a stationary housing 60.

The housing 60 defines an arcuate hot water bath or heating reservoir 62 and an arcuate cold water bath or cooling reservoir 64. The reservoirs each extend generally along a half circle. Fluid seals 66 are provided between the hot and cold water baths to block intermixing of the hot and cold water while allowing the pressure vessels to move therethrough. The rollers on the ends of the pistons engage an eccentric member 68 which is mounted to the stationary body 60. The eccentric member is mounted offset closest to one junction between the hot and cold water baths. When a pressure vessel first enters the hot water bath, the compound starts changing from its solid to its liquid state causing the piston to extend. Extension of the piston against the stationary eccentric member forces the actuator to move to a position where it is more remote from the eccentric member, i.e. rotate counterclockwise in the illustrated embodiment. As the fluid chamber becomes warmer, the piston extends still further until it reaches its point of maximum extension at the other interface between the hot and cold water baths. Once in the cold water bath, the composition starts to solidify, retracting the piston and allowing continued rotation about the eccentric member.

With reference to FIG. 7, rotary motion can also be produced by a pair of oppositely mounted stationary actuators 72. The piston 42 of each actuator is pivotally connected with a rotatably mounted crankshaft 72. A heat transfer means 74, preferably a vapor phase heat pump, transfers heat alternately between the two actuators causing them to cycle out of phase. Each actuator includes a coil 76 which is able to function as either an evaporator coil or a condenser coil. A reversible compressor or valve arrangement 78 for reversing flow pumps heat from one actuator to the other during about 180.degree. rotation of the crankshaft. During the second 180.degree. of rotation of the crankshaft, the compressor reverses and pumps the heat in the other direction. More specifically, freon gas is compressed by the compressor. The compressing elevates the temperature of the compressed gas or freon liquid, which hot freon liquid carries heat to one of the coils which is functioning as a condenser. The condenser coil heats the associated actuator. An expansion valve so allows the freon liquid to evaporate, it adsorbs heat, becoming cold. The cold freon gas flows through the other of coils 76 which is functioning as a condenser coil, removing heat from the other actuator. Once 180 of rotation is completed, the compressor reverses, reversing which of coils 76 functions as the condenser and which functions as the evaporator. In this manner, heat is moved in the other direction. Because a heat pump works most efficiently when moving heat between two reservoirs of substantially the same temperature, the heat pump system works near optimal efficiency.

A pair of additional heat transfer means 82, preferably vapor phase heat pumps, are provided to replace heat losses at the two actuators. Specifically, each of the heat pumps 82 include a compressor 84 which selectively compresses freon removing heat from the ambient air or other heat source and discharging it into the associated actuator through a condenser coil 86. An expansion valve 88 allows the freon liquid to expand to the gaseous state, absorbing heat from the ambient air. If the ambient air or other reservoir from which heat is removed is close to the working temperature of the actuators, the heat pump 82 again works at high efficiency.

With reference to FIG. 8, thermoelectric chips 90, such as peltier chips, are placed against faces 18 of the pressure vessel. Heat sinks, such as an array of fins 92 are mounted to opposite sides of the thermoelectric chips. The thermoelectric chips efficiently move heat from the ambient air into the pressure vessel A and from the pressure vessel back out to the ambient air. High and low travel limit switches 94, 96, respectively, monitor for the piston to reach first and second degrees of extension. The first and second degrees of extension may be fully extended and fully retracted configurations. Alternately, the two degrees of extension may be half and fully extended states, or the like.

In the illustrated embodiment, the piston 42 engages a lever 98 which is cammed about a pivot point. The lever is interconnected at one end with associated equipment which is to be powered. The other end of the lever engages the limit switches 94, 96.

With reference to FIGS. 9 and 10, a valve body housing 100 has a valve member 102 biased by a spring 104 across a valve seat 106. In the preferred embodiment, fluid under pressure from an inlet end assists the spring in biasing the valve member 102 against the valve seat 106. An actuator 108 selectively moves the valve member away from the valve seat to permit fluid flow through the valve.

The actuator includes a pressure vessel 110 of substantially the construction illustrated in FIGS. 1-3. That is, a multiplicity of small passages or thin passages 112 filled with the phase change composition funnel to a manifold area 114. The manifold area connects with a bore 116 in which a piston 118 is mounted. A heat transfer means 120, such as a Peltier chip, selectively adds or removes heat from the pressure vessel 110. Depending on the temperature of the fluid flowing through the valve, the fluid in the valve can be used either add or remove heat from the pressure vessel. For example, if cool water flows through the valve, heat can be added by the heat change means, such as electric resistance heating, to change the composition from its solid to its liquid states. Heat continues to be applied until it is desired to allow the valve to close. When heat is no longer applied, the cooling from the water flowing through valve removes heat from the phase change compound solidifying it, allowing the spring 104 to expand closing the valve.

With reference to FIG. 11, a three-way spool valve is provided. A spool member 130 is slidably mounted in a housing 132. An actuator 134, generally of the construction illustrated in FIGS. 9 and 10, but with longer piston travel has a piston 136 for moving the spool member against a spring 138. In the preferred embodiment, the piston has a tapered surface 136a in a confined chamber, against which the phase change compound presses. A monitoring means 140 monitors the position of the spool member hence the extension of the piston. In the illustrated embodiment, the monitoring means includes a spool extension 142 having recesses 144 for engaging a limit switch 146. When the vessel of actuator 134 is heated, the spindle is moved to the right. When the vessel of actuator 134 is cooled, the spring 138 moves the spool member toward the left.

A control means 148 controls the heat transfer means 150 into and out of a phase change compound holding chamber arrangement 152 in an annular ring around the confined piston chamber of the actuator 134. More specifically in a first, left-most position, the heat transfer means cools the vessel. For a middle position of the spool, heat is applied until the monitor means 140 determines the middle position is reached. The control means causes increased heating and decreased heating (or cooling) in response to the monitoring means determining that the spool is shifting left or right, respectively, from the selected position. For the third, right-most position, the control means 148 causes more heat to be added. When the third position is reached, heating of the vessel is again controlled as necessary to maintain the third position. Analogously, the piston 136 can be controlled to move among and hold at four or more degrees of extension.

With reference to FIGS. 12 and 13, a pair of pressure vessels 160, 162 are mounted parallel to each other, with a common temperature transfer means 164 therebetween. Pistons 166, 168 of fluid pressure to mechanical motion converting means 170, 172 associated with each pressure vessel selectively extend and contract. Piston extension sensor means 174 provides an output signal indicative of the degree of relative piston extension. A pressure sensing means 176 senses the pressure within the pressure vessel, hence the pressure with which each piston is being extended. Based on this information, a computer control means selectively supplies electricity to the temperature controlling means 164 to adjust the relative extension and contraction of the pistons. As illustrated in FIG. 13, a multiplicity of these dual piston, dual controlled actuators can be interconnected in various robotic configurations, such as a hand configuration.

With reference to FIGS. 14 and 15, the pressure vessel A can be fabricated with different techniques. For example, a thin sheet of thermally conductive material 180 such as beryllium copper alloy, is accordion pleated. The accordion pleated sheet is coated with the phase change material and compressed between end blocks 182. Alternately, the phase change material may be drawn in its liquid state into the paths after assembly top and bottom plates 184 are brazed at least to the end blocks and preferably to the pleated sheet for thermal conductivity and strength. The open ends of the compressed accordion pleated sheet are connected with a structure (not shown) that defines a manifold area leading to a piston bore as in FIGS. 1 and 2.

Numerous applications of these actuators readily identify themselves. In the automotive area, actuators can readily be used to control windshield wipers, power seats, power windows, power mirrors, power trunk openers, choke actuators, and other mechanisms which require proportional travel or variable rates of movement. The actuators are also suitable for power trunk latches, gas cap latches, rotating headlamp or headlamp covers, starter solenoids, axle shift devices, inter-axle shift devices, and the like which require merely on/off states.

The actuators also find uses in appliances including a number of directly actuated valves, gravity drain valves, dishwasher drain valves, three-way hydraulic-type valves, metering valves, pressure control valves, washing machine valves, video tape cassette ejection mechanisms, power door openers, ventilation duct damper actuators, ice cube dump mechanisms, zone valves, office equipment, and the like. The actuators can also be adapted for use with a variety of powered hand held devices, such as riveters, embossers, shears, hose crimpers, and the like. The technology is also useful for replacing explosive bolts, expandable rivets, one shot safety brake systems, deployable booms, field swaging operations, fly-by-wire actuators, large hydraulic valve actuators, proportional controllers, robotics, and the like.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended to that the invention be construed as including all such alterations and modifications insofar as they come within the scope of the appended claims or the equivalents thereof.