BACKGROUND OF THE INVENTION Microvalves employed to control the flow of fluid are presently in use, with several designs falling within a class known as micro electromechanical systems or "MEMS."It will be appreciated that such microvalves are preferably driven thermally or electrostatically. In either case, slots or other types of openings are placed in an open or closed position, respectively, preferably within a shutter-type configuration so as to permit or prevent fluid from flowing therethrough. Typically, prior art microvalves involve lateral movement of the shutter which is linear. Lateral movement of the shutter may also be non-linear (i. e., rotational), as disclosed in a separate provisional patent application entitled"Microvalve For Controlling Fluid Flow,"having Serial No. 60/146,625, which is owned by the assignee of the present invention and hereby incorporated by reference. In this way, the amount of opening can be maximized by a minimal amount of movement.

To eliminate the need for continuous power to such microvalves, latching systems are preferably employed to maintain the shutter in position.

One example of latching is disclosed in U. S. 5,837,394 to Schumm, Jr., where a detent or ratchet is provided to assist in holding a sliding portion of a semiconductor microactuator in either the open or closed position. As seen therein, though, separate actuators are utilized to move the sliding portion in each direction. In this way, the actuators must overcome the resistance provided by the detent/ratchet so that the sliding portion is able to move into the desired position. This clearly requires a greater force from the actuators, and therefore a greater amount of power to the actuators. Further, it will be seen that the'394 patent relates specifically to electrically activated, thermally responsive semiconductor valves that include and contain a cantilever deformable element which deforms on heating by electrical resistance.

It will further be appreciated that while microvalves of the type disclosed herein may be utilized in any number of environments, one specific application has been in the field of metal-air batteries. Metal-air batteries have decided advantages over other types of electrochemical cells such as typical alkaline (zinc/manganese dioxide) or lithium batteries. The metal-air batteries utilize a gas reactant, such as oxygen or air, which does not have to be stored in the battery like a solid reactant. The gas reactant may enter the cell through vents or holes in the battery case. Thus, metal-air batteries are able to provide a higher energy density (watts per unit mass) that may result in a relatively higher power output and a relatively lower weight. This is particularly useful in applications in which a small, light battery is desired so that more energy is provided in the same size package or the same amount of energy in a smaller package. Metal-air batteries are also environmentally safe and generally leakage-free.

Metal-air batteries are comprised of one or more electrochemical cells. Each cell typically includes a metal anode and an air cathode with a separator electrically isolating the two, where an electrolyte is present in the anode, cathode and separator. The metal anode usually comprises a fine-grained metal powder, such as, but not limited to, zinc, aluminum or magnesium, blended together with an aqueous electrolyte, such as potassium hydroxide, and a gelling agent into a paste. The air cathode is a catalytic structure designed to facilitate the reduction of oxygen and typically comprises active carbon, a binder and a catalyst, which are formed into a sheet together with a metal current collector. The air cathode also commonly incorporates a hydrophobic polymer, such as polytetrafluoroethylene or polypropylene, directly into the cathode sheet and/or as a coextensive film. The hydrophobic polymer prevents the electrolyte from passing through the cathode and leaking from the cell.

In a metal-air battery, oxygen, through a series of reactions, reacts with the metal in the cell producing electrical current. In a zinc-air cell, for example, oxygen enables a charge/discharge reaction at the cathode (positive electrode): I/202+H20+2e~9 20H-.

Meanwhile, a charge/discharge reaction occurs at the anode (negative electrode): Zn+20H~9ZnO+H20+2e~.

Hence, the zinc-air cell has an overall reaction: Zn+l/2029ZnO.

Typically, metal-air batteries utilize ambient air, which contains approximately 21% oxygen, as the reactant for the cells. The ambient air enters through ventilation holes in the housing. In the housing, the oxygen in the ambient air reacts with the cells. The oxygen-depleted air then exits the housing. Thus, ambient air enters or is drawn into the housing in a flow sufficient to achieve the desired power output.

Free flow of ambient air through the metal-air cell, however, creates several problems that may lower the efficiency of a metal-air cell or even cause the cell to fail prematurely. First, ambient air that enters the electrochemical cell will continue to react with the anode regardless of whether the cell is providing electrical energy to a load.

Thus, the capacity of the cell will continue to decrease unless air is excluded while the cell is not providing electrical energy to a load. Another problem with allowing free flow of ambient air as the reactant is the difficulty in maintaining the proper humidity in the battery. Equilibrium vapor pressure of the metal-air battery results in an equilibrium relative humidity that is typically about 50-60%. If the ambient humidity is greater than the equilibrium relative humidity value for the metal-air battery, the metal-air battery will absorb water from the air through the cathode and fail due to a condition called flooding, which may also cause the battery to leak. If the ambient humidity is less than the equilibrium relative humidity value for the metal-air battery, the metal-air cells will release water vapor from the electrolyte through the air cathode and fail due to drying out.

Further, impurities such as carbon dioxide (C02) present in the ambient air may decrease the energy capacity of the cell. Thus, a metal-air cell will operate more efficiently and longer if the flow of ambient air is controlled so that the air enters the cell only when the cell is providing electrical energy to a load.

Air exchange control systems for metal-air batteries have been designed to control the flow of ambient air into and out of metal-air cells for the following reasons: (1) to prevent the cell from continuing to react; (2) to prevent changes in the cell humidity; and, (3) to prevent C02 from entering the cell when the battery is not providing electrical energy to a load. Some designs, for example, use a mechanism physically operated by the user where a valve or vent cover is attached to a switch that turns an electrical device"on" so that when the switch moves, the cover moves. See, e. g., United States Patent No.

2,468,430, issued to Derksen on April 26,1949; United States Patent No. 4,913,983 entitled"Metal-Air Battery Power Supply"and issued to Cheiky on April 3,1990; and, H.

R. Espig & D. F. Porter, Power Sources 4: Research and Development in Non- Mechanical Electrical Power Sources, Proceedings of the 8th International Symposium held at Brighton, September 1972 (Oriel Press) at p. 342. In these designs, however, the air exchange system requires the physical presence of the operator and an electrical device that has a switch compatible with the battery air exchange system.

Automatic air exchange systems that are contained within the battery and operate without the presence of a user, however, typically provide significant parasitic drains on the energy capacity of the cell that may also shorten the life of the cell. One design, such as the one disclosed in U. S. Patent No. 4,177,327 entitled"Metal-Air Battery Having Electrically Operated Air Access Vent Cover"and issued to Mathews et al. on December 4,1979, utilizes a vent cover associated with an electrically operated bimetallic actuator to close the air access vents to prevent ambient air from entering the housing when the battery is not in use. This is accomplished by applying a current to the bimetallic actuator so that the two materials thereof heat up, whereby the different thermal expansion coefficients thereof cause the system to bend up or down. The electrical actuator, however, provides a substantial parasitic drain on the metal-air cells and diminishes the life of the cell.

Additionally, United States Patent No. 5,304,431 entitled"Fluid Depolarized Electrochemical Battery with Automatic Valve"and issued to Brooke Schumm, Jr. on April 19,1994; United States patent No. 5,449,569 entitled Fluid Depolarized Battery with Improved Automatic Valve"and issued to Brooke Schumm, Jr. on September 12, 1995; and United States Patent No. 5,541,016 entitled"Electrical Appliance with Automatic Valve Especially for Fluid Depolarized Electrochemical Battery"and issued to Brooke Schumm, Jr. on July 30,1996 disclose a design incorporating a thermally responsive semiconductor microactuator disposed over a fluid entrance inlet to permit ambient air to enter the cell when the battery is supplying electrical power to a load. In this design, electrical energy on the order of milliwatts is dissipated to heat a resistive element that opens a thermally responsive valve and keeps that valve open while the battery is in use. Thus, as described hereinabove with respect to the'394 patent, the design also provides a continuous parasitic drain on the cell that decreases the life of the cell.

Therefore, there exists a need for a microvalve, particularly one utilized as an air exchange system in a metal-air battery, that eliminates the need for a latching system while still minimizing the power drain on the cell during operation. There also exists a need to minimize the size of microvalves used with a metal-air battery so that it fits within a standard battery package and maximizes the volume of the battery that is available for providing electrical energy. It is also desirable that such microvalves be mass produced to decrease costs, as well as enable large numbers of batteries to be assembled containing them as an air exchange system.

SUMMARY OF THE INVENTION In a first embodiment of the present invention, a microvalve for controlling fluid flow is disclosed as including: a body portion having at least one opening formed therein; a shutter located adjacent to and substantially parallel with the body portion, the shutter having at least one opening formed therein; and, a drive mechanism for causing the shutter to rotate with respect to the body portion so that the shutter opening is brought into and out of alignment with the opening of the body portion, wherein the microvalve is in an open position and a closed position, respectively. The drive mechanism of the microvalve further includes at least one first comb drive positioned adjacent the shutter and a second comb drive positioned adjacent each first comb drive. The first comb drive includes a member which is movable so as to engage and disengage the shutter and the second comb drive includes a member which is movable so as to deflect the first comb drive member, wherein deflection of the first comb drive member causes the shutter to rotate a predetermined amount when the first comb drive member is engaged therewith.

An alternative drive mechanism includes at least one actuator, a rotation gear hub located adjacent to and operatively connected to the actuator, and a rotation gear operatively connected to the rotation gear hub and the shutter, wherein the rotation gear hub is caused to rotate upon being driven by the actuator so that the rotation gear and the shutter are caused to rotate. Yet another alternative drive mechanism includes at least one comb drive for impacting a periphery of the shutter with a predetermined force so as to rotate the shutter a designated amount.

In a second embodiment of the present invention, a fluid-breathing voltaic battery is disclosed as including a container, a voltaic cell disposed within the container, and a fluid exchange system. The fluid exchange system further includes a microvalve having a first state and a second state, wherein the microvalve is disposed in the container such that the microvalve is adapted to allow a fluid into the cell when the microvalve is in the first state and to substantially prevent the fluid from flowing into the cell when the microvalve is in the second state, and a controller electrically connected to the microvalve, wherein the controller is adapted to initiate a change of state in the microvalve. The microvalve further includes a body portion having at least one opening formed therein, a shutter located adjacent to and substantially parallel with the body portion having at least one opening formed therein, and a drive mechanism for causing the shutter to rotate with respect to the body portion so that the shutter opening is brought into and out of alignment with the opening of the body portion.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the present invention, it is believed that the invention will be better understood from the following description, which is taken in conjunction with the accompanying drawings: Figure 1 is a schematic top view of a microvalve in accordance with the present invention, where the shutter is in the closed position and the drive mechanism is not engaged therewith; Figure 2 is a schematic top view of the microvalve depicted in Figure 1, where the shutter is in the closed position and the drive mechanism is engaged therewith; Figure 3 is a schematic top view of the microvalve depicted in Figures 1 and 2, where the shutter is being rotated by the drive mechanism a predetermined amount; Figure 4 is a schematic top view of the microvalve depicted in Figures 1-3, where the drive mechanism is disengaged from the shutter after rotation; Figure 5 is a schematic top view of the microvalve depicted in Figures 1-4, where the drive mechanism returns to its original position; Figure 6 is a schematic top view of the microvalve depicted in Figures 1-5, where the shutter has been rotated by the drive mechanism into an open position; Figure 7 is a schematic side view of the microvalve depicted in Figure 1, where the shutter is in the closed position; Figure 8 is a schematic side view of the microvalve depicted in Figure 6, where the shutter is in the open position; Figure 9 is a schematic top view of a second embodiment for the microvalve of the present invention, where the shutter is in a partially open position; Figure 10 is an enlarged partial schematic top view of the microvalve depicted in Figure 9, where the gearing system thereof is shown; Figure 11 is a schematic side view of the second embodiment for the microvalve depicted in Figures 9 and 10; Figure 12 is a schematic top view of a third embodiment for the microvalve of the present invention, where the shutter is in the closed position; Figure 13 is a schematic cross-sectional view of a metal-air battery including at least one microvalve of the present invention to control flow of air to the cells therein; and Figure 14 is a top view of the metal-air battery depicted in Figure 13.

DETAILED DESCRIPTION OF THE INVENTION A preferred embodiment of the present invention involves an electrostatically- driven MEMS microvalve designed to control fluid flow. In this application, the term "electrostatically-driven"refers to a driving mechanism created from fixed charge due to an electrostatic potential between two surfaces. This differs from a"thermally-driven" microvalve in that the thermally-driven microvalve utilizes a resistive element that provides the heat energy necessary to drive the valve. Such a resistive element either provides a parasitic drain on the cell itself or requires an alternative power source to drive the valves. Magnetic or inductive systems, by contrast, use continuous current in a loop to generate an external magnetic field which in turn creates a magnetic force. An electrostatic valve, however, utilizes the charge of the cell to drive the valve so that the parasitic drain on the cell is much less than for thermal or magnetic valves.

In the preferred embodiments, the microvalve is designed to consume power only during transients, i. e., while changing states from open to closed or vice versa. More specifically, it will be seen in Figures 1-8 that a microvalve, denoted generally by reference number 10, preferably includes a shutter 12 located adjacent to and substantially parallel with a body portion 14, where body portion 14 preferably has at least one opening 18 formed therein. Shutter 12 has one or more openings 16 formed therein corresponding to body opening 18. As seen in Figures 1-6, shutter 12 may include a support member 19 which traverses opening 16 so as to divide it in substantially symmetrical portions.

Shutter 12 also preferably includes a plurality of smaller openings 15 which permit a predetermined amount of leakage flow through shutter 12 when in the closed position as discussed further herein (see Figures 1-6).

It will further be seen that microvalve 10 includes a drive mechanism (shown generally by numeral 17) to rotate shutter 12 with respect to body portion 14 so that shutter opening 16 is brought into and out of alignment with opening 18 of body portion 14, wherein microvalve 10 is in an open position and a closed position, respectively. It will be appreciated that the rotational movement of shutter 12 involves shutter 12 rotating about a hub 24 in either a clockwise or counterclockwise motion. As seen in Figures 1 and 7, shutter 12 is in the closed position (i. e., openings 16 in shutter 12 are not aligned with opening 18 in body portion 14 so as to substantially prevent fluid flow therethrough) and must rotate approximately 180° in either a clockwise or counterclockwise motion to be located in the open position depicted in Figures 6 and 8. Shutter 12 must then continue rotating in the same direction (or rotate in the opposite direction) approximately 180° to go back to the closed position.

Shutter 12 is preferably substantially circular in shape and includes a main circular portion 26 and an opening 28 (see Figures 7 and 8) located substantially at a centerpoint thereof about which shutter 12 is rotated at hub 24. While shutter 12 is shown as being circular in configuration, it will be understood that any shape may be utilized provided shutter opening 16 aligns with opening 18 in body portion 14 when in the open position and does not align with such opening 18 when in the closed position. In this way, a relatively large overall valve opening may be obtained by rotating shutter 12 a relatively short distance. Such a design minimizes the power necessary to drive microvalve 10 by minimizing the distance shutter 12 needs to be displaced. This, in turn, allows the use of electrostatic driving technologies when the power required to drive microvalve 10 is lowered to a level that may be practically delivered by these technologies. It will be understood that other configurations of shutter 12, including the structure thereof and the number and type of openings therein, may be modified as detailed further herein.

It will be appreciated that drive mechanism 17 preferably includes at least one first comb drive 20 positioned adjacent shutter 12 which has a member 25 that is movable so as to preferably frictionally engage and disengage a periphery of shutter 12 (see arrows 30 in Figures 1-4). It will be noted that first comb drive member 25 is frictionally engaged with shutter 12 in Figures 2 and 3 and frictionally disengaged in Figures 1 and 4. Drive mechanism 17 further includes a second comb drive 22 positioned adjacent each first comb drive 20. Second comb drive 22 also includes a member 27, which is preferably oriented substantially perpendicular to first comb drive member 25, that is movable (see arrows 32 in Figures 3-5) so as to deflect first comb drive member 25. It will then be appreciated that deflection of first comb drive member 25 causes shutter 12 to rotate a predetermined amount when first comb drive member 25 is frictionally engaged therewith (see Figure 3). Since first and second comb drive members 25 and 27 are preferably coupled together, second comb drive member 27 is able to deflect first comb drive member 25 by pushing or pulling so as to cause rotation of shutter 12 in a desired direction (i. e., counterclockwise or clockwise, respectively). The amount of shutter rotation created by the deflection of first comb drive member 25 is dependent on an angle of deflection permitted by first comb drive member 25 and preferably is in a range of 1-2 degrees.

It will also be seen that second comb drive member 27 is positioned with respect to first comb drive member 25 so that second comb drive member 27 is deflected when first comb drive member 25 frictionally engages shutter 12 (see Figures 2 and 3).

Alternatively, second comb drive member 27 may be positioned with respect to first comb drive member 25 so that second comb drive member 27 is deflected when first comb drive member 25 is frictionally disengaged from shutter 12. Due to the length of second comb drive member 27, a stabilizer 34 is preferably provided so that deflection occurs adjacent the end of stabilizer 34 nearest first comb drive member 25.

Comb drives 20 and 22 of drive mechanism 17 are preferably electrostatic in design, although a thermal, magnetic or piezoelectric driving mechanism as is known in the art may be utilized. More specifically, each of first and second comb drives 20 and 22 further includes a plurality of suspended ground fingers 21 and a plurality of anchored fingers 23, wherein ground fingers 21 are pulled to anchored fingers 23 when a potential is applied therebetween to create an electrostatic force. It will be seen that members 25 and 27 of first and second comb drives 20 and 22, respectively, are connected in substantially parallel orientation to ground fingers 21 so that they move in the direction of arrows 30 and 32. A resilient beam 29 is also connected to members 25 and 27, which is anchored so as to suspend first and second comb drives 20 and 22. In this way, members 25 and 27, as well as ground fingers 21, are able to move back and forth absent any friction forces thereon. In this application, the term"resilient beams"refer to mechanical structures that undergo displacement so as to provide a spring-like restoring force on the whole system.

An important factor in driving shutter 12 appropriately is that first comb drive member 25 remain deflected by second comb drive member 27 while being frictionally disengaged (or retracted) from shutter 12 (see Figure 4). Otherwise, shutter 12 would merely rotate back to its original position prior to deflection of first comb drive member 25. It will be understood that first comb drive member 25 is then returned to its non- deflected position by second comb drive member 27 once first comb drive member 25 is frictionally disengaged (see Figure 5) so that the cycle can continue until shutter 12 is rotated the desired amount with respect to body portion 14.

It will be seen from Figures 1-6 that drive mechanism 17 preferably includes a pair of first comb drives 20 positioned adjacent to and on opposite sides of shutter 12. In this way, rotation of shutter 12 is better controlled. Accordingly, all first comb drive members 25 will preferably move in substantial conformity so as to be frictionally engaged with or disengaged from shutter 12. Likewise, second comb drive members 27 will preferably move in substantial conformity so as to cause deflection (in the same direction) or non- deflection of their associated first comb drive member 25.

In order for shutter 12 to be rotatable about hub 24 with a minimum of frictional forces thereon, it will be seen in Figures 7 and 8 that hub 24 includes a support 44. More specifically, central opening 28 of shutter 12 fits over support 44 and is retained in position by a cap 45. Thus, support 44 remains stationary as shutter 12 rotates therearound. Further, a pair of dimples 46 and 47 are provided by shutter 12 which also serve to restrict air flow between shutter 12 and body portion 14. It will be appreciated that dimple 46 extends from a lower surface of shutter 12 and is located about the circumference of shutter 12, while dimple 47 extends from a lower surface of shutter 12 and is located around that portion of shutter opening 16 which would otherwise be exposed to leakage from body portion opening 18.

As stated previously, it is preferred that shutter 12 (which is preferably made of a polysilicon material) include a plurality of small openings 15 therein to permit a predetermined amount of leakage flow through shutter 12 when in the closed position.

Openings 15 serve a dual purpose in that they may be used to provide an acid (e. g., hydrofluoric acid) and thus release an initial oxide layer between shutter 12 and body 14 (preferably made of silicon) as is known in the art. In this way, oxide release is accomplished in a more uniform manner than merely along the sides. Thus, the size and configuration of shutter openings 15 is designed to as to maximize the dual functions of leakage flow and uniformity of oxide release. It will also be understood that additional leakage flow control may be performed by altering dimples 46 and 47 so as to extend only partially around the circumference of shutter 12 or shutter opening 16, respectively, such as in arcuate segments.

In operation, it will be appreciated from Figures 1-6 that microvalve 10 is electrostatically actuated in increments between a first (closed) position and a second (open) position. Initially, an electrostatic force is created between ground fingers 21 and anchored fingers 23 in first comb drive 20 so that member 25 frictionally engages shutter 12. Thereafter, an electrostatic force is created between ground fingers 21 and anchored fingers 23 in second comb drive 22 so that member 27 causes first comb drive member 25 to deflect and rotate shutter 12 a predetermined amount in either a clockwise or counterclockwise direction. Upon this incremental rotation of shutter 12, the electrostatic force in first comb drive 20 is discontinued so that ground fingers 21 return to their original position and member 25 is retracted or frictionally disengaged from shutter 12.

The electrostatic force in second comb drive 22 is then discontinued so as to return ground fingers 21 and member 27 to their original position, as well as first comb drive member 25 to the non-deflected position, where it is ready to begin the cycle again for additional incremental rotation of shutter 12 as desired.

A second embodiment of the microvalve of the present invention, indicated generally by reference numeral 100, is depicted in Figures 9-11. As seen therein, microvalve 100 is configured similar to microvalve 10 so as to include a shutter 112 located adjacent to and substantially parallel with a body portion 114, where shutter 112 and body portion 114 each preferably has at least one opening formed therein.

Microvalve 100 further includes a drive mechanism 117, to be discussed in greater detail hereinafter, which rotates shutter 112 with respect to body portion 114 so that the shutter opening is brought into and out of alignment with the opening of body portion 114. In this way, microvalve 100 is placed in an open position and a closed position, respectively.

As discussed above in microvalve 10, the rotational movement of shutter 112 occurs about a hub 124.

Although shutter 112 may be configured like shutter 12 described hereinabove, an alternative design is depicted in Figures 9 and 11. It will be seen that shutter 112 is preferably substantially circular in shape and includes a ring-shaped portion 113 defining the periphery thereof. A plurality of cross members or spokes 115 extend across the inner diameter of ring-shaped portion 113 to define arcuate openings 119 defined by adjacent spokes 115 and a portion of ring-shaped portion 113. Shutter 112 further includes a central portion 126 having an opening 128 located at a centerpoint about which shutter 112 is rotated at hub 124. It will further be seen that circular portions are located within arcuate openings 119, where circular portions 133 are solid and circular portions 135 are open. In this way, shutter 112 is in the open position when circular portions 135 are aligned with corresponding openings 118 in body portion 114 and in the closed position when circular portions 133 are aligned with such body portion openings 118. In order to better depict the relationship of circular portions 133 and 135 with body portion openings 118, Figure 9 shows shutter 112 being in a partially open position. It will be understood that this configuration of shutter 112 requires less rotation (approximately 60°) of shutter 112 to change positions (i. e., from open to closed or vice versa) than shutter 12.

Naturally, the number and size of circular portions 133 and 135 will conform to body portion openings 118; however, it is preferred that they be of an even number and substantially symmetrically spaced.

Contrary to drive mechanism 17 described for microvalve 10, drive mechanism 117 for microvalve 100 has a self-latching, gear-type design. In accordance therewith, drive mechanism 117 includes first and second comb drives 120 and 122 (preferably electrostatic in design) which are positioned so as to interface with a rotation gear hub 136 having a plurality of gear teeth 138. It will be seen from arrow 134 that this may be in either direction. More specifically, it will be appreciated that first and second comb drives 120 and 122 interact with rotation gear hub 136 in a manner like that described in a paper entitled"Surface Micromachined Microengine,"by Ernest J. Garcia and Jeffrey J.

Sniegowski of Sandia National Laboratories, which is hereby incorporated by reference.

By interfacing with rotation gear hub 136 in such manner, first and second comb drives 120 and 122 cause rotation gear hub 136 to rotate (either clockwise or counterclockwise as indicated by arrow 134). Similar to comb drives 20 and 22, it will be understood that comb drives 120 and 122 each include a plurality of suspended ground fingers and a plurality of anchored fingers, wherein ground fingers are pulled to anchored fingers when a potential is applied therebetween to create an electrostatic force. Further, beams are provided with first and second comb drives 120 and 122 which are in substantially parallel orientation to the ground fingers. In this way, such beams interface with rotation gear hub 136 and move in the direction of arrow 134, as applicable. Resilient beams are also connected to the beams and are anchored so as to suspend comb drives 120 and 122 (see Figure 9).

As seen in Figures 9 and 10, rotation gear hub 136, through gear teeth 138, interfaces directly or indirectly (by means of one or more intermediate rotation gears 140) with shutter 112 by means of a plurality of gear teeth 142 located at least about a portion of shutter 112. In this way, shutter 112 is caused to rotate when rotation gear hub 136 is driven to rotate by comb drives 120 and 122. It will be appreciated that intermediate rotation gears 140 preferably act as torque converters, whereby the torque necessary to drive shutter 112 is more easily generated.

It will further be appreciated from Figure 11 that shutter 112, like shutter 12 in Figures 7 and 8, is rotatable about hub 124. More specifically, opening 128 of shutter 112 fits over a support 141 and is retained in position by a cap 143. Thus, support 141 remains stationary as shutter 112 rotates therearound. Further, a dimple 145 preferably extends from and is located about the circumference of each circular portion 133, which also serves to restrict air flow between shutter 112 and body portion 114 when in the closed position. Shutter 112 also preferably includes a plurality of small openings 130 in circular portions 133 (see Figure 9) like openings 15 in shutter 12. Such openings 130 are likewise sized and configured to maximize the dual functions of providing a predetermined leakage flow and an access path for permitting acid to release an oxide layer between shutter 112 and body 114.

In operation, microvalve 100 is electrostatically actuated between a first (closed) position and a second (open) position by creating an electrostatic force between the ground fingers and the anchored fingers in comb drives 120 and 122 so that the respective beams thereof cause rotation gear hub 136 to rotate with force sufficient to rotate intermediate gears 140 a desired amount. The rotation of intermediate gears 140 then causes shutter 112 to rotate clockwise (or counterclockwise) about hub 124 into the open position. Microvalve 100 is electrostatically actuated from the open position to a closed position by creating an electrostatic force between the ground fingers and the anchored fingers in comb drives 120 and 122 so that the beams operate rotation gear hub 136 with force sufficient to rotate intermediate gears 140 a desired amount until shutter 112 rotates counter-clockwise (or clockwise) about hub 124 into the closed position. Although a plurality of intermediate gears 140 are shown in Figures 9 and 10, rotation of shutter 112 may occur through direct interfacing of rotation gear hub 136 and gear teeth 142 of shutter 112.

Yet another alternative drive mechanism 217 may be utilized with microvalve designs 10 and 100 described above. Although either shutter design depicted in Figures 1 and 9 may also be utilized, Figure 12 depicts a microvalve 200 having a shutter 212 and a body portion 214 similar to those shown in Figures 1-8 (note dimples 245 and 247 shown in hidden lines). As seen in Figure 12, shutter 212 and body portion 214 each have an elliptically-shaped opening 216 and 218, respectively, formed therein which are aligned when microvalve 200 is in the open position and misaligned when in the closed position.

It will be seen that drive mechanism 217 is somewhat simpler in design and includes at least one comb drive 220 which is utilized to impact the periphery of shutter 212 adjacent an edge thereof so as to cause shutter 212 to rotate a predetermined amount about hub 224 (either clockwise or counter-clockwise depending on the orientation thereof). A second impact comb drive 222 is preferably provided adjacent shutter 212 opposite comb drive 220.

It will be appreciated that first and second comb drives 220 and 222 are preferably like comb drives 20,22,120 and 122 described above and include a plurality of ground fingers 221 and a plurality of anchored fingers 223, where ground fingers 221 are pulled to anchored fingers 223 when a potential is applied therebetween to create an electrostatic force. It will be seen that members 225 and 227 are connected in substantially parallel orientation to ground fingers 221 so that they move in the same direction thereof (see arrows 231). Resilient beams 229 and 231 are connected to members 225 and 227, respectively, and anchored so as to suspend comb drives 220 and 222. In this way, members 225 and 227, as well as ground fingers 221, are able to move back and forth absent any friction forces thereon.

In operation, microvalve 200 is electrostatically actuated between a closed position and an open position either incrementally or in a single action. This is accomplished by creating an electrostatic force between ground fingers 221 and anchored fingers 223 of comb drives 220 and 222, whereupon members 225 and 227 impact the periphery of shutter 212 at a very slight angle. The electrostatic force created between ground fingers 221 and anchored fingers 223 of comb drives 220 and 222 is then discontinued so that members 225 and 227 return to their original positions. Comb drives 220 and 222 are then able to continue this sequence as necessary to rotate shutter 212 to the desired position with respect to body portion 214.

One aspect of the present invention is directed to an electrostatically-driven MEMS microvalve that may be used to control fluid (gas or liquid) flow into and/or out of a battery, a battery including such a valve, or a method of controlling fluid flow into and/or out of a battery. The battery may include, for example, one or more metal-air cells, one or more fuel cells, one or more voltaic cells, or a combination of these to produce a hybrid cell. In each case, the fluid flow enables or assists the provision of electrical power by providing a fluid cathode such as in the case of a metal-air cell, by providing a fluid anode in the case of a fuel cell, or by providing a fluid electrolyte such as in the case of a voltaic cell used in seawater.

Figure 13 shows a cross-section of an exemplary fluid-breathing voltaic battery 75 having a container 79 and at least one voltaic cell 74 disposed within container 79.

Container 79 may have a cylindrical shape as shown, a prismatic shape, or even a flat round shape (i. e., a button cell). A fluid exchange system for battery 75 includes at least one microvalve of the present invention (designated by numeral 76) and a controller 78 electrically connected thereto to control the flow of fluid in battery 75. It will be understood that controller 78 is preferably like that described in a patent application entitled"Battery Having a Built-in Controller,"filed on April 2,1998 and having Serial No. 09/054,012, which is hereby incorporated by reference. Microvalve 76 may be located adjacent a top portion of an air path 82 in battery 75. Microvalve 76 is retained in position by a valve seat 87 (which also preferably includes a portion for crimping a top seal 111) and preferably has a hydrophobic layer 88 (e. g., polytetrafluoroethylene or polypropylene) located between it and openings 84 in a top metal cover 86 to diffuse air entering path 82. A plurality of openings 84 are preferably spaced circumferentially in top metal cover 86 (see Figure 14), in such quantities and size as needed for a desired air flow into battery 75.

A second microvalve 77 may be located adjacent a bottom portion of air path 82 so as to control air flow entering from openings 92 in a bottom metal cover 94.

Microvalve 77 is likewise retained in position by a valve seat 96 (which, like valve seat 87, preferably includes a portion for crimping a bottom seal 97) and preferably has a hydrophobic layer 98 located between it and openings 92 to diffuse air entering path 82.

While hydrophobic layers 88 and 98 are shown as being located on only one side of microvalves 76 and 77, several additional or alternative locations are also possible. For example, hydrophobic layers could be placed on both sides of each microvalve 76 and 77 in order to limit the flow of water vapor into or through each microvalve. Additionally, hydrophobic layers could be placed in substantial alignment with openings 84 and 92 in top and bottom metal covers 86 and 94, respectively. It will also be understood that materials for removing carbon dioxide could be incorporated in the same positions as the hydrophobic membranes.

Controller 78 is preferably positioned at the negative end of the cell since both positive and negative battery connections are readily accessible at this location. While controller 78 is preferably electrically connected to both microvalve 76 and microvalve 77 (and any other microvalves in battery 75), a separate controller for each microvalve may be utilized. A controller located at the positive end of the cell, however, would require a line to be run from the negative end of the cell to provide a negative connection. Several other alternative locations are possible for controller 78, including the inner surface of top or bottom metal covers 86 and 94, on top of valve seats 87 and 96, or even incorporated in microvalves 76 and 77 themselves.

It will be understood that connections are necessary between the positive and negative terminals of battery 75, microvalves 76 and 77, and controller 78. Of course, valve seats 87 and 96 for microvalves 76 and 77, respectively, are preferably metal assemblies which carry the positive battery charge. A wire connection 85 is preferably provided between top metal cover 86 and valve seat 87, because lowering top metal cover 86 and spot welding it to valve seat 87 could inhibit air flow from openings 84 to air path 82 unless additional measures were taken (i. e., if openings in top metal cover 86 were located in a middle region above hydrophobic layer 88 or if top metal cover 86 was constructed from a metal screen, perforated metal, or expanded metal). Wire connections 89,91 and 93 are then provided between the negative terminal for battery 75 and controller 78, between controller 78 and microvalve 77, and between microvalve 77 and microvalve 76, respectively.

It will be appreciated that additional microvalves, preferably in the form of an array, may be positioned within battery 75 as an alternative manner of controlling the amount of air entering therein. In this way, the amount of airflow (dependent upon the number of microvalves open) permitted to flow therein is able to provide a high current rate without continued exposure to ambient air after the load has been removed. Since the microvalves for such an array can be of a bi-stable design (i. e., open or closed), this is an attractive alternative to having microvalve 76 and/or microvalve 77 be only partially open.

Although not shown, one or more microvalves for battery 75 may be located adjacent a periphery of container 79.

The terms"electrically connected"and"electrical connection"refer to connections that allow for continuous current flow. The terms"electronically connected"and "electronic connection"refer to connections in which an electronic device such as a transistor or a diode are included in the current path."Electronic connections"are considered in this application to be a subset of"electrical connections"such that while every"electronic connection"is considered to be an"electrical connection,"not every "electrical connection"is considered to be an"electronic connection." It will further be seen that voltaic cell 74 of battery 75 preferably includes an air cathode 108, a metal anode 110, and a separator 109 therebetween. Seals 111 and 97 of an insulating material are provided at each end of voltaic cell 74, with valve seats 87 and 96, respectively, being in contact with air cathode 108. Another hydrophobic layer may be located between air path 82 and air cathode 108 if necessary. Of course, other battery configurations may employ the microvalves described herein, including one where the anode is a cylindrical plug in the center of the cell surrounded by an air cathode on the outside. Another alternative design involves the anode and air cathode being configured in a spiral or"jelly roll"configuration. It will be understood that other modifications may be required in order to employ these alternative battery designs, such as including an air channel between the container and the air cathode and having openings formed in a side portion of the case instead of the ends.

Controller 78 individually, or in conjunction with a second controller, is preferably utilized to open and/or close microvalves 76 and 77. The term"controller"as used in this application refers to a circuit that accepts at least one input signal and provides at least one output signal that is a function of the input signal. Controller 78 may monitor and/or manage fluid flow between a metal-air electrochemical cell and the external environment.

For example, controller 78 may allow air into voltaic cell 74 when oxygen is required to provide the current required by the load. When the load is disconnected or demands only a minimal amount of current, controller 78 may close or partially close microvalves 76 and 77 so that the reaction in voltaic cell 74 is stopped or slowed down and the cell is protected until the load demands more current. At that time, controller 78 may open microvalve 76 so that voltaic cell 74 will generate the current demanded by the load. In this regard, it will also be appreciated that voltaic cell 74 preferably provides power to microvalves 76 and 77 and is able to do so due to the leakage flow therethrough even when in the closed position. Optimally, controller 78 and/or a second controller will provide signal conditioning to the power provided by voltaic cell 79 to drive microvalves 76 and 77.

Controller 78 may also be used to perform other functions to further increase the operation efficiency and/or safety of one or more electrochemical cells in addition to controlling fluid flow into and/or out of one or more electrochemical cells. Examples of operations that may be performed by controller 78 include: using a DC/DC converter to extend the service run time of the battery; controlling a charge cycle of the electrochemical cell by directly monitoring the electrochemical properties of that particular cell; providing a safety disconnect in the event of overheating, inverse polarity, short-circuit, over-pressure, overcharge, over-discharge or excessive hydrogen generation; and, monitoring the state of charge of that particular electrochemical cell to provide this information to the user, the device, or for quality assurance purposes. Functions such as these are described in detail in co-pending United States Application Nos. 09/054,012 and 09/054,087, each entitled"Battery Having a Built-in Controller"and filed on April 2, 1998, which are both incorporated by reference in this application.

While particular embodiments and/or individual features of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Further, it should be apparent that all combinations of such embodiments and features are possible and can result in preferred executions of the invention.