Abstract:
A two-stage valve for controlling the flow of fluid from a pressurized fluid supply with an upper main body including a cavity with a contoured inner surface; a lower main body with at least one flow exhaust passage forming a primary flow path through the two-stage valve; a pre-stressed diaphragm sandwiched between the upper and lower main bodies, and pressure control capability for controlling the pressure in the cavity. A first valve opens and closes the flow of gas from the pressurized gas supply to the cavity. A second valve allows the pressure in the cavity to exhaust to the environment. Raising and lowering of the pressure in the cavity causes the pre-stressed diaphragm to open and close the flow of gas from the pressurized gas supply through the primary flow path of the two-stage valve. The design is suitable as a microvalve using Micro-Electro-Mechanical Systems (MEMS) concepts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/862,809 filed May 22, 2001 now U.S. Pat. No. 6,557,820, by Wetzel et al. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to valves for fluids and more specifically to valves suitable for construction as high flow, high-pressure microvalves. 
     Small fluid valves are known in the art that have been developed using Micro-Electro-Mechanical-Systems (MEMS) concepts. These small-scale valves have the advantage of being able to be produced very precisely and inexpensively using fabrication techniques more commonly used in the microelectronics industry. Typically, such valves also consume very low power and have high switching frequencies. While these valves have many ingenious configurations, most are limited to low pressures, e.g., under 200 psig (approximately 1,500 kPa), and all are limited to extremely low flows, e.g., under 10 −4  kg/second. In fact, none of the actuation mechanisms known, such as electromagnetic, electrostatic, piezoelectric, and shape-memory alloys, are capable by themselves of producing both the forces necessary to overcome high pressures, and the deflections needed to provide large flow areas. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a means for switching high flow rates at high pressures, at the expense of response time, by a device that is particularly suitable for fabrication using micro-fabrication techniques. 
     The present invention is a two-stage valve for controlling the flow of fluid, typically a gas from a pressurized gas supply, comprising an upper main body including a cavity therein, the cavity including an inner surface; a lower main body having a plurality of pressurized gas supply exhaust outlet passages forming a primary flow path with the pressurized gas supply, the primary flow path including an inlet passage for the flow of gas from the pressurized gas supply; a pre-stressed diaphragm sandwiched between the upper and lower main bodies, the pre-stressed diaphragm having an upper surface opposite to the inner surface of the cavity in the upper main body, the pre-stressed diaphragm having one side of a portion thereof in fluidic communication with the cavity, and the opposite side of the portion thereof in fluidic communication with the pressurized gas supply, the inner surface of the cavity being contoured to correspond with the upper surface of the pre-stressed diaphragm; and pressure control means fluidically coupled to the cavity for controlling the pressure in the cavity to cause the portion of the pre-stressed diaphragm to open the flow of gas from the pressurized gas supply through the primary flow path of the two-stage valve and to cause the portion of the pre-stressed diaphragm to close the flow of gas from the pressurized gas supply through the primary flow path of the two-stage valve, at least a portion of the inner surface of the cavity in the upper main body providing a resting surface for the upper surface of the pre-stressed diaphragm, at least one of the plurality of supply fluid exhaust outlet passages being directed such that a component of supply fluid exhaust outlet velocity is in a direction opposite to a component of supply fluid exhaust outlet velocity in at least one other of the plurality of supply fluid exhaust outlet passages. 
     The pressure control means comprises the lower main body having a secondary flow path communicating with the pressurized gas supply, the upper main body having a secondary flow path communicating with the secondary flow path in the lower main body, and communicating with the cavity in the upper main body; a first valve providing (a) an isolating means for isolating the flow of gas from the pressurized gas supply to the cavity in the upper main body, and (b) an opening means for allowing the gas from the pressurized gas supply to flow to the cavity in the upper main body, the upper main body having an exhaust passage for fluidically communicating the cavity with an environment at a pressure lower than the pressure of the pressurized gas supply, a second valve installed in the exhaust passage, the second valve providing an isolating means for fluidically isolating the cavity in the upper main body from the environment, and an opening means for opening the cavity in the upper main body to exhaust to the environment. 
     The first valve is installed in one of (a) the secondary flow path in the lower main body, and (b) the secondary flow path in the upper main body. The lower main body can include a cavity. The lower main body further can include a boss formed in the cavity of the lower main body, the boss surrounding a hole acting as the inlet passage for the flow of gas from the pressurized gas supply, the hole fluidically coupled to the opposite side of the portion of the pre-stressed diaphragm. Preferably, the boss formed in the cavity of the lower main body is positioned coincident with the center of the cavity of the lower main body. The inlet passage from the pressurized gas supply can be directed in a direction substantially perpendicular to the pre-stressed diaphragm. The valve has a form factor F defined as a height H/length L wherein the form factor F is not greater than 0.1. The diaphragm is comprised typically of titanium. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the two-stage valve of the first embodiment of the present invention in the closed position. 
     FIG. 2 illustrates cross-sectional plan view  2 — 2  of the two-stage valve of the first embodiment of the present invention. 
     FIG. 3 illustrates the two-stage valve of the first embodiment of the present invention in the open position. 
     FIG. 4 illustrates cross-sectional elevation view  4 — 4  of the two-stage valve of the first embodiment of the present invention. 
     FIG. 5 illustrates a cross-sectional view with characteristic dimensions of a thermodynamic disc steam trap known in the art. 
     FIG. 6 illustrates a cross-sectional elevation view of a second embodiment of the two-stage valve of the present invention in the closed position. 
     FIG. 7 illustrates a cross-sectional elevation view of the two-stage valve of FIG. 6 in the open position. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
     In FIG. 1, the two-stage valve of the first embodiment of present invention is illustrated. The two-stage valve  100  comprises an upper main body  102  which is made typically of one or more laminations of silicon, silicon carbide, or other suitable material compatible with micro-fabrication techniques, and a lower main body  104  typically made of one or more of the same materials. A cavity  106 , hereinafter referred to as the upper cavity  106 , is formed in the upper main body  102 . Another cavity  108 , hereinafter referred to as the lower cavity  108 , is formed in the lower main body  104 . The upper main body  102  and the lower main body  104  sandwich a diaphragm  110 . The diaphragm  110  is pre-loaded so that it is normally sealed on the boss  112  formed in the middle of the lower main body  104 . 
     A hole  114  through the middle of the boss  112  acts as the inlet for the main flow path. Passages (shown in FIG. 2) are formed in the lower main body  104  parallel to the diaphragm  110  to permit the flow to exhaust when the two-stage valve  100  is opened. 
     A secondary flow path  116  is formed in the upper main body  102  and the lower main body  104  to connect the side of the diaphragm  110  facing the upper main body  102 , hereinafter referred to as the upper side of the diaphragm  110  to the high-pressure gas supply  118 . A first small valve  120  is placed in the secondary flow path  116  to connect and disconnect the top cavity  106  with the high-pressure fluid supply  118 . The high-pressure fluid is typically a gas although in some applications, a liquid can become the high-pressure fluid. A second small valve  122  is placed in an exhaust passage  124  on the top of the upper main body  102  to provide a means to release high-pressure gas to the environment. (Small valve  122  is shown in the closed position in FIG.  1 ). Both the first and second small valves,  120  and  122 , are actuated typically by titanium nickel (TiNi) or piezoelectric actuators, not shown. The design of the first and second small valves  120  and  122  is the subject of co-pending U.S. patent application, Ser. No. 10/277,028 filed Oct. 21, 2002 which is incorporated herein by reference. The entire assembly of the two-stage valve  100  typically is mounted on and attached to a pressure vessel  126  that contains the high-pressure gas supply  118 . 
     FIG. 2 illustrates a cross-sectional plan view  2 — 2  of the two-stage valve of the present invention as illustrated in FIG.  1 . Exhaust passages  202 ,  204 ,  206 , and  208 , referred to previously, are formed in the lower main body  104  parallel to the diaphragm  110  to permit the flow to exhaust to thrusters (not shown) when the two-stage valve  100  is opened. Supply gas  118  flows through the center of hole  114  through the middle of the boss  112  that acts as the inlet for the main flow path and the secondary flow path  116 . 
     Referring to FIG. 1, the operations to close the two-stage microvalve  100  are as follows. Second small valve  122  is closed to seal the upper cavity  106  from the atmosphere. First small valve  120  is opened to expose the upper cavity  106  to the high-pressure gas supply  118 , thereby pressurizing the upper side of diaphragm  110 . After a short time, typically 10 milliseconds or less, both the lower side and the upper side of the diaphragm  110  reach essentially the same pressure as the high-pressure gas supply  118 . However, the lower side of the diaphragm  110  will experience slightly lower pressures due to the velocity of the flow passing through the hole  114  that acts as the inlet for the main flow path. Once the gas pressures are equalized across the diaphragm  110 , i.e., the pressure on the upper side of the diaphragm  110  equals the pressure on the lower side of the diaphragm  110 , the stresses in the pre-loaded diaphragm  110  tend to pull the diaphragm  110  closed on the boss  112 . Once the diaphragm  110  is closed on the boss  112 , the pressure on the upper side of the diaphragm  110  acts over the entire surface area of the upper side of the diaphragm  110  while the pressure on the lower side of the diaphragm  110  acts only over the smaller area of hole  114  that acts as the inlet for the main flow path. The pressure acting on the center of the diaphragm  110  in the upper cavity  106  is the same as the high-pressure gas supply  118 , but the pressure at the lower cavity  108  is lower. This pressure imbalance causes the diaphragm  110  to seal tightly against the boss  112 . As a result, the flow of gas through the two-stage valve  100  is shut off. 
     Referring to FIG. 3, the operations to open the two-stage valve  100  are as follows. First small valve  120  is closed, thus isolating the high-pressure gas supply  118  from the upper cavity  106 . Second small valve  122  is opened, thus permitting the upper cavity  106  to communicate with the environment. The high-pressure gas in the upper cavity  106  exhausts to the environment, until, after a short time, typically 10 milliseconds or less, the pressure in the upper cavity  106  approaches the pressure of the environment. In the meantime, the high pressure of the high-pressure gas at the hole  114  that acts as the inlet passage for the main flow path of the high-pressure gas from the high-pressure gas supply  118  starts to force the diaphragm  110  to lift upwards towards the upper cavity  106  and away from the boss  112 , thereby permitting the high-pressure gas to flow through the hole  114  that acts as the inlet passage for the main flow path, and the high-pressure gas then flows in the radial direction away from the hole  114  at the center of the lower main body  104 , and parallel to the diaphragm  110 , through the passages  202 ,  204 ,  206 , and  208  to the thrusters (not shown). The inlet passage  114  from the high-pressure gas supply typically is directed in a direction substantially perpendicular to the lower surface of the pre-stressed diaphragm. The flow of the high-pressure gas in a radial direction permits the high-pressure gas to be exhausted in more than one direction away from the two-stage valve  100 . Although the exhaust passages  202 ,  204 ,  206 , and  208  are illustrated as being aligned and parallel to each other, those skilled in the art recognize that the exhaust passages  202 ,  204 ,  206 , and  208  can be oriented in any radial direction to permit the exhaust gas to flow away from the hole  114  that acts as the main flow path. 
     FIG. 4 illustrates a side elevation view of the two-stage valve  100 . The upper main body  102  and the lower main body  104  sandwich the diaphragm  110 . The exhaust passages  202  and  206  are illustrated as channels permitting the high-pressure gas supply  118  to exhaust to the environment. The entire assembly of the two-stage valve  100  is illustrated as mounted on and attached to the pressure vessel  126  that contains the high-pressure gas supply  118 . 
     Those skilled in the art will recognize that the two-stage valve can be designed for essentially any size application. 
     In particular, with regard to the size, FIG. 5 illustrates a cross-sectional view with characteristic dimensions of a thermodynamic disc steam trap known in the art, specifically a Model TD-300 trap manufactured by the Ogontz Corporation® of Willow Grove, Pa. This type of valve is chosen for illustration because some features superficially resemble the first embodiment of the present invention. Disc trap  500  has a cap  502  mounted on a body  504 . When a pulse of water mixed with the incoming steam enters at inlet port  506  and passes through the strainer  508 , the water passes through channel  510  and raises the disc  512  thereby enabling the water to exit through channel  514  leading to outlet port  516 . For the smallest size of 0.5 inches (12.2 mm) diameter National Pipe Thread (NPT), the total height is represented by the dimensions of B+C, which equals 2.5 inches 63 mm. The length L is 3 inches or 76 mm. 
     In contrast, in the first embodiment of the present invention, as shown in FIG.  1  and FIG. 3, the height H is typically as low as 0.125 inches (3.175 mm), the effective diameter D of the diaphragm  110 , which corresponds to the diameter of the cavity  604  in the upper main body  602 , typically is in the range of 1 inch (25.4 mm) and the length L is typically 1.5×D, or 1.5 inches (37.6 mm). The diaphragm  110  is typically made of titanium, although other materials can be used. The thickness t of the diaphragm  110  is typically in the range of 0.001 inches (0.0254 mm), and can be less than this thickness depending on the particular application. The valve  100  can be scaled larger or even smaller, depending on the required flow rates. Therefore, as can be appreciated by those skilled in the art, with a height H as low as 0.125 inches or 3.175 mm, the present invention of valve  100  enables a very low profile or form factor F=H/L as compared to a comparable type of prior art valve, e.g., disc trap  500 , which has a form factor F=(B+C)/L=63/76=0.83. In the current example, the form factor for the valve  100  of the present invention is F=3.175/37.6=0.0844, or nearly {fraction (1/10)} th  that of the prior art valve. Consequently, the valve  100  can be made very flat, permitting it to fit into application packages where the corresponding dimension accommodating the height H is very small. 
     Second Embodiment 
     FIGS. 6 and 7 illustrate a second embodiment of the two-stage valve of the present invention. For simplicity, only those features which differ from FIGS. 1 to  4  have been renumbered. Valve  600  differs from valve  100  in that, as compared to upper main body  102 , upper main body  602  has a cavity  604  with an inner surface  606  with a contoured or domed shape to correspond to the contoured or domed shape of the upper surface  606  of pre-stressed diaphragm  110 . When the valve  600  is in the open position as shown in FIG. 7, the contoured or domed shape of the inner surface  606  provides a distributed resting surface for at least a portion of upper surface  608  of the diaphragm  110 . 
     The distributed resting surface provided by the inner surface  606  reduces the stress concentration that would otherwise occur at the edge  610  of the inner surface  606 . Reduction of the stress concentration correspondingly reduces the potential for rupture of the diaphragm  110 . This is particularly desirable when the thickness t of the diaphragm  110  must be reduced to provide a greater opening volume by increased flexing to accommodate high-pressure and high-flow conditions, e.g., at pressures equal to or greater than 200 psig (approximately 1,500 kPa) and flows equal to or greater than 10 −4  kg/second. 
     The dimensions H, D and L and the thickness and the material of the diaphragm  110  of the first embodiment as discussed previously are applicable as well to the dimensions H, D and L of the second embodiment as illustrated in FIGS. 6 and 7. Also, the plan view of valve  600  is identical to that shown in FIG. 2 for valve  100 , and is therefore not shown separately for the second embodiment. Similarly, the cross-sectional elevation view  4 — 4  of the two-stage valve of the first embodiment as shown in FIG. 4 is also applicable as an elevation view of valve  600  of the second embodiment, and is therefore not shown separately. 
     As noted previously for the first embodiment, the high-pressure gas can be exhausted in more than one direction away from the two-stage valve  600 . Although the exhaust passages  202 ,  204 ,  206 , and  208  are illustrated as being aligned and parallel to each other, those skilled in the art recognize that the exhaust passages  202 ,  204 ,  206 , and  208  can be oriented in any radial direction to permit the exhaust gas to flow away from the hole  114  that acts as the main flow path. Therefore, at least one of the plurality of supply gas exhaust outlet passages  202 ,  204 ,  206 , and  208  is directed such that a component of supply gas exhaust outlet velocity is in a direction opposite to a component of supply gas exhaust outlet velocity in at least one other of the plurality of supply gas exhaust outlet passages. 
     Although the two-stage valve of both the first and second embodiments is illustrated with the upper main body in the upper position and the lower main body in the lower position, those skilled in the art will recognize that the two-stage valve can be positioned in any orientation. 
     When designed as a microvalve, the two-stage valve overcomes the inherent lack of force in conventional actuation technologies by tapping the high potential energy inherent in the high-pressure gas supply. As noted, the diaphragm  110  is made preferably of titanium. The actuators for the first and second small valves  120  and  122 , respectively, preferably are made of titanium nickel (TiNi) or piezoelectric and can have small dimensions and small throws (valve operation distance parameters). Such requirements are consistent with piezoelectric and shape memory alloy requirements. The first and second small valves switch a small secondary flow, which in turn acts on the large diaphragm to control a larger flow. By seeping this secondary flow through a very small valve, the filling process for the two-stage valve, when designed as a microvalve, is substantially slower than the small valve actuation speed. A proper design optimizes the tradeoff between the small valves controlling a small, high-pressure flow to switch a large, high-pressure flow at the expense of switching time. 
     The invention has now been explained with reference to specific embodiments. Other embodiments will be apparent to those of ordinary skill in the art in view of the foregoing description. It is not intended that this invention be limited except as indicated by the appended claims and their full scope equivalents.