Abstract:
A microvalve includes a first plate having a surface defining an actuator cavity. A second plate has a surface that abuts the surface of the first plate and includes a displaceable member that is disposed within the actuator cavity for movement between a closed position, wherein the displaceable member prevents fluid communication through the microvalve, and an opened position, wherein the displaceable member does not prevent fluid communication through the microvalve. An actuator is connected to the displaceable member and has only one or two pairs of actuator ribs.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/079,892 filed Nov. 14, 2014, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to microvalves for controlling the flow of fluid through a fluid circuit. In particular, this invention relates to an improved structure for such a microvalve that includes an improved actuator, the use of which reduces the power required to operate the microvalve. 
     Generally speaking, a micro-electro-mechanical system is a system that not only includes both electrical and mechanical components, but is additionally physically small, typically including features having sizes that are generally in the range of about ten micrometers or smaller. The term “micro-machining” is commonly understood to relate to the production of three-dimensional structures and moving parts of such micro-electro-mechanical system devices. In the past, micro-electro-mechanical systems used modified integrated circuit (e.g., computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material), which were micro-machined to provide these very small electrical and mechanical components. More recently, however, other micro-machining techniques and materials have become available. 
     As used herein, the term “micro-machined device” means a device including features having sizes in the micrometer range or smaller and, thus, is at least partially formed by micro-machining. As also used herein, the term “microvalve” means a valve including features having sizes in the micrometer range or smaller and, thus, is also at least partially formed by micro-machining. Lastly, as used herein, the term “microvalve device” means a micro-machined device that includes not only a microvalve, but further includes additional components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be either micro-machined components or standard-sized (i.e., larger) components. Similarly, a micro-machined device may include both micro-machined components and standard-sized components. 
     A variety of microvalve structures are known in the art for controlling the flow of fluid through a fluid circuit. One well known microvalve structure includes a displaceable member that is supported within a closed internal cavity provided in a valve body for pivoting or other movement between a closed position and an opened position. When disposed in the closed position, the displaceable member substantially blocks a first fluid port that is otherwise in fluid communication with a second fluid port, thereby preventing fluid from flowing between the first and second fluid ports. When disposed in the opened condition, the displaceable member does not substantially block the first fluid port from fluid communication with the second fluid port, thereby permitting fluid to flow between the first and second fluid ports. 
     In a conventional thermally actuated microvalve structure, it has been found that in some instances it is desirable to reduce the power required to operate the thermally actuated microvalve. Thus, it would be desirable to provide an improved structure for a microvalve that facilitates a reduction of power required to operate the microvalve. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved microvalve that includes an improved actuator structure that provides desired actuator stiffness but reduces the power required to operate the microvalve. The microvalve includes a first plate having a surface defining an actuator cavity. A second plate has a surface that abuts the surface of the first plate and includes a displaceable member that is disposed within the actuator cavity for movement between a closed position, wherein the displaceable member prevents fluid communication through the microvalve, and an opened position, wherein the displaceable member does not prevent fluid communication through the microvalve. An actuator is connected to the displaceable member and has only one or two pairs of actuator ribs. 
     Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a basic structure of a microvalve including a cover plate, an intermediate plate, and a base plate. 
         FIG. 2  is a perspective view of the basic structure of the microvalve illustrated in  FIG. 1  shown assembled. 
         FIG. 3  is a plan view of an inner surface of a conventional cover plate for a prior art microvalve. 
         FIG. 4  is a plan view of a conventional intermediate plate for a prior art microvalve. 
         FIG. 5  is a plan view of an inner surface of a conventional base plate for a prior art microvalve. 
         FIG. 6  is a plan view of a second embodiment of a conventional intermediate plate having an actuator comprising three pairs of actuator ribs. 
         FIG. 7  is a plan view of a first embodiment of an improved intermediate plate having an improved actuator in accordance with this invention. 
         FIG. 8  is a plan view of a second embodiment of an improved intermediate plate having an improved actuator in accordance with this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIGS. 1 and 2  a basic structure of a microvalve  1  that, to the extent shown, is representative of both a conventional structure for a microvalve and an improved structure for a microvalve in accordance with this invention. The illustrated microvalve  1  includes a cover plate  2 , an intermediate plate  3 , and a base plate  4 . The cover plate  2  has an outer surface  5  and an inner surface  6 . The cover plate  2  also has one or more openings (two of such openings  2   a  and  2   b  are shown in the illustrated embodiment) formed therethrough that, in a manner that is well known in the art, allow one or more electrically conductive wires (not shown) to pass therethrough. The intermediate plate  3  has a first surface  7  and a second surface  8 . The base plate  4  has an inner surface  9  and an outer surface  10 . The base plate  4  also has a one or more openings (three of such openings  4   a ,  4   b , and  4   c  are shown in the illustrated embodiment) formed therethrough that, in a manner that is well known in the art, allow fluid to flow in to and out of the microvalve  1 . 
     When the microvalve  1  is assembled as shown in  FIG. 2 , the inner surface  6  of the cover plate  2  engages the first surface  7  of the intermediate plate  3 , and the inner surface  9  of the base plate  4  engages the second surface  8  of the intermediate plate  3 . The cover plate  2 , the intermediate plate  3 , and the base plate  4  can be retained in this orientation in any desired manner. For example, portions of the cover plate  2  and/or the base plate  4  may be bonded to the intermediate plate  3 , such as by fusion bonding, chemical bonding, or physically bonding (such as, for example, mechanical fasteners and/or adhesives). The cover plate  2 , the intermediate plate  3 , and the base plate  4  may be composed of any desired material or combination of materials. For example, the cover plate  2 , the intermediate plate  3 , and the base plate  4  may be composed of silicon and/or similar materials. 
     The structure of the inner surface  6  of a conventional cover plate  2  for a prior art microvalve is illustrated in detail in  FIG. 3 . As shown therein, the conventional cover plate  2  includes an actuator cavity, indicated generally at  11 , that is provided on the inner surface  6  thereof. The illustrated actuator cavity  11  includes an upper actuator arm cavity portion  11   a , a central actuator arm cavity portion  11   b , a lower actuator arm cavity portion  11   c , an actuator rib cavity portion  11   d , an actuator spine cavity portion  11   e , and an actuator hinge cavity portion  11   f . The upper actuator arm cavity portion  11   a  has a pair of recessed areas  12   a  and  12   b  provided therein. The illustrated actuator cavity  11  also has one or more pressure equalization depressions  13  provided therein. 
     The structure of a conventional intermediate plate  3  for a prior art microvalve is illustrated in detail in  FIG. 4 . As shown therein, the conventional intermediate plate  3  includes a displaceable member, indicated generally at  60 , that includes a sealing portion  61  having a pair of openings  61   a  and  61   b  formed therethrough. The sealing portion  61  is connected through an elongated arm portion  62  to a hinge portion  63  that is formed integrally with the conventional intermediate plate  3 . The intermediate plate  3  also includes an actuator  37  including a plurality of actuator ribs  34  that is connected through a central spine  65  to the elongated arm portion  62  at a location that is intermediate of the sealing portion  61  and the hinge portion  63 . As described below and illustrated in  FIG. 8 , conventional microvalves may include actuators having three actuator ribs  34 . 
     As shown in  FIG. 4 , first ends of a first portion of the plurality of actuator ribs  34  (the upper ribs  34  when viewing  FIG. 4 ) are flexibly joined at first ends thereof to a first non-moving part of the intermediate plate  3 . Second ends of the first portion of the plurality of actuator ribs  34  are connected to the central spine  65 . The first non-moving part of the intermediate plate  3  is electrically connected to a first bond pad (not shown) that is provided on the intermediate plate  3 . Similarly, first ends of a second portion of the plurality of actuator ribs  34  (the lower ribs  34  when viewing  FIG. 4 ) are flexibly joined at first ends thereof to a second non-moving part of the intermediate plate  3 . Second ends of the second portion of the plurality of actuator ribs  34  are also connected to the central spine  65 . The second non-moving part of the intermediate plate  3  is electrically connected to a second bond pad (not shown) that is provided on the intermediate plate  3 . The second bond pad is electrically isolated from the first bond pad, other than through the plurality of actuator ribs  34 . 
     In a manner that is well known in the art, electrical current may be passed from the first bond pad through the plurality of actuator ribs  34  to the second bond pad. Such electrical current causes thermal expansion of the plurality of actuator ribs  34 , which causes axial movement of the central spine  65 . As described above, the central spine  65  is connected to the elongated arm portion  62 . Consequently, axial movement of the central spine  65  causes the elongated arm portion  62  (and, therefore, the sealing portion  61 ) of the displaceable member  60  to pivot about the hinge portion  63  or otherwise move relative to the rest of the intermediate plate  3  (such movement occurring within a plane defined by the rest of the intermediate plate  3 ). Thus, the illustrated displaceable member  60  functions as a conventional micro-electro-mechanical system thermal actuator. 
     The structure of the inner surface  9  of a conventional base plate  4  is illustrated in detail in  FIG. 5 . As shown therein, the conventional base plate  4  includes an actuator cavity, indicated generally at  40 , that is provided on the inner surface  9  thereof. The illustrated actuator cavity  40  includes an upper actuator arm cavity portion  40   a , a central actuator arm cavity portion  40   b , a lower actuator arm cavity portion  40   c , an actuator rib cavity portion  40   d , an actuator spine cavity portion  40   e , and a hinge cavity portion  40   f . The illustrated actuator cavity  40  also has one or more pressure equalization depressions  41  provided therein. 
       FIG. 6  illustrates a second embodiment of an intermediate plate  43  for a conventional microvalve, such as the microvalve  1 . The intermediate plate  43  is similar to the intermediate plate  3  and may be used with the cover plate  2  and the base plate  4 , shown in  FIGS. 2, 3, and 5 . Like the intermediate plate  3 , the intermediate plate  43  has a first surface  47  and a second surface (not shown). The intermediate plate  43  includes the displaceable member  60 . The displaceable member  60  includes the sealing portion  61  having the pair of openings  61   a  and  61   b  formed therethrough. The sealing portion  61  is connected through the elongated arm portion  62  to the hinge portion  63  that is formed integrally with the conventional intermediate plate  43 . The intermediate plate  43  differs from the intermediate plate  3  in that the actuator  57  of the intermediate plate  43  comprises three, rather than four, pairs of actuator ribs  56 . As shown in  FIG. 6 , each actuator rib  56  has a width X within the range of about 120 μm to about 130 μm. 
     The three pairs of actuator ribs  56  are connected through the central spine  65  to the elongated arm portion  62  at a location that is intermediate of the sealing portion  61  and the hinge portion  63 . Each rib  56  is disposed at an angle A 1  measured from a line L 1  parallel to a side edge of the intermediate plate  43 . In the illustrated embodiment, the angle A 1  is about 5 degrees. 
     Each pair of actuator ribs  56  is separated from an adjacent pair of ribs  56 , or from the intermediate plate  43  by an elongated opening  72   a ,  72   b ,  72   c , and  72   d . The intermediate plate  43  also includes channels  70   a ,  70   b ,  70   c , and  70   d  formed through the intermediate plate  43 . The channels  70   a ,  70   b ,  70   c , and  70   d  connect the elongated opening  72   a  to the elongated opening  72   d.    
     The channels  70   a ,  70   b ,  70   c , and  70   d , and a longitudinally extending side edge one of the elongated opening  72   d , also define a boundary of an isolation region  74  that physically separates the isolation region  74  from the rest of the intermediate plate  43 , except through the pairs of actuator ribs  56 . 
     As further shown in  FIG. 6 , first ends of a first portion of the plurality of actuator ribs  56  (the upper actuator ribs  56  when viewing  FIG. 6 ) are flexibly joined at first ends thereof to a first non-moving part of the intermediate plate  43 . Second ends of the first portion of the plurality of actuator ribs  56  are connected to the central spine  65 . The first non-moving part of the intermediate plate  43  is electrically connected to a first bond pad (not shown) that is provided on the intermediate plate  43 . Similarly, first ends of a second portion of the plurality of actuator ribs  56  (the lower actuator ribs  56  when viewing  FIG. 6 ) are flexibly joined at first ends thereof to a second non-moving part of the intermediate plate  43 . Second ends of the second portion of the plurality of actuator ribs  56  are also connected to the central spine  65 . The second non-moving part of the intermediate plate  43  is electrically connected to a second bond pad (not shown) that is provided on the intermediate plate  43  within the isolation region  74 . The second bond pad is thus electrically isolated from the first bond pad, other than through the plurality of actuator ribs  56 . 
       FIG. 7  illustrates an intermediate plate, indicated generally at  103 , having an improved actuator  137 , in accordance with a first embodiment of this invention. The intermediate plate  103  is similar to the intermediate plate  43  and may be used with the cover plate  2  and the base plate  4 , shown in  FIGS. 2, 3, and 5 . Like the intermediate plate  43 , the intermediate plate  103  has a first surface  107  and a second surface (not shown). The intermediate plate  103  includes the displaceable member  60  and the sealing portion  61  having the pair of openings  61   a  and  61   b  formed therethrough. The sealing portion  61  is connected through the elongated arm portion  62  to the hinge portion  63 . 
     The intermediate plate  103  differs from the intermediate plate  43  in that it includes an improved actuator  137 . The improved actuator  137  of the intermediate plate  103  comprises two pairs of actuator ribs  134 , rather than three pairs of actuator ribs  56 . Each of the actuator ribs  134  has a width Y 1  that is wider than the width X of a similar rib  56  in the conventional actuator  57  according to the formula: width Y 1 =X+½X, where X=the width of the conventional actuator ribs  56 . As also shown in  FIG. 7 , portions of each rib  134  have been removed to define apertures  136 . The illustrated apertures  136  have a width Z 1  of about ½X, where X=the width of the conventional actuator ribs  56 . Alternatively, the apertures  136  may be other than as illustrated and have any desired size and shape required to achieve the desired actuator stiffness. 
     As shown in  FIG. 6  and described above, the known actuator rib  56  has a width X within the range of about 120 μm to about 130 μm. Accordingly, the actuator ribs  134  may have a width Y 1  within the range of about 184 μm to about 191 μm. Additionally, the apertures  136  formed in the actuator ribs  134  may have a width Z 1  within the range of about 59 μm to about 66 μm. 
     The two pairs of actuator ribs  134  are connected through the central spine  65  to the elongated arm portion  62  at a location that is intermediate of the sealing portion  61  and the hinge portion  63 . Each rib  134  is disposed at an angle A 2  measured from a line L 2  parallel to a side edge of the intermediate plate  103 . In the illustrated embodiment, the angle A 2  is about 5.25 degrees. Alternatively, the angle A 2  may be within the range of about 4.25 degrees to about 6.25 degrees. 
     Each pair of actuator ribs  134  is separated from an adjacent rib pair or from the intermediate plate  103  by an elongated opening  172   a ,  172   b , and  172   c . The intermediate plate  103  also includes channels  170   a ,  170   b ,  170   c , and  170   d  formed through the intermediate plate  103 . The channels  170   a ,  170   b ,  170   c , and  170   d  connect the elongated opening  172   a  to the elongated opening  172   c.    
     The channels  170   a ,  170   b ,  170   c , and  170   d , and a longitudinally extending side edge of the elongated opening  172   c , also define a boundary of an isolation region  174  that physically separates the isolation region  174  from the rest of the intermediate plate  103 , except through the pairs of actuator ribs  134 . 
     As further shown in  FIG. 7 , first ends of a first portion of the plurality of actuator ribs  134  (the upper actuator ribs  134  when viewing  FIG. 7 ) are flexibly joined at first ends thereof to a first non-moving part of the intermediate plate  103 . Second ends of the first portion of the plurality of actuator ribs  134  are connected to the central spine  65 . The first non-moving part of the intermediate plate  103  is electrically connected to a first bond pad (not shown) that is provided on the intermediate plate  103 . Similarly, first ends of a second portion of the plurality of actuator ribs  134  (the lower actuator ribs  134  when viewing  FIG. 7 ) are flexibly joined at first ends thereof to a second non-moving part of the intermediate plate  103 . Second ends of the second portion of the plurality of actuator ribs  134  are also connected to the central spine  65 . The second non-moving part of the intermediate plate  103  is electrically connected to a second bond pad (not shown) that is provided on the intermediate plate  103  within the isolation region  174 . The second bond pad is thus electrically isolated from the first bond pad, other than through the plurality of actuator ribs  134 . 
       FIG. 8  illustrates an intermediate plate, indicated generally at  203 , having an improved actuator  237 , in accordance with a second embodiment of this invention. The intermediate plate  203  is similar to the intermediate plate  103  and may be used with the cover plate  2  and the base plate  4 , shown in  FIGS. 2, 3, and 5 . Like the intermediate plate  103 , the intermediate plate  203  has a first surface  207  and a second surface (not shown). The intermediate plate  203  includes the displaceable member  60  and the sealing portion  61  having the pair of openings  61   a  and  61   b  formed therethrough. The sealing portion  61  is connected through the elongated arm portion  62  to the hinge portion  63 . 
     The intermediate plate  203  differs from the intermediate plate  103  in that the improved actuator  237  includes only one pair of actuator ribs  234 . Each of the actuator ribs  234  has the width Y 2 , wherein Y 2 =2X. Portions of each rib  234  have been removed to define apertures  236 . The illustrated apertures  236  have the width Z 2 , wherein Z 2 =X. Alternatively, the apertures  236  may be other than as illustrated, and have any desired size and shape required to achieve the desired actuator stiffness. In the actuator  237 , the width Y 2  of the ribs  134  in the one pair of ribs  234 , and the size and shape of the apertures  236 , may be determined based on a desired actuator stiffness and resistance level, and through routine experimentation. 
     As shown in  FIG. 6  and described above, the known actuator rib  56  has a width X within the range of about 120 μm to about 130 μm. Accordingly, the actuator ribs  234  may have a width Y 2  within the range of about 245 μm to about 255 μm. Additionally, the apertures  236  formed in the actuator ribs  234  may have a width Z 2  within the range of about 120 μm to about 130 μm. 
     The pair of actuator ribs  234  is connected through the central spine  65  to the elongated arm portion  62  at a location that is intermediate of the sealing portion  61  and the hinge portion  63 . Each rib  234  is disposed at an angle A 3  measured from a line L 3  parallel to a side edge of the intermediate plate  203 . In the illustrated embodiment, the angle A 3  is about 6 degrees. Alternatively, the angle A 3  may be within the range of about 5 degrees to about 7 degrees. 
     The pair of actuator ribs  234  is separated from the intermediate plate  203  by elongated openings  272   a  and  272   b . The intermediate plate  203  also includes channels  270   a ,  270   b ,  270   c , and  270   d  formed through the intermediate plate  203 . The channels  270   a ,  270   b ,  270   c , and  270   d  connect the elongated opening  272   a  to the elongated opening  272   b.    
     The channels  270   a ,  270   b ,  270   c , and  270   d , and a longitudinally extending side edge of the elongated opening  272   b , also define a boundary of an isolation region  274  that physically separates the isolation region  274  from the rest of the intermediate plate  203 , except through the pair of actuator ribs  234 . 
     As further shown in  FIG. 8 , a first end of a first actuator rib  234  (the upper actuator rib  234  when viewing  FIG. 8 ) is flexibly joined to a first non-moving part of the intermediate plate  203 . A second end of the first actuator rib  234  is connected to the central spine  65 . The first non-moving part of the intermediate plate  203  is electrically connected to a first bond pad (not shown) that is provided on the intermediate plate  203 . Similarly, a first end of a second actuator rib  234  (the lower actuator rib  234  when viewing  FIG. 8 ) is flexibly joined to a second non-moving part of the intermediate plate  203 . A second end of the second actuator rib  234  is also connected to the central spine  65 . The second non-moving part of the intermediate plate  203  is electrically connected to a second bond pad (not shown) that is provided on the intermediate plate  203  within the isolation region  274 . The second bond pad is thus electrically isolated from the first bond pad, other than through the actuator ribs  234 . 
     It may be desirable in some applications to reduce the power required to operate a thermally actuated microvalve, such as the microvalve  1  described above, while maintaining the stiffness or spring rate of the ribs. For example, during actuation of the actuator  57 , i.e., when application of electrical current causes thermal expansion of the actuator ribs  56 , the actuator ribs  56  behave as resistors in parallel. Therefore, it may be desirable to reduce the number of pairs of actuator ribs  56  to reduce the power required to operate the microvalve  1 . 
     It will be understood however, that as a result of removing one or more pairs of actuator ribs  56  from the actuator  57 , the stiffness of actuator  57 ; i.e., a spring rate or resistance to induced forces, of the actuator  57  may be undesirably and negatively affected, such that the stiffness of the actuator  57  is undesirably lowered relative to an actuator with  3  or  4  pairs of ribs. As a result, an actuator having only two pairs of the ribs  56  may become susceptible to unwanted movement due to fluid flow forces in the microvalve  1 , or due to other induced forces, such as from friction induced by contamination or stiction. 
     It has been discovered that increasing the width of the actuator ribs  56  in an actuator having only two pairs of the ribs  56  (not shown, but similar to the actuator  57 ), raises the stiffness of the actuator, but lowers the electrical resistance of the actuator. For example, the actuator  57  requires about 10.8 watts of power to operate and has a spring rate of about 0.232 N/μm. A similar actuator with only two pairs of the ribs  56  requires only about 7.2 watts of power to operate. However, the actuator with only two pairs of the ribs  56  experiences a reduction in spring rate from a desired level of about 0.232 N/μm to about 0.178 N/μm. This undesirable reduction in the spring rate increases the susceptibility of the microvalve  1  to flow forces, which can negatively affect the hysteresis and linearity of the microvalve  1 . 
     Advantageously, it has been further discovered that electrical resistance of the actuator may then be raised to a desired level by removing selected portions (embodied as the apertures  136  in  FIG. 7 ) of a center of each rib  134 , while retaining a desired stiffness of the actuator, such as a spring rate of about 0.232 N/μm. 
     It has been further discovered that when a load of 2 Newtons, which simulates the force experienced by a microvalve actuator during electrical actuation, is applied to the actuator  57  and the actuator  137 , displacement of the ribs,  56  and  134  respectively, is substantially the same. Preferably, when subjected to a load of 2 Newtons, the actuator  137  will retain the desired spring rate of about 0.232 N/μm, while only requiring within the range of about 4.5 watts to about 7.0 watts of power to operate. Significantly, when subjected to a load of 2 Newtons, the illustrated actuator  137  retains the desired spring rate of about 0.232 N/μm, while advantageously only requiring about 6.6 watts of power to operate. 
     The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.