SE536813C2 - Integrated pressure programmable reference pressure device - Google Patents

Abstract

lO 14 AB STRAKT The invention presented in this application is a micromechanical support device for other microsystems. The application area is mainly MEMS (MST) based high pressure microsystems, which use an internal reference pressure for measurement or fate control. The small dimensions involved in the MEMS system result in an inevitable problem, namely that the pressure in the small trapped volumes of the reference pressure cavities can be easily changed by very little leakage or diffusion. The invention is a programmable passive mechanical device, which is programmed only by a pressure versus time profile in a programming channel. The pressure programming method allows thousands of gas handling microsystems to be programmed simultaneously in a very convenient manner.

Description

536 813 stored is large, large, heavy and awkward bottles are often used to reduce the amount of high pressure components with associated piping. Micro system technology (MST) is an emerging new technology area, which has the potential to completely change gas storage and handling technology, which means that gas will be much more available as an energy carrier in cars and for other mobile applications in the future. However, in order to handle large flows with small microsystems, it is required that the microsystems are autonomous but can cooperate in parallel in very large numbers. The disadvantage is that if a parameter is changed and all microsystems need to be adjusted, it becomes very impractical. The solution presented in this application provides a method for batch programming an unlimited number of microsystems simultaneously, which solves the problem.

SUMMARY The invention presented herein solves an important problem for cooperating autonomous microsystems such as the Macrosphere concept, which occurs if the same gas handling chip is to be used for different types of gas, see background. The problem that is solved is that the secondary pressure from each Macrosphere can be changed or harmonized each time the spheres are refilled.

The programming method, which uses a filling pressure against time profile, is very suitable for mass programming of microsystems, not only for the Macrospheres but also in many other microsystems for gas handling.

The system consists of three main components outside the closed reference pressure volume, these are the following, a normally closed pressure-controlled valve, a non-return valve and an active flow limiter. The components are tightly integrated in the same stack of micromachined washers, a typical material for the washers is monocrystalline silicon. The system can be quite small a few cubic millimeters with a weight less than 5 milligrams. To prevent contaminants from creeping into the system and causing valve leakage, the gas used in the system must be very well filtered. However, required filters are not seen as part of the invention, since filtration is a standard procedure when dealing with microsystems.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows some application areas for the device.

Figure 2 is a system block diagram.

Figure 3 is a diagram for different pressures against time curves during programming.

Figure 4 is a section through a stack of joined washers with the system integrated. Figure 5A is a section through a normally closed valve integrated in a five tray stack Figure SB is a section through a more compact normally closed valve integrated in a four tray stack.

Figure 6 is a section through a typical non-return valve.

Figure 7 is an illustration of a passive fate limiter.

Figure 8 is a section through an active asymmetric fl fate limiter.

DETAILED DESCRIPTION The device presented in this patent application is a passive support device, which can be very useful in many gas handling systems or even enable a whole new generation of more complex and "smarter" micro-systems, especially for small autonomous systems, in which no possibility of active or manual control is available. The physical size (typically 1-100pm) of the components of a micromechanical system makes mechanical adjustment or trimming very cumbersome, if not impossible, since an adjusting screw is likely to be many times larger than the object to be adjusted. with the same.

The invention is a programmable device, which uses a control pressure versus time profile for programming it can be used regularly to update a given pressure level to compensate for long-term operation. A typical application may be to update the reference pressure in a pressure sensor, a common type is depicted in Figure 1A. It consists of a micromechanically machined washer (100) hermetically sealed together against a main substrate (10 1).

The sensor uses a set of wire strain gauges (104) mounted on top of a diaphragm (103).

The diaphragm bends up or down depending on the differential pressure between the reference cavity (102) and the applied external pressure (115) on the sensor.

The bulge can be used to measure the absolute value of the applied external pressure provided that the reference chamber pressure is well known.

Since the enclosed volume is very small, typically parts of a cubic millimeter, high demands are placed on leakage tightness in the so-called bond joint (105). The accuracy does not get better than how well the reference pressure is known and maintained. A problem associated with joined (bonded) washers is that both bonding and the subsequent heat treatment affect the entrapped pressure to a relatively unknown extent because the outgassing from the activated joining surfaces gives an increase in the internal pressure. An alternative for higher accuracy is that the pressure can be adjusted. That is one of the reasons for the invention.

Another example is a normally closed pressure-controlled bistable valve. A section through such a valve is given in Figure 1B. The valve type is used to control flow sequences in fluidic systems. A rocket engine is a good example where it is important that there is pressure in the combustion chamber before the fuel is allowed to flow into it. The valve consists of three washers (106-108) leak-tightly joined. In the washer (106), a cavity (110) is etched so that the remaining material forms a pressure-sensitive membrane (109), as in the pressure sensor. The jerked fuel enters the valve via a port (113), but cannot pass the valve seat (112) because the diaphragm shuts off the path of fate and because the surface inside the valve seat is very small compared to the active one of the diaphragm. then the valve will remain closed even if the fuel pressure is high, but as soon as there is a sufficiently high pressure at the outlet (1 1 1) the diaphragm begins to bulge down and as soon as the liquid can pass the valve seat the pressure increases further and the valve opens with an avalanche effect.

The valve will remain open as long as there is a fuel pressure in the system. If the cavity is connected to the invention, the integrated pressure programmable reference pressure device, then the opening pressure can be adjusted for different applications, which in turn can be very useful.

The invention can also be used to set new reference values in devices such as. a more normal passive pressure regulator, which may need different secondary pressures for different applications. An application can be in a vehicle that can use different gaseous fuels such as Biogas, LNG, Hydrogen, etc.

A block diagram of the device is given in Figure 2. The device consists of two valves and a flow restrictor between the programming input (201) which follows the system pressure and the supply channel (202) which leads to the reference pressure cavity (203). The non-return valve (204) is a conventional micromechanical valve with a relatively high opening pressure, to be leak-tight under normal conditions. It is used to protect the system when the update or programming sequence starts with a significant pressure increase, well above the maximum operating pressure of the device. The non-return valve must open before the pressure increase reaches a critical level to burst the pressure-sensitive diaphragm in the reference pressure cavity, as soon as the mass flow decreases the valve closes again because the differential pressure across the valve becomes low. The second valve (205) in the system is the key component, it is a pressure controlled normally closed valve, also that valve uses a high contact pressure and a small diameter of the valve seat to be leak tight. The valve has its own small reference pressure chamber connected to the control inlet (206), when the system pressure rises the reference chamber is slowly filled by a flow restrictor (207) but the pressure at the valve inlet (208) rises faster because it is directly connected to the system pressure inlet (201). remains closed. On the other hand, when the system pressure begins to drop, it drops faster at the valve input (208) than at the control input (206) when the differential pressure becomes large enough that the valve opens, resulting in a mass från from the reference arm (203) to the programming input. (201).

Now if the pressure drop is stopped at a predetermined level (setting value) for a period of time, the pressure in the reference volume (203) will be equal to the system pressure at (201). The open normally closed valve (205) will close again when the pressure in its own reference volume has been drained through the flow limiter (207). If the valve closes when the system pressure is still constant at the predetermined level, that pressure will be "locked" in the reference chamber (203). The next time a programming cycle, another reference pressure can be freely selected. The channel pressures as a function of time are given in Figure 3. At the beginning of the process all the channel pressures, the channel pressure in channel (206) are given by curve (302), in channel (209) are given by curve (303), in channel (210) are given by curve (304) at the same high pressure P1 ((301) At the time t1 (305) the inlet pressure in channel (209) begins to fall at a good speed, when the pressure has dropped to P2 (306) at t2 (307) the differential pressure (308) ) so high that the normally closed valve (205) is forced to open and the pressure in duct (210), which is the reference pressure, will approach curve (303) so when the inlet pressure stops falling at t3, the reference pressure will very quickly become the same as the inlet pressure at The pressure in the control channel (206) also begins to fall at tl (305), but at a much lower velocity illustrated as curve (302), when the pressure reaches the level P4 (312) at t4 (311) the differential pressure is (313) so low that the normally closed valve (205) closes, freezing the reference pressure to P3 (312). At point t5 (314), the inlet pressure slowly decreases to the normal ambient pressure followed by the control pressure (302) while the reference pressure (304) remains at P3 (310) until the next program cycle.

The integrated system requires a stack of 4 or 5 joined (bonded) washers depending on the design of the normally closed valve (205). The tiles are probably silicon, but other materials such as ceramic or metal can also be used. Figure 4 is a folded section through a stack of five tiles. The term “unfolded cross-section” should be interpreted so that all parts present in the block diagram are shown with their connections in one plane, in reality the parts are much more joined in a complex 3-D 10 15 20 25 30 536 813 pattern, but the cross-section gives a good picture was in the stack a specific part is located. The system is fully integrated and all parts of the components are co-manufactured in the same manufacturing schedule. The washers are numbered (400) to (404) from top to bottom. The programming input (201) is between washer (402) and (403), the fate limiter structure (407) consisting of a number of parallel connected input channels (209) goes to valves (406), which together form the active fate limiter (207) presented further down in the text. The channel (209) continues to the non-return valve (204) and the normally closed valve (205). The supply channel (206) is also connected to the normally closed valve. The outputs of (204) and (205) are connected to a channel with an additional volume (210) between washer (400) and (401), the channel leading up to the reference pressure outlet (202) which is connected to the reference volume (203) which is located outside the brick stack.

A cross-section through the selected valve design is depicted in Figure 5A, it requires a stack of five washers but is probably more robust and easier to manufacture compared to the more compact four washers design shown in Figure 5B. In Figure 5A, the inlet duct (209) enters the system in the "bond interface" between washer (402) AND (403), the duct leads to the top of a corrugated diaphragm (501), the supply duct (206) fills up the volume (500) below the diaphragm . The diaphragm has a central reinforcement (502) a pillar (503) is attached to the central lining reinforcement, the pillar lifts the valve cover (505) when the corrugated diaphragm curves upwards. The valve seat (504) has the shape of a ring around the large hole in the washer (402). The valve cover (505) is held in position and pressed downwards with relatively large force by means of a spring suspension (506) in the form of a number of curved beams around the valve cover.

The spring suspension is open to prevent the reference pressure from lifting or reducing the contact pressure when the valve cover (505) rests on the valve seat (504), it is important that the contact pressure is as high as possible and that the valve seat diameter is as small as possible to leak valve.

A section through another type of normally closed valve is given in Figure 5B. This valve type only requires micro-machining of two washers (401) and (402) with a cover on each side (400) and (403). The gas entering the system at (510) between (401) and the cylinder head (400) fills up the volume (511) around a suspended beam (512). The beam has a pivot point (513) between itself and washer (401) and is biased to rest on the valve seat (514) with high contact pressure. The free end of the beam has a contact point (515) just above the center of the actuator diaphragm (516). As gas flows in through the control inlet (517), the diaphragm bends upward due to the increasing pressure in the volume (518). The diaphragm soon pushes up the free end of the beam so that the valve opens and gas can flow from the volume (511) past the valve seat (514) and out through the outlet (519).

The diaphragm has a reinforcement (520) with a much larger diameter than the diameter of the open surface around the contact point (521) and because the clearance (522) between the diaphragm and washer (401) is considerably smaller than the clearance (523) between the beam and the cover (400 ) then the deflection will be stopped before the beam is broken. The ratio L1 / L2 (524/525) gives the mechanical reinforcement of the force generated by the diaphragm and acts on the valve seat, this allows very high contact pressures which in turn gives a lower leakage.

The high pressure non-return valve (204) can be of a relatively conventional design, a cross-section is given in Figure 6. The gas inlet duct (600) is between washer (403) and (404), it passes through a hole in washer (403) and fills a cavity (601 ) under the valve cover (603). When the pressure becomes high enough, the valve cover lifts from the valve seat (602) and the gas can leave the valve through the outlet duct (605). The valve cover (603) is suspended in a number of beams (604) around the same, the beams act as springs and are prestressed to give a high contact pressure, to give a leak-tight valve when it is closed.

The valve cover surface inside the valve seat and the spring bias determine the opening pressure.

The flow restrictor (207) fulfills an important function in the system and must be designed with great care in order to achieve a very low but well-determined fl resistance. The conflicting requirements to handle are that it should be relatively insensitive to pollutant particles while the flow should be low, this is not the case for a long and very narrow channel. The problem is solved by means of a number of flow restriction cells connected in series and in parallel in a matrix, as shown in Figure 7. The advantage of a matrix is that if a few cells are blocked by particles, there are alternative ways for the gas to squeeze through the fl limiter as a unit. The configuration shown in Figure 7 is symmetrical, i.e. there is no difference of gas if gas enters the system via the inlet (700) to leave via the outlet (701) or vice versa. In the example, the fate limiter consists of 18 identical cells, but can be any size, the cells are interconnected in a network (703) of coarser channels and have parallel cells at the inputs and outputs. In each individual cell, a very long and narrow channel (704) is folded in a given pattern with an input and an output. If the channel width is lpm with 2 pm c-c between the channels, then 1 square millimeter of cell space will accommodate a 500 mm long channel. To speed up the programming time, the fate limiter can be made asymmetrical, in other words the fate resistance is much lower in one direction compared to the other, this means that the normally closed valve can be pressurized quickly, but kept open for a longer time. A practical way to create an asymmetrical design is to use an flexable membrane as a roof over each cell, so as the pressure over a cell increases, the membrane curves upwards and opens up new fl pathways of fate from a circular channel to a nearby downstream all the way to the exit channel. Such a type of flow limiter is shown in Figure 8. The high level block diagram is the same as for the passive fate limiter with the difference that all cells have been replaced by active ditto. The only high level difference is that the fl direction of fate is predetermined, so there is no increase in the number of cells on the output side, the matrix gets a more pyranide-shaped appearance. The gas to a particular cell comes from upstream cells near the cell in question through the network channels (703), these are relatively large and provide no flow resistance compared to the cells. In the cell, the gas passes through a channel (800) in the washer (404) to the center of a circular pattern (802) through which it flows as the gas leaves the pattern, passing through a small hole (803) in the membrane (804) located in tray (403) near the end of the circular pattern before leaving the cell via the output channel (801), which leads to the next network channel (703). When the differential pressure between the volume (805) and the circular pattern below the diaphragm begins to build up, the diaphragm begins to bend upwards with the start in the center and as soon as it moves upwards a shortcut for gas opens near the entrance to the next circular track downstream. If the gas flows in the other direction, the cavity (805) is filled through the hole (803), whereby no bulging takes place and within a wave wave a local central reinforcement is created to prevent the membrane from bursting if the differential pressure becomes too high.

The gain closes the gap (807) between the same and the washer (402). The view in (808) is a top view through the tray (403) if it is transparent down to the pattern in the tray (404). 10

Claims (9)

What is claimed is:

1. Claim 1. A method for change/ update of a reference pressure in a verysmall closed volume characterized by the use of a micro mechanical microsystem, the system reacts on the control pressure inlet (201) to fill or drainthe reference chamber (203). The micro system acts as a mechanical memoryto freeze the pressure in the reference chamber at a desired level, if thecontrol pressure is raised to a level several times higher than normaloperational pressure for a time period and then decreased with a certain ratethe micro system will be in a read mode, i. e. the pressure in the referencechamber will follow the control pressure, if then the control pressuredecrease is stopped and held constant at a certain level for a time period willthe connection to the reference chamber be disconnected and the pressure in the same will remain at a fixed value for future use.

2. Claim 2. An integrated micro mechanical system with three componentsworking in symbiosis, a pressure controlled normally closed valve (205)between the control pressure inlet (201) and the feed channel (210) to thereference cavity, the valve is controlled by the pressure in a combinedchannel/ reference volume (206), a very efficient flow restrictor (207) isconnected between said channel and the control pressure inlet (201) a checkvalve , with the flow direction towards the feed channel (210) is parallelconnected across the pressure controlled valve (205). The system is characterized by a. The pressure controlled normally closed valve (205) has a highcontact pressure between the valve seat and the valve capcombined with a very small flow capacity in order to have aminimal leakage problem. The contact pressure is determinated bya strong suspension spring (506) and a significant higher pressure than the expected maximum Operating pressure. 12 vER. 4 b. The Check valve (204) with an unusual high crack openingpressure, due to high mechanical preloading, several times themaximum operational pressure,in combination with a very small valve seat area, in order to be as leak tight as possible. c. The flow restrictor (207) is asymmetrical with a much lower flowresistance in the flow direction towards the valve (205) than from the valve. d. all components are integrated in the same micromechanical chip,enabling a controlled change /update of a reference pressure in aclosed volume by use of a pressure versus time profile at the control port (201).

3. Claim 3. A method according to claim 2 characterized by that allsubsystems including the reference volume are co-processed in the same manufacturing scheme.

4. Claim 4. A system according to claim 2, characterized in that saidnormally closed valve is pressure activated by use of a pressure sensitivedeflecting corrugated membrane, in order to have a maximum pressure resistance for a given diameter of the membrane.

5. Claim 5. A system according to claim 4, characterized in that saidnormally closed valve has a high contact pressure when closed, amechanical amplification of the actuator force must be used to overcome the contact pressure and open the valve.

6. Claim 6 A system according to claim 5, characterized in that saidmechanical amplification is provided by use of an internal lever (512) i.e. a beam fixed in one flexure point.

7. Claim 7. A system according to claim 4, characterized in that saidpressure sensitive membrane (516) is burst protected by use of a membraneembossment (521) in plane with the membrane meeting a flat surface on the bulk material.

8. Claim 8. A system according to claim 2, characterized in that said flow restrictor consists of one or several cells in a matrix, each cell consists of two 13 vER. 4 elements, a narrow long channel (802) and a simple check valve (804),making it unsymmetrical, i. e. the flow resistance is highly depending on the flow direction through the flow restrictor.

9. Claim 9. A system according to claim 8, characterized in that said twoelements are integrated in one unit by making one of the walls in the narrowchannel flexible and pressure sensitive opening up a short circuit in the flow path lowering the flow resistance When exposed for high flow pressure