WO1998005871A1

WO1998005871A1 - Valve arrangement

Info

Publication number: WO1998005871A1
Application number: PCT/EP1997/004223
Authority: WO
Inventors: Heinz-Werner Etzkorn
Original assignee: Gaswärme-Institut e.V.
Priority date: 1996-08-06
Filing date: 1997-08-02
Publication date: 1998-02-12
Also published as: DE59702612D1; EP0916028A1; DE19631693A1; EP0916028B1

Abstract

The valve arrangement comprises two silicon wafers placed on top of each other. The downstream wafer contains a majority of etched through openings (6). The upstream wafer (3) is equipped with a majority a swing valves (7). The latter are modelled by etching the silicon and are located in through frame openings (8). They are connected to the wafer (3) by membrane-type webs (9) enabling elastic opening and closing movements. The individual swing valves (7) contain differing amounts and differing sizes of through openings (6), thereby enabling a widely adjustable range of dynamic pressure and flow control through selective actuation of the valves. The swing valves (7) are actuated by electrical means, resulting in capacitive forces of repulsion and attraction.

Description

Valve arrangement

The invention relates to a valve arrangement for pressure and flow control of a fluid. The preferred field of application of the invention is

Control of gas flow to burners, especially atmospheric injector burners.

Conventional valve arrangements of this type have a housing which contains a large number of individual parts, namely springs, membranes, valve elements and, if appropriate, further closure devices which may be driven by additional magnetic coils or the like. The housing, which is usually made of metal, is also penetrated by a large number of bores and channels of different diameters, some of which can be very fine bores. The mechanical manufacture of such valve assemblies is very complex and accordingly expensive.

In addition, the energy content of the gas present under the supply pressure of generally 20-25 mbar is used to carry out the control in order to act on the diaphragm and return springs. The usual valve arrangements therefore work with a corresponding pressure loss, which can easily amount to approximately 30%. The invention has for its object to provide a structurally simple valve arrangement that works with very little pressure loss and allows dynamic control over a wide performance range.

To achieve this object, the valve arrangement of the type mentioned at the outset is characterized according to the invention in that

that a first silicon wafer with a plurality of etched through openings and a second silicon wafer with at least one etched through frame opening are provided, the frame opening being a multiple has a number of flaps produced by etching, which are connected in one piece to the second wafer via membrane-like webs,

- That the wafers are connected to one another in such a way that each flap of the second wafer is assigned at least one of the through openings of the first wafer, and

- That at the location of each of the flaps there are control means which selectively effect the opening and closing movements of the flaps as a function of a control device.

This valve arrangement is extremely simple in construction and, in comparison with conventional "three-dimensional" valve arrangements, can certainly be referred to as "two-dimensional". They essentially consist of the two silicon wafers, which are subjected to a conventional anisotropic or isotropic etching process. This creates the through openings in the first wafer and the flaps in the second wafer, around which the fluid flows in their open position in which they expose the through openings. An extensive housing can be omitted. Rather, the arrangement can be installed directly in a supply line. Accordingly, there are very small sizes, which can also be used in small devices, for example in water heaters, grain brewing devices, heaters for small residential units and the like.

Since the fluid does not have to work against membranes and return springs, the pressure losses are very low. When supplying gas to injector burners, the supply pressure is practically at the injectors. This allows air numbers to be set that contribute to significantly reduced pollutant emissions.

The power-dependent flow is controlled by selectively opening certain flaps of the second wafer and keeping others selectively closed. It was found that a modulating control is possible in this way, which ranges from a few percent to 100% covers. With conventional valve arrangements, the dynamic range has hitherto extended from approximately 60% to 100%.

Different numbers and / or sizes of through openings of the first wafer are preferably assigned to the individual flaps of the second wafer. This allows a maximum range of variation to be achieved. The control ensures that the flow cross-section required in each case is made available by selecting certain numbers and / or sizes of through openings. This advantage, combined with the small size and the inexpensive manufacture, offers the possibility of providing a separate valve arrangement for each injector or burner segment. This enables modulating control to be achieved with optimum accuracy over a maximum range.

Also, several modules of passage openings and associated flaps can be controlled separately from one another in a modulating manner, so that one and the same wafer arrangement supplies several injectors or burners independently of one another.

In a development of the invention it is proposed that at least some of the through-openings of the first wafer are tapered in the flow direction and that the associated flaps of the second wafer are provided in one piece with complementary locking projections. This offers an additional control option in such a way that the passage cross section of the first wafer can be changed. The etching of the tapered through openings and the complementary locking projections presents no difficulties, since the etching process can follow the crystal orientation of the silicon.

When the flaps of the second wafer are etched, the flap thickness is greatly reduced compared to the thickness of the wafer. This applies in particular to the membrane-like webs that connect the flaps to the wafer body. So the wafer is correspondingly hollowed out and perforated, a flap surface lying in the plane of one of the wafer surfaces. During assembly, this surface of the second wafer can then be placed on the first wafer. Under these circumstances, the flaps sealingly cover the associated through openings of the first wafer. In addition, the supply pressure of the fluid contributes to increasing the sealing effect. If, on the other hand, the second wafer is placed on the first wafer in the opposite orientation, the flaps are at a distance from the contact plane of the wafers. In this case in particular, it is advantageous to pretension the mebram-like webs of the flaps in the closing direction by doping the silicon. The bias is sufficient to press the flaps of the second wafer onto the first wafer. In the case of flaps with locking projections, in which only this type of assembly is possible, the pre-tensioning of the membrane-like webs is particularly useful. However, a pretension to increase the sealing effect can also be advantageous if the flaps of the second wafer rest on the surface of the first wafer anyway.

In addition, the two wafers are aligned exactly with one another and connected to one another by suitable adjustment, assembly and bonding techniques, if appropriate with the interposition of sealing materials. The valve arrangement makes consistent use of micromachining technology. The structure is filigree, and the passage cross-sections are extremely fine - with all possible variations. When used on gaseous media, in particular on fuel gases, this results in the requirement to work with gases that are as dust-free as possible. Since this is not always possible, it is proposed in a development of the invention that the second wafer has a third silicon wafer etched as a dust sieve on its side facing away from the first wafer. The sieve openings can be very fine and still ensure the required passage cross section due to their large number. she offer effective protection for the downstream flaps and through-openings, the additional structural and cost-related expenditure being extremely low, since here too, the advantageous technology of micromachining is used consistently.

The control means are preferably provided for selectively effecting the opening and closing movements of the flaps between the first and second wafers and / or between the second and third wafers. If a third wafer is used, there is the possibility of switching between to support the first and the second wafer effective control means or to replace them entirely.

The control means for actuating the flaps can be of different types, always taking into account the fact that work is carried out in the field of micromechanics. A thermally controlled bimetal actuation of the flaps is conceivable, for example. Under certain circumstances, electrical control is simpler, for example using the piezoelectric effect. As a particularly advantageous development of the invention, it is proposed that the control means exert capacitive or magnetic field-induced repulsive or attractive forces on the flaps. To do this, it is only necessary to provide the flaps and the adjacent wafer or wafers with opposite electrical conductors and to polarize them accordingly. The arrangement is preferably such that the flaps assume their closed position when the electrical control means are de-energized. In the event of a power failure, the supply pressure, possibly supported by the pretensioning of the flap webs, automatically closes the entire valve arrangement.

Furthermore, it can be advantageous to provide at least one of the wafers with a coating of thermally expandable material in the region of the openings. If the valve arrangement overheats, the material of the coating swells and leads to an automatic sealing. block the openings. A separate thermal safety shut-off valve can therefore be omitted.

There are various options for arranging the expandable material. In this way, the material can cover the inner walls of the through openings of the first wafer. It can also be arranged around the through openings on one or both sides of the first wafer. Attachment to the sealing surfaces of the flaps is also an option. From a manufacturing point of view, the last two options mentioned are likely to be cheaper than coating the inner walls of the through openings. If the third wafer forming a dust sieve is used, it is particularly advantageous to coat it with the expandable material on one and / or the other side. The individual measures can also be combined with one another.

For correct dynamic pressure and flow control, it is necessary to record both the supply pressure and the working pressure. The valve arrangement in a further development of the invention meets this requirement in that pressure load cells are etched into the first wafer, each of which is closed on the pressure side by a membrane which is integrally connected to the wafer.

It is also necessary for gas devices to record the gas quality. It is proposed that

that a capillary channel is etched into the first wafer and covered except for an inflow-side inlet opening and an outflow-side outlet opening,

- That the flap of the second wafer is assigned to the inlet and the outlet opening of the capillary channel and

- That a pressure sensor or an anemometer can be connected to the outlet opening. The capillary channel must have a predetermined length and is therefore meandered in the first wafer. Before the burner is started, the inlet opening on the upstream side is closed and the outlet opening on the downstream side is opened. In the capillary channel the atmospheric pressure. As soon as this has happened, the outflow-side outlet opening is closed and the upstream-side inlet opening is opened. The gas now flows through the capillary channel at a speed that depends not only on the geometric conditions but also on the viscosity of the gas. The latter in turn is a measure of the upcoming gas quality. Since the gas quality can be recorded and included in the control system before each burner start, there is a further increase in the control quality.

If an anemometer is connected to the outlet opening of the capillary channel, the flow rate that occurs there is detected. On the other hand, if you work with a pressure sensor, the pressure rise is measured.

In the latter case, it is advantageous to design the pressure sensor of the capillary channel as an etched pressure load cell, which is closed by a membrane which is connected in one piece to the first wafer. The invention is explained in more detail below on the basis of preferred exemplary embodiments in conjunction with the accompanying drawing. The drawing shows in:

Fig. L shows a section through a built-in valve assembly consisting of three wafers, the

Design features of the individual wafers are omitted; 2 shows a plan view of one of the wafers; 3 shows a detail from FIG. 2 in a modified embodiment;

4 is a top view of another of the wafers; 5 shows a partial section through the valve arrangement; 6 shows a modified embodiment in a representation corresponding to FIG. 5. θ

1, a valve arrangement 1 consists of three wafers, namely a first wafer 2, a second wafer 3 and a third wafer 4. The valve arrangement is installed in a fuel gas line 5, which in the present case leads to an injector burner . The valve arrangement 1 allows a flow in the direction indicated by arrows.

The wafers 2 to 4 consist of silicon, their shape being produced by conventional etching. 2, the first wafer 2 has a plurality of through openings 6, which can be selectively opened and closed in a manner to be described in order to control the pressure and flow of the gas as a function of a control device, not shown. In Fig. 2, the through openings 6 are shown as smooth openings of the same size, with a circular cross section. Their number is adapted to the respective circumstances.

Fig. 3 shows a modified embodiment in which the through opening 6 has a square cross section and is also tapered in the direction of flow. Smooth through openings with a square or rectangular cross-section are equally possible. It should also be noted that the through openings 6 can also be of different sizes.

FIG. 4 shows the second wafer 3, via which the opening and closing of the through openings 6 is effected. Flaps 7, which have been produced by etching the second wafer 3, are provided as closing elements. Here, a frame opening 8 has formed in the second wafer 3, into which the flaps 7 protrude. Each flap 7 is connected to the body of the wafer 3 via a membrane-like web 9. The membrane-like webs 9 allow selective movement of the flaps 7.

From Fig. 4 it follows that the flaps 7 different numbers of through openings 6 are assigned. Appropriate control of the flaps 7 allows any flow rates to be set. This enables a modular dynamic control that covers an extremely wide control range. An additional fine tuning is made possible by the fact that the through openings 6 are of different sizes. 5 shows a section through the valve arrangement at the location of one of the flaps 7. It follows that the wafers 2 and 3 lie on one another, the flap 7 of the second wafer 3 closing the associated through-opening 6 of the first wafer 2. Electrical control means 10 open the flap 7. The control means 10 are two conductor surfaces, one of which is assigned to the first wafer 2 and the other to the flap 7. A corresponding polarity causes a capacitive repulsive force which brings the flap 7 into the open position while elastically deforming its web 9. As soon as the control means 10 are switched off, the flap 7 closes, the supply pressure of the fuel gas causing an additional closing force. The arrangement works with very little pressure loss. 5 further shows that the third wafer 4 is provided with etched-in sieve openings 11 and thus forms an upstream dust sieve: which protects the downstream valve system against contamination. If the fuel gas is sufficiently dust-free, the third wafer 4 can also be dispensed with.

In the present case, however, the third wafer 4 also fulfills an additional function in that it supports the opening movement of the flap 7. For this purpose, a further set of control means 10 is provided, which are assigned to the third wafer 4 on the one hand and the flap 7 on the other hand. The polarity is such that a capacitive attraction is brought about. Here, too, the action of force ceases as soon as the control means are switched off. Finally, FIG. 5 shows that the through opening 6 is provided with a coating 12. The latter consists of a thermally expandable material, especially a plastic, and serves as a thermal fuse. As soon as the temperature of the valve arrangement rises above a certain value, for example 650 ° C., the coating 12 expands and automatically closes the passage opening 6.

The arrangement of the coating 12 on the inner wall of the passage opening 6 was chosen as an example that can be represented in the drawing. For manufacturing reasons, it may be more advantageous to apply the coating in the area of the passage opening 6 on one and / or other surface of the wafer 2 or else on the sealing surface of the flap 7. A particularly simple possibility is to coat the third wafer 4 on one and / or the other side. A combination of the individual measures is also possible.

In the variant according to FIG. 6, the through opening 6 is tapered conically in the flow direction. In addition, the flap 7 is provided with a complementary locking projection 13. This offers the possibility of changing the cross section of the through opening 6 and thereby further increasing the variability of the dynamic control.

In order to keep the flap 7 according to FIG. 6 in the closed position regardless of the supply pressure of the fuel gas in the currentless control means, the silicon of the second wafer 3 is doped at the location of the web 9 in such a way that the flap 7 is preloaded accordingly.

It should be mentioned that such a pretension can also be generated in the case of the exemplary embodiment according to FIG. 5, but is not absolutely necessary there.

2 that the first wafer 2 is provided with a capillary channel 14. This is etched into the wafer 2 and covered with suitable means. The capillary channel 14 has an inflow-side inlet opening 15 and an outflow-side outlet opening 16, these openings being closable by flaps 7, see FIG The inlet opening 15 can be subjected to the supply pressure, while the outlet opening 16 can be connected to the atmosphere. In addition, the outlet opening 16 forms a pressure cell, which is provided with a membrane. The latter is formed by etching the first wafer 2.

Before each start of the associated burner, the inlet opening 15 of the capillary channel 14 is closed and the outlet opening 16 is connected to the atmosphere, so that the atmospheric pressure is established within the capillary channel 14. Then the outlet opening 16 is closed and the inlet opening 15 is opened. The supply pressure then builds up in the capillary channel 14. The rise in pressure is detected at the pressure transducer assigned to the outlet opening 16 and provides information about the viscosity of the fuel gas and thus about its gas quality.

As can also be seen from FIG. 2, two further pressure transducers 17 and 18 are etched into the first wafer 2. Both pressure transducers 17 and 18 have membranes made of silicon, which are formed in one piece with the wafer 2 during the etching. The pressure cell 17 detects the supply pressure and the pressure cell 18 the working pressure, these values being included in the control. This increases their accuracy.

Modifications are quite possible within the scope of the invention. 2 and 4 show the assignment of a first set of through openings and flaps to an injector burner. Additional sets can be provided in order to control further injector burners or injectors of burner sets independently of one another. Furthermore, in the arrangement according to FIG. 5, the second wafer 3 can be placed on the first wafer 2 in the reverse orientation. The web 9 of the flap 7 is then doped in such a way that the flap assumes its closed position, as is shown with reference to FIG. 6. The control means 10 shown are capacitive control means. Instead of this, inductive control means can also be provided. Further there is the possibility to effect the opening and closing movements of the flaps piezoelectrically. Thermal control using a bimetal element is also conceivable. 2, the capillary channel 14 is provided on the output side with a pressure cell. An anemometer can also be connected here in order to obtain information about the viscosity and thus the quality of the fuel gas via the resulting flow rate.

Although the invention was explained on the basis of a burner control, the valve arrangement can also be used for other gases and also for liquids.

Claims

1. Valve arrangement for pressure and flow control of a fluid, characterized in that

- That a first silicon wafer (2) with a plurality of etched through openings (6) and a second silicon wafer (3) with at least one etched through frame opening (8) are provided, the frame opening a plurality of flaps (7) produced by etching, which are connected in one piece to the second wafer (3) via membrane-like webs (9),

- That the wafers (2, 3) are connected to each other such that each flap (7) of the second wafer (3) is assigned at least one of the through openings (6) of the first wafer (2), and

- That at the location of each of the flaps (7) control means (10) are provided which selectively cause the opening and closing movements of the flaps (7) as a function of a control device.

2. Valve arrangement according to claim 1, characterized in that the individual flaps (7) of the second wafer (3) are assigned different numbers and / or sizes of through openings (6) of the first wafer (2).

3. Valve arrangement according to claim 1 or 2, characterized in that at least some of the through openings (6) of the first wafer (2) are tapered in the direction of flow and that the associated flaps (7) of the second wafer (3) in one piece with complementary trained locking projections (13) are provided.

4. Valve arrangement according to one of claims 1 to 3, characterized in that the membrane-like webs (9) Flaps (7) are biased in the closing direction by doping the silicon.

5. Valve arrangement according to one of claims 1 to 4, characterized in that the second wafer (3) on its side facing away from the first wafer (2) has a third silicon wafer (4) etched as a dust sieve.

6. Valve arrangement according to one of claims 1 to 5, characterized in that the control means (10) for selectively causing the opening and closing movements of the flaps

(7) between the first and the second wafer (2, 3) and / or between the second and the third wafer (3, 4) are provided.

7. Valve arrangement according to one of claims 1 to 6, characterized in that the control means (10) exert capacitive or magnetic field-induced repulsive or attractive forces on the flaps (7).

8. Valve arrangement according to one of claims 1 to 7, characterized in that the flaps (7) assume their closed position when currentless electrical control means (10).

9. Valve arrangement according to one of claims 1 to 8, characterized in that at least one of the wafers (2 to 4) is provided in the region of the openings with a coating (12) made of thermally expandable material.

10. Valve arrangement according to one of claims 1 to 9, characterized in that in the first wafer (2) pressure load cells (17, 18) are etched, each of which is closed on the pressure side by a membrane connected in one piece to the wafer.

11. Valve arrangement according to one of claims 1 to 8, characterized in that

- A capillary channel (14) is etched into the first wafer (2) and is covered except for an upstream inlet opening (15) and an outlet side outlet opening (16).

- That the inlet and the outlet opening (15, 16) of the capillary channel (14) is assigned a flap (7) of the second wafer (3) and

- That a pressure sensor or an anemometer can be connected to the outlet opening (16).

12. Valve arrangement according to claim 11, characterized in that the pressure sensor of the capillary channel (14) is designed as an etched pressure load cell, which is closed by a membrane connected in one piece to the first wafer (2).