EP0707693A1

EP0707693A1 - Fluid flow regulating valve with a control element made of an electrically heatable, shape memory alloy

Info

Publication number: EP0707693A1
Application number: EP94918786A
Authority: EP
Inventors: Günter Voss
Original assignee: Leybold AG
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1993-07-08
Filing date: 1994-05-26
Publication date: 1996-04-24
Also published as: DE4322731A1; WO1995002143A1; JPH08512387A

Abstract

A fluid flow regulating valve has a control element made of an electrically heatable, shape memory alloy which adjusts a closure element against the restoring force of a spring according to a temperature-dependent longitudinal change in its position in relation to the valve seat. In order to keep constant a state of a fluid (for example pressure, flow rate, mixture composition etc.), the control element is a thread (1) heated by a constant current up to a temperature within the phase transition range of the shape memory alloy (SMA) and the valve body (20) which surrounds the thread (1) is designed as a heat exchanger which in co-operation with the thread reacts in a special way to changes in the state of a passing fluid flow. Appropriately, the valve body contains a bore (24) for receiving the SMA thread (1), for guiding the fluid flows to be regulated and for carrying out the heat exchange between the SMA thread (1) and the fluid flows, as well as channels (27) or joints (28).

Description

Valve for regulating fluid flows with an actuator made of electrically heatable, completely clean material

The invention relates to valves for regulating fluid flows with an actuator made of electrically heatable, ge staltseri nne rndem material, which has a closure element against the back L l force of a spring according to a temperature-dependent change in length its position relative to the valve seat.

A compressed air valve L for robot controls is known from the German magazine Management Wissen 8/88, page 59 "Tech-Highlights". This valve is characterized by an extremely small size, simple construction and fast switching 11 mpu l s e. It replaces previously used electromagnetic valves which, on the contrary, are large and expensive, their magnets being often a source of interference for sensors and for sensitive microelectronic circuits.

The new, extremely small valves use memory metals as an active element. In the molecular structure of these alloys, the geometry of a solid phase is impressed, so that geometric changes can take place depending on the temperature. The well-known compressed air valve has a memory metal lsti ft, which is connected to the valve tip, which is held in the closed position by a compression spring. The memory metal pen is integrated in an electrical circuit. When there is no current flowing, the spring keeps the valve closed, the memory metal keeping its comparatively longer geometric shape in the state of low temperature. When heated with electricity, it converts to its second high pressure temperature form and becomes shorter. The spring force is overcome and the valve opened.

The known version of the valve is a pure control element with opening or

Locking function. A regulation of fluid flows is not feasible with the known venti l.

A sensor for measuring and analysis devices is known from EP-A1-0 391 018. It is a sensor element in which the size to be measured has a direct or indirect influence on the condition of the material of the sensor element. The sensor element is made of a material called Gesta Itseri and is heatable in such a way that its operating temperature can be adjusted to a temperature in the range of the structural phase transition of its material. Characteristic of the function of the known measuring and analysis device is that the temperature of the sensor is kept constant with the aid of a controllable heating current, the voltage applied to the wire, the heating current or the heating power, being used as a measured variable. In this known device, the size to be measured has an influence on the temperature of the transition in the area of the phase structure The low temperature eme phature phase into the high temperature phase with the help of a material that keeps the heat from the air, i.e. the heating current is adjusted to a change in temperature of the material.

A direct control of fluid flows is not possible with the known measuring and analysis device, but would require the arrangement of an additional e rect to see romechani or electromagnetic control lung organ for the fluid flow, which would then have to be controlled by the known measuring and ana lysis device. Such an arrangement is complex, prone to failure and therefore unsatisfactory.

The invention is therefore based on the object of specifying a valve for regulating fluid flows with an actuator made of electrically heatable gesta Ltseri material of the type mentioned, which can be used for direct control, in particular in the sense of constant maintenance of a predetermined state of a fluid flow passed through and moreover uncomplicated in construction and extremely small.

The solution to the problem is achieved with a Venti l of the type mentioned in the preamble of claim 1 with the invention in that the actuator a temperature of the Gesta Itungseri nnen material SMA (SMA = Shape Memory Alloy) within the phase transition area by constant ant st ro heated thread and the valve body surrounding the thread in cooperation with it as one in a special way to changes in the state of a through the fluid flow responsive heat exchange device is trained.

With advantage, the valve is suitable for direct control of a fluid flow, which is regulated within a comparatively narrow equilibrium range of its state, for example in a constant pressure range, a constant flow range or a constant gas mixture range or also in a constant temperature range.

One embodiment of the invention provides that the valve has channels or connections which receive the SMA thread, conduct the fluid streams to be regulated and serve to heat exchange between the SMA thread and the fluid streams.

What the valve and its systematic valve variants have in common is that the contraction or elongation of a material made of steel is used to actuate the closing mechanism. Another common feature in the arrangement of the valve or its valve variants is that a change in the length of its actuator caused by a change in a fluid flow in the area of the phase transition results in an immediate change in the conductance or the flow rate of the fluid through the valve, so that this conductance is a monotonous function of the temperature-related length of the actuator. All parameters occurring during operation are responsible for the temperature of the wire, which can influence the heat balance of the system. For example: - temperature T of the fluid

- Thermal conductivity W of the fluid or different fluid components

- You flow rate e q of the fluid

- pressure p of the fluid

- Electronic, in particular constant heating power on the wire P

Assuming that the ambient (wall) temperature of the valve is constant, the conductivity of the valve is a function of one or more of these quantities.

L = f (T, W, q, p, P)

Depending on the construction of the valve and the heating output kept constant, the process medium compensates for the effects of the above-mentioned variables directly through the process medium through the operating mode or constructive measures. For example, a special design of the valve can ensure that the pressure comes into contact with the wire, but not the flow flowing through the valve, and vice versa. The design can vary so that ^' the contracting thread causes either a closure or an opening of the valve.

Some of the valve designs that are of interest for practical applications are given below. For example, this can be designed as a pressure control element and a body made of electrically non-conductive material with a bore receiving the SMA thread, the spring and the closure element and with a Have valve seat with a connecting channel and a side channel branching side receiving head and a closed bottom part l, the spring as a conductor for the current flow between the vent i lse iti gene end of the SMA wire and the other end thereof on the valve bottom are connected to a power source.

In this type of construction, the gas pressure surrounding the thread when the valve is open is equal to the pressure of the fluid flowing from the secondary duct through the connecting duct L. The gas flow can pass through the valve without significantly influencing the SMA wire. In pressure areas in which the heat conduction is pressure-dependent, the valve shows control valve 11. As the pressure drops, the thread temperature increases, the thread contracts and opens the valve. Conversely, if the pressure increases, the gas flow is throttled. It equates to a constant electrical heating output _. increased pressure, which is kept constant within certain limits.

Another embodiment provides that the valve is designed as a flow control member and has an inflow channel in the bottom part 1 and an outflow channel in the top part 1. With this construction, the gas flow flows along the SMA wire and transports heat away. In suitable river areas, the heat dissipated is a function of the flow. With an impressed constant electrical power, which keeps the wire temperature at a predetermined constant flow of the fluid at the phase transition limit, a function is realized in which increasing flow lowers the thread temperature, the thread lengthening and the conductance of the valve being reduced . Decreasing river causes the opposite l. In this way, the flow of the flowing fluid tends to a state of equilibrium, which is kept constant within narrow limits. The resulting flow is approximately proportional to the voltage or heating power fed in. That is why this type of valve is suitable as an actuator in electronic control loops for the pruning of gases. In contrast, Proportion on Ivent i Le manufactured according to the prior art are problematic, extremely complex and prone to failure for the gas flow.

Another embodiment of the invention provides that

Venti l is formed as a Lorgan, and the

Head part of the valve seat with an inlet channel for one

Gas component with a comparatively high thermal conductivity and a secondary channel for the mixture inlet, s-ow-ie the

Bodentei l an outlet channel for the constantly regulated

Mixture. This type of valve uses the thermal conductivity of different types of gas as the physical basis. Moving in

Gas mixtures the concentrations, this generally results in a change in the thermal conductivity. If, when the valve is closed, a gas current from the secondary duct in the

If the valve head flows to the outlet duct in the bottom part, the heating power of the SMA wire is at a predetermined constant flow with predetermined mixture concentrations

Gas components in equilibrium. Here lies the

Gas component with the higher thermal conductivity at the initially closed inlet duct of the head part. If this component is depleted in the mixture, the

Thermal conductivity decreases, the wire increases its temperature and shortens, so that the valve opens and the Component with the higher thermal conductivity is additionally enriched. In this way, the equilibrium of the concentration is within relatively narrow limits.

Another advantageous valve variant is designed as a protective valve for gas leak detectors, in particular for helium leak detectors. It has an inflow channel in the bottom part l, a connection channel to the leak detector in the head part l and a bypass opening in the bypass to the valve seat at the head end of the valve body. With the sniff Lbet ri eb, high helium concentrations can contaminate the leak detector. Usually the responsible gross leak is only recognized when the gas flow with the high

The apparatus has already passed helium concentration. The result is insensitivity and long recovery times. In such a case, the protection valve switches off the gas flow. The heating power is set so that the valve is open at low concentrations. If a gas stream enriched with helium now enters through the inflow channel in the bottom part l, the SMA wire is cooled due to the higher concentration of helium in the gas stream, and cooled due to the increased thermal conductivity of the gas, lengthens and closes the valve l. The gas flow can then only escape through the bypass opening. As soon as the

If the helium concentration has decreased, the valve moves back to the initial state, i.e. it opens.

A further embodiment provides that the valve is designed, for example, as a visual filter, with a central valve body, one Gas inlet channel in the bottom part l and a first, the closure element guiding, with a valve seat in an intermediate wall closable hole, which is followed by a second hole in the valve body, which receives the SMA thread firmly connected to the tip of the valve , which is fastened on the outlet side to the head part 1 having an outlet channel. This is a Schaltventi l, which remains in its state after tripping and must be reset from the outside. If a gas flow passes the valve from the bottom part to the head part, the gas flow is completely switched off when the flow falls below a certain threshold, as a result of which the wire temperature rises further and the valve remains in the closed position.

An advantageous embodiment of the valve in the variant embodied as a through-flow regulator also consists in that for guiding the fluid flow while increasing a flow density which intensifies the heat exchange

I.

For air flow, a comparatively narrow ceramic tube surrounding the SMA wire and extending between the inlet channel in the base part and the valve seat is arranged.

The invention is shown in schematic. Drawings in preferred embodiments, further advantageous details and features of the invention being apparent from the drawings.

Show it :

Fig. 1 is a diagram of a Vent i barrel structure for constant active lung pressure of the gaseous Media,

2 a Schaltbi ld of the Venti running construction according to FIG. 1,

3 is a schematic of the venti structure for constant flow regulation of a gas flow,

4 is a Schaltbi ld of the Venti Laufbaues of FIG. 3,

5 shows a diagram of a valve structure for constant air flow of gases,

6 is a Schaltbi ld of the Venti Laufbaues of FIG. 5,

Fig. 7 is a diagram of Vent i Laufbaues in the function of a Schutzventi ls for Heliumlec ^'ksücher,

8 is a diagram of the Venti Laufbaues in the function of a Sehwe L Iwertscha Lters,

9 shows in section a valve for constant flow control according to FIGS. 3 and 4 with a ceramic tube surrounding the SMA wire,

The Vent i L superstructure variants shown purely schematically in the figures have, as matching or similar features in construction, a valve body (20) made of electrically non-conductive material with a head part (25) having the valve seat (22) and one Soil part (26). The valve body (20) takes in a bore (24) the Versch Luße element (21) with the actuator (1) made of electrically heatable sta Lt se ri nne rende material in the form of the SMA thread and the return spring (23).

Even if the valve variants described below have in common that the contraction or elongation of the wire (1) made of material reminiscent of the shape is used to actuate the closure element (21), where in principle instead of the wire (1) other geometric shapes with changes in shape due to bending or torsion can also be used. Because of the simplicity of the construction and the clarity of the function, the wire principle is preferred and shown as an example. The use of a cone or needle valve body as a locking element (21) is also to be understood as a pure embodiment example and not as a limitation. Basically, other types of valves can also be used here. The arrangement of the drive is fundamentally chosen so that a change in length of the SMA wire (1) used as an actuator in the area of the phase transition results in a change in the conductance and thus the fluid passage in the valve seat (22), so that the master value is a monotonous function of the length of the actuator.

Due to the basic structure) of the valve in the form of a heat exchange device which responds in a special way to a change in the state of the fluid flow being passed through, it is achieved that the respective length of the wire (1) as a function of the thread temperature with a constant heating power of different physical parameters of the fluid flow is therefore responsible for the temperature of the wire (1) all parameters that occur during operation, which have an influence on the thermal balance of the system such as temperature, Thermal conductivity, flow rate, pressure and mixture type of the gases.

Figure 1 shows an arrangement for a pressure constant. The gas pressure surrounding the SMA thread is equal to that at connection A of the secondary duct (28), since it is connected to the bore (24) of the valve body (20). When the Ver rsch Luße element (21) in the high temperature state of the SMA thread (1), a gas flow can flow between the secondary duct (28) and the connecting duct (B, 27) in the head part (25) of the valve. In pressure areas in which the heat conduction is pressure-dependent, the valve shows regu lation. When the pressure drops, the temperature of the thread (1) increases, the thread (1) contracts and opens the valve (21, 22). Conversely, if the pressure increases, the gas flow is throttled. An equilibrium pressure is established for a fixed electrical heating output, which is kept constant within comparatively narrow limits. 1 has a closed bottom part l (26), the spring (23) as a conductor for the current flow between the vent i Lsei ti gene end of the SMA wire (1) and its other end on the valve bottom ( 26) is each connected to a power source (2) via the 'St. Rome connections (3 and 4).

FIG. 2 shows the circuit diagram of the valve assembly according to FIG. 1. The circuit diagram shows the arrangement of a fine vacuum apparatus with a gas flow from B to A and to the vacuum pump (10) via the vacuum container (11) and the valve body (20) with the actuator arranged in the bypass to the fluid flow in the form of the SMA thread ( 1 ) . This is via the power connections (3,4) connected to the power source (2). This is shown as a controllable current source (2), but is constantly regulated for a pressure to be kept constant.

The Venti Laufbau according to Figure 3 shows a system for constant flow control. With this construction, the gas flow passes the SMA wire (1) and transports heat away. In suitable F flow areas, the heat dissipated is a function of the flow. With impressed electrical power corresponding to a wire temperature in the area of the phase transition, increasing flow lowers the fadent empe rat ur, while decreasing flow causes the opposite. Here the river strives for a balance. The valve has on the bottom part (26) an inflow channel (30) with the designation B and in the head part (25) an outlet channel (29) with the designation A. The electrical connections and designations are otherwise the same as those in Fig. 1.

The circuit diagram of the flow control valve according to FIG. 3 is shown in FIG. 4, the same elements also being identified with the same reference numbers. A fluid flow from B along the heated SMA thread (1) is conveyed from the fan (9) via the valve to the outlet duct A. When the flow changes, the temperature of the SMA thread (1) changes as described above when it is constantly heated by the current source (2), the closure element (21) reacting accordingly.

FIG. 5 shows a valve designed as a lively mixture. It has the valve (20) with the closure element (21), the actuator of the SMA wire (1) and the return spring (23). The mixture to be controlled, consisting of at least two components, enters the valve through the inlet channel (A) in the head part (25), flows along the SMA thread (1) and leaves the valve through the outlet channel at the bottom (34) with the designation C. A gas component with a higher thermal conductivity, initially blocked by the Vent i Lve rsch Luß body (21), is present at the inflow channel (32) with the designation B. The gas capacity is gas dependent. If the concentrations of the components shift in the gas mixture, this leads to a change in the thermal conductivity with a constant flow. The one shown uses this effect

Vent i L con struct i on. A binary gas mixture, for example, constantly flows through the connection A to the output C. If the component with the higher thermal conductivity in the mixture is depleted, the conductivity decreases, the SMA wire (1) increases its temperature and shortens, the closure element (21) stands out from the valve seat (22), whereby a flow cross-section of the inflow channel (32) is opened for the component with the higher thermal conductivity and the mixture is adjusted again to constant mixture concentrations.

For this purpose, Figure 6 shows a Schaltbi ld. By the fan (8) a z. B. binary fluid mixture via the inlet channel (33) labeled A through the Venti lkörper (30) through to the outlet channel (34) with the label C. The blower (7) promotes the component with the higher thermal conductivity through the inlet channel (32) with the designation B in the manner described above for enriching the mixture of the fluid mixture when it opens the valve. Further elements are identified by the same reference symbols.

FIG. 7 shows a valve designed as a protective valve for gas leak detectors, in particular for He li um Lee ksuche r. The inflow channel (30), which is connected by a line to a sniffer tip, is located on the bottom part (26). The A ^'laßkanal (30) is called D. On Kopftei l (25), the outlet channel (29) is located with a connection to a leak detector. The outlet channel (29) bears the designation E. Furthermore, there is a bypass opening (35) immediately next to the head part (25). For a specific helium concentration and flow rate of the leak detector, there is a balance between the induced heating power of the SMA wire (1) and the heat dissipation by the leak detector current with the low helium concentration. The valve is open. If a fluid stream enriched with helium occurs at D, more heat is removed from the SMA wire (1) and

I ^* this takes on its elongated geometric shape. As a result, the closure element (21) closes the valve seat (22) and the gas flow can now only escape via the bypass opening (35).

The valve can alternatively also be configured as a visual switch for pressure or flow. FIG. 8 shows such a switch, which has to remain in its state after tripping and must be reset from the outside. The valve is designed with a valve body (20) divided in the middle, with a gas inlet channel (30) in the bottom part ( 26) and with an outlet channel (29) on the head part l (25). At the gas inlet duct (30) with the designation F closes a first, the gas closure element (21) guiding, with a valve seat (22) in an intermediate wall (19) closable bore (24). Furthermore, the valve l has a second bore (18) in the flow direction, which receives the SMA thread (1), which is firmly connected to the tip (17) of the closure element (21), as the actuator of the valve. This is fixed on the outlet side in the head part l (25). The SMA wire is heated via the power connections (3, 4) by the power source (2). During the function, a fluid flow passes through the schematically illustrated valve from F to G. If the flow falls below a certain threshold value, the gas flow is switched off and the heat removal by the gas flow is thus interrupted. As a result, the wire temperature continues to rise and the valve remains in this position.

According to a representation in FIG. 9, a particularly intensive heat exchange between the fluid flow and the SMA thread (1) can be achieved by designing the valve

I can be brought about with a flow guide tube (16). With this arrangement, the thermal equilibrium of the heat exchange between the constantly heated SMA thread (1) and the flowing fluid flow is determined by the dependence between the speed of the fluid flow and the more or less rapid heat transport caused thereby. As a result of the flow bundled by the kerami tube (16) in the immediate vicinity of the SMA thread (1), this balance and thus the function of the valve is extremely sensitive.

The valve types described above have a number of advantages over conventional valve types. It are this

- Simple, comparatively inexpensive construction

- small designs

- Special characteristics, thus simplified appli cations

- Operation with voltages below 0.5 V and currents below 0.5 A possible, therefore usable in hazardous areas

- Avoidance of interference for sensors and sensitive microelectronic circuits due to the elimination of magnets and their magnetic fields.

Claims

Expectations

1. Valve for regulating fluid flows with an actuator made of .electrically heatable shape-remembering material, which adjusts a closure element against the back e L l by force of a spring in accordance with a temperature-related change in length in its position relative to the valve seat, characterized in that the actuator to a temperature of the stacked material (SMA) within the phase transition area by constant current heated thread (1) and the valve body (20) surrounding the thread (1) in cooperation with this as a particular way to changes in Appealing heat exchange is formed in the state of a fluid flow passed through.

2. Valve according to claim 1, characterized in that there is a SMA thread (1) receiving, the <to regulating fluid streams conductive and the heat exchange between the SMA thread (1) and the fluid streams serving bore (24 ) so he has channels (27) or connections (28 - 30; 32 - 35).

3. Valve according to claim 1 or 2, characterized in that it is designed as a pressure regulating member and a body made of electrically non-conductive material (20) with an SMA thread (1) / the spring (23) and the closure element (21st ) receiving bore (24) and with a valve seat (22) with a connecting channel ⁽ 27) and a side channel branching off from it ⁽ 28 ⁾ Receiving head part L (25) and a closed bottom part L (26), the spring (23) as a conductor for the current flow between the vent i Ise iti gene end of the SMA wire (1) and its other end on the valve bottom ( 26) are each connected to a power source (2).

4. Venti l according to claim 1 or 2, characterized in that it is trained as a flow control member and an inflow channel (30) in the bottom part l (26) and one

Ausst romankana L (29) in the head part l (25).

5. Valve l according to claim 1 or 2, characterized in that it is formed as a rain shower lo rgan and the head part l (25) the valve seat (22) with an inlet channel (32) for a gas component with a comparatively high Thermal conductivity and a secondary channel (33) for the Ge ischeinlaß and the bottom part l (26) has an outlet channel (34) for the constantly controlled mixture.

6. Venti l according to claim 1 or 2, characterized in that it is formed as a protective valve for gas leak detectors, in particular for helium leak detectors, with an inflow channel (30) in the bottom part l (26), an outlet channel (29) as a connection to the leak detector in Head part l (25), and a bypass opening (35) in the bypass to the valve seat (22) at the head end of the valve body (20).

7. Venti l according to claim 1 or 2, characterized in that it is designed as a threshold switch, with a centrally divided valve body (20) with a gas inlet channel (30) in the bottom part (26) and a first, the closure element ( 21) leader, with a Valve seat (22) in an intermediate wall (19) closable bore (24), followed by a second bore (18) in the valve body (20), which connects the SMA with the tip (17) of the closure element (21). Thread (1) receives, which is fastened on the outlet side in the head part l (25) having an outlet channel (29).

8. Venti l according to claim 4, characterized in that for guiding the fluid flow while increasing a heat density intensifying flow density of the fluid flow surrounding the SMA wire (1), comparatively narrow, between the inlet channel (30) in the bottom part L ( 26) and the valve seat (22) extending ceramic tube (16).