WO2008108693A1

WO2008108693A1 - A fluid valve arrangement

Info

Publication number: WO2008108693A1
Application number: PCT/SE2007/000222
Authority: WO
Inventors: Mats Lavenius; Bertil Talen
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 2007-03-05
Filing date: 2007-03-05
Publication date: 2008-09-12
Anticipated expiration: 2009-09-05
Also published as: EP2126430A1

Abstract

A fluid valve comprising a valve body (1) having an chamber (2), the chamber (2) confined by a chamber lower end portion (7), a chamber upper end portion (8) and chamber wall(s) (6), the chamber (2) having at least a two ports (3, 4), a first port (3) and a second port (4) for communicating fluid to and from the chamber (2), and further a piezoelectric valve member (5) in the chamber (2) for controlling fluid flow between the at least two ports (3, 4), and the valve member (5) is a piezoelectric ring actuator of bender type which is aligned substantially parallel to the lower end portion (7) and at a distance (hi) from the lower end portion (7), the valve member (5) having a substantially centred opening (9).

Description

A FLUID VALVE ARRANGEMENT DESCRIPTION

TECHNICAL FIELD

The present invention relates to a fluid valve comprising a valve body having an chamber, the chamber confined by a chamber lower end portion, a chamber upper end portion and chamber wall(s), the chamber having at least a two ports, a first port and a second port for communicating fluid to and from the chamber, and further a piezoelectric valve member in the chamber for controlling fluid flow between the at least two ports.

BACKGROUND OF THE INVENTION

Solenoid valves have been commonly used for controlling the fuel supply in combustion engines. Solenoid valves are comparably fast and reliable, and have been proved to be very suitable in fuel injection systems for many kind of engines. However, it would of course be desirable if an even better fuel valve could be found — in particular in relation to its energy consumption. One candidate for such an improved valve is a valve using a piezoelectric valve member.

Piezoelectric valves are known as low energy consuming and they can be very fast in their response times. Piezoelectric actuators could be operated at very low voltages (10-30 V) up to high voltages (100-lOOOV). The most advanced piezoelectric actuators are the ones operated at low voltages, but they are also the most expensive ones.

The desirable characteristics of a fuel valve in e.g. a chainsaw are many. It needs to be fast and reliable as the solenoid valves used today have proven to be. Further the manufacturing costs are vital aspects in products such as chainsaws since these kinds of products are sold at comparably low prices. The size of course is an issue - the smaller the better.

Further, the fuel valve needs to be robust. For instance capable of withstanding high vibrations. A chainsaw can be operated at in cold winter as well as hot summer, and of course this sets high demands on the fuel valve. For instance due to the wide temperature range it is desirable to find a fuel valve which do not use elastic seals when sealing the valve seat, since these tends to have problems with keeping the tolerances in the such wide temperature ranges.

Another aspect when concerning fuel valves is that it should preferably opened or at least somewhat opened when non-activated, i.e. to facilitate the fuel supply during start.

For instance US4340083 shows a valve includes a piezoelectric bar mounted as a cantilevered beam. The free end of the bar is mounted for movement toward and away from a valve seat surrounding a control opening. The beam is initially flexed when in the closed position so as to maintain a fluid-tight seal with the seat. Application of an electrical signal causes the bar to flex further, thereby causing the deflectable beam portion to move away from the valve seat and permitting fluid to flow through the control opening. The valve is closed when inactive.

DE3608550, JPl 120496, JP63190985, US4567394, US6017016, US2001025752, WO8607429, WO9825061 and EP1200761 are further examples of piezoelectric controlled valves.

OBJECTS OF THE INVENTION

One object of the invention is to provide a valve using a piezoelectric valve member which is suitable to be used as a fuel valve in a fuel supply system to the kind of engines used in e.g. chainsaws and lawnmowers.

Several further objects of the present invention, which may be achieved individually or in groups according to various aspects of the present invention, are:

- to provide a fuel valve which can be operated at high voltages.

- to provide a fuel valve which may be manufactured at low costs. - to provide a fuel valve having a design that avoids need of sealing the valve seat.

- to provide a fuel valve having a simple and robust design.

- to provide a fuel valve having a low power consumption.

- to provide a fuel valve which is insensitive to vibrations.

- to provide a fuel valve which is small in size. - to provide a fuel valve having short response times. - to provide a fuel valve which is at least to some extent open when inactive, to provide fuel valve which has low leakage when closed.

SUMMARY OF THE INVENTION At least one of the above mentioned objects are solved by providing a fluid valve comprising a valve body having an chamber, the chamber confined by a chamber lower end portion, a chamber upper end portion and chamber wall(s), the chamber having at least a two ports, a first port and a second port for communicating fluid to and from the chamber, and further a piezoelectric valve member in the chamber for controlling fluid flow between the at least two ports, where that the valve member is a piezoelectric ring actuator of bender type which is aligned substantially parallel to the lower end portion and at a predetermined distance from the lower end portion, the valve member having a substantially centred opening.

According to further aspects of the invention:

- the chamber has the form of a flat cylinder. the edge of the valve member is secured within the chamber by positioning means of the chamber wall(s), preferably the positioning means is a chamber wall groove running along the chamber wall(s) in parallel to first end portion. - One of the ports is centrally located facing the opening of the ring actuator, the other port arranged at a port distance from the centre of the end portions, which port distance is larger than the opening radius of the ring actuator, the end portion comprising the second port further comprises a centred outlet groove, the outlet groove positioned at a radius corresponding to the port distance. - the piezoelectric ring actuator comprises at least two layers, and where at least one of said layers is a piezoelectric active layer, preferably the piezoelectric ring actuator has two piezoelectric active layers which piezoelectric layers are Y-poled, i.e. the polarization vectors for each of the two piezoelectric active layers point in the same direction.

We also propose a fluid valve comprising a valve body having a box-shaped chamber, the chamber confined by a chamber lower end portion, a chamber upper end portion and chamber wall(s) , the chamber having at least a two ports, a first port and a second port, where the first port has a valve seat protruding from the chamber lower end portion, the first port located close to a first chamber wall, a piezoelectric valve member in the form of a flat rectangular bender is cantilevered in or close to an opposite chamber wall so that the free end of the flat rectangular bender hovers above the valve seat, the fluid valve operated at an normal operating voltage Umax where the flat rectangular bender is arranged, at an operating voltage which is lower than the normal operating voltage, to contact the valve seat at a side of the first port facing the cantilevered end of the flat rectangular bender.

Further, the flat rectangular bender is arranged, to contact the valve seat at the side of the first port facing the cantilevered end of the flat rectangular bender and the opposite side beyond the first port, when the operating voltage is the normal operating voltage. This can be achieved by having the flat rectangular bender angle extending at an angle α in its non- actuated state, which angle α is in the range of 0,1-2°, preferably in the range of 0,2-0,6°.

According to even further aspects of the invention; a two stroke internal combustion engine having a magneto powered ignition system, fuel being supplied to the engine via a fuel supply system including an electrically controlled piezoelectric fuel valve of bender type where the fuel valve is arranged to be controlled at operating voltages of at least 60 V, preferably of at least 100V, more preferred of at least 150V and even more preferred of at least 200V. Preferably the operating voltage is supplied from a primary winding of a magneto powered ignition system.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention will be described in more detail with reference to preferred embodiments and the accompanying drawings.

FIG. 1 shows fluid valve connected to a magneto powered ignition system,

FIG. IA shows a charging pulse from the magneto powered ignition system of FIG. 1,

FIG. 2 shows a cross section of fluid valve according to a first embodiment of the present invention, FIG. 3 is a detail of FIG. 2 on a larger scale,

FIG. 4 is a detail of FIG. 2 on a larger scale,

FIG. 5 shows a lower valve body part of a fluid valve according to the first embodiment,

FIG. 6 shows a cross section of a fluid valve according to a second embodiment as seen from above, and FIG. 7 shows a cross section of the second embodiment taken along the line VII-VII, FIG. 8 shows schematically a cantilevered bender of a fuel valve which when inactive extends horizontally, and

FIG. 9 shows schematically a cantilevered bender of a fuel valve which when inactive extends at an angle, and

FIG. 9A shows a zooming of the dotted rectangle of FIG. 9, indicating the angle α between the cantilevered bender and a plane of the valve seat.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a flywheel 10 and a charging coil Ll charging an engine control system 20 of a hand held power tool powered by a two stroke internal combustion engine, Le. the engine uses a magneto powered ignition system. The engine control system 20 is shown schematically as a box and includes circuitry for controlling and powering the ignition of the spark plug 21 and the piezoelectric fuel valve 22. Even though the engine control system 20 is shown as a single box, the circuitry for controlling the ignition and the fuel valve 22 may be two separate systems and having controls units of their own, but of course a single engine control unit may also be utilized. Further, other components of the hand held power may be controlled and powered by the engine control system 20, such as for example warming the handle of the power tool by inductive heating.

The circuitry includes at least one condenser (not shown) from which power can be drawn. When the flywheel 10 is rotated a charging pulse is generated by the primary winding of the charging coil Ll, an example of the generated pulse is shown in FIG. IA, and the at least one condenser is charged by the pulse. For instance the positive part of the pulse indicated by 23 could be used to charge a first condenser Cl (not shown) and the negative pulses 24A, 24B could be used to charge a second condenser C2 (not shown).

In FIG. 1 the flywheel 10 is shown having one magneto 27 and an opposite located counterweight 28 and thus the charging pulse is created once every turn of the fly wheel. However if the energy generation is to be increased it is possible to replace the counterweight 26 with a second magneto and if it is desired to separate the two pulses, the second magneto could have the opposite polarity, i.e. so that the main pulse 23 alternates between negative and positive. Naturally even further magnetos could be used if desired. In FIG.l a single charging coil Ll is shown having a coil core with two pole legs. This is often referred to as the primary winding. However it is also possible to use further windings, e.g. having a coil core with three pole legs having the charging coil, the primary winding, arranged between the first two pole legs of the coil core and the secondary winding arranged between the second and the third pole leg. .

The configuration of the engine control system 20 is not an aspect of the invention and has therefore been shown and described schematically. An inventive feature according to then present invention, however, is the idea of powering the fuel valve 22 directly from the flywheel 10 without the need of lowering the operation voltage, i.e. using a high operating voltage which is at least 60V, preferably at least 150V and even more preferred above 200V. Thereby a more cost effective piezo actuator can be used. In FIG.l the supplied operating voltage is 240V.

The charging pulse from the charging coil Ll charges at least one condenser Cl of the engine control system 20. The condenser Cl is used to provide an operating voltage to a piezoelectric valve member 5 of the fuel valve 22. The piezoelectric valve member 5 has a bimorph structure, i.e. having two piezoelectric active layers 5A, 5B, a first layer 5A and a second layer 5B. The piezoelectric active layers 5A, 5B are poled in the same direction, i.e. Y-poled, and wired to work in parallel mode. The fuel valve 22 is shown merely as an example and the fluid valves of FIG. 2-5 respectively FIG. 6-7 may be operated in the same manner.

The switches Sl, S2, S3 control the piezoelectric valve member 5. When the first switch Sl is deactivated the condenser Cl is charged by the charging pulses of the charging coil Ll. Activating the first switch Sl provides the piezoelectric valve member 5 with an operating voltage.

Having the first switch Sl activated, the second and the third switches S2, S3 determines which layer 5 A, 5B to be activated. When the first switch Sl is deactivated, the second and the third switch S2, S3 will also be deactivated. When the first switch Sl is activated the second switch S2 is activated as the third switch S3 is deactivated and vice versa. Sl activated, S2 activated, S3 deactivated:

When the second switch S2 is activated, a current will flow over the second resistor R2, whereby the voltage over the first layer 5A will be decreasing and voltage over the second layer 5B will be increasing as the current flows over the second resistor R2. This will continue till the second switch S2 is deactivated or till the voltage over the first layer is zero and the voltage over the second layer 5B is equal to the system voltage of the fist condenser Cl, e.g. around 240V. The piezoelectric valve member 5 will bend downwards as a result of the contraction of the second layer 5B, closing the fuel valve 22.

Sl activated, S2 deactivated, S3 activated:

When the second switch S3 is activated, a current will flow over the third resistor R3, whereby the voltage over the second layer 5B will be decreasing and voltage over the first layer 5A will be increasing as the current flows (in negative direction) over the third resistor R3. This will continue till the second switch S3 is deactivated or till the voltage over the second layer 5B is zero and the voltage over the first layer 5 A is equal to the system voltage of the fist condenser Cl, e.g. around 240V. The piezoelectric valve member 5 will bend upwards as a result of the contraction of the first layer 5B, fully opening the fuel valve 22.

Sl deactivated, S2 deactivated, S3 deactivated:

The layers 5 A, 5B will slowly revert to their normal non-expanded states, as the layers are discharged.

In a special embodiment the piezo valve 22 and the ignition system shares the same condenser Cl. The condenser Cl has a capacitance in the range of 500-100OnF and the piezo activated valve member 5 has a capacitance of less than 1/10 of the capacitance of the condenser Cl (50 -10OnF). Since the capacitance of the piezo activated valve member 5 is so much lower than the capacitance of condenser Cl - the ignition will not be affected.

FIG. 2-5 shows a fluid valve 22 comprising a valve body 1 according to a first embodiment of the present invention, the fluid valve shown in its inactive state. The valve body 1 comprises an upper valve body part IA and a lower valve body part IB forming a chamber 2 in between the two valve body parts IA, IB. The lower valve body part IB having a first port 3 and a second port 4 to the chamber 2 for communicating fluid to and from the chamber 2.

The chamber 2 has the shape of a wide and flat cylinder providing a cylinder wall 6 and two opposite circular cylinder end portions 7, 8, a lower end portion 7 of the lower valve body part IB and a upper end portion 8 of the upper valve body part IA. The cylinder end portions 7, 8 having a cylinder radius r3. The cylinder radius r3 is preferably in the range of 5 - 25 mm, typically around 10mm.

The cylinder wall 6 has a wall groove 6A for positioning a piezoelectric valve member 5, preferably a piezoelectric ring actuator, in the chamber 2, i.e. by having the periphery of the ring actuator 5 positioned in the wall groove 6A. The wall grove 6A is positioned at a first height distance hi from the lower end portion 7 and a second height distance h2 from the upper end portion 8. Typically hl=h2. The thickness of the piezoelectric ring actuator 5 determines the width of the wall groove 6A, i.e. the piezoelectric ring actuator 5 is secured in the wall groove 6A.The radius of the ring actuator 5 is larger than the cylinder radius r3, but somewhat smaller than the cylinder radius r3 and the depth of the wall groove 6A taken together. For example the ring actuator 5 having a radius of 10 mm, the cylinder radius r3 being 9mm and the depth of the wall groove 6 A being 2mm - the larger diameter functioning as a tolerance gap both for manufacturing tolerances as well as thermal expansion.

The ring actuator 5 has a centred circular opening 9 with an opening radius r2. The ring actuator 5 having an upper rim 13 and a lower rim 14 at its opening. The shown ring actuator 5 has a bimorph structure, i.e. having two piezoelectric active layers 5A, 5B, a first layer 5a and a second layer 5b. The piezoelectric active layers 5A, 5B are poled in the same direction, i.e. Y-poled, and wired to work in parallel mode. The electrical wires connects to the ring actuator 5 through a first connection 15 at the upper side of the first layer 5A, a second connection 16 at the lower side of the second layer 5B, and a third connection 17 in-between the two layers 5A, 5b. The piezoelectric active layers 5A, 5B and its electrical connections 15, 16, 17 are sealed in relation to the chamber 2. In the figures the electrical connections 15, 16, 17 and their wires have only been shown schematically. The first port 3 is centrally positioned at the lower end portion 7 facing the opening 9 of the ring actuator 5. The second port 4 is positioned at the lower end portion 7 at a predetermined port distance rl from the centre of the lower end portion 7, which port distance rl is larger than the opening radius r2 of the ring actuator 5. Preferably the first port 3 is operated as an inlet port for the valve fluid and the second port 4 as an outlet port 4. The lower end portion 7 further comprises a centred circular outlet groove 11 positioned at a radius corresponding to said port distance rl, i.e. the second port 4 has its orifice to the chamber 2 in the outlet groove 11. The cross section of the outlet grove 11 has preferably the form of a semi circle having a typical radius of about 0, 5 -1 mm.

The fuel flow from the inlet port 3 towards the outlet port 4 is limited by area defined by the opening radius r2 of the ring actuator 5 and the gap between the lower rim 14 and the lower end portion 7. When the ring actuator 5 is inactive as shown in figure 2-4 - the fuel valve is partly opened and the gap between the lower rim 14 and the lower end portion 7 corresponds to the first height distance hi. Preferably the first height distance hi is less than 0,2 mm, more preferably less than 0,1 mm and typically around 0,05mm. The opening radius r2 could typically be around 4 mm, but this should of course be seen as a mere example.

When the ring actuator 5 is actuated for closure the centre of the ring actuator 5 will curve downwards closing the gap between the lower rim 14 and the lower end portion 7, preventing fluid to flow from the first port 3 towards the second port 4. When the ring actuator 5 is actuated to open the fluid valve, the centre of the ring actuator 5 will curve upwards increasing the gap between the lower rim 14 and the lower end portion 7. At maximum the ring actuator 5 can curve till the upper rim 13 meets the upper end portion 8, whereby the gap between the lower rim 14 and the lower end portion 7 is approximately hl+h2. In practise the first height hi will be modelled to be shorter than the maximum stroke distance of the ring actuator 5, preferably 40-80% of the stroke distance. The reason for this is that since these valves are small in size, safety margins compensating for manufacturing tolerances are advisable, i.e. by having the first height hi shorter than the stroke distance, there is provided a safety margin for a successful closure as well as a active closing force pressing the lower rim 14 against the lower end portion - i.e. the fuel valve will be able to better resist a counter flow. FIG 6-7 shows a fluid valve 22 according to a second embodiment of the invention, the fluid valve 22 shown in its inactive state. The fluid valve comprises a valve body 1 having a chamber 2. The chamber 2 is confined by a chamber lower end portion 7, and a chamber upper end portion 8 and chamber walls 6. The chamber 2 has two ports, a first port 3 and a second port 4. The first port 3 has a valve seat 3A protruding from the chamber lower end portion 7. The fluid valve further comprises a piezoelectric valve member 5 in the form of a flat rectangular bender which is cantilevered in one of the chamber walls 6 for opening and closing against the valve seat 3A. As can be seen in FIG. 7 there is a gap between the free end of the flat rectangular bender 5 and the valve seat 3A, i.e. the valve is not closed when the rectangular bender 5 is non-active. To provide a good closure while maintaining a valve which is at least somewhat opened while non-activated, the flat rectangular bender 5 extends at angle α in relation to a plane defined by the valve seat 3A. The angle α is preferably in the range of 0,1 -2°, more preferably in the range of 0,2-0,6°.

The reason for the flat rectangular bender 5 to extend at the angle α is indicated in FIG 8 and 9. These two figures, FIG. 8 and 9, shows the principle behind having the flat rectangular bender 5 extending at the angle α. When the flat rectangular bender 5 is actuated for closure the free end of the flat rectangular bender 5 will move towards the valve seat 3A as shown by the first dotted lined labelled Z. The second dotted line is labelled X indicates an upward stroke, i.e. moving to a fully opened fuel valve: Thus the fuel valve has three positions; closed Z, somewhat opened Y (i.e. the piezo actuator non- active), and fully opened X. FIG. 9A shows a zooming of the dotted rectangle of FIG. 9, indicating the angle α between the cantilevered bender 5 and a plane A-A of the valve seat 3A, the second dotted line X has however been removed in this zooming.

In FIG. 8, when the flat rectangular bender 5 is actuated from the somewhat opened position Y towards the closed position Z, the free end of the rectangular bender 5 will contact the valve seat 3A at a first position 25 which is beyond the port opening 3, as seen from the secured end of the flat rectangular bender 5. As can be seen the closing is far less perfect than the one seen in FIG. 9, described below. Consider the case that the free end of the rectangular bender 5 first contacts the valve seat 3A, at the first position 25, when the rectangular bender 5 is subjected to half Umax/2 of its operating voltage Umax. When subjecting the rectangular bender 5 for the operating voltage Umax, the free end will first reach the first position 25, which thereafter acts as a momentum point and the gap between the flat rectangular bender 5 and the valve seat 3A actually increases as the free end of the bender curves even more.

As seen in FIG. 9 and 9A; when the flat rectangular bender 5 is actuated from the somewhat opened position Y towards the closed position Z, the rectangular bender 5 first contacts the valve seat 3 A at a second position 26 at a side of the first port facing the cantilevered end of the flat rectangular bender. Continuing actuating the flat rectangular bender 5, the end of the flat rectangular bender 5 will move towards the first position 25, where the second position 26 acts as a momentum point. The result is only a small gap between the flat rectangular bender 5 and the valve seat 3A. The small gap occurs since the bender is slightly upwardly curved between the first and the second position 25, 26. Thus by arranging the flat rectangular bender 5 to first reach the second position 26, e.g. by having the flat rectangular bender 5 extending at an angle α in relation to the plane A-A of the valve seat 3A - an improved closure of the valve seat is achieved. The flat rectangular bender 5 is preferably arranged to reach the second position 26 at an operating voltage in the range of 0,4-0,9* Umax, where Umax is the operating voltage. It should be realised that in the drawings the angle α is exaggerated in order to show the principle behind the inventive feature of having the cantilevered flat rectangular bender 5 extend at a slight angle α when a fluid valve, which is somewhat opened when non-active, is desired. The plane A-A of the valve seat 3 A is defined by a plane extending through the two contacts points 25 and 26

As an alternative approach, it would of course be possible to machine the rim of the valve seat 3A to provide an angle α in relation to the flat rectangular bender 5. I.e. having a sloping valve seat 3A. In such case it would be possible to have the flat rectangular bender 5 extend horizontally as in FIG. 8. The angle α between the flat rectangular bender 5 and the valve seat 3 A, would still be present since the plane A-A of the valve seat, in this situation, would be tilted.

Whereas the invention has been shown and described in connection with the preferred embodiments thereof it will be understood that many modifications, substitutions, and additions may be made which are within the intended broad scope of the following claims. From the foregoing, it can be seen that the present invention accomplishes at least one of the stated objectives. For instance, the piezoelectric active layers 5A, 5B may be separated by an inactive inner layer, e.g. a brass shim.

Further; even though the piezoelectric valve member 5 of the first and second embodiment was shown as having two parallel connected piezoelectric active layers 5 A, 5B, it would of course be possible to have the piezoelectric active layers 5A, 5B poled in opposite directions, i.e. X-poled. In such case the piezoelectric valve members 5 should be wired for serial mode, i.e. 2-wired, removing the third connection 17. Further would also be possible to use only one piezoelectric active layer and having an inactive second layer, i.e. an unimorph piezo actuator. Of course an unimorph actuator would be 2-wired, i.e. the first connection 15 at the upper side of the active layer and the second connection 16 at the lower side of the active layer. Further having a unimorph actuator the fuel valve will of course be fully opened when the unimorph actuator is non-activated. Further, the piezoelectric valve member 5 could also be a multilayered actuator.

Naturally, the flat rectangular bender of the second embodiment could also be a bimorph actuator which is either X-poled or Y-poled, an unimorph actuator or a multilayered actuator

Further, the fluid valve of the first embodiment would of course function without having the outlet groove 11.

Further the first port 3 of the first embodiment could be placed at the opposite side, i.e. at the upper valve body IA, its orifice still facing the opening of the ring actuator 5.

Further, relating to the first embodiment, by having a third port is positioned at the upper end portion 8 at a predetermined second port distance from the centre of the upper end portion 8, which second port distance is larger than the opening radius r2 of the ring actuator 5. I.e. proving a three way valve. Of course the third port could optionally also has a corresponding outlet groove.

Further, relating to the first embodiment, further ports could be equally distributed at the port distance rl, functioning as the second port 4. I.e. in order to equalise the flow through the gap. An advantage using a valve with a ring actuator in comparison to cantilevered rectangular bender is that the response time of a ring actuator is much faster and much stronger. The disadvantage is that the useful stroke distance is less. However the lesser stroke distance can be compensated by increasing the valve diameter.

Claims

1. A fluid valve comprising a valve body (1) having an chamber (2), the chamber (2) confined by a chamber lower end portion (7), a chamber upper end portion (8) and chamber wall(s) (6), the chamber (2) having at least a two ports (3, 4), a first port (3) and a second port (4) for communicating fluid to and from the chamber (2), and further a piezoelectric valve member (5) in the chamber (2) for controlling fluid flow between the at least two ports (3, 4), characterised in that the valve member (5) is a piezoelectric ring actuator of bender type which is aligned substantially parallel to the lower end portion (7) and at a distance (hi) from the lower end portion (7), the valve member (5) having a substantially centred opening (9).

2. A fluid valve according to claim 1 wherein the chamber (2) has the form of a flat cylinder.

3. A fluid valve according to according to claim 1 or 2 wherein the edge of the valve member (5) is secured within the chamber (2) by positioning means (6a) of the chamber wall(s) (6).

4. A fluid valve according to claim 3 wherein the positioning means (6a) is a chamber wall groove running along the chamber wall(s) in parallel to lower end portion (7).

5. A fluid valve according any one of claim 1-3 wherein the first port (3) is positioned at the lower end portion (7) facing the opening (9) of the valve member (5).

6. A fluid valve according to any one of claim 1-3 wherein the first port (3) is positioned at the upper end portion (8) facing the opening (9) of the valve member (5).

7. A fluid valve according to any one of claim 5-6 wherein the second port (4) is positioned at the lower end portion (7) at a predetermined port distance (rl) from the centre of the lower end portion (7).

8. A fluid valve according to any one of claim 5-6 wherein the second port (4) is positioned at the upper end portion (8) at a predetermined port distance (rl) from the centre of the upper end portion (8).

9. A fluid valve according to anyone of claim 7 or 8 wherein the end portion (7, 8) that comprises the second port (4) further comprises a centred outlet groove (11), the groove (11) having a first radius corresponding to said port distance (rl).

10. A fluid valve according to anyone of claim 7 -9 wherein the opening (9) of the valve member (5) is circular having a second radius (r2) which second radius is smaller than port distance (rl).

11. A fluid valve according to anyone of claim 1-10 wherein the first port (3) is an inlet port and the second port is an outlet port (4).

12. A fluid valve according to anyone of claim 1-10 wherein the first port (3) is an outlet port and the second port is an inlet port (4).

13. A fluid valve according to anyone of claim 1-12 wherein the piezoelectric ring actuator (5) comprises at least two layers (5 A, 5B), and where at least one of said layers (5A, 5B) is a piezoelectric active layer.

14. A fluid valve according to claim 13 wherein the piezoelectric ring actuator (5) has two piezoelectric active layers (5 A, 5B) which piezoelectric active layers (5 A, 5B) are X-poled, i.e. the polarization vectors for each of the two piezoelectric active layers (5A, 5B) point in opposite directions.

15. A fluid valve according to claim 13 wherein the piezoelectric ring actuator (5) has two piezoelectric active layers (5A, 5B) which piezoelectric layers (5A, 5B) are Y- poled, i.e. the polarization vectors for each of the two piezoelectric active layers

(5 A, 5B) point in the same direction.

16. A fluid valve comprising a valve body (1) having an chamber (2), the chamber (2) confined by a chamber lower end portion (7), a chamber upper end portion (8) and chamber wall(s) (6A, 6B, 6C, 6D), the chamber (2) having at least a two ports (3, 4), a first port (3) and a second port (4), where the first port (3) has a valve seat (3A) protruding from the chamber lower end portion (7), the first port (3) located close to a first chamber wall (6C), a piezoelectric valve member (5) in the form of a flat rectangular bender is cantilevered in or close to an opposite chamber wall (6A) so that the free end of the flat rectangular bender (5) hovers above the valve seat (3A), the fluid valve operated at an normal operating voltage Umax characterised in that the flat rectangular bender (5) is arranged, at an operating voltage which is lower than the normal operating voltage, to contact the valve seat (3A) at a side (26) of the first port (3) facing the cantilevered end of the flat rectangular bender

(5) .

17. A fluid valve according to claim 16 wherein the flat rectangular bender (5) is arranged, to contact the valve seat (3A) at the side of the first port (3) facing the cantilevered end of the flat rectangular bender (5) and the opposite side (25) beyond the first port (3), when the operating voltage is the normal operating voltage.

18. A fluid valve according to claim 16 or claim 17 wherein the flat rectangular bender (5) when non-actuated extends at an angle (α) in relation to the plane of the valve seat (3A), which angle (α) is in the range of 0,1-2°, preferably in the range of 0,2- 0,6°.

19. A two stroke internal combustion engine having a magneto powered ignition system, fuel being supplied to the engine via a fuel supply system including an piezoelectrically controlled fuel valve (22) of bender type characterised that fuel valve (22) is arranged to be controlled at operating voltages of at least 60V, preferably of at least 100V, more preferred of at least 150V, and even more preferred at least 200V.

20. A two stroke internal combustion engine according to claim 19 wherein the operating voltage is supplied from a primary winding (Ll) of a magneto powered ignition system.

21. A two stroke internal combustion engine according to claim 17 or claim 18 wherein the fuel valve (22) and an ignition system of the engine is powered from a common condenser (Cl).