Arrangement and method for fluid injection The present invention relates to an arrangement and method for fluid injection, comprising an injector, with a chamber for fluid, an opening and a device to change the volume within the chamber. The arrangement further comprises a reservoir to store fluid and a pipe for a fluidic connection between the chamber and the reservoir.

The injection of fluids is an important part of many

industrial and daily life processes. Examples for the

injection of fluids are the fuel supply for internal

combustion engines and turbines, drug delivery into soft tissues in medicine and for dentistry applications, ink delivery during printing and solder delivery in

microelectronic productions. Many of these applications require high speed injection of liquids under high pressure and in a controlled manner. High frequency, i.e. higher than 10 Hz and high pressure injectors are complex electro- hydraulic systems. They comprise moving parts like valves and actuators, which are required for refilling the injection volume and for keeping fluid within the volume. Moving parts increase the risk of failures and are wear parts, increasing service costs and maintenance effort.

Several attempts have been made to design injectors without valves, which can be operated in pulse mode. Pulse mode is used in the following in the meaning of a periodic injection, with a fluid injection for a certain period of time, followed by a time without fluid injection, and a following next injection after the time without injection. In the time without injection the injector can be refilled. The injector is refilled after each injection from a storage tank, the so called reservoir, which is connected to the injector by a supply pipe. Pulse mode injection is known from the state of the art, for example described in US5437255, where a fluid is injected for fuel supply. Fuel, which is stored in a

pressurized fuel tank, is supplied through a straight pipe to the injection volume, driven by capillary forces. A nozzle, in form of a hole in the injector to supply fluid for a working volume, keeps liquid inside the injector by means of surface tension, until the pressure is high enough to

overcome the surface tension. After transcending the surface tension the elevated pressure inside the injector causes an injection of fuel through the nozzle.

Since no valve is arranged between fuel tank and injector, liquid is flowing backward to the fuel tank during injection. The frequency of the injector operation depends on loss of liquid during injection, i.e. injected liquid volume and liquid volume flowing back, and on the refilling rate. The back flow of liquid is in the described arrangement only limited by friction, causing pressure resistance to fluid flow inside the straight pipe connecting fuel tank and injector. However, since the injection pressure is usually several orders of magnitude higher than the refilling

pressure, fluid outflow is sufficiently high and it takes plenty of time to refill the injector.

In US2002/0007143 and in PCT/US2007/019247 , injectors for high repetition rate high speed jet generation are described. The field of application for this kind of injectors is for example medical drug delivery to soft tissues without use of needles. Contrary to above described injectors, these

injectors comprise a one-way valve, i.e. a check-valve arranged in the supply pipe between the storage tank and the injector. The valve limits the back flow of fluid during injection. Check-valves comprise moving parts, as there are springs and/or closing bodies, for example discs, balls and so on, limiting the reliability and adding sufficient

resistance to the system, limiting the performance and operating frequency of the system. In US2009/0074595 an injector is described, limiting the liquid backflow by a complex planar cross section arrangement of the supply pipe, exhibiting different hydraulic resistance to fluid flow for forward and backward flow. However, such arrangement is bulky and expensive to manufacture.

The object of the present invention is to present an

arrangement and method for fluid injection solving the above described problems. Particularly the object is to present an easy to use, cheap to produce, reliable arrangement and a method with an injector to inject fluid and being refilled from a reservoir without the need of moving parts like valves to prevent a high amount of fluid to flow back to the

reservoir during injection, not blocking refilling. A further object is to present an arrangement without high complexity, which is long lasting due to a reduction of wear parts, even in high frequency injection applications.

The above objects are achieved by an arrangement for fluid injection according to claim 1 and a method for fluid

injection according to claim 9.

Advantageous embodiments of the present invention are given in dependent claims. Features of the main claims can be combined with each other and with features of dependent claims, and features of dependent claims can be combined together.

The arrangement for fluid injection according to the present invention comprises an injector, with a chamber for fluid, an opening and a device to change the volume within the chamber. The arrangement further comprises a reservoir to store fluid and a pipe for a fluidic connection between the chamber and the reservoir. The pipe comprises a part with curved and/or angled shape in fluid flow direction.

The curved and/or angled shape of the pipe, which extends in the direction of fluid flow, allows during refilling a fluid to flow from the reservoir to the chamber of the injector, and blocks a fluid flow back from the chamber to the

reservoir during injection. No moving parts like for example valves are needed to block a flow of fluid back to the reservoir during injection.

The fluidic connection between the chamber and the reservoir can be an uninterrupted direct connection through the pipe and/or permanent. This means, there are no valves or other fluidically disrupting components arranged in the fluidic connection between the chamber and the reservoir. A pipe with curved and/or angled shape without moving parts like valves is easy to use, cheap to produce, and reliable, without high complexity, and is long lasting due to no moving parts, reducing wear.

The pipe can comprise a part in form of a repeated loop, particularly the pipe comprises a part with spiral shape. This design is easy to produce without high costs. The repeated loops are well able to block fluid flow back to the reservoir during injection, even when fluid would flow with high velocity in a pipe without loops.

The pipe can comprise a part with spiral shape with a number of full loops in the range of 5 to 15, and/or a predefined radius of curvature and cross-section to result in a limited and/or turbulent fluid flow in direction to the reservoir in a phase of injection and to a laminar fluid flow in direction to the chamber during a phase of refilling. Turbulent flow is blocking fluid from flowing back to the reservoir from the injector chamber during injection. A laminar flow allows a good refilling of the chamber in the injector with fluid from the reservoir due to a good flow of fluid from the reservoir to the injector. A number of loops between 5 to 15 is high enough to block fluid flow during injection and low enough to allow a good fluid flow within the pipe during refilling without high resistance to the fluid to flow. Depending among others on the kind of fluid used, the dimensions of the injector and reservoir, the material of the pipe, the cross- section and radius of curvature as well as number of loops needed to block fluid flow during injection can be

calculated.

The fluid can be a liquid. Depending on application, the liquid can be among others water, ink, solder or mixtures of liquids. The whole arrangement can be arranged in vacuum or air. Depending on the surrounding the dimensions and form of the injector, pipe and reservoir should be chosen.

The injector can be designed for high pressure pulsed fluid injection, particularly with an injection frequency in the range of 10 to 1000 Hz. At this frequency the use of valves is difficult to handle and involves a high amount of wear.

The curved and/or angled shape part in the pipe is well able to block fluid flow during injection due to a hydraulic hammer effect. The device can comprise a metal sheet, a membrane and/or a piezo element for a volume change within the chamber, particularly with a frequency in the range of 10 to 1000 Hz and/or to produce a high pressure within the chamber for pulsed fluid injection through the opening.

The injector can comprise a nozzle cup, particularly with a sharp edge orifice, and/or a clamped circular membrane, and/or a piston particularly driven by a piezo-actuator . A Method for fluid injection according to the present

invention, particularly using an arrangement as described above, comprises the steps injecting fluid through an opening from a chamber comprised by an injector. The injection is effected by changing the volume of the chamber with a device, producing a high pressure in the fluid in the chamber. A further comprised step is refilling the chamber with fluid from a reservoir, the fluid flowing from the reservoir to the chamber through the pipe. The fluid flow in the pipe is limited by a part of the pipe with curved and/or angled shape in fluid flow direction during injection.

The fluid flow in the pipe can be laminar during refilling and at least partly turbulent during injection.

A pulsed fluid injection, particularly with a frequency of injection pulses in the range of 10 to 1000 Hz, can follow in time to a refilling of the chamber with fluid from the reservoir, particularly with liquid fluid.

The device can produce high fluid pressure in the chamber for injection and low fluid pressure during refilling, effecting suction of fluid from the reservoir to the chamber.

During injection fluid flow from the chamber to the reservoir can be limited and/or blocked by the part of the pipe with curved and/or angled shape, particularly with the form of a spiral .

During injection a piston driven by a piezo-actuator can produce high pressure in the chamber by compressing a

hydraulic liquid volume, deforming a membrane, particularly a clamped circular membrane, to reduce the volume of the chamber with fluid being ejected from the chamber through an opening, particularly in form of a nozzle cup with sharp edge orifice, and fluid being blocked from flowing to the

reservoir by the part of the pipe with curved and/or angled shape .

During refilling a piston driven by a piezo-actuator can produce low pressure in the chamber by expanding a hydraulic liquid volume, deforming a membrane, particularly a clamped circular membrane, to increase the volume of the chamber with fluid being sucked from the reservoir to the chamber through the pipe. The advantages in connection with the described method for fluid injection according to the present invention are similar to the previously, in connection with the arrangement for fluid injection described advantages and vice versa.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the

accompanying drawings, in which: FIG 1 illustrates an arrangement 1 according to the

present invention, with a pipe 7 comprising a spiral part 9 fluidically connecting an injector 2 and a reservoir 6, and FIG 2 shows the spiral part 9 of the pipe 7 in FIG 1 in more detail, and

FIG 3 shows an embodiment of the injector of FIG 1 in

more detail with an opening in form of a nozzle cup 10 with sharp edge orifice.

In FIG 1 an arrangement 1 according to the present invention is shown, with an injector 2 and a reservoir 6 fluidically connected by a pipe 7. The pipe comprises a spiral part 9 to allow laminar fluid flow during refilling of the injector 2 with liquid from the reservoir 6, and to block fluid flow from the injector 2 to the reservoir 6 during injection of fluid from the injector 2. The injector 2 comprises a chamber 3 filled with fluid to be injected. The volume of the chamber 3 is for example in the range of 1 cm ³ . The fluid can be among others a liquid like ink, liquid solder, or fuel. Injected means ejected from the chamber 3 via an opening 4 in the chamber 3 to the outside of the chamber 3, i.e. the outside of the injector 2. The injector 2 comprises a device 5 to change the volume within the chamber 3. The device 5 can be for example a piezoelectric device, formed to reduce the volume of the chamber 3 for example after applying a first electrical voltage. The volume reduction increases the pressure in the chamber 3 and a fluid stream with a flow direction 8 as shown in Fig 1 is ejected out of the chamber 3 through the opening 4. The fluid stream is injected when the surface tension of the liquid at the opening 4 is overcome. The injection leads to a reduction of pressure in the chamber 3 up to a point the pressure is below a value to overcome the surface tension, where the injection stops.

In a next step the device 5, for example the piezo-electric device can increase the volume of the chamber 3 for example after applying a second electrical voltage, particularly with opposite sign of the electrical voltage. The volume increase leads to a pressure reduction in the chamber 3. Fluid is sucked from the reservoir 6, which is filled with fluid, through the pipe 7 to the chamber 3 of the injector 2. The chamber 3 is refilled with fluid and the process can start again from the beginning, injecting fluid. As a result a pulsed injection of fluid can be generated continuously or interrupted. Various periods of injection and refilling can be chosen according to the application of the arrangement 1. The injection and refilling can be periodical with the same time intervals or with changing time intervals.

The pressure in reservoir 6 is chosen to be low enough, not to overcome surface tension at the opening 4 without moving of parts of device 5. As long pressure in the reservoir 6 is below a limit, set by the diameter of opening 4 and fluid surface tension, no fluid is leaving the arrangement 1. The limit depends among others from the environment of the arrangement 1, particularly the pressure for example in vacuum or air. For a laminar fluid flow during refilling, which results in a fluid flow with low friction and a high refilling rate, the cross section of the pipe 7 is larger than the cross section of the opening 4 in the chamber 3. With circular diameter of the opening 4 Dl and pipe 7 D2, an example for an inner diameter of the pipe 7 D2 is 200 Micrometer and a diameter of the opening 4 Dl is 50 Micrometer. For a fluid flow to be blocked during injection, the time interval to refill is for example in the order of ten times longer than the time interval to inject. A short time

interval to inject fluid, i.e. eject fluid from the chamber, results from a fast volume change by device 5, inducing a fluid flow pulse breaking through the opening 4 after

overcoming the surface tension of the fluid and pushing fluid in the pipe 7 in direction from the chamber 3 to the

reservoir 6. The fluid pushed fast into the pipe 7 from the camber 3, particularly into the pipe with higher cross- section than the cross-section of the opening 4, results in a kind hydraulic hammer and/or turbulent flow, which is blocked by the spiral part 9 of the pipe 7. In contrast, the more slow laminar flow during refilling is no or at least only very little reduced by the spiral part 9 of the pipe 7.

In FIG 2 a spiral part of pipe 7 is shown in more detail. The number of windings of the spiral 9, the cross-section for fluid flow in the pipe 7 in relation to the cross-section of opening 4 and/or the volume of the chamber 3, particularly depending on the speed of volume change by device 5 and/or the time interval for refilling and injection, are calculated and/or predefined to get an injection of fluid from the injector 2, particularly overcoming the surface tension of the fluid at opening 4, and to result in a blocking of fluid flow in the pipe 7 at the spiral part 9 during injection. The values, particularly the cross-section, i.e. inner cross- section of the pipe 7, the refilling time period and the number of windings of the spiral 9 are chosen to result during refilling in a laminar fluid flow to refill the chamber 3 from the reservoir 6 without or with little flow resistance and/or friction losses. A good refilling results from the described arrangement 1 during refilling, with a high amount of injected fluid without and/or with little fluid flowing from the chamber 3 to the reservoir 6 during injection.

In FIG 3 an embodiment of the injector 2 is shown, with an opening 10 in form of a nozzle cup with sharp edge orifice. The device 5 to change the volume within the chamber 3 comprises a hydraulic liquid volume 13, for example filled with air, oil or water, enclosed by a clamped circular membrane 11, particularly steel membrane, and a piston driven by a piezo-actuator 12. Other parts like the pipe 7 or reservoir 6 are not shown for reasons of simplicity. With a first voltage applied, for example with positive sign, the piezo-actuator drives the piston 12 down, in direction to the membrane 11. The hydraulic liquid volume is pushed in

direction to the membrane 11, deforming the membrane 11 in the direction away from the piston 12. The chamber 3 with fluid to be injected by the injector is arranged opposite to the hydraulic liquid volume 13, separated by the membrane 11. The membrane 11 compresses the fluid in the chamber 3, increasing the pressure to a value above the fluid surface tension at the opening 10. Fluid breaks trough and is ejected from the chamber 3, i.e. injected by the injector 2.

With a second voltage applied to the piezo-actuator, for example with negative sign, the piston 12 moves up, in the direction away from the membrane 11. The hydraulic liquid volume is expanded, deforming the membrane 11 towards the piston 12. The membrane 11 expands the fluid in the chamber 3, decreasing the pressure slowly to suck fluid from the reservoir 6 via the pipe 7 to the chamber 3 without

overcoming the surface tension of the fluid at the opening 10. If the surrounding of the injector is air, no air is sucked into the chamber 3 via the opening 10. A slow movement of the membrane 11, i.e. slow expansion of the volume in chamber 3 and fluid sucking results in a laminar fluid flow in the pipe 7 without blocking of the fluid by the spiral part 9. The chamber 3 is refilled with fluid from the

reservoir 6, to be ready for the next injection. The process can be repeated as long fluid is in the reservoir 6, which can be refilled.

The refilling of chamber 3 can be actively, directly induced by the device 5 with fluid flow synchronous with device 5 movements. In high frequency operation, the refilling can be slow over time after a fast movement of device 5 inducing a pressure difference between chamber 3 and reservoir 6. With piezo-electric stacks high frequency movements are possible, depending on electric voltage change and its frequency. Typical expansion distances of piezo-electric stacks in devices 5 are for example in the range of 0.1 mm, with a force in the range of 50 kN, creating pressure up to 500 to 1000 Atm. This allows high pressure injection in pulsed manner at high frequencies, for example 10 to 1000 Hz. A linear piezo-actuator is able at high voltage changes to expand and/or contract with high frequency, pushing and/or pulling a piston 12 with high constant force. This force is converted to high pressure changes of for example a hydraulic liquid in a hydraulic liquid volume 13. A pressure difference between hydraulic liquid volume 13 and chamber 3 deforms for example a clamped disc membrane, particularly made of a thin steel sheet. The deformation induces high or low pressure in the chamber 3, inducing the fluid injection pulse

respectively refilling.

The dimension of opening 10 in a chamber 3 is for example in the order of 0.01 to 0.1 mm and can be produced for example by laser drilling. The opening 10 can have conical shape with a cone base at the inner side of chamber 3, to provide a vena contracta flow. High injection pressure and small diameter of the opening 10 provides a high speed microjet, which can be used in different applications like for example ink jet printing.

The arrangement 1 as shown in FIG 1 allows a fluid flow, for example liquid injection via opening 4 and refilling from reservoir 6, at high frequency without the use of vales or moving parts to prevent air to be sucked into the chamber 3 during refilling and/or fluid to be pushed back into the reservoir 6 form chamber 3 during injection. The arrangement 1 is less complex than with moving parts like valves to block fluid flow, easier to produce, less expensive in production, and long lasting without wear parts like valves.

The change of direction of fluid flow in the pipe 7 part with curved and/or angled shape 9, with the pipe 7 being curved and/or angled shaped along the fluid flow direction, will cause significant hydraulic losses in addition to friction losses occurring in the pipe 7 along the length of the pipe 7. These losses during injection phase are orders of

magnitude higher than during the refilling phase. This is caused by the fact that during injection the liquid outflow will be turbulent opposite to a laminar low speed refilling flow, i.e. charging of the chamber 3. A part of the pipe with spiral shape 9 can be made, i.e.

produced by spiraling a capillary tube with for example an inner diameter of 0.1 to 1 mm around a cylindrical rod with for example a diameter of 16 mm. A spiraled tube with 1 mm inner diameter and 2 mm outer diameter with 15 x 360 grad full turns will results in a pipe 7 with a length of

approximately 0.85 m, and in 60 x 90 curved and/or angled shaped parts. Hydraulic losses in the curved and/or angled shape parts, which can also be called elbows and sum up to the spiral part 9, will give rise to additional 50 % losses compared to pure friction losses in the pipe 7, assuming high speed turbulent flow when the pressure difference between the injector and reservoir 6 is high, e.g. 100 Atm. During refilling, i.e. charge phase the curved and/or angled shape parts will not generate any additional losses due to laminar regime of fluid flow.

With pressure inside chamber 3 being increased very fast, the effect of hydraulic hammer in the pipe 7 will appear, particularly in the spiral part 9 of the pipe 7. This effect originates from the fact that any disturbances in the fluid are propagating through the fluid with finite speed, which corresponds to the specific velocity of sound in the fluid, depending on physical and thermodynamics properties of the fluid and mechanical properties of the pipe 7. Due to the hydraulic hammer effect, a compression wave moves in

direction from the injector 2 to the reservoir 6, and an expansion wave moves in reverse direction. Fluid is

accelerated behind the front of the waves, taking a certain period of time to establish the outflow of the fluid to the reservoir 6. The propagation of shock waves in spiraled tubes is more complex than in straight tubes . This fact requires additional time to establish the outflow, minimizing total fluid losses during the injection and increasing a possible operating frequency.

This allows an operation of the fluid injector 2 in pulse mode, with a high frequency depending on the ratio of liquid loss during injection and compensation during refilling.

Spiraled pipes 9 are easy to manufacture and limit the fluid outflow to the reservoir 7, i.e. storage tank, during

injection phase when the flow regime is turbulent, but do not bring any essential fluid flow losses during refilling when the flow regime is laminar.

The above described features of embodiments according to the present invention can be combined with each other and/or can be combined with embodiments known from the state of the art. For example, the dimension of components and frequencies can be chosen according to the application and fluid used. The membrane material can for example be instead of steel made of other metals and/or non metallic materials. The arrangement 1 can be used in inert atmosphere instead of air or vacuum, the atmosphere influencing the surface tension of the fluid and necessary dimensions of the opening 4, 10. List of Reference Characters

1 arrangement for fluid injection

2 injector

3 chamber of injector for fluid

4 opening of chamber

5 device to change the volume within the chamber

6 reservoir to store fluid

7 pipe for a fluidic connection between the chamber and the reservoir

8 direction of pulsed fluid injection/stream from chamber

9 spiral part of pipe

10 opening in form of a nozzle cup with sharp edge orifice

11 clamped circular membrane

12 piston driven by a piezo-actuator

13 hydraulic liquid volume