DE10003892A1 - Piezoelectric micro valve, especially for combustion engine fuel injection, has mechanical lever element causing displacement conversion between actuation element and valve needle - Google Patents

Abstract

The micro valve has a valve needle (20) movably mounted for opening and closing a valve opening, a piezo-actuator (30) for driving the valve needle and an actuation element (40) that transfers movement caused by the piezo-actuator to the valve needle. A mechanical lever element (50) couples the actuation element to the valve needle so that a displacement conversion occurs between the actuation element and valve needle. Independent claims are also included for the following: an injection method and a lever element for force transfer between an actuator and a displaceable element.

Description

The present invention relates to a piezoelectric microvalve, in particular for Fuel injection in internal combustion engines, according to the preamble of Claim 1, and an injection method, in particular for Internal combustion engines is suitable, according to the preamble of claim 14. Furthermore, the invention relates to a lever element according to the preamble of Claim 17.

Microvalves are generally required to hold defined amounts of liquids to deliver or to other institutions. For example Internal combustion engines or internal combustion engines operated with fuel injection systems, the fuel being injected into a combustion chamber through micro valves.

DE 197 02 066 C2 describes a piezoelectric injector for fuel injection systems shown by internal combustion engines, in which a piezo actuator via a pressure pin Valve opens so that fuel in the expanded state of the piezo actuator from the Escape vector or be injected into the combustion chamber of an internal combustion engine can. The piezo actuator is compressed by a prestressed compression spring, if it is not loaded.

Although piezo injectors have certain advantages over electromagnetic injectors have such. B. higher speed, less space or injector diameter and higher closing force, they still have considerable disadvantages. One problem is e.g. B. in the relatively small expansion of piezo elements, which is generally around 1 ‰. In order to realize a movement of a valve needle of approx. 100 µm one needs an at least 10 cm long piezo stack or stack of piezo elements. It follows a large length of the piezo injector, which makes it unwieldy and the Freedom of design considerably restricted. Furthermore, there are very high costs because the Piezostacks are currently the price-determining components of piezo injectors.  

Another problem lies in the high preload that is necessary in order to do so long piezo stacks. This requires springs with a large restoring force or high spring constant, which in turn requires an increased installation space.

An additional problem is that the piezo actuator generates heat during operation, the thermal expansion of the injection valve or individual components leads, and which also increases with increasing length of the piezo actuator. To High loads from thermal expansion can cause precision valve lift is impaired or malfunctions occur.

On the other hand, however, very small piezo actuators become in such micro valves used, there is too little movement of the valve needle and beyond insufficient closing force or opening force of the valve. A possible solution that in Integrating multiple valves into one injector is too expensive and requires too much Installation space.

It is therefore the object of the present invention to provide a piezoelectric microvalve create that particularly suitable for fuel injection in internal combustion engines is, however, the piezo actuator has a reduced size without the Reliability and accuracy of liquid delivery or fuel injection affect. Furthermore, an injection method is to be specified that is particularly suitable for internal combustion engines, and with which a reliable and precise injection with a piezo actuator of small size or length can.

This object is achieved by the piezoelectric microvalve according to claim 1, by the injection method according to claim 14, and by the lever element solved according to claim 17. Other advantageous features, aspects and details of Invention result from the dependent claims, the description and the Drawings. Advantages and features arising from the description of the device result, also apply to the method and likewise apply advantages and features that differ  result from the description of the method according to the invention, also for the Contraption.

The piezoelectric microvalve according to the present invention is particularly for Suitable for fuel injection in internal combustion engines and includes a valve needle is slidably mounted, for opening and closing a valve opening, a piezo Actuator, for driving the valve needle, and an actuator that one through the piezo Actuator causes the stroke transmitted to the valve needle, the piezoelectric Microvalve further has a mechanical lever element, which is the actuating element couples to the valve needle, so that a stroke ratio between the actuator and the valve needle takes place.

This solution ensures that a piezo injector with very small dimensions can be realized, in particular the piezo actuator having a very short length. Despite this reduced length, the valve needle achieves a sufficiently large stroke that ensures reliable and accurate operation of the fuel injector. in addition comes that the heat generated by the piezo actuator due to its smaller size is reduced. This also results in increased reliability and accuracy due to the reduced thermal problems. Furthermore, the invention Construction at significantly reduced costs, since the piezostacks or stacks of Piezo elements can be designed much shorter than before.

The lever element is preferably a flat, elastic spring. This will achieves a very effective stroke ratio in a particularly small installation space. in addition comes that the restoring force of the spring z. B. is directed in the closing direction of the valve and even to reset the piezo actuator in its compressed state can contribute.

Advantageously, the lever element is disc-shaped, z. B. extend a plurality of slots in the radial direction to form segments which are called Lever arms work. This gives a uniform power transmission from the piezo Actuator on the valve needle via a variety of levers that are particularly space-saving  are arranged. That is, a single disk is required, which e.g. B. as an elastic spring acts and through a variety of levers that extend radially from the outside inwards, is characterized. Overall, this results in a very uniform space in the smallest space and reliable power transmission in stroke translation.

For example, a lever arm between the valve needle and the actuation point of the Lever element larger than a lever arm between a fixation of the lever element and the operating point of the lever element. An actuation point is advantageously located of the lever element radially further outward than the valve needle. There is a stroke ratio possible by a factor of 2.5 to 3 or even higher, d. H. the valve needle stroke is essential larger than the expansion of the piezo actuator and can e.g. B. be 180 microns.

Preferably, the piezoelectric microvalve comprises a beam-shaping element which, for. B. creates a swirl in the injected liquid or fuel. For example, the beam-shaping element is a swirl plate that is in a special preferred embodiment also serves as a valve needle guide. The swirl plate or Swirl or swirl plate causes good atomization of the injected Liquid or fuel due to a rotation of the fuel as it emerges from the Microvalve. Because the swirl plate is also the valve needle guide continue to save installation space, which still reduces the size of the microvalve additionally contributes.

The power transmission between the control element and the Lever element through one or more rings. The lever element is preferably on Adjusting element fastened by one or more pressure clamps. This creates the strength evenly transmitted between the lever element and the actuating element, since they according to the ring shape is circular, for example, on the lever element act. Thus, a plurality of levers that are arranged radially can be smooth be actuated by the control element. With the pressure clips it is possible to very small space a power transmission between the lever element and actuator in to reach two opposite directions. The pressure clamps z. B. reach through openings in the lever element and engage with one behind the  Lever element located ring, so that a tensile force on the pressure clip is transmitted via the ring from the pressure clip to the lever element, for example to close the valve.

Advantageously, the valve needle z. B. on its circumference an annular groove in the the lever element engages. Thus, with a relatively low design effort and small space required an effective power transmission between the lever element and Valve needle.

The piezo actuator is preferably at least partially biased hydrostatically. there acts z. B. a hydrostatic pressure on the piezo element or the piezo actuator to him to crush. This reduces the preload of the piezo actuator by means of springs, which at the same time means a profit in the stroke of the valve needles. In contrast to one This is because spring tension occurs when the piezo actuator is preloaded hydrostatically regardless of the path essentially the same counterforce is needed to get the To overcome bias. The hydrostatic bias can, for. B. by the Liquid or fuel in the microvalve to be injected. It is therefore advantageously the fuel pressure for upsetting the piezo actuator used.

A hydraulic force in the closing direction preferably acts on the valve needle. It can e.g. B. the piezo actuator and the valve needle by pressure in a liquid be, wherein an area for pressurizing the piezo actuator is larger than one Area to pressurize the Venil needle. The liquid is advantageously the fuel to be injected. For example, the liquid pressure has an opening effect on the Valve needle over a relatively small area, but in the compression direction of the piezo actuator on a relatively large area, so that the valve needle through the compressed piezo actuator is held in their seat. By this distribution of the hydraulic forces or by The hydraulic balance can be the mechanical preload of the piezo stack or the piezo actuator with springs or disc springs can be kept low. So that will the stroke of the valve needle also increases because of a high mechanical preload of the Piezo actuators with disc springs would lead to considerable losses during the stroke.  

The piezoelectric microvalve advantageously has a supply channel for the liquid to be injected, which is thermally coupled to the piezo actuator for heat transfer from the piezo actuator to the liquid. This will cool the piezo Actuator reached for example by fuel flowing past. Due to the thermal Coupling the piezo actuator to the fuel is the thermal one Problems are further reduced, on the other hand, the fuel is preheated, resulting in a leads to more effective combustion. The supply channel of the fuel can e.g. B. in the form of a Be designed envelope that surrounds the piezo actuator.

The injection method according to the invention is in particular for internal combustion engines suitable. In the method, a valve needle is driven by a piezo actuator to carry out an injection process, with an expansion and / or Contraction of the piezo actuator a stroke translation takes place while the stroke of the piezo Actuator is transferred to the valve needle. This allows small dimensions the piezo actuator and a corresponding device an effective and reliable injection take place, with sufficient movement of the Valve needle can be achieved when actuated by an actuator reduced in length can.

The piezo actuator is advantageously cooled by the liquid to be injected, which further increases reliability.

The valve needle and / or the piezo actuator is preferred for prestressing with the pressure charged with a liquid, the z. B. the liquid to be injected or injected Is fuel. This creates an otherwise required pre-tension by disc springs reduced and a higher closing force achieved. According to another aspect of Invention is a lever element for power transmission between an actuator and displaceable element created, in particular for actuating a piezo Is suitable injector, wherein the lever element is disc-shaped, and wherein radially extending slots divided the lever element into a plurality of segments Form lever arms.  

As a result, an effective stroke transmission can take place in a particularly small installation space. Forces and movements are transmitted quickly and with high accuracy, so that Lever element is particularly suitable for use in a piezoelectric microvalve.

The slots preferably each extend from one in the center of the lever element located opening to radially further outward openings or continuous Holes, z. B. circular a plurality of the radially outer openings is located around the center.

The circularly arranged or radially outer openings can be round or be oval in shape, with partial areas of the Lever element z. B. are resiliently bendable to deflect segments that are attached to it connect.

Due to the special features of the construction of the lever element, the accuracy, Reliability and speed of the stroke ratio improved.

The lever element is preferably in a piezoelectric according to the invention Micro valve arranged, and it is advantageous in an inventive Injection method used.

A preferred embodiment of the invention is described below by way of example with reference to Figures described. Show it:

Fig. 1 a longitudinal section in a schematic representation of a microvalve, which is a preferred embodiment of the invention;

Fig. 2 is a view of a lever element as used in the preferred embodiment of the invention; and

Fig. 3 is a schematic perspective view in a partial exploded view to illustrate the internal structure of the microvalve.

In Fig. 1 is a longitudinal section through an inventive micro valve 10 as a preferred embodiment of the invention. The microvalve 10 has a valve needle 20 with a valve needle head 21 which closes a valve opening 22 . The valve needle 21 is movably mounted in its longitudinal direction, so that the valve opening 22 opens when it moves outwards. A piezo actuator 30 is used to drive the valve needle, an actuating element 40 being arranged between the piezo actuator 30 and the valve needle 20 in order to transmit a stroke caused by the piezo actuator 30 to the valve needle 20 . A mechanical lever element 50 is arranged between the control element 40 and the valve needle 20 , which couples the control element 40 to the valve needle 20 .

A lever transmission between the actuating element 40 and the valve needle 20 is caused by the lever element 50 . For example, an expansion of the piezo actuator 30 causes the actuating element 40 to move forward or in the direction of the valve opening 22 and thereby actuate the lever element 50 , which is a very large deflection in comparison with the expansion of the piezo actuator 30 with its Valve needle 20 experienced end.

A jet-forming element 23 forms the guide for the valve needle 20 , so that it can move back and forth in the direction of the longitudinal axis of the microvalve or in the direction of its own longitudinal axis. The jet-forming element 23 is a swirl plate or swirl generator, which sets the fuel in rotation upon exiting the valve opening 22 and causes particularly good atomization of the fuel. The beam-shaping element 23 or the Swirler is integrated in the needle guide or itself part of the needle guide, so that the space requirement is reduced. The swirl plate has a disk-shaped or circular design and has a continuous, circular opening in its center through which the valve needle 11 extends.

The valve needle 11 has at its inner end a groove 24 or a depression which extends in the circumferential direction of the valve needle 20 . That is, the groove 24 is circular in the circumference of the valve needle 20 . The lever element 50 engages with its radially inner end in the groove 24 and is thereby firmly connected to the valve needle 20 . The lever element 50 is designed as a disk, with individual segments engaging in the groove 24 from different radial directions. The valve needle 20 extends with its inner end through an opening in the center of the disc which forms the lever element 50 and is in mutual engagement with the lever element 50 through its groove 24 .

The disk-shaped lever element 50 is fixed on its outer edge by two outer retaining rings 51 , 52 in the microvalve 10 . The radially outer region of the lever element 50 is located between the two retaining rings 51 , 52 and is fastened together with these in a recess 11 within the microvalve 10 . The recess 11 is circular or annular and extends in the circumferential direction inside the microvalve 10 .

An inner retaining ring 53 , 54 is located on both sides of the lever element 50 radially further inward, so that a region of the lever element 50 located radially further inward is accommodated between the two inner retaining rings 53 , 54 . The two inner retaining rings 53 , 54 are fastened to the lever element 50 and to the adjusting element 40 by pressure clips 41 . The pressure clips 41 extend from the adjusting element 40 in the longitudinal direction of the microvalve 10 or parallel to the valve needle through openings in the disk-shaped lever element and enclose the retaining ring 54 located there from the side of the lever element 50 facing away from the adjusting element 40 .

The region of the lever element 50 located between the inner retaining rings 53 , 54 forms an actuation point 55 for the respective lever, while the region of the lever element 50 located radially further out, which is located between the outer retaining rings 51 , 52 , forms a circular, outer fixation 56 of the lever element 50 or the plurality of levers.

A force acting on the actuating element 40 in the longitudinal direction of the microvalve 10 is transmitted to the actuation point 55 via the inner retaining ring 53 , which is located between the actuating element 40 and the lever element 50 . The actuation point is pushed forward, whereby the lever arms engaging in the groove 24 push the valve needle 20 forward. A lever mechanism is actuated, which opens the valve needle 20 . If the force acts on the actuating element 40 in the opposite direction, the valve needle 20 is closed.

The lever element 50 is designed as an elastic spring that bends in the area between the actuation point 55 and the fixation 56 when a force acts on the actuation point 55 . Due to the round cross-section of the retaining rings 51 , 52 , the area of the spring or the lever element 55 located there can roll over the respective retaining ring 51 , 52 , so that the spring is evenly bent. In other words, the force is introduced into the spring via the retaining rings 51 , 52 , 53 , 54 in order to actuate the respective lever.

The distance from the groove 24 , ie the radially inner end of the lever element 50 , to the respective actuation point 55 is large compared to the distance between the respective actuation point 55 and the fixation 56 . Movement of the actuating element 40 in the axial direction thus causes a much greater movement of the valve needle 20 in the axial direction, as a result of which a valve needle stroke is achieved which is very much greater than the stroke of the actuating element 40 . There is a stroke ratio, which corresponds to the ratio of the distances between the starting point of the lever on the valve needle 20 and the actuation points 55 and between the actuation points 55 and the fixation 56 .

Instead of connecting the lever element 50 to the valve needle 20 via the groove 24 , it is also possible to provide another type of connection here, such as, for example, a screw connection or other fixing or fastening, which is known to the person skilled in the art. It is also possible to design the lever element 50 rigidly, in which case, however, a pivotable holder must be provided as a fixation 56 , which allows the lever to be deflected.

When the lever element 50 is reset, ie with a force which acts on the actuating element 40 to the left in the closing direction or in FIG. 1, the force is applied via the pressure clips 41 and via the inner retaining ring 54 which is enclosed by the pressure clip 41 is transferred to the lever element 50 . As a result, the valve needle 20 is withdrawn, ie the valve needle head 21 is withdrawn onto its valve seat 12 , which is configured in the front area of the microvalve 10 and forms the valve opening 22 .

The actuating element 40 is movably mounted in a guide element 13 in the axial direction. The actuating element 40 is formed by a pressure pin or rod 44 which extends in the longitudinal direction of the microvalve 10 or in the axial direction, and by a disk-shaped plate 42 which is aligned parallel to the lever element 50 or perpendicular to the rod 44 . On the outer edge of the plate 42 , a plurality of the pressure clips 41 are formed, which are arranged in a ring.

The guide element 13 for guiding the adjusting element 40 is also designed in a ring shape and has a step-like gradation on its inside. As a result, a guide is formed both for the plate 42 with a relatively large radius and for the rod 44 with a relatively small radius. The stepped gradation in the guide element 13 forms an internal annular space 13 a, in which a sealing element 43 is arranged in the form of an O-ring made of rubber, which surrounds the rod 44 and is used for sealing in the region of the guide element 13 . This can, for. B. get no fuel from the area of the valve needle 20 to the piezo actuator 30 . Instead of an O-ring, however, the sealing can also take place via a membrane which separates the two spaces or areas from one another and is flexible in order to allow the actuating element 40 to move.

The piezo actuator 30 is connected to the rod 44 of the actuating element 40 by a coupling member 31 . The coupling member 31 comprises an inner region 31 a for power transmission between the piezo actuator 30 and the actuating element 40 and an outer region 31 b for guiding on an inner wall 14 of the microvalve 10 . The coupling member 31 is fixedly connected to the actuating element 40 and the piezo actuator 30 , so that when the piezo actuator 30 expands or contracts, it moves together with the actuating element 40 in the axial direction or in the longitudinal direction of the microvalve 10 .

The coupling member 31 is designed in a step-like manner, with six disk springs 32 being arranged in a ring in its radially outer region. The plate springs 32 are in the prestressed state between the guide element 13 and the outer region 31 b of the coupling member 31 and thus press the coupling member 31 against a front surface 33 of the piezo actuator 30 . As a result, the piezo actuator is compressed against its direction of expansion if it is not subjected to current or voltage. Thus, a force acts on the valve needle 20 in the closing direction via the actuating element 40 and the lever element 50 .

The piezo actuator 30 is formed from piezo stacks and is in a neutral liquid such as. B. Oil. The inner wall 14 encloses the piezo actuator stored in oil in the form of an inner, cylindrical shell. Due to the special pressure conditions inside the microvalve 10 , the necessary preload is reduced by the plate springs 32 . In operation, the fuel or the liquid that is to be injected through the microvalve 10 is located in a space 60 into which both the front of the actuating element 40 and the rear of the valve needle 20 extend. The liquid or the fuel is in the space 60 under pressure, which acts on the Venil needle and on the actuating element 40 . Since the area of the valve needle 20 exposed to the liquid pressure is smaller than the area of the adjusting element 40 exposed to the liquid pressure, the force on the adjusting element 40 predominates overall, so that the valve needle 20 is withdrawn in order to close the valve opening 22 .

Due to the relatively large area of the plate 42 of the actuating element 40 in the space 60, the liquid pressure compresses the piezo actuator 30 and thus holds the valve needle 20 in the valve seat 12 . This hydraulic balance enables the mechanical pre-tensioning of the piezo stack by the plate springs 32 to be kept low. Due to the reduced preload of the plate springs 32 , an additional gain in the stroke is achieved. In other words, a considerable loss in the stroke, which would result from a large preload of the plate springs 32 , is avoided.

The restoring force on the piezo actuator 30 and the force on the valve needle 20 are adjusted via the ratio of the area of the front of the plate 42 to the area of the rear of the valve needle 20 , the areas perpendicular to the respective direction of movement being decisive. Overall, a hydrostatic prestressing of the piezo actuator 30 is effected against its direction of expansion. At the same time, there is a force on the valve needle 20 in the closing direction, which, however, is less than the restoring force on the piezo actuator 30 .

The fuel is supplied to the space 60 and thus to the valve opening 22 via one or more fuel channels which are thermally coupled to the piezo actuator 30 . As a result, the heat generated by the piezo actuator 30 during operation is transferred via the liquid in which it is stored to the fuel flowing past it. On the one hand, this cools the piezo actuator 30 , and on the other hand, the fuel or the liquid to be injected is preheated. The supply channel for the fuel is formed by a space between the inner wall 14 , which encloses the piezo actuator 30 , and an outer wall 15 . The outer wall 15 is also cylindrical, ie it runs parallel to the inner wall 14 . This cooling of the piezo actuator 30 due to the fuel flowing past increases the reliability of the microvalve 10 even further. At the same time, the fuel is burned more effectively due to the preheating.

Fig. 2 shows a perspective view of the lever member 50 in a schematic representation. The lever element 50 is a spring which is designed in the form of a disk. At its center, it has a through opening 57 for receiving a portion of the valve needle 20 . Starting from the opening 57 , a plurality of slots 58 extend radially outward, each opening into an opening 59 . The openings 59 are ring-shaped in a region of the spring or the lever element 50 which is located radially further outward. The radially extending slots 58 and the annularly arranged outer openings 59 extend continuously through the thickness of the spring, so that a segment 63 of the disk-shaped spring is formed between two slots 58 and forms a lever arm.

The openings 59 are oval, their respective extent in the circumferential direction being longer than their extent in the radial direction. Between each two openings 59 there is a partial area 64 of the spring or deflection spring, to which a segment 63 is connected integrally or in one piece. An edge region 65 of the spring or of the lever element 50 lies radially further outward than the openings 59 and thus forms a ring on the outer edge of the spring, which is integrally or integrally connected to a plurality of arrow-shaped segments 63 located radially further inward via the partial regions 64 is. The partial areas 64 are narrow in comparison to the radially outer edge of the respective segment 63 , which adjoins it. Due to the oval configuration of the openings 59 , the edges of the partial areas 64 are curved. Dotted lines are drawn in FIG. 2 for the purpose of representing the different areas.

The special design of the lever element 50 or the spring enables very high frequencies when opening and closing the valve needle 20 , ie very short switching times are achieved, for example 20 microseconds. The spring or the lever element 50 is made of steel, but it can also be made of other materials or an alloy suitable for the respective application.

In the valve or injection valve shown in Fig. 1, the spring shown here is arranged so that in the edge region 65 on the front and on the back of the spring there is an outer edge ring 51 , 52, respectively. The edge area 65 is thus fixed between the two outer retaining rings 53 , 54 in the microvalve 10 .

The inner retaining rings 53 , 54 (see FIG. 1) adjoin the radially inner sides of the openings 59 so that they accommodate the eight segments 63 shown in FIG. 2 between them. One of the pressure clamps 41 discussed above extends through each of the eight openings, one end of which in each case surrounds or engages around the retaining ring 54 located there. The circular contacts between the inner retaining rings 53 , 54 and the outer regions of the eight segments 63 form points of attack or surfaces in order to deflect the segments 63 perpendicular to the surface of the lever element 50 . Since the lever element 50 is fixed in its edge region 65 by the outer retaining rings 51 , 52 , the partial regions 64 bend elastically when the segments 63 are deflected. Through the lever arms, which form the segments 63 in the radial direction, a stroke translation takes place, so that with a relatively small movement of the inner retaining rings 53 , 54, a relatively large deflection takes place at the radially inner ends of the segments 63 . As a result, the valve needle 20 coupled there experiences an increased stroke in comparison to the original actuating movement.

Fig. 3 is a perspective, partially exploded view showing the microvalve according to the invention. The lever element 50 is located in a front part of the microvalve 10 . The pressure clips 51 extend through the openings 59 in the lever element 50 and encompass the inner retaining ring 54 located on the front side of the lever element 50 . The lever element 50 is fixed in the microvalve 10 by the two outer retaining rings 51 , 52 . The individual segments 63 of the lever element 50 represent the stroke ratio to the valve needle 20 , the valve needle head 21 of which closes the valve seat 12 . If the valve needle 20 is pressed outwards, the valve needle head 21 lifts off from the valve seat 12 and fuel can e.g. B. are injected into the combustion chamber of an internal combustion engine. The guide element 13 for guiding the valve needle 20 is designed as a swirl generator or swirl plate.

The piezo actuator 30 is arranged in the rear area of the microvalve 10 . It is located in a chamber, which is enclosed by the inner wall 14 , in an oil bath. At its front, the piezo actuator 30 is non-positively connected to a plurality of disc springs 32 , which are compressed due to a current or voltage pulse when the piezo actuator expands. Otherwise, the plate springs 32 generate a restoring force in order to compress the piezo actuator 30 against its direction of expansion.

The annular sealing element 43 tightly separates the space in which the piezo actuator 30 is located from the space in the front area of the microvalve 10 in which the lever element 50 and the valve needle 20 are located. Thus, no fuel can get to the piezo actuator 30 from there. The actuating element 40 connects the lever element 50 to the piezo actuator 30 via the pressure clips 41 and the retaining rings 53 , 54 .

When the piezo actuator 30 is expanded, the actuating element 40 is moved forwards against the spring force of the plate springs 32 and against the fuel pressure in the region of the valve needle 20 , as a result of which the lever element 50 is actuated and the segments 63 are deflected forward. As a result, the valve needle 20 is moved forward and the valve needle head 21 stands out from the valve seat 12 . If the piezo actuator 30 is not activated, it is compressed on the one hand by the restoring force of the plate springs 31 and on the other hand by the fuel pressure which acts on the actuating element 40 from the front. As a result, the valve needle 20 is moved back by means of the pressure clips 41 and the retaining ring 54 .

The fuel is supplied in the direction of arrow F in FIG. 3 along the inner wall 14 in a supply channel, which is not shown here. This feed channel is e.g. B. formed in the form of a further wall or sheath, which is spaced from the wall 14 so that the fuel can pass between these two walls in the front region and then to the valve needle 20 . As a result, the fuel flowing past the wall 14 can absorb the heat generated by the piezo actuator 30 and thus effect cooling.

The piezo injector shown here or the microvalve according to the invention is 50 mm long in the preferred embodiment and has a diameter of 7 mm. The piezo injector has a very high resonance frequency and therefore very short sound times in the range of 20 µsec. It can also switch very high pressures, for example in the range of 200 bar and more. To open the microvalve, the piezo actuator experiences a current surge, which, for. B. is up to 50 A at 150 V voltage. The current surge can e.g. B. have a duration of 15 microseconds. The piezo stroke experiences through the lever element 50 that z. B. is a deflection spring, a reinforcement. The fuel flow to the valve seat is provided by the swirl plate, which also represents the valve needle guide.

To close the valve, the piezo stack or the piezo actuator 30 contracts when unloading. The valve pin 20 is pulled back by the pressure clips 41 and the valve is closed.

The present invention provides a microvalve with small dimensions, which can even be implemented with a length of 50 mm and less. Switching times with a duration of less than 20 µsec can be realized. The valve needle 20 is deflected by the piezo actuator 30 . The operating pressure is z. B. 200 bar. The valve needle stroke is greater than the extent of the piezo actuator 30 , with a 2.5-fold stroke gain, for example. In the example realized here, the valve needle stroke is 180 µm. The microvalve according to the invention has an outwardly opening nozzle and offers the possibility of beam shaping using swirl plates. The piezo actuator 30 is cooled by means of fuel. Overall, a high closing and opening force is made possible with an increased valve needle stroke. The space required is greatly reduced and only short piezo stacks are required. The microvalve can thus be manufactured very inexpensively and is therefore suitable for series production. It is also possible to integrate several valves in one injector. The shape of the lever element or the spring design would be optimized by a Venite element analysis.

The microvalve and the injection method are general for injecting a variety suitable for liquids.  

reference numeral

10th

Microvalve

11

Recess

12th

Valve seat

13

Guide element

13

a annulus

14

inner wall

15

outer wall

20th

Valve needle

21

Valve needle head

22

Valve opening

23

Beam shaping element

24th

Groove

30th

Piezo actuator

31

Coupling link

31

a inner area

31

b outer area

32

Belleville washers

33

front surface (of the piezo actuator)

40

Actuator

41

Pressure clamp

42

plate

43

Sealing element

44

Rod

50

Lever element

51

Bracket, outside

52

Bracket, outside

53

Bracket, inside

54

Bracket, inside

55

Actuation point

56

circular fixation

57

Opening (in the center of the spring)

58

Slits

59

openings

60

room

63

segment

64

Sub-areas

65

Marginal areas

Claims (20)

1. Piezoelectric microvalve, in particular for fuel injection in internal combustion engines, with
a valve needle ( 20 ), which is slidably mounted, for opening and closing a valve opening ( 22 );
a piezo actuator ( 30 ) for driving the valve needle ( 20 ); and
an actuating element ( 40 ) which transmits a stroke caused by the piezo actuator ( 30 ) to the valve needle ( 20 );
marked by
a mechanical lever element ( 50 ) which couples the actuating element ( 40 ) to the valve needle ( 20 ) so that a stroke ratio between the actuating element ( 40 ) and the valve needle ( 20 ) takes place. 2. Piezoelectric microvalve according to claim 1, characterized in that the lever element ( 50 ) is a flat, elastic spring. 3. Piezoelectric microvalve according to claim 1 or 2, characterized in that the lever element ( 50 ) is disc-shaped, wherein a plurality of slots ( 58 ) extend in the radial direction to form segments ( 63 ) which act as lever arms. 4. Piezoelectric microvalve according to one or more of the preceding claims, characterized in that a lever arm between the valve needle ( 20 ) and the actuation point ( 55 ) of the lever element ( 50 ) is larger than a lever arm between a fixation ( 56 ) of the lever element ( 50 ) and the actuation point ( 55 ). 5. Piezoelectric microvalve according to one or more of the preceding claims, characterized by a beam-shaping element ( 23 ) for generating a swirl in an injected liquid. 6. Piezoelectric microvalve according to claim 5, characterized in that the beam-shaping element ( 23 ) is a swirl plate which serves as a valve needle guide. 7. Piezoelectric microvalve according to one or more of the preceding claims, characterized by one or more rings ( 51 , 52 , 53 , 54 ) for power transmission between the actuating element ( 40 ) and the lever element ( 50 ). 8. Piezoelectric microvalve according to one or more of the preceding claims, characterized by one or more pressure clips ( 41 ) for fastening the lever element ( 50 ) on the actuating element ( 40 ). 9. Piezoelectric microvalve according to one or more of the preceding claims, characterized in that the valve needle ( 20 ) has an annular groove ( 24 ) into which the lever element ( 50 ) engages. 10. Piezoelectric microvalve according to one or more of the preceding claims, characterized in that the piezo actuator ( 30 ) is at least partially hydrostatically biased. 11. Piezoelectric microvalve according to one or more of the preceding claims, characterized in that a hydraulic force acts in the closing direction on the valve needle ( 20 ). 12. Piezoelectric microvalve according to one or more of the preceding claims, characterized in that the piezo actuator ( 30 ) and / or the valve needle ( 20 ) are acted upon by pressure in a liquid, a surface for pressurizing the piezo actuator ( 30 ) is larger than an area for pressurizing the valve needle ( 20 ). 13. Piezoelectric microvalve according to one or more of the preceding claims, characterized by a feed channel for the liquid to be injected, which is thermally coupled to the piezo actuator ( 30 ) in order to transfer heat from the piezo actuator ( 30 ) to the liquid. 14. Injection method, in particular for internal combustion engines, in which a valve needle ( 20 ) is driven by a piezo actuator ( 30 ) to carry out an injection process, characterized in that when the piezo actuator ( 30 ) expands and / or contracts, a stroke ratio takes place while the stroke of the piezo actuator ( 30 ) is transmitted to the valve needle ( 20 ). 15. Injection method according to claim 14, characterized in that the piezo actuator ( 30 ) is cooled by the liquid to be injected. 16. The injection method according to claim 14 or 15, characterized in that the valve needle ( 20 ) and / or the piezo actuator ( 30 ) are acted upon by prestressing with the pressure of a liquid. 17. lever element for power transmission between an actuator and a displaceable element, in particular for actuating a piezo injector, characterized in that the fog element ( 50 ) is disc-shaped, with radially extending slots ( 58 ) the lever element ( 50 ) in a variety of Segments ( 63 ) divided, which form lever arms. 18. Lever element according to claim 17, characterized in that the slots ( 58 ) each extend from an opening ( 57 ) located in the center of the lever element ( 50 ) to radially further outward openings ( 59 ), a plurality of the radially further outward openings ( 59 ) are arranged in a circle around the center. 19. Lever element according to claim 17 or 18, characterized by a plurality of circularly arranged openings ( 59 ) which are round or oval in shape, partial regions ( 64 ) of the lever element ( 50 ) located between the openings ( 59 ) being elastically bendable around which deflect the adjacent segments ( 63 ). 20. Lever element according to one of claims 17 to 19, characterized in that it in a piezoelectric microvalve according to one of claims 1 to 13 is arranged and / or in an injection method according to one of claims 14 to 16 is used.