DE102006014768A1 - Piezo electric actuator for high pressure fuel injection system, has torus-shaped and cylindrical coupling units arranged coaxial to each other, where torus-shaped coupling unit cooperates with ring actuator and has large diameter - Google Patents

Abstract

The actuator has several piezoelectric ceramic layers, where an electrode layer is provided between the layers. A coupler (25) is arranged between the actuator and an actuating unit e.g. nozzle needle. The actuator has a circular cross section such that the unit is coaxially arranged to the actuator. A torus-shaped coupling unit (27) and a cylindrical coupling unit (29) are arranged coaxial to each other, where the unit (27) cooperates with a ring actuator and has large diameter. The units are hydraulically connected such that the coupler is filled with an incompressible fluid e.g. oil.

Description

State of technology

Piezoceramic Components are becoming increasingly important in mechatronic applications, especially as actuators or sensors. In high-pressure fuel injection systems for internal combustion engines Piezo actuators are used to make the nozzle needle very fast and very precise head for.

in the The following will be representative of a variety of actuators always talked about piezo injectors, although the invention does not occur naturally Limited piezoinjectors is, but everywhere can be used at a profit, where an actuator with high dynamics and high precision over the entire life of the actuator must be controlled.

Because of the small stroke of piezo actuators is in many applications, especially in the known from the prior art piezoelectric actuators required to provide a coupler or travel distance enhancer, which the stroke of the piezoelectric actuator in a sufficiently large adjusting movement implements. These couplers are for example as a hydraulic translator executed with a stepped piston. In these couplers occur naturally leaks, so that the Piezo actuator must be sealed against fuel. If that is the Piezo actuator surrounding housing leaking, the injector becomes inoperable.

By the required sealing of the piezoelectric actuator and of a variety component hydraulic pressure intensifiers increase the number of needed Components and the manufacturing costs.

Of Another is in the known from the prior art piezo injectors with hydraulic pressure booster the direction of movement of the actuator and the actuator rectified, so that the piezoelectric actuator must be energized to close the nozzle needle. Only for opening the nozzle needle the voltage applied to the piezoelectric actuator is reduced. This means, that the piezoelectric actuator a large part its operating time loaded with an electric field with high field strength will, and only during the proportionately very short injections is de-energized. As a result, the piezoelectric actuator becomes electric and mechanically stressed, and its electrical power consumption is relatively large. In As a result, its life is reduced.

Of the Invention is based on the object, a relation to the State of the art to provide improved piezoelectric actuator or piezoinjector, It is simple, compact and electric and mechanical stress is reduced. Furthermore, should reliability and life of the piezoelectric actuator can be improved.

epiphany the invention

These Task is according to the invention in a piezoelectric actuator with a stack of several piezoelectric Ceramic layers, wherein between the ceramic layers in each case an electrode layer is provided with an actuated by the piezoelectric actuator actuator and with a arranged between the actuator and actuator coupler solved by that the actuator is designed as a ring actuator with an annular cross-section, that the actuator is arranged coaxially with the actuator that the Coupler a first toroidal coupling element and a coaxially arranged second toroidal or cylindrical coupling element includes that the first coupling element and the second coupling element hydraulically communicate with each other, and that the coupler with an incompressible fluid, in particular oil, is filled.

Advantages of the invention

By the coaxial arrangement and the formation of the piezoelectric actuator as ring actuator Movement reversal by the coupler is easily possible.

Thereby will it be possible for example, with a piezo injector, only to energize the actuator, when fuel is to be injected. As a result, the sink electrical and mechanical load piezoelectric actuator clearly and the Life of the piezo actuator increases.

One Another advantage of the ring actuator according to the invention is that because of the large diameter the cooperating with the ring actuator first coupling element already a small stroke of the piezoelectric actuator to a significant volume displacement leads to the coupler. As a result, can be a high gear ratio with be realized the coupler. This means that either one very big Stroke of the actuator can be achieved or it can, if the Stroke of the actuator is sufficient, reduces the length of the piezoelectric actuator become. This results in considerable economic and manufacturing technology Advantages.

By it is the two coaxially arranged coupling elements in a simple way possible, to reverse the direction of movement of the actuator with the coupler. If you may want the Movements of the actuator and the actuator are rectified.

at an advantageous variant is provided that first coupling element two cylindrical walls includes and that of the walls the first coupling element enclosed space through an annular cover plate is limited. This allows the Hubbwegung the Ringaktors to simple and efficient manner in a volume displacement of the first coupling element be implemented.

The same applies to the second coupling element. For example, when the actuator goes through the second coupling element is passed, the recommended Use a toroidal second coupling element. Otherwise, the second coupling element also as a cylinder with only one outer wall and a circular cover plate be formed. This can reduce the number of components become.

at small actuator strokes or actuating paths of the actuator, the transmission and conversion of the Aktorhubs in an actuating movement of the actuator by the elasticity of the cylindrical Walls of the coupling elements respectively.

Around the elasticity to increase the coupling elements, can in a further embodiment of the coupler according to the invention cylindrical Walls of the first Coupling element and / or the second coupling element as a bellows accomplished be. In this case, the transfer is also great Actuator strokes and Travel ranges of the actuator possible, without being too inadmissible high strains in the walls the coupling elements comes.

In addition, the Cover plates curved be educated. Thereby can the cover plates at least partially for transmission and translation the Aktorhubs be used on the actuator.

It has proven to be advantageous if the outer wall of the first coupling element, the inner wall of the second coupling element and a bottom plate Forming, in particular by deep drawing, made in one piece become. By Abweiselfiefziehen can thereby different wall thickness the various components are realized.

The same applies to the inner wall of the first coupling element, the outer wall of the second coupling element and an intermediate plate.

The various components of the coupler, in particular the walls of the Coupling elements, the cover plates, the bottom plate and / or the intermediate plate are welded together in an advantageous manner. Thereby a 100% freedom from leaks is achieved.

Usually lies in a piezoelectric according to the invention Actuator one end of the ring actuator on the cover plate of the first Coupling element on while the actuator rests on the cover plate of the second coupling element. In this case, a compression spring is further provided which the actuator stops in contact with the coupler.

A preferred application of the piezoelectric actuator according to the invention is the application in an injector of an internal combustion engine. In In this case, the actuator is a nozzle needle of the injector. On a hydraulic control valve can - partly because of the large transmission ratio of the coupler according to the invention - completely omitted become. This allows the control of the nozzle needle with greater dynamics and accuracy. Furthermore, space and costs saved and because of the reduced number of components and the Reliability increased.

It has further proven to be advantageous when a compression spring provided is, and the compression spring, the actuator in contact with the coupler holds. Thereby is guaranteed that, first, the actuator the predetermined by the piezoelectric actuator movements immediately follows and secondly, that over the coupler from the Compression spring over the actuator exerts force on the coupler to bias the ring actuator. As a result, a separate biasing device, such as a Bourdon tube, omitted.

Further Advantages and advantageous embodiments of the invention are the subsequent drawing, the description and the claims can be removed. All features disclosed in the drawings, the description and the claims can be essential to the invention both individually and in any combination.

drawings

It demonstrate:

1 a longitudinal section through an embodiment of a piezoelectric actuator according to the invention and

2 to 5 Embodiments of inventive coupler.

Description of the embodiments

In 1 an embodiment of a piezoelectric actuator according to the invention is shown in longitudinal section. In 1 is a piezo injector 1 represented, the a Ringaktor invention 3 having.

The ring actuator 3 has a variety of ceramic layers 5 on, between each of which an electrode layer 7 respectively 9 is arranged. For reasons of clarity, not all ceramic layers and electrode layers are provided with reference symbols. The electrode layers 7 are electrically with a first outer electrode 11 connected while the electrode layers 9 electrically with a second outer electrode 13 are connected. The operation of a piezoelectric actuator are well known, so that is dispensed with a detailed description in this context.

Of importance for the claimed invention is that the ring actuator 3 has an annular cross-section, so that in its center space for a sleeve 15 is available. In the sleeve 15 is a high pressure connection 17 intended. A nozzle needle 19 sticks out with a head 21 in the sleeve 15 ,

Between a front side 23 of the ring actuator 3 and the head 21 the nozzle needle 19 is a coupler 25 arranged. In the 2 and 3 are different versions of the coupler 25 shown. For a better understanding of the function of the piezoelectric actuator according to the invention 1 are the structure and function of the coupler 25 based on 2 and 3 explained.

The coupler 25 comprises a first coupling element 27 and a second coupling element 29 , The first coupling element 27 covers an outer wall 31 and an inner wall 33 as well as a cover plate 35 , The outer wall 31 and the concentrically arranged inner wall 33 be through the circular cover plate 35 connected with each other. The cover plate is preferred 35 on the outside wall 31 and on the inner wall 33 welded watertight. On the cover plate 35 lies the face 23 of the ring actuator (see 1 ) on. Once the ring actuator 3 energized, it expands and pushes the cover plate 35 in the direction of the arrow 43 ,

The second coupling element 29 in principle has the same structure as the first coupling element 27 on. It has an outer wall 37 , an interior wall 39 and an annular cover plate 41 ,

Since the first coupling element 27 a larger diameter than the second coupling element 29 and the interior of the coupler 25 as shown by the hatching in 2 indicated, completely and without air inclusion with oil, especially with hydraulic oil, is filled, the Aktorhub or the movement of the cover plate 35 of the first coupling element 27 through the hydraulic oil on the second cover plate 41 of the second coupling element 29 transfer. The movement of the cover plate 41 of the second coupling element 29 is through the arrows 45 indicated. The gear ratio of the coupler 25 is by the different lengths of the arrows 43 and 45 indicated.

The hydraulic connection between the first coupling element 27 and the second coupling element 29 is through an annular bottom plate 47 and an annular connecting plate 49 produced. The bottom plate 47 as well as the outer wall 31 of the first coupling element 27 and the inner wall 39 of the second coupling element 29 can be manufactured in one piece, for example by deep drawing. The same applies to the inner wall 33 of the first coupling element 27 , the intermediate plate 49 and the outer wall 37 of the second coupling element 29 , Alternatively, the components can also be manufactured individually and then welded. By welding on the cover plates 35 and 41 This creates a hermetically sealed interior in the coupler 25 who in 2 dotted is shown.

This interior (without reference numeral) is filled with oil, in particular hydraulic oil, so that no air bubbles are present. Because oil is almost completely incompressible, any displacement of oil caused by the stroke of the piezoactuator will be in the region of the first coupling element 27 in an expansion of the second coupling element 29 implemented. This is the first coupling element 27 displaced volumes as large as the expansion of the second coupling element 29 , In the embodiments according to 2 and 3 Simultaneously with the translation, a reversal of the direction of movement takes place.

Depending on the material used, preferably a metal with suitable mechanical properties, the stroke of the piezoelectric actuator and the required path of the actuator, the outer walls 31 and 37 as well as the interior walls 33 and 39 the first and the second coupling element 27 and 29 be performed as a cylindrical tube section, as in 2 is shown. This is a manufacturing technology particularly advantageous solution that also has the advantage that the coupling element 25 is very stiff in the radial direction.

However, if the strain in the region of the first coupling element 27 and the second coupling element 29 Due to the stroke of the piezoelectric actuator is too large, it can cause cracks. In these cases, it is beneficial to the outer walls 31 and 37 and / or the interior walls 33 and 39 the coupling elements 27 and 29 form as a bellows. In 3 are exemplary the outer wall 37 and the inner wall 39 of the second coupling element 29 designed as a bellows. If necessary, of course, the outer wall 31 and the inner wall 33 of the first coupling element 27 be formed as a bellows.

In 1 is below the coupler 25 a guide sleeve 51 and a clamping nut 53 intended. In the clamping nut 53 is a nozzle needle seat 55 with one or more spray holes 57 educated.

A compression spring 59 who are at the head one evening 21 the nozzle needle 19 and at the other end at a paragraph 61 in the sleeve 15 supports, presses the nozzle needle 19 against the nozzle needle seat 55 , This will be the injector 1 closed, and there is no injection of fuel into the combustion chamber of an internal combustion engine, not shown.

The sleeve 15 simultaneously seals the ring actuator 3 against the in the high pressure connection 17 available fuel. This requires the ring actuator 3 not be enclosed in a separate liquid-tight housing. As a result, among other things, the heat dissipation is improved.

The clamping nut 51 is with a nozzle holder 58 bolted to his in 1 upper end both the ring actuator 3 as well as the sleeve 15 fixed in the axial direction. By tightening the clamping nut 53 can the required preload of the ring actuator 3 be set.

The in the high pressure connection 17 The pending fuel is in a pressure chamber 63 the clamping nut 53 directed. The guidance of the fuel through the nozzle needle 19 through or past it and through the guide sleeve 51 through is in 1 not shown in detail. Incidentally, the invention is of course not on the in 1 exemplified structural design of the below the coupler 25 located part of the piezoelectric actuator 1 limited.

If now the ring actuator of the invention 3 energized, it expands and pushes the first coupling element 27 of the coupler 25 together. By doing so in the coupler 25 arising pressure increase, the second coupling element expands 29 against the contact pressure of the compression spring 59 out. As a result, the nozzle needle lifts 19 from the nozzle needle seat 55 and gives the spray holes 57 free. At this moment, an injection of fuel in the combustion chamber, not shown, of an internal combustion engine.

As soon as the energizing of the ring actuator 3 is interrupted, reduces the ring actuator 3 its length and the compression spring 59 closes the nozzle needle 19 again. Thus, the injection is ended.

In the injector according to the invention 1 can be dispensed with a hydraulic servo valve, because of the coupler according to the invention 25 first, the stroke of the piezoelectric actuator 3 is sufficiently enlarged and secondly, a reversal of motion takes place. This makes it possible, when the nozzle needle is closed 19 the ring actuator 3 de-energized and only in the short time intervals during which injections occur, the ring actuator 3 to energize. This reduces the electrical power consumption of the ring actuator according to the invention 3 , and the life of the ring actuator 3 is increasing.

The coupler according to the invention 3 may also, if necessary, make a travel magnification or a force amplification without reversing the motion. In the 3 and 4 exemplary embodiments of such couplers are shown. The essential difference between the embodiments according to 2 and 3 such as 4 and 5 is that in the embodiments according to 4 and 5 the adjusting movement of the second coupling element 29 rectified is like the stroke of the ring actuator 3 , This rectification of the movements is achieved in that the second coupling element 29 compared to the embodiments according to the 2 and 3 is turned "upside down".

This also applies to the embodiment according to 5 , In the embodiment according to 5 is the second coupling element not as a toroidal coupling element 29 formed, but as a cylindrical coupling element, in which only an outer wall 37 is available. This embodiment is advantageous when the actuator (not shown) is not through the coupler 25 must be passed.

Claims (11)

Piezoelectric actuator with a stack of several piezoelectric ceramic layers ( 5 ), whereby between the ceramic layers ( 5 ) is provided in each case one electrode layer, with an actuated by the piezoelectric actuator actuator ( 19 ) and with an between actuator ( 3 ) and actuator ( 19 ) arranged couplers ( 25 ), characterized in that the actuator as ring actuator ( 3 ) is formed with an annular cross section, that the actuator ( 19 ) coaxial with the actuator ( 3 ) is arranged that the coupler ( 25 ) a first toroidal coupling element ( 27 ) and a coaxially arranged second toroidal or cylindrical coupling element ( 29 ), that the first toroidal coupling element ( 27 ) and the second toroidal coupling element ( 29 ) are hydraulically connected to each other, and that the coupler ( 25 ) is filled with an incompressible fluid, in particular oil. Piezoelectric actuator according to claim 1, characterized in that the first coupling element ( 27 ) two cylindrical walls ( 31 . 33 ), and that of the walls ( 31 . 33 ) of the first coupling element ( 27 ) enclosed space by an annular cover plate ( 41 ) is limited. Piezoelectric actuator according to claim 1, characterized in that the second coupling element ( 29 ) at least one cylindrical walls ( 37 . 39 ) and that of the wall or walls ( 37 . 39 ) of the second coupling element ( 29 ) enclosed space by a circular or annular cover plate ( 41 ) is limited. Piezoelectric actuator according to claim 3, characterized in that the annular cover plate ( 41 ) is curved. Piezoelectric actuator according to one of claims 2 to 5, characterized in that the cylindrical walls ( 31 . 33 . 37 . 39 ) of the first coupling element ( 27 ) and / or the second coupling element ( 29 ) are designed as a bellows. Piezoelectric actuator according to one of the preceding claims, characterized in that the outer wall ( 31 ) of the first coupling element ( 27 ), the inner wall ( 39 ) of the second coupling element ( 29 ) and a bottom plate ( 47 ) are made by forming, in particular by deep drawing, in one piece. Piezoelectric actuator according to one of the preceding claims, characterized in that the inner wall ( 33 ) of the first coupling element ( 27 ), the outer wall ( 37 ) of the second coupling element ( 29 ) and an intermediate plate ( 49 ) are made by forming, in particular by deep drawing, in one piece. Piezoelectric actuator according to one of the preceding claims, characterized in that the components of the coupler ( 25 ), especially the walls ( 31 . 33 . 37 . 39 ) of the coupling elements ( 27 . 29 ), the cover plates ( 35 ), the bottom plate ( 47 ) and / or the intermediate plate ( 49 ) are welded together. Piezoelectric actuator according to one of the preceding claims, characterized in that an end face ( 23 ) of the ring actuator ( 3 ) on the cover plate ( 35 ) of the first coupling element ( 27 ) and that the actuator ( 19 ) on the cover plate ( 35 ) of the second coupling element ( 29 ) rests. Piezoelectric actuator according to one of the preceding claims, characterized in that a compression spring ( 59 ) is provided, and that the compression spring ( 59 ) the actuator ( 19 ) in contact with the coupler ( 25 ) holds. Piezoelectric actuator according to one of the preceding claims, characterized in that the actuator comprises a nozzle needle ( 19 ) of an injector ( 1 ) is for an internal combustion engine.