Abstract:
A stroke translator or an injector having a solid-state actuator for generating a stroke and a hydraulic system for the hydraulic transmission of the stroke of the solid-state actuator to a control element such as a jet needle of a valve. The hydraulic system has hydraulic volumes hermetically sealed to the outside by metal bellows and constitute a hydraulic bearing with compensation for play. The advantages over known hydraulic levers are such that a complete metal seal is provided, and that a lower-wear design can be realized. Furthermore, a modular structure can be produced.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of International Application No. PCT/EP2010/052363, filed Feb. 25, 2010 and claims the benefit thereof. The International Application claims the benefits of German Application No. 102009015738.731 filed on Mar. 31, 2009, both applications are incorporated by reference herein in their entirety. 
     BACKGROUND 
     Described below is a hydraulic stroke transmitter which forwards a stroke predetermined by a solid state actuator. Generally, stroke translation is combined therewith in order to increase the originally short stroke of the solid state actuators. 
     For introducing a desired quantity of fuel into any combustion processes, injectors are generally required, by which a quantity of fuel may be metered. As very many combustion processes are performed by the direct injection of fuel under high pressure, frequently actuators are used which operate particularly rapidly and which drive injectors. This means that an actuator generates a stroke which, for example, actuates an injector needle which in turn opens a valve and releases fuel at predetermined time intervals and at adjustable flow rates for a combustion process. In this case, combustion air is supplied separately. 
     Injectors for high-pressure direct injection frequently use rapid actuators in this situation, such as for example piezoelectric multilayer actuators (PMA). The actuators are solid state actuators, the central element thereof having a plurality of piezoelectric layers. Moreover, so-called magnetostrictive solid state actuators are known which utilize a magnetic mechanical effect for generating a stroke. For generating a stroke it is important that such solid state actuators have a sufficiently small stroke in order to open an injector needle to such an extent that the desired quantity of fuel is introduced. This leads to a substantial problem, particularly in gas injectors which require a larger stroke than injectors which meter liquid fuel. As a result, only designs with a stroke translator are considered. 
     Where hydrogen is used as fuel, it is a drawback that the small and lightweight hydrogen molecule easily diffuses through non-metallic elements such as rubber membranes. Thus, the choice of a suitable stroke translator becomes a crucial issue in the design of the injector. This is also due to the fact that a stroke translator determines many properties of an injector and, in contrast to an actuator, may be structurally redesigned. 
     In previous solutions to the problem, the stroke is increased by mechanical translation or by partial hydraulic stroke translation sealed in a non-metallic manner. Mechanical stroke translators which, for example, use a mechanical lever are generally susceptible to wear and to undesirable vibrations. This applies, in particular, when an idle stroke is necessary between the actuator and the stroke translator, for example in order to prevent a leakage which could occur in the event of thermal alteration to the length due to heating. As a result, the actuator strikes against a jet needle, for example, whereby the injector is negatively affected. Uneven injection and unreliable opening and closing characteristics result. An idle stroke between the actuator and the stroke translator is also undesirable as the displacement of the actuator as far contact with the jet needle remains unexploited. 
     An increase of the stroke of an actuator with a transmission ratio of less than 1:2 is often implemented by mechanical levers. In injectors for diesel engines, for example, the mechanical transmission ratio may be 1:1.6. Gas injectors typically require higher transmission ratios. In gas injectors, hydraulic stroke translators, also denoted as hydraulic levers, are generally used. In the direct injection of CNG (compressed natural gas), for example, a stroke transmission ratio of 1:6 is used. 
     By the use of a hydraulic stroke translator, the idle stroke may be avoided so that the functional chain between the actuator and jet needle is continuously present. This is directly reflected in the structural design. In other words, the displacement of the actuator is exploited and implemented to a greater extent by the injector. 
     In motor vehicle technology, a drawback in the related art is, for example, the wide temperature range which has to be taken into account and which may range from −40° C. to +150° C. This may involve considerable alterations to the volume in the case of fluid volumes. Peak values may be considerably above 30% of the volume increase. For this reason, hydraulic stroke translators generally require a connection to a reservoir. 
     In the German published patent application DE 10 2005 042 786 A1, for example, a fuel injector is disclosed which is provided with a hermetically sealed hydraulic system. In this publication, so-called guided pistons are used. Such guided pistons require high mechanical precision in manufacture and are very susceptible to wear. 
     SUMMARY 
     described below is a hydraulic stroke translator which has a sealed hydraulic system, forms a hydraulic bearing and is designed to be low-wear. 
     A hydraulic stroke translator described below has the advantage that guides for guided pistons, which are susceptible to wear and which are very costly both in production and in operation, are avoided. The new design of hydraulic stroke translator acts in the short periods during the injection phase of an injector as a known hydraulic stroke translator, namely as a rigid bearing. Additionally, the new hydraulic stroke translator compensates for alterations in length which, as before, are present as a result of temperature fluctuations. This is based on the variable coefficients of expansion of the different materials. 
     It is advantageous that a hydraulic stroke transmitter is constructed with a low-wear design. This has the result that no pistons or piston guides, which are costly to produce and which are also susceptible to wear during operation, have to be fitted. 
     The hermetic seal of a hydraulic system is advantageously improved by the use of metal bellows which define a plurality of hydraulic volumes hermetically sealed to the outside. The hydraulic volumes are connected together either in a throttled or unthrottled manner. 
     If initially the nature of a hydraulic stroke transmitter is considered, so-called hydraulic bearings ensure compensation for play, with compensation for an idle stroke which occurs. Thus, for example, an actuator continues to bear against a jet needle. A further advantage is achieved by a metal seal in the form of the metal bellows, which provides the substantial advantage of a leakage-free seal. Both advantages are associated with different time constants of the hydraulic system. 
     In the brief periods of injection carried out, for example, by an injector, the hydraulic bearing functions as a support acting on a fixed bearing, during the injection process of the injector. To this end, a throttle is provided in the hydraulic system. Over longer time periods, however, it is possible to compensate for the variable expansion of the different materials, by slow compensation processes in the hydraulic system taking place over throttled paths. 
     For completing the optimized hermetic seal of the hydraulic system, the metal bellows are connected in each case via welded seams to their adjacent components. 
     It is also associated with particular advantages if greater hydraulic volumes, which are not able to be produced otherwise, are reduced by displacement elements. Thus it is ensured that a low-loss stroke transmitter may be produced. This is based on the fact that so-called incompressible fluids have a finite coefficient of temperature expansion. This can have a negative effect with larger quantities of liquid in the event of fluctuating temperature and/or fluctuating pressure. 
     For the advantageous configuration of the hydraulic system, the positioning of the metal bellows is arranged concentrically to the solid state actuator axis of the solid state actuator. 
     The hydraulic system has only one movable piston which is not moved in the event of a stroke transmission or stroke transformation, but only in the event of temperature alterations, in particular in the hydraulic fluid in the hydraulic volumes. In this case, the possibility of predetermining the pressure in the hydraulic fluid is very advantageous. In particular, a mechanical spring is advantageous for setting the pressure. 
     For reducing the volume of hydraulic fluid, at least one displacement element may be inserted into at least one of the hydraulic volumes ( 11 ,  12 ,  13 ). 
     The advantages over known hydraulic levers are such that a complete metal seal is provided and a low-wear design may be implemented. 
     Moreover, a modular design may be produced. The use of metal bellows has the advantage that a completely sealed and low-friction hydraulic stroke transmitter may be produced. 
     A stroke translator or even a stroke reducer may be easily constituted by the layout of the pressure-effective surfaces in the hydraulic system. This produces a hydraulic bearing with stroke transformation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments with reference to the accompanying drawings of which: 
         FIG. 1A  is a schematic, partial cross-section of a hydraulic stroke transmitter with compensation for play, which is connected to a jet needle, at the temperature T 1 , 
         FIG. 1B  is a shows is a schematic, partial cross-section view, according to  FIG. 1A , of the metallically sealed hydraulic stroke transmitter with compensation for play being at a lower operating temperature T 2 , 
         FIG. 1C  is a detail view, according to  FIG. 1B , of the annular gap between the hollow cylinder of the movable piston and the central opening in the fixed bearing being illustrated, 
         FIG. 2A  is a schematic, partial cross-section of a metallically sealed hydraulic stroke transmitter with compensation for play in combination with a jet needle, through which a valve is actuated, 
         FIG. 2B  is a schematic, partial cross-section of the open state of the valve in a view according to  FIG. 2A , 
         FIG. 3  is a schematic, partial cross-section of an embodiment which includes displacement devices in a large hydraulic volume. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIGS. 1A and 1B  show in principle the same design, the operating temperature T 1  being present in  FIG. 1A , which is higher than the operating temperature T 2  according to  FIG. 1B . Both figures have substantially the same components denoted by the same reference numerals. A solid state actuator  4  is present which may be a piezoelectric actuator or a magnetostrictive actuator. The actuator is supported at the rear with its rear end  61  on a fixed bearing  7 . At the front end  62  of the solid state actuator, the solid state actuator has an end plate  8  which may be connected via a welded seam to the first metal bellows  1 . In this case, the first hydraulic volume  11  is shown. 
     The first metal bellows  1  is connected at its other end, viewed in the axial direction of the solid state actuator  4 , to a fixed bearing  71 , in a fixed and hermetically sealed manner which may be produced by a welded seam. 
     The fixed bearing  71  is provided with a central opening  19 , into which a hollow cylinder  10  forming part of a movable piston  9  axially runs and extends at least as far as the first hydraulic chamber  11 . The internal volume of the hollow cylinder  10  forms part of the third hydraulic chamber  13 . A second hydraulic chamber  12  is shown, by a second metal bellows  2  being positioned concentrically to the hollow cylinder  10 , and is welded to the fixed bearing  71  and to the top of the movable piston  9 . To this end, the piston  9  has a part of greater diameter than the hollow cylinder  10  and includes a central opening, the diameter thereof approximately corresponding to the internal diameter of the hollow cylinder. 
     A third metal bellows  3  is, on the one hand, welded to the movable piston and, on the other hand, to an end plate  81 . The hydraulic system  18  of the stroke transmitter is produced in this manner. For constituting an injector, in each case the rear end of a jet needle  16  which opens and closes a valve  20  may be in contact with or connected to the end plate  81 . 
     By the spring  14 , supported by the fixed bearing  72 , the movable piston  9  is subjected to pressure, the pressure being able to be set via the spring. Thus the pressure which is present in the entire hydraulic system  18  and which may be set in a uniform manner in the hydraulic chambers  11 ,  12 ,  13 , may be predetermined via the spring  14 . The spring  15  acts as a restoring spring for the valve  20 . 
     In the detail which is indicated in  FIG. 1B  and which is shown enlarged in  FIG. 1C , it may be seen that the first metal bellows  1  and the second metal bellows  2  on opposing sides of the fixed bearing  71  are in each case fixedly attached and coupled in a hermetically sealed manner by a welded seam. In this case, a first hydraulic volume  11  is defined by the first metal bellows  1  and a second hydraulic volume  12  is defined by the second metal bellows  2 . Moreover, the opening  19  in the fixed bearing  71  is indicated at the central position, the hollow cylinder  10  which is part of the movable piston  9  being partially shown. The annular gap  5  is formed between the hollow cylinder  10  and the edge of the opening  19  of the fixed bearing  71 . This annular gap  5  forms the throttle between the first and the second hydraulic volume  11 ,  12 . 
     The third hydraulic volume  13  is radially defined by the movable piston  9 , shown as a whole as a hollow body, as well as the third metal bellows  3  which, at its end remote from the solid state actuator  4 , is terminated by an end plate  81 . Thus it is clear that the first hydraulic volume  11  is connected in a throttled manner to the second hydraulic volume  12  and is connected in an unthrottled manner to the third hydraulic volume  13 . 
     For producing an injector, a jet needle which controls a valve  20  is additionally attached to the end plate  81 . 
     By the operation of the solid state actuator  4 , the hydraulic fluid contained in the hydraulic volumes  11 ,  12 ,  13  in each case is compressed during a stroke and ensures a corresponding stroke translation via the ratio of the pressure-effective surfaces in the first hydraulic volume  11  and in the third hydraulic volume  13 . Significant here is the ratio of the annular surfaces on the underside of the first hydraulic volume  11  and on the underside of the third hydraulic volume  13 , i.e. on the end plate  81 . 
     It may be seen in  FIG. 1B  that as a result of the temperature T 2 , which is lower than the temperature T 1  according to  FIG. 1A , a contraction of the hydraulic fluid has resulted in a shortening of the second metal bellows  2 . There is no idle stroke between the actuator and jet needle. This means that a compensation of the mechanical play which occurs as a result of temperature fluctuations has been compensated by the hydraulic stroke transmitter, in particular the hydraulic stroke translator. With a further stroke of the solid state actuator  4 , the hydraulic stroke transmitter briefly picks up on a fixed hydraulic bearing and/or a fixed hydraulic lever, as the flow rate of hydraulic fluid in the annular gap  5  is throttled and thus limited. 
     In  FIG. 2A , a closed injector is shown and in  FIG. 2B  an open injector is shown with the open valve  20 . The design of the stroke transmitter in  FIGS. 2A ,  2 B corresponds without alteration to that of  FIG. 1A  or  FIG. 1B . When comparing  FIGS. 2A and 2B , the difference is that the solid body actuator  4  in  FIG. 2B  is shown in the elongated state. In other words, its dimensions are greater in the longitudinal direction than in  FIG. 2A . Thus the hydraulic fluid is compressed in the first hydraulic volume  11  and the first metal bellows  1  is also compressed. The increased pressure in the first hydraulic volume  11  continues into the third hydraulic volume  13  in an unthrottled manner. Thus the third metal bellows  3  is lengthened by a specific amount due to the ratios of the pressure-effective surfaces, as disclosed above. The same occurs with the jet needle  16  which is correspondingly displaced. 
     In order to eliminate the susceptibility of the hydraulic system  18  to temperature fluctuations, it is advantageous to adapt large hydraulic volumes as far as possible. This generally means reducing the hydraulic volume, which is directed to such regions which do not hinder the required hydraulic flows. 
       FIG. 3  shows a hydraulic stroke transmitter or hydraulic stroke translator according to  FIGS. 1A ,  1 B,  2 A with a closed valve, whereby an injector is produced. In this case, at least one displacement element  17  is accommodated and/or formed in one or more hydraulic volumes. In  FIG. 3 , the displacement element  17  is initially of cuboidal or annular configuration in the first hydraulic volume  11 , the displacement element  17  being part of the fixed bearing  71 . In the view according to  FIG. 3 , the fixed bearing  1  is also provided with cuboidal or annular displacement elements  17 , which protrude in the direction of the jet needle into the second hydraulic volume  12 . It is significant here that elements which have been moved, such as for example the movable piston  9 , are not hindered in their movement. 
     A further displacement element in  FIG. 3  is positioned in the third hydraulic volume  13 , the displacement element being able to be connected to the end plate  81 , and thus the pressure-effective surface on the end plate  81  being displaced in the direction of the actuator. 
     The new design acts as a known hydraulic lever in the brief periods during which the injector injects. Additionally, the design compensates for alterations in length which, for example, occur as a result of temperature alterations. The design itself is a closed unit, able to be produced separately and thus without leakages. It is completely metallically sealed and does not require any guides. 
     The advantages of stroke translation, compensation for play in order to avoid an idle stroke, freedom from leakage by the use of metal seals and the absence of guides which are susceptible to wear. Many advantages are present relative to embodiments using mechanical levers. A hydraulic system has the advantage that the actuator continues to bear against a jet needle, so that no idle stroke occurs. Thus only small vibrations are produced, no idle stroke is generated and the activity of the actuator is utilized in an optimized manner. 
     The metallically sealed, hydraulic stroke transmitter with compensation for play includes three metal bellows  1 ,  2 ,  3 . The metal bellows are filled with a hydraulic fluid. Moreover, a fixed bearing is included as well as a spring between the fixed bearing and the piston, and/or a movable piston. The fixed bearings denoted hereinafter as the fixed bearings  7 ,  71 ,  72 ,  73 , may, for example, all form part of a housing for a hydraulic stroke transmitter, hydraulic stroke translator or an injector. 
     The first metal bellows  1  is welded to an end plate  8  of the solid state actuator  4  and to a fixed bearing  71 . The end plate  8  may be part of the actuator. The second metal bellows  2  is welded to the fixed bearing  71  and to the movable piston  9 . The third metal bellows  3  is welded to the movable piston  9  and to an end plate  81 . The end plate  81  seals the third hydraulic volume and serves for transmitting force to the jet needle  16 . 
     Via an opening  19  which may be centrally positioned in the fixed bearing  71 , a fluid path is provided for the hydraulic fluid in the first hydraulic volume  11  in the metal bellows  1  for connecting to the hydraulic fluid in the third hydraulic volume in the third metal bellows  3 . 
     The first hydraulic volume  11  in the first metal bellows  1  is also connected to the second hydraulic volume  12  of the second metal bellows  2 , but only via the annular gap  5  acting as a throttle, on the fixed bearing  71  between the first metal bellows  1  and the second metal bellows  2 . Slow compensation processes may take place via this annular gap  5 , whereby the movable piston  9  is displaced. Over time, therefore, the same pressure generally prevails in all three hydraulic volumes  11 ,  12 ,  13 . This is determined by the spring  14  between the housing and the movable piston  9 . This is also the case when the volume of the hydraulic fluid is altered by temperature fluctuation. In  FIG. 1B , this is shown in the case of cooling. The first metal bellows  3  expands, but the larger second metal bellows  2  is compressed. Overall, the second and third hydraulic volumes  12 ,  13  are so much smaller that the thermal effects are compensated. The first hydraulic volume  11  in this case remains constant, secondary effects, such as the rigidity of the actuator, being negligible. No leakage occurs as the entire hydraulic system  18  is enclosed in metal bellows. The pressure in the hydraulic fluid remains constant, at least as long as the spring  14  operates in a proportional area. The thermal longitudinal compensation is an advantage, but compensation is also provided for such longitudinal alterations, which are not thermally generated. Included therein are ageing processes in the solid state actuator, for example, which can alter the polarization thereof and thus the length thereof. As a result of the compensation for play all elements remain in contact. 
     With rapid processes, a quite different behavior of the system is exhibited. During the brief actuation period of the actuator, the flow resistance in the annular gap  5  is sufficiently high for practically no fluid exchange to take place between the first and the second hydraulic volumes  11 ,  12 . Typical injection processes during fuel injection in the motor vehicle, however, only last a few milliseconds. 
     Thus the two desirable properties: “hydraulically sealed with compensation for play” and “metallically sealed in a leakage-free manner” are combined in one arrangement. The separation of the functions takes place over the different time constants. In this case, the time constants of the compensation for play may be set by the dimensioning of the size of the annular gap  5  and the viscosity of the hydraulic fluid. Only metal bellows are moved. These require no particular guides and also are not particularly susceptible to wear. 
     The exemplary embodiment with reduced hydraulic volume corresponding to  FIG. 3  shows the solution to one possible practical problem, which may occur in the preceding figures. With a relatively large volume of hydraulic fluid, firstly the requirement for compensated volumes in the event of temperature alterations may be directly proportional to the filled quantity of hydraulic fluid. Secondly, the hydraulic rigidity of a fluid column reduces with height. A low-loss stroke transmitter, however, is intended to have a characteristic which is as rigid as possible. Both problems may be reduced if the space inside the metal bellows is partially filled by one or more displacement bodies. The shape of the displacement elements is freely selectable, as long as the required bellows movement for compensation for play according to  FIGS. 1A and 1B  and for the injection according to  FIGS. 2A and 2B  is not hindered.  FIG. 3  shows an exemplary embodiment with two displacement bodies  17 , both displacement elements being rotary parts which may be easily produced, and simply being enlargements of components which are otherwise necessary. 
     The system also includes permanent or removable storage, such as magnetic and optical discs, RAM, ROM, etc. on which the process and data structures of the present invention can be stored and distributed. The processes can also be distributed via, for example, downloading over a network such as the Internet. The system can output the results to a display device, printer, readily accessible memory or another computer on a network. 
     A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).