Patent Publication Number: US-9429119-B2

Title: Injection valve with direct and servo drive

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage application of International Application No. PCT/EP2011/059542 filed Jun. 9, 2011, which designates the United States of America, and claims priority to DE Application No. 10 2010 023 698.5 filed Jun. 14, 2010, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The disclosure relates to a valve apparatus for delivering lubricating and non-lubricating liquids, e.g., for use in the field of fuel injection in an internal combustion engine. The valve apparatus may have a two-stage drive device which comprises both an electric direct drive and also a hydraulic servo drive. Here, the servo drive may be activated in addition to the direct drive if a greater valve needle stroke is required. 
     BACKGROUND 
     Valve apparatuses are used for the delivery and/or distribution of a wide variety of liquids. Such valve apparatuses may be formed for example as so-called injection valves, in which the opening of an injection nozzle is controlled very precisely by means of a valve needle. By means of a modern injection valve, it is thus possible for even extremely small liquid quantities to be accurately metered. Such accuracy is required for example in internal combustion engines in which fuel is injected at high pressure into the combustion chamber by means of corresponding fuel injectors. Here, the fuel must be supplied in precisely predefined quantities and at predefined times. For the conditioning of the combustion process, the fuel injection valve of a modern internal combustion engine generally performs multiple injections, wherein the fuel quantity used is varied depending on the injection phase. Relatively small fuel quantities are typically injected for the pilot injection, whereas relatively large fuel quantities are delivered into the combustion chamber during the main injection. 
     The spectrum of fuel quantities required in the individual phases of the fuel injection in an internal combustion engine constitutes an important criterion in the design of a suitable injection valve. For example, the drive device provided for moving the valve needle must be designed to be large enough to ensure the maximum needle stroke required during the main injection. On the other hand, it must also be possible for the valve needle to be controlled quickly and precisely enough to permit an optimum injection of small or extremely small fuel quantities during the pilot injection. 
     A drive device typically used for deflecting the valve needle therefore has an electric drive means, for example a piezoelectric or electromagnetic actuator. In said drive concept, the actuator acts as a direct drive, wherein the valve needle, owing to mechanical contact with components of the drive, is deflected out of its closed position by directly following the deflection or expansion of the actuator. The direct drive thus permits particularly fast switching times and precise regulability, in particular in combination with closed loop regulation. The switching travel that can be realized in this way is however limited to the maximum deflection of the actuator. In the case of a piezo stack, this is for example only approximately 60 to 70 micrometers. Such a small needle stroke is however not expedient for the delivery of relatively large liquid quantities. To overcome said disadvantage, a more complex construction of the direct drive is required, which manifests itself inter alia in high production costs. 
     To realize a greater valve needle stroke, use may also be made of hydraulic drive devices. In said drive concept, a hydraulic force which effects the deflection of the valve needle is generated utilizing different pressure conditions within the valve apparatus. In the hydraulic drive activated for example by means of a servo valve, the deflection of the valve needle takes place in the form of ballistic flight, thus permitting a considerably greater needle stroke in relation to the electric direct drive. However, owing to the indirect response of the valve needle to the control, the possibilities for closed loop regulation and thus also a precise injection of extremely small liquid quantities are severely limited with said drive concept. 
     SUMMARY 
     In one embodiment, a valve apparatus is provided for delivering a liquid, having a housing, having a valve needle which is arranged, such that it can be deflected, in a valve needle chamber of the housing, and having a drive device for the valve needle, wherein the drive device comprises an electric drive component which effects a direct deflection of the valve needle, wherein the drive device also comprises a hydraulic drive component which can be activated in addition to the electric drive component and which effects a ballistic deflection of the valve needle. 
     In a further embodiment, the drive device is designed to effect the activation of the hydraulic drive component by means of the electric drive component. In a further embodiment, the hydraulic drive component is in the form of a servo valve which connects the valve needle chamber to a low-pressure duct, wherein the servo valve comprises a valve element which can be moved from a closed position into an open position by the deflection of the electric drive component. In a further embodiment, the deflection of the electric drive component leads to an activation of the hydraulic drive component only after an activation threshold is overcome, and the activation threshold is predefined by a tolerance in the mechanical transmission path from the electric drive component to the valve element. In a further embodiment, the mechanical transmission path from the electric drive component to the valve element comprises at least one mechanical transmission element which transmits the deflection of the electric drive component to the valve element of the hydraulic drive component. In a further embodiment, the transmission element is of pin-like form. In a further embodiment, the mechanical transmission path comprises a lever-like transmission element which is actuated by the pin-like transmission element. In a further embodiment, between the two transmission elements, a tolerance is provided which permits a deflection of the valve needle by a predefined distance without an activation of the hydraulic drive component taking place. 
     In a further embodiment, the electric drive component comprises a piezo element which effects the desired deflection when an electrical voltage is applied. In a further embodiment, the electric drive component is operated by means of closed loop regulation. In a further embodiment, the valve apparatus is formed as an injection valve for injecting fuel into a combustion chamber of an internal combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will be explained in more detail below on the basis of the schematic drawings, wherein: 
         FIG. 1  shows a valve apparatus which is formed as an injection valve and which has a drive device according to an example embodiment; 
         FIG. 2  shows the drive device of the injection valve apparatus of  FIG. 1  in a rest position; 
         FIG. 3  shows the drive device of  FIG. 2 , with a valve needle deflected slightly by means of the direct drive, 
         FIG. 4  shows the drive device of  FIGS. 2 and 3  in servo operation, with a valve needle in ballistic flight, 
         FIG. 5  shows a time diagram illustrating, by way of example, an injection process of the injection valve according to an example embodiment with pilot injection and main injection, and 
         FIG. 6  shows a possible injection process, during which fuel is injected into the combustion chamber of an internal combustion engine in a plurality of individual injections by means of the injection valve. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments provide a drive concept for a valve apparatus for delivering liquids, which drive concept permits both precise dispensing of small liquid quantities and also a greater valve needle stroke for delivering greater liquid quantities. 
     In some embodiments, a valve apparatus for delivering a liquid has a housing, a valve needle which is arranged, such that it can be deflected, in a valve needle chamber of the housing, and a drive device for the valve needle. Here, the drive device comprises an electric drive component which effects a direct deflection of the valve needle, and a hydraulic drive component which can be activated in addition to the electric drive component and which effects a ballistic deflection of the valve needle. As a result of the combination of the two drive concepts in the drive device, it is possible for the advantages of both drives to be utilized. The electric drive component which acts as a direct drive permits highly precise valve needle control for the injection of small liquid quantities. Owing to the fast response behavior of the valve needle, the direct drive can also be combined with closed loop regulation, whereby the precision of the valve needle control can be increased. By contrast, by means of the hydraulic drive component, it is possible to realize a relatively large deflection of the valve needle, and thus the injection of relatively large liquid quantities, for example during the main injection phase. The combination of the two drive concepts is also associated with a reduction in production costs, because only a relatively short piezo stack is required. 
     In a first embodiment, it is provided that the drive device is designed to effect the activation of the hydraulic drive component by means of the electric drive component. An automatic activation of the hydraulic drive component is permitted in this way. Since, in this case, the two operating modes, specifically “purely electric operation” and “mixed operation” are controlled merely by the means used for controlling the electric drive component, a simplified and thus also less expensive design is thus made possible. 
     In a further embodiment, it is provided that the hydraulic drive component is in the form of a servo valve which connects the valve needle chamber to a low-pressure duct, wherein the servo valve comprises a valve element which is moved from a closed position into an open position by the deflection of the electric drive component. Such servo valves permit a relatively large needle stroke. The direct activation of the valve element by the deflection of the electric drive component makes it possible to realize a particularly simple automatic activation of the hydraulic drive component. 
     A further embodiment provides that the deflection of the electric drive component leads to an activation of the hydraulic drive component only after an activation threshold is overcome, wherein the activation threshold is predefined by a tolerance in the mechanical transmission path from the electric drive component to the valve element. By determining the tolerance, it is possible in a particularly simple manner to define the maximum needle stroke that can be effected by means of the electric drive component without activation of the hydraulic drive. 
     In a further embodiment, it is provided that the mechanical transmission path from the electric drive component to the valve element comprises at least one mechanical transmission element, by means of which the deflection of the electric drive component is transmitted to the valve element of the hydraulic drive component. The use of mechanical transmission elements permits an optimization of the transmission of the movement of the electric drive to the valve element and thus of the opening behavior of the valve element. Furthermore, with mechanical transmission elements, it is particularly easily possible to realize tolerances which permit an activation of the hydraulic component only after a predefined needle stroke is overcome. 
     A further embodiment provides that the transmission element is of pin-like form. This permits a direct and therefore simple transmission of the movement of the electric drive to the valve element. 
     A further embodiment provides that the mechanical transmission path comprises a lever-like transmission element which is actuated by the pin-like transmission element. By means of the lever-like transmission element, the deflection of the electric drive component can be converted as desired into a movement for activating the valve element. In particular, it is possible to reverse the movement direction, such that the valve element is opened counter to the deflection direction of the electric drive component. 
     A further embodiment provides that, between the two transmission elements, a tolerance is provided which permits a deflection of the valve needle by a predefined distance without an activation of the hydraulic drive component taking place. In this way, it is possible in a simple manner to realize an automatic activation of the hydraulic drive component which takes place only beyond a predefined needle stroke, that is to say only after an activation threshold is overcome. 
     In a further embodiment, the electric drive component comprises a piezo element which effects the desired deflection when an electrical voltage is applied. Such piezo elements have a fast response behavior, as a result of which they can be used optimally, in particular in combination with suitable regulation, for precise control of the valve needle. This is advantageous in particular for the injection of extremely small liquid quantities. Furthermore, piezo elements can be produced relatively inexpensively. 
     In a further embodiment, it is provided that the electric drive component is operated by means of closed loop regulation. The precision of the valve needle control can be increased considerably in this way. 
     Finally, a further embodiment provides that the valve apparatus is formed as an injection valve for injecting fuel into a combustion chamber of an internal combustion engine. Owing to the combined properties of the two drive concepts, the valve apparatus may be particularly suitable for the pilot injection and the main injection in an internal combustion engine. In the case of an injection valve, the increased needle stroke of the combined drive in relation to the purely electric drive furthermore permits a more expedient nozzle needle angle, which can have a positive effect on the combustion parameters. 
       FIG. 1  shows a valve apparatus  100  according to an example embodiment for delivering lubricating and non-lubricating liquids. The valve apparatus illustrated here may be a fuel injection valve for an internal combustion engine of a motor vehicle. The injection valve  100  comprises a housing  110 . The housing, which is generally of multi-part construction, comprises an upper and a lower housing part  111 ,  112 , wherein the division of the housing may vary depending on the application. The valve apparatus  100  also comprises a valve needle  120  which is arranged in a valve needle chamber  113  in the interior of the housing  110 . The valve needle  120  controls an injection nozzle (not shown here) which is provided in the lower part of the housing  110  and through which highly pressurized fuel is discharged into the combustion chamber. Here, the fuel is supplied via a high-pressure duct  116  which runs in the housing  110 . 
     The valve needle  120  is mounted so as to be movable in the axial direction and typically comprises a shank-like portion  121 , on the lower end of which is formed a valve needle tip  125  which serves as a closure element for the orifice of the injection nozzle. To ensure that the injection valve closes fully, the valve needle  120  may be held in its valve seat by means of spring force. For this purpose, in the present example, a spiral compression spring  130  is provided which is accommodated in a spring chamber  150  formed by a part of the valve needle chamber  113 . The compression spring  130 , which acts on a collar-like valve needle part  124 , exerts a pressure in the downward direction on the valve needle  120 . To open the injection valve, the valve needle  120  is therefore deflected upward counter to the spring force of the compression spring  130 . For this purpose, a drive device  200  is provided which may be integrated in the housing  110  of the valve apparatus  100 . The drive device  200  comprises an electric drive component  210  which serves as a direct drive. For this purpose, use may be made of basically any suitable electrically operated actuator that is controlled by means of electrical signals, for example current or voltage pulses. In injection valves, therefore, use is often made of actuators which are composed of piezoelectric materials and in which a change in the electrical voltage applied thereto leads to an expansion or contraction. Such piezo actuators are typically produced as so-called piezo stacks which are formed from a plurality of piezoelectric layers arranged one above the other. Furthermore, use is also made of electromagnetic actuators in which the desired deflection is effected by application of corresponding current pulses. 
     In the present case, the electric drive component is formed by a piezo stack  210 . The piezo stack  210 , which is accommodated in an inner housing chamber, is of cylindrical form and has a central bore  211  for receiving the shank-like part  121  of the valve needle  120 . As shown in  FIG. 1 , the piezo stack  210  does not completely fill out the inner housing chamber, as a result of which a pressure chamber  114  for receiving a plate structure  121  of the valve needle  120  is formed above the piezo stack  210 . Here, the plate structure  121  forms the upper termination of the valve needle  120  and is connected to the shank-like valve needle part  121 , which runs within the bore  211 . Against the cylindrical piezo stack  210  there bears a disk-like annular element  212 , which serves to support the valve needle plate  121 . During the expansion of the piezo stack  210 , the valve needle plate  122  is driven by the annular element  212  arranged thereunder, whereby the valve needle  120  is deflected counter to the force of the compression spring  130 , and the nozzle orifice is opened up. Owing to the mechanical contact between the piezo stack  210 , annular element  212  and valve needle plate  122  during the deflection, the valve needle  120  reacts directly to the movement of the piezo stack  210 . Very fast and precise control of the valve needle  120  is thus possible in particular in combination with closed loop regulation. In purely direct operation, however, the deflection of the valve needle  120  is limited by the maximum deflection of the piezo stack  210 . 
     The drive device  200  may therefore additionally include a hydraulic drive  220  which, in the present case, is in the form of a servo valve which connects the pressure chamber  114  to a low-pressure duct  117 . Here, the servo valve  220  comprises a conical valve element  221  which closes off a likewise conically shaped valve orifice in the upper cover element of the pressure chamber  114 . A curved lever element  223  which is arranged in a side chamber  118  of the low-pressure duct  117  serves to open the servo valve  220 , which lever element acts on the valve element  221  and is actuated by means of a pin-like transmission element  213 . The pin-like transmission element  213  is arranged so as to be guided in a bore of the upper cover element of the pressure chamber  114  and bears with its lower end on the annular element  212 . For this purpose, a corresponding opening with a tolerance adequate for the pin-like transmission element  213  is provided in the plate-like termination element  122  of the valve needle  120 . Here, the two transmission elements  213 ,  223  may be formed such that they do not make contact when the valve apparatus  200  is in the closed state, and the actuation of the curved transmission element  223  thus takes place only after a distance predefined by the spacing  214  of said transmission element is overcome. It may be ensured in this way that the hydraulic drive component  220  is activated only after an activation threshold is overcome, that is to say only beyond a relatively large deflection of the valve needle  120  by means of the piezo stack  210 . An activation threshold of the hydraulic drive component  220  is thus realized by means of the gap  214  formed between the two transmission elements  213 ,  223 . Here, the gap width determines the maximum valve needle stroke that can be realized without activation of the hydraulic drive  220 . A corresponding activation threshold may however also be realized by means of corresponding tolerances at other points in the mechanical transmission path, which includes the two transmission elements  213 ,  223 , from the electric drive component  210  to the valve element  221 . 
     An example mode of operation of the disclosed valve apparatus will be described in more detail below. In this regard,  FIG. 2  shows a detail of the drive device  200  from  FIG. 1 . To ensure that the valve needle sealingly closes off the nozzle orifice when the injection valve is in the closed state, the plate-like termination element  122  of the valve needle  120  does not bear directly against the annular element  212 . The two elements are rather separated from one another by a small gap, which defines a so-called idle stroke. Only after the idle stroke is overcome do the two elements come in contact with one another (not shown here).  FIG. 2  illustrates the initial situation in which the valve needle  120  is pressed into the valve seat by the force of the compression spring  130  and consequently holds the injection nozzle closed. Since the entire valve needle chamber  113  communicates hydraulically with the high-pressure duct  116 , the high fuel pressure also prevails in the pressure chamber  114  at this time. Since the servo valve  220  is also still closed, the pressure conditions in the entire pressure chamber  114 , that is to say above and below the plate-like termination element  122  of the valve needle  120 , are substantially balanced. 
     By activation of the direct drive, which is realized in the present example by application of a corresponding electric voltage to the piezo stack, the piezo actuator  210  expands in the direction of the valve needle plate  122 . After the idle stroke is overcome, the valve needle plate  122  is driven by the annular element  212 , which leads to a deflection of the valve needle  120  out of its rest position. A corresponding situation is illustrated in  FIG. 3 . It can be seen here that a small deflection of the valve needle  120  reduces the gap width  214  between the two transmission elements  213 ,  223  without the servo valve  220  being activated. Therefore, by application of a correspondingly low voltage to the piezo stack  210 , it is possible to effect a precise opening of the injection valve, for example in order to inject an extremely small fuel quantity into the combustion chamber during the pilot injection. 
     By contrast, if an adequately high voltage is applied to the direct drive  210 , a correspondingly large expansion of the piezo stack results in contact between the two transmission elements  213 ,  223  and subsequently in activation of the servo valve  220 , wherein the conical valve element  221  is raised out of its valve seat by means of the lever  223 . Said situation is shown in  FIG. 4 . As a result of the opening of the servo valve  220 , an abrupt pressure drop occurs in the upper part of the pressure chamber  114 , because here, the pressurized liquid can escape through the servo valve  220  and the low-pressure duct  117  faster than it can flow in via the connection to the high-pressure duct  116 . Since high pressure substantially still prevails at this time in the lower part of the pressure chamber  114 , the sudden pressure drop in the upper part of the pressure chamber  114  causes a force to act on the valve needle plate  122 , and consequently on the valve needle  120  as a whole, in the direction of the pressure gradient. In the second drive phase of the valve needle  120  initiated in this way, the valve needle plate  122  lifts up from the annular element  212  and, together with the valve needle  120  as a whole, covers a distance dependent on the respective hydraulic parameters in ballistic flight. The considerably greater deflection of the valve needle  120  during the ballistic flight phase generates a correspondingly large opening of the injection nozzle, as a result of which a greater liquid quantity is delivered. Said hydraulically assisted operating mode is thus particularly well suited for fuel injection during the main injection phase of an internal combustion engine. 
     When the pressure conditions within the pressure chamber  114  have been substantially compensated as a result of the follow-up inflow of liquid, the valve needle is forced back in the direction of the valve orifice by the compression spring  130  and the injection valve is closed again. Said process can be influenced by early closing of the servo valve  220 , which may be effected by means of a corresponding contraction of the piezo stack  210 . Here, the valve element  221  is pressed into its valve seat again by the pressure difference prevailing between the pressure chamber  114  and low-pressure duct  117 , as a result of which the pressure drop via the low-pressure duct  117  is abruptly ended. Here, said closing process may be assisted by means of a spring element which presses the valve element  221  into its valve seat (not shown here). 
       FIG. 5  shows a further alternative embodiment of the valve apparatus  100  according to an example embodiment, in which the valve needle  120  is likewise set in ballistic flight in a hydraulically assisted manner when the deflection of the valve needle  120  exceeds a predefined needle stroke. Here, the electric drive component  210  is designed substantially analogously to the corresponding drive component from  FIGS. 1 to 4 . By contrast to the exemplary embodiments shown in the preceding figures, the servo valve of the injection valve  200  shown here is however arranged such that the opening of the valve element  221  now takes place in the direction of expansion of the piezo stack  210 . In this way, the deflection of the piezo element  210  can be transmitted directly to the valve element  221  by means of a simple pin-like transmission element  224 . As shown in  FIG. 5 , the transmission element  224  is in this case not seated directly on the annular element  214 . The gap  214  provided between the two elements  212 ,  224  correspondingly determines the activation threshold, that is to say the maximum distance by which the valve needle  120  can be deflected only by means of the direct drive  210  without assistance by the hydraulic drive component  220 . When the activation threshold is reached, contact occurs between the annular element  212  and the transmission element  224 , which, during a further deflection of the piezo stack  210 , leads to the valve element  221  being lifted out of its valve seat. In this way, similarly to the first exemplary embodiment, a hydraulic connection of the pressure chamber  114  to the low-pressure duct  117  is produced through the duct  119  and the servo valve  220 . 
       FIG. 6  shows a possible injection process, during which fuel is injected into the combustion chamber of an internal combustion engine in a plurality of individual injections by means of the injection valve according to an example embodiment. Here, for the conditioning of the internal combustion engine small or extremely small fuel quantities  301  are injected already during the course of a pilot injection which takes place prior to the main injection. Here, the injection of extremely small quantities may take place in the purely electric operating mode in which the deflection of the valve needle is effected exclusively by the direct drive. For this purpose, the piezo actuator is activated only to a small extent, such that its small deflection does not lead to an activation of the servo valve. By contrast, during the subsequent main injection phase, a relatively high electrical voltage is applied to the piezo actuator in order to attain an activation of the servo valve as a result of the correspondingly large deflection of the piezo actuator. After activation of the servo valve, the valve needle attains a greater needle stroke in ballistic flight, which is manifested in considerably larger injection quantities  302 . 
     The main injections may also be followed by so-called post-injections in order to increase the energy content of the exhaust gases for exhaust-gas aftertreatment. Since likewise only very small fuel quantities are injected into the combustion chamber during a post-injection, it is sufficient in this case for the injection valve to be opened only by means of the direct drive. 
     The embodiments explained on the basis of the figures constitute merely preferred or exemplary embodiments of the invention. In addition to the embodiments described and shown, further embodiments are conceivable which may encompass further modifications and combinations of features. In particular, the valve device disclosed here in conjunction with fuel injection may also be used for the delivery or metering of other lubricating or non-lubricating liquids.