Patent Publication Number: US-2017350356-A1

Title: Injector for injecting a fluid, use of an injector and method for manufacturing an injector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the national stage of International Pat. App. No. PCT/EP2015/079898 filed Dec. 15, 2015, and claims priority under 35 U.S.C. § 119 to DE 10 2014 226 811.7, filed in the Federal Republic of Germany on Dec. 22, 2014, the content of each of which are incorporated herein by reference in their entireties. 
     FIELD OF THE INVENTION 
     The present invention relates to an injector for injecting a fluid, in particular a fuel fluid, into an intake manifold or into a combustion chamber of a cylinder of an internal combustion engine, the injector having an electromagnetic actuator including a magnetic circuit. The present invention also relates to a use of such an injector and a method for manufacturing such an injector. 
     BACKGROUND 
     Electromagnetically actuated injectors of the type mentioned at the outset are usable in general for metering fluids. These injectors are preferably used in fuel systems of internal combustion engines for injecting fuel into a combustion chamber or into an intake manifold (of a cylinder) of the internal combustion engine, the internal combustion engine typically including a plurality of cylinders. Precisely maintaining a predefined injection quantity is crucial for the emission behavior and the consumption behavior of the internal combustion engine. The injected fuel quantity is a function of the opening duration of the valve and thus, in particular, also of an actual hydraulic opening and closing point in time of the valve which may significantly differ from an electrical activation start of the actuator in real valves. Therefore, a precise fluid metering in general cannot take place if only the electrical activation start and end are known. Although it is known in general to carry out the electrical activation of injectors in a controlled manner, the injectors are nowadays typically designed for a purely controlled operation in which an electronic control unit predefines a fixed activation time and the injector responds to it via its magnetic circuit (i.e., opens for the injection of fuel). In this case, the magnetic properties are designed in such a way that the magnetic circuit makes possible preferably short switching times and small tolerances for the injection. 
     SUMMARY 
     It is an object of the present invention to provide an improved injector for injecting a fluid, in particular a fuel fluid, into an intake manifold or into a combustion chamber of a cylinder of an internal combustion engine, the injector being optimized toward a controlled operation. In the case of a controlled operation of the injector, the electromagnetic actuator of the injector is activated in a controlled manner, in particular in a way that is individually adapted to the particular injector. The chronological profile of at least one electrical operating variable of the electromagnetic actuator—in particular during a test activation of the injector which, in an example, is carried out repeatedly—is detected in this case, thus providing information about at least one operating state of the injector and/or about at least one state change of the injector. By detecting at least one feedback signal, different properties of the injection process are detectable, in particular the determination of the opening point in time and/or the closing point in time of the injector. It is therefore an object of the present invention to help improve the feature recognition in the feedback signal so that at least one operating state of the injector and/or at least one state change of the injector is/are better, in particular more precisely or using less signal evaluation effort, detectable based on an analysis of the detected signals or, in particular, of the feedback signal. Based on the feedback of the specific valve behavior (for example the points in time of the valve opening or closing or also of other system functions such as decelerations for the purpose of minimizing noise) the process is controlled toward the setpoint variable, thus increasing the accuracy. 
     According to the present invention, the injector is designed in such a way that the feedback of the injector—detectable with the aid of the feedback signal or by detecting the chronological profile of at least one electrical operating variable of the electromagnetic actuator—is improved in particular with regard to the current and voltage profiles. A better detection of the opening and closing points in time may then be used to increase the control accuracy, i.e., make it possible in the first place. 
     The injector according to the present invention, the use of the injector according to the present invention, and the method for manufacturing an injector according to the present invention have the advantage over the related art that an improved feature manifestation in the feedback signal or in the current and voltage signals can be effectuated at the injector for the opening or closing of the injector or the valve needle with the aid of targeted measures. Here, the electromagnetic properties of the injector are given priority. The goal of the measures is, in particular, to preferably increase the portion of the magnetic flux through a gap (i.e., the working air gap) of the valve and/or also to preferably increase the restoring force of the valve spring in order to make possible shorter injection times or shorter opening time intervals of the injector. This means that the injector is not optimized as an independent component—as is the case in the related art—but for the purpose of interacting with the controlled operation or a controlled operating mode. The manifestation of the features (detected signals of the injector or in the feedback signal) which are needed to carry out the control has a pivotal role in this case. The injector is not optimized—as is the case in the related art—with regard to the properties of an independent component, but for the purpose of interacting with the control or the controlled operation. A central aspect represents maximizing the magnetic flux in the gap of the magnetic actuator (working air gap). In this way, the effect of the armature or needle movement on the current and voltage signals is maximized in the form of the kink intensity in the signal. According to the present invention, it is tolerated that individual measures—as contemplated from the point of view of the conventionally used purely controlled operating mode of the injector—initially negatively affect the valve properties (such as the accuracy of the quantity metering). The controlled operation of the injector makes it, however, possible to overall improve the accuracy, reproducibility as well as the lifetime stability of the valve properties. 
     Against this background, it is provided according to the present invention that the valve sleeve has either continuously—in the area and outside the area of the gap between the internal pole and the magnet armature—paramagnetic material properties, or else has paramagnetic material properties in the area of the gap between the internal pole and the magnet armature and ferromagnetic material properties outside of this area, it being provided according to the present invention that the effort involved in the latter case is comparably small, i.e., a valve sleeve of this type being cost-effectively manufacturable. It is in particular provided that the valve sleeve is designed as a deep-drawn part and continuously has (i.e., essentially over its entire length) paramagnetic material properties and is continuously not annealed, in particular it is not annealed in a temperature range between 350° C. and 700° C. In this way, the valve sleeve is manufacturable particularly cost-effectively, but the magnetic flux in the working air gap (due to the overall paramagnetic properties of the valve sleeve) is still increased or, in any case, not reduced. According to the present invention, it is furthermore in particular preferably provided that the valve sleeve is implemented as a deep-drawn part, the valve sleeve having paramagnetic material properties in the area of the gap between the internal pole and the magnet armature and ferromagnetic material properties outside of this gap area, the valve sleeve being annealed outside of the gap area, in particular annealed in a temperature range between 350° C. and 550° C., the gap area being subjected to a cooling during the annealing process, in particular with the aid of cooled nitrogen. In this way, it is advantageously achieved overall that the valve sleeve is treated in the area of the working air gap—in a comparably cost-effective manner—in such a way that the magnetic resistance is increased there so that the magnetic flux is increased in the area of the working air gap because only a minor portion of the magnetic flux (as a result of the greater magnetic resistance of the material of the valve sleeve) gets lost via the material of the valve sleeve (bypass) and thus does not act in the working air gap. 
     According to one alternative embodiment of the injector according to the present invention—which can, however, also be advantageously implemented together with the measures for designing the material properties of the valve sleeve—it is provided that the injector includes a valve spring, the spring force of the valve spring being greater than 4 N, in particular greater than 4.5 N. This makes it particularly advantageously possible according to the present invention to preferably precisely meter the fluid quantity or the fuel quantity in the case of one or multiple activation periods of the injector. As a result of a comparably great spring force of the valve spring, it is advantageously possible that a comparably great linear metering range is implementable so that the spring force may be optimally adjusted for the linearity and the accuracy of the fluid quantity or fuel quantity may be ensured by the control. 
     Advantageous embodiments and refinements of the present invention can be derived from the description with reference to the drawings. 
     According to one preferred refinement, it is provided that the electromagnetic actuator is activated in a controlled manner by detecting the chronological profile of at least one electrical operating variable of the electromagnetic actuator and thus by obtaining information about at least one operating state of the injector and/or about at least one state change of the injector so that by detecting at least one feedback signal different features of the injection process are detectable, in particular the determination of the opening point in time and/or of the closing point in time of the injector. As a result, it is advantageously possible according to the present invention to increase the accuracy during the operation of the injector overall, although the reproducibility of the injector manufacture is reduced, i.e., the variation with regard to component tolerances is increased, due to individual constructive measures. 
     Another aspect of the present invention relates to the use of an injector according to the present invention in a method for operating the injector, the electromagnetic actuator being activated in a controlled manner by detecting the chronological profile of at least one electrical operating variable of the electromagnetic actuator—in particular during a test activation of the injector—and thus by obtaining information about at least one operating state of the injector and/or about at least one state change of the injector so that by detecting at least one feedback signal different features of the injection process are detectable, in particular the determination of the opening point in time and/or of the closing point in time of the injector. 
     This principle according to the present invention makes it possible within the scope of the test activation(s) according to the present invention to particularly precisely establish the occurrence of an operating state or of an operating state change of the injector which requires monitoring. In this way, it is also possible in particular to ascertain an actual hydraulic opening point in time of the valve by predefining appropriate characteristic features. 
     Another aspect of the present invention relates to a method for manufacturing an injector according to the present invention, the valve sleeve having paramagnetic material properties in the area of the gap between the internal pole and the magnet armature and ferromagnetic material properties outside of this gap area, the valve sleeve being annealed outside of the gap area, in particular annealed in a temperature range between 350° C. and 550° C., the gap area being cooled during the annealing process, in particular with the aid of cooled nitrogen. 
     It is advantageously possible in this way that the area of the valve sleeve, in which the formation of a ferromagnetic behavior (or a corresponding material property) is prevented, is for the most part limited to the area of the gap (i.e., of the working air gap), for example, on the order of magnitude between 0.5 mm to 3 mm, preferably between 0.8 mm and 1.2 mm, the gap (i.e., the working air gap of the magnetic actuator) being essentially situated in the center with regard to the area in which the formation of a ferromagnetic behavior is prevented. 
     Additional advantages, features and details are derived from the following description, in which different exemplary embodiments of the present invention are illustrated with reference to the drawing. The features mentioned in the claims and in the description may each be provided either individually or in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic representation of an internal combustion engine having multiple injectors operated according to an example embodiment of the present invention. 
         FIGS. 2 a  and 2 b    show schematic representations of a detailed view of an injector from  FIG. 1  in two different operating states, according to an example embodiment of the present invention. 
         FIG. 3  schematically shows a chronological profile of the different operating variables of the injector operated according to an example embodiment of the present invention. 
         FIG. 4  schematically shows an example of an injector according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , an internal combustion engine is identified as a whole by reference numeral  10 . It includes a tank  12  out of which a delivery system  14  delivers fuel to a distribution system  16 , which is a common rail, for example. Connected to the latter are multiple electromagnetically actuated injectors  18  which inject the fuel directly into combustion chambers  20  assigned to them or also into the intake manifolds of combustion chambers  20 . The operation of internal combustion engine  10  is controlled or regulated by a control and regulating system  22 , which activates injectors  18 , among other things. 
       FIGS. 2 a  and 2 b    show schematic representations of injector  18  according to  FIG. 1  in two different operating states. Injector  18  has an electromagnetic actuator which includes a solenoid  26  and a magnet armature  30  which cooperates with solenoid  26 . Magnet armature  30  is operatively connected to a valve needle  28  of injector  18 , for example, in such a way that magnet armature  30  is movable relative to valve needle  28  in a non-vanishing mechanical clearance in relation to a vertical direction of movement of valve needle  28  in  FIG. 2 a   . This results, for example, in a two-part mass system  28 ,  30 , which drives valve needle  28  with the aid of electromagnetic actuator  26 ,  30 . This two-part configuration improves the mountability of injector  18  and reduces undesirable rebounding of valve needle  28  when it strikes its valve seat  38 . In the present configuration illustrated in  FIG. 2 a   , the axial clearance of magnet armature  30  on valve needle  28  is limited by two stops  32  and  34 . As shown in  FIG. 2 a   , a corresponding elastic force against valve seat  38  is applied to valve needle  28  in the area of the housing by a valve spring  36 . In  FIG. 2 a   , injector  18  is shown in its closed state in which no fuel injection takes place. In order to effectuate a fuel injection, actuator  26 ,  30  is acted on by an activating current over a predefinable activation period. Magnet armature  30  is moved upward by this energization of solenoid  26  in  FIG. 2 b   , so that it moves valve needle  28  out of its valve seat  38  against the elastic force by engaging with stop  32 . This enables fuel  42  to be injected into combustion chamber  20  ( FIG. 1 ) by injector  18 . As soon as the energization of solenoid  26  by control unit  22  ( FIG. 1 ) is terminated at the end of the predefined activation period, valve needle  28  moves back toward its valve seat  38  under the effect of the elastic force applied by valve spring  36 , and entrains magnet armature  30 . A power transmission from valve needle  28  to magnet armature  30 , in turn, takes place with the aid of upper stop  32 . When valve needle  28  terminates its closing movement by striking valve seat  38 , magnet armature  30  can continue to move downward as a result of the axial clearance in  FIG. 2 b   , until it rests against second stop  34 . This corresponds again to the closed state of injector  18  illustrated in  FIG. 2 a   . 
     According to an example embodiment of the present invention, an operating method is carried out for the purpose of obtaining information about at least one operating state or state change of injector  18 . In a first step, at least one test activation is carried out, during which actuator  26 ,  30  is acted on by a predefinable activating current I. At the same time as the test activation is carried out, at least one chronological profile of at least one electrical operating variable of actuator  26 ,  30  is preferably detected during the test activation. In the case of electromagnetic actuator  26 ,  30 , a chronological profile of a voltage which is applied at solenoid  26  of the actuator and/or a chronological profile of activating current I which flows through the solenoid is in particular taken into consideration. Subsequently, the detected chronological profiles are evaluated for the presence of a predefinable operating state and/or a predefinable operating state change of a feature characterizing injector  18 . A feature in the sense of the present invention can be in particular a local extreme and/or a sequence of multiple local extremes and/or another type of a particular chronological profile of the operating variables current and/or voltage. The characteristic feature of interest is found during the evaluation and the obtained information about the operating state or the operating state change is further used to control a future operation of injector  18 , for example. A plurality of test activations is also possible according to the present invention. It is, in particular, advantageously possible according to the present invention to ascertain an actual hydraulic opening point in time of injector  18 . 
     The hydraulic opening point in time of injector  18  is determined by valve needle  28  lifting from its valve seat  38 . This lifting of valve needle  28  correlates with a special chronological profile of the first chronological derivation of activating current I through solenoid  26 .  FIG. 3  shows, in this regard, a first chronological profile I 1  of an activating current I which is used to activate solenoid  26 —starting from the closed state of valve  18  shown in  FIG. 2 a   —for the purpose of putting injector  18  in its open state. A chronological profile hl of needle lift h resulting during the activation using first activating current I is also illustrated in  FIG. 3 . After starting to apply activating current I to actuator  26 ,  30 , non-vanishing values for lift profile h 1  occur for the first time at point in time T 1  (i.e., an operating state change of injector  18  takes place from its closed state toward its open state at point in time T 1 .) Accordingly, at least the chronological profile I 1  of activating current I is detected and first chronological derivation dI 1  of previously detected first activating current I is formed during the evaluation. As a result, by knowing ascertained opening point in time T 1 , it is possible to carry out a subsequent operation of injector  18  in a controlled manner, for example, with regard to an equalization of the injection characteristic of multiple injectors  18 . If local minimum Min 1  has not been already detected after carrying out the first test activation, it is possible to carry out another test activation, if necessary. 
     In addition to first activating current I 1 ,  FIG. 3  also shows a chronological profile of a second activating current I 2  resulting during the activation of actuator  26 ,  30  using a slightly reduced activating voltage. As is to be expected, the operating state change characterizing the transition from the closed state to the open state takes place in a slightly delayed manner with regard to lift profile h 1  which results during the activation using a greater activating voltage. According to the present invention, point in time T 2 , which, in turn, corresponds to a local minimum Min 2  in first chronological derivation dI 2  of second activating current I 2 , may be ascertained for the activation process by using second activating current I 2  as the actual hydraulic activation start, i.e., opening point in time. 
     In  FIG. 4 , an electromagnetically actuatable injector  18  is illustrated by way of example in the form of a fuel injector for fuel injection systems, for example, for the use in mixture-compressing, spark ignition internal combustion engines. Injector  18  includes a, for the most part, tubular core  2  which is surrounded by a solenoid  1  and which is used as the internal pole and partially as the fuel through-flow. Solenoid  1  is completely surrounded in the circumferential direction by an external, sleeve-shaped ferromagnetic valve jacket  5 , for example, which is designed in a stepped manner and which represents an external component of the magnetic circuit serving as an external pole. Solenoid  1 , core  2 , and valve jacket  5  together form an electrically excitable operating element or a magnetic circuit or an electromagnetic actuator. While a winding  4  of solenoid  1 , the latter being embedded in a coil body  3 , surrounds a valve sleeve  6  from the outside, core  2  is inserted in an internal opening  11  of valve sleeve  6  which runs concentrically to a valve longitudinal axis  10 ′. Valve sleeve  6  is elongated and thin-walled. Opening  11  serves, among other things, as the guiding opening for a valve needle  28  which is axially movable along valve longitudinal axis  10 ′. Valve sleeve  6  extends in the axial direction over approximately half of the axial overall extension of the injector, for example. In the example of  FIG. 4 , valve needle  28  is connected in one piece to magnet armature  30  and is formed from tubular magnet armature  30 , a likewise tubular needle section, and a spherical valve closing body. The injector is actuated electromagnetically in a manner known per se. 
     The electromagnetic circuit including solenoid  1 , internal core  2 , external valve jacket  5 , and magnet armature  30  is used for axially moving valve needle  14  and thus for opening the injector against the spring force of restoring spring  36  acting on valve needle  28  and for closing the injector. Magnet armature  30  is oriented toward core  2 . Instead of core  2 , a cover part, which closes the magnetic circuit, can also be provided as the internal pole, for example. 
     Apart from restoring spring  36 , an adjusting element in the form of an adjusting sleeve  29  is inserted into a flow bore  28  of core  2  which runs concentrically to valve longitudinal axis  10 ′ and which is used to supply the fuel in the direction of valve seat area  38 . Adjusting sleeve  29  is used to adjust the spring preload of restoring spring  36  which is applied to adjusting sleeve  29  and which, in turn, is supported at its opposite side on valve needle  28  in the area of magnet armature  30 . 
     According to the present invention, valve sleeve  6  continuously has either—in and outside the area of the gap between internal pole  2  and magnet armature  30 —paramagnetic material properties, or else has paramagnetic material properties in the area of the gap between internal pole  2  and magnet armature  30  and ferromagnetic material properties outside of this area. According to the first alternative (paramagnetic material properties in and outside the area of the gap between internal pole  2  and magnet armature  30 ), it is preferably provided that valve sleeve  6  is implemented as a deep-drawn part, valve sleeve  6  continuously having paramagnetic material properties and continuously being not annealed, in particular not annealed in a temperature range between 350° C. and 550° C. According to the second alternative (paramagnetic material properties in the area of the gap between internal pole  2  and magnet armature  30  and ferromagnetic material properties outside of this area), it is preferably provided that valve sleeve  6  is implemented as a deep-drawn part, valve sleeve  6  having paramagnetic material properties in the area of the gap between internal pole  2  and magnet armature  30  and ferromagnetic material properties outside of this gap area, valve sleeve  6  being annealed outside of the gap area, in particular annealed in a temperature range between 350° C. and 550° C., the gap area being subjected to a cooling during the annealing process, in particular with the aid of cooled nitrogen. 
     Alternatively or additionally to these measures, it is provided according to the present invention that injector  18  includes a valve spring  36 , the spring force of valve spring  36  being greater than 4 N, in particular greater than 4.5 N. 
     In this way, the control quality of the injector can be improved overall by combining certain properties of the magnetic circuit and a control function, so that a control function for injecting a fluid through the injector is implementable. The pot surrounding the solenoid and the sleeve of the magnetic circuit together with its magnetic resistance R m  are in particular significant features according to the present invention for manifestation in the feedback signal of the injector. In conventionally used injectors which are based on the purely controlled operating mode, these components are typically annealed for the purpose of obtaining a reduced magnetic resistance R m . According to an example embodiment of the present invention, an annealed operation of this type is avoided during the manufacture of the injector, thus improving the manifestation of the feature for control and detectability of the feature for the control.