Patent Publication Number: US-10330062-B2

Title: Injector for injecting fluid

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This U.S. patent application claims the benefit of PCT patent application No. PCT/EP2015/071198, filed Sep. 16, 2015, which claims the benefit of European patent application No. 14189105.1, filed Oct. 15, 2014, all of which are hereby incorporated by reference herein. 
     FIELD OF INVENTION 
     The invention relates to an injector for injecting fluid and relates particularly to an injector for injecting fuel into an internal combustion engine. 
     BACKGROUND 
     Injection valves are in widespread use, in particular for internal combustion engines where they may be arranged in order to dose the fluid into an intake manifold of the internal combustion engine or directly into the combustion chamber of a cylinder of the internal combustion engine. 
     Injection valves are manufactured in various forms in order to satisfy the various needs for the various combustion engines. Therefore, for example, their length, diameter as well as various elements of the injection valve, which are responsible for the way the fluid is dosed, may vary within a wide range. In addition to that, injection valves may accommodate an actuator for actuating a valve needle of an injection valve, which may, for example, be an electromagnetic actuator. 
     In order to enhance the combustion process with regard to the reduction of unwanted emissions, the respective injection valve may be suited to dose fluids under very high pressure. The pressure may be, in the case of a gasoline engine, for example, in the range of up to 500 bar, and in the case of diesel engines in the range of up to 3500 bar. 
     SUMMARY 
     One object of the invention is to create an injector for injecting fluid that contributes to a controllability of an amount of injected fluid and enables efficient operation of the injector. 
     According to one aspect, an injector for injecting fluid comprises a valve assembly with a valve body and a valve needle. The valve body has a longitudinal axis and comprises a cavity with a valve seat. The valve needle is in particular solid, i.e., not hollow. 
     Furthermore, the valve needle comprises an armature retainer that is coupled in a fixed way to the valve needle. Moreover, the armature retainer comprises an armature retainer constriction surface. 
     The cavity is operable to take in the valve needle. The cavity and the valve needle are operable to prevent an injection of fluid from the cavity to external to the injector in a closing position of the valve needle, in which the valve needle is seated on the valve seat. Moreover, the cavity and the valve needle are operable to enable the injection of fluid when the valve needle is spaced apart from the closing position. 
     The injector further comprises an electromagnetic actuator assembly, which is operable to exert a force for influencing a position of the valve needle. The electromagnetic actuator assembly comprises a pole piece and an armature. The pole piece is received in the cavity and positionally fixed within the valve body. The pole piece comprises a pole piece constriction surface facing towards the armature. 
     The armature is received in the cavity and operable to be axially displaced relative to the pole piece. The armature is further operable to take along the armature retainer when being displaced towards the pole piece. 
     A hydraulically effective restriction is preferably formed between the armature retainer constriction surface and the pole piece constriction surface, in particular in at least a range of an axial displacement of the valve needle from a maximum displacement away from the closing position to a restriction displacement. The hydraulically effective restriction in particular effects a first damping force which is exerted on the valve needle. In this context, the “restriction displacement” is in particular an axial position of the valve needle between the closing position and that axial position which corresponds to the maximum displacement away from the closing position. 
     In other words, a fluid channel is defined by a surface of the armature retainer—which is referred to as the armature retainer constriction surface—and a surface of the pole piece—which is referred to as the pole piece constriction surface. The fluid channel can be also be referred to as a gap. The hydraulically effective restriction is in particular represented by said fluid channel. In a preferred embodiment, fluid, which enters the cavity at a fluid inlet end of the valve body and flows to a fluid outlet end of the valve body where the valve seat is positioned, has to pass through the fluid channel. 
     A hydraulic diameter of the fluid channel is dependent on the axial displacement of the valve needle from the closing position. Specifically, the hydraulic diameter decreases with increasing displacement of the valve needle from the closing position. For example, the hydraulic diameter of the fluid channel is at least twice at large—and in one embodiment at least three times or four times as large—when the valve needle is in the closing position compared to the hydraulic diameter when the valve needle is at the maximum displacement away from the closing position. The reduction of the hydraulic diameter by the movement of the armature retainer against the hydraulic force of the fluid in the fluid channel may generate the first damping force. 
     Advantageously, a velocity of the valve needle is decreased by the first damping force such that an amount of injected fluid is suitably influenced. In particular, the first damping force contributes to a controllability of the injector in a ballistic phase of an opening phase of the injector. Particularly, a variation of the amount of injected fluid within a given time window is kept low. In other words, it is contributed to a controllability of the amount of injected fluid. 
     The restriction displacement of the valve needle away from the closing position may be greater than zero; for example, it has a value of one third of the maximum displacement or more. Moreover, the range in which the hydraulically effective restriction is formed may be greater than zero; for example, it has a value of 15% or more, in particular of 30% or more of the maximum displacement. In particular, the restriction displacement, respectively the range is dimensioned as to enable exertion of a desired damping force on the valve needle. Particularly, it is further dimensioned such that the velocity of the valve needle is substantially uninfluenced in a first portion of the opening phase of the injector, hence enabling efficient operation of the injector. 
     In one embodiment, the armature retainer constriction surface and the pole piece constriction surface comprise a smallest distance between the pole piece and the armature retainer at least when the valve needle is axially displaced in the range from the maximum displacement away from the closing position to the restriction displacement. Particularly, the armature retainer constriction surface and the pole piece constriction surface may comprise the smallest distance between the pole piece and the armature retainer when the valve needle is axially displaced to the maximum displacement and/or the restriction displacement. 
     In particular, the maximum displacement of the valve needle away from the closing position may be reached when the valve needle is in an opening position, in which the armature abuts the pole piece. 
     According to one embodiment, the armature retainer constriction surface has a first sloped shape. According to a further embodiment, the pole piece constriction surface has a second sloped shape. The first and/or second sloped shape may be a conical shape, for example, in particular a truncated conical shape. The second sloped shape may be equally sloped to the first sloped shape; in this case, the width of the fluid channel—i.e., the distance between the two constriction surfaces—is in particular independent from a position in the fluid channel along a flow direction of the fluid through the fluid channel. In particular, the armature retainer constriction surface with its first sloped shape and the pole piece constriction surface with its second sloped shape face each other in order to enable a suitable formation of the hydraulically effective restriction. 
     According to a further embodiment, the armature retainer constriction surface has a first curvature. Advantageously, the first curvature contributes to a prevention of jamming of the armature retainer, particularly when the valve needle is tilted. Particularly, the armature retainer is constructed convex, at least at the armature retainer constriction surface. 
     According to a further embodiment, the pole piece constriction surface has a second curvature. Advantageously, the second curvature contributes to a prevention of jamming of the armature retainer, particularly when the valve needle is tilted. Particularly, the pole piece is constructed concave, at least at the pole piece constriction surface. 
     According to a further embodiment, the second curvature is less than or equal to the first curvature. This enables the effective hydraulic restriction with merely a small section of the armature retainer, hence contributing to a reliable operation of the injector, particularly in the case when the valve needle is tilted. 
     According to a further embodiment, the first damping force exerted on the valve needle is dependent on the position of the valve needle. Advantageously, this allows for reliably decreasing the velocity of the valve needle in order to achieve a suitably controllable amount of injected fluid, particularly within the range between the maximum displacement of the valve needle and the restriction displacement, while keeping it substantially uninfluenced in the first instant of the opening phase of the injector which contributes to an efficient operation of the injector. 
     According to a further embodiment, the armature retainer comprises an armature retainer guiding surface. Moreover, the pole piece comprises a pole piece guiding surface. The armature retainer is operable for axially guiding the valve needle with the armature retainer guiding surface gliding along the pole piece guiding surface when the valve needle is axially displaced. In other words, the armature retainer has a side surface—referred to as the armature retainer guiding surface—and the pole piece has a side surface—referred to as the pole piece guiding surface—which are in sliding contact for axially guiding the valve needle. Advantageously, the axial guiding of the valve needle contributes to a prevention of tilting of the valve needle, thus enabling efficient operation of the injector. 
     According to a further embodiment, the armature retainer guiding surface is convexly curved with respect to the valve needle. A convex curvature of the armature retainer guiding surface contributes to a prevention of jamming of the armature retainer, particularly when the valve needle is tilted. Thus an efficient operation of the injector is enabled. 
     According to a further embodiment, the armature retainer guiding surface is substantially spherically shaped, i.e. it has the basic shape of a sphere. Advantageously, a spherical curvature of the armature retainer guiding surface contributes to a reliable prevention of jamming of the armature retainer, particularly when the valve needle is tilted, thus enabling an efficient operation of the injector. 
     According to a further embodiment, the armature retainer guiding surface comprises at least one axial channel for enabling a fluid flow axially through the cavity. This has the advantage that reliable guiding of the valve needle is enabled while also enabling efficient operation of the injector. 
     According to a further embodiment, the armature is axially movable relative to the valve needle. Advantageously, particularly when the armature abuts the pole piece or when the valve needle comes in contact with the valve seat, an axial movement of the valve needle may be decoupled from an axial movement of the armature. This, for example, contributes to a prevention of a transmission of an undesired bouncing of the armature to the valve needle, hence enabling efficient operation of the injector. 
     According to a further embodiment, the armature retainer comprises an armature retainer limiting surface for limiting an axial displacement of the armature relative to the valve needle. The armature retainer limiting surface is a surface of the armature retainer which faces towards the armature and laterally extends away from the valve needle. According to a further embodiment, the armature comprises an armature impact area facing towards the armature retainer limiting surface. The armature retainer limiting surface is operable to engage with the armature impact area. To put it differently, the armature retainer is in particular operable to limit the axial displacement of the armature relative to the valve needle by means of a form-fit engagement between a surface portion of the armature—referred to as the armature impact area—and the armature retainer limiting surface. 
     Particularly, the armature retainer limiting surface allows for a reliable force transmission of the armature to the valve needle. Particularly in the case that the armature is axially movable relative to the valve needle, the armature retainer limiting surface enables the valve needle to engage with the armature and to be taken along with the armature when the armature is axially displaced towards the pole piece. In the case that the injector further comprises a disc element, wherein the disc element is coupled in a fixed way to the valve needle for limiting an axial displacement of the armature relative to the valve needle away from the pole piece, the armature may be coupled to the valve needle by the disc element and the armature retainer limiting surface so that it has an axial play between the armature retainer limiting surface and the disc element. 
     In one embodiment, a lateral extension of the armature retainer limiting surface away from the valve needle is constructed such that a relative movement between the armature and the armature retainer is damped. 
     Advantageously the armature retainer limiting surface contributes to a prevention of bouncing of the valve needle, particularly when the armature abuts the pole piece. This contributes to an efficient operation of the injector. 
     For example, the armature impact area and the armature retainer limiting surface may be parallel. In particular, a lateral extension of the armature impact area away from the valve needle is constructed such that the relative movement between the armature and the armature retainer is damped. For this reason, the lateral extension of the armature impact area may be greater than or equal to the lateral extension of the armature retainer limiting surface. 
     In one embodiment, the armature retainer limiting surface and the armature retainer constriction surface are comprised by a stopper portion of the armature retainer and on opposite axial sides of the stopper portion. The armature retainer limiting surface and the armature retainer constriction surface are preferably inclined or curved relative to one another in such fashion that the stopper portion tapers in the radial outward direction. 
     In one development, the armature retainer further has a guiding portion which comprises the armature retainer guiding surface as its outer surface or as a portion of its outer surface. The guiding portion may expediently be arranged on the axial side of the stopper portion which is remote from the armature and in particular merges with the stopper portion. Preferably, the armature retainer has a constriction in a region where the guiding portion and the stopper portion merge. 
     In an advantageous development, the stopper portion—and therefore in particular the armature retainer limiting surface and the armature retainer constriction surface which both preferably extend radially to an outer contour of the stopper portion—projects radially beyond the guiding portion. Preferably, the maximum radial dimension of the stopper portion is at least twice as large as the maximum radial dimension of the guiding portion. Such dimensions are particularly advantageous for efficient damping of the relative movement between the armature and the armature retainer. 
     According to a further embodiment, the injector comprises a return spring, which is operable to bias the armature in an axial direction away from the armature retainer. For example, the armature return spring is seated in precompressed fashion against the armature retainer and the armature. 
     Advantageously, a large impulse transfer to the valve needle is enabled when the armature comes into contact with the armature retainer. This also enables an opening of the valve needle against a large hydraulic load with only limited actuator power. The return spring may particularly be seated on the armature retainer limiting surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are explained in the following with the aid of schematic drawings and reference numbers. Identical reference numbers designate elements or components with identical functions. In the drawings: 
         FIG. 1  is a longitudinal section view of a first embodiment of an injector, 
         FIG. 2  is an enlarged longitudinal section view of the injector according to  FIG. 1 , 
         FIG. 3 a    is a first graph of an amount of injected fluid over time, by the injector of  FIG. 1 , 
         FIG. 3 b    is a second graph and a third graph of amounts of injected fluid over time by conventional injectors, and 
         FIG. 4  is another enlarged longitudinal section view of the injector according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first embodiment of an injector  1  with a valve assembly  3  and an electromagnetic actuator assembly  19 . The valve assembly  3  comprises a valve body  5  and a valve needle  7 . The valve body  5  has a longitudinal axis  9  and comprises a cavity  11  with a valve seat  13 . 
     The valve needle  7  is received in the cavity  11  and is axially movable relative to the valve body  5 . The valve needle  7  comprises an armature retainer  15  that is coupled in a fixed way to the valve needle  7 . The valve needle  7  may further comprise a disc element  41  being axially displaced to the armature retainer  15  and coupled in a fixed way to the valve needle  7 . 
     The valve needle  7  is operable to prevent an injection of fluid in a closing position, in which the valve needle  7  is seated on the valve seat  13 , from the cavity  11  external to the injector  1 , for example into a combustion chamber. The valve needle  7  is further operable to enable the injection of fluid when it is apart from the closing position. The injector  1  may comprise a valve spring  43  for biasing the valve needle  7  towards the closing position, for example in order to contribute to a leak tightness of the injector  1 . 
     The electromagnetic actuator assembly  19  comprises a pole piece  21 , an armature  23  and a magnetic coil  45 , in particular solenoid, positioned in a housing which laterally surrounds at least a portion of the valve body  5 . The magnetic coil  45 , together with the armature  23  and the pole piece  21  forms a magnetic circuit of the electromagnetic actuator assembly  19  when the magnetic coil  45  is energized. In this context, the electromagnetic actuator assembly  19  may further comprise a yoke  47  for shaping the magnetic circuit of the electromagnetic actuator assembly  19 . 
     The electromagnetic actuator assembly  19  is thus operable to exert a force for influencing a position of the valve needle  7 . Particularly, the valve needle  7  may be axially displaced by the electromagnetic actuator assembly  19  relative to the valve body  5 , for example in reciprocating fashion. 
       FIG. 2  shows an enlarged longitudinal section view of the injector according to  FIG. 1 , particularly of the electromagnetic actuator assembly  19 . The pole piece  21  is received in the cavity  11  and positionally fixed with the valve body  5 . In other embodiments, the pole piece  21  may be comprised by the valve body  5 . The armature  23  is received in the cavity  11  and operable to be axially displaced relative to the pole piece  21 . The armature  23  is further operable to take along the armature retainer  15  when being displaced towards the pole piece  21 . 
     In this embodiment, the armature  23  is axially movable relative to the valve needle  7 , particularly between the armature retainer  15  and the disc element  41 , which both limit an axial displacement of the armature  23  relative to the valve needle  7 . The armature  23  may comprise a return spring  39  in this context in order to enable a large impulse transfer to the valve needle  7  when the armature  23  comes into contact with the armature retainer  15 . The return spring may further enable an opening of the valve needle  7  against large hydraulic loads with limited actuator power, for example 350 bar. In other embodiments, the armature  23  may be arranged to be positionally fixed to the valve needle  7 . The armature  23  may further comprise at least one bore in order to allow an axial fluid flow through the cavity  11 . 
     In this embodiment, the pole piece  21  comprises a pole piece guiding surface  33 . Furthermore, the armature retainer  15  may comprise an armature retainer guiding surface  31 . In this context, the pole piece  21  may comprise a recess with the pole piece guiding surface  33  in order to receive the armature retainer  15  with its armature retainer guiding surface  31 . An axial guiding of the valve needle  7  is thereby provided, with the armature retainer guiding surface  31  gliding along the pole piece guiding surface  33  when the valve needle  7  is axially displaced. 
     Particularly, the armature retainer guiding surface  31  is convexly curved with respect to the valve needle  7 . In particular, it is, for example, substantially spherically shaped in order to avoid jamming of the armature retainer  15  when the valve needle  7  is tilted, as shown in  FIG. 4 . 
     Particularly, the armature retainer guiding surface  31  comprises at least one channel for enabling a fluid flow axially through the cavity  11 . The at least one channel may be an axial recess of the armature retainer  15 . In the representation of  FIG. 2 , the channels are visible on the left and right sides of the armature retainer  15  so that the spherical basic shape is not visible in  FIG. 2 . 
     The armature retainer guiding surface  31  defines a guiding portion of the armature retainer  15 . The guiding portion merges with a stopper portion of the armature retainer  15  at a downstream axial end of the guiding portion. In the interface region between the guiding portion and the stopper portion, the armature guide  15  has a circumferential constriction. In the present embodiment, the stopper portion is in the basic shape of a disc having a rounded outer contour. In another embodiment, it has a wedged shape in a longitudinal section view, i.e., it tapers in the radial outward direction. 
     The stopper portion of the armature retainer  15  comprises an armature retainer limiting surface  35  of the armature retainer  15  for limiting the axial displacement of the armature  23  relative to the valve needle  7 . The armature retainer limiting surface  35  enables, for example, an engagement with an armature impact area  37  of the armature  23  in order to allow the valve needle  7  to be taken along with the armature  23  when the armature  23  is axially displaced towards the pole piece  21 . 
     In particular, the armature retainer limiting surface  35  laterally extends away from the valve needle  7 , particularly projecting away from the armature retainer guiding surface  31 . A lateral extension of the armature retainer limiting surface  35  is constructed such that a relative movement between the armature  23  and the armature retainer  15  is hydraulically damped. In the present embodiment this is achieved by the radial extension of the armature retainer limiting surface  35 —which is also the radial extension of the stopper portion of the armature retainer  15 —being at least twice as large as the radial extension of the guiding portion of the armature retainer  15 . 
     The pole piece  21  further comprises a pole piece constriction surface  25  that is facing towards the armature  23 . Moreover, the armature retainer  15  comprises an armature retainer constriction surface  17 , towards which the pole piece constriction surface  25  is facing. The armature retainer constriction surface  17  is arranged at an axial side of the stopper portion opposite of that axial side on which the armature retainer limiting surface  35  is arranged. 
     Particularly, at least when the valve needle  7  is axially displaced in a range from a maximum displacement away from the closing position to a restriction displacement, the armature retainer constriction surface  17  and the pole piece constriction surface  25  comprise a smallest distance between the pole piece  21  and the armature retainer  23  in the axial region of the stopper portion, forming a hydraulically effective restriction between the armature retainer constriction surface  17  and the pole piece constriction surface  25 . 
     In other words, a gap between the pole piece  21  and the armature retainer  15 , through which fluid may flow, changes depending on the axial displacement of the armature retainer  15 . In particular, an axial distance between the pole piece constriction surface  25  and the armature retainer constriction surface  17  decreases when the armature retainer  15  is axially displaced towards the pole piece  21 . A hydraulic diameter of the hydraulically effective restriction is dependent on the axial displacement of the valve needle  7  from the closing position and is at least twice at large when the valve needle  7  is in the closing position compared to the hydraulic diameter when the valve needle  7  is at the maximum displacement away from the closing position. 
     In particular, the maximum displacement of the valve needle  7  away from the closing position may be reached when the valve needle  7  is in an opening position, in which, for example, the armature  23  abuts the pole piece  21 . 
     Moreover, the restriction displacement of the valve needle  7  away from the closing position may particularly be greater than zero. In particular, the restriction displacement, respectively the range is dimensioned as to allow a formation of the hydraulically effective restriction between the armature retainer constriction surface  17  and the pole piece constriction surface  25 , while still enabling fluid to flow through the cavity  11  such that a pressure difference in the axial direction is small enough to allow for a reliable and efficient injection of the injector  1 . 
     The valve needle  7  is solid so that the fluid has to flow axially along the valve needle  7  on the outside of the valve needle from a fluid inlet end of the valve body  5  through the cavity  11 —and thus through the hydraulically effective restriction—to a fluid outlet end of the valve body  5  to the valve seat  13 . Due to the hydraulically effective restriction between the armature retainer constriction surface  17  and the pole piece constriction surface  25 , a first damping force is exerted on the valve needle  7  when the armature retainer  15  is axially displaced towards the pole piece  21 . Advantageously, a velocity of the valve needle  7  is thereby decreased such that a controllability of the injection, particularly in a ballistic phase  63  (see  FIG. 3 a   ) of an opening phase of the injector is contributed to. Particularly, a variation of an amount of injected fluid within a given time window  61  (see  FIG. 3 a   ) is kept low. 
     Particularly, the restriction displacement, respectively the range is dimensioned as to enable an exertion of a desired damping force on the valve needle  7 . Particularly, it is further dimensioned such that the velocity of the valve needle  7  is substantially uninfluenced in a first instant of the opening phase of the injector  1   
     In one embodiment, the armature retainer constriction surface  17  has a first sloped shape. Particularly, the pole piece constriction surface  25  may have a second sloped shape. This enables the effective hydraulic restriction to be formed by merely a small section of the armature retainer  15 , allowing the first damping force to be reliably provided, particularly in the case when the valve needle  7  is tilted. The second sloped shape may be equally sloped to the first sloped shape. 
     In one embodiment, the armature retainer constriction surface  17  has a first curvature. Particularly, the pole piece constriction surface  25  has a second curvature. The second curvature may be less than or equal to the first curvature. This enables the effective hydraulic restriction to be formed by merely a small section of the armature retainer  15 , allowing the first damping force to be reliably provided, particularly in the case when the valve needle  7  is tilted. Moreover, this contributes to a prevention of jamming of the valve needle  7 . 
       FIG. 3 a    shows a first graph  49  of an amount of injected fluid per activation over time of the injector  1  according to  FIG. 1 . Compared to a second graph  51  ( FIG. 3 b   ) of a fast opening injector and a third graph  53  of a slow opening injector, wherein no hydraulically effective restriction is formed between a respective armature retainer and a respective pole piece, it can be seen that a respective variability  55 ,  57 ,  59  of the amount of injected fluid within the given time window  61  of the first graph  49  is minimized, similar to the slow opening injector depicted in graph  53 . Thus, it is contributed to the controllability of the injection, particularly in the ballistic phase  63 . The given time window  61  is particularly given by an electrical pulse width. Moreover, the velocity of the valve needle  7  in the first instant of the opening phase is maintained, similar to the fast opening injector depicted in graph  51 , thus contributing to a spray stability of the injector  1 .