Patent Publication Number: US-9903328-B2

Title: Solenoid valve with improved opening and closing behavior

Description:
FIELD OF THE INVENTION 
     The present invention relates to a solenoid valve for controlling fluids, particularly fuel, with improved opening behavior and also improved closing behavior, at the same time. 
     BACKGROUND 
     Solenoid valves are known as injection valves, for example, from the related art, in different embodiments. Magnetic injection valves, which, in the area of the armature in the housing, include a nonmagnetic separation, i.e., a nonmagnetic region, are able to open faster than valves without such a separation of the magnetic circuit under the same conditions. However, because of the separation of the magnetic circuit, the closing times are worse. 
     SUMMARY 
     Example embodiments of the present invention provide a solenoid valve for controlling fluids, with improved opening times and the closing times of the solenoid valve, and producible particularly simply and cost-effectively, so that mass production is possible. This is achieved in that the solenoid valve includes a magnetic circuit with an armature, an internal pole, and a magnetic return path. The magnetic circuit includes a nonmagnetic separating element for interrupting the magnetic circuit, and at least one magnetic crosspiece, which runs in the axial direction of the valve and closes the magnetic circuit at the nonmagnetic separating element. The magnetic crosspiece thus functions as a magnetic bypass situated on the nonmagnetic separating element. 
     The magnetic crosspiece is preferably situated radially inside the nonmagnetic separating element, and therefore a harder region than the magnetic separating element can be provided also at an inner surface of the nonmagnetic separating element by the positioning of the magnetic crosspiece. 
     Particularly preferably, the magnetic crosspiece is formed to be in one piece with the magnetic separating element. Particularly preferably, the one-piece component, including the magnetic crosspiece and the nonmagnetic separating element, in this case, is a MIM component (metal injection molding component). Thereby, the magnetic crosspiece can be developed very individually and suitable for use. 
     In a preferred example embodiment, the magnetic crosspiece is in contact with the internal pole of the magnetic circuit. It is especially preferred if, between the magnetic crosspiece and the internal pole, a force-locking connection, especially a clamping connection, is developed. 
     According to a further preferred example embodiment of the present invention, the magnetic crosspiece, the nonmagnetic separating element, and a housing part that is a part of the magnetic circuit are developed as a one-piece component. This one-piece component is particularly preferably a MIM component. Further preferred, in this one-piece component, the housing part is made of ferrite, the nonmagnetic separating element is made of austenite, and the magnetic crosspiece is made of martensite. Especially preferred, in this case, the housing part of ferrite is magnetically stronger than the magnetic crosspiece of martensite. 
     Preferably, a plurality of magnetic crosspieces and the nonmagnetic separating element are provided in the form of a sleeve with a constant inner diameter. Alternatively, the magnetic crosspieces and the nonmagnetic separating element are developed in such a way that they are also provided in the basic form of a sleeve, but that the magnetic crosspieces project radially inwards from the magnetic separating element. 
     For as rapid as possible a closing time, there is further preferred a cross sectional area of the nonmagnetic separating element that is greater than a cross sectional area of a magnetic choke device. 
     The solenoid valve, according to example embodiments of the present invention, is used especially preferably as a fuel injection valve, particularly for direct injection into a combustion chamber. In this context, fuel is conveyed through the armature of the valve. 
     Preferred example embodiments of the present invention are described in detail below, with reference to the accompanying drawings. In the drawings, the same or functionally the same parts in each case denote the same parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic sectional view of a solenoid valve according to a first example embodiment of the present invention. 
         FIG. 2  shows a schematic perspective partial view of a part of a magnetic circuit of the solenoid valve of  FIG. 1 , according to an example embodiment of the present invention. 
         FIG. 3  shows an enlarged sectional view of a subsection of the magnetic circuit of  FIG. 1 , according to an example embodiment of the present invention. 
         FIG. 4  shows a schematic perspective partial view of a part of a magnetic circuit according to a second example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A solenoid valve for controlling a fluid, according to a first example embodiment of the present invention, is described in detail below with reference to  FIGS. 1-3 . 
     In  FIG. 1 , the solenoid valve includes a closing element  2  in the form of a valve needle with a ball on the closing side, which opens and closes outlet openings  4  on a valve seat  3 . 
     The solenoid valve also includes a magnetic circuit  5  that includes an armature  6 , an internal pole  7 , and a magnetic return path  8 . In this example embodiment, magnetic return path  8  is a part of a housing  14  of the solenoid valve, the housing  14  including a plurality of parts. In this instance, the two housing parts  15 ,  16  are parts of magnetic circuit  5 . 
     The solenoid valve  1  further includes a coil  9 , which attracts armature  6  when current is applied to it. After the supply of current to coil  9  is terminated, a restoring element  17  sets armature  6  back to its initial position.  FIG. 1  shows the open state of the solenoid valve, in which armature  6  lies against internal pole  7 . Armature  6  is connected in a known manner to closing element  2 , in order to effect the lifting motion of the closing element. 
     Magnetic circuit  5  of the solenoid valve further includes a nonmagnetic separating element  10 , which is sleeve-shaped in this example embodiment. Nonmagnetic separating element  10  makes possible a magnetic separation of the magnetic circuit, and ensures that, upon operation of the coil for opening the valve, the magnetic circuit is closed rapidly via armature  6 , so that a very rapid opening time of the solenoid valve is achieved. Nonmagnetic separating element  10  is, however, problematic with respect to the closing times of the solenoid valve, which increase because of nonmagnetic separating element  10 . 
     This is why, according to the present invention, a plurality of magnetic crosspieces  13  are provided, which produce a connection between housing part  16  of housing  14  and internal pole  7 . These crosspieces  13  provide a magnetic bridging of the nonmagnetic separating element. 
     In the first example embodiment, altogether four magnetic crosspieces  13  are provided, which are situated on the inside of a nonmagnetic separating element  10 . The four crosspieces  13 , in this instance, are provided along the inner circumference at the same distance apart. The width of crosspieces  13  in the circumferential direction is the same as an intermediate space between two adjacent crosspieces  13 , in this context. 
     In this example embodiment, nonmagnetic separating element  10  is made of austenite and crosspieces  13  are lightly magnetized and made of martensite. By contrast, housing part  16  is made of ferrite and is magnetically stronger than crosspieces  13 . In this case, housing part  16 , nonmagnetic separating element  10 , and crosspieces  13  form a one-piece component, which is provided as a MIM component. Crosspieces  13 , in this case, are situated on sleeve-shaped nonmagnetic separating element  10  such that a cylinder-shaped, smooth, cylindrical inner surface of the component is achieved. Since crosspieces  13  are produced from martensite, they are harder than the nonmagnetic separating element  10 . 
     Furthermore, according to an example embodiment of the present invention, a clamping connection  21  (as shown in  FIG. 3 ) is provided between the one-piece component of the magnetic circuit, including nonmagnetic separating element  10 , crosspieces  13 , and housing part  16 , and internal pole  7 . 
     As is made particularly clear in  FIG. 3 , magnetic crosspieces  13  are each arranged such that a first section of the respective crosspiece  13  is in contact with internal pole  7  and a second section of the respective crosspiece  13  is in contact with armature  6 . Because of that, crosspieces  13  are in addition still able to take over a guidance function for the armature  6 . Consequently, a subsection of crosspieces  13  is provided as guidance for armature  6 . Since crosspieces  13  are harder than separating element  10 , reduced wear thereby comes about. 
     By introducing crosspieces  13 , the magnetic flux is reduced in comparison with a region provided completely at the inner circumference of the component. Thereby, in particular, even more rapid opening times are possible, without a negative effect on the closing times of the valve. Thus, the magnetic crosspieces  13 , which are harder compared to nonmagnetic separating element  10 , also provide advantages in the guidance of armature  6  and during pressing internal pole  7  into the component. Since crosspieces  13  are only partially present, the magnetic flux is nevertheless significantly reduced, in comparison to a magnetic ring on the inner circumference of the component. 
     Thus, by providing the magnetic crosspieces  13 , running in the axial direction X-X of the valve, a magnetic bridging of nonmagnetic separating element  10  is achieved. This has the effect that the closing times of the solenoid valve significantly improve, without the rapid opening times of the solenoid valve becoming worse. In an example embodiment, a thickness of nonmagnetic separating element  10  is many times greater than the cross section of magnetic crosspieces  13 . 
       FIG. 4  shows the one-piece component of magnetic return path  8  according to a second example embodiment. In  FIG. 4 , crosspieces  23  provided for nonmagnetic separating element  10  project radially inwards, so that crosspieces  23  are somewhat set off inwards from the internal surface of nonmagnetic separating element  10 . This one-piece component is also preferably produced using an MIM method. Crosspieces  23  of this example embodiment preferably project inwards by ca 0.2 mm from the inner circumference of the nonmagnetic separating element  10 . A further advantage of the second example embodiment is that the nonmagnetic separating element  10  can be provided as a cylindrical sleeve that can, for instance, also be provided as an insertion part in MIM methods. Thereby, the cylindrical sleeve can be executed very cost-effectively as a geometrically simple component.