Abstract:
The invention relates to a magnet assembly for a magnet valve. The assembly has an inner pole and an outer pole as well as a coil. The coil is arranged between the inner pole and the outer pole and the coil wound directly onto the inner pole. According to the invention, the magnet assembly is used for actuating a closing element in a magnet valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/051489 filed on Feb. 16, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a magnet assembly for a magnet valve. 
     2. Description of the Prior Art 
     A magnet valve is used for instance for controlling the opening and closing motion of an injection valve member of a fuel injector. The magnet valve includes a magnet assembly, which includes an inner pole, an outer pole, and a coil located between them In magnet assemblies of the kind produced in the prior art, the coil is wound onto an electrically insulating coil holder. The coil, together with the coil holder, is inserted into an annular groove in a magnet core. The wall of the groove, which points toward the axis of the magnet core, forms the inner pole, and the opposite wall forms the outer pole. The width of the groove should be selected such that with an internally located coil holder, a gap is embodied between the individual windings of the coil and the outer pole. A disadvantage of the magnet assembly of the kind known from the prior art, particularly for use in fuel injectors, is that it requires a large amount of installation space. The magnet assembly determines the diameter of the magnet valve. Moreover, because of the coil holder made from insulating material, there is only limited thermal conductivity. Particularly in fast-switching magnet valves, this can lead to overheating of the coil. Moreover, because of the need for compactness and because of the dimensions of the coil holder, only a small number of windings is possible. Increasing the number of windings would necessitate a large coil diameter and thus lead to a larger magnet assembly. 
     SUMMARY OF THE INVENTION 
     In a magnet assembly embodied according to the invention for a magnet valve, which includes an inner pole, and outer pole, and a coil, the coil being located between the inner pole and the outer pole, the coil is wound directly onto the inner pole. By winding the coil directly onto the inner pole, the installation space occupied by the coil holder in the versions known from the prior art is smaller. As a result, less installation space is required for the magnet assembly. Moreover, to increase the magnetic force, it is possible to provide a larger number of windings in the same installation space. 
     To prevent a short circuit from being created, whenever the inner pole is made of an electrically conductive material, the inner pole is coated with an electrically insulating coating on the side pointing toward the coil. The coating is preferably a Parylene coating. This is an inert, hydrophobic, optically transparent, polymeric coating, which assures very good electrical installation with a high voltage strength and a low dielectric constant. The coating is micropore-free even beginning at a layer thickness of 0.2 μm. The coating is generally applied in a vacuum by condensation from the gas phase. As a result, even regions and structures that cannot be coated with liquid-based methods are achieved. The layer thickness that is applied according to the invention to the inner pole is preferably approximately 10 μm. The coil is then wound directly onto the coating of the inner pole. Because of the slight thickness of the coating, the heat produced in switching of the magnet valve is dissipated via the inner pole. 
     An outward-protruding enlargement that is press-fitted into the outer pole is preferably embodied on the inner pole. The outside diameter of the outward-protruding enlargement is greater than the outside diameter of the coil, so that once the magnet assembly is assembled between the coil and the outer pole, a gap is embodied. This prevents a short circuit from occurring between the coil and the outer pole. 
     To connect the coil to a voltage source, contact lugs are preferably embodied on the coil. So that the contact lugs can be connected to the voltage source, in a preferred embodiment a recess is embodied in the outward-protruding enlargement on the inner pole, by which recess the contact lugs are guided. This makes it possible to provide an individual recess for each contact lug or for all the contact lugs to be guided by the same recess. Care must merely be taken that the contact lugs not come into contact with the inner pole, the outer pole, or one another. 
     The contact lugs are preferably each connected to a contact pin, by way of which the magnet assembly can be electrically connected to the voltage source. The contact pins are preferably received, electrically insulated from one another, in a pin holder that is received in the recess in the outward-protruding enlargement of the inner pole. The electrical insulation is preferably attained by providing that the pin holder is made from an electrically insulating material. If the pin holder is not made from an electrically insulating material, then it is preferably provided with an electrically insulating coating. 
     The magnet assembly embodied according to the invention is preferably used for actuating a closing element in a magnet valve. In an especially preferred embodiment, the magnet valve, with the magnet assembly embodied according to the invention, is used in a fuel injector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in further detail below in conjunction with the drawings, in which: 
         FIG. 1  is a section through a magnet assembly in accordance with the prior art; 
         FIG. 2  is a perspective view of an inner pole; 
         FIG. 3  is a section through a magnet assembly embodied according to the invention; 
         FIG. 4  shows a plan view on an inner pole with a coil and contact pins; 
         FIG. 5  shows a perspective detail view of the electrical connection of the coil; 
         FIG. 6  shows a perspective view of a wound inner pole with contact pins; 
         FIG. 7  shows a perspective view of an assembled magnet assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a magnet assembly in accordance with the prior art. 
     A magnet assembly  1  in accordance with the prior art includes a magnet core  2 , in which a groove  3  is embodied. In the groove  3 , a coil  4  is received that is wound onto a coil holder  5 . The coil holder  5  is preferably made from an electrically insulating material, so that no electrical connection occurs between the coil  4  and the magnet core  2 . On the outer circumference, a gap  6  is embodied between the coil  4  and the wall of the groove  3 . By means of the gap, a short circuit is prevented from occurring between the coil  4  and the magnet core  2 . The power supply to the coil  4  is effected via contact pins  7 . The contact pins  7  are connected to the coil  4  with the aid of contact lugs  8 , which are each wound around the contact pin  7 . A welded sleeve  9  is disposed around the winding of the contact lug  8  around the contact pin  7 . By means of the welded sleeve  9 , the contact lug  8  is prevented from becoming detached from the contact pin  7 . 
     Because of the coil holder  5 , onto which the coil  4  is wound, additional installation space in the magnet assembly  1  is required. As a result, the necessary diameter of the magnet assembly  1  is increased. This is disadvantageous especially whenever magnet valves must that are as small as possible have to be used, because of the lack of installation space. 
     In  FIG. 2 , an inner pole embodied according to the invention is shown in perspective. 
     On an inner pole  11  embodied according to the invention, an outward-protruding enlargement  12  is embodied. A recess  13  is embodied in the outward-protruding enlargement  12 . The inner pole  11  furthermore includes a cylindrical body  14 , onto which a coil, not shown in  FIG. 2 , is wound. To prevent a short circuit from occurring between the coil and the cylindrical body  14 , the cylindrical body  14  is coated. The coating is preferably done with Parylene. As a result, even a coating with a thickness of only approximately 10 μm is sufficient to assure an adequate electrical insulation. Because of the slight thickness of the coating, however, the thermal insulation effect is only very slight, and thus the heat generated in the coil in the operation of the magnet assembly can be dissipated via the inner pole. In the interior of the cylindrical body  14 , a bore  15  is provided, in which a valve spring, for example, can be guided, if the magnet assembly is used for actuating a magnet valve. 
       FIG. 3  shows a section through a magnet assembly embodied according to the invention. 
     A magnet assembly  20  embodied according to the invention includes the inner pole  11 , onto the coated cylindrical body  14  of which a coil  21  is wound. The diameter of the coil  21  is less than the outside diameter of the outward-protruding enlargement  12 . In this way, once an outer pole  22  has been pressed onto the outward-protruding enlargement  12 , a gap  23  is embodied between the coil  21  and the outer pole  22 . 
     The power supply to the coil  21  is effected via a contact lug  24 , which is connected to a contact pin  25 . For connecting the contact lug  24  to the contact pin  25 , the contact lug  24  is wound around the contact pin  25  and then enclosed with a welded sleeve  26 . A firm seat of the welded sleeve  26  is attained by securing it, for instance by resistance welding, to the winding by which the contact lug  24  is secured to the contact pin  25 . However, any other mode of securing the welded sleeve is also conceivable. For instance, it may be secured by crimping. The contact pin  25  is received in a pin holder  27 . To prevent current from being able to flow from the contact pin  25  to the inner pole  11  or to the outer pole  22 , the pin holder  27  is preferably made from an insulating material. The preferred material is plastic. However, it is also possible to form the pin holder  27  of an electrically conductive material, which is then provided with an insulating coating. 
     In the embodiment shown in  FIG. 3 , the height h of the inner pole is less than the height H of the outer pole. This makes it possible to adjust a remnant air gap between the cylindrical body  14  of the inner pole  11  and an armature, not shown here, without making the total height of the magnet assembly greater than the height H of the outer pole  22 . 
       FIG. 4  shows a plan view on an inner pole, embodied according to the invention, with a coil and contact pins. 
     In the plan view shown in  FIG. 4 , it can be seen that the outside diameter d of the outward-protruding enlargement  12  of the inner pole  11  is greater than outside diameter D of the coil  21 . The width of the gap  23  is the result of the difference between the outer diameter d of the outward-protruding enlargement  12  and the outer diameter D of the coil  21 . 
     It can also be seen in the plan view shown in  FIG. 4  that for supplying voltage to the coil  21 , two contact pins  25  are provided. The two contact pins  25  are received in the pin holder  27 . To put the coil  21  into electrical contact with the contact pins  25 , the contact lugs  24  are wound around the contact pins  25  and then surrounded with the welded sleeves  26 . The welded sleeves  26  are welded, for example by resistance welding, around the coiled contact lugs  24 , so as to attain a stable connection. 
       FIG. 5  shows a perspective view of the pin holder with the contact pins and contact lugs. 
     It can be seen from  FIG. 5  how the contact lugs  24  are wound around the contact pins  25 . Because the contact pins  25  are wrapped with the contact lugs  24 , they are pre-fixed, even before the actual connection by material or positive engagement is done. A stable electrical connection is then preferably attained by resistance welding. 
     In the embodiment shown here, the contact pins  25  are retained in receptacles  28  in the pin holder  27 . The diameter of the receptacles  28  is less than the diameter of the contact pins  25 , so that the latter are clamped in the receptacle  28 . Tabs  29  are embodied on the receptacles  28 , and the contact pins  25  are guided in the tabs. At the same time, the tabs  29  serve the purpose of electrical insulation from the outer pole  22 . 
     The pin holder  27  is received in the recess  13  in the outward-protruding enlargement  12 . To make the installation of the inner pole  11  in the outer pole  22  possible, which is not shown in  FIG. 5 , the diameter of the outer face  30  must not be any larger than the diameter of the outward-protruding enlargement  12 . 
       FIG. 6  shows a perspective view of an inner pole, embodied according to the invention, with a coil and contact pins. 
     In the perspective view in  FIG. 6 , it can be seen that the outer face  30  of the pin holder  27  does not protrude past the outward-protruding enlargement  12  of the inner pole  11 . However, it is possible for the outer face  30  to protrude past the outside diameter of the coil  21  to the same extent as the outward-protruding enlargement  12 . 
     In the view shown in  FIG. 6 , the contact lugs  24  (not visible) wound around the contact pins  25  are enclosed by the welded sleeves  26 . As can be seen from  FIG. 6 , the welded sleeves  26  are installed over the windings of the contact lugs  24  (not visible), so as to attain a stable connection. 
       FIG. 7  shows a completely assembled magnet assembly. 
     In the completely assembled magnet assembly  20 , the inner pole  11 , onto which the coil  21  is wound, is press-fitted with the outward-protruding enlargement  12  into the outer pole  22 . By press-fitting the outward-protruding enlargement  12  into the outer pole  22 , a stable connection is attained. 
     For producing the magnet assembly  20  embodied according to the invention, an inner pole  11  is preferably first made from a highly permeable, resistive material, preferably a soft magnetic powder composite material, by compaction. In a next step, the inner pole  11  is provided with an electrically insulating coating. Parylene is preferably used for this. After the coating, the outward-protruding enlargement  12  is ground to its outside diameter d. Next, the coil  21  is wound onto the cylindrical body  14  of the inner pole  11 . After the coil has been wound, it is put into electrical contact with the contact pins  25 , which are received in the pin holder  27 . 
     In a first step, the outer pole  22  is ground on its inside diameter and on the contact and stop faces to a fit to the inner pole  11 . Next, in a further step, the stop face may be chromium-plated. Finally, the inner pole  11  is press-fitted into the outer pole  22 . 
     In a preferred embodiment, after the inner pole  11 , with the coil  21  and the contact pins  25 , is joined to the outer pole  22 , the entire magnet assembly  20  is extrusion-coated with a plastic, preferably a thermoplastic, or encapsulated with a reaction resin. 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.