Patent Publication Number: US-7721416-B2

Title: Method for installing a magnet valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/EP 2005/050210 filed on Jan. 19, 2005. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a unit fuel injector (UFI) and to a pump-line-nozzle unit (PLNU) for an internal combustion engine, with a pump element, the pump element having a pump chamber, and with a magnet valve, the magnet valve having a valve member and an armature; the magnet valve opens or closes a hydraulic connection between the pump chamber and a low-pressure region of the unit fuel injector. 
   2. Description of the Prior Art 
   In connection with the invention, the following discussion will refer only to the unit fuel injector (UFI), although pump-line-nozzle units (PLNUs) are always intended as well. The most essential distinction between unit fuel injectors and pump-line-nozzle units is that a pump-line-nozzle unit has a short high-pressure line between the pump element and the injection nozzle. For the present invention, this distinction does not matter, and hence the invention applies equally for unit fuel injectors and pump-line-nozzle units. 
   A unit fuel injector is known for instance from German Patent Disclosure DE 198 37 333 A1. In this unit fuel injector, the valve and the armature of the magnet valve are connected to one another nonpositively by a compression spring. Because the valve member and the armature are coupled only nonpositively, the dynamic performance of the magnet valve is difficult to control, and it is hardly avoidable that during operation, the armature and the valve member will repeatedly briefly separate from one another and after that collide again. This process is known as “bouncing”. The bouncing is unwanted, since it has an adverse effect on the precision with which the magnet valve opens and closes. Moreover, the bouncing causes high wear to the armature, which is of a soft material, so that the valve stroke and thus also the operating performance of the magnet valve vary over the course of time. Finally, it should also be mentioned that the armature must be guided in a capsule, and for structural reasons this guide can only be relatively short. As a consequence, the armature has a tendency to tilting, and the armature guide wears down relatively quickly. 
   In a unit fuel injector and a pump-line-nozzle unit according to the invention for an internal combustion engine, with a pump element, the pump element having a pump chamber, and with a magnet valve, the magnet valve having a valve member and an armature, and in which the magnet valve opens or closes a hydraulic connection between the pump chamber and a low-pressure region, it is provided that the armature is fixedly connected to the valve member. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   As a result of fixedly connecting the armature and valve member, bouncing of the armature on the valve member can be effectively averted. Because of the rigid, fixed connected between the armature and the valve member, a separate guide of the armature can be omitted, since the armature is guided by the valve member. Tipping or tilting of the armature in its guide during operation and the resultant functional problems of the unit fuel injector therefore no longer occur. 
   An especially advantageous aspect of the embodiment according to the invention is also that the number of components needed is reduced, since a separate compression spring that keeps the armature in contact with the valve member can be omitted. As a result, the manufacturing and installation costs are reduced, and less installation space is required. 
   In an advantageous feature of the invention, it is provided that a receiving mandrel is embodied on the valve member, and that the armature is fixedly connected to the receiving mandrel. In particular, it is advantageous if the armature is connected to the receiving mandrel by nonpositive engagement, in particular by pressing. As a result of this structural embodiment of the connection between the valve member and the armature, a secure and economical connection between the armature and the valve member can be made in a simple way. It is also possible to position the armature with high precision relative to the valve seat of the valve member. As a result, production tolerances in mass production can be compensated for by a suitable mounting of the armature on the receiving mandrel. The operating performance of various individual examples in a large-scale series is consequently virtually identical. This advantage is of considerable significance, since controlling the unit fuel injector of the invention is based on a certain predetermined, programmed-in operating performance of the unit fuel injector. Any deviation of the unit fuel injector from this programmed-in, predetermined operating performance makes the operating performance of the engine worse. 
   The range of deviation in operating performance of the unit fuel injector of the invention can be further improved by providing that a sealing face and a stroke stop are embodied on the valve member, and that the maximum stroke of the valve member is defined by the spacing in the axial direction between the sealing face and the stroke stop. This means that even during production of the valve member of the invention, the maximum stroke of the valve member is predetermined. Since the spacing in the axial direction between the sealing face and the stroke stop is easy to accomplish in production and can also be well monitored by measuring instruments, the deviation in the valve stroke from one example to another in a series is virtually zero. 
   As with other magnet valves as well, it has proved advantageous to embody the sealing face frustoconically, so that with a likewise frustoconical valve seat embodied in the valve housing, it forms a conical sealing seat. 
   To improve the operating performance of the magnet valve of the invention, a magnet plate cooperating with a coil of the magnet valve is provided between the armature and the stroke stop, and the receiving mandrel of the valve member protrudes through a bore in the magnet plate. With the aid of the magnet plate, it is possible to optimize the magnetic flux of the coil, so that the magnetic forces exerted on the armature of the magnet valve as a consequence of an electric current flowing through the coil are maximized, and the electrical power loss is minimized. 
   To enable adjusting the operating performance of the magnet valve in the installed state, a compression spring acting on the valve member is provided, whose prestressing force is very easily adjustable with the aid of an adjusting disk. By replacing this adjusting disk with another adjusting disk of a different thickness, the operating performance of different examples of magnet valves of the invention can be further improved, and the variations from one another among various examples in a series can be further reduced. 
   So that no fuel can reach the coil, the armature is embodied in encapsulated form. This can be done especially advantageously according to the invention by providing that the armature is surrounded by a capsule; that a spacer ring of a nonmagnetic material, in particular stainless steel, is provided between the capsule and the magnet plate; and that the capsule, spacer ring, and magnet plate are connected in sealing fashion to one another. Especially preferably, the capsule, spacer ring and magnet plate are welded or soldered to one another. 
   To assure high functional reliability and a long service life, the valve member is guided at least one point, but preferably at two points, in a housing. As a result, it is assured that the sealing face of the valve member always strikes the valve seat in the valve housing parallel to the valve seat, and moreover the armature does not rest on the capsule, which does not move relative to the valve housing, and as a result the armature does not wear down. 
   So that the magnet valve of the invention will assume its open position when the coil is made currentless, a compression spring is provided between the valve member and the valve housing. 
   The magnet valve of the invention can be installed especially advantageously by means of a method in which the fully machined valve member is locked in a receptacle of a fixed installation device; the magnet plate and the spacer plate are mounted on the receiving mandrel; the magnet plate, spacer plate and valve member are pressed against the receptacle; next, the magnet plate and the spacer plate are displaced by a predetermined amount relative to the valve member; and the armature is secured to the receiving mandrel of the valve member in such a way that the armature rests on the magnet plate. 
   By means of this method, it is easily possible, despite the production tolerances that occur in every mass production, to adjust the valve stroke exactly and with very great repeatability. In the process, production tolerances among individual components do not adversely affect the precision of the adjusted valve stroke. 
   It has proved advantageous if the magnet plate and the spacer plate are displaced by an amount that corresponds to the sum of the valve stroke and a desired remanent air gap between the armature and the magnet plate in the closed state of the magnet valve. 
   To prevent fuel from being able to reach the coil of the magnet valve, a spacer ring and a capsule are then slipped onto the magnet plate and tightly welded to one another. 
   For calibrating the magnet valve, the compression spring and the valve member are then inserted into the valve housing; a coil of the magnet is triggered with a current which is selected such that the magnetic force exerted on the armature is greater than the spring force that is to be exerted by the compression spring on the valve member; the spring force exerted by the compression spring on the valve member is recorded as a function of the position of the magnet valve in the housing; the recorded spring force and travel graph is evaluated; and if needed, a correction is made in the thickness of the adjusting disk. 
   By means of this method for calibrating the magnet valve of the invention, it can be assured in a simple way that the current with which the coil must be triggered for closing the magnet valve will be virtually identical in all examples in a series. As a result, there is a very uniform operating performance of the magnet valve of the invention. Once the initial tension of the compression spring has been adjusted, function monitoring can be performed, and if needed, another correction of the thickness of the adjusting plate is made. This step is done until such time as the function of the unit fuel injector is in accordance with the required demands. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and advantageous features of the invention can be learned from the ensuing description, taken in conjunction with the drawings, in which: 
       FIG. 1  is a unit fuel injector of the invention, with an only schematically shown magnet valve; 
       FIG. 2 , one exemplary embodiment of a magnet valve of the invention in the assembled state; and 
       FIGS. 3-7  show structural details of the magnet valve of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a unit fuel injector is identified overall by reference numeral  1 . The unit fuel injector  1  serves to inject fuel into a combustion chamber of a direct-injection internal combustion engine (not shown). It has a pump element  2 , which builds up the requisite injection pressure. Via an injection nozzle  3 , the fuel, brought at high pressure from the pump element  2 , is injected into the combustion chamber (not shown). 
   The unit fuel injector  1  is controlled by a 2/2-way control valve  5  which is shown in the form of a block circuit diagram in  FIG. 1 . 
   The control valve  5  is triggered by an actuator, not shown in  FIG. 1 , in particular an electromagnetic actuator. 
   As in every unit fuel injector, the pump element  2  and the injection nozzle  3  form a unit. For each cylinder of the engine, one unit fuel injector  1  is built into the cylinder head  7  of the engine and driven, either directly via a tappet or indirectly via tilt levers, by a camshaft of the engine (not shown) via an actuating element  8 . 
   A pump chamber  9  of the pump element  2  communicates, via a fuel inlet  11 , with a low-pressure fuel supply  12 . The low-pressure fuel supply  12  may for instance comprise an electrically driven prefeed pump  15  and a fuel filter (not shown), which aspirate fuel from a fuel tank  13  via a line. 
   The control valve  5  splits the fuel inlet into two portions  11   a  and  11   b . The control valve  5  is triggered by a control unit, not shown, and opens the hydraulic connection between the pump chamber  9  and the tank  13 , as shown in  FIG. 1 , or closes it (not shown). The portion of the fuel inlet  11  that is located between the control valve  5  and the prefeed pump  15  is identified in  FIG. 1  by reference numeral  11   a , while the portion between the control valve  5  and the pump chamber  9  is identified by reference numeral  11   b.    
   When the control valve  5  is opened, fuel can flow into the pump chamber  9  during the intake stroke of the pump piston  10 . In the ensuing pumping stroke of the pump piston  10 , the fuel previously pumped into the pump chamber  9  is pumped back into the tank  13 , as long as the control valve  5  is open. This also means that a pressure sufficient to open the injection nozzle  3  does not build up in the pump chamber  9 . 
   When fuel is to be injected via the injection nozzle  3  into the combustion chamber, not shown, of the engine, the control valve  5  is closed during the pumping stroke of the pump piston  10 . As a result, the fuel can no longer be pumped out of the pump chamber  9  back into the tank  13 , and in the pump chamber  9  a high pressure builds up, which finally leads to the opening of the injection nozzle  3  and hence to the injection of fuel into the combustion chamber (not shown) of the engine. The onset of the injection of fuel into the combustion chamber can be determined by the closing time of the control valve  5 . The injection of fuel into the combustion chamber is terminated by opening the control valve  5  again. 
   In  FIG. 2 , a magnet valve  5  is shown in section. As  FIG. 1  shows, the magnet valve  5  is integrated into the housing  17  of the unit fuel injector  1 . It is understood that it would also be possible for this magnet valve  5  to be built into a separate valve housing (not shown). 
   The magnet valve  5  comprises a 2/2-way valve with a valve member  21 . The valve member  21  has a frustoconical portion, on which a sealing face  23  is located. The valve member  21  is guided in a bore  25  of the housing  17 . On its lower end in terms of  FIG. 2 , the valve member  21  has a guide portion  27 , which cooperates without play with the bore  25 , so that the valve member  21  is securely guided. 
   As needed, a second guide portion  29  may also be embodied on the valve member  21 , in the vicinity of the sealing face  23 . In this second guide portion  29 , there is a plurality of flat faces  31 , distributed over the circumference of the valve member  21 . The flat faces  31  may for instance be distributed over the circumference at intervals of 120° or 90°. The flat faces  31  serve to establish a hydraulic connection between the portion  11   a  of the fuel inlet  11  and the portion  11   b  of the fuel inlet  11  when the magnet valve  5  is open. Above the second guide portion  29  in the housing  17 , a valve seat  33  is provided. When the valve member  21  moves downward in terms of  FIG. 2 , until the sealing face  23  rests on the valve seat  33 , the hydraulic connection between the portions  11   a  and  11   b  of the fuel inlet  11  is interrupted, and the control valve  5  is closed. 
   In the lower portion of the bore  25 , there is a closure element  28 , which is secured in the housing  17 . On the lower end of the valve member  21 , a compression spring  54  is provided in the bore  25 ; this spring is braced on one end against an adjusting disk  26  for adjusting the spring force and on the other against the valve member  21  and lifts the valve member from the valve seat  33  when a coil  37  is made currentless. The adjusting disk  26  in turn rests on the closure element  28 , and if the needs arises, it can be very easily replaced. 
   The coil  37  has two electrical terminals  39 , by way of which the coil  37  can be supplied with electric current. The delivery of current to the coil  37  is controlled by a control unit, not shown, of the unit fuel injector or of the engine. 
   In the interior of the toroidal coil  37 , there is an armature  41 . The armature  41  is pressed onto a receiving mandrel  43  of the valve member  21 . Below the coil  37 , a magnet plate  45  is provided, which comprises a material which is a good conductor of the magnetic field lines of the coil  37 . By means of the magnet plate  45 , the heat generated in the coil  37  is dissipated, and the magnetic force exerted by the coil  37  on the armature  41  is increased. A spacer ring  47  of a nonmagnetic material, such as stainless steel, and a capsule  49  are slipped onto on the magnet plate  45 . The capsule  49  and the spacer ring  47 , like the spacer ring  47  and the magnet plate  45 , are joined together in fluid-tight fashion by weld seams  51 . 
   The armature  41  does not rest with its outer diameter on the capsule  49 , so that it can move freely in the axial direction of the valve member  21 . In the middle, the magnet plate  45  has a through bore  53 , through which the receiving mandrel  43  protrudes into the chamber (not identified by reference numeral) that is defined by the capsule  49  and the magnet plate  45 . 
   Between the magnet plate  45  and a stroke stop  55  embodied on the valve member  21 , a spacer plate  57  is provided. The spacer plate  57  has a hole  59 . The hole  59  may also be embodied as an oblong slot, which extends radially outward from the center point of the spacer plate  57  as far as its outer diameter. As a result, it is possible as needed to replace the spacer plate  57  with another spacer plate  57  of a slightly different thickness D, and as a result, by way of the remanent air gap, to adjust the resultant magnetic force of the magnet valve  5  in a simple way. 
   The magnet valve  5  functions as follows: 
   When the coil  37  is made currentless, the compression spring  54  opens the magnet valve  5 , by lifting the sealing face  23  of the valve member  21  from the sealing seat  33 . As a result, a hydraulic connection is made between the portions  11   a  and  11   b  of the fuel inlet. As soon as current is flowing through the coil  37 , a magnetic force exerted by the coil  37  on the armature  41  pulls the valve member  21  downward counter to the force of the compression spring  54 , so that the sealing face  23  of the valve member  21  rests on the valve seat  33  of the magnet valve  5 . As a consequence, the hydraulic connection between the portions  11   a  and  11   b  of the fuel inlet  11  is interrupted, so that a pressure buildup can take place in the pump chamber  9  of the pump element  2  (see  FIG. 1 ). 
   The connection of the armature  41  to the receiving mandrel  43  by means of a cylindrical press fit has the advantage that the armature  41  can be pressed onto the receiving mandrel  43  far enough until it has reached the desired position relative to the stroke stop  55  of the valve member  21 . 
   In  FIG. 3 , a valve member  21  is shown without a housing and without an armature. From this view it becomes clear that even in the manufacture of the valve member  21 , the valve stroke of the magnet valve  5  is predetermined by the spacing of the sealing face  23  from the stroke stop  55  in the axial direction. This axial spacing of the sealing face  23  and stroke stop  55  is easy to control from a production standpoint, so that the variation among various examples in a series is only very slight. Even this is already an important precondition for assuring that the magnet valves  5  in one series of unit fuel injectors  1  according to the invention will have a virtually identical operating performance. 
   From  FIGS. 4 through 7 , the installation and calibration of a magnet valve  5  will now be described. From the description of  FIGS. 4 through 7 , the advantages of the method claimed according to the invention for installing a magnet valve can also be made clear. 
   The installation and calibration of the magnet valve  5  are done in an installation device or fixture  61 . This installation device  61  includes a cylindrical receptacle  63 , in which the valve member  21  is received. The valve member  21  rests with the underside of the stroke stop  55  on one end of the receptacle  63 . Next, the spacer plate  57 , which may be of simple steel, and the magnet plate  45  are placed on the valve member  21  in such a way that the spacer plate  57  rests on the stroke stop  55 , and with the aid of a pressing sleeve  65 , the magnet plate  45  and the spacer plate  57  are pressed against the stroke stop  55 . 
   In a further step, an installation sleeve  67  is driven from below against the spacer plate  57 . Once the installation sleeve  67  has been driven from below against the spacer plate  57 , without the spacer plate  57  lifting from the stroke stop  55  as a result, the position of the installation sleeve  67  is detected. Next, the installation sleeve  67  in  FIG. 4  is moved upward counter to the force of the pressing sleeve  65  by an amount A (see  FIG. 5 ). Because of the force of gravity, the valve member  21  continues to rest on the receptacle  63  in the position shown in  FIG. 4 . In other words: 
   The spacer plate  57  and the magnet plate  45  move away from the stroke stop  55  by an amount A relative to the valve member  21 . This position of the spacer plate  57  and magnet plate  45  is shown in  FIG. 5 . The amount A is equivalent to the desired maximum valve stroke, plus a required remaining gap between the armature  41  and the magnet plate  45  in the closed state (not shown). 
   The installation sleeve  67  is locked in the position shown in  FIG. 5  relative to the receptacle  63 . Next, the armature  41  is pressed from above onto the receiving mandrel  43  of the valve member  21  (see  FIG. 6 ). As a result, the valve stroke of the magnet valve  5  is thus adjusted and production inaccuracies in the manufacture of the valve member, the spacer plate  57 , the magnet plate  45 , and the armature  41  do not affect the adjusted valve stroke. 
   A plurality of longitudinal bores  42  are provided in the armature  41 , so that the motion of the armature  41  in the capsule  49  is not hindered by the fuel (not shown) located in the capsule. At the same time, the design of these longitudinal bores  42  is utilized to achieve the optimal damping of the motion of the armature  41  and the valve member  21  at the end of the stroke. To that end, the longitudinal bores  42  may have one or more throttle restrictions, not shown. 
   In  FIG. 7 , the structural group, comprising the valve member  21 , spacer plate  57 , magnet plate  45  and armature  41 , that is preassembled as shown in  FIGS. 4 through 6  is shown. Next, the spacer ring  47  and the capsule  49  are welded onto the magnet plate, as shown in  FIG. 2 . This structural group can now be inserted into the housing  17 . 
   Since the compression spring  54  has a certain variation in terms of its dimensions and spring rate, it is advantageous to calibrate the magnet valve when the valve member  21  and the compression spring  54  are built into the housing  17 . To that end, in a first step, the coil  37  is supplied with a predetermined current. This current is so great that the coil  37  exerts a magnetic force on the armature  41  that is greater than the desired prestressing force of the compression spring  54 . In a second step, the structural group, together with the compression spring  54 , is pushed into its installed position in the housing  17 , and the spring force exerted in the process on the valve member  21  by the compression spring  54  is measured and recorded as a function of the position of the valve member  21  in the housing  17 . Next, the current supply to the coil  37  is interrupted. By evaluating the previously ascertained spring force and travel graph, it can be found whether, in the desired installed position, the spring force exerted by the compression spring  54  is correct. 
   If that proves not to be the case, then the spring force of the compression spring  54  can be adjusted by replacing the adjusting disk  26  with an adjusting disk  26  (see  FIG. 2 ) of a different thickness. 
   Next, it is checked whether the magnet valve  5  closes when the coil  37  is supplied with the desired current intensity I set . If the function of the magnet valve  5  proves not to be satisfactory, then the desired closing performance and opening performance of the magnet valve  5  can be adjusted by means of a further replacement of the adjusting disk  26 . This operation is repeated until such time as the magnet valve  5  functions correctly. 
   By means of the magnet valve  5  of the invention, essentially the following advantages are obtained: 
   The bouncing between the armature  41  and the valve member  21  is entirely avoided. 
   There is therefore now only one compression spring  54  that acts on the valve member  21 , with a favorable effect on the manufacturing costs and on the space required for the compression spring  54 . In the prior art, two compression springs are necessary, one of which acts on the armature  41  and keeps it in contact with the valve member  21 . 
   The adjusting disk  26  is a component that is relatively unproblematic to manufacture, and there is no need, as in the prior art, to pair different components in order to adjust the magnet valve  5 . The desired opening and closing performance of the magnet valve  5  can be adjusted merely by replacing the adjusting disk  26 . Moreover, adjusting the magnet valve  5  is made markedly simpler by the provision that the armature  41  and the valve member  21  form a component that is solidly joined together and whose dynamic performance is comparatively simple to control. 
   The armature  41  is guided by the valve member  21 , so that in the region of the armature  41  and the capsule  49 , separate guidance of the armature is no longer necessary, which reduces the costs and increases the functional reliability of the unit fuel injector of the invention. 
   Moreover, the advantage, known from the prior art, of a dry coil  37  can also be retained in the magnet valve  5  of the invention. 
   The foregoing relates to a 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.