Abstract:
A freeze-resistant metering valve is provided that comprises a magnetic part and a hydraulic part. The magnetic part has an armature biased by a spring. The hydraulic part has an annular space for receiving and conveying a liquid as well as a tappet facing a valve seat. The valve seat comprises a nozzle opening on the side facing away from the tappet. In a currentless state, the tappet blocks the annular space in the direction of an opening (nozzle opening) until a freezing pressure exerted onto the armature generates a sufficient force by virtue of the solidifying liquid. This force is used to counteract the spring force until a freeze expansion space is created by way of a relieving motion.

Description:
[0001]    This application is a divisional of U.S. patent application Ser. No. 11/417,538, filed on May 3, 2006, which application is a continuation of International patent application No. PCT/EP2005/052226 filed on May 13, 2005, and which application claims priority of German patent application No. 10 2004 025 062.6 filed on May 18, 2004, each of which is incorporated herein and made a part hereof by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a freeze-resistant metering valve which can be used in automotive engineering, in particular utility vehicles. The freeze-resistant metering valve is, in particular, suitable for exhaust gas after treatment systems and/or exhaust systems. 
         [0003]    Motor vehicles, in particular utility vehicles which are intended to be used in regions with a temperate climate or even arctic regions, have to be designed so that they can withstand temperatures below zero degrees Celsius without sustaining damage. This is generally possible by the choice of suitable materials. Alternatively, for many years an additional source of heat has been used when temperatures fall too low. 
         [0004]    In order to reduce Nitrogen Oxide (NOx) in the exhaust gas of motor vehicles, in particular diesel vehicles, automobile manufacturers and suppliers have agreed to use a 32.5% urea-water solution (UWS). Due to the high proportion of water in the solution, even at low negative temperatures (degrees Celsius), the solution which is pressurized during operation freezes. 
         [0005]    For many years now, the industry has been concerned with how the problem of the freezing of the urea-water solution can be handled. One solution consists of removing all the UWS by means of compressed air when switching off the motor vehicle. Such a system requires the presence of an air compressor on board the vehicle. An air pressure generator is typically incorporated in large utility vehicles. No specific air supply system is provided in small utility vehicles and automobiles which are equipped with a diesel engine. 
         [0006]    The costly algorithms with which a control device is to be programmed, so that faulty behavior due to freezing can be identified, can be seen from DE 10256169 A (Toyota Motor Corporation Ltd). 
         [0007]    DE 10139139 A (Robert Bosch GmbH) proposes to provide the reducing agent line with electrical heating in order to eliminate freezing of the reducing agent. The fact that this is impractical can be seen from DE 19935920 A (Siemens AG). It can be seen from this publication that the heating power requirement for the reducing agent reservoir alone would exceed one kilowatt. Therefore, it can be further seen from the publication that a heat exchanger can be incorporated. According to DE 10139142 A (Robert Bosch GmbH) the heat exchanger has to prevent freezing, even at temperatures below −11° C. The requirements of automobile manufacturers go even further. They require the valves to work perfectly even at an outside temperature of −40° C. It has been considered, therefore, as in DE 4432577 A (Siemens AG), to incorporate a special back-flow prevention valve with variable control operation. DE 4432576 A (Siemens AG) also refers to the difficulty of using frost protection agents. Operating with different volumes is therefore possible. 
         [0008]    What all these solutions have in common is that additional measures have to be taken to overcome the risk of freezing. It would be desirable to have a freeze-resistant metering valve which operates perfectly at the high temperatures of the exhaust gas stream which can exceed 700° C. and is simultaneously freeze-resistant. Even at an outside temperature of −40° C., the metering valve still has to be able to be operated, provided that the UWS is present in liquid form. Therefore, the entire system in which the metering valve is incorporated is to be of energy efficient design. 
       SUMMARY OF THE INVENTION 
       [0009]    These and other advantages are fulfilled by a freeze-resistant metering valve according to the invention and a corresponding exhaust gas cleaning system. Various advantageous embodiments are disclosed herein. 
         [0010]    The freeze-resistant metering valve is intended to be electrically controllable. As a result, the vehicle controller or a control device particularly appropriate for the exhaust gas stream can meter the correct amount of UWS. The invention can also be used for other liquids which are to be metered. Aspects of the invention are also therefore explained for other liquids. In normal operation, when the entire exhaust gas stream, including exhaust pipes and mufflers, is heated by the waste heat of the engine, no particular attention has to be paid to the risk of freezing. However, it is dangerous when the vehicle is no longer, or not, in operation. In every state under particular consideration, no control signal, i.e. no current, is passed through the valve. The tappet in the metering valve closes the opening through which the UWS is to be conveyed. When the temperature is lowered, for example, from 700° C. to temperatures below the freezing point of the UWS (approximately −11° C.) the metering valve would be permanently damaged, due to the expansion of the UWS, which can be approximately 9 to 11%. The freezing forces of the UWS can be advantageously used in a passive system, by being converted into a relieving motion. The relieving motion produces a freeze expansion space. One possibility is that the relieving motion acts in a controlled manner. The relieving motion acts indirectly or directly on the armature in order to produce a freeze expansion space by a movement of the tappet. The freeze expansion space has to be established within the valve. The freeze expansion space can be located at different positions. In one embodiment, therefore, the freeze expansion space is the region which is produced by lifting the tappet from the valve seat. However, a specific annular space region can also be provided or a space which is only accessible to the liquid by means of the relieving motion. When the pressure in one of the freeze expansion spaces is great enough, the resulting force exceeds the opposing spring force. As a result, the armature can be displaced against the spring force and the tappet is lifted from the seat. 
         [0011]    The invention is further characterized in that the amount of liquid which is present in the metering valve is reduced to a minimum. By a clever design of the valve, the space receiving the liquid is minimized, the tappet filling a portion of the space which is designed for conveying the liquid further into the exhaust gas stream, the annular space. Moreover, unnecessary hollow spaces are filled by filling pieces, sleeves, bearings and other closure members. The minimizing of the annular space should be taken even further from the point of view of freeze resistance. However, the minimizing of the annular space should not impede the flow of the material to be metered, the liquid. In other words, the pressure loss should not be noticeable. The pressure loss would be noticeable at a pressure loss of more than 5% of the nominal pressure of the metering valve. Preferably the pressure loss should be under 1% of the nominal pressure of the metering valve. For example, it can be shown that at a nominal pressure of 5 bar absolute, the pressure loss along the entire annular channel should not be over 250 mbar, preferably under 50 mbar. 
         [0012]    In a further advantageous embodiment, moreover, the metering valve offers flexible expansion surfaces. Such expansion surfaces can be resilient bases or diaphragms. Due to the freezing pressure, a freeze expansion space bulges out in the region of the resilient base or the diaphragm. If the liquid melts, such as for example the UWS, the resilient base or the diaphragm returns again to its original position. The original position is the operating position. 
         [0013]    Moreover, according to a further advantageous aspect, in some embodiments of a freeze-resistant metering valve deliberate undercuts are avoided. Undercuts are avoided in the valves as, in the regions of the undercut, forces can be produced in all directions by the freezing pressure which can lead to damage. The spring which holds the tappet in the currentless state in the locked position is supported such that, in its supported region, no undercuts are necessary. By avoiding undercuts, the freezing liquid is not obstructed. 
         [0014]    Additional expansion spaces can be produced, for example, by the nozzle plate, which is present for the equal distribution of the liquid to be metered and is capable of expansion, being able to be lifted from the nozzle opening. 
         [0015]    The spring can optionally be located in the liquid. 
         [0016]    By means of special seals and special rings, regions in the metering valves are sealed relative to the liquid and thus the amount of liquid present in the valve is reduced. 
         [0017]    According to a further advantageous aspect, the metering valve can be designed such that the supply line discharges into a sleeve via an expandable hose. The sleeve exterior thereof can be ribbed. The expandable hose can be slipped over the sleeve exterior. By means of the ribbing of the sleeve exterior, the surroundings are sealed against the UWS. If the UWS freezes in the supply line or in the sleeve, the expandable hose offers an additional compensation space. On the one hand, the hose itself can expand. On the other hand, it can easily be lifted away from several ribs of the sleeve exterior and yet be sealingly held by the remaining ribs of the sleeve exterior. 
         [0018]    A further outlet can be provided for the valves. The outlet undertakes two tasks. As, during operation, the metering valve has to be heat resistant and the UWS should not overheat on the inside (a desired temperature of less than 90° C. has to be maintained) it can be necessary to prevent overheating that the nozzle neck of the hydraulic part is cooled by additional liquid. To this end, during the constant circulation of the UWS, said hydraulic part is cooled by the UWS. In the case of freezing of the liquid, the additional outlet undertakes the task of switching the valve to the unpressurized state and also offers an additional expansion space. 
         [0019]    By pressing the tappet with stop plates, sleeve armatures or annular armatures, a large surface is provided for bearing the freezing pressure. The large surface converts the force of the freezing pressure of the minimal liquid present into a large force which can act against the spring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    For better understanding, reference is made to the following Figures, whereby 
           [0021]      FIG. 1  discloses a first example embodiment of the present invention, 
           [0022]      FIG. 2  discloses a second example embodiment of the present invention, 
           [0023]      FIG. 3  discloses a third example embodiment of the present invention, and 
           [0024]      FIG. 4  illustrates a section through a nozzle neck of an example embodiment of the present invention according to  FIG. 1  or  2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    In the Figures, similar components are numbered with the same reference numerals, even when there are small structural differences. 
         [0026]      FIG. 1  discloses a metering valve  1 . The metering valve  1  comprises a hydraulic part  3  and a magnetic part  5 . The magnetic part  5  has a coil  7 , which has numerous windings and is arranged on a coil support  9 . On the corners of the coil support are provided seals  49  which can be, for example, O-rings. The seals  49  seal the coil support relative to the magnet housing  11  around the pole core  61 . The metering valve is, as a whole, rotationally symmetrically constructed. A bore is provided in its center. The tappet  17  moves in the bore. The space which remains of the bore is an annular space  19 . The tappet is partially surrounded by an armature which is a sleeve armature  13 ′. The tappet  17  which leads into the valve seat  21  at its one end, is rounded at the end. On the other end, the tappet  17  leads into an armature sleeve  51 . The valve seat  21  is a part of the end piece  23  which also surrounds the nozzle opening  25 . Optionally, a nozzle plate  27  can be arranged on the end piece  23 . The nozzle plate  27  attenuates the droplets of liquid which are already atomized by the funnel-shaped nozzle opening  25  and by the nozzle  73 . The UWS is introduced without compressed air into the exhaust gas stream. It can therefore be necessary for the liquid to be atomized further. A bearing  57  is provided in the vicinity of the end piece  23  by means of which the liquid space is minimized. The bearing  57  guides the tappet  17 . The liquid space is further minimized by the sleeve  59 . Compensation spaces are intentionally provided on the other side. The opening  45 , for example, which is a second opening, serves to relieve the pressure and in the frozen state serves as an outlet to a compensation space, for example in an expansion hose which can be optionally present. The ring  47  undertakes a plurality of tasks: it circulates the magnetic flow, by interrupting the direct flow and seals the supply line and/or the annular space  19  relative to the coil support. Undercuts are avoided by means of the projections  43 , on which the spring  15  can be supported. The projections  43  are of such a size that the spring  15  is supported in a stable manner but no effect is produced on the liquid in the supply line  35 . On the other side of the spring  15 , the spring presses against the armature  13  which is a sleeve armature  13 ′. Threaded projections are provided on the nozzle neck  67 . By means of its nozzle exterior  39  which has a Christmas tree profile, the sleeve  37  is not only provided for the receipt of a resilient hose, but is also simultaneously the pole core  61  for the magnetic end of the coil  7  on the armature  13 ′. In the currentless state, i.e. the state in which no current flows through the coil  7 , the spring  15 , via the armature  13 ′, presses the tappet  17  against the valve seat  21 . The biasing of the spring  15  is permanently present, provided that the spring is not restricted in its expansion by freezing of the liquid in the supply line  35 . The tappet  17  is pressed via the sleeve  51  in the currentless state by the spring force of the spring  15  against the valve seat  21  of the end piece  23 . The annular space which, in this embodiment, is 5/10 mm (i.e., 0.5 mm) in total, receives only a minimal amount of liquid. If this minimal amount of liquid freezes, the liquid is pressed against the deformable diaphragm  33  and/or base  33 ′. The liquid can also be pressed into the resilient hose. If the force exceeds that which is formed by the internal pressure produced on the corresponding surface, the tappet  17  is displaced against the spring force and the tappet  17  is lifted from the valve seat  21 . As a result, compensation spaces are opened up. A first compensation space  29  and a second compensation space  31  are provided in this embodiment. Moreover, the opening  45  is provided. The freezing liquid can be diverted into the compensation spaces  29  and  31  which are located in the supply line  35  and the valve seat  21 . The magnet housing  11  is flanged at its ends and therefore presses the pole core  61  and the hydraulic part  3  against the ring  47 . The magnetic diverter, which the ring  47  represents, seals the two parts of the valve and is optionally welded. The shape of the valve housing  69  corresponds to the receiving unit, for example the exhaust of the motor vehicle, by means of recesses and projections depending on the contour. 
         [0027]    In contrast to the metering valve  1  according to  FIG. 1  which is provided with an axial supply connector for the supply line  35 , the metering valve  1  according to  FIG. 2  is equipped with a lateral connector. The two valves have a long metering valve neck, the nozzle neck  67 , to ensure at a corresponding temperature gradient that, in the rear portion of the valve, materials which are not so heat resistant are used for the spring  15  and the coil  7  as well as the supply line  35 . The metering valve  1  also has a hydraulic part  3  and a magnetic part  5 . The spring  15  is supported on the one hand against the magnet housing  11  and on the other hand relative to the armature  13 , which is a flat armature. A coil  7  is located in the magnet housing  11 . The tappet  17  which leads into the valve seat  21  via its rounded tip, has a shrink-fitted sleeve  51  on its other end. The valve seat  21  in the end piece  23  leads into the nozzle opening  25  which is covered by an optional nozzle plate  27  for distributing the liquid. The metering valve  1  comprises two compensation spaces  29  and  31  and has a further optional outlet  45 . The first space  29  is delimited by a diaphragm  33 . The space  29  adopts the function of an compensation space by means of the diaphragm  33 . On the side opposing the compensation space  29 , a hollow space  55  is provided. The diaphragm  33  is connected by spot welds or by t hick welds to the valve housing  69  and the tappet  17 . The diaphragm is made of metal. The liquid is transferred to the metering valve from a resilient hose via the supply line  35  in the sleeve  37  which has the sleeve side  39 . In a less advantageous embodiment, a metal pipe can be provided instead of a resilient hose. As a result, however, a further compensation space is lost. The liquid, which is present in the supply line  35 , flows via the annular space  19  along the tappet  17  to the valve seat  21 . When current is applied to the coil  7 , the armature  13  is pulled onto the coil  7 . In the open state of the metering valve  1 , the hollow space  55  is reduced or disappears. The spring  15  is pressed together by the armature  13 . At the end of the operation of the motor vehicle, the coil  7  is switched to the currentless state. The tappet  17  is lowered onto its valve seat  21 . The liquid which is present in the compensation space  31  is dispensed via the nozzle plate  27  into the exhaust gas stream of the vehicle. If the liquid in the annular space  19  is frozen by corresponding cooling of the metering valve  1 , the freezing liquid presses against the diaphragm  33 . The force of the freezing pressure is transferred via the disc  71  to the armature  13 . The armature  13  presses against the spring  15 . The tappet  17  is lifted from the valve seat  21  via the sleeve  51 . The compensation space  31  is therefore opened up. The further compensation space  29  which may be enlarged by the diaphragm  33 , offers additional space for the expansion of the frozen liquid. Moreover, the opening  45  which, however, does not have to be present, provides a compensation space. The hydraulic part  3  is narrower than the magnetic portion  5 . As the hydraulic portion  3  has to be produced from heat resistant material, it would be preferable to use as little as possible of the valuable material. The bearing  57  delimits the possible amount of liquid which can be present in the annular space  19 . The bearing guides the needle and/or the tappet which is optionally provided with holes. 
         [0028]    In  FIG. 3  a further embodiment of a metering valve  1  according to the invention is disclosed. The entire metering valve  1  consisting of a hydraulic part  3  and a magnetic part  5  is, for example, shorter than the metering valves according to  FIGS. 2 and 1 . It is, however, wider. The geometry of the valve part is adapted to requirements. The metering valve is also rotationally symmetrically constructed, with a few exceptions. The armature  13 ″ is a tappet armature which leads into a tappet  17  and has an armature bore  53 . The spring  15 , which is supported relative to the seal pot  63 , engages on one side of the tappet armature  13 ″. The seal pot  63  is equipped with a hollow space  55  which is intended to provide an expansion space for the volume from the space  29 . The supply line  35  runs laterally to the tappet  17  which is partially surrounded by the inner space  19 . The tappet  17  leads into the valve seat  21  of the end piece  23 . The end piece  23 , in this embodiment, is not equipped with a nozzle plate. Also, the compensation space  31  in the region of the nozzle opening  25  is smaller than in the metering valves according to  FIG. 1  or  2 . The bearing  57  delimits the maximum amount of liquid which can be located in the annular space  19  and in the supply line  35 . If current is applied to the coil  7 , the armature  13  is moved by the magnetic field against the spring force of the spring  15  in the direction of the pole core  61 . As a result, the tappet  17  is lifted from the valve seat  21 . In the currentless state, the tappet  17  sinks onto the valve seat  21 . If the fluid freezes in the supply line  35  or the annular space  19 , the freezing liquid presses against the tappet armature  13 ″, the tappet armature  13 ″ is moved against the spring  15 . As a result, the UWS in the space  29  is forced in the direction of the resilient base  33 . The spring  15  is pressed together. The tappet  17  is lifted from the valve seat  21 . The liquid can be diverted into the compensation space  31 . When the compensation space is not sufficient, an additional compensation space can be created by the resilient base  33  in the region of the spring  15 . The magnet housing  11  is simultaneously the valve housing. The hollow space which is also a first compensation space  29 , is in fluidic connection with the supply line  35  and the annular space  19  via the armature bore  53 . The armature  13 ″ is supported or surrounded on both sides by the liquid. 
         [0029]    In  FIG. 4  a further alternative possibility is shown of how the amount of liquid present can be further reduced. 
         [0030]    Instead of having a completely circumferential annular space  19  along the entire tappet  17 , the tappet  17  is only partially provided with grooves and projections  65   a ,  65   b ,  65   c  and  65   d . The remaining volume of the nozzle neck  67  is made from solid material. Only the minimal liquid present in the eccentric openings  65   a ,  65   b ,  65   c  and  65   d  can then still freeze. The solid material of the nozzle neck  67  further contributes to the strength of the nozzle neck  67 . A nozzle neck shown can be present in the valves according to  FIG. 1 ,  FIG. 2  and also  FIG. 3 . The nozzle neck only has to be correspondingly adapted in each case. 
         [0031]    The valves according to the invention are preferably connected to a resilient hose through which the liquid is conveyed to the metering valve. The valve seat opens into the exhaust gas stream of the motor vehicle. With vehicles driven by diesel engines, a 32.5% urea-water solution is conveyed through the valve. The freeze-resistant valves are, however, developed advantageously such that other liquids can also be conveyed through the metering valves. Thus pure water or salt water or even diesel can be conveyed just as efficiently through the valves. 
         [0032]    The valve is characterized in that, on the one hand, it can operate in an environment which may reach more than 700° C. and, on the other hand, even at temperatures as low as −40° C. it undergoes no permanent damage. To this end, it contributes to minimizing the amount of liquid inside the valve. Moreover, only selected components are wetted by the liquid. The entire system operates passively in the frozen state. The system itself is relieved during freezing. No additional sources of energy are required. The liquid wettable spaces and liquid containing spaces are designed without undercuts or interfering contours. Even when valves have only one or other of the previously summarized features, they fall within the protective scope of this invention. 
       LIST OF REFERENCE NUMERALS 
       [0033]      
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                  1 
                 Metering valve 
               
               
                   
                  3 
                 Hydraulic part 
               
               
                   
                  5 
                 magnetic part 
               
               
                   
                  7 
                 coil (with windings) 
               
               
                   
                  9 
                 coil support 
               
               
                   
                 11 
                 magnet housing 
               
               
                   
                 13 
                 armature as flat armature 
               
               
                   
                 13′ 
                 armature as sleeve armature 
               
               
                   
                 13′′ 
                 armature as tappet armature 
               
               
                   
                 15 
                 spring (helical compression spring) 
               
               
                   
                 17 
                 tappet 
               
               
                   
                 19 
                 annular space 
               
               
                   
                 21 
                 valve seat 
               
               
                   
                 23 
                 end piece 
               
               
                   
                 25 
                 nozzle opening 
               
               
                   
                 27 
                 nozzle plate (optional) 
               
               
                   
                 29 
                 first compensation space (as part of the freeze 
               
               
                   
                   
                 expansion space) 
               
               
                   
                 31 
                 second compensation space (as part of the freeze 
               
               
                   
                   
                 expansion space) 
               
               
                   
                 33 
                 diaphragm 
               
               
                   
                 33′ 
                 resilient base 
               
               
                   
                 35 
                 supply line 
               
               
                   
                 37 
                 sleeve (ribbed exterior) 
               
               
                   
                 39 
                 sleeve exterior 
               
               
                   
                 41 
                 spot welds 
               
               
                   
                 43 
                 projections 
               
               
                   
                 45 
                 opening (second) 
               
               
                   
                 47 
                 ring 
               
               
                   
                 49 
                 O-ring seal 
               
               
                   
                 51 
                 armature sleeve 
               
               
                   
                 53 
                 armature bore 
               
               
                   
                 55 
                 hollow space 
               
               
                   
                 57 
                 bearing 
               
               
                   
                 59 
                 sleeve 
               
               
                   
                 61 
                 pole core 
               
               
                   
                 63 
                 seal pot 
               
               
                   
                 65 
                 annular space openings (65a, 65b, 65c, 65d) 
               
               
                   
                 67 
                 nozzle neck 
               
               
                   
                 69 
                 valve housing 
               
               
                   
                 71 
                 disc 
               
               
                   
                 73 
                 nozzle