Abstract:
A system for exhaust gas treatment for internal combustion engines has a pump ( 1 ) for metered supply of a freezable substance, particularly a urea solution, to a supply device ( 23 ) introducing the substance into the exhaust gas flow. A compensation device ( 25 ) is provided as protection against damage to the system due to volume expansion when the substance freezes. The compensation device compensates for the volume expansion accompanying an increase of the fluid pressure when the substance freezes.

Description:
FIELD OF THE INVENTION 
     The invention relates to a system for exhaust gas treatment for internal combustion engines, comprising a pump for a metered supply of a freezable substance. In particular, an aqueous urea solution is conveyed to a supply device introducing the substance into the exhaust gas flow. 
     BACKGROUND OF THE INVENTION 
     Such systems, which are also referred to in technical language as the Adblue system, can be used in automotive engineering to reduce nitrogen oxides contained in the exhaust gas flow to nitrogen. This reduction takes place by the metered supply of an aqueous urea solution from a supply tank, via a supply device, to the exhaust gas flow. Ammonia is obtained from the urea by hydrolysis. The ammonia functions as a selective reducing agent in the exhaust gas flow. To optimize the efficiency of the reduction, the aqueous urea solution is supplied to the exhaust gas flow in a metered manner by a pump, which pump is controlled by a control device in a load-dependent manner. 
     The water content of the urea solution, which functions as an additional working substance, has a disadvantageous effect on the operating behavior. If the aqueous solution should freeze, the entire system could fail, in particular as a result of the pump and the supply device connected thereto becoming damaged or destroyed. This risk exists, in particular, during immobilization times at frost temperatures. 
     SUMMARY OF THE INVENTION 
     In light of these issues, the problem addressed by the invention is provide an improved Adblue system in which the risk of damage due to the effects of frost is minimized. 
     According to the invention, this problem is solved by a system having, as an essential special feature of the invention, a compensation device provided as protection against damage to the system due to volume expansion when the substance freezes. The compensation device compensates for the volume expansion accompanying an increase of the fluid pressure when the substance freezes. The risk that would exist otherwise is thereby avoided, namely that, if an aqueous substance freezes, as is the case with an aqueous urea solution under frost conditions, the resultant increase in volume causes walls to burst or, in particular, damages or destroys the pump and/or the valve devices that belong thereto. 
     In a particularly advantageous manner, the compensation device can comprise at least one component that is connected to the fluid chamber of the system and that has predetermined resilience that enables the fluid chamber to enlarge in a pressure-dependent manner. 
     To provide such resilience, in the case of exemplary embodiments comprising a displacement-type pump having at least one displacement element that can be moved by an actuator, the displacement element can interact with the actuator via a resilient coupling device that permits a pressure-dependent relative motion to take place. 
     In particularly advantageous exemplary embodiments, a piston pump comprising at least one pump piston can be provided. The coupling device has a compression spring installed between the respective pump piston and the actuator and allowing the piston to move, against the spring force of the compression spring and relative to the actuator. The fluid chamber is then enlarged. 
     Particularly advantageously, the actuator can be formed by an actuating part of a magnet piston, which can move axially in the pole tube of a solenoid device. 
     In particularly advantageous exemplary embodiments, the pump piston can be lengthened, on the side facing away from the fluid chamber, by a sleeve part that is guided in the pump cylinder and that is open toward the actuating part of the magnet piston. The compression spring is disposed in the interior space of the sleeve part. Due to the fact that the lengthened piston guide is used simultaneously as the spring housing, a compact design of the pump can be obtained. 
     In an advantageous manner, the solenoid device can be designed as a pressing magnet. When current flows through the magnet coil, the magnet presses the magnet piston, together with the actuating part, against the compression spring and moves the pump piston for a delivery stroke. 
     The arrangement is preferably designed such that, when current is not supplied to the magnet coil, a return spring acts on the pump piston and moves the pump piston for a return stroke. 
     To preload the actuating part of the magnet piston against the compression spring in a force-locking manner when current is not supplied to the magnet coil, a spring that acts counter to the return spring can act on the magnet piston. The spring force of this spring is less than that of the return spring. 
     In particularly advantageous exemplary embodiments, a magnet coil that heats up when supplied with current is provided as a heat source, to function as freeze protection and as a thawing device via a thermal coupling to the pump. In a particularly advantageous manner, when a cold start of the internal combustion engine is attempted under frost conditions, with the urea solution frozen and, therefore, the pump blocked, the cold-running phase, in which exhaust gas treatment does not take place, lasts only for as long as the time required for the pump to be automatically thawed out by the heat of the magnet coil. The pump can then begin operating, and exhaust gas treatment can begin. By the heat provided by the magnet coil, in the event that the ambient temperature drops into the frost range during operation, the pump is then prevented from freezing. The failure of the exhaust gas treatment that would result is also prevented. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure: 
         FIG. 1  is a side view in section only of the region of system according to a first exemplary embodiment of the invention that is adjacent to the pump, being enlarged and cut off with respect to a practical embodiment; 
         FIG. 2  is a side view in section of the region of the system of  FIG. 1  adjacent to the pump, shown on a smaller scale than in  FIG. 1  and being rotated by 90° relative thereto, wherein a filter device allocated thereto is incompletely shown; 
         FIG. 3  is a side view in section of the region of a system according to a second exemplary embodiment of the invention, adjacent to the pump wherein a filter device is incompletely shown; 
         FIG. 4  is a schematically simplified, side view in section of only the filter device for the exemplary embodiments of the system according to the invention; and 
         FIG. 5  is an enlarged, schematically simplified, partial side view in section of only of the region of a system according to a third exemplary embodiment of the invention that is adjacent to an end region of the filter device and that comprises sensors. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Proceeding from an exemplary embodiment of the system according to the invention,  FIG. 1  shows a pump  1  as a component of a supply device. The supply device extends from a non-illustrated supply tank containing a supply of an aqueous urea solution, via the pump  1  to a filter device, which is best shown in  FIG. 4 , and, from the filter device to an injection nozzle (likewise not illustrated). The injection nozzle sprays a metered amount of the urea solution into the exhaust gas stream. In addition, a further or second pump or another type of delivery system that increases the pressure to the final injection pressure can be provided. The urea solution reaches the pump  1  via an inlet line  3 . The pump delivers a metered amount of the urea solution from the pump outlet  5  to the filter inlet  7  of the filter device  9 , which is depicted in greater detail in  FIG. 4 . As is clear from  FIGS. 2 and 3 , the pump  1  is designed as a piston pump, the cylinder  11  of which is visible in  FIGS. 2 and 3  and, in each case, is rotated 90° relative to the plane of the drawing of  FIG. 1 . As shown in  FIG. 1 , non-return valves  13  and  15 , respectively, having spring-loaded closing bodies  17  and  19 , respectively, are located at the inlet line  3  and at the outlet  5  of the pump  1 . The non-return valve  13  opens during the intake stroke of the pump  1 , and the non-return valve  15  opens during the delivery stroke of the pump  1 . Sealing rings  21  form the seal at the non-return valves  13 ,  15 . The urea solution emerging from the filter device  9  reaches the exhaust gas stream via an outlet line  23 . 
     As mentioned previously, the pump  1  is a piston pump. The pump piston  25  is guided in the cylinder  11 , and is lengthened at the end thereof facing away from the fluid chamber  27  of the pump  1  by a sleeve part  29 . By sleeve part  29 , the piston  25  is guided in an axially movable manner at the wall of the cylinder  11 , with a piston seal  31  being provided for sealing. The inner space  33  of the sleeve part  29  is open at the end opposite the fluid chamber  27 . A compression spring  35  is inserted into the inner space  33  from the open end. This compression spring  35  is supported on one side at the closed base of the sleeve part  29  and on the other side at a thrust element  37 . Thrust element  37  is displaceable in the sleeve part  29  at the open end of the sleeve part. As an alternative, the thrust element could also be disposed on the inside, although the thrust element would then have to be sealed off from this inner space, for example, by an O ring. 
     An actuating part  39  interacts with the free side of the thrust element  37 , with the actuating part being formed by an extension of a magnet piston  41 . This actuating part  39  is displaceably guided in a pole body  43  of a solenoid device  45 . The pole body  43  transitions into a pole tube  49  via a tapering point  47  having a reduced material cross section, which forms a magnetic gap. The magnet piston  41  connected to the actuating part  39 , can move in the pole body  43 . The magnet coil  51 , which can be supplied with current via a connecting device  53 , is located in a ferromagnetic magnet housing  55  having a pole plate  57 . The solenoid device  45  is designed as a “pressing” magnet, wherein, when current is supplied to the magnet coil  51 , the magnet piston  41  presses the actuating part  39  against the thrust element  37  and therefore presses the compression spring  35 . As a result, the pump piston  25  is moved via the compression spring  35  to the left, as shown in the drawing, for a delivery stroke, by which a dosed amount of the urea solution is dispensed from the fluid chamber  27  via the non-return valve  15  at the pump outlet  5 .  FIGS. 2 and 3  each show the currentless state of the solenoid device  45 . When current is supplied to the coil  51 , the actuating part  39  moves the piston  25 , for a delivery stroke, to the left as shown in the drawing against the force of a return spring  59 . Return spring  59  is located in the fluid chamber  27 . When the current supply to the coil  51  is halted, the actuating part moves the pump piston  25  back toward the right, into the starting position shown in  FIGS. 2 and 3 . In the exemplary embodiment of  FIG. 2 , the free end of the magnet piston  41  rests against an end stop, which is formed by a terminating element  61  at the end of the pole tube  49 . 
     The pump piston  25  can perform a reciprocating motion even when the magnet piston  41  is located in an end position, as shown in  FIG. 2 . Further motion of the actuating part  39  is blocked in a direction that corresponds to the enlargement of the volume of the fluid chamber  27 , because the compression spring  35  is a resilient component that can be compressed when the pressure increase in the fluid chamber  27  is excessive, thereby enabling the pump piston  25  to make a motion to the right as shown in the drawing, which enlarges the volume of the fluid chamber  27 . The end  63  of the sleeve part  29  moves into a free space  65  at the pole body  43 . Due to the thusly formed resilience, the increase in volume that occurs when the urea solution freezes in the fluid chamber  27  can be safely compensated. A diaphragm seal  67 , as an additional sealing element, is located in the free space  65 . 
       FIG. 3  shows a variant in which an additional spring  69  is provided instead of the fixed end stop of the magnet piston  41  formed by the end piece  61  in  FIG. 2 . The additional spring constantly holds the actuating part  39  of the magnet piston  41  against the thrust element  37  of the compression spring  35  in a force-locking manner, but has a weaker spring effect than the return spring  59 . 
       FIG. 4  shows additional details of the filter device  9 , which comprises a filter housing  71  in the form of a circular cylindrical pot having a closed base  73 . The housing  71  is closed at the open end by an end cap  75  of a filter element  77 , which is accommodated in the housing  71 . The filter element  77  comprises a hollow cylindrical filter medium  81 , which surrounds an inner filter cavity  79 . The inner side of said filter medium rests against a support tube  83  and is enclosed on the outer side by a support body  85 . Within the filter housing  71 , the support body  85  delimits a partial volume that delimits the fluid chamber as a partial volume of the housing  71  that is in fluidic connection with the inner filter cavity  79 . The inlet (filter inlet  7  of  FIGS. 2 and 3 ) and the outlet  90  of the fluid chamber of the filter housing  71  are located at the end cap  75  of the filter element  77 . An electric heating rod  87  extends through a central opening  86  of the end cap  75  and into the inner filter cavity  79 . For the purpose of thermal coupling with the heating rod  87 , a metallic filler piece  89  adjoins the heating rod  87  at the end thereof. 
     To allow the partial volume to enlarge relative to the remaining volume in the filter housing  71  when the aqueous urea solution freezes in the partial volume forming the fluid chamber, a casing  91  made of a material having a predefined compressibility is provided as a resilient element between the inner wall of the housing  71  and the outer side of the filter element  77 . In the present exemplary embodiment, a casing  91  made of microcellular rubber is provided for this purpose and, in the example shown, completely surrounds the filter element  77 , proceeding from the end cap  75 . The casing  91  therefore fills all the residual volume within the filter housing  71 . The residual volume decreases relative to the partial volume that forms the fluid chamber when the casing  91  is compressed to allow the partial volume formed by the fluid chamber to safely increase when the urea solution freezes in the fluid chamber. 
       FIG. 5  shows, in an exemplary embodiment of the system according to the invention, the connecting piece  92  comprising the inlet line  3 , which leads to the pump  1 , and the outlet line  23  for the metered delivery of the urea solution. A temperature sensor  93  and a pressure sensor  94  are connected to the outlet line  23 . Each of the  FIGS. 2 to 4  show plug caps  96  on the electric plug connection  95  of the sensors  93 ,  94 , while  FIG. 5  shows a plug cap  96  on only the pressure sensor  94 . Both sensors  93 ,  94  are embodied as screw-in sensors and are screwed into the connecting piece  92  by screw-in threads  97  and  98 . The measurement probe  99  of the temperature sensor  93  thereby extends into the outlet line  23 . A pressure-transferring element, for example, in the form of a diaphragm  88 , is fluidically connected to the outlet line  23  on the side having the pressure sensor  94 . 
     A resilient component is assigned to each sensor  93  and  94  as freeze protection. The resilient component forms a resilient wall part at the fluid region of the respective sensor  93 ,  94 . To this end, in the case of the temperature sensor  93 , a resilient cushion  100 , which is in the form of a cube made of microcellular rubber in the present example, is provided at the part of the outlet line  23  opposite the measurement probe  99 . On the side having the pressure sensor  94 , a cushion  101  in the form of a plate is disposed at a corresponding point of the outlet line  23 . The plate is also made of microcellular rubber and forms a resilient wall part of the outlet line  23  at the inlet region of the sensor  94 . Due to this resilience, the increase in volume that results when the aqueous urea solution freezes in the outlet line  23  can be compensated, thereby preventing damage to the connecting regions of the sensors  93 ,  94 , such as the measurement probe  99  and the screw-in threads  97 ,  98 . 
     Instead of a compressible body, such as the microcellular-rubber cushion, a resilient wall part could be provided at the outlet line  23  or at the sensor  93 ,  94 , such as a component that is supported by a spring element, as shown in  FIGS. 2 and 3 . 
     While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.