Abstract:
The invention relates to a device for injecting a fluid ( 2 ), in particular into the exhaust-gas section of an internal combustion engine, having a reservoir ( 4 ) for storing the fluid ( 2 ) to be injected; an injection and metering module ( 10 ); a pump ( 8 ) which is configured for conveying fluid ( 2 ) during operation out of the reservoir ( 4 ) to the injection and metering module ( 10 ); and a return line ( 16 ) which makes an outflow of fluid ( 2 ) out of the injection and metering module ( 10 ) possible, wherein a switchable throttling valve ( 14 ) which is suitable for pumping fluid out of the injection and metering module ( 10 ) is arranged in the return line ( 16 ).

Description:
BACKGROUND OF INVENTION 
     The invention relates to a multifunctional device for injecting a fluid, in particular into the exhaust tract of an internal combustion engine. 
     It is known to inject aqueous urea solution (AdBlue®) into the exhaust tract of internal combustion engines, in particular diesel engines, in order to reduce the nitrogen oxides contained in the exhaust gases. If a delivery module provided for injecting the aqueous urea solution into the exhaust tract has a pump with a non-volumetric delivery action, a return line is required in order for excess amounts of urea solution delivered by the pump to be delivered from the pressure side of the pump back to the suction side, and for the injection pressure to be kept constant. A variable throttle is preferably provided in the return line such that the injection pressure can be adjusted by variation of the throttle cross section. 
     To remove air (bubbles) from the delivery module, it is necessary for the return line to be fully closed. 
     To make the delivery module resistant to ice pressure, it is known for a small amount of air to be sucked in through the injection opening in a pulsed manner, and for an air-filled compensation volume for the aqueous urea solution to thus be created in the delivery module. To trigger such a pulsed sucking-in process, the cross section of the controllable throttle which is arranged in the return line is enlarged very quickly (for example within approximately 40 ms) by a factor of more than 100. 
     The three described functions (pressure regulation, venting of the delivery module and sucking-in of air in order to improve resistance to ice pressure) may be realized by means of a 2/3 directional valve that has two ports and the stated three functions. 
     In addition to the stated three functions, there is often a requirement for the injection system to be fully evacuated. For this purpose, use is conventionally made of the pump that is provided for the injection of the fluid during normal operation. For this purpose, by means of an additional 4/2 directional valve, the pump is switched such that the inlet and outlet of said pump are interchanged, and the urea solution is sucked out of the delivery module, and delivered back into the tank, by operation of the pump. 
     In an injection system of said type, two switchable valves, a 2/3 directional valve and a 4/2 directional valve, are required in order to realize the desired four functions. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an injection system which is of simple construction and by means of which the stated functions, including a complete evacuation of the system, can be realized. 
     A device according to the invention for injecting a fluid, in particular into the exhaust tract of an internal combustion engine, has a reservoir for storing the fluid to be injected, has an injection and dosing module designed to inject the fluid into the exhaust tract, and has a pump designed such that, during operation, it delivers fluid from the reservoir to the injection and dosing module. A return line is also provided through which excess fluid can be discharged from the injection and dosing module. In the return line there is arranged a switchable throttle valve which can be operated in a pumping mode in which the throttle valve acts as a pump and pumps fluid out of the injection and dosing module. 
     By virtue of the fact that, according to the invention, the throttle valve is suitable for pumping fluid out of the injection and dosing module, it is possible to dispense with an additional switchable valve that switches the pump between an injection mode for injecting the fluid into the exhaust tract and a suction mode for sucking the fluid out of the injection and dosing module. A device according to the invention can therefore be realized more easily and at lower cost than the injection devices known from the prior art. 
     In one embodiment, the throttle valve can be switched into further operating states in which the throttle valve is selectively fully closed, fully open or partially open. By means of a switchable throttle valve of said type, alternatively to the pumping-out of the fluid (pumping mode), the injection pressure in the injection and dosing module can be controlled and/or regulated (throttle valve partially open), the injection and dosing module can be vented (throttle valve fully closed), and/or air can be sucked into the injection and dosing module in pulsed fashion (throttle valve fully open) in order to increase the resistance thereof to ice pressure. By means of a throttle valve of said type, all of the functions required during operation can be realized by means of a single valve. In particular, it is possible to dispense with a second valve for switching the delivery direction of the pump. 
     In one embodiment, the throttle valve has a throttle chamber with at least one first port and at least one second port, wherein a movable throttle element is arranged in the throttle chamber. The throttle valve can be closed and fully or partially opened by movement of the throttle element in the throttle chamber. In particular, by means of a dosed movement of the throttle element, the opening cross section of the throttle valve can be variably adjusted in order to set the injection pressure to a desired value. 
     In one embodiment, the throttle valve has in each case one check valve in the first port and in the second port respectively into and out of the throttle chamber, which check valve defines the possible flow direction in the first port and in the second port respectively and prevents a fluid flow counter to the defined delivery direction. Check valves arranged in the first port and in the second port make it possible for the throttle valve to be operated as a pump by means of a continuous oscillating movement of the throttle element, and thus for the function of pumping fluid out of the injection and dosing module to be realized by means of the throttle valve, without an external pump being used for this purpose. In this case, the throttle element performs the function of a pump piston. 
     In one embodiment, the throttle chamber is delimited, and closed off in a fluid-tight manner, on at least one side by a flexible diaphragm. A flexible diaphragm makes it possible for the throttle chamber to be reliably sealed off, and for leaks through which fluid could escape from the throttle chamber to be eliminated. Owing to the flexibility of the diaphragm, it is possible for the volume of the throttle chamber to be varied by movement of the diaphragm. 
     In one embodiment, at least one spring element is provided which is designed to push the throttle element into its closed position in which no fluid flow through the throttle valve is possible. By means of a spring element of said type, the throttle valve is reliably closed when it is not actuated. 
     In one embodiment, a drive, which is for example in the form of a linear magnet drive, is provided for moving the throttle element from its closed position into an open position during operation. By means of dosed actuation of the drive, the throttle element can be moved into a desired open position in a precise manner. This makes it possible to set a desired opening cross section at the throttle valve in order to realize a predefined injection pressure. 
     The invention also encompasses a method for operating a device according to the invention, wherein the method includes pumping fluid out of the injection and delivery module by means of suitable actuation of the throttle valve. The injection and delivery module can thus be fully evacuated without an external pump and without an additional valve for switching the pumping direction of the injection pump. 
     In one embodiment, the method according to the invention additionally includes adjusting the pressure in the injection and dosing module by partially opening the throttle valve in a controlled manner. The injection pressure can thus also then be set to a desired value in a precise manner if the injection and delivery pump is not a pump with a volumetric delivery action. 
     One embodiment of the method includes sucking air into the injection and dosing module by deactivating the pump and fully opening the throttle valve, in order to create an air volume in the injection and dosing module and thus increase the resistance of the injection and dosing module to ice pressure. 
     One embodiment of the method additionally includes fully closing the throttle valve in order to vent the injection and dosing module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below on the basis of the appended figures, in which: 
         FIG. 1  shows a schematic block diagram of a conventional injection device; 
         FIG. 2  shows a schematic block diagram of an injection device according to the invention; and 
         FIG. 3  shows a schematic sectional view through a 2/4 directional throttle valve according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic block diagram of a conventional device for injecting a fluid  2 . 
     The device has a reservoir  4  in which the fluid  2  to be injected is stored. The fluid  2  to be injected is extracted from the reservoir  4  via a fluid extraction line  5  in which a filter  6  is arranged, and said fluid is supplied to the inlet of a pump  8  through a 4/2 directional switching valve  12  which, during normal operation, is switched into a first position  12   a . The pump pressurizes the fluid  2  and conducts the fluid  2  to be injected at elevated pressure through a second duct of the 4/2 directional switching valve  12  to the injection and dosing module  10 , the latter being arranged on an exhaust tract (not shown) and being designed to inject the fluid supplied to it into the exhaust tract. The pressure of the fluid can be continuously measured and monitored by means of a pressure sensor  18  arranged in or on the supply line  13 . 
     Also connected to the injection and dosing module  10  is a return line  16  which makes it possible for fluid to be conducted from the injection and dosing module  10  back to the inlet side of the pump  8  and/or into the reservoir  4 . In the return line  16  there is arranged a 2/3 directional throttle valve  14  which can be switched between the following three states:  14   a —shutting-off of the return line,  14   b —dosing function for setting a desired setting pressure, and  14   c —complete opening for pulsed suction of air. One of the three operating states can selectively be set by switching the throttle valve  14  in the return line  16 . In the dosing function  14   b , the opening cross section of the throttle valve  14  can be varied in order to set a desired injection pressure. 
     In order to pump fluid out of the injection and dosing module  10  when required, the 4/2 directional switching valve  12  is switched into the second operating state  12   b , in which the injection and dosing module  10  is connected to the inlet of the pump  8  and the filter  6  is connected to the outlet of the pump  8  such that, by operation of the pump  8 , fluid is sucked out of the injection and dosing module  10  and pumped back into the reservoir  4  through the filter  6 . 
     In the case of a device of said type, in addition to the throttle valve  14 , a second switchable valve  12  is required in order to enable fluid to be pumped out of the injection and dosing module  10 . 
       FIG. 2  shows a schematic block diagram of an exemplary embodiment of an injection device according to the invention. 
     Those constituent parts of the injection device which correspond to the constituent parts of a conventional injection device such as is shown in  FIG. 1  are denoted by the same reference signs and will not be described in detail again. Instead, reference is made to the description of  FIG. 1 . 
     An injection device according to the invention does not have a 4/2 directional switching valve  12  in order to connect the inlet and the outlet of the pump  8  selectively to the filter  6  or to the injection and dosing module  10 . Instead, the inlet of the pump  8  (suction line) is connected permanently, that is to say without an interposed (switching) valve, to the filter  6 , and the outlet of the pump  8  (pressure line) is connected permanently to the injection and dosing module  10 . 
     An injection device according to the invention has a modified throttle valve  14  which is in the form of a 2/4 directional throttle valve  4  with two ports and four functions. In addition to the three functions of a conventional throttle valve  14 , such as have been described in conjunction with  FIG. 1 , a 2/4 directional throttle valve  14  according to the invention can be switched into a pumping mode  14   d . In the pumping mode  14   d , it is made possible for fluid to be pumped out of the injection and dosing module  10  to the inlet of the pump  8 , or back into the reservoir  4  through the filter  6 . 
       FIG. 3  shows a sectional view of a 2/4 directional throttle valve  14  according to the invention. 
     The throttle valve  14  has a valve plate  22  in which, as shown in  FIG. 2 , there are formed a valve chamber  28 , a first port  24  which in the assembled state is connected to the injection and dosing module  10 , and a second port  26  which in the assembled state is connected to the inlet of the pump  8  and to the filter  6 . 
     In the valve chamber  28  there is arranged a valve body  32  which is movable along an axis A. The point at which the first port  24  issues into the valve chamber  28  can be selectively opened and closed by movement of the valve body  32 . In particular, the cross section of the opening and thus the throttling action of the throttle valve  14  can be variably adjusted by movement of the valve body  32  between a fully open state and a fully closed state. 
     The valve body  32  is mechanically connected to a slide  34  such that, by movement of the slide  34 , the valve body  32  can be moved parallel to the axis A between the closed position and an open position. The slide  34  is guided to the outside through a flexible diaphragm  37  by means of which one side of the valve chamber  28  is delimited and closed off in a fluid-tight manner, and said slide can be driven by an external drive  38 , which is for example in the form of a linear magnet drive. 
     In the rest state, that is to say when the drive  38  is deactivated, spring elements  30 ,  36  which are arranged in the form of spiral springs around the valve element  32  and the slide  34  and which are supported on these push the valve element  32  and the slide  34  respectively into the closed position, in which the first port  24  into the throttle chamber  28  is closed off in a fluid-tight manner by the valve element  32 . 
     A projection  35  formed on the slide  34  interacts with the flexible diaphragm  37  that delimits at least one side of the valve chamber  28 , such that, when the slide  34  is moved from the closed position into an open position (from bottom to top in the illustration of  FIG. 3 ), the diaphragm  37  is turned out toward the outer side situated opposite the valve chamber  28 . As a result of the flexible diaphragm  37  being turned out, the volume of the valve chamber  28  is enlarged, and the pressure in the valve chamber  28  is reduced. 
     In the first port  24  into the valve chamber  28 , there is arranged a first check valve  40  which permits a fluid flow from the first port  24  into the valve chamber  28  and prevents a return flow of fluid from the valve chamber  28  into the first port  24 . 
     Likewise, in the second port  26  out of the valve chamber  28 , there is provided a second check valve  42  which permits a fluid flow out of the valve chamber  28  into the second port  26  and prevents a fluid flow from the second port  26  into the valve chamber  28 . 
     When the drive  38  is deactivated, the valve body  32  and the slide  34  are pushed by the spring elements  30 ,  36  (downward) into the closed position in which the throttle valve  14  is fully closed, for example in order to enable the injection device to be fully vented. 
     Activation of the drive  38  causes the slide  34  and the valve element  32  to be moved (upward) into an open position. Abrupt complete opening of the throttle valve  14  with a fast movement of the valve body  32  into the fully open position causes air to be sucked into the injection and dosing module  10  in a pulsed manner, whereby there is created in the latter an elastic air volume which can receive the additional volume of freezing fluid and which thereby increases the resistance of the injection and dosing module  10  to ice pressure. 
     The throttle function of the throttle valve  14  can be realized by means of an incomplete opening of the throttle valve  14 . Precise actuation of the throttle valve  14  in an incompletely opened state makes it possible to set a desired injection pressure in the injection and dosing module  10 . 
     The pump function according to the invention of the throttle valve  14  can be realized by periodic movement of the slide  34 . If the slide  34  is moved (upward) in the direction of the drive  38  by actuation of the drive  38 , not only is the valve body  32  moved into an open position, but it is also the case that the flexible diaphragm  37  is turned outward and the volume of the valve chamber  28  is enlarged. 
     Owing to the pressure drop in the valve chamber  28  caused by the enlargement of the volume of the valve chamber  28 , fluid  2  flows out of the first port  24  into the valve chamber  28  through the check valve  40  which opens in said flow direction. After the valve chamber  28  has been filled with fluid in this way, the slide  34  is, by corresponding actuation of the drive  38  or after the deactivation of the drive  38 , moved in the opposite direction (downward) by the force of the spring elements  30 ,  36 . In this case, the elastic diaphragm  37  that is connected to the slide  34  is also moved downward in the direction of the valve plate  22  and, in so doing, reduces the volume of the valve chamber  28 . The reduction of the volume of the valve chamber  28  causes the pressure in the valve chamber  28  to be increased, and the fluid flows out of the valve chamber  28  into the second port  26  through the second check valve  42  arranged in the second port  26 , and flows from there to the inlet side of the pump or back into the fluid reservoir  4  (see  FIG. 2 ). 
     By virtue of the slide  34  being periodically driven in an oscillating movement, it is thus possible to realize a pumping function, and fluid can be pumped out of the first port  24  into the second port  26  through the pump chamber  28 . The two check valves  40 ,  42  are preferably designed such that they can be opened with the least possible force or least possible fluid pressure, in order that they constitute a negligible resistance during the “pulsed back-suction” function, in which fast opening of the valves is of importance. 
     Owing to the flexible diaphragm  37 , the volume of the valve chamber  28  is variable. In particular, the volume of the valve chamber  28  can increase, by expansion of the diaphragm  37 , if the fluid in the pump chamber  28  freezes. The invention thus provides an injection device with a throttle valve  14  which is resistant to ice pressure. 
     The expansion according to the invention of the controllable throttle valve  14  from a 2/3 directional throttle valve  14  to a 2/4 directional throttle valve  14  with additional pumping function reduces considerably the outlay and the costs for an injection device which permits a suction of fluid out of the injection and dosing module  10 .