Abstract:
The invention relates to an injection device ( 1 ), designed in particular for injecting fluid into an exhaust tract of an internal combustion engine, having a valve needle ( 14 ), an injection chamber ( 12 ) having at least one injection opening ( 44 ), and a control chamber ( 20 ). The injection device ( 1 ) is designed such that a pressure differential between the injection chamber ( 12 ) and the control chamber ( 20 ) brings about a displacement of the valve needle ( 14 ) between an open position in which a fluid flow through the injection opening ( 44 ) from the injection chamber ( 12 ) is released, and a closed position, in which the injection opening ( 44 ) is closed off. The injection chamber ( 22 ) and the control chamber ( 20 ) are hydraulically connected to an inlet ( 40, 42; 9 ), such that a pressure rise in the inlet ( 40, 42; 9 ) results in a pressure rise in the injection chamber ( 12 ), and a pressure rise in the control chamber ( 20 ) delayed in time relative to the pressure rise in the injection chamber ( 12 ), and said pressure differential brings about a displacement of the valve needle ( 14 ) from the closed position into an open position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The demands placed on the exhaust-gas quality of internal combustion engines, in particular of internal combustion engines for driving motor vehicles, have steadily increased in recent years. In the case of diesel engines in particular, NO x  emissions constitute a problem, which is counteracted by means of so-called SCR catalytic converters. In an SCR catalytic converter, environmentally harmful NO x  is converted with the aid of NH 3 , which is supplied to the catalytic converter generally in the form of an aqueous urea solution, into N 2  and H 2 O. 
         [0002]    To supply the urea solution to the exhaust gases of the internal combustion engine, a dosing system is required, which conventionally comprises an electrically operated pump and an electrically actuated dosing valve. Such dosing systems are cumbersome and expensive to produce, assemble and maintain. 
         [0003]    EP 1 878 920 A1 discloses a liquid pump having an inlet, an outlet, a pump chamber for receiving the liquid, and an actuator which is movable between a first position and a second position and which is designed to pump liquid from the pump chamber into the outlet. The inlet and the outlet are fluidically connected to a supply passage when the actuator is in the first position. The supply passage runs around the actuator in order to permit a transfer of heat from the actuator to the liquid. 
         [0004]    U.S. 2007/0295003 A1 describes a high-pressure dosing pump which is designed to provide a reducing agent to an exhaust-gas reduction system. The high-pressure dosing pump has an electromagnet for driving a piston which is arranged in a movable manner in an inner bore of a valve housing of the pump. The inner bore has a pressure chamber with an inlet one-way valve and with an outlet one-way valve. Movement of the piston causes reducing agent to be supplied at high pressure to an injection nozzle. The injection nozzle is arranged at a location which permits a maximum reduction of undesired pollutants in the exhaust gases. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the invention to provide an improved dosing system which permits an effective injection of fluid and which is inexpensive to produce, assemble and maintain. 
         [0006]    An injection device according to the invention, which is designed in particular for injecting fluid into an exhaust tract of an internal combustion engine, has a valve needle, an injection chamber with at least one injection orifice, and a control chamber. The injection device is designed such that a pressure difference between the injection chamber and the control chamber causes a movement of the valve needle between an open position, in which the valve needle permits a flow of fluid out of the injection chamber through the injection orifice, and a closed position, in which the valve needle closes the injection orifice. The injection chamber and the control chamber are hydraulically connected to a fluid inlet in such a way that a pressure increase in the fluid inlet results in a pressure increase in the injection chamber and, after a time delay in relation to the pressure increase in the injection chamber, a pressure increase in the control chamber. In this way, a pressure difference is temporarily generated between the injection chamber and the control chamber, which pressure difference results in a movement of the valve needle from the closed position into an open position. 
         [0007]    An injection device of said type is of simple and inexpensive construction and operates reliably. Since the opening and closing of the nozzle needle is realized hydraulically by means of a pressure difference between the injection chamber and the control chamber, an injection device of said type makes do without active actuators which act directly on the nozzle needle and which, owing to the high injection pressures, are complex, expensive and susceptible to failure. 
         [0008]    In one embodiment, the control chamber is hydraulically connected via a control chamber inlet throttle to the inlet. By means of such an inlet throttle, the fluid inflow into the control chamber can be regulated. In particular, it is possible for the pressure increase in the control chamber to be delayed by means of a throttled fluid inlet, and for the opening and closing behavior of the nozzle needle to be adjusted through the dimensioning of the control chamber inlet throttle. 
         [0009]    In one embodiment, the control chamber is hydraulically connected via a control chamber outlet throttle to an outlet through which fluid can be discharged from the control chamber. By means of such an outlet throttle, the fluid outflow out of the control chamber can be regulated in a targeted manner. In particular, the opening and closing behavior of the nozzle needle can be adjusted through the dimensioning of the control chamber outlet throttle. 
         [0010]    In one embodiment, an injection chamber outlet duct (bypass duct) having an injection chamber outlet throttle (bypass throttle) is provided and fluid can be discharged from the injection chamber through the injection chamber outlet duct and the injection chamber outlet throttle. By means of an injection chamber outlet duct of said type, the fluid pressure in the injection chamber below the nozzle needle can be quickly depleted, such that high closing speeds can be realized. 
         [0011]    In one embodiment, the inlet is hydraulically connected via a one-way valve to a pressure chamber. The pressure chamber is designed for increasing the pressure of the fluid. The one-way valve prevents a return flow of fluid from the pressure chamber into the inlet. Such a return flow would impair or even prevent an increase of the pressure in the pressure chamber. 
         [0012]    In one embodiment, the volume of the pressure chamber can be varied by movement of a pressure element. The injection pressure can thus be increased beyond the pressure of the fluid in the fluid supply. In particular, the fluid need not be supplied to the injection device at a high (injection) pressure, and it is possible to dispense with an external high-pressure pump and complex, expensive high-pressure lines which are susceptible to failure. 
         [0013]    In one embodiment, the injection chamber outlet duct is hydraulically connected to the pressure chamber. Fluid from the injection chamber can thus be discharged from the injection chamber into the pressure chamber through the injection chamber outlet duct, in particular when the volume of the pressure chamber is increased during a suction process, in order to increase the speed of the closing process. 
         [0014]    In one embodiment, a one-way valve is provided in the injection chamber outlet duct. The one-way valve prevents a fluid flow from the pressure chamber into the injection chamber through the injection chamber outlet duct. Such a fluid flow could uncontrollably influence the opening and closing behavior of the nozzle needle. 
         [0015]    In one embodiment, the pressure element is designed as a diaphragm which delimits the pressure chamber. A diaphragm provides a proven and easily actuable pressure element. The diaphragm may be produced from a material which comprises plastic and/or metal. A diaphragm produced from plastic has a low mass and can be moved quickly with low force. A diaphragm which comprises metal is particularly resistant to high pressures and temperatures of the fluid in the injection device. 
         [0016]    In one embodiment, the injection chamber outlet duct is hydraulically connected to the outlet. Such an injection chamber outlet duct which is connected to an outlet makes it possible for fluid to be discharged from the injection chamber particularly effectively and quickly. 
         [0017]    In one embodiment, an actuable switching valve is formed in the injection chamber outlet duct. By means of an actuable switching valve in the injection chamber outlet duct, the injection chamber outlet duct can be opened and closed in a targeted manner. This permits an effective and simple actuation of the nozzle needle by opening and closing of the switching valve. 
         [0018]    In one embodiment, the control chamber is also hydraulically connected via the controllable switching valve to the outlet. This permits an even more effective actuation of the nozzle needle by opening and closing of the switching valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention will be explained in more detail below on the basis of the appended figures. 
           [0020]      FIG. 1  shows a sectional view of a first exemplary embodiment of an injection device according to the invention. 
           [0021]      FIG. 2  shows a sectional view of a second exemplary embodiment of an injection device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    In the following description of the figures, expressions such as “top” and “bottom” serve for improved explanation of the schematic illustrations of an exemplary embodiment of the invention shown in the respective figure, without restricting the invention to the exemplary embodiment shown or to a certain orientation or installation position. 
         [0023]      FIG. 1  shows a sectional view of a first exemplary embodiment of an injection device  1  according to the invention. 
         [0024]    An injection device  1  according to the invention has a nozzle body  7  which is for example of cylindrical form about a longitudinal axis A and along the longitudinal axis A of which is formed an injection chamber  12 . The injection chamber  12  has a first cylindrical region  12   a  illustrated at the bottom in  FIG. 1  and has a second cylindrical region  12   c  arranged thereabove. 
         [0025]    In a plane which is oriented at right angles to the longitudinal axis A, the first cylindrical region  12   a  has a smaller cross section than the second cylindrical region  12   c.  Between the first and the second cylindrical region  12   a,    12   c  there is formed a frustoconical region  12   b,  the cross section of which widens along the longitudinal axis A from the cross section of the first cylindrical region  12   a  to the cross section of the second cylindrical region  12   c.    
         [0026]    At the face end, illustrated at the bottom in  FIG. 1 , of the first cylindrical region  12   a  of the injection chamber  12 , there is formed an injection orifice  44  through which fluid emerges from the injection chamber  12  during an injection process. 
         [0027]    In the injection chamber  12  there is arranged a nozzle needle  14  which is of substantially cylindrical form and the longitudinal axis of which is oriented along the longitudinal axis A of the nozzle body  7 . The nozzle needle  14  is formed with a lower cylindrical region  14   a  and an upper cylindrical region  14   b,  wherein, in a plane arranged at right angles to the longitudinal axis A of the nozzle needle  14 , the upper cylindrical region  14   b  of the nozzle needle  14  has a larger cross section than the lower cylindrical region  14   a.  Between the lower cylindrical region  14   a  and the upper cylindrical region  14   b  there is formed a frustoconical transition region  14   c,  the cross section of which increases in size in its profile parallel to the longitudinal axis A from the cross section of the lower cylindrical region  14   a  to the cross section of the upper cylindrical region  14   b  of the nozzle needle  14 . 
         [0028]    The nozzle needle  14  is movable along the longitudinal axis A between a lower, closed position and an upper, open position. When the nozzle needle  14  is situated in the lower, closed position, the lower cylindrical region  14   a  of the nozzle needle  14  rests on a valve seat  46  formed above the injection orifice  44  on the nozzle body  7  and closes the valve seat  46  in a substantially fluid-tight manner, such that no fluid can escape from the injection chamber  12  through the injection orifice  44 . 
         [0029]    An upper end  14   d  of the nozzle needle  14  is surrounded by a cylindrical control chamber sleeve  18 . Within the control chamber sleeve  18 , there is formed above the upper end  14   d  of the nozzle needle  14  a control chamber  20 , the volume of which can be varied by movement of the nozzle needle  14  along the longitudinal axis A. Conversely, the nozzle needle  14  can be moved by variation of the pressure difference between the control chamber  20  and the injection chamber  12 . 
         [0030]    On the circumference of the upper cylindrical region  14   b  of the nozzle needle  14 , a support ring  15  is formed below the control chamber sleeve  18 . Between the support ring  15  and the control chamber sleeve  18  there is arranged around the circumference of the nozzle needle  14  a cylindrical nozzle needle spring element  16  which is supported with its face sides against the control chamber sleeve  18  at one side and against the support ring  15  on the other side and which presses the nozzle needle  14  elastically in the direction of the lower, closed position. 
         [0031]    On its upper side which faces away from the nozzle needle  14 , the control chamber  20  is delimited by a throttle plate  6 . Within the throttle plate  6  there are formed a number of fluid ducts  22 ,  24 ,  26 ,  30 . 
         [0032]    Above the throttle plate  6  there is arranged a valve plate  5 . In the valve plate  5  there are formed three one-way valves  32 ,  34 ,  36 , wherein each of the one-way valves  32 ,  34 ,  36  is hydraulically connected to at least one of the fluid ducts  22 ,  24 ,  26 ,  30  formed in the throttle plate  6 . The one-way valves  32 ,  34 ,  36  may be formed for example as check valves. 
         [0033]    Above the valve plate  5  there is arranged a control plate  4  in which a pressure chamber  50  and three fluid ducts  36 ,  40  and  42  are formed. Each of the three fluid ducts  36 ,  40  and  42  connects the pressure chamber  50  hydraulically to in each case one of the one-way valves  32 ,  34 ,  36  formed in the valve plate  5 . 
         [0034]    In particular, the pressure chamber  50  is hydraulically connected via an inlet duct  42  and an inlet valve  36  to a fluid inlet  9  through which fluid can be supplied to the injection device  1  from an external fluid source. The inlet valve  36  is formed as a one-way valve such that it permits a fluid flow from the fluid inlet  9  into the pressure chamber  50  and prevents a return flow of fluid from the pressure chamber  50  into the fluid inlet  9 . 
         [0035]    The pressure chamber  50  is hydraulically connected to the control chamber  20  via a pressure duct  40  formed in the valve plate  4 , via a pressure valve  34  formed in the valve plate  5 , and via a control chamber duct  24  which is formed in the throttle plate  6  and in which a control chamber throttle  25  is provided. Furthermore, an injection chamber duct  22  which is formed in the throttle plate  4  hydraulically connects the pressure valve  34  to the injection chamber  12 . The pressure valve  34  is formed as a one-way valve such that it permits a fluid flow from the pressure chamber  50  into the control chamber  20  and into the injection chamber  12  and prevents a fluid flow from the control chamber  20  and/or from the injection chamber  12  into the pressure chamber  50 . 
         [0036]    The injection chamber  12  is additionally hydraulically connected to the pressure chamber  50  by an injection chamber outlet duct (bypass duct)  30 , which is formed in the throttle plate  6  and which has an injection chamber outlet throttle (bypass throttle)  31 , and by an injection chamber outlet valve (bypass valve)  32  formed in the valve plate  5 . The injection chamber outlet valve  32  is formed as a one-way valve such that it permits a fluid flow from the injection chamber  12  into the pressure chamber  50  and prevents a fluid flow in the opposite direction, that is to say from the pressure chamber  50  into the injection chamber  12 . 
         [0037]    A side, which faces away from the control plate  4 , of the pressure chamber  50  is delimited by an elastic diaphragm  2 . The elastic diaphragm  2  is arranged above the valve plate  5  so as to span a plane arranged substantially at right angles to the longitudinal axis A. A central region  2   a  of the diaphragm  2 , which is formed around the longitudinal axis A, is connected to an armature  10  arranged on that side of the diaphragm  2  which faces away from the control plate  4 . 
         [0038]    Around an upper region, which faces away from the diaphragm  2 , of the armature  10  there is arranged an electromagnet  11  which is spaced apart from the elastic diaphragm  2  in a direction parallel to the longitudinal axis A by a spacer  3 . The armature  10  can be moved in a direction parallel to the longitudinal axis A by activation or deactivation of the electromagnet  11 . By means of such a movement of the armature  10 , the elastic diaphragm  2  is moved such that the volume of the pressure chamber  50  is varied. 
         [0039]    The electromagnet  11 , the spacer  3 , the armature  10  and the diaphragm  2  are surrounded, in the circumferential direction and on the side facing away from the nozzle needle  4 , by a cup-shaped nozzle clamping nut  8  which is open in the downward direction. The nozzle body  7  is inserted into the open side of the nozzle clamping nut  8  and screwed together with the nozzle clamping nut  8  in such a way that the injection device  1  is closed in a fluid-tight manner. 
         [0040]    For the suction of fluid into the pressure chamber  50 , the electromagnet  11  is deactivated. The elastic diaphragm  2 , which is deformed when the electromagnet  11  is activated, moves into its starting and suction position owing to its inherent elasticity. Fluid from a fluid inlet  9  which is hydraulically connected to the inlet valve  36  formed in the valve plate  5  flows into the pressure chamber  50  through the inlet valve  36 , which opens for a fluid flow in this direction, and through an inlet duct  42  formed in the control plate  4 . 
         [0041]    As long as the pressure in the pressure chamber  50  is not higher than the pressure in the injection chamber  12  or in the control chamber  20 , the injection chamber outlet valve  32  and the pressure valve  34  are closed. The injection chamber outlet valve  32  and the pressure valve  34  thereby prevent fluid from flowing out of the injection chamber  12  and/or out of the control chamber  20  into the pressure chamber  50 . 
         [0042]    To initiate an injection process, the electromagnet  11  is activated (energized) such that the magnetic force generated by the electromagnet  11  moves the armature  10 , and with it the central region  2   a  of the elastic diaphragm  2 , “downward” in the direction of the control plate  4 . The elastic diaphragm  2  reduces the volume of the pressure chamber  50 , and the pressure in the pressure chamber  50  increases. 
         [0043]    As a result of the increased pressure in the pressure chamber  50 , the pressure valve  34  opens and fluid flows from the pressure chamber  50  into the injection chamber  12  through the open pressure valve  34  and through an inlet duct  22  formed in the throttle plate  6 . 
         [0044]    At the same time, fluid flows from the pressure chamber  50  into the control chamber  20  through the open pressure valve  34  and through a control chamber duct  24  formed in the throttle plate  6 . 
         [0045]    In the control chamber duct  24  there is formed a control chamber throttle  25 , whereby the fluid flow from the pressure chamber  50  into the control chamber  20  is throttled, and the pressure increase caused in the control chamber  20  by the fluid flow is delayed in terms of time in relation to the pressure increase in the injection chamber  12  caused by said fluid flow from the pressure chamber  50  into the injection chamber  12 . 
         [0046]    As a result of the fluid pressure which increases more quickly in the injection chamber  12  than in the control chamber  20 , an upwardly directed force is exerted on the nozzle needle  14 , which force moves the nozzle needle  14  from the closed position into an open position counter to the force of the nozzle needle spring  16  and counter to the pressure in the control chamber  20 , which has not increased to as great an extent owing to the control chamber throttle  25 . The lower region  14   a  of the nozzle needle  14  lifts from the valve seat  46  and fluid escapes from the injection chamber  12  through the injection orifice  44  (injection process). 
         [0047]    Fluid which is displaced out of the control chamber  20  by the opening movement of the nozzle needle  14  escapes from the control chamber  20  through an outlet duct  26 , which is formed in the throttle plate  6  and in which is provided an outlet throttle  28 , and through an outlet not visible in  FIG. 1 . 
         [0048]    Fluid at elevated pressure flows out of the injection chamber  12  through the open injection orifice  44  until, owing to the fluid escaping from the injection chamber  12 , the fluid pressure in the injection chamber  12  has fallen to such an extent that it is no longer sufficient to hold the nozzle needle  14  in an open position counter to the combination of the fluid pressure in the control chamber  20  and the force of the nozzle needle spring element  16 . The nozzle needle  14  is pushed by the fluid pressure in the control chamber  20  and by the force of the nozzle needle spring element  16  into the lower closed position again, in which the lower region  14   a  of the nozzle needle  14  rests on the valve seat  46  and closes the injection orifice  44 . 
         [0049]    The electromagnet  11  is deactivated and the diaphragm  2  moves into its starting and suction position again. The volume of the pressure chamber  50  is increased and the pressure in the pressure chamber  50  reduced, such that, by means of an additional fluid flow from the injection chamber  12  through the injection chamber outlet duct  30  into the pressure chamber  50 , the pressure in the injection chamber  12  can be depleted more quickly in order to increase the speed of the closing process of the nozzle needle  14 . 
         [0050]    The injection chamber outlet duct  30 , the injection chamber outlet throttle  31  and the injection chamber outlet valve  32  are optional for accelerating the closing process. The opening and closing behavior of the nozzle needle  14  and in particular the opening and closing speed can be adjusted in a targeted manner through the dimensioning of the control chamber throttle  25 , the outlet throttle  28  and if appropriate the injection chamber outlet throttle  31 . 
         [0051]      FIG. 2  shows a second exemplary embodiment of an injection device  51  according to the invention. 
         [0052]    The nozzle body  7  with the injection chamber  12  and with the nozzle needle  14  and also the throttle plate  6  of the second exemplary embodiment are of exactly the same design as in the first exemplary embodiment shown in  FIG. 1 , and therefore will not be described again in detail. 
         [0053]    The pressure-generating part of the injection device  51 , which generates the desired injection pressure, of the second exemplary embodiment is not shown in the detail shown in  FIG. 2 . 
         [0054]    To initiate an injection process, fluid at injection pressure is conducted into the inlet  9  which is formed in the valve plate  5  and in which, in this exemplary embodiment, no one-way valve is provided. As in the first exemplary embodiment, the fluid flows into the injection chamber  12  through the inlet duct  22  formed in the throttle plate  6 , and into the control chamber  20  through the control chamber duct  24  and the control chamber throttle  25 . 
         [0055]    The control chamber  20  is connected via a control chamber outlet duct  26 , in which a control chamber outlet throttle  28  is provided, to a valve chamber of a switching valve  52  formed in the valve plate  5 . The injection chamber  12  is hydraulically connected via an injection chamber outlet duct  30 , in which an injection chamber outlet throttle  31  is formed, to the valve chamber of the switching valve  52 . The switching valve  52  issues at the outflow side into an outlet (not shown) which is designed to discharge fluid from the injection device  51 . 
         [0056]    The switching valve  52  has a movable closing body  54  which, in the rest state, is pushed into an upper, closed position, in which it prevents a fluid flow from the valve chamber into the outlet, by a switching valve spring element  56  which surrounds the closing body  54 . 
         [0057]    By contrast to the valves  32 ,  34 ,  36  of the first exemplary embodiment, the switching valve  52  is not a passive one-way valve controlled by the fluid flow or by a difference in fluid pressure. Instead, the closure body  54  of the switching valve  52  is mechanically connected to an actuator  58  which is arranged above the valve plate  5  and which is designed for example as an electromagnetic or piezo actuator. By activation of the actuator  58 , the closure body  54  can be moved counter to the force of the switching valve spring element  56  into an open position in which it permits a fluid flow through the switching valve  52 . When the switching valve  52  is open, fluid can flow out of the control chamber  20  through the outlet duct  26  and the outlet throttle  28 , and out of the injection chamber  12  through the injection chamber outlet duct  30  and the injection chamber outlet throttle  31 , into the outlet (not shown in  FIG. 2 ) arranged downstream of the switching valve  52 . 
         [0058]    To initiate an injection process, fluid at injection pressure is supplied to the inlet  25  of the injection device  51  when the switching valve  52  is closed. As in the first exemplary embodiment, the control chamber throttle  25  formed in the control chamber duct  24  has the effect that the supplied fluid flows more quickly into the injection chamber  12  than into the control chamber  20 , and the pressure increases more quickly in the injection chamber  12  than in the control chamber  20 . When the pressure difference between the injection chamber  12  and the control chamber  20  exceeds a predefined critical value, the nozzle needle  14  moves from the closed position into an open position and opens up the injection orifice  44 , such that fluid flows out of the injection chamber  12  through the injection orifice  44  (injection process). 
         [0059]    To end the injection process, the actuator  58  is actuated such that it opens the switching valve  52  and fluid flows out of the injection chamber  12  through the injection chamber outlet duct  30  and the injection chamber outlet throttle  31  and out of the control chamber  20  through the control chamber outlet duct  26  and the control chamber outlet throttle  28 . The injection chamber outlet throttle  31  and the control chamber outlet throttle  28  are dimensioned here such that the pressure falls more quickly in the injection chamber  12  than in the control chamber  20 . The pressure in the control chamber  20  is thus temporarily higher than the pressure in the injection chamber  12 . As a result of said pressure difference between the control chamber  20  and the injection chamber  12 , the nozzle needle  14  is pushed, in interaction with the nozzle needle spring element  16 , into the closed position in which the nozzle needle  14  closes the injection orifice  44 , and the injection process is ended. 
         [0060]    The components of an injection device  1 ,  51  according to the invention, and in particular the diaphragm  2  and the valves  32 ,  34 ,  36 ,  52 , can be produced inexpensively and in a weight-saving manner from plastic. In the case of elevated demands being placed on pressure resistance and temperature resistance, metal parts may also be used. In particular, as valves, use may be made of metal valves such as are known from common rail fuel injectors.