Injection system, metering pump, exhaust gas treatment device, method

Abstract

The invention relates to an injection system ( 2 ) for metered injection of a fluid, particularly for an exhaust gas treatment device ( 1 ) in a motor vehicle, said system having: a tank ( 3 ) for storing the fluid; a metering valve ( 19 ); an actuatable venting valve ( 25 ) for admitting gas into or releasing gas from the injection system ( 2 ); and a metering pump ( 7 ) which is connected to the tank ( 3 ) and the metering valve ( 19 ) in order to convey the fluid from the tank ( 3 ) to the metering valve ( 19 ). The metering pump ( 19 ) is designed as a piston pump ( 8 ) and has a piston ( 10 ) axially movable in a cylinder ( 9 ) between an upper and a lower dead centre and forming, together with the cylinder ( 9 ), a pump chamber ( 12 ). Associated with the pump chamber ( 12 ), the cylinder ( 9 ) has a first connection ( 14 ) which is connected to the tank ( 3 ) via a tank line ( 6 ), a second connection ( 17 ) which is connected to the metering valve ( 19 ) via a conveying line ( 18 ), and a third connection ( 23 ) which is connected to the venting valve ( 25 ) via a venting line ( 24 ). The invention further relates to a metering pump and an exhaust gas treatment system. The invention additionally relates to a method for operating a corresponding injection system.

1 . An injection system ( 2 ) for metered injection of a liquid, said system having a tank ( 3 ) for storing the liquid, a metering valve ( 19 ), an actuable ventilation valve ( 25 ) for admitting gas into or releasing gas from the injection system ( 2 ), and a metering pump ( 7 ), which is connected to the tank ( 3 ) and the metering valve ( 19 ) in order to deliver the liquid from the tank ( 3 ) to the metering valve ( 19 ), characterized in that the metering pump ( 19 ) is a piston pump ( 8 ) and has a piston ( 10 ) axially movable in a cylinder ( 9 ) between an upper dead center and a lower dead center and forming, together with the cylinder ( 9 ), a pump chamber ( 12 ), wherein, assigned to the pump chamber ( 12 ), the cylinder ( 9 ) has a first connection ( 14 ), which is connected to the tank ( 3 ) via a tank line ( 6 ), a second connection ( 17 ), which is connected to the metering valve ( 19 ) via a delivery line ( 18 ), and a third connection ( 23 ), which is connected to the ventilation valve ( 25 ) via a ventilation line ( 24 ). 
     
     
         2 . The injection system as claimed in  claim 1 , characterized in that the second connection ( 17 ) is arranged in an end region ( 26 ) of the cylinder ( 9 ) adjacent to the upper dead center. 
     
     
         3 . The injection system as claimed in  claim 1 , characterized in that the third connection ( 23 ) is arranged in an end region ( 26 ) of the cylinder adjacent to the upper dead center. 
     
     
         4 . The injection system as claimed in  claim 1 , characterized in that the first connection ( 14 )—as seen in the direction of motion of the piston ( 10 )—is formed between the third connection ( 23 ) and the lower dead center of the piston ( 10 ) in a circumferential wall ( 13 ) of the cylinder ( 9 ). 
     
     
         5 . The injection system as claimed in  claim 1 , characterized in that the first connection ( 14 ) is arranged on an end face of the cylinder ( 9 ). 
     
     
         6 . The injection system as claimed in  claim 5 , characterized in that the first connection ( 14 ) is assigned an automatic suction valve ( 30 ), which opens during a movement of the piston ( 10 ) in the direction of the lower dead center and closes at least substantially during a movement of the piston ( 10 ) in the direction of the upper dead center. 
     
     
         7 . The injection system as claimed in  claim 6 , characterized in that the suction valve ( 30 ) is a spring-loaded check valve ( 31 ). 
     
     
         8 . The injection system as claimed in  claim 6 , characterized in that the suction valve ( 30 ) is a diaphragm valve ( 43 ). 
     
     
         9 . The injection system as claimed in  claim 6 , characterized in that the suction valve ( 30 ) is a piston valve ( 50 ) with an integrated restrictor ( 53 ). 
     
     
         10 . The injection system as claimed in  claim 1 , characterized in that the ventilation valve ( 25 ) is connected to a gas connection ( 27 ). 
     
     
         11 . The injection system as claimed in  claim 10 , characterized in that at least one hydrophobic diaphragm ( 32 ) is arranged between the ventilation valve ( 25 ) and the gas connection ( 27 ). 
     
     
         12 . The injection system as claimed in  claim 11 , characterized in that the hydrophobic diaphragm ( 32 ) is assigned at least one reservoir ( 33 ,  34 ) for liquid or gaseous medium. 
     
     
         13 . A metering pump ( 7 ) for an injection system ( 2 ), which is a piston pump ( 8 ) and has a piston ( 10 ) axially movable in a cylinder ( 9 ) between an upper dead center and a lower dead center and the piston forming, together with the cylinder ( 9 ), a pump chamber ( 12 ), wherein, assigned to the pump chamber ( 12 ), the cylinder ( 9 ) has a first connection ( 14 ) for a tank line ( 6 ), which is configured to be connected to a tank ( 3 ) of the injection system ( 2 ), a second connection ( 17 ) for a delivery line ( 18 ) connected to a metering valve ( 19 ) of the injection system ( 2 ), and a third connection ( 23 ) for a ventilation line ( 24 ), connected to a ventilation valve ( 25 ), of the injection system ( 2 ). 
     
     
         14 . An exhaust gas treatment system ( 1 ) for a motor vehicle, having an injection system ( 2 ) claimed in  claim 1  for injecting a liquid exhaust gas treatment medium ( 4 ) into the exhaust gas produced by an internal combustion engine. 
     
     
         15 . A method for operating an injection system ( 2 ) for the metered injection of a liquid as claimed in  claim 1 , characterized in that, to switch over from a liquid-delivering normal mode to an ice-pressure-resistant state, the piston ( 10 ) continues to be operated at least substantially as in the normal mode, and the ventilation valve ( 25 ) is opened and closed in such a way, in accordance with the position of the piston ( 10 ), that a gas is introduced into the injection system ( 2 ). 
     
     
         16 . The injection system as claimed in  claim 1 , characterized in that the second connection ( 17 ) is arranged on an end face of the cylinder ( 9 ) adjacent to the upper dead center. 
     
     
         17 . The injection system as claimed in  claim 16 , characterized in that the third connection ( 23 ) is arranged in a circumferential wall ( 13 ) of the cylinder ( 9 ) adjacent to the upper dead center. 
     
     
         18 . The injection system as claimed in  claim 17 , characterized in that the first connection ( 14 )—as seen in the direction of motion of the piston ( 10 )—is formed between the third connection ( 23 ) and the lower dead center of the piston ( 10 ) in the circumferential wall ( 13 ) of the cylinder ( 9 ). 
     
     
         19 . The injection system as claimed in  claim 18 , characterized in that the first connection ( 14 ) is arranged on the end face of the cylinder ( 9 ). 
     
     
         20 . The injection system as claimed in  claim 19 , characterized in that the first connection ( 14 ) is assigned an automatic suction valve ( 30 ), which opens during a movement of the piston ( 10 ) in the direction of the lower dead center and closes at least substantially during a movement of the piston ( 10 ) in the direction of the upper dead center. 
     
     
         21 . The injection system as claimed in  claim 1 , characterized in that the ventilation valve ( 25 ) is connected to a gas connection ( 27 ), which is an ambient air connection, an exhaust pipe connection, being connected to an exhaust pipe ( 20 ) of the motor vehicle, or a ventilation connection, being connected to the tank ( 3 ).