Delivery unit for a liquid additive, method for operating a delivery unit and motor vehicle having a delivery unit

1. A delivery unit for a liquid additive, the delivery unit comprising:

first, second and third line systems;

a first pump with a first suction port and a first pressure port;

a second pump with a second suction port and a second pressure port;

a feed device connected through said first line system to said first pressure port, said first line system connected through said second suction port to said second pump;

a tank for the liquid additive;

said first suction port connected through said second line system to said tank;

said second pressure port connected through said third line system to said tank; and

said second line system and said third line system being separated from one another, said first pump having a first electric drive and said second pump having a second electric drive.

2. The delivery unit according to claim 1 , which further comprises a filter separating said second line system from said tank.

3. The delivery unit according to claim 1 , which further comprises a pulsation damper provided for at least said first line system.

4. The delivery unit according to claim 1 , wherein said second line system and said third line system each have a hose line connected to said tank.

5. The delivery unit according to claim 1 , wherein said second pump is connected between said first line system and said third line system.

6. The delivery unit according to claim 1 , wherein said second pump is constructed to act as a valve.

7. The delivery unit according to claim 6 , wherein said second pump separates said first line system and said third line system from one another in a direction from said second suction port to said second pressure port when said second pump is deactivated.

8. A method for operating a delivery unit, the method comprising the following steps:

providing a delivery unit according to claim 1 ;

a) simultaneously operating said first pump and said second pump to purge said first line system, said second line system and said third line system;

b) deactivating said second pump to end said purging step; and

c) operating said first pump to dose liquid additive through said feed device.

9. The method according to claim 8 , which further comprises dosing liquid additive through the feed device during step a).

10. A motor vehicle, comprising:

an internal combustion engine;

an exhaust-gas treatment device configured to purify exhaust gases of said internal combustion engine;

a delivery unit according to claim 1 ; and

a feed device disposed at said exhaust-gas treatment device, connected to said delivery unit and configured to dose liquid additive from said delivery unit into said exhaust-gas treatment device.

11. A delivery unit for a liquid additive, the delivery unit comprising:

first, second and third line systems;

a first pump with a first suction port and a first pressure port;

a second pump with a second suction port and a second pressure port;

a feed device connected through said first line system to said first pressure port, said first line system connected through said second suction port to said second pump;

a pulsation damper provided for at least said first line system, said pulsation damper being provided directly upstream of said feed device;

a tank for the liquid additive;

said first suction port connected through said second line system to said tank;

said second pressure port connected through said third line system to said tank; and

said second line system and said third line system being separated from one another, said first pump having a first electric drive and said second pump having a second electric drive.

12. The delivery unit according to claim 11 , wherein said second pump is connected between said first line system and said third line system.