Method for operating a delivery device for a reducing agent and motor vehicle having a delivery device

1. A method for operating a delivery device for a reducing agent, the method comprising the following steps:

providing the delivery device with a tank for a liquid reducing agent, an injector for supplying the liquid reducing agent to an exhaust gas treatment device of an internal combustion engine, and a reducing agent line running from the tank to the injector and having at least one pump for delivering reducing agent in a delivery direction from the tank to the injector and at least one pressure sensor;

a) determining and providing an adequate and achievable supply pressure for the injector in the delivery device with the pump;

b) calculating an injector opening time from a defined injection quantity and the achievable supply pressure;

c) opening the injector for the calculated injector opening time; and

carrying out, at a predefined point in time, an air removal procedure including at least the following steps:

i) determining an actual slope of a pressure/delivery volume characteristic in the delivery device;

ii) calculating an air bubble volume by comparing the determined slope to a target slope; and

iii) delivering a delivery volume through the injector if the air bubble volume calculated in step ii) is greater than a maximum permissible air bubble volume.

2. The method according to claim 1 , which further comprises:

operating the at least one pump in a pulsed manner; and

detecting an air bubble in the at least one pump in step a) by using the at least one pressure sensor to detect and evaluate at least one pressure signal to be associated with a single pump stroke.

3. The method according to claim 1 , which further comprises repeating steps b) and c) more frequently than step a).

4. The method according to claim 1 , which further comprises:

operating the at least one pump in a pulsed manner; and

at least in step iii), operating the at least one pump with a maximum delivery stroke or at a reduced frequency relative to a regular operation.

5. The method according to claim 1 , which further comprises repeating steps i) to ii) several times in succession as part of the air removal procedure until the slope determined in step i) and a theoretical slope are approximately equal.

6. The method according to claim 1 , which further comprises setting the delivery volume delivered in step iii) to be less than the air bubble volume calculated in step ii).

7. The method according to claim 1 , which further comprises carrying out the air removal procedure using steps i) to iii) if at least one of the following states was present immediately prior to carrying out the air removal procedure:

initial startup of the delivery device;

filling of the tank of the delivery device;

a motor vehicle traveling at an oblique angle with a filling level in the tank below a threshold value;

changing of a reducing agent filter in the delivery device; and

restarting after a freezing process.

8. A motor vehicle, comprising:

an internal combustion engine;

an exhaust gas treatment device associated with said internal combustion engine;

a reducing agent delivery device configured to supply reducing agent to said exhaust gas treatment device; and

a controller connected to said delivery device and configured to carry out the method according to claim 1 .