Method for operating a delivery device for a reducing agent and delivery device for a reducing agent

1. A method for delivering a reducing agent from a reducing agent tank into an exhaust-gas treatment device of an internal combustion engine of a motor vehicle, the method comprising the following steps:

at least intermittently ventilating a delivery device during operation of the internal combustion engine to carry air bubbles and gas bubbles out of the delivery device by using a controller to:

a) perform a ventilation of the delivery device at a present point in time by operating a delivery pump to deliver reducing agent to and circulate reducing agent in the delivery device and registering the ventilation;

b) activate a timer for a predefined preset time interval after the present point in time independently of any pressure measurement carried out in the delivery device;

c) determine whether a special event takes place, and prevent an ensuing ventilation of the delivery device until the predefined preset time interval has elapsed or until it is determined that the special event has taken place, said special event comprising one or more of the following:

an occurrence of a predetermined driving state of the motor vehicle;

an occurrence of at least one of a predetermined fill level or a predetermined fill level change in the reducing agent tank;

a start of operation of the internal combustion engine;

an exchange of a filter or of another component of the delivery device; or

a thawing of frozen reducing agent in at least one of the reducing agent tank or the delivery device; and

d) return to step a).

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

providing the delivery device with a delivery line running from the reducing agent tank to the exhaust-gas treatment device;

providing a return line branching off from the delivery line and opening in the reducing agent tank; and

during the ventilation of the delivery device, further using the controller to operate the delivery pump to circulate reducing agent through the delivery line and the return line.

3. The method according to claim 1 , wherein the predefined preset time interval is varied as a function of at least one of the following parameters:

fill level in the reducing agent tank;

temperature of the reducing agent;

mass flow per unit time of reducing agent supplied to the exhaust-gas treatment device;

speed of the motor vehicle;

rotational speed of the internal combustion engine of the motor vehicle; or

outside temperature.

4. The method according to claim 2 , which further comprises carrying out step b) by activating the timer with the preset time interval, and only counting phases during the operation of the internal combustion engine towards the time interval.

5. The method according to claim 3 , which further comprises carrying out step b) by activating the timer with the preset time interval, and only counting phases during the operation of the internal combustion engine towards the time interval.

6. The method according to claim 2 , which further comprises carrying out step b) by activating the timer with the preset time interval, and setting the time interval to last at least 5 min [minutes] and at most 2 hours.

7. The method according to claim 3 , which further comprises carrying out step b) by activating the timer with the preset time interval, and setting the time interval to last at least 5 min [minutes] and at most 2 hours.

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

providing the exhaust-gas treatment device with a storage capacity for reducing agent; and

delivering an increased quantity of reducing agent, before the ventilation, to fill the storage capacity with reducing agent.

9. The method according to claim 1 , which further comprises interrupting a delivery of reducing agent while a ventilation process of the delivery device is taking place.