Method for operating an exhaust-gas treatment device having a heater and motor vehicle having the device

1. A method for operating an exhaust-gas treatment device, the method comprising the following steps:

providing an electric heater for heating at least one exhaust-gas stream or a surface in the exhaust-gas treatment device;

providing a controller for activating and deactivating the electric heater;

providing a feed point for feeding an additive into the exhaust-gas treatment device causing the additive to impinge on the electric heater;

a) feeding the additive at the feed point;

b) identifying, based on at least one state variable, an operating state of the exhaust-gas treatment device in which deposits can form on the electric heater;

c) setting a cycle frequency as a function of the operating state if the operating state identified in step b) lies in a predefined operating state range; and

d) the controller cyclically activating and deactivating the electric heater at the set cycle frequency if the operating state identified in step b) lies in the predefined operating state range.

2. The method according to claim 1 , which further comprises providing the heater with an electrically heatable honeycomb body.

3. The method according to claim 1 , which further comprises providing a reducing agent as the additive, and providing at least one SCR catalytic converter in the exhaust-gas treatment device downstream of the feed point in an exhaust-gas flow direction.

4. The method according to claim 1 , which further comprises identifying the operating state in step b) by using at least one of the following state variables:

at least one temperature;

a mass flow of the additive through the feed point into the exhaust-gas treatment device; or

a mass flow of an exhaust-gas stream in the exhaust-gas treatment device.

5. The method according to claim 1 , which further comprises, in step c), setting a heating period, over which the heater is operated during each cycle length of the cycle frequency, in addition to setting the cycle frequency.

6. The method according to claim 1 , which further comprises selecting the cycle frequency to activate the heater for less than 20 percent of an operating time of the exhaust-gas treatment device during which the operating state of the exhaust-gas treatment device lies in the predefined operating state range.

7. The method according to claim 1 , which further comprises raising a temperature of an exhaust-gas stream in the exhaust-gas treatment device by less than 50° C. as a result of the cyclic operation of the heater.

8. The method according to claim 1 , which further comprises placing the feed point upstream of the heater in an exhaust-gas flow direction through the exhaust-gas treatment device, and metering-in the additive in the exhaust-gas flow direction.

9. The method according to claim 1 , which further comprises placing the feed point downstream of the heater in an exhaust-gas flow direction through the exhaust-gas treatment device, and metering-in the additive counter to the exhaust-gas flow direction.

10. A method for operating an exhaust-gas treatment device, the method comprising the following steps:

providing an electric heater for heating at least one exhaust-gas stream or a surface in the exhaust-gas treatment device;

providing a controller for activating and deactivating the electric heater;

providing a feed point for feeding an additive into the exhaust-gas treatment device causing the additive to impinge on the electric heater;

a) feeding the additive at the feed point;

b) identifying, based on at least one state variable, an operating state of the exhaust-gas treatment device in which deposits can form on the electric heater;

c) setting a cycle frequency as a function of the operating state if the operating state identified in step b) lies in a predefined operating state range; and

d) the controller cyclically activating and deactivating the electric heater at the set cycle frequency if the operating state identified in step b) lies in the predefined operating state range;

feeding the additive in step a) at least at one predefined injection time, and adapting the at least one predefined injection time at least to the cycle frequency of the activation of the heater.

11. A motor vehicle, comprising:

an internal combustion engine;

an exhaust-gas treatment device configured to purify a stream of exhaust gases of said internal combustion engine, said exhaust-gas treatment device having a surface, an electric heater configured to heat the exhaust-gas stream or said surface in said exhaust-gas treatment device, and a feed point configured to feed an additive into said exhaust-gas treatment device causing the additive to impinge on said electric heater; and

a controller constructed and configured to operate said exhaust-gas treatment device by carrying out the following steps:

a) feeding the additive at said feed point;

b) identifying, based on at least one state variable, an operating state of said exhaust-gas treatment device in which deposits can form on said electric heater;

c) setting a cycle frequency as a function of the operating state if the operating state identified in step b) lies in a predefined operating state range; and

d) cyclically activating and deactivating said electric heater at the set cycle frequency if the operating state identified in step b) lies in the predefined operating state range.

12. The motor vehicle according to claim 11 , wherein said controller activates said electric heater to reach a temperature that effectively burns off or erodes deposits on said electric heater.

13. The method according to claim 1 , wherein the controller activates the electric heater to reach a temperature that effectively burns off or erodes deposits on the electric heater.

14. The motor vehicle according to claim 11 , which further comprises said controller constructed and configured for feeding the additive in step a) at least at one predefined injection time, and adapting the at least one predefined injection time at least to the cycle frequency of the activation of the heater.

15. The motor vehicle according to claim 11 , which further comprises placing the feed point downstream of said heater in an exhaust-gas flow direction through the exhaust-gas treatment device, and said feed point metering-in the additive counter to the exhaust-gas flow direction.