Method for draining a delivery unit for liquid additive, delivery unit and motor vehicle having a delivery unit

Abstract

A method for draining a delivery unit for a liquid additive, in particular a urea-water solution, includes at least: a) producing an electrical connection by using a currentless switch which is constructed to produce an electrical connection when a temperature falls below a threshold temperature; and b) draining the delivery unit when, in step a), the electrical connection has been produced. The method can be used, in particular, in SCR systems for exhaust-gas aftertreatment for motor vehicles. A delivery unit and a motor vehicle having a delivery unit are also provided.

1 . A method for draining a delivery unit for liquid additive, the method comprising the following steps:
 a) producing an electrical connection using a currentless switch constructed to produce an electrical connection when a temperature falls below a threshold temperature; and   b) draining the delivery unit when, in step a), the electrical connection has been produced.   
     
     
         2 . The method according to  claim 1 , which further comprises activating a control unit by using the switch in step a), and controlling the draining in step b) by using the control unit. 
     
     
         3 . The method according to  claim 2 , which further comprises automatically deactivating the control unit after execution of the method. 
     
     
         4 . The method according to  claim 1 , which further comprises:
 performing a temperature measurement between step a) and step b) by using a temperature sensor in order to check if a threshold temperature has actually been undershot; and   removing the liquid additive from the delivery unit in step b) only if the threshold temperature has actually been undershot.   
     
     
         5 . The method according to  claim 1 , which further comprises:
 storing the drainage of the delivery unit in a memory after step b);   at least one of before step a) or after step a), checking if the delivery unit has already been drained based on information in the memory; and   at least carrying out step b) only when the delivery unit has not been drained.   
     
     
         6 . The method according to  claim 1 , which further comprises carrying out the step of draining the delivery unit by back-suction of the liquid additive into a tank. 
     
     
         7 . The method according to  claim 1 , which further comprises selecting the switch at least from the following group:
 a bimetal switch,   a switch including a shape memory alloy,   a temperature switch with a liquid, and   a prestressed switch.   
     
     
         8 . The method according to  claim 1 , which further comprises executing the method during a standstill phase of an internal combustion engine. 
     
     
         9 . A delivery unit for delivering a liquid additive, the delivery unit comprising:
 a tank;   a delivery line connected to said tank;   a pump configured to deliver liquid additive through said delivery line from said tank; and   a currentlessly activatable switch connected to said pump and configured to produce an electrical connection when a threshold temperature is undershot.   
     
     
         10 . A motor vehicle, comprising:
 an internal combustion engine;   an exhaust-gas treatment device configured to purify exhaust gases of said internal combustion engine; and   a delivery unit according to  claim 9  associated with said exhaust-gas treatment device.