Method of controlling urea dosing in an exhaust system of a vehicle

Abstract

The present application relates to a method of controlling urea dosing in an exhaust system of a vehicle. The method includes adjusting the urea dosing based on the severity of urea deposition on an SCR catalyst, where the urea dosing is reduced as the severity increases.

1 . A method of controlling urea dosing in an exhaust system of a vehicle wherein said urea is injected into an exhaust gas flow in said exhaust system for selective catalytic reduction, said method comprising:
 establishing an allocation rule for a group of parameters that characterize an operating condition in said exhaust system, and for a value of a urea deposition severity index suited to characterize an urea deposition severity in said exhaust system;   determining a current value combination for said group of parameters for a current operation condition of said exhaust system;   based on said allocation rule, allocating a current value combination for said group of parameters for a current operation condition of said exhaust system, to a current value of said urea deposition severity index; and   based on said current value of said urea deposition severity index, controlling urea dosing in said exhaust system.   
     
     
         2 . The method according to  claim 1 , wherein said group of parameters comprises an exhaust gas mass flow rate, a urea dosing rate, and a characteristic temperature in said exhaust system. 
     
     
         3 . The method according to  claim 1 , wherein said group of parameters comprises one parameter dependent on a ratio between the urea dosing rate and the exhaust gas mass flow rate. 
     
     
         4 . The method according to  claim 1 , wherein said group of parameters comprises two parameters, a first parameter being dependent on a ratio between a urea dosing rate and an exhaust gas mass flow rate, and a second parameter being a characteristic temperature in said exhaust system. 
     
     
         5 . The method according to  claim 4 , wherein said exhaust system comprises a selective catalytic reduction catalyst, wherein said characteristic temperature is a temperature of exhaust gas upstream of the selective catalytic reduction catalyst. 
     
     
         6 . The method according to  claim 1 , wherein said urea deposition severity index suited to characterize an urea deposition severity in said exhaust system is defined based on a percentage of deposits initially formed during urea dosing that are not removed within a predetermined period after stopping urea dosing. 
     
     
         7 . The method according to  claim 1 , wherein said allocation rule is established as a look-up table. 
     
     
         8 . The method according to  claim 1 , wherein controlling urea dosing in said exhaust system comprises reducing a urea dosing rate if said current value of said urea deposition severity index exceeds a predetermined threshold value. 
     
     
         9 . A system for controlling urea dosing in an exhaust system of a vehicle, comprising a controller with a chip including non-transitory computer instructions to operate a urea dosing system in a first reductant dosing mode when a urea deposition severity index is less than a threshold, the first reductant dosing mode including adjusting reductant injection into engine exhaust to a first amount based on a plurality of operating conditions, and operate the urea dosing system in a second reductant dosing mode when the urea deposition severity index is greater than the threshold, the second reductant dosing mode being a restricted urea dosing mode including reducing the first amount to a second, lower, amount. 
     
     
         10 . The system of  claim 9 , wherein the controller with the chip further includes non-transitory computer instructions for determining the urea deposition severity index. 
     
     
         11 . The system of  claim 10 , wherein determination of the urea deposition severity index comprises calculation of a ratio of an exhaust gas mass flow rate to a urea dosing rate, measurement of a characteristic exhaust temperature, and referencing a predetermined map of the ratio between the exhaust gas mass flow rate and the urea dosing rate versus the characteristic exhaust temperature. 
     
     
         12 . The system of  claim 9 , wherein the controller with the chip further includes non-transitory computer instructions for determining the first amount in the first reductant dosing mode based on one or more of the exhaust gas mass flow rate, the exhaust temperature, the urea dosing rate, a remaining amount of stored urea, an engine speed/torque, an allowable urea slip, and a plurality of properties of a SCR catalyst. 
     
     
         13 . The system of  claim 12 , wherein the plurality of properties of the SCR catalyst comprise one or more of conversion efficiency, catalyst conditions, and ageing status. 
     
     
         14 . A method of urea injection into an exhaust gas flow, comprising:
 in a first mode, dosing a first urea amount to an SCR catalyst based on a plurality of operating parameters; and   in a second mode, different than the first mode, dosing a second urea amount to the SCR catalyst based on an exhaust temperature and a ratio between an exhaust gas mass flow rate and a urea dosing rate.   
     
     
         15 . The method of  claim 14 , wherein the plurality of operating parameters comprises one or more of the exhaust gas mass flow rate, the exhaust temperature, the urea dosing rate, a remaining amount of stored urea, an engine speed/torque, an allowable urea slip, and a plurality of properties of a SCR catalyst. 
     
     
         16 . The method of  claim 15 , wherein the plurality of properties of the SCR catalyst comprise one or more of conversion efficiency, catalyst conditions, and ageing status. 
     
     
         17 . The method of  claim 14 , further comprising determining a urea deposition severity index, and further adjusting urea dosing to either of the first mode or the second mode based on the urea deposition severity index. 
     
     
         18 . The method of  claim 14 , wherein determination of the urea deposition severity index comprises calculating the ratio of the exhaust gas mass flow rate to the urea dosing rate, determining the exhaust temperature, and referencing a predetermined map of the ratio between the exhaust gas mass flow rate and the urea dosing rate versus the exhaust temperature. 
     
     
         19 . The method of  claim 18 , wherein if the urea deposition severity index is greater than a threshold, the first urea amount is delivered, and if the severity index is less than the threshold, the second urea amount is delivered. 
     
     
         20 . The method of  claim 14 , wherein the second urea amount is less than the first urea amount.