Method and Apparatus for Controlling an Exhaust Gas After-Treatment System

Abstract

A combustion engine exhaust gas after-treatment device includes a first selective catalytic reduction (SCR) device, a second SCR device downstream of the first and a diesel particulate filter (DPF) between the first and second SCR devices. A method of dosing the after-treatment device includes: allowing dosing of the first SCR device with reductant only when its temperature is within its the operating temperature range; and allowing dosing of the second SCR device with reductant only when its temperature is within its different operating temperature range; and reducing the level of dosing of the first SCR device when requiring DPF regeneration.

1 . A method of dosing an exhaust gas after treatment device comprising a first selective catalytic reduction (SCR) device, a second SCR device downstream of the first SCR device and a diesel particulate filter (DPF) located between the first SCR device and the second SCR device, wherein an operating temperature range of the first SCR device is different to an operating temperature range of the second SCR device, the method comprising the steps of:
 allowing dosing of the first SCR device with reductant when a temperature of the first SCR device is within the operating temperature range of the first SCR device, and preventing dosing of the first SCR device with reductant when the temperature of the first SCR device is outside the operating temperature range of the first SCR device; and   allowing dosing of the second SCR device with reductant when a temperature of the second SCR device is within the operating temperature range of the second SCR device, and preventing dosing of the second SCR device with reductant when the temperature of the second SCR device is outside the operating temperature range of the second SCR device; and   reducing the level of dosing of the first SCR device when regeneration of the DPF is required.   
     
     
         2 . The method of  claim 1 , wherein a lower bound of the operating temperature range of the first SCR device is below a lower bound of the operating temperature range of the second SCR device. 
     
     
         3 . The method of  claim 1 , wherein an upper bound of the operating temperature range of the first SCR device is greater than a lower bound of the operating temperature range of the second SCR device and less than an upper bound of the operating temperature range of the second SCR device. 
     
     
         4 . The method of  claim 1 , wherein an upper bound of the operating temperature range of the first SCR device is below a regeneration temperature of the DPF. 
     
     
         5 . A controller to control the dosing of an exhaust gas after treatment device comprising a first selective catalytic reduction (SCR) device, a second SCR device downstream of the first SCR device and a diesel particulate filter (DPF) located between the first SCR device and the second SCR device, wherein an operating temperature range of the first SCR device is different to an operating temperature range of the second SCR device, the controller being configured to:
 allow dosing of the first SCR device with reductant when a temperature of the first SCR device is within the operating temperature range of the first SCR device, and prevent dosing of the first SCR device with reductant when the temperature of the first SCR device is outside the operating temperature range of the first SCR device; and   allow dosing of the second SCR device with reductant when a temperature of the second SCR device is within the operating temperature range of the second SCR device, and prevent dosing of the second SCR device with reductant when the temperature of the second SCR device is outside the operating temperature range of the second SCR device; and   reduce the level of dosing of the first SCR device when regeneration of the DPF is required.   
     
     
         6 . An engine unit comprising the controller of  claim 5 . 
     
     
         7 . A vehicle comprising the engine unit of  claim 6 . 
     
     
         8 . An exhaust gas after treatment device comprising:
 a first selective catalytic reduction (SCR) device dosable by a first reductant injector upstream of the first SCR device;   a second SCR device downstream of the first SCR device, the second SCR device being dosable by a second reductant injector; and   a diesel particulate filter (DPF) located between the first and second SCR devices;   wherein, the second reductant injector is located between the DPF and the second SCR device; and   an operating temperature range of the first SCR device is different to an operating temperature range of the second SCR device.   
     
     
         9 . The exhaust gas after treatment device of  claim 8 , wherein a lower bound of the operating temperature range of the first SCR device is below a lower bound of the operating temperature range of the second SCR device. 
     
     
         10 . The exhaust gas after treatment device of  claim 8 , wherein an upper bound of the operating temperature range of the first SCR device is greater than a lower bound of the operating temperature range of the second SCR device and less than an upper bound of the operating temperature range of the second SCR device. 
     
     
         11 . The exhaust gas after treatment device of  claim 8 , wherein a regeneration temperature of the DPF is above an upper bound of the operating temperature range of the first SCR device. 
     
     
         12 . An internal combustion engine comprising the exhaust gas after treatment device of  claim 8 . 
     
     
         13 . A vehicle comprising the internal combustion engine of  claim 12 . 
     
     
         14 . The exhaust gas after treatment device of  claim 9 , wherein an upper bound of the operating temperature range of the first SCR device is greater than a lower bound of the operating temperature range of the second SCR device and less than an upper bound of the operating temperature range of the second SCR device. 
     
     
         15 . The exhaust gas after treatment device of  claim 9 , wherein a regeneration temperature of the DPF is above an upper bound of the operating temperature range of the first SCR device. 
     
     
         16 . An internal combustion engine comprising the exhaust gas after treatment device of  claim 9 . 
     
     
         17 . The method of  claim 2 , wherein an upper bound of the operating temperature range of the first SCR device is greater than a lower bound of the operating temperature range of the second SCR device and less than an upper bound of the operating temperature range of the second SCR device. 
     
     
         18 . The method of  claim 17 , wherein an upper bound of the operating temperature range of the first SCR device is below a regeneration temperature of the DPF. 
     
     
         19 . The method of  claim 2 , wherein an upper bound of the operating temperature range of the first SCR device is below a regeneration temperature of the DPF. 
     
     
         20 . The method of  claim 3 , wherein an upper bound of the operating temperature range of the first SCR device is below a regeneration temperature of the DPF.