Method and arrangement for improving the hydrolysis of a reduction agent in an exhaust gas post treatment system

1. A method of improving the hydrolysis of a reduction agent in an exhaust gas post treatment system for the selective catalytic reduction of NOx in the exhaust gas of an internal combustion engine ( 1 ) that is operated with excess air, including the steps of:

providing an SCR catalytic converter ( 9 );

upstream of said SCR catalytic converter ( 9 ), branching off from an exhaust gas stream ( 2 ) a partial exhaust gas stream ( 3 ) that is quantitatively smaller than said exhaust gas stream ( 2 );

disposing in said partial exhaust gas stream ( 3 ) a metering arrangement ( 17 ) for supplying a reduction agent to said partial exhaust gas stream ( 3 );

disposing a hydrolysis catalytic converter ( 16 ) in said partial exhaust gas stream ( 3 ) downstream of said metering arrangement ( 17 );

conveying said partial exhaust gas stream ( 3 ) back to said exhaust gas stream ( 2 ) downstream of said hydrolysis catalytic converter ( 16 ) and upstream of said SCR catalytic converter ( 91 );

disposing a flow control device ( 12 ) in said partial exhaust gas stream ( 3 ) upstream or downstream of said hydrolysis catalytic converter ( 16 ), wherein a degree of opening of said flow control device ( 12 ) is adapted to be controlled or regulated;

maintaining the temperature at said hydrolysis catalytic converter ( 16 ) within prescribed limits by actively controlling or regulating the quantity of exhaust gas conveyed via said partial exhaust gas stream ( 3 ) by entirely or partially blocking or opening said partial exhaust gas stream ( 3 ): via said flow control device ( 12 ), if

measured or indirectly determined temperature values at said hydrolysis catalytic converter ( 16 ) and in said exhaust gas stream ( 2 ) and/or in said partial exhaust gas

stream exceed or do not reach specified threshold values, and/or if certain operating

conditions and/or operating condition changes of the internal combustion engine ( 1 )

occur;

increasing the quantity of exhaust gas conveyed via said partial exhaust gas stream ( 3 ) by opening said flow control device ( 12 ) at a low temperature of said hydrolysis catalytic converter ( 16 ) and in the presence of a high temperature exhaust gas stream upstream of said hydrolysis catalytic converter ( 16 ), and/or at operating parameters and/or operating parameter changes of the internal combustion engine ( 1 that lead to such a high exhaust gas temperature, in order to effect heating up of said hydrolysis catalytic converter ( 16 ); and

at a low temperature at said hydrolysis catalytic converter ( 16 ) and with the presence of a low exhaust gas temperature and/or operating parameters and/or operating parameter changes of the internal combustion engine ( 1 ) that lead to a low exhaust gas temperature, the exhaust gas quantity conveyed via the partial exhaust gas stream ( 3 ), by means of a partial closing of said flow control device ( 12 ), is reduced to such an extent that the reduction agent quantity that is to be supplied still makes it possible to ensure a proper receipt of the reduction agent into said partial exhaust gas stream ( 3 ).

2. A method according to claim 1 , which, when the temperature at said hydrolysis catalytic converter ( 16 ) drops below a first predetermined temperature threshold value at said hydrolysis catalytic converter, includes the steps of partially shutting off said partial exhaust gas stream ( 3 ) and, via appropriate activation of said metering arrangement ( 17 ), reducing or eliminating the supply of the reduction agent, independently of an actual requirement for complete reduction of the nitrogen oxides.

3. A method according to claim 1 , which, when the temperature at said hydrolysis catalytic converter ( 16 ) drops below a predetermined lower temperature threshold, and with the simultaneous presence of an exhaust gas temperature below a prescribed threshold value, includes the further steps of entirely closing said flow control device ( 12 ) and eliminating the supply of reduction agent via said metering arrangement ( 17 ).

4. A method according to claim 1 , which, upon a closing of said flow control device ( 12 ) and an elimination of the supply of reduction agent, and if the exhaust gas temperatures increase to a value above a prescribed threshold value, and/or operating parameters and/or operating parameter changes of the internal combustion engine ( 1 ) are present that lead to such an increase of the exhaust gas temperature, includes the further steps of opening said control flow device ( 12 ) and releasing a supply of reduction agent via said metering arrangement ( 17 ).

5. A method according to claim 1 , which, if the temperature of the hydrolysis catalytic converter exceeds a prescribed upper temperature threshold, includes the further step, by at least partially closing said flow control device ( 12 ), of reducing the exhaust gas quantity conveyed via the partial exhaust gas stream ( 3 ) to such an extent that any further temperature increase at said hydrolysis catalytic converter ( 16 ) is avoided.

6. A method according to claim 1 , which includes the step of metrologically determining the temperature at said hydrolysis catalytic converter ( 16 ) directly via a temperature sensor provided at said hydrolysis catalytic converter.

7. A method according to claim 1 , which includes the step of determining the temperature at said hydrolysis catalytic converter ( 16 ) indirectly by means of two temperature sensors for determining the exhaust gas temperature upstream and downstream of said hydrolysis catalytic converter.

8. A method according to claim 1 , which includes the further steps of:

determining the temperature at said hydrolysis catalytic converter ( 16 ) and/or the exhaust gas temperature via a model, wherein said model is comprised of characterizing values, performance characteristic values, mathematical functions, or neuronal networks, which are stored in a control unit of the internal combustion engine ( 1 ) and that represent the temperature curves at the hydrolysis catalytic converter ( 16 ) and/or exhaust gas temperatures, and wherein the temperature curves are determined at a reference internal combustion engine as a function of operating parameters of the internal combustion engine ( 1 ), such as fuel injection quantity and/or exhaust gas pressure and/or intake pressure and/or oil temperature and/or engine coolant temperature and/or surrounding temperature and/or engine speed and/or metering quantity for the reduction agent; and

if certain operating parameters of the internal combustion engine ( 1 ) and/or their periodic sequence are present, indirectly determining the temperature of said hydrolysis catalytic converter ( 16 ) and/or the exhaust gas temperatures upstream and/or downstream of said hydrolysis catalytic converter ( 16 ) by a logical operation undertaken with the stored characterizing values or performance characteristic values or mathematical functions or neuronal networks.