Method and apparatus for measuring and controlling the EGR rate in a combustion engine

1. A method for measuring and controlling an EGR rate in a combustion engine system, the system comprising engine cylinders, at least an EGR cooler, an EGR valve and a turbine, the method comprising:

determining an EGR mass flow (dm EGR ) indirectly from the difference between a total exhaust gas mass flow (dm Tot ) across the engine cylinders calculated through an cylinder model, and a turbine mass flow (dm Turb ) across the turbine calculated through a turbine model;

wherein the cylinder model calculates the total exhaust gas mass flow as the sum of an actual gas mass flow and a fuel mass flow, the actual gas mass flow being calculated from an engine speed and a total gas charge in a cylinder per stroke, the total gas charge in a cylinder per stroke being calculated using a boost air pressure and a boost air temperature at the engine inlet;

wherein the turbine model calculates the turbine mass flow across the turbine from an upstream pressure, a downstream pressure, and an upstream temperature; and

adjusting the EGR valve based on the determined EGR mass flow (dm EGR ).

2. The method according to claim 1 , wherein, in a further step of adaptation, the turbine mass flow (dm Turb ) or total exhaust gas mass flow (dm Tot ) are adjusted such that they are equal when the EGR valve is closed.

3. The method according to claim 2 , further comprising the following steps:

adding or multiplying a feedback correction value or a feedback correction factor with the turbine mass flow (dm Turb ), with the feedback correction value or with a feedback correction factor coming from an integrator;

adding the result of the previous step to the value of the exhaust gas mass flow (dm Tot );

applying a gain correction to the result of the previous step;

feeding the integrator with the result of the previous step, only if the EGR valve is closed; if the EGR valve is not closed, the input of the integrator is zero.

4. The method according to claim 3 , wherein said turbine mass flow (dm Turb ) and said exhaust gas mass flow (dm Tot ) are reciprocally exchanged.

5. The method according to claim 1 , wherein, in case of a variable geometry turbine (VGT), the turbine model calculates the turbine mass flow additionally from a VGT position.

6. The method according to claim 1 , wherein, in case of a waste gate turbine, the turbine model calculates the turbine mass flow additionally from an opening of a waste gate.

7. The method according to claim 1 , wherein, in case of more than one turbine, the turbine model additionally calculates the turbine mass flow (dm Turb ) of a turbine downstream of an EGR connection.

8. The method according to claim 7 , wherein, for high pressure EGR, the turbine mass flow (dm Turb ) of any turbine has to be determined, for mid pressure EGR, the turbine mass flow (dm Turb ) of a more downstream turbine has to be determined.

9. An apparatus for measuring and controlling an EGR rate in a combustion engine system having at least an EGR cooler, an EGR valve and a turbine, the apparatus comprising:

a boost air pressure sensor for determining a boost air pressure;

a boost air temperature sensor for determining a boost air temperature;

a turbine inlet pressure sensor for determining a turbine inlet pressure;

a turbine upstream pressure sensor for determining a turbine upstream pressure;

a turbine downstream pressure sensor for determining a turbine downstream pressure; and

a turbine upstream temperature sensor for determining a turbine upstream temperature;

wherein the apparatus indirectly determines an EGR mass flow from the difference between a total exhaust gas mass flow across engine cylinders calculated through a cylinder model having as inputs at least the boost air pressure and the boost air temperature, and a turbine mass flow across the turbine calculated through a turbine model having as inputs at least the turbine upstream pressure, the turbine downstream pressure, and the turbine upstream temperature.

10. The apparatus of claim 9 , wherein the apparatus is configured to measure and control the EGR rate in a combustion engine system of a motor vehicle.

11. An article of manufacture comprising a non-transitory computer readable medium, the computer readable medium tangibly embodying one or more programs of instructions executable to perform the method of:

determining an EGR mass flow (dm EGR ) indirectly from the difference between a total exhaust as mass flow (dm Tot ) across the engine cylinders calculated through an cylinder model and a turbine mass flow (dm Turb ) across the turbine calculated through a turbine model;

wherein the cylinder model calculates the total exhaust gas mass flow as the sum of an actual gas mass flow and a fuel mass flow, the actual gas mass flow being calculated from an engine speed and a total gas charge in a cylinder per stroke, the total gas charge in a cylinder per stroke being calculated using a boost air pressure, and a boost air temperature at the engine inlet;

wherein the turbine model calculates the turbine mass flow across the turbine from an upstream pressure, a downstream pressure, and an upstream temperature; and

adjusting the EGR valve based on the determined EGR mass flow (dm EGR ).

12. The apparatus according to claim 9 , wherein the cylinder model calculates total exhaust gas mass flow as the sum of an actual gas mass flow and a fuel mass flow, wherein the actual gas mass is calculated from an engine speed and a total gas charge in a cylinder per stroke, and wherein the total gas charge in a cylinder per stroke is calculated using the boost air pressure and the boost air temperature.

13. An apparatus according to claim 9 , wherein, the turbine has a fixed geometry.

14. An apparatus according to claim 9 , wherein the turbine has a variable geometry, and wherein the turbine model calculates the turbine mass flow additionally from a turbine variable geometry position.

15. The method according to claim 1 , wherein the total gas charge in a cylinder per stroke is additionally calculated using turbine inlet pressure and turbine inlet temperature.

16. The apparatus according to claim 9 , wherein the total gas charge in a cylinder per stroke is additionally calculated using turbine inlet pressure and turbine inlet temperature.