Method for zone controlling a wastegate in a turbocharged internal combustion engine

1. A method for controlling the wastegate ( 16 ) in a internal combustion engine ( 1 ) turbocharged by means of a turbocharger ( 12 ); the control method comprises the steps of:

determining, during a design phase, a control law (CL) which provides an objective opening of a controlling actuator ( 35 ) of the wastegate ( 16 ) according to the supercharging pressure (P);

determining an objective supercharging pressure (P obj );

measuring an actual supercharging pressure (P);

determining a first open loop contribution (WG OL ) of an objective position (WG obj ) of the controlling actuator ( 35 ) of the wastegate ( 16 ) through the control law (CL) and according to the objective supercharging pressure (P obj );

determining a second closed loop contribution (WG CL1 ) of the objective position (WG obj ) of the controlling actuator ( 35 ) of the wastegate ( 16 );

calculating the objective position (WG obj ) of the controlling actuator ( 35 ) of the wastegate ( 16 ) by adding the two contributions (WG OL , WG CL1 );

controlling the controlling actuator ( 35 ) of the wastegate ( 16 ), so as to pursue the objective position (WG obj ) of the controlling actuator ( 35 ) of the wastegate ( 16 );

dividing the operation field of the wastegate ( 16 ) into at least two different operation zones according to the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ): an intermediate-supercharging-pressure operation zone (B) in which the position of the wastegate ( 16 ) and the possibility of controlling the position of the wastegate ( 16 ) by means of the controlling actuator ( 35 ) are uncertain, and a high-supercharging-pressure operation zone (C) in which the position of the wastegate ( 16 ) can be controlled by means of the controlling actuator ( 35 ); and

differentiating the kind of control according to the fact that the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ) is in the intermediate-supercharging-pressure operation zone (B) or in the high-supercharging-pressure operation zone (C).

2. The control method as set forth in claim 1 further including the steps of:

dividing the operation field of the wastegate ( 16 ) according to the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ) also into a low-supercharging-pressure operation zone (A) in which the wastegate ( 16 ) remains substantially closed irrespective of the controlling action of the controlling actuator ( 35 ); and

avoiding any kind of control of the controlling actuator ( 35 ) when the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ) is in the low-supercharging-pressure operation zone (A).

3. The control method as set forth in claim 1 further including the step of switching off the feedback controls zeroing the closed loop contributions (WG CL1 , WG CL2 ) and using only the open loop control when the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ) is in the intermediate-supercharging-pressure operation zone (B).

4. The control method as set forth in claim 1 further including the step of assigning to the objective position (WG obj ) of the controlling actuator ( 35 ) of the wastegate ( 16 ) a constant and predetermined value which is independent from the objective supercharging pressure (P obj ).

5. The control method as set forth in claim 1 further including the step of differentiating the operative parameters of the regulators ( 44 , 45 ) according to the fact that the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ) is in the intermediate-supercharging-pressure operation zone (B) or in the high-supercharging-pressure operation zone (C).

6. The control method as set forth in claim 5 further including the step of using in the intermediate-supercharging-pressure operation zone (B) a slower control with respect to the control used in the in the high-supercharging-pressure operation zone (C).

7. The control method as set forth in claim 5 further including the step of using in the intermediate-supercharging-pressure operation zone (B) proportional, integral and/or derivative coefficients of the regulators ( 44 , 45 ) which are lower than the similar coefficients used in the high-supercharging-pressure operation zone (C).

8. The control method as set forth in claim 5 further including the step of using in the intermediate-supercharging-pressure operation zone (B) saturations thresholds which are lower than the similar saturation thresholds used in the high-supercharging-pressure operation zone (C).

9. The control method as set forth in claim 1 further including the step of zeroing the integral term of the regulators ( 44 , 45 ) when the difference between the actual supercharging pressure (P) and the atmospheric pressure (P atm ) decreases passing from the high-supercharging-pressure operation zone (C) to the intermediate-supercharging-pressure operation zone (B).

10. The control method as set forth in claim 1 further including the step of zeroing or freezing the integral term of the regulators ( 44 , 45 ) when a rapid variation of the objective supercharging pressure (P obj ) occurs.

11. The control method as set forth in claim 10 further including the steps of:

determining a gradient (ΔP obj ) of the objective supercharging pressure (P obj ) by calculating the difference between the objective supercharging pressure (P obj ) and the filtered objective supercharging pressure (P obj-F ) which has been filtered by means of a fifth low-pass filter ( 49 ); and

establishing the presence of a rapid variation of the objective supercharging pressure (P obj ) when the gradient (ΔP obj ) of the objective supercharging pressure (P obj ) is higher than a threshold value.

12. The control method as set forth in claim 10 further including the step of zeroing or freezing the integral term of the regulators ( 44 , 45 ) when a rapid variation of the objective supercharging pressure (P obj ) occurs, only if the absolute value of the integral term is higher than a threshold value.

13. The control method as set forth in claim 1 further including the steps of:

learning a border supercharging pressure (P BORDER ) beneath which wastegate ( 16 ) remains substantially closed irrespective of the control action of the controlling actuator ( 35 ); and

establishing the borders of the intermediate-supercharging-pressure operation zone (B) according to the difference between the border supercharging pressure (P BORDER ) and the atmospheric pressure (P atm ).

14. The control method as set forth in claim 13 further including the step of centering the intermediate-supercharging-pressure operation zone (B) on the difference between the border supercharging pressure (P BORDER ) and the atmospheric pressure (P atm ).

15. The control method as set forth in claim 13 wherein the step of learning the border supercharging pressure (P BORDER ) further includes the steps of:

closing completely the controlling actuator ( 35 ) of the wastegate ( 16 ) for a given learning time interval in which a reduced mass flow rate (M R ) of the supercharger ( 14 ) exceeds the predetermined threshold value; and

assuming the border supercharging pressure (P BORDER ) to be substantially equal to the maximum actual supercharging pressure (P) during the learning time interval.