Method to control a wastegate valve in a turbocharged internal combustion engine

1. A method to control a wastegate valve in an internal combustion engine turbocharged by a turbocharger provided with a turbine and with a compressor; the internal combustion engine comprising a number of cylinders, an intake manifold and an exhaust manifold and being suited to allow air to directly flow from the intake manifold to the exhaust manifold such that a pressure upstream of the compressor can be measured; the method comprises:

determining an objective supercharging pressure;

measuring an actual supercharging pressure;

experimentally determining a control law for obtaining an objective value for an opening of a solenoid valve controlling the wastegate valve by determining a first objective opening

of the solenoid valve corresponding to a position of the wastegate valve in an absence of air flowing from the intake manifold directly into the exhaust manifold; and by determining a second objective opening of the solenoid valve corresponding to a position of the wastegate valve when a quantity of air is flowing from the intake manifold into the exhaust manifold; wherein the control law is a data map or table or a mathematical function;

wherein the first objective opening of the solenoid valve is calculated as a function of an actual reduced mass flow rate and an objective compression ratio which is equal to a ratio between the objective supercharging pressure and the pressure upstream of the compressor; and

wherein the second objective opening of the solenoid valve is calculated as a function of an indicator of the quantity of air flowing from the intake manifold to the exhaust manifold, the actual reduced mass flow rate and the objective compression ratio;

calculating the objective value for the opening of the solenoid valve controlling the wastegate valve by adding a first contribution and a second contribution, wherein the first contribution is an open loop contribution and the second contribution is a closed loop contribution; the step of calculating further including the sub steps of:

determining the first contribution based on the first objective opening of the solenoid valve and the second objective opening of the solenoid; and

determining the second contribution by using a fictitious position of the wastegate valve as a feedback variable in the control law and comparing the second closed loop contribution with the first contribution;

wherein the fictitious position of the wastegate valve is based on the first objective opening of the solenoid valve and the second objective opening of the solenoid valve.

2. The control method according to claim 1 , further including providing a third contribution which represents a position that the wastegate valve has in conjunction with the air flowing from the intake manifold directly into the exhaust manifold; wherein the third and the first contributions are variable as a function of a mass flow rate of the compressor and the objective compression ratio or an actual compression ratio resulting from a ratio between the actual supercharging pressure and the pressure upstream of the compressor.

3. The control method according to claim 1 further comprising:

determining the second contribution as a function of the third contribution.

4. The control method according to claim 1 further comprising:

determining the second contribution as a function of the first contribution.

5. The control method according to claim 1 further comprising:

determining the second contribution as a function of a difference between the third contribution and the first contribution.

6. The control method according to claim 1 further comprising:

determining an indicator of the quantity of air directly flowing from the intake manifold to the exhaust manifold; and

determining the second contribution using the indicator of the quantity of air directly flowing from the intake manifold to the exhaust manifold.

7. The control method according to claim 5 further comprising:

determining the second contribution by determining a product between the indicator of the quantity of air directly flowing from the intake manifold to the exhaust manifold and the difference between the third contribution and the first contribution.

8. The control method according to claim 6 further comprising:

determining a rotation speed of the turbocharger as a function of the objective compression ratio and of a mass flow rate of the compressor and determining the indicator as a function of the rotation speed of the turbocharger.

9. The control method according to claim 8 further comprising:

determining the rotation speed of the turbocharger as a function of the mass flow rate of the compressor and the objective compression ratio or an actual compression ratio resulting from a ratio between the actual supercharging pressure and the pressure upstream of the compressor.

10. The control method according to claim 6 further comprising:

determining the indicator as a function of the ratio between an actual efficiency calculated from the ratio between a mass flow rate of total air flowing through the internal combustion engine and a mass flow rate of air trapped in the cylinders, which participates in the combustion, and an efficiency under conditions of air flowing directly from the intake manifold to the exhaust manifold.

11. The control method according to claim 10 , wherein the efficiency under conditions of air flowing directly from the intake manifold to the exhaust manifold can vary as a function of a mass flow rate of the compressor and the objective compression ratio or an actual compression ratio resulting from a ratio between the actual supercharging pressure and the pressure upstream of the compressor.

12. The control method according to claim 1 , wherein determining the second contribution further comprises:

determining an opening of the solenoid valve controlling the wastegate valve which corresponds to a position that the wastegate valve has in conjunction with the supercharging ratio and the actual reduced mass flow rate of the compressor;

calculating an opening error by determining a difference between the first contribution and the opening of the solenoid valve corresponding to the position of the wastegate valve has in conjunction with the supercharging ratio and the reduced mass flow rate of the compressor; and

determining the second contribution as a function of the opening error.