Method of determining opening of an internal combustion engine intake valve

1. A method of determining opening of an intake valve of an internal combustion engine; the method comprising:

determining the time pattern of an intake pressure in an intake manifold of the internal combustion engine;

determining an intake-frequency component of the intake pressure; and

determining opening of the intake valve as a function of the intake-frequency component of the intake pressure;

further determining the time pattern of a rotation speed of a drive shaft of the internal combustion engine, or the time pattern of a voltage at the terminals of a battery of the internal combustion engine;

determining an intake-frequency component of the rotation speed or voltage; and

determining opening of the intake valve as a function of the intake-frequency component of the intake pressure, and also as a function of the intake-frequency component of the rotation speed or voltage.

2. A method as claimed in claim 1 , and comprising the further step of establishing opening of the intake valve, if at least one intake-frequency component exceeds a first threshold value.

3. A method as claimed in claim 1 , and comprising the further step of only establishing non-opening of the intake valve, if both the intake-frequency components are below respective first threshold values.

4. A method as claimed in claim 1 , wherein opening of an intake valve is determined at start-up of the internal combustion engine.

5. A method as claimed in claim 4 , and comprising the further step of closing a throttle valve of the internal combustion engine if, within a given time interval from starting the start-up procedure, the internal combustion engine does not start, and correct opening of the intake valve is not established.

6. A method as claimed in claim 5 , and comprising the further steps of:

cutting off fuel injection when the throttle valve is closed; and

restarting fuel injection and reopening the throttle valve, if correct opening of the intake valve is established after the throttle valve is closed.

7. A method as claimed in claim 1 , and comprising, at start-up of the internal combustion engine, the further steps of:

determining a rotation speed of a drive shaft of the internal combustion engine; and

establishing opening of the intake valve independently of the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage, if the rotation speed exceeds a second threshold value higher than the maximum speed of a starter motor.

8. A method as claimed in claim 1 , and comprising, at start-up of the internal combustion engine, the further steps of:

determining an intake pressure in an intake manifold of the internal combustion engine; and

establishing opening of the intake valve independently of the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage, if the intake pressure is below a third threshold value lower than atmospheric pressure.

9. A method as claimed in claim 1 , and comprising the further step, when the internal combustion engine is running, of waiting for the internal combustion engine to reach a steady condition, in particular the cut-off condition, before determining opening of the intake valve.

10. A method as claimed in claim 9 , and comprising, when the internal combustion engine is running, the further steps of:

determining a stationary wave in the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage; and

determining opening of the intake valve as a function of the stationary wave in the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage.

11. A method as claimed in claim 10 , and comprising the further step of establishing abnormal opening of the intake valve when the amplitude of the stationary wave in the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage is too small.

12. A method as claimed in claim 10 , and comprising the further step of establishing abnormal opening of the intake valve when the stationary wave in the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage shows cyclic irregularities.

13. A method as claimed in claim 1 , wherein the intake frequency equals the rotation speed of a drive shaft of the internal combustion engine multiplied by the number of intakes for each complete turn of the drive shaft.

14. A method as claimed in claim 1 , and comprising, when the internal combustion engine is running and with direct fuel injection into the cylinders, the further steps of:

determining the strength of the exhaust gases produced by combustion in the cylinders; and

determining opening of the intake valve as a function of the intake-frequency component of the intake pressure, of the rotation speed, or of the voltage, and also as a function of the strength of the exhaust gases.

15. A method as claimed in claim 14 , and comprising the further step of only confirming abnormal opening of the intake valve if the strength of the exhaust gases indicates an excess of fuel.