Spark timing control and method
A spark control system and method for an engine having an intake cam phaser and/or an exhaust cam phaser, and having engine sensors, comprises a principal calculation module that determines a principal spark advance value based upon actual rotational position of the cam phasers, and an output calculation module that determines an output spark advance value based upon the principal spark advance value and spark modifiers determined from the engine sensors. The actual rotational positions of the cam phasers are obtained from predictive calculations or rotational position sensors on the cam phasers. The principal calculation module includes two separately calibrated look-up tables, indexed by the actual rotational position of the cam phasers, whose outputs are scaled and combined to determine the principal spark advance. The spark modifiers include temperature base, coolant, induction air temperature, equivalence ratio, and piston slap.
1. A spark control system for an engine having at least one of an intake cam phaser and an exhaust cam phaser, and having at least one engine sensor, comprising:
a principal calculation module that determines a principal spark advance value based upon actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser, wherein said principal calculation module includes an n-dimensional first look-up table to determine said principal spark advance, said first look-up table is indexed by said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser, and n equals two when both intake and exhaust cam phasers are present, and n equals one otherwise; and
an output calculation module that determines an output spark advance value based upon said Principal spark advance value and data from the at least one engine sensor.
2. The spark control system of claim 1 wherein said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser is obtained from at least one rotational position sensor on each of the at least one of an intake cam phaser and an exhaust cam phaser.
3. The spark control system of claim 1 wherein said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser is obtained from predictive calculations.
4. The spark control system of claim 1 wherein said principal calculation module further includes an n-dimensional second look-up table to determine said principal spark advance, said second look-up table is indexed by said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser, and n equals two when both intake and exhaust cam phasers are present, and n equals one otherwise.
5. The spark control system of claim 4 wherein said second look-up table is calibrated using low-octane fuel.
6. The spark control system of claim 4 wherein scaled outputs of said first and second look-up tables are combined to produce said principal spark advance value.
7. The spark control system of claim 6 wherein said output of said first look-up table is scaled by an octane scalar and said output of said second look-up table is scaled by one minus said octane scalar before being combined to produce said principal spark advance value.
8. The spark control system of claim 7 wherein said octane scalar varies between zero and one, and increases with higher knock intensity and decreases with lower knock intensity, and the at least one engine sensor comprises a knock sensor.
9. The spark control system of claim 1 wherein said principal spark advance value includes a scalar offset selected from a two-dimensional table indexed by engine speed and engine load.
10. The spark control system of claim 1 wherein said principal calculation module selectively combines said principal spark advance value with at least one spark modifier.
11. A spark control system for an engine having at least one of an intake cam phaser and an exhaust cam phaser, and having at least one engine sensor, comprising:
a principal calculation module that determines a principal spark advance value based upon actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser, wherein said principal calculation module combines said principal spark advance value with at least one spark modifier only when a failure signal is not being received from an electronic throttle control system; and
an output calculation module that determines an output spark advance value based upon said principal spark advance value and data from the at least one engine sensor.
12. The spark control system of claim 10 wherein said at least one spark modifier includes at least one of temperature base, coolant, induction air temperature, equivalence ratio, and piston slap.
13. A method of determining spark timing for an engine having at least one of an intake cam phaser and an exhaust cam phaser, and having at least one engine sensor, comprising:
determining a principal spark advance from an output of a first look-up table that is indexed by an actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser; and
calculating an output spark advance value based upon said principal spark advance value and data from the at least one engine sensor.
14. The method of claim 13 further comprising determining said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser by analyzing information from at least one rotational position sensor on each of the at least one of an intake cam phaser and an exhaust cam phaser.
15. The method of claim 13 further comprising performing predictive calculations to determine said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser.
16. The method of claim 13 further comprising modifying said principal spark advance with an output of a second look-up table that is indexed by said actual rotational position of the at least one of an intake cam phaser and an exhaust cam phaser.
17. The method of claim 16 further comprising scaling said output of said first look-up table by a first scalar, scaling said output of said second look-up table by a second scalar, and combining said scaled outputs to produce said principal spark advance value.
18. The method of claim 13 further comprising combining said principal spark advance value with at least one spark modifier.