초록 ▼

Methods and arrangements are described for controlling transitions between firing fractions during skip fire operation of an engine in order to help smooth the transitions. Generally, firing fractions transitions are implemented gradually, preferably in a manner that relatively closely tracks manifo

Methods and arrangements are described for controlling transitions between firing fractions during skip fire operation of an engine in order to help smooth the transitions. Generally, firing fractions transitions are implemented gradually, preferably in a manner that relatively closely tracks manifold filling dynamics. In some embodiments, the commanded firing fraction is altered each firing opportunity. Another approach contemplates altering the commanded firing fraction by substantially the same amount each firing opportunity for at least a portion of the transition. These approaches work particularly well when the commanded firing fraction is provided to a skip fire controller that includes an accumulator functionality that tracks the portion of a firing that has been requested, but not delivered, or vice versa. In various embodiments, commanded firing fraction changes are delayed relative to initiation of the change in throttle position to help compensate for inherent delays associated with changing the manifold air pressure.

대표청구항 ▼

1. A method of controlling the transition of an engine between different firing fractions, the method comprising: while the engine is operating at a first firing fraction, determining a second target firing fraction that is different than the first firing fraction; andtransitioning from the first fi

1. A method of controlling the transition of an engine between different firing fractions, the method comprising: while the engine is operating at a first firing fraction, determining a second target firing fraction that is different than the first firing fraction; andtransitioning from the first firing fraction to the target firing fraction by gradually altering a commanded firing fraction from the first firing fraction to the second firing fraction, wherein the commanded firing fraction is altered each firing opportunity. 2. A method of controlling the transition of an engine between different firing fractions, the method comprising: while the engine is operating at a first firing fraction, determining a second target firing fraction that is different than the first firing fraction; andtransitioning from the first firing fraction to the target firing fraction by gradually altering a commanded firing fraction from the first firing fraction to the second firing fraction, wherein the commanded firing fraction is altered by substantially the same amount each firing opportunity. 3. A method as recited in claim 1 wherein: the commanded firing faction has an associated skip fraction which is a complementary fraction of the commanded firing fraction; andthe commanded firing fraction is altered in a manner such that a product of the skipping fraction and the intake manifold pressure remains substantially constant throughout the transition. 4. A method as recited in claim 1 wherein the firing fraction is changed at substantially the same rate throughout the transition. 5. A method as recited in claim 1 wherein the commanded firing fraction is provided to a skip fire firing timing determining module that includes an accumulator functionality that tracks a portion of a firing that has been requested, but not delivered, or that has been delivered, but not requested. 6. A method as recited in claim 1 wherein the commanded firing fraction is changed each firing opportunity using a linear slew rate such that the amount that the commanded firing fraction is changed each firing opportunity is the same throughout the transition. 7. A method as recited in claim 2 wherein the commanded firing fraction is changed each firing opportunity using a linear slew rate such that the amount that the commanded firing fraction is changed each firing opportunity is the same throughout the transition. 8. A method as recited in claim 6 wherein the linear slew rate is in the range of 1-5% such that the commanded firing fraction increases in the range of 1 to 5 percent each firing opportunity. 9. A method as recited in claim 6 wherein the magnitude of the linear slew rate is selected at least in part based on the magnitude of the change in firing fraction and at least one engine operating parameter. 10. A method as recited in claim 1, wherein the transition period is in the range of 150 to 300 milliseconds. 11. A method as recited in claim 1, wherein the engine includes a multiplicity of working chambers and an intake manifold that supplies air to at least a plurality of the working chambers, the intake manifold having a manifold air pressure, the method further comprising: changing a commanded throttle position in conjunction with the transition between different firing fractions to facilitate operation at the target firing fraction, wherein initiation of the altering of the commanded firing fraction is delayed relative to initiation of the change in throttle position by a plurality of firing opportunity, thereby helping compensate for inherent delays associated with changing the manifold air pressure. 12. A method as recited in claim 1, wherein the engine includes a multiplicity of working chambers and an intake manifold that supplies air to at least a plurality of the working chambers, the method further comprising: determining a target manifold pressure associated with the target firing fraction, the target manifold pressure being different than an initial manifold pressure that exists when a decision to change firing fractions is made; andutilizing feed forward throttle control in conjunction with the transition to accelerate the transition of the manifold pressure to the target manifold pressure. 13. A method as recited in claim 1, wherein the engine includes a plurality of cylinders, a plurality of intake valves, each intake valve being associated with an associated one of the cylinders, a camshaft arranged to open and close the intake valves; and an intake manifold that supplies air to the cylinders through the intake valves, the method further comprising: determining a target air charge associated with the target firing fraction, the target air charge being different than an initial air charge that exists when a decision to change firing fractions is made; andutilizing feed forward camshaft control in conjunction with the transition to accelerate the transition of the air charge to the target air charge. 14. A method as recited in claim 1, wherein the engine includes a multiplicity of working chambers, each working chamber having an associated spark source, the method further comprising: determining a target spark timing associated with the target firing fraction, the target spark timing potentially being different than an initial spark timing that exists when a decision to change firing fractions is made; andretarding the spark relative to both the initial spark timing and the target spark timing for selected fired working chambers during the transition to mitigate or prevent a torque surge that would otherwise occur during the transition. 15. A method as recited in claim 14 wherein at least one of the initial and target spark timings is a spark timing that causes the engine to generate the maximum brake torque at the associated engine settings. 16. A method as recited in claim 1 wherein: the engine includes an intake manifold, an exhaust and a multiplicity of working chambers, each working chamber being arranged to operate in a succession of working cycles;at least one of the first and target firing fraction has a complementary skip fire firing fraction in which selected skipped working cycles are not fired;air is pumped through the engine from the intake manifold to the exhaust during selected skipped working cycles that occur during the firing fraction transition to more quickly reduce manifold pressure during the transition; andwherein air is generally not pumped through the engine during skipped working cycles that occur outside the firing fraction transition. 17. A method as recited in claim 1 further comprising changing at least one commanded engine operating parameter that affects a working chamber air charge in conjunction with the transition between different firing fractions to facilitate operation at the target firing fraction, wherein initiation of the altering of the commanded firing fraction is delayed relative to initiation of the change in the commanded engine operating parameter by a plurality of firing opportunity, thereby helping compensate for inherent delays associated with increasing or decreasing the amount of air in an intake manifold that provides air to the working chamber. 18. A method of controlling the transition of an engine from an initial firing fraction to a target firing fraction, there being an initial manifold pressure and a target manifold pressure, the target manifold pressure being lower than the initial manifold pressure and the target firing fraction being higher than the initial firing fraction, the method comprising: operating the engine in a skip fire manner during the transition; andpumping air through the engine from an intake manifold to an exhaust during selected skipped working cycles that occur during the transition to more quickly reduce intake manifold pressure to the target manifold pressure; andwherein air is generally not pumped through the engine during skipped working cycles that occur outside the firing fraction transition. 19. A method of controlling the transition of an engine between different firing fractions, the engine including a multiplicity of working chambers, an intake manifold and an exhaust, the intake manifold having a manifold air pressure and being arranged to supply air to at least a plurality of the working chambers, the method comprising: while the engine is operating at a first operational firing fraction, receiving a request to transition to a target second operational firing fraction that is different than the first operational firing fraction;transitioning from the first operational firing fraction towards the target second operational firing fraction by gradually altering a commanded firing fraction from the first operational firing fraction towards the target second operational firing fraction; andchanging a commanded throttle position in conjunction with the transition between the different firing fractions to facilitate operation at the target second operational firing fraction, wherein initiation of the altering of the commanded firing fraction is delayed relative to initiation of the change in throttle position by a plurality of firing opportunity, thereby helping compensate for inherent delays associated with changing the manifold air pressure. 20. A method as recited in claim 19 wherein when a request is received to transition to a third operational firing fraction before the transition to the target second operational firing fraction is completed, the method further comprises: changing the commanded throttle position to a throttle position that facilitates operation at the third operational firing fraction in response to the request to transition to the third operational firing fraction;continuing to transition towards the target second operational firing fraction during a designated delay period; andafter the designated delay period has expired, transitioning from the then current firing fraction to the third operational firing fraction by gradually altering the commanded firing fraction from the then current operation firing fraction towards the third operation firing fraction. 21. A method as recited in claim 20 wherein the designated delay period is a defined time period. 22. A method as recited in claim 20 wherein the designated delay period is a defined number of firings or firing opportunities. 23. A method as recited in claim 19 wherein the commanded firing fraction is altered each firing opportunity. 24. A method as recited in claim 19 wherein the commanded firing fraction is altered by substantially the same amount each firing opportunity.