Engine idle speed and turbocharger speed control
Various methods are described for controlling engine operation for an engine having a turbocharger and direction injection. One example method includes performing at least a first and second injection in response to a driver action. The first and second injection may be performed during a cylinder cycle, the first injection generating a lean combustion and the second injection injected after combustion such that it exits the cylinder unburned into the exhaust upstream of a turbine of the turbocharger.
1. A method for controlling an engine having a turbocharger and direct cylinder injection, comprising:
in response to a driver input, during a cylinder cycle, performing a first injection generating a lean combustion, and a second injection injected after the first injection at least partially exiting the cylinder unburned into an exhaust upstream of a turbocharger turbine; and
adjusting an amount of the first or second injection to maintain exhaust air-fuel ratio about stoichiometry.
2. The method of claim 1 , where said first and second injections are further performed responsive to turbocharger speed, and wherein the first injection is adjusted responsive to engine idle speed, and where if the first injection is increased in response to a decrease in engine idle speed, the second injection is decreased by a corresponding amount, and where the driver input includes actuation of a brake pedal.
3. The method of claim 1 , where said first and second injection are further performed responsive to turbocharger speed, and wherein an amount of the first and second injections are selected to maintain increased turbine speed at least under selected conditions responsive to the driver input and including at least some idle operation, the method further comprising adjusting throttle angle based on an amount of the first and second injections to maintain sufficient torque reserve with respect to the first injection relative to a maximum injection that corresponds to stoichiometric combustion; and where the driver input includes release of a brake pedal.
4. The method of claim 1 , wherein the lean combustion is spark ignited, the method further comprising reducing a spark retard reserve during idle speed operation when performing the first and second injections, where if the second injection falls below a threshold value, the second injection is disabled and the spark reserve is increased, and where the driver input includes release of a brake pedal, and where the engine is in an idle condition.
5. The method of claim 1 where said adjusting is further responsive to exhaust air-fuel ratio, and where the second injection is adjusted responsive to the exhaust air-fuel ratio, the method further comprising adjusting a throttle angle responsive to turbocharger speed, and where the driver input includes release of a brake pedal, and whether a vehicle including the engine is in a deceleration condition.
6. The method of claim 1 where the driver input includes actuation of a brake pedal.
7. The method of claim 1 where the driver input includes actuation of a gas pedal.
8. The method of claim 1 where the driver input includes actuation of a gear position.
9. The method of claim 1 where the driver input includes release of a brake pedal, and where the engine is in an idle condition during the cylinder cycle.
10. The method of claim 1 where the driver input includes release of a brake pedal, and where a vehicle including the engine is in a deceleration condition during the cylinder cycle.