Pressurized air induction system
Methods and systems are provided for boosted engine systems. In one example, a system may include a pressurized air induction system with two pathways, the first for delivering ambient and the second for delivering boosted air to the engine. The pressurized air induction system is also adapted to store boosted air for faster supply of boost pressure in the event of demand for greater engine torque.
1. A method for boosting an engine, comprising:
estimating a position of an accelerator pedal via an accelerator pedal position sensor,
responsive to a tip-in of the accelerator pedal, increasing, via an electronic controller, an opening of a second air throttle to draw cool, compressed air from downstream of a charge air cooler (CAC) into the engine via a second air passage, the cool, compressed air generated by compressing ambient air at a compressor upstream of the CAC and then cooling the compressed ambient air at the CAC;
responsive to a tip-out of the accelerator pedal, increasing, via the electronic controller, an opening of a first air throttle to draw ambient air from upstream of the CAC into the engine via a first air passage while retaining the cool, compressed air in the second air passage; and
opening, via the electronic controller, the second air throttle following the tip-out of the accelerator pedal based on an estimated heat transfer to the cool, compressed air in the second air passage relative to a torque demand by an operator.
2. The method of claim 1 , wherein opening the second air throttle following the tip-out includes:
opening the second air throttle in response to the estimated heat transfer to the cool, compressed air in the second air passage being higher than a threshold amount while torque demand is below a threshold demand; and
opening the second air throttle in response to an increase in torque demand to higher than the threshold demand while the estimated heat transfer to the cool, compressed air in the second air passage is lower than the threshold amount.
3. The method of claim 2 , further comprising, responsive to opening the second air throttle while torque demand is below the threshold demand, adjusting one or more engine operating parameters to reduce engine torque output, the adjusting including retarding spark timing, adjusting fuel injection timing, adjusting valve timing, and adjusting a split ratio of fuel delivered via direct injection relative to port injection.
4. The method of claim 1 , wherein the second air passage includes a pressure relief valve upstream of the compressor, wherein the second air passage is coupled to the first air passage upstream of the pressure relief valve, wherein increasing the opening of the second air throttle includes decreasing the opening of the first air throttle, and wherein increasing the opening of the first air throttle includes decreasing the opening of the second air throttle.
5. The method of claim 1 , wherein the estimated heat transfer to the cool, compressed air is estimated based on each of an ambient temperature and an ambient humidity, the heat transfer increased as the ambient temperature increases and the ambient humidity decreases.