Method and system for controlling fuel usage

#The present application relates to methods and systems for controlling use of various fuels in an internal combustion engine.

#Alternate fuels have been developed to mitigate the rising prices of conventional fuels and for reducing exhaust emissions. For example, alcohol and alcohol-containing fuel blends have been recognized as attractive alternative fuels, in particular for automotive applications. Various engine systems may be used with alcohol fuels, utilizing various engine technologies and injection technologies. Further, various approaches may be used to control such alcohol-fuelled engines to take advantage of the charge-cooling effect of the high octane alcohol fuel, in particular to address engine knocking. For example, engine control methods may include adjustment of boost or spark timing in dependence upon the alcohol fuel, and various other engine operating conditions.

#One example approach for controlling an alcohol-fuelled engine is illustrated by Oda et al. in U.S. Pat. No. 6,951,202. Therein, in response to engine knocking, an engine controller determines whether to inject a high octane fuel (e.g., ethanol fuel) into an engine cylinder to address the knock based on an amount of the high octane fuel in the fuel tank. Specifically, when a larger amount of high octane fuel is available, fuel injection is used instead of spark retard to address the knock. In comparison, when a smaller amount of fuel is available, spark retard is used instead of ethanol injection to address the knock.

#FIG. 1 shows an example embodiment of an engine combustion chamber;

#FIG. 2 shows a map depicting variations in fuel economy loss and torque ratio with varying spark retard;

#FIG. 3 shows a map that may be used to identify an adjustment threshold point by comparing fuel economy losses due to spark retard with fuel economy losses due to an ethanol fuel injection;

#The following description relates to systems and methods for improving the efficiency of fuel usage in flex-fueled engines, such as the engine of FIG. 1. In response to engine knocking, an amount of spark retard and a knock control fluid injection may be used to address the knock. Specifically, spark may be retarded up to a predetermined amount of retard (such as a predetermined timing, or threshold point), up to which it may be more advantageous (e.g., more fuel economical) to use spark retard, and beyond which it may be more advantageous to inject a knock control fluid to address engine knock. As shown in FIGS. 2-5, based on a driver-selected cost function, a controller may adjust usage of spark retard and usage of direct injected and/or port injected fuels, or knock control fluids, to address knock. The usage may be further based on a combination of the inherent octane content, dilution effect, and charge cooling effect of the available knock control fluid(s), for example, as inferred from a composition (e.g., molar or volumetric) of the injected knock control fluid. As shown in FIGS. 7-8, at selected engine operating conditions (such as speed-load conditions), engine limitations (such as torque, temperature, and emissions limitations) may be determined, and the predetermined timing may be further adjusted accordingly. As shown in FIG. 9, in response to knocking, the controller may use spark retard up to the predetermined timing to address the knock, after which, the controller may use the injection of a knock control fluid to address knock. As shown in FIGS. 10-11, the adjustments between use of spark retard and knock control fluid injection may also be based on the amount of the injected knock control fluid, as compared to pulse width injection limitations of the injector. As shown in FIGS. 6 and 12, additional engine adjustments may be performed based on the dilution effect of the injected knock control fluid so as to better coordinate the engine dilution advantages and knock suppressing advantages of the injected fluid. Further, as shown in FIG. 13, throttle adjustments may be made based on a timing of the direct injection relative to intake valve closing, so as to better compensate for torque transients. In this way, by improving the use of spark retard and injection of fuel or knock control fluid in addressing knock, knock control fluid may be used more judiciously while engine performance is improved.

#FIG. 1 depicts an example embodiment of a combustion chamber or cylinder of internal combustion engine 10. Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder (herein also “combustion chamber’) 14 of engine 10 may include combustion chamber walls 136 with piston 138 positioned therein. Piston 138 may be coupled to crankshaft 140 so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor may be coupled to crankshaft 140 via a flywheel to enable a starting operation of engine 10.

#Cylinder 14 can receive intake air via a series of intake air passages 142, 144, and 146. Intake air passage 146 may communicate with other cylinders of engine 10 in addition to cylinder 14. In some embodiments, one or more of the intake passages may include a boosting device such as a turbocharger or a supercharger. For example, FIG. 1 shows engine 10 configured with a turbocharger including a compressor 174 arranged between intake passages 142 and 144, and an exhaust turbine 176 arranged along exhaust passage 148. Compressor 174 may be at least partially powered by exhaust turbine 176 via a shaft 180 where the boosting device is configured as a turbocharger. However, in other examples, such as where engine 10 is provided with a supercharger, exhaust turbine 176 may be optionally omitted, where compressor 174 may be powered by mechanical input from a motor or the engine. A throttle 20 including a throttle plate 164 may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle 20 may be disposed downstream of compressor 174 as shown in FIG. 1, or alternatively may be provided upstream of compressor 174.