The present disclosure relates to fuel injection in an engine.
Fuel injection amounts are typically set based on a desired air/fuel ratio and adapted using feedback from one or more exhaust gas sensors in the exhaust. Fueling errors may occur, however, during operating conditions where fuel vapors are present in the intake. For example, fuel vapor canisters designed to trap fuel vapors from the fuel tank are periodically purged to the intake, and these vapors may result in an excess amount of fuel in the cylinders, wasting fuel and degrading emissions.
Previous solutions to account for the amount of fuel originating from the fuel vapor canister have relied on purge flow estimates, based on purge duration and other parameters. However, these estimates are frequently inaccurate. Further, these estimates don't take into account additional sources of intake fuel, such as fuel from the positive crankcase ventilation system or pushback fuel.
The inventors have recognized the issues with the above approach and offer a method to at least partly address them. In one embodiment, a method comprises adjusting fuel injection based on fuel concentration in an engine intake manifold, and during idle and when EGR is disabled, adjusting fuel injection based on the fuel concentration and a fuel pushback amount. In this way, fuel injection may be adjusted based on fuel vapors present in the intake, for example, from both a fuel vapor canister purge and from a positive crankcase ventilation system. In one example, these fuel vapor amounts may be determined based on an oxygen sensor present in the intake. Further, the fuel injection may be additionally adjusted based on an amount of pushback fuel, for example from fuel evaporated from a fuel puddle on an intake valve or port.
By determining the amount of fuel in the intake based on a signal from an oxygen sensor, fuel injection amounts may be adjusted to maintain desired air/fuel ratio in the cylinder. Depending on operating conditions, the intake oxygen concentration may be able to provide an indication of an amount of ambient humidity, fuel vapors from various sources, and/or an amount of exhaust gas recirculation in the intake. By determining these amounts in some conditions and modeling them in other conditions, optimal air/fuel ratio may be maintained, improving fuel economy and reducing emissions. Further, the amount of vapors can also be adjusted based on feedback from exhaust air-fuel ratio sensors, purge flow estimates, purge duration, and other parameters if desired.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
An oxygen sensor positioned in the intake of an engine may be able to provide information regarding various parameters of the intake air, including ambient humidity, EGR, and fuel vapor amounts in the intake. Under some conditions, the reading from the intake oxygen sensor may be directly used to determine one or more of the above parameters. In other conditions, the intake oxygen amount may be determined and the relative contribution of the above parameters to the intake oxygen concentration may be modeled. Together, this information may be used to maintain the air/fuel ratio in each cylinder at an optimal level to improve fuel economy and reduce emissions.
Engine 10 may be virtually any volatile-liquid or gas-fueled internal combustion engine, e.g., a port- or direct-injection gasoline engine or diesel engine. In one, non-limiting embodiment, the engine may be adapted to consume an alcohol-based fuel—ethanol, for example.
Engine system 1 includes at least two sensors depicted in
Intake manifold 44 is configured to supply intake air or an air-fuel mixture to a plurality of combustion chambers of engine 10. The combustion chambers may be arranged above a lubricant-filled crankcase 130, in which reciprocating pistons of the combustion chambers rotate a crankshaft. The reciprocating pistons may be substantially isolated from the crankcase via one or more piston rings, which suppress the flow of the air-fuel mixture and of combustion gasses into the crankcase. Nevertheless, a significant amount of fuel vapor may ‘blow by’ the piston rings and enter the crankcase over time. To reduce the degrading effects of the fuel vapor on the viscosity of the engine lubricant and to reduce the discharge of the vapor into the atmosphere, the crankcase may be continuously or periodically ventilated, as further described hereinafter. In the configuration shown in
Engine system 1 includes fuel tank 34, which stores the volatile liquid fuel combusted in engine 10. To avoid emission of fuel vapors from the fuel tank and into the atmosphere, the fuel tank is vented to the atmosphere through adsorbent canister 136. The adsorbent canister may have a significant capacity for storing hydrocarbon-, alcohol-, and/or ester-based fuels in an adsorbed state; it may be filled with activated carbon granules and/or another high surface-area material, for example. Nevertheless, prolonged adsorption of fuel vapor will eventually reduce the capacity of the adsorbent canister for further storage. Therefore, the adsorbent canister may be periodically purged of adsorbed fuel, as further described hereinafter. In the configuration shown in
To provide venting of fuel tank 34 during refueling, adsorbent canister 136 is coupled to the fuel tank via refueling tank vent 140. The refueling tank vent may be a normally closed valve which is held open during refueling. To provide venting of the fuel tank while the engine is running, engine-running tank vent 142 is provided. The engine-running tank vent may be a normally closed tank vent which is held open while the engine is running. The engine-running tank vent, when open, may conduct vapors from the fuel tank to the intake manifold via buffer 144. The buffer may be any structure configured to reduce or restrict the admission of transient slugs of fuel vapor into the clean air intake conduit. Such slugs of fuel vapor could be caused by tank slosh, for example. The buffer may comprise one or more baffles, screens, orifices, etc.
The configuration illustrated in
Continuing in
Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and may exhaust combustion gases via exhaust passage 48. Intake manifold 44 and exhaust passage 48 can selectively communicate with combustion chamber 30 via respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and/or two or more exhaust valves.
In this example, intake valve 52 and exhaust valves 54 may be controlled by cam actuation via respective cam actuation systems 51 and 53. Cam actuation systems 51 and 53 may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller 12 to vary valve operation. The position of intake valve 52 and exhaust valve 54 may be determined by position sensors 55 and 57, respectively. In alternative embodiments, intake valve 52 and/or exhaust valve 54 may be controlled by electric valve actuation. For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems.
Fuel injector 66 is shown coupled directly to combustion chamber 30 for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 68. In this manner, fuel injector 66 provides what is known as direct injection of fuel into combustion chamber 30. The fuel injector may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector 66 by a fuel system (not shown in
Intake passage 42 may include a throttle 62 having a throttle plate 64. In this particular example, the position of throttle plate 64 may be varied by controller 12 via a signal provided to an electric motor or actuator included with throttle 62, a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle 62 may be operated to vary the intake air provided to combustion chamber 30 among other engine cylinders. The position of throttle plate 64 may be provided to controller 12 by throttle position signal TP. Intake passage 42 may include a mass air flow sensor 120 and a manifold air pressure sensor 122 for providing respective signals MAF and MAP to controller 12.
Ignition system 88 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA from controller 12, under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber 30 or one or more other combustion chambers of engine 10 may be operated in a compression ignition mode, with or without an ignition spark.
Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstream of emission control devices 71 and 72. Sensor 126 may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Emission control devices 71, 72 are shown arranged along exhaust passage 48 downstream of exhaust gas sensor 126. Devices 71, 72 may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof. In some embodiments, during operation of engine 10, emission control devices 71, 72 may be periodically reset by operating at least one cylinder of the engine within a particular air/fuel ratio.
Controller 12 is shown in
Storage medium read-only memory 106 can be programmed with computer readable data representing instructions executable by processor 102 for performing the methods described below as well as other variants that are anticipated but not specifically listed.
As described above,
Further, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may route a desired portion of exhaust gas from exhaust passage 48 to intake manifold 44 via EGR passage 170. The amount of EGR provided to intake manifold 44 may be varied by controller 12 via EGR valve 174. Further, an EGR sensor 172 may be arranged within the EGR passage and may provide an indication of one or more pressure, temperature, and concentration of the exhaust gas. Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within the combustion chamber, thus providing a method of controlling the timing of ignition during some combustion modes. Further, during some conditions, a portion of combustion gases may be retained or trapped in the combustion chamber by controlling exhaust valve timing, such as by controlling a variable valve timing mechanism.
Thus, the system of
Turning to
At 302, fuel injection parameters are determined based on engine operating parameters. The fuel injection parameters may include fuel injection amount and timing, as well as other parameters such as spark timing. The fuel injection parameters may be based on engine speed, engine load, manifold absolute temperature, engine temperature, etc. Further, the fuel injection parameters may be adapted based on feedback from one or more downstream air/fuel ratios, such as sensor 126. In some examples, a desired air/fuel ratio, such as a stoichiometric air/fuel ratio, may be determined based on the various engine operating parameters, and the fuel amount injected may be adapted based on the air/fuel ratio determined by the downstream sensors in order to maintain the desired air/fuel ratio.
As explained previously, under certain conditions such as fuel vapor canister purging, additional fuel may be present in the intake manifold. When adaptive fuelling strategies are based on feedback from downstream sensors, this fuel in the intake may not be accounted for, resulting in over-fueling in some conditions. To avoid this, feedback from an intake gas sensor may also be used to determine fuel injection parameters. As such, at 304, the concentration of oxygen in the intake is determined based on a gas sensor in the intake. At 306, it is determined if the measured oxygen concentration is different from a baseline oxygen concentration stored in the memory of the controller. This baseline oxygen concentration may be determined under conditions where no fuel or EGR is present in the intake, such as immediately following a cold engine start. This baseline concentration may also account for ambient humidity present in the air. In other embodiments, the baseline concentration may be a preset amount based only the amount of oxygen typically present in the atmosphere, and the humidity corrected for using a humidity sensor in the intake.
If the oxygen concentration is not different from baseline, routine 300 proceeds to 307 to maintain the current fueling parameters determined at 302. If the measured oxygen concentration is different from the baseline concentration, routine 300 proceeds to 308 to determine the intake fuel concentration based on the intake oxygen concentration. As shown in
Determining the intake fuel concentration may include, in some conditions, correcting the fuel concentration based on operating parameters at 310. EGR present in the intake may lower intake oxygen concentration, and ambient humidity in the air may also alter intake oxygen amounts. Further, the intake fuel may derive from multiple sources, such as from the PCV system, fuel puddles on the intake ports, and pushback fuel arising during certain events such as intake/exhaust valve overlap. While the oxygen sensor may be able to detect fuel from all these sources, under some conditions the sensor may not detect them all, or may be subject to too much noise to accurately determine the fuel concentration. Additionally, adaptive fuel strategies may compensate for evaporating fuel from a fuel puddle that is then also measured by the intake gas sensor, resulting in fueling errors. The conditions likely to confound the determination of the fuel concentration, and mechanisms for correcting the fuel concentration based on the conditions, are discussed in more detail below with respect to
At 312, the fuel injection parameters set at 302 may be adjusted based on the determined intake fuel concentration. Adjusting the fuel injection may include adjusting a fuel injection amount at 314. If the intake air includes an appreciable amount of fuel, the fuel injection amount may be reduced to compensate for this additional fuel. Additionally, because the intake fuel is likely to already be vaporized and homogenized by the time it enters the cylinder, under some conditions, the dynamics of the when the fuel is injected and ignited may be altered as a result of the fuel in the intake. Further, the intake gas sensor may be able to detect EGR and/or humidity, and these factors may also effect injection and spark timing. Thus, to maintain optimal combustion conditions, fuel injection may be adjusted at 316 and spark timing may be adjusted at 318. Upon either maintaining fuel injection at 307 or adjusting fuel injection at 312, routine 300 ends.
Turning to
At 416, it is determined if conditions are present for additional fuel in the intake from a fuel vapor canister purge and/or from the positive crankcase ventilation system. Purge conditions may include the fuel vapor canister being in a regeneration state, e.g., the canister may be at its capacity to store fuel vapors. This may be determined by a position of a valve controlling the fuel vapor canister, or by an amount of time since a previous purge. Fuel from the PCV system may be present in the intake when oil temperature is below standard warmed up temperature, and so may be present if engine temperature is below a threshold (such as the cold start temperature discussed above with respect to 406 of
If it is determined that conditions indicative of PCV and/or purge fuel are present, routine 400 proceeds to 418 to attribute the measured change in oxygen concentration from a baseline oxygen concentration to all external fuel sources, including fuel from pushback and from PCV and/or purge. The intake oxygen sensor cannot differentiate these sources from each other, but can adjust the fuel injection amount based on the total fuel concentration in the intake. However, the relative contribution of each source may be determined under other conditions, which will be described in more detail below.
If it is determined that conditions indicative of PCV and/or purge fuel are not present, routine 400 proceeds to 420 to attribute the change in oxygen concentration in the intake from a baseline concentration to fuel from pushback only.
Returning to 410, if it is determined that conditions resulting in fuel pushback are not present, routine 400 proceeds to 422 to determine if conditions for purge and/or PCV are present, similar to the conditions determined at 416. If purge and/or PCV fuel are present in the intake, routine 400 proceeds to 428 to estimate EGR percentage based on EGR valve position and other intake flow parameters. At 430, the oxygen sensor reading is corrected to account for the estimated EGR percentage. At 432, the change in oxygen concentration detected by the sensor is attributed to vapors from purge and/or PCV only.
If it is determined at 422 that purge and/or PCV fuel is not present in the intake, routine 400 proceeds to 434 attribute the change in oxygen concentration detected by the sensor to the EGR present in the intake. As no fuel is present in the intake, this reading may be used directly to monitor the EGR percentage in the intake and used to adjust the EGR valve at 436 to maintain a desired EGR percentage in the intake. After determining what fuel sources are present in the intake at 418, 420, or 432, or after adjusting the EGR valve at 436, routine 400 exits.
Thus,
If it is determined at 438 that fuel pushback conditions are not present, routine 400 proceeds to 446 to determine if canister purge vapors and/or PCV fuel is present in the intake. If yes, routine 400 proceeds to 448 to determine if the engine is operating at idle or low load conditions. During idle or low load conditions, the amount of airflow through the intake is relatively low compared to higher load operating conditions. As a result, if the fuel vapor canister is in a purge condition, the purge flow may comprise a significant enough proportion of the airflow to be accurately measured by the oxygen sensor. If the engine is not operating in idle or low load, the conditions may not be optimal for accurate purge flow determination, and routine 400 proceeds to attribute the fuel in the intake to purge and/or PCV at 454, without storing the determination for future use.
If the engine is operating at idle or low load, at 450 it is determined if oil temperature is above a threshold, based on a determination of engine temperature. When oil temperature is above the threshold, it may be possible to accurately determine the purge flow amount, as the fuel from PCV system will not be present in the intake. The threshold may be warmed-up engine temperature or another suitable threshold that indicates a lack of appreciable fuel deriving from the PCV system (as fuel from the PCV system tends to be present in the intake only while the oil in the engine is warming up). If oil temperature is above the threshold, routine 400 proceeds to 452 to attribute the change in measured oxygen concentration to fuel only from the fuel vapor canister purge, and store this amount in memory for future use. If oil temperature is not above the threshold, routine 400 proceeds to 454 to attribute the fuel in the intake to purge and/or PCV. However, under some circumstances, if the amount of fuel in the intake during a fuel vapor purge is known based on previous measurements (such as the amount determined at 452), this amount may be subtracted out from the amount determined at 454, and the remaining amount attributed to just fuel from the PCV system.
Returning to 446 of
Thus, routine 400 as depicted in
Intake oxygen readings can be used to provide information on various parameters, including ambient humidity, the amount of EGR in the intake, and the amount of fuel vapors in manifold (from fuel vapor, PCV, and/or pushback). During selected conditions, intake oxygen can provide information on each of the above singly. For example, when EGR is disabled and there is no canister vapor purge and no PCV, the intake oxygen reading provides the amount of fuel in the intake from pushback. When EGR is disabled and there is no pushback or PCV fuel in the intake, the intake oxygen reading provides the amount of fuel in the intake from the fuel vapor canister purge. In another example, when EGR is enabled but there is no fuel from a canister purge, pushback or the PCV system, the intake oxygen reading may provide the amount of EGR in the intake.
When conditions are present that allow for the determination of the concentration of intake oxygen due to a single factor (e.g. only pushback) this determined concentration can be used to directly determine the amount of fuel in the intake from that source, and that amount stored in the memory of the controller. Each of the above factors that affect the intake oxygen concentration may also be modeled, e.g., EGR flow may be modeled from EGR pressures and/or valve position, pushback can be estimated from valve timing and fuel injection parameters from the previous cycle, etc. By storing the amount of fuel present from each source in some conditions and modeling the amount from each source in other conditions, fuel amounts in the intake may be determined even if too much noise is present to accurately use the sensor for intake fuel determination. For example, if there is a significant amount of pushback fuel and the fuel vapor canister is in purge state during high engine load, the sensor may have a low signal-to-noise ratio and thus not provide an accurate determination of the intake fuel amount. In such conditions, the amount of fuel vapors released to the intake during a purge can be estimated based on previous determinations in better conditions, and the amount of pushback modeled based on valve timing and fuel injection parameters from the previous cycle, to provide an estimation of the fuel present in the intake.
Thus, the routines of FIGS. 3 and 4A-4C may provide for a method comprising, during purging of fuel vapors from a fuel vapor storage system, adjusting fuel injection to an engine based on an amount of fuel vapors indicated from an intake oxygen amount measured by a sensor; and fuel pushback into the intake only during positive valve overlap. FIGS. 3 and 4A-4C may also provide a method comprising, during EGR operation without fuel-vapor purging, adjusting an EGR valve to maintain a desired EGR amount, during fuel vapor purging without EGR, adjusting fuel injection based on intake oxygen concentration to maintain a desired air-fuel ratio, and during pushback without fuel vapor purging and without EGR, adjusting fuel injection based on intake oxygen concentration to compensate for fuel pushback from other cylinders.
In some embodiments, adjusting the EGR valve may comprise during pushback, adjusting the EGR valve to decrease EGR percentage by a first amount based on a decrease in intake oxygen concentration, and without pushback, adjusting the EGR valve to decrease EGR percentage by a second amount, greater than the first, based on the decrease in intake oxygen concentration. In this way, the EGR valve may be adjusted based on the determined intake oxygen concentration. If the intake air includes fuel vapors from pushback, for example, the EGR valve may adjusted by a different amount than if the intake air does not include fuel vapors, for the same determined intake oxygen concentration.
In another example, the method may further comprise, during fuel vapor purging with EGR, adjusting fuel injection based on intake oxygen concentration and further based on an estimated EGR flow. In some embodiments, this may further comprise correcting the intake oxygen concentration for the estimated EGR flow, and if the corrected intake oxygen concentration is lower than a baseline oxygen concentration, then decreasing a fuel injection amount.
In another example, the method may comprise adjusting fuel injection based on intake oxygen concentration and fuel pushback into the intake during positive valve overlap, and the adjusting fuel inject may further comprise decreasing a fuel injection amount if the intake oxygen concentration is less than a baseline oxygen concentration.
Thus, the fuel injection amount may be decreased if the measured intake oxygen concentration is less than a baseline oxygen concentration. A decrease in the oxygen concentration from baseline is indicative of fuel vapors present in the intake, and thus the fuel injection amount may be decreased to compensate for the fuel in the intake.
It will be appreciated that the configurations and methods disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.