Fuel feedback control for a two-way exhaust system

Abstract

Systems and procedures for controlling the fuel supplied to the cylinders of an internal combustion engine are described. In one example, the fuel is controlled in response to an output from two different fuel control units on an external circuit. The fuel can be controlled according to the individual, separate outputs of the external circuit's control units or the combined outputs of the two different fuel control units.

Description

Field of InterestThe present description relates to a system and method for regulating fuel supplied to engine cylinders. The methods and systems implement fuel control operation according to various ways that exhaust travels in an exhaust system.General State of the ArtA V8 engine includes a first cylinder bank and a second cylinder bank. The first cylinder bank may be coupled to a first exhaust passage including a first catalyst. Similarly, the second cylinder bank may be coupled to a second exhaust passage including a second catalyst. The first exhaust passage may include two oxygen sensors and the second exhaust passage may include two oxygen sensors. The two oxygen sensors in the first exhaust passage may provide feedback for regulating fuel injected into the first cylinder bank and the two oxygen sensors in the second exhaust passage may provide feedback for regulating fuel injected into the second cylinder bank. However, when exhaust gas is transferred from the first cylinder bank to a portion of the second exhaust passage and when exhaust gas is transferred from the second cylinder bank to a portion of the first exhaust passage to decrease the catalyst temperature, the control of the air-fuel ratio may be impaired and the stability of the fuel control may be impaired.SummaryThe inventors of the present invention have recognized the above-mentioned disadvantages and developed a fuel control method, comprising: in a first mode, setting a first inner circuit target value in response to a first outer circuit correction and setting a second inner circuit target value in response to a second outer circuit correction; in a second mode, setting the first inner circuit target value in response to the second outer circuit correction and setting a second inner circuit target value in response to the first outer circuit correction; and supplying fuel to an engine via control according to the first inner circuit target value and the second inner circuit target value.By adjusting the inner loop setpoint based on the first outer loop correction and the second outer loop correction, it may be possible to maintain the stability of the fuel control loop and reduce engine emissions even in the presence of alternating exhaust flow paths. For example, during low loads and / or during an engine cold-start, exhaust may be directed from a first cylinder bank to a first catalyst via a short path. During high engine speeds and engine loads and after the catalysts reach light-off, exhaust may be directed from the first cylinder bank via a longer path to a second catalyst. As exhaust flows from the first cylinder bank to the first catalyst, fuel flow to the first cylinder bank may be adjusted according to a correction generated via an outer loop first control responsive to a first downstream oxygen sensor positioned downstream of the first catalyst. Conversely, as exhaust gas flows from the first cylinder bank to the second catalyst, a fuel flow to the first cylinder bank may be adjusted according to a correction generated via an outer loop second control responsive to a second downstream oxygen sensor positioned downstream of the second catalyst. This control approach allows fuel supplied to a cylinder bank to follow the respective catalyst that processes exhaust gases from the cylinder bank, thereby adjusting fuel to the cylinder according to the most relevant catalyst state to control emissions of the cylinder bank.The present description may provide several advantages. In particular, the approach may reduce engine emissions while enabling shorter catalyst light-off times and high load, high speed engine operation. Further, the approach may maintain or increase catalyst efficiency even in the presence of exhaust path switching.The foregoing advantages, as well as other advantages and features of the present specification, will be readily apparent from the following detailed description when taken alone or in conjunction 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 intended to identify key 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 address any of the disadvantages listed above or in any part of this disclosure.Brief Description of the DrawingsThe advantages described herein will become more fully apparent from reading an example of an embodiment referred to herein as the detailed description when taken alone or with reference to the drawings in which: FIG. 1 is a schematic illustration of a single cylinder of an engine; FIG. 2 is a schematic illustration of an eight cylinder engine with valves arranged in a first configuration in an exhaust system to provide a straight exhaust flow through a catalyst; FIG. 3 is a schematic illustration of an eight cylinder engine with valves arranged in a first configuration in an exhaust system to provide a crossed exhaust flow through a catalyst; FIG. 4 is a schematic diagram of an eight cylinder engine with valves arranged in a second configuration in an exhaust system to provide a straight exhaust flow through a catalyst; FIG. 5 is a schematic illustration of an eight cylinder engine with valves arranged in a second configuration in an exhaust system to provide a crossed exhaust flow through a catalyst; FIG. 6 illustrates an example first fuel control system including an inner fuel control loop and an outer fuel control loop for each cylinder bank; and FIG. 7 illustrates an example second fuel control system that includes an inner fuel control loop and an outer fuel control loop for each cylinder bank.Detailed DescriptionThe present description relates to rules of fuel of an engine that includes two cylinder banks. The cylinder banks are coupled to an exhaust system including two valves that allow exhaust flow to change direction so that catalyst light-off shortened and high speed / high load engine operation may be facilitated. Fuel may be controlled for an internal combustion engine of the type shown in FIG. 1. The exhaust system of the engine and the valves in the exhaust system may be configured with crossover pipes as shown in FIGS. 2-5. Fuel may be regulated via a control system, as shown in FIG. 6. Alternatively, the fuel may be controlled via an alternative control system, as shown in FIG. 7.Referring to FIG. 1, an internal combustion engine 10 including a plurality of cylinders, one cylinder of which is shown in FIG. 1, is controlled by an electronic engine controller 12. Engine 10 includes a combustion chamber 30 and cylinder walls 32 with a piston 36 positioned therein and connected to a crankshaft 40. A flywheel 97 and a ring gear 99 are coupled to the crankshaft 40. A starter 96 includes a pinion shaft 98 and a pinion gear 95. the pinion shaft 98 can selectively advance the pinion gear 95 to engage the ring gear 99. The starter 96 may be mounted directly on the front of the engine or the rear of the engine. In one example, the starter 96 is in a ground state when not engaged with the engine crankshaft. Combustion chamber 30 is shown communicating with intake manifold 44 and exhaust manifold 48 via corresponding intake valve 52 and exhaust valve 54. Each intake and exhaust valve may be operated by an intake cam 51 and an exhaust cam 53. The position of the intake cam 51 may be determined by an intake cam sensor 55. The position of the exhaust cam 53 may be determined by an exhaust cam sensor 57.As shown, a direct fuel injector 66 is positioned to directly inject fuel into the cylinder 35, known to those skilled in the art as direct injection. Fuel injector 66 delivers liquid fuel in proportion to a voltage pulse width or fuel injection pulse width of a signal from controller 12. Fuel is delivered to fuel injector 66 through a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail (not shown). Moreover, intake manifold 44 is shown communicating with an optional electronic throttle 62 that adjusts a position of a throttle plate 64 to control air flow from an air inlet 42 to intake manifold 44.A distributorless ignition system 88 provides spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12. A first upstream oxygen sensor 126 (e.g., universal exhaust gas oxygen (UEGO) sensor, which may be referred to as a wide-band oxygen sensor) is shown coupled to exhaust manifold 48 upstream of a catalyst 70. Alternatively, the first upstream oxygen sensor 126 may be replaced with a two-state (e.g., narrowband) exhaust oxygen sensor.The catalyst 70 may include multiple catalyst honeycomb bodies in one example. In another example, multiple emission control devices each having multiple honeycomb bodies may be used. The catalyst 70 may be a three-way catalyst in one example.The controller 12 is shown in FIG. 1 as a conventional microcomputer including: a microprocessor unit 102, input / output ports 104, read-only memory 106 (e.g., persistent memory), random access memory 108, keep alive memory 110, and a conventional data bus. As shown, controller 12 receives various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including: an engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; a position sensor 134 coupled to a driver demand pedal 130 to sense a displacement path through a human 132; a position sensor 154 coupled to a caliper actuation pedal 150 to sense a displacement path through a human 132; a measurement of manifold pressure (MAP) from a pressure sensor 122 coupled to intake manifold 44; an engine position sensor 118 sensing a position of crankshaft 40; a measurement of mass air entering the engine from a sensor 120; and a measurement of throttle position from a sensor 58. In a preferred aspect of the present description, the engine position sensor 118 produces a predetermined number of equally spaced pulses each revolution of the crankshaft from which the engine speed (rpm) can be determined.In some examples, the engine may be coupled to an electric motor / battery system in a hybrid vehicle. Further, in some examples, other engine configurations may be employed, for example, a diesel engine with multiple fuel injectors. Further, the controller 12 may receive input and communicate conditions such as degradation of components to light or to a human / machine interface 171.During operation, each cylinder within engine 10 typically undergoes a four stroke cycle, the cycle including the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, generally, the exhaust valve 54 closes and the intake valve 52 opens. air is introduced into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves to the bottom of the cylinder to increase the volume within the combustion chamber 30. The position at which the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, the intake valve 52 and the exhaust valve 54 are closed. The piston 36 moves toward the cylinder head to compress the air within the combustion chamber 30. The point at which the piston 36 is closest to the cylinder head at the end of its stroke (e.g., when the combustion chamber 30 has its smallest volume) is commonly referred to by those of skill in the art as top dead center (TDC). In a process referred to as injection hereinafter in this specification, fuel is introduced into the combustion chamber. In a process referred to as ignition hereinafter, the injected fuel is ignited by known igniting means such as the spark plug 92, resulting in combustion. During the power stroke, the expanding gases push the piston 36 back to BDC. The crankshaft 40 converts the piston motion into a torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve 54 opens to deliver the combusted air-fuel mixture to the exhaust manifold 48, and the piston returns to TDC. It should be appreciated that the foregoing is shown merely as an example and that timings for opening and / or closing the intake and exhaust valves may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples.Referring now to FIG. 2, a top view 200 of the engine 10 is shown. The engine 10 is the same engine as shown in FIG. 1, but all engine cylinders are shown in FIG. 2. In this example, the cylinders of the engine are numbered 1-8. The cylinders are supplied with air via the intake manifold 44. A right cylinder bank includes cylinders 1- 4 and a left cylinder bank includes cylinders 5- 8. Cylinders 1- 4 are shown in fluid communication with exhaust manifold 48 and cylinders 5- 8 are shown in fluid communication with exhaust manifold 202. The right cylinder bank exhaust system 276 includes an exhaust manifold 48 and a first upstream oxygen sensor 126. The left cylinder bank exhaust system 275 includes an exhaust manifold 202 and a second upstream oxygen sensor 204. Each of the cylinders 1- 8 includes a fuel injector, a spark plug, and intake / exhaust valves as shown in FIG. 1.The engine 10 of FIG. 2 includes catalysts 70 and 270 (e.g., close-coupled catalysts) that enable a rapid catalyst light-off when the engine 10 is cold-started. However, under conditions where the engine is warm and operated at high loads and high speeds for extended periods of time, the flow of exhaust gas from the left cylinder bank 250 to the catalyst 270 may cause degradation of the catalyst 270. To reduce a possibility of catalyst 270 degradation during high speed / high load conditions, a position of valve 220 (e.g., the left valve of the left cylinder bank) may be adjusted to direct exhaust gas to left-right crossover pipe 251, resulting in exhaust gas flowing from left cylinder bank 250 to catalyst 70. Also, to reduce a possibility of catalyst 70 degradation during high speed / high load conditions, a position of the valve 222 (e.g., the right right cylinder bank valve) may be adjusted to direct exhaust gas to the right-left crossover pipe 253, resulting in exhaust gas flowing from the right cylinder bank 252 to the catalyst 270. The left-right crossover pipe 251 selectively fluidly couples the left cylinder bank exhaust system 275 to the right cylinder bank exhaust system 276. Similarly, right-left crossover pipe 253 selectively fluidly couples right cylinder bank exhaust system 276 to left cylinder bank exhaust system 275.In FIG. 2, a first valve configuration is illustrated in which the valve 220 is positioned at an inlet 251 iof the left-right crossover pipe 251 and the valve 222 is positioned at an inlet 253 iof the right-left crossover pipe 253. The valve 220 is shown in a first position (e.g., a pass-through state) where exhaust from the left cylinder bank 250 bypasses the left-right crossover pipe 251 and flows a short distance to the catalyst 270, thereby reducing the light-off time of the catalyst 270 so that engine exhaust pipe emissions may be reduced. Similarly, valve 222 is shown in a first position where exhaust from the right cylinder bank bypasses right-left crossover pipe 253 and flows a short distance to catalyst 70, thereby reducing light-off time of catalyst 70, so that engine exhaust pipe emissions may be reduced. Arrows 240 represent a direction of exhaust flow from the left cylinder bank 250 when the valve 220 blocks exhaust flow from the left-right crossover pipe 251 as shown. Arrows 230 represent a direction of exhaust flow from right cylinder bank 252 when valve 222 blocks exhaust flow from right-left crossover pipe 253 as shown.The first upstream oxygen sensor 126 (e.g., a wide band upstream oxygen sensor (UEGO)) is shown configured to detect exhaust gases from cylinders numbered 1-4 of the right cylinder bank 252. The second upstream oxygen sensor 204 (e.g., a wide band upstream oxygen sensor (UEGO)) is shown configured to detect exhaust gases from cylinders 5- 8 of the left cylinder bank 250. A third oxygen sensor 210 (e.g., a narrowband downstream oxygen sensor (HEGO)) is shown configured to detect exhaust gases from within the catalyst 70 or alternatively at location 212. A fourth oxygen sensor 206 (e.g., a narrowband downstream oxygen sensor (HEGO)) is shown configured to detect exhaust gases from within the catalyst 270 or, alternatively, at a location 208.The output of the first upstream oxygen sensor 126 may be applied as air-fuel or equivalence ratio feedback (e.g., λ=air-fuel ratio / stoichiometric air-fuel ratio) for regulating fuel supplied to the cylinders numbered 1-4. The output of the second upstream oxygen sensor 204 may be applied as air-fuel or equivalence ratio feedback for regulating fuel supplied to the cylinders numbered 5-8. The output of the third oxygen sensor 210 may be applied as a voltage signal, air-fuel ratio, or equivalence ratio feedback for an outer loop fuel control. The output of the fourth oxygen sensor 206 (e.g., a downstream oxygen sensor) may be applied as air-fuel or equivalence ratio feedback for outer loop fuel regulation.Referring now to FIG. 3, the top view 200 of the engine 10 is again shown. The components of the engine 10 are the same as shown in FIG. 2, and the components of the engine 10 operate as described above. Therefore, for brevity, the description of the engine 10 and its components will be omitted in FIG. 3.In FIG. 3, the valve 220 is positioned at an inlet 251 iof the left-right crossover pipe 251, and the valve 222 is positioned at an inlet 253 iof the right-left crossover pipe 253. Valve 220 is shown in a second position (e.g., a bypass condition) where entry of exhaust from left cylinder bank 250 into catalyst 270 is blocked. Instead, exhaust gases are directed from the left cylinder bank 250 to the left-right crossover pipe 251 and the exhaust gas flows to the catalyst 70 over a longer distance, thereby reducing a quantity of heat that can be transferred to the catalyst 70, so that a possibility of catalyst degradation can be reduced. Similarly, valve 222 is shown in a second position blocking entry of exhaust from right cylinder bank 252 into catalyst 70. Instead, exhaust gases are directed from the right cylinder bank 252 to the right-left crossover pipe 253 and the exhaust gas flows to the catalyst 270 for a longer distance so that a possibility of catalyst degradation may be reduced. Arrows 240 represent a direction of exhaust flow from the left cylinder bank 250 when the valve 220 blocks exhaust flow from the left cylinder bank 250 to the catalyst 270 as shown. Arrows 230 represent a direction of exhaust flow from right cylinder bank 252 when valve 222 blocks exhaust flow from right cylinder bank 252 to catalyst 70. Thus, FIG. 3 illustrates a configuration in which exhaust gases from the left cylinder bank are processed via catalyst 70 and exhaust gases from the right cylinder bank are processed via catalyst 270.Referring now to FIG. 4, the top view 200 of the engine 10 is again shown. The components of the engine 10 are the same as shown in FIG. 2, and the components of the engine 10 operate as described above. Therefore, for brevity, the description of the engine 10 and its components will be omitted in FIG. 4.In FIG. 4, a second valve configuration is illustrated in which the valve 220 is positioned at an outlet 253 oof the right-left crossover pipe 253 and the valve 222 is positioned at an outlet 251 oof the left-right crossover pipe 251. The valve 220 is shown in a first position where exhaust from the right cylinder bank 252 bypasses the right-left crossover pipe 253 and flows a short distance to the catalyst 70, thereby reducing the light-off time of the catalyst 70, such that engine exhaust pipe emissions may be reduced. Similarly, valve 222 is shown in a first position where exhaust from left cylinder bank 250 bypasses left-right crossover pipe 253 and flows a short distance to catalyst 270, thereby reducing catalyst 270 light-off time, so that engine exhaust pipe emissions may be reduced. Arrows 240 represent a direction of exhaust flow from the left cylinder bank 250 when the valve 222 blocks exhaust flow from the left-right crossover pipe 251 as shown. Arrows 230 represent a direction of exhaust flow from right cylinder bank 252 when valve 220 blocks exhaust flow from right-left crossover pipe 253 as shown.Referring now to FIG. 5, the top view 200 of the engine 10 is again shown. The components of the engine 10 are the same as shown in FIG. 2, and the components of the engine 10 operate as described above. Therefore, for brevity, the description of the engine 10 and its components will be omitted in FIG. 5.In FIG. 5, the second configuration in which the valve 220 is positioned at the outlet 253 oof the right-left crossover pipe 253 and the valve 222 is positioned at the outlet 251 oof the left-right crossover pipe 251 is illustrated a second time. Valve 220 is shown in a second position where exhaust from left cylinder bank 250 is blocked by catalyst 270 and allowed to flow through left-right crossover tube 251 and catalyst 70. Similarly, valve 222 is shown in a second position where exhaust from right cylinder bank 252 is blocked by catalyst 70 and allowed to flow through right-left crossover tube 253 and catalyst 270. The second position of these valves allows the catalyst 70 and the catalyst 270 to remain cooler even at high engine speeds and loads. Arrows 240 represent a direction of exhaust flow from the left cylinder bank 250 when the valve 220 blocks exhaust flow from the left cylinder bank 250 to the catalyst 270 as shown. Arrows 230 represent a direction of exhaust flow from right cylinder bank 252 when valve 222 blocks exhaust flow from right cylinder bank 252 to catalyst 70, as shown.Thus, the system of FIGS. 1-5 provides for an engine system, comprising: an engine including a left cylinder bank and a right cylinder bank; a right cylinder bank exhaust system coupled to the right cylinder bank; a left cylinder bank exhaust system coupled to the left cylinder bank; a right-left crossover pipe coupling the right cylinder bank exhaust system to the left cylinder bank exhaust system; a left-right crossover pipe coupling the left cylinder bank exhaust system to the right cylinder bank exhaust system; a right valve positioned along the right cylinder bank exhaust system; a left valve positioned along the left cylinder bank exhaust system; a left upstream oxygen sensor; a right upstream oxygen sensor; a left downstream oxygen sensor; a right downstream oxygen sensor; and a controller including executable instructions stored in persistent memory that cause the controller to adjust a first inner loop setpoint in response to outer loop corrections generated among two different outer loop controls. In a first example, the engine system further comprises additional executable instructions that cause the controller to adjust a second inner loop setpoint in response to the outer loop corrections generated via the two different outer loop controllers. In a second example, which may include the first example, the engine system includes where the first inner loop setpoint is adjusted in response to an output of a first of the two different outer loop controls in response to a first command or position of the right valve or the left valve. In a third example, which may include one or both of the first and second examples, the engine system includes where the first inner loop setpoint is adjusted responsive to an output of a second of the two different outer loop controls responsive to a second command or position of the right valve or the left valve. In a fourth example, which may include one or more of the first through third examples, the motor system includes where the first inner loop setpoint is adjusted according to a weighting of the outer loop corrections generated via the two different outer loop controls. In a fifth example, which may include one or more of the first through fourth examples, the engine system includes where the weighting is adjusted as a function of time or exhaust flow since the left valve or right valve moved from or was commanded to move from position. In a sixth example, which may include one or more of the first through fifth examples, the engine system further comprises additional executable instructions that cause the controller to adjust an amount of fuel supplied to the right cylinder bank based on the first inner circle threshold.Referring now to FIG. 6, a block diagram 600 of a first fuel control method and system including a right cylinder bank fuel control 601 and a left cylinder bank fuel control 603 is shown. Right cylinder bank fuel control 601 controls the amounts of fuel supplied to the right engine cylinder bank and left cylinder bank fuel control 603 controls the amounts of fuel supplied to the left engine cylinder bank. This fuel control system allows corrections of the outer circuit control to be switched or exchanged between the left cylinder bank fuel control 603 and the right cylinder bank fuel control 601 so that the corrections of the outer circuit control change with the positions of the left cylinder bank left valve 220 and the right cylinder bank valve 222.It should be appreciated that FIG. 6 illustrates a simplified version of a fuel control method and system that includes inner and outer circuits for the left and right cylinder banks. Other versions of fuel control systems with inner and outer control loops for the left and right cylinder banks are also anticipated. At least portions of the fuel control method and system shown in FIG. 6 may be generated via executable instructions stored in persistent memory of a controller (e.g., 12 of FIG. 1 ).The right cylinder bank fuel control 601 includes a right cylinder bank inner control loop 652 and a right cylinder bank outer control loop 650. A desired or requested lambda value (e.g., lambda=air-fuel ratio / stoichiometric air-fuel ratio) for the right cylinder bank is input to the right cylinder bank summing junction 602, where it is added with a right cylinder bank inner circle correction lambda value. The right cylinder bank summing junction 602 outputs a right cylinder bank desired lambda value input at block 604, and block 604 generates a fuel mass for the right cylinder bank 252 in response to the right cylinder bank desired lambda value and a mass air flow rate into the engine. Block 604 outputs a mass of fuel that is delivered to the right cylinder bank 252 of the engine 10. The engine 10 burns the fuel mass with air to generate torque and exhaust gas. The exhaust from the right cylinder bank is detected via the first upstream oxygen sensor 126 before the exhaust is processed by the catalyst 70 or the catalyst 270, depending on the positions of the valves 220 and 222.The right cylinder bank outer loop 650 receives input from the downstream oxygen sensor 210, and the output from the downstream oxygen sensor 210 is subtracted from the output of a desired voltage table 608 at junction 610. The downstream oxygen sensor voltage error value generated at junction 610 is input to outer loop controller 606, where a first outer loop correction value is generated. The first correction value of the outer loop may be applied to either summing junction 615 or, alternatively, to summing junction 633 via a switch 688. In this example, the control logic is shown as switch 688, which is configured as a two-pole double throw switch whose operating state is controlled via positions of or commands to valves in the outlet (e.g., valves 220 and 222). When valves 220 and 222 are commanded or positioned so that exhaust gas may flow from right cylinder bank 252 to catalyst 70, the first outer loop correction value is input to summing junction 615. When valves 220 and 222 are commanded or positioned so that exhaust gas may flow from left cylinder bank 250 to catalyst 70, the first outer loop correction value is input to summing junction 633.The right cylinder bank inner control loop 652 receives input from the first upstream lambda probe 126, and this is subtracted from the desired lambda value and the right cylinder bank outer control loop output or the left cylinder bank outer control loop output at summing junction 615. The output of summing junction 615 is input to the right cylinder bank inner circle controller 612. The right cylinder bank inner circle controller 612 outputs an inner circle correction and this output is input to the summing junction 602 where it is added with the desired lambda value.The right cylinder bank fuel control 603 includes a right cylinder bank inner control loop 656 and a right cylinder bank outer control loop 654. A desired or requested lambda value (e.g., lambda=air-fuel ratio / stoichiometric air-fuel ratio) for the left cylinder bank is input to the left cylinder bank summing junction 620, where it is added with a left cylinder bank inner circle correction lambda value. The left cylinder bank summing junction 620 outputs a left cylinder bank desired lambda value that is input at block 622, and block 622 generates a fuel mass for the left cylinder bank 250 in response to the left cylinder bank desired lambda value and a mass air flow rate into the engine. Block 622 outputs a mass of fuel delivered to the left cylinder bank 250 of the engine 10. The engine 10 burns the fuel mass with air to generate torque and exhaust gas. The exhaust from the left cylinder bank is detected via the second upstream oxygen sensor 204 before the exhaust is processed by the catalyst 70 or the catalyst 270, depending on the positions of the valves 220 and 222.The left cylinder bank outer loop 654 receives input from the downstream oxygen sensor 206 and the output from the downstream oxygen sensor 206 is subtracted from the output of a desired voltage table 626 at junction 628. The downstream oxygen sensor voltage error value generated at junction 628 is input to outer loop controller 624, where a second outer loop correction value is generated. The second correction value of the outer loop may be applied to either summing junction 633 or alternatively to summing junction 615 via switch 688. When valves 220 and 222 are commanded or positioned so that exhaust gas may flow from left cylinder bank 250 to catalyst 270, the second outer loop correction value is input to summing junction 633. When valves 220 and 222 are commanded or positioned so that exhaust gas may flow from right cylinder bank 252 to catalyst 270, the second outer loop correction value is input to summing junction 615.The left cylinder bank inner control loop 656 receives input from the second upstream lambda probe 204 and this is subtracted from the desired lambda value and the left cylinder bank outer control loop output or the right cylinder bank outer control loop output at summing junction 633. The output of summing junction 633 is input to left cylinder bank inner circle controller 630. The left cylinder bank inner circle controller 630 outputs an inner circle correction and this output is input to the summing junction 620 where it is added with the desired lambda value.Thus, as illustrated and discussed with respect to FIG. 6, outer loop corrections (Δλ c,OL, e.g., output of block 606) may be applied as a modification of an inner loop setpoint λ (λ t,IL, e.g., input in block 612) such that: λ t,IL= λ des+ Δλ c,OL, where λ des is the desired lambda value. Because valves and the exhaust system reciprocate from a direct or straight flow (e.g., a direct exhaust path that does not include flow through a cross-tube) to a cross exhaust flow (e.g., exhaust flows from a cylinder bank through a cross-tube), the corrections of the outer circle may be assigned to correction targets of different inner loops according to the following equations:For Direct Exhaust Flow Paths:For crossed exhaust flow paths: where [R] identifies the right cylinder bank, [L] identifies the left cylinder bank, Δλ c,OL corresponds to lambda correction for an outer circle, λ des is the desired lambda, λ t,IL is the desired lambda for inner circle regulation. During a time when the valves in the outlet are moving, the corrections of the outer circuit can be kept at their last value.It should be appreciated that instead of switching the output of the outer loop right controller 606 from the summing junction 615 to the summing junction 633 and switching the output of the inner loop left controller 624 from the summing junction 633 to the summing junction 615 in response to the position of the valves 220 and 222 changing, the output of the right downstream oxygen sensor 210 may be switched from the summing junction 610 to the summing junction 628 and the output of the left downstream oxygen sensor 206 is switched from the summing junction 628 to the summing junction 610 to perform substantially a same function and achieve a substantially similar result as switching the target of the outputs of the outer loop controllers 606 and 624. Moreover, the output of the desired voltage table 626 may be switched to the summing junction 610, and the output of the desired voltage table 608 may be switched to the summing junction 628.Turning now to FIG. 7, a block diagram of an alternative fuel control method and system for an engine having two cylinder banks is shown. Instead of switching outer loop corrections to set inner loop setpoints as performed by the control of FIG. 6, FIG. 7 illustrates a method by which outer loop corrections may be gradually shifted. Block diagram 700 of a second fuel control system includes a right cylinder bank fuel control 701 and a left cylinder bank fuel control 703. The right cylinder bank fuel control 701 controls the amounts of fuel supplied to the right engine cylinder bank, and the left cylinder bank fuel control 703 controls the amounts of fuel supplied to the left engine cylinder bank. This fuel control system allows corrections of the outer circuit control between the left cylinder bank fuel control 703 and the right cylinder bank fuel control 701 to be gradually changed, so that the corrections of the outer circuit control gradually change with positions of the left left cylinder bank valve 220 and the right cylinder bank valve 222.It should be appreciated that FIG. 7 illustrates a simplified version of a fuel control method and system that includes inner and outer circuits for the left and right cylinder banks. Other versions of fuel control methods and systems with inner and outer control loops for the left and right cylinder banks are also anticipated. At least portions of the fuel control method and system depicted in FIG. 7 may be generated via executable instructions stored in persistent memory of a controller (e.g., 12 of FIG. 1 ).The right cylinder bank fuel control 701 includes a right cylinder bank inner control loop 752 and a right cylinder bank outer control loop 750. A desired or requested lambda value (e.g., lambda=air-fuel ratio / stoichiometric air-fuel ratio) for the right cylinder bank is input to the right cylinder bank summing junction 702, where it is added with a right cylinder bank inner circle correction lambda value. The right cylinder bank summing junction 702 outputs a right cylinder bank desired lambda value input at block 704, and block 704 generates a fuel mass for the right cylinder bank 252 in response to the right cylinder bank desired lambda value and a mass air flow rate into the engine. Block 704 outputs a mass of fuel that is delivered to the right cylinder bank 252 of the engine 10. The engine 10 burns the fuel mass with air to generate torque and exhaust gas. The exhaust from the right cylinder bank is detected via the first upstream oxygen sensor 126 before the exhaust is processed by the catalyst 70 or the catalyst 270, depending on the positions of the valves 220 and 222.The right cylinder bank outer loop 750 receives input from the downstream oxygen sensor 210, and the output from the downstream oxygen sensor 210 is subtracted from the output of a desired voltage table 708 at junction 710. The downstream oxygen sensor voltage error value generated at junction 710 is input to outer loop controller 706, where a first outer loop correction value is generated. The first outer loop correction value is provided to block 760, where a weighting function mixes the first outer loop correction value with a second outer loop correction to produce a weighted correction which is provided to summing junction 715. The weighting value (w) may be adjusted as a function of time since the last movement or command of a valve (e.g., valves 220 and 222) and / or exhaust flow rate and / or valve position (e.g., positions of valves 220 and 222). The weighting value may vary between 0 and 1 depending on time, exhaust gas flow rate or valve position.The right cylinder bank inner control loop 752 receives input from the first upstream lambda probe 126, and this is subtracted from the desired lambda value and the output of block 760 (e.g., weighted outer control loop correction for the right cylinder bank inner loop) at summing junction 715. The output of summing junction 715 is input to the right cylinder bank inner circle regulator 712. The right cylinder bank inner circle controller 712 outputs an inner circle correction and this output is input to the summing junction 702 where it is added with the desired lambda value.The right cylinder bank fuel control 703 includes a right cylinder bank inner control loop 756 and a right cylinder bank outer control loop 754. A desired or requested lambda value for the left cylinder bank is input to the left cylinder bank summing junction 720, where it is added to a left cylinder bank inner circle correction lambda value. The left cylinder bank summing junction 720 outputs a left cylinder bank desired lambda value that is input at block 722, and block 722 generates a fuel mass for the left cylinder bank 250 in response to the left cylinder bank desired lambda value and a mass air flow rate into the engine. Block 722 outputs a mass of fuel that is delivered to the left cylinder bank 250 of the engine 10. The engine 10 burns the fuel mass with air to generate torque and exhaust gas. The exhaust from the left cylinder bank is detected via the second upstream oxygen sensor 204 before the exhaust is processed by the catalyst 70 or the catalyst 270, depending on the positions of the valves 220 and 222.The left cylinder bank outer loop 754 receives input from the downstream oxygen sensor 206 and the output from the downstream oxygen sensor 206 is subtracted from the output of a desired voltage table 726 at the junction 728. The downstream oxygen sensor voltage error value generated at junction 728 is input to outer loop controller 724, where a second outer loop correction value is generated. The second outer loop correction value is applied to block 760, where a weighting function mixes the second outer loop correction value with the first outer loop correction to produce a weighted correction which is provided to summing junction 733. The weighting value (w) may be adjusted as a function of time since the last movement or command of a valve (e.g., valves 220 and 222) and / or exhaust flow rate and / or valve position (e.g., positions of valves 220 and 222). The weighting value may vary between 0 and 1 depending on time, exhaust gas flow rate or valve position.The left cylinder bank inner control loop 756 receives input from the second upstream lambda probe 204 and this is subtracted from the desired lambda value and the left cylinder bank outer control loop output or the left cylinder bank outer control loop weighted correction value output at summing junction 733. The output of summing junction 733 is input to left cylinder bank inner circle controller 730. The left cylinder bank inner circle controller 730 outputs an inner circle correction and this output is input to the summing junction 720, where it is added with the desired lambda value.Thus, as shown and discussed with respect to FIG. 7, a weighted average of outer loop corrections of the right and left cylinder banks may be applied to inner loop setpoints of the right and left cylinder banks according to the following equations: where [R] identifies the right cylinder bank, [L] identifies the left cylinder bank, Δλ c,OL corresponds to lambda correction for an outer circle, λ des is the desired lambda, λ t,lL is the desired lambda for inner circle control.For Direct Exhaust Flow Paths:For crossed exhaust flow paths: During a time that the valves are moving in the outlet, the value of the weighting factor (w) may be adjusted depending on one or more of a valve position (e.g., valve 222 or 222), an exhaust flow, and / or a latest time since a change in valve movement was commanded.The methods of FIGS. 6 and 7 provide a fuel control method, comprising: in a first mode, setting a first inner circuit set point in response to a first outer circuit correction and setting a second inner circuit set point in response to a second outer circuit correction; in a second mode, setting the first inner circuit set point in response to the second outer circuit correction and setting a second inner circuit set point in response to the first outer circuit correction; and supplying fuel to an engine via control according to the first inner circuit set point and the second inner circuit set point. In a first example, the fuel control method includes where the engine includes a first upstream oxygen sensor, a second upstream oxygen sensor, a first downstream oxygen sensor, and a second downstream oxygen sensor. In a second example, which may include the first example, the fuel control method includes where the first outer loop correction is based on an output of the first downstream oxygen sensor and where the second outer loop correction is based on the output of the second downstream oxygen sensor. In a third example, which may include one or both of the first and second examples, the fuel control method includes where fuel supplied to a right cylinder bank is based on the first inner circuit setpoint and where fuel supplied to a left cylinder bank is based on the second inner circuit setpoint. In a fourth example, which may include one or more of the first through third examples, the fuel control method further includes a first inner circuit control and a second inner circuit control. In a fifth example, which may include one or more of the first through fourth examples, the fuel control method includes where the first inner loop control receives input from the first upstream oxygen sensor and where the second inner loop control receives input from the second upstream oxygen sensor. In a sixth example, which may include one or more of the first through fifth examples, the fuel control method includes activating the first mode based on a valve in an exhaust passage of the engine being in a first position or commanded to the first position. In a seventh example, which may include one or more of the first through sixth examples, the fuel control method includes activating the second mode based on a valve in an exhaust passage of the engine being in a second position or commanded to the second position.The methods of FIGS. 6 and 7 provide a fuel control method comprising: adjusting a quantity of fuel supplied to a cylinder bank of an internal combustion engine in response to a first output of the outer loop control and a second output of the outer loop control. In a first example, the fuel control method includes where the first output of the outer loop control is mixed with the second output of the outer loop control and where a weighting factor adjusts the mixing between the first output of the outer loop control and the second output of the outer loop control. In a second example, which may include the first example, the fuel control method includes adjusting the amount of fuel supplied to the cylinder bank via switching between the first outer loop control output and the second outer loop control output. In a third example, which may include one or both of the first and second examples, the fuel control method further comprises adjusting the amount of fuel supplied to the cylinder bank further in response to a position or command of a valve in an exhaust system of the internal combustion engine. In a fourth example, which may include one or more of the first through third examples, the fuel control method further comprises adjusting the position or command in response to a temperature or an exhaust flow rate.It should be appreciated that the example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. Moreover, although the methods herein relate to lambda control, the approaches herein may be applied to other units. For example, the approaches herein describe lambda control, but in other examples, the controls and methods may be configured to control the air-fuel ratio. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be executed by the control system including the control in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. Thus, various illustrated acts, acts, and / or functions may be performed in the illustrated sequence, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the examples described herein, but rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may / may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations, and / or functions may graphically represent code to be programmed into a non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.Thus, the description is completed. Many changes and modifications would be apparent to those skilled in the art upon reading them without departing from the spirit and scope of the description. For example, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could take advantage of the present description.According to the present invention, a fuel control method includes: in a first mode, setting a first inner circuit target value in response to a first outer circuit correction and setting a second inner circuit target value in response to a second outer circuit correction; in a second mode, setting the first inner circuit target value in response to the second outer circuit correction and setting the second inner circuit target value in response to the first outer circuit correction; and supplying fuel to an engine via control according to the first inner circuit target value and the second inner circuit target value.In one aspect of the invention, the engine includes a first upstream oxygen sensor, a second upstream oxygen sensor, a first downstream oxygen sensor, and a second downstream oxygen sensor.In one aspect of the invention, the first outer loop correction is based on an output of the first downstream oxygen sensor, and wherein the second outer loop correction is based on the output of the second downstream oxygen sensor.In one aspect of the invention, fuel supplied to a right cylinder bank is based on the first inner circuit setpoint and fuel supplied to a left cylinder bank is based on the second inner circuit setpoint.In one aspect of the invention, the method includes a first inner circuit control and a second inner circuit control.In one aspect of the invention, the first inner loop control receives input from the first upstream oxygen sensor and the second inner loop control receives input from the second upstream oxygen sensor.In one aspect of the invention, the first mode is activated based on a valve in an exhaust passage of the engine being in a first position or commanded to the first position.In one aspect of the invention, the first mode is activated based on the valve in the exhaust passage of the engine being in a second position or commanded to the second position.According to the present invention, there is provided an engine system comprising: an engine including a left cylinder bank and a right cylinder bank; a right cylinder bank exhaust system coupled to the right cylinder bank; a left cylinder bank exhaust system coupled to the left cylinder bank; a right-left crossover pipe coupling the right cylinder bank exhaust system to the left cylinder bank exhaust system; a left-right crossover pipe coupling the left cylinder bank exhaust system to the right cylinder bank exhaust system; a right valve positioned along the right cylinder bank exhaust system; a left valve positioned along the left cylinder bank exhaust system; a left upstream oxygen sensor; a right upstream oxygen sensor; a left downstream oxygen sensor; a right downstream oxygen sensor; and a controller including executable instructions stored in persistent memory that cause the controller to adjust a first inner loop setpoint in response to outer loop corrections generated among two different outer loop controls.According to an embodiment, the invention is further characterized by additional executable instructions that cause the controller to adjust a second inner loop setpoint in response to the outer loop corrections generated via the two different outer loop controllers.According to an embodiment, the first inner circuit setpoint is adjusted in response to an output of a first of the two different outer circuit controls in response to a first command or position of the right valve or the left valve.According to an embodiment, the first inner circuit setpoint is adjusted in response to an output of a first of the two different outer circuit controls in response to a second command or position of the right valve or the left valve.According to an embodiment, the first inner circuit set point is adjusted according to a weighting of the outer circuit corrections generated via the two different outer circuit regulations.According to one embodiment, the weighting is adjusted as a function of time or exhaust flow since the left valve or the right valve is moving from or commanded to move from a position.According to one embodiment, the invention is further characterized by additional executable instructions that cause the controller to adjust a fuel amount supplied to the right cylinder bank based on the first inner loop setpoint.According to the present invention, a fuel control method includes: adjusting a quantity of fuel supplied to a cylinder bank of an internal combustion engine in response to a first output of the outer circuit control and a second output of the outer circuit control.In one aspect of the invention, the output of the outer loop control is mixed with the second output of the outer loop control, and wherein a weighting factor adjusts the mixing between the first output of the outer loop control and the second output of the outer loop control.In one aspect of the invention, the amount of fuel supplied to the cylinder bank is adjusted via switching between the first output of the outer loop control and the second output of the outer loop control.In one aspect of the invention, the method includes adjusting the amount of fuel supplied to the cylinder bank further in response to a position or command of a valve in an exhaust system of the internal combustion engine.In one aspect of the invention, the method includes adjusting the position or command in response to a temperature or an exhaust flow rate.

Claims

A fuel control method comprising: in a first mode, setting an inner circuit first target value in response to a first outer circuit correction and setting an inner circuit second target value in response to a second outer circuit correction; in a second mode, setting the inner circuit first target value in response to the second outer circuit correction and setting the inner circuit second target value in response to the first outer circuit correction; and supplying fuel to an engine via control according to the inner circuit first target value and the inner circuit second target value.The fuel control method of claim 1, wherein the engine includes a first upstream oxygen sensor, a second upstream oxygen sensor, a first downstream oxygen sensor, and a second downstream oxygen sensor.The fuel control method of claim 2, wherein the first outer loop correction is based on an output of the first downstream oxygen sensor and wherein the second outer loop correction is based on an output of the second downstream oxygen sensor.The fuel control method of claim 3, wherein fuel supplied to a right cylinder bank is based on the first inner circuit target value, and wherein fuel supplied to a left cylinder bank is based on the second inner circuit target value.The fuel control method according to claim 4, further comprising a first inner circuit control and a second inner circuit control.The fuel control method of claim 5, wherein the first inner loop control receives input from the first upstream oxygen sensor and wherein the second inner loop control receives input from the second upstream oxygen sensor.The fuel control method of claim 1, wherein the first mode is activated based on a valve in an exhaust passage of the engine being in a first position or commanded to the first position.The fuel control method of claim 7, wherein the second mode is activated based on the valve in the exhaust passage of the engine being in a second position or commanded to the second position.An engine system, comprising: an engine including a left cylinder bank and a right cylinder bank; a right cylinder bank exhaust system coupled to the right cylinder bank; a left cylinder bank exhaust system coupled to the left cylinder bank; a right-left crossover pipe coupling the right cylinder bank exhaust system to the left cylinder bank exhaust system; a left-right crossover pipe coupling the left cylinder bank exhaust system to the right cylinder bank exhaust system; a right valve positioned along the right cylinder bank exhaust system; a left valve positioned along the left cylinder bank exhaust system; a left upstream oxygen sensor; a right upstream oxygen sensor; a left downstream oxygen sensor; a right downstream oxygen sensor; and a controller including executable instructions stored in persistent memory that cause the controller to adjust a first inner loop setpoint in response to outer loop corrections generated via the two different outer loop controllers.The engine system of claim 9, further comprising additional executable instructions that cause the controller to adjust a second inner loop setpoint in response to the outer loop corrections generated via the two different outer loop controllers.The engine system of claim 10, wherein the first inner circuit setpoint is adjusted in response to an output of a first of the two different outer circuit controls in response to a first command or position of the right valve or the left valve.The engine system of claim 11, wherein the first inner circuit setpoint is adjusted in response to an output of a second of the two different outer circuit controls in response to a second first command or a second position of the right valve or the left valve.The motor system of claim 9, wherein the first inner circle setpoint is adjusted according to a weighting of the outer circle corrections generated via the two different outer circle controls.The engine system of claim 13, wherein the weighting is adjusted as a function of time or exhaust flow since the left valve or the right valve has moved from or has been commanded to move from the position.The engine system of claim 9, further comprising additional executable instructions that cause the controller to adjust a quantity of fuel supplied to the right cylinder bank based on the first inner loop setpoint.

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