Split-cycle exhaust engine with idle check valve

Abstract

The present disclosure provides "Split Exhaust Engine with Idle Check Valve". Methods and systems are provided for reducing exhaust residuals in a split exhaust engine during light load conditions via a check valve. In one example, a scavenge exhaust manifold can be maintained above a threshold pressure by introducing fresh air into the scavenge exhaust manifold during a valve overlap period, the scavenge exhaust manifold being coupled to a cylinder of an engine and to an intake passage of the engine.

Description

Technical Field

[0001] This specification generally relates to methods and systems for increasing combustion stability and reducing exhaust valve opening losses in the operation of split-flow exhaust engines utilizing direct-fired exhaust. Background Technology

[0002] Engines can use supercharging devices, such as turbochargers, to increase engine power density. However, engine knocking can occur due to the increased combustion temperature. Knocking is particularly problematic under supercharged conditions due to the high charging temperature. The inventors here have recognized that engine systems with a split exhaust system can reduce knocking and improve engine efficiency, in which a first exhaust manifold directs exhaust gas recirculation (EGR) upstream of the turbocharger compressor to the engine's intake passage, and a second exhaust manifold directs exhaust gas to the turbocharger turbine in the engine's exhaust passage. In such an engine system, each cylinder may include two intake valves and two exhaust valves, wherein a first set of cylinder exhaust valves (e.g., bleed exhaust valves) connected only to the first exhaust manifold can operate at different timings than a second set of cylinder exhaust valves (e.g., scavenging exhaust valves) connected only to the second exhaust manifold, thereby isolating the bleed portion and the scavenging portion of the exhaust gas. The timing of the second set of cylinder exhaust valves can also be coordinated with the timing of the cylinder intake valves to form a positive valve overlap period, during which fresh intake air (or a mixture of fresh intake air and EGR) (referred to as direct blow) can flow through the cylinder and return to the intake passage upstream of the compressor via an EGR passage connected to the first exhaust manifold. Direct blow air can remove residual exhaust gas from the cylinder (referred to as scavenging). The inventors of this paper have recognized that by allowing a first portion of the exhaust gas (e.g., higher-pressure exhaust) to flow through the turbine and a higher-pressure exhaust passage, and by allowing a second portion of the exhaust gas (e.g., lower-pressure exhaust) and direct blow air to flow to the compressor inlet, combustion temperatures can be reduced while improving turbine efficiency and engine torque.

[0003] However, the inventors of this paper have recognized the potential problems of such systems. As an example, in the aforementioned engine system, the timing of the two exhaust valve openings results in a relatively long cylinder exhaust event (e.g., the total amount of exhaust valve opening time), which interacts with / overlaps with the intake valve opening. This valve overlap period can negatively impact fuel economy and combustion stability under light engine loads. While the valve overlap period can be reduced or eliminated at low loads by advancing the exhaust valve timing, the resulting exhaust valve opening losses may reduce fuel economy, thus offsetting any potential benefits of reducing valve overlap. On the other hand, if exhaust valve timing is delayed to reduce exhaust valve losses, internal exhaust residues may increase, thereby reducing combustion stability. Therefore, a mechanism is needed that minimizes exhaust valve losses during low engine loads while reducing internal residues to maintain combustion stability and reduce fuel economy. Summary of the Invention

[0004] In one example, the above problem can be addressed by a method that includes maintaining the scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during the valve overlap period. The scavenging manifold is connected to both the engine cylinders and the engine's intake passage. In this way, the scavenging manifold can remain oxygen-rich during idling or in other conditions where a vacuum may occur in the scavenging manifold, thereby reducing or preventing exhaust gas from entering the scavenging manifold during valve overlap, thus reducing combustion instability.

[0005] In another example, one approach includes: during low engine load conditions, delaying the closing timing of both the venting exhaust valve that connects the engine cylinder to the turbine and the scavenging exhaust valve that connects the cylinder to the engine intake passage via the scavenging manifold; and reducing exhaust residue in the cylinder by allowing intake air into the scavenging manifold during the valve overlap period.

[0006] In this way, during low engine load conditions such as idling, the closing timing of the bleed exhaust valve and the scavenging exhaust valve can each be delayed, thereby reducing exhaust valve losses associated with earlier closing timing. Because the bleed valve closes at a later timing (e.g., closer to top dead center), all exhaust gas from the cylinder is directed to the turbine via the bleed valve (which is connected to a separate bleed exhaust manifold). This can result in low-pressure conditions in the scavenging manifold, which, if maintained, can draw exhaust gas from subsequent combustion events into the scavenging manifold. Ultimately, the scavenging manifold can become filled with exhaust residue, leading to unstable combustion. By filling the scavenging manifold with intake air, these exhaust residues can be reduced, allowing the engine to operate with delayed exhaust valve closing, thus reducing exhaust valve losses.

[0007] In one example, intake air may be allowed to enter the scavenging manifold via a check valve positioned upstream of the throttle valve between the scavenging manifold and the intake passage. For example, the check valve may be positioned in a conduit connected around an exhaust recirculation valve and may be configured to allow only air from the intake passage into the scavenging manifold during other engine operating conditions and prevent exhaust gas from flowing back from the scavenging manifold into the intake passage.

[0008] It should be understood that the foregoing summary is provided to present a simplified version of a series of concepts that will be further described in the detailed description section. This does not imply representation of key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to embodiments that address any shortcomings pointed out in the foregoing or any part of this disclosure. Attached Figure Description

[0009] Figure 1A and Figure 1B A schematic diagram of a turbocharged engine system with a split exhaust system is shown.

[0010] Figure 2 It shows Figure 1A and Figure 1B An example of an engine system cylinder.

[0011] Figure 3 An exemplary cylinder intake and exhaust valve timing of one engine cylinder in a split-flow exhaust engine system is shown.

[0012] Figure 4 This is a flowchart illustrating an exemplary method for operating a split-flow exhaust engine system.

[0013] Figure 5 This is an exemplary illustration showing the proportion of scavenged manifold exhaust residue as a function of exhaust valve closing timing.

[0014] Figure 6 This is an exemplary diagram illustrating the check valve flow rate and manifold pressure in the engine cycle.

[0015] Figure 7A and Figure 7B It shows that it can be executed Figure 4 An exemplary timing diagram of the operating parameters observed during the method. Detailed Implementation

[0016] The following description relates to systems and methods for operating a split-flow exhaust engine using direct blow and exhaust gas recirculation (EGR) via a scavenging exhaust manifold to the intake passage. For example... Figure 1A and Figure 1BAs shown, the split-flow exhaust engine includes a first exhaust manifold (referred to herein as the bleed exhaust manifold) connected only to a bleed exhaust valve for each cylinder. The bleed exhaust manifold is connected to the engine's exhaust passage, which includes a turbocharger turbine and one or more emission control devices (which may include one or more catalysts). The split-flow exhaust engine also includes a second exhaust manifold (referred to herein as the scavenging exhaust manifold), which is connected only to a scavenging exhaust valve for each cylinder. The scavenging manifold is connected to the intake passage upstream of the turbocharger compressor via an EGR passage including an EGR valve (referred to herein as the scavenging EGR valve). Additionally, in some embodiments, the split-flow exhaust engine system may include various valve actuation mechanisms and may be installed in hybrid vehicles, such as... Figure 2 As shown in the diagram. For each cylinder, the scavenging exhaust valve and the venting exhaust valve open and close at different times during the engine cycle to isolate the scavenging and venting portions of the combustion exhaust and direct these portions to the scavenging manifold and venting manifold, respectively. Figure 3 As shown, there may be an overlap period between the intake valve and the scavenging exhaust valve of each cylinder, during which these valves open simultaneously. Therefore, fresh direct-flow air can flow into the EGR passage via the scavenging exhaust valve. Thus, during each engine cycle, the EGR passage can receive a combination of combusted exhaust, direct-flow air, and unburned fuel, and recirculate this combined gas mixture back into the intake passage.

[0017] The specific structure of a split-exhaust engine system (e.g.) Figure 1A and Figure 1B As illustrated in the example, the timing of the cylinder valves leads to an increased proportion of direct-flow air in the gas recirculated to the intake manifold via the EGR passage (compared to conventional engines utilizing EGR), making it challenging to maintain combustion stability and reduce fuel economy during low engine load periods, such as idling. For example, fuel economy can be improved by reducing exhaust valve losses that occur when the exhaust valve closes at a relatively early timing (e.g., before top dead center). Exhaust valve losses can be reduced by delaying exhaust valve closing (e.g., after top dead center). However, delaying exhaust valve closing during the valve overlap period when both the scavenging exhaust valve and intake valve are open can lead to a decrease in pressure in the scavenging manifold. This pressure decrease may allow exhaust gas to enter the scavenging manifold. Because both the scavenging EGR valve and the scavenging wastegate are closed during idling, the reduced scavenging manifold pressure can lead to the buildup of exhaust residue in the scavenging manifold, which can reduce combustion stability.

[0018] Therefore, according to the embodiments disclosed herein, the check valve can be positioned parallel to the scavenging EGR valve, such as... Figure 1A and Figure 1BAs shown in the diagram. The check valve can open to introduce fresh air into the scavenging manifold when the intake valve is open, as... Figure 4 As described in the flowchart, measures are taken to prevent excessive residue from accumulating in the scavenging manifold, and to improve stability and minimize exhaust valve opening losses, such as... Figure 5 (It shows exhaust residue as a function of exhaust valve closure) and Figure 6 (It shows an exemplary check valve flow rate and manifold pressure as a function of engine position) as illustrated in the figure. Figure 7A and Figure 7B The text shows that it can be executed Figure 4 Exemplary operating parameters observed during the method.

[0019] Figure 1A A schematic diagram of a multi-cylinder internal combustion engine 10 is shown, which can be included in the propulsion system of a vehicle. The engine 10 includes multiple combustion chambers (i.e., cylinders), the tops of which can be covered by cylinder heads (not shown). Figure 1A In the example shown, engine 10 includes cylinders 11, 14, 16, and 18 arranged in an inline 4-cylinder configuration. However, it should be understood that although... Figure 1A Four cylinders are shown, but engine 10 can also include any number of cylinders in any configuration, such as V-6, I-6, V-12, opposed 4-cylinder, etc. Furthermore, Figure 1A The cylinder shown may have, for example, Figure 2 The cylinder configuration shown is further described below. Each of cylinders 11, 14, 16, and 18 includes two intake valves and two exhaust valves, the intake valves including a first intake valve 2 and a second intake valve 4, and the exhaust valves including a first exhaust valve (referred to herein as a venting exhaust valve or vent valve) 8 and a second exhaust valve (referred to herein as a scavenging exhaust valve or scavenging valve) 6. Intake valves and exhaust valves may refer herein to cylinder intake valves and cylinder exhaust valves, respectively. See below for reference. Figure 2 To further explain, the timing of each of the intake valves (e.g., opening timing, closing timing, opening duration, etc.) can be controlled via various camshaft timing systems. In one embodiment, both the first intake valve 2 and the second intake valve 4 can be controlled to the same valve timing (e.g., such that they open and close simultaneously during the engine cycle). In an alternative embodiment, the first intake valve 2 and the second intake valve 4 can be controlled with different valve timings. Furthermore, the first exhaust valve 8 can be controlled with a different valve timing than the second exhaust valve 6 (e.g., such that the first and second exhaust valves of the same cylinder open at different times and close at different times), as discussed further below.

[0020] Each cylinder receives intake air (or a mixture of intake air and recirculated exhaust air, as explained further below) from the intake manifold 44 via intake passage 28. The intake manifold 44 is connected to the cylinder via intake ducts (e.g., flow paths). For example, the intake manifold 44 is located in... Figure 1A The cylinder is shown as being connected to each first intake valve 2 of each cylinder via a first intake passage 20. Furthermore, an intake manifold 44 is connected to each second intake valve 4 of each cylinder via a second intake passage 22. In this way, each cylinder intake passage can selectively communicate with its connected cylinder via either the first intake valve 2 or the second intake valve 4. Each intake passage can supply air and / or fuel to its connected cylinder for combustion.

[0021] As mentioned in this article, direct-flow air or direct-flow combustion cooling can refer to intake air that flows from one or more intake valves of each cylinder to the second exhaust valve 6 (and into the second exhaust manifold 80) without combustion during the valve opening overlap period between the intake valve and the second exhaust valve 6 (e.g., the period when the intake valve and the second exhaust valve 6 are open at the same time).

[0022] High-pressure two-stage fuel systems (such as) Figure 2 The fuel system shown can be used to generate fuel pressure in injector 66. Therefore, fuel can be injected directly into the cylinders via injector 66. Distributorless ignition system 88 provides ignition sparks to cylinders 11, 14, 16, and 18 via spark plug 92 in response to controller 12. Cylinders 11, 14, 16, and 18 are each connected to two exhaust ports for guiding the venting and scavenging portions of the combustion gases, respectively. Specifically, as... Figure 1A As shown, cylinders 11, 14, 16, and 18 discharge combustion gases (e.g., scavenging portion) to a second exhaust manifold (referred to herein as scavenging manifold) 80 via a second exhaust passage (e.g., exhaust passage) 82, and discharge combustion gases (e.g., venting portion) to a first exhaust manifold (referred to herein as venting manifold) 84 via a first exhaust passage (e.g., exhaust passage) 86. The second exhaust passage 82 extends from cylinders 11, 14, 16, and 18 to the second exhaust manifold 80. Additionally, the first exhaust manifold 84 includes a first manifold portion 81 and a second manifold portion 85. The first exhaust passage 86 of cylinders 11 and 18 (referred to herein as outer cylinders) extends from cylinders 11 and 18 to the second manifold portion 85 of the first exhaust manifold 84. Additionally, the first exhaust passage 86 of cylinders 14 and 16 (referred to herein as inner cylinders) extends from cylinders 14 and 16 to the first manifold portion 81 of the first exhaust manifold 84.

[0023] Each exhaust passage may be selectively connected to its corresponding cylinder via an exhaust valve. For example, a second exhaust passage 82 is connected to its corresponding cylinder via a second exhaust valve 6, and a first exhaust passage 86 is connected to its corresponding cylinder via a first exhaust valve 8. When at least one exhaust valve of each cylinder is in the closed position, the second exhaust passage 82 is isolated from the first exhaust passage 86. Exhaust may not flow directly between exhaust passages 82 and 86. The exhaust system described herein may be referred to as a split exhaust manifold system, wherein a first portion of the exhaust from each cylinder is output to a first exhaust manifold 84, and a second portion of the exhaust from each cylinder is output to a second exhaust manifold 80, and wherein the first and second exhaust manifolds are not directly connected to each other (e.g., there is no passage directly connecting the two exhaust manifolds to each other, so the first and second portions of the exhaust do not mix within the first and second exhaust manifolds).

[0024] Engine 10 includes a turbocharger comprising a two-stage exhaust turbine 164 and an intake compressor 162 coupled to a common shaft. The two-stage turbine 164 includes a first turbine 163 and a second turbine 165. The first turbine 163 is directly coupled to a first manifold portion 81 of a first exhaust manifold 84 and receives exhaust gas from cylinders 14 and 16 only via first exhaust valves 8 of cylinders 14 and 16. The second turbine 165 is directly coupled to a second manifold portion 85 of the first exhaust manifold 84 and receives exhaust gas from cylinders 11 and 18 only via first exhaust valves 8 of cylinders 11 and 18. The rotation of the first and second turbines drives the rotation of the compressor 162, which is disposed within an intake passage 28. Therefore, intake air is pressurized (e.g., compressed) at the compressor 162 and travels downwards into the intake manifold 44. Exhaust gas exits from the first turbine 163 and the second turbine 165 into a common exhaust passage 74. A wastegate may be coupled across the two-stage turbine 164. Specifically, the wastegate 76 may be included in a bypass 78, which connects each of the first manifold portion 81 and the second manifold portion 85 (upstream of the inlet of the two-stage turbine 164) to the exhaust passage 74 (downstream of the inlet of the two-stage turbine 164). In this way, the position of the wastegate valve (referred to herein as the turbine wastegate) 76 controls the amount of boost provided by the turbocharger. In an alternative embodiment, the engine 10 may include a single-stage turbine, wherein all exhaust from the first exhaust manifold 84 is directed to the same turbine inlet.

[0025] Exhaust gas exiting the two-stage turbine 164 flows downstream in exhaust passage 74 to a first emission control device 70 and a second emission control device 72, the second emission control device 72 being arranged downstream of the first emission control device 70 in exhaust passage 74. In one example, emission control devices 70 and 72 may include one or more catalyst blocks. In some examples, emission control devices 70 and 72 may be three-way catalysts. In other examples, emission control devices 70 and 72 may include one or more diesel oxidation catalysts (DOC) and selective catalytic reduction catalysts (SCR). In yet another example, the second emission control device 72 may include a gasoline particulate filter (GPF). In one example, the first emission control device 70 may include a catalyst, and the second emission control device 72 may include a GPF. After passing through emission control devices 70 and 72, the exhaust gas may be directed to an exhaust tailpipe.

[0026] The exhaust passage 74 also includes multiple exhaust sensors that communicate electronically with the controller 12 of the control system 15, as further described below. Figure 1A As shown, the exhaust passage 74 includes a first oxygen sensor 90 positioned between the first emission control unit 70 and the second emission control unit 72. The first oxygen sensor 90 can be configured to measure the oxygen content of the exhaust gas entering the second emission control unit 72. The exhaust passage 74 may include one or more additional oxygen sensors positioned along the exhaust passage 74, such as a second oxygen sensor 91 located between the two-stage turbine 164 and the first emission control unit 70 and / or a third oxygen sensor 93 located downstream of the second emission control unit 72. Thus, the second oxygen sensor 91 can be configured to measure the oxygen content of the exhaust gas entering the first emission control unit 70, and the third oxygen sensor 93 can be configured to measure the oxygen content of the exhaust gas leaving the second emission control unit 72. In one embodiment, the one or more oxygen sensors 90, 91, and 93 may be universal exhaust oxygen (UEGO) sensors. Alternatively, a dual-state exhaust oxygen sensor may replace oxygen sensors 90, 91, and 93. The exhaust passage 74 may include various other sensors, such as one or more temperature and / or pressure sensors. For example, as Figure 1AAs shown, pressure sensor 96 is positioned within exhaust passage 74 between first emission control unit 70 and second emission control unit 72. Therefore, pressure sensor 96 can be configured to measure the exhaust pressure entering second emission control unit 72. Both pressure sensor 96 and oxygen sensor 90 are arranged within exhaust passage 74 at the point where a flow passage connects to exhaust passage 74. This flow passage may be referred to herein as scavenging manifold bypass passage (SMBP) 98. Scavenging manifold bypass passage 98 is directly connected to and between second exhaust (e.g., scavenging) manifold 80 and exhaust passage 74. Valve 97 (referred to herein as scavenging manifold bypass valve, SMBV) is disposed within scavenging manifold bypass passage 98 and is actuated by controller 12 to adjust the exhaust flow from second exhaust manifold 80 to exhaust passage 74 at a position between first emission control unit 70 and second emission control unit 72.

[0027] The second exhaust manifold 80 is directly connected to the first exhaust gas recirculation (EGR) passage 50. The EGR passage 50 is directly connected upstream of the compressor (e.g., a turbocharger compressor) 162 between the second exhaust manifold 80 and the intake passage 28 (and can therefore be referred to as a low-pressure EGR passage). Thus, exhaust gas (or direct-flow air, as explained further below) is guided from the second exhaust manifold 80 upstream of the compressor 162 to the intake passage 28 via the EGR passage 50. The EGR passage 50 is located in... Figure 1A The diagram shows no EGR cooler, but in an alternative embodiment, an EGR cooler may be arranged in the EGR passage 50 to cool the exhaust gas flowing from the second exhaust manifold 80 to the intake passage 28 and the EGR valve 54 (which may be referred to herein as the scavenging EGR valve 54). The controller 12 is configured to actuate the EGR valve 54 and adjust its position to control the airflow through the EGR passage 50. When the EGR valve 54 is in the closed position, no exhaust or intake air can flow from the second exhaust manifold 80 upstream of the compressor 162 to the intake passage 28. Furthermore, when the EGR valve 54 is in the open position, exhaust and / or direct-flow air can flow from the second exhaust manifold 80 upstream of the compressor 162 to the intake passage 28. The controller 12 may additionally adjust the EGR valve 54 to multiple positions between fully open and fully closed.

[0028] Within the intake passage 28, an ejector 56 is positioned at the outlet of the EGR passage 50. The ejector 56 may include a constriction or venturi tube that provides a pressure increase at the inlet of the compressor 162. Thus, the EGR from the EGR passage 50 can be mixed with the fresh air flowing to the compressor 162 through the intake passage 28. Therefore, the EGR from the EGR passage 50 can be used as a motive flow on the first ejector 56. In an alternative embodiment, there may be no ejector at the outlet of the EGR passage 50. Instead, the outlet of the compressor 162 may be shaped as an ejector, which reduces the gas pressure to assist the EGR flow (therefore, in this embodiment, air is the motive flow and EGR is the auxiliary flow). In yet another embodiment, the EGR from the EGR passage 50 may be introduced at the trailing edge of the blades of the compressor 162, thereby allowing direct airflow through the EGR passage 50 to the intake passage 28.

[0029] Conduit 190 may branch off from EGR passage 50 downstream of the scavenging manifold. Conduit 190 may fluidly connect EGR passage 50 to intake passage 28 upstream of compressor 162. Conduit 190 may include a one-way check valve 192. In this way, check valve 192 may be positioned parallel to EGR valve 54. Check valve 192 may be configured to open when the pressure between check valve 192 and intake passage 28 is greater than the pressure between check valve 192 and scavenging manifold 80, thereby allowing gas (e.g., intake air) to enter scavenging manifold 80 from intake passage 28 under conditions where, for example, the compressor inlet pressure is greater than the scavenging manifold pressure. Although conduit 190 is in Figure 1A The diagram shows the intake passage 28 being connected upstream of the ejector 56, but other configurations are possible. For example, the duct 190 may be connected to the EGR passage 50 on each side of the EGR valve 54, or it may be connected to the intake passage 28 at other locations downstream of the ejector 56 and upstream of the compressor 162.

[0030] The intake passage 28 includes a boost air cooler (CAC) 40. The CAC 40 is configured to cool the intake air (which may be a mixture of fresh intake air and exhaust air from outside the engine system) as it passes through the CAC 40. Thus, recirculated exhaust air from the first EGR passage 50 can be cooled via the CAC 40 before entering the intake manifold 44.

[0031] The intake passage 28 also includes an electronic intake throttle valve 62 connected to the intake manifold 44. For example... Figure 1AAs shown, the intake throttle valve 62 is positioned downstream of the CAC 40. The position of the throttle plate 64 of the throttle valve 62 can be adjusted by the control system 15 via a throttle actuator (not shown) communicatively connected to the controller 12. By adjusting the intake throttle valve 62, a certain amount of fresh air can be introduced from the atmosphere and / or a certain amount of recirculated exhaust gas can be introduced from the EGR passage into the engine 10, cooled by the CAC 40 and delivered to the engine cylinders at compressor (or boost) pressure via the intake manifold 44. To reduce compressor surge, at least a portion of the air compressed by the compressor 162 can be recirculated to the compressor inlet. A compressor recirculation passage 41 can be provided for recirculating compressed air from the compressor outlet to the compressor inlet upstream of the CAC 40. A compressor recirculation valve (CRV) 42 can be provided for adjusting the recirculation flow rate to the compressor inlet. In one example, in response to an actual or anticipated compressor surge, the CRV 42 can be actuated via a command from the controller 12.

[0032] The second exhaust manifold 80 and / or the second exhaust passage 82 may include one or more sensors disposed therein (such as pressure, oxygen, and / or temperature sensors). For example, as Figure 1A As shown, the second exhaust manifold 80 includes pressure sensors 34 and 53, a temperature sensor 52, and an oxygen sensor 36, which are disposed within the second exhaust manifold 80 and configured to measure the pressure, temperature, and oxygen content of the exhaust and direct-flow (e.g., intake) air exiting the second exhaust valve 6 and entering the second exhaust manifold 80, respectively. In addition to or as an alternative to oxygen sensor 36, each second exhaust passage 82 may include a separate oxygen sensor disposed therein. Therefore, the oxygen content of the exhaust and / or direct-flow air exiting each cylinder via the second exhaust valve 6 can be determined based on the output of one or more oxygen sensors.

[0033] The intake passage 28 may include one or more additional sensors (such as additional pressure, temperature, flow, and / or oxygen sensors). For example, as Figure 1AAs shown, the intake passage 28 includes a mass air flow (MAF) sensor 48 and a first intake air temperature sensor 3, which are disposed upstream of the compressor 162, with the EGR passage 50 connected to the intake passage 28. A first intake pressure sensor 51 may be arranged immediately upstream of the venturi tube of the ejector 56. A second intake pressure sensor 31 and a second intake air temperature sensor 33 are positioned in the intake passage 28 upstream of the compressor 162 and downstream of the location where the EGR passage 50 is connected to the intake passage 28. An intake oxygen sensor 35 and an intake air temperature sensor 43 may be located in the intake passage 28 downstream of the compressor 162 and upstream of the CAC 40. An additional intake pressure sensor 37 may be positioned in the intake passage 28 downstream of the CAC 40 and upstream of the throttle valve 62. In some embodiments, such as Figure 1A As shown, an additional intake oxygen sensor 39 can be positioned in the intake passage 28 between the CAC 40 and the throttle valve 62. Furthermore, an intake manifold pressure (e.g., MAP) sensor 122 and an intake manifold temperature sensor 123 are positioned within the intake manifold 44 upstream of all engine cylinders.

[0034] In some examples, engine 10 can be coupled to the electric motor / battery system in a hybrid vehicle (e.g., Figure 2 (As shown in the diagram). Hybrid vehicles can have parallel configurations, series configurations, or variations or combinations thereof. Furthermore, in some embodiments, other engine configurations, such as diesel engines, may be employed.

[0035] The engine 10 can be at least partially controlled by a control system 15 including a controller 12 and via an input device ( Figure 1A (Not shown) The control system 15 is controlled by input from the vehicle driver. It receives information from multiple sensors (various examples of which are described herein) and sends control signals to multiple actuators 83. As an example, the sensors may include pressure, temperature, and oxygen sensors located within the intake passage 28, intake manifold 44, exhaust passage 74, and second exhaust manifold 80, as described above. Other sensors may include a throttle inlet pressure (TIP) sensor coupled downstream of the throttle valve in the intake passage for estimating throttle inlet pressure (TIP) and / or a throttle inlet temperature (TCT) sensor for estimating throttle air temperature (TCT). References below... Figure 2 The additional system sensors and actuators are described in detail. As another example, actuator 83 may include a fuel injector, valves 63, 42, 54, 97, 76, and throttle valve 62. Actuator 83 may also include various camshaft timing actuators coupled to the cylinder intake and exhaust valves (see reference below). Figure 2(Further description). Controller 12 can receive input data from various sensors, process the input data, and trigger actuators in response to the processed input data based on instructions or codes corresponding to one or more programs programmed in the memory of controller 12. This document... Figure 4 Exemplary control routines (e.g., methods) are described herein. For example, adjusting the EGR flow from the second exhaust manifold 80 to the intake passage 28 may include adjusting the actuator of the EGR valve 54 to adjust the exhaust flow from the second exhaust manifold 80 upstream of the compressor 162 to the intake passage 28. In another example, adjusting the EGR flow from the second exhaust manifold 80 to the intake passage 28 may include adjusting the actuator of the exhaust valve camshaft to adjust the opening timing of the second exhaust valve 6.

[0036] In this way, Figure 1A The first and second exhaust manifolds can be configured to separately guide the venting and scavenging portions of exhaust gas. The first exhaust manifold 84 can direct exhaust gas venting pulses to the two-stage turbine 164 via a first manifold section 81 and a second manifold section 85, while the second exhaust manifold 80 can direct the scavenging portion of exhaust gas to the intake passage 28 via the EGR passage 50 and / or to the exhaust passage 74 downstream of the two-stage turbine 164 via a flow passage. For example, the first exhaust valve 8 directs the exhaust gas venting portion through the first exhaust manifold 84 to both the two-stage turbine 164 and both the first emission control device 70 and the second emission control device 72, while the second exhaust valve 6 directs the scavenging portion of exhaust gas through the second exhaust manifold 80 and via the EGR passage to the intake passage 28 or via a flow passage to the exhaust passage 74 and the second emission control device 72.

[0037] Figure 1B An alternative embodiment of engine 10 is shown, wherein a conduit housing a check valve is connected to the intake system downstream of compressor 162. Similar to... Figure 1A The components shown are given the same reference numerals, and further description of these components is omitted. No further reference is made. Figure 1B Description Figure 1A The description of the components is applicable Figure 1B Components.

[0038] Conduit 190' is shown as fluidly connecting EGR passage 50 to intake passage 28 downstream of compressor 162 and upstream of CAC 40. However, other locations for the connection between conduit 190' and intake passage 28 are also possible, such as downstream of CAC 40. Conduit 190' includes check valve 192', configured to open when the pressure between compressor 162 and check valve 192' is greater than the pressure between check valve 192' and scavenging manifold 80, thereby allowing gas (e.g., intake air) to enter scavenging manifold 80 from intake passage 28 under conditions where, for example, the compressor inlet pressure is greater than the scavenging manifold pressure. To prevent compressed intake air from entering scavenging manifold 80 under non-idle conditions or other undesirable conditions, conduit 190' may include shut-off valve 54. Shut-off valve 54 may be controlled by controller 12 to open under certain conditions, such as at idle or other low load conditions, when it is desired to allow intake air into scavenging manifold 80.

[0039] Now for reference Figure 2 It depicts a partial view of a single cylinder of an internal combustion engine 10 that can be installed in a vehicle 100. Therefore, previously in Figure 1A and / or Figure 1B The components described herein are indicated by the same reference numerals and will not be repeated. Engine 10 is depicted as having a combustion chamber (cylinder) 130, a coolant sleeve 114, and cylinder walls 132, wherein a piston 136 is located in the cylinder and connected to a crankshaft 140. Combustion chamber 130 is shown communicating with intake passage 146 and exhaust passage 148 via corresponding intake valves 152 and exhaust valves 156. As previously described... Figure 1A As described, each cylinder of engine 10 can discharge combustion products along two ducts. In the depicted view, exhaust passage 148 represents a first exhaust flow path (e.g., a port) leading from the cylinder to the turbine (such as...). Figure 1A The first exhaust channel 86), while the second exhaust channel is not visible in this view.

[0040] In addition, as previously stated Figure 1AAs described in detail, each cylinder of engine 10 may include two intake valves and two exhaust valves. In the depicted view, intake valve 152 and exhaust valve 156 are located in the upper region of combustion chamber 130. Intake valve 152 and exhaust valve 156 can be controlled by controller 12 using a corresponding cam actuation system including one or more cams. The cam actuation system may utilize one or more of a cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) system to change valve operation. In the depicted example, each intake valve 152 is controlled by intake cam 151, and each exhaust valve 156 is controlled by exhaust cam 153. Intake cam 151 can be actuated via intake valve timing actuator 101 according to the set intake valve timing and exhaust valve timing, respectively, and exhaust cam 153 can be actuated via exhaust valve timing actuator 103. In some examples, the intake and exhaust valves can be deactivated via intake valve timing actuator 101 and exhaust valve timing actuator 103, respectively. For example, the controller can send a signal to exhaust valve timing actuator 103 to deactivate exhaust valve 156, causing exhaust valve 156 to remain closed and not open at its set timing. The positions of intake valve 152 and exhaust valve 156 can be determined by valve position sensors 155 and 157, respectively. As described above, in one example, all exhaust valves of each cylinder can be controlled on the same exhaust camshaft. Therefore, the timing of the scavenging (second) exhaust valve and the waste (first) exhaust valve can be adjusted together via a single camshaft, but they can each have different timings relative to each other. In another example, the scavenging exhaust valve of each cylinder can be controlled on a first exhaust camshaft, and the waste exhaust valve of each cylinder can be controlled on a different second exhaust camshaft. In this way, the valve timings of the scavenging valve and the waste valve can be adjusted separately from each other. In an alternative embodiment, one or more cams or valve timing systems for the scavenging exhaust valve and / or the bleed exhaust valve may employ cams in a cam system, an electro-hydraulic system on the scavenging valve, and / or an electromechanical valve lift control on the scavenging valve.

[0041] For example, in some embodiments, the intake and / or exhaust valves may be controlled by electric valve actuation. For instance, cylinder 130 may alternatively include an intake valve controlled by electric valve actuation and an exhaust valve controlled by cam actuation including a CPS and / or VCT system. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system.

[0042] In one example, the intake cam 151 includes separate and distinct cam lobe angles that provide different valve profiles (e.g., valve timing, valve lift, duration, etc.) for each of the two intake valves of the combustion chamber 130. Similarly, the exhaust cam 153 may include separate and distinct cam lobe angles that provide different valve profiles (e.g., valve timing, valve lift, duration, etc.) for each of the two exhaust valves of the combustion chamber 130. In another example, the intake cam 151 may include a common cam lobe angle or similar cam lobe angles that provide substantially similar valve profiles for each of the two intake valves.

[0043] Furthermore, different exhaust valve profiles can be used to separate exhaust gases discharged at low cylinder pressure from those discharged at high exhaust pressure. For example, a first exhaust valve profile can open from the closed position (e.g., a bleed valve) just before the bottom dead center (BDC) of the power stroke in combustion chamber 130 and close the same exhaust valve before the top dead center (TDC) to selectively discharge bleed gases from the combustion chamber. Additionally, a second exhaust valve profile can be positioned to open from the closed position (e.g., a scavenging valve) before the midpoint of the exhaust stroke and close after the TDC to selectively discharge the scavenging portion of the exhaust gas.

[0044] Therefore, the timing of the first and second exhaust valves isolates the cylinder exhaust gases from the scavenging portion of the exhaust, while utilizing the direct-flow fresh intake air during the positive valve overlap between the intake and scavenging exhaust valves to purge any residual exhaust gas from the cylinder clearance volume. By directing the first portion of the exhaust gas leaving the cylinder (e.g., higher-pressure exhaust) to one or more turbines and a higher-pressure exhaust passage, and directing the subsequent second portion of the exhaust gas (e.g., lower-pressure exhaust) and direct-flow air to the compressor inlet, engine system efficiency is improved. Turbo energy recovery can be enhanced by increasing EGR and reducing knock, thus improving engine efficiency.

[0045] continue Figure 2 Exhaust sensor 126 is shown coupled to exhaust passage 148. Sensor 126 can be positioned within the exhaust passage relative to one or more emission control devices (such as...). Figure 1A Upstream of devices 70 and 72. Sensor 126 may be selected from a variety of suitable sensors to provide an indication of the exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust oxygen), a dual-state oxygen sensor or EGO (as depicted), HEGO (heated EGO), NOx, HC, or CO sensors. Downstream emission control devices may include one or more of a three-way catalytic converter (TWC), a NOx trap, a GPF, and a combination thereof of various other emission control devices.

[0046] Exhaust temperature can be estimated using one or more temperature sensors (not shown) located in exhaust passage 148. Alternatively, exhaust temperature can be inferred based on engine operating conditions such as engine speed, load, air-fuel ratio (AFR), spark delay, etc.

[0047] Cylinder 130 may have a compression ratio, which is the volume ratio when piston 136 is at bottom dead center versus top dead center. Typically, the compression ratio is in the range of 9:1 to 10:1. However, in some examples using different fuels, the compression ratio may be increased. This may occur, for example, when using fuels with higher octane ratings or higher latent enthalpy of vaporization. The compression ratio may also be increased if direct injection is used due to its effect on engine knock.

[0048] In some embodiments, each cylinder of the engine 10 may include a spark plug 92 for initiating combustion. In a selected operating mode, the ignition system 188 may provide an ignition spark to the combustion chamber 130 via the spark plug 92 in response to a spark advance signal SA from the controller 12. However, in some embodiments, the spark plug 92 may be omitted, such as when the engine 10 can initiate combustion by automatic ignition or by fuel injection (as is the case with some diesel engines).

[0049] In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors for supplying fuel thereto. As a non-limiting example, cylinder 130 is shown as including a fuel injector 66. Fuel injector 66 is shown as being directly coupled to combustion chamber 130 for injecting fuel directly into the combustion cylinder in proportion to the pulse width (FPW) of a signal received from controller 12 via electronic actuator 168. In this way, fuel injector 66 provides so-called direct fuel injection (hereinafter also referred to as "DI") into combustion cylinder 130. Although Figure 2 Injector 66 is shown as a side injector, but it can also be located on top of the piston, such as near spark plug 92. Because some alcohol-based fuels are less volatile, such a location can promote mixing and combustion when the engine is operated with an alcohol-based fuel. Alternatively, the injector can be located at the top and close to the intake valve to promote mixing. In an alternative embodiment, injector 66 can be an intake manifold injector that supplies fuel to the intake manifold upstream of cylinder 130.

[0050] Fuel can be delivered from a high-pressure fuel system 180, including a fuel tank, fuel pump, and fuel rail, to the fuel injector 66. Alternatively, fuel can be delivered at a lower pressure by a single-stage fuel pump, in which case direct fuel injection timing during the compression stroke can be more restrictive than when using a high-pressure fuel system. Furthermore, although not shown, the fuel tank may have a pressure sensor that provides a signal to the controller 12. The fuel tank in the fuel system 180 can hold fuels with different fuel qualities, such as different fuel compositions. These differences may include different alcohol contents, different octane numbers, different heats of vaporization, different fuel mixtures, and / or combinations thereof. In some embodiments, the fuel system 180 may be coupled to a fuel vapor recovery system including a filter canister for storing replenishment fuel and daytime fuel vapor. When purging conditions are met, fuel vapor can be purged from the filter canister into the engine cylinders during engine operation. For example, purging vapor can be naturally drawn into the cylinders via a first intake passage at atmospheric pressure or below.

[0051] The engine 10 can be at least partially controlled by the controller 12 and by input from the vehicle driver 113 via input devices 118, such as the accelerator pedal 116. The input devices 118 send pedal position signals to the controller 12. Figure 2The microcomputer shown includes a microprocessor unit (CPU) 102, input / output ports (I / O) 104, an electronic storage medium for executing programs and calibration values, shown in this particular example as read-only memory (ROM) 106, random access memory (RAM) 108, keep-alive memory (KAM) 110, and a data bus. The read-only memory 106 can be programmed with computer-readable data representing instructions executable by the microprocessor 102 to perform the methods and programs described below, as well as other anticipated but not specifically listed variations of the instructions. In addition to the signals previously discussed, controller 12 may also receive various signals from sensors coupled to engine 10, including: the measured intake mass airflow (MAF) from mass airflow sensor 48; engine coolant temperature (ECT) from temperature sensor 112 coupled to coolant sleeve 114; surface ignition sensing signal (PIP) from Hall effect sensor 120 (or other type) coupled to crankshaft 140; throttle position (TP) from throttle position sensor; manifold absolute pressure signal (MAP) from sensor 122; cylinder AFR from EGO sensor 126; abnormal combustion from knock pressure sensor; and crankshaft acceleration sensor. Engine speed signal RPM can be generated by controller 12 based on signal PIP. Manifold pressure signal MAP from manifold pressure sensor can be used to provide an indication of vacuum or pressure in the intake manifold.

[0052] Based on inputs from one or more of the aforementioned sensors, controller 12 can adjust one or more actuators, such as fuel injector 66, throttle valve 62, spark plug 92, intake / exhaust valves, and camshafts. The controller can receive input data from various sensors, process the input data, and trigger the actuators in response to the processed input data based on instructions or codes programmed into the actuators corresponding to one or more programs.

[0053] In some examples, vehicle 100 may be a hybrid vehicle with multiple torque sources available for one or more wheels 160. In other examples, vehicle 100 is a conventional vehicle with only an engine or an electric vehicle with only an electric motor. Figure 2In the example shown, vehicle 100 includes engine 10 and electric motor 161. Electric motor 161 can be a motor or a motor / generator, and therefore may also be referred to herein as an electric motor. When one or more clutches 166 are engaged, the crankshaft 140 of engine 10 and electric motor 161 are connected to wheels 160 via transmission 167. In the depicted example, a first clutch 166 is disposed between crankshaft 140 and electric motor 161, while a second clutch 166 is disposed between electric motor 161 and transmission 167. Controller 12 can send signals to the actuators of each clutch 166 to engage or disengage the clutches, thereby connecting or disconnecting crankshaft 140 from electric motor 161 and its connected components, and / or connecting or disconnecting electric motor 161 from transmission 167 and its connected components. Transmission 167 can be a gearbox, a planetary gear system, or another type of transmission. The powertrain can be configured in various ways, including parallel, series, or series-parallel hybrid vehicles.

[0054] Motor 161 receives power from power battery 170 to provide torque to wheel 160. Motor 161 can also operate as a generator to provide power to charge battery 170, for example, during braking operation.

[0055] Figures 1A to 2Exemplary configurations with the relative positioning of various components are shown. If shown as directly contacting or directly connected to each other, then in at least one example such components may be referred to as directly contacting or directly connected, respectively. Similarly, components shown as connected or adjacent to each other may be connected or adjacent to each other, respectively, in at least one example. As an example, components laid out in coplanar contact with each other may be referred to as coplanar contact. As another example, components positioned apart from each other with only space between them and no other components may be referred to as such in at least one example. Furthermore, components shown above / below each other, on opposite sides of each other, or to the left / right of each other may be referred to as coplanar contact relative to each other. Moreover, as shown, in at least one example, the topmost component or the highest vertex of the component may be referred to as the “top” of the component, while the bottommost component or the lowest point of the component may be referred to as the “bottom” of the component. As used herein, top / bottom, upper / lower, above / below may be relative to the vertical axis of the figures and are used to describe the positioning of the components in the figures relative to each other. Thus, in one example, an component shown above other components is vertically positioned above the other components. As yet another example, the shapes of the elements depicted in the figure can be described as having these shapes (e.g., circular, straight, planar, curved, rounded, chamfered, angled, etc.). Furthermore, in at least one example, elements shown intersecting each other can be described as intersecting elements or intersecting each other. Additionally, in one example, an element shown as being inside another element or an element shown as being outside another element can be described as such.

[0056] Now for reference Figure 3 Figure 300 depicts exemplary valve timing with respect to piston position for an engine cylinder comprising four valves: two intake valves and two exhaust valves, as shown in the reference above. Figures 1A to 2 As stated above. Figure 3 The examples are drawn to scale, even though each point is not labeled with a numerical value. This allows the relative variation in timing to be estimated by plotting the dimensions. However, other relative timings can be used if needed.

[0057] continue Figure 3 The cylinder is configured to receive intake air via two intake valves and exhaust air via a first exhaust valve (e.g., such as...). Figure 1A The first or venting exhaust valve 8 shown discharges the first vent portion into the turbine inlet via the second exhaust valve (e.g., such as...). Figure 1AThe second or scavenging exhaust valve 6 shown discharges a second scavenging portion into the intake passage and unburned direct-flow air is discharged into the intake passage via the second exhaust valve. By adjusting the opening and / or closing timing of the second exhaust valve with these two intake valves, residual exhaust gas in the cylinder clearance volume can be removed and recirculated as EGR along with fresh intake direct-flow air.

[0058] Figure 300 shows the engine positions along the x-axis in crank angles (CAD). Figure 302 depicts the piston positions (along the y-axis) relative to their positions from top dead center (TDC) and / or bottom dead center (BDC), and further relative to their positions within the four strokes of the engine cycle (intake, compression, power, and exhaust).

[0059] During engine operation, each cylinder typically undergoes a four-stroke cycle, including the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, the exhaust valve is typically closed and the intake valve is open. Air is introduced into the cylinder via the corresponding intake passage, and the piston moves to the bottom of the cylinder to increase the volume within the cylinder. The position of the piston near the bottom of the cylinder at the end of its stroke (e.g., when the combustion chamber is at its maximum volume) is generally referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, both the intake and exhaust valves are closed. The piston moves toward the cylinder head to compress the air in the combustion chamber. The point at the end of the piston's stroke and closest to the cylinder head (e.g., when the combustion chamber is at its minimum volume) is generally referred to by those skilled in the art as top dead center (TDC). In what is referred herein as injection, fuel is introduced into the combustion chamber. In what is referred herein as ignition, the injected fuel is ignited by a known ignition device such as a spark plug, thereby causing combustion. During the expansion stroke, the expanding gas pushes the piston back to the BDC. The crankshaft converts this piston motion into rotational torque on the rotating shaft. During the exhaust stroke, in conventional designs, the exhaust valve opens to release the remaining combusted air-fuel mixture into the corresponding exhaust passage, and the piston returns to the TDC. In this specification, the second exhaust (scavenging) valve can open after the start of the exhaust stroke and remain open until the end of the exhaust stroke, while the first exhaust (venting) valve closes and the intake valve opens to flush away any remaining exhaust with direct-flow air.

[0060] Curve 304 depicts the first intake valve timing, lift, and duration of the first intake valve (Int_1), while curve 306 depicts the second intake valve timing, lift, and duration of the second intake valve (Int_2) connected to the intake passage of the engine cylinder. Curve 308 depicts the first exhaust manifold connected to the engine cylinder (e.g., Figure 1A The first exhaust valve (Exh_1) of the venting exhaust manifold 84 shown in the figure can correspond to Figure 1AThe exemplary exhaust valve timing, lift, and duration of the first or venting exhaust valve 8 shown are illustrated, while curve 310 depicts the second exhaust manifold connected to the engine cylinder (e.g., Figure 1A The second exhaust valve (Exh_2) of the scavenging manifold 80 shown can correspond to Figure 1A The exemplary exhaust valve timing, lift, and duration of the second or scavenging exhaust valve 6 shown are illustrated. As previously described, the first exhaust manifold connects the first exhaust valve to the inlet of the turbine in the turbocharger, and the second exhaust manifold connects the second exhaust valve to the intake passage via the EGR passage. As mentioned above, the first and second exhaust manifolds can be separate from each other.

[0061] In the depicted example, the first and second intake valves are fully opened from the closed position at a common timing (curves 304 and 306), begin to close just after CAD2 (e.g., at or just after intake stroke TDC), and close after the subsequent compression stroke begins past CAD3 (e.g., after BDC). Additionally, when fully open, both intake valves can open with the same amount of valve lift L1 for the same duration D1. In other examples, the two valves can be operated at different timings by adjusting the phase, lift, or duration based on engine conditions.

[0062] Referring now to the exhaust valves, the timings of the first and second exhaust valves are staggered relative to each other. Specifically, the first exhaust valve opens from the closed position at a first timing (curve 308), which is earlier in the engine cycle than the timing of the second exhaust valve opening from its closed position (curve 310). Specifically, the first timing for opening the first exhaust valve is between the TDC and BDC of the power stroke, before CAD1 (e.g., before the exhaust stroke BDC), while the timing for opening the second exhaust valve is exactly after the exhaust stroke BDC, after CAD1, but before CAD2. The first exhaust valve (curve 308) closes before the end of the exhaust stroke, and the second exhaust valve (curve 310) closes after the end of the exhaust stroke. Therefore, the second exhaust valve remains open to slightly overlap with the opening of the intake valves.

[0063] In detail, the first exhaust valve can be fully opened from the closed position before the start of the exhaust stroke (e.g., between 90 and 40 degrees before BDC), remain fully open through the first part of the exhaust stroke, and can be fully closed before the end of the exhaust stroke (e.g., between 50 and 0 degrees before TDC) to collect the venting portion of the exhaust pulse. The second exhaust valve (curve 310) can be fully opened from the closed position just after the start of the exhaust stroke (e.g., between 40 and 90 degrees after BDC), remain open through the second part of the exhaust stroke, and can be fully closed after the start of the intake stroke (e.g., between 20 and 70 degrees after TDC) to expel the scavenging portion of the exhaust. Additionally, the second exhaust valve and the intake valve (e.g., ... Figure 3 The cycle (as shown) can have a positive overlap phase (e.g., between 20 degrees before TDC and 40 degrees after TDC until between 40 and 90 degrees past TDC) to allow direct EGR blowing. This cycle (where all four valves are operable) can repeat automatically based on engine operating conditions.

[0064] Additionally, the first exhaust valve can open at a first timing with a first valve lift L2, while the second exhaust valve can open with a second valve lift L3 (curve 310), where L3 is less than L2. Furthermore, the first exhaust valve can be open and held for a first timing duration D2, while the second exhaust valve can be open and held for a duration D3, where D3 is less than D2. It should be understood that, in alternative embodiments, the two exhaust valves can have the same valve lift and / or the same opening duration, but open at different phasing timings.

[0065] In this way, by using staggered valve timing, engine efficiency and power can be increased by separating exhaust gas released at higher pressures (e.g., expanded venting exhaust gas in the cylinder) from residual exhaust gas at lower pressures (e.g., exhaust gas remaining in the cylinder after venting) and directing it into different channels. By delivering low-pressure residual exhaust gas as EGR along with direct-flow air to the compressor inlet (via the EGR passage and the second exhaust manifold), combustion chamber temperatures can be reduced, thereby minimizing knocking and spark delay from maximum torque. Furthermore, since exhaust gas at the end of the stroke is directed downstream of the turbocharger or upstream of the compressor (both at lower pressures), exhaust pumping losses can be minimized to improve engine efficiency.

[0066] Therefore, exhaust gas can be used more efficiently than simply directing all the exhaust gas from the cylinders through a single common exhaust port to the turbocharger turbine. Several advantages can be achieved as a result. For example, by separating and directing the bleed pulses to the turbine inlet to increase turbocharger output, the average exhaust pressure supplied to the turbocharger can be increased. Additionally, fuel economy can be improved because the direct-flow air is directed to the compressor inlet instead of the catalytic converter, and therefore, excessive fuel may not be injected into the exhaust to maintain the stoichiometric ratio.

[0067] Exhaust gas is recirculated back to the engine intake passage through the scavenging manifold and flows out from the second exhaust valve during the exhaust stroke of the cylinder, as described above. Figure 3 The mixture may include fresh air, combustion gases (e.g., combusted exhaust gas), and recirculated fuel (e.g., unburned fuel). The EGR dilution rate can be estimated based on engine operating conditions, such as the ratio of combustion gases (generated from recirculated exhaust gas) in the air mass at the compressor inlet to the combined exhaust gas, fresh direct-flow air, and recirculated fuel at the engine intake passage. For example, engine speed and load may affect the combustion rate and thus the amount of exhaust gas produced. A certain amount of scavenging gas (a mixture of fresh direct-flow air, combustion gases, and recirculated fuel) recirculated from the scavenging manifold to the intake passage can be adjusted by the timing of the exhaust cam coupled to the scavenging exhaust valve. Additionally, the proportion of combustion gases recirculated to the engine cylinders can vary with the temperature of the scavenging gas.

[0068] Therefore, the two exhaust valves open and close at staggered timings to efficiently utilize exhaust gases. This staggered timing results in a long combined exhaust event that begins when the bleed exhaust valve (the first exhaust valve mentioned above) opens and ends when the scavenging exhaust valve (the second exhaust valve) closes. While this exhaust timing configuration provides the aforementioned advantages, during very light engine loads, such as during engine idling, the long combined exhaust event overlaps with the intake valve opening, which may adversely affect fuel economy and / or engine stability under light loads.

[0069] One method for mitigating fuel economy and / or engine stability under light loads in a split-flow exhaust engine system involves keeping the scavenging wastegate open (e.g., valve 97) and advancing the exhaust camshaft (which results in an earlier exhaust valve closing timing for both exhaust valves) to eliminate intake valve overlap. While this approach may benefit engine stability, the advanced exhaust valve opening (EVO) leads to losses, thus reducing fuel economy. If, alternatively, the exhaust camshaft is delayed to improve EVO losses, internal residues in the cylinder increase, thereby impairing combustion stability.

[0070] Therefore, as described in more detail below, a check valve (e.g., check valve 192) positioned parallel to the EGR valve can open during certain conditions to introduce fresh air into the scavenging manifold at the intake valve opening. Filling the scavenging manifold prevents excessive residue from accumulating in it and improves stability while minimizing EVO loss. With this increased stability, the bleed exhaust valve can open closer to the BDC to further minimize EVO loss.

[0071] Figure 4 A method 400 for operating a split-flow exhaust engine system is shown, such as Figure 1A or Figure 1B The engine system includes a check valve (e.g., valve 192) parallel to the EGR valve (e.g., valve 54). This can be controlled by a controller based on instructions stored in the controller's memory and in conjunction with data from sensors in the engine system (such as those mentioned above). Figures 1A to 2 The sensor described receives signals to execute instructions for performing method 400 and the remaining methods included herein. The controller can adjust engine operation using the engine actuator of the engine system according to the methods described below.

[0072] At 402, method 400 includes determining engine operating conditions. The determined operating conditions may include, but are not limited to, engine speed, engine load and / or torque, current operating mode, engine temperature, and other operating parameters. At 404, method 400 includes determining whether the engine is operating at idle (or under other low-load conditions where the engine load is below a lower threshold load, such as less than 20% of the maximum rated load). If the engine is not operating at idle or under other low-load conditions (e.g., if the load is above the lower threshold load), method 400 proceeds to 406 to adjust the actuators of the split-flow exhaust engine system based on the current engine speed and load and / or other parameters.

[0073] For example, the scavenging manifold bypass valve (SMBV, such as SMBV 97) and the exhaust valve (such as exhaust valve 76) can be adjusted based on engine speed and load (e.g., the SMBV can remain closed until the engine speed and load each reach a corresponding higher threshold). Cylinder valve timings (such as the opening and / or closing timings of intake valves, bleed exhaust valves, and scavenging exhaust valves) can be adjusted based on the current operating mode, which may be a function of engine speed and load. As a non-limiting example, during steady-state engine operation where both engine speed and engine load are in the intermediate range (e.g., engine speed at 2000 RPM and engine load at 50% of maximum load), the cylinder valve timings can be set to... Figure 3The timing shown provides optimal fuel economy. Cylinder valve timing can be adjusted from optimal timing based on the desired EGR rate (e.g., if the desired EGR rate is relatively low, exhaust valve timing can be delayed). In another example, during high engine speed and load conditions where compressor flow is limited (e.g., due to compressor operating temperature and / or flow being at or near maximum temperature or flow), exhaust valve timing can be delayed relative to optimal timing, and intake valve timing can be advanced relative to optimal timing. EGR valve position (such as the position of EGR valve 54) can be adjusted based on the desired EGR rate (which can be a function of engine speed and load), and in some examples, further adjustments can be made based on exhaust valve timing. Furthermore, in a configuration where a check valve is positioned in a conduit downstream of the compressor connected to the intake system (such as...) Figure 1B The configuration shown can close a shut-off valve (such as shut-off valve 54) to prevent unwanted compressed intake airflow into the scavenging manifold. The following section discusses... Figure 7A and Figure 7B Additional details regarding cylinder valve timing and exhaust system valve position adjustments during non-idling conditions are presented. Method 400 then returns.

[0074] Returning to 404, if it is determined that the engine is operating at idle or other low-load conditions, method 400 proceeds to 408 to close (or keep closed) the wastegate (such as wastegate 76) across the turbine coupling and close (or keep closed) the SMBV (such as SMBV 97) to direct all exhaust gas to the turbine. At 410, method 400 includes closing (or keeping closed) the EGR valve (such as EGR valve 54). By closing the EGR valve, the intake air is prevented from being diluted with exhaust residue, thereby improving combustion stability. Furthermore, in a configuration where a duct housing a check valve is coupled downstream of the compressor to the intake system, a shut-off valve can be opened.

[0075] Because the EGR valve is closed, and because the scavenging manifold bypass valve is closed, any exhaust gas discharged from the scavenging exhaust valve accumulates in the scavenging manifold. Specifically, if the exhaust valve timing is advanced to allow the bleed exhaust valve (e.g., Figure 1A If the first exhaust valve (8) closes prematurely while the piston is still moving upwards, pressure builds up in the cylinder and scavenging manifold. This pressure can be relieved by opening the scavenging manifold bypass valve, but this configuration results in exhaust valve losses due to the premature closing timing. Delaying exhaust valve timing can mitigate these valve losses, but due to the low pressure present in the scavenging manifold during valve overlap, excessive exhaust residue may still build up in the system. For example, some exhaust may pass through the scavenging exhaust valve (e.g., Figure 1AThe second exhaust valve 6) is released, and during the low-pressure conditions that occur during valve overlap, the exhaust can be pulled back into the cylinder, causing exhaust residue to accumulate in the cylinder, which may reduce combustion stability.

[0076] However, due to the presence of a check valve in the exhaust system (e.g., check valve 192 or 192' parallel to the EGR valve), a large amount of intake / fresh air is allowed to flow into the scavenging manifold when the scavenging exhaust valve overlaps with the intake valve. This keeps the scavenging manifold at ambient pressure and prevents exhaust residue from accumulating in the system.

[0077] Therefore, at 412, method 400 includes delaying the release exhaust valve timing and the scavenging exhaust valve timing. For example, a common exhaust cam can be adjusted to delay the release exhaust valve ( Figure 1A First exhaust valve (8) and scavenging exhaust valve ( Figure 1A The closing timing of both the second exhaust valve (6) and the scavenging exhaust valve. The timing can be delayed so that the bleed exhaust valve closes close near the TDC of the corresponding exhaust stroke, resulting in more exhaust gas from the cylinder being discharged into the bleed manifold and also reducing losses associated with early exhaust valve closure. The timing of the scavenging exhaust valve can be delayed to allow for a relatively high valve overlap duration, such as a valve overlap period of 70 degrees of crank angle. At 414, method 400 includes allowing intake air into the scavenging manifold via a check valve during the valve overlap period. For example, intake / fresh air from upstream of the compressor can be drawn into the scavenging manifold via the check valve, since the check valve is configured to open when the compressor inlet pressure is greater than the scavenging manifold pressure. Method 400 then returns.

[0078] Figure 5 This is a diagram 500 illustrating an exemplary graph of the proportion of combustion mass (e.g., exhaust residues) present in a given cylinder at the start of combustion as a function of exhaust valve closing timing in a multi-engine configuration during idle engine operation. Diagram 500 depicts exhaust valve closing in crank angles (for scavenging exhaust valves in a configuration with multiple exhaust valves) after top dead center along the x-axis, and depicts exhaust products (percentage of combustion mass at the start of combustion, including EGR and residues) along the y-axis. A first curve 502 shows the proportion of combustion mass as a function of exhaust valve closing in a standard non-split exhaust system configuration. A standard exhaust system configuration may include a single exhaust manifold coupled to each cylinder, where each cylinder may have only one exhaust valve. A standard exhaust system configuration may also include a turbocharger turbine coupled to the exhaust manifold. Figure 5During idle operation, the turbine's exhaust valve remains fully closed. As shown in curve 502, the proportion of combustion increases with a delayed exhaust valve closing timing. Similarly, as shown in curve 504, in a split-flow exhaust engine system without a check valve, the proportion of combustion increases with a delayed scavenging exhaust valve closing time when the exhaust valve remains closed and the SMBV is open. For both curves 502 and 504, the proportion of combustion may exceed the stability limit (e.g., greater than 40%) at very delayed exhaust valve closing timings (such as 70 degrees ATDC and later).

[0079] Curves 506 and 508 illustrate the combustion mass ratio of the split-exhaust engine system of this disclosure, such as Figure 1A or Figure 1B The system, in which the check valve is positioned parallel to the EGR valve. Curve 506 shows the combustion mass ratio when the SMBV remains open, and curve 508 shows the combustion mass ratio when the SMBV is closed. In both examples, the combustion mass ratio is reduced by means of the check valve. For example, for Figure 5 With any exhaust valve closed, the combustion mass ratio can not exceed 35%. As understood from curve 508, the combustion mass ratio decreases significantly when the SMBV is closed. For example, the combustion mass ratio can peak at a scavenged exhaust valve closed (SC-EVC) timing of 50 degrees ATDC and then decrease as SC-EVC is delayed beyond 50 degrees. At approximately 74 degrees CA ATDC, the combustion mass ratio can be as low as the combustion mass ratio at SC-EVC timing of TDC (e.g., 14%). Conversely, at 74 degrees EVC / SC-EVC, the combustion mass ratio can be 33% when the SMBV is open (shown by curve 506); and 47% when there is no check valve and the SMBV is open (shown by curve 504).

[0080] Figure 6 This is a graph 600 showing the mass flow rate and exhaust pressure as a function of engine position in a single engine cycle during idling operation for a split-flow exhaust engine system with a check valve, as referenced above. Figure 1A or Figure 1B As described above, the SMBV is off. Figure 600 depicts the engine position along the x-axis in crank angles, and along the first y-axis (in... Figure 6 The mass flow rate (in kg / s) on the right side and along the second y-axis (in Figure 6The pressure (in bar) on the left side of the cylinder. For a given cylinder, the depicted engine cycle may include a compression stroke between -180° and 0° CA, a power stroke between 0° and 180° CA, an exhaust stroke between 180° and 360° CA, and an intake stroke between 360° and 540° CA. The piston of a given cylinder may be located at BDC at -180° CA, TDC at 0° CA, BDC at 180° CA, TDC at 360° CA, and BDC at 540° CA.

[0081] The first curve 602 shows the intake pressure (e.g., intake manifold pressure), which remains relatively stable and below ambient pressure during the depicted engine cycle. The second curve 604 shows the exhaust pressure in the bleed manifold, which also remains relatively stable during the engine cycle. The bleed manifold is connected to each cylinder via a corresponding bleed valve and receives exhaust gas whenever the bleed valve opens. The bleed manifold then directs the exhaust gas to the turbine. The bleed manifold remains near ambient pressure during the engine cycle. The third curve 606 shows the exhaust pressure in the scavenging manifold, which exhibits a larger pressure variation than the bleed manifold. During each valve overlap period, the pressure in the scavenging manifold can decrease (e.g., below ambient pressure) before increasing. For example, Figure 6 The diagram shows the intake pressure, exhaust pressure, and check valve mass flow rate during an engine cycle, where each cylinder (including the first cylinder) experiences a combustion event. The first cylinder, which experiences the start of combustion near 0° CA, may have a valve overlap period starting near 360° CA, and therefore, the scavenging manifold pressure may decrease at 360° CA and increase once the overlap period ends (e.g., around 430° CA).

[0082] Curve 608 illustrates the mass flow rate through the check valve (e.g., the mass flow rate of intake / fresh air drawn into the scavenging manifold via check valve 192 or 192'). As understood from curve 608, the mass flow rate through the check valve pulses whenever an overlap period occurs, a result of the reduced pressure in the scavenging manifold. For the overlap period of the first cylinder, occurring between 360° CA and 430° CA, the mass flow rate through the check valve increases from zero to a peak of approximately 0.015 kg / s. The mass flow rate through the check valve can be proportional to the valve overlap amount; for example, the mass flow rate through the check valve can increase as the duration of the overlap period (e.g., crank angles) increases. After the overlap period (once the scavenging exhaust valve of the cylinder is closed), the flow rate through the check valve decreases back to zero. A similar pulse occurs whenever another cylinder has an overlap period. The engine configuration described herein includes four cylinders, thus four flow pulses are observed.

[0083] Figure 7A and Figure 7B This shows that in the execution of, for example Figure 4 Timing diagrams of exemplary operating parameters that can be observed during method 400. Figure 7A The engine load, EGR valve position, and SMBV / exhaust valve position were plotted as they increased over time to five periods of interest. Figure 7B An exemplary cylinder valve timing is shown during each period of interest. Figure 7A and Figure 7B A unified description will be provided.

[0084] Figure 7A The timing diagram 700 includes: a first curve showing engine load starting from the top; a second curve showing engine speed starting from the top; a third curve showing EGR valve position (including the position of EGR valve 54 upstream of the compressor that connects the scavenging manifold to the intake passage) starting from the top; and a fourth curve showing SMBV and turbocharger wastegate valve positions starting from the top. Engine load is depicted in relevant terms, starting at a minimum of 0% and increasing along the y-axis to 100%. The time of interest is depicted along the x-axis.

[0085] Figure 7B Timing diagram 750 includes a first curve 752 starting from the top, the first curve 752 showing the timing diagram at the top. Figure 7A The timing of the first exhaust valve (venting exhaust valve BDV), second exhaust valve (scavenging exhaust valve SV), and intake valve (IV) of the cylinder during the operation period between time t0 and t1. The second curve 754 shows the exhaust valve timing during this period. Figure 7A The timing of the exhaust and intake valves of the cylinder during the operation period between time t1 and t2. Curve 756 shows the timing of the exhaust and intake valves of the cylinder during this time period. Figure 7A The timing of the exhaust and intake valves of the cylinder during the operation period between time t2 and t3. Curve 758 shows the timing of the exhaust and intake valves during this time period. Figure 7A The timing of the exhaust and intake valves of the cylinder during the operation period between time t3 and t4. Curve 760 shows the timing of the exhaust and intake valves during this time period. Figure 7A The timing of the exhaust and intake valves of the cylinder during the operation period between time t4 and t5.

[0086] Before time t1, the engine operates in a first low-load mode, where the engine load is within a first load range (e.g., 25%–50% of maximum load), as shown in curve 702. Engine speed is also relatively low (e.g., below 2500 RPM), as shown in curve 703. In some examples, the engine may operate in boost mode, such that the intake manifold pressure is greater than the compressor inlet pressure. During the first low-load mode, the EGR valve is partially open, as shown in curve 704. Both the turbine wastegate and the SMBV are fully closed, as shown in curves 710 (for the turbine wastegate) and 712 (for the SMBV).

[0087] During operation in the first low-load mode (e.g., at least some time points between t0 and t1), the cylinder valve timing can be adjusted / controlled to a relatively delayed timing configuration. For example... Figure 7B As shown in curve 752, the bleed exhaust valve can begin to open just before -180° CA, and the scavenging exhaust valve can begin to open when the bleed exhaust valve reaches its peak lift (approximately -90° CA). The bleed exhaust valve can close at 0° CA, and the scavenging exhaust valve can close near 70° CA. The intake valve can open just after TDC (approximately 20° CA), resulting in a relatively long valve overlap period (e.g., 50° CA).

[0088] Around time t1, the engine load increases to the second load range (e.g., 50%-75% of maximum load) and the engine speed is stable and moderate (e.g., 2000-3000 RPM). The exhaust valve and SMBV can remain closed. The EGR valve can remain open and the EGR rate can be adjusted by adjusting the EGR valve position (as shown in the figure, the opening of the EGR valve can be increased) and / or by adjusting the exhaust valve and / or intake valve timing.

[0089] During operation in stable EGR mode (e.g., at least some time points between t1 and t2), cylinder valve timing can be adjusted / controlled to a relatively advanced timing configuration. For example... Figure 7BAs shown in curve 754, the exhaust valve can begin to open as early as -180° CA, and the scavenging valve can begin to open when the exhaust valve reaches its peak lift (approximately -160° CA). The exhaust valve can close before 0° CA, and the scavenging valve can close exactly after 0° CA. The intake valves can open exactly after TDC (approximately 20° CA), resulting in a relatively short valve overlap period. By advancing the valve timing, a relatively large amount of EGR can flow into the intake passage, for example, resulting in a lower amount of direct flow due to the small valve overlap period. If a lower EGR is desired, or if increased direct flow is desired (e.g., if the compressor inlet temperature is high, the engine is knocking, etc.), the exhaust valve timing can be delayed and / or the intake valve timing can be advanced to increase the valve overlap period.

[0090] Starting at time t2, the engine load increases again to the third load range (e.g., 75%-100% of maximum rated load). When engine speed is also high (e.g., 4000-5000 RPM), the exhaust flow may be high enough to exceed the limits of the turbocharger and engine dilution tolerances. Therefore, the SMBV opens to guide exhaust gas from the scavenging manifold to the atmosphere (after passing through the emission control unit), and the wastegate opens to reduce the exhaust flow through the turbine. The SMBV can open before the turbine wastegate opens, for example, as engine speed increases. The EGR valve can also close. Figure 7B As shown in curve 756, during at least some time points between t2 and t3, the exhaust valve timing can return to a delayed timing, similar to curve 752 above.

[0091] At time t3, the accelerator pedal may be released (e.g., when the vehicle operator begins to decelerate and then eventually brings the vehicle to a stop), causing a drop in engine load and engine speed. The wastegate can close to direct all exhaust gas from the bleed manifold to the turbocharger. The SMBV can remain open and the EGR valve can remain closed to prevent exhaust gas from flowing into the engine. Figure 7B As shown in curve 758, during at least some time points between t3 and t4, the exhaust valve timing can return to advanced timing, similar to curve 754 above.

[0092] The engine load continues to decrease, and around time t4, the engine load is in the low load / idle load range (e.g., below 25% of maximum load). The EGR valve can remain closed, and the SMBV can be shut off. Air enters the engine via the overlap of the scavenging exhaust valve and the intake valve. Figure 7B As shown in curve 760, during at least some time points between t4 and t5, the exhaust valve timing can return to a delayed timing, similar to curve 752 above.

[0093] Therefore, the systems and methods described herein provide a secondary path (e.g., a secondary EGR passage) for connecting a scavenging manifold to the intake system, which allows the scavenging manifold to maintain an oxygen-rich / lean EGR at idle or other low-load conditions. The secondary path can be connected to the scavenging manifold at a first end (e.g., via an EGR passage connected to the scavenging manifold) and can be connected to the intake system at a second end. The secondary path can be connected to the intake system along the intake passage at a suitable location where the intake air is above ambient pressure, such as before or at the compressor inlet, at or after the compressor outlet, or at other locations upstream of the intake throttle. The secondary path is controlled via a one-way check valve configured to open to allow intake air into the scavenging manifold but to prevent exhaust gas from flowing from the scavenging manifold into the intake passage. In this way, the vacuum in the scavenging manifold that may occur during valve overlap at idle can be avoided by allowing intake air to enter the scavenging manifold via a check valve during valve overlap, thereby preventing or reducing exhaust dilution in the scavenging manifold.

[0094] The technical effect of providing a check valve that is parallel to the EGR valve and fluidly connects the scavenging exhaust manifold to the intake passage upstream of the throttle valve is to reduce dilution of the scavenging manifold during the valve overlap period at idle, thereby reducing combustion instability and allowing exhaust valve timing retardation, reducing losses associated with earlier valve timing.

[0095] One example provides a method comprising maintaining a scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during a valve overlap period, the scavenging manifold being coupled to a cylinder of an engine and to an intake passage of the engine. In a first example of the method, maintaining the scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during a valve overlap period comprises maintaining the scavenging exhaust manifold at ambient pressure. In a second example of the method (which optionally includes the first example), maintaining the scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during a valve overlap period comprises: allowing fresh air into the scavenging manifold via a check valve positioned in a duct during the valve overlap period, the duct being fluidly coupled to the scavenging manifold at a first end and to an intake passage at a second end, the duct being fluidly coupled to the intake passage upstream of the intake throttle valve. In a third example of the method (which may optionally include one or both of the first and second examples), the cylinder is connected to the scavenging manifold via a scavenging exhaust valve, and the valve overlap period includes the period of the engine cycle when both the scavenging exhaust valve and the cylinder's intake valve are open. In a fourth example of the method (which may optionally include one or each of the first to third examples), the method further includes: during low engine load conditions, delaying the closing timing of both the bleed exhaust valve and the scavenging exhaust valve that connect the cylinder to the turbine. In a fifth example of the method (which may optionally include one or each of the first to fourth examples), the method further includes: during low engine load conditions, closing an exhaust gas recirculation (EGR) valve located upstream of the compressor between the scavenging manifold and the intake passage, with the check valve connected in parallel to the EGR valve. In a sixth example of the method (which may optionally include one or each of the first to fifth examples), the method further includes: when the engine load is higher than the low engine load condition, adjusting the position of the EGR valve based on a commanded EGR rate.

[0096] One example provides a system for an engine comprising: a first set of exhaust valves connected only to a first exhaust manifold, the first exhaust manifold being connected upstream of a turbocharger compressor to an intake passage via an exhaust gas recirculation (EGR) passage including an EGR valve; a second set of exhaust valves connected only to a second exhaust manifold, the second exhaust manifold being connected upstream of a turbocharger turbine disposed in an exhaust passage; a plurality of engine cylinders, each engine cylinder including one of the first set of exhaust valves and one of the second set of exhaust valves; and a check valve positioned in a conduit parallel to the EGR valve. In a first example of the system, the first set of exhaust valves and the second set of exhaust valves open at different timings, and there is a valve overlap period between the first set of exhaust valves and the intake valves of the plurality of engine cylinders, wherein when the second set of exhaust valves is closed, both the exhaust valve and the intake valve of each cylinder are open. In a second example of the system (which may optionally include the first example), the check valve is positioned to draw in intake air from the intake passage upstream of the turbocharger compressor and direct the intake air to the first exhaust manifold during valve overlap periods when the engine load is below a threshold load. In a third example of the system (which may optionally include one or both of the first and second examples), the system further includes a bypass passage downstream of the turbocharger turbine connecting the first exhaust manifold and the exhaust passage, and a scavenging exhaust gas valve positioned within the bypass passage. In a fourth example of the system (which may optionally include one or more of the first to third examples), the system further includes a controller configured to close the scavenging exhaust gas valve and the EGR valve when the engine load is below a threshold load. In a fifth example of the system (which may optionally include one or more of the first to fourth examples), the controller is further configured to adjust the first closing timing of the first set of exhaust valves and the second closing timing of the second set of exhaust valves when the engine load is below a threshold load.

[0097] Another example provides a method comprising: during low engine load conditions, delaying the closing timing of both the exhaust valve of the bleed exhaust valve that connects the engine cylinder to the turbine and the scavenging exhaust valve that connects the cylinder to the engine intake passage via the scavenging manifold; and reducing exhaust residue in the cylinder by allowing intake air into the scavenging manifold during the valve overlap period. In a first example of the method, the valve overlap period includes the period of an engine cycle when both the scavenging exhaust valve and the intake valve of the cylinder are open. In a second example of the method (which optionally includes the first example), allowing intake air into the scavenging manifold includes allowing intake air into the scavenging manifold via a check valve positioned upstream of the compressor between the scavenging manifold and the intake passage. In a third example of the method (which optionally includes one or both of the first and second examples), the method further comprises: during low engine load conditions, closing an exhaust gas recirculation (EGR) valve positioned upstream of the compressor between the scavenging manifold and the intake passage, and the check valve being connected in parallel to the EGR valve. In a fourth example of the method (which may optionally include one or more of the first to third examples), the low engine load condition includes engine operation with the engine load below a first threshold load, and further includes opening the EGR valve to allow exhaust gas to flow from the scavenging manifold to the intake passage upstream of the compressor during EGR activation operation when the engine load is above the first threshold load. In a fifth example of the system (which may optionally include one or more of the first to fourth examples), delaying the exhaust valve closing timing of both the bleed exhaust valve and the scavenging exhaust valve includes closing the bleed exhaust valve at a first timing and closing the scavenging exhaust valve at a second timing later than the first timing, and further includes closing the bleed exhaust valve at a third timing and closing the scavenging exhaust valve at a fourth timing when the commanded EGR is greater than a threshold EGR rate during EGR activation operation, wherein the third timing is earlier than the first timing and the fourth timing is earlier than the second timing. In a sixth example of the method (which may optionally include one or more of the first to fifth examples), the method further includes: during low engine load conditions, closing a scavenging exhaust valve that connects the scavenging manifold to the engine's exhaust passage downstream of the turbine, and closing a turbine exhaust valve that crosses the turbine connection.

[0098] Another representation provides a method comprising, during a first condition, adjusting the position of an exhaust gas recirculation (EGR) valve based on a commanded EGR rate; allowing gas to flow from a first set of exhaust valves to the intake passage; and allowing combusted exhaust gas to flow from a second set of exhaust valves to a turbine disposed in the exhaust passage instead of flowing into the intake passage, wherein each of a plurality of engine cylinders includes one valve from the first set of exhaust valves and one valve from the second set of exhaust valves. The method further comprises, during a second condition, closing the EGR valve; allowing intake gas to flow from the intake passage to the plurality of engine cylinders via a check valve positioned parallel to the EGR valve and via the first set of exhaust valves; and allowing combusted exhaust gas to flow from the second set of exhaust valves to the turbine instead of flowing into the intake passage. In a first example of the method, the first condition includes an engine load within a first load range, and the second condition includes an engine load within a second load range, the second load range being lower than the first load range. In a second example of the method (which optionally includes the first example), the method further comprises, during the first condition, closing the first set of exhaust valves at a first timing; and during the second condition, closing the first set of exhaust valves at a second timing later than the first timing. In a third example of the method (which may optionally include one or both of the first and second examples), the method further includes opening a set of intake valves at a third timing earlier than the second timing during both the first and second states, wherein each cylinder includes at least one intake valve from the set. In a fourth example of the method (which may optionally include one or more of the first to third examples), the method further includes adjusting the closing timing of the first set of exhaust valves based on a commanded EGR rate during the first state. In a fifth example of the method (which may optionally include one or more of the first to fourth examples), the method further includes adjusting the position of a scavenging manifold bypass valve based on exhaust mass flow rate during the first state, the bypass valve fluidly connecting the first set of exhaust valves to the exhaust passage downstream of the turbine; and closing the scavenging manifold bypass valve during the second state.

[0099] Note that the exemplary control and estimation programs included herein can be used in conjunction with various engine and / or vehicle system configurations. The control methods and programs disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific programs described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threaded processing strategies, etc. Therefore, the various actions, operations, or functions shown can be executed in the order shown, in parallel, or in some cases omitted. Similarly, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the shown actions, operations, and / or functions can be repeatedly executed according to the specific strategy used. Furthermore, the described actions, operations, and / or functions can be graphically represented as code to be programmed into the non-transitory memory of a computer-readable storage medium in the engine control system, wherein the described actions are implemented by executing instructions in conjunction with an electronic controller in a system including various engine hardware components.

[0100] It will be understood that the configurations and procedures disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, as many variations are possible. For example, the above-described techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of various systems and configurations, as well as other features, functions, and / or properties disclosed herein.

[0101] The following claims specifically point to certain combinations and sub-combinations considered novel and non-obvious. These claims may relate to an “a” element or a “first” element or its equivalents. These claims should be understood to include combinations 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 by amendments to these claims or by setting new claims in this application or related applications. Such claims, whether broader or narrower in scope than the original claims, identical or different, are considered to be included within the subject matter of this disclosure.

[0102] According to the present invention, a method includes maintaining a scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during a valve overlap period, the scavenging manifold being connected to a cylinder of an engine and to an intake passage of the engine.

[0103] According to an embodiment, maintaining the scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during the valve overlap period includes maintaining the scavenging exhaust manifold at ambient pressure.

[0104] According to an embodiment, maintaining the scavenging manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during the valve overlap period includes: allowing fresh air into the scavenging manifold via a check valve positioned in a duct during the valve overlap period, the duct being fluidly connected to the scavenging manifold at a first end and fluidly connected to the intake passage at a second end, the duct being fluidly connected to the intake passage at a position upstream of the intake throttle valve.

[0105] According to an embodiment, the cylinder is connected to the scavenging manifold via a scavenging exhaust valve, and the valve overlap period includes the period of engine cycle when both the scavenging exhaust valve and the cylinder's intake valve are open.

[0106] According to an embodiment, the invention is further characterized in that, during low engine load conditions, the closing timing of both the venting exhaust valve and the scavenging exhaust valve that connect the cylinder to the turbine is delayed.

[0107] According to an embodiment, the invention is further characterized in that, during low engine load conditions, the exhaust gas recirculation (EGR) valve located upstream of the compressor between the scavenging manifold and the intake passage is closed, and the check valve therebetween is connected in parallel to the EGR valve.

[0108] According to an embodiment, the invention is further characterized in that, during a period when the engine load is higher than that of a low engine load condition, the position of the EGR valve is adjusted based on the commanded EGR rate.

[0109] According to the present invention, a system for an engine is provided, comprising: a first set of exhaust valves connected only to a first exhaust manifold, the first exhaust manifold being connected upstream of a turbocharger compressor to an intake passage via an exhaust gas recirculation (EGR) passage including an EGR valve; a second set of exhaust valves connected only to a second exhaust manifold, the second exhaust manifold being connected upstream of a turbocharger turbine disposed in an exhaust passage; a plurality of engine cylinders, each engine cylinder including one of the first set of exhaust valves and one of the second set of exhaust valves; and a check valve positioned in a conduit parallel to the EGR valves.

[0110] According to an embodiment, the first group of exhaust valves and the second group of exhaust valves open at different times, and there is a valve overlap period between the first group of exhaust valves and intake valves of the plurality of engine cylinders, wherein when the second group of exhaust valves is closed, one exhaust valve and one intake valve of each cylinder are open.

[0111] According to an embodiment, the check valve is positioned to draw in intake air from the intake passage upstream of the turbocharger compressor and to direct the intake air to the first exhaust manifold during valve overlap periods when the engine load is below a threshold load.

[0112] According to an embodiment, the invention is further characterized by a bypass passage connected downstream of the turbocharger turbine between the first exhaust manifold and the exhaust passage, and a scavenging exhaust valve positioned in the bypass passage.

[0113] According to an embodiment, the invention is further characterized by a controller configured to close the scavenging exhaust valve and the EGR valve when the engine load is below a threshold load.

[0114] According to an embodiment, the controller is further configured to adjust the first closing timing of the first set of exhaust valves and the second closing timing of the second set of exhaust valves when the engine load is below a threshold load.

[0115] According to the present invention, a method includes: during low engine load conditions, delaying the closing timing of both the exhaust valve of the venting exhaust valve that connects the engine cylinder to the turbine and the scavenging exhaust valve that connects the cylinder to the engine intake passage via the scavenging manifold; and reducing exhaust residue in the cylinder by allowing intake air to enter the scavenging manifold during the valve overlap period.

[0116] According to an embodiment, the valve overlap period includes the period of the engine cycle when both the scavenging exhaust valve and the cylinder intake valve are open.

[0117] According to an embodiment, allowing intake air into the scavenging manifold includes allowing intake air into the scavenging manifold via a check valve located upstream of the compressor between the scavenging manifold and the intake passage.

[0118] According to an embodiment, the invention is further characterized in that, during low engine load conditions, the exhaust gas recirculation (EGR) valve located upstream of the compressor between the scavenging manifold and the intake passage is closed, and the check valve therebetween is connected in parallel to the EGR valve.

[0119] According to an embodiment, the low engine load condition includes engine operation with engine load below a first threshold load, and also includes opening the EGR valve to allow exhaust gas to flow from the scavenging manifold upstream of the compressor to the intake passage during EGR activation operation with engine load above the first threshold load.

[0120] According to an embodiment, the delayed exhaust valve closing timing of both the release exhaust valve and the scavenging exhaust valve includes closing the release exhaust valve at a first timing and closing the scavenging exhaust valve at a second timing later than the first timing, and further includes closing the release exhaust valve at a third timing and closing the scavenging exhaust valve at a fourth timing when the commanded EGR is greater than a threshold EGR rate during EGR-enabled operation, wherein the third timing is earlier than the first timing and the fourth timing is earlier than the second timing.

[0121] According to one embodiment, the invention is further characterized in that, during low engine load conditions, a scavenging exhaust valve is closed, which connects the scavenging manifold to the engine's exhaust passage downstream of the turbine, and a turbine exhaust valve connecting across the turbine is closed.

Claims

1. A method for an engine, the method comprising: The scavenging exhaust manifold is maintained above a threshold pressure by introducing fresh air into it during the valve overlap period. The scavenging exhaust manifold is connected to the engine cylinder via a scavenging exhaust valve and to the engine intake passage upstream of the turbocharger compressor via an exhaust gas recirculation (EGR) passage. Maintaining the scavenging exhaust manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during the valve overlap period includes: allowing the fresh air into the scavenging exhaust manifold via a check valve positioned in a duct during the valve overlap period, the duct being fluidly connected to the scavenging exhaust manifold at a first end and fluidly connected to the intake passage at a second end, the duct being fluidly connected to the intake passage upstream of the intake throttle valve; The valve overlap period includes the time period of the engine cycle when both the scavenging exhaust valve and the cylinder's intake valve are open; and During low engine load conditions, the closing timing of both the venting exhaust valve and the scavenging exhaust valve that connect the cylinder to the turbine is delayed.

2. The method of claim 1, wherein maintaining the scavenging exhaust manifold above a threshold pressure by introducing fresh air into the scavenging exhaust manifold during the valve overlap period includes maintaining the scavenging exhaust manifold at ambient pressure.

3. The method of claim 1, further comprising: During the low engine load condition, the exhaust gas recirculation (EGR) valve located upstream of the compressor between the scavenging exhaust manifold and the intake passage is closed, wherein the check valve is connected in parallel to the EGR valve.

4. The method of claim 3, further comprising adjusting the position of the EGR valve based on the commanded EGR rate during a period when the engine load is higher than the low engine load condition.

5. A system for an engine, comprising: The first set of exhaust valves is connected only to the first exhaust manifold, which is connected to the intake passage upstream of the turbocharger compressor via an exhaust gas recirculation (EGR) passage, the EGR passage including an EGR valve. The second set of exhaust valves is connected only to the second exhaust manifold, which is connected to the exhaust passage upstream of the turbocharger turbine located in the exhaust passage. Multiple engine cylinders, each engine cylinder including one of the first group of exhaust valves and one of the second group of exhaust valves; as well as A check valve is positioned in a conduit parallel to the EGR valve.

6. The system of claim 5, wherein the first set of exhaust valves and the second set of exhaust valves open at different times, and wherein there is a valve overlap period between the first set of exhaust valves and intake valves of the plurality of engine cylinders, wherein when the second set of exhaust valves is closed, the one exhaust valve and the one intake valve of each cylinder are open.

7. The system of claim 6, wherein the check valve is positioned to draw in intake air from the intake passage upstream of the turbocharger compressor and direct the intake air to the first exhaust manifold during the valve overlap period when the engine load is below a threshold load.

8. The system of claim 7, further comprising a bypass passage downstream of the turbocharger turbine, connected between the first exhaust manifold and the exhaust passage, and a scavenging exhaust valve located in the bypass passage.

9. The system of claim 8, further comprising a controller configured to close the scavenging exhaust valve and the EGR valve when the engine load is below the threshold load.

10. The system of claim 9, wherein the controller is further configured to adjust the first closing timing of the first set of exhaust valves and the second closing timing of the second set of exhaust valves when the engine load is below the threshold load.

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