Engine systems and methods for EGR control

Abstract

Method for an engine (10), comprising: selectively opening a plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) of a dedicated EGR cylinder group or a dedicated EGR cylinder (4) to recirculate exhaust gas at each of a pre-compressor and a post-compressor location to engine cylinders (1, 2, 3), wherein the selective opening is based on one or more of engine load and boost pressure, where selective opening includes: Opening a first exhaust valve (EV1, 64) at lower load or lower boost pressure, while remaining exhaust valves (EV2, EV3; 65, 66) of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) are kept closed, to recirculate exhaust gas from the dedicated EGR cylinder (4) to a post-compressor location; and Opening a second, different exhaust valve (EV2, 65) at higher load or higher boost pressure, while remaining exhaust valves (EV1, EV3; 64, 66) of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) are kept closed to recirculate exhaust gas from the dedicated EGR cylinder (4) to a pre-compressor location.

Description

Area

[0001] This description relates to systems and methods for improving EGR control in engine systems designed with a dedicated cylinder group for providing external EGR to other engine cylinders. Background and brief presentation

[0002] Engines can be designed with exhaust-gas recirculation (EGR) systems to divert at least some exhaust gas from an engine exhaust manifold to an engine intake manifold. By providing a desired engine dilution, such systems reduce engine knock, in-cylinder heat losses, throttle losses, and NOx emissions. As a result, fuel economy is improved, particularly at high levels of engine boost pressure. However, cooled EGR is limited by the combustion system's ability to maintain acceptable stability and burn rates during EGR dilution.

[0003] Engines have also been designed with a single cylinder (or cylinder group) dedicated to providing external EGR to other engine cylinders. Exhaust gas is recirculated only from the dedicated cylinder group to the remaining engine cylinders. Accordingly, this allows a substantially fixed amount (e.g., percent) of EGR to be provided to engine cylinders under most operating conditions. By adjusting the fueling of the dedicated EGR cylinder group, the EGR composition can be altered. In particular, the dedicated cylinder can be operated fuel-richer than stoichiometry to produce more combustible species, such as hydrogen and carbon monoxide, which, when redirected to the engine intake, can increase EGR tolerance.Accordingly, this further improves the fuel economy benefit resulting from EGR by reducing combustion instability and combustion times while increasing permissible EGR rates.

[0004] An example of a turbocharged engine system with dedicated EGR cylinder capabilities is presented by Gingrich et al. in US 2012 / 0 204 844 A1. Exhaust gas from the dedicated EGR cylinder is mixed with pre-compressed air from a compressor at a location upstream of an intercooler and upstream of an intake throttle, allowing cooled EGR to be delivered to the engine.

[0005] From DE 60 2004 004 947 T2 and DE 10 2015 100 183 A1, engine control methods are known, wherein exhaust gas can be recirculated to a pre-compressor point and / or to a post-compressor point by selectively opening a plurality of exhaust valves of a dedicated EGR cylinder group or a dedicated EGR cylinder, wherein the selective opening of the exhaust valves is based on an engine load.

[0006] However, the inventors hereof have recognized potential problems with such dedicated EGR cylinder configurations. In particular, EGR may be at the wrong level during transients. For example, if there is a sudden increase in torque demand and a change in throttle position to a wider open position with a consequent drop in EGR demand, there may be manifold fill delays due to the specific EGR delivery location, resulting in more residual EGR gases remaining in the manifold than desired. The long delay in cleaning the residual EGR gases can lead to a drop in the power of the boosted engine.As another example, if there is a sudden decrease in torque demand and a change in throttle position to a more closed position with a consequent increase in EGR demand, there may be less EGR residual exhaust gas than desired due to the EGR delivery location and resulting manifold fill delays. The long delay in filling the manifold with EGR can lead to a drop in engine power. In both cases, combustion stability issues can also occur. Although diverter valves can be used to divert some or all of the exhaust gas from the dedicated EGR cylinder to an exhaust point under conditions where EGR is not required, the use of diverter valves may be prohibitively expensive, in addition to the associated consistency issues.

[0007] The inventors have recognized these and other problems and at least partially solved them with a method for an engine that allows exhaust gas to be directed from the dedicated EGR cylinder to a plurality of locations based on engine operating conditions. The method includes selectively opening a plurality of exhaust valves of a dedicated EGR cylinder group to recirculate exhaust gas at each of a pre-compressor and a post-compressor location to remaining engine cylinders. In this way, EGR delivery locations and rates can be easily varied as engine operating conditions change.

[0008] In one example, an engine system may be configured with a single dedicated EGR (DEGR) cylinder to provide external EGR to all engine cylinders. The engine may further include a charge air cooler (CAC) integrated into the intake manifold, enabling compaction of the boosted engine system. The dedicated EGR cylinder may include a plurality of exhaust valves, for example, three exhaust valves, and a single intake valve. A first exhaust valve may direct exhaust gas from the DEGR cylinder downstream of the charge air cooler and downstream of an intake throttle to the engine intake, thereby enabling discharge of hot EGR at a location further downstream of the intake manifold.A second exhaust valve may direct exhaust gas from the DEGR cylinder upstream of the intake compressor to the engine intake, thereby allowing cooled EGR to be recirculated at a location further upstream of the intake manifold. Because the engine includes an integrated CAC, both hot and cooled EGR are exhausted into a smaller manifold volume, reducing manifold fill delays and accelerating EGR fill, even when throttle position changes suddenly. A third exhaust valve may direct hot exhaust gas from the DEGR cylinder to the exhaust manifold, bypassing the remaining engine cylinders, at a location upstream of an exhaust catalyst. Accordingly, the third exhaust valve allows no EGR to be delivered to the engine. The plurality of exhaust valves may be configured with variable valve timing, such as through the use of a cam profile shifting (CPS) mechanism.cam profile switching) such that one or more of the exhaust valves are selectively activated at a particular time. For example, the CPS mechanism may be used to operate the dedicated EGR cylinder in one of a plurality of modes based on engine operating conditions, where the mode determines when and for how long each exhaust valve is opened during an exhaust stroke in the dedicated EGR cylinder group. As one example, under low load and / or low boost pressure conditions, the dedicated EGR cylinder may be operated in a first mode wherein only the first exhaust valve is opened during the exhaust stroke such that hot EGR is delivered to the engine intake at a post-compressor location.Under high load and / or high boost conditions, the dedicated EGR cylinder may then be operated in a second mode, where only the second exhaust valve is opened during the exhaust stroke, and cooled EGR is delivered to the engine intake at a pre-compressor location. Conversely, during engine cold-start or catalyst warm-up conditions, or when engine dilution is not required, the dedicated EGR cylinder may be operated in a third mode, where only the third exhaust valve is opened during the exhaust stroke to deliver hot exhaust gas to the catalyst while bypassing the engine cylinders. In still further examples, the timing of each of the exhaust valves may be adjusted to operate with different degrees of overlap (e.g., only partial overlap).

[0009] In this way, the EGR delivery location from a dedicated EGR cylinder group can be changed as operating conditions change in a turbocharged engine system. By enabling selective delivery of EGR to a pre-compressor and / or post-compressor location based on engine load and boost conditions, combustion stability issues and EGR failures during transient throttle position changes can be reduced. By introducing EGR to a pre-compressor location at higher engine loads and higher EGR rates, cylinder-to-cylinder EGR balancing is improved while also providing additional EGR cooling from an intercooler. Furthermore, the risk of compressor surge is reduced.By changing the EGR delivery location based on engine operating conditions, the discrepancy between where EGR is required under those conditions and where EGR is introduced is reduced, thereby reducing the amount of EGR delivery errors generated and shortening manifold fill times. Accordingly, this reduces the likelihood of EGR being at the incorrect level. Furthermore, the approach allows for simultaneous drawing of cooled and uncooled EGR at a reduced rate, along with some exhaust flow to the catalyst for light-off servicing. By adjusting the opening of a plurality of exhaust valves of a dedicated EGR cylinder group, the pre-exhaust portion of an exhaust stroke can be advantageously utilized for improved EGR controllability. Furthermore, the exhaust gas can be routed to a pre-turbine location for improved turbocharger performance.Likewise, the exhaust port can be adjusted to take advantage of the scavenging portion of the exhaust stroke to achieve a higher concentration of unburned and partially burned hydrocarbons for improved EGR tolerance in the engine. By reducing EGR errors during transients, turbocharged engine performance is improved, even at high engine dilution.

[0010] It should be understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts that are described in more detail in the detailed description. It is not intended to reveal critical or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any of the disadvantages noted above or in any part of this disclosure. Short description of the drawings

[0011] The advantages described herein will be better understood by reading an example of an embodiment, referred to herein as the "Detailed Description", alone or with reference to the drawings, in which: Fig. 1 is a schematic representation of an engine system including a dedicated EGR donor cylinder group. Fig. Figure 2 shows a schematic representation of the multiple exhaust valves of the dedicated EGR donor cylinder group in the different operating modes. Fig. 3 is a schematic representation of a combustion chamber of the engine. Fig. 4 illustrates an example method for adjusting exhaust valve actuation of the dedicated EGR cylinder group to change EGR flow based on engine operating conditions. Fig. 5 illustrates an example routine for switching between the various operating modes of the dedicated EGR cylinder group in response to changes in engine operating conditions. Fig. Figure 6 shows a table listing the different operating modes of the dedicated EGR cylinder group. Fig. 7 and Fig. 8 illustrate example exhaust valve timing for a dedicated EGR cylinder group in different operating modes. Detailed description

[0012] This description concerns EGR control in an engine operating with highly diluted cylinder mixtures, such as the engine systems of Fig. 1 to 3. The cylinder mixtures may be diluted using recirculated exhaust gases (EGR), which are byproducts of the combustion of air-fuel mixtures. A dedicated EGR cylinder (or a dedicated EGR cylinder group) of the engine may be designed with a plurality of exhaust valves, wherein the opening of each exhaust valve is controlled via a cam profile switching mechanism such that the number and identity of each open exhaust valve, as well as a duration of exhaust valve opening, can be changed with engine operating conditions. A controller may be designed to implement a control routine, such as the routine of Fig. 4, to selectively open a plurality of exhaust valves based on an EGR demand such that a location and rate of EGR delivery may be changed. For example, the controller may operate the dedicated EGR cylinder group in one of a plurality of modes ( Fig. 2 and Fig. 6) and switch between the majority of modes ( Fig. 5) switch when operating conditions change to change the EGR delivery location between a pre-compressor, a post-compressor, and an exhaust catalyst location. Example exhaust valve adjustments for EGR control in a turbocharged engine system are described with reference to Fig. 7 and Fig. 8 shown.

[0013] Fig. 1 schematically illustrates aspects of an exemplary engine system 100 including an engine 10 with four cylinders (1 through 4). As further explained herein, the four cylinders are configured as a first cylinder group 18 consisting of a dedicated EGR cylinder 4 and a second cylinder group 17 consisting of non-dedicated EGR cylinders 1 through 3. A detailed description of each combustion chamber of the engine 10 will be described with reference to Fig. 3. The engine system 100 may be coupled in a vehicle designed for road travel, such as a passenger car.

[0014] In the illustrated embodiment, the engine 10 is a supercharged engine coupled to a turbocharger 13 including a compressor 74 driven by a turbine 76. Specifically, fresh air is introduced into the engine 10 along an intake passage 42 via an air cleaner 53 and flows to the compressor 74. A flow rate of ambient air entering the intake system through the intake air passage 42 may be controlled, at least in part, by adjusting an intake throttle 20. The compressor 74 may be any suitable intake air compressor, such as an electric motor-driven or driveshaft-driven supercharger compressor. However, in the engine system 10, the compressor is a turbocharger compressor mechanically coupled to the turbine 76 via a shaft 19, with the turbine 76 driven by expanding engine exhaust.In one embodiment, the compressor and turbine may be coupled within a dual-scroll turbocharger. In another embodiment, the turbocharger may be a variable geometry turbocharger (VGT), where the turbine geometry is actively varied as a function of engine speed.

[0015] As in Fig. 1, the compressor 74 is coupled to the intake throttle body 20 through the charge air cooler (CAC) 78. The CAC 78 may be integrated into the intake manifold 25 and enable downsizing of the boosted engine. For example, the engine system may be manufactured in a first configuration (Configuration A) wherein the CAC is not integrated. Alternatively, the engine system may be manufactured in a second configuration (Configuration B) wherein the CAC is integrated. As described with reference to the table of Fig. As further detailed in Section 6, each configuration can be operated in one of three operating modes, achieving different HP-EGR and LP-EGR benefits.

[0016] The intake throttle valve 20 is coupled to the engine intake manifold 25. From the compressor, the compressed air flows through the charge air cooler and the throttle valve to the intake manifold. The charge air cooler can be, for example, an air-to-air or air-to-water heat exchanger. Fig. 1, the pressure of the air charge within the intake manifold is measured by a manifold air pressure (MAP) sensor 24. A compressor bypass valve (not shown) may be coupled in series between the inlet and outlet of the compressor 74. The compressor bypass valve may be a normally closed valve configured to open under selected operating conditions to relieve excessive boost pressure. For example, the compressor bypass valve may be opened under conditions of decreasing engine speed to avert compressor surge.

[0017] The intake manifold 25 is connected by a series of intake valves (see Fig. 3) is coupled to a series of combustion chambers 30. The combustion chambers are further connected to a series of exhaust valves (see Fig. 3) coupled to an exhaust manifold 36. Each cylinder 30 may be served by one or more valves. In the present example, the cylinders of the second cylinder group (cylinders 1 through 3) may each include at least one intake valve and at least one exhaust valve (not shown). In contrast, the cylinders of the first cylinder group (cylinder 4) may be configured with a single intake valve 62 and a plurality of exhaust valves. In the illustrated embodiment, the first cylinder group includes each of first, second, and third exhaust valves 64 through 66. In the illustrated embodiment, the plurality of exhaust valves 64 through 66 of the dedicated EGR cylinder group are configured symmetrically. However, in alternative embodiments, the plurality of exhaust valves of the dedicated EGR cylinder group may be configured asymmetrically.As one example, a larger exhaust valve may feed the exhaust route, while smaller exhaust valves may feed the pre- and post-compressor recirculation routes. As another example, exhaust valves 64 and 65 may be configured to be larger than exhaust valve 66, such that more exhaust gas is recirculated to the pre-compressor and post-compressor locations of the intake manifold than exhaust gas is diverted to the exhaust turbine or exhaust catalyst.

[0018] In the illustrated embodiment, the exhaust manifold 36 includes a plurality of exhaust manifold sections that allow exhaust gas from different combustion chambers to be directed to different locations in the engine system. In particular, exhaust gas from the second cylinder group 17 (cylinders 1 through 3) is directed through the turbine 76 of the exhaust manifold 36 before being processed by an exhaust catalyst of an exhaust control device 170. Exhaust gas from the first cylinder group 18 (cylinder 4), on the other hand, is redirected to the intake manifold 25 via an EGR passage 54 and a water gas shift catalyst 70. The water gas shift (WGS) catalyst 70, positioned in the EGR passage 54, is configured to generate hydrogen gas from rich exhaust gas received in passage 54 from cylinder 4.

[0019] Each of cylinders 1 through 4 may include internal EGR by capturing exhaust gases from a combustion event in the respective cylinder and allowing the exhaust gas to remain in the respective cylinder during a subsequent combustion event. The amount of internal EGR may be changed by adjusting the intake and / or exhaust valve opening and / or closing timing. For example, by increasing intake and exhaust valve overlap, additional EGR may be retained in the cylinder during a subsequent combustion event. External EGR is provided to cylinders 1 through 4 only via exhaust flow from the first cylinder group 18 (herein, cylinder 4) and the EGR passage 54. In another example, external EGR may be provided only to cylinders 1 through 3 and not to cylinder 4. External EGR is not provided by the exhaust flow from cylinders 1 through 3.Accordingly, in this example, cylinder 4 is the only source of external EGR for engine 10 and is therefore referred to as the dedicated EGR cylinder (or cylinder group). By recirculating exhaust gas from one cylinder of the four-cylinder engine to the engine intake manifold, a nearly constant EGR rate (e.g., of about 25%) can be provided. Cylinders 1 through 3 are also referred to herein as the non-dedicated EGR cylinder group. It should be understood that although the current example depicts the dedicated EGR cylinder group as having a single cylinder, in alternative engine configurations, the dedicated EGR cylinder group may include multiple engine cylinders.

[0020] The EGR passage 54 may include an EGR cooler 52 for cooling EGR delivered to the engine intake. In some embodiments, the dedicated EGR cylinder 4 may have variable valve timing on the intake and / or exhaust valves to change the EGR rate. Furthermore, the EGR passage 54 may include an exhaust gas sensor or exhaust catalyst for estimating an air-fuel ratio of the exhaust gas recirculated from the first cylinder group to the engine intake. Optionally, a second exhaust gas sensor (not shown) may be positioned downstream of the exhaust manifold sections of the first cylinder group for estimating an air-fuel ratio of exhaust gas in the first cylinder group. There may be further exhaust gas sensors in the engine system of Fig. 1 must be included.

[0021] It should be understood that in some examples, the integrated charge air cooler 78 may also be configured to provide EGR cooling. In such embodiments, an EGR cooler is not required.

[0022] The EGR passage 54 may include a first conduit 57 that allows the recirculated exhaust gas to be delivered to a post-compression location (downstream of the throttle valve 20), and a second conduit 55 that allows the recirculated exhaust gas to be delivered to a pre-compression location (upstream of the compressor 74 near a compressor inlet). The EGR cooler 52 may be disposed in the EGR passage 54, and more particularly in the EGR conduit 55, such that exhaust gas recirculated to the pre-compression location is cooled prior to delivery, while exhaust gas recirculated to the post-compression location is not cooled prior to delivery. As a result, cooled low-pressure (LP) EGR from the second exhaust valve is delivered to the pre-compression location, while uncooled EGR from the first exhaust valve is delivered to the post-compression location.Alternatively, the EGR cooler 54 may be relocated upstream and / or the CAC 78 may be integrated into the intake manifold, allowing delivery of cooled EGR to either the pre- or post-compressor locations. Optionally, at least a portion of the exhaust gas from the first cylinder group may be redirected to the exhaust manifold 48 via a bypass conduit 56. In the depicted example, the conduit redirects exhaust gas to the exhaust manifold upstream of the turbine 76. However, in alternative examples, the exhaust gas may be redirected to a location downstream of the turbine 76 and upstream of an exhaust catalyst of an exhaust control device 170. As further explained herein, by changing the exhaust valve actuation timing of the first cylinder group 18, exhaust gas from the dedicated EGR cylinder group may be recirculated to the intake via conduits 55, 57 and / or redirected to the exhaust catalyst via conduit 56.

[0023] A hydrogen concentration in the external EGR from cylinder 4 may be increased by enriching an air-fuel mixture combusted in cylinder 4. In particular, the amount of hydrogen gas produced at the WGS catalyst 70 may be increased by increasing the richness of exhaust gas received in passage 50 from cylinder 4. Accordingly, to provide hydrogen-enriched exhaust gas to engine cylinders 1 through 4, the fueling of the second cylinder group 18 may be adjusted to enrich cylinder 4. In one example, the hydrogen concentration of the external EGR from cylinder 4 may be increased under conditions where engine combustion stability is less than desired. This measure increases the hydrogen concentration in the external EGR and may improve engine combustion stability, particularly at lower engine speeds and loads (e.g., idle).In addition, hydrogen-enriched EGR allows the engine to tolerate significantly higher EGR levels than conventional EGR (with lower hydrogen concentration) before combustion stability issues even arise. By increasing the range and amount of EGR utilization, the engine's fuel economy is improved.

[0024] The engine system 100 further includes one or more camshafts for actuating the intake and exhaust valves of the combustion chambers. For example, an intake camshaft (not shown) may be coupled to the intake valve of the first cylinder group and the intake valve of each cylinder of the second cylinder group via different cam lobes. The camshaft may be actuated to actuate the corresponding intake valves via adjustments to the timing of the corresponding cam lobes. Each intake valve may be actuated between an open position admitting intake air into the corresponding cylinder and a closed position substantially excluding intake air from the cylinder. The intake camshafts may be included as part of an intake valve actuation system.

[0025] Likewise, an exhaust camshaft 68 may be included in an exhaust valve actuation system 69. The exhaust camshaft 68 may be coupled to the exhaust valves 64-66 of the first cylinder group 18 (herein, cylinder 4). The exhaust camshaft 68 may include an exhaust cam 67 having a cam lobe profile for varying the timing and duration of opening of the exhaust valve 64 during an exhaust stroke of the first cylinder group. Likewise, exhaust cams with similar or different cam lobe profiles may be included to be coupled to the exhaust valves 65 and 66. Each exhaust valve 64-66 may be actuated between an open position, which allows exhaust gas to flow from the corresponding cylinder, and a closed position, which substantially retains gas within the cylinder.Based on the lobe profile of each exhaust cam, the corresponding exhaust valve may be opened at a different timing and for a different duration. The lobe profile may affect cam lift, cam duration, and / or cam timing. A controller may be capable of switching between exhaust valve actuation by longitudinally moving exhaust camshaft 68 and switching between cam profiles. Although exhaust camshaft 68 is shown coupled to the exhaust valves of first cylinder group 18, a similar exhaust camshaft (not shown) may be coupled to the exhaust valves of each cylinder of second cylinder group 17, with the common exhaust camshaft being actuated to actuate the exhaust valves of all coupled cylinders.

[0026] The exhaust valve actuation system 69 and the intake valve actuation system (not shown) may further include pushrods, rocker arms, lifters, etc. Such devices and features may control the actuation of the intake valves and the exhaust valves by converting the rotational motion of the cams into translational motion of the valves. As previously mentioned, the valves may also be actuated via additional cam lobe profiles on the camshafts, where the cam lobe profiles may provide different cam lift height, cam duration, and / or cam timing between the various valves. However, alternative camshaft arrangements (overhead and / or pushrod) may also be used if desired. In still further examples, each of the exhaust valves and intake valves of one or more cylinders may be actuated by a common camshaft.Additionally, in some examples, some of the intake valves and / or exhaust valves may be actuated by their own independent camshaft or other device.

[0027] The engine system 100 may include variable valve timing systems, for example, a variable exhaust cam timing (VCT) system 80. The VCT system 80 may be configured to open the first exhaust valve 64 at a first timing and for a first duration during a first operating mode. The first operating mode may occur at lower engine load and / or lower boost pressures. The first conduit 57 couples the first exhaust valve 64 of the first cylinder group to the intake manifold downstream of the intake compressor 74 (at a location after the compressor). The second conduit 55 couples the second exhaust valve 65 of the first cylinder group to the intake manifold upstream of the intake compressor (at a location before the compressor). The third conduit 56 couples the third exhaust valve 66 of the first cylinder group to the exhaust manifold upstream of an exhaust catalyst of the exhaust control device 170.As in . Fig. 2 and Fig. 4, by changing the operation of the camshaft 68, the opening and closing of the exhaust valves 64 to 66 can be changed to thereby change the EGR discharge location and the EGR discharge rate.

[0028] The VCT system 80 may include an exhaust camshaft phaser 81 coupled to the exhaust camshaft 68 for changing exhaust valve timing. The VCT system may similarly include an intake camshaft phaser coupled to an intake camshaft for changing intake valve timing. The VCT system 80 may be configured to advance or retard valve timing by advancing or retarding camshaft timing, and may be controlled by the controller 12. The VCT system 80 may be configured to change the timing of valve opening and closing events by changing the relationship between crankshaft position and camshaft position. For example, the VCT system 80 may be configured to rotate the intake camshaft 68 independently of the crankshaft to advance or retard valve timing.In some embodiments, the VCT system 80 may be a cam-torque-actuated device configured to rapidly change cam timing. In some embodiments, valve timing, such as intake valve closing (IVC) and exhaust valve closing (EVC), may be changed by a continuously variable valve lift (CVVL) device.

[0029] The valve / cam control devices and systems described above may be hydraulically driven or electrically actuated, or combinations thereof. In one example, camshaft position may be changed via cam phasing of an electric actuator (e.g., an electrically actuated cam phaser) with an accuracy exceeding that of most hydraulically actuated cam phasers. Signal lines may send control signals to the VCT system 80 and receive a cam timing and / or cam selection measurement at the actuator therefrom.

[0030] The combustion chambers 30 may be supplied with one or more fuels, such as gasoline, alcoholic fuel blends, diesel, biodiesel, compressed natural gas, etc. The fuel may be delivered to the combustion chambers via an injector 66. The fuel injector 66 may draw fuel from a fuel tank. In the depicted example, the fuel injector 66 is configured for direct injection, although in other embodiments, the fuel injector 66 may be configured for port injection or throttle body injection. Further, each combustion chamber may include one or more fuel injectors of various configurations to enable each cylinder to receive fuel via direct injection, port injection, throttle body injection, or combinations thereof. Combustion within the combustion chambers may be initiated via spark ignition and / or compression ignition.

[0031] Exhaust gas from the exhaust manifold 36 is directed to the turbine 76 to drive the turbine. If reduced turbine torque is desired, some exhaust gas may instead be directed by bypassing the turbine through a wastegate (not shown). The combined flow from the turbine and wastegate then flows through the exhaust control device 170. In general, one or more emission control devices 170 may include one or more exhaust aftertreatment catalysts configured to catalytically treat exhaust gas flow and thereby reduce an amount of one or more substances in the exhaust stream. For example, an exhaust aftertreatment catalyst may be configured to X from the exhaust gas stream when the exhaust gas stream is lean, and the captured NO X reduced when the exhaust flow is rich. In other examples, an exhaust aftertreatment catalyst may be designed to reduce NO Xdisproportionate or NO X selectively reduced using a reducing agent. In other examples, an exhaust aftertreatment catalyst may be configured to oxidize residual hydrocarbons and / or residual carbon monoxide in the exhaust stream. Various exhaust aftertreatment catalysts having any such functionality may be disposed in intermediate layers or elsewhere in the exhaust aftertreatment stages, either separately or together. In some embodiments, the exhaust aftertreatment stages may include a regenerable soot filter configured to capture and oxidize soot particulates in the exhaust stream. All or a portion of the treated exhaust gas from the emission control device 170 may be discharged to the environment via the outlet conduit 35.

[0032] The engine system 100 further includes a control system 14. The control system 14 includes a controller 12, which may be any electronic control system of the engine system or the vehicle in which the engine system is installed. The controller 12 may be configured to make control decisions based at least in part on inputs from one or more sensors 16 within the engine system and to control actuators 83 based on the control decisions. For example, the controller 12 may store computer-readable instructions in memory, and the actuators 83 may be controlled by executing the instructions. Example sensors include MAP sensor 24, MAF sensor 49, exhaust temperature and pressure sensors 128 and 129, and exhaust oxygen sensor 51. Example actuators include throttle body 20, fuel injector 66, intake valve 62, and exhaust valves 64-66.Additional sensors and actuators may be included, as described in . Fig. 2 to 3. The read-only memory storage medium in the controller 12 may be programmed with computer-readable data representing instructions executable by a processor for performing the methods described hereinafter, as well as other variants anticipated but not specifically listed. An exemplary method is described herein with reference to Fig. 4 described.

[0033] Fig. Figure 2 illustrates a detailed embodiment 200 of the exhaust flow from the dedicated EGR cylinder group to various locations in the engine during various operating modes. Accordingly, the components previously described in Fig. 1, similarly numbered. It should be understood that, although the illustrated embodiment appears to depict the dedicated EGR cylinder (cylinder 4) separate from the remaining engine cylinders (cylinders 1 through 3), this is intended to represent a functional distinction. Accordingly, the cylinders may actually be arranged adjacently on an engine block, as in Fig. 1. However, in alternative examples, the dedicated engine cylinder group may be physically separated from the remaining engine cylinders, such as on a different bank or even on a separate engine.

[0034] Embodiment 200 shows the engine 10 with an intake manifold 25 and an exhaust manifold 36, a turbocharger including an intake compressor 74 driven via a shaft by an exhaust turbine 76; and an intercooler 78 integrated into the intake manifold in a pre-throttle position, as shown by solid lines, or alternatively in a post-throttle position, as shown by dashed lines. The first dedicated EGR cylinder group 18 (cylinder number 4 herein) includes an intake valve 62 and each of a first exhaust valve 64, a second exhaust valve 65, and a third exhaust valve 66. The intake valve 62 draws intake air into the first cylinder group 18 from upstream of the intake compressor, or it could alternatively draw pre-compressed air from the intake manifold 25.

[0035] A first conduit 57 couples the first exhaust valve 64 of the first cylinder group to the intake manifold downstream of the intake compressor. The first conduit may be contained within the EGR passage 54. In this case, the EGR is also discharged downstream of the intake throttle 20. In this way, the dedicated EGR cylinder group is configured to return hot EGR to the engine intake at a post-compressor location via the first exhaust valve and first conduit when the CAC is not integrated into the intake manifold, or to return cooled EGR to the engine intake at the post-compressor location via the first exhaust valve and first conduit. In one example, in a first operating mode at lower engine load and lower boost pressure, the first exhaust valve may be selectively opened to provide hot EGR to the engine via the first conduit.By delivering the hot EGR (or cooled EGR in the configuration with the integrated CAC) to the engine downstream of the compressor in a smaller volume, EGR filling is accelerated and EGR errors during transients are reduced. Furthermore, the hot (or cooled) EGR is delivered closer to where it is desired. Alternatively, the EGR cooler 52 could be contained in passage 57, or the CAC 78 could be integrated into the intake manifold 25, allowing delivery of cooled EGR after the compressor.

[0036] A second conduit 55 couples the second exhaust valve 65 of the first cylinder group to the air intake upstream of the intake compressor. The second conduit may also be contained within the EGR passage 54 and disposed at least partially adjacent to the first conduit 57. Here, the EGR is also discharged upstream of the intake throttle 20. In this manner, the dedicated EGR cylinder group is configured to return cooled EGR to the engine intake at a pre-compressor location via the second exhaust valve and the second conduit. The EGR may be cooled via the CAC either at the pre-throttle location (if the CAC is not integrated) or at the post-throttle location (if the CAC is integrated). In one example, in a second operating mode at higher engine load and higher boost pressure, the second exhaust valve may be selectively opened to provide cooled low-pressure EGR to the engine via the second conduit.By delivering the cooled EGR to the engine upstream of the compressor, longer mixing lengths are available, allowing for more even distribution of EGR to the engine cylinders and avoiding compressor surge problems during boosted operation.

[0037] A third conduit 56 couples the third exhaust valve 66 of the first cylinder group to the exhaust manifold at a location upstream of an exhaust catalyst 192 of the emission control device. The third conduit may also be contained within the EGR passage 54, but may be offset from the first and second conduits 55 and 57. In the embodiment of Fig. 2, the line 56 is coupled downstream of the turbine 76, although in alternative examples, such as in Fig. 1, conduit 56 may be coupled upstream of turbine 76. In this way, the dedicated EGR cylinder group is configured to divert exhaust gas to the exhaust catalyst to accelerate catalyst warm-up and / or provide substantially no engine dilution. In one example, in a third operating mode, the third exhaust valve may be selectively opened during an engine cold start to not provide EGR to the engine. Routing exhaust gas to the pre-turbine location may also improve engine boost performance.

[0038] A cam profile switcher actuator may be coupled to each of the first, second, and third exhaust valves of the first cylinder group. A controller with computer-readable instructions may be included in the engine system and configured with code to adjust a timing of opening each of the first, second, and third exhaust valves during an exhaust stroke of the first cylinder group based on one or more of engine load, boost pressure, and engine dilution. For example, at lower engine load and lower boost pressure, adjusting may include opening and closing the first exhaust valve prior to closing the second and third exhaust valves during an exhaust stroke of the first cylinder group. The adjusting may further include, at higher engine load and higher boost pressure, opening and closing the second exhaust valve prior to closing the first and third exhaust valves.Furthermore, adjusting during an engine cold start may include opening and closing the third exhaust valve prior to closing the first and second exhaust valves. Here, the controller may adjust an opening duration of each of the first and second exhaust valves based on an engine dilution demand, while adjusting an opening duration of the third exhaust valve based on a temperature of an exhaust catalyst coupled to the exhaust manifold. For example, the opening duration of the first and second exhaust valves may be increased as the engine dilution demand increases, while the opening duration of the third exhaust valve may be increased as the exhaust catalyst temperature drops below a threshold.

[0039] The timing of exhaust valve opening can be adjusted so that there is no overlap between valve actuations, or at least only partial overlap. By adjusting the valve opening timing, the valve opening duration, and the timing overlap between the exhaust valves, the rate and location of EGR delivery can be changed as engine operating conditions change. This allows EGR delivery to each of a pre-compressor and a post-compressor location while simultaneously changing a ratio of EGR delivery between the locations based at least on engine load and boost pressure, and while still meeting engine dilution requirements. For example, under conditions of higher engine load and boost pressure, a larger portion of EGR may be delivered to a pre-compressor location, while a smaller portion of EGR is delivered to a post-compressor location.As another example, under conditions of lower engine load and lower boost pressure, a larger portion of EGR may be delivered to the post-compression location while a smaller portion of EGR is delivered to the pre-compression location.

[0040] Now with reference to Fig. 3, a cylinder of an internal combustion engine 10 comprising a plurality of cylinders (as in Fig. 1-2). The engine 10 includes a combustion chamber 30 and cylinder walls 132 with a piston 136 positioned therein and connected to a crankshaft 40. A flywheel 197 and a ring gear 199 are coupled to the crankshaft 40. A starter 196 includes a pinion shaft 198 and a pinion gear 195. The pinion shaft 198 can selectively advance the pinion gear 195 to engage the ring gear 199. The starter 196 can be mounted directly to the front of the engine or the rear of the engine. In some examples, the starter 196 can selectively supply torque to the crankshaft 40 via a belt or chain. In one example, the starter 196 is in a ground state when not engaged with the engine crankshaft.

[0041] The combustion chamber 30 is shown communicating with an intake manifold 144 and an exhaust manifold 148 via an intake valve 152 and an exhaust valve 154, respectively. Each intake and exhaust valve can be independently actuated by an intake cam 151 and an exhaust cam 153. An intake valve timing device 85 advances or retards the phase of the intake valve 152 with respect to a position of the crankshaft 40. In addition, the intake valve timing device 85 can advance or retard an intake valve lift. An exhaust valve timing device 83 advances or retards the phase of the exhaust valve 154 with respect to a position of the crankshaft 40. Furthermore, the exhaust valve timing device 83 can advance or retard an exhaust valve lift. The position of the intake cam 151 can be determined by the intake cam sensor 155. The position of the exhaust cam 153 can be determined by the exhaust cam sensor 157.In cases where the combustion chamber 30 is part of a dedicated EGR cylinder, the timing and / or lift height of valves 152 and 154 can be adjusted independently of other engine cylinders so that the cylinder air charge of the dedicated EGR cylinder can be increased or decreased relative to other engine cylinders. In this way, external EGR supplied to the engine cylinders can exceed 25 percent of the cylinder charge mass. External EGR is exhaust gas pumped from a cylinder's exhaust valves and recirculated to the cylinders via cylinder intake valves. Furthermore, the amount of internal EGR from cylinders other than the EGR cylinder can be adjusted independently of the dedicated EGR cylinder by adjusting the valve timing of those respective cylinders. Internal EGR is exhaust gas that remains in a cylinder after a combustion event and is part of a mixture in the cylinder for a subsequent combustion event.

[0042] In the illustration, fuel injector 66 is positioned to inject fuel directly into cylinder 30, known to those skilled in the art as direct injection. Alternatively, fuel may be injected into an intake port, known to those skilled in the art as port injection. In some example engine configurations, one or more cylinders may receive fuel from both direct and port fuel injectors.

[0043] In one example, fuel injector 66 may be a selectively deactivatable fuel injector. Accordingly, an engine cylinder may be selectively deactivated by shutting off fuel to that cylinder. In some embodiments, the dedicated EGR cylinder may be deactivated by shutting off air instead of, or in addition to, shutting off fuel. For example, one of the intake valve and the exhaust valve(s) of the dedicated EGR cylinder may be deactivated, but not both. By deactivating either the intake valve or the exhaust valve, the pumping work of the cylinder may be increased. Maximizing the pumping work of the dedicated EGR cylinder may also include adjusting cam phasing, valve lift, position of an intake throttle or charge motion control device, etc.

[0044] The intake manifold 144 is illustrated as communicating with an optional electronic throttle 162 that adjusts a position of the throttle plate 164 to control airflow from the air intake 42 into the intake manifold 144. In some examples, the throttle plate 162 and the throttle plate 164 may be positioned between the intake valve 152 and the intake manifold 144 such that the throttle plate 162 is a port throttle. A driver-requested torque may be determined from a position of the accelerator pedal 180 sensed by the accelerator pedal sensor 184. A voltage or current indicative of the driver-requested torque is output from the accelerator pedal sensor 184 when the driver's foot 182 depresses the accelerator pedal 180.

[0045] A distributorless ignition system 88 provides an ignition spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12. A universal exhaust gas oxygen (UEGO) sensor 126 is shown coupled to the exhaust manifold 148 upstream of a catalytic converter 170. Alternatively, a dual-state exhaust gas oxygen sensor may be employed in place of the UEGO sensor 126.

[0046] In one example, the catalyst 170 may include multiple catalyst blocks. In another example, multiple emission control systems, each with multiple blocks, may be used. In one example, the catalyst 170 may be a three-way catalyst.

[0047] The control 12 is in Fig. 3 as a conventional microcomputer including: a microprocessor unit 102, input / output (I / O) ports 104, a (non-transitory) read-only memory 106, a random access memory 108, a keep alive memory (KAM) 110, and a conventional data bus. The controller 12 is shown receiving, in addition to the signals previously discussed, various signals from sensors coupled to the engine 10, including: an engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 113; a measurement of engine manifold pressure (MAP) from a temperature sensor 112 coupled to a cooling sleeve 113; and a measurement of engine coolant pressure (ECT) from a temperature sensor 114 coupled to a cooling sleeve 115.manifold pressure) from a pressure sensor 122 coupled to the intake manifold 144; an engine position sensor from a Hall-effect sensor 115 that measures the position of the crankshaft 40; a measurement of air mass entering the engine from a sensor 119; and a measurement of throttle position (TP) from a sensor 158. Barometric pressure may also be sensed for processing by the controller 12 (sensor not shown). In a preferred aspect of the present description, the engine position sensor 115 generates a predetermined number of evenly spaced pulses during each revolution of the crankshaft from which the engine speed (RPM) can be determined.

[0048] During operation, each cylinder within the engine 10 typically experiences a four-stroke cycle: the cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, the exhaust valve 154 generally closes and the intake valve 152 opens. Air is introduced into the combustion chamber 30 via the intake manifold 144, and the piston 136 moves to the bottom of the cylinder to increase the volume within the combustion chamber 30. The position at which the piston 136 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, the intake valve 152 and the exhaust valve 154 are closed. The piston 136 moves towards the cylinder head to compress the air in the combustion chamber 30.The point at which the piston 136 is at the end of its stroke and closest to the cylinder head (e.g., when the combustion chamber 30 has its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC).

[0049] In a process referred to below as injection, fuel is introduced into the combustion chamber. In a process referred to below as ignition, the injected fuel is ignited by known ignition means, such as spark plug 92, resulting in combustion. During the power stroke, expanding gases push piston 136 back to BDC. Crankshaft 40 converts piston motion into rotating shaft torque. Finally, during the exhaust stroke, exhaust valve 154 opens to release the combusted air-fuel mixture to exhaust manifold 148, and the piston returns to TDC.It should be noted that the foregoing is presented merely as an example, and that the timing of intake and exhaust valve opening and / or closing may vary to provide, for example, positive or negative valve overlap, late intake valve closing, among various other examples.

[0050] Accordingly, the components of Fig. 1 to 3 for an engine system configured to selectively open a plurality of exhaust valves of a dedicated EGR cylinder group to recirculate exhaust gas at each of a pre-compressor and a post-compressor location to remaining engine cylinders. The system further allows for (e.g., simultaneously) routing a portion of the exhaust gas from the dedicated EGR cylinder to an exhaust catalyst while bypassing the remaining engine cylinders.

[0051] Fig. Figure 6 illustrates a table 600 listing various operating modes of the dedicated EGR cylinder group. Configuration A lists the various operating modes for the engine configuration that does not have an integrated CAC, while Configuration B lists the various operating modes for the engine configuration that does have an integrated CAC.

[0052] For both configurations, the engine control unit can operate the dedicated EGR cylinder group in a first mode (Mode A), with a first exhaust valve open and each of a second and third exhaust valve closed to recirculate exhaust gas at a post-compressor location to an intake manifold. Consequently, in Configuration A, hot, high-pressure EGR can be delivered to the engine, while in Configuration B, cooled, high-pressure EGR can be delivered to the engine.

[0053] The controller may further operate the dedicated EGR cylinder group in a second mode (Mode B), with the second exhaust valve open and each of the first and third exhaust valves closed to recirculate exhaust gas to the intake manifold at a pre-compressor location. Thus, in Configuration A, low-pressure EGR cooled via the CAC may be delivered to the engine at a pre-throttle location, while in Configuration B, low-pressure EGR cooled via the integrated CAC may be delivered to the engine at a post-throttle location.

[0054] The controller may further operate the dedicated EGR cylinder group in a third mode (Mode C) wherein the third exhaust valve is open and each of the first and second exhaust valves is closed to redirect exhaust gas to an exhaust manifold while bypassing engine cylinders.

[0055] Now with reference to Fig. 4 illustrates an exemplary method 400 for adjusting exhaust valve actuation of a dedicated EGR cylinder group of a multi-cylinder engine based on engine operating conditions to change a location and rate of EGR flow based on varying EGR demand. The method enables recirculating exhaust gas from a dedicated EGR cylinder group to each of a pre-compressor and a post-compressor location. Further, the method enables redirecting at least some exhaust gas to an exhaust catalyst, bypassing engine cylinders.

[0056] At 402, the routine includes estimating and / or measuring engine operating conditions, such as engine speed, torque demand, engine load, boost pressure, MAP, intake airflow, ambient conditions such as ambient pressure, temperature, humidity, exhaust catalyst temperature, etc. At 404, an engine dilution demand is determined based on the engine operating conditions. In one example, the engine dilution demand may be lower at lower engine loads and boost pressures and higher at higher engine loads and boost pressures.

[0057] At 405, fueling of the dedicated EGR cylinder group may be adjusted based on the engine dilution demand and further based on the engine's combustion stability limit under the current operating conditions. For example, if the engine's combustion stability limit is lower, the engine's EGR tolerance may be lowered. Under such conditions, the dedicated EGR cylinder group may be rich-fueled to operate the dedicated EGR (DEGR) cylinder group at an air-fuel ratio richer than stoichiometry. The WGS catalyst may use the hydrocarbon-rich exhaust from the DEGR cylinder group to produce more combustible species, such as CO and H2, which, when redirected into the engine via the intake manifold, may increase the engine's EGR tolerance by reducing combustion instability and combustion durations.Accordingly, this increases the allowable EGR rate, thereby improving the fuel economy benefit of EGR. In one example, the richness of the DEGR cylinder fuel supply is increased as the combustion stability limit decreases for a given engine dilution requirement.

[0058] At 406, an operating mode for the dedicated EGR cylinder is determined based on the engine dilution demand and further based on the engine operating conditions. For example, the mode selection may be based on one or more of engine load and boost pressure. Selecting the mode may include determining whether to meet the engine dilution demand with hot EGR or cooled low-pressure EGR. If both, a relative ratio of the hot EGR and cooled LP EGR may be determined. Accordingly, the hot EGR includes EGR recirculated from the DEGR cylinder at a post-compressor location downstream of the intake throttle and substantially directly into the intake manifold without passing through an EGR cooler to the engine intake. This direct delivery into the intake manifold reduces the manifold's EGR fill time.Cooled LP-EGR includes EGR recirculated from the DEGR cylinder to the engine intake after cooling after passing through an EGR cooler at a pre-compressor location. Delivering cooled EGR to the pre-compressor location reduces cylinder heat losses, mitigates engine knock, and lowers exhaust temperatures to reduce enrichment requirements. The pre-compressor injection point also improves cylinder-to-cylinder EGR balancing and provides additional EGR cooling by the CAC, both of which are required at higher EGR rates and high loads. Selecting the mode may further include determining whether no engine dilution is required and / or whether catalyst warm-up is required. If catalyst warm-up is required, a heat flow amount required at the exhaust catalyst may also be determined.Accordingly, based on the heat flux required at the exhaust catalyst, an amount of hot exhaust gas to be diverted to the exhaust catalyst of the emission control device when bypassing engine cylinders can be determined. In particular, when the catalyst temperature drops below a threshold temperature (such as a light-off temperature below which the exhaust catalyst is not activated), the required heat flux increases, and more exhaust gas may need to be diverted to the catalyst. Similarly, under conditions where a rapid reduction in engine dilution is required, more of the exhaust gas from the DEGR cylinder group can be diverted away from the intake manifold and into the exhaust manifold.Based on the mode selection, the controller may actuate a cam profile switching (CPS) device including lobes each coupled to the plurality of exhaust valves of the DEGR cylinder group to change an opening timing and an opening duration of each of the plurality of exhaust valves.

[0059] At 408, it may be determined whether a first mode has been selected. In one example, control may operate the dedicated EGR cylinder group in the first mode in response to one or more of lower engine load (e.g., lower than a threshold load) and lower boost pressure (e.g., lower than a threshold boost pressure) conditions. The routine includes, if the first mode is confirmed at 410, adjusting the CPS device coupled to the exhaust valves of the DEGR cylinder group to selectively open the first exhaust valve and release hot EGR from the DEGR cylinder to the intake manifold at the post-compressor location. Specifically, control may operate the dedicated EGR cylinder group in a first mode with the first exhaust valve open and each of the second and third exhaust valves closed to recirculate exhaust gas to the intake manifold at the post-compressor location downstream of an intake throttle.

[0060] In one example, in the first mode, the first exhaust valve is opened and closed prior to opening (and / or closing) each of the second and third valves during an exhaust stroke of the dedicated EGR cylinder group. For example, in the first mode, only the first exhaust valve may be opened during the exhaust stroke, while the second and third valves are kept closed during the exhaust stroke. That is, the valves may be actuated mutually exclusive and without valve overlap. In an alternative example, the valves may be actuated with at least some overlap such that the first valve is opened and closed before the other valves are opened or before the other valves are closed.For example, the first exhaust valve may be opened and closed during an earlier portion of the exhaust stroke, while the remaining exhaust valves are opened and / or closed during a later portion of the exhaust stroke. The earlier opening exhaust valve could take advantage of the pre-exhaust portion of the exhaust stroke for improved EGR control capability or be routed to the pre-turbine location for improved turbocharger performance. The later opening exhaust valve could take advantage of the scavenging portion of the exhaust stroke for a higher concentration of unburned and partially burned hydrocarbons for improved EGR tolerance in the engine.

[0061] In addition to adjusting the opening timing of the first exhaust valve, the opening duration of the first exhaust valve can also be adjusted based at least on the EGR demand, with the opening duration being extended as the EGR demand increases. The opening duration can be extended by increasing the valve lift of the first exhaust valve, for example, by adjusting the CPS device.

[0062] If the first mode is not confirmed, a determination may be made at 412 as to whether a second mode has been selected. In one example, the controller may operate the dedicated EGR cylinder group in the second mode in response to one or more of higher engine load (e.g., higher than a threshold load) and higher boost pressure (e.g., higher than a threshold boost pressure) conditions. The routine includes, at 414, if the second mode is confirmed, adjusting the CPS device coupled to the exhaust valves of the DEGR cylinder group to selectively open the second exhaust valve and deliver cooled EGR from the DEGR cylinder at the pre-compressor location to the intake manifold.In particular, the controller may operate the dedicated EGR cylinder group in a second mode with the second exhaust valve open and each of the first and third exhaust valves closed to recirculate exhaust gas at the pre-compressor location upstream of the intake compressor to the intake manifold.

[0063] In one example, in the second mode, the second exhaust valve is opened and closed prior to opening (and / or closing) each of the first and third valves during an exhaust stroke of the dedicated EGR cylinder group. For example, in the second mode, only the second exhaust valve may be opened during the exhaust stroke, while the first and third valves are kept closed during the exhaust stroke. That is, the valves may be actuated mutually exclusive and without valve overlap. In an alternative example, the valves may be actuated with at least some overlap such that the second valve is opened and closed before the other valves are opened or before the other valves are closed.For example, the second exhaust valve can be opened and closed during an earlier part of the exhaust stroke, while the remaining exhaust valves are opened and / or closed during a later part of the exhaust stroke. This would allow simultaneous drawing of cooled and uncooled EGR at a reduced rate, along with some exhaust flow to the catalyst for light-off servicing.

[0064] In addition to adjusting the opening timing of the second exhaust valve, the opening duration of the second exhaust valve can also be adjusted based at least on the EGR demand, with the opening duration being extended as the EGR demand increases. The opening duration can be extended by increasing the valve lift of the second exhaust valve, for example, by adjusting the CPS device.

[0065] By selecting between the first and second modes, the controller may selectively open a plurality of exhaust valves of a dedicated EGR cylinder group to recirculate exhaust gas at each of a pre-compressor and a post-compressor location to remaining engine cylinders. For example, the controller may adjust an opening timing of the plurality of exhaust valves during an exhaust stroke of the dedicated EGR cylinder group such that recirculating exhaust gas to the pre-compressor location and recirculating exhaust gas to the post-compressor location are mutually exclusive. Alternatively, the controller may adjust an opening timing of the plurality of exhaust valves during an exhaust stroke of the dedicated EGR cylinder group such that recirculating exhaust gas to the pre-compressor location at least partially overlaps with recirculating exhaust gas to the post-compressor location.

[0066] If the second mode is not affirmed, a determination may be made at 416 whether a third mode has been selected. In one example, the controller may operate the dedicated EGR cylinder group in the third mode in response to one of engine cold start, catalyst warm-up, and engine idle conditions (where engine dilution is not required). The routine includes, at 418, if the third mode is affirmed, adjusting the CPS device coupled to the exhaust valves of the DEGR cylinder group such that the third exhaust valve is selectively opened to direct exhaust from the DEGR cylinder group to an exhaust catalyst while bypassing the remaining engine cylinders.In particular, the controller may operate the dedicated EGR cylinder group in a third mode with the third exhaust valve open and each of the first and second exhaust valves closed to direct exhaust gas away from the intake manifold and into the exhaust manifold upstream of an exhaust catalyst and / or upstream of an exhaust turbine.

[0067] In one example, in the third mode, the third exhaust valve is opened and closed prior to opening (and / or closing) each of the first and second valves during an exhaust stroke of the dedicated EGR cylinder group. For example, in the third mode, only the third exhaust valve may be opened during the exhaust stroke, while the first and second valves are kept closed during the exhaust stroke. That is, the valves may be actuated mutually exclusive and without valve overlap. In an alternative example, the valves may be actuated with at least some overlap such that the third valve is opened and closed before the other valves are opened or before the other valves are closed.For example, the third exhaust valve can be opened and closed during an earlier part of the exhaust stroke, while the remaining exhaust valves are opened and / or closed during a later part of the exhaust stroke. This would be advantageous if the third mode is directed to the pre-turbine location so that the energy from the pre-exhaust pulse improves turbo performance, or if the hottest gases are directed to the post-turbine catalyst location for improved catalyst performance. In addition to adjusting the opening timing of the third exhaust valve, the opening duration of the third exhaust valve can also be adjusted based at least on the temperature of the exhaust catalyst, with the opening duration being extended when the exhaust catalyst temperature drops below a threshold temperature (e.g., light-off temperature). The opening duration can be extended by increasing the valve lift of the third exhaust valve, for example, by adjusting the CPS device.

[0068] From each of 410, 414, and 418, the routine proceeds to 420 to determine if there is a change in operating conditions that requires a change in operating mode. For example, the routine may switch operation between the various modes in response to changes in one or more of engine load, boost pressure, or EGR demand. If no switching is required, the routine ends, maintaining the current DEGR cylinder operating mode. Otherwise, at 422, an engine dilution demand may be updated based on the updated engine operating conditions. The CPS device may then be actuated to switch between modes based on the updated engine dilution demand. As described with reference to the routine of Fig. 5, this may include, as non-limiting examples, switching from the first mode to the second mode in response to an increase in engine load, switching from the second mode to the first mode in response to a decrease in engine load, and switching from the third mode to the first mode in response to insufficient exhaust catalyst warm-up.

[0069] Now turning to Fig. 5, an example routine 500 for selecting an operating mode and switching between operating modes of a dedicated EGR cylinder group in response to engine operating conditions is shown.

[0070] At 502, engine operating conditions may be estimated and / or measured, as at 402. At 504, it may be determined whether an engine cold start condition exists. In one example, an engine cold start may be confirmed when an exhaust catalyst temperature is lower than a threshold, such as lower than a light-off temperature. If an engine cold start condition is confirmed, then at 506, the routine includes operation in the third mode, wherein the third exhaust valve is open to redirect exhaust gas to the exhaust manifold upstream of an exhaust catalyst while bypassing engine cylinders. The first and second exhaust valves may be closed simultaneously during the exhaust stroke.

[0071] At 508, it may be determined whether the exhaust catalyst is warm enough, for example, whether the exhaust catalyst temperature is higher than the threshold. If not, the dedicated EGR cylinder group may continue operating in the third mode. Otherwise, at 510, the dedicated EGR cylinder group may be switched to a first mode, with the first exhaust valve open to recirculate hot exhaust gas to the engine intake at a post-compressor location. The second and third exhaust valves may be closed simultaneously during the exhaust stroke.

[0072] Returning to 504, if no engine cold start condition is confirmed, at 512 the routine includes operating the dedicated EGR cylinder group in the first mode with the first exhaust valve open to return hot exhaust gas to the engine intake at a post-compressor location. The second and third exhaust valves may be closed simultaneously during the exhaust stroke. In one example, the first mode may be a default operating mode of the dedicated EGR cylinder group. The first mode exhaust valve could be configured to provide a smaller amount of EGR than 25% to the engine cylinders due to typically lower EGR tolerance and lower engine loads. Additionally, if the first mode EGR is uncooled or moderately cooled, this would be ideal for low load conditions to improve combustion stability and reduce pumping losses.

[0073] From 512 and 510, the routine moves to 514 to determine if a tip-in to higher engine loads is present. If so, at 516, the routine includes switching the dedicated EGR cylinder group from the first mode to a second mode with the second exhaust valve open to return cooled exhaust gas at a pre-compressor location to the engine intake. The first and third exhaust valves may be closed simultaneously during the exhaust stroke. At higher engine loads, EGR cooling is critical, and according to the low-pressure configuration, the EGR is cooled via the EGR cooler and again by the CAC. Additionally, at higher engine speeds and loads, there is less time for EGR mixing, so the longer route traversed by the EGR provides equal distribution from cylinder to cylinder, smoother turbo operation, and less risk of compressor surge.

[0074] If tip-in to higher loads is not confirmed at 514, the routine proceeds to 518, just as it did from 516, to determine if idle tip-out conditions exist. If idle tip-out conditions are not confirmed, the routine includes a switch back to the first mode at 520 once the tip-out event is complete. If idle tip-out conditions are confirmed, the routine includes a switch to the third mode to deliver exhaust to the catalyst while bypassing engine cylinders.

[0075] This allows exhaust gas from the dedicated EGR cylinder to be diverted to the main exhaust stream for rapid catalyst light-off and rapid engine warm-up. Similarly, when EGR is not required, the exhaust valve is activated, feeding the main exhaust stream. This improves engine efficiency. Furthermore, the engine can be equipped with high-pressure or low-pressure EGR as needed.

[0076] Now turning to Fig. 7, a map 700 illustrates a set of example exhaust valve timing for a dedicated EGR cylinder during various operating modes. Map 700 illustrates the piston position at various engine strokes at curve 702. Profiles 750 through 770 represent example profiles for modes 1 through 3, respectively. In each mode, only one of the plurality of exhaust valves is selectively opened during the exhaust stroke, while the other exhaust valves are held closed for the entire duration of the exhaust stroke. In other words, the exhaust valves are actuated in a mutually exclusive manner. In each profile, the intake valve timing is represented by a solid line (curve 710, 720, 730), and the exhaust valve timing is represented by various dashed lines (curve 704, 706, 708).

[0077] Curve 702 represents piston positions (along the y-axis) with respect to their position from top dead center (TDC) and / or bottom dead center (BDC), and further with respect to their position within the four strokes (intake, compression, power, and exhaust) of an engine cycle. As indicated by a sinusoidal curve 602, a piston moves incrementally downward from TDC and impacts BDC by the end of the power stroke. The piston then returns to the top at TDC at the end of the exhaust stroke. Thereafter, the piston moves downward again to BDC during the intake stroke and finally returns to its top starting position at TDC at the end of the compression stroke.

[0078] Curves 710, 720, and 730 represent valve timing for an intake valve (solid line) during a first, second, and third mode of DEGR cylinder operation at profiles 750, 760, and 770, respectively. As shown, in each mode, the intake valve can be opened at or before the beginning of an intake stroke and remain open at least until a subsequent compression stroke has begun. Furthermore, the intake valve can be actuated at various values ​​of valve lift and duration.

[0079] Profile 750 illustrates exhaust valve timing during a first mode, where exhaust gas is redirected to the engine intake via a first conduit at a location downstream of the compressor and downstream of an intake throttle. As illustrated, in the first mode, only the first exhaust valve (curve 704) can open and close during the exhaust stroke, while the second and third exhaust valves are held closed throughout the exhaust stroke. Here, the actuation of the first valve and the actuation of the second and third valves are mutually exclusive during each exhaust stroke. In one example, the engine in this mode runs primarily on uncooled EGR in a high-pressure configuration.

[0080] Profile 760 illustrates exhaust valve timing in a second mode where exhaust gas is redirected to the engine intake via a second conduit at a location upstream of the compressor. As illustrated, in the second mode, only the second exhaust valve (curve 706) may open and close during the exhaust stroke, while the first and third exhaust valves are held closed throughout the exhaust stroke. Here, the actuation of the second valve and the actuation of the first and third valves during each exhaust stroke are mutually exclusive. In one example, this mode may be used at higher engine loads where larger amounts of cooled EGR are desired.

[0081] Profile 770 illustrates exhaust valve timing in a third mode, where exhaust gas is redirected to the engine exhaust manifold via a third conduit while bypassing the engine cylinders at a location upstream of an exhaust catalyst. As illustrated, in the third mode, only the third exhaust valve (curve 708) may open and close during the exhaust stroke, while the first and second exhaust valves are held closed throughout the exhaust stroke. Here, the actuation of the third valve and the actuation of the first and second valves during each exhaust stroke are mutually exclusive. In one example, the third mode is executed during an engine cold start.

[0082] In each of the profiles 750 through 770, the closing point of the exhaust valve lift is immediately after TDC. However, in alternative examples, the closing point may also be immediately at TDC.

[0083] It is understood that although the example of Fig. 7 illustrates only a single exhaust valve active at a given time, in alternative examples two or all of the exhaust valves may be active at a given time.

[0084] For example, in a first mode, where exhaust gas is diverted to the engine intake via a first conduit at a location downstream of the compressor and downstream of an intake throttle, the first exhaust valve may open and close first during an earlier portion of the exhaust stroke, while the second and third exhaust valves are held closed. In particular, the first exhaust valve may open immediately as the piston reaches the end of the power stroke. The second valve may open and close next, followed by the actuation of the third exhaust valve. In particular, the third valve may close as the piston completes the exhaust stroke. Here, the actuation of each valve does not overlap with the actuation of any other exhaust valve during a given exhaust stroke. In alternative examples, the actuation of the exhaust valves may at least partially overlap.By changing the valve lift, the duration and degree of valve opening are changed, thereby changing the amount of exhaust gas released through each exhaust valve. For example, the valve lift of the first exhaust valve can be increased relative to the valve lift of the remaining exhaust valves so that the engine runs primarily on uncooled EGR in a high-pressure configuration, but mixed with some cooled EGR in a low-pressure configuration, as well as a small amount of exhaust gas to the catalyst for warming.

[0085] In a second mode, where exhaust gas is redirected to the engine intake via a second conduit at a location upstream of the compressor, the second exhaust valve may open and close first during an earlier portion of the exhaust stroke, while the first and third exhaust valves are held closed. In particular, the second exhaust valve may open immediately as the piston reaches the end of the power stroke. The first valve may open and close next, followed by actuation of the third exhaust valve. In particular, the third valve may close as the piston completes the exhaust stroke. Here, the actuation of each valve does not overlap with the actuation of any other exhaust valve during a given exhaust stroke. In alternative examples, the actuation of the exhaust valves may at least partially overlap.By changing the valve lift, the duration and degree of valve opening are altered, thereby changing the amount of exhaust gas released through each exhaust valve. For example, the valve lift of the second exhaust valve can be increased relative to the valve lift of the remaining exhaust valves. Accordingly, these scenarios can also exist at higher engine loads, where larger amounts of EGR are desired while still maintaining some uncooled HP EGR and some flow to the exhaust for catalyst warming.

[0086] In a third mode, where exhaust gas is redirected to the engine exhaust manifold via a third conduit while bypassing the engine cylinders at a location upstream of an exhaust catalyst, the third exhaust valve may open and close first during an earlier portion of the exhaust stroke while the first and second exhaust valves are held closed. In particular, the third exhaust valve may open immediately as the piston reaches the end of the power stroke. The first valve may open and close next, followed by actuation of the second exhaust valve. In particular, the second valve may close as the piston completes the exhaust stroke. Here, the actuation of each valve does not overlap with the actuation of any other exhaust valve during a given exhaust stroke. In alternative examples, the actuation of the exhaust valves may at least partially overlap.By changing the valve lift height, a duration and degree of valve opening are changed, thereby changing an amount of exhaust gas released via each exhaust valve. For example, the valve lift of the third exhaust valve may be increased relative to the valve lift of the remaining exhaust valves. For example, during an engine cold start, the third exhaust valve may be actuated with a greater valve lift but for a shorter duration to allow for faster warm-up. In one example, the third mode scenario is the most likely mode, with only a single exhaust valve open, as normally the engine would not run fuel-rich, as desired in EGR modes, and would also send rich exhaust gas to the catalytic converter.

[0087] Now turning to Fig. 8 illustrates exemplary engine operation with EGR adjustment via selectively opening one of a plurality of exhaust valves of a dedicated EGR cylinder. Specifically, a map 800 illustrates engine speed at curve 802, boost pressure at curve 804, exhaust temperature (Texh) at curve 806, and EGR demand at curve 808. Curve 810 illustrates when a first exhaust valve (EV1) of a DEGR cylinder, which couples the cylinder to an intake manifold downstream of the intake compressor, is active. Curve 812 illustrates when a second exhaust valve (EV2), which couples the DEGR cylinder to the intake manifold upstream of the intake compressor, is active. Curve 814 represents when a third exhaust valve (EV3), which couples the DEGR cylinder to the exhaust manifold bypassing engine cylinders, is active.

[0088] It is understood that a particular exhaust valve being active for a duration does not mean that the exhaust valve is open for that duration. Exhaust valve being active means that the respective exhaust valve is operating and continuously transitioning between open and closed states throughout each combustion event, as represented by dashed lines 811. It is further understood that when a particular exhaust valve is active, the opening duration and degree may vary. In one example, the valve parameters may be adjusted by changing the valve lift.

[0089] At t0, an engine restart may be initiated. The engine restart may be a cold engine start, where the temperature of an exhaust catalyst is below its activation temperature. Accordingly, engine dilution may not be desired during this time. Accordingly, between t0 and t1, when the engine is restarted and as the exhaust temperature and the exhaust catalyst temperature increase, the third exhaust valve is activated, while the first and second exhaust valves of the dedicated EGR cylinder remain inactive. Consequently, exhaust gas from the dedicated EGR cylinder is routed to the exhaust catalyst, bypassing the engine cylinders.

[0090] At t1, the exhaust temperature may be high enough, and the exhaust catalyst temperature may be above its activation temperature. Furthermore, at t1, engine speed and load may be at lower speed and load conditions. For example, the engine speed may be at or above idle, and the engine load may be lower than a threshold load such that no boost pressure is required. Under such lower speed and load conditions, the EGR demand may be higher. Thus, to provide the required engine dilution, the third exhaust valve may be deactivated at t1 while the first exhaust valve is activated. Further, the second exhaust valve may be kept inactive. The first valve may be kept active until t2. Consequently, exhaust gas from the dedicated EGR cylinder is recirculated to a post-compressor location to provide high-pressure EGR.

[0091] At t2, engine speed and load may increase due to a change in the operator's torque demand. For example, the engine load may be higher than a threshold load. Additionally, boost pressure may be increased to meet the operator's demand. Under such high-speed and load conditions, EGR demand may be lower. Accordingly, to provide the required lower engine dilution, the first exhaust valve may be deactivated at t2, while the second exhaust valve is activated. Furthermore, the third exhaust valve may be kept inactive. The second valve may be kept active until t3. Consequently, exhaust gas from the dedicated EGR cylinder is recirculated to a pre-compressor location to provide cooled, low-pressure EGR.

[0092] At t3, engine operating conditions may change, and engine speed and load may return to a lower range, with higher EGR demand and lower boost pressure. Thus, at t3, the second exhaust valve may be deactivated while the first exhaust valve is reactivated. Furthermore, the third exhaust valve may be kept inactive. Additionally, the engine may resume receiving EGR at a post-compressor location from the dedicated EGR cylinder.

[0093] It is understood that although the example of Fig. 8 illustrates only a single exhaust valve active at a given time; in alternative examples, two or all of the exhaust valves may be active at a given time. As one example, the first and second exhaust valves may be activated so that a relative amount of EGR delivered to pre- and post-compressor locations may be changed.

[0094] In this way, exhaust gas from the dedicated EGR cylinder group can be recirculated to an engine intake to provide either high-pressure or low-pressure EGR. Further, the exhaust gas can be recirculated to provide either hot EGR or cooled EGR as desired. By activating one or more exhaust valves that feed exhaust gas from a dedicated EGR cylinder into an EGR passage when EGR is required, unique problems associated with low and high loads and EGR can be solved. By activating an exhaust valve that feeds exhaust gas from a dedicated EGR cylinder into an exhaust passage while bypassing an EGR passage, a drop in engine dilution can be accelerated when EGR is not required. In addition, exhaust gas can be redirected to an exhaust manifold to accelerate turbine start-up and catalyst warm-up under cold conditions.By delivering EGR to various locations in an engine with an integrated intercooler, the manifold fill volume is reduced, allowing EGR level changes to be quickly achieved as desired during transients. By reducing EGR errors during transients, the performance of the boosted engine is improved, even at high engine dilution.

[0095] It should be noted that the exemplary control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-volatile memory. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated acts, operations, and / or functions may be performed in the illustrated order, in parallel, or in some cases, omitted.Likewise, the order of processing is not required to achieve the features and advantages of the embodiments described herein, but is provided merely for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Furthermore, the described acts, operations, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer-readable storage medium in the engine control system.

[0096] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be interpreted in a limiting sense, as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, horizontally opposed four-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

[0097] The following claims particularly point out certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be understood to encompass the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims are also considered to be included within the subject matter of the present disclosure, whether broader, narrower, equal, or different in scope.

Claims

[1] A method for an engine (10) comprising: selectively opening a plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) of a dedicated EGR cylinder group or a dedicated EGR cylinder (4) to recirculate exhaust gas at each of a pre-compressor and a post-compressor location to engine cylinders (1, 2, 3), wherein the selective opening is based on one or more of engine load and boost pressure, where selective opening includes: Opening a first exhaust valve (EV1, 64) at lower load or lower boost pressure, while remaining exhaust valves (EV2, EV3; 65, 66) of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) are kept closed, to recirculate exhaust gas from the dedicated EGR cylinder (4) to a post-compressor location; and Opening a second, different exhaust valve (EV2, 65) at higher load or higher boost pressure, while remaining exhaust valves (EV1, EV3; 64, 66) of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) are kept closed to recirculate exhaust gas from the dedicated EGR cylinder (4) to a pre-compressor location. [2] The method of claim 1, wherein the selective opening comprises adjusting an opening timing of the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) during an exhaust stroke of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) such that the recirculation of exhaust gas to the pre-compressor location and the recirculation of exhaust gas to the post-compressor location are mutually exclusive. [3] The method of claim 1, wherein the selective opening comprises adjusting an opening timing of the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) during an exhaust stroke of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) such that the recirculation of exhaust gas to the pre-compressor location at least partially overlaps with the recirculation of exhaust gas to the post-compressor location. [4] The method of claim 1, further comprising selectively opening a third exhaust valve (EV3; 66) during an engine cold start or when no EGR is required while keeping remaining exhaust valves (EV1, EV2; 64, 65) of the dedicated EGR cylinder group or cylinder (4) closed to direct exhaust gas from the dedicated EGR cylinder group or cylinder (4) to an exhaust catalyst while bypassing the engine cylinders (1, 2, 3). [5] The method of claim 1, wherein selectively opening a plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) comprises actuating a cam profile switching device comprising lobes coupled to each of the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) to change an opening timing and an opening duration of each of the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66). [6] The method of claim 5, wherein the opening duration of each of the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) is based on at least one EGR demand of the engine (10), the opening duration being increased as the EGR demand of the engine (10) increases. [7] The method of claim 6, wherein extending the opening duration of an exhaust valve (EV1, EV2, EV3; 64, 65, 66) comprises increasing a valve lift of the exhaust valve (EV1, EV2, EV3; 64, 65, 66) by adjustments of the cam profile switching device. [8] The method according to claim 1, wherein the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) are designed symmetrically. [9] Method according to claim 1, wherein the plurality of exhaust valves (EV1, EV2, EV3; 64, 65, 66) of the dedicated EGR cylinder group or the dedicated EGR cylinder (4) are designed asymmetrically. [10] A method comprising: Operating a dedicated EGR cylinder group or cylinder (4) in a first mode (Mode A), wherein a first exhaust valve (EV1; 64) is open and each of a second (EV2; 65) and third exhaust valve (EV3; 66) is closed to recirculate exhaust gas at a post-compressor location to an intake manifold (25); Operating the dedicated EGR cylinder group or the dedicated EGR cylinder (4) in a second mode (Mode B), wherein a second exhaust valve (EV2; 65) is open and each of a first (EV1; 64) and third exhaust valve (EV3; 66) is closed to recirculate exhaust gas at a pre-compressor location to an intake manifold (25); and Operating the dedicated EGR cylinder group or cylinder (4) in a third mode (Mode C), wherein a third exhaust valve (EV3; 66) is open and each of a first (EV1; 64) and second exhaust valve (EV2; 65) is closed to redirect exhaust gas to an exhaust manifold (36) while bypassing engine cylinders (1, 2, 3). [11] The method of claim 10, further comprising switching operation between the modes (AC modes) in response to one or more of engine load, boost pressure, and EGR demand. [12] The method of claim 11, wherein operating in the first mode (Mode A) is in response to one of lower load and lower boost pressure conditions, operating in the second mode (Mode B) is in response to one of higher engine load and higher boost pressure conditions, and operating in the third mode (Mode C) is in response to one of engine cold start, catalyst warm-up, and engine idle conditions. [13] The method of claim 10, wherein in the first mode (Mode A) the first exhaust valve (EV1, 64) is opened and closed prior to opening each of the second (EV2; 65) and third valves (EV3; 66) during an exhaust stroke of the dedicated EGR cylinder group or the dedicated EGR cylinder (4), wherein in the second mode (Mode B) the second valve (EV2; 65) is opened and closed prior to opening each of the first (EV1; 64) and third valves (EV3; 66) during an exhaust stroke, and wherein in the third mode (Mode C) the third valve (EV3; 66) is opened and closed prior to opening each of the first (EV1; 64) and second valves (EV2; 65) during an exhaust stroke. [14] The method of claim 10, wherein diverting to the exhaust manifold (36) when operating in the third mode (Mode C) comprises diverting to the exhaust manifold (36) upstream of an exhaust turbine and upstream of an exhaust catalyst. [15] Engine system comprising: an engine having an intake manifold (25) and an exhaust manifold (36); a turbocharger (13) comprising an inlet compressor (74) driven by an exhaust turbine (76); a charge air cooler (78) integrated into the intake manifold (25); a first cylinder (4) comprising an intake valve (62) and each of a first, second and third exhaust valve (EV1, EV2, EV3; 64, 65, 66); a first line (57) coupling the first exhaust valve (EV1; 64) of the first cylinder (4) to the intake manifold (25) downstream of the intake compressor (74); a second line (55) coupling the second exhaust valve (EV2; 65) of the first cylinder (4) to the intake manifold (25) upstream of the intake compressor (74); a third line (56) coupling the third exhaust valve (EV3; 66) of the first cylinder (4) to the exhaust manifold (36); a cam profile switching device actuator coupled to each of the first, second and third exhaust valves (EV1, EV2, EV3; 64, 65, 66) of the first cylinder (4); a second cylinder having an intake valve and an exhaust valve coupled to the exhaust manifold (36); and a controller (12) with computer-readable instructions for: Adjusting an opening timing of each of the first, second and third exhaust valves (EV1, EV2, EV3; 64, 65, 66) during an exhaust stroke of the first cylinder (4) based on one or more of engine load, boost pressure and engine dilution. [16] The engine system of claim 15, wherein said adjusting comprises: Opening and closing the first exhaust valve (EV1; 64) before closing the second (EV2; 65) and third exhaust valve (EV3; 66) at lower engine load and lower boost pressure; Opening and closing the second exhaust valve (EV2; 65) before closing the first (EV1; 64) and third exhaust valve (EV; 66) at higher engine load and higher boost pressure; and Opening and closing the third exhaust valve (EV; 66) before closing the first (EV1; 64) and second exhaust valve (EV2; 65) during an engine cold start. [17] The engine system of claim 16, wherein the controller (12) further comprises instructions for adjusting an opening duration of each of the first (EV1; 64) and second exhaust valves (EV2; 65) based on an engine dilution demand and for adjusting an opening duration of the third exhaust valve (EV3; 66) based on a temperature of an exhaust catalyst coupled to the exhaust manifold (36). [18] Engine system according to claim 17, wherein the opening duration of the first (EV1; 64) and second exhaust valve (EV2; 65) is extended with increasing engine dilution demand, and wherein the opening duration of the third exhaust valve (EV3; 66) is extended when the exhaust catalyst temperature drops below a threshold.

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