Dedicated EGR engine with dynamic load control

An internal combustion engine comprises a first engine bank and a second engine bank. A first intake valve is disposed in an intake port of a cylinder of the first engine bank, and is configured for metering the first flow of combustion air by periodically opening and closing according to a first intake valve lift and duration characteristic. A variable valve train control mechanism is configured for affecting the first intake valve lift and duration characteristic. Either a lift or duration of the first intake valve is modulated so as to satisfy an EGR control criterion.

FIELD OF THE INVENTION

The subject invention relates to internal combustion engines with exhaust gas recirculation, and more particularly to an internal combustion engine that may be operated in various EGR modes with widely varying ranges of EGR.

BACKGROUND

In today's world, it is desirable to have internal combustion engines with improved fuel economy and reduced emissions while producing acceptable levels of power. A means for simultaneously achieving these objectives is to use exhaust gas recirculation (EGR). Unfortunately, conventional engines are typically unable to operate in a wide range of displacements while allowing for the relatively high levels of EGR that may be necessary in some operating modes to mitigate spark knock and to also improve fuel economy. In addition, it has thus far not been practical to provide for symmetric, or near symmetric, delivery of hydrogen rich EGR to all cylinders of an engine with the ability to reduce throttling losses at light loads so as to provide for a reduction in fuel consumption.

Accordingly, it is desirable to provide an invention that addresses these and other deficiencies in the prior art.

SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention an internal combustion engine comprises a first engine bank defining a first combustion chamber with a first intake port for providing a first flow of combustion air to the first combustion chamber and with a first exhaust port for providing a first flow of combustion products from the first combustion chamber. A second engine bank defines a second combustion chamber with a second intake port for providing a second flow of combustion air to the second combustion chamber and with a second exhaust port for providing a second flow of combustion products from the second combustion chamber. A first intake valve is disposed in the first intake port, and the first intake valve is configured for metering the first flow of combustion air by periodically opening and closing according to a first intake valve lift and duration characteristic.

A second intake valve is disposed in the second intake port, and the second intake valve is configured for metering the second flow of combustion air by periodically opening and closing according to a second intake valve lift and duration characteristic. An intake manifold defines an intake plenum, and the intake manifold also defines an air inlet, a first intake runner, a second intake runner, and an EGR duct, each being in fluid communication with the intake plenum. The air inlet is in fluid communication with a supply of ambient air and configured for carrying the supply of ambient air for delivery to the intake plenum. The first intake runner is in fluid communication with the first intake port and configured for carrying the first flow of combustion air from the intake plenum to the first intake port. The second intake runner is in fluid communication with the second intake port and configured for carrying the second flow of combustion air from the intake plenum to the second intake port. The EGR duct is in fluid communication with the first exhaust port and configured for carrying the first flow of combustion products from the first exhaust port to the intake plenum.

In another exemplary embodiment of the invention a variable valve train control mechanism is provided that is configured for affecting the first intake valve lift and duration characteristic. Either a lift or duration of the first intake valve is modulated so as to satisfy an EGR control criterion.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawing, which is a schematic drawing showing an internal combustion engine in accordance with an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. In accordance with an exemplary embodiment of the invention, an internal combustion engine100comprises a first engine bank102defining a first combustion chamber104with a first intake port106for providing a first flow of combustion air108to the first combustion chamber104. The first engine bank102also defines a first exhaust port110for providing a first flow of combustion products112from the first combustion chamber104. A second engine bank114defines a second combustion chamber116with a second intake port118for providing a second flow of combustion air120to the second combustion chamber116. The second engine bank114also defines a second exhaust port122for providing a second flow of combustion products124from the second combustion chamber116.

A first intake valve126is disposed in the first intake port106and is configured for metering the first flow of combustion air108by periodically opening and closing according to a first intake valve lift and duration characteristic. It should be appreciated that the first intake valve126may comprise a single poppet valve, a plurality of poppet valves, or any apparatus suitable for performing the function of metering the first flow of combustion air108according to a desired characteristic. A second intake valve128is similarly disposed in the second intake port118. The second intake valve128is configured for metering the second flow of combustion air120by periodically opening and closing according to a second intake valve lift and duration characteristic. It should be appreciated that the second intake valve128may comprise a single poppet valve, a plurality of poppet valves, or any apparatus suitable for performing the function of metering the second flow of combustion air120according to a desired characteristic.

The engine also includes an intake manifold130, which defines an intake plenum132. In addition, the intake manifold130defines an air inlet134, a first intake runner136, a second intake runner138, and an EGR duct140. Each of the air inlet134, the first intake runner136, the second intake runner138, and the EGR duct140is in fluid communication with the intake plenum132. The air inlet134is in fluid communication with a supply of ambient air142and is configured for carrying the supply of ambient air142for delivery to an inlet mixer144, where the supply of ambient air142is combined with a pre-boost EGR stream146carried by the boost leg148to create boost-inlet stream150, which is delivered to a supercharger172and subsequently to the intake plenum132. The intake plenum132provides a common supply of combustion air154, which is split to create the first flow of combustion air108in the first intake runner136and the second flow of combustion air120in the second intake runner138. A throttle valve156may be disposed in the first intake runner136for controlling the relationship between first flow of combustion air108and second flow of combustion air120, which are each extracted from the common supply of combustion air154traveling through the intake plenum132. The first intake runner136is in fluid communication with the first intake port106and is configured for carrying the first flow of combustion air108from the intake plenum132to the first intake port106.

The second intake runner138is in fluid communication with the second intake port118and is configured for carrying the second flow of combustion air120from the intake plenum132to the second intake port118. The EGR duct140is in fluid communication with the first exhaust port110and is configured for carrying the first flow of combustion products112from the first exhaust port110to an EGR splitter178, where the combustion products112are divided between a post-boost EGR stream158and the pre-boost EGR stream146. The post-boost EGR stream158is directed through a direct return leg160to the intake plenum132. The pre-boost EGR stream146is directed through boost leg148and is combined with the ambient air142at an inlet mixer144to form the boost-inlet stream150. A recuperator162may be disposed (e.g., upstream from the EGR splitter178) for extracting heat from the combustion products112prior to their reintroduction to the intake plenum132.

In an exemplary embodiment, the internal combustion engine100comprises a variable valve train control mechanism164that is configured for affecting the first intake valve126lift and duration characteristic by modulating a lift of the first intake valve126, by modulating a duration of the first intake valve126, or by modulating a lift and a duration of the first intake valve126.

In an exemplary embodiment, the internal combustion engine100comprises an EGR vent166that is in fluid communication with the EGR duct140and that is configured for carrying at least a portion of the first flow of combustion products112from the EGR duct140to be discharged to atmosphere176. An EGR vent flow control valve168may be disposed in the EGR vent166, and the EGR vent flow control valve168may be configured for allowing at least a portion of the first flow of combustion products112to be vented to the atmosphere176when the EGR vent flow control valve168is in an open mode and to prevent release of the first flow of combustion products112to the atmosphere176when the EGR vent flow control valve168is in a closed mode.

In an exemplary embodiment, the internal combustion engine100comprises an EGR return flow control valve170disposed in the EGR duct140. In accordance with this embodiment, the EGR return flow control valve170is configured for allowing at least a portion of the first flow of combustion products112to be delivered directly to the intake plenum132when the EGR return flow control valve170is in an open mode and to prevent flow of the first flow of combustion products112directly to the intake plenum132when the EGR return flow control valve170is in a closed mode.

In an exemplary embodiment, the EGR duct140has a boost leg148and a direct return leg160, the direct return leg160being in fluid communication with the intake plenum132. The boost leg148is in fluid communication with an inlet152of a supercharger172, and is configured for carrying the first flow of combustion products112to be mixed with the supply of ambient air142, to create a boost-inlet stream150and to deliver the boost-inlet stream150to the inlet152of the supercharger172. The supercharger172is in fluid communication with the inlet152of the supercharger172and with the intake plenum132. The supercharger172is configured for compressing the combined flow of combustion air150and delivering the combined flow of combustion air150to the intake plenum132.

In an exemplary embodiment, an EGR boost flow control valve174is disposed in the direct return leg160. The EGR boost flow control valve174is configured and arranged for allowing at least a portion of the first flow of combustion products112to be delivered through the direct return leg160to the intake plenum132when the EGR boost flow control valve174is in an open mode and to prevent flow through the direct return leg160to or from the intake plenum132when the EGR boost flow control valve174is in a closed mode.

In one embodiment, the internal combustion engine100comprises an EGR vent166that is in fluid communication with the EGR duct140and that is configured for carrying at least a portion of the first flow of combustion products112from the EGR duct140to be discharged to atmosphere176. In addition, the internal combustion engine100comprises an EGR vent flow control valve168disposed in the EGR vent166. The EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be vented to the atmosphere176when the EGR vent flow control valve168is in an open mode and to prevent release of the first flow of combustion products112to the atmosphere176when the EGR vent flow control valve168is in a closed mode. In addition, in accordance with this embodiment, an EGR return flow control valve170is disposed in the EGR duct140, and the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be delivered directly to the intake plenum132when the EGR return flow control valve170is in an open mode and to prevent flow of the first flow of combustion products112directly to the intake plenum132when the EGR return flow control valve170is in a closed mode.

In yet another exemplary embodiment, an internal combustion engine100includes an EGR vent166that is in fluid communication with the EGR duct140and that is configured for carrying at least a portion of the first flow of combustion products112from the EGR duct140to be discharged to atmosphere176. An EGR vent flow control valve168is disposed in the EGR vent166, and the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be vented to the atmosphere176when the EGR vent flow control valve168is in an open mode and to prevent release of the first flow of combustion products112to the atmosphere176when the EGR vent flow control valve168is in a closed mode. In addition, the EGR duct140has a boost leg148and a direct return leg160, the direct return leg160being in fluid communication with the intake plenum132. The boost leg148is in fluid communication with an inlet152of a supercharger172and is configured for carrying the first flow of combustion products112to be mixed with the supply of ambient air142, to create a combined flow of combustion air150, and to deliver the combined flow of combustion air150to the inlet152of the supercharger172. The supercharger172is in fluid communication with the inlet152of the supercharger172and with the intake plenum132and is configured for compressing the combined flow of combustion air150and delivering the combined flow of combustion air150to the intake plenum132. Still further, an EGR boost flow control valve174is disposed in the direct return leg160, and the EGR boost flow control valve174is configured for allowing at least a portion of the first flow of combustion products112to be delivered through the direct return leg160to the intake plenum132when the EGR boost flow control valve174is in an open mode and to prevent flow through the direct return leg160to or from the intake plenum132when the EGR boost flow control valve174is in a closed mode.

In yet another exemplary embodiment, an internal combustion engine100includes an EGR return flow control valve170disposed in the EGR duct140, and the EGR return flow control valve170is configured for allowing at least a portion of the first flow of combustion products112to be delivered directly to the intake plenum132when the EGR return flow control valve170is in an open mode and to prevent flow of the first flow of combustion products112directly to the intake plenum132when the EGR return flow control valve170is in a closed mode. In addition, the EGR duct140has a boost leg148and a direct return leg160, with the direct return leg160being in fluid communication with the intake plenum132. The boost leg148is in fluid communication with an inlet152of a supercharger172and is configured for carrying the first flow of combustion products112to be mixed with the supply of ambient air142, to create a combined flow of combustion air150, and to deliver the combined flow of combustion air150to the inlet152of the supercharger172. The supercharger172is in fluid communication with the inlet152of the supercharger172and with the intake plenum132and is configured for compressing the combined flow of combustion air150and delivering the combined flow of combustion air150to the intake plenum132. An EGR boost flow control valve174is disposed in the direct return leg160, and is configured for allowing at least a portion of the first flow of combustion products112to be delivered through the direct return leg160to the intake plenum132when the EGR boost flow control valve174is in an open mode and to prevent flow through the direct return leg160to or from the intake plenum132when the EGR boost flow control valve174is in a closed mode.

In yet another exemplary embodiment, an internal combustion engine100includes an EGR vent166in fluid communication with the EGR duct140and configured for carrying at least a portion of the first flow of combustion products112from the EGR duct140to be discharged to atmosphere176. An EGR vent flow control valve168is disposed in the EGR vent166, and the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be vented to the atmosphere176when the EGR vent flow control valve168is in an open mode and to prevent release of the first flow of combustion products112to the atmosphere176when the EGR vent flow control valve168is in a closed mode. An EGR return flow control valve170is disposed in the EGR duct140and is configured for allowing at least a portion of the first flow of combustion products112to be delivered directly to the intake plenum132when the EGR return flow control valve170is in an open mode and to prevent flow of the first flow of combustion products112directly to the intake plenum132when the EGR return flow control valve170is in a closed mode.

The EGR duct140has a boost leg148and a direct return leg160, and the direct return leg160is in fluid communication with the intake plenum132. The boost leg148is in fluid communication with an inlet152of a supercharger172and is configured for carrying the first flow of combustion products112to be mixed with the supply of ambient air142, to create a combined flow of combustion air150, and to deliver the combined flow of combustion air150to the inlet152of the supercharger172. The supercharger172is in fluid communication with the inlet152of the supercharger172and with the intake plenum132and is configured for compressing the combined flow of combustion air150and delivering the combined flow of combustion air150to the intake plenum132. An EGR boost flow control valve174is disposed in the direct return leg160. The EGR boost flow control valve174is configured for allowing at least a portion of the first flow of combustion products112to be delivered through the direct return leg160to the intake plenum132when the EGR boost flow control valve174is in an open mode and to prevent flow through the direct return leg160to or from the intake plenum132when the EGR boost flow control valve174is in a closed mode.

A method for controlling an internal combustion engine100comprises providing a first engine bank102defining a first combustion chamber104with a first intake port106for providing a first flow of combustion air108to the first combustion chamber104and with a first exhaust port110for providing a first flow of combustion products112from the first combustion chamber104. A second engine bank114is also provided, defining a second combustion chamber116with a second intake port118for providing a second flow of combustion air120to the second combustion chamber116and with a second exhaust port122for providing a second flow of combustion products112from the second combustion chamber116. A first intake valve126is disposed in the first intake port106, and the first intake valve126is configured for metering the first flow of combustion air108by periodically opening and closing according to a first intake valve126lift and duration characteristic.

A second intake valve128is disposed in the second intake port118, and the second intake valve128is configured for metering the second flow of combustion air120by periodically opening and closing according to a second intake valve lift and duration characteristic. An intake manifold130is provided defining an intake plenum132. The intake manifold130also defines an air inlet134, a first intake runner136, a second intake runner138, and an EGR duct140, each being in fluid communication with the intake plenum132. The air inlet134is in fluid communication with a supply of ambient air142and configured for carrying the supply of ambient air142for delivery to the intake plenum132, and the first intake runner136is in fluid communication with the first intake port106and configured for carrying the first flow of combustion air108from the intake plenum132to the first intake port106. The second intake runner138is in fluid communication with the second intake port118and is configured for carrying the second flow of combustion air120from the intake plenum132to the second intake port118. The EGR duct140is in fluid communication with the first exhaust port110and is configured for carrying the first flow of combustion products112from the first exhaust port110to the intake plenum132.

In accordance with this exemplary method, a variable valve train control mechanism164is provided, the mechanism being configured for affecting the first intake valve126lift and duration characteristic. Finally, either a lift or a duration of the first intake valve126is modulated so as to satisfy an EGR control criterion. It should be appreciated that a duration of the first intake valve126may be modulated or a lift of the first intake valve126may be modulated or both a lift and a duration of the first intake valve126may be modulated.

In an exemplary embodiment, an EGR vent166may be provided so as to be in fluid communication with the EGR duct140. The EGR vent166is configured for carrying at least a portion of the first flow of combustion products112from the EGR duct140to be discharged to atmosphere176. An EGR vent flow control valve168may also be disposed in the EGR vent166such that the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be vented to the atmosphere176when the EGR vent flow control valve168is in an open mode and to prevent release of the first flow of combustion products112to the atmosphere176when the EGR vent flow control valve168is in a closed mode. An EGR return flow control valve170may also be disposed in the EGR duct140such that the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be delivered directly to the intake plenum132when the EGR return flow control valve170is in an open mode and to prevent flow of the first flow of combustion products112directly to the intake plenum132when the EGR return flow control valve170is in a closed mode. In an exemplary embodiment, the EGR duct140is provided with a boost leg148and a direct return leg160, the direct return leg160being in fluid communication with the intake plenum132such that the boost leg148is in fluid communication with an inlet152of a supercharger172. The boost leg148is configured for carrying the first flow of combustion products112to be mixed with the supply of ambient air142, to create a combined flow of combustion air150, and to deliver the combined flow of combustion air150to the inlet152of the supercharger172. The supercharger172is provided so at to be in fluid communication with the inlet152of the supercharger172and with the intake plenum132and to be configured for compressing the combined flow of combustion air150and delivering the combined flow of combustion air150to the intake plenum132.

In accordance with this exemplary method, an EGR boost flow control valve174is provided so as to be disposed in the direct return leg160. The EGR boost flow control valve174is configured for allowing at least a portion of the first flow of combustion products112to be delivered through the direct return leg160to the intake plenum132when the EGR boost flow control valve174is in an open mode and to prevent flow through the direct return leg160to or from the intake plenum132when the EGR boost flow control valve174is in a closed mode. To facilitate operating the internal combustion engine100in a normally aspirated mode, producing power in both the first engine bank102and the second engine bank114, the method includes closing the EGR return flow control valve170. In a further embodiment, the EGR vent flow control valve168may be closed so as to operate the internal combustion engine100with the first engine bank102deactivated. Further still, the EGR boost flow control valve174may be closed so as to operate the internal combustion engine100in a boosted mode while the first engine bank102is operated at a relatively light load in accordance with the first intake valve126lift and duration characteristic while the second engine bank114is operated at a relatively heavy load.

In an exemplary embodiment, an internal combustion engine100may be provided with an EGR vent166in fluid communication with the EGR duct140and configured for carrying at least a portion of the first flow of combustion products112from the EGR duct140to be discharged to atmosphere176. An EGR vent flow control valve168, may then be disposed in the EGR vent166such that the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be vented to the atmosphere176when the EGR vent flow control valve168is in an open mode and to prevent release of the first flow of combustion products112to the atmosphere176when the EGR vent flow control valve168is in a closed mode. An EGR return flow control valve170may be disposed in the EGR duct140such that the EGR vent flow control valve168is configured for allowing at least a portion of the first flow of combustion products112to be delivered directly to the intake plenum132when the EGR return flow control valve170is in an open mode and to prevent flow of the first flow of combustion products112directly to the intake plenum132when the EGR return flow control valve170is in a closed mode.

In further accordance with this method, the EGR duct140is provided with a boost leg148and a direct return leg160, the direct return leg160being in fluid communication with the intake plenum132, and the boost leg148being in fluid communication with an inlet152of a supercharger172such that the boost leg148is configured for carrying the first flow of combustion products112to be mixed with the supply of ambient air142, to create a combined flow of combustion air150, and to deliver the combined flow of combustion air150to the inlet152of the supercharger172. The supercharger172is provided to be in fluid communication with the inlet152of the supercharger172and with the intake plenum132and is configured for compressing the combined flow of combustion air150and delivering the combined flow of combustion air150to the intake plenum132. An EGR boost flow control valve174is disposed in the direct return leg160and configured for allowing at least a portion of the first flow of combustion products112to be delivered through the direct return leg160to the intake plenum132when the EGR boost flow control valve174is in an open mode and to prevent flow through the direct return leg160to or from the intake plenum132when the EGR boost flow control valve174is in a closed mode.

In accordance with this exemplary method, the EGR vent flow control valve168is closed so as to operate the internal combustion engine100in a normally aspirated dedicated EGR mode. In a further exemplary embodiment, the EGR boost flow control valve174is closed so as to operate the internal combustion engine100in a boosted mode while the first engine bank102is operated at a relatively light load in accordance with the first intake valve126lift and duration characteristic, producing a dedicated supply of EGR, while the second engine bank114is operated at a relatively heavy load.

Accordingly, the engine may be operated in a number of modes such as: (a) a dual bank operating mode in which the EGR boost flow control valve174and the EGR vent flow control valve168are open and the EGR return flow control valve170is closed. In this mode, the engine operates as a normally aspirated dual bank engine such as a V6 engine having three operating cylinders in each bank; (b) a single bank mode in which the EGR boost flow control valve174is open and both the EGR return flow control valve170and the EGR vent flow control valve168are closed. In this mode, the engine operates with one bank of the engine deactivated such as wherein a V6 engine is operated on only three cylinders; (c) a CVVL mode with natural aspiration and without a dedicated supply of EGR in which the EGR return flow control valve170is closed and both the EGR boost flow control valve174and the EGR vent flow control valve168are closed. In this mode, the engine may be operated with one bank of cylinders at a heavy load and with the CVVL modulated cylinders operated at a light load; (d) a CVVL mode with natural aspiration and with a dedicated supply of EGR in which the EGR vent flow control valve168is closed and both the EGR boost flow control valve174and the EGR return flow control valve170are open. In this mode, the engine operates with one bank at a heavy load and with the CVVL bank at a lighter load providing EGR to the intake manifold130as a dedicated supply of EGR; (e) a CVVL boosted mode with a non-dedicated supply of EGR in which the EGR boost flow control valve174, the EGR return flow control valve170, and the EGR vent flow control valve168are all closed. In this mode, the engine operates in a boosted mode with one bank of cylinders at a heavier load and the other bank of cylinders at a lighter load controlled by the CVVL mechanism; and (f) a CVVL boosted mode with a dedicated supply of EGR in which the EGR boost flow control valve174is closed and both the EGR return flow control valve170and the EGR vent flow control valve168are open. In this mode, the engine operates in boosted mode with one bank of cylinders at a heavy load and with the other cylinders at a lighter load controlled by the CVVL mechanism and providing EGR to the intake manifold130in a dedicated EGR mode.

As a result, an engine is provided wherein one bank of cylinders may be operated at high loads while the other bank is operated as a supply of dedicated EGR to all of the cylinders. The cylinders providing dedicated EGR may be operated with full CVVL capability (lift and duration) to control the amount of effective displacement and EGR as called for depending on the load (i.e., power output) sought by the operator. The invention provides a simplified engine wherein a plurality of cylinders, half (or potentially less than half), have their valve train controlled by a continuously variable valve train control mechanism164to allow for variation in valve lift and valve event duration. Cylinders equipped with the CVVL capability are utilized to supply EGR via a path from the exhaust port of the CVVL equipped cylinders to the intake manifold130of the engine.

As a further result, the invention provides for: symmetric torque delivery at the flywheel for improved performance (unlike trying to run a V6 in 4 cylinder mode for example); cost reduction by requiring CVVL on only one cylinder bank as opposed to CVVL on both cylinder banks; and the ability to run a single bank of cylinders at optimal combustion efficiency throughout a broad range of operating conditions. The invention enables a dual-bank engine to operate with only a single bank, producing a wide range of available displacements for significant reductions in fuel consumption.

Continuous Variable Valve Lift (CVVL) systems employ mechanisms such as switching between slow and fast cams to achieve speed-dependent variations in valve lift. An ideal variable valve lift system may be capable of varying valve lift continuously such that at higher rpm, higher lift is provided by supplying the engine more air to breathe. At low rpm, lift may be reduced to increase air flow velocities, thereby improving air/fuel mixing to provide improved fuel economy and emissions. CVVL may be used to regulate engine output, reducing dependence on throttle butterfly and reducing attendant pressure losses.

The invention provides for a symmetric or near symmetric delivery of hydrogen rich EGR to all cylinders of the engine with the ability to reduce throttling losses at light loads for a reduction in fuel consumption.