Engine assembly

Abstract

Engine assembly (10) comprising: an inlet assembly (14) comprising an exhaust gas recirculation (EGR) mixer (26) and a charge air cooler (28) having an inlet (88) and an outlet, the EGR mixer (26) being coupled to the inlet (88) of the charge air cooler (28); a spark-ignited internal combustion engine (12) defining a plurality of cylinders (20) and configured to combust a fuel; wherein each of the plurality of cylinders (20) is coupled to the outlet (82) of the charge air cooler (28); wherein the combustion of the fuel occurs in the plurality of cylinders (20) and produces an exhaust gas (40, 64); an exhaust assembly (16) in fluid communication with a first subset of the plurality of cylinders (20); a dedicated exhaust gas recirculation system (60) in fluid communication with a second subset of the plurality of cylinders (20) and with the EGR mixer (26), wherein the dedicated exhaust gas recirculation system (60) is configured to direct all of the exhaust gas (64) from the second subset of the plurality of cylinders (20) to the EGR mixer (26); and a backpressure valve (70) arranged between the outlet of the charge air cooler (28) and the plurality of cylinders (20), wherein the backpressure valve (70) is configured to maintain a minimum pressure difference between the inlet (88) of the charge air cooler (28) and an outlet (82) of the backpressure valve (70), wherein the charge air cooler (28) is arranged between the EGR mixer (26) and the back pressure valve (70), characterized in that the engine assembly (10) further comprises a throttle (30) arranged between the backpressure valve (70) and the spark-ignited internal combustion engine (12), the back pressure valve (70) comprises an actuator (84) in communication with the inlet (88) of the charge air cooler (28) and the actuator (84) closes the backpressure valve (70) to increase the pressure difference when the pressure difference between the inlet (88) of the charge air cooler (28) and the outlet (82) of the backpressure valve (70) is below a predetermined amount.

Description

TECHNICAL FIELD

[0001] The present invention generally relates to turbocharged internal combustion engines with dedicated exhaust gas recirculation. BACKGROUND

[0002] Internal combustion engines (ICE) can combust a mixture of air and fuel in one or more combustion chambers to produce mechanical output. During combustion, various exhaust gases are generated and expelled into the atmosphere. In some cases, a portion of the exhaust gas may be recirculated to the engine cylinders (using an exhaust gas recirculation system). In a gasoline engine, this inert exhaust gas can displace some of the combustible mixture in the cylinder, resulting in improved engine efficiency. In a diesel engine, the exhaust gas can replace some of the excess oxygen in the pre-combustion mixture. In both cases, the recirculated exhaust gas can lower the combustion temperature in the cylinder and / or reduce the production of certain gaseous byproducts.

[0003] Internal combustion engines are often required to reliably produce significant levels of power for extended periods of time. Many such ICE assemblies utilize a turbocompressor device, such as an exhaust-turbine-driven turbocharger, to compress the airflow before it enters the engine's intake manifold to improve performance and efficiency.

[0004] Specifically, a turbocharger is a centrifugal gas compressor that forces more air, and therefore more oxygen, into the combustion chambers of the ICE than would otherwise be achievable at ambient atmospheric pressure. The additional mass of oxygen-containing air forced into the ICE improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle and thus produce more power.

[0005] A typical turbocharger features a central shaft supported by one or more bearings that transmits rotational motion between an exhaust-driven turbine wheel and an air compressor wheel. Both the turbine and compressor wheels are attached to the shaft, which, in combination with various bearing components, constitutes the rotating assembly of the turbocharger.

[0006] From US 2012 / 0 204 844 A1 an engine assembly with the features according to the preamble of claim 1 is known.

[0007] DE 10 2009 022 938 A1 describes an engine assembly with a turbocharger and an exhaust gas recirculation system, in which actuators are provided on a throttle valve and / or on an exhaust gas flap in order to increase a pressure difference across the exhaust gas recirculation system.

[0008] DE 199 51 096 A1 also describes an engine assembly with a turbocharger and exhaust gas recirculation, in which throttle valves are provided between the exhaust gas recirculation and an internal combustion engine.

[0009] An object of the invention is to provide an engine assembly with exhaust gas recirculation in which the occurrence of knocking is prevented and uniform combustion is achieved. SUMMARY

[0010] This object is achieved by an engine assembly having the features of claim 1.

[0011] The engine assembly includes an intake assembly, a spark-ignited internal combustion engine, and an exhaust assembly. The intake assembly includes a charge air cooler disposed between an exhaust gas recirculation (EGR) mixer and a backpressure valve. The charge air cooler has both an inlet and an outlet, and the backpressure valve is configured to maintain a minimum pressure differential between the charge air cooler inlet and an outlet of the backpressure valve.

[0012] A dedicated exhaust gas recirculation system is provided in fluid communication with at least one cylinder and with the EGR mixer. The dedicated exhaust gas recirculation system is configured to route all exhaust gas from the at least one cylinder to the EGR mixer for recirculation back to the engine.

[0013] The intake assembly can supply air to each of the plurality of cylinders at a desired flow rate. The supplied air can include both atmospheric air and the recirculated exhaust gas from the dedicated exhaust gas recirculation system. The exhaust gas can have a pressure pulse, which can be due to the sequential firing nature of the internal combustion engine. The charge air cooler can be configured to dampen the exhaust pulse when the flow rate is above a predetermined rate, while the backpressure valve can be configured to dampen the pulse when the flow rate is below the predetermined rate.

[0014] The engine assembly may further include a turbocharger having a compressor in fluid communication with the intake assembly and a turbine in fluid communication with the exhaust assembly. The compressor and turbine may be operatively connected by a shaft such that the turbine can drive the compressor to compress the atmospheric air before it is mixed with the recirculated exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of an internal combustion engine assembly with dedicated exhaust gas recirculation. Fig. Figure 2 is a schematic diagram of an air intake system including an exhaust gas recirculation mixer, an intercooler, and a backpressure valve. DETAILED DESCRIPTION

[0015] Referring to the drawings, in which like reference numerals are used to identify like or identical components in the several views, Fig. 1 schematically illustrates an engine assembly 10 including an internal combustion engine 12, an air intake system 14, and an exhaust system 16. The air intake system 14 and the exhaust system 16 may each be in fluid communication with the engine 12, and they may be mechanically connected to each other via a turbocharger 18.

[0016] The internal combustion engine 12 (i.e., the motor 12) may be a spark-ignited internal combustion engine or a combustion-ignited diesel engine, and it may define a plurality of cylinders 20 (referred to as cylinders 1-4). Each of the respective cylinders 20 may include one or more fuel injectors 22 that can selectively introduce liquid fuel (as an aerosol) into each cylinder for combustion. Each of the cylinders 20 may be in selective fluid communication with the air intake system 14 to receive fresh / oxygen-rich air, and various ones of the cylinders 20 may be in selective fluid communication with the exhaust system 16 to expel the byproducts of combustion. Although the illustrated engine 12 shows a 4-cylinder engine, the present technology is equally applicable to inline three- and six-cylinder engines, as well as engines with V8, V10, and V12 configurations, among others.

[0017] The air intake system 14 may generally include a fresh air inlet 24, an exhaust gas recirculation (EGR) mixer 26, a charge air cooler 28, a throttle 30, and an intake manifold 32. As can be appreciated, during operation of the engine 12, fresh air 34 may be drawn through the air intake system 14 from the atmosphere (or from an associated air cleaner assembly) via the fresh air inlet 24. The throttle 30 may include a controllable baffle configured to selectively regulate the overall airflow through the intake system 14 and ultimately into the cylinders 20 (via the intake manifold 32).

[0018] In a typical 4-cylinder engine, combustion in the various engine cylinders 20 may occur in a sequential manner. For example, the firing order may be sequential: cylinder 1; cylinder 3; cylinder 4; cylinder 2. As can be appreciated, the engine 12 may subsequently expel gas from the cylinders in the same sequential order; and therefore, the exhaust flow may be more like a series of pulses than a continuous flow.

[0019] It has been found that engine efficiency is maximized when exhaust pulses are separated from each other. In addition to reducing interference between the pulses, the separation can reduce the occurrence of knock and / or irregular combustion. To achieve sufficient pulse separation, the exhaust flow can be divided into different flows that can be separately routed to the turbocharger 18 via multiple exhaust manifolds. Therefore, in one configuration, the exhaust system 16 can include a first exhaust manifold 36 and a second exhaust manifold 38 that can direct flowing exhaust gases 40 away from the engine 12. The exhaust gases 40 can finally pass through an aftertreatment device 42 to catalyze and / or remove certain byproducts before exiting the exhaust system 16 via an exhaust 44.

[0020] As mentioned above, the air intake system 14 and the exhaust system 16 may be in mechanical communication via a turbocharger 18. The turbocharger 18 may include a turbine 50 in fluid communication with the exhaust system 16 and a compressor 52 in fluid communication with the intake system 14. The turbine 50 and the compressor 52 may be mechanically coupled via a rotatable shaft 54. The turbocharger 18 may use the energy of the exhaust gases 40 flowing from the engine 12 to rotate the turbine 50 and the compressor 52. The rotation of the compressor 52 may then draw fresh air 34 from the intake 24 and compress it into the rest of the intake system 14.

[0021] The engine assembly 10 may further include a dedicated EGR system 60 that may direct the exhaust gas 64 from one or more cylinders of the engine 12 directly (e.g., via an EGR manifold 62) back into the intake system 14.

[0022] This recirculated exhaust gas 64 may be mixed with the fresh air 34 in the EGR mixer 26, and may accordingly dilute the oxygen content of the mixture. The use of EGR is known to increase efficiency in spark-ignition engines. EGR is also known to reduce combustion temperature and NOx production by the engine 12. The use of a separate EGR manifold 62 to redirect all of the exhaust gas from one or more cylinders back to the intake assembly 14 is referred to herein as "dedicated EGR."

[0023] With further reference to Fig. 1, one of the cylinders 20 (i.e., cylinder 4) is a dedicated EGR cylinder capable of returning 100% of its exhaust gas 64 back to the intake assembly 14. The exhaust gas 40 from the remaining three cylinders 20 (i.e., cylinders 1-3) is exhausted from the engine 12 via the exhaust assembly 16.

[0024] In a similar manner to cylinders 1-3, the dedicated EGR cylinder 4 may similarly expel combustion gases in a pulsed manner. Although an engine operating with dedicated EGR may exhibit an increase in fuel efficiency, the full benefit may not be available if the recirculated exhaust gas 64 is not properly mixed with the intake air 34. For example, if 80% of the available exhaust gas were drawn exclusively into cylinder 3 (e.g., due to intake timing and exhaust pulsing), then the benefits of EGR for cylinders 1, 2, and 4 would be greatly reduced. Similarly, the power output of cylinder 3 would be noticeably reduced due to the comparatively small amount of combustible air / combustible exhaust gas in that cylinder.

[0025] As is generally the case in Fig.2, the charge air cooler 28 may therefore be disposed between the EGR mixer 26 and a backpressure valve 70 to suppress / damp the pulsation of the recirculated exhaust gas 64 across all flow rates. Generally, the charge air cooler 28 may be a radiator-style heat exchanger that may utilize a flow of atmospheric air 72 or a liquid coolant to cool the fresh air / exhaust gas mixture 74. As can be appreciated, the gas mixture 74 may be warmer than atmospheric temperature due to the pressurization by the compressor 52 along with mixing with the high-temperature exhaust gases 64. The charge air cooler 28 may cool the gas mixture 74 to increase its density / volumetric efficiency while equally reducing the likelihood of erratic combustion.

[0026] The charge air cooler 28 may include a plurality of closed cooling passages 76 fluidly coupling an inlet volume 78 to an outlet volume 80. The cooling passages 76 may be formed from a thermally conductive material, such as aluminum, and may further include a plurality of heat transfer features, such as fins or wires, that may promote heat transfer between the externally flowing atmospheric air or the externally flowing liquid coolant 72 and the internally contained gas mixture 74.

[0027] During high-flow rate scenarios where a significant amount of the gas mixture 74 is drawn into the engine 12, the intake volume 78 and cooling passages 76 of the charge air cooler 28 may act as a gas damper to reduce the pulsation of the recirculated exhaust gas 64. This damping may occur due to acoustic and / or flow impedance effects.

[0028] With specific reference to the charge air cooler 28, due to the reduced cross-sectional area of ​​the cooling passages 76 (compared to the inlet volume 78), a flow impedance is established and acoustic tuning effects are generated. These flow impedances and acoustic tuning effects can serve to dampen the exhaust pulses created upstream of the charge air cooler 28 to create a more uniform flow downstream (i.e., on the engine side). Unfortunately, if the upstream flow rate is below the rate at which the flow impedance and acoustic tuning are effective, the charge air cooler 28 may lose the ability to dampen the exhaust pulses.

[0029] To dampen exhaust pulses at low flow, the air intake system 14 may include a backpressure valve 70 disposed between the charge air cooler 28 and the engine 12. The backpressure valve 70 may serve to ensure a minimum pressure differential between a reference pressure and a pressure at the outlet 82 of the valve 70.

[0030] The backpressure valve 70 may include or be in communication with an actuator 84 configured to regulate the valve 70 as a function of a monitored pressure differential. According to one configuration, the actuator 84 may be in communication with an inlet 88 of the charge air cooler 28 (e.g., via a signal line 86), which may serve as a reference pressure. When the pressure differential between the inlet 88 of the charge air cooler 28 and the outlet 82 of the valve 70 is below a predetermined amount, the actuator 84 may close the valve 70 to increase the pressure differential. Once the pressure differential exceeds the minimum allowable pressure differential, the actuator 84 may adjust the valve 70 while allowing the cooled gas mixture 90 to flow into the cylinders 20. According to one configuration, the minimum allowable pressure differential may be in the range of 2 kPa - 10 kPa.

[0031] During operation at high flow rates, the flow may result in a pressure buildup near the inlet 78 of the charge air cooler 28. Thus, the pressure differential between the inlet 78 of the charge air cooler 28 and the outlet 82 of the valve 70 may exceed the minimum allowable pressure differential, and the valve 70 may be fully open (i.e., presenting no or minimal flow restriction). If the flow rate should drop to a point where 100% of the flow is freely passing through the cooling passages 76, the pressure at the inlet 78 of the charge air cooler 28 may drop to a level where no damping occurs. In response to this pressure drop at the inlet volume 78, the backpressure valve 70 may be closed until the desired pressure at the inlet equals the regained differential (i.e., between the inlet 78 of the charge air cooler 28 and the throttle 30 / cylinders 20).

Claims

[1] Engine assembly (10) comprising: an inlet assembly (14) comprising an exhaust gas recirculation (EGR) mixer (26) and a charge air cooler (28) having an inlet (88) and an outlet, the EGR mixer (26) being coupled to the inlet (88) of the charge air cooler (28); a spark-ignited internal combustion engine (12) defining a plurality of cylinders (20) and configured to combust a fuel; wherein each of the plurality of cylinders (20) is coupled to the outlet (82) of the charge air cooler (28); wherein the combustion of the fuel occurs in the plurality of cylinders (20) and produces an exhaust gas (40, 64); an exhaust assembly (16) in fluid communication with a first subset of the plurality of cylinders (20); a dedicated exhaust gas recirculation system (60) in fluid communication with a second subset of the plurality of cylinders (20) and with the EGR mixer (26), wherein the dedicated exhaust gas recirculation system (60) is configured to direct all of the exhaust gas (64) from the second subset of the plurality of cylinders (20) to the EGR mixer (26); and a backpressure valve (70) arranged between the outlet of the charge air cooler (28) and the plurality of cylinders (20), wherein the backpressure valve (70) is configured to maintain a minimum pressure difference between the inlet (88) of the charge air cooler (28) and an outlet (82) of the backpressure valve (70), wherein the charge air cooler (28) is arranged between the EGR mixer (26) and the backpressure valve (70), characterized by , that the engine assembly (10) further comprises a throttle (30) arranged between the backpressure valve (70) and the spark-ignited internal combustion engine (12), the back pressure valve (70) comprises an actuator (84) in communication with the inlet (88) of the charge air cooler (28) and the actuator (84) closes the backpressure valve (70) to increase the pressure difference when the pressure difference between the inlet (88) of the charge air cooler (28) and the outlet (82) of the backpressure valve (70) is below a predetermined amount. [2] The engine assembly (10) of claim 1, further comprising a turbocharger (18) comprising: a compressor (52) in fluid communication with the inlet assembly (14); a turbine (50) in fluid communication with the exhaust assembly (16); and wherein the compressor (52) and the turbine (50) are functionally connected via a shaft (54). [3] Engine assembly (10) according to claim 1, wherein the intake assembly (14) supplies air to each of the plurality of cylinders (20) at a flow rate; wherein the supplied air comprises both atmospheric air (34) and the exhaust gas (64) from the second subset of the plurality of cylinders (20). [4] Engine assembly (10) according to claim 3, wherein the exhaust gas (64) from the second subset of the plurality of cylinders (20) has a pressure pulse; wherein the charge air cooler (28) is configured to dampen the pressure pulse when the flow rate is above a predetermined rate; and wherein the backpressure valve (70) is configured to dampen the pressure pulse in communication with the charge air cooler (28) when the flow rate is below the predetermined rate.

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