Exhaust system having parallel asymmetric turbochargers and EGR

An exhaust system for a use with a combustion engine is provided. The exhaust system may have a first exhaust manifold configured to receive exhaust from the engine, and at least one turbocharger driven by exhaust from the first exhaust manifold. The exhaust system may also have a second exhaust manifold configured to receive exhaust from the engine in parallel with the first exhaust manifold, and at least two turbochargers driven by exhaust from the second exhaust manifold. The exhaust manifold may further have an exhaust gas recirculation circuit in fluid communication with only the first exhaust manifold. A number of turbochargers that receives exhaust from the first exhaust manifold may be less than a number of turbochargers that receives exhaust from the second exhaust manifold.

TECHNICAL FIELD

The present disclosure is directed to an exhaust system and, more particularly, to an exhaust system having parallel asymmetric turbochargers and exhaust gas recirculation (EGR).

BACKGROUND

Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output. In order to maximize the power output generated by this combustion process, the engine is often equipped with a divided exhaust manifold in fluid communication with a turbocharged air induction system.

The divided exhaust manifold increases engine power by helping to preserve exhaust pulse energy generated by the engine's combustion chambers. Preserving the exhaust pulse energy improves turbocharger operation, which results in a more efficient use of fuel. In addition, the turbocharged air induction system increases engine power by forcing more air into the combustion chambers than would otherwise be possible. This increased amount of air allows for enhanced fueling that further increases the power output generated by the engine.

In addition to the goal of maximizing engine power output and efficiency, it is desirable to simultaneously minimize exhaust emissions. That is, combustion engines exhaust a complex mixture of air pollutants as byproducts of the combustion process. And, due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.

One method that has been implemented by engine manufacturers to comply with the regulation of exhaust emissions includes utilizing an exhaust gas recirculating (EGR) system. EGR systems operate by recirculating a portion of the exhaust produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture has a lower combustion temperature and, subsequently, produces a reduced amount of regulated pollutants.

EGR systems require a certain level of backpressure from the exhaust system to push a desired amount of exhaust back to the intake of the engine. And, the backpressure needed for adequate operation of the EGR system varies with engine load. Although effective, utilizing exhaust backpressure to drive EGR can adversely affect turbocharger operation, thereby reducing the air compressing capability of the air induction system. The reduced air compressing capability may, in turn, reduce the engine's fuel economy and possibly the amount of power generated by the engine. Thus, a system is required that provides sufficient and variable exhaust backpressure to drive EGR flow without adversely affecting turbocharger or engine operation.

An example of a turbocharged engine have exhaust gas recirculation is disclosed in U.S. Pat. No. 6,694,736 (the '736 patent) issued to Pflüger on Feb. 24, 2004. In particular, the '736 patent discloses an engine with a common intake manifold and divided exhaust manifolds. Two high-pressure turbochargers having respective high-pressure compressors connected to and driven by high-pressure turbines are separately associated with the common intake manifold and the two exhaust manifolds, and a single low-pressure turbocharger receives exhaust from each of the two high-pressure turbochargers (i.e., the engine of the '736 patent includes three turbochargers arranged into two stages). In addition, exhaust return pipes are connected to the intake manifold downstream of the high-pressure compressors to direct exhaust from upstream of the high-pressure turbines back into the engine.

The disclosed exhaust system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the disclosure is directed toward an exhaust system for an engine. The exhaust system may include a first exhaust manifold configured to receive exhaust from the engine, and at least one turbocharger driven by exhaust from the first exhaust manifold. The exhaust system may also include a second exhaust manifold configured to receive exhaust from the engine in parallel with the first exhaust manifold, and at least two turbochargers driven by exhaust from the second exhaust manifold. The exhaust manifold may further include an exhaust gas recirculation circuit in fluid communication with only the first exhaust manifold. A number of turbochargers that receives exhaust from the first exhaust manifold may be less than a number of turbochargers that receives exhaust from the second exhaust manifold.

In another aspect, the disclosure is directed toward another exhaust system for an engine. This exhaust system may include a first exhaust manifold configured to receive exhaust from the engine, a second exhaust manifold configured to receive exhaust from the engine in parallel with the first exhaust manifold, and a balance valve configured to selectively allow exhaust from the first exhaust manifold to pass to the second exhaust manifold. The exhaust system may also include at least one turbocharger, each of the at least one turbocharger being driven by exhaust from only one of the first and second exhaust manifolds. The exhaust system may further include an exhaust gas recirculation circuit in fluid communication with only the first exhaust manifold. A number of turbochargers that receives exhaust from the first exhaust manifold may be less than a number of turbochargers that receives exhaust from the second exhaust manifold.

In yet another aspect, the disclosure is directed toward a method of handling exhaust from an engine. The method may include receiving exhaust from a first plurality of combustion chambers, and dividing the exhaust received from the first plurality of combustion chambers into a first flow of exhaust and a second flow of exhaust. The method may further include removing energy from the first flow of exhaust, and removing energy from the second flow of exhaust in parallel with a removal of energy from the first flow of exhaust. The method may also include receiving exhaust from a second plurality of combustion chambers, and removing energy from the exhaust received from the second plurality of combustion chambers in parallel with a removal of energy from the first and second flows of exhaust. The method may additionally include directing a portion of the exhaust received from only the second plurality of combustion chambers back into the engine.

DETAILED DESCRIPTION

FIG. 1illustrates a power system10having a power source12, an air induction system14, and an exhaust system16. For the purposes of this disclosure, power source12is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that power source12may be any other type of combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine. Power source12may include an engine block18that at least partially defines a plurality of cylinders20. A piston (not shown) may be slidably disposed within each cylinder20to reciprocate between a top-dead-center position and a bottom-dead-center position, and a cylinder head (not shown) may be associated with each cylinder20. Each cylinder20, piston, and cylinder head may together at least partially define a combustion chamber22. In the illustrated embodiment, power source12includes eight such combustion chambers22arranged in a V-configuration (i.e., a configuration having two banks or rows of combustion chambers22). However, it is contemplated that power source12may include a greater or lesser number of combustion chambers22and that combustion chambers22may be arranged in an in-line configuration, if desired.

Air induction system14may include components configured to introduce charged air into power source12. For example, air induction system14may include at least one compressor, and an air cooler28. Each included compressor may embody a fixed geometry compressor, a variable geometry compressor, or any other type of compressor configured to receive air and compress the air to a predetermined pressure level before it enters power source12. In one embodiment, air induction system14includes three substantially identical compressors (a first compressor25, a second compressor26, and a third compressor27) disposed in a parallel relationship and connected to power source12via a fluid passageway32(i.e., fluid passageway32may function as a common intake manifold). Air cooler28may embody an air-to-air heat exchanger, an air-to-liquid heat exchanger, or a combination of both, and be configured to facilitate the transfer of thermal energy to or from the compressed air directed into power source12. Air cooler28may be disposed within fluid passageway32, between power source12and compressors25-27.

Exhaust system16may include components configured to direct exhaust from power source12to the atmosphere. Specifically, exhaust system16may include a first exhaust manifold34and a second exhaust manifold36in separate communication with combustion chambers22, an exhaust gas recirculation (EGR) circuit38fluidly communicating first exhaust manifold34with air induction system14, and at least one turbine associated with first and second exhaust manifolds34,36. It is contemplated that exhaust system16may include components in addition to those listed above such as, for example, particulate traps, constituent absorbers or reducers, and attenuation devices, if desired.

Exhaust produced during the combustion process within combustion chambers22may exit power source12via either first exhaust manifold34or second exhaust manifold36. In the embodiment shown, first exhaust manifold34may fluidly connect a first plurality of combustion chambers22of power source12(e.g., the four combustion chambers22shown in the lower bank ofFIG. 1) to a first turbine40. Second exhaust manifold36may fluidly connect a second plurality of combustion chambers22of power source12(e.g., the four combustion chambers shown in the upper bank ofFIG. 1) to a second turbine41and to a third turbine42in parallel. In one example, each of first, second, and third turbines40-42may be substantially identical.

EGR circuit38may include components that cooperate to redirect a portion of the exhaust produced by power source12from first exhaust manifold34to air induction system14. Specifically, EGR circuit38may include an inlet port52, an EGR cooler54, a recirculation control valve56, and a discharge port58. Inlet port52may be fluidly connected to first exhaust manifold34upstream of first turbine40, and fluidly connected to EGR cooler54via a fluid passageway60. Discharge port58may receive exhaust from EGR cooler54via a fluid passageway62, and discharge exhaust to air induction system14at a location upstream or downstream of air cooler28. Recirculation control valve56may be disposed within fluid passageway62, between EGR cooler54and discharge port58. It is further contemplated that a check valve (not shown), for example a reed-type check valve may be situated within fluid passageway62upstream or downstream of recirculation control valve56at a location where exhaust mixes with inlet air to provide for a unidirectional flow of exhaust through EGR circuit38(i.e., to inhibit bidirectional exhaust flows through EGR circuit38), if desired.

Recirculation control valve56may be located to regulate a recirculated flow of exhaust through EGR circuit38. Recirculation control valve56may be any type of valve known in the art such as, for example, a butterfly valve, a diaphragm valve, a gate valve, a ball valve, a poppet valve, or a globe valve. In addition, recirculation control valve56may be solenoid-actuated, hydraulically-actuated, pneumatically-actuated or actuated in any other manner to selectively restrict or completely block the flow of exhaust through fluid passageways60and62.

EGR cooler54may be configured to cool exhaust flowing through EGR circuit38. EGR cooler54may include a liquid-to-air heat exchanger, an air-to-air heat exchanger, or any other type of heat exchanger known in the art for cooling an exhaust flow.

First turbine40may be a fixed geometry turbine having a single volute and being configured to receive exhaust from first exhaust manifold34to drive one or more of compressors25-27. For example, first turbine40may be directly and mechanically connected to first compressor25by way of a shaft64to form a first turbocharger66. As the hot exhaust gases exiting power source12move through first turbine40and expand against blades (not shown) therein, first turbine40may rotate and drive the connected first compressor25to pressurize air directed into power source12. It is contemplated that first turbine40may alternatively be a variable geometry turbine having an adjustable nozzle ring or adjustable vane members, if desired.

Second turbine41may also be connected to one of compressors25-27to form a fixed or variable geometry turbocharger92. For example, second turbine41may be directly and mechanically connected to second compressor26by way of a shaft65to form second turbocharger92. In the depicted arrangement, second turbine41may be a single volute turbine situated to receive exhaust from second exhaust manifold36. As the hot exhaust gases exiting power source12move through second turbine41and expand against blades (not shown) therein, second turbine41may rotate and drive the connected second compressor26to pressurize air directed into power source12.

Third turbine42may similarly be connected to one of compressors25-27to form a third fixed or variable geometry turbocharger94. For example, third turbine42may be directly and mechanically connected to third compressor27by way of a shaft68to form third turbocharger94. In the depicted arrangement, third turbine42may be a single volute turbine situated to receive exhaust from second exhaust manifold36in parallel with second turbine41. As the hot exhaust gases exiting power source12move through third turbine42and expand against blades (not shown) therein, third turbine42may rotate and drive third compressor27to pressurize air directed into power source12.

First turbocharger66may have a flow capacity different than a combined flow capacity of second and third turbochargers92,94(i.e., exhaust system16may be asymmetric both in a number of turbochargers associated with each of first and second exhaust manifolds34,36and in a total flow capacity of the associated turbochargers). Specifically, first turbocharger66may restrict exhaust flow to a degree greater (i.e., have a lower flow capacity) than a combined restriction of second and third turbochargers92,94. This substantially decreased flow capacity may function to increase a back pressure within first exhaust manifold34by an amount greater than a pressure within second exhaust manifold36. The increased back pressure of first exhaust manifold34may help force exhaust through EGR circuit38and back into power source12for subsequent combustion. In one example, the decreased flow capacity of first turbocharger66may be due to a decreased cross-sectional flow area or area/radius (A/R) ratio at a housing opening of first turbine40(as compared to a combined cross-sectional flow area or A/R ratio). In another example, the decreased flow capacity may be due to a smaller volute area or A/R ratio, turbine wheel diameter, trim profile, or nozzle vane orientation or setting. It is contemplated that other ways of providing the decreasing the flow capacity of first turbine40may also be possible.

A balance passageway86and an associated balance valve87may also be included within exhaust system16and utilized to fluidly communicate exhaust from first exhaust manifold34with second exhaust manifold36. Balance valve87may be disposed within balance passageway86and configured to regulate the pressure of exhaust flowing through first exhaust manifold34by selectively allowing exhaust to flow from first exhaust manifold34to second exhaust manifold36(i.e., by selectively adjusting a restriction placed on the flow through balance passageway86). It should be understood that the pressure within first exhaust manifold34may affect the amount of exhaust directed through EGR circuit38. That is, when a greater amount of exhaust flows from first exhaust manifold34to second exhaust manifold36by way of balance passageway86, a pressure within first exhaust manifold34may be reduced and, as a result of the pressure reduction, an amount of exhaust passing from first exhaust manifold34through EGR circuit38may be reduced proportionally.

Balance valve87may be any type of valve such as, for example, a butterfly valve, a diaphragm valve, a gate valve, a ball valve, a globe valve, a poppet valve, or any other valve known in the art. Furthermore, balance valve87may be solenoid-actuated, hydraulically-actuated, pneumatically-actuated or actuated in any other manner to selectively restrict or completely block the flow of exhaust between first and second exhaust manifolds34,36.

INDUSTRIAL APPLICABILITY

The disclosed exhaust system may be implemented into any power system application where charged air induction and exhaust gas recirculation are utilized. The disclosed exhaust system may be suitable for both high- and low-boost applications, be simple, and offer enhanced efficiency. Specifically, the asymmetric nature of exhaust system16may offer adequate boosting at both low and high engine speeds, without the need for extensive valving or flow path changing. Further, because exhaust system16may maintain a level of separation between first and second exhaust manifolds34,36, the exhaust pulse preservation provided by divided manifolds may also be maintained. Also, the disclosed exhaust system may allow for one bank of combustion chambers22to operate at a substantially lower back pressure than an intake of power system10, while still providing sufficient EGR flow from the remaining bank of combustion chambers22to meet low emissions requirements. By not having to increase the back pressure of all combustion chambers22, engine efficiency may be improved. In addition, the location of recirculation control valve56downstream of EGR cooler54may result in cool operating temperatures and extended component life.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed exhaust system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed exhaust system. For example, althoughFIG. 1shows three turbochargers being associated with power system10, any number of turbochargers may be included as long as a number of turbochargers associated with first exhaust manifold34is less than a number of turbochargers associated with second exhaust manifold36. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.