Air and fuel supply system for combustion engine

A method of operating an internal combustion engine, including at least one cylinder and a piston slidable in the cylinder, may include supplying a mixture of pressurized air and recirculated exhaust gas from an intake manifold to an air intake port of a combustion chamber in the cylinder, selectively operating an air intake valve to open the air intake port to allow pressurized air to flow between the combustion chamber and the intake manifold substantially during a majority portion of a compression stroke of the piston, and operably controlling a fuel supply system to inject fuel into the combustion chamber after the intake valve is closed.

TECHNICAL FIELD

The present invention relates to a combustion engine and, more particularly, to an air and fuel supply system for use with an internal combustion engine.

BACKGROUND

An internal combustion engine may include one or more turbochargers for compressing a fluid, which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor driven by the turbine. The compressor receives the fluid to be compressed and supplies the compressed fluid to the combustion chambers. The fluid compressed by the compressor may be in the form of combustion air or an air/fuel mixture.

An internal combustion engine may also include a supercharger arranged in series with a turbocharger compressor of an engine. U.S. Pat. No. 6,273,076 (Beck et al., issued Aug. 14, 2001) discloses a supercharger having a turbine that drives a compressor to increase the pressure of air flowing to a turbocharger compressor of an engine. In some situations, the air charge temperature may be reduced below ambient air temperature by an early closing of the intake valve.

Early or late closing of the intake valve, referred to as the “Miller Cycle,” may reduce the effective compression ratio of the cylinder, which in turn reduces compression temperature, while maintaining a high expansion ratio.

Consequently, a Miller cycle engine may have improved thermal efficiency and reduced exhaust emissions of, for example, oxides of Nitrogen (NOx). Reduced NOxemissions are desirable. In a conventional Miller cycle engine, the timing of the intake valve close is typically shifted slightly forward or backward from that of the typical Otto cycle engine. For example, in the Miller cycle engine, the intake valve may remain open until the beginning of the compression stroke.

While a turbocharger may utilize some energy from the engine exhaust, the series supercharger/turbocharger arrangement does not utilize energy from the turbocharger exhaust. Furthermore, the supercharger requires an additional energy source.

SUMMARY OF THE INVENTION

According to one exemplary aspect of the invention, a method of operating an internal combustion engine, including at least one cylinder and a piston slidable in the cylinder, is provided. The method may include supplying a mixture of pressurized air and recirculated exhaust gas from an intake manifold to an air intake port of a combustion chamber in the cylinder, selectively operating an air intake valve to open the air intake port to allow pressurized air to flow between the combustion chamber and the intake manifold substantially during a majority portion of a compression stroke of the piston, and operably controlling a fuel supply system to inject fuel into the combustion chamber after the intake valve is closed.

According to another exemplary aspect of the invention, a variable compression ratio internal combustion engine may include an engine block defining at least one cylinder, a head connected with the engine block, wherein the head includes an air intake port and an exhaust port, and a piston slidable in each cylinder. A combustion chamber may be defined by the head, the piston, and the cylinder. The engine may include an air intake valve controllably movable to open and close the air intake port, an air supply system including at least one turbocharger fluidly connected to the air intake port, an exhaust gas recirculation system operable to provide a portion of exhaust gas from the exhaust port to the air supply system, and a fuel supply system operable to controllably inject fuel into the combustion chamber at a selected timing. A variable intake valve closing mechanism may be configured to keep the intake valve open by selective actuation of the variable intake valve closing mechanism.

According to still another exemplary aspect of the invention, a method of controlling an internal combustion engine having a variable compression ratio is provided. The engine may have a block defining a cylinder, a piston slidable in the cylinder, a head connected with the block, and the piston, the cylinder, and the head defining a combustion chamber. The method may include pressurizing a mixture of air and exhaust gas, supplying the air to an intake manifold, maintaining fluid communication between the combustion chamber and the intake manifold during a portion of an intake stroke and through a portion of a compression stroke, and supplying a pressurized fuel directly to the combustion chamber during a portion of an combustion stroke.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Referring toFIG. 1, an exemplary air supply system100for an internal combustion engine110, for example, a four-stroke, diesel engine, is provided. The internal combustion engine110includes an engine block111defining a plurality of combustion cylinders112, the number of which depends upon the particular application. For example, a 4-cylinder engine would include four combustion cylinders, a 6-cylinder engine would include six combustion cylinders, etc. In the exemplary embodiment ofFIG. 1, six combustion cylinders112are shown. It should be appreciated that the engine110may be any other type of internal combustion engine, for example, a gasoline or natural gas engine.

The internal combustion engine110also includes an intake manifold114and an exhaust manifold116. The intake manifold114provides fluid, for example, air or a fuel/air mixture, to the combustion cylinders112. The exhaust manifold116receives exhaust fluid, for example, exhaust gas, from the combustion cylinders112. The intake manifold114and the exhaust manifold116are shown as a single-part construction for simplicity in the drawing. However, it should be appreciated that the intake manifold114and/or the exhaust manifold116may be constructed as multi-part manifolds, depending upon the particular application.

The air supply system100includes a first turbocharger120and may include a second turbocharger140. The first and second turbochargers120,140may be arranged in series with one another such that the second turbocharger140provides a first stage of pressurization and the first turbocharger120provides a second stage of pressurization. For example, the second turbocharger140may be a low pressure turbocharger and the first turbocharger120may be a high pressure turbocharger. The first turbocharger120includes a turbine122and a compressor124. The turbine122is fluidly connected to the exhaust manifold116via an exhaust duct126. The turbine122includes a turbine wheel128carried by a shaft130, which in turn may be rotatably carried by a housing132, for example, a single-part or multi-part housing. The fluid flow path from the exhaust manifold116to the turbine122may include a variable nozzle (not shown) or other variable geometry arrangement adapted to control the velocity of exhaust fluid impinging on the turbine wheel128.

The compressor124includes a compressor wheel134carried by the shaft130. Thus, rotation of the shaft130by the turbine wheel128in turn may cause rotation of the compressor wheel134.

The first turbocharger120may include a compressed air duct138for receiving compressed air from the second turbocharger140and an air outlet line152for receiving compressed air from the compressor124and supplying the compressed air to the intake manifold114of the engine110. The first turbocharger120may also include an exhaust duct139for receiving exhaust fluid from the turbine122and supplying the exhaust fluid to the second turbocharger140.

The second turbocharger140may include a turbine142and a compressor144. The turbine142may be fluidly connected to the exhaust duct139. The turbine142may include a turbine wheel146carried by a shaft148, which in turn may be rotatably carried by the housing132. The compressor144may include a compressor wheel150carried by the shaft148. Thus, rotation of the shaft148by the turbine wheel146may in turn cause rotation of the compressor wheel150.

The second turbocharger140may include an air intake line136providing fluid communication between the atmosphere and the compressor144. The second turbocharger140may also supply compressed air to the first turbocharger120via the compressed air duct138. The second turbocharger140may include an exhaust outlet154for receiving exhaust fluid from the turbine142and providing fluid communication with the atmosphere. In an embodiment, the first turbocharger120and second turbocharger140may be sized to provide substantially similar compression ratios. For example, the first turbocharger120and second turbocharger140may both provide compression ratios of between 2 to 1 and 3 to 1, resulting in a system compression ratio of at least 4:1 with respect to atmospheric pressure. Alternatively, the second turbocharger140may provide a compression ratio of 3 to 1 and the first turbocharger120may provide a compression ratio of 1.5 to 1, resulting in a system compression ratio of 4.5 to 1 with respect to atmospheric pressure.

The air supply system100may include an air cooler156, for example, an aftercooler, between the compressor124and the intake manifold114. The air cooler156may extract heat from the air to lower the intake manifold temperature and increase the air density. Optionally, the air supply system100may include an additional air cooler158, for example, an intercooler, between the compressor144of the second turbocharger140and the compressor124of the first turbocharger120. Intercooling may use techniques such as jacket water, air to air, and the like. Alternatively, the air supply system100may optionally include an additional air cooler (not shown) between the air cooler156and the intake manifold114. The optional additional air cooler may further reduce the intake manifold temperature. A jacket water pre-cooler (not shown) may be used to protect the air cooler156.

Referring now toFIG. 2, a cylinder head211may be connected with the engine block111. Each cylinder112in the cylinder head211may be provided with a fuel supply system202. The fuel supply system202may include a fuel port204opening to a combustion chamber206within the cylinder112. The fuel supply system202may inject fuel, for example, diesel fuel, directly into the combustion chamber206.

The cylinder112may contain a piston212slidably movable in the cylinder. A crankshaft213may be rotatably disposed within the engine block111. A connecting rod215may couple the piston212to the crankshaft213so that sliding motion of the piston212within the cylinder112results in rotation of the crankshaft213. Similarly, rotation of the crankshaft213results in a sliding motion of the piston212. For example, an uppermost position of the piston212in the cylinder112corresponds to a top dead center position of the crankshaft213, and a lowermost position of the piston212in the cylinder112corresponds to a bottom dead center position of the crankshaft213.

As one skilled in the art will recognize, the piston212in a conventional, four-stroke engine cycle reciprocates between the uppermost position and the lowermost position during a combustion (or expansion) stroke, an exhaust stroke, and intake stroke, and a compression stroke. Meanwhile, the crankshaft213rotates from the top dead center position to the bottom dead center position during the combustion stroke, from the bottom dead center to the top dead center during the exhaust stroke, from top dead center to bottom dead center during the intake stroke, and from bottom dead center to top dead center during the compression stroke. Then, the four-stroke cycle begins again. Each piston stroke correlates to about 180° of crankshaft rotation, or crank angle. Thus, the combustion stroke may begin at about 0° crank angle, the exhaust stroke at about 180°, the intake stroke at about 360°, and the compression stroke at about 540°.

The cylinder112may include at least one intake port208and at least one exhaust port210, each opening to the combustion chamber206. The intake port208may be opened and closed by an intake valve assembly214, and the exhaust port210may be opened and closed by an exhaust valve assembly216. The intake valve assembly214may include, for example, an intake valve218having a head220at a first end222, with the head220being sized and arranged to selectively close the intake port208. The second end224of the intake valve218may be connected to a rocker arm226or any other conventional valve-actuating mechanism. The intake valve218may be movable between a first position permitting flow from the intake manifold114to enter the combustion cylinder112and a second position substantially blocking flow from the intake manifold114to the combustion cylinder112. A spring228may be disposed about the intake valve218to bias the intake valve218to the second, closed position.

A camshaft232carrying a cam234with one or more lobes236may be arranged to operate the intake valve assembly214cyclically based on the configuration of the cam234, the lobes236, and the rotation of the camshaft232to achieve a desired intake valve timing. The exhaust valve assembly216may be configured in a manner similar to the intake valve assembly214and may be operated by one of the lobes236of the cam234. In an embodiment, the intake lobe236may be configured to operate the intake valve218in a conventional Otto or diesel cycle, whereby the intake valve218moves to the second position from between about 10° before bottom dead center of the intake stroke and about100after bottom dead center of the compression stroke. Alternatively, the intake valve assembly214and/or the exhaust valve assembly216may be operated hydraulically, pneumatically, electronically, or by any combination of mechanics, hydraulics, pneumatics, and/or electronics.

The intake valve assembly214may include a variable intake valve closing mechanism238structured and arranged to selectively interrupt cyclical movement of and extend the closing timing of the intake valve218. The variable intake valve closing mechanism238may be operated hydraulically, pneumatically, electronically, mechanically, or any combination thereof. For example, the variable intake valve closing mechanism238may be selectively operated to supply hydraulic fluid, for example, at a low pressure or a high pressure, in a manner to resist closing of the intake valve218by the bias of the spring228. That is, after the intake valve218is lifted, i.e., opened, by the cam234, and when the cam234is no longer holding the intake valve218open, the hydraulic fluid may hold the intake valve218open for a desired period. The desired period may change depending on the desired performance of the engine110. Thus, the variable intake valve closing mechanism238enables the engine110to operate under a conventional Otto or diesel cycle or under a variable late-closing Miller cycle.

As shown inFIG. 4, the intake valve218may begin to open at about 360° crank angle, that is, when the crankshaft213is at or near a top dead center position of an intake stroke406. The closing of the intake valve218may be selectively varied from about 540° crank angle, that is, when the crank shaft is at or near a bottom dead center position of a compression stroke407, to about 650° crank angle, that is, about 70° before top center of the combustion stroke508. Thus, the intake valve218may be held open for a majority portion of the compression stroke407, that is, for the first half of the compression stroke407and a portion of the second half of the compression stroke407.

The fuel supply system202may include a fuel injector assembly240, for example, a mechanically-actuated, electronically-controlled unit injector, in fluid communication with a common fuel rail242. Alternatively, the fuel injector assembly240may be any common rail type injector and may be actuated and/or operated hydraulically, mechanically, electrically, piezo-electrically, or any combination thereof. The common fuel rail242provides fuel to the fuel injector assembly240associated with each cylinder112. The fuel injector assembly240may inject or otherwise spray fuel into the cylinder112via the fuel port204in accordance with a desired timing.

A controller244may be electrically connected to the variable intake valve closing mechanism238and/or the fuel injector assembly240. The controller244may be configured to control operation of the variable intake valve closing mechanism238and/or the fuel injector assembly240based on one or more engine conditions, for example, engine speed, load, pressure, and/or temperature in order to achieve a desired engine performance. It should be appreciated that the functions of the controller244may be performed by a single controller or by a plurality of controllers. Similarly, spark timing in a natural gas engine may provide a similar function to fuel injector timing of a compression ignition engine.

Referring now toFIG. 3, each fuel injector assembly240may be associated with an injector rocker arm250pivotally coupled to a rocker shaft252. Each fuel injector assembly240may include an injector body254, a solenoid256, a plunger assembly258, and an injector tip assembly260. A first end262of the injector rocker arm250may be operatively coupled to the plunger assembly258. The plunger assembly258may be biased by a spring259toward the first end262of the injector rocker arm250in the general direction of arrow296.

A second end264of the injector rocker arm250may be operatively coupled to a camshaft266. More specifically, the camshaft266may include a cam lobe267having a first bump268and a second bump270. The camshafts232,266and their respective lobes236,267may be combined into a single camshaft (not shown) if desired. The bumps268,270may be moved into and out of contact with the second end264of the injector rocker arm250during rotation of the camshaft266. The bumps268,270may be structured and arranged such that the second bump270may provide a pilot injection of fuel at a predetermined crank angle before the first bump268provides a main injection of fuel. It should be appreciated that the cam lobe267may have only a first bump268that injects all of the fuel per cycle.

When one of the bumps268,270is rotated into contact with the injector rocker arm250, the second end264of the injector rocker arm250is urged in the general direction of arrow296. As the second end264is urged in the general direction of arrow296, the rocker arm-250pivots about the rocker shaft252thereby causing the first end262to be urged in the general direction of arrow298. The force exerted on the second end264by the bumps268,270is greater in magnitude than the bias generated by the spring259, thereby causing the plunger assembly258to be likewise urged in the general direction of arrow298. When the camshaft266is rotated beyond the maximum height of the bumps268,270, the bias of the spring259urges the plunger assembly258in the general direction of arrow296. As the plunger assembly258is urged in the general direction of arrow296, the first end262of the injector rocker arm250is likewise urged in the general direction of arrow296, which causes the injector rocker arm250to pivot about the rocker shaft252thereby causing the second end264to be urged in the general direction of arrow298.

The injector body254defines a fuel port272. Fuel, such as diesel fuel, may be drawn or otherwise aspirated into the fuel port272from the fuel rail242when the plunger assembly258is moved in the general direction of arrow296. The fuel port272is in fluid communication with a fuel valve274via a first fuel channel276. The fuel valve274is, in turn in fluid communication with a plunger chamber278via a second fuel channel280.

The solenoid256may be electrically coupled to the controller244and mechanically coupled to the fuel valve274. Actuation of the solenoid256by a signal from the controller244may cause the fuel valve274to be switched from an open position to a closed position. When the fuel valve274is positioned in its open position, fuel may advance from the fuel port272to the plunger chamber278, and vice versa. However, when the fuel valve274is positioned in its closed positioned, the fuel port272is isolated from the plunger chamber278.

The injector tip assembly260may include a check valve assembly282. Fuel may be advanced from the plunger chamber278, through an inlet orifice284, a third fuel channel286, an outlet orifice288, and into the cylinder112of the engine110.

Thus, it should be appreciated that when one of the bumps268,270is not in contact with the injector rocker arm16, the plunger assembly258is urged in the general direction of arrow296by the spring259thereby causing fuel to be drawn into the fuel port272which in turn fills the plunger chamber278with fuel. As the camshaft266is further rotated, one of the bumps268,270is moved into contact with the rocker arm250, thereby causing the plunger assembly258to be urged in the general direction of arrow298. If the controller244is not generating an injection signal, the fuel valve274remains in its open position, thereby causing the fuel which is in the plunger chamber278to be displaced by the plunger assembly258through the fuel port272. However, if the controller244is generating an injection signal, the fuel valve274is positioned in its closed position thereby isolating the plunger chamber278from the fuel port272. As the plunger assembly258continues to be urged in the general direction of arrow298by the camshaft266, fluid pressure within the fuel injector assembly240increases. At a predetermined pressure magnitude, for example, at about 5500 psi (38 MPa), fuel is injected into the cylinder112. Fuel will continue to be injected into the cylinder112until the controller244signals the solenoid256to return the fuel valve274to its open position.

As shown in the exemplary graph ofFIG. 5, the pilot injection of fuel may commence when the crankshaft213is at about 675° crank angle, that is, about 45° before top dead center of the compression stroke407. The main injection of fuel may occur when the crankshaft213is at about 710° crank angle, that is, about 10° before top dead center of the compression stroke407and about 45° after commencement of the pilot injection. Generally, the pilot injection may commence when the crankshaft213is about 40–50° before top dead center of the compression stroke407and may last for about 10–15° crankshaft rotation. The main injection may commence when the crankshaft213is between about 10° before top dead center of the compression stroke407and about 12° after top dead center of the combustion stroke508. The main injection may last for about 20–45° crankshaft rotation. The pilot injection may use a desired portion of the total fuel used, for example about 10%.

FIG. 6is a combination diagrammatic and schematic illustration of a second exemplary air supply system300for the internal combustion engine110. The air supply system300may include a turbocharger320, for example, a high-efficiency turbocharger capable of producing at least about a 4 to 1 compression ratio with respect to atmospheric pressure. The turbocharger320may include a turbine322and a compressor324. The turbine322may be fluidly connected to the exhaust manifold116via an exhaust duct326. The turbine322may include a turbine wheel328carried by a shaft330, which in turn may be rotatably carried by a housing332, for example, a single-part or multi-part housing. The fluid flow path from the exhaust manifold116to the turbine322may include a variable nozzle (not shown), which may control the velocity of exhaust fluid impinging on the turbine wheel328.

The compressor324may include a compressor wheel334carried by the shaft330. Thus, rotation of the shaft330by the turbine wheel328in turn may cause rotation of the compressor wheel334. The turbocharger320may include an air inlet336providing fluid communication between the atmosphere and the compressor324and an air outlet352for supplying compressed air to the intake manifold114of the engine110. The turbocharger320may also include an exhaust outlet354for receiving exhaust fluid from the turbine322and providing fluid communication with the atmosphere.

The air supply system300may include an air cooler356between the compressor324and the intake manifold114. Optionally, the air supply system300may include an additional air cooler (not shown) between the air cooler356and the intake manifold114.

FIG. 7is a combination diagrammatic and schematic illustration of a third exemplary air supply system400for the internal combustion engine110. The air supply system400may include a turbocharger420, for example, a turbocharger420having a turbine422and two compressors424,444. The turbine422may be fluidly connected to the exhaust manifold116via an inlet duct426. The turbine422may include a turbine wheel428carried by a shaft430, which in turn may be rotatably carried by a housing432, for example, a single-part or multi-part housing. The fluid flow path from the exhaust manifold116to the turbine422may include a variable nozzle (not shown), which may control the velocity of exhaust fluid impinging on the turbine wheel428.

The first compressor424may include a compressor wheel434carried by the shaft430, and the second compressor444may include a compressor wheel450carried by the shaft430. Thus, rotation of the shaft430by the turbine wheel428in turn may cause rotation of the first and second compressor wheels434,450. The first and second compressors424,444may provide first and second stages of pressurization, respectively.

The turbocharger420may include an air intake line436providing fluid communication between the atmosphere and the first compressor424and a compressed air duct438for receiving compressed air from the first compressor424and supplying the compressed air to the second compressor444. The turbocharger420may include an air outlet line452for supplying compressed air from the second compressor444to the intake manifold114of the engine110. The turbocharger420may also include an exhaust outlet454for receiving exhaust fluid from the turbine422and providing fluid communication with the atmosphere.

For example, the first compressor424and second compressor444may both provide compression ratios of between 2 to 1 and 3 to 1, resulting in a system compression ratio of at least 4:1 with respect to atmospheric pressure. Alternatively, the second compressor444may provide a compression ratio of 3 to 1 and the first compressor424may provide a compression ratio of 1.5 to 1, resulting in a system compression ratio of 4.5 to 1 with respect to atmospheric pressure.

The air supply system400may include an air cooler456between the compressor424and the intake manifold114. Optionally, the air supply system400may include an additional air cooler458between the first compressor424and the second compressor444of the turbocharger420. Alternatively, the air supply system400may optionally include an additional air cooler (not shown) between the air cooler456and the intake manifold114.

Referring toFIG. 8, an exemplary exhaust gas recirculation (EGR) system804in an exhaust system802in a combustion engine110is shown. Combustion engine110includes intake manifold114and exhaust manifold116. Engine block111provides housing for at least one cylinder112.FIG. 8depicts six cylinders112. However, any number of cylinders112could be used, for example, three, six, eight, ten, twelve, or any other number. The intake manifold114provides an intake path for each cylinder112for air, recirculated exhaust gases, or a combination thereof. The exhaust manifold116provides an exhaust path for each cylinder112for exhaust gases.

In the embodiment shown inFIG. 8, the air supply system100is shown as a two-stage turbocharger system. Air supply system100includes first turbocharger120having turbine122and compressor124. Air supply system100also includes second turbocharger140having turbine142and compressor144. The two-stage turbocharger system operates to increase the pressure of the air and exhaust gases being delivered to the cylinders112via intake manifold114, and to maintain a desired air to fuel ratio during extended open durations of intake valves. It is noted that a two-stage turbocharger system is not required for operation of the present invention. Other types of turbocharger systems, such as a high pressure ratio single-stage turbocharger system, a variable geometry turbocharger system, and the like, may be used instead.

A throttle valve814, located between compressor124and intake manifold114, may be used to control the amount of air and recirculated exhaust gases being delivered to the cylinders112. The throttle valve814is shown between compressor124and an aftercooler156. However, the throttle valve814may be positioned at other locations, such as after aftercooler156. Operation of the throttle valve814is described in more detail below.

The EGR system804shown inFIG. 8is typical of a low pressure EGR system in an internal combustion engine. Variations of the EGR system804may be equally used with the present invention, including both low pressure loop and high pressure loop EGR systems. Other types of EGR systems, such as for example by-pass, venturi, piston-pumped, peak clipping, and back pressure, could be used.

An oxidation catalyst808receives exhaust gases from turbine142, and serves to reduce HC emissions. The oxidation catalyst808may also be coupled with a De-NOxcatalyst to further reduce NOxemissions. A particulate matter (PM) filter806receives exhaust gases from oxidation catalyst808.

Although oxidation catalyst808and PM filter806are shown as separate items, they may alternatively be combined into one package.

Some of the exhaust gases are delivered out the exhaust from the PM filter806. However, a portion of exhaust gases are rerouted to the intake manifold114through an EGR cooler810, through an EGR valve812, and through first and second turbochargers120,140. EGR cooler810may be of a type well known in the art, for example a jacket water or an air to gas heat exchanger type.

A means816for determining pressure within the PM filter806is shown. In the preferred embodiment, the means816for determining pressure includes a pressure sensor818. However, other alternate means816may be employed. For example, the pressure of the exhaust gases in the PM filter806may be estimated from a model based on one or more parameters associated with the engine110. Parameters may include, but are not limited to, engine load, engine speed, temperature, fuel usage, and the like.

A means820for determining flow of exhaust gases through the PM filter806may be used. Preferably, the means820for determining flow of exhaust gases includes a flow sensor822. The flow sensor822may be used alone to determine pressure in the PM filter806based on changes in flow of exhaust gases, or may be used in conjunction with the pressure sensor818to provide more accurate pressure change determinations.

INDUSTRIAL APPLICATION

During use, the internal combustion engine110operates in a known manner using, for example, the diesel principle of operation. Referring to the exemplary air supply system shown inFIG. 1, exhaust gas from the internal combustion engine110is transported from the exhaust manifold116through the inlet duct126and impinges on and causes rotation of the turbine wheel128. The turbine wheel128is coupled with the shaft130, which in turn carries the compressor wheel134. The rotational speed of the compressor wheel134thus corresponds to the rotational speed of the shaft130.

The exemplary fuel supply system200and cylinder112shown inFIG. 2may be used with each of the exemplary air supply systems100,300,400. Compressed air is supplied to the combustion chamber206via the intake port208, and exhaust air exits the combustion chamber206via the exhaust port210. The intake valve assembly214and the exhaust valve assembly216may be controllably operated to direct airflow into and out of the combustion chamber206.

In a conventional Otto or diesel cycle mode, the intake valve218moves from the second position to the first position in a cyclical fashion to allow compressed air to enter the combustion chamber206of the cylinder112at near top center of the intake stroke406(about 360° crank angle), as shown inFIG. 4. At near bottom dead center of the compression stroke (about 540° crank angle), the intake valve218moves from the first position to the second position to block additional air from entering the combustion chamber206. Fuel may then be injector from the fuel injector assembly240at near top dead center of the compression stroke (about 720° crank angle).

In a conventional Miller cycle engine, the conventional Otto or diesel cycle is modified by moving the intake valve218from the first position to the second position at either some predetermined time before bottom dead center of the intake stroke406(i.e., before 540° crank angle) or some predetermined time after bottom dead center of the compression stroke407(i.e., after 540° crank angle). In a conventional late-closing Miller cycle, the intake valve218is moved from the first position to the second position during a first portion of the first half of the compression stroke407.

The variable intake valve closing mechanism238enables the engine110to be operated in both a late-closing Miller cycle and a conventional Otto or diesel cycle. Further, injecting a substantial portion of fuel after top dead center of the combustion stroke508, as shown inFIG. 5, may reduce NOxemissions and increase the amount of energy rejected to the exhaust manifold116in the form of exhaust fluid. Use of a high-efficiency turbocharger320,420or series turbochargers120,140may enable recapture of at least a portion of the rejected energy from the exhaust. The rejected energy may be converted into increased air pressures delivered to the intake manifold114, which may increase the energy pushing the piston212against the crankshaft213to produce useable work. In addition, delaying movement of the intake valve218from the first position to the second position may reduce the compression temperature in the combustion chamber206. The reduced compression temperature may further reduce NOxemissions.

The controller244may operate the variable intake valve closing mechanism238to vary the timing of the intake valve assembly214to achieve desired engine performance based on one or more engine conditions, for example, engine speed, engine load, engine temperature, boost, and/or manifold intake temperature. The variable intake valve closing mechanism238may also allow more precise control of the air/fuel ratio. By delaying closing of the intake valve assembly214, the controller244may control the cylinder pressure during the compression stroke of the piston212. For example, late closing of the intake valve reduces the compression work that the piston212must perform without compromising cylinder pressure and while maintaining a standard expansion ratio and a suitable air/fuel ratio.

The high pressure air provided by the exemplary air supply systems100,300,400may provide extra boost on the induction stroke of the piston212. The high pressure may also enable the intake valve assembly214to be closed even later than in a conventional Miller cycle engine. In the present invention, the intake valve assembly214may remain open until the second half of the compression stroke of the piston212, for example, as late as about 80° to 70° before top dead center (BTDC). While the intake valve assembly214is open, air may flow between the chamber206and the intake manifold114. Thus, the cylinder112experiences less of a temperature rise in the chamber206during the compression stroke of the piston212.

Since the closing of the intake valve assembly214may be delayed, the timing of the fuel supply system may also be retarded. For example, the controller244may controllably operate the fuel injector assembly240to supply fuel to the combustion chamber206after the intake valve assembly214is closed. For example, the fuel injector assembly240may be controlled to supply a pilot injection of fuel contemporaneous with or slightly after the intake valve assembly214is closed and to supply a main injection of fuel contemporaneous with or slightly before combustion temperature is reached in the chamber206. As a result, a significant amount of exhaust energy may be available for recirculation by the air supply, system100,300,400, which may efficiently extract additional work from the exhaust energy.

Referring to the exemplary air supply system100ofFIG. 1, the second turbocharger140may extract otherwise wasted energy from the exhaust stream of the first turbocharger120to turn the compressor wheel150of the second turbocharger140, which is in series with the compressor wheel134of the first turbocharger120. The extra restriction in the exhaust path resulting from the addition of the second turbocharger140may raise the back pressure on the piston212. However, the energy recovery accomplished through the second turbocharger140may offset the work consumed by the higher back pressure. For example, the additional pressure achieved by the series turbochargers120,140may do work on the piston212during the induction stroke of the combustion cycle. Further, the added pressure on the cylinder resulting from the second turbocharger140may be controlled and/or relieved by using the late intake valve closing. Thus, the series turbochargers120,140may provide fuel efficiency via the air supply system100, and not simply more power

It should be appreciated that the air cooler156,356,456preceding the intake manifold114may extract heat from the air to lower the inlet manifold temperature, while maintaining the denseness of the pressurized air. The optional additional air cooler between compressors or after the air cooler156,356,456may further reduce the inlet manifold temperature, but may lower the work potential of the pressurized air. The lower inlet manifold temperature may reduce the NOxemissions.

Referring again toFIG. 8, a change in pressure of exhaust gases passing through the PM filter806results from an accumulation of particulate matter, thus indicating a need to regenerate the PM filter806, i.e., burn away the accumulation of particulate matter. For example, as particulate matter accumulates, pressure in the PM filter806increases.

The PM filter806may be a catalyzed diesel particulate filter (CDPF) or an active diesel particulate filter (ADPF). A CDPF allows soot to burn at much lower temperatures. An ADPF is defined by raising the PM filter internal energy by means other than the engine110, for example electrical heating, burner, fuel injection, and the like.

One method to increase the exhaust temperature and initiate PM filter regeneration is to use the throttle valve814to restrict the inlet air, thus increasing exhaust temperature. Other methods to increase exhaust temperature include variable geometry turbochargers, smart wastegates, variable valve actuation, and the like. Yet another method to increase exhaust temperature and initiate PM filter regeneration includes the use of a post injection of fuel, i.e., a fuel injection timed after delivery of a main injection.

The throttle valve814may be coupled to the EGR valve812so that they are both actuated together. Alternatively, the throttle valve814and the EGR valve812may be actuated independently of each other. Both valves may operate together or independently to modulate the rate of EGR being delivered to the intake manifold114.

CDPFs regenerate more effectively when the ratio of NOxto particulate matter, i.e., soot, is within a certain range, for example, from about 20 to 1 to about 30 to 1. It has been found, however, that an EGR system combined with the above described methods of multiple fuel injections and variable valve timing results in a NOxto soot ratio of about 10 to 1. Thus, it may be desirable to periodically adjust the levels of emissions to change the NOxto soot ratio to a more desired range and then initiate regeneration. Examples of methods which may be used include adjusting the EGR rate and adjusting the timing of main fuel injection.

A venturi (not shown) may be used at the EGR entrance to the fresh air inlet. The venturi would depress the pressure of the fresh air at the inlet, thus allowing EGR to flow from the exhaust to the intake side. The venturi may include a diffuser portion which would restore the fresh air to near original velocity and pressure prior to entry into compressor144. The use of a venturi and diffuser may increase engine efficiency.

An air and fuel supply system for an internal combustion engine in accordance with the exemplary embodiments of the invention may extract additional work from the engine's exhaust. The system may also achieve fuel efficiency and reduced NOxemissions, while maintaining work potential and ensuring that the system reliability meets with operator expectations.