BACKGROUND OF THE INVENTION [0002] It is well known that many spark-ignition four-stroke reciprocating piston internal combustion engine designs have a lower efficiency at low/partial load.

The loss of efficiency is caused by a number of factors including : losses due to the throttling of the intake mixture, slow combustion due to lower density of the throttled mixture, and excessive heat loss to the combustion chamber walls. In addition to low efficiency at low/partial load, some engines emit unacceptable levels of nitrogen oxides (NOx) and hydrocarbons (HC) during partial-load operation.

[0003] Engine designs that use exhaust gas recirculation (EGR) have been developed as one solution to the efficiency and emission problems associated with low/partial load operation. It has been well documented that the use of exhaust gas recirculation in engines provides some reduction in throttling losses and significant reductions in engine NOx emissions because the peak combustion temperature is reduced. It is also known that exhaust gas recirculation can be used with stoichiometric air-fuel mixtures to allow the use of conventional three-way catalysts for effective exhaust emission control.

[0004] A number of engine configurations that implement homogeneous exhaust gas recirculation are known in the art. For example, in U. S. Patent No.

4,870,941 linethere is disclosed a basic type of an engine EGR system wherein the engine exhaust manifold is placed in fluid communication with the intake manifold by way of an EGR passage. In this configuration, exhaust gas is recirculated or fed back to the intake manifold through the EGR passage and an EGR valve. Another type of engine EGR system is disclosed in U. S. Patent No. 5, 404,844 wherein a first portion of the exhaust gas in an upper portion of the cylinder is expelled into an exhaust port and a second portion of the exhaust gas from a lower portion of the intake stroke. Yet another type of engine EGR system is disclosed in U. S. Patent No.

5,005,552 wherein exhaust gas is recirculated into the cylinder by opening the exhaust valve during the intake stroke thereby drawing a backflow of exhaust gas into the cylinder.

[0005] Stratified exhaust gas recirculation (EGR) has been developed as yet another solution to the efficiency and emission problems associated with low/partial load operation. U. S. Patent Nos. 4,393,853,5,870,993,5,894,826 and 5,918,577 all represent various forms of stratified exhaust gas recirculation (EGR).

[0006] In U. S. Patent No. 4,393,853, there is disclosed an engine which implements stratified exhaust gas recirculation (EGR) methods. In the engine configuration described in this patent, a swirling fuel-air mixture is introduced through an intake valve into the center of the cylinder near the spark plug, and exhaust gas is directed from another cylinder or the exhaust gas manifold through a tangential port located in the middle of the cylinder wall. This engine configuration creates radial stratification wherein exhaust gas swirls adjacent the cylinder wall and the fuel-air mixture swirls in the center of the cylinder.

[0007] U. S. Patent No. 5,870,993 discloses an engine configuration wherein exhaust gas is recirculated into the cylinder by opening the exhaust valve during the intake stroke thereby drawing a backflow of exhaust gas into the cylinder. A chamfer on the exhaust valve opening creates a swirling flow of recirculated exhaust gas that rotates about an axis parallel to the direction of motion of the reciprocating piston. A fuel-air mixture is also introduced into the cylinder in a manner that creates a tumble flow in the center region of the cylinder. The swirling exhaust gas flow and the tumbling fuel-air flow create stratification in the combustion chamber.

[0008] In U. S. Patent No. 5,894,826, there is disclosed an engine with a first inlet port for introducing air tangentially into the cylinder to produce a generally circular motion in a peripheral region of the cylinder and a second inlet port to introduce air and recirculated exhaust gas, which is provided to the second inlet by way of an EGR passageway, toward the center of the cylinder.

[0009] U. S. Patent No. 5, 918,577 discloses another stratified EGR engine wherein exhaust gas is recirculated into the cylinder by opening the exhaust valve during the intake stroke thereby drawing a backflow of exhaust gas into the cylinder. A helical exhaust port creates a swirling flow of recirculated exhaust gas that rotates about an axis parallel to the direction of motion of the reciprocating piston. The exhaust gas remains substantially on the piston surface and along the cylinder wall to create a cup- shaped region. A fuel-air mixture is also introduced into the cylinder in a manner such that the fuel-air mixture swirls in the center of the cylinder. The swirling exhaust gas flow and fuel-air flow create a stratification in the combustion chamber.

[0010] While the engine configurations in U. S. Patent Nos. 4,393,853,5,870,993, 5,894,826 and 5,918,577 can provide improved engine efficiency and lower emissions, there are certain disadvantages with these prior stratified EGR systems. It is well known that the air-fuel ratio has a significant effect on engine torque and emissions.

Particularly, one specific air-fuel ratio, the stoichiometric mixture, is highly significant and corresponds to an air and fuel combination such that if combustion were perfect all of the hydrogen and carbon in the fuel would be converted by the burning process to H20 and C02. Accordingly, it is preferred that an ignitable mixture be present in the cylinder near the spark plug before the end of the compression stroke when ignition occurs so that emissions can be decreased. As a result, an ideal stratified EGR system should maintain a stratified flow during intake and compression such that an ignitable mixture is present in the cylinder near the spark plug before ignition occurs. One disadvantage with the engine configurations disclosed in U. S. Patent Nos. 4,393,853, 5,870,993,5,894,826 and 5,918,577 is that these engine configurations may not maintain a stratified flow during intake and compression which can have negative effects on spark ignition combustion quality and emissions.

[0011] For example, the engine configuration in U. S. Patent No. 4,393,853 provides some level of stratification, but significant mixing of the air-fuel mixture and recirculated exhaust gas is inevitable with this design. As a result, it may be difficult to achieve a near stoichiometric mixture in the cylinder near the spark plug before ignition occurs. Likewise, the engine configuration in U. S. Patent No. 5,870,993 provides stratification, but mixing of the air-fuel mixture and recirculated exhaust gas is inevitable because of the swirling flow of recirculated exhaust gas and the tumbling flow of the air- fuel mixture. With respect to the engine design in U. S. Patent No. 5,894,826, significant mixing of air, fuel and exhaust gas will occur in this engine as the fuel is injected through exhaust gas and into air at the peripheral region of the cylinder. Lastly, while the engine configuration in U. S. Patent No. 5, 918,577 provides an improvement in the control of air-fuel mixture and exhaust gas mixing compared to the engines disclosed in U. S. Patent Nos. 4,393,853,5,870,993, and 5,894,826, the engine disclosed in U. S.

Patent No. 5,918,577 will also experience some mixing of the air-fuel mixture and recirculated exhaust gas as any recirculated exhaust gas existing on the top of the piston will be mixed with the air-fuel mixture when the piston pushes up on the recirculated exhaust gas and air-fuel mixture during the compression stroke.

[0012] Thus, there is a continuing need for a four-stroke reciprocating piston internal combustion engine that optimally implements stratified exhaust gas recirculation (EGR) methods to provide a solution to the efficiency and emission problems associated with low/partial load engine operation. More particularly, there is a need for a four-stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods and can maintain a stratified flow during intake and compression such that an ignitable and fully combustible mixture is present in a specific region of the cylinder before ignition occurs.

SUMMARY OF THE INVENTION [0013] The foregoing disadvantages of prior art stratified exhaust gas recirculation (EGR) methods are overcome by providing a four-stroke reciprocating internal combustion engine with variable valve lift and timing for producing a stratified EGR/air-fuel mixture within the combustion chamber defined by the engine cylinder, the cylinder head and the piston. The stratified exhaust gas/air-fuel mixture produced by the engine comprises recirculated exhaust gas which rotates about an exhaust vortex axis extending substantially in the direction of reciprocation of the piston within the combustion chamber and an air-fuel mixture which rotates about an intake fluid vortex axis extending substantially in the direction of reciprocation of the piston within the combustion chamber. The engine enables precise control of the motion of the stratified recirculated exhaust gas/air-fuel mixture during intake and compression such that no or minimal mixing occurs between the air-fuel mixture and the recirculated exhaust gas. As a result, recirculated exhaust gas is positioned adjacent a stoichiometric air-fuel mixture which resides in the cylinder near the spark plug during ignition thereby achieving stable ignition and substantially complete combustion within the chamber. In addition, because of the stoichiometric operation of the engine, conventional three-way catalysts can be used for emission control.

[0014] One version of a four-stroke reciprocating internal combustion engine in accordance with the invention includes a combustion chamber that is defined by a cylinder, a reciprocating piston contained within the cylinder, and a cylinder head. The combustion chamber is in fluid communication with an exhaust port and an intake port.

The exhaust port includes an exhaust valve that opens during the intake stroke at part load, an exhaust flow motion generating device and optionally, an associated exhaust flow direction control device. The exhaust flow motion generating device creates an exhaust fluid flow in a first portion of the combustion chamber adjacent the exhaust port during the intake stroke at part load. The intake port includes an associated intake valve, an intake flow motion generating device and optionally, an associated intake flow direction control device. The intake flow motion generating device creates an intake fluid flow in a remaining portion of the combustion chamber adjacent the intake port.

The flow motion generating devices may be helical ports, and the flow direction control devices may be valve masks or valve shrouds. The engine includes a variable valve lift and timing system for operating the exhaust valve and the intake valve, at least one sensor for sensing an engine operating condition, and an engine controller. The engine controller receives and processes signals from each sensor and outputs a control signal to the variable valve lift and timing system for operating each intake valve and each exhaust valve such that an exhaust residual flow is inducted through the exhaust port into the combustion chamber and an air-fuel mixture is simultaneously inducted through the intake port into the combustion chamber during the intake stroke to produce the stratified exhaust gas and air-fuel mixture described above.

[0015] Another version of a four-stroke reciprocating internal combustion engine in accordance with the invention includes a combustion chamber that is defined by a cylinder, a reciprocating piston contained within the cylinder, and a cylinder head. The combustion chamber is in fluid communication with an intake port and an exhaust port.

The exhaust port includes an exhaust valve that opens during the intake stroke at part load, an exhaust flow motion generating device and optionally, an associated exhaust flow direction control device. The exhaust flow motion generating device creates an exhaust fluid flow in a first portion of the combustion chamber adjacent the exhaust port during the intake stroke at part load. The intake port includes an associated intake valve, an intake flow motion generating device and optionally, an associated intake flow direction control device. The intake flow motion generating device creates an intake air fluid flow in a remaining portion of the combustion chamber adjacent the intake port.

The flow motion generating devices may be helical ports, and the flow direction control devices may be valve masks or valve shrouds. The engine includes a fuel injector mounted in the cylinder head or in a side wall of the cylinder for directing fuel into the air in the combustion chamber, a variable valve lift and timing system for operating the exhaust valve and the intake valve, at least one sensor for sensing an engine operating condition, and an engine controller. The engine controller receives and processes signals from each sensor and outputs a control signal to the variable valve lift and timing system for operating the intake valve and the exhaust valve such that an exhaust residual flow is inducted through the exhaust port into the combustion chamber and air is simultaneously inducted through the intake port into the combustion chamber and fuel is directly injected into the air in the combustion chamber to produce the stratified exhaust gas and air-fuel mixture described above.

[0016] In one aspect of the invention, the stratified exhaust gas and air-fuel mixture comprises recirculated exhaust gas which rotates about an exhaust vortex axis in a first portion of the combustion chamber and an air-fuel mixture which rotates about an intake fluid vortex axis in the remaining portion of the combustion chamber.

Preferably, the exhaust gas rotates about the exhaust vortex axis substantially parallel to a plane normal to the cylinder axis and the air-fuel mixture rotates about the intake fluid vortex axis substantially parallel to the plane. Most preferably, the exhaust gas and the air-fuel mixture rotate in opposite directions and with substantially the same angular velocity thereby eliminating or significantly minimizing mixing between the recirculated exhaust gas and the air-fuel mixture.

[0017] It is therefore an advantage of the present invention to provide a four- stroke reciprocating piston internal combustion engine that optimally implements stratified exhaust gas recirculation (EGR) methods to provide a solution to the efficiency and emission problems associated with low/partial load engine operation.

[0018] It is another advantage of the present invention to provide a four-stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods and can maintain a stratified flow during intake and compression such that a near stoichiometric mixture is present in the cylinder near the spark plug before ignition occurs.

[0019] It is still another advantage of the present invention to provide a four- stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods to maintain stable combustion with less fuel and reduced pumping losses thereby increasing fuel economy.

[0020] It is yet another advantage of the present invention to provide a four- stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods to lower the temperature of combustion thereby reducing NOx emissions.

[0021] It is a further advantage of the present invention to provide a four-stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods to reduce the effective size of the cylinder while maintaining reliable combustion at low and partial engine loads.

[0022] It is still another advantage of the present invention to provide a four- stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods to create a layer of exhaust gas that acts as a thermal barrier between the combustion reaction and a portion of the cylinder wall thereby reducing thermal losses.

[0023] It is yet another advantage of the present invention to provide a four- stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods to provide a solution to the efficiency and emission problems associated with low/partial load engine operation and that allows for the use of conventional three-way catalysts for exhaust emission control.

[0024] It is a further advantage of the present invention to provide a four-stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods to isolate a portion of the crevice region above the piston ring from the air-fuel mixture.

[0025] It is still another advantage of the present invention to provide a four- stroke reciprocating piston internal combustion engine that uses stratified exhaust gas recirculation (EGR) methods and does not require a centrally mounted fuel injector.

[0026] Another advantage of the present invention is that increased levels of EGR are tolerated. Another, more specific, advantage of the present invention is that pumping losses are reduced resulting in greater fuel economy. Yet another, more specific, advantage of the present invention is that NOx and hydrocarbon emissions of an engine are significantly reduced and that because of the stoichiometric operation of the engine, conventional three-way catalysts can be used for emission control. Still another advantage of the present invention is that heat transfer through the cylinder walls and piston is reduced, thereby increasing the thermodynamic efficiency of the engine. A further advantage of the present invention is that fuel economy is increased.

BRIEF DESCRIPTION OF THE DRAWINGS [0027] These and other features, aspects, objects, and advantages of the present invention will become better understood upon consideration of the following detailed description, appended claims and accompanying drawings where: [0028] Figure 1 is a schematic representation of a variable valve controlled engine according to the present invention; [0029] Figure 1A is a schematic representation of another version of a variable valve controlled engine according to the present invention; [0030] Figure 2 is a block diagram of a control system according to the present invention; [0031] Figure 3 is a schematic representation of an engine including helical intake and exhaust ports for creating swirling intake flow and exhaust gas flow that are introduced into the combustion chamber of an engine according to the present invention; [0032] Figure 4 is a bottom plan view of a cylinder head having means for directing intake and exhaust flow into the combustion chamber of an engine according to the present invention; [0033] Figure 5 is a sectional view of the cylinder head of Figure 4 taken along line 5-5; [0034] Figure 5A is a sectional view of the cylinder head of Figure 5 taken along line 5A-5A; [0035] Figure 6 is a bottom plan view of an alternative cylinder head having means for directing intake and exhaust flow into the combustion chamber of an engine according to the present invention; [0036] Figure 7 is a sectional view of the cylinder head of Figure 6 taken along line 7-7; [0037] Figure 7A is a sectional view of the cylinder head of Figure 6 taken along line 7A-7A; [0038] Figure 8A is a schematic illustration of a top plan view of the charge within the combustion chamber of the engine according to the present invention taken along line 8A-8A of Figure 9; [0039] Figure 8B is another schematic illustration of a top plan view of the charge within the combustion chamber of the engine according to the present invention taken along line 8B-8B of Figure 9; [0040] Figure 9 is a schematic illustration of a side sectional view of the charge within the combustion chamber of the engine according to the present invention; and [0041] Figure 10 is a depiction of the velocity vector distribution for an engine in accordance with the invention taken along line 8A-8A of Figure 9.

[0042] It should be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein.

[0043] Like reference numerals will be used to refer to like or similar parts from Figure to Figure in the following description of the drawings.

DETAILED DESCRIPTION OF THE INVENTION [0044] As shown in Figure 1, one cylinder of a multi-cylinder four-stroke cycle reciprocating internal combustion engine 10 has a cylinder 11, a crankshaft 12 with a connecting rod 14 and a piston 16 disposed within the cylinder 11. A cylinder head 17 closes an end of the cylinder 11 and cooperates with the piston 16 to define a combustion chamber 19. The combustion chamber 19 communicates with an intake port 18 and an exhaust port 22 by an intake valve 20 and an exhaust valve 24, respectively. The intake valve 20 is operated by an intake valve actuator 25 and the exhaust valve 24 is operated by an exhaust valve actuator 26. A fuel injector 29 is arranged in fluid communication with the intake port 18 for injecting fuel into air in the intake port 18. While one cylinder, one intake valve, one exhaust valve, one intake port, and one exhaust port are shown in Figure 1, it should be understood that the present invention can be used with an engine having multiple cylinders, intake valves, exhaust valves, intake ports, and exhaust ports.

[0045] Figure 1A shows another version of one cylinder of a multi-cylinder four-stroke cycle reciprocating internal combustion engine 10A. The engine 10A has a cylinder 11, a crankshaft 12 with a connecting rod 14, a piston 16, a cylinder head 17, an intake port 18, an exhaust port 22, an intake valve 20, an exhaust valve 24, an intake valve actuator 25, and an exhaust valve actuator 26 as in the engine 10 of Figure 1.

However, in the engine 10A of Figure 1A, a fuel injector 29a is mounted in the cylinder head 17 for injecting fuel directly into the combustion chamber 19. Alternatively, the fuel injector 29a may be mounted in a side wall of the cylinder 11 for injecting fuel directly into the combustion chamber 19. It can be appreciated that either location of the fuel injector 29a is advantageous as the engine 10A does not require a centrally mounted fuel injector. While one cylinder, one intake valve, one exhaust valve, one intake port, and one exhaust port are shown in Figure 1A, it should be understood that the present invention can be used with an engine having multiple cylinders, intake valves, exhaust valves, intake ports, and exhaust ports. [0046] Figure 2 illustrates an engine control system according to the present invention. An engine controller 30 receives a variety of inputs from engine operating sensors 32, which include many of the types of sensors known to those skilled in the art of engine control and suggested by this disclosure. For instance, the engine operating sensors 32 may sense parameters such as engine speed, engine load, air-fuel ratio, intake manifold absolute pressure, engine intake air mass flow rate, engine exhaust temperature, exhaust manifold absolute pressure, engine temperature, vehicle speed, vehicle gear selection, accelerator position, and other parameters known to those skilled in the art and suggested by this disclosure. The engine controller 30, which may comprise an electronic engine operating controller drawn from many types known to those skilled in the art of automotive electronic engine controllers, compares sensed operating parameters with predetermined values and outputs electrical signals that control various engine actuators. For example, in the present invention, the engine controller 30 is electrically connected to the intake valve actuator 25 and the exhaust valve actuator 26, and the engine controller 30 outputs electrical signals that are used by the intake valve actuator 25 and the exhaust valve actuator 26 to control motion of the intake valve 20 and exhaust valve 24, respectively.

[0047] The intake valve 20, the exhaust valve 24, the intake valve actuator 25 and the exhaust valve actuator 26 form part of a variable lift and timing valve system known in the art. For example, valvetrains controlled by a variable lift and timing electrohydraulic camless valve system are shown in U. S. Patent Nos. 5,404,844 and 5,255,641; valvetrains controlled by a variable lift and timing electromagnetic camless valve system are shown in U. S. Patent Nos. 5,743,221 and 5,692,463; and valvetrains controlled by a variable lift and timing mechanical valve system are shown in U. S.

Patent No. 5,592,906. Each of these patents is incorporated herein by reference.

These types of valvetrains provide flexibility in which both the timing and lift of the intake valve 20 and the exhaust valve 24 can be varied. Accordingly, as used herein, the term"variable valve lift and timing system"will be used to describe a valvetrain in which both the timing and the lift of the intake valve 20 and the exhaust valve 24 can be varied. For instance, in the preferred version of the present invention, the intake valve actuator 25 and the exhaust valve actuator 26 receive signals from the engine controller 30 and enable variable timing and lift of the intake valve 20 and the exhaust valve 24.

[0048] The intake valve actuator 25 and the intake valve 20 are used to induct an air-fuel mixture from the intake port 18 during the intake stroke of the engine 10 shown in Figure 1. The engine controller 30 compares sensed operating parameters with load demand and predetermined values and sends an electrical signal to the intake valve actuator 25. The intake valve actuator 25 then operates the intake valve 20 so that the air-fuel mixture may flow from the intake port 18 into predetermined regions of combustion chamber 19 during the intake stroke.

[0049] The intake valve actuator 25 and the intake valve 20 are used to induct air from the intake port 18 during the intake stroke of the engine 10A shown in Figure 1A.

The engine controller 30 compares sensed operating parameters with load demand and predetermined values and sends an electrical signal to the intake valve actuator 25.

The intake valve actuator 25 then operates the intake valve 20 so that air may flow from the intake port 18 into predetermined regions of combustion chamber 19 during the intake stroke.

[0050] The exhaust valve actuator 26 and the exhaust valve 24 are used to induct exhaust gas from the exhaust port 22 during the intake stroke of the engine 10 or 10A. The engine controller 30 compares sensed operating parameters with load demand and predetermined values and sends an electrical signal to the exhaust valve actuator 26. The exhaust valve actuator 26 then operates the exhaust valve 24 so that exhaust gas residual may flow from the exhaust port 22 into predetermined regions of combustion chamber 19 during the intake stroke. As used herein, the flow of exhaust gases into the combustion chamber will be termed"exhaust residual".

[0051] One particular advantage of using a variable valve lift and timing system wherein the intake valve actuator 25 and the exhaust valve actuator 26 receive signals from the engine controller 30 and enable continuously variable timing and lift of the intake valve 20 and the exhaust valve 24 is that the amount of intake air or air-fuel mixture inducted into the combustion chamber 19 through the intake port 18 may be varied in response to load demand and a sensed engine load or a derived engine load value and the amount of exhaust inducted into the combustion chamber 19 through the exhaust port 22 may be varied in order to fill the combustion chamber and thereby reduce pumping losses.

[0052] According to the present invention, the intake port 18 and the exhaust port 22 contain a flow motion generating device that works in conjunction with the variable valve lift and timing system to generate a particular motion in the air or air-fuel mixture and exhaust gas inducted into the combustion chamber 19. Referring to Figure 3, there is shown a helical intake port 48 and a helical exhaust port 50 that may be used in conjunction with the variable valve lift and timing system as a means to generate a swirling motion in the intake air or air-fuel mixture and the exhaust residual inducted into specific regions of combustion chamber 19. Alternatively, an irregular surface in the flow cross-section of the intake port 18 and the exhaust port 22 may be used to generate a swirling motion in the air or air-fuel mixture and exhaust residuals inducted into the combustion chamber 19.

[0053] According to a most preferred version of the present invention, the intake port 18 and the exhaust port 22 each contain an associated flow direction control device. The flow direction control devices work in conjunction with the variable valve lift and timing system to direct air or air-fuel mixture and exhaust residuals into specific regions of the combustion chamber 19. Figures 4,5 and 5A show one version of a flow direction control device. Looking at Figures 4,5 and 5A, there is shown a valve shroud 58 on a portion of the exhaust valve 24 that serves to direct exhaust residuals into specific regions of the combustion chamber 19 when the exhaust valve 24 is opened.

Of course, the same type of valve shroud can be used on the intake valve 20 to direct intake air or air-fuel mixture into specific regions of the combustion chamber 19 when the intake valve 20 is opened. Figures 6,7 and 7A show another version of a flow direction control device. Looking at Figures 6,7 and 7A, there is shown a valve mask 42 on one side of the flow cross section of the exhaust port 22 and a valve mask 42a on one side of the flow cross section of the intake port 18. The valve masks 42 and 42a direct air or air-fuel mixture and exhaust residuals into specific regions of the combustion chamber 19 when the intake valve 20 and the exhaust valve 24 are opened.

While four valves/cylinder are shown in Figures 3-7A, it will be appreciated by those skilled in the art that any number of valves/cylinder may be used, provided that the port structure or valve structure is used to obtain the desired air and exhaust gas motion or direction within combustion chamber 19.

[0054] During operation of the engine 10 of Figure 1 in accordance with the present invention, fuel is injected into air in the intake port 18 from fuel injector 29 either while the intake valve 20 is closed or open to produce an air-fuel mixture. The engine controller 30 receives and processes sensed parameters, and the engine controller 30 commands the intake valve actuator 25 to operate the intake valve 20 to induce varied levels of the air-fuel mixture into the combustion chamber 19 during the intake stroke to achieve the required load. For instance, the engine controller 30 typically receives load demand signals and receives or derives engine load signals and then commands the intake valve actuator 25 to operate the intake valve 20 to induce a specific level of air- fuel mixture into the combustion chamber that depends on the load demand and the measured engine load. Also during the intake stroke, the engine controller 30 commands the exhaust valve actuator 26 to operate the exhaust valve 24 to induce varied levels of exhaust gas residual from the exhaust port 22 into the combustion chamber 19. The exhaust gas residuals serve to fill the combustion chamber 19 and reduce pumping losses. The ratio of exhaust gas mass to air mass varies between 0 and 1 depending on the operating conditions. The exhaust residual is directed by way of the helical exhaust port 50 and the valve shroud 58 or the valve mask 42 into a first portion of the combustion chamber 19 adjacent the exhaust port 22 and rotates about an exhaust vortex axis that extends substantially in the direction of reciprocation of the piston 16 within the combustion chamber 19. At the same time, the air-fuel mixture inducted through the intake port 18 is directed by way of the helical intake port 48 and a valve shroud or the valve mask 42a into the remaining portion of the combustion chamber 19 adjacent the intake port 18 and rotates about an intake fluid vortex axis extending substantially in the direction of reciprocation of the piston 16 within the combustion chamber 19. This produces a stratified exhaust and air-fuel mixture within combustion chamber 19.

[0055] During operation of the engine 10A of Figure 1A in accordance with the present invention, the engine controller 30 receives and processes sensed parameters, and the engine controller 30 commands the intake valve actuator 25 to operate the intake valve 20 to induce varied levels of air into the combustion chamber 19 during the intake stroke to achieve the required load. For instance, the engine controller 30 typically receives load demand signals and receives or derives engine load signals and then commands the intake valve actuator 25 to operate the intake valve 20 to induce a specific level of air into the combustion chamber that depends on the load demand and the measured engine load. Also during the intake stroke, the engine controller 30 commands the exhaust valve actuator 26 to operate the exhaust valve 24 to induce varied levels of exhaust gas residuals from the exhaust port 22 into the combustion chamber 19. The exhaust gas residuals serve to fill the combustion chamber 19 and reduce pumping losses. The ratio of exhaust gas mass to air mass varies between 0 and 1 depending on the operating conditions. The exhaust residual is directed by way of the helical exhaust port 50 and the valve shroud 58 or the valve mask 42 into a first portion of the combustion chamber 19 adjacent the exhaust port 22. The exhaust residual rotates about an exhaust vortex axis that extends substantially in the direction of reciprocation of the piston 16 within the combustion chamber 19. At the same time, air inducted through the intake port 18 is directed by way of the helical intake port 48 and a valve shroud or the valve mask 42a into the remaining portion of the combustion chamber 19 adjacent the intake port 18. The air rotates about an intake fluid vortex axis extending substantially in the direction of reciprocation of the piston 16 within the combustion chamber 19. Fuel is directly injected into the air in the combustion chamber 19 from fuel injector 29a during the intake stroke to produce a stratified exhaust and air-fuel mixture within the combustion chamber 19. Preferably, the fuel droplet diameter from the fuel injector 29a is less than 20 microns, and the cone angle and the penetration are optimized to prevent fuel from entering the exhaust residual in the first portion of the combustion chamber 19 and to prevent wetting of the piston 16 and/or cylinder head 17.

[0056] Referring now to Figures 8A, 8B and 9, the stratified mixture produced by the engines 10 and 10A is shown. Through the use of two identical inverse helical ports, that is, helical intake port 48 and helical exhaust port 50 shown in Figure 3, two strong inverse gas flow vortices are created in the combustion chamber 19. The exhaust residual gas flow 70 rotates about an exhaust vortex axis 93 that extends substantially in the direction of reciprocation of the piston within the combustion chamber 19. The exhaust residual 70 resides along a first portion of the inner wall of the cylinder 11 and within the volume defined by the piston 16, the cylinder head 17, the first portion of the inner wall of the cylinder 11, and an interface 91 that extends between locations 94 and 95 where the exhaust residual 70 meets the air-fuel mixture flow 80 along opposite sides of the inner wall of the cylinder 16. The air-fuel mixture flow 80 rotates about an intake fluid vortex axis 92 that extends substantially in the direction of reciprocation of the piston 16 within the combustion chamber 19. The air- fuel mixture flow 80 resides along a second portion of the inner wall of the cylinder 11 and within the volume defined by the piston 16, the cylinder head 17, the second portion of the inner wall of the cylinder 11, and an interface 91 that extends between locations 94 and 95 where the exhaust residual 70 meets the air-fuel mixture flow 80 along opposite sides of the inner wall of the cylinder 16. The exact amount of air or air-fuel mixture and exhaust residual to be induced into the combustion chamber 19 is dependent upon a variety of engine operation conditions. As shown in Figure 9, the exhaust residual 70 also covers a portion of the crevice region 72 above the piston ring (s) such that the air-fuel mixture cannot enter a portion of the crevice region 72.

This serves to reduce hydrocarbon emissions from the engine.

[0057] The double inverse vortices shown in Figures 8A, 8B and 9, that is, the exhaust residual flow 70 and the air-fuel mixture flow 80, display stable separation during the entire intake stroke. A clear stratification interface 91 exists between the exhaust residual flow 70 and the air-fuel mixture flow 80, and it has been determined that the turbulent kinetic energy on the interface 91 is quite small (about teens m2/s2 level), which means that there is minimal mixing opportunity between the exhaust residual flow 70 and the air-fuel mixture flow 80 at this interface 91. This double inverse vortex flow structure is quite advantageous. One of the major reasons that other prior art flow structures fail to maintain stratification is because of high relative velocity between two anti-clockwise flow vortices, which causes high turbulence levels (greater than 1200 m2/s2) in the center of the cylinder. This high turbulence flow accelerates fresh air and EGR mixing at their interface area. It has been discovered that in order to reduce this relative movement of the two vortices to attain a maintainable exhaust residual flow and air-fuel mixture flow separation in the cylinder, the exhaust residual flow vortex and the air-fuel mixture flow vortex should rotate in opposite directions as described above.

[0058] As detailed above, during operation of the engines 10 and 10A of the present invention, the controller 30 and the variable lift and timing valve system operate both the exhaust valve 24 and the intake valve 20 to induce exhaust residuals and air or air-fuel mixture into the cylinder during the intake stroke. The double helical ports, helical intake port 48 and helical exhaust port 50 shown in Figure 3, produce two strong almost identical inverse vortices in the cylinder 16. During movement of the piston 16 from top dead center to bottom dead center in the intake stroke, the air or air-fuel vortex and the exhaust residual vortex are stable and maintain their coherent structure. The turbulence kinetic energy keeps on the low level (approximately teens m2/s2) in their interface area. Looking at Figure 10, there is shown a velocity vector distribution at a cutaway plane under a 120 degree crank angle from top dead center. At other cutaway planes and crank angles, similar velocity vector distributions were observed.

[0059] Improved engine efficiency and reduced emissions can be achieved by an engine 10 in accordance with the present invention (as shown in Figure 1) because the stratified mixture shown in Figures 8A, 8B and 9 can be maintained during the intake and the compression stroke. During operation of the engine 10 of Figure 1, exhaust gas may be inducted during the intake stroke into the combustion chamber 19 through the exhaust port 22 and the exhaust residual rotates in a first portion of the combustion chamber adjacent the exhaust port about an exhaust vortex axis that extends substantially in the direction of reciprocation of the piston within the combustion chamber, while the air-fuel mixture is inducted through the intake port 18 and rotates in a remaining portion of the combustion chamber adjacent the intake port about an intake fluid vortex axis extending substantially in the direction of reciprocation of the piston within the combustion chamber. It has been discovered that by inducting the exhaust gas and the air-fuel mixture into the combustion chamber 19 during the intake stroke such that there is minimal mixing between the exhaust residual and the air-fuel mixture, spark ignition combustion quality and reliability can be improved. Preferably, there is no mixing between the exhaust residual and the air-fuel mixture, and the result of the intake stroke and the compression stroke is a swirling flow of exhaust gas (near 0% air-fuel mixture) in a first portion of the cylinder and a swirling homogeneous stoichiometric air-fuel mixture (near 0% exhaust) in the remaining portion of the cylinder before the end of the compression stroke.

[0060] Improved engine efficiency and reduced emissions can also be achieved by an engine 10A in accordance with the present invention (as shown in Figure 1A) as the stratified mixture shown in Figures 8A, 8B and 9 can be maintained during the intake and the compression stroke. During operation of the engine 10A of Figure 1A, exhaust gas may be inducted during the intake stroke into the combustion chamber 19 through the exhaust port 22 and the exhaust residual rotates in a first portion of the combustion chamber adjacent the exhaust port about an exhaust vortex axis that extends substantially in the direction of reciprocation of the piston within the combustion chamber, while air is inducted through the intake port 18 and rotates in a remaining portion of the combustion chamber adjacent the intake port about an intake fluid vortex axis extending substantially in the direction of reciprocation of the piston within the combustion chamber. Fuel is directly injected into the air in the combustion chamber by way of fuel injector 29a. It has been discovered that by inducting the exhaust gas and the air during the intake stroke into the combustion chamber 19 such that there is minimal mixing between the exhaust residual and the air-fuel mixture created when fuel is injected into the air, spark ignition combustion quality and reliability can be improved.

Preferably, there is no mixing between the exhaust residual and the air-fuel mixture, and the result of the intake stroke and the compression stroke is a swirling flow of exhaust gas (near 0% air-fuel mixture) in a first portion of the cylinder and a swirling homogeneous stoichiometric air-fuel mixture (near 0% exhaust) in the remaining portion of the cylinder before the end of the compression stroke.

[0061] An engine 10 or an engine 10A in accordance with the present invention is particularly useful in eliminating or minimizing mixing between the swirling exhaust gas and air-fuel mixture as the engine 10 and the engine 10A can create and maintain a stratified exhaust gas/air-fuel mixture wherein the exhaust gas and the air-fuel mixture rotate as separate vortices in the cylinder in the opposite direction and with substantially the same angular velocity. When the exhaust gas and the air-fuel mixture rotate in the opposite direction and with substantially the same angular velocity, there is minimal relative movement at the exhaust gas/air-fuel interface and therefore, there is minimal mixing between the exhaust gas and the air-fuel mixture. By creating and maintaining a stratified exhaust gas/air-fuel mixture wherein the exhaust gas and the air-fuel mixture rotate as separate vortices in the cylinder in the opposite direction and with substantially the same angular velocity, the engine design assures that at the moment of spark ignition, a swirling flow of exhaust gas (near 0% air-fuel mixture) exists in a first portion of the cylinder and a swirling homogeneous stoichiometric air-fuel mixture (near 0% exhaust) exists in the remaining portion of the cylinder near the spark plug.

[0062] By incorporating an engine load sensor or other sensors from which an engine load value can be derived, an intake air mass flow rate sensor, an engine exhaust temperature sensor, an exhaust manifold absolute pressure sensor, a controller responsive to these sensors, and a variable lift and timing valve system into the engine 10 or the engine 10A, it is possible to precisely control the engine load and corresponding EGR rate and create and maintain a stratified exhaust gas/air-fuel mixture wherein the exhaust gas and the air-fuel mixture rotate in separate vortices in opposite directions with substantially the same angular velocity thereby minimizing mixing between the exhaust gas and the air-fuel mixture. The engine load sensor or other sensors from which an engine load value can be derived provide a signal that is used to control the fuel injector and the exact amount of air and exhaust gas residual entering the combustion chamber. The intake air mass flow rate sensor, the engine exhaust temperature sensor, and the exhaust manifold absolute pressure sensor also provide signals that are used the control the amount of air and exhaust gas residual entering the combustion chamber 19. It has been discovered that it is preferable to open the intake valve 20 and the exhaust valve 24 at the same time and for the same duration in order to create the stratified exhaust gas/air-fuel mixture described above.

[0063] Therefore, by: (1) providing the intake port 18 and the exhaust port 22 with a flow motion generating device and optionally, an associated flow direction control device; (2) measuring or deriving engine load, intake air mass flow rate, engine exhaust temperature, and engine exhaust manifold absolute pressure, (3) using the variable timing feature of the variable lift and timing valve system to open and close the intake valve 20 and the exhaust valve 24 at substantially the same time during the intake stroke, and (4) using the variable lift feature of the variable lift and timing valve system to allow variable amounts of air or air-fuel and exhaust gas to flow through the intake port 18 and the exhaust port 22 respectively into the combustion chamber 19 when the intake valve 20 and the exhaust valve 24 are open, it is possible to create a stratified exhaust gas/air-fuel mixture wherein the exhaust gas and the air-fuel mixture rotate in separate vortices in opposite directions with substantially the same angular velocity.

[0064] An engine in accordance with the present invention has many advantages.

For example, (1) the recirculated exhaust gas effectively reduces the volume of the combustion chamber and thereby reduces the amount of fuel/air required as no extra power is required to offset pumping losses ; (2) the smaller mass of air/fuel mixture in the cylinder during part load operation and the adjacent uncombusted exhaust gas lower the peak temperature of combustion thereby reducing NOx emissions; (3) engine efficiency is improved because the exhaust residual resides along a portion of the inner wall of the cylinder thereby decreasing heat transfer from the combustion chamber; (4) in one version of the invention, stable combustion can be achieved with mixtures of very high overall dilution by arranging for the air-fuel mixture drawn in through the intake port 18 to be stoichiometric while drawing in exhaust gas residual from the exhaust port 22; (5) in another version of the invention, stable combustion can be achieved with mixtures of very high overall dilution by drawing in air through the intake port 18 and directly injecting fuel into the air in the cylinder such that a stoichiometric air-fuel mixture is formed while drawing in exhaust gas residual from the exhaust port 22; (6) by maintaining precise control of the motion of the stratified exhaust gas residual/air-fuel mixture during intake and compression, a stoichiometric air-fuel mixture resides near the spark plug during ignition thereby achieving near complete combustion; (7) by filling the combustion chamber with an air/fuel mixture and uncombusted exhaust gas, pumping losses are minimized; (8) because of the stoichiometric operation of the engine, conventional three-way catalysts can be used for emission control ; and (9) the air-fuel mixture in the present invention provides more reliable combustion than a homogeneous exhaust/air/fuel mixture thereby allowing for more EGR.

[0065] Although the present invention has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.