Patent Application
20070107706
The present invention relates to a system for controlling the mixture of an inlet air flow and an exhaust gas return flow in an engine. More specifically, the invention relates to a system for controlling the quantity of each flow and the ratio of one flow to the other.
It is generally recognized that the production of noxious oxides of nitrogen (NOx), which pollute the atmosphere, are undesirable and, in many cases, are controlled by limits established by local, state and federal governmental regulations. The formation of NOx constituents in the exhaust gas products of an internal combustion engine must therefore be eliminated, minimized, or at least maintained below some threshold limit or level.
It is generally understood that the presence of NOx in the exhaust of internal combustion engines is determined by combustion temperature and pressure as well as by the air/fuel ratio (lambda). An increase in combustion temperature causes an increase in the amount of NOx present in the engine exhaust. Therefore, it is desirable to control the combustion temperature in order to limit the amount of NOx present in the exhaust of an internal combustion engine.
One method suggested by the prior art for limiting or controlling the combustion temperature has been to recirculate a portion of the exhaust gas back to the engine air intake. It was reasoned in these early methods that since the exhaust gas is low in oxygen, this will result in a dilute combustion mixture which will burn at a lower temperature. The lower combustion temperature, it was reasoned, would, in turn, reduce the amounts of NOx produced during combustion.
Also, it had, until recently, been common practice to run an internal combustion engine at or near an ignition timing that produces peak combustion pressures, which maximize combustion efficiency. However, unacceptably high levels of NOx may be produced in the combustion chambers when the engine operates at or near such conditions. Therefore, in order to inhibit the formation and emission of NOx, it is necessary to limit the peak combustion pressure to a threshold value.
One technique suggested by the prior art for limiting combustion pressure involves the recirculation of exhaust gases through the induction passage of the combustion chamber since it is well-known that an increase in recirculation of exhaust gases will reduce peak combustion pressure, and thus, the attendant levels of undesirable NOx.
Therefore, it has become generally well-known that the formation of undesirable oxides of nitrogen may be reduced by recirculating a portion of the exhaust gas back to the engine air/fuel intake passage so as to dilute the incoming air/fuel mixture with inert H2O, and CO2. The molar specific heat of these gases, and especially of CO2, absorbs substantial thermal energy so as to lower peak cycle temperatures and/or pressures to levels conducive to reducing NOx formation.
While NOx formation is known to decrease as the exhaust gas recirculation (EGR) flow increases to where it represents a threshold percentage of the exhaust gas constituents, it is also known that this is accompanied by a deterioration in engine performance including, but not limited to, an increase in engine roughness with increasing EGR. Therefore, one factor limiting the magnitude of EGR is the magnitude of EGR-induced performance deterioration or roughness that can be tolerated before vehicle drivability becomes unacceptable.
Accordingly, various systems have been suggested to control the amount of exhaust gas flowing through the system, such as those disclosed in U.S. Pat. No. 5,333,456 to Bollinger and U.S. Pat. No. 6,502,397 to Lundqvist. These systems uses valves or sleeves to partially block the flow of exhaust gas before it mixes with inlet air, thereby controlling the amount of exhaust gas versus inlet air existing in the resultant mixture.
However, these arrangements result in a number of disadvantages. One problem with these devices is that they require extra components in addition to the standard piping for the inlet air and exhaust gas flows that, in addition to increasing the cost and difficulty of manufacture and assembly, requires additional space in the vehicle. Moreover, the specific components employed and the arrangement thereof do not facilitate as efficient of a mixing of the two gas flows as is possible. Additionally, the particular arrangements of these parts result in systems that are less accurate than desirable in obtaining both precise amounts of both gas flows and a precise ratio between the two different flows. Finally, such systems are unable to completely terminate the flow for whichever of the gas flows it may be desired to do so.
What is desired, therefore, is a system for controlling the mixture of inlet air and recirculating exhaust gas that optimizes the mixing efficiency of the two flows. What is further desired is a system for controlling the mixture of inlet air and recirculating exhaust gas that does not require additional components connecting to the existing piping requiring excess additional cost and space. What is also desired is a system for controlling the mixture of inlet air and recirculating exhaust gas that can precisely control the ratio of inlet air versus exhaust gas, including the complete termination of whichever gas flow may be required.
Accordingly, it is an object of the present invention to provide a system for controlling the mixture of inlet air and recirculating exhaust gas that minimizes pressure losses when mixing the two gas flows.
It is a further object of the present invention to provide a system for controlling the mixture of inlet air and recirculating exhaust gas that minimizes the amount of external components added to the main piping for the gas flows.
It is yet another object of the present invention to provide a system for controlling the mixture of inlet air and recirculating exhaust gas that can accurately and precisely control the ratio of inlet air versus exhaust gas being mixed together and communicated through the system.
It is another object of the present invention to provide a system for controlling the mixture of inlet air and recirculating exhaust gas that can accurately and precisely control the amounts of inlet air and exhaust gas being communicated through the system.
It is still another object of the present invention to provide a system for controlling the mixture of inlet air and recirculating exhaust gas that can terminate the flow of whichever gas may be required.
In order to overcome the deficiencies of the prior art and to achieve at least some of the objects and advantages listed, the invention comprises a system for controlling the mixture of air and recirculating exhaust gas, including an air conduit defined by a wall for communicating air therethrough, an exhaust gas inlet passing through the wall of the air conduit for introducing exhaust gas into the air conduit, and a sleeve at least partly disposed in the air conduit, the sleeve having an inlet end through which air enters the sleeve and an outlet end through which air flowing through the sleeve exits the sleeve into the air conduit, the outlet end of the sleeve being disposed in the air conduit, wherein the outlet end of the sleeve is positionable along the air conduit to at least partly occlude the exhaust gas inlet and is movable along a portion of the air conduit to vary the extent of occlusion of the exhaust gas inlet in order to regulate flow of exhaust gas into the air conduit.
In another embodiment, the invention comprises a system for controlling the mixture of air and recirculating exhaust gas, including an air conduit defined by a wall for communicating air therethrough, an exhaust gas inlet for introducing exhaust gas into the air conduit, and a sleeve at least partly disposed in the air conduit, the sleeve having an inlet end through which air enters the sleeve and an outlet end through which air flowing through the sleeve exits the sleeve into the air conduit, the outlet end of the sleeve being disposed in the air conduit, wherein the cross-sectional area of the outlet end of the sleeve is reduced, and wherein the outlet end of the sleeve is positionable along the air conduit to at least partly occlude the exhaust gas inlet and is movable along the air conduit to vary the extent of occlusion of the exhaust gas inlet in order to regulate flow of exhaust gas into the air conduit.
In yet another embodiment, the invention comprises a system for controlling the mixture of air and recirculating exhaust gas, including an air conduit defined by a wall for communicating air therethrough, an exhaust gas inlet for introducing exhaust gas into the air conduit, and a sleeve at least partly disposed in the air conduit, the sleeve having an inlet end through which air enters the sleeve and an outlet end through which air flowing through the sleeve exits the sleeve into the air conduit, the outlet end of the sleeve being disposed in the air conduit, wherein the outlet end of the sleeve is positionable along the air conduit to at least partly occlude the exhaust gas inlet, the sleeve is movable along the air conduit to vary the extent of occlusion of the exhaust gas inlet in order to regulate flow of exhaust gas into the air conduit, and the sleeve is positionable to fully occlude the exhaust gas inlet in order to prevent flow of exhaust gas into the air conduit.
In still another embodiment, the invention comprises a system for controlling the mixture of air and recirculating exhaust gas, including an air conduit defined by a wall for communicating air therethrough, an exhaust gas inlet for introducing exhaust gas into the air conduit, and a sleeve at least partly disposed in the air conduit, the sleeve having an inlet end through which air enters the sleeve and an outlet end through which air flowing through the sleeve exits the sleeve into the air conduit, the outlet end of the sleeve being disposed in the air conduit, and a streamlined body disposed in the air conduit, wherein the outlet end of the sleeve is positionable along the air conduit to at least partly occlude the exhaust gas inlet and is movable along the air conduit to vary the extent of occlusion of the exhaust gas inlet in order to regulate flow of exhaust gas into the air conduit.
In some of these embodiments, the outlet end of the sleeve is tapered, and has, for example, a frustoconical shape.
In certain embodiments, the cross-sectional area of at least part of the portion of the air conduit in which the outlet end of the sleeve moves is reduced. In some of these embodiments, the reduced part of the air conduit is tapered.
In certain embodiments, a portion of the wall of the air conduit is threaded, and the sleeve has a corresponding threaded surface for engaging this portion of the wall.
The basic components of one embodiment of a system for controlling the mixture of inlet air and recirculating exhaust gas in accordance with the invention are illustrated in
The system 10 includes an air conduit 22 defined by a wall 23, through which inlet air is communicated to an engine (not shown). An exhaust gas inlet 30 passes through the wall 23, through which recirculating exhaust gas is introduced from an exhaust gas conduit 24 into the air conduit 22 (indicated by arrows B).
A sleeve 70, through which the inlet air flows, has an inlet end 66 and an outlet end 68, and at least the outlet end 68 is positioned within the conduit wall 23. Accordingly, inlet air enters the sleeve 70 via inlet end 66, flows through the sleeve 70, and exits the sleeve 70 via outlet end 68 (indicated by arrows A). The sleeve 70 can be positioned such that the outlet end 68 at least partially occludes the inlet 30, thereby decreasing the flow of exhaust gas into the air conduit 22. At least a portion of the sleeve 70 can be displaced longitudinally along the air conduit 22 to alter the extent to which the outlet end 68 occludes the inlet 30, allowing the introduction of exhaust gas into the air conduit 22 to be regulated.
In certain advantageous embodiments, a portion of the sleeve 70 has a threaded outer surface 71, and a portion of the conduit wall 23 has a corresponding, threaded inner surface 72 for engaging the threaded sleeve surface 71. As a result, the outlet end 68 can be displaced along the air conduit 22 by simply rotating the sleeve 70. In this way, the flow of exhaust gas into the conduit 22 can be accurately and precisely controlled. In certain advantageous embodiments, the sleeve 70 and the conduit 22 are coaxial.
Various drive mechanisms may be employed to drive the sleeve 70 back and forth through the air conduit 22. For example, as shown in
In certain advantageous embodiments, the cross-sectional area of the outlet end 68 is smaller than the cross-sectional area of the inlet end 66, such that some throttling of the inlet air flowing through the sleeve 70 occurs in this reduced portion. In certain embodiments, this reduced portion is simply a necked portion of the sleeve 70, and in some embodiments, it comprises a tapered section 74, which, for example, may have a frustoconical shape. Likewise, in some embodiments, the cross-sectional area of a portion of the conduit 22 in which the outer end 68 of the sleeve 70 moves is also reduced, providing a similar throttling effect. In some embodiments, this reduced section is necked or tapered, resulting in a venturi 54.
When the sleeve 70 is rotated longitudinally in the direction of the venturi 54, the annular, tapered section 74 of the sleeve 70 approaches the annular, tapered wall of the venturi 54. In this way, the sleeve 70, in conjunction with the venturi 54, acts as a flow regulator for the exhaust gas entering the conduit 22 and mixing with the inlet air. The tapered section 74 of the sleeve 70 is designed with a cross-sectional area that decreases towards the tip of the outlet end 68. Similarly, the venturi 54 has a cross-sectional area that decreases in the direction of flow of the conduit 22. Furthermore, this reduction in the cross-sectional area of the venturi 54 is greater than the reduction in the cross-sectional area of the outlet end 68. Because of this arrangement, as the sleeve 70 is rotated in the direction of the flow through the conduit 22, the inlet 30 becomes smaller, restricting the amount of exhaust gas that is communicated into the air conduit 22.
Moreover, as the size of the inlet 30 changes in accordance with the movement of the outlet end 68 of the sleeve 70, the point of entry of the exhaust gas into the flow of inlet air likewise changes. Accordingly, the greatest throttling of the inlet air flowing through the air conduit 22 (i.e., passing through the outlet end 68 of the sleeve 70) is always achieved at the point at which the exhaust gas enters the conduit 22, independently of the position of the sleeve 70.
In some embodiments, a streamlined body 90 is disposed in the conduit 22 that may be positioned to at least partly occlude the outlet end 68 of the sleeve 70. Accordingly, in addition to the reduction resulting from the tapered section 74, further throttling of the inlet air flowing through the conduit 22 can be achieved by limiting the amount of air exiting the sleeve 70 by employing the streamlined body 90. In certain advantageous embodiments, the streamlined body 90 has a tapered end 91, which may, for example, be ovoid in shape. Due to this shape of the tapered end 91, the space between the perimeter of the outlet end 68 and the body 90 may be decreased and increased by moving the sleeve 70 forward and backward along the conduit 22.
In some embodiments, the streamlined body 90 is fixed to the conduit 22 such that it remains stationary with respect to the conduit 22. Accordingly, the flow of fresh air through the conduit 22 can be controlled by moving the sleeve 70 back and forth over the end of the body 90 to partly occlude, and vary the extent of occlusion of, the outlet end 68 of the sleeve 70. In this way, the flow of fresh air through the conduit 22 can be rapidly increased with minimal movement of the sleeve 70 due to the sharp curve of the body 90.
In other embodiments, an actuator 92 in provided for displacing the streamlined body 90 backwards and forwards along the conduit 22, causing the tapered end 91 to move back and forth through the outlet end 68. In this way, the flow of inlet air through the conduit 22 can be altered independently of the alteration of the recirculating exhaust gas flow. The actuator 92 may be located outside of the conduit 22 and connected to the body 90, or may located within the streamlined body 90 itself, as is further described below.
With this arrangement, in addition to generally providing desirable mixing and pumping effects, the sleeve 70 can be used to control the speed of the recirculating exhaust gas, while the body 90 can be used to control the speed of the inlet air, and relative speed between the two can be controlled by coordinating the movement of the two. Furthermore, in certain embodiments, the sleeve 70 may be advanced far enough along the conduit 22 such that the flow of exhaust gas into the conduit 22 is completely shut off. Refering to
In some embodiments, the streamlined body 90 is disposed in the conduit 22 such that the maximum diameter of the body 90 is located downstream of the sleeve 70, and the body 90 is positioned substantially outside of the sleeve 70, as shown in
Another embodiment of the system 10 is illustrated in
In this particular embodiment, the system 10 includes a first pipe section 120, a supply part 124, and a second pipe section 122, through which inlet air flows (indicated by arrows C). Recirculating exhaust gas is introduced into the flow of inlet air via the supply part 124, which creates an inlet 130 for this flow (indicated by arrows D).
In certain advantageous embodiments, the supply part 124 includes two parts 140, 142, which are inserted between two flanges 144,146 of the two pipe sections 120,122, respectively. However, in other embodiments, the supply part 124 is a single, integral piece having a single, radial opening or a plurality of openings arranged in an annular fashion. Moreover, in some embodiments, the supply part 124 is separate from the pipe sections 120, 122, while in other embodiments, the supply part 124 is integrally formed with the piping 120, 122.
This arrangement results in a radial gap 152, through which the exhaust gas is communicated from the supply part 124 to the pipe section 122. In certain advantageous embodiments, the system includes a venturi part 154, such that a portion of the inner, annular wall of the piping 122 adjacent to the gap 152 is tapered, thereby extending the essentially planar gap 152 into an essentially frustoconical opening. A continuous, cylindrical cavity 156 exists around the gap 152, and a gasket 158 is placed between the two parts 140,142. Accordingly, a desired distance for the gap 152 can be achieved by selecting the thickness of the gasket 158. A supply pipe (not shown) for the EGR supply flow can be mounted to an inlet port 160 of the supply part 124 to deliver the exhaust gases of the engine to the system 10.
A sleeve 170, as previously described, is moveably disposed fully within the pipe section 120. The sleeve 170 has a threaded outer surface 171 for engaging a threaded inner surface 172 of the pipe section 120, thereby enabling the sleeve 170 to be precisely displaced longitudinally therealong, and the sleeve 170 has a tapered end for throttling the inlet air flowing through the sleeve 170.
As illustrated in
As noted above and shown in
For example, as shown in
As shown in
In operation, the inlet air is typically cooled in the conventional manner downstream of a turbocharger by an intercooler (not shown), and the recirculated exhaust gases are cooled in the same way via a separate EGR cooler before being mixed with the inlet air flow. The above-described system for regulating flow can be placed at any location downstream of the turbocharger. However, in certain advantageous embodiments, the flow regulator is preferably located downstream of the intercooler to prevent the latter from becoming contaminated with soot or being corroded by the acidic exhaust gases.
It should be understood that the foregoing is illustrative and not limiting, and that obvious modifications may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, reference should be made primarily to the accompanying claims, rather than the foregoing specification, to determine the scope of the invention.
