The present invention relates to an engine exhaust gas diverter and a method of operating such a diverter. In particular, the invention relates to an exhaust gas diverter, suitable for use in a combustion engine exhaust after-treatment system, which alternately obstructs the exhaust stream from flowing into one of two outlet ports, and a method of actuating the diverter. The engine can be part of a vehicular or non-vehicular system. The gas diverter can be useful in other fields and applications.
Lean NOx Trap (LNT) exhaust after-treatment systems reduce nitrogen oxide (NOx) exhaust emissions from lean burn combustion engines such as diesel engines. LNTs comprise catalysts and adsorbents and work by adsorbing and storing NOx during normal lean (excess oxygen) exhaust stream conditions while releasing and converting NOx into benign constituents during rich (oxygen deficient) exhaust stream conditions. The capacity of the adsorbents to adsorb and store NOx is limited. Other contaminants in the exhaust stream such as sulfur (S) may also be adsorbed, further contributing to the reduction in capacity. However the capacity can be regenerated by inducing a rich exhaust stream condition for example, the introduction of a hydrogen- and/or carbon monoxide-containing gas mixture and at elevated temperatures, for example, 350° to 500° C.
a is a simplified illustration of a LNT configuration where at least the majority of the engine exhaust stream continuously passes through a single LNT during engine operation. In
b and 1c illustrate a multiple leg LNT configuration comprising two LNTs arranged in parallel with an exhaust gas diverter.
Engine systems and components are designed to comply with various constraints, for example, product cost, operating cost, weight, volume, and durability. Components that handle engine exhaust streams are subjected to severe operating conditions which should be taken into consideration. Some of these challenging operating conditions include the presence of particulates and contaminants in the exhaust stream; a wide operating temperature range, for example, −40° to +500° C.; high temperatures; thermal cycling; thermal gradients; low exhaust stream pressures; vibration; and a corrosive environment. Degradation of materials as a result of prolonged exposure to such conditions can diminish diverter performance significantly, ultimately leading to diverter failure and in some cases system failure. Additional requirements of an exhaust gas diverter may include a need or desire for low internal leak rates, low external leak rates, low pressure loss across the diverter, fast cycle times, high cycle quantities, rapid thermal cycling, minimal maintenance and operation without the use of lubricants.
Many valve designs are unsuitable for automotive or other mobile applications due to excessive size, prohibitive cost, slow response and the required actuation force. Several valve designs have been used for various engine exhaust applications. These include butterfly, ball, poppet, gate and flapper type valves. Each valve design poses specific challenges for the exhaust gas diverter application. A disadvantage of the butterfly design is the high internal leak rates across the valve due to the clearances required between the valve plate and the internal sealing surfaces that are needed to accommodate thermal expansion. A disadvantage of the ball design is the size, weight and cost. A disadvantage of the poppet design is the high pressure drop across the valve, or large valve size required, as the poppet remains in the direct path of the exhaust gas stream acting as a restrictor. A disadvantage of the gate design is the high internal leak rates due to the clearances required for thermal expansion and actuation. A disadvantage of conventional flapper designs is also the high internal leak rates.
In certain embodiments a gas diverter comprises at least one port circumscribed by a port seat, and a valve sub-assembly for selectively obstructing the port. The valve sub-assembly comprises an actuation arm, a disk coupled to the arm, and an actuator for selectively causing the disk to be urged against the port seat to obstruct the port. The gas diverter is constructed so that the disk deforms elastically as it is urged against the port seat.
In more specific embodiments a gas diverter comprises an inlet port, and a first outlet port, circumscribed by a first port seat, and a second outlet port, circumscribed by a second port seat. The gas diverter further comprises a valve sub-assembly for selectively obstructing the first and second outlet ports. The valve subassembly comprises a pivotable arm and first and second disks coupled to the arm. An actuator causes the arm to pivot, such that in a first position the first disk is urged against the first outlet port seat to obstruct the first outlet port, and in a second position the second disk is urged against the second outlet port seat to obstruct the second outlet port. The gas diverter is constructed so that the first and second disks deform elastically during the obstruction of the outlet ports.
The first and second disks are preferably not parallel to each other and are oriented at less than a 90° angle to one another. The first and second outlet ports can be arranged side-by-side in substantially the same plane as one another. The first and second outlet ports can be arranged so that the plane of the first port seat is at an angle of 160°-180° to the plane of the second port seat, and/or so that the planes of the first and second port seats extend through the pivot axis of the pivotable arm.
In the above embodiments, the disk can be coupled to the arm via a rod. Preferably the rod is resilient and also elastically deforms during actuation of the valve sub-assembly. Preferably the port seat is essentially rigid. The actuation force for urging the disk toward the port seat respectively is preferably applied substantially perpendicularly to the plane of the port seat.
The above-described gas diverters are particularly suitable as engine exhaust gas diverters wherein they are connected to receive exhaust gas from an internal combustion engine. An engine system can comprise such a gas diverter. In an engine system comprising an exhaust after-treatment system that includes at least two exhaust after treatment devices, the gas diverter can be used to direct at least a portion of an exhaust stream from the engine selectively to the at least two devices.
In a preferred method of operating the above described gas diverters, the actuator causes the disk to decelerate as it approaches the port seat to obstruct the port, during operating of the valve subassembly.
a is an illustration of a single lean NOx trap exhaust after-treatment system.
b is an illustration of a dual lean NOx trap exhaust after-treatment system illustrating an exhaust gas diverter directing an engine exhaust gas stream through an outlet port and lean NOx trap.
c is an illustration of a dual lean NOx trap exhaust after-treatment system illustrating an exhaust gas diverter directing an engine exhaust gas stream through the alternate outlet port and lean NOx trap as illustrated in
a is a transparent illustration of an exhaust gas diverter actuated to direct a gas stream through a first outlet port.
b is a transparent illustration of the exhaust gas diverter of
a-c are described in the Background section above.
a and 2b are transparent views of a preferred embodiment of an exhaust gas diverter 200 comprising inlet port 201, duct 202, plate 210, first outlet port 211, second outlet port 212, shaft 221, arm 222, first rod 223 and first disk 225, second rod 224 and second disk 226.
a and 2b illustrate the same exhaust gas diverter actuated to alternately obstruct one of two outlet ports, 211 and 212.
In
In
In
In
In a preferred embodiment arm 222, and the outlet ports 211 and 212 are designed with a high degree of stiffness, with minimal deformation occurring along the axis of the port, while rod 223, rod 224, disk 225 and disk 226 are designed to elastically deform under designed operating conditions as the valve sub-assembly is actuated against the port seats. A certain degree of elastic deformation of the rods and disks helps to provide a more uniform circumferential contact between the disk and port seat allowing for increased tolerance in the relative location of the valve sub-assembly and the port seats. For example, the elasticity of the rod and disk can be about 50-300 lbf/in (pounds force per inch) where the force is applied through the axis of the rod with the disk seated against the port and the deflection is measured as a differential displacement between opposing edges of the disk.
In a preferred embodiment, first and second disks 225 and 226 are circular, and comprise an essentially convex-concave cross-sectional profile (one face substantially convex, while the opposing face is substantially concave), with the convex face seating against the port seats of outlet ports 211 and 212 respectively. A circular disk with a convex-concave profile offers several advantages, for example; increased stiffness and reduced buckling due to thermal gradients and thermal cycling. The disks are preferably manufactured from a light gauge material that can withstand the high temperatures typical in the exhaust gas applications. For example, 22 gauge stainless steel sheet has been used, but stainless steel in the range of 18-28 gauge will typically also be suitable. A light gauge material offers several advantages for example:
In the embodiment of
The pair of outlet ports can be arranged so that the port seats are roughly in the same plane (that is, so that the axes of the two outlet ports are substantially parallel), or the ports can be arranged at an angle to one another (for example, down to 90° or even less). In many applications it is desirable to have the outlet ports side-by-side in roughly the same plane. However, with a valve sub-assembly of the type described in
The actuation profile can be different from the one shown in
Aspects of the present approach can be employed in gas diverters with one, two or more outlet ports, and with one, two or more inlet ports. In some applications, the gas diverter can be orientated with a reversed gas stream flow, for example, so that as illustrated in
As discussed above, preferably the disk is actuated axially in relation to the port. In alternative, but generally less preferred embodiments of the diverter, the disk can be oriented with the concave side of the disk contacting the port the port can have a seat on the outside perimeter of the port and/or the seat profile can be straight.
In some applications it is important that the disk forms a tight seal against the port seat so that gas leak rate across the closed disk is minimal or insignificant. In other applications, a small amount of leakage can be tolerated, and in some applications the diverter can be designed to deliberately allow a certain amount of gas leakage through the obstructed port. In some applications, the disks can be actuated to one or more intermediate positions in addition to the fully open or closed positions. When the disk is actuated to an intermediate position, the disk can function to partially obstruct a port therefore restricting or modulating the flow of the engine exhaust stream through the port.
Alternative ways to actuate the valve sub-assembly can be employed. The actuator can provide a linear or rotary motion. The actuator can be coupled to the shaft by various mechanisms, for example, directly coupled or coupled through mechanical linkages, levers and/or cams. The actuator can be powered in different ways; for example, pneumatic, electrical, hydraulic and/or mechanical means. Sensors can be employed to detect and control open, closed and intermediate positions of actuator and/or valve sub-assembly utilizing an open and/or closed loop control protocols. Examples of alternative actuators include stepper motors, multi-position pneumatics and proportional pneumatics.
The diverter duct or interior of the diverter body can be shaped and/or comprise vanes to reduce turbulence and pressure drop across the diverter and/or to evenly distribute the gas stream into the outlet ports.
The gas diverter designs and the actuation methods described herein are particularly suited for directing engine exhaust gas within an exhaust after-treatment system. The exhaust after-treatment system can comprise various after-treatment devices and/or after-treatment device combinations for example, lean NOx traps, selective catalytic reduction (SCR), oxidation catalysts and particulate filters. Embodiments of the present designs and methods could also be employed in other engine exhaust gas applications, for example, in exhaust gas recirculation (EGR), and/or for selective bypass of a muffler, heat exchanger or other device in the engine exhaust system. The engine can be part of a vehicular or non-vehicular system. In such systems, the combustion engine can be fueled by diesel, gasoline, kerosene, natural gas, liquid propane gas (LPG), hydrogen or other similar fuels.
Furthermore, although they were developed to specifically to address some of the shortcomings of existing exhaust gas flow diverter technology, the diverter designs and actuation methods described herein could be employed for other gases besides engine exhaust gas, and in other applications. One such potential application is to regulate air flow in regenerative thermal oxidizer systems.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.
The present application is related to and claims priority benefits from U.S. Provisional Patent Application Ser. No. 60/945,342, entitled “Exhaust Gas Diverter”, filed on Jun. 20, 2007. The present application is also related to and claims priority benefits from U.S. patent application Ser. No. 11/676,499, entitled “Combustion Engine Exhaust After-treatment System Incorporating Syngas Generator”, filed on Feb. 19, 2007. The '342 and '499 applications are each hereby incorporated by reference in their entirety.
Number | Date | Country | |
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60945342 | Jun 2007 | US |