US20080314037A1

US20080314037A1 - Exhaust Gas Diverter

Info

Publication number: US20080314037A1
Application number: US12/033,620
Authority: US
Inventors: Jacobus Neels; Orlando Christopher Janzen
Original assignee: Individual
Current assignee: Westport Power Inc
Priority date: 2007-06-20
Filing date: 2008-02-19
Publication date: 2008-12-25
Also published as: WO2008101336A1

Abstract

A gas diverter includes at least one port circumscribed by a port seat, and a valve subassembly for selectively obstructing the port. The valve subassembly comprises: (a) an actuation arm; (b) a disk coupled to the arm, and (c) an actuator for selectively causing the disk to be urged against said port seat to obstruct said port. In operation, the disk deforms elastically as it is urged against the port seat.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

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.

FIELD OF THE INVENTION

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.

BACKGROUND OF THE INVENTION

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.
FIG. 1 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 FIG. 1 a, engine 1 produces an exhaust stream which flows via exhaust conduit 2 into LNT 3, and exits into the atmosphere via conduit 4. To create the rich exhaust stream condition for regeneration of the LNT, a reducing agent can be introduced into the engine exhaust stream prior to the LNT 3. The primary disadvantage of this configuration is that a substantial amount of reducing agent is required to create sufficiently rich exhaust stream conditions because of the high engine exhaust stream flow rates. This leads to an undesirably high operating cost.
FIGS. 1 b and 1 c illustrate a multiple leg LNT configuration comprising two LNTs arranged in parallel with an exhaust gas diverter. FIGS. 1 b and 1 c represent the same engine and exhaust after-treatment system, however, FIG. 1 b illustrates the exhaust gas diverter actuated to obstruct the exhaust stream flow from flowing through a first outlet port, while FIG. 1 c illustrates the exhaust gas diverter actuated to obstruct the exhaust stream flow from flowing through a second outlet port. The exhaust gas diverter periodically and alternatively directs the exhaust gas stream via an outlet port into each of the two LNTs. In FIG. 1 b, engine 11 produces an exhaust stream which flows via exhaust conduit 12 and into exhaust gas diverter 13. Exhaust gas diverter 13, is actuated to direct the engine exhaust stream through LNT 14, trapping NOx from the exhaust stream, and from there via conduit 16 to exit into the atmosphere. Exhaust gas diverter 13 at the same time obstructs or prevents the exhaust stream from flowing into LNT 15, reducing the amount of exhaust gas, more particularly the oxygen (O₂), from diluting and reacting with the reducing agent that is introduced into LNT 15 during the regeneration process. This reduces the amount of reducing agent required for regeneration and thereby reduces the operating cost compared to a single LNT configuration. Before LNT 14 reaches its adsorbing capacity, the exhaust gas diverter 13 is actuated to redirect the exhaust stream flow into LNT 15, and at the same to obstruct or prevent the exhaust stream from flowing into LNT 14, allowing LNT 14 to be regenerated. This is illustrated in FIG. 1 c where engine 11 produces exhaust stream which flows via exhaust conduit 12 and into exhaust gas diverter 13. Exhaust gas diverter 13, is actuated to direct the engine exhaust stream through LNT 15, trapping NOx from the exhaust stream, and then to exit into the atmosphere via conduit 16. Exhaust gas diverter 13 obstructs the exhaust stream from flowing into LNT 14, while a reducing agent is introduced into LNT 14 during the regeneration process. The LNTs are switched between the adsorbing and regenerating modes in part by actuating the exhaust gas diverter which is typically controlled by a controller, various sensors and associated software.
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.

SUMMARY OF THE INVENTION

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.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 a is an illustration of a single lean NOx trap exhaust after-treatment system.

FIG. 1 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.

FIG. 1 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 FIG. 1 b.

FIG. 2 a is a transparent illustration of an exhaust gas diverter actuated to direct a gas stream through a first outlet port.

FIG. 2 b is a transparent illustration of the exhaust gas diverter of FIG. 2 a, actuated to direct an exhaust gas stream through a second outlet port.

FIG. 3 is a cross-sectional illustration of a valve sub-assembly and a port seat of an exhaust gas diverter.

FIG. 4 is a graph illustrating an actuation velocity profile of a valve sub-assembly as it is actuated from an open to a closed position.

FIG. 5 is a cross-sectional illustration of a valve sub-assembly and a port seat that are part of an exhaust gas diverter, with an alternative configuration where the disk is linearly actuated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

FIGS. 1 a-c are described in the Background section above.
FIGS. 2 a and 2 b 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.
FIGS. 2 a and 2 b illustrate the same exhaust gas diverter actuated to alternately obstruct one of two outlet ports, 211 and 212. FIG. 2 a illustrates the diverter actuated with first disk 225 obstructing first outlet port 211 while FIG. 2 b illustrates the diverter actuated with second disk 226 obstructing second outlet port 212.
In FIGS. 2 a and 2 b, a main exhaust stream conduit (not shown) from the combustion engine is connected to inlet port 201 which is attached to the main body of the diverter which comprises duct 202 and plate 210. In one particular application, a lean NOx trap (not shown) can be connected to each of first outlet port 211 and second outlet port 212. The (dual) valve sub-assembly, which comprises arm 222, first rod 223 and associated disk 225, and second rod 224 and associated disk 226, is assembled in plate 210 to pivot with rotation of shaft 221.
In FIG. 2 a valve sub-assembly is positioned with first disk 225 obstructing first outlet port 211. The engine exhaust stream enters diverter 200 via inlet port 201, and flows via duct 202 to second outlet port 212, exiting into a lean NOx Trap (not shown in FIG. 2 a).
In FIG. 2 b, the valve sub-assembly is illustrated with second disk 226 obstructing second outlet port 212. Engine exhaust stream enters diverter 200 via inlet port 201, and flows via duct 202 to first outlet port 211, exiting into another lean NOx Trap (not shown in FIG. 2 b).
In FIGS. 2 a and 2 b, plate 210, comprise shaft bushings (not visible in FIGS. 2 a and 2 b), shaft seal (not visible in FIGS. 2 a and 2 b), shaft 221, and first and second outlet ports 211 and 212. One end of shaft 221 is located by a shaft bushing (not visible in FIGS. 2 a and 2 b) and sealed by a blind hole in plate 210. The opposite end of shaft 221 is also located by a shaft bushing (not visible in FIGS. 2 a and 2 b) sealed to the external atmosphere by a mechanical seal (not visible in FIGS. 2 a and 2 b), and attached to an actuator, for example, an external pneumatic linear actuator and linkage (both not shown in FIGS. 2 a and 2 b) which actuates and pivots shaft 221. The valve sub-assembly is located and actuated by shaft 221.
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:

- (a) low thermal mass, which increases the heat transfer rate, reducing thermal gradients and reducing thermal deformation during rapid thermal cycles;
- (b) lightweight, which reduces inertia and stress;
- (c) improved manufacturability, as use of a lighter gauge material can allow the disk to be fabricated by inexpensive non-machined processes, such as stamping or spinning;
- (d) low stiffness, which increases sealing performance due to disk conformance to the port seat.

FIG. 3 illustrates a cross-section of the valve sub-assembly and port seat (area where the disk comes into contact with the port). In a preferred embodiment, the cross-sectional profile of the port seat is substantially convex which, along with the convex profiled disk, provides essentially a narrow line contact between port 311 and disk 325 creating a high contact load. The convex-to-convex (disk to port seat) contact offers several advantages. For example, it can increase the location and manufacturing tolerances while maintaining the ability to achieve or exceed an ANSI Class IV sealing standard without the use of a grinding or lapping manufacturing process, it can assist in the displacement of particulates such as carbon or soot that can tend to accumulate around the port seat and disk, thereby providing some self-cleaning capability within the valve sub-assembly, and it can assist in reducing the pressure drop across a port when the port is in an open position.
In the embodiment of FIG. 3 the two outlet ports are side-by-side and slightly angled towards one another. In preferred embodiments of a diverter that has a pair of ports in this configuration, the theoretical port seat plane 331 is essentially perpendicular to the theoretical axis 332 of a first outlet port 311. Port seal plane 331 extends through the axis of shaft 321, upon or about which the valve subassembly pivots. This geometry is representative also of the second exhaust gas diverter outlet port (not shown in FIG. 3). Also as illustrated in FIG. 3, first and second disks 325 and 326 are configured by the arrangement of arm 322, and first and second rods 323 and 324, to be at an angle of less than 90° to one another, for example 60°. Both of these features provide the following advantages:

- (1) An actuation force that is essentially perpendicular to the planes of the port seats is applied, assisting in applying a more uniform force around the essentially circumferential contact area between the disk and port seat;
- (2) By choosing an appropriate angle, the non-sealing disk can be positioned to aid in directing the exhaust stream toward and into the open outlet port, when the sealing disk is seated against the other port;
- (3) By positioning the non-sealing disk to re-direct the exhaust stream as described in point 2 above, the exhaust stream can assist in increasing the sealing force between the sealing disk and port;
- (4) The travel distance of the valve sub-assembly between the pair of outlet ports is reduced. This can increase the response time of the diverter, and also decrease the stress on components and increase durability.

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 FIG. 2, even with a side-by-side port configuration, it is advantageous to angle the ports slightly toward one another, in relation to the inlet port (for example, so that the angle between the planes of the two port seats is less than 180°; say, for example 160-178°). This allows an actuation force that is essentially perpendicular to the planes of the port seats to be applied, while not adding significantly to the thickness of plate 310 and overall volume of the exhaust gas diverter. With this slightly angled arrangement, the pivot point for the valve sub-assembly (the axis of the shaft 321) can be recessed into the thickness of the plate, rather than protruding above the plate or being embedded in a thicker plate.
FIG. 4 is a graphical illustration of the actuation velocity over distance profile of an actuator, or in turn, of the valve sub-assembly. The graph represents the velocity of the valve sub-assembly, disk or actuator as one of the valves or disks moves from an open to a closed position, from port seat to port seat. In a preferred method, the actuation velocity of the valve sub-assembly is non-linear, and comprises a gradual deceleration at the end of travel (as one of the disk approaches one of the port seats). The gradual deceleration of the valve sub-assembly prior to the disk contacting the port seat offers advantages including, for example, reducing shock loads, increasing durability and reducing noise levels. If a pneumatic linear actuator is employed to actuate the diverter, a restrictor placed in the exhaust stream of the pneumatic linear actuator can be used to decelerate the actuation force of the actuator and the force of the exhaust stream pushing on the disk as it is nears the port. The desired degree of deceleration should be weighed against the desired response time or speed of open/close of the valve sub-assembly. An actuation method which comprises decreasing the velocity of the valve as it moves towards a closed position can offer advantages in conventional exhaust gas flow diverter designs with single, dual or multiple valves/ports, as well as in diverters of the type described herein.
The actuation profile can be different from the one shown in FIG. 4 and need not be symmetrical. The diverter can be actuated by different devices or mechanisms, for example, suitable options include: an electrical linear actuator, electrical motor with a mechanical linkage or cam assembly, pneumatic motor with a mechanical linkage or cam assembly, a hydraulic linear actuator or a hydraulic motor with a mechanical linkage or cam assembly.
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 FIG. 2 b inlet gas stream enters from either port 211 and port 212, with port 201 as the outlet port.
FIG. 5 is a cross-sectional illustration of a valve sub-assembly and a port seat that are part of an exhaust gas diverter. This embodiment illustrates an alternative configuration where the disk is linearly actuated (shown with the port in the open position). In FIG. 5, the engine exhaust stream enters assembly 500 through an inlet port (not shown in FIG. 5), flowing inside cavity or duct 530, through port 511 and exiting into conduit 512. In order to open port 511 (as shown in FIG. 5), linear actuator assembly 520 moves rod 521 and disk 522, along a theoretical port axis 510 away from port 511. In order to obstruct port 511 linear actuator assembly 520 moves rod 521 and disk 522, along a theoretical port axis 510, allowing disk 522 to come into contact with port 511.
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.

Claims

1. A gas diverter comprising at least one port circumscribed by a port seat, and a valve sub-assembly for selectively obstructing said port, said valve sub-assembly comprising:

(a) an actuation arm;

(b) a disk coupled to said arm;

(c) an actuator for selectively causing said disk to be urged against said port seat to obstruct said port;

wherein said disk deforms elastically as it is urged against said port seat.

2. The gas diverter of claim 1, wherein said disk is primarily convex in profile wherein the convex face of said disk contacts said port seat during obstruction of said port.

3. The gas diverter of claim 2, wherein port seat has a convex surface, whereby during obstruction of said port the convex surface of said disk is urged against said convex surface of said port seat.

4. The gas diverter of claim 1, wherein the actuation force for urging said disk toward said port seat respectively is applied substantially perpendicularly to the plane of said port seat.

5. The gas diverter of claim 1, wherein said port seat is essentially rigid.

6. The gas diverter of claim 1, wherein said disk is coupled to said arm via a rod.

7. The gas diverter of claim 6, wherein said rod is resilient and elastically deforms during actuation of said valve sub-assembly.

8. The gas diverter of claim 1, wherein said disk comprises stainless steel.

9. The gas diverter of claim 1, wherein said disk is made from 18-28 gauge stainless steel material.

10. The gas diverter of claim 1, wherein said disk is manufactured by a spinning process.

11. The gas diverter of claim 1, wherein said disk is manufactured by a stamping process.

12. The gas diverter of claim 1, wherein said actuator comprises a pneumatic linear actuator.

13. The gas diverter of claim 1, wherein said gas diverter is an engine exhaust gas diverter.

14. The gas diverter of claim 14, wherein said port is connected to receive exhaust gas from an internal combustion engine.

15. The gas diverter of claim 1, wherein the contact between said disk and said port seat is a line contact during obstruction of said port.

16. An engine system comprising a gas diverter, said gas diverter comprising at least one port circumscribed by a port seat, and a valve sub-assembly for selectively obstructing said port, said valve sub-assembly comprising:

(a) an actuation arm;

(b) a disk coupled to said arm;

wherein said disk deforms elastically as it is urged against said port seat.

17. A method of operating the gas diverter, said gas diverter comprising at least one port circumscribed by a port seat, and a valve sub-assembly for selectively obstructing said port, said valve sub-assembly comprising:

(a) an actuation arm;

(b) a disk coupled to said arm;

wherein said disk deforms elastically as it is urged against said port seat;

wherein during operating of said valve subassembly said actuator causes said disk to decelerate as it approaches said port seat to obstruct said port.

18. A gas diverter comprising:

(a) an inlet port;

(b) a first outlet port, circumscribed by a first port seat;

a second outlet port, circumscribed by a second port seat;

a valve sub-assembly for selectively obstructing said first and second outlet ports, said valve subassembly comprising:

(1) a pivotable arm;

(2) a first disk coupled to said arm;

(3) a second disk coupled to said arm;

an actuator for causing said arm to pivot, such that in a first position said first disk is urged against said first outlet port seat to obstruct said first outlet port, and in a second position said second disk is urged against said second outlet port seat to obstruct said second outlet port;

wherein said first and second disks deform elastically during said obstruction of said outlet ports.

19. The gas diverter of claim 18, wherein said first and second disks are primarily convex in profile wherein the convex face of said first disk contacts said first port seat during obstruction of said first outlet port and the convex face of said second disk contacts said second port seat during obstruction of said second outlet port.

20. The gas diverter of claim 19, wherein port seats have a convex surface, whereby in said first position the convex surface of said first disk is urged against the convex surface of said first port seat, and in said second position the convex surface of said second disk is urged against the convex surface of said second port seat.

21. The gas diverter of claim 18, wherein the actuation force for urging said first and second disks toward said first and second port seats respectively is applied substantially perpendicularly to the plane of said port seats.

22. The gas diverter of claim 18, wherein said first and second port seats are essentially rigid.

23. The gas diverter of claim 18, wherein said first disk is coupled to said arm via a first rod and said second disk is coupled to said arm via a second rod.

24. The gas diverter of claim 23, wherein said first and second rods are resilient and elastically deform during actuation of said valve sub-assembly.

25. The gas diverter of claim 18, wherein said first and second disks are not parallel to each other.

26. The gas diverter of claim 25, wherein said first and second disks are at less than a 90° angle to one another.

27. The gas diverter of claim 18, wherein said first and second outlet ports are arranged side-by-side in substantially the same plane as one another.

28. The gas diverter of claim 18, wherein said first and second outlet ports are arranged so that the plane of said first port seat is at an angle of 160-180° to the plane of said second port seat.

29. The gas diverter of claim 18, wherein the planes of said first and second port seats extend through the pivot axis of said pivotable arm.

30. The gas diverter of claim 18, wherein in said first position said second disk is pivoted away from said second outlet port providing a substantially unobstructed gas stream path through said second outlet port, and in said second position said first disk is pivoted away from said first outlet port providing a substantially unobstructed gas stream path through said first outlet port.

31. The gas diverter of claim 18, wherein said actuator selectively causes said arm to pivot, such that said first and second disks rest in at least one intermediate position between said first and second positions.

32. The gas diverter of claim 18, wherein said first and second disks comprise stainless steel.

33. The gas diverter of claim 18, wherein said first and second disks are made from 18-28 gauge stainless steel material.

34. The gas diverter of claim 18, wherein said first and second disks are manufactured by a spinning process.

35. The gas diverter of claim 18, wherein said first and second disks are manufactured by a stamping process.

36. The gas diverter of claim 18, wherein said actuator comprises a pneumatic linear actuator.

37. The gas diverter of claim 18, wherein the contact between said disk and said port seat is a line contact during obstruction of said port.

38. The gas diverter of claim 18, wherein said gas diverter is an engine exhaust gas diverter.

39. The gas diverter of claim 38, wherein said inlet port is connected to receive exhaust gas from an internal combustion engine.

40. An engine system comprising the gas diverter, said gas diverter comprising:

(a) an inlet port;

(b) a first outlet port, circumscribed by a first port seat;

a second outlet port, circumscribed by a second port seat;

(1) a pivotable arm;

(2) a first disk coupled to said arm;

(3) a second disk coupled to said arm;

41. The engine system of claim 40, wherein said engine system comprises an exhaust after-treatment system comprising at least two exhaust after treatment devices, and said gas diverter is for selectively directing at least a portion of an exhaust stream from said engine selectively to said at least two devices.

42. A method of operating the gas diverter, said gas diverter comprising:

(a) an inlet port;

(b) a first outlet port, circumscribed by a first port seat;

a second outlet port, circumscribed by a second port seat;

(1) a pivotable arm;

(2) a first disk coupled to said arm;

(3) a second disk coupled to said arm;

wherein said first and second disks deform elastically during said obstruction of said outlet ports;