Patent Application
20060283173
A problem relating to catalytic converters for internal combustion engines, such as the prior art reversing flow catalytic converter for internal combustion engines disclosed in U.S. Pat. No. 6,148,613, is overheating Lean burn combustion systems for fuel-efficient vehicles are particularly hard on exhaust after-treatment systems because excessive oxygen is always present in the exhaust. For example, the exhaust of diesel dual fuel (DDF) engines, which is one type of diesel engine, normally contains more than 5% volumetric oxygen after combustion. Under partial load the surplus of oxygen in the exhaust may be higher than 10% by volume. Under such circumstances, any engine management problems that result in excessive fuel in the exhaust, will generally damage exhaust after-treatment system due to overheating.
If a fuel management problem occurs, a large amount of the excess fuel delivered to the engine can pass through it and into the engine exhaust. That fuel will burn inside the catalyst if sufficient oxygen is available and the catalyst has reached catalytic temperature. For example, the complete burning of 2% of methane in the exhaust, can raise the temperature of exhaust gases by about 420° C., in addition to the 600° C. temperature of the exhaust as it is ejected from the engine. Consequently, the rate of temperature rise in the catalyst can reach 20 to 30° C./second, if the monoliths are metallic. Besides the catalytic burning of methane, any combustible matter such as soot accumulated on the catalyst surface, will also be rapidly oxidized under such high temperatures. The burning of accumulated soot will escalate and prolong the temperature rise. The thermal wave oscillation produced by the reverse flow process will also expedite the rise of the peak temperature of the catalyst substrate. Once the catalyst temperature reaches 1200° C., a metallic substrate will begin to soften and subsequently lose mechanical strength. Further temperature rise will cause collapse of the substrate and eventual melt-down will occur when it is heated to 1400-1450° C. A detrimental uncontrolled temperature rise can damage a catalyst in less than 20 seconds.
In the prior art, when a catalyst protection mode is required for a gasoline engine, an extremely rich fuel/air mixture is delivered to the engine. Since all oxygen is basically consumed inside the engine during the over-rich combustion process, the engine exhaust contains no oxygen. The large amount of excessive fuel from the engine pulls down the catalyst temperature. In this type of catalyst protection mode, however, the carbon monoxide content of the exhaust gas is undesirably very high.
However, for lean burn systems such as diesel or dual fuel engines, the excessive fuel will not cool down the catalyst temperature because of the presence of a high concentration of oxygen in the exhaust. Furthermore, lean burn systems cannot burn stoichiometric fuel/air mixtures because of knocking restrictions. For knock-free operation of a dual fuel engine, the original compression ratio of the baseline diesel engine requires the pre-mixed natural gas/air mixture to be generally leaner than λ=1.5.
As well, the concept of the reversing flow catalytic converter has been found to offer nearly continuous oxidation of exhaust components, mainly unburned hydrocarbons and carbon monoxide, when used after natural gas or dual fuel engines, in a 13 mode test cycle. For this reason, such a catalytic converter will likely not require supplementary heat added to the converter to maintain oxidation temperature. However, for a diesel engine there are fewer hydrocarbons and CO in the exhaust stream providing less fuel in the emissions. Engine fuel will need to be added to the exhaust stream during idle and low power operation of the engine in order to maintain an oxidation temperature sufficient to convert CO and hydrocarbons (including particulates), however, a considerably lesser amount of fuel than would be required by a conventional uni-directional oxidation catalyst. For this reason, addition of fuel can also result in overheating of the catalyst, if too much fuel is added.
U.S. Pat. No. 6,148,613 discloses a prior art reversing flow catalytic converter for internal combustion engines. Such device 10 includes a valve housing 14 which reversibly directs exhaust gases through a “U” shaped passage having a catalytic material therein. A valve disk 42 having two openings 48 therein rotates around a central axis, wherein in a first position of such rotatable valve disk 42 the exhaust gases enter the exhaust cavity from an exhaust pipe and pass through one of the openings in valve disk 42 into the “U” shaped passage. In the second position of the rotatable valve disk 42, the disk 42 and corresponding openings 48 therein are rotated 90° so that each opening 48 communicates with the same cavity within the valve housing 14, but a different one of the ports communicating with the U-shaped passage, so that gas flow through the u-shaped passage is thereby able to be reversed.
Disadvantageously, prior art devices such as the type disclosed in U.S. Pat. No. 6,148,613 lack a safeguard system to protect such reversing flow catalytic converter from overheating, as may arise under any one or more of the conditions explained above.
Further, there exists a need for a continuously oxidizing filter particulate trap for diesel engine exhausts.
An improved patent application Ser. No. 11/212,608 addresses the above problems and disadvantages and presents solutions and improvements.
The improved patent however, suffers from use of a rotating compact valve that is prone to having a high degree of friction drag due to its design and requirement for low leakage of exhaust gas across the valve. For each percent of exhaust gas leakage across the valve, the effectiveness of the destruction of exhaust methane or exhaust particulates diminishes by about one percentage point. Leakage and drag at the valve are reduced in this new invention by a re-configuration of the valve rotor and stator ports from being rotated as a sliding assembly perpendicular to and rotated about a shaft, to the rotor now being a symmetrical flapper and four stator ports now being fixed in the two conjoined inner valve walls parallel to the shaft intersecting each other at the center of the valve at the shaft area, and the rotor flapper being rotated about the shaft between two stator walls with four ports. The improved valve is divided into four cavities separated from each other by the internal valve walls The valve cavities extending from container chambers one and two and constrained between valve bottom ports one and two, the two valve inner walls, the outer wall and the cover plate are now better described as extended cavities to chambers one and two of the container. The valve cavities extending from the inlet and outlet piping ports and constrained by the valve top and bottom covers and between two valve walls are now better called inlet and outlet cavities through which the flapper moves to redirect flow as directed by the controller, actuator, spring return and rotor The rotor is now better described as a symmetrical flapper without ports and the stator is now better described as two pairs of conjoined walls intersecting at the center of the valve housing, each wall section having a valve port which the flapper covers two at a time while leaving the other two completely uncovered on a cyclic basis This type of valve action occurs with very little drag even at operating temperature, and the flapper is able to cover valve ports effectively and in this manner improve exhaust component destruction efficiency. The valve action of the flapper alternately covering two ports and uncovering the other two ports on a cyclic basis, is controlled by a temperature control system and has the effect of reversing the flow of exhaust gas cyclically flowing through the monolith in the container.
The improved patent application also suffers from a neutralizing spring return design with two compressed springs such that the spring return is not force-balanced at the shaft and therefore prone to shaft wear. Therefore an improvement is made to create a force-balanced spring return with the use of four compressed springs mounted in such a way as to balance out forces on the shaft that were prevalent with the original two spring design.
The improved patent application used diesel injection as required into the inlet pipe taking exhaust gases from the diesel engine into the valve and oxidation or filter monolith and also mentioned that injection of diesel was alternately possible into the space at the central core of the monolith. It is preferred to add diesel fuel within the central core since the heat in this area is prevalently greater than in the inlet to the monolith, giving greater opportunity for complete diesel vaporization within the core thereby effecting a greater oxidation efficiency of the added fuel.
It is accordingly an object of the present invention to provide a further improved reversing flow catalytic converter system for treating exhaust gases from an internal combustion engine, which system includes an improved compact valve structure incorporated in the converter as well as an improved safeguard system to protect the catalyst and converter from overheating and including an improved method for monolith heat addition by diesel injection into the central core of the monolith.
Another object of the present invention is to provide a further improved reversing flow catalytic converter system for treating exhaust gases from an internal combustion engine which has a compact structure for efficient performance, minimal heat loss, and mechanical simplicity.
Yet another object of the present invention is to provide an improved three-way valve for a further improved reversing flow catalytic converter which overcomes the shortcomings of the prior art discussed above.
A further object of the present invention is to provide a further improved reversing flow catalytic converter having an improved bypass system to protect the further improved reversing flow catalytic converter from overheating.
A still further object of the present invention is to provide an improved three-way valve for a further improved reversing flow catalytic converter that is maintained in a neutral position to permit exhaust gases to bypass the further improved catalytic converter when the improved valve is not actuated.
A further object of the present invention is to optionally provide a further improved reversing flow catalytic converter with an oxidizing filter trap that may or may not be coated with catalytic material, to trap, hold and oxidize particulates, in place of the oxidation catalytic substrate within the further improved reversing flow catalytic converter.
A further object of the present invention is to provide a further improved reversing flow catalytic converter with an improved means of injecting a controlled amount of diesel engine fuel within the core of the further improved reversing flow catalytic converter, when required to maintain a continuous oxidation temperature. The catalytic converter monolith may or may not be coated with catalytic material, depending on the application and upon the amount of fuel normally present in the exhaust stream and additionally injected into the middle of the further improved reversing flow catalytic converter.
A still further object of the present invention is the provision of an improved force-balanced spring return design component such that the improved valve can be reliably and quickly returned to a neutral or bypass position upon detection of damaging impending temperatures within the monolith of the further improved reversing flow catalytic converter.
Accordingly, in one broad aspect of the invention, a further improved reversing flow catalytic converter for treating exhaust gases from an internal combustion engine is provided, comprising:
Alternatively, in another aspect of such first aspect, the present invention comprises a further improved reversing flow catalytic converter for treating exhaust gases from an internal combustion engine is provided, comprising:
Preferably, the improved valve housing has an interior cavity with two openings in the bottom plate and two transverse walls that divide the cavity into four parts, two parts that, with the outer wall and cover plate, respectively form cavity extensions of the container chambers one and two, and the other two parts that respectively connect to the engine exhaust valve inlet pipe and the engine tailpipe outlet pipe The improved valve component may include a flapper plate which is symmetrical and rotatably mounted to the center of the valve housing at the shaft, and rotates about a central axis that is perpendicular to the improved valve cover plate and the two openings therein that communicate with one of the inlet and exhaust cavities. The improved valve bottom plate has a first opening and second opening therethrough which communicate respectively with each of the two container chambers.
More preferably, the gas flow passage is formed within an interior chamber of the container, the interior chamber being separated by a transverse plate into two parts which respectively form a first chamber section and a second chamber section. The two sections communicate with each other, and each of the chamber sections communicates with one of the first and second valve openings. The container further comprises a gas permeable material which contains the catalytic material. The gas permeable material preferably comprises a plurality of monoliths having a plurality of cells extending therethrough, the monoliths being coated with a catalytic material.
According to a second aspect of the present invention, there is provided a further improved reversing flow catalytic converter for exhaust gases, the converter comprising a container which has a top end with a first chamber and a second chamber that are in fluid communication with each other so that the exhaust gases introduced into one of the first and second chambers flow through a catalytic material in the container. The improved valve structure comprises an improved valve housing including two openings in the bottom plate of the improved valve housing, opening one that connects to the first chamber of the container and opening two that connects to the second chamber of the container and two extended valve cavities, one connected to container chamber one through improved valve opening one and the other connected to chamber two through improved valve opening two, and an improved intake cavity and an improved exhaust cavity. The improved intake and exhaust cavities are separated from the container first and second chambers and their associated extended valve cavities by two conjoined walls that intersect at the center of the improved valve housing, each wall making two wall sections and each section containing one opening such that two of the four openings are blocked by the flapper alternately as dictated by the controller. The improved intake cavity is adapted for connection of an exhaust gas pipe and the improved exhaust cavity is adapted for connection of a tail pipe. An improved valve component is provided for reversing gas flow operably mounted in the valve housing. The improved valve is adapted to move the flapper between a first position in which the improved intake cavity communicates with the first container chamber through its associated extended valve cavity and the improved exhaust cavity communicates with the second container chamber through its associated extended valve cavity, and a second position in which the improved intake cavity communicates with the second container chamber through its associated extended valve cavity and the improved exhaust cavity communicates with the first container chamber through its associated extended valve cavity. The improved valve structure further includes an improved center return mechanism associated with the improved valve component for moving the improved valve component to a third position in which the improved intake cavity communicates with the improved exhaust cavity through the improved valve component when the improved valve component is not actuated to move to one of the first and second positions. Alternatively, the third position may be achieved by positive action of a controller and actuator.
According to a third aspect of the present invention, there is provided a further improved reversing flow catalytic converter for treating exhaust gases from an internal combustion engine. The catalytic converter includes a container having a gas flow passage therein and a top end having a first chamber and a second chamber which respectively communicate with the passage. A catalytic material is provided in the gas flow passage and contacts the exhaust gases which flow through the passage. The further improved catalytic converter has an improved valve for reversing the exhaust gas flow through the gas flow passage, including an improved valve housing with an improved intake cavity and an improved exhaust cavity, and two extended valve cavities mounted to the top end of the container. The improved intake cavity is adapted for connection of an exhaust gas pipe and the improved exhaust cavity is adapted for connection of a tail pipe. The improved valve also includes an improved valve component for reversing gas flow, operably mounted in the improved valve housing, and adapted to be moved between the first, second, and third positions.. In the first position, the improved intake cavity communicates with the first container chamber through its associated extended valve cavity and the improved exhaust cavity communicates with the second container chamber through its associated extended valve cavity In the second position, the improved intake cavity communicates with the second container chamber through its associated extended valve cavity and the improved exhaust cavity communicates with the first container chamber through its associated extended valve cavity. In the third position, the improved intake cavity communicates with the improved exhaust cavity. A controller controls movement of the improved valve component between the first and second positions, and movement of the improved valve component to the third position, if required to protect the catalytic material from overheating.
According to a fourth aspect of the present invention, a safeguard system is provided to inhibit overheating the further improved reversing flow catalytic converter. In addition to controlling the improved valve component for reversing flow bypass operation, the controller is also adapted to indirectly control fuel supply to the engine, in order to protect the catalytic material from overheating.
According to fifth aspect of the invention, there is provided a method for preventing overheating of the further improved reversing flow catalytic converter. The further improved reversing flow catalytic converter includes an improved valve adapted for connection of an exhaust gas pipe and a tail pipe, and associated with first and second ports of a container and their respective associated extended valve cavities for reversing exhaust gas flow through a catalytic material in the container. The method comprises steps of monitoring temperatures of the catalytic material, and controlling an improved valve mechanism to permit the exhaust gases to flow from the exhaust gas pipe to the tail pipe without passing through the catalytic material when the temperature of the catalytic converter exceeds a predetermined threshold. The method also preferably includes steps of calculating the rate of temperature rise in the catalytic material, and controlling the improved valve mechanism to permit the exhaust gases to flow from the exhaust gas pipe to the tail pipe without passing through the catalytic material when the rate of temperature rise exceeds a predetermined threshold. A further optional step adjusts engine operation to reduce total hydrocarbon and carbon monoxide volume in the exhaust gas flow.
The safeguard system in accordance with the present invention, protects the catalytic material from overheating when an abnormal rate of temperature rise is detected. The bypass of exhaust gases around the catalyst is the primary safeguard mechanism. During bypass, the exhaust gases do not flow through the monoliths in the catalytic converter. Thus, the inner catalyst is shielded from the flow of the fuel-oxygen mixture contained in the engine exhaust. Extensive testing has shown that once the exhaust flow to the catalyst is stopped by the improved bypass mechanism, the catalyst center temperature comes down quickly even if the exhaust gases are rich in both fuel and oxygen. However, if overheating occurs, the engine fuel supply is preferably adjusted to reduce the total hydrocarbon and carbon monoxide volume in the exhaust, as well as the temperature of the exhaust gases. In bypass mode, exhaust gases rich in fuel and oxygen will burn in the improved valve housing if the temperature of the improved valve housing is high enough The high temperature resulting from the burning of the fuel in the improved valve housing retards cooling of the catalyst, and may damage the improved valve structure. Therefore, control of the fuel supply is preferable when overheating occurs. Besides, in the bypass mode, the exhaust gases are not treated by the catalyst and therefore, the concentrations of hydrocarbons and carbon monoxide in the exhaust gas generally increases.
According to a sixth aspect of the invention, there is provided an option to replace the oxidation catalyst within the further improved reversing flow catalytic converter with a catalytic filter trap. In this variation of the reversing flow catalytic converter, a method is provided to entrap particulates and to hold them for a period of time to allow effective oxidation of the particulate matter when the trap is held at a continuous oxidation temperature by the temperature monitoring and control system. In this sixth aspect and as a second option, the oxidation catalyst may be replaced by a filter monolith that is not coated with catalyst.
According to a seventh aspect of the invention, there is provided a method by which diesel engine fuel may be injected through an injector valve that provides vaporized engine fuel into the central area of the further improved reversing flow catalytic converter within the flow redirection bowl. Diesel engine fuel passes into the flow redirection bowl through a bulkhead fitting into a coiled small diameter tubing section that provides sufficient heating surface to vaporize diesel fuel components into the flow redirection bowl. Diesel fuel is provided to the bulkhead fitting from a connecting pipe that connects a diesel fuel supply manifold that in turn receives diesel fuel supply from the high pressure diesel injector low pressure supply pump. The manifold contains the diesel injector, an associated flow orifice to control diesel flow, an associated check valve to block diesel flow during air purge and an associated strainer to filter diesel fuel within the manifold block before the injector. The manifold also contains an air injection solenoid valve that purges diesel fuel from the line downstream of the diesel injector by briefly injecting vehicle air into the diesel injection line when the engine is shut down. The method comprises of steps of monitoring temperature of the monolith material and controlling a fuel injector valve mounted on the flow redirection bowl of the further improved reversing flow converter to inject metered quantities of fuel required to maintain a preset oxidation temperature of the monolith material. The method includes the provision of a control interlock such that in the event of overheating for any reason, the power to the fuel injector valve will be locked out until the overheat condition is removed. Additionally, when an overheat event occurs, the engine fuel supply will be adjusted to reduce total hydrocarbons and carbon monoxide volume in the exhaust.
According to an eighth aspect of the invention, there is optionally provided, a three position valve and rotary stepper motor actuator which includes valve positions for; forward, reverse and bypass flow. In this aspect, the valve position is determined by a pneumatic or electric stepper motor that is driven by a control method similar to that described earlier for the reverse flow oxidizing catalytic converter, comprised of steps of monitoring temperature and rate of temperature rise of the oxidizing filter trap and controlling valve position such that exhaust gases are permitted to flow from the engine to the tail pipe without passing through the oxidizing filter trap when the temperature of the monolith exceeds a predetermined threshold. This is the third or bypass valve position
Other features and advantages of the invention will be more clearly understood with reference to the preferred embodiments described below.
The invention will now be further described by way of example only, and with reference to the accompanying drawings, in which:
a is a cross-sectional plan view taken along line B-B of the improved bypass mechanism 316 of
b is a cross-sectional plan view taken along line B-B of the improved bypass mechanism 316 of
a is a top plan view of the improved valve housing 301, showing the inlet and outlet piping with flanges and the actuator and improved spring return in a stack mounted at the center of the improved valve top cover plate.
b is a elevation view of the improved valve housing 301, showing the inlet and outlet piping with flanges and the actuator and improved spring return stack mounted on the improved valve top cover.
c is a bottom plan view of the improved valve housing 301 showing the improved valve bottom plate and its two openings to communicate with the two container chambers.
a is an elevational view of the oxidation catalyst or filter catalyst monolith of the further improved reverse flow catalytic converter showing the monolith and transverse separation wall of the inlet section of the can in dashed lines.
b shows the can top plan view of the can and monolith 302 (section E-E of
a shows the flow re-direction bowl 303 in elevational view with capillary tubing shown in dashed lines.
b shows the flow re-direction bowl 303 from its top plan view (section G-G of
c is a schematic showing the injection manifold 347 with its associated flow components.
a is an elevational cross-sectional view (section H-H of
b is an elevational cross-sectional view (section J-J of
c is an elevational cross-sectional view (section K-K of FOG. 7) showing wall sections 352 and 353 within the improved valve structure housing 301 in a second direction.
a is a bottom diagrammatic plan view of the bottom of the improved valve 301 showing exhaust flow paths for one position of the improved valve flapper in which exhaust gas from the engine enters the bottom inlet pipe and is redirected to the right hand side bottom plate valve opening and into the monolith and the flow that leaves the monolith enters the valve through the left hand opening of the improved valve bottom plate and is directed into the valve exhaust piping to the tail pipe.
With reference to
As shown in
As shown in
a, 4b and 4c illustrate features of the improved valve housing.
c is is a bottom view cross-sectional along line D-D of
a, 5b and 5c illustrate the further improved reversing flow catalytic converter can and substrate section 302.
a, 6b and 6c illustrate the further improved reversing flow catalytic converter flow re-direction bowl 303 and diesel fuel injection capillary tubing 337 as well as a schematic showing the diesel injection block 347 with its integral components.
a, 8b and 8c all illustrate cross-sectional elevations of the internal improved valve structure of wall sections and flapper sections.
a, 9b and 9c illustrate the valve flapper sections 348 and 349 in their three positions, for respectively forward and reverse exhaust flow through the container 302 and for bypassing the oxidation or filter catalytic material. For clearer illustration, these figures illustrate only a bottom plan schematic view of the valve housing with valve bottom plate 309 removed exposing flapper sections 348 and 349, wall sections 350, 351, 352 and 353 and valve inlet opening 329 and valve outlet 328. The four wall sections divide the interior cavity of the valve housing 301 into the intake cavity and exhaust cavity, and into two other valve cavities that are essentially extensions of the two can cavities.
When the valve flapper sections 348 and 349 are in the first position as shown in
As shown in
If during the reversing flow operation of the further improved catalytic converter 300, the temperature of the catalyst material rises too quickly or is predicted to overheat the catalytic material, a controller places the catalytic converter in bypass mode. In bypass mode, the rotary actuator is deactivated by interrupting the pressurized fluid supply (not shown) or electric power Supply. When the rotary actuator 202 is deactivated, the swivel arm 322 of the improved center return mechanism 316 is forced by two of the springs 317, 318, 319 or 320, to return to its central position as shown in
The further improved catalytic converter 300 described above with reference to
As long as the temperature measured is within a predetermined range, the controller controls the rotary actuator 202 to achieve cyclic reverse flow through the catalytic converter by periodically rotating valve 301 so that the reverse flow valve 301 is moved between the first and second positions. If an abnormally sharp rise in temperature is detected, or if the temperature of the catalytic material rises above a threshold that will predictably damage the catalytic material, the controller 250 enters the bypass mode. During the bypass mode, the controller 250 deactivates the rotary actuator 202. When the rotary actuator 202 is deactivated, the improved center return mechanism 316 forces the reverse flow valve 301 into the third position to cause the gas flow to bypass the catalytic converter 302/303, as described above with reference to
Exhaust flow bypass is a first safeguard action to prevent damage to the reversing flow catalytic converter. Adjusting engine fuel supply is another. Therefore, when the controller enters bypass mode, it sends a signal to the engine controller 252. The engine controller responds to the signal by adjusting the engine fuel supply to reduce total hydrocarbon and carbon monoxide volume in the exhaust gases.
As seen in
A look-up table 258 may be accessed at the controller 250. The look-up table 258 stores data defining a dynamic limit of a rate of rise of the temperature of the catalytic converter 300. Each time the controller 250 samples the temperature of the catalyst using the RTDs 307, the controller 250 calculates the dynamic rate of rise in the temperature and compares the dynamic rate of rise in the temperature with entries in the look-up table 258, to obtain an early indication of overheating in the catalyst. The controller 250 must promptly respond to an indication of overheating in the catalytic material. The more quickly the controller 250 responds to the prediction of overheating in the catalytic converter, the better the catalyst is protected. A quick response will protect the washcoat from damage whereas a delayed response may only protect the monolith from meltdown. The control system therefore needs to be sensitive enough to protect the washcoat most of time and invariably prevent meltdown of the monolith substrate. However, over-sensitivity will trigger catalyst protection when it is not required. Frequent triggering of unwarranted catalyst protection will compromise engine performance in the case of engine management-systems and unnecessarily increase emissions in the case where bypass protection is used.
The control algorithm used by the controller 250 therefore determines when to enter bypass mode based on catalyst temperature thresholds. Appropriate setting of the temperature thresholds will safeguard the catalyst from overheating provided there is a slow climb in catalyst temperature. However, static temperature thresholds are not sufficient to prevent the catalytic washcoat from damage if operating conditions cause a serious fuel management problem. Serious fuel management problems may result in a sustained rate of temperature rise over 20-30° C./second. Due to the inherent delay in temperature sensing and processing, and a slight delay in the response of the bypass mechanism, an early prediction of overheating is required to protect the washcoat.
It should be noted that only catalyst temperatures are used to predict overheating by the control algorithm. The catalyst temperature and the rate of temperature rise in the catalyst temperature are used by the control algorithm. The engine exhaust temperature is not measured or considered, because exhaust temperatures vary at a much greater rate than catalyst temperature variation during normal engine operating conditions.
As an example, described below is a safeguard system for preventing overheating of a reversing flow catalytic converter used for a diesel/natural gas duel fuel engine.
Three Type-K thermocouples were installed in the catalytic converter, one at each side of the boundary layers, that is, inside the catalyst substrate, and a third one at the bottom center of the container structure. Type-K thermocouples are commonly used to measure temperatures of 0° to 1250° C. in various industrial processes. For balancing control of a catalyst flow-path temperature profile, two boundary thermocouples are preferred so that heat is measured more efficiently. For catalyst overheat protection, the two boundary thermocouples and the central thermocouple are required to provide early warning of any fuel management faults. The control algorithm used by the controller 250 provides the system with the following functionality:
The effectiveness of the safeguard system is ensured by multiple thresholds and the combination of static and dynamic temperature tracking. A performance evaluation test for the safeguard system was conducted to test the effectiveness of the catalyst temperature control and the durability of control functionality under a wide range of engine and vehicle operating conditions, including fuel management system failures. Evaluation tests demonstrated that the safeguard system reliably activated each time the controller determined that protection mode was required. For slow temperature rise, the onset of the bypass mode was triggered by either inlet or outlet catalyst temperature readings exceeding the static temperature threshold. Test results showed that the onset of bypass mode almost immediately stopped monolith temperature rise under slow temperature rise conditions. If an abnormal rate of temperature rise triggers bypass mode, the onset of bypass mode rapidly reduces and subsequently reverses the temperature rise. The tests indicted that the safeguard system reliably prevented meltdown of the catalyst under these conditions.
The protection of the catalyst washcoat is more difficult, mainly because of the narrow line between optimized working catalyst temperatures and washcoat damage temperatures. The catalyst tested worked best when bed temperatures were maintained between 580° and 640° C. and peaked at 720° C. Catalyst ageing is accelerated above 730° C. and reactivity deteriorated over 760° C. If high concentrations of hydrocarbons are present in the exhaust gases, a flame may be sustained in the valve housing for some time during bypass mode. Under such circumstances, the cavity of the valve housing is the hottest zone and conducts heat to the top of the monolith. However, the flame does not propagate to the inside of the catalyst because bypass mode stops gas flow through the catalyst. Rapidly adjusting the engine fuel supply provides improved protection for the washcoat.
The monolith material 336 of
In
In the cases of both the oxidizing catalytic converter and the oxidizing catalytic filter, it may be feasible to reduce the amount of catalytic loading and maintain temperature at oxidizing levels by the use of incremental fuel injection by way of fuel injector valve 339. In the limit, with sufficient exhaust fuel injection, catalytic coating may not be required. The amount of catalytic material may be balanced against the amount of fuel consumed in a case by case assessment of each application
The control schematic of
The advantages of the further improved catalytic converter described above are apparent. No plumbing is required between the converter unit and the valve unit, which makes the catalytic converter compact and inhibits heat loss between the valve and the catalyst. The valve flapper is rotated about a perpendicular axis, which provides a smooth and reliable valve operation in a minimum of space. The unique arrangement of the monolith improves catalyst life and conversion performance. And the reversing exhaust gas flow ensures maximum efficiency of conversion by keeping the catalyst material uniformly heated and in addition small incremental fuel additions help to increase catalytic activity for pollutant reduction. Furthermore, the safeguard system including the improved spring return mechanism used with the catalytic converter effectively safeguards the catalytic converter from damage due to overheating and effectively improves catalyst life. An additional advantage is the ability of the reverse flow catalytic converter to be optionally modified to work effectively and efficiently as a continuous oxidation particulate filter trap.
In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. Various changes could be made in the above methods and constructions without departing from the scope of the invention, which is limited solely by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,508,159 | May 2005 | CA | national |
The present invention relates to catalytic converters for internal combustion engines, and in particular, to a further improved reversing flow catalytic converter over that disclosed in U.S. patent application Ser. No. 11/218,608 filed Aug. 29, 2005 in the name of some of the inventors herein for treating exhaust gases from internal combustion engines.
