Abstract:
A further improved compact reversing flow catalytic converter with protection from overheating includes an improved valve unit which directs exhaust gases through a container filled with catalytic material to permit a bypass of catalytic material when a temperature of the material exceeds a predetermined threshold. The container defines a U-shaped gas passage that communicates with two chambers at the top of the container. The improved valve unit is mounted to the top of the container and includes two container chamber extension cavities, an improved intake cavity and an improved exhaust cavity. The improved valve unit includes an improved valve flapper and two conjoined valve walls each wall with two openings therethrough. The improved valve flapper rotates around normal central axis between a first, a second and third positions. When overheating of the catalytic material is predicted, a controller relinquishes control of the improved valve flapper and an improved center return mechanism rotates the improved valve flapper to a third position, in which each of the valve openings communicates with both inlet and exhaust ports so that the exhaust gas flow bypasses catalytic material. A fuel injection system under control of the controller is used so that measured amounts of fuel can be injected into the container reaction core to enhance oxidation. The catalytic material is thus protected from damage due to overheating. The advantage is a compact, reliable, highly efficient further improved catalytic converter that is inexpensive to manufacture, durable, and adapted for extended service life. The improved valve may driven by a stepper motor that moves and holds the valve to its three positions including bypass, forward and reverse flow. An alternate version also replaces the oxidizing flow-through monolith with an oxidizing filter trap.

Description:
[0001]     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. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     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.  
         [0003]     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.  
         [0004]     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.  
         [0005]     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.  
         [0006]     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.  
         [0007]     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.  
         [0008]     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.  
         [0009]     Further, there exists a need for a continuously oxidizing filter particulate trap for diesel engine exhausts.  
         [0010]     An improved patent application Ser. No. 11/212,608 addresses the above problems and disadvantages and presents solutions and improvements.  
         [0011]     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.  
         [0012]     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.  
         [0013]     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.  
       SUMMARY OF THE INVENTION  
       [0014]     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.  
         [0015]     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.  
         [0016]     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.  
         [0017]     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.  
         [0018]     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.  
         [0019]     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.  
         [0020]     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.  
         [0021]     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.  
         [0022]     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: 
        a container having a gas flow passage therein and a top end having a first chamber and a second chamber that respectively communicate with the gas flow passage;     a catalytic material in the gas flow passage adapted for contacting the exhaust gases that flow through the gas flow passage;     an improved valve for reversing an exhaust gas flow through the gas flow passage, including an improved valve housing with two extended valve cavities connecting to chambers one and two of the container and mounted to the top end of the container, an improved intake cavity and an improved exhaust cavity, the improved intake cavity adapted for connection to an exhaust gas pipe from said engine and the improved exhaust cavity adapted for connection to a tail pipe for egress of said exhaust gas from said converter; and     an improved valve component for reversing gas flow operably mounted to the improved valve housing, adapted to move between a first position in which the intake cavity communicates with the first valve opening and container chamber and the exhaust cavity communicates with the second valve opening and container chamber, a second position in which the intake cavity communicates with the second valve opening and container chamber and the exhaust cavity communicates with the first valve opening and container chamber, and a third position which allows the intake cavity to communicate with the exhaust cavity; and     a controller for controlling movement of the improved valve component between the first and second positions during normal operating temperatures for the further improved reversing flow catalytic converter and otherwise permitting movement of the improved valve component to the third position for abnormal operating temperatures.        
 
         [0028]     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: 
        a container having a gas flow passage therein and a top end having a first chamber and a second chamber that respectively communicate with the gas flow passage;     a catalytic material in the gas flow passage adapted for contacting the exhaust gases that flow through the gas flow passage;     an improved valve for reversing an exhaust gas flow through the gas flow passage, including an improved valve housing with a bottom plate mounted to the top end of the container and containing two openings, one connecting to each of the first and second container chambers, and extended valve cavities within the valve connecting the container chambers to an improved intake cavity and an improved exhaust cavity, separated from the container chambers and associated extended valve cavity by two conjoined walls intersecting at the center of the valve housing, each wall section having an opening that allows communication between the container first and second chambers and connected extended valve cavities and the intake and exhaust cavities when the valve flapper is positioned to allow such communication. The improved intake cavity is adapted for connection to an exhaust gas pipe from said engine and the improved exhaust cavity is adapted for connection to a tail pipe for egress of said exhaust gas from said converter; and     an improved valve component for reversing gas flow operably mounted to the improved valve housing, adapted to the be moved between a first position in which the improved intake cavity communicates with the first chamber of the container through the first extended valve cavity and the improved exhaust cavity communicates with the second chamber of the container through the second extended valve cavity, a second position in which the improved intake cavity communicates with the second chamber of the container through the second extended valve cavity and the improved exhaust cavity communicates with the first chamber of the container through the first extended exhaust cavity, and a third position which allows the improved intake cavity to communicate with the improved exhaust cavity; and     a controller for controlling movement of the improved valve component between the first and second positions during normal operating temperatures for the further improved reversing flow catalytic converter and to the third position to permit bypass of exhaust gas without passing through said catalyst material during certain other temperatures for the further improved reversing flow catalytic converter.        
 
         [0034]     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.  
         [0035]     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.  
         [0036]     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.  
         [0037]     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.  
         [0038]     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.  
         [0039]     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.  
         [0040]     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.  
         [0041]     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.  
         [0042]     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.  
         [0043]     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  
         [0044]     Other features and advantages of the invention will be more clearly understood with reference to the preferred embodiments described below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]     The invention will now be further described by way of example only, and with reference to the accompanying drawings, in which:  
         [0046]      FIG. 1  is a side elevation view of the further improved reverse flow catalytic converter of the present invention which includes an improved bypass mechanism to control overheating of the catalytic material in the catalytic converter, an improved valve to operate with low drag and low leakage and an improved diesel fuel injection system;  
         [0047]      FIG. 2  is a cross-sectional plan view taken along line A-A of the actuator  202  of  FIG. 1  to show the structure of a rotary actuator for driving the valve;  
         [0048]      FIG. 3   a  is a cross-sectional plan view taken along line B-B of the improved bypass mechanism  316  of  FIG. 1  to illustrate an improved center return mechanism in a first position corresponding to that of the actuator shown in  FIG. 2 , and in dashed lines in a second position corresponding to a second position of the actuator shown in dashed lines in  FIG. 2 ;  
         [0049]      FIG. 3   b  is a cross-sectional plan view taken along line B-B of the improved bypass mechanism  316  of  FIG. 1  to illustrate an improved center return mechanism in position for bypass mode corresponding to the actuator neutral position shown in dashed lines in  FIG. 2 ;  
         [0050]      FIG. 4   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.  
         [0051]      FIG. 4   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.  
         [0052]      FIG. 4   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.  
         [0053]      FIG. 5   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.  
         [0054]      FIG. 5   b  shows the can top plan view of the can and monolith  302  (section E-E of  FIG. 1 ) and  FIG. 5   c  shows the bottom plan view of the can and monolith  302 .  
         [0055]      FIG. 6   a  shows the flow re-direction bowl  303  in elevational view with capillary tubing shown in dashed lines.  
         [0056]      FIG. 6   b  shows the flow re-direction bowl  303  from its top plan view (section G-G of  FIG. 1 ) showing the diesel injection capillary tubing and bulkhead fitting as well as an RTD mounted within the bowl.  
         [0057]      FIG. 6   c  is a schematic showing the injection manifold  347  with its associated flow components.  
         [0058]      FIG. 7  is a cross-sectional plan view (section C-C of  FIG. 1 ) of the improved valve housing  301  with inlet and outlet openings in the valve cover plate superimposed in dashed lines and the flapper shown covering two wall ports.  
         [0059]      FIG. 8   a  is an elevational cross-sectional view (section H-H of  FIG. 7 ) showing wall sections  350  and  351  within the improved valve structure housing  301  in a first direction.  
         [0060]      FIG. 8   b  is an elevational cross-sectional view (section J-J of  FIG. 7 ) of the flapper  348  mounted within the improved valve structure housing  301  in a second direction.  
         [0061]      FIG. 8   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.  
         [0062]      FIG. 9   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.  FIG. 9   b  is a similar improved valve  301  bottom view showing the flapper in the second position redirecting engine exhaust flow into the monolith on the left hand side and out of the monolith on the right hand side and into the valve exhaust opening into the tail pipe.  FIG. 9   c  is a similar bottom plan view of the improved valve  301  with the flapper in the bypass position allowing direct communication from the engine exhaust to the tail pipe directly through the valve and bypassing the monolith.  
         [0063]      FIG. 10  is a schematic plan for the control system  262  employed by the further improved reversing flow catalytic converter  300 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0064]      FIG. 1  illustrates a further improved catalytic converter  300  in accordance with an embodiment of the present invention which incorporates a safeguard system to inhibit overheating the catalyst monoliths, an improved valve assembly, an improved spring return and an improved monolith can and re-direction bowl with improved diesel fuel injection.  
         [0065]     With reference to  FIG. 1 , the catalytic converter  300  comprises a improved container  302  and improved valve housing  301  with a similar function as described in U.S. patent application Ser. No. 11/212,608. A rotary actuator  202  and a center return mechanism  316  are mounted on the drive shaft  50  of the valve flapper parts  348  and  349 . The rotary actuator  202  is controlled to periodically rotate the valve flapper parts  348  and  349  between the first and the second positions to reverse gas flow through the container  302 .  
         [0066]     As shown in  FIG. 2 , the rotary actuator  202  includes a housing  206  which encloses a pressure chamber  208 . A moveable vane  210  is mounted to drive shaft  212  which is adapted to be connected to the shaft  50  of the valve flapper parts  348  and  349  to rotate together therewith. The housing  206  has a first opening  214  and a second opening  216  in the respective side walls of the housing  206  so that the moveable vane  210  rotates clockwise until it abuts a left stop member  218  when pressurized fluid is injected into the pressure chamber  208  through the first opening  214 . This position of the moveable vane  210  corresponds to the first position of the valve flapper parts  348  and  349  as shown in  FIGS. 7 and 9   b , to permit the exhaust gases to flow through the container in a first direction. Similarly, the moveable vane  218  rotates counter clockwise until it abuts a right stop member  220 , as shown in broken lines at the right side, when the pressurized fluid is injected into the pressure chamber  208  through the second opening  216 . This position corresponds to the second position of the valve flapper parts  348  and  349 , as shown in  FIG. 9   a , to permit the exhaust gases to flow through the container  302  in the opposite direction.  
         [0067]     As shown in  FIGS. 3   a  and  3   b , the center return mechanism  316  includes a base block  323  having a circular bore  321  at an apex of triangular cavities  324  and  325 . A swivel arm  322  is connected on both ends to a pivot shaft  358  that is rotatably mounted in the bore  321  of the base block. Four coil springs  317 , 318 , 319  and  320  are retained in the annular grooves  359  and  360 , each is restrained between one end of the grooves  359  and  360  and one side of the swivel arm  322 . A connector (not shown) is integrally formed with the pivot shaft  358 , having a square cross-section adapted to receive a square top end of pivot shaft  212 (not shown) of the rotary actuator  202 . The swivel arm members  322  are adapted to swivel within the triangular cavities  324  and  325  and compress two of the springs  317 ,  318 ,  319  and  320  as they swivel. The other of the springs  317 ,  318 ,  319  and  320  are free to expand within the annular grooves. A cover  243  (not shown) is provided to retain the swivel arms  322  and springs  317 ,  318 ,  319  and  320  within the base block  323 . When the pressure vane  210  of the rotary actuator  202  is at the left side, corresponding to the first position of the valve flapper  348  shown in  FIGS. 7 and 9   b , the swivel arm  322  of the center return mechanism  316  compresses springs  317  and  318 . When the pressure vane  210  of the rotary actuator  202  pivots to the right side as shown in the broken line at the right side of  FIG. 2 , the valve flapper parts  348  and  349  are in the second position as shown in  FIG. 9   a . However, when the rotary actuator  202  is deactivated (no fluid pressure is applied to either side of the pressure vane  210 ), the swivel arm  322  of the center return mechanism  316  is forced by two of the springs  317  and  318 , to return to the central position shown in  FIG. 3b . This moves the pressure vane  210  of the rotary actuator  202  to the central position shown in broken lines in  FIG. 2 . It also moves the valve flapper parts  348  and  349  to the bypass position shown in  FIG. 9   c.    
         [0068]      FIGS. 4   a ,  4   b  and  4   c  illustrate features of the improved valve housing.  FIG. 4   a  is a plan view of the valve housing showing inlet flange  312  and inlet pipe  313  receiving exhaust gas from a diesel engine and outlet pipe  315  and outlet flange  314  discharging purified exhaust gas to the vehicle tail pipe.  FIG. 4   a  also illustrates valve cover plate  310  and the two openings in the cover plate  329  and  328  allowing gas to pass into and out of the valve housing inlet and outlet compartments formed by valve interior walls  350 ,  351 ,  352  and  353  of  FIG. 7   FIGS. 4   a  and  4   b  also show improved spring return  316  and actuator  202  mounted to the valve cover  310  and to each other by a bracket (not shown) and connected to shaft  50  that also connects to improved valve flapper parts  348  and  349  of  FIG. 7 .  FIG. 4   b  also shows the outer improved valve outer assembly consisting of outer wall  330  that is welded to top flange  311  that fastens to valve cover plate  310  and valve bottom flange  309  that also is welded to outer wall  330 .  
         [0069]      FIG. 4   c  is is a bottom view cross-sectional along line D-D of  FIG. 1  showing the valve bottom plate  309  and its two ports  326  and  327  that connect to can chambers  333  and  334  of  FIG. 5   b.    
         [0070]      FIGS. 5   a ,  5   b  and  5   c  illustrate the further improved reversing flow catalytic converter can and substrate section  302 .  FIG. 5   a  is an elevational view of the can and substrate section  302  including can upper and lower flanges  308  and  306  respectively attached to wall section  331 , and transverse wall section  335  in dashed lines and attached to flange  308  and wall  331  and sealed to the upper surface of monolith or substrate  336  surface also in dashed line.  FIG. 5   a  also shows the preferred mountings of resistance temperature detectors (RTDs)  307 , approximately ¼ and ½ of the way down the substrate on each side of the transverse wall and below the substrate  336  surface.  FIG. 5   b  is a top plan view of the can or cross-sectional vied along line E-E of  FIG. 1  showing the transverse wall  335  and the substrate  336  visible through can chamber openings  333  and  334 .  FIG. 5   c  is a bottom can or cross-sectional view along line F-F of  FIG. 1  showing the exposed substrate  336  mounted flush with bottom flange  306 .  
         [0071]      FIGS. 6   a ,  6   b  and  6   c  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.  FIG. 6   a  shows an elevational view of the flow re-direction bowl  303  comprised of flange  305  and bowl container  332 . Also shown in  FIG. 6   a  is a tubing bulkhead fitting  304 , internal coiled tubing  337  in dashed lines supported by a bracket (not shown) and RTD  307 .  FIG. 6   b  is a plan view of cross-sectional area along line G-G of  FIG. 1 , showing flange  305  and bowl container  332 , bulkhead fitting  304 , coiled tubing  337  and RTD  307 . The schematic shown in  FIG. 6   c  reveals the manifold block  347  with internally mounted components; check valves  342 , filter screen  340  and orifice  341 . A diesel supply from the diesel fuel supply pump  345  enters the manifold block  347 , is filtered by screen  340  before passing to a diesel injector valve  339  that is under control of converter controller  262  of  FIG. 10  and then passing through a flow control orifice  341  and check valve  342  and thence out of the manifold block into tubing leading directly to bulkhead fitting  304 . The manifold block  347  also contains flow passages tha direct air from vehicle air supply  346  directly to air purge solenoid  344  and then through check valve  343  and directly to tubing leading to bulkhead fitting  304 . When the vehicle is shut down, the converter controller  262  will de-activate diesel injection solenoid  339  blocking diesel flow and briefly activate air purge solenoid  344  sufficient to clear diesel fuel from the tubing leading to bulkhead filling  304  and from capillary tubing  337  so that caking of the tubing is prevented.  
         [0072]      FIG. 7  is a cross-sectional plan view along line C-C of  FIG. 1  illustrating the internal wall system consisting of walls  350 ,  351 ,  352  and  353  that converge near the center of the valve and around valve shaft  50  that is connected to valve flapper sections  348  and  349 . The angles subtended by the wall system are about 60 degrees in the directions of inlet opening  328  and outlet opening  329  in valve cover plate  311  and about 120 degrees in the directions of valve bottom plate  309  openings  326  and  327  that connect to can cavities  333  and  334  of  FIG. 5   b . As shown in  FIG. 7 , valve flapper section  348  completely covers the opening  354  of  FIG. 8   a  in wall  350  and valve flapper section  349  completely covers the opening  356  of  FIG. 8   c  in wall  352 .  
         [0073]      FIGS. 8   a ,  8   b  and  8   c  all illustrate cross-sectional elevations of the internal improved valve structure of wall sections and flapper sections.  FIG. 8   a  shows the internal cross-sectional elevation along line H-H of  FIG. 7  displaying wall sections  350  and  351  and wall openings  354  and  355  respectively. This view also shows top cover plate opening  329  that connects to the inlet pipe  313  and bottom plate opening  326  that connects to can inlet cavity  334  of  FIG. 5   b.    FIG. 8   b  shows the valve internal cross-sectional elevation along line J-J of  FIG. 7  displaying the flapper sections  348  and  349  with connected shaft  50  and wall sections  352  and  353  in behind the flapper sections and also showing wall openings  356  and  357  in dashed lines. In this illustration, the flapper section completely seals wall opening  356  in wall section  352  and completely uncovers wall section opening  357  in wall section  353 .  FIG. 5   c  shows the valve internal cross-sectional elevation along line K-K of  FIG. 7  displaying wall sections  352  and  353  along with wall section openings  356  and  357  respectively. In the position of valve flapper sections  348  and  349  shown in  FIG. 7 , opening  356  of wall section  352  is completely sealed by flapper section  349  and opening  357  of wall section  353  is completely uncovered. With the valve flapper position shown in  FIG. 7 , engine exhaust gases enter the valve housing through opening  329  and then through wall opening  355  of wall section  351  and then through opening  326  of the valve bottom plate into can cavity  334  and into the oxidation or filter monolith  336  down the left hand side in  FIG. 5   b  and then into the flow re-direction bowl  303  of  FIG. 6   a  and then up and into the oxidation or filter monolith right hand side of  FIG. 5   b  and into can cavity  333  and then through valve bottom plate opening  327  and then through opening  357  of wall section  353  and out of the valve housing through top valve cover opening  328 .  
         [0074]      FIGS. 9   a ,  9   b  and  9   c  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.  
         [0075]     When the valve flapper sections  348  and  349  are in the first position as shown in  FIG. 9   a , the gas flow enters intake cavity from the inlet opening  329 . The gas flow passes through the valve wall opening  355  in wall section  351  to enter the container through valve bottom plate opening  326  and disperse container cavity  334  and into the cells of the catalytic material above within the container on the left hand side of the transverse wall  335 . After the exhaust gas flow is forced through the catalytic material it exits on the opposite side of the container transverse wall which is on the right hand side of the transverse wall  335 , and passes first through second container cavity  333  and then through the valve bottom plate opening  327  to the exhaust cavity through wall opening  357  in wall section  353 . The gas flow then exits through the outlet opening  328 .  
         [0076]     As shown in  FIG. 9   b , when the valve flapper sections are in the second position, it is rotated about 60° counter-clockwise so that the gas flow entering the intake cavity through the inlet opening  329  passes through valve wall opening  356  in wall section  352 . Therefore the gas flow must enter the container through the valve bottom plate opening  327  and first move into container cavity  333  and exit the container through container cavity  334  and then through valve bottom plate opening  325  and through valve exhaust opening  328  so that the gas flow in the container is reversed, in comparison to the gas flow shown in  FIG. 9   a    
         [0077]     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  FIG. 3   b . Thus, the center return mechanism  316  moves the valve flapper sections  348  and  349  to the third (bypass) position which is between the first and second positions, as shown in  FIG. 9   c . The valve flapper sections  348  and  349  are maintained in the third position until the rotary actuator  202  is reactivated. When the valve flapper sections  348  and  349  are in the third position, the valve wall openings  354 ,  355 ,  356  and  357  communicate with both the intake cavity and the exhaust cavity. Thus, the gas flow entering the intake cavity through the inlet opening  329  passes directly through the valve wall openings, enters the valve exhaust cavity, and exits the valve outlet opening  328 . Even though the valve wall openings  354 ,  355 ,  356  and  357  communicate through the first and second valve bottom plate openings  326  and  327  with the container, the gas flow through the valve wall openings does not enter the container  302  because the gas pressure at the first valve bottom plate opening  326  is equal to the gas pressure at the second valve bottom plate opening  327 . Thus, when the valve flapper sections  348  and  349  are in the third position, the exhaust gases bypass the container  302 .  
         [0078]     The further improved catalytic converter  300  described above with reference to  FIGS. 1 through 9   c  is preferably controlled by a control system, a preferred embodiment of which is illustrated in  FIG. 10 . During normal engine operation and normal reverse flow catalytic converter operation, a controller  250  monitors the temperature of the catalytic material in the catalytic converter. Resistance temperature detectors (RTDs)  307  attached to the catalytic converter  302  and  303 , or imbedded in the catalytic material, are preferably used to measure temperatures of the catalytic material.  
         [0079]     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  FIG. 9   c.    
         [0080]     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.  
         [0081]     As seen in  FIG. 10 , an auxiliary catalytic converter  254  connected in series to the engine exhaust system downstream of the reverse flow catalytic converter  302 / 303  may be optionally installed During bypass mode, the controller  250  activates the valve  256  to direct the exhaust flow to pass through the auxiliary catalytic converter  254 , which will oxidize at least a part of the carbon monoxide and hydrocarbons during the bypass mode. The auxiliary catalytic converter may be smaller and less expensive than the reversing flow catalytic converter  300 .  
         [0082]     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.  
         [0083]     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.  
         [0084]     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.  
         [0085]     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.  
         [0086]     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 reverse flow mode is terminated when all three thermocouples measure catalyst temperatures lower than 300° C. When any one of the three thermocouples measure a catalyst temperature higher than 350° C., the reverse flow mode is turned on.     The controller continuously computes rates of temperature rise in the catalyst and compares each computed rate of rise with predetermined values in the look-up table  258 . The controller  250  triggers the system into bypass mode if a rate of temperature rise listed in the look-up table is exceeded by a computed rate. After entering bypass mode, the reverse flow catalyst converter is bypassed, as explained above. A prediction that the catalyst is about to overheat also triggers the engine controller  252  to switch to diesel mode. This shuts off the natural gas fuel supply and causes the engine controller to begin self-diagnostics. The engine controller  252  is also preferably programmed to operate the engine in a special diesel mode, in which the diesel injection timing is advanced as compared to normal diesel mode in order to lower engine exhaust temperature The reverse flow mode is resumed after the catalyst has cooled down to a predetermined restart threshold, 580° C., for example. If each of thermocouples indicate temperatures that are lower than the restart threshold, and a catalyst damage flag has not been set, the reverse flow mode is resumed. The controller  250  sets a damage flag when any one of the thermocouples indicates a temperature that exceeds a temperature that might damage the catalyst. If a damage flag is set, the reverse flow mode is not resumed until the catalytic material has cooled to temperature below a predetermined threshold.        
 
         [0089]     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.  
         [0090]     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.  
         [0091]     The monolith material  336  of  FIG. 5  can be either an oxidation substrate or a particulate filter substrate with or without a catalyst washcoat.. The replacement of the oxidation monolith with an oxidation particulate filter trap in  FIG. 5  monolith  336 . When used with a diesel engine, the oxidizing filter trap will trap and hold particulate matter to allow effective oxidation of the carbon kernel as well as the volatile organic fractions of the particulates.  
         [0092]     In  FIG. 6 , the location and mounting of a fuel injection valve  339  is illustrated on a diesel injection manifold  347 . For a dual fuel engine, it is not likely that supplementary fuel injection will be needed, but if it is deemed useful, the injector valve  339  will be one designed for gaseous fuel injection in time duration pulses. If the reverse flow oxidizing converter is to treat exhaust gases from a diesel engine, then the injector valve  339  will be one designed for diesel fuel injection as a fine mistor vapour. The injector valve  339  supply  345  and a manifold block  347  complete with filter  340 , fuel flow control orifice  341  and check valve  342 . The manifold block will also have an air purge system momentarily activated on engine shut down to clean out the diesel lines feeding the converter. An air supply  346  is connected to the manifold block  347  along with a check valve  343  and air purge solenoid  344 . A wiring harness for power to activate the injector valve  339  and air purge solenoid  344  under command of the converter controller  250  shown in  FIG. 10 . Power will be applied to the injector valve  339  when the temperature profile is insufficient for oxidation and power will be locked off the injector valve  339  when the controller  250  is reacting to an overheat event. It is preferable to install diesel injector valve manifold diesel piping to bulkheads fitting  304  on the flow re-direction bowl  303 . The air purge solenoid will normally not be activated and will only be momentarily activated on engine shutdown sufficient to blow all diesel fuel from the diesel injection circuit including coiled capillary tubing  337  within the flow re-direction bowl  303 .  
         [0093]     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  
         [0094]     The control schematic of  FIG. 10  shows a means of diesel injection with reverse flow controller  250  that can be used for the oxidizing converter or for the oxidizing particulate trap reverse flow controller. When the RTDs  307  detect a monolith temperature moving downward and approaching the catalytic light off temperature, the converter controller  250  will command the fuel injection valve  339  to pulse a metered volume of fuel into the converter re-direction bowl through bulkhead fitting  304 . As the temperature moves upward from the added heat of the oxidizing fuel, the controller  250  will monitor the rate of temperature rise, and if below a selected threshold rate of rise, the controller will pulse more fuel into the converter. This action will continue until the monolith temperature is detected to be sufficiently above catalytic light off temperature to sustain continuous oxidation of particulate matter. Under conditions of catalyst overheat, the power to the fuel injector  339  will be disconnected until the overheat event is over. The control algorithm earlier described will act on both static temperature measurements and rate of temperature rise calculations for the oxidizing filter monolith in the same manner as for the oxidizing flow through catalyst monolith.  
         [0095]     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.  
         [0096]     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.