Abstract:
A compact reversing flow catalytic converter with protection from overheating includes a 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 ports at the top of the container. The valve unit is mounted to the top of the container and includes an intake and an exhaust cavity. The valve unit includes a valve disk having two openings therethrough. The valve disk rotates around perpendicular central axis between a first, a second and third positions. When overheating of the catalytic material is predicted, a controller relinquishes control of the valve disk and a center return mechanism rotates the valve disk to a third position, in which each of the openings communicates with both ports so that the exhaust gas flow bypasses catalytic material. The catalytic material is thus protected from damage due to overheating. The advantage is a compact, reliable, highly efficient catalytic converter that is inexpensive to manufacture, durable, and adapted for extended service life. An alternate version of the compact reversing flow controller is also described wherein the valve unit and container are essentially as described above but the valve disk is a four position disk with the fourth position blocking communication between the valve housing and the container isolating the monolith so that maximum heat is retained during engine shut down. The valve is driven by a stepper motor that moves and holds the valve to its four positions including block, bypass, forward and reverse flow. The alternate version also replaces the oxidizing flow-through monolith with an oxidizing filter trap and adds a fuel injection system under control of the controller so that measured amounts of fuel can be injected into the valve inlet to enhance oxidation.

Description:
INTRODUCTION 
   The present invention relates to catalytic converters for internal combustion engines, and in particular, to an improved reversing flow catalytic converter for treating exhaust gases from internal combustion engines. 
   BACKGROUND OF THE INVENTION 
   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. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the present invention to provide an improved reversing flow catalytic converter system for treating exhaust gases from an internal combustion engine, which system includes a compact valve structure incorporated in the converter as well as a safeguard system to protect the catalyst and converter from overheating. 
   Another object of the present invention is to provide an 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 a three-way valve for a 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 reversing flow catalytic converter having a bypass system to protect the reversing flow catalytic converter from overheating. 
   A still further object of the present invention is to provide a three-way valve for a reversing flow catalytic converter, that is maintained in a neutral position to permit exhaust gases to bypass the catalytic converter when the valve is not actuated. 
   A further object of the present invention is to optionally provide a 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 reversing flow catalytic converter. 
   A further object of the present invention is to optionally provide a reversing flow catalytic converter with a means of injecting a controlled amount of engine fuel upstream of the 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 and additionally injected upstream of the reversing flow catalytic converter. 
   A still further object of the present invention is the optional provision of an alternate four or more way valve that is actuated by a rotary stepping motor to at least four distinct valve positions including: forward, reverse, bypass and blocked flow positions. 
   A further object of the present invention is the optional provision of a means with a blocking valve to thermally isolate the oxidizing monolith of the reversing flow converter when the internal combustion engine is shut down, and to return the blocking valve to normal operation before the internal combustion engine is started up. 
   Accordingly, in one broad aspect of the invention, a 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 port and a second port 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;   a valve for reversing an exhaust gas flow through the gas flow passage, including a valve housing with an intake cavity and an exhaust cavity, mounted to the top end of the container, the intake cavity adapted for connection to an exhaust gas pipe from said engine and exhaust cavity adapted for connection to a tail pipe for egress of said exhaust gas from said converter; and   a valve component for reversing gas flow operably mounted to the valve housing, adapted to moved between a first position in which the intake cavity communicates with the first port and the exhaust cavity communicates with the second port, a second position in which the intake cavity communicates with the second port and the exhaust cavity communicates with the first port, and a third position which allows the intake cavity to communicate with the exhaust cavity; and   a controller for controlling movement of the valve component between the first and second positions during normal operating temperatures for the catalytic converter and otherwise permitting movement of the valve component to the third position for abnormal operating temperatures.       

   Alternatively, in another aspect of such first aspect, the present invention comprises a 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 port and a second port 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;   a valve for reversing an exhaust gas flow through the gas flow passage, including a valve housing with an intake cavity and an exhaust cavity, mounted to the top end of the container, the intake cavity adapted for connection to an exhaust gas pipe from said engine and exhaust cavity adapted for connection to a tail pipe for egress of said exhaust gas from said converter; and   a valve component for reversing gas flow operably mounted to the valve housing, adapted to the be moved between a first position in which the intake cavity communicates with the first port and the exhaust cavity communicates with the second port, a second position in which the intake cavity communicates with the second port and the exhaust cavity communicates with the first port, and a third position which allows the intake cavity to communicate with the exhaust cavity; and   a controller for controlling movement of the valve component between the first and second positions during normal operating temperatures for the catalytic converter and to the third to permit bypass of exhaust gas without passing through said catalyst material during certain other temperatures for the catalytic converter.       

   Preferably, the valve housing has an interior cavity with an open bottom and a transverse wall that divides the cavity into two halves that respectively form the intake cavity and the exhaust cavity. The valve component may include a plate which is rotatably mounted to the valve housing at the open bottom, and rotates about a central axis that is perpendicular to the plate, the plate having a first opening and second opening therethrough which communicate respectively with each of the ports, and one of the intake and exhaust cavities. 
   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 ports. 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 reversing flow catalytic converter for exhaust gases, the converter comprising a container which has top end with a first port and a second port that are in fluid communication with each other so that the exhaust gases introduced into one of the first and second ports flow through a catalytic material in the container. The valve structure comprises a valve housing including an intake cavity and an exhaust cavity, adapted to be mounted to the top end of the container. The intake cavity adapted for connection of an exhaust gas pipe and the exhaust cavity is adapted for connection of a tail pipe. A valve component is provided for reversing gas flow operably mounted in the valve housing. The valve is adapted to be moved between a first position in which the intake cavity communicates with the first port and the exhaust cavity communicates with the second port, and a second position in which the intake cavity communicates the second port and the exhaust cavity communicates with the first port. The valve structure further includes a center return mechanism associated with the valve component for moving the valve component to a third position in which the intake cavity communicates with the exhaust cavity through the valve component when the 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 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 port and a second port 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 catalytic converter has a valve for reversing the exhaust gas flow through the gas flow passage, including a valve housing with an intake cavity and an exhaust cavity, mounted to the top end of the container. The intake cavity is adapted for connection of an exhaust gas pipe and the exhaust cavity is adapted for connection of a tail pipe. The valve also includes a valve component for reversing gas flow, operably mounted in the valve housing, and adapted to be moved between the first, second, and third positions. In the first position, the intake cavity communicates with the first port and the exhaust cavity communicates with the second port. In the second position, the intake cavity communicates with the second port and the exhaust cavity communicates with the first port. In the third position, the intake cavity communicates with the exhaust cavity. A controller controls movement of the valve component between the first and second positions, and movement of the 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 a reversing flow catalytic converter. In addition to controlling the 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 a reversing flow catalytic converter. The reversing flow catalytic converter includes a valve adapted for connection of an exhaust gas pipe and a tail pipe, and associated with first and second ports of a container 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 a 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 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 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 valve housing if the temperature of the valve housing is high enough. The high temperature resulting from the burning of the fuel in the valve housing retards cooling of the catalyst, and may damage the 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 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 optionally provided a method by which engine fuel may be injected through an injector valve that provides a mist of engine fuel into the inlet piping of the reversing flow converter at a location downstream of the inlet flange and upstream of the valve housing, or into the central area of the reversing flow converter within the flow redirection bowl. The method comprises of steps of monitoring temperature of the monolith material and controlling a fuel injector valve mounted on the inlet piping of the 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 four or more position valve and rotary stepper motor actuator which includes as a minimum, valve positions for; forward, reverse, bypass and blocked exhaust 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. Further, according to the eighth aspect of the invention, there is also provided a fourth or blocking position of the valve. The control method and stepper motor position the valve to this fourth position when the engine ignition key is in the “off” position. This aspect allows the oxidizing filter container to be completely blocked or isolated so that heat entrapped within the monolith will be retained to the maximum extent of time while the engine is shut down. The control method allows the blocking position to be changed to either the forward or reverse flow positions when the ignition key is in the “on” position. 
   The improved reversing flow catalytic converter of the present invention, having an appropriate controller, actuator means, and valve, will act to isolate and block the passages leading to the filter monolith when the engine is shut down, such that heat will be further retained within the monolith so that when the engine is restarted, the monolith will be able to oxidize fuel components quickly for short engine shut down periods. 
   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 
     The invention will now be further described by way of example only, and with reference to the accompanying drawings, in which: 
       FIG. 1  is a side elevation view of the improved reverse flow catalytic converter of the present invention which includes a bypass mechanism to control overheating of the catalytic material in the catalytic converter; 
       FIG. 2  is a cross-sectional view taken along line A-A of  FIG. 1  to show the structure of a rotary actuator for driving the valve; 
       FIG. 3   a  is a cross-sectional view taken along line B-B of  FIG. 1  to illustrate a center return mechanism in a position corresponding to that of the actuator shown in  FIG. 2 ; 
       FIG. 3   b  is a cross-sectional view of the center return mechanism shown in  FIG. 3   a,  with the center return mechanism in position for bypass mode; 
       FIG. 4  is a longitudinal cross-sectional view of the center return mechanism taken along line C-C of  FIG. 3   b;    
       FIG. 5   a  is a bottom plan view of the improved valve disk and housing, showing the valve disk in a first position in which exhaust gases are routed in a first direction through the catalytic converter; 
       FIG. 5   b  is a bottom plan view of the improved valve disk and housing, showing the valve disk in a second position in which exhaust gases are routed in an opposite direction through the catalytic converter; 
       FIG. 5   c  is a bottom plan view of the improved valve disk and housing, showing the valve disk in a third position in which the exhaust gases bypass the catalytic material of the catalytic converter; 
       FIG. 6  is a block diagram illustrating the control system for the reversing flow valve of the embodiment of the invention shown in  FIG. 1 ; 
       FIG. 7  is a longitudinal cross-sectional view of the canister portion of the improved catalytic converter along the line D-D of  FIG. 8 , showing an alternate arrangement for the monolith in which a catalytic particulate filter trap is installed within the reverse flow catalytic converter. In some applications the particulate filter trap monolith will not be coated with catalytic material; 
       FIG. 8  is an elevational view of the preferred embodiment of an improved reverse flow catalytic converter showing a mounting location of an optional fuel injector valve for injecting fuel upstream of the reverse flow catalytic converter. The injector valve may alternatively be mounted in a spool piece immediately upstream of the converter inlet flange or mid-way through the catalytic converter flow path such that fuel is injected within the flow redirection bowl; 
       FIG. 9  is a block diagram illustrating the optional control system for the reversing flow oxidizing filter for the embodiment of the alternate invention shown in  FIGS. 6 and 7 ; 
       FIG. 10  is a top plan view of the valve disk optionally modified for utilization in a fourth position, showing the two openings reduced by about 30% therein compared to the improved three position oxidizing catalytic converter valve disk that is similar to the bottom plan view of the two position valve disk shown in FIG. 4 of U.S. Pat. No. 6,148,613; 
       FIG. 11  is a top plan view of the container of the oxidizing filter taken along the line E-E of  FIG. 7 , showing the optionally modified adapter plate (or valve stator) made up of a ring and modified diametrical beam. This modified adapter plate flares out from the center to the ring in two diametrically opposed directions along the axis of the separating wall within the container, and reduces the area of each port by about 30% compared to the oxidizing catalytic converter adapter plate shown in FIG. 5 of U.S. Pat. No. 6,148,613. In doing so, the flared portion of the adapter plate creates a blocking area for the valve, when its reduced openings overlap the adapter plate in the flared area; 
       FIG. 12   a  is a bottom plan view of the optionally modified valve disk and housing with the adapter plate superimposed above the valve disk showing the valve disk in the first position in which exhaust gases are routed in a first direction through the filter trap; 
       FIG. 12   b  is a bottom plan view of the optionally modified valve disk and housing with the adapter plate superimposed above the valve disk showing the valve disk in the second position in which exhaust gases are routed in a second or reverse direction through the filter trap; 
       FIG. 12   c  is a bottom plan view of the optionally modified valve disk and housing with the adapter plate superimposed above the valve disk showing the valve disk in the third position in which exhaust gases bypass the filter trap; and 
       FIG. 12   d  is a bottom plan view of the optionally modified valve disk and housing with the adapter plate superimposed above the valve disk showing the valve disk in the fourth position in which the filter trap is completely enclosed and separated from the valve and the engine exhaust and tail pipe. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates an improved catalytic converter  200  in accordance with an embodiment of the present invention which incorporates a safeguard system to inhibit overheating the catalyst monoliths. 
   With reference to  FIG. 1 , the catalytic converter  200  comprises a container  40  and valve housing  42  with a similar structure and components as described in U.S. Pat. No. 6,148,613. A rotary actuator  202  and a center return mechanism  204  are mounted on the drive shaft  50  of the valve disk  18 . The rotary actuator  202  is controlled to periodically rotate the valve disk  18  between the first and the second positions to reverse gas flow through the container  40 . 
   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 disk  18  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 disk  18  as shown in  FIG. 5   a,  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 disk  18 , as shown in  FIG. 5   b,  to permit the exhaust gases to flow through the container  40  in the opposite direction. 
   As shown in  FIGS. 3   a,    3   b  and  4 , the center return mechanism  204  includes a base block  222  having a circular bore  224  at an apex of triangular cavity  226 . An annular groove  228  is formed in the block along an outer side of the triangular cavity  226  the annular groove  228  is recessed further than the triangular cavity  226 . A swivel arm  230  is connected on one end to a pivot shaft  232  that is rotatably mounted in the bore  224  of the base block. A depending leg  231  depends from a free end of the swivel arm  230 . Two coil springs  234  and  236  are retained in the annular groove  228 , each is restrained between one end of the groove  228  and one side of the swivel arm  230 . A connector  238  is integrally formed with the pivot shaft  232 , 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 member  230  is adapted to swivel within the triangular cavity  226  and compress one of the springs  234 ,  236  as it swivels. The other of the springs  234 ,  236  is retained between the other end of the annular groove and stop members  240 ,  242  that extend from opposite sides of the groove  228 . The stop members  240  and  242  are spaced apart from each other to permit the depending leg  231  of the swivel arm  230  to pass through when the swivel arm  230  pivots from one side to the other. A cover  243  is provided to retain the swivel arm  230  and springs  234 ,  236  within the base block  222 . When the pressure vane  210  of the rotary actuator  202  is at the left side, corresponding to the first position of the valve disk  18  shown in  FIG. 5   a,  the swivel arm  230  of the center return mechanism  204  is located on the left side and compresses spring  234 . 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 disk  18  is in the second position as shown in  FIG. 5   b.  However, when the rotary actuator  202  is deactivated (no fluid pressure is applied to either side of the pressure vane  210 ), the swivel arm  230  of the center return mechanism  204  is forced by one of the springs  234 ,  236  to return to the central position shown in  FIG. 3   b.  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 disk  18  to the bypass position shown in  FIG. 5   c.    
     FIGS. 5   a ,  5   b  and  5   c . illustrate the valve disk  18  in its three positions, for respectively forward and reverse exhaust flow through the container  40  and for bypassing the catalytic material. For clearer illustration, these figures illustrate only a bottom plan view of the valve disk  18  sitting above the valve housing and below the adapter plate  46 . With respect to  FIGS. 5   a ,  5   b , and  5   c , references to “above” or “over” refer to portions of the reverse flow catalytic converter nearer to the bottom of  FIG. 1 , while references to “below” or “under” refer to portions of the reverse flow catalytic converter nearer to the top of  FIG. 1 . The exhaust gas inlet  43  and exhaust gas outlet  44  which are located below the valve disk  18 , and the first port  27  and the second port  28  of adapter plate  46  which are located above the valve disk  18  are shown in broken lines. The vertical center line  51  indicates the position of the valve housing transverse wall which is also below the valve disk  18  and divides the interior cavity of the valve housing  42  into the intake cavity and exhaust cavity, similar to that shown in FIG. 3 of U.S. Pat. No. 6,148,613. The horizontal central line  52  indicates the position of the container transverse plate which is located above the valve disk  18  and separates the interior of the container into the first and second compartments, as shown in  FIG. 7 . 
   When the valve disk  18  is in the first position as shown in  FIG. 5   a,  the gas flow enters intake cavity from the inlet  43  which is at the left side of central line  51  (valve housing separating wall) below the valve disk  18 . The gas flow passes through the valve opening  22  (upper left) to enter the container through first port  27  and disperse into the cells of the catalytic material above within the container on the upper side of the transverse wall indicated by line  52 . 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 lower side of line  52 , and passes first through second port  28  and then through the valve opening  22  (lower right) to the exhaust cavity which is on the right side of line  51 . The gas flow then exits through the outlet  44 . 
   As shown in  FIG. 5   b,  when the valve disk  18  is the second position, it is rotated 90° clockwise so that the gas flow entering the intake cavity through the inlet  43  passes through valve opening  22  which is now at the lower left quadrant. Therefore the gas flow must enter the container through the second port  28  and exit the container through the first port  27  so that the gas flow in the container is reversed, in comparison to the gas flow shown in  FIG. 5   a.    
   If during the reversing flow operation of the catalytic converter  40 , 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  230  of the center return mechanism  204  is forced by one of the springs  234  or  236 , to return to its central position as shown in  FIG. 3   b.  Thus, the center return mechanism  204  moves the valve disk  18  to the third (bypass) position which is between the first and second positions, as shown in  FIG. 5   c . The valve disk  18  is maintained in the third position until the rotary actuator  202  is reactivated. When the valve disk  18  is in the third position, the valve openings  22  communicate with both the intake cavity to the left of line  51 , over the valve housing transverse wall (located on line  51 ) and the exhaust cavity to the right of line  58 . Thus, the gas flow entering the intake cavity through the inlet  43  passes directly over the valve housing transverse wall (located on line  51 ), enters the exhaust cavity, and exits the outlet  44 . Even though the valve openings  22  communicate through the first and second ports  27  and  28  with the container, the gas flow through the openings  22  does not enter the container  40  because the gas pressure at the first port  27  is equal to the gas pressure at the second port  28 . Thus, when the valve disk  22  is in the third position, the exhaust gases bypass the container  40 . 
   The catalytic converter  200  described above with reference to  FIGS. 1 through 5   c  is preferably controlled by a control system, a preferred embodiment of which is illustrated in  FIG. 6 . 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. Thermocouples  49  attached to the catalytic converter  200 , or imbedded in the catalytic material, are preferably used to measure temperatures of the catalytic material. 
   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  18  so that the reverse flow valve  18  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 center return mechanism  204  forces the reverse flow valve  18  into the third position to cause the gas flow to bypass the catalytic converter  200 , as described above with reference to  FIG. 5   c.    
   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  FIG. 6 , an auxiliary catalytic converter  254  connected in series to the engine exhaust system downstream of the reverse flow catalytic converter  200  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  200 . 
   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  200 . Each time the controller  250  samples the temperature of the catalyst using the thermocouples  49 , 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 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.       

   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 replacement of the oxidation flow through catalyst with an oxidation particulate filter trap  260  is illustrated in  FIG. 7 . The oxidizing filter trap sections  260  are shown located near the center of the reactor core on both sides of the flow redirection bowl section  269 . The sections immediately upstream and downstream of the central core sections  260  are sections  261  and may be an oxidizing catalytic section of monolith as used in the reverse flow oxidizing catalyst. Sections  262  may be sections of monolith without catalytic coating. When used with a diesel engine, the oxidizing filter trap sections  260  will trap and hold particulate matter to allow effective oxidation of the carbon kernel as well as the volatile organic fractions of the particulates. 
   In  FIG. 8 , the location and mounting of a fuel injection valve  259  is illustrated at the inlet side  43  of the reverse flow oxidizing converter. 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  259  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  259  will be one designed for diesel fuel injection as a fine mist. The injector valve  259  will have a fuel line  261  connected to it as well as a wiring harness for power to activate the injector valve  259  under command of the converter controller  250  shown in  FIG. 9 . Power will be applied to the injector valve  259  when the temperature profile is insufficient for oxidation and power will be locked off the injector valve  259  when the controller  250  is reacting to an overheat event. Alternatively, it may be preferable to install diesel injector valve  259  at a location such that the additional fuel is injected into the flow redirection bowl  269  ( FIG. 7 ). 
   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  259 . 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 optional control schematic for the oxidizing particulate trap reverse flow controller  250  is illustrated in  FIG. 9 . When the thermocouples  49  detect a monolith temperature moving downward and approaching the catalytic light off temperature, the converter controller  250  will command the fuel injection valve  259  to pulse a metered volume of fuel  261  into the converter inlet piping  43  or redirection bowl  269 . 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  259  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. 
   The valve disk  263  as optionally modified for inclusion of the fourth or blocking position, is shown in  FIG. 10 . Both valve openings  264  have been reduced by about 30% in order to allow for the blocking position. When the internal combustion engine is shut down by moving the ignition key to the “off” position, the valve actuator will move the valve to the fourth or block position. 
     FIG. 11  shows the optionally modified adapter plate  265  and its smaller ports  266  and  267  which have also been reduced by about 30% to accommodate the blocking position when valve openings  264  are directly over the flared sections  268  of the diametrical beam. In this fourth position of the valve, the converter monolith is completely isolated and contained so that heat trapped within the monolith in the container, is maximally retained for the duration of the block position, or while the engine is shut down. Only when the engine ignition key is switched to start the engine, is the valve moved from the fourth or blocking position to the first or second position as required for forward or reverse flow. 
     FIG. 12   a  shows the first or forward flow position of the optionally modified valve wherein engine exhaust gas enters valve housing inlet pipe  43  into the valve housing inlet cavity and then passes through rotor valve opening  264  and then through port  267  (in phantom)in adapter plate  265  and then into and through the oxidizing filter, then through port  267  (in phantom) in adapter plate  265  and rotor valve opening  264  into the valve housing outlet cavity and finally to valve housing outlet pipe  44  and into the exhaust tail pipe. 
     FIG. 12   b  shows the second or reverse flow position of the optionally modified valve wherein engine exhaust gas enters valve housing inlet pipe  43  into the valve housing inlet cavity and then passes through rotor valve opening  264  and then through port  267  (in phantom) in adapter plate  265  and then into and through the oxidizing filter in a direction reversed from the forward flow direction, then through port  266  (in phantom) in adapter plate  265  and rotor valve opening  264  into the valve housing outlet cavity and finally to valve housing outlet pipe  44  and into the exhaust tail pipe. 
     FIG. 12   c  shows the third or bypass position of the optionally modified valve wherein the engine exhaust gas enters valve housing inlet pipe  43  into the valve housing inlet cavity and then passes through both valve openings  264  and  264  and both adapter plate ports  266  and  267  over the valve housing transverse wall and directly through adapter plate ports  266  and  267  and both valve openings  264  into the valve housing outlet cavity and then to valve housing outlet pipe  44  and into the exhaust tail pipe. 
     FIG. 12   d  shows the optional fourth or blocked flow position wherein after the engine is shut down, the ignition system signals the valve control system to position rotor valve openings  264  directly over the pie shaped flared areas  268  of the adapter plate  265  such that the oxidizing filter container is completely blocked and isolated allowing maximum heat retention within the container for the duration of engine shut down. Valve openings  264  will automatically be positioned to either the forward or reverse flow direction prior to engine start, providing the highest oxidizing filter temperature possible after shut down. For short engine shut downs such as prevalent with delivery vehicles or hybrid diesel electric vehicles, the filter monolith will achieve early oxidation after a short engine shut down. 
   The four position valve can also be optionally achieved by modifying the adapter plate  265  such that the diametrical beam connects to the ring of the adapter plate  265  as for the three way valve application but the flared or pie shaped portions  268  are extended from the center of the adapter plate  265  in two diametrically opposite directions along a diametrical line at right angles to the diametrical beam  56 . With a valve rotor the same as for the four position valve described earlier in  FIG. 11 , the combination of modified valve rotor and optionally modified adapter plate will also act effectively the same as described in the text for  FIG. 12   d . There may be advantages in some applications for the optionally modified valve. 
   The advantages of the 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 lose between the valve and the catalyst. The valve disk 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 series improves catalyst life and conversion performance. And the reversing exhaust gas flow ensures maximum efficiency of conversion by keeping the catalyst material uniformly heated to increase catalytic activity for pollutant reduction. Furthermore, the safeguard system 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.