Abstract:
A method for controlling temperature of a catalytic converter in an automobile exhaust system is disclosed. The method includes establishing a reference temperature for the catalytic converter, distributing a stream of exhaust gases through the catalytic converter, obtaining a measured temperature of the catalytic converter and converting thermal energy from the stream of exhaust gases into electrical energy when the measured temperature exceeds the reference temperature. An apparatus for controlling temperature of a catalytic converter in an automobile exhaust system is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to catalytic converters used in automobile exhaust systems to treat unburned hydrocarbons, carbon monoxide and various nitrogen oxides in an exhaust stream. More particularly, the present invention relates to a method and apparatus for thermoelectrically capturing thermal energy from an exhaust stream in an automobile exhaust system to control the temperature and prolong the lifetime of a catalytic converter in the system, which would lead to significant cost reduction. 
     BACKGROUND OF THE INVENTION 
     Automotive vehicles have used catalytic converters to treat unburned hydrocarbons, carbon monoxide and various nitrogen oxides produced from the combustion of hydrocarbon fuels in the engine. The engine exhaust gases flow through a catalytic converter that contains a very small quantity of noble metal catalysts such as palladium, platinum and rhodium coated on the surface of ceramic substrate inside the catalytic converter. The hydrocarbon and oxide constituents are oxidized and/or reduced by these catalysts. 
     A challenge often encountered in preparing exhaust treatment catalysts for catalytic converters lies in making the most efficient use of the relatively expensive noble metals. The noble metals must be distributed in the catalytic converter in such a manner that all of the metal is exposed to exhaust gas flowing through the converter. Due to heat and vibration, the precious noble metal particles have a tendency to agglomerate and grow over time to form larger crystalline particles with reduced conversion efficiency. Thus, it is necessary to incorporate a sufficient excess quantity of the noble metals onto the surface of ceramic substrate inside the catalytic converter to ensure continuous catalytic activity over the lifetime of the vehicle. 
     The cost of emission control systems could be reduced if the optimum dispersion of platinum group metals (PGM) nanoparticles can be achieved. It is also important to maintain optimum dispersion of the noble metals on the surface of ceramic substrate inside catalytic converter surfaces over time. For automotive applications, it would be much easier to maintain optimum dispersion of the PGM nanoparticles over the vehicle lifetime if the temperature of catalytic converters can be controlled to within a maximum temperature range of typically about 500˜650 degrees C. This requires the use of additional mechanisms to control the maximum converter temperature, which can reach temperatures of up to 1,000 degrees C. under some operating conditions if not controlled. 
     Accordingly, a method and apparatus are needed to maintain the temperature of a catalytic converter within an optimal temperature range in order to prolong the lifetime of the catalytic converter, which would lead to significant cost reduction. 
     SUMMARY OF THE INVENTION 
     The present invention is generally directed to a novel method for maintaining the temperature of a catalytic converter in an automobile exhaust system within an optimal temperature range to prevent overheating and prolong the lifetime of the catalytic converter, which would lead to significant cost reduction. In one embodiment, the method includes providing alternate exhaust flow pathways for exhaust gases generated by an internal combustion engine; providing a thermoelectric energy recovery system (ERS) in one of the exhaust flow pathways; providing a main exhaust flow pathway for receiving exhaust gas from the alternate exhaust flow pathways; and providing a catalytic converter in the main exhaust flow pathway. When the temperature of the catalytic converter is low, the exhaust gas is initially distributed through the alternate exhaust flow pathway without the ERS until the catalytic converter reaches a preset reference temperature. At that point, the exhaust gas is distributed through the alternate exhaust flow pathway having the ERS to convert most of the exhaust heat energy into electrical energy and prevent over-heating of the catalytic converter. 
     In another embodiment, the method includes providing a main exhaust flow pathway having a catalytic converter and providing at least one thermoelectric energy recovery system (ERS) in thermally-conductive relationship to the catalytic converter. Under exhaust system operation, the ERS must be cooled with a coolant to facilitate proper thermal-to-electrical conversion functioning. At low converter temperatures, the flow of coolant to the ERS is terminated to prevent functioning of the ERS and cause the temperature of the catalytic converter to rise rapidly. After the temperature of the catalytic converter reaches a preset reference temperature, flow of coolant to the ERS is resumed to resume functioning of the ERS and convert most of the exhaust heat into electrical energy. 
     The present invention is further directed to an apparatus for thermoelectrically capturing thermal energy from an exhaust stream in an automobile exhaust system to control the temperature and prolong the lifetime of a catalytic converter in the system, which would lead to significant cost reduction. In one embodiment, the apparatus includes an exhaust outlet conduit which receives exhaust gases from an automobile engine. A thermoelectric ERS conduit, in which is provided a thermoelectric ERS (energy recovery system), and an ERS bypass conduit branch from the exhaust outlet conduit. The thermoelectric ERS conduit and the ERS bypass conduit merge into a main exhaust flow conduit, in which is provided a catalytic converter. During operation of the automobile, exhaust gases initially flow through the ERS bypass conduit to the catalytic converter until the catalytic converter reaches a preset reference temperature. At that point, the exhaust gases are diverted from the ERS bypass conduit through the thermoelectric ERS in the thermoelectric ERS conduit such that most of the exhaust heat energy is converted into electrical energy. This maintains the catalytic converter within an optimum temperature range to prevent overheating and prolong the lifetime of the catalytic converter, which would lead to significant cost reduction. A battery in the automobile may be connected to the thermoelectric ERS to store the converted electrical energy for operation of automobile components. 
     In another embodiment of the invention, the apparatus for thermoelectrically capturing thermal energy from an exhaust stream in an automobile exhaust system includes an exhaust outlet conduit which receives exhaust gases from an internal combustion engine in an automobile. A catalytic converter is provided in the exhaust outlet conduit, and at least one thermoelectric ERS is provided in thermal contact with the catalytic converter. A coolant flow circuit is provided to distribute a coolant through the thermoelectric ERS for proper functioning of the ERS. During operation of the automobile, exhaust gases flow through the exhaust outlet conduit and through the catalytic converter. At low temperatures of the catalytic converter, flow of coolant is diverted from the ERS such that the ERS does not function and the temperature of the catalytic converter rises rapidly. As the temperature of the catalytic converter rises to a preset reference temperature, coolant is distributed through the ERS such that the ERS resumes functioning and most of the exhaust heat energy is converted into electrical energy. This maintains the temperature of the catalytic converter within an optimal temperature range. A battery in the automobile may be connected to the thermoelectric ERS to store the converted electrical energy for operation of automobile components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of an automobile which incorporates a thermoelectric catalytic converter temperature control apparatus according to a first embodiment of the present invention; and 
         FIG. 2  is a schematic view of an automobile which incorporates a thermoelectric catalytic converter temperature control apparatus according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , an illustrative embodiment of the apparatus for thermoelectrically capturing thermal energy from an exhaust stream in an automobile exhaust system, hereinafter apparatus, of the present invention is generally indicated by reference numeral  10 . The apparatus  10  is shown in  FIG. 1  as being a part of an automobile  31  having an internal combustion engine  32 , a transmission  34  and a drive shaft  36  which transmit rotation from the engine  32  to rear wheels  40  mounted on a rear axle  38 . A front axle  42  mounts a pair of front wheels  44 . A radiator  46  is provided for cooling the engine  32 , in conventional fashion. However, it is understood that the automobile  31  is just one example of an automobile which is suitable for implementation of the present invention. Accordingly, the invention is equally adaptable to front-wheel drive automobiles and automobiles having a drive and radiator configuration which varies from that shown in  FIG. 1 . 
     The apparatus  10  includes an exhaust outlet conduit  12  which receives exhaust gases from the engine  32  during operation of the automobile  31 . An ERS conduit  14  and an ERS bypass conduit  18  branch from the exhaust outlet conduit  12 . A thermoelectric ERS (energy recovery system)  16 , which may be conventional, is provided in the ERS conduit  14  for converting exhaust heat energy from the exhaust gases into electrical energy, as will be hereinafter described. An onboard vehicle battery  27  may be connected to the thermoelectric ERS  16 , typically through wiring  27   a , to store electrical energy generated by the thermoelectric ERS  16 . 
     The ERS conduit  14  and ERS bypass conduit  18  merge into a main exhaust flow conduit  20 . A catalytic converter  22 , which may be conventional, is provided in the main exhaust flow conduit  20 . A thermoelectric ERS  24  may be provided in the main exhaust flow conduit  20 , downstream of the catalytic converter  22 . Like the thermoelectric ERS  16 , the thermoelectric ERS  24  may be connected to the onboard vehicle battery  27 , typically through wiring  27   a , for the storage of electrical energy generated by the thermoelectric ERS  24 . 
     An actuator plate  30  is provided in the exhaust outlet conduit  12 , at the inlet of the ERS conduit  14  and of the ERS bypass conduit  18 . The actuator plate  30  is capable of being positioned in such a manner as to block the inlet of the ERS conduit  14 , as shown by the solid lines, or alternatively, to block the inlet of the ERS bypass conduit  18 , as indicated by the phantom lines. A controller  26  operably engages an actuator  29 , which in turn, operably engages the actuator plate  30  to selectively block the inlet of the ERS conduit  14  or the ERS bypass conduit  18 . A temperature sensor  28  is provided in thermal contact with the catalytic converter  22 . The temperature sensor  28  is further operably connected to the controller  26  to transmit temperature signals to the controller  26  during operation of the vehicle  31 . Accordingly, depending on the temperature of the catalytic converter  22  as measured by the temperature sensor  28 , the controller  26  causes the actuator  29  to position the actuator plate  30  in such a manner that exhaust gases flow through either the ERS conduit  14  or the ERS bypass conduit  18 , as will be hereinafter further described. It is understood that the actuator plate  30  represents one possible mechanism for alternately blocking the flow of exhaust gases through the ERS conduit  14  and the ERS bypass conduit  18  and that alternative mechanisms known by those skilled in the art may be used for the purpose. 
     Typical operation of the apparatus  10  is as follows. A reference temperature, such as about 500˜650 degrees C., for example, is initially programmed into the controller  26 . The reference temperature corresponds to the maximum temperature desired for the catalytic converter  22  during operation of the automobile  31 . After initial start-up of the automobile  31 , exhaust gases flow from the engine  32  into the exhaust outlet conduit  12 . Initially, due to the relatively low temperature of the catalytic converter  22  as measured by the temperature sensor  28 , the controller  26  causes the actuator  29  to position the actuator plate  30  in the exhaust outlet conduit  12  in such a manner that the actuator plate  30  blocks the inlet of the ERS conduit  14 . Accordingly, the exhaust gases flow through the ERS bypass conduit  18 , bypassing the thermoelectric ERS  16 . The exhaust gases flow from the ERS bypass conduit  18  and into the main exhaust flow conduit  20 ; through the catalytic converter  22  and thermoelectric ERS  24 , respectively; and are discharged from the discharge end  21  of the main exhaust flow conduit  20 . 
     After the automobile  31  has been operating for a period of typically several minutes, the temperature of the catalytic converter  22  rises substantially due to the continual flow of the exhaust gases through the catalytic converter  22 . Eventually, the temperature of the catalytic converter  22  reaches the preset reference temperature programmed into the controller  26 . Accordingly, the temperature sensor  28  relays this information, in the form of a temperature data signal, to the controller  26 , which causes the actuator  29  to change the position of the actuator plate  30  from the position indicated by the solid lines to the position indicated by the phantom lines. Therefore, the actuator plate  30  uncovers the inlet of the ERS conduit  14  and blocks the inlet of the ERS bypass conduit  18 . This facilitates flow of the exhaust gases from the exhaust outlet conduit  12  and through the ERS conduit  14  and thermoelectric ERS  16 . The thermoelectric ERS  16  converts most of the thermal energy from the exhaust gases into electrical energy. The electrical energy generated by the thermoelectric ERS  16  is typically transmitted to the onboard vehicle battery  27 , which stores the electrical energy for the powering of various components in the automobile  31 . 
     After it flows through the thermoelectric ERS  16 , the exhaust gases flow from the ERS conduit  14  and into the main exhaust flow conduit  20 ; through the catalytic converter  22  and thermoelectric ERS  24 , respectively; and out the discharge end  21  of the main exhaust flow conduit  20 . Because the thermoelectric ERS  16  converts most of the thermal energy of the flowing exhaust gases into electrical energy, the temperature of the exhaust gases as the gases subsequently flow through the catalytic converter  22  is substantially reduced. Consequently, the temperature of the catalytic converter  22  eventually drops below the preset reference temperature programmed into the controller  26 . At that point, the controller  26 , upon receiving temperature data input from the temperature sensor  28 , causes the actuator  29  to re-position the actuator plate  30  from the position indicated by the dashed lines (wherein the actuator plate  30  blocks the inlet of the ERS bypass conduit  18 ) to the position indicated by the solid lines (wherein the actuator plate  30  blocks the inlet of the ERS conduit  14 ). Accordingly, the exhaust gases again flow through the ERS bypass conduit  18 , thereby bypassing the thermoelectric ERS  16  such that the temperature of the catalytic converter  22  again rises to the preset temperature. At that point, the controller  26  again re-positions the actuator plate  30  to block the ERS bypass conduit  18  and allow flow of the exhaust gases through the thermoelectric ERS  16 , reducing the temperature of the exhaust gases prior to flow of the gases through the catalytic converter  22 . 
     Throughout operation of the automobile  31 , the foregoing cycle continues to maintain the temperature of the catalytic converter  22  at or as close as possible to the reference temperature. This prevents the temperature of the catalytic converter  22  from rising to temperatures at which agglomeration of catalysts in the catalytic converter  22  tends to occur. Accordingly, the lifetime of the catalytic converter  22  is substantially prolonged. Furthermore, the thermoelectric ERS  16  and thermoelectric ERS  24  provide an additional source of electricity for the onboard vehicle battery  27 . 
     Referring next to  FIG. 2 , another illustrative embodiment of the apparatus for thermoelectrically capturing thermal energy from an exhaust stream in an automobile exhaust system, hereinafter apparatus, of the present invention is generally indicated by reference numeral  50 . The apparatus  50  is shown in  FIG. 2  as being a part of an automobile  66  having a rear-wheel drive mechanism. However, it will be appreciated that the invention is equally adaptable to front-wheel drive automobiles and automobiles having a drive and radiator configuration which varies from that shown in  FIG. 2 . 
     The apparatus  50  typically includes an exhaust outlet conduit  52  which extends from the internal combustion engine  32  of the automobile  66 . A catalytic converter  54 , which may be conventional, is provided in the exhaust outlet conduit  52 . At least one thermoelectric ERS  56  is provided in thermal contact with the catalytic converter  54 . Preferably, a pair of thermoelectric ERS  56  is provided in thermal contact with the catalytic converter  54 . Accordingly, the catalytic converter  54  may be sandwiched between the thermoelectric ERS  56 , as shown in  FIG. 2 . Each thermoelectric ERS  56  includes a coolant system (not shown) through which a coolant (not shown) is distributed for proper functioning of the thermoelectric ERS  56 . Each thermoelectric ERS  56  may be connected, typically through wiring  68   a , to an onboard vehicle battery  68  for the storage of electrical energy generated by the thermoelectric ERS  56 . A main exhaust flow conduit  58 , having a discharge end  58   a , extends from the outlet of the catalytic converter  54 . 
     A controller  60  operably engages an actuator  62 , which in turn operably engages the coolant system (not shown) of each thermoelectric ERS  56 , according to the knowledge of those skilled in the art. A temperature sensor  64  is provided in thermal contact with the catalytic converter  54  to measure the temperature of the catalytic converter  54 . The temperature sensor  64  is operably connected to the controller  60  and relays a temperature data signal which indicates the temperature of the catalytic converter  54  to the controller  60 . Accordingly, depending on the temperature of the catalytic converter  54  as measured by the temperature sensor  64 , the controller  60  either actuates or terminates operation of each thermoelectric ERS  56  through the coolant system of each, as will be hereinafter further described. 
     Typical operation of the apparatus  50  is as follows. A reference temperature, which corresponds to the maximum temperature desired for the catalytic converter  54  during operation of the automobile  66 , is initially programmed into the controller  60 . The reference temperature is typically about 500˜650 degrees C. After initial start-up of the automobile  66 , exhaust gases flow from the engine  32  into the exhaust outlet conduit  52 ; through the catalytic converter  54  and main exhaust flow conduit  58 ; and from the discharge end  58   a  thereof, respectively. Initially, the temperature of the catalytic converter  54  as measured by the temperature sensor  64  is relatively low. Therefore, the controller  60  causes the actuator  62  to terminate flow of coolant at the cool side of each thermoelectric ERS  56 . This prevents each thermoelectric ERS  56  from converting thermal energy of the exhaust gases into electrical energy, and therefore, facilitates heating of the catalytic converter  54 . 
     After the automobile  66  has been operating for a period of typically several minutes, the temperature of the catalytic converter  54  rises substantially due to the continual flow of the exhaust gases through the catalytic converter  54 . Eventually, the temperature of the catalytic converter  54  reaches the preset reference temperature programmed into the controller  60 . Accordingly, the temperature sensor  64  relays this information, in the form of a temperature data signal, to the controller  60 . In turn, the controller  60  causes the actuator  62  to resume flow of coolant at the cool side of each thermoelectric ERS  56 . This causes each thermoelectric ERS  56  to convert thermal energy from the flowing exhaust gases into electrical energy, which is typically stored in the onboard vehicle battery  68 . Therefore, the temperature of the exhaust gases flowing through the catalytic converter  54  is reduced, causing a corresponding reduction in the temperature of the catalytic converter  54  below the reference temperature. At that point, the controller  60 , responsive to a temperature input signal from the temperature sensor  64 , causes the actuator  62  to terminate further flow of coolant at the cool side of each thermoelectric ERS  56 . Therefore, each thermoelectric ERS  56  no longer converts thermal energy from the exhaust gases into electrical energy. Consequently, the temperature of each thermoelectric ERS  56  again increases to the reference temperature, at which point the controller  60  resumes operation of each thermoelectric ERS  56 , and the cycle is repeated to maintain the temperature of the catalytic converter  54  as close as possible to the reference temperature. 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.