Abstract:
An exhaust treatment system comprises M three-way catalysts and N electrically heated catalysts (EHCs). The M three-way catalysts are arranged to receive exhaust gas output by an engine of a hybrid vehicle. M is an integer greater than one. The N EHCs are arranged to receive the exhaust gas and provide radiant heat to the M three-way catalysts when the N EHCs are powered. N is an integer greater than one.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. patent application Ser. No. [INSERT APP. # OF 8540P-000882] filed on [INSERT FILING DATE OF 8540P-000882]. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to internal combustion engines and more particularly to exhaust treatment systems. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Internal combustion engines combust an air and fuel mixture within cylinders to produce drive torque. A byproduct of combustion is exhaust gas. The exhaust gas may include various components, such as nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). An exhaust treatment system includes a catalyst that converts the NOx, CO, and HC to carbon dioxide and water. 
         [0005]    Conversion efficiency of the catalyst refers to the catalyst&#39;s ability to react with or convert one or more components of the exhaust gas. The conversion efficiency of the catalyst is related to the temperature of the catalyst. The catalyst may operate at a reduced conversion efficiency when the catalyst temperature is less than a threshold temperature. The catalyst efficiency may be increased by increasing the catalyst temperature to be greater than or equal to the threshold temperature. 
         [0006]    The catalyst temperature may be increased using various methods. For example only, heat from the exhaust gas exiting the engine may increase the catalyst temperature. The exhaust gas transfers heat to the catalyst via convection, thereby increasing the catalyst temperature. Fueling to the engine may also be adjusted to increase the catalyst temperature. For example only, unburned fuel from the engine may enter the catalyst where the fuel combusts with oxygen in the catalyst to increase the catalyst temperature. Air may be pumped into the exhaust gas and/or catalyst to increase the amount of oxygen in the catalyst. 
         [0007]    Hybrid vehicles generally have two power sources: the internal combustion engine and an electric motor. The electric motor is used more often as a power source in city driving where vehicle kinetic energy can be recovered by regenerative braking, converted to electric and chemical form, and stored in a battery, from which the motor is driven. The internal combustion engine is more suitable during highway driving, during which braking and opportunities for energy recovery are infrequent, and the engine operates at its greatest efficiency. In mixed city and highway driving conditions, the electric motor and combustion engine may be used together to transmit power to a transmission input shaft, depending on driving conditions and the magnitude of the battery capacity. 
         [0008]    Hybrid vehicles may experience long periods of engine off-time during idling and driving scenarios. During the period that the engine is off, the catalyst temperature may fall below the threshold temperature. Accordingly, catalyst heating may be required to obtain the peak efficiency of the catalyst. Maintaining the catalyst temperature at approximately the threshold temperature during engine-off periods increases the conversion efficiency of the catalyst when the engine is started. 
       SUMMARY 
       [0009]    An exhaust treatment system comprises M three-way catalysts and N electrically heated catalysts (EHCs). The M three-way catalysts are arranged to receive exhaust gas output by an engine of a hybrid vehicle. M is an integer greater than one. The N EHCs are arranged to receive the exhaust gas and provide radiant heat to the M three-way catalysts when the N EHCs are powered. N is an integer greater than one. 
         [0010]    A hybrid vehicle system comprises the exhaust treatment system and an engine control module (ECM). The ECM applies power to the N EHCs when an event occurs. 
         [0011]    In other features, the ECM applies power to all of the N EHCs when the event occurs. 
         [0012]    In still other features, the event occurs when combustion within the engine is disabled. 
         [0013]    In further features, the event occurs when combustion within the engine is disabled and torque transfer to one or more wheels of a hybrid vehicle is controlled by one or more electric motors. 
         [0014]    In still further features, the event occurs when an exhaust flowrate in an exhaust system is zero. 
         [0015]    In other features, the ECM regulates temperature of the M three-way catalysts based on a predetermined catalyst temperature when the events occurs. 
         [0016]    In still other features, the ECM warms the M three-way catalysts to the predetermined catalyst temperature before combustion within the engine is enabled. 
         [0017]    In further features, the ECM controls the power to regulate the temperatures of the M three-way catalysts based on the predetermined catalyst temperature. 
         [0018]    In still further features, N is less than nine. 
         [0019]    An exhaust treatment method comprises: implementing M three-way catalysts to receive exhaust gas output by an engine of a hybrid vehicle, wherein M is an integer greater than one; implementing N electrically heated catalysts (EHCs) to receive the exhaust gas, wherein N is an integer greater than one; and providing radiant heat to the M three-way catalysts using the N EHCs. 
         [0020]    In other features, the exhaust treatment method further comprises providing the radiant heat by selectively applying power to the N EHCs when an event occurs. 
         [0021]    In still other features, the exhaust treatment method further comprises providing the radiant heat by applying power all of the N EHCs when the event occurs. 
         [0022]    In further features, the event occurs when combustion within the engine is disabled. 
         [0023]    In still further features, the event occurs when combustion within the engine is disabled and torque transfer to one or more wheels of a hybrid vehicle is controlled by one or more electric motors. 
         [0024]    In other features, the event occurs when an exhaust flowrate in an exhaust system is zero. 
         [0025]    In still other features, the exhaust treatment method further comprises regulating temperature of the M three-way catalysts based on a predetermined catalyst temperature when the events occurs. 
         [0026]    In further features, the exhaust treatment method further comprises warming the M three-way catalysts to the predetermined catalyst temperature before combustion within the engine is enabled. 
         [0027]    In still further features, the exhaust treatment method further comprises regulating the temperature of the M three-way catalysts based on the predetermined catalyst temperature by controlling the application of power. 
         [0028]    In other features, N is less than nine. 
         [0029]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0031]      FIG. 1  is a functional block diagram of an exemplary hybrid vehicle system according to the principles of the present disclosure; 
           [0032]      FIG. 2  is an exemplary segmented, cross-sectional perspective of a catalyst assembly including a plurality of electrically heated catalysts (EHCs) according to the principles of the present disclosure; 
           [0033]      FIG. 3  is an exemplary graph of temperature versus time for the EHCs and passive, three-way catalysts according to the principles of the present disclosure; and 
           [0034]      FIG. 4  is a flowchart depicting an exemplary method performed by an engine control module according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0036]    As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0037]    A hybrid vehicle includes an engine and one or more electric motors that control drive torque output to wheels of the vehicle. In some circumstances, the engine is disabled and torque output to the wheels is controlled by the one or more electric motors. The engine may be disabled to, for example, increase the vehicle&#39;s fuel efficiency. 
         [0038]    An exhaust system that receives exhaust gas output by the engine includes a plurality of electrically heated catalysts (EHCs) and a plurality of three-way catalysts (TWCs). The EHCs and the TWCs include a catalyst material that reacts with various components of the exhaust gas to reduce the amount of those components in the exhaust gas. The catalysts of the EHCs and the TWCs, however, react with the targeted components of the exhaust gas at temperatures at or above a predetermined (i.e., threshold) temperature, such as 300° C. While the engine is disabled, the temperature of the catalysts may fall below the predetermined temperature. 
         [0039]    Accordingly, power is applied to the EHCs to heat the catalyst of the EHCs to or above the predetermined temperature while the engine is disabled. The application of power to the EHCs also generates radiant heat that radiates to the TWCs to warm the catalysts of the TWCs to or above the predetermined temperature. The electrical heating of the EHCs and the radiant heating of the TWCs increases the volume of catalyst that is at or above the predetermined temperature when the engine is re-enabled. 
         [0040]    Implementation of more than one smaller EHC and TWC rather than a single larger EHC and TWC also decreases the period necessary to increase the temperature of the catalysts to the predetermined temperature. The implementation of more than one smaller EHC and TWC rather than the single larger EHC and TWC also provides more uniform heating and enables a lesser amount of power to be drawn to heat the catalysts to the predetermined temperature. 
         [0041]    Referring now to  FIG. 1 , a functional block diagram of an exemplary hybrid vehicle system  100  is presented. The hybrid vehicle system  100  includes an engine  102  that combusts an air/fuel mixture to produce a drive torque based on a driver input module  104 . Air is drawn into an intake manifold  110  through a throttle valve  112 . For example only, the throttle valve  112  may include a butterfly valve having a rotatable blade. An engine control module (ECM)  114  may control a throttle actuator module  116 , which regulates opening of the throttle valve  112  to control the amount of air drawn into the intake manifold  110 . 
         [0042]    Air from the intake manifold  110  is drawn into cylinders of the engine  102 . While the engine  102  may include multiple cylinders, for illustration purposes a single representative cylinder  118  is shown. For example only, the engine  102  may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. Air from the intake manifold  110  is drawn into the cylinder  118  through an intake valve  122 . 
         [0043]    The ECM  114  controls a fuel actuator module  124 , which regulates fuel injection to achieve a desired air/fuel ratio. Fuel may be injected into the intake manifold  110  at a central location or at multiple locations, such as near the intake valve of each of the cylinders. In various implementations not depicted in  FIG. 1 , fuel may be injected directly into the cylinders or into mixing chambers associated with the cylinders. The injected fuel mixes with air and creates an air/fuel mixture in the cylinder  118 . 
         [0044]    A piston (not shown) within the cylinder  118  compresses the air/fuel mixture. Based upon a signal from the ECM  114 , a spark actuator module  126  may energize a spark plug  128  in the cylinder  118 , which ignites the air/fuel mixture. The timing of the spark may be specified relative to the time when the piston is at its topmost position, referred to as top dead center (TDC). In diesel and compression ignition engines, compression by the piston may ignite the air/fuel mixture. The spark actuator module  126  may be controlled by a timing signal indicating how far before or after TDC the spark should be provided. Operation of the spark actuator module  126  may therefore be synchronized with crankshaft rotation. 
         [0045]    The combustion of the air/fuel mixture drives the piston down, thereby driving a rotating crankshaft (not shown). The piston then begins moving up again and expels the byproducts of combustion through an exhaust valve  130 . The byproducts of combustion are exhausted from the hybrid vehicle via an exhaust system  134 . 
         [0046]    The intake valve  122  may be controlled by an intake camshaft  140 , while the exhaust valve  130  may be controlled by an exhaust camshaft  142 . In various implementations, multiple intake camshafts may control multiple intake valves per cylinder and/or may control the intake valves of multiple banks of cylinders. Similarly, multiple exhaust camshafts may control multiple exhaust valves per cylinder and/or may control exhaust valves for multiple banks of cylinders. 
         [0047]    The exhaust system  134  includes a catalyst assembly  136 . The catalyst assembly  136  includes a plurality of electrically heated catalysts (EHCs) and three-way catalysts (TWCs). The catalyst assembly  136  is discussed in detail below. A muffler (not shown) may be implemented in the exhaust system  134  downstream of the catalyst assembly  136 . A heater actuator module  138  selectively applies power to one or more of the EHCs based on signals from the ECM  114 . 
         [0048]    The ECM  114  may use signals from various sensors to make control decisions for the hybrid vehicle system  100 . The ECM  114  also controls operation of the engine  102  and the torque output of the engine  102 . The ECM  114  may communicate with a hybrid control module  196  to coordinate operation of the engine  102  and an electric motor  198 . While only the electric motor  198  is shown, the hybrid vehicle system  100  may include more than one electric motor. 
         [0049]    In some circumstances, the electric motor  198  may be used to produce drive torque that supplements torque output by the engine  102 . In other circumstances, the engine  102  may be shutdown (i.e., disabled) to increase fuel economy of the hybrid-vehicle. The electric motor  198  supplies drive torque for the hybrid vehicle during periods when the engine  102  is shutdown. 
         [0050]    The electric motor  198  may also function as a generator. The electric motor  198  may be used to generate electrical energy for use by the various components of the hybrid vehicle system  100  and/or storage. In various implementations, various functions of the ECM  114  and the hybrid control module  196  may be integrated into one or more modules. 
         [0051]    The ECM  114  selectively operates the hybrid vehicle in a combustion mode. The combustion mode includes using the engine  102  to produce drive torque. The ECM  114  also selectively operates the hybrid vehicle in an electric mode. The electric mode includes using the electric motor  198  to produce drive torque. The ECM  114  may operate the hybrid vehicle in a blended mode by using both the engine  102  and the electric motor  198  to produce drive torque. The ECM  114  may select the mode of operation based on a desired torque output, which may be based on a driver input. 
         [0052]    Referring now to  FIG. 2 , an exemplary segmented, cross-sectional perspective of the catalyst assembly  136  is presented. The catalyst assembly  136  includes a housing  202  that is coupled with the exhaust system  134  to receive exhaust gas output from the engine  102 . The catalyst assembly  136  receives exhaust gas output by the engine  102  at an inlet  204 . 
         [0053]    A plurality of electrically heated catalysts (EHCs) are implemented within the housing  202  of the catalyst assembly  136 . For example only,  FIGS. 2-3  depict three EHCs  206 ,  208 , and  210 . While the three EHCs  206 - 210  are described and shown, the catalyst assembly  136  may include two or more EHCs. For example only, the number of EHCs implemented in a vehicle may be based on a battery load, load on the electric motor  198 , an alternator/generator electrical output, and/or other electrical components associated with the electrical system of the vehicle. 
         [0054]    Each of the EHCs  206 - 210  includes a substrate, such as cordierite, aluminum, and/or another suitable material. The substrates may be formed in a honeycomb arrangement or in another suitable arrangement. A catalyst is applied to each of the substrates of the EHCs  206 - 210 . The catalyst may include, for example, platinum, rhodium, and/or another three-way catalyst. The catalyst reacts with various components of the exhaust gas to reduce the amount of those components in the exhaust gas. 
         [0055]    A plurality of passive, three-way catalysts (TWCs) are also implemented within the housing  202  of the catalyst assembly  136 . For example only, the catalyst assembly  136  includes four passive TWCs  212 ,  214 ,  216 , and  218 . While the four TWCs  212 - 218  are described and shown, the catalyst assembly  136  may include two or more TWCs. Each of the TWCs  212 - 218  also includes a substrate, such as cordierite, aluminum, and/or another suitable substrate. These substrates may also be formed in a honeycomb arrangement or in another suitable arrangement. 
         [0056]    A catalyst is also applied to each of the substrates of the TWCs  212 - 218 . The catalyst may include, for example, platinum, rhodium, and/or another suitable three-way catalyst. In some implementations, the same three-way catalyst is applied to both the TWCs  212 - 218  and the EHCs  206 - 210 . The catalyst of the TWCs  212 - 218  also reacts with various components of the exhaust gas to reduce the amount of those components in the exhaust gas. 
         [0057]    The EHCs  206 - 210  and TWCs  212 - 218  of the catalyst assembly  136  are arranged in a way to maximize radiant heat energy provided by the EHCs  206 - 210 . For example only, in the exemplary implementation of  FIG. 2 , the EHCs  206 - 210  and the TWCs  212 - 218  are arranged to alternate between EHCs and passive TWCs. More specifically, the EHCs  206 - 210  and the TWCs  212 - 218  are arranged in the following order starting nearest to the inlet  204 : first, the TWC  212 ; second, the EHC  206 ; third, the TWC  214 ; fourth, the EHC  208 ; fifth, the TWC  216 ; sixth, the EHC  210 ; and seventh, the TWC  218 . 
         [0058]    Each of the EHCs  206 - 210  is separated from each of the TWCs  212 - 218 . In other words, a buffer zone is provided between each of the EHCs  206 - 210  and the TWCs  212 - 218 . Exemplary buffer zones between the EHCs  206 - 210  and the TWCs  212 - 218  are illustrated by buffer zones  220 . The buffer zones  220  may be implemented to, for example, prevent electrical grounding of the EHCs  206 - 210 . 
         [0059]    The catalysts of the EHCs  206 - 210  and the TWCs  212 - 218  are effective in reacting with the exhaust gas when the temperature of the catalyst is greater than the threshold temperature (e.g., 300° C.). The heater actuator module  138  selectively applies power to the EHCs  206 - 210  based on signals from the ECM  114 . The heater actuator module  138  applies power to the EHCs  206 - 210  via electrical connectors that are associated with each of the EHCs  206 - 210 . For example only, electrical connectors  222  and  224  are associated with the EHC  206 . Electrical connectors  226  and  228  are associated with the EHC  208 , and electrical connectors  230  and  232  are associated with the EHC  210 . 
         [0060]    Power is applied to each of the EHCs  206 ,  208 , and  210  via the associated electrical connectors  222 ,  226 , and  230 , respectively. The power may be supplied by, for example, the electric motor  198 , an energy storage device (e.g., a battery), and/or another suitable power source. Power flows through the EHCs  206 ,  208 , and  210  to the electrical connectors  224 ,  228 , and  232 , respectively. The electrical connectors  224 ,  228 , and  232  are electrically connected to a ground source  234 , such as a ground source that is common to the power source. 
         [0061]    The application of power to the electrically resistive EHCs  206 - 210  causes each of the EHCs  206 - 210  to generate (resistive) heat. The EHCs  206 - 210  in turn radiate heat to the TWCs  212 - 218 . In this manner, the radiant heating provided by the EHCs  206 - 210  increases the volume of catalyst (EHC and TWC) that may be heated to the threshold temperature and effectively react with exhaust gas when the engine  102  is started. 
         [0062]    The ECM  114  selectively applies power to the EHCs  206 - 210  when the engine  102  is disabled (i.e., shutdown) and the electric motor  198  is enabled (i.e., outputting torque). In other words, the ECM  114  selectively applies power to the EHCs  206 - 210  during operation in the electric mode. The heater actuator module  138  applies the power to all of the EHCs  206 - 210 . The heater actuator module  138  may apply a predetermined amount of power to the EHCs  206 - 210 . The predetermined power amount may be set based on characteristics of the EHCs  206 - 210  and/or the TWCs  212 - 218  and may be set to, for example, 3.1 kW. 
         [0063]    Resistively heating the EHCs  206 - 210  to or above the threshold temperature enables the catalyst of the EHCs  206 - 210  to react with exhaust gas when the engine  102  is started (i.e., turned on). When power has been applied to the EHCs  206 - 210  for long enough to allow the radiant heat to increase the TWCs  212 - 218  to or above the threshold temperature, the catalysts of the TWCs  212 - 218  will also be able to react with the exhaust gas when the engine  102  is started. In this manner, the radiant heat provided by the EHCs  206 - 210  increases the effective volume of catalyst capable of reacting with exhaust gas when the engine  102  is started. 
         [0064]    Implementation of multiple EHCs and passive TWCs rather than a single larger EHC and TWC also decreases the period necessary to increase the catalyst temperatures to or above the threshold temperature. The implementation of multiple EHCs and passive TWCs rather than the single larger EHC and TWC also provides more uniform heating and enables a lesser amount of power to be drawn to heat the catalysts to the threshold temperature. Smaller EHCs and TWCs may also manufactured more easily than larger EHCs and TWCs. 
         [0065]    Referring now to  FIG. 3 , an exemplary graph of temperature versus time for an EHC and a passive TWC is presented. The passive TWC is arranged to receive radiant heat from the EHC. Exemplary trace  302  tracks the temperature of the EHC, and exemplary trace  304  tracks the temperature of the passive TWC. 
         [0066]    The ECM  114  applies power to the EHC starting at time zero. Time zero corresponds to when the engine  102  is disabled and the electric motor  198  is producing drive torque. The EHC temperature  302  increases as time passes and power is applied to the EHC. Application of power to the EHC produces radiant heat that radiates to the passive TWC, thereby increasing the passive TWC temperature  304 . 
         [0067]    In this manner, the ECM  114  increases the EHC temperature  302  and the passive TWC temperature  304  to or above the threshold temperature while the engine  102  is disabled and not producing exhaust. The catalysts of the EHC and the passive TWC will therefore likely be capable of reacting with exhaust gas output by the engine  102  with a high conversion efficiency when the engine  102  is started. In this manner, the radiant heat provided to the passive TWC while the engine  102  is disabled increases the volume of catalyst (EHC and TWC) that is capable of reacting with the exhaust gas when the engine  102  is started. 
         [0068]    At time  306 , power is removed from the EHC. The EHC temperature  302  accordingly decreases after time  306 . The passive TWC temperature  304  plateaus shortly after power is removed from the EHC as no more radiant heat is being provided to the passive TWC. Accordingly, the passive TWC temperature  304  thereafter decreases. 
         [0069]    Referring now to  FIG. 4 , a flowchart depicting an exemplary method  400  performed by the ECM  114  is presented. The method  400  determines whether the electric motor  198  is enabled in step  402 . In other words, the method  400  determines whether the electric motor  198  is operable to produce drive torque for the vehicle in step  402 . If true, the method  400  continues to step  404 ; if false, the method  400  remains in step  402 . 
         [0070]    The method  400  determines whether the engine  102  is disabled in step  404 . In other words, the method  400  determines whether the engine  102  is combusting the air/fuel mixture or producing drive torque in step  404 . In one implementation, the method  400  may determine whether the engine  102  is disabled based on whether an exhaust flow rate in the exhaust system  134  is greater than zero. If true, the method  400  continues to step  406 ; if false, the method  400  returns to step  402 . The method  400  applies power to all of the EHCs in step  406 . 
         [0071]    The method  400  determines whether the engine  102  is starting or will be started in step  408 . If true, the method  400  ends; if false, the method returns to step  406  and continues to apply power to the EHCs. In one implementation, the method  400  may also adjust the power applied to the EHCs to avoid possible overheating of the EHCs or the associated passive TWCs. 
         [0072]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.