Abstract:
An emissions control method may include operating a hybrid vehicle in a first mode during which a combustion engine is off and an electric motor powers propulsion of the vehicle. An electrically heated catalyst (EHC) may be energized during the first mode. The method may further include determining an operating temperature of an additional catalyst in communication with exhaust gas from the combustion engine and operating the vehicle in a second mode after the first mode during which the engine powers propulsion of the vehicle. The engine may operate in a catalyst combustion mode during the second mode when the operating temperature is below a first predetermined limit. The catalyst combustion mode may include operating the engine at an air-fuel ratio of less than stoichiometry and injecting air into exhaust gas from the engine at a location before the additional catalyst to create an exothermic reaction within the additional catalyst.

Description:
FIELD 
     The present disclosure relates to hybrid vehicle exhaust control strategies. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Hybrid vehicles may include an internal combustion engine and a hybrid power assembly. Hybrid vehicles may be operated during extended periods of time in a hybrid mode using only the hybrid power assembly. During operation in the hybrid mode, the engine may be off. When the vehicle is switched to an engine operating mode, exhaust gas exiting the engine passes through an exhaust aftertreatment system. Components of the exhaust aftertreatment system may require minimum operating temperatures for proper operation. The engine may be powered on during the hybrid mode, even when not needed for additional power output, in order to maintain the exhaust aftertreatment system at a desired operating temperature. This results in reduced fuel economy. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     An emissions control method may include operating a hybrid vehicle in a first mode during which a combustion engine is off and an electric motor powers propulsion of the vehicle. An electrically heated catalyst (EHC) may be energized during the first mode. The method may further include determining an operating temperature of an additional catalyst in communication with exhaust gas from the combustion engine and operating the vehicle in a second mode after the first mode during which the engine powers propulsion of the vehicle. The engine may operate in a catalyst combustion mode during the second mode when the operating temperature is below a first predetermined limit. The catalyst combustion mode may include operating the engine at an air-fuel ratio of less than stoichiometry and injecting air into exhaust gas from the engine at a location before the additional catalyst to create an exothermic reaction within the additional catalyst. 
     A control module may include a hybrid vehicle mode control module, an EHC control module in communication with the hybrid mode control module and an electrically heated catalyst (EHC), a catalyst temperature evaluation module, and an engine combustion control module in communication with the hybrid vehicle mode control module and the catalyst temperature evaluation module. The hybrid vehicle mode control module may control vehicle operation between first and second modes. The first mode may include a combustion engine being off and an electric motor powering propulsion of the vehicle and the second mode may include the engine being operated and powering propulsion of the vehicle. The EHC control module may energize the EHC during the first mode. The catalyst temperature evaluation module may determine an operating temperature of the additional catalyst. The engine combustion control module may operate the engine in a catalyst combustion mode during the second mode when the operating temperature is below a first predetermined limit. The catalyst combustion mode may include operating the engine at an air-fuel ratio of less than stoichiometry and injecting air into exhaust gas from the engine at a location before the additional catalyst to create an exothermic reaction within the additional catalyst. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic illustration of a vehicle according to the present disclosure; 
         FIG. 2  is a schematic illustration of a control module of the vehicle of  FIG. 1 ; and 
         FIG. 3  is an illustration of control logic for operation of the vehicle of  FIG. 1 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, 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 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, or other suitable components that provide the described functionality. 
     Referring to  FIG. 1 , an exemplary vehicle  10  may include an engine assembly  12 , a hybrid power assembly  14 , a transmission  16 , a driveline assembly  18 , an exhaust assembly  20 , and a control module  22 . The engine assembly  12  may include an internal combustion engine  24  having a crankshaft  26  rotationally driven by pistons  28 , an intake manifold  30  providing an air flow to the engine  24  and exhaust manifolds  32 ,  34  receiving exhaust gas exiting the engine  24 . 
     The hybrid power assembly  14  may include an electric motor  36  and a rechargeable battery  38 . The electric motor  36  and the rechargeable battery  38  may form a drive mechanism for the hybrid power assembly  14 . The motor  36  may be in electrical communication with the battery  38  to convert power from the battery  38  to mechanical power. The motor  36  may additionally be powered by the engine  24  and operated as a generator to provide power to charge the battery  38 . The hybrid power assembly  14  may be incorporated into and engaged with the transmission  16 . Alternatively, the hybrid power assembly  14  may be external to the transmission  16 . 
     The driveline assembly  18  may include an output shaft  40  and a drive axle  42 . The motor  36  may be coupled to the output shaft  40  via the transmission  16  to power rotation of the drive axle  42 . The engine  24  may be coupled to the transmission  16  via a coupling device  44 . The coupling device  44  may include a friction clutch or a torque converter. The transmission  16  may use the power from the engine  24  and/or the motor  36  to drive the output shaft  40  and power rotation of the drive axle  42 . 
     The vehicle  10  may be operable in a variety of modes depending on power requirements. In a first operating mode, the engine  24  may be decoupled from the transmission  16  and the electric motor  36  may drive the output shaft  40 . In a second operating mode, the crankshaft  26  may drive the output shaft  40  through combustion within the engine  24 . In the second operating mode, the engine  24  may drive the output shaft  40  by itself or in combination with the electric motor  36 . In a third operating mode, the engine  24  may drive the electric motor  36  to charge the battery  38  and may drive the output shaft  40 . 
     The exhaust assembly  20  may include an air injection assembly  46 , an exhaust conduit  48 , an electrically heated catalyst (EHC)  50 , an additional catalyst  52 , first and second oxygen sensors  54 ,  56  and first and second temperature sensors  58 ,  60 . The air injection assembly  46  may include an air pump  62  and an air injection conduit  63  in fluid communication with the air pump  62  and the exhaust manifolds  32 ,  34 . The exhaust conduit  48  may provide fluid communication between the exhaust manifolds  32 ,  34  and the EHC  50  and the additional catalyst  52 . The EHC  50  may be located upstream of the additional catalyst  52 . The EHC  50  may be powered by the battery  38 . The additional catalyst  52  may include a three-way catalyst. 
     The first and second oxygen sensors  54 ,  56  may be in communication with an exhaust gas flow upstream of the EHC  50 . More specifically, the first oxygen sensor  54  may be located in the exhaust conduit  48  proximate the outlet of the exhaust manifold  32  and the second oxygen sensor  56  may be located in the exhaust conduit  48  proximate the outlet of the exhaust manifold  34 . The first and second oxygen sensors  54 ,  56  may be in communication with the control module  22  and may provide signals thereto indicative of the oxygen concentration in the exhaust gas exiting the engine  24 . 
     The first temperature sensor  58  may be coupled to the EHC  50  and may be in communication with the control module  22 , providing a signal to the control module  22  indicative of the temperature of the EHC  50 . The second temperature sensor  60  may be coupled to the additional catalyst  52  and may be in communication with the control module  22 . The second temperature sensor  60  may provide a signal to the control module  22  indicative of the temperature of the additional catalyst  52 . 
     The control module  22  may additionally be in communication with the air pump  62  and the hybrid power assembly  14 . The control module  22  may include a hybrid vehicle mode control module  64 , an EHC control module  66 , an EHC temperature evaluation module  68 , an engine combustion control module  70 , an engine exhaust oxygen concentration evaluation module  72 , and a catalyst temperature evaluation module  74 . The hybrid vehicle mode control module  64  may control operation of the vehicle in the first, second, and third operating modes discussed above, as well as switching between the operating modes. 
     The hybrid vehicle mode control module  64  may be in communication with the EHC control module  66 . The EHC control module  66  may be in communication with the EHC temperature evaluation module  68  and may receive a signal therefrom indicating power requirements for operating the EHC at a desired temperature. The EHC temperature evaluation module  68  may receive signals from the first temperature sensor  58  indicative of the EHC operating temperature. 
     The hybrid vehicle mode control module  64  may be in communication with the engine combustion control module  70  and may command engine operation when needed. The engine combustion control module  70  may be in communication with the engine exhaust oxygen concentration evaluation module  72  and the catalyst temperature evaluation module  74 . The engine exhaust oxygen concentration evaluation module  72  may be in communication with the first and second oxygen sensors  54 ,  56  and may receive signals therefrom indicative of the oxygen concentration in the exhaust gas. The engine exhaust oxygen concentration evaluation module  72  may provide a signal to the engine combustion control module  70  indicative of the oxygen concentration in the exhaust gas. 
     The catalyst temperature evaluation module  74  may be in communication with the second temperature sensor  60  and may receive a signal therefrom indicative of the temperature of the catalyst  52 . The catalyst temperature evaluation module  74  may provide a signal to the engine combustion control module  70  indicative of the temperature of the catalyst  52 . The engine combustion control module  70  may control combustion parameters and operation of the air injection assembly  46  based on the inputs from the engine exhaust oxygen concentration evaluation module  72  and the catalyst temperature evaluation module  74 . 
     Control logic  110  for operation of the vehicle  10  is illustrated in  FIG. 3 . The hybrid vehicle mode control module  64  may initially operate the vehicle  10  in the first operating mode at start-up. Control logic  110  may begin at block  112  where the EHC temperature evaluation module  68  determines the temperature of EHC  50  during vehicle operation in the first operating mode. Control logic  110  then proceeds to block  114  where the EHC temperature is evaluated. If the EHC temperature is above a predetermined limit (T EHC     -     Desired ), control logic  110  proceeds to block  116  where EHC temperature is maintained by the EHC control module  66 . The predetermined limit (T EHC     -     Desired ) may include a temperature where the EHC  50  maintains nominal hydrocarbon (HC) treatment efficiency, such as two hundred degrees Celsius. The temperature of the EHC  50  may be maintained by controlling the powering of the EHC  50  by the battery  38 . Control logic  110  may then proceed to block  120 . 
     If the EHC temperature is below the predetermined limit (T EHC     -     Desired ), control logic  110  proceeds to block  118  where EHC temperature is increased by the EHC control module  66 . The temperature of the EHC  50  may be increased by controlling the powering of the EHC  50  by the battery  38 . For example, when the EHC is operating at a temperature below the predetermined limit (T EHC     -     Desired ), the battery  38  may provide fully power to the EHC  50 . The EHC  50  may remain powered (or energized) throughout operation in the first operating mode. Control logic  110  may then proceed to block  120 , where the vehicle operating mode is evaluated by the hybrid vehicle mode control module  64 . More specifically, control logic  110  determines whether engine operation is required. If engine operation is not required, control logic  110  may terminate and the vehicle may continue operation in the first operating mode. Otherwise, control logic  110  may proceed to block  122  where the temperature of the catalyst  52  is determined by the catalyst temperature evaluation module  74 . The temperature of the catalyst  52  may be determined before operation of the vehicle in the second operating mode. 
     The catalyst temperature evaluation module  74  may then evaluate the temperature of the catalyst  52  at block  124 . If the catalyst temperature is above a predetermined limit (T CAT     -     Desired ), control logic  110  may proceed to block  126  where operation of the vehicle in the second operating mode is initiated by the engine combustion control module  70  using a normal combustion strategy. The predetermined temperature limit (T CAT     -     Desired ) may correspond to a temperature at which the catalyst  52  is fully functional, such as at or above four hundred degrees Celsius. The normal combustion strategy may include closed loop operation of the engine using a generally stoichiometric air-fuel ratio (an air-fuel ratio of between 14.2-to-1 and 14.8-to-1). Control logic  110  may then terminate. 
     If the catalyst temperature is below the predetermined limit (T CAT     -     Desired ), control logic  110  may proceed to block  128  where operation of the vehicle  10  in the second operating mode is initiated using a catalyst combustion strategy. The catalyst combustion strategy may include operating the engine using an air-fuel ratio that is less than stoichiometric (rich operation) to produce higher carbon monoxide (CO) and hydrocarbon (HC) content in the exhaust gas relative to stoichiometric air-fuel ratio operation. More specifically, the catalyst combustion strategy includes operating the engine at an air-fuel ratio between 8-to-1 and 14.2-to-1. The EHC  50  may be operating at or above the predetermined limit (T EHC     -     Desired ) before air injection. The catalyst combustion strategy may additionally include the injection of air into the exhaust gas using the air injection assembly  46 . The engine exhaust oxygen concentration evaluation module  72  may monitor the oxygen concentration in the exhaust gas exiting the engine and control the air injection assembly  46  to provide an exhaust gas stream having a desired oxygen concentration. 
     The introduction of oxygen into the exhaust gas stream may provide increased carbon monoxide (CO) and hydrocarbon (HC) oxidation in the catalyst  52 . The carbon monoxide (CO) and hydrocarbon (HC) oxidation produces an exothermic reaction in the catalyst  52 , raising the temperature of the catalyst. After the catalyst combustion strategy has run for a predetermined time, control logic  110  may proceed to block  130  where the temperature of the catalyst  52  is again evaluated. 
     If the catalyst temperature is below the predetermined limit (T CAT     -     Desired ), control logic  110  may proceed to block  132  where engine operation is maintained in the catalyst combustion strategy. Control logic  110  may then return to block  130  where the temperature of the catalyst  52  is again evaluated. If the catalyst temperature is above the predetermined limit (T CAT     -     Desired ), control logic  110  may proceed to block  126  where the normal combustion strategy is initiated. Control logic  110  may then terminate. 
     Control logic  110  may loop back to start again at block  112  after termination. More specifically, control logic  110  may wait a predetermined time and restart at block  112 . By way of non-limiting example, the predetermined time may be at least 12.5 milliseconds (ms). Therefore, control logic  110  may run continuously during vehicle operation.