Abstract:
A method comprises modifying combustion parameters of an engine of a hybrid vehicle to provide an engine power level insufficient to maintain crankshaft rotation at a desired speed including increasing a temperature of an exhaust gas and reducing an emissions content of the exhaust gas; and supplementing the engine power level with an electric machine of the hybrid vehicle to maintain crankshaft rotation at the desired speed. A control module comprises a cold start combustion control module that modifies combustion parameters of an engine of a hybrid vehicle to provide an engine power level insufficient to maintain crankshaft rotation at a desired speed, wherein the modifying includes increasing a temperature of an exhaust gas, and reducing an emissions content of the exhaust gas; and an electric machine control module that supplements the engine power level using an electric machine of the hybrid vehicle to maintain crankshaft rotation at the desired speed.

Description:
FIELD 
     The present disclosure relates to hybrid vehicles, and more specifically, to cold start emissions in hybrid vehicles. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Hybrid vehicles may utilize an electric machine and an internal combustion engine to selectively produce torque that is transferred to a drivetrain to operate a vehicle. Energy may also be transferred between the internal combustion engine and electric machine. In its normal operation the internal combustion engine of a hybrid vehicle may produce gas emissions. Catalytic converters may reduce exhaust gas emissions in vehicles using an internal combustion engine. 
     A catalytic converter may be three-way catalytic converter and may include a substrate with a coating of catalyst materials that stimulate the oxidation of hydrocarbons and carbon monoxide, and the reduction of nitrogen oxides, in the exhaust gas. The catalysts may operate optimally when the temperature of the catalysts is above a minimum level. Emissions control using a catalytic converter may be difficult at cold vehicle startup because the catalysts have not reached the minimum operating temperature. Cold start emissions may also be affected by engine-out emissions. 
     Catalytic converter warm-up time may be reduced at an engine cold start by generating high engine-out energy. The energy may be dependent on exhaust temperature and mass flow rate. Retarding ignition timing and increasing engine idle speed may reduce cold start emissions by increasing these parameters. However, the impact of these strategies may be limited since retarding ignition timing lowers engine efficiency and may eventually result in engine stalling. 
     SUMMARY 
     A method comprises modifying combustion parameters of an engine of a hybrid vehicle to provide an engine power level insufficient to maintain crankshaft rotation at a desired speed including increasing a temperature of an exhaust gas and reducing an emissions content of the exhaust gas; and supplementing the engine power level with an electric machine of the hybrid vehicle to maintain crankshaft rotation at the desired speed. 
     A control module comprises a cold start combustion control module that modifies combustion parameters of an engine of a hybrid vehicle to provide an engine power level insufficient to maintain crankshaft rotation at a desired speed, wherein the modifying includes increasing a temperature of an exhaust gas, and reducing an emissions content of the exhaust gas; and an electric machine control module that supplements the engine power level using an electric machine of the hybrid vehicle to maintain crankshaft rotation at the desired speed. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples 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 illustration purposes only and are not intended to limit the scope of the present disclosure in any way. The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of an exemplary hybrid vehicle; 
         FIG. 2  is a block diagram of a control module for a hybrid vehicle; 
         FIG. 3  is a flow diagram describing the steps in cold start emissions control for a hybrid vehicle. 
     
    
    
     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, and/or a processor (shared, dedicated, or group) and memory that execute one or more software or firmware program. 
     Referring now to  FIG. 1 , an exemplary hybrid vehicle  10  is schematically illustrated. Hybrid vehicle  10  may include engine  12 , electric machine  14 , transmission  16 , fuel system  18 , energy storage device (ESD)  20 , coupling  22 , control module  24 , belt-alternator system (BAS)  26 , crankshaft  28 , intake system  30 , throttle  32 , ignition system  34 , exhaust manifold  36 , and catalytic converter  38 . 
     Engine  12  may be an internal combustion engine and may be in communication with intake system  30 , exhaust manifold  36 , fuel system  18 , ignition system  34 , BAS  26 , and coupling  22 . A crankshaft  28  of engine  12  may be engaged with electric machine  14  through BAS  26 . BAS  26  may include a belt and pulleys that transfer drive torque between crankshaft  28  and electric machine  14 . Alternatively, BAS  26  may be replaced by a flywheel-alternator-starter (FAS) system (not shown), wherein electric machine  14  is operably disposed between engine  12  and transmission  16 . It is anticipated that other systems may be implemented to couple engine  12  and electric machine  14  including, but not limited to, a chain or gear system that is implemented between electric machine  14  and crankshaft  28  of engine  12 . Electric machine  14  may have an electrical connection with ESD  20  to provide electrical power to operate electric machine  14 . ESD  20  may include a rechargeable battery. 
     Engine  12  and electric machine  14  may selectively drive transmission  16  through BAS  26 , crankshaft  28  and coupling  22 . In one mode of vehicle  10  operation, electric machine  14  and engine  12  may provide drive torque to drive transmission  16  through BAS  26 , crankshaft  28  and coupling  22 . In another mode of operation, engine  12  may drive electric machine  14  through crankshaft  28  and BAS  26  to generate power used to recharge ESD  20 . In another mode of operation, electric machine  14  may use energy from ESD  20  to drive crankshaft  28  of engine  12  through BAS  26  to provide all or substantially all drive torque to transmission  16  through coupling  22 . 
     Fuel system  18  may control a fuel flow into engine  12 , throttle  32  may control an air flow into engine  12  from intake system  30 , and ignition system  34  may ignite the air/fuel mixture in engine  12 . Exhaust manifold  36  may receive exhaust gas from engine  12  and catalytic converter  38  may receive exhaust gas from exhaust manifold  36 . Catalytic converter  38  may reduce exhaust gas emissions from engine  12 . 
     Catalytic converter  38  may be a three-way catalytic converter including a substrate with a coating of catalyst materials that stimulate the oxidation of hydrocarbons and carbon monoxide, and the reduction of nitrogen oxides, in the exhaust gas. Catalytic converter  38  may begin to operate optimally when the temperature of catalytic converter  38  is at a minimum temperature. Catalytic converter  38  operating temperatures may vary based on the catalysts, construction, or other materials used in the particular catalytic converter  38 . 
     Control module  24  may be in communication with electric machine  14 , throttle  32  of intake system  30 , fuel system  18 , ignition system  34  and engine  12 , as well as other components of hybrid vehicle  10 . Control module  24  may monitor and control components of hybrid vehicle  10 . 
     Referring now to  FIG. 2 , control module  24  may include cold start combustion control module  40 , electric machine control module  42  and timing control module  50 . Cold start combustion control module  40  may include fuel control module  44 , intake control module  46  and ignition timing control module  48 . 
     Timing control module  50  may be in communication with cold start combustion control module  40 , electric machine control module  42 , and components and systems of vehicle  10 . Timing control module  50  may compare conditions such as ignition status, timing measurements related to engine operation, and temperatures that correspond to a catalytic converter  38  temperature to predetermined thresholds to determine whether vehicle  10  should be operated pursuant to a cold start strategy, as will be described in more detail with respect to control logic  100  below. Timing control module  50  may communicate a cold start status to cold start combustion control module  40  and electric machine control module  42 . 
     Cold start combustion control module  40 , fuel control module  44 , intake control module  46  and ignition timing control module  48  may be in communication with and control engine  12 , fuel system  18 , throttle  32  of intake system  30 , and ignition system  34 . Engine  12 , throttle  32  of intake system  30 , fuel system  18 , and ignition system  34  may be controlled to operate under normal conditions such that engine  12  may receive air and fuel from intake system  30  and fuel system  18 , and ignition system  34  may provide a spark such that the fuel and air are ignited within engine  12  to provide combustion power to maintain rotation of crankshaft  28  of engine  12  at a desired speed. 
     Indicated mean effective pressure (IMEP) is a measurement of the useful pressure produced by combustion and may be measured in units of kilopascals (kPa). In such normal operating conditions the IMEP of engine  12  may be in excess of 300 kPa. As will be described below with respect to the operation of control logic  100 , cold start combustion control module  40 , fuel control module  44 , intake control module  46  and ignition timing control module  48  may not operate under normal conditions when a cold start strategy is indicated by timing control module  50 . 
     Electric machine control module  42  may be in communication with cold start combustion control module  40 , timing control module  50  and electric machine  14 . Electric machine control module  42  may control electric machine  14  to selectively provide power to transmission  16  through BAS  26 , crankshaft  28  of engine  12 , and coupling  22 . 
     Referring now to  FIG. 3 , a flow chart illustrates control logic  100  providing a method of cold start emissions reduction in hybrid vehicle  10 . Block  102  may determine whether the cold start strategy is to be executed. Timing control module  42  may consider whether the vehicle is being started or may invoke more complex control strategies involving timing or measured parameters. Timing parameters may include parameters such as the elapsed time since the engine  12  was last operated while measured parameters may include a measured temperature corresponding to a temperature of catalytic converter  38 . If timing control module  42  determines that the cold start strategy is to be executed, control logic  100  may continue to block  104 . If the cold start strategy is not to be executed, control logic  100  is complete. 
     At block  104  engine  12 , fuel system  18 , intake system  30  and ignition system  34  may be operated by cold start combustion control module  40 , fuel control module  44 , intake control module  46  and ignition timing control module  48  to execute the cold start emissions strategy by operating the engine to provide exhaust with an increased temperature and reduced emissions content to catalytic converter  38 . Engine  12  may receive air and fuel from intake system  30  and fuel system  18 , and ignition system  34  may provide a spark such that the fuel and air are ignited within exhaust manifold  36  or within engine  12  during the exhaust stroke of engine  12 . 
     The timing of these events may be such that most of the combustion energy is converted to heat in the exhaust gas rather than work to provide power to maintain rotation of crankshaft  28 . When engine  12  is operated in this manner, the work provided by engine  12  may not be adequate to maintain rotation of crankshaft  28  and engine  12  may not continue to operate at a desired speed and may stall without the aid of electric machine  14 , as will be described below. In a typical engine  12  during normal operation, an IMEP of 140 kPa or less may cause engine  12  to shake and eventually misfire and stall. At a typical cold start, the minimum IMEP at which the engine may misfire and stall may be 200 kPa. Even an engine  12  that is specifically designed to operate at a low IMEP may stall at 80 kPa or less. 
     When operated with electric machine  14  as described below the IMEP of engine  12  may be 30 kPa or less. The resulting exhaust that may be received by catalytic converter  38  may have a decreased emissions content and increased temperature compared to normal operation. In an exemplary hybrid vehicle  10  the exhaust gas temperature from engine  12  may exceed normal exhaust gas temperatures by approximately 50%. For example, at five seconds after a cold start the exhaust gas temperature may be approximately 400 degrees (C.) compared to approximately 250 degrees (C.) under normal operating conditions. Hydrocarbon content of exhaust gas from engine  12  may be approximately 25% of normal exhaust hydrocarbon emissions. For example, the concentration of hydrocarbons in the exhaust gas from engine  12  may be less than 200 parts per million compared to approximately 800 parts per million under normal operating conditions. Control logic  100  may then proceed to block  106 . 
     Block  106  may operate electric machine  14  to provide supplementary drive power to engine  12 . While the cold start strategy is being executed at block  104  engine  12  may not produce enough useful power to continue rotation of crankshaft  28  at a desired speed as described above. Without supplemental power, engine  12  may stall and may not be able to assist with rotation of crankshaft  28  or propulsion of hybrid vehicle  10 . Electric machine control module  42  may control electric machine  14  to operate in combination with engine  12  to prevent a stall. As engine  12  output power is reduced to provide a heated exhaust with low emissions content, power may be provided by electric machine  14  through BAS  26  to maintain rotation of crankshaft  28  of engine  12  to prevent engine  12  from stalling. Control logic  100  may then proceed to block  108 . 
     Block  108  may determine whether the cold start strategy is complete. The determination may include timing control module  50  communicating with electric machine control module  42  and cold start combustion control module  40  to cease cold start operation and return to normal operation of electric machine  14  and engine  12  based on parameters such as timing parameters and measured parameters. 
     Timing parameters may include a predetermined cold start run time. A predetermined cold start run time may be a time necessary to heat the catalytic converter  38  of the particular hybrid vehicle  10 . Measured parameters may include measurements corresponding to emissions content of the exhaust gas or the temperature of catalytic converter  38 . If the cold start run time has elapsed, the emissions content is less than a predetermined maximum, or if the temperature of catalytic converter  38  exceeds a predetermined minimum, timing control module  50  may communicate to cold start combustion control module  40  and electric machine control module  42  that the cold start strategy is complete and control logic  100  may end. If the cold start strategy is not complete, control logic  100  may return to block  104 . 
     Those skilled in the art may now appreciate from the foregoing description that the broad teachings of the present disclosure may be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure 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.