Abstract:
A method comprises operating an engine of a vehicle to provide output torque to an input of a torque converter, determining whether the engine is in a cold start condition, fixing an input shaft of a transmission when the engine is in the cold start condition, and coupling the input shaft of the transmission to an output of the torque converter. A control module comprises a combustion control module that operates an engine of a vehicle to provide output torque to an input of a torque converter, a NPD module that determines whether the engine is in a cold start condition, and a transmission control module that fixes an input shaft of a transmission when the engine is in the cold start condition, wherein the input shaft of the transmission is in communication with an output of the torque converter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/032,234, filed on Feb. 28, 2008. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present invention relates to catalytic converter performance in a vehicle, and more specifically to reducing catalytic converter light-off time. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Catalytic converters may reduce emissions in vehicles with an internal combustion engine. The catalytic converter may be a three-way catalytic converter and may include a substrate with a coating of catalyst materials. The catalytic converter may stimulate oxidation of hydrocarbons and carbon monoxide and reduction of nitrogen oxides. The catalysts may operate optimally when a temperature of the catalytic converter is above a minimum temperature that is in a range between 200° C. to 300° C. Emissions control using a catalytic converter may be difficult during a cold start because the catalytic converter has not reached the optimal temperature. 
     Catalytic converter warm-up (or “light-off”) time may be reduced during a cold start by generating high engine-out energy. The engine-out energy may be dependent on the exhaust temperature and mass flow rate of the exhaust. Retarding ignition timing and increasing engine idle speed may reduce cold start emissions by increasing exhaust temperature and mass flow rate. However, the impact of these strategies may be limited since retarding ignition timing lowers engine efficiency and may be perceived by the driver as approaching an engine stall. 
     SUMMARY 
     A method comprises operating an engine of a vehicle to provide output torque to an input of a torque converter, determining whether the engine is in a cold start condition, fixing an input shaft of a transmission when the engine is in the cold start condition, and coupling the input shaft of the transmission to an output of the torque converter. 
     A control module comprises a combustion control module that operates an engine of a vehicle to provide output torque to an input of a torque converter, a NPD module that determines whether the engine is in a cold start condition, and a transmission control module that fixes an input shaft of a transmission when the engine is in the cold start condition, wherein the input shaft of the transmission is in communication with an output of the torque converter. 
     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 vehicle; 
         FIG. 2  is a block diagram of a control module for a vehicle; and 
         FIG. 3  is a flow diagram describing steps that provide for enhanced catalyst performance by engine load adjustment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the present teachings, applications, or uses. For purposes of clarity, the same reference numbers may 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. 
     An exemplary vehicle  10  may include engine  12 , torque converter  14 , transmission  16 , fuel system  18 , throttle  20 , intake manifold  22 , control module  24 , ignition system  26 , exhaust manifold  28 , and catalytic converter  30 . Engine  12  may be in communication with fuel system  18 , intake manifold  22 , and ignition system  26  to receive air, fuel, and a spark, respectively, to combust the air and fuel within cylinders (not shown) of engine  12 . The air input may be controlled by throttle  20  and received by intake manifold  22  to be provided to engine  12 . Fuel may be provided to engine  12  by fuel system  18  which may include a fuel pump (not shown), a fuel rail (not shown), and fuel injectors (not shown) to provide the fuel to the cylinders of engine  12 . The spark may be provided by ignition system  26 . 
     Control module  24  may be in communication with engine  12 , fuel system  18 , throttle  20 , and ignition system  26  to control the amount and timing of fuel, air, and spark delivered to the cylinders of engine  12 . The combustion may provide power to drive pistons (not shown) within the cylinders which in turn rotate a crankshaft (not shown) of engine  12  to provide an output torque. The output torque of engine  12  may be provided to an input of torque converter  14 . Torque converter  14  may transmit output torque from engine  12  to transmission  16 . 
     Transmission  16  may be an automatic transmission. An input shaft of transmission  16  may receive a torque converter  14  output. In normal operation, brakes or bands (not shown) and clutches (not shown) within transmission  16  may be hydraulically controlled to selectively engage or fix gears of a planetary gear (not shown) within transmission  16  to change a gear ratio or drive mode. 
     In order to allow engine load adjustment when the vehicle is in park or neutral, the input shaft of transmission  16  may be fixed by the selective operation of brakes or bands and clutches within transmission  16 . In such a condition torque converter  14  may slip and the engine  12  may load against torque converter  14 . When vehicle  10  is operated in this manner, the operation may be referred to as neutral pseudo drive (NPD). When vehicle  10  is in NPD mode, exhaust gas from engine  12  may have an increased temperature and mass flow rate due to the increased loading of the engine output. 
     Exhaust gas from engine  12  may exit engine  12  through exhaust manifold  28  to catalytic converter  30 . Catalytic converter  30  may be a three-way catalytic converter including a substrate with a coating of catalyst materials. The catalytic converter may stimulate the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides. Catalytic converter  30  may begin to operate optimally when the temperature of catalytic converter  30  is at a minimum temperature that is in a range between 200° C. to 300° C. The time it takes to reach this temperature may be referred to as catalyst light-off time, and may vary based on the catalysts, construction, or other materials used in the particular catalytic converter  30 . By increasing engine  12  loading in NPD mode as was described above, catalyst light-off time may be decreased. 
     Referring now to  FIG. 2 , control module  24  is depicted. Control module  24  may include combustion control module  40 , neutral pseudo drive (NPD) module  42 , and transmission control module  50 . Combustion control module  40  may include fuel control module  44 , intake control module  46 , and spark control module  48 . 
     NPD module  42  may be in communication with combustion control module  40 , transmission control module  50 , and sensors (not shown) throughout vehicle  10 . NPD module  42  may receive input parameters such as whether the vehicle ignition is ON or OFF, temperature measurements throughout the vehicle including measurements correlating to a catalytic converter  30  temperature, and may include stored values such as predetermined thresholds related to catalytic converter  30  light-off time and temperature. NPD module  42  may communicate to combustion control module  40  and transmission control module  50  whether to operate in NPD mode based on vehicle conditions. 
     Combustion control module  40 , fuel control module  44 , intake control module  46 , and spark control module  48  may control the supply and timing of fuel, air, and spark to operate engine  12  in a desired manner. This may include creating output power in response to driver commands under normal operation. Engine  12  may also be operated to provide late spark timing such that the fuel and air are ignited late in the combustion cycle to provide a reduced power to drive the pistons of engine  12  and a high temperature exhaust to exhaust manifold  28 . Engine  12  may also be operated to provide output torque that is loaded against torque converter  14  in NPD mode, thereby producing a high-temperature exhaust with a high mass flow rate to exhaust manifold  28  and catalytic converter  30 . 
     Transmission control module  50  may be in communication with torque converter  14  and transmission  16 . Transmission control module  50  may operate torque converter  14  and transmission  16  in a normal manner in response to user commands. Torque converter  14  may transfer output torque from engine  12  to transmission  16  and desired gear ratios and drive modes may be selected with transmission  16 . In response to a signal from NPD module  42  to enter NPD mode, transmission control module  50  may operate transmission  16  to fix brakes or bands and/or engage clutches of transmission  16  to fix an input shaft of transmission  16  such that the output torque of engine  12  is tied up within torque converter  14 . 
     Referring now to  FIG. 3 , control logic  100  for enhanced catalyst performance by engine load adjustment is depicted. At block  102 , NPD module  42  may determine whether NPD mode is required. NPD module  42  may consider whether the vehicle ignition has just turned from OFF to ON and may consider other parameters such as a catalytic converter temperature to determine whether heated exhaust should be supplied to catalytic converter  30 . If NPD mode is not required, control logic  100  may end. If NPD mode is required, control logic  100  may continue to block  104 . 
     At block  104 , NPD module  42  may determine whether the vehicle  10  transmission  16  is in neutral or park. NPD module  42  may prevent NPD mode from fixing the input shaft of transmission  16  when the driver places the transmission  16  in drive or reverse. If transmission  16  is in neutral or park, control logic  100  may continue to block  106 . If transmission  16  is not in neutral or park, control logic  100  may continue to block  112 . 
     At block  106 , NPD module  42  may communicate to combustion control module  40  and transmission control module  50  that NPD mode is required. Transmission control module  50  may fix an input shaft of transmission  16  such that torque converter  14  receives an output torque from engine  12 . Any output torque from engine  12  may be tied up within torque converter  14  which may slip as an input shaft to torque converter  14  may rotate while an output shaft may not. In this manner, even though engine  12  may be loaded against torque converter  14 , torque may not be transmitted through transmission  16 . Because transmission  16  does not output torque, a driver may not perceive a difference in vehicle  10  operation during NPD mode from a conventional idle. Control logic  100  may then continue to block  108 . 
     At block  108 , combustion control module  40 , fuel control module  44 , intake control module  46 , and spark control module  48  may provide combustion within cylinders of engine  12  to provide an increased output torque that is loaded against torque converter  14 . The exhaust gas provided by the loaded engine  12  during catalyst  30  light-off may be in excess of 300° Celsius. As compared to a standard neutral or park operating mode where the engine is idled, this loaded condition may increase the heat of the exhaust, the mass flow rate of the exhaust, and the exhaust manifold  28  pressure. This may result in more heat delivered from engine  12  to catalytic converter  30 , resulting in a reduced time until catalyst light-off. 
     Although the loading of engine  12  against torque converter  14  in park or neutral may reduce the need for late spark timing strategies to provide increased heat, late spark timing may also be used in conjunction with engine  12  loading to decrease catalyst light-off time. Reducing the need for late spark timing may provide for more stable combustion and reduce engine vibration during catalyst light-off. Loading engine  12  in NPD mode may also allow the engine  12  to be operated in a manner such that a shift from park or neutral to drive or reverse may be less noticeable to a driver. Control logic  100  may continue to block  110 . 
     At block  110 , NPD module  42  may determine whether NPD mode is complete. NPD module  42  may compare the time of NPD operation to a predetermined time associated with catalyst  30  light-off in a particular vehicle configuration. NPD module  42  may also consider catalyst  30  temperature. A desired catalyst  30  temperature may be 200° C.-300° C. If NPD mode is complete, control logic  100  may continue to block  112 . If NPD mode is not complete control logic  100  may return to block  104 . 
     At block  112 , transmission control module  50  may release the input shaft to transmission  16  such that torque converter  14  may transfer torque from engine  12  to transmission  16 . Control logic  100  may then end. 
     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.