Abstract:
An engine processor ( 38 ) processes data for inferring temperature of exhaust gas at an exhaust manifold ( 18 ) of an internal combustion engine ( 10 ) whose exhaust system ( 16 ) contains an after-treatment device ( 26, 28 ) for treating exhaust gas and a sensor ( 30 ) for providing data for temperature of exhaust gas entering the after-treatment device. The processor processes data from the sensor and other data to infer temperature of exhaust gas at the exhaust manifold by executing an algorithm (FIGS.  3  and  4 ) that models temperature of exhaust gas at the exhaust manifold as a function of data from the sensor and the other data, including certain constants, certain geometry of the exhaust system, and certain variables related to operation of the engine.

Description:
REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM 
       [0001]    This application claims the priority of Provisional Patent Application No. 61/078,135, filed on 03 Jul. 2008, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The subject matter of this disclosure relates to internal combustion engines, especially diesel engines like those used to propel large trucks. In particular it relates to a strategy for inferring temperature of exhaust gas at an engine exhaust manifold from a measured temperature of exhaust gas entering a diesel oxidation catalyst (DOC) and using the inferred temperature as an engine control parameter, such as for control of recirculation of exhaust gas through an exhaust gas recirculation (EGR) system. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    A representative diesel engine comprises an exhaust system through which diesel exhaust gas is conveyed from the engine&#39;s cylinders to the tailpipe where it enters the surrounding atmosphere. Before passing through and out of the tailpipe, the exhaust gas is treated by an after-treatment system that comprises one or more after-treatment devices. Examples of such devices are diesel oxidation catalysts (DOC&#39;s) and diesel particulate filters (DPF&#39;s). 
         [0004]    Diesel engines that are manufactured today for use in automotive vehicles such as trucks are typically turbocharged. Heat energy in exhaust gas leaving an engine exhaust manifold is converted into mechanical energy as it passes through a turbine portion of a turbocharger to operate a compressor in the compression portion that draws air into the intake system to deliver charge air to the engine cylinders. 
         [0005]    For controlling NOx content in the exhaust gas, a portion of the exhaust gas can be recirculated from the exhaust system through an EGR system to the intake system. When the entrance to an EGR system is upstream of the turbocharger turbine, it may be appropriate for the EGR system to comprise one or more heat exchangers for cooling the exhaust gas being recirculated. Cooling of the exhaust gas can increase the effectiveness of the EGR system in limiting the generation of NOx. 
         [0006]    However, it is recognized in the industry that cooling of recirculated exhaust gas creates the potential for condensation of certain gaseous constituents in the exhaust gas. Over time such condensates may accumulate sufficiently to have a detrimental effect on performance and/or components. For example, coolant passageways in coolers may become restricted, components may corrode, and moving parts may stick. 
         [0007]    Condensation may be more extreme and/or perhaps even unavoidable at certain times, such as when a cold-soaked engine is warming after having been started and portions of its EGR system have not yet reached operating temperature. When condensation occurs along an EGR flow path and temperature of surrounding parts is sufficiently low, condensate may freeze and consequently restrict, or even block, the flow until the parts warm sufficiently to thaw the frozen condensate. 
         [0008]    Condensation may also occur regardless of whether any cooler is present in the EGR system, for example when the engine is running at low idle and exhaust gas temperatures are low. 
         [0009]    To address such situations, known practices in EGR control strategies include delaying and/or limiting EGR when conditions are conducive for condensation, and while such measures may be helpful in slowing the accumulation of condensates as an engine ages, they do impact the quantity of NOx in tailpipe emissions. 
       SUMMARY OF THE DISCLOSURE 
       [0010]    A temperature sensor associated with a diesel oxidation catalyst, or DOC, provides a measurement of the temperature of engine exhaust gas entering the DOC as an input to a processor in an engine controller. The present disclosure describes a model that enables the temperature of exhaust gas at the exhaust manifold to be inferred, or estimated, from the temperature measured by the sensor. The model is embodied, by way of illustration, as an algorithm that is executed by the processor. 
         [0011]    Briefly, the model processes data for a number of parameters related to engine operation, to ambient conditions, and to exhaust system characteristics such as its geometry. Some parameters are constants; others are variables, such as engine speed and load, that are taken into account because exhaust gas temperature will vary as engine operation changes, and variables, such as air temperature and barometric pressure, which change with changing ambient conditions. 
         [0012]    A general aspect of the disclosure relates to an internal combustion engine comprising an exhaust system which conveys exhaust gas created in engine combustion chambers to atmosphere and which comprises an exhaust manifold through which exhaust gas enters from the combustion chambers, an after-treatment device for treating exhaust gas before passing into the atmosphere, and a sensor providing data for temperature of exhaust gas entering the after-treatment device. 
         [0013]    A processor comprises an algorithm that models temperature of exhaust gas at the exhaust manifold as a function of the data from the sensor and other data, including certain thermodynamic constants, certain geometry of the exhaust system, and certain variables related to operation of the engine, and that when executed, processes the data from the sensor and the other data to calculate temperature of exhaust gas at the exhaust manifold. 
         [0014]    Another general aspect relates to a method for inferring temperature of exhaust gas at an exhaust manifold of an internal combustion engine that has an exhaust system comprising an after-treatment device for treating exhaust gas passing through the exhaust system from the exhaust manifold and a sensor providing data for temperature of exhaust gas entering the after-treatment device. 
         [0015]    The method comprises processing the data from the sensor and other data to infer temperature of exhaust gas at the exhaust manifold by executing an algorithm that models temperature of exhaust gas at the exhaust manifold as a function of data from the sensor and the other data, including certain constants, certain geometry of the exhaust system, and certain variables related to operation of the engine. 
         [0016]    The foregoing summary, accompanied by further detail of the disclosure, will be presented in the Detailed Description below with reference to the following drawings that are part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a general schematic diagram that is representative of portions of a diesel engine in a motor vehicle. 
           [0018]      FIG. 2  is a general block diagram of the strategy that is the subject of this disclosure. 
           [0019]      FIG. 3  is a schematic diagram showing more detail of one of the blocks of  FIG. 2 . 
           [0020]      FIG. 4  is a schematic diagram showing more detail of another block of  FIG. 2 . 
           [0021]      FIG. 5  is diagram defining certain parameters that appear in various Figures. 
           [0022]      FIGS. 6 through 10  are enlarged views of correspondingly numbered blocks in the block diagram of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows an example of a turbocharged diesel engine  10  having an intake system  12 , including an intake manifold  14 , through which charge air enters, and an exhaust system  16 , including an exhaust manifold  18 , through which exhaust gas resulting from combustion exits, not all details of those two systems that are typically present being shown. 
         [0024]    Engine  10  also comprises a number of cylinders  20  forming combustion chambers into which fuel is injected by fuel injectors to combust with the charge air that has entered from intake manifold  14 . Energy released by combustion in cylinders  20  powers the engine via pistons connected to a crankshaft (not specifically shown). 
         [0025]    When used in a motor vehicle, such as a truck, engine  10  is coupled through a drivetrain to driven wheels that propel the vehicle. Intake valves control the admission of charge air into cylinders  20  from intake manifold  14 , and exhaust valves control the outflow of exhaust gas into exhaust manifold  18 , through exhaust system  16 , and ultimately to ambient atmosphere via a tailpipe. 
         [0026]    Turbocharging is provided by a turbocharger  22  that comprises a turbine  22 T for converting heat energy in exhaust gas passing through the turbine after leaving exhaust manifold  18  into mechanical energy as to operate a compressor  22 C that draws air into intake system  12  through an air cleaner  23  to deliver charge air for cylinders  20 . Because the compression of the air elevates its temperature, the compressed air flows through a charge air cooler  24  where some of the heat is rejected before the charge air enters cylinders  20 . 
         [0027]    After leaving turbine  22 T and before entering the atmosphere, the exhaust gas is treated by one or more after-treatment devices in an after-treatment system  26  that includes a DOC  28  and a temperature sensor  30  for measuring temperature of exhaust gas entering the DOC. 
         [0028]    Engine  10  also comprises an EGR system  32  for recirculating some exhaust gas from exhaust system  16  successively through a cooler  34  and an EGR control valve  36  to intake system  12  for entrainment with the charge air flow to cylinders  20 . EGR valve  36  meters an appropriate amount of exhaust gas into fresh air passing through intake system  12  so that the air is diluted, consequently limiting in-cylinder temperatures and the quantity of NOx in the exhaust gas created by combustion. 
         [0029]    For inferring the temperature of exhaust gas leaving manifold  18  to enter EGR system  32 , the temperature of exhaust gas measured by sensor  30  is processed by a processor  38  according to a mathematical model that will be described with reference to  FIGS. 2 through 10 . 
         [0030]    For modeling temperature of exhaust gas at exhaust manifold  18 , heat lost during passage through the turbo down pipe from turbine  22 T and heat lost in turbine  22 T are modeled, as indicated by the respective heat-loss models shown in blocks  40  and  42  respectively of  FIG. 2 . Exhaust manifold temperature T ExhMnf  is considered to equate to the sum of temperature measured by sensor  30 , temperature lost during passage through the turbo down pipe, and temperature lost during passage through turbine  22 T. 
         [0031]    Heat loss through the turbo down pipe comprises a radiant component and a convective component. The convective component is large in comparison to the radiant component. Heat loss through turbine  22 T is due predominantly to work that it performs to operate compressor  22 C. 
         [0032]      FIG. 3  shows detail of the heat-loss model represented by block  40  in  FIG. 2 . The model is implemented in processor  38  as an algorithm that when executed calculates a value for a parameter T STACK  that represents exhaust gas temperature leaving turbine  22 T to enter the down pipe. The algorithm uses certain constants and variables to perform various preliminary calculations that include calculating an external heat transfer coefficient, h ext , and calculating an internal heat transfer coefficient, h int . 
         [0033]    External heat transfer coefficient h ext  is calculated using a mathematical model  44 . The variables used in the calculation are the nominal outside diameter of the turbo downpipe DO, velocity of the exhaust gas flowing through the downpipe U, and the temperature measurement T DOC  provided by sensor  30 . The model uses a parameter DOC_In_Temp Signal corresponding to T DOC  as the input to each of two converters  46 ,  48  for converting the DOC inlet temperature into a parameter V representing the kinematic viscosity of air and a parameter K representing thermal conductivity of air. 
         [0034]    Internal heat transfer coefficient h int  is calculated using a mathematical model  50 . The variables used in the calculation are the nominal inside diameter of the turbo downpipe DI, the nominal internal transverse cross sectional area of the downpipe A in     —     cross     —     section , ambient air temperature Ambient_Temp_Signal, engine speed N, engine torque TQI_SP, and ambient air pressure Ambient_Pres_Signal. Constants used in the calculation are the specific heat of air C p , the viscosity of air μ, and the Prandtl number P r . 
         [0035]    Ambient air temperature Ambient_Temp_Signal, engine speed N, engine torque TQI_SP, and ambient air pressure Ambient_Pres_Signal are used in a mathematical model  52  for calculating the mass flow rate of exhaust gas M exh  that is one of the parameters in model  50 . 
         [0036]    In addition to the external heat transfer coefficient h ext  and the internal heat transfer coefficient h int , ambient air temperature Ambient_Temp_Signal, the nominal transverse cross sectional area bounded by the outer surface of the downpipe Across_section, and DOC inlet temperature DOC_In_Temp Signal are used in a mathematical model  54  to yield a value, Q, for heat lost in the down pipe due to convection. Because the radiant heat loss is small in comparison to the convective heat loss, the former is not worth modeling. 
         [0037]    The lost heat Q, the mass flow rate of exhaust gas M exh , the DOC inlet temperature DOC_In_Temp Signal, and the specific heat of air C p  are used in a mathematical model  56  for calculating a data value for T STACK  representing the temperature of exhaust gas leaving turbine  22 T. 
         [0038]      FIG. 4  shows detail of the model represented by block  42  in  FIG. 2 . The model is implemented as an algorithm in processor  38  that uses the calculated value for T STACK  as one variable used in a mathematical model  58  for calculating a value for T ExeMnf  that represents exhaust gas temperature at exhaust manifold  18 . The calculation also uses DOC inlet temperature DOC_In_Temp Signal to map a parameter           representing Specific Heat Ratio of gases, exhaust back-pressure measured by a sensor at exhaust manifold  18  and converted to a corresponding value for a parameter P exh     —     mnf , ambient air pressure measured by a barometric pressure sensor and converted to a corresponding value for a parameter P amb , and pressure loss across a diesel particulate filter that is downstream of DOC  30  in after-treatment system  26 , P dpf . 
         [0039]    A calculation  60  sums P dpf  and P amb  to provide the pressure parameter P stack.  The efficiency of turbine  22 T is a parameter ηt. 
         [0040]      FIG. 5  is a chart that gives definitions of and units for thermodynamic constants that appear in the mathematical model that has been described.