Patent Publication Number: US-2012023932-A1

Title: System and method for calculating a vehicle exhaust manifold pressure

Description:
TECHNICAL FIELD 
     The invention relates to a system and a method for calculating a vehicle exhaust manifold pressure. 
     BACKGROUND 
     In a vehicle having an internal combustion engine, exhaust gas is discharged from each engine cylinder and collected by an exhaust manifold. The exhaust manifold ultimately directs the collected exhaust gas from the engine to the vehicle&#39;s exhaust system, where it is typically processed through one or more catalysts and a particulate filter before being discharged as processed exhaust gas to the surrounding atmosphere through a tail pipe. Exhaust manifold pressure is an important feedback value for the regulation of the fuel combustion process, with this value typically measured in the exhaust manifold using a temperature-resistant pressure transducer. 
     SUMMARY 
     Accordingly, an apparatus and a method are disclosed herein for virtually sensing or calculating exhaust manifold pressure aboard a vehicle. Due to the harsh operating conditions present within an exhaust manifold, physical sensors used to directly measure exhaust pressure at that location in the conventional manner may be less than optimal both in cost and functionality. Virtual sensing technology can therefore be used instead of physical pressure sensors for this purpose. However, the robustness of virtual sensing methods can likewise be less than optimal due to the rapidly varying conditions within the exhaust system of a vehicle. 
     Therefore, a vehicle is provided herein that includes an engine, an air intake assembly, an exhaust manifold, and a controller. The air intake assembly has a variable geometry turbine (VGT) with inlet and outlet sides, with the VGT being controllable using a calibrated turbine mass flow map accessible by the controller. The controller calculates an exhaust pressure ratio between the inlet and outlet sides of the VGT, as well as first and second exhaust manifold pressures. The first and second exhaust manifold pressures are calculated using respective first and second mathematical models, with each of the models extracting information from the turbine mass flow map and calculating the exhaust manifold pressure in different manners. The controller then executes a control action using the first exhaust manifold pressure when the calculated pressure ratio exceeds a calibrated threshold, and using the second exhaust manifold pressure when the ratio does not exceed the threshold. 
     A controller is also disclosed herein that may be used with the vehicle noted above. The controller includes a host machine and the first and second mathematical models for calculating the exhaust manifold pressure in two different manners. The host machine calculates a pressure ratio between the inlet and outlet sides of the VGT, as well as a first and a second exhaust manifold pressure using the respective first and second mathematical models, and then executes a control action using the first exhaust pressure manifold pressure when the pressure ratio exceeds a calibrated threshold, and using the second exhaust pressure manifold pressure when the ratio does not exceed the threshold. 
     A method for controlling an engine operation aboard the vehicle noted above includes using the host machine to calculate a pressure ratio between the inlet and outlet side of the VGT, and to calculate a first and a second exhaust manifold pressure using the respective first and second mathematical models, wherein each of the models extracts information from the turbine mass flow map. The method further includes executing a control action via the host machine using the first exhaust manifold pressure when the pressure ratio exceeds a calibrated threshold, and using the second exhaust manifold pressure when the ratio does not exceed the threshold. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a vehicle having a controller adapted for calculating an exhaust manifold pressure as disclosed herein; 
         FIG. 2  is a schematic logic diagram for the controller shown in  FIG. 1 ; and 
         FIG. 3  is a flow chart describing an algorithm for calculating exhaust manifold pressure aboard the vehicle shown in  FIG. 1 . 
     
    
    
     DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components, a vehicle  10  is shown in  FIG. 1 . Vehicle  10  includes an electronic control unit or controller  50  adapted to calculate an exhaust manifold pressure, abbreviated P EM  hereinafter, in one of two different manners. That is, the controller  50  selects and executes one of a pair of different mathematical models  64 ,  66  (see  FIG. 2 ) in order to calculate the exhaust manifold pressure (P EM ), as explained in detail below with reference to  FIGS. 2 and 3 . 
     The particular model to be used is automatically selected by controller  50  by comparing the value of a calculated exhaust pressure ratio, abbreviated hereinafter as P R , to a calibrated threshold and then selecting one of the models  64  or  66  depending on whether or not the exhaust pressure ration (P R ) exceeds the calibrated threshold. The controller  50  can then execute an engine control action, such as regulate an air intake rate aboard the vehicle  10 , as needed using the exhaust manifold pressure (P EM ) as calculated via the respective selected first or second mathematical model  64 ,  66 . 
     The vehicle  10  includes an internal combustion engine  12 , an intake manifold  14 , an exhaust manifold  15 , an exhaust system  16 , a tail pipe  18 , and an air intake assembly  22  having an air compressor  36  and a variable geometry turbine (VGT)  38 . Vehicle  10  also includes a plurality of physical sensors, including: a flow sensor  73  positioned at an inlet side of air intake assembly  22 , a position sensor  75  sufficiently positioned to measure a vane position of VGT  38 , and a temperature model or temperature sensor  77  sufficiently positioned to measure or otherwise determine the outlet temperature of exhaust stream  37  as it passes into the VGT. Flow sensor  73  generates a flow signal  21 , the position sensor  75  generates a position signal  23 , and temperature sensor  77  generates a temperature signal  19 , each of which is relayed to controller  50  for use in calculating the exhaust manifold pressure (P EM ) as set forth below. 
     Engine  12  combusts fuel to generate engine torque, which drives an engine output shaft  24 . Output shaft  24  is selectively connectable to an input member  26  of a transmission  28  via a clutch  30 . Transmission  28  has an output member  32  which ultimately delivers drive torque from the engine  12 , and/or from one or more motor/generator units (not shown) when vehicle  10  is configured as a hybrid electric vehicle, to a set of wheels  34 , with only one of the wheels being shown in  FIG. 1  for simplicity. 
     Air, which is represented in  FIG. 1  by arrow  11 , is drawn into the engine  12  via the air intake assembly  22 . Air intake assembly  22  includes the air compressor  36  and VGT  38  noted above, with the VGT being a turbocharger device having an inlet side  90 , an outlet side  91 , and multiple vanes each with a variable geometry or turbine angle. As understood by those of ordinary skill in the art, a VGT such as the VGT  38  shown in  FIG. 1 , is a turbocharger turbine which converts the gasses of the exhaust stream  37  into mechanical energy suitable for driving the air compressor  36 . VGT  38  regulates the volume and rate of air being fed into engine  12  via its blade or vane position, which may be automatically adjusted by controller  50 . This vane position is hereinafter abbreviated as VGT POS , a value which is communicated to controller  50  as the position signal  23 . 
     Still referring to  FIG. 1 , controller  50  is in communication with the engine  12 , an exhaust gas recirculation (EGR) valve  42 , and the various components of air intake assembly  22  via a set of control signals  13 , some of which are processed by the controller using an algorithm  100  in order to calculate the exhaust manifold pressure (P EM ) as set forth below. EGR valve  42  can be controlled as needed to selectively direct a portion of the exhaust stream  37  discharged via the exhaust manifold  15  back into the intake manifold  14  as needed. The remaining exhaust stream  37  passes into the exhaust system  16  where devices such as one or more oxidation catalysts, a particulate filter, a selective reduction catalyst, a muffler, and the like (not shown) further process the exhaust gas before it is ultimately discharged to atmosphere via tailpipe  18 . 
     Controller  50  may be configured as a control module or a host machine programmed with or having access to algorithm  100 . Controller  50  is configured to calculate the exhaust manifold pressure (P EM ) at or in the exhaust manifold  15  in each of two different manners depending on the value of the exhaust pressure ratio (P R ), and to use the calculated exhaust manifold pressure to control an operation of vehicle  10 . 
     Controller  50  may be configured as a digital computer acting as a vehicle controller, and/or as a proportional-integral-derivative (PID) controller device having a microprocessor or central processing unit (CPU), read-only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and any required input/output circuitry and associated devices, as well as any required signal conditioning and/or signal buffering circuitry. Algorithm  100  and any required reference calibrations are stored within or readily accessed by controller  50  to provide the functions described below with reference to  FIGS. 2 and 3 . 
     Referring to  FIG. 2 , algorithm  100  can be broadly explained with reference to a schematic logic flow diagram  60 . Diagram  60  includes a pressure ratio calculation block  62 , respective first and second mathematical models  64  and  66 , a delay block  63 , and a software switch  68 . The software switch  68  uses the result of a threshold comparison to determine which of the respective first and second mathematical models  64  or  66  will be used to calculate the exhaust manifold pressure (P EM ), which is ultimately used as an output signal  70  for subsequent engine control or air intake regulation. 
     Pressure ratio calculation block  62  calculates and holds a data value for the exhaust pressure ratio (P R ), i.e., the ratio of pressure at the inlet side  90  of the VGT  38  to the pressure at the outlet side  91  of the VGT, or 
     
       
         
           
             
               
                 P 
                 turb_in 
               
               
                 P 
                 turb_out 
               
             
             , 
           
         
       
     
     as calculated by the controller  50  shown in  FIG. 1 . This function may be performed by first calculating the mass flow ({dot over (m)}) of the exhaust stream  37  flowing through the VGT  38 , and then by solving for the exhaust manifold pressure ratio (P R ), e.g., using the following equation: 
         {dot over (m)}=k   1 √{square root over ( 1 − P   R   k     2   )},
 
     where the terms k 1  and k 2  are traces extracted or derived from a calibrated turbine mass flow map  80 . As understood by one of ordinary skill in the art, a turbine mass flow map is a set of curves plotting the pressure ratio across the VGT  38  versus turbine mass flow and efficiency, thus describing how turbine performance changes with respect to the pressure drop across the VGT  38 . Map  80  is of the type typically provided by a manufacturer of the VGT  38  upon delivery of the VGT. The values k 1  and k 2  are functions of the measured vane position of the VGT  38 , a value which is made available to the controller  50  as the position signal  23  as transmitted by position sensor  75  (also see  FIG. 1 ). The exhaust pressure ratio (P R ) is then relayed as a signal  69  to the software switch  68 . Software switch  68  then determines which of the respective first and second mathematical models  64  and  66  to use in calculating the exhaust manifold pressure (P EA ) based on the results of a comparison of the exhaust pressure ratio (P R ) to a calibrated threshold. 
     To determine mass flow ({dot over (m)}) through the VGT  38 , the first mathematical model  38  delays the exhaust manifold pressure (P EM ), i.e., the output signal  70 , using delay block  63  by applying a suitable lag or time delay. A delayed pressure signal  170  is thus generated. First mathematical model  64  uses as input signals the delayed pressure signal  170 , which may be calculated in a previous control loop, the temperature signal  19  measured at the inlet side of VGT  38  by the temperature sensor  77 , and the position signal  23  measured by the position sensor  75  as described above. Controller  50  calculates the turbine mass flow ({dot over (m)}), i.e., the mass flow of the exhaust stream  37  passing through VGT  38 , using the following equation: 
     
       
         
           
             
               m 
               · 
             
             = 
             
               
                 
                   
                     T 
                     turb_inlet 
                   
                 
                 
                   P 
                   EM 
                 
               
                
               
                 
                   m 
                   · 
                 
                 exh 
               
             
           
         
       
     
     with the value of the exhaust pressure (P EM ) being initially predefined or calibrated, and the mass flow rate of the exhaust gas, i.e., {dot over (m)} exh , calculated using the data from flow sensor  73 , the specific heat of the gasses comprising the exhaust stream  37 , etc. Using the pressure ratio (P R ) from calculation block  62 , the controller  50  can then calculate the exhaust manifold pressure (P EM ) as the output signal  70 . 
     The second model  66  calculates exhaust manifold pressure (P EM ) in a different manner from that of first model  64 , in particular by mathematically inverting the mass flow map  80  for the VGT  38 . Second model  66  uses as input signals the turbine inlet temperature signal  19  and the position signal  23 . Controller  50  then calculates a transferred turbine mass flow ({dot over (m)} tran ) value as follows: 
     
       
         
           
             
               
                 m 
                 · 
               
               tran 
             
             = 
             
               
                 
                   P 
                   R 
                 
                  
                 
                   
                     m 
                     · 
                   
                   c 
                 
               
               = 
               
                 
                   
                     P 
                     R 
                   
                    
                   
                     
                       
                         T 
                         turb_inlet 
                       
                     
                     
                       P 
                       EM 
                     
                   
                    
                   
                     
                       m 
                       · 
                     
                     turb 
                   
                 
                 = 
                 
                   
                     
                       
                         T 
                         turb_inlet 
                       
                     
                     
                       P 
                       turb_outlet 
                     
                   
                    
                   
                     
                       m 
                       · 
                     
                     turb 
                   
                 
               
             
           
         
       
     
     where the value {dot over (m)} c  is the corrected mass flow rate, which can be determined as a function of the pressure ratio (P R ) and VGT vane position (VGT POS ), and where {dot over (m)} turb  is taken from the turbine mass flow map  80  after it has been transferred to a new coordinate system. Controller  50  then calculates the exhaust manifold pressure (P EM ) in a second manner as: 
     
       
         
           
             
               P 
               EM 
             
             = 
             
               
                 P 
                 turb_outlet 
               
                
               
                 f 
                 ( 
                 
                   
                     
                       
                         
                           T 
                           turb_inlet 
                         
                       
                       
                         P 
                         turb_outlet 
                       
                     
                      
                     
                       
                         m 
                         · 
                       
                       turb 
                     
                   
                   , 
                   
                     VGT 
                     POS 
                   
                 
                 ) 
               
             
           
         
       
     
     Software switch  68  then takes the output signals  74  and  76  from first and second mathematical models  64 ,  66 , respectively, and the pressure ratio signal  69  from calculation block  62 , and then compares the exhaust pressure ratio (P R ) of signal  69  to a calibrated threshold. If the exhaust pressure ratio (P R ) exceeds the calibrated threshold, controller  50  passes the exhaust manifold pressure output value  70  using the value calculated via the first mathematical model  64 . Otherwise, the controller  50  passes the exhaust manifold pressure as the output value  70  calculated via the second mathematical model  66 . 
     Referring to  FIG. 3 , algorithm  100  begins at step  102 , wherein the pressure ratio (P R ) is calculated and stored in memory. The algorithm  100  then proceeds to step  104 , wherein the exhaust pressure (P EM ) is calculated via two different approaches, i.e., the first and second mathematical models  64  and  66 , respectively, which are explained in detail above. 
     At step  106 , the calculated values are fed forward to the software switch  68  of  FIG. 2 , and logic is applied in order to determine which of the respective first or second mathematical models  64 ,  66  to use. In one embodiment, the controller  50  compares the pressure ratio (P R ) to a calibrated threshold. The algorithm  100  proceeds to step  108  when the pressure ratio (P R ) exceeds the calibrated threshold, and to step  110  when the pressure ratio does not exceed the calibrated threshold. 
     At steps  108  and  110 , the controller  50  feeds forward the exhaust pressure (P EM ) from a respective one of the first mathematical model  64  (step  108 ) and the second mathematical model  66  (step  110 ), and uses this value in controlling an operation of the engine  12  of  FIG. 1 , e.g., by regulating the air intake rate. Algorithm  100  may continue in a loop having a suitable period, thereby continuously controlling the operation of engine  12  and the air intake assembly  22 . 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.