Abstract:
An EGR system is disclosed for reducing NO x  emissions and that may eliminate the need for a SCR system. The disclosed EGR system includes dual valves, including a hot EGR valve disposed in the exhaust manifold and a cold EGR valve disposed upstream of the intake manifold. A VGT turbine with adjustable vanes may also be employed with a low pressure turbine. Intake air may proceed through both a high pressure compressor as well as a low pressure compressor and the high pressure compressor may be substantially bypassed by way of a bypass valve disposed between the low pressure compressor and the air intake. The EGR system may be controlled by adjusting the positions of the valves and VGT turbine vanes.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to exhaust gas recirculation (EGR) systems for reducing NO x  emissions. More specifically, this disclosure relates to EGR systems that recirculate large volumes of exhaust to eliminate or at least reduce the need for a catalytic system in addition to the disclosed EGR systems. 
       BACKGROUND 
       [0002]    An internal combustion (IC) engine may include an exhaust gas recirculation (EGR) system for controlling the generation of undesirable pollutant gases and particulate matter. EGR systems recirculate exhaust gases and particular matter into the intake air supply of the IC engine. The exhaust gases, which are recirculated to the engine cylinders, reduce the concentration of oxygen in the cylinders, which lowers the maximum combustion temperature in the cylinders and slows the chemical reaction of the combustion process. As a result, a decrease in nitrous oxides (NO x ) formation is achieved. Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned upon recirculation the engine cylinder and which further reduces the emission of exhaust gas by-products. 
         [0003]    An IC engine may also include one or more turbochargers for compressing air which is supplied to one or more combustion chambers of corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the air to be compressed and supplies the compressed air to the combustion chambers. The compressor may also be used to compress a fuel/air mixture as well as air. 
         [0004]    When utilizing EGR in a turbocharged diesel engine, the exhaust gases to be recirculated may be removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted by a poppet-type EGR valve downstream from the exhaust manifold. The percentage of the total exhaust flow which is diverted for introduction into the intake manifold of the engine is known as the “EGR rate” of the engine. One example of an EGR system can be found in U.S. Pat. No. 6,128,902, which discloses an EGR valve  34  disposed in a conduit  32  that connects the exhaust manifold  28  to the intake manifold  26 . 
         [0005]    Variable-geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (sometimes called A/R ratio) of the VGT turbine to be altered as conditions change. A VGT turbine typically has a set of movable vanes to control pressure of the exhaust flowing through the VGT turbine. At low engine speeds when exhaust flow is low, the vanes are partially closed to accelerate the VGT turbine. Accelerating the VGT turbine increases boost pressure delivered by the compressor that is driven by the VGT turbine. As the engine speed increases, the vanes are opened to slow down the VGT turbine. Slowing down the VGT turbine prevents the boost pressure provided by the compressor from reaching excessive levels. 
         [0006]    VGTs have proven useful because an optimum aspect ratio at low engine speeds is different from an optimum aspect ratio at high engine speeds. If the aspect ratio is too large, the turbocharger may fail to create boost at low speeds; if the aspect ratio is too small, the turbocharger may choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. 
         [0007]    By altering the vane positions as the engine accelerates, the aspect ratio of the VGT turbine can be maintained at its optimum. As a result, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs tend to be much more common on diesel engines because the lower exhaust temperatures of diesel engines means the VGTs are less prone to failure. 
         [0008]    Selective catalytic reduction (SCR) systems catalytically convert NO x  to nitrogen and water. A gaseous reductant, typically urea or ammonia, is added to the exhaust gas stream where it is adsorbed onto the catalyst. Carbon dioxide is a reaction product when urea is used as the reductant. Because of the need to supply both a reductant and a catalyst, SCR systems tend to be space intensive and are most appropriate for large utility boilers, industrial boilers, and municipal solid waste boilers. However, due to increasingly stringent emission standards, recent applications include diesel engines. Further, because current EGR systems do not meet Tier4 admission standards, the combination of EGR and SCR systems in diesel engine designs has become common. 
         [0009]    However, an SCR system requires the driver or maintenance staffer to replenish an on-board urea or ammonia tank that contains the reactant in an aqueous solution. Further, operators must buy and store the solution or have drivers find it while on the road. A pump pushes the solution out of the tank. Because the solution is about two-thirds purified water, a heater is used in the tank or line between it and the dosing chamber, where solution is injected downstream of the particulate filter. This equipment plus the solution, which weighs about 9 pounds per gallon, adds 200 to 400 pounds and occupies precious space on a truck. This can be a major drawback to any weight-conscious owner and presents packaging problems for manufacturers of diesel trucks and other equipment that includes an SCR. 
         [0010]    Thus, there is a need for an improved emission control system for internal combustion engines that can meet the new stringent emission requirements in terms of NO x , yet avoid the disadvantages of SCR systems and the combination of EGR and SCR systems. 
       SUMMARY OF THE DISCLOSURE 
       [0011]    In one aspect, a method for controlling an internal combustion engine is disclosed. The engine may include an engine block that defines a plurality of cylinders, an intake manifold, an exhaust manifold, a controller and an exhaust gas recirculation (EGR) system. The EGR system may include a cold EGR valve in combination with the intake manifold and a hot EGR valve in communication with the exhaust manifold. The EGR system may circulate a portion of the exhaust gases from the exhaust manifold to the intake manifold through the cold EGR valve. The controller may communicate with hot and cold EGR valves. The method may include adjusting the cold EGR valve and adjusting the hot EGR valve to vary a portion of the exhaust gases directed from the exhaust manifold to the intake manifold, depending upon a load condition of the engine. As a result, the portion of the exhaust gases provided to the plurality of cylinders by the EGR system may be greater than 40% of the total exhaust gases output from all of the cylinders. 
         [0012]    In another aspect, an internal combustion engine is disclosed. The engine may include a cold exhaust gas recirculation (EGR) valve that is adjustable between an open position and a closed position. The engine may also include an intake manifold that receives recirculated exhaust gas from the cold EGR valve when the cold EGR valve is not in the closed position. The engine may further include at least one combustion cylinder in communication with the intake manifold and an exhaust manifold in communication with the at least one combustion cylinder and a turbine. The engine may further include a hot EGR valve disposed in the exhaust manifold and that may be adjustable between a closed position wherein the at least one cylinder is isolated from the turbine and in communication with the cold EGR valve and an open position where the at least one cylinder is in communication with the turbine. 
         [0013]    In yet another aspect, an internal combustion engine is disclosed that may include a cold exhaust gas recirculation (EGR) valve and an intake manifold that receives recirculated exhaust gas from the cold EGR valve. The engine may further include a plurality of combustion cylinders in communication with the intake manifold and an exhaust manifold in communication with the combustion cylinders as well as a variable geometry turbocharger (VGT) that includes a VGT turbine in communication with the exhaust manifold and that is coupled to a low pressure compressor (LPC) that is in communication with the intake manifold. The engine may further include a hot EGR valve that may be disposed in the exhaust manifold and that may have a closed position wherein at least one of the cylinders is isolated from the VGT turbine and in communication with the cold EGR valve. The hot EGR valve may also have an open position wherein the plurality of combustion cylinders are in communication with the VGT turbine. The hot EGR valve may also be adjustable between the open and closed positions. The LPC may also be in communication with an air inlet and a high pressure compressor (HPC). The air inlet may also be in communication with a bypass valve disposed between the LPC and the air inlet. The bypass valve may have a closed position that directs all incoming air to a high pressure compressor and an open position that provides at least some communication between the air inlet and the LPC. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  schematically illustrates a disclosed EGR system associated with a six cylinder internal combustion engine. 
           [0015]      FIG. 2  is an operating map for the engine shown in  FIG. 1  equipped with the EGR system shown in  FIG. 1 , particularly illustrating the sixteen data points listed in Table 1 below. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Turning to  FIG. 1 , an internal combustion engine  10  is shown that is equipped with an exhaust gas recirculation (EGR) system  11  and an engine control module (ECM)  12 . The engine  10  is shown with six cylinders  13 - 18 , but the number of cylinders for purposes of this disclosure is largely irrelevant. The disclosed EGR system  11  may be employed with engines having a single or at least one cylinder or more than six cylinders as shown in  FIG. 1 . The cylinders  13 - 18  are in communication with an intake manifold  19  that directs a combination of incoming air and recirculated exhaust to each cylinder as shown in  FIG. 1 . Specifically, the intake manifold  19  is in communication with an air inlet line  21  that may pass through a cooler  22  before it reaches the intake manifold  19 . The air inlet line  21  may also receive air from a low pressure compressor (LPC)  24  which may receive incoming air from an air intake  25  via a bypass valve  26  and a high pressure compressor (HPC)  27 . The HPC  27  may be equipped with a vaned diffuser. The bypass valve  26 , when open, allows air from the air intake  25  to pass through the conduit  28 , through the valve  26  and to the LPC  24 . When closed, the bypass valve  26  prevents fresh air from passing through the conduit  28  to the LPC  24 . Thus, air enters the air intake  25  and proceeds through the conduit  29  to the HPC  27 , which then may pressurize and propel the air through the conduit  31  to the LPC  24 . 
         [0017]    The LPC  24  and HPC  27  are driven by a pair of turbines as shown in  FIG. 1 . Specifically, a low pressure turbine (LPT)  32  may be coupled to the HPC  27  via a shaft  33  or other arrangement that will be apparent to those skilled in the art. A high pressure turbine (HPT)  34  may be used to drive the LPC  24  via a shaft  35  or other arrangement that will also be apparent to those skilled in the art. The HPT  34  may be part of a variable geometry turbocharger (VGT), wherein the distance between the vanes (not shown) and the rotors (not shown) of the HPT  34  may be varied to alter the performance of the EGR system  11 . Therefore, the HPT  34  will hereinafter be referred to as the “VGT turbine”  34 , although the use of a variable-geometry turbocharger is not required. 
         [0018]    The VGT turbine  34  is driven by exhaust gases exiting the dual exhaust manifolds  36 ,  37  that deliver exhaust gases to the conduits  40 ,  41  as shown in  FIG. 1 . The conduit  41  may include a control valve referred to herein as the hot EGR valve  42 . When closed, the hot EGR valve  42  blocks flow from the exhaust manifold  37  to the conduit  41  thereby causing the exhaust gases from the cylinders  16 ,  17 ,  18  to be recirculated through the manifold  37 , through an optional EGR cooler  43  and into the conduit  44 . The conduit  44  includes another control valve, referred to herein as the cold EGR valve  45 . The hot EGR valve  42 , cold EGR valve  45  and bypass valve  26  may be linked to the ECM  12  as shown in  FIG. 1 . 
         [0019]    Thus,  FIG. 1  illustrates the use of three valves, including a bypass valve  26 , a hot EGR valve  42  and a cold EGR valve  45  for controlling the EGR system  11 . In addition to the valves  26 ,  42 ,  45 , other components of the EGR system  11  may be used to control the EGR system  11 . For example, the VGT turbine  34 , as discussed above, may include adjustable vanes which enables the operator to adjust the spacing between the vanes (not shown) and the rotors (not shown). When the vanes are extended so that they are close to, but not engaging, the rotating rotors, the vane position is considered closed or assigned a valve of zero (0) in Table 1 below. When the vanes are fully retracted away from the rotating rotors, the vanes are considered to be in an open position and assigned a value of 1.00 in Table 1 below. The vane positions of the VGT turbine  34  for various torques and engine speeds are listed below in Table 1 under the column heading “VGT turbine  34  vanes”. 
         [0020]    Similarly, when one of the valves  26 ,  42 ,  45  is fully open, it is assigned a value of 1.00 in Table 1 below and when such a valve  26 ,  42  or  45  is fully closed, it is assigned a value of 0.00 in Table 1. The valves  26 ,  42  and  45  are adjustable between fully open (1.00) and fully closed (0.00) positions and these adjustable positions are assigned numerical values that range from 0.00 to 1.00 in Table 1. Table 1 also shows the exhaust gas recirculation percentage that exceeds 50% at numerous torque speeds A100, A75, A50, ANTE+, B100, B50, BNTE+, C100, C75, C50 and CNTE+. The only values in Table 1 where the EGR % drops below 50% are the data points designated as ANTE−, BNTE− and CNTE−, which are disposed outside of the not to exceed boundary line  47  of  FIG. 2 . Table 1 also lists the air-to-fuel ratio (AFR) for each data point. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Hot 
                 Cold 
                 VGT 
                   
                   
                   
               
               
                   
                 EGR 
                 EGR 
                 turbine 
                 Bypass 
                 EGR 
               
               
                   
                 valve 42 
                 valve 45 
                 34 vanes 
                 valve 26 
                 % 
                 AFR 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Low Idle 
                 1.00 
                 0.00 
                 0.45 
                 1.00 
                 7 
                 60 
               
             
          
           
               
                 Peak Torque Speeds 
               
             
          
           
               
                 A100 
                 0.00 
                 1.00 
                 0.75 
                 0.00 
                 50 
                 20 
               
               
                 A75 
                 0.15 
                 1.00 
                 0.64 
                 0.15 
                 51.5 
                 25 
               
               
                 A50 
                 0.17 
                 1.00 
                 0.57 
                 0.25 
                 52 
                 20 
               
               
                 ANTE+ 
                 0.20 
                 1.00 
                 0.50 
                 1.00 
                 56 
                 40 
               
               
                 ANTE− 
                 1.00 
                 0.00 
                 0.60 
                 1.00 
                 7 
                 37 
               
             
          
           
               
                 Intermediate Speeds 
               
             
          
           
               
                 B100 
                 0.00 
                 1.00 
                 0.77 
                 0.00 
                 50 
                 25 
               
               
                 B50 
                 0.15 
                 1.00 
                 0.69 
                 0.00 
                 52 
                 24 
               
               
                 BNTE+ 
                 0.20 
                 1.00 
                 0.57 
                 1.00 
                 56 
                 45 
               
               
                 BNTE− 
                 1.00 
                 0.00 
                 0.67 
                 1.00 
                 7 
                 40 
               
             
          
           
               
                 Rated Speeds 
               
             
          
           
               
                 C100 
                 0.00 
                 1.00 
                 0.80 
                 0.00 
                 50 
                 22 
               
               
                 C75 
                 0.15 
                 1.00 
                 0.75 
                 0.00 
                 51.5 
                 20 
               
               
                 C50 
                 0.17 
                 1.00 
                 0.70 
                 0.00 
                 53 
                 40 
               
               
                 CNTE+ 
                 0.20 
                 1.00 
                 0.65 
                 1.00 
                 56 
                 50 
               
               
                 CNTE− 
                 1.00 
                 0.00 
                 0.75 
                 1.00 
                 7 
                 45 
               
               
                 High Idle 
                 1.00 
                 0.00 
                 0.65 
                 1.00 
                 7 
                 60 
               
               
                   
               
             
          
         
       
     
         [0021]    Turning to  FIG. 2 , a series of peak or high torque speeds A100, A75, A50 and ANTE+ (i.e. high loads) are achievable with the valves  26 ,  42 ,  45  and the VGT turbine vanes appropriately adjusted to enable the EGR system  11  to achieve EGR flow rates exceeding 50%. Similarly,  FIG. 2  and Table 1 illustrate that a variety of intermediate speeds B100, B50 and BNTE+ with an EGR % of greater than 50% can be achieved with appropriate adjustment of the valves  26 ,  42 ,  45  and the vanes of the VGT turbine  34 . Similarly, various rated, low torque speeds C100, C75, C50 and CNTE+ with an EGR % of greater than 50% can also be achieved using appropriate adjustment of the valves  26 ,  42 ,  45  and the vanes of the VGT turbine  34 . 
         [0022]    Still referring to Table 1 and  FIG. 2 , at low idle (LI), the cold EGR valve  45  is fully closed and the hot EGR valve  42  is fully open. Further, the bypass valve  26  is also fully open. The vanes of the VGT turbine  34  are also closed to provide adequate back pressure for the EGR system  11 . As the engine speed is increased, the cold EGR valve  45  is opened and the hot EGR valve  42  is also opened as shown by the data point ANTE− in Table 1. Further, the vanes of the VGT turbine  34  are also opened from the low idle starting position of 0.45. As the engine load or torque increases, the cold EGR valve  45  remains fully open and the hot EGR valve  42  is adjusted towards its closed position as can be seen by comparing the hot EGR valve  42  positions for the data points ANTE−, ANTE+, A50, A75 and A100 in Table 1. The hot EGR valve  42  is closed to limit the EGR %. The bypass valve  26  remains open at minimum loads and is closed as the load increases which, again, can be seen by comparing the bypass valve  26  positions of the data points ANTE−, ANTE+, A50, A75 and A100. 
         [0023]    Thus, the hot EGR valve  42  remains fully open at low torques and fully closed at full or high torque (compare ANTE− and A100; BNTE− and B100; and CNTE− and C100). An algorithm that can be used to calculate the hot EGR valve  42  position can be expressed as follows: hot EGR valve  42  position=1−(actual engine torque)/(max engine torque). 
         [0024]    Further, the cold EGR valve  45  generally remains open at sea level and may be closed with increases in altitude. It will be noted that the only data points for which the cold EGR valve  45  is closed in Table 1 are the data points that fall outside of the not to exceed line  47 , that is ANTE−, BNTE−, CNTE−, LI and HI. An algorithm that may be used to calculate the position of the cold EGR valve  45  may be expressed as follows: cold EGR valve  45  position=1−(actual engine altitude)/(max engine altitude). 
         [0025]    The vanes of the VGT turbine  34  are generally positioned about half open at low idle (LI) and are adjusted to reach peak efficiencies at full speed at sea level. An algorithm that may be used to calculate the positions of vanes of the VGT turbine  34  may be expressed as follows: vane position of VGT turbine  34 =(actual engine speed−min engine speed)/(max engine speed−min engine speed)×(max turbine efficiency vane position−low idle vane position)+(low idle vane position). 
         [0026]    Finally, the bypass valve  26  position is generally fully open at low torque or low loads and is fully closed at full torque or high loads. An algorithm for calculating the correct position of the bypass valve  26  may be expressed as follows: bypass valve  26  position=1−(actual engine torque−min engine torque)/(max engine torque−min engine torque). 
       INDUSTRIAL APPLICABILITY 
       [0027]    By controlling airflow and the EGR system  11  independently, a zero NO x  or reduced NO x  exhaust treatment solution is provided. The EGR system  11  includes the use of dual EGR valves including a hot EGR valve  42  as well as a cold EGR valve  45 . By associating the hot EGR valve with the exhaust manifold  37 , the exhaust gases from half of the cylinders  16 ,  17 ,  18  can be fully recycled reaching an EGR % of 50% as shown by the data points A100, B100, C100 in Table 1 above. Further, while the cold EGR valve  45  may remain open, the hot EGR valve  42  may be partially opened as the VGT turbine  34  vanes and bypass valve  26  are adjusted to achieve EGR rates exceeding 50%. For example, referring to the peak torque speeds of Table 1, and comparing the EGR percentages for the peak torque speeds A75, A50 and ANTE+, as the hot EGR  42  is opened and the VGT turbine  34  vanes are moved towards a closed position while the bypass valve  26  is moved towards an open position, the EGR rate increases to a level exceeding 50%. Similar results are also obtained for the intermediate speeds B100, B50, BNTE+ and the rated speeds C75, C50 and CNTE+ as shown in Table 1. 
         [0028]    The increased EGR % can enable a manufactures to reach the Tier4 emission standards without resulting to a selective catalytic reduction (SCR) system thereby saving space, weight as well as costs.