Abstract:
A method for driving exhaust gas recirculation comprising the steps of restricting exhaust gas flow into the turbine inlet to create backpressure in the exhaust system under low engine operating conditions, and providing an unrestricted exhaust gas flow to the turbine under normal engine operating conditions. Restriction of exhaust gas flow is accomplished through the use of an exhaust gas throttle valve disposed upstream of the turbine inlet. The valves can be adjustable knife edge flap valves or D-shaped valves situated in each passageway of a divided exhaust manifold, which are closed to varying degrees to generate desired levels of backpressure while allowing exhaust gas to pass though open regions of the partially obstructed flow pathway to reach the engine turbocharger. This allows the turbine to continue to spin, while at the same time exhaust gas back pressure upstream of the turbocharger is used to drive exhaust gas recirculation.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to internal combustion engines, in particular to exhaust gas recirculation systems for an internal combustion engine. 
       BACKGROUND OF THE INVENTION 
       [0002]    Multi-cylinder internal combustion engines, particularly diesel engines for large tractor-trailer trucks, may include an exhaust-gas turbocharger. The turbocharger includes a turbine that drives a compressor via a shaft, which generates an increased intake air pressure in the intake duct during normal operation. 
         [0003]    Many internal combustion engines use an exhaust gas recirculation (EGR) system to reduce the production of nitrogen oxides (NOx) during the combustion process in the cylinders. EGR systems typically divert a portion of the exhaust gases exiting the cylinders for mixing with intake air. The exhaust gas generally lowers the combustion temperature of the fuel below the temperature where nitrogen combines with oxygen to form nitrogen oxides. 
         [0004]    Achieving low levels of NOx emissions in compliance with EPA standards without using NOx after treatment systems requires good EGR driving capabilities at low engine speeds. Typically, good EGR driving capabilities at low engines speeds is accomplished by the use of a variable geometry turbine (VGT) to create the backpressure when needed. The backpressure generated by the VGT becomes the driving means of the EGR at low engine speeds. However, the design complexity and the cost associated with a VGT system is higher than for fixed turbocharger geometry systems. In addition, the lifespan of a VGT used in heavy duty engines can be limited. 
         [0005]    Alternatively, other means for driving the EGR have included the use of the intake throttle to drive the EGR. The intake throttle is at least partially closed to reduce the charge air boost pressure that limits the EGR gas flow. While this method eliminates the need for using VGT systems, the air to fuel (NF) ratio deteriorates. For heavy duty applications, this decreased fuel economy is a factor in leading to decreased customer satisfaction. 
         [0006]    The present inventors have recognized the need for an efficient method for driving EGR gas flow during low engine speeds without requiring the use of a VGT. 
         [0007]    The present inventors have recognized the need for a method of driving EGR gas flow which functions efficiently and satisfactorily under a wide range of engine operating conditions. 
         [0008]    The present inventors have recognized the need for a low-cost method of driving EGR gas flow. 
       SUMMARY OF THE INVENTION 
       [0009]    According to an exemplary embodiment of the present invention, an exhaust gas throttle valve (EGTV) is located in the exhaust system upstream of a turbine of the engine turbocharger. For exhaust systems utilizing a divided exhaust manifold system with a divided turbocharger turbine inlet, an EGTV is present in each gas flow passageway. The EGTV can be knife edge flap valves or D-shaped valves which rotate about a horizontal axis to adjust the amount of exhaust gas supplied to the turbine, and the amount of gas restricted to generate sufficient back pressure to drive the exhaust gas recirculation (EGR). The EGTV is adjusted to provide a restricted flow to the turbine inlet during low engine operating conditions. A portion of the restricted flow provides the backpressure of exhaust gas to drive the EGR. Under normal engine operating conditions, the EGTV is in an open position to provide an unrestricted flow of exhaust gas to the turbine. 
         [0010]    By using adjustable backpressure EGTVs upstream of the turbocharger, the system is capable of generating high levels of backpressure. Closing the EGTV increases exhaust manifold pressure to improve EGR drive. Adjusting the valves to a position such that a gap remains between the valves and the exhaust manifold will allow a portion of exhaust gas to flow through, allowing the turbine and the compressor to continue to spin because engine mass flow is not choked off. 
         [0011]    Placing the EGTV in the exhaust system upstream of the turbochargers provides a more favorable corrected turbine flow rate, which results in higher expansion ratios, turbine speeds, and compressor boost. The higher compressor boost allows the air system to achieve higher air/fuel (NF) ratios while achieving the desired EGR flow rate. As a result, there is little to no deterioration in the NF ratio, thus eliminating BSFC and soot penalties. 
         [0012]    Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic diagram of an engine system that includes a turbocharger and an exhaust gas recirculation system in accordance with an exemplary embodiment of the invention; 
           [0014]      FIG. 2  is a schematic vertical side sectional diagram of a valve assembly useful in an engine exhaust gas recirculation system, taken generally along line  2 - 2  of  FIG. 1 . 
           [0015]      FIG. 3  is a schematic plan view of the valve assembly of  FIG. 2 , with a top wall portion removed to view underlying components. 
           [0016]      FIG. 3A  is a view along line  3 A- 3 A of  FIG. 3 . 
           [0017]      FIG. 4  is a schematic front vertical sectional diagram of an alternate valve assembly useful in an engine exhaust gas recirculation system, taken generally along line  4 - 4  of  FIG. 1 . 
           [0018]      FIG. 5  is a schematic vertical side sectional diagram of the valve assembly shown in  FIG. 4 , taken generally along line  2 - 2  of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
         [0020]    An engine  100  is shown schematically in  FIG. 1 . The engine  100  has a block  101  that includes a plurality of cylinders. The cylinders in the block  101  are fluidly connected to an intake system  103  and to an exhaust system  105 . The exhaust system includes a first pipe  105   a  from cylinders  1 ,  2  and  3  of one bank of cylinders and a second pipe  105   b  from cylinders  4 ,  5  and  6 . Although an inline arrangement of six cylinders is illustrated, inline or V-arrangements or other arrangements of plural cylinders of any number of cylinders are also encompassed by the invention. 
         [0021]    A turbocharger  107  includes a turbine  109 . The turbine  109  shown has a dual turbine inlet port  113  connected to the exhaust system  105 . The turbocharger  107  includes a compressor  111  connected to the intake system  103  through an inlet air passage  115 . The turbine can be a divided housing turbine. 
         [0022]    During operation of the engine  100 , air may enter the compressor  111  through an air inlet  117 . Compressed air may exit the compressor  111  through a discharge nozzle  207 , pass through the inlet air passage  115 , and pass through an optional charge air cooler  119  and an optional inlet throttle  120  before entering an intake air mixer  121  and an intake air manifold  122  of the intake system  103 . The compressed air enters the engine cylinders  1 - 6 . 
         [0023]    A stream of exhaust gas from the exhaust system  105  may be routed through an exhaust gas recirculation (EGR) passage or conduit  124 , through an exhaust gas recirculation (EGR) valve  125 , through an EGR cooler  126  and pass through a further EGR conduit  127  before meeting and mixing with air from the inlet throttle  120  at the mixer  121 . A more complete description of exhaust gas recirculation systems can be found in U.S. Pat. Nos. 7,140,357; 7,028,680; and 7,032,578, all herein incorporated by reference. 
         [0024]    The inlet port  113  of the turbine  109  may be connected to the exhaust pipes  105   a,    105   b  in a manner that forms a divided exhaust manifold  129 . Exhaust gas passing through the turbine  109  may exit the engine  100  through a tailpipe  134 . Emissions and sound treating components can be arranged to receive the exhaust gas from the tailpipe, before exhausting to atmosphere, as is known. 
         [0025]    At times when the EGR valve  125  is at least partially open, exhaust gas flows through pipes  105   a,    105   b,  through the conduit  124 , through the EGR valve  125 , through the EGR cooler  126 , through the further conduit  127  and into the mixer  121  where it mixes with air from the inlet throttle  120 . An amount of exhaust gas being re-circulated through the EGR valve  125  may depend on a controlled opening percentage of the EGR valve  125 . 
         [0026]    An exhaust gas throttle valve  133  ( FIG. 1 ) is arranged within the exhaust manifold  129 . The exhaust gas throttle valve  133  includes valve elements  136   a  that are adjustable between a closed position, shown in solid, for driving EGR operation, and an open position, shown in dashed ( FIG. 2 ). During normal engine operating speeds where the EGR does not need the additional backpressure, the valve is moved to a horizontal position, as illustrated by dashed lines in  FIG. 2 , parallel to the direction of exhaust gas flow, to allow exhaust gas to pass through the passage with minimal restriction. 
         [0027]    During low engine speeds, the valve elements  136   a  are adjusted from their open position to a position which restricts at least a portion of the exhaust gas flow, shown in solid lines ( FIG. 2 ). Exhaust gas which passes through the exhaust manifold  129  reaches the turbocharger to maintain turbine speed to maintain a high volume of compressed air from the compressor  111  into the intake system  103 . 
         [0028]    As shown in  FIGS. 2 and 3 , exhaust gas throttle valve elements can be knife edge flap valve elements  136   a  which are hinged at the top  138  to a horizontal shaft  248  in a divided manifold system. The valve elements  136   a  pivot with respect to each channel of the divided manifold allowing gas to enter a divided turbocharger turbine inlet  113 . As illustrated in  FIG. 2 , the knife edge flap valve in its open position is tucked in a recessed portion of the exhaust manifold  129  to minimize the restriction of air flow through the exhaust manifold  129 . 
         [0029]    The shaft  248  penetrates the manifold  129  through a top thereof and is sealed within the penetration. As illustrated in  FIGS. 3 and 3A , a crank  252  is fixed to an end of the shaft  248  at a base end  254  of the crank  252  and is pivotally connected at a distal end  256  to a linear actuator  260 . The actuator  260  can be an electric solenoid powered actuator for reciprocal movement of an actuator arm  262  into, and out of, an actuator body  264 . The distal end  256  of the crank is pivotally connected to a ball joint or pivotal joint  266  of the arm  262 . The actuator  260  is pivotally connected at a base end  268  thereof to a support plate  272  mounted on the manifold  129 . The pivotal connection of the actuator  260  allows a small degree of pivoting of the actuator  260  as the arm  262  is moved into, or out of, the body  264 . As the arm  262  moves with respect to the body  264 , the crank  252  is turned and the valves  136   a  open or close. 
         [0030]    As alternatives to an electrical solenoid powered actuator, a pneumatic cylinder actuator, a hydraulic oil powered actuator, other types of electrical powered actuators, or other known actuators are possible. 
         [0031]    As illustrated in  FIG. 2 , knife edge flap valve elements  136   a  have a bottom edge  135  which is angled. The angled bottom edge  135  allows for exhaust gas not restricted by the valves in its closed position to flow around the bottom edge  135  towards the turbine inlet in direction A. Without wishing to be bound by any particular theory, it is believed that by blocking flow to the upper half of the turbine housing, and directing flow towards the bottom of the turbine, the expansion of gas as it passes into the turbine housing is minimized and the flow of exhaust gas is directed into the turbine housing with exhaust gas flow directed in a tangential direction to the turbine wheel, at a location that is farthest from the wheel center, to maximize angular velocity of the turbine wheel. 
         [0032]    The knife edge flap valve element  136   a  in  FIG. 2  is show in its substantially closed position in solid lines. The closed position can be defined by a stop mechanism situated near shaft  248  to prevent the knife flap valve element  136   a  from further rotating in a counterclockwise position. Alternatively, the closed position can be defined by the actuator by only allowing the shaft to rotate up to a certain degree of rotation from the open position. 
         [0033]    In another embodiment, as illustrated in  FIGS. 4 and 5 , an exhaust gas throttle valve  133   a  has D-shaped valve elements  136   b  to accommodate circular, divided exhaust passages  300 , separated by a dividing wall  128 . D-shaped valve elements  136   b  pivot about a shaft  248   a  passing through the center of each D-shaped valve at its widest region, allowing the D-shaped valve element  136   b  to rotate between a closed position, shown dashed in  FIG. 5 , and an open position, shown solid in  FIG. 5 . The shaft  284   a  may be rotated by an actuator  260  attached, and operated as described with respect to  FIGS. 3 and 3A . The D-shaped valve elements  136   b  have a bottom edge  135   a  which has been truncated so as to allow greater exhaust gas flow at the bottom region  137   a  of the passage compared to the exhaust gas flow that would flow through the bottom region  137  of the valve in its open position without the truncated bottom edge  135   a.  The truncated bottom edge  135   a  allows for more exhaust gas flow from the bottom of the passageway towards the turbine when the valve is adjusted to one of its opened positions. In an alternative embodiment, D-shape valves without the truncated bottom edge  135   a  can also be used. 
         [0034]    The valves  133 ,  133   a  can be adjusted to any position within a range between a closed position, where maximum restriction of flow occurs, and an open position, where minimum flow restriction occurs, depending on engine operating conditions and desired degree of EGR drive. 
         [0035]    In another embodiment, valves  133 ,  133   a  could be a separate assembly that can be attached upstream of the turbocharger, and not as part of the exhaust manifold. 
         [0036]    The optimal position of the adjustable valves  133 ,  133   a  can be calibrated and optimized according to various operating conditions to which the engine is subjected. 
         [0037]    In addition to providing a simple, efficient system for exhaust gas recirculation, the valves  133 ,  133   a  disclosed can be closed to promote engine warm up during light loads or cold start conditions to increase exhaust back pressure and exhaust gas temperatures. In this mode, the valve functions as a cold aid device. The valves  133 ,  133   a,  when closed, also enhance engine braking. The EGVT can be used in combination with a compression release or bleeder brake to create high boost levels, thus resulting in increased engine retarding power. The EGTV can also be used for A/T thermal management by replacing an exhaust valve located downstream of the turbochargers with the EGTV to increase exhaust temperatures, particularly at low engine load conditions, to promote passive regeneration in engine map areas where fuel dosing is needed. Minimizing active regeneration assists in improving fuel economy. 
       PARTS LIST 
       [0000]    
       
           100  engine 
           101  block 
           103  intake system 
           105  exhaust system 
           105   a  first exhaust pipe 
           105   b  second exhaust pipe 
           107  turbocharger 
           109  turbine 
           111  compressor 
           115  inlet air passage 
           119  optional charge air cooler 
           120  optional inlet throttle 
           121  inlet air mixer 
           122  intake manifold 
           124  EGR conduit 
           125  EGR valve 
           126  cooler 
           127  further conduit 
           128  dividing wall 
           129  divided exhaust manifold 
           132  divided turbine inlet 
           133 ,  133   a  exhaust gas throttle valve 
           134  tailpipe 
           135  bottom edge of knife edge flap valves 
           135   a  bottom edge of D-shaped valves 
           136   a  knife edge flap valve element 
           136   b  D-shaped valve element 
           137  gas flow path at the bottom region of flow passage 
           137   a  gas flow path at the bottom region of flow passage 
           138  top region of knife edge flap valve 
           201  compressor housing 
           248  shaft 
           252  crank 
           254  base end of crank 
           256  distal end of crank 
           260  linear actuator 
           262  actuator arm 
           264  actuator body 
           266  pivotal joint 
           268  base end of body  264   
           272  support plate 
       
     
         [0079]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.