Patent Publication Number: US-2004045281-A1

Title: Turbocharged engine with turbocharger compressor recirculation valve

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to turbocharged internal combustion engines and more particularly to such an engine with an exhaust gas recirculation system and a turbocharger compressor recirculation valve to lower turbocharger compressor discharge pressure and thereby assist exhaust gas recirculation flow.  
       BACKGROUND OF THE INVENTION  
       [0002] It is known in the art of controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines to use an exhaust gas recirculation (EGR) system. EGR systems recirculate exhaust gas into the engine intake air supply reducing the concentration of oxygen, which lowers the combustion temperature within the cylinder and slows the chemical reaction of a combustion process, decreasing the formation of nitrous oxides (NO x ). Additionally unburned hydrocarbons contained in exhaust gas are re-introduced into the engine cylinders which further reduces the emission of undesirable hydrocarbons.  
       [0003] In some internal combustion engines and particularly diesel engines a turbocharger is used to increase engine performance. Therein the exhaust gas to be recirculated is diverted upstream of the exhaust gas turbine associated with the turbocharger.  
       [0004] In a high pressure system exhaust gas is pumped directly into the intake manifold. However, under lower speed and high torque conditions, the boost pressure is higher than the exhaust manifold pressure and recirculation of exhaust gases is not possible. A present method of generating EGR flow to correct this problem has been to use various devices such as back pressure valves or restrictive turbines such as a variable nozzle turbine (VNT).  
       [0005] With a variable nozzle turbine its vanes are adjustably closable to restrict exhaust gas flow through the turbine. Thereby turbine inlet pressure is increased to a point where it exceeds the intake manifold pressure as generated by the turbocharger compressor. During the process the exhaust gas that does pass between the vanes of the turbine has a higher velocity, due to the reduced cross-sectional area between the vanes. This increased gas velocity, when it strikes the turbine wheel, causes higher wheel rotational speed. This higher speed on the compressor side causes increased boost or compressor discharge pressures. The overall impact, therefore, is that the very concept used to increase EGR flow by increasing the turbine inlet pressure, also increases the compressor discharge and intake manifold pressure, thereby hindering further increases in EGR flow.  
       [0006] The result is that compressor discharge and intake manifold pressures become unacceptably high in the effort to generate higher EGR flow rates for reduced NO x emissions. These high intake manifold pressures tax the capability of the charge cooling system and associated ducting to withstand the higher pressures and contribute to unacceptably high combustion peak firing pressures. Another unwanted result is that the turbocharger rotation speeds can become unacceptably high during high load engine operation.  
       SUMMARY OF THE INVENTION  
       [0007] The present invention provides an internal combustion engine having means to lower turbocharger compressor discharge and intake manifold pressure allowing an appropriate EGR flow rate to be more readily generated at lower turbocharger rotational speeds and reducing combustion peak firing pressure.  
       [0008] The present invention also provides an intake air bypass that allows turbocharger compressor discharge air to be recirculated back into the turbocharger compressor inlet. A control valve may be provided to control bypass flow.  
       [0009] The present invention optionally provides a pressure relief device for bypassing charge air back to the turbocharger compressor inlet as a function of engine operating conditions. At lower engine loads, the device is closed and EGR systems operate normally. At sufficiently high engine loads, the compressor discharge pressure will rise to the level of the pressure relief devices opening pressure, allowing charge air to be recirculated back to the turbocharger compressor inlet. This recirculated charge air allows the intake manifold pressure to remain low enough to cause the pressure difference between the turbine inlet and the intake manifold to be sufficiently large to allow the proper EGR flow.  
       [0010] In engines using a variable nozzle turbine, a more open VNT vane position allows the turbocharger to rotate at a lower speed which is beneficial to turbocharger durability. The lowering of the intake manifold results also in a decrease in the combustion peak firing pressure, which is beneficial to engine durability.  
       [0011] Accordingly an internal combustion engine in accordance with the invention includes a block having a plurality of cylinders. An intake manifold is fluidly connected to the block for supplying charge air to the cylinders. An exhaust manifold is fluidly connected to the plurality of cylinders for conducting exhaust gas away from the cylinders. A turbocharger including a turbine having an exhaust gas inlet is fluidly connected with the exhaust manifold. The turbocharger also includes a compressor having a compressor air inlet and air outlet. The compressor air outlet is fluidly connected to the intake manifold to pressurize the charge air during high power levels of engine operation.  
       [0012] An EGR bypass is fluidly connected between the turbine exhaust gas inlet and the intake manifold to recirculate a portion of the exhaust gases to the cylinders. An intake air bypass is fluidly connected between the compressor air outlet and the compressor air inlet. The intake air bypass is adapted to recirculate a portion of compressor outlet air back to the compressor air inlet to reduce compressor outlet pressure and aid EGR flow through the EGR bypass to the cylinders during high power operation of the engine.  
       [0013] In one embodiment of the invention the turbocharger includes a variable geometry turbine operable to raise engine exhaust pressure by restricting exhaust gas flow to the turbine. The intake air bypass includes a control valve operable to control bypass flow. The control valve may be a pressure relief valve that is opened by excess pressure from the compressor outlet. Alternatively the control valve may be operated by suitable engine control apparatus.  
       [0014] The engine may include a charge air cooler fluidly connected between the compressor air outlet and the intake manifold for cooling compressed charge air prior to delivery into the cylinders. The intake air bypass may be fluidly connected with an outlet of the charge air cooler to provide cool air to the compressor inlet.  
       [0015] The EGR bypass can be fluidly connected with the intake manifold after the connection of the intake air bypass with the compressor air outlet to avoid recirculating exhaust gas to the compressor air inlet.  
       [0016] The EGR bypass may include a cooler to cool hot exhaust gas prior to entering the intake manifold.  
       [0017] These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018] In the drawings:  
     [0019]FIG. 1 is a perspective view of a turbocharged diesel internal combustion engine adapted to include an EGR system and a turbocharger compressor recirculation valve system in accordance with the present invention;  
     [0020]FIG. 2 is a schematic illustration of an internal combustion engine similar to that of FIG. 1 including an EGR system and a turbocharger compressor recirculation valve system; and  
     [0021]FIG. 3 is a schematic view of one embodiment of the turbocharger compressor recirculation valve system in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0022] Referring to FIGS. 1 and 2, there is shown a representative internal combustion engine  10 . Internal combustion engine  10  includes a block  12  having a plurality of cylinders  14 . An intake manifold  16  is fluidly connected to the block for supplying charge air to the cylinders  14 . An exhaust manifold  18  having a plurality of exhaust gas inlet ports  20  is fluidly connected to the plurality of cylinders  14  for conducting exhaust gases from the cylinders. Exhaust manifold  18  also has an exhaust gas outlet port  22 .  
     [0023] A turbocharger  24  includes a turbine  26  and a compressor  28 . Turbine  26  is driven by exhaust gas received from exhaust manifold  18 . Turbine  26  in turn drives compressor  28  through a mechanical connection as is generally known. Turbine  26  includes an exhaust gas inlet  30  and an exhaust gas outlet  32 . Turbine exhaust gas inlet  30  is connected by a fluid conduit  34  to the manifold exhaust gas outlet port  22 . The turbine exhaust gas outlet  32  is connected to an exhaust system fluid conduit  36 . Turbine  26  may be a variable geometry turbine operable to raise engine exhaust pressure by restricting exhaust gas flow to the turbine.  
     [0024] Compressor  28  includes a compressor air inlet  38  for receiving ambient air and a compressor air outlet  40 . Compressor air outlet  40  is connected by a fluid conduit  42  to an air intake port  44  of intake manifold  16  to pressurize the charge air during high power levels of engine operation. An air cooler  46  may be disposed in the air flow along conduit  42  to cool compressed charge air prior to delivery into the cylinders  14 .  
     [0025] An EGR bypass  48  of known construction is fluidly connected between the turbine exhaust gas inlet  30  and intake manifold  16  to recirculate a portion of the exhaust gases to the cylinders  14 . EGR bypass  48  includes an EGR inlet  50  fluidly connected to fluid conduit  34  and an EGR outlet  52  fluidly connected to the air intake side of the intake manifold  16 . An air cooler  54  may be disposed in the air flow through EGR bypass  48  to cool hot exhaust gas prior to entering the intake manifold  16 .  
     [0026] An intake air bypass  60  includes a fluid conduit  62  having a compressed charge air inlet  64  and a discharge outlet  66  fluidly connecting the compressor air outlet  40  with the compressor air inlet  38 . The compressed charge air inlet  64  is fluidly connected to the compressor air outlet along fluid conduit  42  and the discharge outlet  66  is fluidly connected to the compressor air inlet  38 .  
     [0027] The intake air bypass  60  is adapted to recirculate a portion of compressor outlet air back to the compressor air inlet  38  to reduce compressor outlet pressure and aid EGR flow through the EGR bypass  48  to the cylinders  14  during high power operation of the engine  10 .  
     [0028] Preferably the intake bypass charge air inlet  64  is connected downstream of air cooler  44 , if provided, to thereby provide cooled compressed air to the compressor air inlet  38 .  
     [0029] With further reference to FIG. 2 and with reference to FIG. 3 in one embodiment of the invention, the intake air bypass  60  includes a control valve  70  operable to control bypass flow. Control valve  70  may be a pressure relief valve that is opened by excess air pressure from the compressor outlet  40 . Control valve  70  may be a spring release valve or other known pressure release device. Alternatively, control valve  70  may be an operable pressure relief valve that may be operated by suitable engine control apparatus  74  that operates the control valve in response to defined, sensed engine operating parameters. If desired fluid conduit  62  may be provided with a separate shutoff valve  76  (FIG. 3) to deactivate the compressor bypass system.  
     [0030] In a preferred embodiment of the invention, the EGR bypass  48  is connected via EGR outlet  52  to the intake manifold  16  downstream or after the connection of the intake air bypass charge air inlet  64  to avoid recirculating exhaust gas to the compressor air inlet  38 .  
     [0031] In use, the intake air bypass  60  recirculates a portion of the compressed charge air back to the compressor air inlet  38  when the pressure of the charge air exceeds a specified predetermined pressure. Such recirculation lowers the intake manifold pressure to assure appropriate EGR flow rates at lower turbocharger rotational speeds and reduces combustion peak firing pressure.  
     [0032] Although the invention has been described by reference to a specific embodiment, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiment, but that it have the full scope defined by the language of the following claims.