Abstract:
An exhaust gas recirculating system for a turbocharged diesel engine utilizes an electrically driven compression pump to boost exhaust gas pressure before return to the engine induction system. Exhaust gas is drawn from the exhaust system or stack some distance removed and downstream from the outlet from the exhaust turbine, compressed to overcome the intake manifold boost pressure, and returned to the intake system along an extended pipe to cool the gas. The compressor is energized from the vehicle battery during periods of demand for peak pressure demand on the engine thereby recycling recaptured energy from the battery to boost engine output. Exhaust turbine performance during periods of peak loading is also improved.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The invention relates to exhaust gas recirculating systems for internal combustion engines and more particularly to an exhaust gas recirculating system for a turbocharged diesel engine.  
         [0003]     2. Description of the Problem  
         [0004]     Turbocharging is a well known method for increasing the efficiency and boosting the peak power output of an internal combustion engine. An exhaust energy recovery turbine is positioned in the exhaust stream from the engine and uses energy from the exhaust gas to drive a supercharger disposed in the engine&#39;s air intake system. The supercharger boosts the density of air delivered to the engine&#39;s intake manifold. The increased air density allows additional fuel to be introduced to the cylinders and combusted, increasing engine output. Turbocharging, while used occasionally with spark ignition engines, is more commonly found in compression ignition engines, i.e. diesel engines.  
         [0005]     Complicating the application of turbocharging to diesel engines is the need to meet government emission standards, particularly those relating to NO x  emissions. One way in which emissions are reduced is through the use of exhaust gas recirculating systems (EGR) in which exhaust gas is returned to the air intake system. The air intake system for a supercharged diesel engine includes the compressor pump and, usually, an intercooler between the supercharger and the engine&#39;s intake manifold. Exhaust gas can be returned ahead of the supercharger, into the intercooler, or directly into the intake manifold. Exhaust gas may be drawn from the exhaust manifold ahead of the energy recovery turbine, or from some point further down the exhaust system. The most common arrangement is to draw exhaust gas directly from the exhaust manifold and to deliver the gas to intake manifold, usually passing the exhaust gas through an intercooler in the EGR line. See, by way of example, U.S. Pat. No. 6,470,864 to Kim et al., U.S. Pat. No. 6,247,311 to Itoyama et al., and U.S. Pat. No. 6,412,278 to Matthews. It is usually considered undesirable to return the exhaust gas to the intake system ahead of the supercharger or the intake intercooler due to the potential of corrosion the exhaust gas poses for these components. The exhaust gas is considerably hotter than ambient air and this reduces the flow mass through the supercharger compressor and reduces the power output of the engine. While Kim et al. and Itoyama et al. provided no pressure boost for the exhaust gas, Matthews stated that the exhaust gas from the exhaust manifold may not have sufficient pressure to allow smooth delivery of the gas into the intake manifold due to pressures in the intake manifold. Matthews provided a hydraulically driven pump in the exhaust gas recirculating line to assure sufficient exhaust gas pressure for delivery to the intake manifold.  
         [0006]     Many prior art EGR systems have the disadvantages of introducing an extremely high temperature gas to the engine induction system and of diverting exhaust air flow from the exhaust turbine, reducing the turbine&#39;s effectiveness. While all position an intercooler in the EGR line to reduce exhaust gas temperature, these systems still release a great deal of heat into a vehicle&#39;s engine compartment, promoting engine overheating. In addition, the need for an intercooler in the EGR line adds substantial expense to the systems.  
         [0007]     Cook, U.S. Pat. No. 6,470,866 proposed diverting exhaust gas from the exhaust pipe downstream from the exhaust turbine. This was achieved by restricting flow through the exhaust pipe to boost the pressure of the gas. However, this arrangement increases exhaust system back pressure which again reduces exhaust turbine performance. The prior art proposals considered have all had the disadvantage of reducing peak engine output.  
       SUMMARY OF THE INVENTION  
       [0008]     According to the invention there is provided an internal combustion engine having an air intake system and an exhaust system. Air drawn into the air intake system is boosted by an exhaust gas driven supercharger. An intercooler is usually disposed between the air outlet from the supercharger and an engine intake manifold to increase charge air density. Exhaust gas is drawn from the exhaust system downstream from the exhaust turbine and compressed for return to the air intake system. Pressurized exhaust gas is introduced to the intake system above the intake manifold and after the intake system intercooler. An electric compressor motor drives the recirculated exhaust gas compressor. Power for the compressor motor is supplied from the vehicle electrical system and during periods of highest pressure demand on the engine, almost exclusively from the vehicle&#39;s battery plant. When peak engine output is required the compressor avoids reduction in the pressure drop across the exhaust turbine, improving vehicle performance. Battery recharging is directed toward periods when engine load is negative allowing the exhaust gas recirculating system to cooperate with the battery charging system as a vehicle kinetic energy recovery system. Exhaust gas is drawn from the exhaust pipe well outside the engine compartment, after particulate removal (if used) and NO x  reduction, which reduces the temperature of the exhaust gas and the pollution levels thereof without the need for a supplemental EGR line intercooler. This arrangement helps transport waste heat from the engine compartment and reduces the corrosiveness of the recirculated exhaust gas.  
         [0009]     Additional effects, features and advantages will be apparent in the written description that follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a plan view of a vehicle chassis.  
         [0012]      FIG. 2  is a schematic diagram showing a turbocharged engine assembly with boosted exhaust gas recirculating. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Referring now to the figures and in particular to  FIG. 1 a  vehicle chassis  10  is illustrated. Vehicle chassis  10  includes a frame  11  which supports an internal combustion engine  12  and its drive train  13 . Engine  12  has an air intake or induction system  14  into which air is drawn from the ambient environment and compressed for delivery to the engine&#39;s cylinders. A high pressure stage exhaust system  16  from engine  12  includes an exhaust manifold and at least a first stage exhaust turbine. The first stage exhaust turbine is mechanically coupled to a compressor/supercharger in the air intake system  14  to compress air for the air intake system. Engine  12  and high pressure stage exhaust system  16  are located toward the front of vehicle chassis  10  in an engine compartment  15 . Engine  12  is preferably an ignition compression engine.  
         [0014]     Extending toward the back of vehicle chassis  10  from high pressure stage exhaust system  16  is a low pressure exhaust system  19  which is illustrated as including an exhaust pipe  20 , a particulate trap  22 , an SCR catalytic converter or NO x  adsorber  24  and a muffler  26 . Typically an exhaust system will include either the particulate trap  22 , or the muffler  26 , but not both. An exhaust gas recirculating (EGR) line  21  is connected via sampling line  18  to exhaust pipe  20  at a point downstream from NO x  adsorber  24  and between the adsorber and muffler  26  (if present). Preferably, the point of connection is as far removed from the engine compartment  15  as feasible to allow for cooling of the exhaust gas in the exhaust pipe  20  and EGR recirculating line  21 . Exhaust gas is drawn into EGR sampling line  18  by an electrically driven compressor pump  28  located in return line  21 . Compressor  28  is likewise located at a point relatively removed from engine compartment  15 . EGR return line  21  extends between compressor  28  and air intake system  14  and is made relatively long to allow cooling of the compressed exhaust gas before introduction to the air intake system. Preferably, EGR return line  21  delivers exhaust gas to the engine intake manifold  34 . Exhaust gas can be returned to other points in the intake system, such as upstream from supercharger  30  (as shown in phantom in  FIG. 2 ) and still provide energy recycling and improved efficiency as described below, but such an arrangement is not considered desirable.  
         [0015]     Referring now to  FIG. 2 , a preferred embodiment of an engine assembly  100  incorporating a diesel engine  12 , turbocharging and exhaust gas recirculating is shown. Engine assembly  100  draws air from the ambient environment (typically through an air filtration system which is not shown) into a supercharger  30 . Compressed air is discharged from supercharger  30  to an intercooler  32  to reduce the temperature of the gas and thereby increase its density for introduction to an intake manifold  34  for diesel engine  12 . Fuel from fuel injectors  48  is mixed in the cylinders of engine  12  with air drawn from intake manifold  34 . Compression ignition of the mixture occurs in the cylinders and exhaust gas is generated. The exhaust gases pass to an exhaust manifold  36  in the high pressure stage of the exhaust system. The exhaust gases are under considerable pressure and are used to drive an exhaust turbine  38  which is mechanically coupled to drive supercharger  30 . Exhaust gas is typically discharged from the exhaust turbine  38  to an exhaust pipe  20 , although in some vehicles incorporating turbocompounding, a second stage exhaust turbine (not shown) may be present which is mechanically coupled to an engine drive shaft (not shown). Exhaust gas temperature falls on passage through the exhaust turbine as work is extracted from the gas.  
         [0016]     From the exhaust turbine  38  exhaust gas passes down exhaust pipe  20  through a particulate trap  22  (if used) and through an NO x  adsorber or SCR catalytic converter  24 . After discharge from SCR catalytic converter  24  into exhaust pipe  20  the exhaust gas passes to a muffler  26  (when no particulate trap is used) and finally out of the exhaust system into the environment. Exhaust gas for recirculating is drawn from exhaust pipe  20  downstream from SCR catalytic converter  24  into an EGR sampling line  18  by a electrically driven compressor pump  28  in EGR return line  21 . The exhaust gas is pressurized sufficiently by compressor  28  for delivery to intake manifold  34 , overcoming the pressurized intake air in the intake manifold. The discharge of pressurized exhaust gas from EGR return line  21  into intake manifold  34  is usually controlled by an exhaust gas recirculating metering valve  44  positioned between the discharge of compressor  28  and the intake manifold. Metering valve  44  may be replaced by a fixed diameter orifice if the output of compressor  28  is subject to variable control by engine controller  46 . Since exhaust gas is drawn from exhaust pipe  20  by a pipe the back pressure in the exhaust pipe is reduced and the operation of exhaust turbine  38  is not negatively affected, and may be improved. By tapping energy from battery  52  to drive motor  42  for compressor  28  the output of engine  12  is increased during periods when peak output is demanded of the engine. In addition, exhaust gas is introduced to intake manifold  34  with no turbocharger induced lag thereby improving transient response.  
         [0017]     Engine controller  46  is programmed to provide control over exhaust gas recirculating responsive to engine operating conditions. Exhaust gas pressure is set at a level to obtain a fixed ratio of the recirculated exhaust gas pressure to the pressure of the air in the air intake manifold  34 . Pressure sensor  40  in EGR return line  21  and a intake manifold pressure sensor included in engine sensor package  49  provide the required pressure readings. Electrically driven compressor  28  is driven by electric motor  42  which is mechanically coupled to compressor  28 . Compressor  28  itself is preferably an electrically operated free piston device or a scroll compressor. These devices exhibit high efficiency without the need for lubrication, which prevents the possibility of passing lubricating oil from the compressor to the intake manifold  34 . Engine controller  46  controls energization of electric motor  42  and may control the speed or output of the motor. If used, the position of exhaust gas recirculating metering valve  44  is also determined by control signals provided by engine controller  46 . Where valve  44  has been replaced by fixed diameter orifices, the speed of motor  42  is varied by engine controller  46  to obtain the desired exhaust gas pressure. In either case EGR pressure is adjusted in response to intake manifold pressure to obtain a fixed pressure ratio. Engine controller receives inputs from a power demand input source and from a number of engine sensors  49 , including cam position sensing, engine oil operating temperature, coolant temperature, propeller shaft speed, intake manifold pressure, exhaust manifold pressure, etc., to effect the desired control. The engine controller  46  also controls fuel injection timing and quantity, and can, accordingly, estimate engine load and determine periods of peak system pressure or output demand. Energization of electric motor  42  exclusively from battery  52  occurs during transient conditions, e.g. vehicle launch, which are characterized by low engine RPMs and high demands for pressure.  
         [0018]     A vehicle electrical system conventionally includes a battery charging system  50  and a battery  52 . The battery charging system  50  typically includes an alternator which is belt driven from engine  12 . Motor  42  is energized from the vehicle electrical system, either from the battery charging system  50  or by discharge from battery  52  should the output of the battery charging system  50  be diverted by the engine controller  46 . Diversion may be by means of a switch  58 , which shifts the power source to battery  52  during periods of high pressure demand on engine  12 . Engine controller  46  monitors the charge state of battery  52  using appropriate instrumentation, such as a voltmeter  54 . Engine controller  46  effects energy recapture by emphasizing charging of battery  52  during periods when the engine  12  is under a negative load. In effect the charging system  50  is then used as a brake. Such negative loading occurs when the vehicle is going downhill or stopping. By use of the term “emphasizing” it is meant that a programmable device, such as the engine controller  46  or another on board computer tends to limit battery charging to periods of negative load by only allowing charging during those periods or when the battery exhibits an undesirably low state of charge. The invention provides for tapping this recovered energy during vehicle transient or launch conditions when engine RPMs are low and the call for all pressures is higher. On these occasions energy is drawn from battery  52 .  
         [0019]     Exhaust gas recirculating with the present invention avoids EGR heat release in the vehicle engine compartment. Improved engine output under high demand conditions is met while maintaining the pressure drop across the exhaust turbine under peak load conditions. In some applications as much as 15 HP can be recovered during peak load conditions on engine  12 . Exhaust gases are recovered for recirculating after treatment, making the gases both cleaner and cooler than in prior art EGR systems. Energy recovered and stored as electrical power is recycled to drive the EGR compression pump during periods of high pressure demand on the engine, e.g. during vehicle launch from a standing start. Engine controller  46  is otherwise programmed to implement with conventional exhaust gas recirculating control algorithms minimizing the modifications required to implement the invention.  
         [0020]     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.