Abstract:
A two stage cooled EGR system for a turbocharged internal combustion engine with an intake air charge air cooler. The first EGR cooler is a liquid-to-air cooler and the second, low temperature EGR cooler, is an air-to-air cooler combining with the gas flow downstream of the intake air cooler. The system bypasses EGR flow through the low temperature EGR cooler during certain engine conditions such as low engine coolant temperature and a check valve allows a limited portion of un-cooled, pressurized intake air to be passed through the low temperature EGR cooler for scavenging of any residual moisture and ultimate consumption by the engine.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to internal combustion engines, and, more specifically, to an exhaust gas recirculation (EGR) system for such engines. 
     2. Description of the Related Art 
     In an ever increasing effort that began more than 30 years ago, systems have been provided for internal combustion engines to recirculate a portion of the exhaust gas in order to reduce the combustion temperatures and, in turn, reduce the generation of oxides of nitrogen or NOx. Initial developments were undertaken for spark ignition engines but subsequent research has caused this technique to be applied to compression ignition, or diesel engines. In an effort to increase the density of the EGR gasses, and thus the impact on efficiency, cooled EGR has been proposed. Such a system enables a greater quantity of recirculated products of combustion without adversely affecting performance. However, systems of this type have problems, among those being the lowering of the EGR gas to the point moisture in the air condenses thus forming water particles. These water particles combine with the components in the combustion gasses to produce various acids that have an adverse effect on materials used for heat exchanges and air carrying conduits, as well as combustion chamber components. 
     In an effort to provide even greater quantities of EGR, additional coolers have been proposed to increase the gas density even more to minimize the effect on combustion efficiency. The additional cooling process, while providing a benefit, carries with it the occurrence of additional condensation and generation of water particles. It has been proposed in various systems to bypass the secondary cooling function during conditions when generation of water particles would occur to avoid the adverse problem of water ingestion in uncontrolled amounts into the combustion cylinders. However, these systems fail to address the problem of moisture that has collected in the heat exchangers. 
     Therefore, what is needed in the art is an EGR system in which the moisture in heat exchangers for such systems is effectively purged without adverse impact on the engine. 
     SUMMARY OF THE INVENTION 
     In one form, the invention is an exhaust gas recirculation (EGR) system for an air breathing, fuel consuming turbocharged internal combustion engine (IC) engine producing a work output and having products of combustion, said system having a conduit for delivering intake air from the turbocharger to the IC engine for combustion, and a heat exchanger interposed in the inlet air conduit for cooling air delivered to the IC engine. An EGR conduit receives a controlled portion of the products of combustion from the IC engine and selectively introduces the products of combustion into the intake air conduit. At least one heat exchanger is interposed in the EGR conduit for reducing the temperature of products of combustion passing to the intake air conduit. A first valve is responsive to a signal input for bypassing flow around the at least one heat exchanger during predetermined engine conditions, and a second valve responsive to the bypass flow condition delivers air from a point upstream of said charge air cooler to the at least one heat exchanger for purging moisture from the heat exchanger. 
     In another form, the invention includes a power system with an air breathing, fuel consuming internal combustion engine producing a work output with products of combustion. A fuel system supplies fuel to the IC engine for combustion. A turbocharger has a turbine for receiving products of combustion and a compressor for pressurizing air for delivery to the IC engine for combustion. A conduit delivers intake air from the turbocharger compressor to the IC engine for combustion. A heat exchanger interposed in the intake air conduit cools air delivered to the IC engine. An exhaust conduit extends from the IC engine to the turbine for said turbocharger and an exhaust gas recirculation (EGR) conduit is connected to the exhaust conduit for receiving a controlled portion of the products of combustion from said IC engine and is connected to the intake conduit for selectively introducing the products of combustion into the intake air conduit. At least one heat exchanger is interposed in the EGR conduit for reducing the temperature of products of combustion passing to the intake air conduit. A first valve is responsive to a signal input for bypassing flow around said at least one heat exchanger during predetermined engine conditions and a second valve responsive to the bypass flow condition delivers air from a point upstream of the intake air cooler to said at least one heat exchanger for purging moisture from said heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a schematic view of an internal combustion engine system employing an EGR system embodying the present invention, 
         FIG. 2  is a view of a portion of the engine system of  FIG. 1  and, 
         FIG. 3  is an alternative view of the portion of the engine system shown in  FIG. 2 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , there is shown an internal combustion engine  10  which is an air breathing, fuel consuming engine providing a rotary output through shaft  12 . Engine  10  may be of the compression engine, spark ignition type or a combination thereof. In any of these cases, the products of combustion are discharged through an exhaust manifold  14  into an exhaust conduit  16  leading to the turbine  18  of a turbocharger  20 . The discharge from turbine  18  extends through a conduit  21  which may include a diesel particulate filter  22  before leading to ambient A. It should be noted that the diesel particulate filter  22  may be employed at any point in the exhaust system including a position upstream of the turbine  18 . 
     Turbine  18  provides a rotary output through a shaft  24  to a compressor  26  that receives air from ambient A through an inlet conduit  28 . Typically, such air is filtered in an appropriate fashion. The air pressurized by compressor  26  extends through an intake air conduit  30  past a charge air cooler (CAC), or a intake air heat exchanger  32  to a second intake air conduit  34  leading to an intake manifold  36  for engine  10 . The function of the charge air cooler  32  is to decrease the temperature of the air flowing therethrough and thus increase its density to enable a greater power output from engine  10 . 
     Engine  10  receives fuel from a fuel system  38  to provide fuel in predetermined amounts at predetermined intervals in the operating cycle of the engine to provide controlled power from the engine  10 . Fuel system  38  receives control inputs from an electronic control module (ECM)  40  via signal line  42 . It should be noted that the ECM  40  receives engine operating parameter inputs from multiple locations on the engine  10  and total system to provide precise control of fuel. These connections have been omitted to simplify the understanding of the present invention. 
     As noted above, emissions controls have prompted the use of exhaust gas recirculation (EGR) to reduce the temperature of the products of combustion and to accordingly reduce the production of oxides of nitrogen. Such a system is shown by a valve  44  interposed in the exhaust conduit  16  and controlled by signal line  46  from ECM  40  to provide controlled amounts of the products of combustion, or exhaust gas, through EGR conduit  48 . EGR conduit  48  leads to a high temperature EGR cooler  60  and then to a second EGR conduit  52  to a bypass valve  54 . One fluid output from bypass valve  54  passes through conduit  56  to a low temperature EGR cooler  58  and, finally, through conduit  60  to fluidly connect with conduit  34  leading to the intake manifold  36 . Valve  54  selectively directs flow through conduit  56  in one position and through a conduit  62  in a second position to bypass the low temperature EGR cooler  58  and direct the EGR flow to intake air conduit  34 . Bypass valve  54  receives a signal input from ECM  40  via signal line  64  to bypass flow when around the low temperature EGR cooler when engine conditions are such that excessive moisture will be generated due to the cooling of the EGR flow. Typically, this, among other conditions may be when the engine coolant temperature is at a low level. 
     As illustrated, the engine  10  is a liquid cooled engine and requires a radiator  66  positioned generally in the ambient air flow passing through the charge air cooler and the low temperature EGR cooler. Radiator  66  is an air-to-liquid heat exchanger and includes a coolant flow path internal to the engine  10  and which passes through a coolant conduit  68 , through the high temperature EGR cooler  50 , and through coolant conduit  70  to radiator  66  and returns to the engine  10  via coolant conduit  72 . A liquid coolant pump (not shown) provides circulation of the liquid coolant. Thus, the high temperature EGR cooler  50  is a liquid-to-air cooler and the low temperature EGR cooler  58  is an air-to-air cooler, as is the charge air cooler  32 . The charge air cooler  32  and low temperature EGR cooler are air-to-air coolers because they enable the heat sink for the thermal dynamic heat transfer to be ambient air which is significantly lower than the engine coolant temperature found in the liquid control circuit for engine  10 . By utilizing an air-to-air low temperature EGR cooler, EGR percentages may be significantly increased to provide a beneficial effect on the emissions generated by the engine. However, with the second stage of EGR cooling, the combustion products from the engine passing through the exhaust conduit  16  have moisture and the subsequent cooling reduces the temperature so that water condenses out of the air flow stream. This water combines with other products of combustion to have an adverse effect on the materials commonly used in the intake and combustion chamber of engines. The bypass valve  54  is provided to direct flow around the low temperature EGR cooler  58  so as to avoid the occurrence of condensation of moisture as stated above. However, with existing systems, there may be residual moisture within the low temperature EGR cooler which can pass in an uncontrolled manner to the inlet conduit  34 . 
     In accordance with the present invention, the charge air cooler  32  and low temperature EGR cooler  58  illustrated in  FIGS. 2 and 3  minimize, if not eliminate, the adverse accumulation of moisture. The charge air cooler  32  has an inlet end  74  connected to intake air conduit  30  and an outlet end  76  connected to intake air conduit  34 . Charge air cooler  32  is an air-to-air heat exchanger and includes flow passages (not shown) for providing heat exchange through the surface of internal flow directing passages to provide the cooling function. The low temperature after cooler  58  likewise has an inlet end  78  connected to EGR conduit  56  and an outlet  80  connected to conduit  60  at a low point in the EGR cooler  58  to permit any moisture to pass to conduit  60 . The low temperature EGR cooler  58  has similarly configured passages to provide heat exchange flow. As illustrated, the charge air cooler  32  and low temperature EGR cooler  58  are contiguous with the charger cooler  32  being higher than the low temperature EGR cooler  58 . A valve  82  interconnects the inlet end  74  of charge air cooler  32  to the inlet end  78  of low temperature EGR cooler  58 . The inlet end  74  is upstream of the internal passages in charge air cooler  32  and is thus upstream of charge air cooler, and is exposed to the pressures and temperatures from the outlet of the compressor  28 . Valve  82  operates on a pressure differential so that higher pressure in inlet end  74  than inlet  78  causes gas flow from a point upstream of the charge air cooler through the low temperature EGR cooler  58 . As illustrated, valve  82  is a check valve only permitting flow from end  74  to end  78  so that any moisture generated within the low temperature EGR cooler  58  would not pass to the charge air cooler  32 . Valve  82  permits a flow of air from a point upstream of the charge air cooler through the low temperature EGR cooler to purge it of any accumulated moisture. The air upstream of the charger cooler  32  is at a high temperature and passing it through the low temperature EGR cooler  58  evaporates and carries with it any accumulated moisture. Since the charge air cooler and the low temperature after cooler are contiguous and connected by the one way flow of valve  82 , moisture does not flow from the low temperature cooler  58  into the charge air cooler  32 . As such, the charge air cooler  32  can continue to be made of materials optimized for charge air cooling without the need for special selection to resist the effects of acids generated with moisture in the EGR stream. 
     The orientation of the charge air cooler  32  and low temperature EGR cooler  58  shown in  FIG. 2  is that the charge air cooler  32  is on top.  FIG. 3  shows the reverse orientation with duplicate numbers designated with a prime superscript. Thus, charge air cooler  32 ′ is below low temperature EGR cooler  58 ′. The valve  82 ′ permits only one way flow from the charge air cooler end  74 ′ to the low temperature EGR cooler end  78 ′. The outlet  80 ′ connects to conduit  60 ′ at a low point in EGR cooler  58 ′. The advantage of this orientation is that the moisture droplets in the low temperature EGR cooler  58 ′ fall by gravity into the higher velocity airstream from the charge air cooler  32 ′ are entrained in the airflow in conduit  34 ′ as a fine mist. In order to facilitate the entrainment, a mixer such as a nozzle  84 , shown in dashed lines, may be incorporated into the system. 
     The above arrangements have the beneficial effect of utilizing a simple differential pressure check valve between the charge air cooler and the low temperature EGR cooler to provide effective purging of moisture from the low temperature EGR cooler without an elaborate control mechanism. The existing control mechanism to initiate bypass flow around the low temperature charge air cooler is retained but the added benefit is an effective purging of the low temperature charge air cooler without providing puddles of moisture in the main flow to the engine that could cause intermittent slugs of moisture to be ingested by the engine. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.