Abstract:
A compression ignition engine comprising at least one combustion chamber, an air intake system, a fuel system, an exhaust system and an exhaust gas recirculation system. The air intake system conveys air to the chamber. The exhaust system conveys exhaust gases from the combustion chamber. The exhaust gas recirculation system is capable of recirculating a portion of the exhaust gases into air intake system. The exhaust gas recirculation system comprises a cooler package and a valve. The valve controls the amount of air flow through the cooler package. The cooler package includes a first portion, a second portion and a control valve. The control valve of the cooler package is configured to control whether the air that flows through the cooler package flows only through one of the first or the second portion or through both of the first portion and the second portion in parallel.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of patent application Ser. No. 11/933,603, filed Nov. 1, 2007, the subject matter of which are hereby expressly incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure generally relates to diesel engines and more particularly to the arrangement of coolers utilized in exhaust gas recirculation in diesel engines. 
       BACKGROUND 
       [0003]    Diesel engines include cylinders that combust a mixture of compressed air and diesel fuel. Frequently, exhaust gas recirculation (EGR) is utilized to minimize unfavorable emissions, such as NOx emissions, for the combustion of the diesel fuel. The usage of exhaust gas recirculation often impacts fuel economy, especially in turbocharged diesel engines. Moreover, in large duty trucks, the extra heat energy transferred to the coolant requires that the size of the radiators and cooling fans generally be increased in order to maintain engine temperature. 
         [0004]    Traditionally, EGR systems have been described as a “high pressure loop” wherein the exhaust is extracted on the high-pressure side of a turbocharger turbine. The exhaust is then returned to the high pressure side of the turbocharger compressor. Accordingly, in order for the exhaust gas to flow in the proper direction, the exhaust manifold pressure must be higher than the intake manifold pressure. In order to achieve this, crankshaft power may be used to deliver power during the pumping loop portion of the engine cycle. Since the EGR in a high pressure loop requires a reversal of the manifold pressure differential as compared to normal engines, the pumping loop portion of the cycle consumes power, rather than delivers power. Thus, the amount of power consumed in the pumping loop portion depends upon the manifold pressure differential. In addition, the flow restriction of the EGR path may also affect the manifold pressure differential. 
         [0005]    Much of the flow restriction of an EGR system occurs in the EGR cooler. The size of the cooler generally depends upon several factors. For example, the system may require a cooler large enough (i.e. with sufficient surface area for heat transfer) to deliver low temperature EGR at high power/high flow conditions in order to prevent NOx limits from being exceeded. Unfortunately, large coolers often result in a larger pressure drop, and further require more space for mounting. Moreover, at low power/low flow, the gas flowing through the cooler may deposit soot on the cooler surfaces. As these deposits build up on the surface of the cooler, the deposits insulate the surfaces and impede heat transfer. During laminar flow, the deposits may accumulate to the point where the flow passages become completely blocked, but with turbulent flow, the deposits stabilize at a certain thickness and typically do not block the passages of the cooler. 
         [0006]    Furthermore, the first portion of the cooler generally provides a greater reduction in air temperature than the second portion downstream from the first portion. At relatively higher power, the reduction of temperature in the second portion may be necessary to cool the gas, but at lower power with the initial temperature of the gas being lower, the second portion may not effectively cool the gas but still reduce the pressure of the gas as it passes through the cooler. 
         [0007]    Additionally, as mentioned above EGR cooler designs attempt to accommodate the lower emission requirements by increasing cooling of the EGR gas, which requires a larger cooler. The increase in cooler package size has reduced the available space for other components on the “hot side’ of the engine. Accordingly, it is desirable to increase the effectiveness of the EGR cooler, while maintaining a compact package configuration. 
       SUMMARY 
       [0008]    An embodiment of the present disclosure relates to a compression ignition engine comprising at least one combustion chamber, an air intake system, a fuel system, an exhaust system and an exhaust gas recirculation system. In one variation, the air intake system conveys air to at least one combustion chamber. In addition, the fuel system conveys fuel into at least on combustion chamber. Furthermore, the exhaust system conveys exhaust gases from at least one combustion chamber. The exhaust gas recirculation system is capable of recirculating a portion of the exhaust gases into the air intake system. The exhaust gas recirculation system comprises a first exhaust gas recirculation cooler, a second exhaust gas recirculation cooler and a valve positioned intermediate the first cooler and the second cooler. The valve, when opened, allows the exhaust gas to flow in parallel through both the first cooler and the second cooler. When closed, the valve prevents exhaust gas from flowing through the second cooler. 
         [0009]    In one variation of the disclosure, the first cooler and the second cooler are liquid cooled. The first cooler is arranged in a parallel relationship with the second cooler. In another variation, a controller is capable of controlling whether the valve is opened or closed. In an extension of this variation, the controller includes a sensor configured to determine the speed of the engine. 
         [0010]    In another variation of the disclosure, the engine further includes a third exhaust gas recirculation cooler connected to the first and second exhaust gas recirculation coolers. The third exhaust gas recirculation cooler is further connected to the intake, and the third exhaust gas recirculation cooler is connected in series with the first and second exhaust gas recirculation coolers. In yet another variation, the third exhaust gas recirculation cooler is air cooled. It should be understood, however, that any of the exhaust gas recirculation coolers may be liquid cooled, air cooled, or cooled using any other suitable technique. 
         [0011]    As such, a staged arrangement EGR cooler according to the teachings of the present disclosure may incorporate a pair of independent cooler sections and a valve to control the amount of cross-sectional cooler area (by directing EGR gas to one or both cooler sections) as a function of engine load. Additionally, the EGR cooler package may be formed in a compact shape (such as a U-shape) to reduce the space required for mounting the cooler package and permit alternate mounting orientations (e.g. vertical instead of horizontal). 
         [0012]    The features and advantages of the present disclosure described above, as well as additional features and advantages, will be readily apparent to those skilled in the art upon reference to the following description and the accompanying drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above-mentioned and other features of this disclosure and the manner of obtaining them will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawing, wherein: 
           [0014]      FIG. 1  depicts a general schematic diagram of portions of an exemplary diesel engine embodying principles of the present disclosure; 
           [0015]      FIG. 2  depicts an embodiment of a cooling package in accordance with the principles of the present disclosure; and 
           [0016]      FIG. 3  depicts another embodiment of a cooling package in accordance with the principles of the present disclosure. 
       
    
    
       [0017]    Although the drawings represents embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the concepts presented herein. The exemplifications set out herein illustrate embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. 
       DETAILED DESCRIPTION 
       [0018]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, which are described below. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. The disclosure includes any alterations and further modifications in the illustrated devices and described methods and further applications of the principles of the disclosure, which would normally occur to one skilled in the art to which the disclosure relates. Moreover, the embodiments were selected for description to enable one of ordinary skill in the art to practice the invention. 
         [0019]      FIG. 1  depicts a portion of an exemplary diesel engine  10  for powering a motor vehicle operating in accordance with an embodiment of the present disclosure. In the depicted embodiment, engine  10  comprises a plurality of cylinders  12  within which pistons (not shown) reciprocate in a known manner. Each piston may be coupled to a respective throw of a crankshaft (not shown) by a corresponding connecting rod (not shown) in an known manner. 
         [0020]    Engine  10  further includes an intake system, indicated by numeral  14 . Intake system  14  delivers the intake air into each of the cylinders in a known manner. In the depicted embodiments, intake system  14  comprises a fresh air inlet  16 . Fresh air inlet  16  conveys ambient air to a compressor  18 C of a turbocharger  18 . After compressor  18 C has compressed the fresh air, a charge air cooler, also known as an intercooler,  20  cools the fresh air before the air passes to an intake manifold  22 . In a known manner, air enters a respective cylinder  12  when a respective intake valve or valves of the cylinder  12  is open. 
         [0021]    In the depicted embodiment, engine  10  includes an exhaust gas recirculation (EGR) system, indicated by numeral  24 , and an exhaust system, generally indicated by numeral  26 . EGR  24  provides controlled recirculation of engine exhaust gases from exhaust system  26  of engine  10  to intake system  14  for purposes of emission control. 
         [0022]    Exhaust system  26  comprises an exhaust manifold  28  and a turbine  18 T of turbocharger  18 . Exhaust manifold  28  may be any suitable manifold known in the art. Exhaust system  26  may also include one or more exhaust treatment devices (not shown) such as a diesel particulate filter (DPF) for trapping soot present within the exhaust air in order to prevent the trapped soot from escaping to the surrounding atmosphere, for example. 
         [0023]    In the depicted embodiment, EGR system  24  comprises an EGR cooler package, generally indicated by numeral  30 , an EGR intercooler  32  and an EGR valve  34 . EGR cooler package  30  includes a housing  31 , a first portion  40 , a second portion  42 , a divider wall  44 , and a control valve  45 . Housing  31  includes an inlet  30   i  and an outlet  30   o . As shown, inlet  30   i  is in flow communication with first portion  40 . Inlet  30   i  is also in flow communication with a flow path  43  to second portion  42 . Flow path  43  is bounded by first portion  40 , housing  31  and divider wall  44 . The outlet side of first portion  40  is in flow communication with flow path  47 , which is bounded by divider wall  44 , second portion  42  and housing  31 . Flow path  47  and the outlet side of second cooler  42  are in flow communication with outlet  30   o  of EGR cooler package  30 . As indicated above, EGR cooler package  30  may be cooled in any suitable manner, such as jacket water cooling, for example. First portion  40  and second portion  42  of EGR cooler package  30  are each generally configured to cool the air passing through cooler package  30 . 
         [0024]    In the depicted embodiment, control valve  45  controls the manner in which air flows through cooler package  30 . For example, when control valve  45  is in a closed position as depicted in dotted lines and indicated by numeral  45   c , all of the air entering package  30  flows through first portion  40  prior to exiting the cooler package  30 . None of the air (or at least substantially none of the air) flows through second package  42 . Conversely, when control valve  45  is in an opened position as depicted in solid lines and indicated by numeral  45   o , a portion of the air flowing through package  30  travels through first portion  40  and the remainder of the air travels through second portion  42  in parallel prior to exiting the cooler package  30 . It should be understood that control valve  45  may be configured for controllable positioning in a plurality of positions intermediate the closed position  45   c  and the opened position  45   c  referenced above. 
         [0025]    EGR charge air cooler, or EGR intercooler,  32 , may also be utilized to further cool the air. EGR intercooler  32  may be any type of suitable intercooler, such as an air-cooled, or direct, intercooler, for example. It should be noted that in an alternate embodiment, EGR intercooler  32  may be omitted from engine  10 . 
         [0026]    Intercooler  32  includes an inlet  32   i  and an outlet  32   o , and valve  34  includes an inlet  34   i  and outlets  34   o  and  34   o ′. In the depicted embodiment, inlet  30   i  conveys air from exhaust manifold  28  to cooler package  30 . Air exiting cooler package  30  travels through outlet  30   o  and is then conveyed to valve  34  by way of inlet  34   i . Air exiting valve  34  may travel from outlet  34   o  to inlet  32   i  and then enters intercooler  32 . In addition, air exiting valve  34  may travel from outlet  34   o ′ to join with the air traveling though outlet  32   o  at junction  35 . Outlet  32   o  conveys air from intercooler  32  to junction  35 , and air travels through outlet  35   o  from junction  35  to intake  14 . 
         [0027]    It should be noted that in the depicted embodiment, valve  34  controls the flow of air through the EGR system  24 . Specifically, valve  34  may direct air into outlet  34   o  and consequently into intercooler  32 , or valve  34  may direct air into outlet  34   o ′ in order to allow the air to bypass intercooler  32 . Furthermore, valve  34  may be fully closed thereby preventing air from flowing through inlet  30   i  and consequently, preventing air from traveling through cooler package  30 . Accordingly, air from exhaust manifold  28  will be communicated to inlet  30   i  whenever valve  34  is at least partially open. Thus, whenever valve  34  is at least partially open, the air flows through EGR system  24  and into intake  14 . 
         [0028]    It should be noted that in embodiments of the invention, valve  34  may be replaced with a plurality of valves capable of collectively performing the same function. For example, valve  34  may be replaced with a first valve capable of selectively preventing the flow of air through cooler package  30 , and a second valve capable of directing air from input  34   i  into either output  34   o  or output  34   o ′. Moreover, these valves may be placed in any number of suitable positions within the EGR system  24 . 
         [0029]    In operation, whenever valve  34  is opened and directs air into at least one of output  34   o  or output  34   o ′ thereby allowing air to flow through the EGR system  24 , cooler package  30  may be in at least one of two different configurations. For example, at low power and low flow, wherein less cooling is necessary, valve  45  may be closed so that air only flows through first portion  40 . First portion  40  is configured to ensure the air remains in turbulent flow in order to reduce the amount of soot deposited on first portion  40 . When the engine is at a high flow and high power condition, valve  44  may be opened in order to allow the air flowing through the cooler package  30  to flow in parallel through both first portion  40  and second portion  42 , i.e. such that a portion of the air flowing through package  30  travels through the first portion  40  and a portion of the air travels through second portion  42 . In high power/high pressure conditions, the air flowing through cooler package  30  remains in a turbulent flow state in order to minimize the soot deposited on the portions  40 ,  42  of the cooler package  30 . 
         [0030]    In either instance, once the air exits from cooler package  30  by way of outlet  30   o , the air passes into valve  34  by way of inlet  34   i . Valve  34  may be configured to direct the air into outlet  34   o  and into intercooler  32  by way of inlet  32   i . The passage of the air through intercooler  32  allows the temperature of the air to be lowered prior to the air being conveyed to intake  14  via outlet  32   o.    
         [0031]    It should be noted that in certain instances, valve  34  may be switched so that the air bypasses intercooler  32 . For example, when intercooler  32  is air cooled and the ambient air is below freezing, valve  34  may be switched so that the air bypasses intercooler  32  in order to prevent the condensation of the moisture within the air. 
         [0032]    In alternative embodiments, intercooler  32  may be removed from the engine  10 , thereby allowing air to pass from cooler package  30  through valve  34  and into intake  14 . In embodiments in which intercooler  32  is not present, valve  34  may be located at any suitable position within the EGR system  24 . 
         [0033]    It should be noted that the valves  34 ,  45  may be controlled in any suitable manner. For example, an engine control unit (not shown) may be used to control the degree to which the valves  34 ,  45  are opened. The engine control unit may also include a sensor configured to sense the power output and flow of the engine, in order to ensure the valves  34 ,  45  are opened appropriately and proper turbulent air flow is maintained through the cooler package  30  in order to minimize the deposit of soot. 
         [0034]      FIG. 2  depicts another embodiment of a cooling package according to the teachings of the present disclosure, generally indicated by numeral  130 . In the depicted embodiment, cooling package  130  includes a first cooler  140 , a second cooler  142  and a valve  144 . Gas enters valve  144  of cooling package  130  by way of inlet  130   i , and at least a portion of the gas passes through valve  144  and into first cooler  140 . The first cooler  140  cools the gas in a conventional manner. 
         [0035]    Valve  144  may also be configured to direct a portion of the gas passing through the valve  144  into second cooler  142 . Generally, when valve  144  directs a portion of the gas to second cooler  142 , valve  144  continues to direct a portion of the gas to the first cooler  140 . In the depicted embodiment of cooling package  130 , the gas flowing through first cooler  140  and second cooler  142  recombines at junction  141  in a suitable manner. The recombined gas may then exit cooling package  130  via outlet  130   o . It should be noted that in embodiments of the invention, first cooler  140  and second cooler  142  may be liquid cooled. 
         [0036]    Referring now to  FIG. 3 , another embodiment of an EGR cooler is shown. Cooler package  150  includes a housing  152 , a first cooler core (first portion  154 ), a second cooler core (second portion  156 ), a divider wall  158 , and a control valve  160 . As shown, first portion  154  and second portion  156  are enclosed within housing  152 , which is formed in a U-shape. Accordingly, first portion  154  includes a substantially straight inlet segment  154 A, a curved segment  154 B, and a substantially straight outlet segment  154 C. Similarly, second portion  156  includes a substantially straight inlet segment  156 A (disposed substantially parallel to inlet segment  154 A), a curved segment  156 B (disposed substantially parallel to inlet segment  154 B), and a substantially straight outlet segment  156 C (disposed substantially parallel to inlet segment  154 C). Housing  152  includes an inlet  162  and an outlet  164 . As shown, inlet  162  is in flow communication with inlet segment  154 A of first portion  154 . First portion  154  is entirely separated from second portion  156  from inlet  162  to outlet  164  by the combination of divider wall  158  and control valve  160 . Both outlet segment  154 C of first portion  154  and outlet segment  156 C of second portion  156  are in flow communication with outlet  164 . 
         [0037]    Control valve  160  is depicted in this embodiment as a flapper valve, with a movable portion  166  coupled to a pivotal connection  168  that is mounted to housing  152 . Movable portion  166  is configured to obstruct, when valve  160  is in the closed position shown in solid lines in  FIG. 3 , an opening in divider wall  158  between inlet segment  154 A and inlet segment  156 A. Thus, when valve  160  is in the closed position, gas is substantially prevented from flowing through second portion  156  of package  150 . When valve  160  is in the opened position as shown in dotted lines in  FIG. 3 , the opening in divider wall  158  is unobstructed, and gas is permitted to flow in parallel through both first portion  154  and second portion  156 . While control valve  160  is depicted as a hinged-type valve, it should be understood that any suitable valve configuration may readily be employed by a person skilled in the art. Moreover, it should be understood that valve  160  may be configured for controllable positioning in a plurality of positions intermediate the closed position and the open position. 
         [0038]    In operation, under low load conditions (i.e., when the EGR flow rate is low), control valve  160  is in the closed position to inhibit flow through second portion  156  and provide a relatively smaller flow area (i.e., the cross-sectional area of first portion  154 ). This smaller flow area ensures sufficiently turbulent flow to reduce the amount of soot deposited (i.e., fouling) on first portion  154 . Under high load conditions (i.e., when the EGR flow rate is high), control valve  160  is in the opened position to permit flow through second portion  156  in parallel with the flow through first portion  154 , thereby providing a relatively larger flow area (i.e., the sum of the cross-sectional areas of first portion  154  and second portion  156 ). In this manner, the level of turbulence is maintained within an acceptable range to prevent a large pressure drop through cooler package  150 . 
         [0039]    It should be understood that by facilitating a variable cooler cross-section using control valve  160  in the manner described above, cooler package  150  can be controlled to maintain a Reynolds number in the turbulent flow range under low flow conditions without experiencing the undesirable effects of very high Reynolds numbers under high flow conditions. Moreover, it should be understood that the compact design of a U-shaped cooler package may reduce the space needed to receive the package, and may permit alternate mounting orientations such as vertical instead of horizontal. 
         [0040]    While these embodiments have been described as having exemplary designs they may 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 disclosed 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 application pertains.