Abstract:
An apparatus for a vehicle with an engine is provided that accomplishes exhaust heat recovery and exhaust gas recirculation with a common heat exchanger used for both purposes. The apparatus includes an exhaust system through which exhaust gas is discharged from the engine. A heat exchanger is positioned within the exhaust system. Coolant flow passages are provided in thermal communication with the engine and with the heat exchanger. A bypass valve is operable in a first position to direct the exhaust gas through the heat exchanger to transfer heat to the coolant flow passages in a coolant heating mode, and operable in a second position in which the exhaust gas bypasses the heat exchanger in a bypass mode during which no significant coolant heating occurs via the heat exchanger. A portion of the exhaust gas is recirculated to the engine after cooling via the heat exchanger.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to an exhaust heat recovery system and an exhaust gas recirculation system for a vehicle. 
       BACKGROUND OF THE INVENTION 
       [0002]    Rapid warm-up of engine coolant, engine oil, and transmission fluid is important to fuel economy during a cold start (i.e., when the vehicle has not been running and the engine and transmission are relatively cold). Engine warm-up is especially challenging for diesel and hybrid applications, as less fuel is burned. Exhaust gas recirculation (EGR) systems are used to reduce emissions by recirculating some of the exhaust gas back to the engine. Cooled EGR gas can improve fuel economy by allowing more spark advance. Additionally, engine warm-up may be more rapid with warm EGR gas, which may be advantageous in some engine applications. 
       SUMMARY OF THE INVENTION 
       [0003]    An apparatus for a vehicle with an engine is provided that accomplishes exhaust heat recovery and exhaust gas recirculation with a common heat exchanger used for both purposes. The apparatus includes an exhaust system through which exhaust gas is discharged from the engine. A heat exchanger is positioned within the exhaust system, and coolant flow passages are provided in thermal communication with the engine and with the heat exchanger. A bypass valve is operable in a first position to direct the exhaust gas through the heat exchanger to transfer heat to the coolant flow passages in a coolant heating mode, and operable in a second position in which the exhaust gas bypasses the heat exchanger in a bypass mode during which no significant coolant heating occurs via the heat exchanger. A portion of the exhaust gas is recirculated to the engine after cooling via the heat exchanger. Thus, both exhaust gas recirculation and exhaust heat recovery thereby being accomplished via the heat exchanger, and a separate heat exchanger for cooling of recirculated exhaust gas is not required. Cost savings and reduced system complexity may be realized by the elimination of a separate heat exchanger. Additionally, mass may be reduced, improving fuel economy. 
         [0004]    For example, the exhaust system may have an exhaust gas recirculation port in fluid communication with the engine for recirculating a portion of the exhaust gas to the engine. A portion of the exhaust gas flows through the heat exchanger for cooling prior to flowing through the exhaust gas port when the bypass valve is in the bypass mode. Various embodiments accomplish these two functions via a single heat exchanger using different exhaust gas recirculation ports, valve bodies and valves. 
         [0005]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic illustration of a first embodiment of a vehicle with a first embodiment of an apparatus for exhaust heat recovery and exhaust gas recirculation with a common heat exchanger; 
           [0007]      FIG. 2  is a schematic illustration of the apparatus of  FIG. 1  in a coolant heating mode; 
           [0008]      FIG. 3  is a schematic illustration of the apparatus of  FIG. 1  in a heat exchanger bypass mode; 
           [0009]      FIG. 4  is a schematic illustration of an alternative apparatus for exhaust heat recovery and exhaust gas recirculation with a common heat exchanger and in a coolant heating mode; 
           [0010]      FIG. 5  is a schematic illustration of the apparatus of  FIG. 4  in a heat exchanger bypass mode; 
           [0011]      FIG. 6  is a schematic perspective illustration of the apparatus of  FIG. 4  in partial cross-sectional view; 
           [0012]      FIG. 7  is a schematic perspective illustration of the apparatus of  FIG. 5  in partial cross-sectional view; 
           [0013]      FIG. 8  is a schematic illustration of another alternative apparatus for exhaust heat recovery and exhaust gas recirculation with a common heat exchanger and in a coolant heating mode; and 
           [0014]      FIG. 9  is a schematic illustration of the apparatus of  FIG. 8  in a heat exchanger bypass mode. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,  FIG. 1  shows a vehicle  10  that has an engine  12  for propelling the vehicle  10 . The engine  10  is an internal combustion engine of the gasoline or diesel type. An apparatus  14  is operatively connected to the engine  12  and is operable to accomplish both exhaust heat recovery and exhaust gas recirculation using only a single heat exchanger  16 , as shown and described further with respect to  FIG. 2 . The engine  12  generates exhaust gas in an exhaust system  18  that includes an exhaust manifold  20  and an exhaust pipe  22  extending therefrom. Referring to  FIG. 2 , the relatively hot exhaust gas exits the manifold  20  via an inlet  24  of the exhaust pipe  22  and passes through the apparatus  14  before exiting via an outlet  26  of the exhaust pipe  22 . A catalytic converter (not shown) may be positioned in the exhaust system  18  between the manifold  20  and the apparatus  14 . Engine coolant flows between the engine  12  and the apparatus  14  via conduits forming an engine coolant inlet flow passage  28  and an engine coolant outlet flow passage  30 , as indicated by coolant flow arrows I and O. The conduits may be flexible or rigid tubing, or bored, drilled, cast or otherwise formed passages in any vehicle component. Furthermore, exhaust gas is recirculated from the apparatus  14  to an intake manifold  32  of the engine  12  via exhaust gas recirculation passage  34 . The exhaust system  18  has an exhaust gas recirculation port  35  through which exhaust gas is provided to the exhaust gas recirculation passage  34 , 
         [0016]    The apparatus  14  includes a wall  40  partially dividing the exhaust pipe  22 . A bypass valve  30  is pivotally connected to the wall  40  and pivots about an axis extending along pivot post  44 . An exhaust bypass actuator (not shown), such as an electric servo motor, is controllable to selectively move the valve  42  between the first position of  FIG. 2  and the second position of  FIG. 3 . Alternatively, the actuator may also be a vacuum diaphragm, or a wax motor that can be activated by coolant temperature flowing therethrough (in which case the actuator might be activated without input from a controller). Stops  46 A,  46 B extend within the exhaust pipe  22  to limit movement of valve  42  and thereby define the first and second positions of the valve  42 . An electronic controller (not shown) is operatively connected to the actuator (depending on the type of actuator used, as described above), and controls the actuator according to vehicle operating conditions received as input signals from various sensors placed on the vehicle  10 , such as an exhaust heat recovery coolant temperature sensor and an engine coolant temperature sensor. The information received by the controller is indicative of such operating conditions as temperature of coolant flowing through the engine and temperature of coolant exiting the heat exchanger. The sensors may directly measure the operating conditions, or may provide information used in a predictive model that predicts or estimates these operating conditions. A person of ordinary skill in the art would readily understand the various ways to provide such information indicative of vehicle operating conditions to the controller, and would readily understand various algorithms that may be stored on the controller to process the information. Furthermore, electronically, thermally, or pneumatically actuated valves are well understood by those skilled in the art. 
         [0017]    Referring to  FIG. 2 , when the valve  42  is in the first position, a coolant heating mode is established as a majority of the exhaust gas is directed through the heat exchanger  16 , as indicated by flow arrows A showing exhaust gas entering the heat exchanger  16 , and flow arrows B indicating exhaust gas exiting the heat exchanger  16 . In the Figures, flow arrows indicating relatively warm exhaust gas are shaded, while flow arrows indicating relatively cool exhaust gas are unshaded. Some heat is transferred from the exhaust gas to the engine coolant via the heat exchanger  16 , so that coolant in flow passage  30  is warmer than coolant in flow passage  28 . In the coolant heating mode of  FIG. 2 , a small portion of the exhaust gas enters the exhaust gas recirculation passage  34  prior to passing through the heat exchanger  16 , as indicated by flow arrow C. Thus, the recirculated exhaust gas indicated by arrow C is not cooled during the coolant heating mode. Relatively warm EGR gas may facilitate rapid engine warm-up. 
         [0018]    When the engine  12  is sufficiently warmed, the valve  42  is moved to a second position shown in  FIG. 3  in which the flow path indicated by arrows A in  FIG. 2  is blocked, and exhaust gas cannot pass to the exhaust gas recirculation passage  34  without first passing through the heat exchanger  16 . When the valve  42  is in the second position, the apparatus is in a bypass mode. Exhaust gas flow is directed along an opposite side of wall  40  from the heat exchanger  16  than when the valve  42  is in the first position, as indicated by flow arrow D. Most of the exhaust gas passes out of the exhaust gas outlet  26 , bypassing the heat exchanger. A small portion of the exhaust gas flows through the heat exchanger  16 , as indicated by arrows E. Some heat is extracted from the exhaust gas and transferred to the engine coolant in flow passage  30 ; however, warming of the coolant is minimal in comparison to the coolant heating mode, because only a portion of the exhaust gas is routed through the heat exchanger  16  in the bypass mode. Accordingly the exhaust gas indicated by flow arrows F exiting the heat exchanger  16  and entering the exhaust gas recirculation passage  34  via port  35  is cooled. Thus in the bypass mode, the apparatus  14  cools recirculated exhaust gas via the common heat exchanger  16  used for heating engine coolant in the coolant heating mode. 
         [0019]    Referring to  FIGS. 4-7 , another embodiment of an apparatus  114  operatively connectable to the engine  12  is operable to accomplish both exhaust heat recovery and cooled exhaust gas recirculation using only a single heat exchanger  16 . Furthermore, EHR and cooled EGR are achieved during the same mode (coolant heating mode), i.e., during engine warm-up. Components of the apparatus  114  that are the same as those of apparatus  14  are referred to using like reference numbers. The apparatus  114  has an exhaust system  118  with a valve body  143  that has a first exhaust gas recirculation inlet port  145 , a second exhaust gas recirculation inlet port  147 , and an exhaust gas recirculation outlet port  135  that is in selective fluid communication with both the first and the second exhaust gas recirculation inlet ports  145 ,  147 , depending on the position of valve  142 . An exhaust bypass actuator (not shown), such as an electric servo motor, is controllable to selectively move the valve  142  between the first position of  FIGS. 4 and 6  and the second position of  FIGS. 5 and 7 . The actuator may also be a wax motor or a vacuum diaphragm. 
         [0020]    As best shown in  FIGS. 6 and 7 , the valve  142  has a first portion  142 A extending toward the exhaust inlet  24  from pivot post  144 , and a second portion  142 B that extends toward the exhaust outlet  26  from the pivot post  144 . The first and second portions  142 A,  142 B pivot in unison with one another about pivot post  144 , as both are integrally connected with one another via the pivot post  144 . The first portion  142 A lies in a portion of the interior of exhaust pipe  122 , level with the exhaust inlet  24 , the wall  40  and the heat exchanger  16 . The second portion  142 B lies above the wall  40  within a cavity formed by the valve body  143 . The valve body  143  also has barrier walls  151 ,  152  partially surrounding the exhaust gas recirculation inlet ports  145 ,  147 , respectively. 
         [0021]    When the valve  142  is in the first position of  FIGS. 4 and 6 , valve portion  142 A directs the exhaust gas from the exhaust pipe inlet  24  to flow through the heat exchanger  16 , as indicated by flow arrows A and B, establishing a coolant heating mode to transfer heat from the exhaust gas to engine coolant flowing through passages  28 ,  30 . The valve portion  142 B rests against the barrier wall  152  when in the first position, thus preventing fluid communication between the exhaust gas recirculation inlet port  147  and the exhaust gas recirculation outlet port  135 . A portion of the exhaust gas exiting the heat exchanger  16  flows along the opposite side of wall  40 , as indicated by flow arrows G, and then flows through exhaust gas recirculation inlet port  145  to exhaust gas recirculation outlet port  135 , as indicated by flow arrow H. From the exhaust gas recirculation outlet port  135 , the cooled recirculated exhaust gas, indicated by flow arrow J, is directed to the engine  12  through an exhaust gas recirculation passage, not shown but similar to passage  34  of  FIG. 1 . Thus, during the coolant heating mode, cooled exhaust gas recirculation is accomplished using exhaust gas cooled via the same heat exchanger  16  as used for coolant heating. 
         [0022]    When the engine  12  is sufficiently warmed, the valve  142  is moved to the second position of  FIGS. 5 and 7 , and valve portion  142 A directs the exhaust gas from the exhaust pipe inlet  24  to the opposite side of wall  40  from the heat exchanger  16 , as indicated by flow arrows K, establishing a bypass mode in which most of the exhaust gas passes out of the exhaust gas outlet  26 , bypassing the heat exchanger  16 . The valve portion  142 B rests against the barrier wall  151  when in the second position, thus preventing fluid communication between the exhaust gas recirculation inlet port  145  and the exhaust gas recirculation outlet port  135 . A portion of the exhaust gas flows around the wall  40 , as indicated by flow arrows L, and then flows through heat exchanger  16 , as indicated by flow arrow M. This small cooled portion of exhaust gas then flows through the exhaust gas recirculation inlet port  147 , as indicated by flow arrow N, and then through the exhaust gas recirculation outlet port  135  (as indicated by flow arrow P), which is in fluid communication with inlet port  147  when the valve  142  is in the second position. From the exhaust gas recirculation outlet port  135 , the cooled recirculated exhaust gas is directed to the engine  12  through an exhaust gas recirculation passage, not shown but similar to passage  34  of  FIG. 1 . Thus, during the bypass mode, exhaust gas recirculation is also accomplished using exhaust gas cooled via the same heat exchanger  16  as used for heating coolant in the coolant heating mode. Exhaust gas recirculation flow is directed to the engine  12  generally perpendicular to exhaust flow through the exhaust system  118 , as indicated by flow arrows J and P generally perpendicular to flow arrows A, B, G, K, L and M. 
         [0023]    Referring to  FIGS. 8 and 9 , another embodiment of an apparatus  214  operatively connectable to the engine  12  is operable to accomplish both exhaust heat recovery and exhaust gas recirculation using only a single heat exchanger  16 . EHR and cooled EGR are both accomplished during the same mode (engine warm-up). Components of the apparatus  214  that are the same as those of apparatus  14  are referred to using like reference numbers. 
         [0024]    The apparatus  214  includes an exhaust pipe  222  having exhaust inlet  24  and exhaust outlet  26 . The exhaust pipe  222  forms a first exhaust gas recirculation port  234  and a second exhaust gas recirculation port  236  on an opposing side of the heat exchanger  16  from the first exhaust gas recirculation port  234 . A first exhaust gas recirculation valve  237  is positioned in the first exhaust gas recirculation port  234  and is selectively openable and closable, such as via an electronic control signal from a controller (not shown). When the first exhaust gas recirculation valve  237  is opened, exhaust flow through the first exhaust gas recirculation port  234  is permitted. When the first exhaust gas recirculation valve  237  is closed, exhaust flow through the first exhaust gas recirculation port  234  is not permitted. In  FIGS. 8 and 9 , an “X” through valve  237  or  239  indicates that the valve is closed. 
         [0025]    Similarly, a second exhaust gas recirculation valve  239  is positioned in the second exhaust gas recirculation port  236  and is selectively openable and closable, such as via an electronic control signal from a controller (not shown). When the second exhaust gas recirculation valve  239  is opened, exhaust flow through the second exhaust gas recirculation port  236  is permitted. When the second exhaust gas recirculation valve  239  is closed, exhaust flow through the second exhaust gas recirculation port  236  is not permitted. 
         [0026]    When the valve  42  is in the first position shown in  FIG. 8 , a coolant heating mode is established as a majority of the exhaust gas is directed through the heat exchanger  16 , as indicated by flow arrows A showing exhaust gas entering the heat exchanger  16 , and flow arrows B indicating exhaust gas exiting the heat exchanger  16 . Some heat is transferred from the exhaust gas to the engine coolant via the heat exchanger  16 , so that coolant in flow passage  30  is warmer than coolant in flow passage  28 . When the valve  42  is in the first position, exhaust gas recirculation valve  237  is opened, and exhaust gas recirculation valve  239  is closed. A small portion of the exhaust exiting the heat exchanger flows through the exhaust gas recirculation port  234 , as indicated by flow arrow Q, and is directed to the engine  12  through open valve  237 , as indicated by flow arrow R, and through an exhaust gas recirculation passage, not shown but similar to passage  34  of  FIG. 1 . Thus in the coolant heating mode, the apparatus  214  accomplishes recirculation of cooled exhaust gas via the common heat exchanger  16 . 
         [0027]    When the engine  12  is sufficiently warmed, the valve  42  is moved to a second position shown in  FIG. 9  in which the flow path indicated by arrows A in  FIG. 8  is blocked. When the valve  42  is in the second position, the apparatus  214  is in a bypass mode. Exhaust gas flow is directed along an opposite side of wall  40  from the heat exchanger  16  than when the valve  42  is in the first position, as indicated by flow arrow D. Most of the exhaust gas passes out of the exhaust gas outlet  26 , bypassing the heat exchanger  16 . A small portion of the exhaust gas flows through the heat exchanger  16 , as indicated by arrows S. Some heat is extracted from the exhaust gas and transferred to the engine coolant in flow passage  30 ; however, warming of the coolant is minimal in comparison to the coolant heating mode, because only a portion of the exhaust gas is routed through the heat exchanger  16  in the bypass mode. When the valve  42  is in the second position, exhaust gas recirculation valve  239  is opened, and exhaust gas recirculation valve  237  is closed. Accordingly the exhaust gas indicated by flow arrows T exits the heat exchanger and is directed to the engine  12  through exhaust gas recirculation port  236  and open valve  239 , as indicated by flow arrow U, and through an exhaust gas recirculation passage, not shown but similar to passage  34  of  FIG. 1 . The exhaust gas entering the recirculation port  236  is cooled. Thus, in the bypass mode, the apparatus  214  accomplishes recirculation of cooled exhaust gas via the common heat exchanger  16 . 
         [0028]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.