Patent Publication Number: US-2020291905-A1

Title: Exhaust system with exhaust gas heat recovery assembly and method for operation of the exhaust system

Description:
FIELD 
     The present description relates generally to an exhaust system with exhaust gas heat recovery capabilities and a method for operating an exhaust system. 
     BACKGROUND/SUMMARY 
     Engine exhaust systems have been designed with exhaust gas heat recovery (EGHR) heat exchangers to capture thermal energy from exhaust gases. In certain exhaust systems, EGHR heat exchangers are operated during cold starts to decrease emissions and increase engine efficiency and are shut down after the engine is warmed up. 
     One example approach is shown by Speer, in U.S. Pat. No. 7,353,865. Speer&#39;s system uses an exhaust conduit branching off a primary conduit with an EGHR heat exchanger positioned therein and valving designed to vary gas flow through the branch conduit with the heat exchanger or the primary exhaust conduit. However, when the EGHR heat exchanger is not in operation, unwanted heat may be transferred to the heat exchanger. For instance, the heat transferred to the heat exchanger may come from heat recirculating into the heat exchanger from either the entry or exit ports as well as heat conducted through housing and other structures connecting the heat exchanger to the exhaust system. The engine cooling system therefore experiences unwanted thermal loading when the EGHR heat exchanger is not in operation, thereby decreasing cooling system efficiency. As such, Speer&#39;s system may be forced to balance tradeoffs between the heat exchanger&#39;s efficiency while the device is active and parasitic losses while the device is shut down. Towing and other high load conditions exacerbate the thermal loading on the cooling system when the heat exchanger is not in operation and may, in some cases, lead to elevated engine temperatures, increasing the chance of thermal damage to engine components, reducing combustion efficiency, and increasing emissions. 
     In one example, the issues described above may be at least partially addressed by an exhaust system for an internal combustion engine including a first exhaust conduit receiving exhaust gas from a cylinder during internal combustion engine operation and an EGHR heat exchanger coupled to an exterior surface of the first exhaust conduit and including an inlet and an outlet extending through a housing of the first exhaust conduit. The exhaust system further includes a second exhaust conduit arranged in a parallel flow arrangement with the first exhaust conduit and including a conduit body spaced away from the first exhaust conduit, a first flow control valve designed to adjust exhaust gas flow through the EGHR heat exchanger, and a second flow control valve coupled to the second exhaust conduit and designed to adjust exhaust gas flow through the second exhaust conduit. In this way, the benefits of an EGHR heat exchanger can be achieved while reducing the amount of heat transferred to the heat exchanger during periods of heat exchanger inactivity. For instance, while the EGHR heat exchanger is active, the engine&#39;s coolant may be warmed up more rapidly, increasing engine efficiency, reducing emissions, and providing a larger thermal reservoir from which cabin heat can be drawn from. In this way, the tradeoffs between EGHR heat exchanger efficiency and parasitic losses caused by thermal loading of the cooling system during EGHR heat exchanger shutdown may be diminished. As a result, engine efficiency is increased, emissions are reduced, and cabin heating can be increased during cold starts without increasing thermal loads on the cooling system when the heat exchanger is shut down, for instance. 
     In one example, the exhaust system may further include a controller with computer readable instructions stored on non-transitory memory that when executed cause the controller to operate the exhaust system in a first mode where exhaust gas flow through the EGHR heat exchanger is permitted and exhaust gas flow through the second exhaust conduit is inhibited. The controller may further include instructions stored on the non-transitory memory that when executed cause the controller to operate the exhaust system in a second mode where exhaust gas flow through the EGHR heat exchanger is inhibited and exhaust gas flow through the second exhaust conduit is permitted. In this way, the exhaust system may selectively flow exhaust gas through the first or second conduit based on engine operating conditions. For instance, the second mode may be implemented during higher speed and/or higher load conditions and the first mode may be implemented during lower speed and/or lower load conditions. Consequently, heat transfer from the first exhaust conduit to the heat exchanger may be reduced, during high flow conditions for example, while EGHR heat exchanger heat recovery benefits can be achieved during lower load operation, such as cold start operation. 
     In another example, the exhaust system may further include an insulated union at the inlet of the EGHR heat exchanger. The insulated union may further reduce the amount of heat transferred from the housing of the first exhaust conduit to the EGHR heat exchanger. As a result, the thermal loading on the cooling system during periods of heat exchanger shutdown is further decreased. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic depiction of an engine including an exhaust system. 
         FIG. 2  shows a schematic depiction of a hybrid vehicle. 
         FIG. 3  shows an example of an exhaust system with an exhaust gas heat recovery (EGHR) heat exchanger. 
         FIGS. 4-5  show the exhaust system, depicted in  FIG. 3 , in different operating modes. 
         FIGS. 6-7  show different detailed views of a flow control valve in the exhaust system, illustrated in  FIG. 3 . 
         FIGS. 8-9  show detailed views of another example of a flow control valve that may be included in the exhaust system, shown in  FIG. 3 . 
         FIGS. 10-11  show detailed views of an example of a flow control valve that may be included in the exhaust system, shown in  FIG. 3 . 
         FIGS. 12-13  show another example of a flow control valve that may be included in the exhaust system, shown in  FIG. 3 . 
         FIG. 14  shows an example of an EGHR assembly with insulated unions. 
         FIG. 15  shows another example of an EGHR assembly with insulated unions. 
         FIG. 16  shows a cross-section view of one of the insulated unions, shown in  FIG. 15 . 
         FIG. 17  shows a method for operation of an exhaust system. 
         FIG. 18  shows a more detailed method for operation of an exhaust system. 
         FIG. 19  shows a timing diagram for an exhaust system control scheme. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to an engine exhaust system leveraging benefits of an exhaust gas heat recovery (EGHR) heat exchanger (e.g., increased engine efficiency, reduced engine emissions, and increased cabin heating, if desired) during selected operating conditions, such as cold starts. Additionally, the exhaust system also reduces energy transfer from the exhaust gas to the EGHR heat exchanger while the heat exchanger is shut down. Reducing the flow of heat between the exhaust system and the EGHR heat exchanger reduces parasitic losses in the engine during periods when the heat exchanger is disabled. Consequently, the impacts of tradeoffs between the heat exchanger&#39;s efficiency when active and parasitic losses while the heat exchanger is disabled may be drastically reduced or avoided, in certain cases. 
     The exhaust system includes a first exhaust conduit with an exterior surface having the EGHR heat exchanger attached thereto. The heat exchanger receives exhaust gas from an inlet and expels exhaust gas through an outlet. The inlet and outlet of the heat exchanger each extend through an exhaust conduit housing. A heat exchanger flow control valve is coupled to the first exhaust conduit and regulates the flow of exhaust gas through the heat exchanger. For example, to accomplish the heat exchanger flow regulation, the flow control valve may be positioned between the inlet and outlet of the heat exchanger. The exhaust system further includes a branch conduit arranged in a parallel flow arrangement with the first conduit. A branch flow control valve coupled to the branch conduit (e.g., positioned at the upstream confluence of the branch conduit and the first conduit) regulates exhaust gas flow through the branch conduit. The branch flow control valve, for example, may block flow through the first conduit and permit flow through the branch conduit, during, for example, higher speed and/or load conditions. Conversely, in some examples, during lower speed and/or load conditions the branch flow control valve inhibits gas flow through the branch conduit and permits gas flow through the first conduit. It will be appreciated that the heat exchanger may be activated or deactivated while gas flows through the first conduit. 
       FIG. 1  shows a schematic depiction of an engine with an exhaust system having an EGHR assembly.  FIG. 2  shows a schematic depiction of a hybrid vehicle.  FIG. 3  shows an example of an exhaust system with an EGHR heat exchanger in a first operating mode where the EGHR heat exchanger is active.  FIG. 4  shows the exhaust system, depicted in  FIG. 3 , in a second operating mode where the EGHR heat exchanger is deactivated.  FIG. 5  shows the exhaust system, depicted in  FIG. 3 , in a third operating mode where the EGHR heat exchanger is deactivated and exhaust is routed further away from the heat exchanger.  FIGS. 6-7  illustrate different views of a flow control valve included in the exhaust system shown in  FIG. 3 .  FIGS. 8-9  show different views of another example of a flow control valve that may be included in the exhaust system, shown in  FIG. 3 .  FIGS. 10-11  show different views of yet another example of a flow control valve that may be included in the exhaust system, shown in  FIG. 3 .  FIGS. 12-13  show different views of another example of a flow control valve that may be included in the exhaust system, shown in  FIG. 3 .  FIG. 14  shows a detailed illustration of an example of an EGHR heat exchanger with insulated unions.  FIG. 15  shows yet another example of an EGHR heat exchanger with insulated unions.  FIG. 16  shows a cross-sectional view of the EGHR heat exchanger, depicted in  FIG. 15 .  FIG. 17  shows a method for operation of an exhaust gas system to augment the amount of heat transferred to an EGHR heat exchanger based on engine operating conditions.  FIG. 18  shows a more detailed method for operation of an exhaust system with an EGHR assembly.  FIG. 19  shows a graphical representation of an exemplary exhaust system control routine. 
       FIG. 1  shows a schematic representation of a vehicle  100  including an internal combustion engine  102 . Although,  FIG. 1  provides a schematic depiction of various engine and engine system components, it will be appreciated that at least some of the components may have different spatial positions and greater structural complexity than the components shown in  FIG. 1 . 
     An intake system  104  providing intake air to a cylinder  106 , is also depicted in  FIG. 1 . It will be appreciated that the cylinder may be referred to as a combustion chamber. A piston  108  is positioned in the cylinder  106 . The piston  108  is coupled to a crankshaft  110  via a piston rod  112  and/or other suitable mechanical component. It will be appreciated that the crankshaft  110  may be coupled to a transmission that provides motive power to a drive wheel. Although,  FIG. 1  depicts the engine  102  with one cylinder. The engine  102  may have additional cylinders, in other examples. For instance, the engine  102  may include a plurality of cylinders that may be positioned in banks. 
     The intake system  104  includes an intake conduit  114  and a throttle  116  coupled to the intake conduit. The throttle  116  is configured to regulate the amount of airflow provided to the cylinder  106 . For instance, the throttle  116  may include a rotatable plate varying the flowrate of intake air passing there through. In the depicted example, the throttle  116  feeds air to an intake conduit  118  (e.g., intake manifold). In turn, the intake conduit  118  directs air to an intake valve  120 . The intake valve  120  opens and closes to allow intake airflow into the cylinder  106  at desired times. The intake valve  120 , may include, in one example, a poppet valve with a stem and a valve head seating and sealing on a cylinder port in a closed position. 
     Further, in other examples, such as in a multi-cylinder engine additional intake runners may branch off the intake conduit  118  and feed intake air to other intake valves. It will be appreciated that the intake conduit  118  and the intake valve  120  are included in the intake system  104 . Moreover, the engine  102 , shown in  FIG. 1 , includes one intake valve and one exhaust valve. However, in other examples, the cylinder  106  may include two or more intake and/or exhaust valves. 
     An exhaust system  122  configured to manage exhaust gas from the cylinder  106  is also included in the vehicle  100 , depicted in  FIG. 1 . The exhaust system  122  includes an exhaust valve  124  designed to open and close to allow and inhibit exhaust gas flow to downstream components from the cylinder. For instance, the exhaust valve may include a poppet valve with a stem and a valve head seating and sealing on a cylinder port in a closed position. 
     The exhaust system  122  also includes an emission control device  126  coupled to an exhaust conduit  128  downstream of another exhaust conduit  130  (e.g., exhaust manifold). The emission control device  126  may include filters, catalysts, absorbers, combinations thereof, etc., for reducing tailpipe emissions. The engine  102  also includes an ignition system  132  including an energy storage device  134  designed to provide energy to an ignition device  136  (e.g., spark plug). For instance, the energy storage device  134  may include a battery, capacitor, flywheel, etc. Additionally or alternatively, the engine  102  may perform compression ignition. 
     The exhaust system  122  also includes an EGHR assembly  150  including another exhaust conduit  152  and another exhaust conduit  154  arranged in a parallel flow configuration with the exhaust conduit  152 . As such, the first and second exhaust conduits merge at an upstream confluence  156  and a downstream confluence  158 . 
     An EGHR heat exchanger  160  is attached to the exhaust conduit  152 . The heat exchanger includes a gas inlet  162  and an outlet  164  allowing exhaust gas to flow through the heat exchanger. The heat exchanger  160  also includes coolant conduits (not shown) routed therethrough. The internal coolant conduits are fluidly coupled to coolant conduits routing coolant through the EGHR heat exchanger and to/from an engine cooling system  168 . Specifically, in the illustrated example, an outlet coolant conduit  166  routes coolant to passages (e.g., cylinder head and/or block coolant jackets) in the engine  102  from the EGHR heat exchanger  160 . An inlet coolant conduit  167  directs coolant into the heat exchanger  160  from another heat exchanger  170  (e.g., cabin heat exchanger). The heat exchanger  170  is fluidly coupled to a flow diverter  171  (e.g., passive crossover flow diverter) designed to adjust the amount of coolant flowing to the heat exchanger  170  or a radiator  172 . Thus, flow may be directed to the EGHR heat exchanger from the cabin heat exchanger, for example. For instance, plates, seals, shafts, and/or other suitable mechanical components in the flow diverter  171  may be used to direct coolant flow to the heat exchanger  170  or the radiator  172  based on engine operating conditions, cabin heating requests, etc. In one example, a portion of the coolant from coolant passages in the engine may be directed to both the heat exchanger  170  and the radiator  172 . A pump  174  is coupled to the coolant line  175  fluidly connecting the flow diverter  171  and the engine coolant passages. A thermostat  177  may be coupled to a coolant line  179  extending between the flow diverter  171 . The thermostat  177  is designed to regulate the engine coolant temperature. Coolant lines  169  direct coolant from the thermostat  177  and the radiator  172  back to the engine coolant passages in the engine. However, it will be appreciated that the engine cooling system  168  may include additional or alternative components, such as valves, filters, etc. Furthermore, coolant routing arrangements differing from the routing illustrated in  FIG. 1 , have been envisioned. 
     A first flow control valve  176  is coupled to the exhaust conduit  152 . Specifically, in the illustrated example, the first flow control valve  176  is positioned between the gas inlet  162  and the  164  of the EGHR heat exchanger  160  with regard to a downstream exhaust gas flow direction. The first flow control valve  176  is designed to adjust the amount of exhaust gas flow through the first exhaust conduit. For example, the first flow control valve  176  may block the exhaust conduit  152 . When the first flow control valve block the first exhaust conduit, exhaust gas is directed through the EGHR heat exchanger  160 . On the other hand, the first flow control valve  176  may also be designed to permit exhaust gas flow through the exhaust conduit  152 . In this configuration, exhaust gas flow through the EGHR heat exchanger  160  may be substantially inhibited. As such, the first flow control valve  176  may be used to activate/deactivate the EGHR heat exchanger  160 . It will be appreciated that the first flow control valve  176  may also be arranged in partially opened or closed configurations where a portion of exhaust gas flows through the EGHR heat exchanger  160  and another portion of exhaust gas flows through the exhaust conduit  152 . 
     A second flow control valve  178  is coupled to the exhaust conduit  154 . Specifically, as illustrated, the second flow control valve  178  is positioned at the upstream confluence  156  of the exhaust conduit  152  and the exhaust conduit  154 . The first flow control valve  176  and the second flow control valve  178  may include plates, springs, hinges, pivots, bearings, solenoids, other suitable components, etc., facilitating the aforementioned flow control functionality. Examples of the first and second flow control valves are illustrated in detail in  FIGS. 6-13  and discussed in greater detail herein. 
       FIG. 1  also shows a fuel delivery system  138 . The fuel delivery system  138  provides pressurized fuel to a fuel injector  140 . In the illustrated example, the fuel injector  140  is a direct fuel injector coupled to cylinder  106 . Additionally or alternatively, the fuel delivery system  138  may also include a port fuel injector designed to inject fuel upstream of the cylinder  106  into the intake system  104 . For instance, the port fuel injector may be an injector with a nozzle spraying fuel into an intake port at desired times. The fuel delivery system  138  includes a fuel tank  142  and a fuel pump  144  designed flow pressurized fuel to downstream components. For instance, the fuel pump  144  may be an electric pump with a piston and an inlet in the fuel tank that draws fuel into the pump and delivers pressurized fuel to downstream components. However, other suitable fuel pump configurations have been contemplated. Furthermore, the fuel pump  144  is shown positioned within the fuel tank  142 . Additionally or alternatively the fuel delivery system may include a second fuel pump (e.g., higher pressure fuel pump) positioned external to the fuel tank. A fuel line  146  provides fluidic communication between the fuel pump  144  and the fuel injector  140 . The fuel delivery system  138  may include additional components such as a higher-pressure pump, valves (e.g., check valves), return lines, etc., to enable the fuel delivery system to inject fuel at desired pressures and time intervals. 
     During engine operation, the cylinder  106  typically undergoes a four-stroke cycle including an intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve closes and intake valve opens. Air is introduced into the combustion chamber via the corresponding intake conduit, and the piston moves to the bottom of the combustion chamber so as to increase the volume within the combustion chamber. The position at which the piston is near the bottom of the combustion chamber and at the end of its stroke (e.g., when the combustion chamber is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, the intake valve and the exhaust valve are closed. The piston moves toward the cylinder head so as to compress the air within the combustion chamber. The point at which the piston is at the end of its stroke and closest to the cylinder head (e.g., when the combustion chamber is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process herein referred to as injection, fuel is introduced into the combustion chamber. In a process herein referred to as ignition, the injected fuel in the combustion chamber is ignited via a spark from an ignition device, resulting in combustion. However, in other examples, compression may be used to ignite the air fuel mixture in the combustion chamber. During the expansion stroke, the expanding gases push the piston back to BDC. A crankshaft converts this piston movement into a rotational torque of the rotary shaft. During the exhaust stroke, in a traditional design, exhaust valve is opened to release the residual combusted air-fuel mixture to the corresponding exhaust passages and the piston returns to TDC. 
       FIG. 1  also shows a controller  180  in the vehicle  100 . Specifically, controller  180  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  181 , input/output ports  182 , read-only memory  183 , random access memory  184 , keep alive memory  185 , and a conventional data bus. Controller  180  is configured to receive various signals from sensors coupled to the engine  102 . The sensors may include engine coolant temperature sensor  179 , exhaust gas composition sensor  186 , exhaust gas airflow sensor  187 , an intake airflow sensor  188 , manifold pressure sensor  189 , engine speed sensor  190 , ambient temperature sensor  192 , etc. Additionally, the controller  180  is also configured to receive throttle position (TP) from a pedal position sensor  193  coupled to a pedal  194  actuated by an operator  195 . 
     Additionally, the controller  180  may be configured to trigger one or more actuators and/or send commands to components. For instance, the controller  180  may trigger adjustment of the throttle  116 , fuel injector  140 , fuel pump  144 , flow control valves  176  and  178 , pump  174 , etc. Specifically in one example, the controller  180  may send signals to an actuator in the first and/or second flow control valves that opens and/or closes the valve to facilitate valve adjustment. Furthermore, the controller  180  may be configured to send control signals to actuators in the fuel pump  144  and the fuel injector  140  to control the amount and timing of fuel injection provided to the cylinder  106 . The controller  180  may also send control signals to the throttle  116  to vary engine speed. The other adjustable components receiving commands from the controller may also function in a similar manner. Therefore, the controller  180  receives signals from the various sensors and employs the various actuators to adjust engine operation based on the received signals and instructions stored in memory (e.g., non-transitory memory) of the controller. Thus, it will be appreciated that the controller  180  may send and receive signals from the exhaust system  122  and the EGHR assembly  150 . 
     In one specific example, the controller  180  may be designed to implement different exhaust system operating modes. In a first mode exhaust flow through the EGHR heat exchanger  160  may be permitted. In this way, heat may be recovered from the exhaust gas during cold starts, for example, allowing the engine temperature to be increased more rapidly, provide cabin heating, etc. In such an example, at least the second flow control valve  178  may be configured to block the exhaust conduit  154 . Additionally, in the first mode, the first flow control valve  176  may be placed in a configuration where the valve blocks (e.g., fully blocks) or partially blocks the exhaust conduit  152  to direct exhaust gas through the EGHR heat exchanger  160 . It will be appreciated that the degree to which the valve blocks the exhaust conduit  152  may determine the amount of exhaust gas flowing through the EGHR heat exchanger  160 . 
     Additionally, the controller  180  may be designed to implement a second mode where exhaust gas flow through the EGHR heat exchanger  160  is substantially inhibited and gas flow through the exhaust conduit  152  is permitted. Additionally, in the second mode, exhaust gas flow through the exhaust conduit  154  may be substantially inhibited. Thus, in the second mode the first flow control valve  176  may arrange a valve plate in a position allowing gas to flow through the exhaust conduit  152  and may also block the inlet and/or outlet of the EGHR heat exchanger  160 . In this way, the heat exchanger may be deactivated, when desired. 
     Furthermore, the controller  180  may be designed to implement a third mode where exhaust gas flow through the exhaust conduit  154  is permitted and exhaust gas flow through the exhaust conduit  152  is substantially inhibited. Thus, in the third mode, the second flow control valve  178  may reposition a valve plate to substantially block the exhaust conduit  152 . Therefore, in the third mode exhaust gas is directed further away from the EGHR heat exchanger to reduce the amount of heat transferred to the heat exchanger and then the cooling system. 
     An entry condition for the first mode may be a threshold engine temperature. For instance, when the engine temperature drops below a threshold value (e.g., 60°, 63°, 65°, 70°, 80°, etc.). Conversely, in such an example, the second mode may be implemented when the engine is above the threshold value. Additionally, an entry condition for the third mode may be a threshold engine speed (e.g., 2,500 RPM, 3,000 RPM, 3,500 RPM, etc.,) and/or engine load (e.g., 25 CFM, 50 CFM, 100 CFM, 150 CFM, etc.) It will be appreciated that in some instances, the aforementioned thresholds may be selected based on engine design and EGHR package configuration. As such, the threshold may vary based on the end-use operating environment of the system. 
     When the engine is above the threshold speed and/or the threshold load the third mode may be implemented. In this way, during high exhaust flow conditions exhaust gas may be routed through a bypass conduit more thermally isolated than the primary conduit. Consequently, the amount of heat transferred to the EGHR heat exchanger during periods of inactivity is reduced to decrease thermal loading on the cooling system. Therefore, parasitic losses in the engine may be reduced during periods of EGHR heat exchanger inactivity. Conversely, when the engine is not operating at a speed and/or load above the threshold value(s) and the engine is above the threshold temperature, the second mode may be implemented. However, other entry condition sets for the different modes have been envisioned. For instance, exhaust manifold pressure, exhaust gas composition, turbine speed in the case of a turbocharged engine, etc. It also will be understood that the aforementioned controller functions may be stored in non-transitory memory that when executed by the processor cause the controller to implement the control commands. 
     In yet another example, the amount of component, device, actuator, valve, etc., adjustment may be empirically determined and stored in predetermined lookup tables and/or functions. For example, one table may correspond to conditions related to a position of the first flow control valve  176  and another table may correspond to conditions related to a position of the second flow control valve  178 . Moreover, it will be appreciated that the controller  180  may be configured to implement the methods, control strategies, etc., described herein. 
     Referring to  FIG. 2 , the figure schematically depicts a vehicle  201  with a hybrid propulsion system  200 . Hybrid propulsion system  200  includes an internal combustion engine  202 . It will be appreciated that the hybrid propulsion system  200  may be included in the vehicle  100  shown in  FIG. 1 . Thus, the vehicle  201  and the engine  202  shown in  FIG. 2  may include at least a portion of the features, components, systems, etc., of the vehicle  100  and engine  102  described above with regard to  FIG. 1  or vice versa. 
     The engine  202  is coupled to a transmission  204 . The transmission  204  may be a manual transmission, automatic transmission, or combinations thereof. Further, various additional components may be included, such as a torque converter, and/or other gears such as a final drive unit, etc. The transmission  204  is shown coupled to a drive wheel  206 , which in turn is in contact with a road surface  208 . 
     In this example embodiment, the hybrid propulsion system  200  also includes an energy conversion device  210 , which may include a motor, a generator, among others and combinations thereof.  FIG. 2  also shows an inverter  211  connected to the energy storage device and the energy conversion device. The inverter  211  is configured to condition electrical energy in and out of the energy storage device (e.g., high voltage battery). However, in other examples, the vehicle may not include an inverter. The energy conversion device  210  is further shown coupled to an energy storage device  212 , which may include a battery, a capacitor, a flywheel, a pressure vessel, etc. The energy conversion device can be operated to absorb energy from vehicle motion and/or the engine and convert the absorbed energy to an energy form suitable for storage by the energy storage device (i.e., provide a generator operation). The energy conversion device can also be operated to supply an output (power, work, torque, speed, etc.,) to the drive wheel  206  and/or engine  202  (i.e., provide a motor operation). It should be appreciated that the energy conversion device may, in some embodiments, include only a motor, only a generator, or both a motor and generator, among various other components used for providing the appropriate conversion of energy between the energy storage device and the vehicle drive wheel and/or engine. 
     The depicted connections between engine  202 , energy conversion device  210 , transmission  204 , and drive wheel  206  indicate transmission of mechanical energy from one component to another, whereas the connections between the energy conversion device and the energy storage device may indicate transmission of a variety of energy forms such as electrical, mechanical, etc. For example, torque may be transmitted from engine  202  to drive the vehicle drive wheel  206  via transmission  204 . As described above energy storage device  212  may be configured to operate in a generator mode and/or a motor mode. In a generator mode, the hybrid propulsion system  200  absorbs some or all of the output from engine  202  and/or transmission  204 , which reduces the amount of drive output delivered to the drive wheel  206 , or the amount of braking torque to the drive wheel  206 . Such operation may be employed, for example, to achieve efficiency gains through regenerative braking, increased engine efficiency, etc. Further, the output received by the energy conversion device may be used to charge energy storage device  212 . In the motor mode, the energy conversion device may supply mechanical output to engine  202  and/or transmission  204 , for example, by using electrical energy stored in an electric battery. 
     Hybrid propulsion embodiments may include full hybrid systems, in which the vehicle can run on just the engine, just the energy conversion device (e.g., motor), or a combination of both. Assist or mild hybrid configurations may also be employed, in which the engine is the primary torque source, with the hybrid propulsion system acting to selectively deliver added torque, for example during tip-in or other conditions. Further still, starter/generator and/or smart alternator systems may also be used. The various components described above with reference to  FIG. 2  may be controlled by a vehicle controller such as the controller  180 , shown in  FIG. 1 . 
     From the above, it should be understood that the exemplary hybrid propulsion system  200  is capable of various modes of operation. In a full hybrid implementation, for example, the propulsion system may operate using energy conversion device  210  (e.g., an electric motor) as the only torque source propelling the vehicle. This “electric only” mode of operation may be employed during braking, low speeds, while stopped at traffic lights, etc., in one example. However, in other examples the “electric only” mode may be implemented over a wider range of operating conditions such as at higher speeds. In another mode, engine  202  is turned on, and acts as the only torque source powering drive wheel  206 . In still another mode, which may be referred to as an “assist” mode, energy conversion device  210  may supplement and act in cooperation with the torque provided by engine  202 . As indicated above, energy conversion device  210  may also operate in a generator mode, in which torque is absorbed from engine  202  and/or transmission  204 . Furthermore, energy conversion device  210  may act to augment or absorb torque during transitions of engine  202  between different combustion modes (e.g., during transitions between a spark ignition mode and a compression ignition mode). Additionally, an external energy source  214  may provide power to the energy storage device  212 . The external energy source  214  may be a charging station outlet or other suitable power outlet, a solar panel, a portable energy storage device, etc., for instance. 
       FIG. 3-5  show an example of an EGHR assembly  300  in an exhaust system  302  in different operating modes. It will be appreciated that the EGHR assembly  300 , the exhaust system  302 , and/or corresponding components, depicted in  FIGS. 3-5 , may be examples of the EGHR assembly  150 , the exhaust system  122 , and/or the corresponding components, shown in  FIG. 1 . As such, different structural and/or functional features of the EGHR assemblies and the exhaust systems may be combined, substituted, etc., to form other assembly/system embodiments. Additionally, the components described with regard to  FIGS. 3-5  as well as  FIGS. 6-16  may be controller by a controller, such as the vehicle controller  180 , shown in  FIG. 1 . 
       FIG. 3  shows the EGHR assembly  300  with a first exhaust conduit  304 . The first exhaust conduit  304  may receive exhaust gas from upstream exhaust system components such as an exhaust manifold, cylinder(s), etc. 
     A second exhaust conduit  306  is coupled in a parallel flow arrangement with the first exhaust conduit  304 . As described herein a parallel flow arrangement is an arrangement where two conduits include sections fluidly separated from one another between an upstream and downstream intersection and flow fluid in a common general direction. As such, the first and second exhaust conduits  304  and  306  merge at an upstream confluence  308  and a downstream confluence  310 . 
     An EGHR heat exchanger  312  is coupled to an exterior surface  313  of the first exhaust conduit  304 . In the illustrated example, a housing  314  of the EGHR heat exchanger  312  is coupled to the first exhaust conduit  304  via a gas inlet  316  and a gas outlet  318 . Specifically, as illustrated, the inlet  316  and outlet  318  extend through a housing  319  of the first exhaust conduit  304  and open into an interior flow channel  321  of the conduit. However, in other examples, the heat exchanger housing  314  may be directly coupled an exterior surface  313  of the first exhaust conduit  304 . The EGHR heat exchanger  312  includes a coolant inlet conduit  320  and a coolant outlet conduit  322 . Therefore, the EGHR heat exchanger  312  may also include coolant passages routing coolant through the heat exchanger to remove heat therefrom. As previously discussed, the coolant from the heat exchanger  312  may be routed to an engine cooling system, such as the engine cooling system  168 , shown in  FIG. 1 . In one particular example, the heat extracted from the EGHR heat exchanger  312  may be routed to a cabin heat exchanger. In this way, additional heat may be provided to the cabin (during cold starts, for instance). However, other coolant routing arrangements in the cooling system may be used, in other instances. 
     The first and second exhaust conduits  304  and  306  each include bodies  324  between the upstream confluence  308  and the downstream confluence  310  of the first and second exhaust conduits  304  and  306 . As shown, the bodies  324  of the conduits are spaced away from one another. Specifically, a gap  326  is formed between the bodies  324 , in the depicted example. In this way, heat transferred from the second exhaust conduit to the first exhaust conduit may be decreased. However, in other examples, the housings of the first and second exhaust conduits may be at least partially attached along their lengths. 
     A first flow control valve  328  is also depicted in  FIG. 3 . The first flow control valve  328  is an example of the first flow control valve  176 , shown in  FIG. 1 . The first flow control valve  328  is positioned in the first exhaust conduit  304  between the inlet  316  and outlet  318  of the EGHR heat exchanger  312 . However, other valve positions and/or configurations have been envisioned. For instance, a first valve may be positioned upstream of the heat exchanger inlet  316  and downstream of the upstream confluence and a second valve may be located at the inlet. In the depicted embodiment, the first flow control valve  328  includes a plate  330  rotating about a pivot  332  at one end. The plate  330  may be profiled to obstruct gas flow, in selected positions. However, other valve designs may be used in other embodiments such as butterfly valves, solenoid valves, flap valves, spring driven valves with wax actuators, etc. 
     A second flow control valve  334 , is also shown in  FIG. 3 . The second flow control valve  334  is an example of the second flow control valve  178 , shown in  FIG. 1 . The second flow control valve  334  is positioned in the upstream confluence  308  between the first and second exhaust conduits. However, in other examples, the second flow control valve  334  may be positioned at a downstream location in the second exhaust conduit  306  between the upstream and downstream confluence of the conduits. Again, the second flow control valve  334  also includes a plate  336  rotating about a pivot  338  at one end and the plate  336  may be profiled to obstruct gas flow, in selected positions. However, other valve designs such as the valve designs listed above regarding the first flow control valve may be used, in other embodiments. The second flow control valve  334  is also shown including a spring-loaded flap  340  (e.g., pressure actuated flap). The spring-loaded flap  340  may open when the pressure in the first exhaust conduit  304  exceeds a threshold pressure (e.g., a range between 6 kPa and 28 kPa, 10 kPa, 20 kPa, 28 kPa, etc.) The threshold may be determined as a product of gas temperature, flowrate, and/or a function of engine size and package location (e.g., whether the exhaust system includes a one or two bank manifold), for instance. In this way, the chance of overpressure conditions in the first exhaust conduit  304  may be reduced when, for example, the EGHR heat exchanger is activated. Detailed illustrations of the second flow control valve  334  are depicted in  FIGS. 6-7 . 
     As shown in  FIG. 6  the second flow control valve  334  includes the plate  336  and the flap  340  partially extending across the plate. The flap  340  rotates about a spring-loaded pivot  600 . In this way, the flap  340  may open when the pressure in the first exhaust conduit  304 , shown in  FIG. 3 , exceeds the spring force. However, other suitable passive valving arrangements allowing for over pressure conditions to be avoided may be used, such as check valves. Still further in other examples, active valve components may be used to reduce the likelihood of overpressure conditions. Additionally, the flap has a semi-circular shape, in the illustrated example. However, numerous suitable flap shapes have been envisioned such as polygonal shapes, circular shapes, oval shapes, etc. 
       FIG. 7  illustrates a side view of the second flow control valve  334 . Again, the plate  336  and flap  340  are depicted. A rotational axis  700  of the spring-loaded pivot  600  is also depicted in  FIG. 7 . The flap&#39;s actuation path  702  (e.g., arc) is shown to exemplify flap movement from an open position to a closed position. It will be appreciated that gas flows through a central region of the flap when it is in the open position and conversely when it is closed gas is inhibited from flowing through the central flap region. 
       FIGS. 8-9  show a different example of a flow control valve  800 . The flow control valve  800  may an example of the second flow control valve  334 , shown in  FIG. 3 . The flow control valve  800  includes a first section  802  and a second section  804 . A torsion spring  806  is coupled to the first section  802  and the second section  804 . The torsion spring  806  is designed to allow the second section  804  to pivot and allow gas flow into the branch exhaust conduit, such as the second exhaust conduit  306 , shown in  FIG. 3 . The torsion spring  806  may function in this manner when a threshold pressure (e.g., 6 kPa-28 kPa, 10 kPa, 20 kPa, 28 kPa, etc.,) in the first exhaust conduit, such as the first exhaust conduit  304 , shown in  FIG. 3 , exceeds the threshold pressure. In this way, the flow control valve  800  passively allows exhaust gas flow through the first and second exhaust conduits, during certain engine operating conditions.  FIG. 9  also shows the pivot point  900  of the second section  804  and a path  902  of the second section  804  during actuation. 
       FIGS. 10-11  show different views of another example of a flow control valve  1000 . Thus, the flow control valve  1000  may be the first flow control valve  328 , shown in  FIG. 3 , in some examples. 
       FIG. 10  shows a side view of the flow control valve  1000  in an exhaust conduit  1002  with housing  1004  enclosing an exhaust airflow. Arrow  1006  depicts the general direction of exhaust gas flow through the conduit  1002 . The flow control valve  1000  includes a spring  1008  (e.g., toroid spring). The spring  1008  and the plate  1012  rotate about a hinge  1013 . The spring&#39;s torque direction is indicated by arrow  1010 . Thus, the spring action urges the valve into a closed position. However, other valve designs may be used, in other examples. The spring  1008  is coupled to a flow direction plate  1012 . The flow direction plate  1012  allows the valve to block exhaust flow through the conduits in some positions and in other positions allows exhaust gas to flow through the exhaust conduit. A lever  1014  is also coupled to the spring  1008 . The lever  1014  is coupled to a wax actuator  1016  via a pin  1017  or other suitable mechanical coupling in a groove  1019  of the lever. The wax actuator  1016  designed to actuate the level  1014  based on the temperature of coolant flowing through the actuator. For instance, the wax actuator  1016  may be designed to actuate the lever  1014  to move the plate  1012  into a position where exhaust gas is allowed to flow through the conduit  1012  when the coolant temperature is above a threshold value (e.g., 55° C. to 85° C., 60° C., 63° C., 70° C., etc.) Continuing with such an example, the wax actuator  1016  may be designed to actuate the lever to move the plate into a position obstructing exhaust gas flow through the conduit when the coolant temperature is below the threshold value. In this way, the wax valve opens at a predetermined temperature and stays open as long as the coolant temperature stays above the predetermined temperature. However, other valve designs have been envisioned such as valves designed with active control schemes. 
     The wax actuator  1016  is shown including a coolant inlet  1018  and a coolant outlet  1020 . Thus, the coolant inlet receives coolant from the engine&#39;s cooling system, such as the cooling system  168 , shown in  FIG. 1 , and the coolant outlet expels coolant into the engine cooling system. A base  1022  (e.g., welded base) is also shown coupled to the wax actuator  1016 . The base  1022  is attached to the housing  1004  of the conduit  1002 . 
       FIG. 11  shows a front view of the flow control valve  1000 . Again the plate  1012 , the spring  1008 , the hinge  1013 , the lever  1014 , the wax actuator  1016 , the coolant inlet  1018 , the coolant outlet  1020 , and the base  1022 . 
       FIGS. 12-13  show another example of a flow control valve  1200 . The flow control valve  1200  is an example of the first flow control valve  328 , shown in  FIG. 3 . The flow control valve  1200  includes a wax actuator  1202  with a coolant inlet  1204  and outlet  1206 . Thus, the wax actuator  1202  receives coolant from an engine cooling system, such as the cooling system  168 , shown in  FIG. 1 . The coolant flow through the wax actuator initiates valve actuation in the valve when the coolant temperature surpasses a threshold value or threshold range. An output shaft  1207  of the wax actuator  1202  is coupled to a flow plate  1208  via mechanical linkage  1210 . The mechanical linkage  1210  includes a gear  1212  rotationally coupled to the output shaft  1207  via a lever  1213 . The mechanical linkage  1210  also includes a shaft  1214  (e.g., serrated shaft) attached to the flow plate  1208  and the gear  1212 . The shaft  1214  is spring loaded via a torsion spring  1300 , shown in  FIG. 13 . The direction of spring loading of the shaft  1214  is indicated via arrow  1216 . In one specific example, the wax actuator  1202  may expand to push the shaft  1207  in an axial direction to actuate the mechanical linkage  1210 , thereby opening the valve to allow exhaust gas flow through the exhaust conduit  1222  and prevent exhaust gas flow through the EGHR heat exchanger inlet passage  1224 . It will be appreciated that the valve  1200  may stay open as long as the coolant temperature stays above the threshold value. However, when the coolant temperature decreasing the torsion spring  1300 , shown in  FIG. 13 , gradually compresses the wax back into a reservoir, causing the plate  1208  to block gas flow in the conduit  1222 . In this way, the valve allows gas to flow through the EGHR inlet when the engine coolant temperature is below a desired value. However, other valve actuation designs have been contemplated. Arrow  1226  depicts the general flow of exhaust gas in an upstream portion of the conduit  1222 . 
     Additionally, a spring loaded door  1218  is coupled to the flow plate  1208 . Specifically, a spring  1220  is coupled to the spring loaded door  1218  and the flow plate  1208 . The spring loaded door  1218  opens and allows exhaust gas to flow through exhaust conduit  1222  when the pressure in the exhaust conduit exceeds a threshold value (e.g., 6 kPa-28 kPa, 10 kPa, 20 kPa, etc.) Arrow  1226  indicates the direction of rotation of the door  1218  when moving into a position allowing gas to pass downstream through the conduit  1222 . In this way, when engine speed increases the valve  1200  opens to reduce the likelihood of overpressure conditions in the exhaust conduit. 
       FIG. 13  shows a rear view of the flow control valve  1200 . The spring  1300  (e.g., torsion spring) coupled to the flow plate  1208  via a hinge  1302  is shown in  FIG. 13 . The wax actuator  1202  is also shown in  FIG. 13 . The wax actuator  1202  includes a welded plate  1304  and as previously discussed a coolant inlet  1204  and a coolant outlet  1206 . The lever  1213  in the mechanical linkage  1210  is also shown in  FIG. 13 . The springs  1306  interacting with the door  1218 , are also shown in  FIG. 13 . As previously discussed, the springs  1306  function to allow the door to rotate and allow exhaust gas pass through the conduit  1222 , shown in  FIG. 12 , when the pressure in the conduit exceeds the threshold value. The springs  1306  are positioned on lateral sides of the door, but other positions of the springs have been contemplated. 
     Returning to  FIG. 3 , the EGHR assembly  300  and exhaust system  302  are depicted in first operating mode (e.g., active mode) where the first flow control valve  328  directs exhaust gas through the EGHR heat exchanger  312  and blocks flow through the first exhaust conduit  304 . Additionally, in the first mode the second flow control valve  334  is shown blocking the second exhaust conduit  306 . Additionally, in the first mode of operation the first flow control valve  328  and/or second flow control valve  334  may be partially opened to modulate exhaust flow through the EGHR heat exchanger  312 . Arrows  350  depict the general flow direction of exhaust gas in the system. However, it will be appreciated that the actual flow patterns in the exhaust system have greater complexity than is depicted. 
       FIG. 4 , shows the EGHR assembly  300  and the exhaust system  302  in a second operating mode (e.g., lower flow bypass mode) and  FIG. 5  shows the EGHR assembly  300  and the exhaust system  302  in a third operating mode. The EGHR assembly  300  and exhaust system  302  are shown in  FIGS. 4 and 5 . 
     Referring specifically to  FIG. 4 , in the second operating mode the first flow control valve  328  is positioned to permit exhaust gas flow through the first exhaust conduit  304 . Additionally, as illustrated in  FIG. 4  the plate  330  of the first flow control valve  328  substantially blocks (e.g., completely blocks) the outlet of the heat exchanger  312 . However, in other examples, the first flow control valve  328  may block the inlet of the heat exchanger or the plate may not block the heat exchanger outlet or inlet. Additionally, as shown in  FIG. 4  the second flow control valve  334  blocks the second exhaust conduit  306 . As such exhaust gas travels through the first exhaust conduit  304 . Arrows  450  depict the general direction of exhaust gas flow in  FIG. 4 . 
     Referring specifically to  FIG. 5 , in the third operating mode, the second flow control valve  334  is positioned to block exhaust gas flow through the first exhaust conduit  304  and permits exhaust gas flow through the second exhaust conduit  306 . In this way, exhaust gas flow may be routed further away, with regard to conduit housing material, from the EGHR heat exchanger  312 . Consequently, the amount of heat transferred to the EGHR heat exchanger during the third mode may be reduced. It will be appreciated that coolant may be routed through the EGHR heat exchanger  312  in the second and/or third operating modes. Arrows  550  depict the general direction of exhaust gas flow in  FIG. 5 . It will be appreciated, that the second flow control valve  334  may also function as a back-up with regard to the first flow control valve  328  malfunctions (e.g., fails), in certain circumstances. 
       FIGS. 14 and 15  show different examples of exhaust systems with EGHR heat exchangers with insulated unions in different locations in the system. It will be appreciated that one or more of the functional and/or structural features of the previously described exhaust systems may be included in the exhaust systems depicted in  FIGS. 3-5  or vice versa. 
     Specifically,  FIG. 14  shows an EGHR assembly  1400  with insulated unions  1402  at locations upstream and downstream of an inlet  1404  and an outlet  1406  of the EGHR heat exchanger  1408 . The insulated unions reduce the amount of heat transferred from a housing  1410  of the exhaust conduit  1412  to the EGHR heat exchanger  1408 . Consequently, the insulated unions provide greater thermal isolation to the heat exchanger to reduce heat transfer to the device shutdown. The insulated unions may therefore include insulation material at least partially circumferentially surrounding the exhaust conduit acting as an insulative interface between different sections of the conduit&#39;s housing.  FIG. 14  also shows the coolant conduits  1414  routed through a housing  1416  of the EGHR heat exchanger  1408 . Coolant inlets and outlets  1418  connect the heat exchanger to an engine cooling system, such as the cooling system  168 , shown in  FIG. 1 . The coolant conduits  1414  laterally traverse the housing. However, numerous types of suitable heat exchanger types may be used such as counter-flow heat exchangers, shell and tube heat exchangers, etc. Arrows  1450  depict the general direction of coolant flow into and out of the heat exchanger  1408 . Arrows  1452  depict the general direction of exhaust gas flow through the EGHR assembly  1400 . As shown, a flow control valve  1420  is blocking an exhaust conduit  1422  to induce gas flow into the EGHR heat exchanger  1408 . 
       FIG. 15  shows an EGHR assembly  1500  similar to the EGHR assembly  1400 , depicted in  FIG. 14 . Therefore, redundant description is omitted for brevity. The EGHR assembly  1500 , shown in  FIG. 15 , includes insulated unions  1502  at the inlet  1504  and the outlet  1506  of the EGHR heat exchanger  1508 . In this way, the thermal isolation of the EGHR heat exchanger  1508 , when inactive, may be further increased, when compared to the EGHR assembly, shown in  FIG. 14 . 
       FIG. 15  also shows a flow control valve  1510  in a configuration blocking the inlet  1504 . As such, gas flow through the exhaust conduit  1512  is permitted and gas flow through the heat exchanger  1508  is substantially inhibited. The general flow pattern of gas through the exhaust conduit is indicated at  1514 . Arrows  1516  also indicate the general direction of coolant flow through the heat exchanger  1508 . It will be appreciated that in one example, coolant may be continuously flowed through the heat exchanger  1508  regardless of the position of the flow control valve  1510 . As such, coolant may be flowed through the heat exchanger while it is shut down and exhaust gas is substantially prevented from flowing therethrough, in some embodiments. 
       FIG. 16  shows a cross-sectional view of an example of an insulation union  1502  in the EGHR assembly  1500 , depicted in  FIG. 15 .  FIG. 16  specifically shows the insulated union  1502  at the inlet  1504  of the EGHR heat exchanger. However, the other unions in the EGHR assembly may have a similar configuration, in some instances. The insulated union  1502  may include an insulated ring  1602  and a clamp  1604  designed to exert compressive force on the union. The insulated ring  1602  may specifically be in the shape of a donut, in one example. Thus, the insulation ring  1602  may circumferentially surround the EGHR heat exchanger inlet. However, other shapes of the ring have been contemplated. Additionally, in one example, the clamp  1604  may be constructed out of a metal such as stainless steel. Sections  1606  connect the union to the EGHR main body and the EGHR heat exchanger  1508 , shown in  FIG. 15 . Section  1609  connects to the housing of the conduit  1512 , shown in  FIG. 15 . The EGHR main body may be constructed out of a metal such as stainless steel, for instance. In some examples, the unions may be constructed out of Alumina (Al2O3) or Silicon Nitride (Si3N4), combinations thereof, etc. The insulated unions may be particularly beneficial with regard to reducing heat transfer to the heat exchanger when the exhaust conduit housing is constructed out of metal or other material with high thermal conductivity. 
     Arrow  1650  depicts the general direction of exhaust gas flow through the inlet  1504  of the EGHR heat exchanger. It will be appreciated that due to the configuration of the insulated union a decreased amount of heat may be transferred from the exhaust conduit&#39;s housing to the EGHR heat exchanger. As a result, parasitic losses in the system when the EGHR heat exchanger is shutdown are reduced. 
     Sections  1608  may provide additional insulation in the union. The sections  1608  may be in the shape of half-moons, in one example. However, other shapes of sections  1608  have been envisioned. Sections  1610  may also be in the shape of a half-moon, in some examples. Section  1610  may be constructed out of a metal such as stainless steel, in some instances. 
       FIGS. 1-16  show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. 
       FIG. 17  shows a method  1700  for operation of an exhaust system with an EGHR assembly. The method  1700  as well as the remainder of the methods described herein may be implemented via the exhaust systems, EGHR assemblies, components, etc., described above with regard to  FIGS. 1-16 . However, in other examples, the method  1700  and/or the other methods described herein may be implemented via other suitable exhaust systems and EGHR assemblies. Instructions for carrying out method  1700  may be executed by a controller based on instructions stored in non-transitory memory of the controller. 
     At  1702  the method includes determining operating conditions that may include engine speed, engine temperature, engine load, ambient temperature, exhaust gas airflow, MAP, etc. Next at  1704  the method includes determining an exhaust system operating mode using the operating conditions. At  1706  the method includes implementing a first operating mode in which a first valve is adjusted to direct exhaust gas flow through the EGHR heat exchanger at  1708  and a second valve is adjusted to block exhaust gas flow through the second exhaust conduit at  1710 . The entry conditions for the first mode may include a condition where engine temperature is below a threshold value (e.g., 60°, 63°, 65°, 70°, 80°, etc.,) in one example. However, other suitable entry conditions may be used, such as engine load. The first operating mode may also include a step of opening (e.g., passively opening) the flap in the second valve to reduce backpressure (e.g., sudden backpressure) in the exhaust stream. 
     At  1712  the method includes implementing a second operating mode where the first valve is adjusted to permit exhaust gas flow through the first exhaust conduit at  1714  and where the second valve is adjusted to block exhaust gas flow through the second exhaust conduit at  1716 . In this way, the operation of the EGHR heat exchanger may be shut down and exhaust gas may be directed through the first exhaust conduit. The entry conditions for the second mode may include a condition where engine temperature is above a threshold value and the engine speed is below a threshold value (e.g., 3,000-6,000 RPM, 3,000 RPM, 4,000 RPM, etc.) In this way, when the EGHR heat exchanger is shut down and the engine is operating at a low speed, exhaust gas may be directed through the first exhaust conduit. Thus, exhaust gas is directed through the first exhaust conduit when the amount of heat transferred from the exhaust gas to the heat exchanger is below a desired value due to the lower exhaust gas flowrate. The second operating mode may also include a step of opening (e.g., passively opening) the flap in the second valve to reduce backpressure (e.g., sudden backpressure) in the exhaust stream. 
     At  1716  the method includes implementing a third operating mode where the method includes adjusting the first valve to inhibit exhaust gas flow through the first exhaust conduit at  1718  and adjusting the second valve to permit exhaust gas flow through the second exhaust conduit at  1720 . The entry conditions for the third mode may include a condition where engine temperature is above a threshold value and the engine speed is above the threshold value. In this way, heat transfer from the exhaust gas to the EGHR heat exchanger may be reduced because the exhaust gas is routed further away from the heat exchanger. Consequently, parasitic losses in the engine can be reduced due to the decrease thermal load on the engine cooling system. It will be appreciated, that the different operating modes may be transitioned between depending on the operating conditions. As such, one mode is implemented while the other modes are temporarily disabled. In the third operating mode the second flow control valve may also be configured to inhibit the flap in the valve from opening, in some examples. Thus, the third operating mode may include the step of inhibiting (e.g., passively inhibiting) a flap in the second flow control valve from opening. 
     In another example operating strategy the first flow control valve may be held closed and the EGHR heat exchanger may be continuously in an active mode until a threshold engine coolant temperature (e.g., maximum engine coolant temperature (e.g., approximately 88 degrees Celsius)) is reached. At that point the second flow control valve may be opened. Therefore, backpressure may be handled by the second flow control valve. 
       FIG. 18  shows another method  1800  for operating an exhaust system. At  1802  the method includes determining operating conditions, similar to step  1702 , shown in  FIG. 17 . Next at  1804  the method includes determining if the engine is operating below a threshold temperature (e.g., 60 degrees Celsius, 63 degrees Celsius, 70 degrees Celsius, etc.) 
     If it is determined that the engine is operating below the threshold temperature (YES at  1804 ) the method includes implementing the first operating mode at  1806 . Implementing the first mode includes steps  1808 - 1810  similar to steps  1708 - 1710 , shown in  FIG. 17 . In this way, exhaust heat may be captured by the heat exchanger to warm up the engine, provide cabin heating, etc., during a cold-start, for instance. 
     On the other hand, if it is determined that the engine is not operating below the threshold temperature (NO at  1804 ) the method moves to  1812 . At  1812  the method includes determining if the engine speed is above a threshold value. 
     If it is determined that the engine speed is not above the threshold value (NO at  1812 ) the method advances to  1814  where the method includes implementing the second operating mode. Implementing the second operating mode includes steps  1816 - 1818 , similar to steps  1714 - 1716 , shown in  FIG. 17 . Thus, in the second mode the EGHR heat exchanger is deactivated and exhaust gas is routed through the first exhaust conduit. 
     Conversely, if it is determined that the engine speed is above the threshold value (YES at  1814 ) the method moves to  1820  where the method includes implementing the third operating mode. The third operating mode includes steps  1822 - 1824  similar to steps  1718 - 1720 , shown in  FIG. 17 . As previously, discussed when the third operating mode is implemented parasitic losses in the engine are decreased, thereby increasing engine efficiency. 
     Now turning to  FIG. 19 , depicting examples of pressure graphs and control signal graphs during an exhaust system control routine, such as the exhaust systems and control methods described above with regard to  FIGS. 1-18 . The example of  FIG. 19  is drawn substantially to scale, even though each and every point is not labeled with numerical values. As such, relative differences in timings can be estimated by the drawing dimensions. However, other relative timings may be used, if desired. Furthermore, in each of the graphs time is represented on the abscissa. Additionally, the graphical control strategy of  FIG. 19  is illustrated as a use case example and that numerous control strategies for the exhaust systems described herein, have been contemplated. 
     A temperature plot is indicated at  1900  and an engine speed is indicated at  1902 . An engine temperature threshold value  1904  and an engine speed threshold value  1906 . Surpassing the engine temperature threshold value  1904  may trigger a transition between the previously described first and second exhaust system operating modes or vice versa. Furthermore, surpassing the engine speed threshold may trigger a transition from the previously described second and third operating modes or vice versa. 
     A first valve control signal is indicated at  1908 . Signals blocking the first exhaust conduit and unblocking the first exhaust conduit are indicated on the ordinate. A second valve control signal is indicated at  1910 . Signals blocking the first exhaust conduit and blocking the second exhaust conduit are indicated on the ordinate. 
     At t 0 , the first flow control valve is configured to block the first exhaust conduit and the second flow control valve is configured to block the second exhaust conduit. In this way, the EGHR heat exchanger is in an active mode recovering heat from the exhaust. 
     As shown, at t 1  the engine temperature surpasses the threshold value and in response the second control valve is reconfigured to block the second exhaust conduit and the first control valve is reconfigured to unblock the first exhaust conduit. 
     At t 2  the engine speed surpasses the threshold value and in response the second flow control valve is switched into a configuration where the first exhaust conduit is blocked. In this way, hot exhaust gas is routed further away from the EGHR heat exchanger to reduce heat transfer thereto during high exhaust flow conditions. As a result, the thermal loading on the engine cooling system during periods of EGHR heat exchanger inactivity is reduced. 
     The technical effect of providing an exhaust system with two conduits in a parallel flow arrangement and an EGHR heat exchanger coupled to one of the conduits with valving designed to vary the flow in each conduit is that the EGHR heat exchanger may be more efficiently operated during selected operating conditions and also that heat transferred to the EGHR heat exchanger during other operating conditions may be reduced, thereby decreasing thermal loading of the cooling system. 
     The invention will be further described in the following paragraphs. In one aspect, an exhaust system for an internal combustion engine is provided that comprises: a first exhaust conduit receiving exhaust gas from a cylinder during internal combustion engine operation; an EGHR heat exchanger coupled to an exterior surface of the first exhaust conduit and including an inlet and an outlet extending through a housing of the first exhaust conduit; a second exhaust conduit arranged in a parallel flow arrangement with the first exhaust conduit and including a conduit body spaced away from the first exhaust conduit; a first flow control valve coupled to the first exhaust conduit and designed to adjust exhaust gas flow through the EGHR heat exchanger; and a second flow control valve coupled to the second exhaust conduit and designed to adjust exhaust gas flow through the second exhaust conduit. 
     In another aspect, a method for operating an exhaust system is provided that comprises implementing a first operating mode where a first flow control valve positioned in a first exhaust conduit is adjusted to flow exhaust gas through an EGHR heat exchanger from an inlet extending through a housing of the first exhaust conduit and a second flow control valve positioned in a second exhaust conduit is adjusted to inhibit exhaust gas flow through the second exhaust conduit. In one example, the method may further include implementing a second operating mode where the first flow control valve positioned in the first exhaust conduit is adjusted to inhibit exhaust gas through the EGHR heat exchanger coupled to the first exhaust conduit and the second flow control valve positioned in the second exhaust conduit is adjusted to inhibit exhaust gas flow through the second exhaust conduit. Further, in one example, the method may include implementing a third operating mode where the second flow control valve positioned in the second exhaust conduit is adjusted to permit exhaust gas flow through the second exhaust conduit and inhibit exhaust gas flow through the first exhaust conduit. 
     In another aspect, an exhaust system for an internal combustion engine is provided that comprises a first exhaust conduit receiving exhaust gas from a cylinder during internal combustion engine operation; an EGHR heat exchanger coupled to an exterior surface of the first exhaust conduit and including an inlet and an outlet extending through a housing of the first exhaust conduit; a second exhaust conduit arranged in a parallel flow arrangement with the first exhaust conduit and including a conduit body spaced away from the first exhaust conduit; a first flow control valve positioned within the first exhaust conduit and adjusting exhaust gas flow through the EGHR heat exchanger; a second flow control valve coupled to the second exhaust conduit and adjusting exhaust gas flow through the second exhaust conduit; and a controller with computer readable instructions stored on non-transitory memory that when executed during an engine-off condition, cause the controller to; operate the exhaust system in a first mode where exhaust gas flow through the EGHR heat exchanger is permitted and exhaust gas flow through the second exhaust conduit is inhibited by adjusting the first and second flow control valves; and operate the exhaust system in a second mode where exhaust gas flow through the EGHR heat exchanger is inhibited and exhaust gas flow through the second exhaust conduit is permitted by closing the first flow control valve and opening the second flow control valve. 
     In any of the aspects or combinations of the aspects, the exhaust system may further comprise a controller with computer readable instructions stored on non-transitory memory that when executed cause the controller to; operate the exhaust system in a first mode where exhaust gas flow through the EGHR heat exchanger is permitted and exhaust gas flow through the second exhaust conduit is inhibited by adjusting the first and second flow control valves. 
     In any of the aspects or combinations of the aspects, the controller may further include computer readable instructions stored on the non-transitory memory that when executed cause the controller to; operate the exhaust system in a second mode where exhaust gas flow through the EGHR heat exchanger is inhibited and exhaust gas flow through the second exhaust conduit is permitted by adjusting the first and second flow control valves. 
     In any of the aspects or combinations of the aspects, the second mode may be implemented when exhaust gas flow through the first exhaust conduit exceeds a threshold value. 
     In any of the aspects or combinations of the aspects, the controller may further include computer readable instructions stored on the non-transitory memory that when executed cause the controller to; operate the exhaust system in a third mode where exhaust gas flow through the EGHR heat exchanger is inhibited and exhaust gas flow through the second exhaust conduit is permitted by adjusting the first and/or second flow control valves. 
     In any of the aspects or combinations of the aspects, the EGHR heat exchanger may include an insulated union positioned in at least one of the inlet and the outlet of the EGHR heat exchanger. 
     In any of the aspects or combinations of the aspects, the second flow control valve may include a pressure-actuated flap designed to open when a pressure in the first exhaust conduit exceeds a threshold value. 
     In any of the aspects or combinations of the aspects, the exhaust system may further comprise an insulated joint in the first exhaust conduit upstream of the EGHR heat exchanger inlet and an upstream confluence between the first exhaust conduit and the second exhaust conduit. 
     In any of the aspects or combinations of the aspects, the first exhaust conduit may be fluidly coupled to the second exhaust conduit in a parallel flow configuration and where the first exhaust conduit includes a body spaced away from a body of the second exhaust conduit. 
     In any of the aspects or combinations of the aspects, the second operating mode may be implemented responsive to an exhaust gas flow through the first exhaust conduit exceeding a threshold value. 
     In any of the aspects or combinations of the aspects, during implementation of the first operating mode, a pressure-actuated flap in the second flow control valve may be passively opened responsive to a pressure in the first exhaust conduit exceeding a threshold value. 
     In any of the aspects or combinations of the aspects, the third operating mode may be transitioned into responsive to an exhaust gas flow through the first exhaust conduit being less than a threshold value. 
     In any of the aspects or combinations of the aspects, the first operating mode may be transitioned into responsive to a temperature of the internal combustion engine coolant being below a threshold value. 
     In any of the aspects or combinations of the aspects, the controller may further include computer readable instructions stored on the non-transitory memory that when executed cause the controller to; operate the exhaust system in a third mode where exhaust gas flow through the EGHR heat exchanger is inhibited and exhaust gas flow through the second exhaust conduit is permitted by adjusting the first and second flow control valves. 
     In any of the aspects or combinations of the aspects, the second flow control valve may include a flap passively opening when pressure in the first exhaust conduit exceeds a threshold value. 
     In any of the aspects or combinations of the aspects, the exhaust system may further comprise an EGHR insulated union at each of the inlet and the outlet of the EGHR heat exchanger and an exhaust conduit insulated joint in the first exhaust conduit upstream of the EGHR heat exchanger inlet and an upstream confluence between the first exhaust conduit and the second exhaust conduit. 
     In any of the aspects or combinations of the aspects, the exhaust system may be included in a hybrid vehicle. 
     In another representation, an EGHR assembly is provided with parallel flow conduits and a heat exchanger directly coupled to one of the conduits and flow control valves routing exhaust gas through the flow conduits spaced away from the heat exchanger during selected operating conditions to reduce heat transfer to the EGHR heat exchanger. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     As used herein, the terms “approximately” and “substantially” are construed to mean plus or minus five percent of the range unless otherwise specified. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.