Method and system for an exhaust gas catalyst

Abstract

A method for controlling an engine (10), comprising: during non-fueling conditions of the engine (10) sensed by a sensor (175, 177), flowing exhaust gas through a bypass passage (173) having a heat exchanger (174) while bypassing an underbody catalyst (176) positioned in a main exhaust passage (102, 202) via a valve positioned downstream of the underbody catalyst (176) and controlled by a controller (12) responsive to the sensor (175, 177); characterized in that the method further comprises: during fueling conditions of the engine (10), selectively flowing exhaust gas through the bypass passage (173) based on each of a temperature and water content of the exhaust gas; Estimating the water content of the exhaust gas based on each of an ambient humidity, an air-fuel ratio of the exhaust gas and an EGR level of the engine (10) and Predicting a condensation hazard on the underbody catalyst (176) based on each of the estimated water content of the exhaust gas and a substrate temperature of the underbody catalyst (176), wherein the hazard increases as the estimated water content increases or the substrate temperature decreases.

Description

Area

[0001] This description generally relates to methods and systems for controlling a vehicle engine to increase the efficiency of an exhaust aftertreatment system and reduce engine emissions. General state of the art / brief description

[0002] Emissions control devices, such as an underbody catalyst coupled to an exhaust passage of an internal combustion engine, reduce combustion byproducts such as oxides of nitrogen, carbon monoxide, and hydrocarbons. Engine cold-start emissions generated before the underbody catalyst is activated can contribute a significant percentage of total exhaust emissions. The efficiency of the underbody catalyst can be affected by exhaust gas temperature and may be suboptimal outside a specific temperature range. Furthermore, the functionality of the catalyst can be compromised by a higher than threshold oxygen supply to the catalyst.

[0003] Accordingly, various approaches have been developed to selectively direct exhaust gas through an exhaust catalyst based on exhaust gas temperature.

[0004] JP 2008 - 2 376 A provides an engine system having the features of the preamble of claim 1.

[0005] DE 10 2011 113 905 A1 shows a method comprising: during fueling conditions of an engine, selectively flowing exhaust gas through a bypass passage based on each of a temperature and water content of the exhaust gas.

[0006] US 8 468 805 B2 teaches a control depending on the moisture stored in an adsorber.

[0007] An exemplary approach, shown by Servati et al. in US Pat. No. 5,377,486, involves, during cold-start conditions, passing exhaust gas first through a smaller catalyst before passing exhaust gas through the underfloor (main) catalyst, and after reaching the light-off temperature of the main catalyst, bypassing the smaller catalyst and passing exhaust gas directly through the main catalyst. The smaller catalyst may achieve light-off earlier than the main catalyst, and by flowing exhaust gas first through the smaller catalyst, emissions quality may be increased. By bypassing the smaller catalyst after reaching the light-off temperature of the main catalyst, damage to the smaller catalyst from a higher than threshold exhaust temperature may be reduced.

[0008] However, the inventors have recognized potential problems with such a system. For example, the system configuration does not bypass the main catalyst, regardless of the exhaust gas temperature. This allows the catalyst to exhibit higher conversion efficiencies within a defined exhaust gas temperature range due to a coating on the underfloor catalyst surface. Consequently, the functionality of the underfloor catalyst may be reduced at exhaust temperatures below or above the defined range. Additionally, the flow of hot exhaust gas can cause damage to the catalyst components.As another example, when exhaust gas flows through the catalyst during cold-start conditions, water from the exhaust components upstream of the main catalyst can condense on the catalyst and extract energy from the catalyst for vaporization, which can further impact the functionality of the catalyst and delay the attainment of light-off temperature. Furthermore, during engine operating conditions such as fuel shut-off (DFSO), the engine may be operating without fuel while air is still being pumped through the cylinders. Consequently, a higher concentration of oxygen may reach the catalyst, leading to oxygen saturation of the underbody catalyst. This oxygen saturation can lead to a reduction in the catalyst's ability to convert NOx absorbed on the catalyst, thereby impacting emissions quality.

[0009] The inventors of the present invention have discovered an approach that can at least partially address the problems described above. According to the invention, a method and an engine system are provided with the features of the independent claims. Advantageous developments of the invention are described in the subclaims.

[0010] Accordingly, the problems described above can be addressed by a method for an engine comprising: during non-fueling conditions of the engine, flowing exhaust gas through a bypass passage while bypassing an underbody exhaust catalyst positioned in a main exhaust passage via a valve positioned downstream of the catalyst; and during fueling conditions of the engine, selectively flowing exhaust gas through the bypass passage based on each of a temperature and water content of the exhaust gas. In this way, emissions quality can be improved by opportunistically bypassing the underbody catalyst during conditions that may impair the functionality of the catalyst.

[0011] In one example, the exhaust system may include a front catalyst and a main underbody catalyst coupled to the main exhaust passage downstream of the exhaust manifold. A bypass passage may be coupled to the main exhaust passage, parallel to the underbody catalyst, wherein the bypass includes a switching device. After flowing through the front catalyst, exhaust gas may either flow through the underbody catalyst or flow through the bypass passage, bypassing the underbody catalyst. The routing of exhaust gas through the main passage or the bypass passage may be regulated via adjustments to a position of the switching valve.For example, during cold-start conditions, the switching valve may be adjusted to allow exhaust gas to first bypass the underbody catalyst until water in the exhaust stream has evaporated, and then the switching valve may be adjusted again to allow exhaust gas to be directed through the underbody catalyst. Heat from the exhaust gas may be used to heat the underbody catalyst and achieve light-off temperature. Conversely, during higher cylinder air mass conditions as well as higher exhaust temperature conditions, exhaust gas may be directed through the underbody catalyst. In one example, during cooler exhaust temperature conditions, exhaust gas may be directed to bypass the underbody catalyst to maintain the operating temperature of the underbody catalyst above a desired operating temperature as well as to reduce water in the exhaust by lowering the catalyst temperature.Similarly, during hotter exhaust temperature conditions, exhaust gas may be routed to bypass the underbody catalyst to reduce catalyst overheating. Furthermore, during engine operating conditions such as DFSO, where there is a potential for oxygen saturation at the underbody catalyst, exhaust gas may be routed to bypass the underbody catalyst. Further, a heat exchanger may be coupled to the bypass passage to transfer heat from exhaust gas flowing through the bypass passage to a coolant circulating through the heat exchanger. The heat recovered at the heat exchanger may be used to provide heat to vehicle components, such as a cylinder head and a passenger cabin.

[0012] In this way, by selectively bypassing an underfloor catalyst immediately after an engine cold start, water condensation and subsequent evaporation at the underfloor catalyst can be reduced, thereby reducing energy consumption at the catalyst. Consequently, catalyst light-off delays caused by water condensation-evaporation cycles are reduced. Additionally, unwanted drops in catalyst temperature from exhaust condensate are reduced. The technical effect of effectively utilizing exhaust heat to accelerate water evaporation from the underfloor catalyst and increase catalyst temperature is to accelerate catalyst light-off, thereby reducing the use of spark retardation for catalyst warm-up and increasing fuel efficiency.The technical effect of bypassing the underbody catalyst during conditions (such as below-threshold exhaust temperatures and DFSO events) where the catalyst operating temperature may decrease and / or where oxygen saturation of the catalyst may occur is that catalyst efficiency can be maintained above a threshold. By using a heat exchanger in the bypass passage to recover heat from the exhaust gas, exhaust heat can be effectively used to accelerate engine warm-up and provide heat to the passenger compartment, thereby reducing engine power losses. Overall, emissions quality and fuel efficiency can be improved in an engine system by regulating the flow of exhaust gas through the exhaust catalyst and a bypass passage that houses a heat exchanger. Short description of the drawings Fig. 1 shows an exemplary embodiment of an engine system including an exhaust catalyst system. Fig. 2A shows an exemplary embodiment of the exhaust gas catalyst system of Fig. 1, which operates in a first mode. Fig. 2B shows an exemplary embodiment of the exhaust gas catalyst system of Fig. 1, which operates in a second mode. Fig. Figure 3 shows a flow diagram illustrating an exemplary method that can be implemented to reduce exhaust flow through the exhaust catalyst system from Fig. 1 to set. Fig. 4 shows a table showing different operating modes of the exhaust gas catalyst system from Fig. 1 illustrates. Fig. 5 shows an exemplary operation of the exhaust gas catalyst system from Fig. 1. Detailed description

[0013] The following description relates to systems and methods for increasing the efficiency of an exhaust catalyst system and reducing engine emissions. An exemplary engine system including an exhaust catalyst system with a bypass passage that houses a heat exchanger is described in Fig. 1. The different operating modes of the exhaust gas catalyst system Fig. 1 is made with reference to the Fig. 2A and Fig. 2B. A motor controller may be configured to execute a control routine, such as the example routines from Fig. 3, to perform the position of a switching valve coupled to the main exhaust passage to direct exhaust flow through the exhaust catalyst system in the system from Fig. 1. The different operating modes of the exhaust gas catalyst system are described in Fig. 4 is shown in a table. An example of the operation of the exhaust gas catalyst system from Fig. 1 is made with reference to Fig. 5 shown.

[0014] Fig. 1 schematically illustrates aspects of an exemplary engine system 100 including an engine 10. In the depicted embodiment, the engine 10 is a boosted engine connected to a turbocharger 13 including a compressor 114 driven by a turbine 116. Specifically, fresh air is introduced into the engine 10 along the intake passage 42 via the air cleaner 112 and flows to the compressor 114. The compressor may be any suitable intake air compressor, such as an engine-driven or driveshaft-driven supercharger compressor. In the engine system 10, the compressor is a turbocharger compressor mechanically coupled to the turbine 116 via a shaft 19, with the turbine 116 driven by expanding engine exhaust gases.

[0015] As in Fig. 1, the compressor 114 is connected to the throttle valve 20 through the charge air cooler (CAC) 21. The throttle valve 20 is connected to the intake manifold 22 of the engine. From the compressor, the compressed air flow flows through the charge air cooler 21 and the throttle valve to the intake manifold. In the Fig. In the embodiment shown in Figure 1, the pressure of the air charge within the intake manifold is sensed by the manifold air pressure (MAP) sensor 124. The mass air flow within the intake manifold is sensed by a manifold air flow (MAF) sensor 125. A cylinder air mass may be estimated based on inputs from each of the MAP sensor 124 and the MAF sensor 125.

[0016] One or more sensors may be coupled to an inlet of compressor 114. For example, a temperature sensor 55 may be coupled to the inlet for estimating a compressor inlet temperature, and a pressure sensor 56 may be coupled to the inlet for estimating a compressor inlet pressure. As another example, a humidity sensor 57 may be coupled to the inlet for estimating a humidity of an air charge entering the compressor. Still other sensors may include, for example, air-fuel ratio sensors, etc. In other examples, one or more of the compressor inlet conditions (such as humidity, temperature, pressure, etc.) may be inferred based on engine operating conditions.Additionally, when exhaust gas recirculation (EGR) is enabled, the sensors can estimate a temperature, pressure, humidity, and air-fuel ratio of the air charge mixture, including fresh air, recirculated compressed air, and exhaust residues, taken in at the compressor inlet.

[0017] A wastegate actuator 92 may be actuated to open to vent at least a portion of the exhaust pressure from upstream of the turbine through the wastegate 90 to a location downstream of the turbine. By reducing the exhaust pressure upstream of the turbine, the turbine speed may be reduced, which in turn helps reduce compressor surge.

[0018] The intake manifold 22 is coupled to a series of combustion chambers 30 through a series of intake valves (not shown). The combustion chambers are further connected to the exhaust manifold 36 via a series of exhaust valves (not shown). In the illustrated embodiment, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold may include a plurality of exhaust manifold sections. Designations including a plurality of exhaust manifold sections may allow wastewater from different combustion chambers to be directed to different locations in the engine system.

[0019] In one embodiment, each of the exhaust and intake valves may be electronically actuated or controlled. In another embodiment, each of the exhaust and intake valves may be cam-actuated or controlled. Whether electronically actuated or cam-actuated, the timing of the exhaust and intake valve opening and closing can be adjusted as required to achieve the desired combustion and emissions control performance.

[0020] One or more fuels, such as gasoline, alcohol-fuel blends, diesel, biodiesel, compressed natural gas, etc., can be supplied to the combustion chambers 30 via an injector 66. The fuel can be supplied to the combustion chambers via direct injection, port injection, throttle body injection, or a combination thereof. Combustion in the combustion chambers can be initiated via spark ignition and / or compression ignition.

[0021] As in Fig. 1, exhaust gas from one or more exhaust manifold sections is directed to the turbine 116 to drive the turbine. The combined flow from the turbine and the wastegate may then flow through a front catalyst 170 housed within the main exhaust passage 102. Generally, the front catalyst 170 may include one or more exhaust aftertreatment catalysts configured to catalytically treat the exhaust stream and thereby reduce an amount of one or more substances in the exhaust stream.

[0022] All or a portion of the exhaust exiting the front catalyst 170 may then flow over an underbody catalyst 176 coupled to the main exhaust passage downstream of the front catalyst 170. The underbody catalyst 176 may be configured to xfrom the exhaust gas stream when the exhaust gas stream is lean, and the stored NO x to reduce when the exhaust flow is rich. In further examples, the underbody catalyst 176 may be configured to NO x to disproportionate or NO x selectively reduce with the aid of a reducing agent. In still further examples, the underbody catalyst 176 may be configured to oxidize hydrocarbon and / or carbon monoxide residues in the exhaust stream. Various exhaust aftertreatment catalysts with such functionality may be disposed in washcoats or elsewhere within the underbody catalyst 176.

[0023] The efficiency of the underfloor catalyst 176 may be affected by the exhaust temperature and may be suboptimal outside of a specific temperature range. For example, the underfloor catalyst 176 may not activate quickly enough during a cold-start condition where exhaust gas flowing through the catalyst is not hot enough. Consequently, the catalyst may not operate optimally until the temperature of the catalyst has been increased to the light-off temperature. As exhaust gas flows through the underfloor catalyst 176 during cold-start conditions, water from exhaust components upstream of the underfloor catalyst 176 may condense on the catalyst and extract energy from the catalyst for vaporization, further impacting the functionality of the catalyst and further delaying the attainment of the light-off temperature.Thus, the water content in the exhaust gas can be influenced by various engine operating conditions, such as exhaust gas temperature, EGR level, ambient conditions, etc. For example, due to one or more of a lower threshold exhaust gas temperature, a higher than threshold ambient humidity, a substrate temperature of the underbody catalyst relative to the exhaust gas temperature, and EGR flow and composition, an increased risk of water condensation on the underbody catalyst may arise, which may impair catalyst efficiency. A higher than upper threshold exhaust gas temperature may also reduce catalyst functionality.Furthermore, the functionality of the catalyst may be compromised by a higher than threshold oxygen supply to the catalyst, such as during a fuel shutoff (DFSO) event when the engine is operating without fuel while the valves continue to pump air through the catalyst. As discussed herein, exhaust flow through the underbody catalyst may be bypassed during engine operating conditions when the functionality of the underbody catalyst 176 may be compromised due to one or more of a risk of water condensation on the underbody catalyst, exhaust temperature, and / or oxygen content.

[0024] In particular, the exhaust catalyst system 160 may include a bypass passage 173 coupled to the exhaust passage 102. The bypass passage 173 may extend from downstream of the underbody catalyst 176 to upstream of a muffler 172. After flowing through the front catalyst 170, exhaust gas may either flow through the underbody catalyst 176 or flow through the bypass passage 173, bypassing the underbody catalyst 176. The flow of exhaust gas through the main exhaust passage 102 or the bypass passage 173 may be regulated via adjustments to a position of a switching valve 182 coupled to the main exhaust passage 102 at a junction of the main exhaust passage 102 and the bypass passage 173 downstream of the underbody catalyst 176.For example, the exhaust catalyst system 160 may be operated in a first mode, with the switching valve 182 switched to a first position to flow exhaust gas over the underbody catalyst 176. As another example, the exhaust catalyst system 160 may be operated in a second mode, with the switching valve 182 switched to a second position to flow exhaust gas over the bypass passage 173, bypassing the underbody catalyst 176. In one example, the exhaust catalyst system 160 may be operated in the first mode during conditions including less than a threshold risk of water condensation in the underbody catalyst, greater than a threshold cylinder air mass, less than an upper threshold exhaust temperature, and greater than a threshold exhaust temperature.In another example, the exhaust catalyst system 160 may be operated in the second mode during conditions including a fuel shutoff condition. Engine fueling conditions where the second operating mode may be used may include conditions where there is a greater than threshold risk of water condensation in the underbody catalyst, a greater than upper threshold exhaust temperature (e.g., during a warm start where the exhaust is too hot), and a less than lower threshold exhaust temperature (e.g., during a cold start where the exhaust is too cold).

[0025] One or more temperature sensors and oxygen sensors may be coupled to the exhaust catalyst system 160 to determine the temperature and oxygen content of the exhaust gas entering and exiting the underbody catalyst 176. In one example, a first temperature sensor 177 and a first oxygen sensor 175 may be coupled to the main exhaust passage 102 downstream of the underbody catalyst 174, and a second oxygen sensor 179 may be coupled downstream of the underbody catalyst 176. A second temperature sensor 178 may be coupled to the underbody catalyst 176 to estimate the temperature of the catalyst substrate. Each of the first and second oxygen sensors 175 and 179 may be a linear oxygen sensor, a UEGO (wideband exhaust gas oxygen) sensor, a dual-state oxygen sensor, or an EGO or HEGO (heated EGO) sensor.From downstream of the underbody catalyst 176 and from the bypass passage 173, exhaust gas can flow towards a muffler 172 and exit the exhaust system via the tailpipe 35.

[0026] A heat exchanger 174 may be coupled to the bypass passage 173 to cool the exhaust gas flowing through the bypass passage 173. As the exhaust gas flows through the heat exchanger 174, heat may be transferred from the hot exhaust gas to a coolant circulating through the heat exchanger 174. In one example, the heat exchanger 174 may be a water-to-gas exchanger. Upon transfer of heat from the exhaust gas to the coolant, the warmed coolant may be circulated back to the engine (such as when heating the engine is required) and / or through a heater core to heat a passenger cabin of the vehicle (such as when cabin heating is requested). Alternatively, when there are no heating requirements, the warmed coolant may flow through a radiator to dissipate heat to the atmosphere. A detailed description of the operation and structure of the exhaust catalyst system 160 will be described with reference to Fig. 2A-2B, 3, 4 and 5.

[0027] In some embodiments, a regenerable soot filter may be incorporated into the main exhaust passage 102 downstream of the underbody catalyst 176 to capture and oxidize soot particles in the exhaust stream.

[0028] An exhaust gas recirculation (EGR) discharge passage 180 may be coupled to the main exhaust passage 102 upstream of the front catalyst 170 to provide external low-pressure (NP) EGR by capturing exhaust gas from downstream of the turbine 116. The discharge passage may accommodate an EGR cooler to cool the exhaust gas prior to delivery to the intake manifold upstream of the compressor 114. The EGR valve 52 may be opened to admit a controlled amount of exhaust gas to the compressor inlet for desired combustion and emissions control performance. The EGR valve 52 may be configured as a continuously variable valve. However, in an alternative example, the EGR valve 52 may be configured as an on / off valve. In further embodiments, the engine system may include a high pressure EGR flowpath wherein exhaust gas is drawn from upstream of the turbine 116 and recirculated to the engine intake manifold downstream of the compressor 114.

[0029] One or more sensors may be coupled to the EGR passage 180 to provide details regarding the composition and condition of the EGR. For example, a temperature sensor may be provided to determine an EGR temperature, a pressure sensor may be provided to determine an EGR pressure, a humidity sensor may be provided to determine a humidity or water content of the EGR, and an air-fuel ratio sensor may be provided to estimate an EGR air-fuel ratio. Alternatively, EGR conditions may be inferred by the one or more temperature, pressure, humidity, and air-fuel ratio sensors 55-57 coupled to the compressor inlet. In one example, the air-fuel ratio sensor 57 is an oxygen sensor.

[0030] The engine system 100 may further include the control system 14. The control system 14 is shown receiving information from a plurality of sensors 16 (for which various examples are described in this disclosure) and sending control signals to a plurality of actuators 18 (for which various examples are described in this disclosure).As one example, sensors 16 may include a first exhaust temperature sensor 177 positioned upstream of underbody catalyst 176, a second exhaust temperature sensor 178 positioned on underbody catalyst 176, a first exhaust oxygen sensor 175 positioned upstream of underbody catalyst 176, a second exhaust oxygen sensor 179 positioned downstream of underbody catalyst 176, exhaust pressure sensor 128, MAP sensor 124, MAF sensor 125, compressor inlet temperature sensor 55, compressor inlet pressure sensor 56, compressor inlet humidity sensor 57, and EGR sensor. Other sensors, such as additional pressure, temperature, air-fuel ratio, and composition sensors, may be coupled at various locations in engine system 100. The actuators 81 may include, for example, a switching valve 182, a throttle 20, an EGR valve 52, a wastegate 92, and a fuel injector 66.The control system 14 may include a controller 12.

[0031] The controller 12 may receive input data from the various sensors, process the input data, and trigger various actuators in response to the processed input data based on an instruction or code programmed therein according to one or more sequences. For example, the controller 12 may predict a threat of condensate formation on the underbody catalyst 176 based on inputs from one or more of the underbody catalyst temperature sensor 178, the exhaust temperature sensor 177, the intake temperature, pressure, humidity, and air-fuel ratio sensors 55-57, and the EGR sensors. In response to a greater than threshold threat of water condensation on the underbody catalyst, the controller 12 may adjust the position of the diverter valve 182 to direct exhaust gas via the bypass passage 173, thereby bypassing the underbody catalyst 176.As another example, the controller 12 may estimate an exhaust oxygen content based on inputs from one or more exhaust oxygen sensors 175 and 179 and based on an exhaust oxygen content greater than a threshold, wherein the controller 12 may adjust the position of the switching valve 182 to direct exhaust gas via the bypass passage 173, bypassing the underbody catalyst 176.

[0032] Fig. 2A further introduces the Fig. 1 introduced underbody catalyst system and shows an exemplary embodiment 200 for operating the underbody catalyst system of Fig. 1 in a first operating mode, wherein the exhaust gas flow is directed through the underbody catalyst. In one example, the assembly 200 is an embodiment of the exhaust catalyst system 160 of Fig. 1 and may therefore share similar features and / or designs as those already described for the exhaust catalyst system 160.

[0033] Exhaust gas flowing from the engine flows through the front catalyst 170 and reaches the underfloor catalyst system 200. A larger portion of the combustion byproducts can be absorbed and processed at the front catalyst. The front catalyst may include a higher loading of precious metals compared to the underfloor catalyst to facilitate optimal treatment of the byproducts. The underfloor catalyst may have higher efficiency compared to the front catalyst during conditions where the cylinder air mass is higher and the catalyst loading of exhaust gas flowing through each of the front catalyst and the underfloor catalyst is higher. When EGR is required, a portion of the exhaust gas may be drawn from downstream of the front catalyst for recirculation to the engine intake manifold.An exhaust gas recirculation (EGR) discharge passage 228 may be coupled to the main exhaust passage 202 downstream of the front catalyst 170 to provide low-pressure (NP) EGR. The EGR valve 52 may be opened to admit a controlled amount of exhaust gas to the intake manifold for desired combustion and emissions control performance. The EGR valve 52 may be configured as a continuously variable valve or as an on / off valve.

[0034] The underbody catalyst 176 may be coupled to the main exhaust passage 202 upstream of the front catalyst 170. In one example, the underbody catalyst 176 may be configured to x from the exhaust gas stream when the exhaust gas stream is lean, and the stored NO x to reduce when the exhaust flow is rich. The underbody catalyst 176 may also be configured to NO x to disproportionate or NO xto selectively reduce using a reducing agent. In another example, the underfloor catalyst 176 may be configured to oxidize hydrocarbon and / or carbon monoxide residues in the exhaust stream. A variety of sensors may be coupled to the exhaust catalyst system 200 to determine the temperature and oxygen content of the exhaust gas entering and exiting the underfloor catalyst 176 and catalyst substrate temperature. In one example, a first temperature sensor 177 and a first oxygen sensor 175 may be coupled to the main exhaust passage 202 downstream of the underfloor catalyst 176, and a second oxygen sensor 179 may be coupled to the main exhaust passage 202 downstream of the underfloor catalyst 176. A second temperature sensor 178 may be coupled to the underbody catalyst 176 to estimate the catalyst substrate temperature.The water content of the exhaust gas and a risk of condensate formation on the underbody catalyst 176 may be estimated based on the catalyst substrate temperature as estimated by the second temperature sensor 178 and further based on factors including ambient humidity, EGR level, exhaust gas temperature, etc.

[0035] An inlet pipe 210 of an underfloor catalyst bypass assembly 205 may be coupled to the exhaust passage 202 at junction 206 downstream of the front catalyst 170 and upstream of the underfloor catalyst 176. The inlet pipe may lead to a bypass passage 212 that houses a heat exchanger 174. The heat exchanger may be coupled to an engine coolant system. Coolant may be circulated through the heat exchanger 174 to recover heat from the exhaust gas. Upstream of the heat exchanger 174, the bypass passage 212 may terminate in an inlet pipe 216 that leads back to the exhaust passage 202. The inlet 210 and outlet pipes 216 may be perpendicular to the passage 212 and the main exhaust passage 202. The outlet pipe 216 may connect the exhaust passage 202 to the underbody catalyst 176 at a junction 218 located downstream of the junction 206.A switching valve may be coupled to the main exhaust passage 302 at junction 218 to regulate the flow of exhaust through one of the main exhaust passage 202 and the bypass passage 212. In one example, the switching valve may be set to a first position to direct exhaust through the main exhaust passage 202 and the underbody catalyst. In another example, the switching valve may be set to a second position to direct exhaust through the bypass passage 212 and the heat exchanger 174. Further downstream of junction 218, a muffler 272 may be coupled to the main exhaust passage 202. After passing through the muffler 272, the exhaust may be exhausted to the atmosphere through a tailpipe 235.

[0036] Thus, the first operating mode represents a first setting of the switching valve 182, which enables exhaust flow control. In the first operating mode, due to the first position of the switching valve 182, the exhaust gas can flow to the muffler without entering the underbody catalyst bypass assembly 205. For this reason, all exhaust gas exiting the front catalyst 170 can flow through the underbody catalyst 176. After passing through the underbody catalyst 176, the exhaust gas can flow through the muffler 272 and exit to the atmosphere via the tailpipe 235. Thus, exhaust heat cannot be recovered at the heat exchanger 174 during operation in the first operating mode because exhaust gas cannot flow through the heat exchanger 174, which is housed in the bypass passage 212.

[0037] The first operating mode may be selected during conditions when exhaust flow over the underbody catalyst 176 is desired. In one example, the first mode may be selected during cold-start conditions after the risk of water condensation on the underbody catalyst 176 has been reduced below a threshold. During conditions where the risk of condensation is higher than the threshold, water may condense on the underbody catalyst 176 and extract energy from the catalyst for vaporization, which may impair the functionality of the catalyst by reducing the catalyst temperature. The water content of the exhaust gas may be estimated based on each of an ambient temperature, an exhaust air-fuel ratio, an exhaust temperature, and an engine EGR level. The water content of the exhaust gas may increase as humidity increases and the EGR level / flow increases.The risk of condensation on the underfloor catalyst may be predicted based on each of the estimated water content of the exhaust gas and a substrate temperature of the underfloor catalyst, and the risk may increase as the estimated water content increases or the substrate temperature decreases. The predicted risk of condensation may be further based on an exhaust air-fuel ratio relative to stoichiometry, with the predicted risk increasing as a duration of engine operation leaner than stoichiometry increases. During cold-start conditions, once the risk of condensation is less than the threshold, the temperature of the catalyst may be increased by flowing warm gas through the underfloor catalyst 176, thereby accelerating the attainment of light-off temperature.

[0038] In another example, the first operating mode may be selected when the cylinder air mass is higher than a threshold. At a cylinder air mass higher than a threshold, exhaust gas may be routed through the underbody catalyst 176 to improve emissions quality and also reduce backpressure exerted by the exhaust system. The cylinder air mass may be derived based on input from one of a manifold air flow (MAF) and manifold air pressure (MAP) sensor.

[0039] In yet another example, the first mode may be selected during conditions where one of the exhaust temperature and the exhaust temperature is higher than a lower threshold and the exhaust temperature is lower than an upper threshold. Due to a coating on the underbody catalyst surface, the underbody catalyst may exhibit higher efficiencies within a defined exhaust temperature range, which may further reduce the functionality of the catalyst depending on the exhaust temperature range (above or below the range).

[0040] Fig. Figure 2B shows a schematic view 250 of an exemplary embodiment of the underbody catalyst system 200 in a second operating mode in which exhaust flow bypasses the underbody catalyst. Components previously described in Fig. 2A are similarly numbered and will not be reintroduced.

[0041] Thus, the second operating mode represents a second setting of the switching valve 182, which enables exhaust flow control. In the second operating mode, due to the second position of the switching valve 182, exhaust gas may flow into the underbody catalyst bypass assembly 205 through the inlet tube 210 (as shown by the arrows), bypassing the underbody catalyst 176. In the second operating mode, exhaust gas flows through the heat exchanger 174 from a first end of the heat exchanger proximal to the inlet tube 210 to the second end of the heat exchanger 174 proximal to the outlet tube 216. At the heat exchanger 174, heat may be transferred from the exhaust gas to a coolant circulating through the heat exchanger 174. The warmed coolant may then be circulated back through the engine (e.g.,through the cylinder head to provide engine heating during cold-start conditions) and / or circulated through a heater core of the vehicle, and thereafter, the recovered heat may be used for functions such as heating the passenger cabin, thereby improving engine efficiency. In circumstances where the heat recovered at heat exchanger 174 is not required to heat vehicle components, the heat may be transferred to a radiator for dissipation to the atmosphere. After passing through heat exchanger 174, the cooled exhaust gas flows through outlet pipe 216 and exits underbody catalyst bypass assembly 205. The exhaust gas re-enters main exhaust passage 202 at junction 218 and flows downstream toward muffler 272. After passing through muffler 272, the exhaust gas exits to the atmosphere through a tailpipe 235.

[0042] The second operating mode may be selected during conditions when exhaust flow over the underfloor catalyst 176 is undesirable. In one example, the second mode may be selected during conditions with a higher than a threshold risk of condensation in the underfloor catalyst 176. During cold-start conditions, the risk of water condensation on the underfloor catalyst may be higher due to the lower temperature of the exhaust gas and the underfloor catalyst 176. For this reason, exhaust gas may be routed during cold-start conditions to flow through the underfloor catalyst 176 for a duration until the risk of condensation decreases below the threshold. In another example, the second mode may be selected during conditions where the exhaust temperature is less than the lower threshold and / or greater than the upper threshold.

[0043] In yet another example, the second mode may be selected during non-fueling engine conditions, such as during a fuel shutoff (DFSO) condition. During such conditions, the oxygen content in the exhaust may rise above a threshold, which may result in oxygen saturation at the underbody catalyst 176. Oxygen saturation may result in a reduction in the catalyst's ability to convert NOx absorbed on the catalyst, thereby impacting emissions quality.

[0044] A transition from operation in the first mode to operation in the second mode may be performed in response to a greater than a threshold risk of condensation on the underbody catalyst 176, a fuel cut-off (DFSO) event, a lower than a lower threshold exhaust gas temperature, and a higher than an upper threshold exhaust gas temperature. A transition from operation in the second mode to operation in the first mode may be performed in response to a less than a threshold risk of condensation on the underbody catalyst 176, a higher than a lower threshold exhaust gas temperature, a lower than an upper threshold exhaust gas temperature, and a higher than a threshold cylinder air mass.Furthermore, in response to the catalyst temperature falling below a threshold temperature while the risk of condensation on the underbody catalyst is lower, the switching valve may be switched to the first position earlier, and in response to the catalyst temperature falling below a threshold temperature while a risk of condensation on the underbody catalyst is higher, the switching valve may be switched to the first position.

[0045] In one example, a transition from the second operating mode to the first operating mode may be performed during a DFSO event if the underfloor catalyst temperature drops below a threshold. Flowing exhaust through the underfloor catalyst during a DFSO event may increase the oxygen concentration in the underfloor catalyst, which may lead to increased fuel consumption during catalyst regeneration. However, if the underfloor catalyst temperature drops below the threshold, spark timing may need to be retarded (also resulting in increased fuel consumption) to increase the exhaust temperature and the underfloor catalyst temperature.For this reason, the control system can consider the potential increase in fuel consumption due to oxygen saturation and the reduction in the temperature of the underbody catalyst and determine whether exhaust gas should be routed through the underbody catalyst or whether the underbody catalyst should be bypassed, depending on which increase is smaller. For example, if the fuel increase associated with retarding the ignition to raise the catalyst temperature is smaller, the underbody catalyst cannot be bypassed. Otherwise, if the fuel increase associated with catalyst regeneration is smaller, the underbody catalyst can be bypassed.During cold-start conditions, the switching valve can be held in the second position for a period based on the water content of the exhaust gas (system operating in second mode). After the period has elapsed, the switching valve can be actuated to the first position (transition to system operation in first mode) to flow exhaust gas over the front catalyst and then to the underbody catalyst in the main exhaust passage. The period can be increased as the water content of the exhaust gas increases.

[0046] In this way, the systems from the Fig. 1 and 2A-2B, an engine system is provided, comprising: an engine intake manifold including each of a mass air flow (MAF) and a manifold pressure (MAP) sensor; an engine exhaust manifold including a main exhaust passage housing a front catalyst upstream of an underfloor catalyst, and a bypass passage coupled to the main exhaust passage from downstream of the front catalyst to downstream of the underfloor catalyst, the bypass passage including a heat exchanger; a coolant system fluidly coupling the heat exchanger to a heater core; a switching valve coupled downstream of the underfloor catalyst at a junction of the main exhaust passage and the bypass passage; and an exhaust gas temperature sensor; an exhaust oxygen sensor;and a controller having computer-readable instructions stored on non-transitory memory to: in response to engine operation below the threshold air-fuel ratio, actuate the switching valve from a first position allowing exhaust flow through the underbody catalyst to a second position allowing exhaust flow through the bypass passage and the heat exchanger while bypassing the underbody catalyst;Estimating a catalyst temperature based on a duration of operation at the threshold air-fuel ratio, in response to the catalyst temperature falling below a threshold temperature while a water content of the exhaust gas is higher, transitioning the switching valve to the first earlier position, and in response to the catalyst temperature falling below a threshold temperature while a water content of the exhaust gas is lower, transitioning the switching valve to the first later position;

[0047] Fig. 3 illustrates an exemplary method 300 for operating an underbody catalyst system (such as an exhaust catalyst system 160 in the Fig. 1 and Fig. 2A-2B) to reduce engine emissions. Instructions for performing method 300 and the other methods included herein may be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those described above with reference to Fig. 1 and 2A-2B. The controller may use motor actuators of the engine system to adjust engine operation according to the methods described below.

[0048] At 302, engine conditions may be estimated by the controller based on inputs from a variety of sensors. The estimated engine operating conditions may include engine temperature, engine load, engine speed, air-fuel ratio, exhaust gas temperature, cylinder air mass, underbody catalyst substrate temperature, etc. Environmental conditions may also be estimated, including ambient temperature, humidity, barometric pressure, etc.

[0049] At 304, the routine includes determining whether the vehicle engine is operating under cold-start conditions. An engine cold-start condition may be confirmed when the engine is started after an extended period of engine inactivity, when the engine temperature is lower than a threshold (such as below an underbody exhaust catalyst light-off temperature), and while ambient temperatures are below a threshold.

[0050] In such a condition, a higher than threshold risk of water condensation on the underbody catalyst may be present due to the lower exhaust gas temperature, a higher exhaust water content, and a lower underbody catalyst substrate temperature. The risk of condensate formation may be determined based on inputs from a variety of sensors, including exhaust gas temperature sensors (such as sensor 177 in the Fig. 2A-2B), underbody catalyst temperature sensor (such as temperature sensor 178 in the Fig. 2A-2B), exhaust gas lambda sensors (such as lambda sensors 175 and 179 in the Fig. 2A-2B) and ambient humidity sensor. The controller may estimate the risk of condensate formation through a determination that directly considers an estimated exhaust water content and a measured underfloor catalyst substrate temperature, such as increasing the risk of condensate formation as the exhaust water content increases and reducing the underfloor catalyst substrate temperature. Alternatively, the controller may determine the risk of condensate formation based on a calculation using a lookup table, where the input is exhaust water content and underfloor catalyst substrate temperature, and the risk of condensate formation is the output. The risk of condensate formation may be further determined based on an exhaust air-fuel ratio relative to stoichiometry, with the predicted risk increasing as a duration of engine operation leaner than stoichiometry increases.

[0051] Under conditions with a higher than threshold risk of water condensation on the underbody catalyst, water condensation and subsequent evaporation may occur on the underbody catalyst, increasing the energy absorption at the catalyst. Consequently, catalyst light-off delays may occur due to water condensation-evaporation cycles.

[0052] If engine cold start conditions are confirmed, the routine continues to 306 to operate the underbody catalyst system in a second operating mode, assuming that the risk of condensation is higher. Operating in the second mode, as described with reference to Fig. 2B, includes switching a switching valve (such as the switching valve 182 in the Fig. 2A-2B) to a second position. Due to the second position of the valve, exhaust flow from the bypass passage into the main passage cannot be blocked, thereby allowing exhaust gas to flow through the bypass passage (such as bypass passage 212 into the Fig. 2A-2B), whereby the underbody catalyst (such as catalyst 176 in the Fig. 2A-2B) accommodated in the main exhaust passage. When exhaust gas is passed through the bypass passage, exhaust gas can be passed through a heat exchanger (such as the heat exchanger 174 in the Fig. 2A-2B). After flowing through the heat exchanger, the exhaust gas can flow further downstream via the bypass passage and then re-enter the main exhaust passage downstream of the underbody catalyst, ultimately exiting to the atmosphere via the tailpipe. Flowing exhaust gas through the passage reduces condensation and evaporation of water on the underbody catalyst, and the exhaust water can condense along the main exhaust passage further downstream of the underbody catalyst.

[0053] During exhaust flow across the heat exchanger coupled to the bypass passage, heat may be transferred at 308 from the exhaust to a coolant circulating through the heat exchanger. The coolant heated via heat transfer at the heat exchanger may be circulated to a heater core so that it may be used to heat other components of the vehicle during engine cold start, such as a cylinder head, an engine block, and a vehicle cabin space. During cold start, the vehicle cabin temperature may be low, and cabin heating may be desired. Accordingly, based on a cabin heat demand, as requested by a vehicle operator (e.g., based on a cabin temperature setting), heat may be transferred from the heater core to the cabin. For example, air may be drawn into the cabin via the heater core, allowing for cabin heating.After the cabin heat demand has been met, the heated coolant can also be circulated to an engine block and cylinder head to raise engine temperatures, thereby improving engine performance in cold conditions.

[0054] At 310, the routine includes determining whether the risk of condensation on the underfloor catalyst has been reduced below a threshold. Due to the higher exhaust temperature resulting in a higher proportion of exhaust water condensation occurring at the main exhaust passage downstream of the underfloor catalyst and / or a higher proportion of exhaust water vaporized during exhaust flow through the underfloor catalyst, the risk of condensation may decrease as engine combustion progresses. Additionally, the exhaust water content may decrease based on changes in ambient conditions, such as ambient humidity. If it is determined that the risk of condensation remains higher than the threshold, the switch valve may be maintained in the second position at 312, and the catalyst system may operate in the second mode (bypassing the underfloor catalyst).

[0055] If it is determined that the risk of condensation has decreased below the threshold, the routine continues to 314 to operate the underbody catalyst system in a first operating mode. Operating in the first mode, as described with reference to Fig. 2A, includes switching a switching valve to a first position at 315. Due to the first position of the valve, exhaust flow from the bypass passage into the main passage may be blocked, allowing exhaust to flow via the main exhaust passage and the underbody catalyst rather than via the exhaust bypass passage. By flowing the hot exhaust through the underbody catalyst, the catalyst temperature may be increased, which may accelerate the attainment of the underbody catalyst's light-off temperature.

[0056] At 316, the process includes determining whether the estimated underbody catalyst temperature is above a threshold temperature. The threshold temperature may correspond to the underbody catalyst light-off temperature. Once the underbody catalyst reaches the light-off temperature, it may operate at optimal functionality. The underbody catalyst temperature may be derived based on inputs from exhaust temperature sensors coupled to the main exhaust passage and the underbody catalyst. Additionally, the underbody catalyst temperature may be estimated based on a duration of engine operation at a stoichiometric or leaner-than-stoichiometric air-fuel ratio.

[0057] Additionally, if it is determined at step 304 that the engine is not operating under cold-start conditions, the routine may proceed directly to step 316. If it is determined that the catalyst temperature is less than a threshold, and further, an increase in temperature is desired for optimal operation, the catalyst system may continue to operate in the first mode and exhaust gas is directed over the underbody catalyst.

[0058] If it is determined that the exhaust gas temperature is higher than a threshold temperature, it can be inferred that the underbody catalyst has reached the light-off temperature and is better able to reduce combustion by-products, such as oxides of nitrogen, carbon monoxide and hydrocarbons, and thereby improve emission quality.

[0059] At 318, the process includes determining whether the cylinder air mass is above a threshold air mass. The cylinder air mass may be a function of intake air flow and engine speed and may be determined based on inputs from one or more of a manifold air flow sensor and a manifold pressure sensor. The threshold air mass may correspond to a cylinder air mass that results in higher than desired exhaust backpressure and further leads to increased tailpipe emissions.

[0060] If it is determined that the engine is operating with less than the threshold cylinder air mass, the routine may continue to step 322, where it may be determined whether the engine is operating without fuel (engine non-fueling condition). Engine non-fueling conditions may include a fuel cutoff (DFSO) condition when the air-fuel ratio is leaner than stoichiometry. During engine non-fueling conditions, an increase in oxygen content in the exhaust may occur, resulting in the underbody catalyst becoming saturated with oxygen. Oxygen saturation at the underbody catalyst may result in a reduction in catalyst functionality. Therefore, if it is determined that the engine is operating without fuel to reduce underbody oxygen deposition, the catalyst system may operate in the second mode at 324.

[0061] To operate the catalyst system in the second mode, the switching valve at 325 may be switched to the second position. Due to the second position of the valve, exhaust gas may flow through the bypass passage, thereby bypassing the underbody catalyst. When exhaust gas is directed through the bypass passage, exhaust gas may flow through the heat exchanger. At 326, heat may be transferred from the exhaust gas to the coolant flowing through the heat exchanger. The heat recovered by the coolant at the heat exchanger may be used to provide heat to vehicle components, such as the cylinder head, and a passenger cabin. The flow rate of the coolant through the heat exchanger, the passenger cabin, and the engine block may be adjusted based on engine and cabin heat demands.In circumstances where the heat recovered at the heat exchanger is not desired for heating vehicle components, the heat can be transferred to a radiator for dissipation.

[0062] If it is determined that the engine is not operating without fuel, the routine includes determining at 328 whether the exhaust temperature is less than a first threshold temperature. It may also be determined whether the exhaust temperature is greater than a second threshold temperature, where the second threshold temperature is greater than the first threshold temperature. When exhaust gas flows through the underfloor catalyst at less than a lower (first) threshold temperature, the operating temperature of the catalyst may decrease, which may impact the performance of the catalyst. Additionally, when exhaust gas flows through the underfloor catalyst at greater than an upper (second) threshold temperature, the functionality of the catalyst may be reduced due to a coating on the catalyst surface.The first threshold temperature may be lower than the second threshold temperature, and for optimal operation of the underbody catalyst, the catalyst temperature may be maintained between the first threshold temperature and the second threshold temperature.

[0063] If it is determined that the exhaust temperature is less than the first threshold temperature or greater than the second threshold temperature, the routine may proceed to step 334 to operate the exhaust system in the second mode. In the second mode, the temperature of the catalyst may not be affected by the exhaust temperature because the exhaust gas is directed to flow over the bypass passage, thereby bypassing the underbody catalyst.

[0064] If it is determined at 328 that the exhaust temperature is higher than the first threshold or less than the second threshold, the exhaust system may continue to operate in the first mode, and exhaust gas may be directed through the underbody catalyst. However, if at any time it is determined that the water content of the exhaust gas has increased due to factors such as increased exhaust gas recirculation, a leaner than stoichiometry air-fuel ratio, and higher ambient humidity, and there is a greater than threshold risk of condensation on the underbody catalyst, the switching valve may be switched to the second position to operate the catalyst system in the second mode, bypassing the underbody catalyst to reduce condensation on the catalyst.

[0065] In this way, the operation of the underbody exhaust catalyst system can be improved by selecting the second mode in response to one of the underbody catalyst condensate risk being higher than a threshold risk, the exhaust gas temperature being less than a lower threshold, the exhaust gas temperature being higher than an upper threshold, and the oxygen concentration in the exhaust gas being higher than a threshold concentration; and selecting the first mode in response to one of the exhaust gas temperature being less than the lower threshold or higher than the upper threshold and the oxygen concentration in the exhaust gas being less than the threshold concentration.

[0066] Fig. 4 is a table 400 showing exemplary operating modes of the exhaust catalyst system from Fig. 1. An engine controller can select one of the operating modes based on engine conditions and heat requirements. The exhaust catalyst is an underfloor catalyst coupled downstream of a front catalyst in the main exhaust passage, with the underfloor catalyst having a higher light-off temperature than the front catalyst. Based on the selected mode, the position of a switching valve coupled to the main exhaust passage downstream of the underfloor catalyst at a junction of the main exhaust passage can be varied to flow exhaust gas either through the catalyst or via the bypass passage.

[0067] In one example, the controller may operate the catalyst system in a first mode. In the first mode, the switching valve may be switched to a first position, blocking exhaust flow from the main passage to the bypass passage. Due to the position of the valve, exhaust gas may flow through the underbody catalyst into the main exhaust passage. Exhaust gas flowing through the catalyst in the main passage includes exhaust gas flowing from downstream of the front catalyst to an exhaust tailpipe via the underbody catalyst through the main passage. The catalyst bypass system may operate in the first mode during one or more conditions, such as less than a threshold risk of water condensation in the underbody catalyst, greater than a threshold cylinder air mass, less than an upper threshold exhaust temperature, and greater than a threshold exhaust temperature.The risk of water condensation in the underfloor catalyst can be predicted based on the water content in the exhaust gas and the catalyst substrate temperature. The water content of the exhaust gas can be estimated based on each of an engine EGR level, an air-fuel ratio, an engine temperature, and an ambient humidity. Predicting a risk of water condensation can involve increasing the predicted risk if one or more of the catalyst substrate temperature decreases, the engine EGR level increases, the engine temperature decreases, and the ambient humidity increases, and reducing the predicted risk if one or more of the catalyst temperature increases, the engine EGR level decreases, the engine temperature increases, and the ambient humidity decreases.

[0068] In another example, the controller may operate the catalyst system in a second mode. In the second mode, the switching valve may be switched to a second position where exhaust flow from the main passage to the bypass passage is not blocked. Due to the position of the valve, exhaust gas may flow through the bypass passage, thereby bypassing the underbody catalyst. Exhaust gas flowing through the bypass passage includes exhaust gas flowing from downstream of the front catalyst to an exhaust tailpipe via the bypass passage without flowing through the underbody catalyst. The catalyst bypass system may operate in the second mode during non-fueling engine conditions and certain fueling engine conditions.The non-fueling engine conditions may include a fuel shutoff condition, and the fueling engine conditions utilizing the second operating mode may include a higher than a threshold risk of water condensation in the underbody catalyst, a higher than an upper threshold exhaust temperature (for example, during a warm start), and a lower than a lower threshold exhaust temperature. During operation in the second mode, exhaust gas may flow through a heat exchanger coupled to the bypass passage, and during exhaust flow through the heat exchanger in the bypass passage, heat may be transferred from the exhaust gas to a coolant circulating through the heat exchanger.In response to an engine heat demand, the warmed coolant may be circulated through an engine block; and in response to a cabin heat demand, the warmed coolant may be circulated through the heater core.

[0069] In this way, the exhaust gas can be routed through the underbody catalyst or a bypass passage, thereby avoiding the underbody catalyst, based on a predicted risk of condensate formation on the underbody catalyst, the exhaust gas temperature and the oxygen content in the exhaust gas.

[0070] Fig. Figure 5 shows an exemplary operating sequence 500 of the underbody exhaust catalyst system. Exhaust flow through the underbody catalyst or bypass passage is determined based on engine operating conditions. The horizontal (x-axis) represents time, and the vertical markers t1-t5 indicate key points in the operation of the exhaust bypass system.

[0071] The first trace, line 502, shows a variation in engine revolutions per minute (RPM) over time. The dotted line 503 shows a threshold engine speed (RPM) below which the engine can operate without fuel. The second trace, line 504, shows the underfloor catalyst substrate temperature. The dotted line 505 shows a threshold catalyst temperature below which the underfloor catalyst cannot be fully functional. The third trace, line 506, shows a change in exhaust temperature over time. The dotted line 507 shows a threshold exhaust temperature below which exhaust gas cannot be passed over the underfloor catalyst. The catalyst substrate temperature and the exhaust temperature can be estimated via exhaust temperature sensor(s). The fourth trace, line 508, shows a deviation in cylinder air mass as determined via a manifold air flow sensor and / or a manifold air pressure sensor.The dotted line 509 shows a threshold cylinder air mass above which exhaust gas can be passed through the underbody catalyst. The fifth trace, line 510, shows a predicted risk of water condensation on the underbody catalyst, as estimated based on the water content in the exhaust gas, and the substrate temperature of the underbody catalyst. The dotted line 511 shows a threshold condensation risk above which a significant amount of condensate can form on the underbody catalyst, thereby impairing the functionality of the catalyst. The sixth trace, line 512, shows the fuel mass (amount of fuel) as injected into an engine cylinder for combustion. The seventh trace, line 514, shows the position of a switching valve coupled to the main exhaust passage downstream of the underbody catalyst at a junction of the main exhaust passage and the bypass passage.

[0072] Shortly after t0, an engine start is requested. Because the engine was started from a standstill after a period of inactivity during which the vehicle was not driven, and furthermore due to cooler ambient conditions, the engine start may be a cold start. The engine may start under cold start conditions with an exhaust gas temperature and the substrate temperature of the underbody catalyst lower than the threshold. Due to cold start conditions and the lower than the threshold exhaust gas temperature, the risk of condensate formation on the underbody catalyst may be higher than the threshold danger level. For this reason, exhaust gas cannot be passed through the underbody catalyst during this time to reduce energy absorption from the catalyst through condensate evaporation.In response to the greater than threshold risk of condensate formation on the underbody catalyst, the controller may send a signal to an actuator coupled to the switching valve to switch the valve to a second position to direct exhaust gas via the bypass passage, thereby avoiding the underbody catalyst.

[0073] Between t0 and t1, the exhaust temperature may steadily increase, and water from the exhaust may condense on the main exhaust passage upstream and / or downstream of the underbody catalyst. Accordingly, the risk of condensate formation on the underbody catalyst may decrease. At time t1, the risk of condensate formation may decrease below the threshold. In response to the reduction in the risk of condensate formation, the controller may send a signal to an actuator coupled to the switching valve to switch the valve to a first position to direct exhaust gas via the main exhaust passage and the underbody catalyst. Between time t1 and t2, as hot exhaust is directed through the underbody catalyst, the temperature of the underbody catalyst may steadily increase.

[0074] At time t2, it can be inferred that the underbody catalyst has reached light-off temperature and is fully functional. At this time, the cylinder air mass may also increase above the threshold, and to maintain a lower exhaust backpressure while improving emissions quality, exhaust gas may continue to be routed through the underbody catalyst between time t2 and t3.

[0075] At time t3, the engine speed (-RPM) may decrease due to operator pedal input and a drop in torque demand below the threshold speed (-RPM), and to improve engine fuel efficiency, the engine may be operated without fuel. In response to the less than threshold engine speed (-RPM), the fuel mass injected to the cylinders may decrease to zero. Due to the engine's non-fueling condition, where fuel delivery is shut off but intake and / or exhaust valves continue to pump air through the engine cylinders, the oxygen content of the exhaust gas may increase. At this time, the exhaust gas temperature may also decrease below the threshold temperature.To reduce the possibility of oxygen saturation at the underbody catalyst and maintain the catalyst temperature at an optimal level, the switching valve can be switched to the second position to direct the cooler, oxygen-rich exhaust gas through the bypass passage, thereby avoiding the underbody catalyst. Between time t3 and t4, when the engine's non-fueling conditions persist, the exhaust gas can continue to be directed to bypass the underbody catalyst.

[0076] At time t4, the engine speed (RPM) may increase due to operator pedal application and an increase in torque demand above the threshold speed (RPM), and accordingly, fueling may continue, resulting in a reduction in the oxygen content in the exhaust. However, at this time, the underbody catalyst temperature may be reduced below the threshold temperature, increasing the risk of condensation on the underbody catalyst. At this time, the exhaust gas temperature may continue to remain below the threshold. Therefore, to reduce the possibility of water condensation on the underbody catalyst and prevent a further reduction in catalyst temperature, the diverter valve may be held in the second position between times t4 and t5, allowing exhaust gas to continue to bypass the underbody catalyst.

[0077] At time t5, the underbody catalyst temperature may increase above the threshold temperature, the exhaust gas temperature may decrease below the threshold temperature, and the risk of condensation may decrease below the threshold. Furthermore, the cylinder air mass may increase above the threshold air mass. Therefore, to direct exhaust gas over the underbody catalyst, the switching valve may be switched to the first position. After time t5, exhaust gas may continue to flow over the underbody catalyst, and combustion byproducts such as oxides of nitrogen, carbon monoxide, and hydrocarbons may be effectively reduced at the catalyst.

[0078] In one example, an engine comprises: during non-fueling conditions of the engine, flowing exhaust gas through a bypass passage while bypassing an underbody exhaust catalyst positioned in a main exhaust passage via a valve positioned downstream of the catalyst; and during fueling conditions of the engine, selectively flowing exhaust gas through the bypass passage based on each of a temperature and water content of the exhaust gas. The above exemplary method may additionally or optionally further comprise estimating the water content of the exhaust gas based on each of an ambient humidity, an air-fuel ratio of the exhaust gas, and an EGR level of the engine.Any or all of the above examples further additionally or optionally include predicting a condensation risk on the underfloor catalyst based on each of the estimated water content of the exhaust gas and a substrate temperature of the underfloor catalyst, wherein the risk increases as the estimated water content increases or the substrate temperature decreases. In any or all of the above examples, selectively flowing additionally or optionally includes: in response to the exhaust gas temperature falling below a lower threshold or exceeding a higher threshold, flowing the exhaust gas through the bypass passage for a duration until the water content of the exhaust gas has been reduced below a threshold level or the substrate temperature of the catalyst has been increased above a threshold temperature.In any or all of the above examples, selectively flowing additionally or optionally includes: in response to the exhaust temperature falling below a lower threshold or exceeding a higher threshold, flowing the exhaust gas through the bypass passage for a duration until the predicted risk of condensation on the underbody catalyst has been reduced, and in response to the exhaust temperature being higher than an upper threshold, flowing the exhaust gas through the bypass passage for a duration until the temperature of the exhaust gas has been reduced below the upper threshold.In any or all of the above examples, selective flow further additionally or optionally includes: in response to one of the exhaust gas temperature exceeding the lower threshold, the exhaust gas temperature falling below the upper threshold, and the predicted risk of condensation being reduced, transitioning to flowing exhaust gas through the catalyst into the main exhaust passage via the valve. In any or all of the above examples, selective flow is further additionally or optionally based on cylinder air mass, wherein selective flow includes flowing exhaust gas through the exhaust catalyst when the cylinder air mass exceeds a threshold mass.In any or all of the above examples, the engine non-fueling conditions additionally or optionally include a delay fuel cut-off condition, wherein the engine fueling conditions when the exhaust temperature falls below the threshold include an engine cold start, and wherein the engine fueling conditions when the exhaust temperature exceeds the threshold include an engine warm start. In any or all of the above examples, the underbody exhaust catalyst is additionally or optionally positioned in the main exhaust passage downstream of a front exhaust catalyst, and wherein the valve is a switching valve coupled downstream of the underbody catalyst at a junction of the main exhaust passage and the bypass passage.In any or all of the above examples, flowing exhaust gas through the main passage additionally or optionally includes actuating the switching valve to a first position blocking exhaust gas flow from the bypass passage into the main passage, and wherein flowing exhaust gas through the bypass passage additionally or optionally includes actuating the switching valve to a second position unblocking exhaust gas flow from the bypass passage into the main passage. In any or all of the above examples, the bypass passage additionally or optionally includes a heat exchanger, and wherein flowing exhaust gas through the bypass passage additionally or optionally includes flowing exhaust gas through the heat exchanger, transferring heat from the flowing exhaust gas to coolant circulating through the heat exchanger, and circulating warmed coolant through an engine block based on engine temperature and through a heater based on cabin heating.

[0079] Another example method includes predicting a risk of condensation on an exhaust catalyst based on each of a catalyst temperature and a water content of exhaust gas; and selecting between operating in a first mode, with exhaust gas flowing through the catalyst in a main exhaust passage, and operating in a second mode, with exhaust gas flowing through a bypass passage while bypassing the catalyst, based on a predicted risk. In the above example method, the predicted risk is further additionally or optionally based on an exhaust air-fuel ratio relative to stoichiometry, with the predicted risk increasing as a duration of engine operation leaner than stoichiometry increases.In any or all of the above examples, the exhaust catalyst is additionally or optionally an underfloor catalyst coupled downstream of a front catalyst in the main exhaust passage, wherein the underfloor catalyst has a higher light-off temperature than the front catalyst, wherein exhaust gas flowing through the catalyst in the main passage includes exhaust gas flowing from downstream of the front catalyst to an exhaust tailpipe via the underfloor catalyst through the main passage, and wherein exhaust gas flowing through the bypass passage includes exhaust gas flowing from downstream of the front catalyst to an exhaust tailpipe via the bypass passage without flowing through the underfloor catalyst.Any or all of the above examples further additionally or optionally include estimating the water content of exhaust gas based on each of an engine EGR level, an engine temperature, and an ambient humidity, wherein predicting includes increasing the predicted hazard when one or more of the catalyst temperature decreases, the engine EGR level increases, the engine temperature decreases, and the ambient humidity increases, and reducing the predicted hazard when one or more of the catalyst temperature increases, the engine EGR level decreases, the engine temperature increases, and the ambient humidity decreases.In any or all of the above examples, selecting additionally or optionally includes: operating in the second mode in response to the predicted hazard being greater than a threshold, and transitioning to the first mode in response to the predicted hazard being less than the threshold. In any or all of the above examples, selecting additionally or optionally includes: selecting the second mode in response to one of the exhaust temperature being less than a lower threshold, the exhaust temperature being higher than an upper threshold, and the oxygen concentration in the exhaust being higher than a threshold concentration; and selecting the first mode in response to one of the exhaust temperature being less than the lower threshold or higher than the upper threshold and the oxygen concentration in the exhaust being less than the threshold concentration.In any or all of the above examples, additionally or optionally, transitioning from operating in the first mode to operating in the second mode in response to a fuel cutoff event and transitioning from operating in the second mode to operating in the first mode in response to one of the exhaust gas temperature exceeding an upper threshold and the cylinder air mass exceeding a threshold air mass.

[0080] In yet another example, an engine system comprises an engine intake manifold including each of a mass air flow (MAF) and a manifold pressure (MAP) sensor; an engine exhaust manifold including a main exhaust passage housing a front catalyst upstream of an underbody catalyst, and a bypass passage coupled to the main exhaust passage from downstream of the front catalyst to downstream of the underbody catalyst, the bypass passage including a heat exchanger; a coolant system fluidly coupling the heat exchanger to a heater core; a switching valve coupled downstream of the underbody catalyst at a junction of the main exhaust passage and the bypass passage, and an exhaust gas temperature sensor; an exhaust gas oxygen sensor; and a controller with computer-readable instructions,stored on a non-volatile memory for: in response to engine operation below the threshold air-fuel ratio, actuating the switching valve from a first position allowing exhaust flow through the underfloor catalyst to a second position allowing exhaust flow through the bypass passage and the heat exchanger while bypassing the underfloor catalyst; estimating a catalyst temperature based on a duration of operation at the threshold air-fuel ratio, in response to the catalyst temperature falling below a threshold temperature while a water content of the exhaust gas is higher, transitioning the switching valve to the first prior position, and in response to the catalyst temperature falling below a threshold temperature while a water content of the exhaust gas is lower,Transition of the switching valve to the first later position. In the above exemplary method, the controller additionally or optionally further includes instructions for: based on input from the exhaust temperature sensor indicating that the exhaust temperature is above a lower threshold and below an upper threshold, actuating the switching valve to the first position; based on input from the exhaust temperature sensor indicating an exhaust temperature less than the lower threshold or greater than the upper threshold, actuating the switching valve from the first position to the second position to flow exhaust gas over the front catalyst, then the bypass passage, and then the heat exchanger; maintaining the switching valve in the second position for a period based on the water content of the exhaust gas; and after the period has elapsed, actuating the switching valve to the first position,to flow exhaust gas over the front catalyst and then the underfloor catalyst in the main exhaust passage. In any or all of the preceding examples, the controller further additionally or optionally includes instructions to: divert the cylinder airflow mass based on input from one of the MAF and the MAP sensor; and in response to a greater than threshold cylinder mass flow while the water content is lower, actuating the switch valve to the first position to flow exhaust gas over the underfloor catalyst in the main exhaust passage. In any or all of the preceding examples, the controller further additionally or optionally includes instructions to: during exhaust flow through the heat exchanger in the bypass passage, transfer heat from the exhaust to the coolant circulating through the heat exchanger; in response to an engine heat demand,Circulating heated coolant through an engine block; and in response to a cabin heat demand, circulating heated coolant through the heater core. By directing exhaust flow to bypass an underbody exhaust catalyst during conditions where there is a greater than a threshold risk of condensate formation on the underbody exhaust catalyst, desired catalyst cooling is reduced. By flowing exhaust through the bypass passage during non-fueling engine conditions, oxygen saturation and the resulting degradation of catalyst functionality can also be reduced. The technical effect of bypassing the underbody catalyst during conditions where the exhaust temperature (greater than an upper threshold or less than a lower threshold) is outside a desired temperature range is tothat the underbody catalyst temperature can be maintained within an optimal range. By using a heat exchanger in the bypass passage to recover heat from the exhaust gas, exhaust heat can be effectively used to accelerate engine warm-up and provide heat to the passenger compartment, thereby reducing engine power losses. By regulating the exhaust flow via an underbody catalyst and a bypass passage that houses a heat exchanger, overall emission quality can be improved and engine efficiency increased.

[0081] It should be noted that the example control and estimation routines included herein may 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-volatile memory and executed 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. Thus, various illustrated acts, operations, and / or functions may be performed in the order illustrated, in parallel, or in some cases, omitted.Likewise, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Further, the described acts, operations, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer-readable storage medium in the internal combustion engine control system, in which the described acts are performed by executing the instructions in a system including the various internal combustion engine hardware components in combination with the electronic controller.

[0082] It is understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technology may be applied to V6, I4, I6, V12, horizontally opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

[0083] The following claims particularly set forth certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as including the inclusion of one or more such elements and neither requiring nor excluding two or more such elements. Further combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by filing new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope than the original claims, are further considered to be included within the subject matter of the present disclosure.

Claims

[1] A method for controlling an engine (10), comprising: during non-fueling conditions of the engine (10) sensed by a sensor (175, 177), flowing exhaust gas through a bypass passage (173) having a heat exchanger (174) while bypassing an underbody catalyst (176) positioned in a main exhaust passage (102, 202) via a valve positioned downstream of the underbody catalyst (176) and controlled by a controller (12) responsive to the sensor (175, 177); characterized by , that the method further comprises: during fueling conditions of the engine (10), selectively flowing exhaust gas through the bypass passage (173) based on each of a temperature and water content of the exhaust gas; Estimating the water content of the exhaust gas based on each of an ambient humidity, an air-fuel ratio of the exhaust gas and an EGR level of the engine (10) and Predicting a condensation hazard on the underbody catalyst (176) based on each of the estimated water content of the exhaust gas and a substrate temperature of the underbody catalyst (176), wherein the hazard increases as the estimated water content increases or the substrate temperature decreases. [2] The method of claim 1, wherein the selective flowing includes: in response to the exhaust gas temperature falling below a lower threshold or exceeding a higher threshold, flowing the exhaust gas through the bypass passage (173) for a duration until the water content of the exhaust gas has been reduced below a threshold content or the substrate temperature of the underbody catalyst (176) has been increased above a threshold temperature. [3] The method of claim 2, wherein the selective flowing includes: in response to the exhaust gas temperature falling below a lower threshold or exceeding a higher threshold, flowing the exhaust gas through the bypass passage (173) for a duration until the predicted risk of condensation on the underbody catalyst (176) has been reduced; and in response to the exhaust gas temperature exceeding an upper threshold, flowing the exhaust gas through the bypass passage (173) for a duration until the temperature of the exhaust gas has been reduced below the upper threshold. [4] The method of claim 3, wherein the selective flow further includes: in response to one of the exhaust gas temperature exceeding the lower threshold, the exhaust gas temperature falling below the upper threshold and the predicted risk of condensation being reduced, transitioning to flow of the exhaust gas through the underbody catalyst (176) into the main exhaust passage (102, 202) via the valve. [5] The method according to the preamble of claim 1, further comprising: during fueling conditions of the engine (10), selectively flowing exhaust gas through the bypass passage (173) based on each of a temperature and water content of the exhaust gas, characterized by that the selective flow is further based on the cylinder air mass, wherein the selective flow includes flowing exhaust gas through the underbody catalyst (176) when the cylinder air mass exceeds a threshold mass. [6] The method of claim 2, wherein the non-fueling conditions of the engine (10) include a delay fuel cut-off condition, wherein the fueling conditions of the engine (10) when the exhaust temperature falls below the threshold include an engine cold start, and wherein the fueling conditions of the engine (10) when the exhaust temperature exceeds the threshold include an engine warm start. [7] The method of claim 1, wherein the underbody catalyst (176) is positioned in the main exhaust passage (102, 202) downstream of a front catalyst (170), and wherein the valve is a switching valve (182) coupled downstream of the underbody catalyst (176) at a junction of the main exhaust passage (102, 202) and the bypass passage (173). [8] The method of claim 7, wherein flowing exhaust gas through the main exhaust passage (102, 202) includes actuating the switching valve (182) to a first position in which exhaust gas flow from the bypass passage (173) into the main exhaust passage (102, 202) is blocked, and wherein flowing exhaust gas through the bypass passage (173) includes actuating the switching valve (182) to a second position in which exhaust gas flow from the bypass passage (173) into the main exhaust passage (102, 202) is not blocked. [9] The method of claim 1, wherein the bypass passage (173) includes the heat exchanger (174), and wherein flowing exhaust gas through the bypass passage (173) includes flowing exhaust gas through the heat exchanger (174), which transfers heat from the flowing exhaust gas to a coolant circulating through the heat exchanger (174), and circulating warmed coolant through an engine block based on engine temperature and through a heater based on cabin heating. [10] Engine system (100), comprising: an engine intake manifold (22) including each of a mass air flow sensor (125) and a manifold pressure sensor (124); an engine exhaust manifold (36) including a main exhaust passage (102, 202) receiving a front catalyst (170) upstream of an underbody catalyst (176), and a bypass passage (173) coupled to the main exhaust passage (102, 202) from downstream of the front catalyst (170) to downstream of the underbody catalyst (176), the bypass passage (173) including a heat exchanger (174); a coolant system fluidly coupling the heat exchanger (174) to a heater core; a switching valve (182) coupled downstream of the underbody catalyst (176) at a junction of the main exhaust passage (102, 202) and the bypass passage (173); an exhaust gas temperature sensor (177); an exhaust gas lambda probe (175); and a controller (12) having computer-readable instructions stored in a non-volatile memory for: in response to engine operation below the threshold air-fuel ratio, Actuating the switching valve (182) from a first position allowing exhaust gas flow through the underbody catalyst (176) to a second position allowing exhaust gas flow through the bypass passage (173) and the heat exchanger (174) while bypassing the underbody catalyst (176); characterized by that the controller (12) further comprises instructions for: estimating a catalyst temperature based on a duration of operation at the threshold air-fuel ratio; in response to the catalyst temperature falling below a threshold temperature while a water content of the exhaust gas is lower, transitioning the switching valve (182) to the first earlier position; and in response to the catalyst temperature falling below a threshold temperature while a water content of the exhaust gas is higher, transitioning the switching valve (182) to the first later position. [11] The system of claim 10, wherein the controller (12) further comprises instructions for: based on an input from the exhaust gas temperature sensor (177) indicating that the exhaust gas temperature exceeds a lower threshold and falls below an upper threshold, actuating the switching valve (182) to the first position; based on an input from the exhaust temperature sensor (177) indicating a lower than the lower threshold exhaust temperature or a higher than the upper threshold exhaust temperature, actuating the switching valve (182) from the first position to the second position to flow exhaust gas over the front catalyst (170), then the bypass passage (173), and then the heat exchanger (174); Maintaining the switching valve (182) in the second position for a period of time based on the water content of the exhaust gas; and after the period of time has elapsed, actuating the changeover valve (182) to the first position to flow exhaust gas over the front catalyst (170) and then the underbody catalyst (176) in the main exhaust passage (102, 202). [12] The system of claim 10, wherein the controller (12) further comprises instructions for: Deriving the cylinder airflow mass based on the input from one of the mass airflow sensor (125) and the manifold pressure sensor (124); and in response to a higher than the threshold cylinder mass flow while the water content is lower, actuating the switching valve (182) to the first position to flow exhaust gas over the underbody catalyst (176) in the main exhaust passage (102, 202). [13] The system of claim 10, wherein the controller (12) further comprises instructions for: during the exhaust gas flow through the heat exchanger (174) in the bypass passage (173), Transferring heat from the exhaust gas to the coolant circulating through the heat exchanger (174); in response to an engine heat demand, circulating heated coolant through an engine block; and In response to a cabin heat demand, circulating heated coolant through the heater core.

Images