Method and system for coolant temperature sensor diagnostics

Abstract

The present invention relates to methods and systems for coolant temperature sensor diagnostics. Methods and systems are provided for on-board diagnostics of components of an exhaust gas heat recovery (EGHR) system, the EGHR system including an engine coolant temperature sensor coupled to the system. Degradation of one or more of a first coolant temperature sensor coupled to an upstream heat exchanger of the EGHR system and a second coolant temperature sensor coupled to a downstream heat exchanger is indicated based on a difference between a modeled coolant temperature and a measured coolant temperature, the modeled coolant temperature being based on one or more of heat transfer between a heater core and a vehicle cabin and heat transfer between exhaust gas flowing through the heat exchanger and coolant flowing through the heat exchanger.

Description

Technical Field

[0001] The present invention generally relates to methods and systems for on-board diagnostics of an engine coolant temperature sensor coupled to an exhaust heat recovery system. Background Art

[0002] The engine can be configured with an exhaust heat recovery (EGHR) system for recovering heat from the exhaust gas. During periods of lower engine temperatures and / or during periods of cabin heating demand, exhaust gas can be routed through the EGHR system and the exhaust heat can be recovered by coolant flowing through a heat exchanger of the EGHR system. The coolant with recovered exhaust heat can be circulated through a heater core of the engine and / or an onboard heating, ventilation, and air conditioning (HVAC) system, and the exhaust heat can be used to provide heat to the engine as well as warm the cabin, thereby improving engine and fuel efficiency. Diagnostic procedures may need to be performed periodically or in a timely manner to monitor different components of the EGHR system, including a coolant temperature sensor housed in a coolant line fluidly coupled to the heat exchanger of the EGHR system.

[0003] Various methods are provided for diagnosing an engine coolant temperature sensor. In one example, as shown in U.S. Patent No. 6,848,434, Li et al. disclose a method for diagnosing a coolant temperature sensor coupled to an engine coolant system. The coolant temperature can be modeled based on each of the energy flow between the engine and the coolant, the energy flow between the coolant and the air, and the energy flow from the coolant to the radiator. Based on an indication of engine warm-up based on the modeled coolant temperature, a diagnosis of the coolant sensor can be performed based on a comparison of the coolant temperature estimated via the coolant temperature sensor and a predetermined regulated temperature.

[0004] However, the inventors of the present invention have recognized potential problems with the above approach. As an example, in an embodiment having an EGHR system, multiple coolant temperature sensors may be housed in a coolant line coupled to the EGHR system, and the rationality of each coolant temperature sensor may need to be monitored independently. The coolant temperature at each location in the EGHR system may be different in different operating modes of the EGHR system, and a single model may not be used to calculate the coolant temperature at each location in the EGHR system during operation of the EGHR system in each operating mode. Further, by modeling the coolant temperature separately based on the energy flow between each of the engine, coolant, air, and radiator, it is not possible to quantify energy losses during heat transfer between the aforementioned components, thereby reducing the accuracy of the temperature model. Summary of the invention

[0005] The inventors of the present invention have recognized a method by which the problems described above can be at least partially solved. An example method includes: during exhaust gas flow from a vehicle engine through / across a heat exchanger having coolant flowing therethrough, in response to a difference above a threshold between a measured coolant temperature and a modeled coolant temperature (the modeled coolant temperature is based on heat transfer between a heat loss source and a vehicle cabin), indicating degradation of a first coolant temperature sensor and / or a second coolant temperature sensor coupled upstream and downstream of the heat exchanger, respectively. In this way, by using separate temperature models to calculate coolant temperatures at different locations in the EGHR system and comparing the measured coolant temperature to the modeled coolant temperature, degradation of one or more coolant temperature sensors can be independently detected.

[0006] In one example, an engine system can be configured to have an exhaust heat recovery (EGHR) system including a heat exchanger. The heat exchanger can be positioned in an exhaust bypass channel that is arranged parallel to the main exhaust channel, and a diverter valve coupled to the main exhaust channel can be used to enable the exhaust gas to be diverted / diverted to the bypass channel or directed through the main channel into the tail pipe. Based on the engine heating and / or cabin heating requirements, the EGHR system can be operated in multiple modes by adjusting the position of the diverter valve. As an example, during higher engine and / or cabin heating requirements, the diverter valve can be actuated to a first position (a first operating mode of the EGHR system) to allow the exhaust gas to flow to the tail pipe via the heat exchanger, and once the engine temperature has been increased above a threshold and cabin heating is no longer desired, the diverter valve can be actuated to a second position (a second operating mode of the EGHR system) to allow the exhaust gas to bypass the heat exchanger and flow directly to the tail pipe. During the flow of the exhaust gas via the heat exchanger, the engine coolant can be transmitted via the heat exchanger, wherein the heat from the exhaust gas can be transferred to the coolant. The coolant with exhaust heat can then be transmitted via the heater core of the engine and the vehicle HVAC system, where the exhaust heat can be used to increase the engine and / or cabin temperature. A first coolant temperature sensor can be coupled to a first coolant line entering the heat exchanger (upstream of the heat exchanger), and a second coolant temperature sensor can be coupled to a second coolant line leaving the heat exchanger (downstream of the heat exchanger). During operation of the EGHR system in the first mode, when the exhaust gas is transmitted via the heat exchanger, the coolant temperature upstream of the heat exchanger can be modeled using two different modeling methods. Each of the two modeling methods for calculating the coolant temperature upstream of the heat exchanger can be based on the heat loss during the heat transfer from the heater core and the coolant line to the cabin. The modeled coolant temperature upstream of the heat exchanger can be calibrated and optimized for multiple HVAC system operating conditions upstream of the heat exchanger. The coolant temperature downstream of the heat exchanger can also be modeled using two different modeling methods. Each of the two modeling methods for calculating the coolant temperature downstream of the heat exchanger can be based on the heat loss during the heat transfer from the exhaust gas to the heat exchanger and the modeled coolant temperature upstream of the heat exchanger. An optimized modeled coolant temperature upstream of the heat exchanger may be compared to a measured coolant temperature, and in response to a difference between the modeled and measured temperatures being above a threshold, degradation of a first coolant temperature sensor may be detected. Similarly, a modeled coolant temperature downstream of the heat exchanger may be compared to a measured coolant temperature, and in response to a difference between the modeled and measured temperatures being above a threshold, degradation of a second coolant temperature sensor may be detected. In addition to diagnosing the coolant temperature sensor, diagnostics of the diverter valve and heat exchanger may also be performed during operation of the EGHR system in exhaust heat.

[0007] In this way, by modeling the coolant temperatures upstream and downstream of the heat exchanger of the EGHR system using different mathematical methods, degradation of a first coolant temperature sensor upstream of the heat exchanger can be distinguished from degradation of a second coolant temperature sensor downstream of the heat exchanger, and appropriate mitigation actions can be performed. By timely diagnosing the coolant temperature sensor, diverter valve, and heat exchanger during specific operating modes of the EGHR system, the possibility of falsely detecting degradation of one or more components of the EGHR system can be reduced. The technical effect of including heat losses between one or more vehicle components (including the heater core, coolant lines, cabin, exhaust, and heat exchanger) in the calculation of the modeled temperatures is that the accuracy of the modeled temperatures upstream and downstream of the heat exchanger can be improved. By enabling the diagnosis of the coolant temperature sensor to be performed reliably and accurately, the tendency of the coolant to overheat can be reduced and the robustness of the HVAC system can be improved.

[0008] It should be understood that the above summary is provided to introduce selected concepts in a simplified form, which will be further described in the detailed description. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the appended claims. In addition, the claimed subject matter is not limited to implementations that address any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A An example embodiment of an engine system including an exhaust gas heat recovery (EGHR) system operating in a first mode is shown.

[0010] Figure 1B An example embodiment of an engine system including an EGHR system operating in a second mode is shown.

[0011] Figure 2 shows a fluidly coupled Figure 1A to Figure 1B An example of an EGHR system in a vehicle heating, ventilation, and air conditioning (HVAC) system.

[0012] Figure 3 An example schematic diagram illustrating a modeling technique used in diagnosing a coolant temperature sensor coupled upstream of an EGHR system heat exchanger.

[0013] Figure 4 An example schematic diagram illustrating a modeling technique used in diagnosing a coolant temperature sensor coupled downstream of an EGHR system heat exchanger.

[0014] Figure 5 A flow chart is shown that illustrates an example method that may be implemented for diagnosing an EGHR system diverter valve and heat exchanger.

[0015] Figure 6 A flow chart is shown that illustrates an example method that may be implemented for diagnosing a coolant temperature sensor coupled upstream of a heat exchanger of an EGHR system.

[0016] Figure 7 A flow chart is shown that illustrates an example method that may be implemented for diagnosing a coolant temperature sensor coupled downstream of a heat exchanger of an EGHR system.

[0017] Figure 8 An example diagnostic performed on a coolant temperature sensor coupled to an EGHR system according to the present disclosure is shown. DETAILED DESCRIPTION

[0018] The following description relates to systems and methods for on-board diagnostics of multiple engine coolant temperature sensors coupled to an exhaust gas heat recovery (EGHR) system. The EGHR system may include a heat exchanger (coupled to a bypass passage) for exhaust gas heat recovery. Figure 1A to Figure 1B The different operating modes of the EGHR system are shown in FIG. Figure 2 An example vehicle HVAC system fluidly coupled to an EGHR system is shown in FIG. Figure 3 to Figure 4 An example schematic diagram of a modeling technique used in diagnosing coolant temperature sensors coupled upstream and downstream of an EGHR system heat exchanger is shown in FIG. The engine controller may be configured to execute control routines such as Figures 5 to 8 An example routine is provided for periodically or opportunistically diagnosing components of an EGHR system including a diverter valve, a heat exchanger, and coolant temperature sensors coupled upstream and downstream of the EGHR system. Figure 8 An example diagnostic procedure is shown.

[0019] Figure 1A A schematic diagram 110 of a vehicle system 101 having an example engine system 100 including an engine 10 is shown. In one example, the engine system 100 can be a diesel engine system. In one example, the engine system 100 can be a gasoline engine system. In the depicted embodiment, the engine 10 is a boosted engine coupled to a turbocharger 13 including a compressor 114 driven by a turbine 116. Specifically, fresh air is introduced into the engine 10 along an intake passage 42 via an air cleaner 112 and flows to the compressor 114. The compressor can be any suitable intake compressor, such as a motor-driven or drive shaft-driven supercharger compressor. In the engine system 10, the compressor is a turbocharger compressor mechanically coupled to a turbine 116 via a shaft 19, and the turbine 116 is driven by expanding engine exhaust.

[0020] like Figure 1AAs shown, compressor 114 is coupled to throttle valve 20 via charge air cooler (CAC) 118. Throttle valve 20 is coupled to engine intake manifold 22. Compressed air charge flows from compressor 114 through charge air cooler 118 and throttle valve 20 to intake manifold 22. Figure 1A In the illustrated embodiment, the pressure of the air charge within the intake manifold 22 is sensed by a manifold air pressure (MAP) sensor 124 .

[0021] One or more sensors may be coupled to the inlet of the compressor 114. For example, a temperature sensor 55 may be coupled to the inlet for estimating the compressor inlet temperature, and a pressure sensor 56 may be coupled to the inlet for estimating the compressor inlet pressure. As another example, a humidity sensor 57 may be coupled to the inlet for estimating the humidity of the air charge entering the compressor. For example, other sensors may include an air-fuel ratio sensor, etc. In other examples, one or more of the compressor inlet conditions (such as humidity, temperature, pressure, etc.) may be inferred based on the engine operating conditions. In addition, when exhaust gas recirculation (EGR) is enabled, the sensor may estimate the temperature, pressure, humidity, and air-fuel ratio of the air charge mixture containing fresh air, recirculated compressed air, and exhaust gas residuals received at the compressor inlet.

[0022] Wastegate actuator 92 may be actuated open to vent at least some exhaust pressure from upstream of the turbine to a location downstream of the turbine via wastegate 91. By reducing exhaust pressure upstream of the turbine, turbine speed may be reduced, which in turn helps reduce compressor surge.

[0023] Intake manifold 22 is coupled to a series of combustion chambers 30 via a series of intake valves (not shown). The combustion chambers are further coupled to exhaust manifold 36 via a series of exhaust valves (not shown). In the depicted embodiment, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold may include multiple exhaust manifold sections. A configuration with multiple exhaust manifold sections may enable outflows from different combustion chambers to be directed to different locations in the engine system.

[0024] In one embodiment, each of the exhaust valve and the intake valve may be electronically actuated or controlled. In another embodiment, each of the exhaust valve and the intake valve may be cam actuated or controlled. Whether electronically actuated or cam actuated, the timing of the opening and closing of the exhaust valve and the intake valve may be adjusted as required for desired combustion and emission control performance.

[0025] One or more fuels such as gasoline, an alcohol fuel blend, diesel, biodiesel, compressed natural gas, etc. may be supplied to combustion chamber 30 via injector 66. Fuel may be supplied to the combustion chamber via direct injection, port injection, throttle body injection, or any combination thereof. Combustion may be initiated in the combustion chamber via spark ignition and / or compression ignition.

[0026] like Figure 1A As shown, exhaust gas from one or more exhaust manifold sections may be directed to turbine 116 to drive the turbine. The combined flow from the turbine and the wastegate then flows through emission control devices 170 and 171. In one example, first emission control device 170 may be a light-off catalyst and second emission control device 171 may be an underbody catalyst. Generally, exhaust aftertreatment devices 170 and 171 are configured to catalytically treat the exhaust flow and thereby reduce the amount of one or more substances in the exhaust flow. For example, exhaust aftertreatment devices 170 and 171 may be configured to capture NO from the exhaust flow when the exhaust flow is lean. x , and reduces the captured NO when the exhaust stream is enriched x In other examples, exhaust aftertreatment devices 170 and 171 may be configured to disproportionate NO x , or selectively reduce NO with the help of a reducing agent x . In other examples, exhaust aftertreatment devices 170 and 171 may be configured to oxidize residual hydrocarbons and / or carbon monoxide in the exhaust flow. Different exhaust aftertreatment catalysts having any such functionality may be arranged separately or together in the washcoat or elsewhere in the exhaust aftertreatment stage. In some embodiments, the exhaust aftertreatment stage may include a regenerable soot filter configured to capture and oxidize soot particles in the exhaust flow.

[0027] Exhaust gas recirculation (EGR) delivery passage 181 can be coupled to exhaust passage 102 downstream of turbine 116 to provide low pressure EGR (LP-EGR) to the engine intake manifold upstream of compressor 114. EGR valve 52 can be coupled to EGR passage 181 at the junction of EGR passage 181 and intake passage 42. EGR valve 52 can be opened to allow a controlled amount of exhaust gas to the compressor inlet for desired combustion and emission control performance. EGR valve 52 can be configured as a continuously variable valve or an on / off valve. In further embodiments, the engine system may include a high pressure EGR flow path, wherein exhaust gas is drawn from upstream of turbine 116 and recirculated to the engine intake manifold downstream of compressor 114. In further embodiments, the engine system may include a high pressure EGR flow path, wherein exhaust gas is drawn from upstream of turbine 116 and recirculated to the engine intake manifold downstream of compressor 114.

[0028] One or more sensors may be coupled to the EGR passage 181 for providing details about the composition and condition of the EGR. For example, a temperature sensor may be provided for determining the temperature of the EGR, a pressure sensor may be provided for determining the pressure of the EGR, a humidity sensor may be provided for determining the humidity or water content of the EGR, and an air-fuel ratio sensor may be provided for estimating the air-fuel ratio of the EGR. Alternatively, the EGR condition may be inferred by one or more temperature sensors, pressure sensors, humidity sensors, and air-fuel ratio sensors 55 to 57 coupled to the compressor inlet. In one example, the air-fuel ratio sensor 57 is an oxygen sensor.

[0029] A plurality of sensors including an exhaust temperature sensor 128, an exhaust oxygen sensor, an exhaust flow sensor, and an exhaust pressure sensor 129 may be coupled to the main exhaust passage 102. The oxygen sensor may be a linear oxygen sensor or UEGO (universal or wide range exhaust gas oxygen sensor), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx sensor, an HC sensor, or a CO sensor.

[0030] Exhaust gas may flow from downstream of second emission control device 171 to muffler 172 via one or more of main exhaust passage 102 and bypass passage 174. For example, after passing through muffler 172, all or a portion of the treated exhaust gas from exhaust aftertreatment devices 170 and 171 may be released to the atmosphere via main exhaust passage 102. Alternatively, all or a portion of the treated exhaust gas from exhaust aftertreatment devices 170 and 171 may be released to the atmosphere via an exhaust heat recovery (EGHR) system 150 coupled to the main exhaust passage. The EGHR system 150 may be operated for exhaust heat recovery for engine heating and cabin heating.

[0031] A bypass passage 174 of the exhaust heat exchange system 150 may be coupled to the main exhaust passage 102 downstream of the second emission control device 171 at junction 106. The bypass passage 174 may extend from downstream of the second emission control device 171 to upstream of the muffler 172. The bypass passage 174 may be arranged parallel to the main exhaust passage 102. A heat exchanger 176 may be coupled to the bypass passage 174 to extract heat from the exhaust gas passing through the bypass passage 174. In one example, the heat exchanger 176 is a water-to-air exchanger.

[0032] A diverter valve 175 at the junction of the main exhaust passage 102 and the inlet of the bypass passage 174 coupled upstream of the heat exchanger 176 can be used to regulate the exhaust gas flow through the bypass passage 174. The position of the diverter valve can be adjusted in response to a signal received from the engine controller to operate the EGHR in a selected operating mode. In one example, the diverter valve can be actuated to a first fully open position to allow the entire volume of the exhaust gas flow to flow from the downstream of the catalyst (second emission control device) 171 to the tail pipe 35 via the exhaust bypass passage 174, thereby enabling the EGHR system to operate in a first mode that provides exhaust heat recovery. As another example, the diverter valve can be actuated to a second fully closed position to direct all exhaust gas to the tail pipe via the main exhaust passage, while disabling the exhaust gas flow from the downstream of the catalyst 171 to the tail pipe 35 via the exhaust bypass passage 174, thereby enabling the EGHR system to operate in a second mode that does not provide exhaust heat recovery. Therefore, the position of the diverter valve 175 can be adjusted to maintain a desired engine coolant temperature, which is based on each of the engine heating demand and the cabin heating. A position sensor 32 may be coupled to the diverter valve 175 to detect the position of the diverter valve.

[0033] The coolant lines of the vehicle's onboard heating, ventilation, and air conditioning (HVAC) system 155 can be fluidly coupled to the exhaust heat exchanger 176 for exhaust heat recovery. The coolant of the HVAC system can flow through the heat exchanger via the coolant inlet line 160, and after circulating through the heat exchanger, the coolant can return to the engine via the coolant outlet line 162. The auxiliary pump 81 can be coupled to the coolant inlet line 160 to enable coolant flow through the heat exchanger 176. A first coolant temperature sensor 180 can be coupled to the coolant inlet line 160 upstream of the heat exchanger 176 to measure the temperature of the coolant entering the heat exchanger. A second coolant temperature sensor 182 can be coupled to the coolant outlet line 162 downstream of the heat exchanger 176 to measure the temperature of the coolant leaving the heat exchanger. Each of the coolant temperature sensors 180 and 182 can be diagnosed from time to time to detect any degradation of the coolant sensor. An example control routine for diagnosing the coolant temperature sensors 180 and 182 is referenced. Figure 6 to Figure 7 Give a description.

[0034] In one example, degradation of the diverter valve 175 may be indicated in response to an actual position of the diverter valve 175 as estimated based on input from the diverter valve position sensor 32 that is different from an expected position of the diverter valve. The expected position of the diverter valve 175 may include one of a first position that enables exhaust gas flow through the heat exchanger 176 during an engine heating demand above a threshold and / or a cabin heating demand above a threshold, and a second position that disables exhaust gas flow through the heat exchanger 176 during an engine heating demand below a threshold and a cabin heating demand below a threshold. Further, degradation of the heat exchanger 176 may be indicated in response to an expected temperature difference between coolant temperatures upstream and downstream of the heat exchanger 176 being different from an actual temperature difference between coolant temperatures upstream and downstream of the heat exchanger, the expected temperature difference being based on each of the actual position of the diverter valve 175, the mass coolant flow rate through the heat exchanger 176, and the exhaust gas flow rate, and the actual difference being based on input from the first coolant temperature sensor 180 and the second coolant temperature sensor 182. For details on the diagnostic diverter valve 175 and heat exchanger 176 refer to Figure 5 Discuss.

[0035] The engine system 100 may further include a control system 14. The control system 14 shown receives information from a plurality of sensors 16 (various examples of which are described herein) and sends control signals to a plurality of actuators 18 (various examples of which are described herein). As an example, the sensors 16 may include a first coolant temperature sensor 180 coupled to the coolant inlet line 160, a second coolant temperature sensor 182 coupled to the coolant outlet line 162, a diverter valve position sensor 32, an exhaust gas sensor 126 located upstream of the turbine 116, a MAP sensor 124, an exhaust gas temperature sensor 128, an exhaust gas pressure sensor 129, a compressor inlet temperature sensor 55, a compressor inlet pressure sensor 56, a compressor inlet humidity sensor 57, and an EGR sensor. Other sensors such as additional pressure sensors, temperature sensors, air / fuel ratio sensors, and composition sensors may be coupled to various locations in the engine system 100. For example, the actuators 18 may include the throttle valve 20, the EGR valve 52, the diverter valve 175, the wastegate 92, and the fuel injector 66. The control system 14 may include a controller 12. The controller 12 may receive input data from various sensors, process the input data, and trigger various actuators in response to the processed input data based on instructions or code programmed therein corresponding to one or more routines. For example, based on engine temperature, the controller 12 may issue a signal command to an actuator coupled to the diverter valve 175 to direct exhaust gas to the tailpipe via the heat exchanger 176. Moreover, the controller may periodically or opportunistically diagnose each of the coolant temperature sensors 180 and 182 based on input from a plurality of HVAC system sensors.

[0036] Figure 1A The EGHR system 150 is shown operating in a first operating mode. Thus, the first operating mode represents a first setting of the diverter valve 175 to achieve exhaust flow control. In the first operating mode, the diverter valve 175 can be in a first (fully open) position. When in the first operating mode, due to the first position of the diverter valve 175, the entire volume of exhaust gas leaving the second emission control device 171 can be diverted into the bypass channel via the open diverter valve 175. The exhaust gas can then flow through the heat exchanger 176 and return to the main exhaust passage. After re-entering the main exhaust passage 102, the exhaust gas can flow through the muffler 172 and then be released into the atmosphere via the tail pipe 35. When the exhaust gas passes through the heat exchanger 176, the heat from the exhaust gas can be transferred to the coolant circulating through the heat exchanger 176. As heat is transferred from the exhaust gas to the coolant, the warmed coolant may be circulated back to the engine and circulated around the engine (such as when engine heating is required) and / or circulated through the heater core via coolant outlet line 162 for use in heating the vehicle's passenger cabin (such as when cabin heating is required).

[0037] During conditions where exhaust heat needs to be recovered for use in heating the engine, such as during an engine cold start condition, the exhaust heat exchange system can be operated in a first operating mode (as described above). By diverting the exhaust gas through the heat exchanger 176 during an engine cold start, heat from the exhaust gas can be recovered at the heat exchanger and transferred to the coolant circulating through the heat exchanger 176. The hot coolant can then circulate around the engine block so that the heat extracted from the exhaust can be used for engine warm-up. In one example, engine heating can be desired when the temperature of the coolant in the coolant inlet (as estimated via the first coolant temperature sensor 180) is below a first threshold temperature. The EGHR system can continue to be operated in the first mode until the temperature of the coolant inlet increases to a second threshold temperature, wherein the second threshold temperature is higher than the first threshold temperature. Once the temperature of the coolant entering the heat exchanger 176 reaches the second threshold temperature, it can be inferred that the engine temperature has reached the optimal operating temperature and heat is no longer being extracted from the heater core for cabin heating purposes, and operation of the EGHR system 150 can be converted from the first mode to the second mode (as described with respect to FIG. 1 ). Figure 1B described).

[0038] By accelerating engine warm-up during cold starts, cold start exhaust emissions can be reduced and engine performance can be improved. In addition, if the operator desires vehicle heating, such as by adjusting the cabin temperature setting, the hot coolant can be circulated around the heater core of the HVAC system 155 for providing heat to the passenger compartment of the vehicle.

[0039] During operation in the first mode, on-board diagnostics of each of the coolant temperature sensors 180 and 182 may be performed using input from the exhaust temperature sensor 128 and a plurality of HVAC system sensors. In one example, if at least one of the first coolant temperature sensor 180 and the second coolant temperature sensor 182 is degraded, the temperature of the coolant entering the heat exchanger 176 and / or exiting the heat exchanger 176 may not be accurately estimated, and therefore the amount of heat transferred to the coolant may not be quantified. An erroneous estimate of the coolant temperature may result in excessive heat being transferred from the exhaust gas to the coolant, resulting in overheating of the coolant. In order to provide the desired mitigation action, each coolant temperature sensor is individually diagnosed to determine which coolant temperature sensor is degraded.

[0040] When the EGHR system is operated in the first mode, the coolant temperature may be measured upstream of the heat exchanger 176 via the first coolant temperature sensor 180, the coolant temperature upstream of the heat exchanger 176 may be modeled, and degradation of the first coolant temperature sensor 180 may be indicated in response to a difference above a threshold between the modeled coolant temperature upstream of the heat exchanger and the measured coolant temperature upstream of the heat exchanger. Similarly, the coolant temperature may be measured downstream of the heat exchanger 176 via the second coolant temperature sensor 182, the coolant temperature downstream of the heat exchanger may be modeled, and degradation of the second coolant temperature sensor 182 may be indicated in response to a difference above a threshold between the modeled coolant temperature downstream of the heat exchanger and the measured coolant temperature downstream of the heat exchanger 176. The modeled coolant temperature upstream of the heat exchanger 176 may be based on one or more of air flow between the heater core and the cabin and coolant flow from the engine to the heater core, and wherein the modeled coolant temperature downstream of the heat exchanger 176 is based on one or more of the modeled coolant temperature upstream of the heat exchanger 176, air flow between exhaust gas flowing through the heat exchanger 176 and coolant flowing through the heat exchanger 176, and coolant flow from the heater core to the heat exchanger. For details of the diagnostic process of the first coolant temperature sensor 180 coupled to the coolant inlet 160, refer to Figure 6 1 and 162. The details of the diagnostic process of the second coolant temperature sensor 182 coupled to the coolant outlet 162 are discussed in detail with reference to FIG. Figure 7 Discuss.

[0041] Figure 1B Schematic diagram 120 of an EGHR system 150 operating in a second mode of operation is shown. Figure 1A Components introduced in are numbered similarly and are not reintroduced.

[0042] Thus, the second operating mode represents a second setting of the diverter valve 175 to achieve exhaust flow control. In the second operating mode, the diverter valve 175 can be in a second (fully closed) position to disable exhaust flow from the main exhaust passage 102 to the bypass passage 174. In the second mode, exhaust gas can flow directly from the catalyst 171 to the muffler 172, bypassing the heat exchanger 176. When the exhaust does not flow via the heat exchanger 176, exhaust heat cannot be recovered at the heat exchanger.

[0043] After engine warm-up and cabin warm-up have been completed and when exhaust heat is no longer desired for engine and / or cabin heating purposes, the EGHR system 150 may be operated in a second operating mode (as described above). During operation in this mode, when recovery of exhaust heat by the coolant is not occurring, the coolant temperature upstream of the heat exchanger may be equal to the coolant temperature downstream of the heat exchanger, and thus diagnostics of each of the coolant temperature sensors 180 and 182 may not be performed. In one example, during operation of the EGHR system 150 in the second mode, the controller may send a signal to an actuator of the auxiliary pump 81 to stop operation of the pump, thereby disabling coolant flow through each of the coolant inlet line 160, the coolant outlet line 162, and the heat exchanger.

[0044] In one example, during operation of the EGHR system 150 in the first mode, the diverter valve 175 may be maintained in the fully open position until the temperature of the coolant entering the heat exchanger 176 reaches a third threshold temperature. The third threshold temperature may be higher than the first threshold temperature, but lower than the second threshold temperature (the third threshold temperature is between the first threshold temperature and the second threshold temperature). In response to the temperature of the coolant entering the heat exchanger 176 reaching the third threshold temperature, it may be inferred that a lower rate of heat transfer from the exhaust gas to the coolant is desired. To reduce the rate of heat transfer from the exhaust gas to the coolant, the position of the diverter valve 175 may be adjusted to a third partially open position, wherein a first portion of the exhaust gas may enter the bypass passage 174 and flow via the heat exchanger 176, while a second remaining portion of the exhaust gas may flow directly from the catalyst 171 to the muffler 172 via the exhaust passage 102. In this manner, the EGHR system 150 may be operated in the third mode, wherein the diverter valve is in the third partially open position. The controller may determine the position of the diverter valve based on the difference between the temperature of the coolant entering the heat exchanger 176 and the second threshold temperature. For example, the controller may consult a lookup table that has as input the difference between the temperature of the coolant entering the heat exchanger 176 and the second threshold temperature, and has as output a signal corresponding to the position of the diverter valve 175. As an example, as the difference between the temperature of the coolant entering the heat exchanger 176 and the second threshold temperature decreases, the opening of the diverter valve may be reduced to reduce exhaust flow through the bypass passage 174 and the heat exchanger 176. Once the temperature of the coolant entering the heat exchanger 176 reaches the second threshold temperature, it may be inferred that the engine temperature has reached the optimal operating temperature and heat is no longer being extracted from the heater core for cabin heating purposes, and the operation of the EGHR system 150 may be transitioned from the third mode to the second mode.

[0045] Figure 2An example embodiment 200 of an onboard heating, ventilation, and air conditioning (HVAC) system 5 (also referred to herein as a coolant system) in a motor vehicle 6 is shown. The coolant system 5 circulates engine coolant and distributes heat recovered from the exhaust heat exchanger 54 by the internal combustion engine 10 and the heater core 90. In one example, the coolant system 5 may be the HVAC system 155, and the exhaust heat exchanger 54 may be Figure 1A to Figure 1B The heat exchanger 176 in.

[0046] Figure 2 A coolant system 5 is shown that is coupled to the engine 10 and circulates engine coolant from the engine 10 through the exhaust heat exchanger 54 via the heater core 90 and circulates it via an engine driven (or electronic) water pump 86 to the radiator 80 and / or radiator bypass line 87, and back to the engine 10. The heat exchanger 54 can be part of the exhaust heat recovery system 150, and exhaust gas from the main exhaust passage 102 can be transferred to the heat exchanger 54 via the bypass passage 174. Coolant from the engine can flow to the heater 90 via the coolant line 89, and heat from the coolant can be transferred to the heater core 90. An auxiliary pump 75 can be coupled to the coolant line 89 to enable coolant flow through the heater core 90 and the heat exchanger 176. In one example, an evaporator can be coupled to the coolant line 89 upstream of the heater core. In one example, the auxiliary pump 75 can be a condenser such as a heat exchanger. Figure 1A to Figure 1B Auxiliary pump 81 is shown. Coolant can be circulated from the heater core to the heat exchanger 54 via a coolant inlet line 84. In one example, as the engine coolant circulates through the heat exchanger 54, heat from the exhaust gas can be transferred to the engine coolant, and then the heated coolant (heated with the extracted exhaust heat) can be sent through the engine 10. Coolant from the heat exchanger can exit via a coolant outlet line 83 and can return to the engine 10. Heat from the engine coolant can be transferred to the engine 10 and / or then transferred to the heater core 90, and the heat extracted from the engine coolant can be used to heat the engine 10 (including the cylinder walls and pistons) and the cabin 4. A first coolant temperature sensor 180 can be coupled to the coolant inlet line 84 to estimate the temperature of the coolant entering the heat exchanger, and a second coolant temperature sensor 182 can be coupled to the coolant outlet line 83 to estimate the temperature of the coolant leaving the heat exchanger.

[0047] The water pump 86 may be coupled to the engine via the front end accessory drive (FEAD) 37 and rotated in proportion to the engine speed via a belt, chain, or the like. In particular, the water pump 86 circulates coolant through passages in the engine block, engine cover, or the like to absorb engine heat, which is then transferred to the ambient air via the radiator 80 as regulated by the thermostatic valve 38. In an example where the pump 86 is a centrifugal pump, the pressure generated (and the resulting flow) may be proportional to the crankshaft speed, which may be directly proportional to the engine speed. The temperature of the coolant may be regulated by the thermostatic valve 38, which may be maintained closed until the coolant reaches a threshold temperature, thereby reducing heat transfer from the radiator 80 to the ambient air when closed.

[0048] After flowing through engine 10, the coolant may exit the engine via coolant line 82 and may flow through radiator 80 as regulated by thermostatic valve 38 or through radiator bypass line 87, with flow being directed through radiator bypass line 87 during conditions when the engine temperature (coolant temperature) is below a threshold temperature.

[0049] The fan 93 can be coupled to the radiator 80 to increase the air flow through the radiator 80 as needed to keep the coolant temperature below the desired threshold. In some examples, the fan speed can be directly controlled by the engine controller. Alternatively, the fan 93 can be coupled to the engine and driven directly from the engine.

[0050] In one example, a climate control system 94 may be coupled to the cabin 4. The climate control system 94 may be part of a heater core, and heat from the heater core may be used for cabin heating via the climate control system 94. An operator may specify a desired cabin temperature via an input to a dashboard switch coupled to the climate control system 94. The climate control system 94 may have blades and / or doors to allow air to circulate between the heater core 90 and the cabin 4. Based on the temperature setting and the fan setting as specified by the operator, one or more of the speed of the fan (blower) and the position of the blades and / or doors may be adjusted. As an example, in response to an increase in the demand for heating the cabin 4, the controller may increase each of the fan speed of the climate control system 94 and the opening of the blades (such as a blending door at the inlet of the heater core) to allow a higher amount of warm air to flow from the heater core 90 to the cabin 4. Similarly, in response to a decrease in the demand for heating the cabin 4, the controller may reduce the opening of the blades of the climate control system 94 to reduce the flow of warm air from the heater core 90 to the cabin 4.

[0051] In this way, Figure 1A to Figure 1B , Figure 2A system for a vehicle is implemented, comprising: an engine; a vehicle cabin, an engine intake manifold, an engine exhaust system comprising an exhaust passage and a bypass passage, the exhaust passage comprising one or more exhaust catalysts and a muffler, the bypass passage being coupled to the exhaust passage from downstream of the one or more exhaust catalysts to upstream of the muffler, the bypass passage comprising a heat exchanger, a diverter valve coupling an inlet of the bypass passage to the exhaust passage, a diverter valve position sensor coupled to the diverter valve, a coolant system having an incoming coolant line and an outgoing coolant line for circulating coolant through the heat exchanger, the coolant system being further coupled to an engine block and each of a heater core of a heating, ventilation and air conditioning (HVAC) system, the incoming coolant line comprising a first coolant temperature sensor for estimating a coolant temperature upstream of the heat exchanger, the outgoing coolant line comprising a second coolant temperature sensor for estimating a coolant temperature downstream of the heat exchanger. The vehicle system further includes a controller having computer-readable instructions stored on a non-volatile memory for performing the following operations when operating in a first mode: shifting the diverter valve to a first position to operate the exhaust system in a first mode in which exhaust flows from downstream of the exhaust catalyst to upstream of the muffler via a heat exchanger; and measuring a coolant temperature upstream of the heat exchanger via a first temperature sensor, indicating degradation of the first coolant temperature sensor in response to a difference above a threshold between a modeled coolant temperature upstream of the heat exchanger and a measured coolant temperature upstream of the heat exchanger, and in response to the degradation indication, estimating the coolant temperature upstream of the heat exchanger using the modeled temperature.

[0052] Figure 5 An example method 500 is shown that may be used to diagnose an exhaust gas heat recovery (EGHR) system such as Figure 1A to Figure 1B An example method implemented by a component of an EGHR system 150) including a diverter valve (such as a EGHR system 150) coupled to a junction of a main exhaust passage and an exhaust bypass passage accommodating a heat exchanger. Figure 1A to Figure 1B diverter valve 175), and a heat exchanger (such as Figure 1A to Figure 1B heat exchanger 176). The controller may be based on instructions stored in the controller's memory and in conjunction with sensors from the engine system (such as reference Figure 1A to Figure 1B The controller may use engine actuators of the engine system to adjust engine operation according to the methods described below.

[0053] At 502, the routine includes estimating and / or measuring engine operating conditions. For example, the conditions evaluated may include engine temperature, engine load, driver torque demand, engine speed, throttle position, exhaust pressure, exhaust air fuel ratio, ambient conditions (including ambient temperature, pressure and humidity), MAP, MAF, boost, etc. The controller may also determine the current cabin heating demand such as whether the operator has requested cabin heating during lower ambient temperature conditions. The operator may request cabin heating via input to a switch of a vehicle climate control system that is coupled to the cabin and a heater core of a heating, ventilation and air conditioning (HVAC) system.

[0054] At 504, the controller may select an operating mode for the EGHR system based on the determined engine operating conditions and cabin heating requirements. Selecting the operating mode includes determining whether engine heating is required and / or whether cabin heating has been requested based on engine temperature, ambient temperature, and / or exhaust catalyst temperature. As an example, during conditions when the engine temperature is low (e.g., below the activation temperature of the exhaust catalyst), such as during an engine cold start condition, engine heating is desired. The heat exchange system may be operated in one of a plurality of modes by adjusting the position of a diverter valve coupled to a main exhaust passage and a bypass passage (such as a bypass passage) housing a heat exchanger. Figure 1A to Figure 1B The position of the diverter valve can be adjusted to obtain the desired engine coolant temperature and then maintain the desired coolant temperature. In one example, when the temperature of the coolant leaving the heat exchanger is as measured by a coolant temperature sensor (such as a coolant temperature sensor) coupled to the coolant outlet downstream of the heat exchanger, Figure 1A to Figure 1B When the temperature of the coolant entering the heat exchanger is lower than the first threshold temperature estimated by the second coolant temperature sensor 182 of the heat exchanger, exhaust heat recovery for engine heating may be desired. The first threshold may correspond to the engine warm-up temperature, and the first threshold may be calibrated based on the activation temperature of the exhaust catalyst during engine operation. In another example, when the temperature of the coolant entering the heat exchanger is as measured by a coolant temperature sensor (such as a coolant temperature sensor) coupled to the coolant inlet upstream of the heat exchanger, the exhaust heat recovery for engine heating may be desired. Figure 1A to Figure 1BWhen the exhaust heat recovery for cabin heating is expected when the first coolant temperature sensor 180) estimates that the exhaust heat recovery for cabin heating is lower than the second threshold coolant temperature. The second threshold coolant temperature can be calibrated based on each of the actual cabin temperature as estimated via the cabin temperature sensor and the desired cabin temperature as specified by the operator. In this way, the operating mode of the EGHR system can be selected based on input from at least one of the first coolant temperature sensor coupled upstream of the heat exchanger and the second coolant temperature sensor coupled downstream of the heat exchanger. As described herein, such methods including determining whether a certain condition occurs and performing an action in response to the condition can include operating in the condition, and determining whether the condition occurs and performing an action in response to the condition, and operating when the condition does not occur, determining that the condition does not occur and performing a different action in response to the condition not occurring.

[0055] At 506, the routine includes determining whether an exhaust heat recovery mode (first mode) has been selected. During cold start conditions when exhaust heat recovery for engine and cabin heating is desired, the exhaust heat exchange system may be operated in the first mode. Thus, exhaust heat recovery for engine heating may be desired until the coolant temperature downstream of the heat exchanger reaches the first coolant temperature, and exhaust heat recovery for cabin heating may be desired until the coolant temperature upstream of the heat exchanger reaches the second coolant temperature. In order to operate in the first exhaust heat recovery mode (as described with respect to FIG. 1 ), the exhaust heat recovery system may be operated in the first mode. Figure 1AIn the embodiment of the present invention, when operating the EGHR system as discussed above, the controller can send a signal to the diverter valve to actuate the diverter valve to a first open position, thereby enabling the entire volume of the exhaust gas to flow from the main exhaust passage to the tail pipe via the bypass passage accommodating the heat exchanger. In the exhaust heat recovery mode, based on the engine heating and cabin heating requirements, the diverter valve can be partially opened to allow a portion of the exhaust gas to enter the bypass passage and flow via the heat exchanger, while the remaining portion of the exhaust gas can bypass the heat exchanger and be directly transmitted from the exhaust catalyst to the tail pipe. In one example, if the difference between the first threshold coolant temperature and the coolant temperature downstream of the heat exchanger increases, the opening of the diverter valve can be increased to allow an increased amount of exhaust gas to flow via the heat exchanger, thereby increasing the exhaust heat recovery for engine heating. In another example, if the difference between the first threshold coolant temperature and the coolant temperature downstream of the heat exchanger decreases, the opening of the diverter valve can be reduced to allow a reduced amount of exhaust gas to flow via the heat exchanger, thereby reducing the exhaust heat recovery for engine heating. Similarly, if the difference between the second threshold coolant temperature and the coolant temperature upstream of the heat exchanger increases, the opening of the diverter valve can be increased to allow an increased amount of exhaust gas to flow through the heat exchanger, thereby increasing exhaust heat recovery for cabin heating, and if the difference between the second threshold coolant temperature and the coolant temperature upstream of the heat exchanger decreases, the opening of the diverter valve can be decreased to allow a reduced amount of exhaust gas to flow through the heat exchanger, thereby reducing exhaust heat recovery for cabin heating.

[0056] If it is determined that a heat recovery mode has been selected for operation of the EGHR system, then at 510, the routine includes determining whether the diverter valve is in a commanded position. Since the first operating mode is selected for the EGHR system, the commanded position may be a first open position. The actual position of the diverter valve may be based on information from a diverter valve position sensor such as Figure 1A to Figure 1B The actual position of the diverter valve may be compared to a commanded position, such as a first position. In one example, during operation in a heat recovery mode, the diverter valve may be commanded to a partially open position to allow a portion of the exhaust gas to enter the bypass passage. During such a condition, the controller may determine whether the actual position of the diverter valve is the same as the commanded partially open position.

[0057] If it is determined that the diverter valve is not in a commanded position, such as in the case where the diverter valve is stuck in a closed position or a partially open position different from the commanded position, then at 512, a diagnostic code indicating that the diverter valve has degraded can be set. Due to the degradation of the diverter valve, the opening of the diverter valve cannot be adjusted to allow at least a portion of the exhaust to flow through the heat exchanger. In response to detecting degradation of the diverter valve, at 508, the EGHR system can be operated in a bypass mode, wherein the diverter valve is actuated to a second fully closed position. In the fully closed position, exhaust gas cannot enter the bypass passage that houses the heat exchanger and can flow directly from downstream of the exhaust catalyst to the tailpipe. In one example, during operation of the EGHR system in the second bypass mode, the coolant temperature sensor cannot be diagnosed because the exhaust does not flow through the heat exchanger. In another example, even during EGHR operation in the second bypass mode, each of the first coolant temperature sensor (located upstream of the heat exchanger) and the second coolant temperature sensor (located downstream of the heat exchanger) can be diagnosed. Diagnostic details of the first coolant temperature sensor are as follows Figure 6 The second coolant temperature sensor diagnostic details are discussed below. Figure 7 Discuss.

[0058] If it is determined at 506 that a heat recovery mode is not selected for operation of the EGHR system, it can be inferred that exhaust heat recovery at the heat exchanger is no longer desired due to lower engine heating and / or cabin heating demands. In one example, exhaust heat recovery for engine heating may no longer be desired when the temperature of the coolant leaving the heat exchanger is higher than a first threshold temperature as estimated via a coolant temperature sensor coupled to a coolant outlet downstream of the heat exchanger. In another example, exhaust heat recovery for cabin heating may no longer be desired when the temperature of the coolant entering the heat exchanger is higher than a second threshold coolant temperature as estimated via a coolant temperature sensor coupled to a coolant inlet upstream of the heat exchanger. Therefore, the routine can proceed to 508 to operate the EGHR system in a bypass mode.

[0059] If it is determined that the system is not operating in the exhaust heat recovery mode, then at 506, it can be inferred that the EGHR system is operating in the bypass mode (second mode). The EGHR system can operate in the bypass mode when engine heating and / or cabin heating is no longer required. In the second bypass mode (as described in relation to FIG. Figure 1B As discussed above, the exhaust heat exchange system is operated with the diverter valve commanded to the second closed position so that the exhaust gas cannot enter the bypass passage from the main exhaust passage. In the bypass mode, since the exhaust gas does not flow through the heat exchanger, heat cannot be transferred from the exhaust gas to the coolant flowing through the heat exchanger.

[0060] In one example, when the EGHR system is operated in bypass mode, the diverter valve may be diagnosed based on input from a diverter valve position sensor. In bypass mode, the controller may command the diverter valve to be actuated to a fully closed position. If it is determined that the actual position of the diverter valve (determined based on input from the diverter valve position sensor) is different from the commanded fully closed position, it may be inferred that the diverter valve is stuck in a partially open position or a fully open position, and a diagnostic code indicating degradation of the diverter valve may be set.

[0061] If at 510, it is confirmed that the diverter valve is in the commanded first open position, then at 514, it can be confirmed that the diverter valve is not degraded and diagnosis of the heat exchanger can be started. At 516, the controller can estimate the expected difference in coolant temperature between the upstream and downstream of the heat exchanger. When the coolant flows through the heat exchanger, the exhaust heat is transferred to the coolant, which causes the coolant temperature to rise. The difference in coolant temperature between the upstream and downstream of the heat exchanger can be a function of the diverter valve position, the coolant flow rate, the exhaust flow rate, and the ambient temperature. When the diverter valve is actuated from a closed position (such as in a first mode) to an open position (such as in a heat recovery mode), the portion of the total exhaust gas volume that flows through the heat exchanger can be adjusted. Therefore, when the total exhaust gas volume and the opening of the diverter valve increase, there can be a corresponding increase in the exhaust gas flow rate through the heat exchanger. In one example, a controller can determine the exhaust flow rate through a heat exchanger based on a calculation using a lookup table, wherein the inputs to the lookup table are the total exhaust volume (the total exhaust flow rate through the main exhaust passage) and the position (degree of opening) of the diverter valve, and the output of the lookup table is the exhaust flow rate through the heat exchanger. The total exhaust volume (the total exhaust flow rate through the main exhaust passage) can be determined based on input from an exhaust pressure sensor coupled to the main exhaust passage, and the diverter valve position can be determined based on input from a diverter valve position sensor coupled to the diverter valve. The total exhaust volume can also be inferred from engine speed, load, ignition timing, and EGR. The coolant flow rate can be determined based on an auxiliary pump (such as a throttle) coupled to the coolant inlet line. Figure 1A to Figure 1B Auxiliary pump 81 in ) or an engine driven coolant pump (such as Figure 2 The controller may determine the expected difference in coolant temperature between upstream and downstream of the heat exchanger based on calculations using a lookup table, wherein the inputs to the lookup table are the ambient temperature, the coolant flow rate, the exhaust temperature at the inlet of the heat exchanger, and the exhaust flow rate through the heat exchanger, and the output of the lookup table is the difference in coolant temperature between upstream and downstream of the heat exchanger.

[0062] At 518 , the difference in coolant temperature between the upstream and downstream sides of the heat exchanger may be based on a first coolant temperature sensor (such as a first coolant temperature sensor) coupled to the coolant inlet line upstream of the heat exchanger. Figure 1A to Figure 1B A first coolant temperature sensor 180 of the heat exchanger and a second coolant temperature sensor (such as Figure 1A to Figure 1B The controller may retrieve a temperature estimate from each of the first coolant temperature sensor and the second coolant temperature sensor and estimate a difference between the coolant temperature downstream of the heat exchanger and the coolant temperature upstream of the heat exchanger.

[0063] At 520, the routine includes determining whether the expected difference in coolant temperature between upstream and downstream of the heat exchanger is substantially equal to the estimated difference in coolant temperature between upstream and downstream of the heat exchanger. The controller may also determine whether the expected difference in coolant temperature is within a specific error range of the estimated difference in coolant temperature. In one example, if there is degradation of the heat exchanger, such as in the event that the heat exchanger is blocked, the exhaust flow through the heat exchanger may be adversely affected, resulting in less than expected exhaust heat transfer from the exhaust to the coolant. Therefore, due to degradation of the heat exchanger, the coolant temperature downstream of the heat exchanger may not increase as expected due to a lower amount of exhaust heat recovery.

[0064] If it is determined that the expected difference in coolant temperature between upstream and downstream of the heat exchanger is substantially different than the measured difference in coolant temperature between upstream and downstream of the heat exchanger (exceeds the error range), a diagnostic code indicating degradation of the heat exchanger may be set at 524. If it is determined that the heat exchanger is degraded, exhaust heat recovery may no longer be performed effectively, and the routine may proceed to step 508 to operate the EGHR system in bypass mode.

[0065] If it is determined that the expected difference in coolant temperature between the upstream and downstream of the heat exchanger is substantially equal to the measured difference in coolant temperature between the upstream and downstream of the heat exchanger (or within a certain error range), then at 522, it can be confirmed that the heat exchanger is not degraded and diagnosis of each of the first coolant temperature sensor upstream of the heat exchanger and the second coolant temperature sensor downstream of the heat exchanger can be initiated. Figure 6 The second coolant temperature sensor diagnostic details are discussed below. Figure 7 Give a description.

[0066] In this way, degradation of the heat exchanger is indicated by the temperature difference of the upstream and downstream coolant temperature sensors and correlating that temperature difference to the diverter valve position, and degradation of the diverter valve function may be indicated by the difference between the measured valve position and the commanded valve position.

[0067] Figure 6 A first coolant temperature sensor (such as a CT sensor) is shown that can be coupled to a coolant inlet line upstream of a heat exchanger of an exhaust gas heat recovery (EGHR) system for diagnostics. Figure 1A to Figure 1B The method 600 may be implemented as follows: Figure 5 A portion of method 500 is described and may be performed at 522 of method 500 .

[0068] At 602, diagnosis of a first coolant temperature sensor upstream of the heat exchanger may be initiated. Diagnosis may be performed when it is confirmed that the EGHR system is operating in an exhaust heat recovery mode, wherein the diverter valve is at least partially open to allow at least a portion of the exhaust gas to flow through the heat exchanger. In one example, when the EGHR system is transitioned from operating in a bypass mode to an exhaust heat recovery mode, the diagnosis may be triggered in response to a (calibratable) change in the position of the diverter valve that is greater than a threshold. Furthermore, the diagnosis may be initiated when it is confirmed that the engine is operating in a steady state, wherein stable engine operating conditions include engine speed and engine load. During transitions in engine operation, there may be frequent changes in engine operating conditions, which may affect the diagnostic routine.

[0069] At 603, diagnosing a first coolant temperature sensor upstream of the heat exchanger includes modeling a first coolant temperature (TU1) upstream of the heat exchanger using a first calculation method (referred to herein as Method 1). The modeled first coolant temperature as calculated using the first method may be based on heat loss sources and a vehicle cabin (such as Figure 2 The heat loss source may include a separate heat loss source such as a heater core of an onboard heating, ventilation, and air conditioning (HVAC) system (such as Figure 2 The EGHR system includes a heater core 90 in the engine and a coolant line of the coolant system that delivers coolant from the engine to the heater core and then to the heat exchanger of the EGHR system. By including the individual heat loss sources into a single heat loss source, the exchange characteristics of each individual heat loss source can be simplified into a single time constant that represents the entire system.

[0070] Figure 3An example schematic diagram 300 is shown of a modeling technique used to diagnose a coolant temperature sensor coupled upstream of an EGHR system heat exchanger. A heat loss source 302 can be fluidly coupled to a cabin 304 to enable air flow between the heat loss source 302 and the cabin 304. In one example, the heat loss source 302 can be fluidly coupled to ambient air, and heat transfer can occur between the heat loss source 302 and the ambient air. Coolant from the engine 10 can enter the heat loss source, and after flowing through the heat loss source, the coolant can exit the heat loss source and flow toward the heat exchanger of the EGHR system. In a first approach, a first coolant temperature upstream of the heat exchanger can be calculated using Equation 1:

[0071]

[0072] where TU1 is the first coolant temperature upstream of the heat exchanger as calculated by the first method, is the temperature of the air entering the heat exchanger (which may be ambient and / or a mixture of ambient and recirculated air from the climate control system), is the temperature of the coolant entering the heat loss source 302 from the engine, m air_1 is the air flow rate between the cabin 304 and the heat loss source 302, m coolant_1 is the mass coolant flow rate through the heat loss source 302 , and k_a is the calibratable time constant of the combined heat loss source 302 . The estimate may be made based on input from one or more of a cabin temperature sensor (when the climate control system is operating), an ambient temperature sensor, and an evaporator outlet temperature sensor (coupled to the evaporator housed in the coolant line upstream of the heater core), and may be used to estimate the temperature of the vehicle. Can be estimated based on input from the engine coolant temperature sensor. air_1 This estimate can be made based on the position of a blend door of a climate control system that allows air flow between the heat loss source 302 and the cabin, and m coolant_1 An engine driven pump (such as a Figure 2 In one example, the controller can determine m based on calculations using a lookup table. air_1 , where the inputs to the lookup table are the position of the blend door of the climate control system and the total mass air flow from the evaporator, and the output of the lookup table is m air_1 In another example, the controller may determine m based on calculations using a lookup table. coolant_1 , where the input to the lookup table is the speed of the coolant pump and the output is m coolant_1 .

[0073] At 604, diagnosing a first coolant temperature sensor upstream of the heat exchanger includes modeling a first coolant temperature (TU2) upstream of the heat exchanger using a second calculation method (referred to herein as Method 2). The modeled first coolant temperature as calculated using the second method can be based on heat transfer between a heat loss source and the cabin. The heat loss source can include separate heat loss sources such as a heater core of an HVAC system and a coolant line of a coolant system that delivers coolant from the engine to the heater core and then to a heat exchanger of the EGHR system. The separate heat loss sources can be combined into one heat loss source by calibrating the efficiency of heat transfer between the heat loss source 302 and the cabin 304.

[0074] In a second method, the first coolant temperature upstream of the heat exchanger can be calculated using Equation 2:

[0075]

[0076] where TU2 is the first coolant temperature upstream of the heat exchanger as calculated by the second method, is the temperature of the air leaving the cabin 304 and entering the heat loss source 302, is the temperature of the coolant entering the heat loss source 302 from the engine, C min is the specific heat capacity of air, C is the specific heat capacity of the coolant flowing through the heat loss source, and ε1 is the efficiency of heat transfer between the heat loss source 302 and the cabin 304. In one example, if the specific heat capacity of the coolant (C) is greater than the specific heat capacity of the air (C min ) is lower, then in equation 2, C min Can be replaced by C. The specific heat capacity (C) of the coolant can be a function of the mass coolant flow rate through the heat loss source as estimated based on the speed of the coolant system pump. The efficiency (ε1) of the heat transfer between the heat loss source 302 and the cabin 304 can be given by Equation 3:

[0077] ε1=k1m coolant_1 m air_1 +k2m coolant_1 2 +k3m air_1 2 +k4m coolant_1 +k5m air_1 +k6 Equation 3

[0078] Where ε1 is the efficiency of heat transfer between the heat loss source and the cabin, k1, k2, k3, k4, k5 and k6 are calibratable coefficients representing the combined efficiency of the system including the heat loss source and the cabin, and m air_1 is the mass air flow rate between the cabin 304 and the heat loss source 302, and mcoolant_1 is the mass coolant flow rate through the heat loss source 302 .

[0079] In this way, the heat transfer between the heat loss source and the cabin is a function of one or more of the mass air flow rate between the heat loss source and the cabin, the temperature of the coolant entering the heat loss source from the engine, the temperature of the air entering the heat loss source from the cabin, the temperature of the air entering the cabin from the heat loss source, and the heat transfer efficiency between the heat loss source and the cabin, the heat transfer efficiency between the heat loss source and the cabin being based on each of the mass air flow rate between the heat loss source and the cabin and the mass coolant flow rate through the heat loss source.

[0080] Once the first coolant temperature upstream of the heat exchanger is calculated using each of the two calculation models, at 606, the modeled coolant temperatures TU1 and TU2 can be optimized under multiple HVAC system operating conditions to obtain a steady-state coolant temperature upstream of the heat exchanger. TU1 and TU2 can be calculated for multiple HVAC system operating conditions, such as at different temperature settings for the cabin. Based on conditions such as ambient temperature, the operator can request different temperatures at the cabin. Based on the requested temperature and the setting of the fan coupled to the climate control system, the amount of heat transfer from the heat loss source (including the heater core) to the cabin can vary. The heat loss from the coolant flowing through the heat loss source can change based on the HVAC system operating conditions. In one example, during cold weather conditions, the operator can request a maximum heat supply to supply an increased amount of warm air to the cabin while increasing the fan speed, thereby increasing the mass air flow rate between the cabin and the heat loss source. In another example, after the cabin is warmed, the operator can reduce the fan speed to maintain a lower stable supply of warm air to the cabin, thereby reducing the mass air flow rate between the cabin and the heat loss source. In yet another example, during warm weather conditions, the operator may not request any heat supply to the cabin, thereby further reducing the mass air flow rate between the cabin and the heat loss source. A rolling average time filter may be applied to obtain an optimized steady state first coolant temperature upstream of the heat exchanger, the optimized first coolant temperature being given by Equation 4:

[0081] TU1(t)=rolledaverage(T01 ss (t), T01 ss (t-1), t c ) Equation 4

[0082] where TU1(t) is the modeled first coolant temperature as calculated using the first method at time t, T01 SS(t) is the first coolant temperature modeled at the steady state as calculated using the first method at time t, T01 SS (t-1) is the modeled first coolant temperature as calculated using the first method at time t-1, and t c is the time constant of the first-order low-pass filter for each of the modeled first coolant temperature at time t and the modeled first coolant temperature at time t-1. Equation 4 can also be used to obtain the optimized first coolant temperature (TU2) as calculated using the second method.

[0083] At 607, the coolant temperature upstream of the heat exchanger can be measured via a first coolant temperature sensor coupled to the coolant inlet line. At 608, a first residual between the measured coolant temperature upstream of the heat exchanger (TU_M) and the modeled first coolant temperature upstream of the heat exchanger can be estimated. At 609, the estimated residual includes estimating the error (Error_TU1) between the measured coolant temperature upstream of the heat exchanger (TU_M) and the modeled coolant temperature (TU1) as calculated using the first method using Equation 5:

[0084] Error_TU1=TU_M-TU1 Equation 5

[0085] Where Error_TU1 is a first error between the measured coolant temperature upstream of the heat exchanger and the modeled coolant temperature as calculated using the first method, TU_M is the measured coolant temperature upstream of the heat exchanger, and TU1 is the modeled coolant temperature upstream of the heat exchanger as calculated using the first method.

[0086] At 610 , estimating the residual further includes estimating the error ( Error_TU2 ) between the measured coolant temperature ( TU_M ) upstream of the heat exchanger and the modeled coolant temperature ( TU2 ) as calculated using the second method using Equation 6:

[0087] Error_TU2=TU_M-TU2 Equation 6

[0088] Where Error_TU2 is a second error between the measured coolant temperature upstream of the heat exchanger and the modeled coolant temperature as calculated using the second method, TU_M is the measured coolant temperature upstream of the heat exchanger, and TU2 is the modeled coolant temperature upstream of the heat exchanger as calculated using the second method.

[0089] At 612, the routine includes determining whether Error_TU1 and / or Error_TU2 are higher than a threshold. The threshold may include a tolerance band having an upper limit and a lower limit. In one example, the tolerance band may have a tolerance of ±5°F, such as an upper limit of the tolerance band may be +5°F relative to zero error, and a lower limit of the tolerance band may be -5°F.

[0090] If it is determined that Error_TU1 and / or Error_TU2 exceeds an upper limit of the tolerance band or falls below a lower limit of the tolerance band, then at 616 , degradation of a first coolant temperature sensor coupled to the coolant inlet line may be indicated.

[0091] In one example, whenever Error_TU1 and / or Error_TU2 exceed the upper limit of the tolerance band or fall below the lower limit of the tolerance band, the error is integrated with respect to time. The integrated error can be compared with a threshold error, and in response to the integrated error of the coolant temperature upstream of the heat exchanger exceeding the threshold error, the degradation of the first coolant temperature sensor coupled to the coolant inlet line can be indicated. In another example, the error Error_TU1 between the output of the first coolant temperature sensor upstream of the heat exchanger and the first modeled coolant temperature within a threshold time period can be accumulated. The accumulated error can be compared with the threshold error, and in response to the accumulated error of the coolant temperature upstream of the heat exchanger exceeding the threshold error, the degradation of the first coolant temperature sensor coupled to the coolant inlet line can be indicated. In yet another example, whenever Error_TU1 and / or Error_TU2 exceed the upper limit of the tolerance band or fall below the lower limit of the tolerance band, an increase can be added to the timer. The timer can be compared with the threshold time, and in response to the timer exceeding the threshold time, the degradation of the first coolant temperature sensor coupled to the coolant inlet line can be indicated.

[0092] When degradation of a first coolant temperature sensor coupled to a coolant inlet line upstream of a heat exchanger is indicated, until the first coolant temperature sensor has been serviced at 618, a modeled temperature upstream of the heat exchanger (TU1 or TU2) can be used for engine operation rather than relying on the output of the degraded first coolant temperature sensor upstream of the heat exchanger for estimating the temperature of the coolant entering the heat exchanger. In one example, based on the modeled temperature of the coolant entering the heat exchanger, a demand for engine heating and / or cabin heating can be estimated, and the position of the diverter valve can be actuated based on the estimated engine heating and / or cabin heating demand. Thus, if the modeled temperature of the coolant entering the heat exchanger is lower than a threshold, it can be inferred that engine heating and / or cabin heating is desired, and the diverter valve can be actuated to a fully open (first) position to enable the entire volume of exhaust gas to flow through the heat exchanger.

[0093] If it is determined that the modeled temperature upstream of the heat exchanger is substantially equal to the measured coolant temperature, or if Error_TU1 and / or Error_TU2 are within a threshold tolerance band, then at 614 , it can be inferred that the first coolant temperature sensor upstream of the heat exchanger is not degraded, and the output from the first coolant temperature sensor can continue to be used to estimate the temperature of the coolant entering the heat exchanger.

[0094] In one example, two methods for modeling the exhaust temperature upstream of a heat exchanger can be compared to determine which method provides a modeled coolant temperature upstream of the heat exchanger with greater accuracy. To compare a first modeling method with a second modeling method, a coolant temperature upstream of the heat exchanger (TU1) as modeled using the first method over a certain time period can be used to fit an actual (measured) coolant temperature upstream of the heat exchanger (fit_U_1) over the same time period. Similarly, a coolant temperature upstream of the heat exchanger (TU2) as modeled using the second method over a certain time period can be used to fit an actual (measured) coolant temperature upstream of the heat exchanger (fit_U_2) over the same time period. The quality of the fit (fit_U_1) including the residual between the modeled temperature (TU1) and the measured temperature can be compared to the quality of the fit_U_2 including the residual between the modeled temperature (TU2) and the measured temperature. If the residual of fit_U_1 is inferred to be lower than the residual of fit_U_2, it can be inferred that the coolant temperature (TU1) upstream of the heat exchanger as modeled using the first method can be more accurate than the coolant temperature (TU1) upstream of the heat exchanger as modeled using the second method. Similarly, if the residual of fit_U_2 is inferred to be lower than the residual of fit_U_1, it can be inferred that the coolant temperature (TU1) upstream of the heat exchanger as modeled using the second method can be more accurate than the coolant temperature (TU1) upstream of the heat exchanger as modeled using the first method.

[0095] At 620 , a second coolant temperature sensor coupled to the coolant outlet line downstream of the heat exchanger may be diagnosed based at least in part on the first modeled coolant temperature upstream of the heat exchanger. Diagnostic details of the second temperature sensor may be found in Figure 7 Discuss.

[0096] Figure 7 An example method 700 is shown that may be used to diagnose a second coolant temperature sensor (such as a second coolant temperature sensor) coupled to a coolant outlet line downstream of a heat exchanger of an exhaust gas heat recovery (EGHR) system. Figure 1A to Figure 1B The method 700 may be implemented as follows: Figure 5A portion of method 500 is described and may be performed at 522 of method 500 .

[0097] At 701, the modeled coolant temperature (TU) upstream of the heat exchanger can be retrieved. In one example, as shown in FIG. Figure 6 As described in method 600 of , based on a comparison of a modeled coolant temperature upstream of a heat exchanger calculated using each of the first method and the second method with a measured coolant temperature upstream of the heat exchanger, a calculation method with a higher accuracy may be determined. If it is determined that the accuracy of the modeled coolant temperature upstream of the heat exchanger calculated using the first method is higher than the accuracy of the modeled coolant temperature upstream of the heat exchanger calculated using the second method, the modeled coolant temperature upstream of the heat exchanger calculated using the first method may be retrieved and used to diagnose the second coolant temperature sensor. If it is determined that the accuracy of the modeled coolant temperature upstream of the heat exchanger calculated using the second method is higher than the accuracy of the modeled coolant temperature upstream of the heat exchanger calculated using the first method, the modeled coolant temperature upstream of the heat exchanger calculated using the second method may be retrieved and used to diagnose the second coolant temperature sensor.

[0098] At 702, a diagnostic of a second coolant temperature sensor downstream of the heat exchanger may be initiated. The diagnostic may be performed when it is confirmed that the EGHR system is operating in an exhaust heat recovery mode, wherein the diverter valve is at least partially open to allow at least a portion of the exhaust gas to flow through the heat exchanger. In one example, the diagnostic may be triggered in response to a (calibratable) change in position of the diverter valve above a threshold when the EGHR system is transitioning from operating in a bypass mode to an exhaust heat recovery mode. Furthermore, the diagnostic may be initiated when it is confirmed that the engine is operating in a steady state, wherein steady engine operating conditions include engine speed and engine load.

[0099] At 703, diagnosing the second coolant temperature sensor upstream of the heat exchanger includes modeling the second coolant temperature (TD1) downstream of the heat exchanger using a first calculation method (referred to herein as the first method). The modeled second coolant temperature as calculated using the first method may be based on the second coolant temperature of the exhaust gas bypass passage (such as the exhaust gas bypass passage). Figure 1A to Figure 1B The heat transfer between the exhaust gas flowing through the bypass passage 174 in the heat exchanger and the heat exchanger (including the coolant line of the coolant system that transports the coolant through the heat exchanger). By including the coolant line of the coolant system that transports the coolant through the heat exchanger and the heat exchanger as a single heat exchange source, the exchange characteristics of each individual heat loss source can be simplified to a single time constant representing the entire system.

[0100] Figure 4An example schematic diagram 400 is shown of a modeling technique used to diagnose a coolant temperature sensor coupled downstream of an EGHR system heat exchanger. The heat exchanger 402 and the coolant line passing through the heat exchanger may be fluidly coupled to an exhaust bypass passage 404 that enables air flow between the exhaust gas flowing through the exhaust bypass passage 404 and the heat exchanger 402. A heater core (such as a Figure 3 The coolant of the heat loss source 302 in the heat exchanger can enter the heat exchanger via the coolant inlet line, and after flowing through the heat exchanger, can leave via the coolant outlet line and flow toward the engine. In the first method, the second coolant temperature downstream of the heat exchanger can be calculated using Equation 7:

[0101]

[0102] where TD1 is the second coolant temperature downstream of the heat exchanger as calculated by the first method, T coolantin_2 is the temperature of the coolant entering the heat exchanger 402 from the heater core, is the temperature of the air leaving the exhaust bypass passage 404 and entering the heat exchanger 402, m air_2 is the mass air flow rate between the exhaust bypass passage 404 and the heat exchanger 402, m coolant_2 is the mass coolant flow rate through the heat exchanger 402, and k_b is a calibratable time constant of the heat exchanger and the coolant line through the heat exchanger. coolantin_2 The modeled first coolant temperature may be upstream of the heat exchanger (as retrieved in step 701 ). The estimate may be based on an exhaust flow model or based on input from an exhaust flow sensor coupled to the exhaust passage. In one example, It can be estimated based on input from the air conditioner (AC) evaporator temperature sensor. air_2 It can be estimated based on the position of the diverter valve and the total amount of exhaust gas flow through the main exhaust passage, and m coolant_2 The coolant system may be based on an engine driven coolant pump (such as a Figure 2 In one example, the controller can determine m based on calculations using a lookup table. air_2 , where the input to the lookup table is each of the position of the diverter valve and the total amount of exhaust gas flow through the main exhaust passage, and the output is m air_2 In another example, the controller may determine m based on calculations using a lookup table. coolant_2 , where the input to the lookup table is the speed of the coolant pump and the output is m coolant_2 In yet another example, mcoolant_2 The coolant inlet line may be coupled to an auxiliary pump such as Figure 1A to Figure 1B The output of the auxiliary pump 81) in coolant_2 As the output of the auxiliary pump increases, m coolant_2 Decreases as the output of the auxiliary pump decreases.

[0103] At 704, diagnosing a second coolant temperature sensor downstream of the heat exchanger includes modeling a second coolant temperature (TD2) downstream of the heat exchanger using a second calculation method (referred to herein as the second method). The modeled second coolant temperature as calculated using the second method may be based on heat transfer between the exhaust gas flowing through the exhaust bypass passage and the coolant flowing through the heat exchanger.

[0104] In a second method, the second coolant temperature downstream of the heat exchanger may be calculated using Equation 8:

[0105]

[0106] where TD2 is the second coolant temperature downstream of the heat exchanger as calculated by the second method, is the temperature of the air leaving the exhaust bypass passage 404 and entering the heat exchanger 402, T coolantin_2 The modeled first coolant temperature upstream of the heat exchanger (as retrieved in step 701), C min is the specific heat capacity of the exhaust gas, C is the specific heat capacity of the coolant flowing through the heat exchanger, and ε2 is the efficiency of heat transfer between the exhaust bypass passage 404 and the heat exchanger 402. In one example, if the specific heat capacity of the coolant (C) is greater than the specific heat capacity of the exhaust gas (C min ) is lower, then in equation 8, C min can be replaced by C. The efficiency (ε2) of heat transfer between the exhaust bypass channel and the heat exchanger can be given by Equation 9:

[0107] ε2=c1m coolant_2 m air_2 +c2m coolant_2 2 +c3m air_2 2 +c4m coolant_2 +c5m air_2 +c6

[0108] Equation 9

[0109] Where ε2 is the efficiency of heat transfer between the exhaust bypass passage and the heat exchanger, c1, c2, c3, c4, c5 and c6 are calibratable coefficients representing the combined efficiency of the EGHR system including the heat exchanger, the coolant line through the heat exchanger and the exhaust bypass passage, mair_2 is the mass exhaust flow rate through the heat exchanger 402, m coolant_2 is the mass coolant flow rate through the heat exchanger 402 .

[0110] In this manner, heat transfer between the exhaust gas and the coolant in the heat exchanger is a function of one or more of a mass exhaust gas flow rate through the heat exchanger, a temperature of the coolant entering the heat exchanger, a temperature of the air entering the heat exchanger from the exhaust gas, a temperature of the air entering the exhaust gas from the heat exchanger, and a heat transfer efficiency between the exhaust gas and the coolant flowing through the heat exchanger, the heat transfer efficiency between the exhaust gas and the coolant flowing through the heat exchanger being based on each of the mass air flow rate between the exhaust gas and the mass coolant flow rate through the heat exchanger.

[0111] At 705, the coolant temperature (TD_M) downstream of the heat exchanger can be measured via a second coolant temperature sensor coupled to the coolant outlet line. At 706, a first residual between the measured coolant temperature (TD_M) downstream of the heat exchanger and the modeled second coolant temperature downstream of the heat exchanger can be estimated. At 707, the estimated residual includes an error (Error_TD1) between the measured coolant temperature (TD_M) downstream of the heat exchanger estimated using Equation 10 and the modeled coolant temperature (TD1) as calculated using the first method.

[0112] Error_TD1=TD_M-TD1 Equation 10

[0113] Where Error_TD1 is a first error between the measured coolant temperature downstream of the heat exchanger and the modeled coolant temperature as calculated using the first method, TD_M is the measured coolant temperature downstream of the heat exchanger, and TD1 is the modeled coolant temperature downstream of the heat exchanger as calculated using the first method.

[0114] At 708 , the estimated residual further includes estimating the error ( Error_TD2 ) between the measured coolant temperature ( TD_M ) downstream of the heat exchanger using Eq. 11 and the modeled coolant temperature ( TD2 ) as calculated using the second method.

[0115] Error_TD2 = TD_M - TD2 Equation 11

[0116] Wherein Error_TD2 is the second error between the measured coolant temperature downstream of the heat exchanger and the modeled coolant temperature as calculated using the second method, TD_M is the measured coolant temperature downstream of the heat exchanger, and TD2 is the modeled coolant temperature downstream of the heat exchanger as calculated using the second method.

[0117] At 710, the routine includes determining whether Error_TD1 and / or Error_TD2 are higher than a threshold. The threshold may include a tolerance band having an upper limit and a lower limit. In one example, the tolerance band may have a tolerance of ±5°F, such as an upper limit of the tolerance band may be +5°F relative to zero error, and a lower limit of the tolerance band may be -5°F.

[0118] If it is determined that Error_TD1 and / or Error_TD2 exceeds the upper limit of the tolerance band or is below the lower limit of the tolerance band, then at 714 , degradation of a second coolant temperature sensor coupled to the coolant outlet line may be indicated.

[0119] In one example, whenever Error_TD1 and / or Error_TD2 exceed the upper limit of the tolerance band or fall below the lower limit of the tolerance band, the error is integrated with respect to time. The integrated error can be compared with a threshold error, and in response to the integrated error of the coolant temperature downstream of the heat exchanger exceeding the threshold error, the degradation of the second coolant temperature sensor coupled to the coolant outlet line can be indicated. In another example, the error Error_TD1 between the output of the second coolant temperature sensor downstream of the heat exchanger and the first modeled coolant temperature within a threshold time period can be accumulated. The accumulated error can be compared with the threshold error, and in response to the accumulated error of the coolant temperature downstream of the heat exchanger exceeding the threshold error, the degradation of the second coolant temperature sensor coupled to the coolant outlet line can be indicated. In yet another example, whenever Error_TD1 and / or Error_TD2 exceed the upper limit of the tolerance band or the lower limit of the tolerance band, an increase can be added to the timer. The timer can be compared with the threshold time, and in response to the timer exceeding the threshold time, the degradation of the second coolant temperature sensor coupled to the coolant outlet line can be indicated.

[0120] When degradation of a second coolant temperature sensor coupled to the coolant inlet line upstream of the heat exchanger is indicated, until the second coolant temperature sensor has been serviced at 716, the modeled temperature (TD1 or TD2) downstream of the heat exchanger can be used for engine operation rather than relying on the degraded second coolant temperature sensor downstream of the heat exchanger for estimating the temperature of the coolant leaving the heat exchanger. Thus, exhaust heat recovery can be continued until the coolant temperature downstream of the heat exchanger reaches a desired coolant temperature (such as a coolant temperature corresponding to a warm engine). The position of the diverter valve can be actuated based on the modeled temperature (TD1 or TD2) downstream of the heat exchanger. In one example, if the difference between the desired coolant temperature and the coolant temperature downstream of the heat exchanger increases, the opening of the diverter valve can be increased to allow an increased amount of exhaust gas to flow through the heat exchanger, thereby increasing exhaust heat recovery. In another example, if the difference between the desired coolant temperature and the coolant temperature downstream of the heat exchanger decreases, the opening of the diverter valve can be reduced to allow a reduced amount of exhaust gas to flow through the heat exchanger, thereby reducing exhaust heat recovery.

[0121] If it is determined that the modeled temperature downstream of the heat exchanger is substantially equal to the measured coolant temperature downstream of the heat exchanger, or if Error_TD1 and / or Error_TD2 are within a threshold tolerance band, then at 712 , it can be inferred that the second coolant temperature sensor downstream of the heat exchanger is not degraded, and the output from the second coolant temperature sensor can continue to be used to estimate the temperature of the coolant exiting the heat exchanger.

[0122] In one example, two methods for modeling the exhaust temperature downstream of a heat exchanger can be compared to determine which of the two methods provides a modeled coolant temperature downstream of the heat exchanger with greater accuracy. To compare a first modeling method with a second modeling method, a coolant temperature downstream of the heat exchanger (TD1) as modeled using the first method over a certain time period can be used to fit an actual (measured) coolant temperature downstream of the heat exchanger (fit_D_1) over the same time period. Similarly, a coolant temperature downstream of the heat exchanger (TD2) as modeled using the second method over a certain time period can be used to fit an actual (measured) coolant temperature upstream of the heat exchanger (fit_D_2) over the same time period. The quality of fit_D_1, which includes the residual between the modeled temperature (TD1) and the measured temperature, can be compared to the quality of fit_D_2, which includes the residual between the modeled temperature (TD2) and the measured temperature. If the residual of fit_D_1 is inferred to be lower than the residual of fit_D_2, it can be inferred that the coolant temperature (TD1) downstream of the heat exchanger as modeled using the first method can be more accurate than the coolant temperature (TD2) downstream of the heat exchanger as modeled using the second method. Similarly, if the residual of fit_D_2 is inferred to be lower than the residual of fit_U_1, it can be inferred that the coolant temperature (TD2) downstream of the heat exchanger as modeled using the second method can be more accurate than the coolant temperature (TD1) downstream of the heat exchanger as modeled using the first method.

[0123] In this way, during exhaust gas flow from a vehicle engine to a tailpipe via a heat exchanger having coolant flowing therethrough, degradation of one or more of the first coolant temperature sensor and the second coolant temperature sensor may be indicated in response to a difference above a threshold between an output of a first coolant temperature sensor located upstream of the heat exchanger and a first modeled coolant temperature based in part on heat transfer between a heat loss source and a vehicle cabin, and in response to a difference above a threshold between an output of a second coolant temperature sensor located downstream of the heat exchanger and a second modeled coolant temperature based in part on the first modeled coolant temperature. As an example, one or more of the first coolant temperature sensor upstream of the heat exchanger and the second coolant temperature sensor downstream of the heat exchanger may be removed, and as based on Figure 6 to Figure 7 The coolant temperature modeled by the method discussed in can be used for engine operation (rather than sensed temperature), thereby reducing engine components and associated costs. Figure 8An example operational sequence 800 is shown that illustrates diagnosing a coolant temperature sensor coupled to an exhaust gas heat recovery (EGHR) system. The horizontal line (x-axis) represents time, and vertical markers t1 through t3 identify significant moments in diagnosing the coolant temperature sensor of the EGHR system.

[0124] A first curve 802 shows the change of cabin temperature over time. A dashed line 803 shows a threshold cabin temperature below which an operator can request cabin heating. A second curve 804 shows the position of a diverter valve coupled to the junction of the main exhaust passage and the exhaust bypass passage, which regulates the exhaust flow from the main exhaust passage to the heat exchanger housed in the exhaust bypass passage. A third curve 806 shows a first modeled temperature upstream of the heat exchanger as calculated using equation 1. A dashed line 805 shows a first measured coolant temperature upstream of the heat exchanger as estimated based on input from a first coolant temperature sensor coupled to the coolant inlet line upstream of the heat exchanger. A fourth curve 808 shows the difference (error_TU1) between the measured coolant temperature upstream of the heat exchanger (as given by dashed line 805) and the first modeled temperature upstream of the heat exchanger (as given by line 806). A dashed line 807 shows an upper limit of a threshold error range, above which it can be inferred that the first temperature sensor coupled to the upstream of the heat exchanger is degraded. The dashed line 809 shows the lower limit of the threshold error range, below which it can be inferred that the first temperature sensor coupled to the upstream of the heat exchanger is degraded. The fifth curve 810 shows the second modeled temperature downstream of the heat exchanger as calculated using equation 7. The dashed line 811 shows the second measured coolant temperature downstream of the heat exchanger as estimated based on the input from the second coolant temperature sensor coupled to the coolant outlet line downstream of the heat exchanger. The sixth curve 812 shows the difference (error_TD1) between the measured coolant temperature downstream of the heat exchanger (as given by the dashed line 811) and the second modeled temperature downstream of the heat exchanger (as given by line 812). The dashed line 813 shows the upper limit of the threshold error range, above which it can be inferred that the second temperature sensor coupled to the downstream of the heat exchanger is degraded. The dashed line 814 shows the lower limit of the threshold error range, below which it can be inferred that the second temperature sensor coupled to the downstream of the heat exchanger is degraded. A seventh curve 816 illustrates the position of a diagnostic marker indicating the health of a first coolant temperature sensor coupled upstream of the heat exchanger, and a dashed line 818 illustrates the position of a diagnostic marker indicating the health of a second coolant temperature sensor coupled downstream of the heat exchanger.

[0125] Prior to time t1, the cabin temperature is higher than threshold 803 and cabin heating is not requested. The diverter valve is maintained in the second closed position to prevent exhaust gas flow from flowing from the main exhaust passage to the heat exchanger via the diverter valve, thereby operating the EGHR system in bypass mode. Because the EGHR system is operated in bypass mode, exhaust heat is not recovered by the heat exchanger, and there is no appreciable difference in coolant temperature upstream and downstream of the heat exchanger. Because exhaust heat recovery is not performed during EGHR operation in bypass mode, diagnosis of the coolant temperature sensor cannot be performed prior to time t1.

[0126] At time t1, the cabin temperature decreases below a threshold value due to the vehicle traveling through an area with a cooler ambient temperature. In response to the decrease in cabin temperature, exhaust heat recovery is requested and the EGHR system is switched from operating in the bypass mode to operating in the exhaust heat recovery mode. To operate the EGHR system in the exhaust heat recovery mode, the diverter valve is actuated from a fully closed position to a fully open first position to enable exhaust gas to flow from the main exhaust passage to the heat exchanger via the diverter valve.

[0127] As the exhaust gas flows through the heat exchanger, the exhaust heat is transferred from the exhaust gas to the coolant flowing through the heat exchanger. The coolant with the exhaust heat then flows through the heater core of the vehicle heating, ventilation and air conditioning (HVAC) system via the engine, and at the heater core, the heat from the exhaust gas is transferred to the cabin, thereby increasing the cabin heat. After flowing through the heater core, the coolant returns to the heat exchanger of the EGHR system via the coolant inlet line. During operation of the EGHR system in exhaust heat recovery mode, at time t1, diagnosis of each of the first coolant temperature sensor coupled to the coolant inlet line upstream of the heat exchanger and the second coolant temperature sensor coupled to the coolant outlet line downstream of the heat exchanger is started. Between t1 and t2, a modeled coolant temperature (TU1) upstream of the heat exchanger is calculated based on the heat transfer between the heater core and the cabin. Moreover, during this time, a modeled coolant temperature (TD1) downstream of the heat exchanger is calculated based on the heat transfer from the exhaust gas flowing through the exhaust bypass passage and the coolant flowing through the heat exchanger.

[0128] Between time t1 and time t2, each of the temperature upstream of the heat exchanger and the temperature downstream of the heat exchanger is measured via the first coolant temperature sensor and the second coolant temperature sensor, respectively. The difference 808 (error_TU1) between the measured coolant temperature upstream of the heat exchanger and TU1 is compared with each of the upper limit 807 and the lower limit 809 of the threshold error range to detect any degradation of the first coolant temperature sensor. Between t1 and t2, error_TU1 remains within the threshold error range, and the mark indicating degradation of the first coolant temperature sensor remains in the closed position. The difference 812 (error_TD1) between the measured coolant temperature downstream of the heat exchanger and TU1 is compared with each of the upper limit 813 and the lower limit 814 of the threshold error range to detect any degradation of the second coolant temperature sensor. Between t1 and t2, error_TD1 remains within the threshold error range, and the mark indicating degradation of the second coolant temperature sensor is maintained in the closed position. Once the exhaust heat is supplied to the cabin, a steady increase in cabin temperature is observed.

[0129] At time t2, based on error_TU1 808 decreasing below the lower limit 809 of the threshold error range, it is inferred that there is a difference above the threshold between the measured coolant temperature upstream of the heat exchanger and the modeled coolant temperature upstream of the heat exchanger. Based on error_TU1 being above the threshold, at time t2, degradation of the first coolant temperature sensor is inferred, and a flag (diagnostic code) 816 indicating degradation of the first coolant temperature sensor is set. In response to degradation of the first coolant temperature sensor, after time t2, the coolant temperature upstream of the heat exchanger is inferred based on the modeled coolant temperature TU1, and coolant temperature measurement based on input from the first coolant temperature sensor is suspended until the first coolant temperature sensor is repaired. Between t2 and t3, error_TD1 remains within the threshold error range, and the flag indicating degradation of the second coolant temperature sensor is maintained in the off position.

[0130] At time t3, based on error_TD1 812 increasing above the upper limit 813 of the threshold error range, it is inferred that there is a difference above the threshold between the measured coolant temperature downstream of the heat exchanger and the modeled coolant temperature downstream of the heat exchanger. Based on error_TD1 being above the threshold, at t3, degradation of the second coolant temperature sensor is inferred, and a flag (diagnostic code) 818 indicating degradation of the second coolant temperature sensor is set. In response to degradation of the second coolant temperature sensor, after time t3, the coolant temperature downstream of the heat exchanger is inferred based on the modeled coolant temperature TD1, and coolant temperature measurement based on input from the second coolant temperature sensor is suspended until the second coolant temperature sensor is repaired.

[0131] In this manner, by opportunistically monitoring the health of EGHR system components (including coolant temperature sensors, diverter valves, and heat exchangers) during different operating modes of the EGHR system, degradation of individual components can be detected and appropriate mitigating actions can be taken. A technical effect of using different mathematical models to calculate coolant temperatures upstream and downstream of a heat exchanger of an EGHR system is that degradation of a first coolant temperature sensor upstream of the heat exchanger can be distinguished from degradation of a second coolant temperature sensor downstream of the heat exchanger. By optimizing the modeled coolant temperature upstream of the heat exchanger under a variety of HVAC system operating conditions, an accurate steady-state coolant temperature can be obtained.

[0132] An example method includes: during exhaust gas flow from a vehicle engine through a heat exchanger having coolant flowing therethrough, in response to a difference above a threshold between a measured coolant temperature and a modeled coolant temperature based on heat transfer between a heat loss source and a vehicle cabin, indicating degradation of one or more of a first coolant temperature sensor and a second coolant temperature sensor coupled upstream and downstream of the heat exchanger, respectively. In any of the foregoing examples, additionally or optionally, wherein the heat loss source includes a heater core and a plurality of coolant lines of an onboard heating, ventilation, and air conditioning (HVAC) system. In any or all of the foregoing examples, additionally or optionally, the measured coolant temperature includes a first measured coolant temperature upstream of the heat exchanger based on input from a first coolant temperature sensor coupled to a coolant line entering the heat exchanger, the modeled coolant temperature includes a first modeled coolant temperature upstream of the heat exchanger, and indicating degradation of the first coolant temperature sensor coupled upstream of the heat exchanger is based on a difference above a threshold between the first measured coolant temperature upstream of the heat exchanger and the first modeled coolant temperature upstream of the heat exchanger, the first modeled coolant temperature being calibrated for a plurality of cabin thermal settings. In any or all of the foregoing examples, additionally or optionally, wherein heat transfer between the heat loss source and the cabin is a function of one or more of a mass air flow rate between the heat loss source and the cabin, a temperature of coolant entering the heat loss source from the engine, a temperature of air entering the heat loss source from the cabin, a temperature of air entering the cabin from the heat loss source, and a heat transfer efficiency between the heat loss source and the cabin, the heat transfer efficiency between the heat loss source and the cabin being based on each of the mass air flow rate between the heat loss source and the cabin and the mass coolant flow rate through the heat loss source. In any or all of the foregoing examples, additionally or optionally, wherein the mass air flow rate between the heater core and the cabin is a function of a position of an air vent that allows air flow between the heater core and the cabin. In any or all of the foregoing examples, additionally or optionally, wherein the measured coolant temperature further includes a second measured coolant temperature downstream of the heat exchanger based on input from a second coolant temperature sensor coupled to a coolant line exiting the heat exchanger, the modeled coolant temperature further includes a second modeled coolant temperature downstream of the heat exchanger, and degradation of the second coolant temperature sensor coupled downstream of the heat exchanger is indicated based on a difference above a threshold between the second measured coolant temperature downstream of the heat exchanger and the second modeled coolant temperature of the heat exchanger, wherein the second modeled coolant temperature downstream of the heat exchanger is based on each of the first modeled coolant temperature upstream of the heat exchanger and heat transfer between the exhaust and the heat exchanger.In any or all of the foregoing examples, additionally or optionally, wherein heat transfer between the exhaust gas and the coolant flowing through the heat exchanger is a function of one or more of an exhaust gas flow rate through the heat exchanger, a temperature of the coolant entering the heat exchanger, a temperature of the air entering the heat exchanger from the exhaust gas, a temperature of the air entering the exhaust gas from the heat exchanger, and a heat transfer efficiency between the exhaust gas and the coolant flowing through the heat exchanger, the heat transfer efficiency between the exhaust gas and the coolant flowing through the heat exchanger being based on each of a mass air flow rate between the exhaust gas and the coolant flowing through the heat exchanger and a mass coolant flow rate through the heat exchanger. In any or all of the foregoing examples, wherein the mass exhaust gas flow rate through the heat exchanger is additionally or optionally a function of each of a position of an exhaust diverter valve and a total exhaust gas flow rate through a main exhaust passage. Additionally or optionally, any or all of the foregoing examples further include using a first modeled coolant temperature for engine operation in response to indicating degradation of a first coolant temperature sensor, and using a second modeled coolant temperature for engine operation in response to indicating degradation of a second coolant temperature sensor. In any or all of the foregoing examples, additionally or optionally, wherein the heat exchanger is coupled to an exhaust bypass, the method further includes adjusting a position of an exhaust diverter valve coupled to a junction of the exhaust bypass and the main exhaust passage to regulate exhaust flow through the heat exchanger to maintain a desired engine coolant temperature of an engine coolant that is in thermal communication with coolant from the heat exchanger, the desired engine coolant temperature being based on each of an engine heating demand and a cabin heating demand. Additionally or optionally, any or all of the foregoing examples further include indicating degradation of the diverter valve in response to an actual position of the diverter valve as estimated based on input from a diverter valve position sensor being different from an expected position of the diverter valve, wherein the expected position of the diverter valve includes one of a first position that enables exhaust flow through the heat exchanger during an engine heating demand above a threshold and / or a cabin heating demand above a threshold, and a second position that disables exhaust flow through the heat exchanger during an engine heating demand below a threshold and a cabin heating demand below a threshold. Additionally or optionally, any or all of the foregoing examples further include indicating degradation of the heat exchanger in response to an expected temperature difference between coolant temperatures upstream and downstream of the heat exchanger being different from an actual temperature difference between coolant temperatures upstream and downstream of the heat exchanger, the expected temperature difference being based on an actual position of the diverter valve, each of a mass coolant flow rate through the heat exchanger, and an exhaust flow rate, and the actual difference being based on inputs from a first coolant temperature sensor and a second coolant temperature sensor.

[0133] Another example method includes, during exhaust gas flow from a vehicle engine to a tailpipe via a heat exchanger having coolant flowing therethrough, indicating degradation of one or more of a first coolant temperature sensor and a second coolant temperature sensor in response to a difference above a threshold between an output of a first coolant temperature sensor located upstream of the heat exchanger and a first modeled coolant temperature based in part on heat transfer between a heat loss source and a vehicle cabin, and in response to a difference above a threshold between an output of a second coolant temperature sensor located downstream of the heat exchanger and a second modeled coolant temperature based at least in part on the first modeled coolant temperature. In any of the foregoing examples, additionally or optionally, wherein the heat transfer between the heat loss source and the vehicle cabin is based on each of a rate of mass air flow between the heat loss source and ambient air and / or the vehicle cabin, a temperature of coolant entering the heat loss source from the engine, a temperature of air entering the heat loss source from the vehicle cabin, and a temperature of air entering the vehicle cabin from the heat loss source, the heat loss source comprising a heater core of an onboard heating, ventilation, and air conditioning (HVAC) system that receives coolant from the engine. In any of the foregoing examples, additionally or optionally, wherein the second modeled coolant temperature is further based on heat transfer between exhaust gas flowing through the heat exchanger and coolant flowing through the heat exchanger, the heat transfer between the exhaust gas and the coolant flowing through the heat exchanger being based on each of a rate of air flow between the exhaust gas and the heat exchanger, a temperature of the coolant entering the heat exchanger, a temperature of air entering the heat exchanger from the exhaust gas, and a temperature of air entering the exhaust gas from the heat exchanger. Additionally or optionally, any of the foregoing examples further include accumulating a first error between an output of a first coolant temperature sensor and the first modeled coolant temperature over a threshold time period, accumulating a second error between an output of a second coolant temperature sensor and the second modeled coolant temperature over a threshold time period, indicating degradation of the first sensor in response to the accumulated first error exceeding the threshold error, and indicating degradation of the second sensor in response to the accumulated second error exceeding the threshold error. In any of the foregoing examples, additionally or optionally, exhaust flow from the vehicle engine to the tailpipe via the heat exchanger includes exhaust flow from a main exhaust passage to the heat exchanger via a diverter valve coupled to a junction of the main exhaust passage and an exhaust bypass accommodating the heat exchanger, and coolant flow through the heat exchanger includes coolant flowing from the vehicle engine to the heat exchanger via a heater core.

[0134] In yet another example, a vehicle system includes: a vehicle system including: an engine, a vehicle cabin, an engine intake manifold, an engine exhaust system including an exhaust passage and a bypass passage, the exhaust passage including one or more exhaust catalysts and a muffler, the bypass passage coupled to the exhaust passage from downstream of the one or more exhaust catalysts to upstream of the muffler, the bypass passage including a heat exchanger; a diverter valve coupling an inlet of the bypass passage to the exhaust passage, a diverter valve position sensor coupled to the diverter valve, a coolant system having an incoming coolant line and an outgoing coolant line for circulating coolant through the heat exchanger, the coolant system further coupled to an engine block and each of a heater core of a heating, ventilation, and air conditioning (HVAC) system, the incoming coolant line including a coolant temperature sensor for estimating a coolant temperature upstream of the heat exchanger; a first coolant temperature sensor for measuring a temperature of the coolant downstream of the heat exchanger, the outgoing coolant line including a second coolant temperature sensor for estimating a coolant temperature downstream of the heat exchanger; and a controller having computer-readable instructions stored on a non-transitory memory, the instructions being used to perform the following operations when operating in a first mode: shifting the diverter valve to a first position to operate the exhaust system in a first mode, wherein exhaust flows from downstream of the exhaust catalyst to upstream of the muffler via the heat exchanger, and measuring the coolant temperature upstream of the heat exchanger via the first coolant temperature sensor, indicating degradation of the first coolant temperature sensor in response to a difference above a threshold between a modeled coolant temperature upstream of the heat exchanger and a measured coolant temperature upstream of the heat exchanger, and in response to the degradation indication, estimating the coolant temperature upstream of the heat exchanger using the modeled temperature. In any of the foregoing examples, additionally or optionally, wherein the controller includes further instructions that, when operating in the first mode, are to: measure a position of the diverter valve via a position sensor, measure a coolant temperature downstream of the heat exchanger via a second coolant temperature sensor, indicate degradation of the second coolant temperature sensor in response to a difference between a modeled coolant temperature downstream of the heat exchanger and the measured coolant temperature downstream of the heat exchanger being above a threshold, indicate degradation of the diverter valve in response to the position of the diverter valve being different than the first position, estimate the coolant temperature downstream of the heat exchanger using the modeled temperature in response to indicating degradation of the second coolant temperature sensor, and disable operation of the exhaust system in the first mode in response to indicating degradation of the diverter valve. In any or all of the foregoing examples, additionally or optionally, wherein the modeled coolant temperature upstream of the heat exchanger is based on one or more of air flow between the heater core and the cabin and coolant flow from the engine to the heater core, and wherein the modeled coolant temperature downstream of the heat exchanger is based on one or more of the modeled coolant temperature upstream of the heat exchanger, air flow between exhaust gas flowing through the heat exchanger and coolant flowing through the heat exchanger, and coolant flow from the heater core to the heat exchanger.

[0135] In a further representation, the vehicle is a hybrid vehicle system.

[0136] 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 can be stored as executable instructions in a non-temporary memory and can be performed by a control system including a controller in combination with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. Therefore, the various actions, operations, and / or functions shown can be performed in the order shown, in parallel, or omitted in some cases. Similarly, the order of processing is not necessary 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 actions, operations, and / or functions shown can be repeatedly performed according to the specific strategy used. Further, the described actions, operations, and / or functions can graphically represent the code in the non-temporary memory of a computer-readable storage medium to be programmed into the engine control system, wherein the described actions are performed by combining electronic controllers in a system including various engine hardware components to execute instructions.

[0137] It should be understood that the configurations and routines disclosed herein are exemplary in nature, as many variations are possible, and these specific embodiments should not be considered limiting. For example, the above techniques may 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.

[0138] The appended claims particularly point out certain combinations and subcombinations 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 subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal to, or different in scope from the original claims, are also deemed to be included in the subject matter of the present disclosure.

Claims

1. A method for coolant temperature sensor diagnosis, the method comprising: During exhaust gas flow from a vehicle engine through a heat exchanger having a coolant flowing therethrough, indicating degradation of a first coolant temperature sensor and / or a second coolant temperature sensor, respectively coupled upstream and downstream of the heat exchanger, in response to a difference between a measured coolant temperature and a modeled coolant temperature that is above a threshold, the modeled coolant temperature being based on heat transfer between a heat loss source and a vehicle cabin; Wherein the heat transfer between the heat loss source and the vehicle cabin is based on one or more of a mass air flow rate between the heat loss source and the vehicle cabin, and a temperature of air entering the vehicle cabin from the heat loss source. 2 . The method of claim 1 , wherein the heat loss sources include a heater core and a plurality of coolant lines of an onboard heating, ventilation, and air conditioning (HVAC) system.

3. The method of claim 1 , wherein the measured coolant temperature comprises a first measured coolant temperature upstream of the heat exchanger based on input from a first coolant temperature sensor coupled to a coolant line entering the heat exchanger, the modeled coolant temperature comprises a first modeled coolant temperature upstream of the heat exchanger, and indicating degradation of the first coolant temperature sensor coupled to the heat exchanger upstream is based on a difference above a threshold between the first measured coolant temperature upstream of the heat exchanger and the first modeled coolant temperature upstream of the heat exchanger, the first modeled coolant temperature being calibrated for a plurality of cabin thermal settings.

4. The method of claim 1 , wherein the heat transfer between the heat loss source and the cabin is further based on one or more of a temperature of coolant entering the heat loss source from the engine, a temperature of air entering the heat loss source from ambient air and / or the cabin, and a heat transfer efficiency between the heat loss source and the cabin, the heat transfer efficiency between the heat loss source and the cabin being based on each of the mass air flow rate between the heat loss source and the cabin and a mass coolant flow rate through the heat loss source. 5 . The method of claim 4 , wherein the mass air flow rate between the heater core of the heat loss source and the vehicle cabin is a function of a location of a vent that allows air flow between the heater core and the vehicle cabin.

6. The method of claim 4 wherein the measured coolant temperature further comprises a second measured coolant temperature downstream of the heat exchanger based on input from a second coolant temperature sensor coupled to a coolant line exiting the heat exchanger, the modeled coolant temperature further comprises a second modeled coolant temperature downstream of the heat exchanger, and indicating degradation of the second coolant temperature sensor coupled to the downstream of the heat exchanger is based on a difference above a threshold between the second measured coolant temperature downstream of the heat exchanger and the second modeled coolant temperature of the heat exchanger, wherein the second modeled coolant temperature downstream of the heat exchanger is based on each of the first modeled coolant temperature upstream of the heat exchanger and heat transfer between exhaust gas and the coolant flowing through the heat exchanger.

7. The method of claim 6, wherein the heat transfer between the exhaust gas and the coolant flowing through the heat exchanger is a function of one or more of a mass exhaust flow rate through the heat exchanger, a temperature of the coolant entering the heat exchanger, a temperature of air entering the heat exchanger from the exhaust gas, a temperature of air entering the exhaust gas from the heat exchanger, and a heat transfer efficiency between the exhaust gas and the coolant flowing through the heat exchanger, the heat transfer efficiency between the exhaust gas and the coolant flowing through the heat exchanger being based on each of the mass exhaust flow rate through the heat exchanger and the mass coolant flow rate through the heat exchanger.

8. The method of claim 7, wherein the heat exchanger is coupled to an exhaust bypass, the method further comprising: A position of an exhaust diverter valve coupled to a junction of the exhaust bypass and main exhaust passage is adjusted to regulate exhaust gas flow through the heat exchanger to maintain a desired engine coolant temperature based on each of an engine heating demand and / or a cabin heating demand.

9. The method according to claim 4, further comprising: In response to indicating degradation of the first coolant temperature sensor, the first modeled coolant temperature is used for engine operation, and in response to indicating degradation of the second coolant temperature sensor, the second modeled coolant temperature is used for engine operation.

10. The method of claim 8, wherein the mass exhaust flow rate through the heat exchanger is a function of each of a position of an exhaust diverter valve and a total exhaust flow rate through the main exhaust passage.

11. The method according to claim 10, further comprising: In response to an actual position of the diverter valve estimated based on input from a diverter valve position sensor being different from an expected position of the diverter valve, degradation of the diverter valve is indicated, wherein the expected position of the diverter valve includes: a first position that enables exhaust flow through the heat exchanger during an engine heating demand that is higher than a threshold and / or a cabin heating demand that is higher than a threshold, and a second position that disables exhaust flow through the heat exchanger during an engine heating demand that is lower than a threshold and a cabin heating demand that is lower than a threshold.

12. The method according to claim 11, further comprising: Degradation of the heat exchanger is indicated in response to an expected temperature difference between coolant temperatures upstream and downstream of the heat exchanger being different from an actual temperature difference between coolant temperatures upstream and downstream of the heat exchanger, the expected temperature difference being based on the actual position of the diverter valve, each of the mass coolant flow rate and the mass exhaust flow rate through the heat exchanger, and the actual temperature difference being based on inputs from the first coolant temperature sensor and the second coolant temperature sensor.

13. A vehicle system comprising: engine; car; Engine intake manifold; an engine exhaust system including an exhaust passage and a bypass passage, the exhaust passage including one or more exhaust catalysts and a muffler, the bypass passage coupled to the exhaust passage from downstream of the one or more exhaust catalysts to upstream of the muffler, the bypass passage including a heat exchanger; a diverter valve coupling an inlet of the bypass passage to the exhaust passage; a diverter valve position sensor coupled to the diverter valve; a coolant system having an incoming coolant line and an outgoing coolant line for circulating coolant through the heat exchanger, the coolant system further coupled to an engine block and each of a heater core of a heating, ventilation, and air conditioning (HVAC) system, the incoming coolant line including a first coolant temperature sensor for estimating a coolant temperature upstream of the heat exchanger, the outgoing coolant line including a second coolant temperature sensor for estimating a coolant temperature downstream of the heat exchanger; as well as A controller having computer readable instructions stored on a non-transitory memory for: displacing the diverter valve to a first position to operate the exhaust system in a first mode in which exhaust gas flows from downstream of the exhaust catalyst to upstream of the muffler via the heat exchanger; and When operating in the first mode, measuring a coolant temperature upstream of the heat exchanger via the first coolant temperature sensor; indicating degradation of the first coolant temperature sensor in response to a difference between the modeled coolant temperature upstream of the heat exchanger and the measured coolant temperature upstream of the heat exchanger being above a threshold; as well as In response to the indication of degradation, a coolant temperature upstream of the heat exchanger is estimated using the modeled coolant temperature.

14. The vehicle system of claim 13, wherein the controller includes further instructions for: When operating in the first mode, measuring the position of the diverter valve via the position sensor; measuring a coolant temperature downstream of the heat exchanger via the second coolant temperature sensor; indicating degradation of the second coolant temperature sensor in response to a difference between the modeled coolant temperature downstream of the heat exchanger and the measured coolant temperature downstream of the heat exchanger being above a threshold; responsive to the position of the diverter valve being different from the first position, indicating degradation of the diverter valve; responsive to the indication of degradation of the second coolant temperature sensor, estimating a coolant temperature downstream of the heat exchanger using the modeled coolant temperature downstream of the heat exchanger; as well as In response to the indication of degradation of the diverter valve, operation of the exhaust system in the first mode is disabled.

15. The vehicle system of claim 13, wherein the modeled coolant temperature upstream of the heat exchanger is based on one or more of air flow between the heater core and the cabin and coolant flow from the engine to the heater core, and wherein the modeled coolant temperature downstream of the heat exchanger is based on one or more of the modeled coolant temperature upstream of the heat exchanger, air flow between exhaust gas flowing through the heat exchanger and coolant flowing through the heat exchanger, and coolant flow from the heater core to the heat exchanger.

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